Transport of U(VI) through sediments amended with phosphate to induce in situ uranium immobilization.

PubMed

Mehta, Vrajesh S; Maillot, Fabien; Wang, Zheming; Catalano, Jeffrey G; Giammar, Daniel E

2015-02-01

Phosphate amendments can be added to U(VI)-contaminated subsurface environments to promote in situ remediation. The primary objective of this study was to evaluate the impacts of phosphate addition on the transport of U(VI) through contaminated sediments. In batch experiments using sediments (<2 mm size fraction) from a site in Rifle, Colorado, U(VI) only weakly adsorbed due to the dominance of the aqueous speciation by Ca-U(VI)-carbonate complexes. Column experiments with these sediments were performed with flow rates that correspond to a groundwater velocity of 1.1 m/day. In the absence of phosphate, the sediments took up 1.68-1.98 μg U/g of sediments when the synthetic groundwater influent contained 4 μM U(VI). When U(VI)-free influents were then introduced with and without phosphate, substantially more uranium was retained within the column when phosphate was present in the influent. Sequential extractions of sediments from the columns revealed that uranium was uniformly distributed along the length of the columns and was primarily in forms that could be extracted by ion exchange and contact with a weak acid. Laser induced fluorescence spectroscopy (LIFS) analysis along with sequential extraction results suggest adsorption as the dominant uranium uptake mechanism. The response of dissolved uranium concentrations to stopped-flow events and the comparison of experimental data with simulations from a simple reactive transport model indicated that uranium adsorption to and desorption from the sediments was not always at local equilibrium. Copyright © 2014 Elsevier Ltd. All rights reserved.

A series of uranium (IV, V, VI) tritylimido complexes, their molecular and electronic structures and reactivity with CO2.

PubMed

Schmidt, Anna-Corina; Heinemann, Frank W; Maron, Laurent; Meyer, Karsten

2014-12-15

A series of uranium tritylimido complexes with structural continuity across complexes in different oxidation states, namely U(IV), U(V), and U(VI), is reported. This series was successfully synthesized by employing the trivalent uranium precursor, [(((nP,Me)ArO)3tacn)U(III)] (1) (where ((nP,Me)ArO)3tacn(3-) = trianion of 1,4,7-tris(2-hydroxy-5-methyl-3-neopentylbenzyl)-1,4,7-triazacyclononane), with the organic azides Me3SiN3, Me3SnN3, and Ph3CN3 (tritylazide). While the reaction with Me3SiN3 yields an inseparable mixture of both the azido and imido uranium complexes, applying the heavier Sn homologue yields the bis-μ-azido complex [{(((nP,Me)ArO)3tacn)U(IV)}2(μ-N3)2] (2) exclusively. In contrast to this one-electron redox chemistry, the reaction of precursor 1 with tritylazide solely leads to the two-electron oxidized U(V) imido [(((nP,Me)ArO)3tacn)U(V)(N-CPh3)] (3). Oxidation and reduction of 3 yield the corresponding U(VI) and U(IV) complexes [(((nP,Me)ArO)3tacn)U(VI)(N-CPh3)][B(C6F5)4] (4) and K[(((nP,Me)ArO)3tacn)U(IV)(N-CPh3)] (5), respectively. In addition, the U(V) imido 3 engages in a H atom abstraction reaction with toluene to yield the closely related amido complex [(((nP,Me)ArO)3tacn)U(IV)(N(H)-CPh3)] (6). Complex 6 and the three tritylimido complexes 3, 4, and 5, with oxidation states ranging from +IV to +VI and homologous core structures, were investigated by X-ray diffraction analyses and magnetochemical and spectroscopic studies as well as density functional theory (DFT) computational analysis. The series of structurally very similar imido complexes provides a unique opportunity to study electronic properties and to probe the uranium imido reactivity solely as a function of electron count of the metal-imido entity. Evidence for the U-N bond covalency and f-orbital participation in complexes 3-6 was drawn from the in-depth and comparative DFT study. The reactivity of the imido and amido complexes with CO2 was probed, and conclusions about the influence of the formal oxidation state are reported.

U(VI) adsorption on aquifer sediments at the Hanford Site.

PubMed

Um, Wooyong; Serne, R Jeffrey; Brown, Christopher F; Last, George V

2007-08-15

Aquifer sediments collected via split-spoon sampling in two new groundwater wells in the 200-UP-1 operable unit at the Hanford Site were characterized and showed typical Ringold Unit E Formation properties dominated by gravel and sand. High iron-oxide content in Fe oxide/clay coatings caused the highest U(VI) adsorption as quantified by batch K(d) values, indicating iron oxides are the key solid adsorbent in the 200-UP-1 sediments that affect U(VI) fate and mobility. Even though U(VI) adsorption on the gravel-sized fraction of the sediments is considered to be negligible, careful characterization should be conducted to determine U(VI) adsorption on gravel, because of presence of Fe oxides coatings and diffusion-controlled adsorption into the gravel particles' interior surfaces. A linear adsorption isotherm was observed up to 10(-6) M (238 microg/L) of total U(VI) concentration in batch U(VI) adsorption tests with varying total U(VI) concentrations in spiked groundwater. U(VI) adsorption decreased with increasing concentrations of dissolved carbonate, because strong anionic aqueous uranium-carbonate complexes formed at high pH and high alkalinity conditions. Noticeable uranium desorption hysteresis was observed in a flow-through column experiment, suggesting that desorption K(d) values for aged uranium-contaminated sediments at the Hanford Site can be larger than adsorption K(d) values determined in short-term laboratory experiments and slow uranium release from contaminated sediments into the groundwater is expected.

Uranium(VI) Scavenging by Amorphous Iron Phosphate Encrusting Sphaerotilus natans Filaments.

PubMed

Seder-Colomina, Marina; Morin, Guillaume; Brest, Jessica; Ona-Nguema, Georges; Gordien, Nilka; Pernelle, Jean-Jacques; Banerjee, Dipanjan; Mathon, Olivier; Esposito, Giovanni; van Hullebusch, Eric D

2015-12-15

U(VI) sorption to iron oxyhydroxides, precipitation of phosphate minerals, as well as biosorption on bacterial biomass are among the most reported processes able to scavenge U(VI) under oxidizing conditions. Although phosphates significantly influence bacterially mediated as well as iron oxyhydroxide mediated scavenging of uranium, the sorption or coprecipitation of U(VI) with poorly crystalline nanosized iron phosphates has been scarcely documented, especially in the presence of microorganisms. Here we show that dissolved U(VI) can be bound to amorphous iron phosphate during their deposition on Sphaerotilus natans filamentous bacteria. Uranium LIII-edge EXAFS analysis reveals that the adsorbed uranyl ions share an equatorial oxygen atom with a phosphate tetrahedron of the amorphous iron phosphate, with a characteristic U-P distance of 3.6 Å. In addition, the uranyl ions are connected to FeO6 octahedra with U-Fe distances at ~3.4 Å and at ~4.0 Å. The shortest U-Fe distance corresponds to a bidentate edge-sharing complex often reported for uranyl adsorption onto iron oxyhydroxides, whereas the longest U-Fe and U-P distances can be interpreted as a bidentate corner-sharing complex, in which two adjacent equatorial oxygen atoms are shared with the vertices of a FeO6 octahedron and of a phosphate tetrahedron. Furthermore, based on these sorption reactions, we demonstrate the ability of an attached S. natans biofilm to remove uranium from solution without any filtration step.

Removing uranium (VI) from aqueous solution with insoluble humic acid derived from leonardite.

PubMed

Meng, Fande; Yuan, Guodong; Larson, Steven L; Ballard, John H; Waggoner, Charles A; Arslan, Zikri; Han, Fengxiang X

2017-12-01

The occurrence of uranium (U) and depleted uranium (DU)-contaminated wastes from anthropogenic activities is an important environmental problem. Insoluble humic acid derived from leonardite (L-HA) was investigated as a potential adsorbent for immobilizing U in the environment. The effect of initial pH, contact time, U concentration, and temperature on U(VI) adsorption onto L-HA was assessed. The U(VI) adsorption was pH-dependent and achieved equilibrium in 2 h. It could be well described with pseudo-second-order model, indicating that U(VI) adsorption onto L-HA involved chemisorption. The U(VI) adsorption mass increased with increasing temperature with maximum adsorption capacities of 91, 112 and 120 mg g -1 at 298, 308 and 318 K, respectively. The adsorption reaction was spontaneous and endothermic. We explored the processes of U(VI) desorption from the L-HA-U complex through batch desorption experiments in 1 mM NaNO 3 and in artificial seawater. The desorption process could be well described by pseudo-first-order model and reached equilibrium in 3 h. L-HA possessed a high propensity to adsorb U(VI). Once adsorbed, the release of U(VI) from L-HA-U complex was minimal in both 1 mM NaNO 3 and artificial seawater (0.06% and 0.40%, respectively). Being abundant, inexpensive, and safe, L-HA has good potential for use as a U adsorbent from aqueous solution or immobilizing U in soils. Copyright © 2017 Elsevier Ltd. All rights reserved.

Bio-precipitation of uranium by two bacterial isolates recovered from extreme environments as estimated by potentiometric titration, TEM and X-ray absorption spectroscopic analyses.

PubMed

Merroun, Mohamed L; Nedelkova, Marta; Ojeda, Jesus J; Reitz, Thomas; Fernández, Margarita López; Arias, José M; Romero-González, María; Selenska-Pobell, Sonja

2011-12-15

This work describes the mechanisms of uranium biomineralization at acidic conditions by Bacillus sphaericus JG-7B and Sphingomonas sp. S15-S1 both recovered from extreme environments. The U-bacterial interaction experiments were performed at low pH values (2.0-4.5) where the uranium aqueous speciation is dominated by highly mobile uranyl ions. X-ray absorption spectroscopy (XAS) showed that the cells of the studied strains precipitated uranium at pH 3.0 and 4.5 as a uranium phosphate mineral phase belonging to the meta-autunite group. Transmission electron microscopic (TEM) analyses showed strain-specific localization of the uranium precipitates. In the case of B. sphaericus JG-7B, the U(VI) precipitate was bound to the cell wall. Whereas for Sphingomonas sp. S15-S1, the U(VI) precipitates were observed both on the cell surface and intracellularly. The observed U(VI) biomineralization was associated with the activity of indigenous acid phosphatase detected at these pH values in the absence of an organic phosphate substrate. The biomineralization of uranium was not observed at pH 2.0, and U(VI) formed complexes with organophosphate ligands from the cells. This study increases the number of bacterial strains that have been demonstrated to precipitate uranium phosphates at acidic conditions via the activity of acid phosphatase. Copyright © 2011 Elsevier B.V. All rights reserved.

Biomineralization of U(VI) phosphate promoted by microbially-mediated phytate hydrolysis in contaminated soils

NASA Astrophysics Data System (ADS)

Salome, Kathleen R.; Beazley, Melanie J.; Webb, Samuel M.; Sobecky, Patricia A.; Taillefert, Martial

2017-01-01

The bioreduction of uranium may immobilize a significant fraction of this toxic contaminant in reduced environments at circumneutral pH. In oxic and low pH environments, however, the low solubility of U(VI)-phosphate minerals also makes them good candidates for the immobilization of U(VI) in the solid phase. As inorganic phosphate is generally scarce in soils, the biomineralization of U(VI)-phosphate minerals via microbially-mediated organophosphate hydrolysis may represent the main immobilization process of uranium in these environments. In this study, contaminated sediments were incubated aerobically in two pH conditions to examine whether phytate, a naturally-occurring and abundant organophosphate in soils, could represent a potential phosphorous source to promote U(VI)-phosphate biomineralization by natural microbial communities. While phytate hydrolysis was not evident at pH 7.0, nearly complete hydrolysis was observed both with and without electron donor at pH 5.5, suggesting indigenous microorganisms express acidic phytases in these sediments. While the rate of hydrolysis of phytate generally increased in the presence of uranium, the net rate of inorganic phosphate production in solution was decreased and inositol phosphate intermediates were generated in contrast to similar incubations conducted without uranium. These findings suggest uranium stress enhanced the phytate-metabolism of the microbial community, while simultaneously inhibiting phosphatase production and/or activity by the indigenous population. Finally, phytate hydrolysis drastically decreased uranium solubility, likely due to formation of ternary sorption complexes, U(VI)-phytate precipitates, and U(VI)-phosphate minerals. Overall, the results of this study provide evidence for the ability of natural microbial communities to liberate phosphate from phytate in acidic sediments, possibly as a detoxification mechanism, and demonstrate the potential utility of phytate-promoted uranium immobilization in subsurface environments. These processes should be investigated in more detail with pure cultures isolated from these sediments.

Bicarbonate Impact on U(VI) Bioreduction in a Shallow Alluvial Aquifer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, Philip E.; Williams, Kenneth H.; Davis, James A.

Field-scale biostimulation and desorption tracer experiments conducted in a uranium (U) contaminated, shallow alluvial aquifer have provided insight into the coupling of microbiology, biogeochemistry, and hydrogeology that control U mobility in the subsurface. Initial experiments successfully tested the concept that Fe-reducing bacteria such as Geobacter sp. could enzymatically reduce soluble U(VI) to insoluble U(IV) during in situ electron donor amendment (Anderson et al. 2003, Williams et al. 2011). In parallel, in situ desorption tracer tests using bicarbonate amendment demonstrated rate-limited U(VI) desorption (Fox et al. 2012). These results and prior laboratory studies underscored the importance of enzymatic U(VI)-reduction and suggestedmore » the ability to combine desorption and bioreduction of U(VI). Here we report the results of a new field experiment in which bicarbonate-promoted uranium desorption and acetate amendment were combined and compared to an acetate amendment-only experiment in the same experimental plot. Results confirm that bicarbonate amendment to alluvial aquifer desorbs U(VI) and increases the abundance of Ca-uranyl-carbonato complexes. At the same time, that the rate of acetate-promoted enzymatic U(VI) reduction was greater in the presence of added bicarbonate in spite of the increased dominance of Ca-uranyl-carbonato aqueous complexes. A model-simulated peak rate of U(VI) reduction was ~3.8 times higher during acetate-bicarbonate treatment than under acetate-only conditions. Lack of consistent differences in microbial community structure between acetate-bicarbonate and acetate-only treatments suggest that a significantly higher rate of U(VI) reduction the bicarbonate-impacted sediment may be due to a higher intrinsic rate of microbial reduction induced by elevated concentrations of the bicarbonate oxyanion. The findings indicate that bicarbonate amendment may be useful in improving the engineered bioremediation of uranium in aquifers.« less

Bicarbonate impact on U(VI) bioreduction in a shallow alluvial aquifer

NASA Astrophysics Data System (ADS)

Long, Philip E.; Williams, Kenneth H.; Davis, James A.; Fox, Patricia M.; Wilkins, Michael J.; Yabusaki, Steven B.; Fang, Yilin; Waichler, Scott R.; Berman, Elena S. F.; Gupta, Manish; Chandler, Darrell P.; Murray, Chris; Peacock, Aaron D.; Giloteaux, Ludovic; Handley, Kim M.; Lovley, Derek R.; Banfield, Jillian F.

2015-02-01

Field-scale biostimulation and desorption tracer experiments conducted in a uranium (U) contaminated, shallow alluvial aquifer have provided insight into the coupling of microbiology, biogeochemistry, and hydrogeology that control U mobility in the subsurface. Initial experiments successfully tested the concept that Fe-reducing bacteria such as Geobacter sp. could enzymatically reduce soluble U(VI) to insoluble U(IV) during in situ electron donor amendment (Anderson et al., 2003; Williams et al., 2011). In parallel, in situ desorption tracer tests using bicarbonate amendment demonstrated rate-limited U(VI) desorption (Fox et al., 2012). These results and prior laboratory studies underscored the importance of enzymatic U(VI)-reduction and suggested the ability to combine desorption and bioreduction of U(VI). Here we report the results of a new field experiment in which bicarbonate-promoted uranium desorption and acetate amendment were combined and compared to an acetate amendment-only experiment in the same experimental plot. Results confirm that bicarbonate amendment to alluvial aquifer sediments desorbs U(VI) and increases the abundance of Ca-uranyl-carbonato complexes. At the same time, the rate of acetate-promoted enzymatic U(VI) reduction was greater in the presence of added bicarbonate in spite of the increased dominance of Ca-uranyl-carbonato aqueous complexes. A model-simulated peak rate of U(VI) reduction was ∼3.8 times higher during acetate-bicarbonate treatment than under acetate-only conditions. Lack of consistent differences in microbial community structure between acetate-bicarbonate and acetate-only treatments suggest that a significantly higher rate of U(VI) reduction in the bicarbonate-impacted sediment may be due to a higher intrinsic rate of microbial reduction induced by elevated concentrations of the bicarbonate oxyanion. The findings indicate that bicarbonate amendment may be useful in improving the engineered bioremediation of uranium in aquifers.

Removal and recovery of uranium(VI) by waste digested activated sludge in fed-batch stirred tank reactor.

PubMed

Jain, Rohan; Peräniemi, Sirpa; Jordan, Norbert; Vogel, Manja; Weiss, Stephan; Foerstendorf, Harald; Lakaniemi, Aino-Maija

2018-05-24

This study demonstrated the removal and recovery of uranium(VI) in a fed-batch stirred tank reactor (STR) using waste digested activated sludge (WDAS). The batch adsorption experiments showed that WDAS can adsorb 200 (±9.0) mg of uranium(VI) per g of WDAS. The maximum adsorption of uranium(VI) was achieved even at an acidic initial pH of 2.7 which increased to a pH of 4.0 in the equilibrium state. Desorption of uranium(VI) from WDAS was successfully demonstrated from the release of more than 95% of uranium(VI) using both acidic (0.5 M HCl) and alkaline (1.0 M Na 2 CO 3 ) eluents. Due to the fast kinetics of uranium(VI) adsorption onto WDAS, the fed-batch STR was successfully operated at a mixing time of 15 min. Twelve consecutive uranium(VI) adsorption steps with an average adsorption efficiency of 91.5% required only two desorption steps to elute more than 95% of uranium(VI) from WDAS. Uranium(VI) was shown to interact predominantly with the phosphoryl and carboxyl groups of the WDAS, as revealed by in situ infrared spectroscopy and time-resolved laser-induced fluorescence spectroscopy studies. This study provides a proof-of-concept of the use of fed-batch STR process based on WDAS for the removal and recovery of uranium(VI). Copyright © 2018 Elsevier Ltd. All rights reserved.

Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium

NASA Astrophysics Data System (ADS)

Zhang, Xiaofei; Wang, Jun

2018-01-01

Uranium(VI) was removed from aqueous solutions using carbon coated Fe3O4 nanoparticles (Fe3O4@C). Batch experiments were conducted to study the effects of initial pH, shaking time and temperature on uranium sorption efficiency. It was found that the maximum adsorption capacity of the Fe3O4@C toward uranium(VI) was ∼120.20 mg g-1 when the initial uranium(VI) concentration was 100 mg L-1, displaying a high efficiency for the removal of uranium(VI) ions. Kinetics of the uranium(VI) removal is found to follow pseudo-second-order rate equation. In addition, the uranium(VI)-loaded Fe3O4@C nanoparticles can be recovered easily from aqueous solution by magnetic separation and regenerated by acid treatment. Present study suggested that magnetic Fe3O4@C composite particles can be used as an effective and recyclable adsorbent for the removal of uranium(VI) from aqueous solutions.

The short-term reduction of uranium by nanoscale zero-valent iron (nZVI): role of oxide shell, reduction mechanism and the formation of U( v )-carbonate phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsarev, Sergey; Collins, Richard N.; Ilton, Eugene S.

Nanoscale zero-valent iron (nZVI) is a potential remediation agent for uranium-contaminated groundwaters, however, a complete mechanistic understanding of the processes that lead to uranium immobilization has yet to be achieved. In this study, the short-term anoxic reaction of U(VI) with fresh, (anoxic) aged and corroded nZVI particles was investigated under aqueous conditions conducive to the formation of thermodynamically stable U(VI)-Ca-CO3 ternary aqueous complexes. The first stage of the reaction between U(VI) and nZVI was assigned to sorption processes with the formation of surface U(VI)-carbonate complexes. Aged nZVI removed U(VI) faster than either fresh or corroded nZVI and it is hypothesizedmore » that U reduction initially occurs through the transfer of one electron from Fe(II) in the nZVI surface oxide layer. Evidence for reduction to U(V) was obtained through X-ray photoelectron spectroscopy and by determination of U-O bond distances of ~2.05 Å and 2.27 Å by U LIII-edge X-ray absorption spectroscopy detection of U-O bond distances at ~2.05 Å and 2.27 Å with these distances , similar to thoseat observed for the U(V) site in the mixed U(V)/U(VI) carbonate mineral wyartite. Scanning transmission electron microscopy also demonstrated that U was present as a nanoparticulate phase after one day of reaction, rather than a surface complex. Further reduction to U(IV), as observed in previous studies, would appear to be rate-limiting and coincident with the transformation of this meta-stable U-carbonate phase to uraninite (UO2).« less

Uranium(VI) Binding Forms in Selected Human Body Fluids: Thermodynamic Calculations versus Spectroscopic Measurements.

PubMed

Osman, Alfatih A A; Geipel, Gerhard; Barkleit, Astrid; Bernhard, Gert

2015-02-16

Human exposure to uranium increasingly becomes a subject of interest in many scientific disciplines such as environmental medicine, toxicology, and radiation protection. Knowledge about uranium chemical binding forms(speciation) in human body fluids can be of great importance to understand not only its biokinetics but also its relevance in risk assessment and in designing decorporation therapy in the case of accidental overexposure. In this study, thermodynamic calculations of uranium speciation in relevant simulated and original body fluids were compared with spectroscopic data after ex-situ uranium addition. For the first time, experimental data on U(VI) speciation in body fluids (saliva, sweat, urine) was obtained by means of cryogenic time-resolved laser-induced fluorescence spectroscopy (cryo-TRLFS) at 153 K. By using the time dependency of fluorescence decay and the band positions of the emission spectra, various uranyl complexes were demonstrated in the studied samples. The variations of the body fluids in terms of chemical composition, pH, and ionic strength resulted in different binding forms of U(VI). The speciation of U(VI) in saliva and in urine was affected by the presence of bioorganic ligands, whereas in sweat, the distribution depends mainly on inorganic ligands. We also elucidated the role of biological buffers, i.e., phosphate (H(2)PO(4−)/HPO(4)(2−)) on U(VI) distribution, and the system Ca(2+)/UO(2)(2+)/PO(4)(3−) was discussed in detail in both saliva and urine. The theoretical speciation calculations of the main U(VI) species in the investigated body fluids were significantly consistent with the spectroscopic data. Laser fluorescence spectroscopy showed success and reliability for direct determination of U(VI) in such biological matrices with the possibility for further improvement.

Sorption of uranium (VI) on homoionic sodium smectite experimental study and surface complexation modeling.

PubMed

Korichi, Smain; Bensmaili, Aicha

2009-09-30

This paper is an extension of a previous paper where the natural and purified clay in the homoionic Na form were physico-chemically characterized (doi:10.1016/j.clay.2008.04.014). In this study, the adsorption behavior of U (VI) on a purified Na-smectite suspension is studied using batch adsorption experiments and surface complexation modeling (double layer model). The sorption of uranium was investigated as a function of pH, uranium concentration, solid to liquid ratio, effect of natural organic matter (NOM) and NaNO(3) background electrolyte concentration. Using the MINTEQA2 program, the speciation of uranium was calculated as a function of pH and uranium concentration. Model predicted U (VI) aqueous speciation suggests that important aqueous species in the [U (VI)]=1mg/L and pH range 3-7 including UO(2)(2+), UO(2)OH(+), and (UO(2))(3)(OH)(5)(+). The concentration of UO(2)(2+) decreased and that of (UO(2))(3)(OH)(5)(+) increased with increasing pH. The potentiometric titration values and uptake of uranium in the sodium smectite suspension were simulated by FITEQL 4.0 program using a two sites model, which is composed of silicate and aluminum reaction sites. We compare the acidity constants values obtained by potentiometric titration from the purified sodium smectite with those obtained from single oxides (quartz and alpha-alumina), taking into account the surface heterogeneity and the complex nature of natural colloids. We investigate the uranium sorption onto purified Na-smectite assuming low, intermediate and high edge site surfaces which are estimated from specific surface area percentage. The sorption data is interpreted and modeled as a function of edge site surfaces. A relationship between uranium sorption and total site concentration was confirmed and explained through variation in estimated edge site surface value. The modeling study shows that, the convergence during DLM modeling is related to the best estimation of the edge site surface from the N(2)-BET specific surface area, SSA(BET) (thus, total edge site concentrations). The specific surface area should be at least 80-100m(2)/g for smectite clays in order to reach convergence during the modeling. The range of 10-20% SSA(BET) was used to estimate the values of edge site surfaces that led to the convergence during modeling. An agreement between the experimental data and model predictions is found reasonable when 15% SSA(BET) was used as edge site surface. However, the predicted U (VI) adsorption underestimated and overestimated the experimental observations at the 10 and 20% of the measured SSA(BET), respectively. The dependence of uranium sorption modeling results on specific surface area and edge site surface is useful to describe and predict U (VI) retardation as a function of chemical conditions in the field-scale reactive transport simulations. Therefore this approach can be used in the environmental quality assessment.

Characterization of U(VI)-carbonato ternary complexes on hematite: EXAFS and electrophoretic mobility measurements

USGS Publications Warehouse

Bargar, John R.; Reitmeyer, Rebecca; Lenhart, John J.; Davis, James A.

2000-01-01

We have measured U(VI) adsorption on hematite using EXAFS spectroscopy and electrophoresis under conditions relevant to surface waters and aquifers (0.01 to 10 μM dissolved uranium concentrations, in equilibrium with air, pH 4.5 to 8.5). Both techniques suggest the existence of anionic U(VI)-carbonato ternary complexes. Fits to EXAFS spectra indicate that U(VI) is simultaneously coordinated to surface FeO6 octahedra and carbonate (or bicarbonate) ligands in bidentate fashions, leading to the conclusion that the ternary complexes have an inner-sphere metal bridging (hematite-U(VI)-carbonato) structure. Greater than or equal to 50% of adsorbed U(VI) was comprised of monomeric hematite-U(VI)-carbonato ternary complexes, even at pH 4.5. Multimeric U(VI) species were observed at pH ≥ 6.5 and aqueous U(VI) concentrations approximately an order of magnitude more dilute than the solubility of crystalline β-UO2(OH)2. Based on structural constraints, these complexes were interpreted as dimeric hematite-U(VI)-carbonato ternary complexes. These results suggest that Fe-oxide-U(VI)-carbonato complexes are likely to be important transport-limiting species in oxic aquifers throughout a wide range of pH values.

Bis(hydroxylamino)triazines: High Selectivity and Hydrolytic Stability of Hydroxylamine-Based Ligands for Uranyl Compared to Vanadium(V) and Iron(III).

PubMed

Hadjithoma, Sofia; Papanikolaou, Michael G; Leontidis, Epameinondas; Kabanos, Themistoklis A; Keramidas, Anastasios D

2018-06-08

The development of ligands with high selectivity and affinity for uranium is critical in the extraction of uranium from human body, radioactive waste, and seawater. A scientific challenge is the improvement of the selectivity of chelators for uranium over other heavy metals, including iron and vanadium. Flat ligands with hard donor atoms that satisfy the geometric and electronic requirements of the U VI O 2 2+ exhibit high selectivity for the uranyl moiety. The bis(hydroxylamino)(triazine) ligand, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H 2 bihyat), a strong binder for hard metal ions (Fe III , Ti IV , V V , and Mo VI ), reacted with [U VI O 2 (NO 3 ) 2 (H 2 O) 2 ]·4H 2 O in aqueous solution and resulted in the isolation of the complexes [U VI O 2 (bihyat)(H 2 O)], [U VI O 2 (bihyat) 2 ] 2- , and {[U VI O 2 (bihyat)(μ-OH)]} 2 2- . These three species are in equilibrium in aqueous solution, and their abundance varies with the concentration of H 2 bihyat and the pH. Reaction of H 2 bihyat with [U VI O 2 (NO 3 ) 2 (H 2 O) 2 ]·4H 2 O in CH 3 CN gave the trinuclear complex [U VI 3 O 6 (bihyat) 2 (μ-bihyat) 2 ] 2- , which is the major species in organic solvents. The dynamics between the U VI O 2 2+ and the free ligand H 2 bihyat in aqueous and dimethyl sulfoxide solutions; the metal binding ability of the H 2 bihyat over pyridine-2,6-dicarboxylic acid (H 2 dipic) or glutarimidedioxime for U VI O 2 2+ , and the selectivity of the H 2 bihyat to bind U VI O 2 2+ in comparison to V V O 4 3- and Fe III in either U VI O 2 2+ /V V O 4 3- or U VI O 2 2+ /Fe III solutions were examined by NMR and UV-vis spectroscopies. The results revealed that H 2 bihyat is a superior ligand for U VI O 2 2+ with high selectivity compared to Fe III and V V O 4 3- , which increases at higher pHs. Thus, this type of ligand might find applications in the extraction of uranium from the sea and its removal from the environment and the human body.

A procedure for quantitation of total oxidized uranium for bioremediation studies

USGS Publications Warehouse

Elias, Dwayne A.; Senko, John M.; Krumholz, Lee R.

2003-01-01

A procedure was developed for the quantitation of complexed U(VI) during studies on U(VI) bioremediation. These studies typically involve conversion of soluble or complexed U(VI) (oxidized) to U(IV) (the reduced form which is much less soluble). Since U(VI) freely exchanges between material adsorbed to the solid phase and the dissolved phase, uranium bioremediation experiments require a mass balance of U in both its soluble and adsorbed forms as well as in the reduced sediment bound phase. We set out to optimize a procedure for extraction and quantitation of sediment bound U(VI). Various extractant volumes to sediment ratios were tested and it was found that between 1:1 to 8:1 ratios (v/w) there was a steady increase in U(VI) recovered, but no change with further increases in v/w ratio.Various strengths of NaHCO3, Na-EDTA, and Na-citrate were used to evaluate complexed U(VI) recovery, while the efficiency of a single versus repeated extraction steps was compared with synthesized uranyl-phosphate and uranyl-hydroxide. Total recovery with 1 M NaHCO3 was 95.7% and 97.9% from uranyl-phosphate and uranyl-hydroxide, respectively, compared to 80.7% and 89.9% using 450 mM NaHCO3. Performing the procedure once yielded an efficiency of 81.1% and 92.3% for uranyl-phosphate and uranyl-hydroxide, respectively, as compared to three times. All other extractants yielded 7.9–82.0% in both experiments.

Effect of bicarbonate on aging and reactivity of nanoscale zerovalent iron (nZVI) toward uranium removal.

PubMed

Hua, Yilong; Wang, Wei; Huang, Xiaoyue; Gu, Tianhang; Ding, Dexin; Ling, Lan; Zhang, Wei-Xian

2018-06-01

Bicarbonate, ubiquitous in natural and waste waters is an important factor regulating the rate and efficiency of pollutant separation and transformation. For example, it can form complexes with U(VI) in the aqueous phase and at the solid-water interface. In this work, we investigated the effect of bicarbonate on the aging of nanoscale zero-valent (nZVI) in the context of U(VI) reduction and removal from wastewater. For fresh nZVI, over 99% aqueous uranium was separated in less than 10 min, of which 83% was reduced from U(VI) to U(IV). When nZVI was aged in water, its activity for U(VI) sequestration and reduction was significantly reduced. Batch experiments showed that for nZVI aged in the presence of 10 mM bicarbonate, only 20.3% uranium was reduced to U(IV) after 6 h reactions. Characterizations of the iron nanoparticles with spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) suggest that in fresh nZVI, uranium was concentrated at the nanoparticle center; whereas in nZVI aged in bicarbonate, uranium was largely deposited on the outer surface of the nanoparticles. Furthermore, aged nZVI without bicarbonate contained more lepidocrocite (γ-FeOOH) while aged nZVI in the presence of bicarbonate had more magnetite/maghemite (Fe 3 O 4 /γ-Fe 2 O 3 ). This could be attributed to the formation of carbonate green rust and pH buffer effect of . Primary mechanisms for U(VI) removal with nZVI include reduction, sorption and/or precipitation. Results demonstrate that bicarbonate alter the aging products of nZVI, and reduces the separation efficiency and reduction capability for uranium removal. Copyright © 2018. Published by Elsevier Ltd.

Remediation of uranium contaminated soils with bicarbonate extraction and microbial U(VI) reduction

USGS Publications Warehouse

Philips , Elizabeth J.P.; Landa, Edward R.; Lovely, Derek R.

1995-01-01

A process for concentrating uranium from contaminated soils in which the uranium is first extracted with bicarbonate and then the extracted uranium is precipitated with U(VI)-reducing microorganisms was evaluated for a variety of uranuum-contaminated soils. Bicarbonate (100 mM) extracted 20–94% of the uranium that was extracted with nitric acid. The U(VI)-reducing microorganism,Desulfovibrio desulfuricans reduced the U(VI) to U(IV) in the bicarbonate extracts. In some instances unidentified dissolved extracted components, presumably organics, gave the extract a yellow color and inhibited U(VI) reduction and/or the precipitation of U(IV). Removal of the dissolved yellow material with the addition of hydrogen peroxide alleviated this inhibition. These results demonstrate that bicarbonate extraction of uranium from soil followed by microbial U(VI) reduction might be an effective mechanism for concentrating uranium from some contaminated soils.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yingjie, E-mail: yzx@ansto.gov.au; Karatchevtseva, Inna; Bhadbhade, Mohan

With the coordination of dimethylformamide (DMF), two new uranium(VI) complexes with either 4-hydroxybenzoic acid (H{sub 2}phb) or terephthalic acid (H{sub 2}tph) have been synthesized under solvothermal conditions and structurally characterized. [(UO{sub 2}){sub 2}(Hphb){sub 2}(phb)(DMF)(H{sub 2}O){sub 3}]·4H{sub 2}O (1) has a dinuclear structure constructed with both pentagonal and hexagonal bipyramidal uranium polyhedra linked through a µ{sub 2}-bridging ligand via both chelating carboxylate arm and alcohol oxygen bonding, first observation of such a coordination mode of 4-hydroxybenzoate for 5 f ions. [(UO{sub 2})(tph)(DMF)] (2) has a three-dimensional (3D) framework built with pentagonal bipyramidal uranium polyhedra linked with µ{sub 4}-terephthalate ligands. The 3Dmore » channeled structure is facilitated by the unique carboxylate bonding with nearly linear C–O–U angles and the coordination of DMF molecules. The presence of phb ligands in different coordination modes, uranyl ions in diverse environments and DMF in complex 1, and tph ligand, DMF and uranyl ion in complex 2 has been confirmed by Raman spectroscopy. In addition, their thermal stability and photoluminescence properties have been investigated. - Graphical abstract: With the coordination of dimethylformamide, two new uranyl complexes with either 4-hydroxybenzoate or terephthalate have been synthesized under solvothermal conditions and structurally characterized. - Highlights: • Solvent facilitates the synthesis of two new uranium(VI) complexes. • A dinuclear complex with both penta- and hexagonal bipyramidal uranium polyhedral. • A unique µ{sub 2}-bridging mode of 4-hydroxybenzoate via alcohol oxygen for 5 f ions. • A 3D framework with uranium polyhedra and µ{sub 4}-terephthalate ligands. • Vibration modes and photoluminescence properties are reported.« less

Different biosorption mechanisms of Uranium(VI) by live and heat-killed Saccharomyces cerevisiae under environmentally relevant conditions.

PubMed

Wang, Tieshan; Zheng, Xinyan; Wang, Xiaoyu; Lu, Xia; Shen, Yanghao

2017-02-01

Uranium adsorption mechanisms of live and heat-killed Saccharomyces cerevisiae in different pH values and biomass concentrations were studied under environmentally relevant conditions. Compared with live cells, the adsorption capacity of heat-killed cells is almost one order of magnitude higher in low biomass concentration and highly acidic pH conditions. To explore the mesoscopic surface interactions between uranium and cells, the characteristic of uranium deposition was investigated by SEM-EDX, XPS and FTIR. Biosorption process of live cells was considered to be metabolism-dependent. Under stimulation by uranyl ions, live cells could gradually release phosphorus and reduce uranium from U(VI) to U(IV) to alleviate uranium toxicity. The uranyl-phosphate complexes were formed in scale-like shapes on cell surface. The metabolic detoxification mechanisms such as reduction and "self-protection" are of significance to the migration of radionuclides. In the metabolism-independent biosorption process of heat-killed cells: the cells cytomembrane was damaged by autoclaving which led to the free diffusion of phosphorous from intracellular, and the rough surface and nano-holes indicated that the dead cells provided larger contact area to precipitate U(VI) as spherical nano-particles. The high biosorption capacity of heat-killed cells makes it become a suitable biological adsorbent for uranium removal. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effects of aqueous uranyl speciation on the kinetics of microbial uranium reduction

DOE PAGES

Belli, Keaton M.; DiChristina, Thomas J.; Van Cappellen, Philippe; ...

2015-02-16

The ability to predict the success of the microbial reduction of soluble U(VI) to highly insoluble U(IV) as an in situ bioremediation strategy is complicated by the wide range of geochemical conditions at contaminated sites and the strong influence of aqueous uranyl speciation on the bioavailability and toxicity of U(VI) to metal-reducing bacteria. In order to determine the effects of aqueous uranyl speciation on uranium bioreduction kinetics, incubations and viability assays with Shewanella putrefaciens strain 200 were conducted over a range of pH and dissolved inorganic carbon (DIC), Ca 2+, and Mg 2+ concentrations. A speciation-dependent kinetic model was developedmore » to reproduce the observed time series of total dissolved uranium concentration over the range of geochemical conditions tested. The kinetic model yielded the highest rate constant for the reduction of uranyl non-carbonate species (i.e., the ‘free’ hydrated uranyl ion, uranyl hydroxides, and other minor uranyl complexes), indicating that they represent the most readily reducible fraction of U(VI) despite being the least abundant uranyl species in solution. In the presence of DIC, Ca 2+, and Mg 2+ is suppressed during the formation of more bioavailable uranyl non-carbonate species and resulted in slower bioreduction rates. At high concentrations of bioavailable U(VI), however, uranium toxicity to S. putrefaciens inhibited bioreduction, and viability assays confirmed that the concentration of non-carbonate uranyl species best predicts the degree of toxicity. The effect of uranium toxicity was accounted for by incorporating the free ion activity model of metal toxicity into the bioreduction rate law. These results demonstrate that, in the absence of competing terminal electron acceptors, uranium bioreduction kinetics can be predicted over a wide range of geochemical conditions based on the bioavailability and toxicity imparted on U(VI) by solution composition. Finally, these findings also imply that the concentration of uranyl non-carbonate species, despite being extremely low, is a determining factor controlling uranium bioreduction at contaminated sites.« less

The effect of calcium on aqueous uranium(VI) speciation and adsorption to ferrihydrite and quartz

USGS Publications Warehouse

Fox, P.M.; Davis, J.A.; Zachara, J.M.

2006-01-01

Recent studies of uranium(VI) geochemistry have focused on the potentially important role of the aqueous species, CaUO2 (CO3)32- and Ca2 UO2(CO3)30(aq), on inhibition of microbial reduction and uranium(VI) aqueous speciation in contaminated groundwater. However, to our knowledge, there have been no direct studies of the effects of these species on U(VI) adsorption by mineral phases. The sorption of U(VI) on quartz and ferrihydrite was investigated in NaNO3 solutions equilibrated with either ambient air (430 ppm CO2) or 2% CO2 in the presence of 0, 1.8, or 8.9 mM Ca2+. Under conditions where the Ca2UO2(CO3)30 (aq) species predominates U(VI) aqueous speciation, the presence of Ca in solution lowered U(VI) adsorption on quartz from 77% in the absence of Ca to 42% and 10% at Ca concentrations of 1.8 and 8.9 mM, respectively. U(VI) adsorption to ferrihydrite decreased from 83% in the absence of Ca to 57% in the presence of 1.8 mM Ca. Surface complexation model predictions that included the formation constant for aqueous Ca2UO2(CO3)30(aq) accurately simulated the effect of Ca2+ on U(VI) sorption onto quartz and ferrihydrite within the thermodynamic uncertainty of the stability constant value. This study confirms that Ca2+ can have a significant impact on the aqueous speciation of U(VI), and consequently, on the sorption and mobility of U(VI) in aquifers. ?? 2005 Elsevier Inc. All rights reserved.

A Uranium Bioremediation Reactive Transport Benchmark

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yabusaki, Steven B.; Sengor, Sevinc; Fang, Yilin

A reactive transport benchmark problem set has been developed based on in situ uranium bio-immobilization experiments that have been performed at a former uranium mill tailings site in Rifle, Colorado, USA. Acetate-amended groundwater stimulates indigenous microorganisms to catalyze the reduction of U(VI) to a sparingly soluble U(IV) mineral. The interplay between the flow, acetate loading periods and rates, microbially-mediated and geochemical reactions leads to dynamic behavior in metal- and sulfate-reducing bacteria, pH, alkalinity, and reactive mineral surfaces. The benchmark is based on an 8.5 m long one-dimensional model domain with constant saturated flow and uniform porosity. The 159-day simulation introducesmore » acetate and bromide through the upgradient boundary in 14-day and 85-day pulses separated by a 10 day interruption. Acetate loading is tripled during the second pulse, which is followed by a 50 day recovery period. Terminal electron accepting processes for goethite, phyllosilicate Fe(III), U(VI), and sulfate are modeled using Monod-type rate laws. Major ion geochemistry modeled includes mineral reactions, as well as aqueous and surface complexation reactions for UO2++, Fe++, and H+. In addition to the dynamics imparted by the transport of the acetate pulses, U(VI) behavior involves the interplay between bioreduction, which is dependent on acetate availability, and speciation-controlled surface complexation, which is dependent on pH, alkalinity and available surface complexation sites. The general difficulty of this benchmark is the large number of reactions (74), multiple rate law formulations, a multisite uranium surface complexation model, and the strong interdependency and sensitivity of the reaction processes. Results are presented for three simulators: HYDROGEOCHEM, PHT3D, and PHREEQC.« less

Fate of Uranium in Wetlands: Impact of Drought Followed by Re-flooding

NASA Astrophysics Data System (ADS)

Gilson, E.; Huang, S.; Koster van Groos, P. G.; Scheckel, K.; Peacock, A. D.; Kaplan, D. I.; Jaffe, P. R.

2014-12-01

Uranium contamination in groundwater can be mitigated in anoxic zones by iron-reducing bacteria that reduce soluble U(VI) to insoluble U(IV) and by uranium immobilization through complexation and sorption. Wetlands often link ground and surface-waters, making them strategic systems for potentially limiting migration of uranium contamination. Little is known about how drought periods that result in the drying of wetland soils, and consequent redox changes, affect uranium fate and transport in wetlands. In order to better understand the fate and stability of immobilized uranium in wetland soils, and how dry periods affect the uranium stability, we dosed saturated wetland mesocosms planted with Scirpus acutus with low levels of uranyl-acetate for 5 months before imposing a 9-day drying period followed by a 13-day rewetting period. Concentrations of uranium in mesocosm effluent increased after rewetting, but the cumulative amount of uranium released in the 13 days following the drying constituted less than 1% of the uranium immobilized in the soil during the 5 months prior to the drought. This low level of remobilization suggests that the uranium immobilized in these soils was not primarily bioreduced U(IV), which could have been oxidized to soluble U(VI) during the drought and released in the effluent during the subsequent flood. XANES analyses confirm that most of the uranium immobilized in the mesocosms was U(VI) sorbed to iron oxides. Compared to mesocosms that did not experience drying or rewetting, mesocosms that were sacrificed immediately after drying and after 13 days of rewetting had less uranium in soil near roots and more uranium on root surfaces. Metal-reducing bacteria only dominated the bacterial community after 13 days of rewetting and not immediately after drying, indicating that these bacteria are not responsible for this redistribution of uranium after the drying and rewetting. Results show that short periods of drought conditions in a wetland may impact uranium distribution, but these conditions may not cause large losses of immobilized uranium from the wetland.

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium

PubMed Central

Thorgersen, Michael P.; Lancaster, W. Andrew; Rajeev, Lara; Ge, Xiaoxuan; Vaccaro, Brian J.; Poole, Farris L.; Arkin, Adam P.; Mukhopadhyay, Aindrila

2016-01-01

ABSTRACT Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC had an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. IMPORTANCE Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Herein, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. While other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an S-layer complex. The UBC provides a potential tool for the microbiological sequestration of uranium for the cleaning of contaminated environments. PMID:27913415

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thorgersen, Michael P.; Lancaster, W. Andrew; Rajeev, Lara

Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC hadmore » an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Here in this paper, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. Finally, while other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an S-layer complex. The UBC provides a potential tool for the microbiological sequestration of uranium for the cleaning of contaminated environments.« less

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium.

PubMed

Thorgersen, Michael P; Lancaster, W Andrew; Rajeev, Lara; Ge, Xiaoxuan; Vaccaro, Brian J; Poole, Farris L; Arkin, Adam P; Mukhopadhyay, Aindrila; Adams, Michael W W

2017-02-15

Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC had an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Herein, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. While other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an S-layer complex. The UBC provides a potential tool for the microbiological sequestration of uranium for the cleaning of contaminated environments. Copyright © 2017 American Society for Microbiology.

Uranium removal from a contaminated effluent using a combined microbial and nanoparticle system.

PubMed

Baiget, Mar; Constantí, Magda; López, M Teresa; Medina, Francesc

2013-09-25

Reduction of soluble uranium(VI) to insoluble uranium(IV) for remediating a uranium-contaminated effluent (EF-03) was examined using a biotic and abiotic integrated system. Shewanella putrefaciens was first used and reduced U(VI) in a synthetic medium but not in the EF-03 effluent sample. Subsequently the growth of autochthonous microorganisms was stimulated with lactate. When lactate was supported on active carbon 77% U(VI) was removed in 4 days. Separately, iron nanoparticles that were 50 nm in diameter reduced U(VI) by 60% in 4 hours. The efficiency of uranium(VI) removal was improved to 96% in 30 min by using a system consisting of lactate and iron nanoparticles immobilized on active carbon. Lactate also stimulated the growth of potential uranium-reducing microorganisms in the EF-03 sample. This system can be efficiently used for the bioremediation of uranium-contaminated effluents. Copyright © 2013 Elsevier B.V. All rights reserved.

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonitemore » edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites (‘spillover’ effect).« less

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

DOE PAGES

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.; ...

2017-10-06

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonitemore » edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites (‘spillover’ effect).« less

Tetra- and Hexavalent Uranium Forms Bidentate-Mononuclear Complexes with Particulate Organic Matter in a Naturally Uranium-Enriched Peatland.

PubMed

Mikutta, Christian; Langner, Peggy; Bargar, John R; Kretzschmar, Ruben

2016-10-04

Peatlands frequently serve as efficient biogeochemical traps for U. Mechanisms of U immobilization in these organic matter-dominated environments may encompass the precipitation of U-bearing mineral(oid)s and the complexation of U by a vast range of (in)organic surfaces. The objective of this work was to investigate the spatial distribution and molecular binding mechanisms of U in soils of an alpine minerotrophic peatland (pH 4.7-6.6, E h = -127 to 463 mV) using microfocused X-ray fluorescence spectrometry and bulk and microfocused U L 3 -edge X-ray absorption spectroscopy. The soils contained 2.3-47.4 wt % organic C, 4.1-58.6 g/kg Fe, and up to 335 mg/kg geogenic U. Uranium was found to be heterogeneously distributed at the micrometer scale and enriched as both U(IV) and U(VI) on fibrous and woody plant debris (48 ± 10% U(IV), x̅ ± σ, n = 22). Bulk U X-ray absorption near edge structure (XANES) spectroscopy revealed that in all samples U(IV) comprised 35-68% of total U (x̅ = 50%, n = 15). Shell-fit analyses of bulk U L 3 -edge extended X-ray absorption fine structure (EXAFS) spectra showed that U was coordinated to 1.3 ± 0.2 C atoms at a distance of 2.91 ± 0.01 Å (x̅ ± σ), which implies the formation of bidentate-mononuclear U(IV/VI) complexes with carboxyl groups. We neither found evidence for U shells at ∼3.9 Å, indicative of mineral-associated U or multinuclear U(IV) species, nor for a substantial P/Fe coordination of U. Our data indicates that U(IV/VI) complexation by natural organic matter prevents the precipitation of U minerals as well as U complexation by Fe/Mn phases at our field site, and suggests that organically complexed U(IV) is formed via reduction of organic matter-bound U(VI).

Study on kinetics of adsorption of humic acid modified by ferric chloride on U(VI)

NASA Astrophysics Data System (ADS)

Zhang, Y. Y.; Lv, J. W.; Song, Y.; Dong, X. J.; Fang, Q.

2017-11-01

In order to reveal the adsorption mechanism of the ferric chloride modified humic acid on uranium, the influence of pH value and contact time of adsorption on uranium was studied through a series of batch experiments. Meanwhile, the adsorption kinetics was analyzed with pseudo-first order kinetic model and pseudo-second order kinetic model. The results show that adsorption is affected by the pH value of the solution and by contract time, and the best condition for adsorption on uranium is at pH=5 and the adsorption equilibrium time is about 80 min. Kinetics of HA-Fe adsorption on uranium accords with pseudo-second order kinetic model. The adsorption is mainly chemical adsorption, and complexes were produced by the reaction between uranium ions and the functional groups on the surface of HA-Fe, which can provide reference for further study of humic acid effecting on the migration of U(VI) in soil.

Uranium(VI) Reduction by Anaeromyxobacter dehalogenans Strain 2CP-C

PubMed Central

Wu, Qingzhong; Sanford, Robert A.; Löffler, Frank E.

2006-01-01

Previous studies demonstrated growth of Anaeromyxobacter dehalogenans strain 2CP-C with acetate or hydrogen as the electron donor and Fe(III), nitrate, nitrite, fumarate, oxygen, or ortho-substituted halophenols as electron acceptors. In this study, we explored and characterized U(VI) reduction by strain 2CP-C. Cell suspensions of fumarate-grown 2CP-C cells reduced U(VI) to U(IV). More-detailed growth studies demonstrated that hydrogen was the required electron donor for U(VI) reduction and could not be replaced by acetate. The addition of nitrate to U(VI)-reducing cultures resulted in a transitory increase in U(VI) concentration, apparently caused by the reoxidation of reduced U(IV), but U(VI) reduction resumed following the consumption of N-oxyanions. Inhibition of U(VI) reduction occurred in cultures amended with Fe(III) citrate, or citrate. In the presence of amorphous Fe(III) oxide, U(VI) reduction proceeded to completion but the U(VI) reduction rates decreased threefold compared to control cultures. Fumarate and 2-chlorophenol had no inhibitory effects on U(VI) reduction, and both electron acceptors were consumed concomitantly with U(VI). Since cocontaminants (e.g., nitrate, halogenated compounds) and bioavailable ferric iron are often encountered at uranium-impacted sites, the metabolic versatility makes Anaeromyxobacter dehalogenans a promising model organism for studying the complex interaction of multiple electron acceptors in U(VI) reduction and immobilization. PMID:16672509

Biosorption and Biomineralization of U(VI) by the Marine Bacterium Idiomarina loihiensis MAH1: Effect of Background Electrolyte and pH

PubMed Central

Morcillo, Fernando; González-Muñoz, María T.; Reitz, Thomas; Romero-González, María E.; Arias, José M.; Merroun, Mohamed L.

2014-01-01

The main goal of this study is to compare the effects of pH, uranium concentration, and background electrolyte (seawater and NaClO4 solution) on the speciation of uranium(VI) associated with the marine bacterium Idiomarina loihiensis MAH1. This was done at the molecular level using a multidisciplinary approach combining X-ray Absorption Spectroscopy (XAS), Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), and High Resolution Transmission Electron Microscopy (HRTEM). We showed that the U(VI)/bacterium interaction mechanism is highly dependent upon pH but also the nature of the used background electrolyte played a role. At neutral conditions and a U concentration ranging from 5·10−4 to 10−5 M (environmentally relevant concentrations), XAS analysis revealed that uranyl phosphate mineral phases, structurally resembling meta-autunite [Ca(UO2)2(PO4)2 2–6H2O] are precipitated at the cell surfaces of the strain MAH1. The formation of this mineral phase is independent of the background solution but U(VI) luminescence lifetime analyses demonstrated that the U(VI) speciation in seawater samples is more intricate, i.e., different complexes were formed under natural conditions. At acidic conditions, pH 2, 3 and 4.3 ([U] = 5·10−4 M, background electrolyte  = 0.1 M NaClO4), the removal of U from solution was due to biosorption to Extracellular Polysaccharides (EPS) and cell wall components as evident from TEM analysis. The L III-edge XAS and TRLFS studies showed that the biosorption process observed is dependent of pH. The bacterial cell forms a complex with U through organic phosphate groups at pH 2 and via phosphate and carboxyl groups at pH 3 and 4.3, respectively. The differences in the complexes formed between uranium and bacteria on seawater compared to NaClO4 solution demonstrates that the actinide/microbe interactions are influenced by the three studied factors, i.e., the pH, the uranium concentration and the chemical composition of the solution. PMID:24618567

Use of spectroscopic techniques for uranium(VI)/montmorillonite interaction modeling.

PubMed

Kowal-Fouchard, A; Drot, R; Simoni, E; Ehrhardt, J J

2004-03-01

To experimentally identify both clay sorption sites and sorption equilibria and to understand the retention mechanisms at a molecular level, we have characterized the structure of hexavalent uranium surface complexes resulting from the interaction between the uranyl ions and the surface retention groups of a montmorillonite clay. We have performed laser-induced fluorescence spectroscopy (LIFS) and X-ray photoelectron spectroscopy (XPS) on uranyl ion loaded montmorillonite. These structural results were then compared to those obtained from the study of uranyl ions sorbed onto an alumina and also from U(VI) sorbed on an amorphous silica. This experimental approach allowed for a clear determination of the reactive surface sites of montmorillonite for U(VI) sorption. The lifetime values and the U4f XPS spectra of uranium(VI) sorbed on montmorillonite have shown that this ion is sorbed on both exchange and edge sites. The comparison of U(VI)/clay and U(VI)/oxide systems has determined that the interaction between uranyl ions and montmorillonite edge sites occurs via both [triple bond]AlOH and [triple bond]SiOH surface groups and involves three distinct surface complexes. The surface complexation modeling of the U(VI)/montmorillonite sorption edges was determined using the constant capacitance model and the above experimental constraints. The following equilibria were found to account for the uranyl sorption mechanisms onto montmorillonite for metal concentrations ranged from 10(-6) to 10(-3) M and two ionic strengths (0.1 and 0.5 M): 2[triple bond]XNa + UO2(2+) <==> ([triple bond]X)2UO2 + 2Na+, log K0(exch) = 3.0; [triple bond]Al(OH)2 + UO2(2+) <==> [triple bond]Al(OH)2UO2(2+), log K0(Al) = 14.9; [triple bond]Si(OH)2 + UO2(2+) <==> [triple bond]SiO2UO2 + 2H+, log K0(Si1) = -3.8; and [triple bond]Si(OH)2 + 3UO2(2+) + 5H2O <==> [triple bond]SiO2(UO2)3(OH)5- + 7H+, log K0(Si2) = -20.0.

Microbial reduction of uranium

USGS Publications Warehouse

Lovley, D.R.; Phillips, E.J.P.; Gorby, Y.A.; Landa, E.R.

1991-01-01

REDUCTION of the soluble, oxidized form of uranium, U(VI), to insoluble U(IV) is an important mechanism for the immobilization of uranium in aquatic sediments and for the formation of some uranium ores1-10. U(VI) reduction has generally been regarded as an abiological reaction in which sulphide, molecular hydrogen or organic compounds function as the reductant1,2,5,11. Microbial involvement in U(VI) reduction has been considered to be limited to indirect effects, such as microbial metabolism providing the reduced compounds for abiological U(VI) reduction and microbial cell walls providing a surface to stimulate abiological U(VI) reduction1,12,13. We report here, however, that dissimilatory Fe(III)-reducing microorganisms can obtain energy for growth by electron transport to U(VI). This novel form of microbial metabolism can be much faster than commonly cited abiological mechanisms for U(VI) reduction. Not only do these findings expand the known potential terminal electron acceptors for microbial energy transduction, they offer a likely explanation for the deposition of uranium in aquatic sediments and aquifers, and suggest a method for biological remediation of environments contaminated with uranium.

Modeling the effectiveness of U(VI) biomineralization in dual-porosity porous media

NASA Astrophysics Data System (ADS)

Rotter, B. E.; Barry, D. A.; Gerhard, J. I.; Small, J. S.

2011-05-01

SummaryUranium contamination is a serious environmental concern worldwide. Recent attention has focused on the in situ immobilization of uranium by stimulation of dissimilatory metal-reducing bacteria (DMRB). The objective of this work was to investigate the effectiveness of this approach in heterogeneous and structured porous media, since such media may significantly affect the geochemical and microbial processes taking place in contaminated sites, impacting remediation efficiency during biostimulation. A biogeochemical reactive transport model was developed for uranium remediation by immobile-region-resident DMRB in two-region porous media. Simulations were used to investigate the parameter sensitivities of the system over wide-ranging geochemical, microbial and groundwater transport conditions. The results suggest that optimal biomineralization is generally likely to occur when the regional mass transfer timescale is less than one-thirtieth the value of the volumetric flux timescale, and/or the organic carbon fermentation timescale is less than one-thirtieth the value of the advective timescale, and/or the mobile region porosity ranges between equal to and four times the immobile region porosity. Simulations including U(VI) surface complexation to Fe oxides additionally suggest that, while systems exhibiting U(VI) surface complexation may be successfully remediated, they are likely to display different degrees of remediation efficiency over varying microbial efficiency, mobile-immobile mass transfer, and porosity ratios. Such information may aid experimental and field designs, allowing for optimized remediation in dual-porosity (two-region) biostimulated DMRB U(VI) remediation schemes.

Uranium(VI) interactions with mackinawite in the presence and absence of bicarbonate and oxygen.

PubMed

Gallegos, Tanya J; Fuller, Christopher C; Webb, Samuel M; Betterton, William

2013-07-02

Mackinawite, Fe(II)S, samples loaded with uranium (10(-5), 10(-4), and 10(-3) mol U/g FeS) at pH 5, 7, and 9, were characterized using X-ray absorption spectroscopy and X-ray diffraction to determine the effects of pH, bicarbonate, and oxidation on uptake. Under anoxic conditions, a 5 g/L suspension of mackinawite lowered 5 × 10(-5) M uranium(VI) to below 30 ppb (1.26 × 10(-7) M) U. Between 82 and 88% of the uranium removed from solution by mackinawite was U(IV) and was nearly completely reduced to U(IV) when 0.012 M bicarbonate was added. Near-neighbor coordination consisting of uranium-oxygen and uranium-uranium distances indicates the formation of uraninite in the presence and absence of bicarbonate, suggesting reductive precipitation as the dominant removal mechanism. Following equilibration in air, mackinawite was oxidized to mainly goethite and sulfur and about 76% of U(IV) was reoxidized to U(VI) with coordination of uranium to axial and equatorial oxygen, similar to uranyl. Additionally, uranium-iron distances, typical of coprecipitation of uranium with iron oxides, and uranium-sulfur distances indicating bidentate coordination of U(VI) to sulfate were evident. The affinity of mackinawite and its oxidation products for U(VI) provides impetus for further study of mackinawite as a potential reactive medium for remediation of uranium-contaminated water.

Post Audit of a Field Scale Reactive Transport Model of Uranium at a Former Mill Site

NASA Astrophysics Data System (ADS)

Curtis, G. P.

2015-12-01

Reactive transport of hexavalent uranium (U(VI)) in a shallow alluvial aquifer at a former uranium mill tailings site near Naturita CO has been monitored for nearly 30 years by the US Department of Energy and the US Geological Survey. Groundwater at the site has high concentrations of chloride, alkalinity and U(VI) as a owing to ore processing at the site from 1941 to 1974. We previously calibrated a multicomponent reactive transport model to data collected at the site from 1986 to 2001. A two dimensional nonreactive transport model used a uniform hydraulic conductivity which was estimated from observed chloride concentrations and tritium helium age dates. A reactive transport model for the 2km long site was developed by including an equilibrium U(VI) surface complexation model calibrated to laboratory data and calcite equilibrium. The calibrated model reproduced both nonreactive tracers as well as the observed U(VI), pH and alkalinity. Forward simulations for the period 2002-2015 conducted with the calibrated model predict significantly faster natural attenuation of U(VI) concentrations than has been observed by the persistent high U(VI) concentrations at the site. Alternative modeling approaches are being evaluating evaluated using recent data to determine if the persistence can be explained by multirate mass transfer models developed from experimental observations at the column scale(~0.2m), the laboratory tank scale (~2m), the field tracer test scale (~1-4m) or geophysical observation scale (~1-5m). Results of this comparison should provide insight into the persistence of U(VI) plumes and improved management options.

Microbial reduction of U(VI) under alkaline conditions: implications for radioactive waste geodisposal.

PubMed

Williamson, Adam J; Morris, Katherine; Law, Gareth T W; Rizoulis, Athanasios; Charnock, John M; Lloyd, Jonathan R

2014-11-18

Although there is consensus that microorganisms significantly influence uranium speciation and mobility in the subsurface under circumneutral conditions, microbiologically mediated U(VI) redox cycling under alkaline conditions relevant to the geological disposal of cementitious intermediate level radioactive waste, remains unexplored. Here, we describe microcosm experiments that investigate the biogeochemical fate of U(VI) at pH 10-10.5, using sediments from a legacy lime working site, stimulated with an added electron donor, and incubated in the presence and absence of added Fe(III) as ferrihydrite. In systems without added Fe(III), partial U(VI) reduction occurred, forming a U(IV)-bearing non-uraninite phase which underwent reoxidation in the presence of air (O2) and to some extent nitrate. By contrast, in the presence of added Fe(III), U(VI) was first removed from solution by sorption to the Fe(III) mineral, followed by bioreduction and (bio)magnetite formation coupled to formation of a complex U(IV)-bearing phase with uraninite present, which also underwent air (O2) and partial nitrate reoxidation. 16S rRNA gene pyrosequencing showed that Gram-positive bacteria affiliated with the Firmicutes and Bacteroidetes dominated in the post-reduction sediments. These data provide the first insights into uranium biogeochemistry at high pH and have significant implications for the long-term fate of uranium in geological disposal in both engineered barrier systems and the alkaline, chemically disturbed geosphere.

The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsenovich, Yelena P.; Cardona, Claudia; Lapierre, Robert

2016-10-01

Remediation of uranium in the deep unsaturated zone is a challenging task, especially in the presence of oxygenated, high-carbonate alkalinity soil and pore water composition typical for arid and semi-arid environments of the western regions of the U.S. This study evaluates the effect of various pore water constituencies on changes of uranium concentrations in alkaline conditions, created in the presence of reactive gases such as NH3 to effectively mitigate uranium contamination in the vadose zone sediments. This contaminant is a potential source for groundwater pollution through slow infiltration of soluble and highly mobile uranium species towards the water table. Themore » objective of this research was to evaluate uranium sequestration efficiencies in the alkaline synthetic pore water solutions prepared in a broad range of Si, Al, and bicarbonate concentrations typically present in field systems of the western U.S. regions and identify solid uranium-bearing phases that result from ammonia gas treatment. In previous studies (Szecsody et al. 2012; Zhong et al. 2015), although uranium mobility was greatly decreased, solid phases could not be identified at the low uranium concentrations in field-contaminated sediments. The chemical composition of the synthetic pore water used in the experiments varied for silica (5–250 mM), Al3+ (2.8 or 5 mM), HCO3- (0–100 mM) and U(VI) (0.0021–0.0084 mM) in the solution mixture. Experiment results suggested that solutions with Si concentrations higher than 50 mM exhibited greater removal efficiencies of U(VI). Solutions with higher concentrations of bicarbonate also exhibited greater removal efficiencies for Si, Al, and U(VI). Overall, the silica polymerization reaction leading to the formation of Si gel correlated with the removal of U(VI), Si, and Al from the solution. If no Si polymerization was observed, there was no U removal from the supernatant solution. Speciation modeling indicated that the dominant uranium species in the presence of bicarbonate were anionic uranyl carbonate complexes (UO2(CO3)2-2 and UO2(CO3)3-4) and in the absence of bicarbonate in the solution, U(VI) major species appeared as uranyl-hydroxide (UO2(OH)3- and UO2(OH)4-2) species. The model also predicted the formation of uranium solid phases. Uranyl carbonates as rutherfordine [UO2CO3], cejkaite [Na4(UO2)(CO3)3] and hydrated uranyl silicate phases as Na-boltwoodite [Na(UO2)(SiO4)·1.5H2O] were anticipated for most of the synthetic pore water compositions amended from medium (2.9 mM) to high (100 mM) bicarbonate concentrations.« less

Uranium(VI) interactions with mackinawite in the presence and absence of bicarbonate and oxygen

USGS Publications Warehouse

Gallegos, Tanya J.; Fuller, Christopher C.; Webb, Samuel M.; Betterton, William J.

2013-01-01

Mackinawite, Fe(II)S, samples loaded with uranium (10-5, 10-4, and 10-3 mol U/g FeS) at pH 5, 7, and 9, were characterized using X-ray absorption spectroscopy and X-ray diffraction to determine the effects of pH, bicarbonate, and oxidation on uptake. Under anoxic conditions, a 5 g/L suspension of mackinawite lowered 5 × 10-5 M uranium(VI) to below 30 ppb (1.26 × 10-7 M) U. Between 82 and 88% of the uranium removed from solution by mackinawite was U(IV) and was nearly completely reduced to U(IV) when 0.012 M bicarbonate was added. Near-neighbor coordination consisting of uranium–oxygen and uranium-uranium distances indicates the formation of uraninite in the presence and absence of bicarbonate, suggesting reductive precipitation as the dominant removal mechanism. Following equilibration in air, mackinawite was oxidized to mainly goethite and sulfur and about 76% of U(IV) was reoxidized to U(VI) with coordination of uranium to axial and equatorial oxygen, similar to uranyl. Additionally, uranium-iron distances, typical of coprecipitation of uranium with iron oxides, and uranium-sulfur distances indicating bidentate coordination of U(VI) to sulfate were evident. The affinity of mackinawite and its oxidation products for U(VI) provides impetus for further study of mackinawite as a potential reactive medium for remediation of uranium-contaminated water.

The use of halloysite functionalized with isothiouronium salts as an organic/inorganic hybrid adsorbent for uranium(VI) ions removal.

PubMed

Gładysz-Płaska, A; Majdan, M; Tarasiuk, B; Sternik, D; Grabias, E

2018-07-15

Elimination of U(VI) from nuclear wastes and from the underground water near the uranium mines is the serious problem. Therefore search for new sorbents for U(VI) is still a big challenge for the scientists. This paper investigates of U(VI) ions sorption on halloysite modified with the isothiouronium salts: S-dodecaneisothiouronium bromide (ligand 1), S,S'-dodecane-1,12-diylbis(isothiouronium bromide) (ligand 2), S-hexadecaneisothiouronium chloride (ligand 3), S,S'-naphthalene-1,4-diylbis(methylisothiouronium) dichloride (ligand 4), and S,S'-2,5-dimethylbenzene-1,4-diylbis(methylisothiouronium) dichloride (ligand 5). It was established that halloysite modified by the ligands with four nitrogen atoms in their structure (ligand-5, 2 and 4) was characterized by higher sorption capacity compared with that modified by the ligands with two donor nitrogens (ligand-1 and 3). The maximum sorption capacity of halloysite-5 toward U(VI) was 157 mg U/g and this places the modified mineral among the most effective sorbents for U(VI) removal from wastes. As follows from ATR, XPS and thermal degradation spectra of the sorption products [R-S-C(NH)(NH 2 )] n = 1-2 (UO 2 2+ ) complexes are formed on the external surface of the halloysite whereas oligomeric hydroxy complexes (UO 2 ) 3 (OH) 5 + and (UO 2 ) 4 (OH) 7 + are present in the interior of halloysite structure and interact predominantly with aluminols. Copyright © 2018 Elsevier B.V. All rights reserved.

Reduction of uranium by cytochrome c3 of Desulfovibrio vulgaris

USGS Publications Warehouse

Lovley, D.R.; Widman, P.K.; Woodward, J.C.; Phillips, E.J.P.

1993-01-01

The mechanism for U(VI) reduction by Desulfovibrio vulgaris (Hildenborough) was investigated. The H2-dependent U(VI) reductase activity in the soluble fraction of the cells was lost when the soluble fraction was passed over a cationic exchange column which extracted cytochrome c3. Addition of cytochrome c3 back to the soluble fraction that had been passed over the cationic exchange column restored the U(VI)-reducing capacity. Reduced cytochrome c3 was oxidized by U(VI), as was a c-type cytochrome(s) in whole-cell suspensions. When cytochrome c3 was combined with hydrogenase, its physiological electron donor, U(VI) was reduced in the presence of H2. Hydrogenase alone could not reduce U(VI). Rapid U(VI) reduction was followed by a subsequent slow precipitation of the U(IV) mineral uraninite. Cytochrome c3 reduced U(VI) in a uranium-contaminated surface water and groundwater. Cytochrome c3 provides the first enzyme model for the reduction and biomineralization of uranium in sedimentary environments. Furthermore, the finding that cytochrome c3 can catalyze the reductive precipitation of uranium may aid in the development of fixed-enzyme reactors and/or organisms with enhanced U(VI)-reducing capacity for the bioremediation of uranium- contaminated waters and waste streams.

Surface complexation modeling of U(VI) adsorption by aquifer sediments from a former mill tailings site at Rifle, Colorado

USGS Publications Warehouse

Hyun, S.P.; Fox, P.M.; Davis, J.A.; Campbell, K.M.; Hayes, K.F.; Long, P.E.

2009-01-01

A study of U(VI) adsorption by aquifer sediment samples from a former uranium mill tailings site at Rifle, Colorado, was conducted under oxic conditions as a function of pH, U(VI), Ca, and dissolved carbonate concentration. Batch adsorption experiments were performed using <2mm size sediment fractions, a sand-sized fraction, and artificial groundwater solutions prepared to simulate the field groundwater composition. To encompass the geochemical conditions of the alluvial aquifer at the site, the experimental conditions ranged from 6.8 ?? 10-8 to 10-5 M in [U(VI)]tot, 7.2 to 8.0 in pH, 3.0 ?? 10-3 to 6.0 ?? 10 -3 M in [Ca2+], and 0.05 to 2.6% in partial pressure of carbon dioxide. Surface area normalized U(VI) adsorption Kd values for the sand and <2 mm sediment fraction were similar, suggesting a similar reactive surface coating on both fractions. A two-site two-reaction, nonelectrostatic generalized composite surface complexation model was developed and successfully simulated the U(VI) adsorption data. The model successfully predicted U(VI) adsorption observed from a multilevel sampling well installed at the site. A comparison of the model with the one developed previously for a uranium mill tailings site at Naturita, Colorado, indicated that possible calcite nonequilibrium of dissolved calcium concentration should be evaluated. The modeling results also illustrate the importance of the range of data used in deriving the best fit model parameters. ?? 2009 American Chemical Society.

Fermentation and Hydrogen Metabolism Affect Uranium Reduction by Clostridia

DOE PAGES

Gao, Weimin; Francis, Arokiasamy J.

2013-01-01

Previously, it has been shown that not only is uranium reduction under fermentation condition common among clostridia species, but also the strains differed in the extent of their capability and the pH of the culture significantly affected uranium(VI) reduction. In this study, using HPLC and GC techniques, metabolic properties of those clostridial strains active in uranium reduction under fermentation conditions have been characterized and their effects on capability variance of uranium reduction discussed. Then, the relationship between hydrogen metabolism and uranium reduction has been further explored and the important role played by hydrogenase in uranium(VI) and iron(III) reduction by clostridiamore » demonstrated. When hydrogen was provided as the headspace gas, uranium(VI) reduction occurred in the presence of whole cells of clostridia. This is in contrast to that of nitrogen as the headspace gas. Without clostridia cells, hydrogen alone could not result in uranium(VI) reduction. In alignment with this observation, it was also found that either copper(II) addition or iron depletion in the medium could compromise uranium reduction by clostridia. In the end, a comprehensive model was proposed to explain uranium reduction by clostridia and its relationship to the overall metabolism especially hydrogen (H 2 ) production.« less

Characterization of uranium redox state in organic-rich Eocene sediments.

PubMed

Cumberland, Susan A; Etschmann, Barbara; Brugger, Joël; Douglas, Grant; Evans, Katy; Fisher, Louise; Kappen, Peter; Moreau, John W

2018-03-01

The presence of organic matter (OM) has a profound impact on uranium (U) redox cycling, either limiting or promoting the mobility of U via binding, reduction, or complexation. To understand the interactions between OM and U, we characterised U oxidation state and speciation in nine OM-rich sediment cores (18 samples), plus a lignite sample from the Mulga Rock polymetallic deposit in Western Australia. Uranium was unevenly dispersed within the analysed samples with 84% of the total U occurring in samples containing >21 wt % OM. Analyses of U speciation, including x-ray absorption spectroscopy and bicarbonate extractions, revealed that U existed predominately (∼71%) as U(VI), despite the low pH (4.5) and nominally reducing conditions within the sediments. Furthermore, low extractability by water, but high extractability by a bi-carbonate solution, indicated a strong association of U with particulate OM. The unexpectedly high proportion of U(VI) relative to U(IV) within the OM-rich sediments implies that OM itself does not readily reduce U, and the reduction of U is not a requirement for immobilizing uranium in OM-rich deposits. The fact that OM can play a significant role in limiting the mobility and reduction of U(VI) in sediments is important for both U-mining and remediation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tetra- and hexavalent uranium forms bidentate-mononuclear complexes with particulate organic matter in a naturally uranium-enriched peatland

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mikutta, Christian; Langner, Peggy; Bargar, John R.

Peatlands frequently serve as efficient biogeochemical traps for U. Mechanisms of U immobilization in these organic matter-dominated environments may encompass the precipitation of U-bearing mineral(oid)s and the complexation of U by a vast range of (in)organic surfaces. The objective of this work was to investigate the spatial distribution and molecular binding mechanisms of U in soils of an alpine minerotrophic peatland (pH 4.7–6.6, E h = –127 to 463 mV) using microfocused X-ray fluorescence spectrometry and bulk and microfocused U L 3-edge X-ray absorption spectroscopy. The soils contained 2.3–47.4 wt % organic C, 4.1–58.6 g/kg Fe, and up to 335 mg/kg geogenic U. Uranium was found to be heterogeneously distributed at the micrometer scale and enriched as both U(IV) and U(VI) on fibrous and woody plant debris (48 ± 10% U(IV),more » $$\\bar{x}$$ ± σ, n = 22). Bulk U X-ray absorption near edge structure (XANES) spectroscopy revealed that in all samples U(IV) comprised 35–68% of total U ($$\\bar{x}$$ = 50%, n = 15). Shell-fit analyses of bulk U L 3-edge extended X-ray absorption fine structure (EXAFS) spectra showed that U was coordinated to 1.3 ± 0.2 C atoms at a distance of 2.91 ± 0.01 Å ($$\\bar{x}$$ ± σ), which implies the formation of bidentate-mononuclear U(IV/VI) complexes with carboxyl groups. We neither found evidence for U shells at ~3.9 Å, indicative of mineral-associated U or multinuclear U(IV) species, nor for a substantial P/Fe coordination of U. As a result, our data indicates that U(IV/VI) complexation by natural organic matter prevents the precipitation of U minerals as well as U complexation by Fe/Mn phases at our field site, and suggests that organically complexed U(IV) is formed via reduction of organic matter-bound U(VI).« less

Tetra- and hexavalent uranium forms bidentate-mononuclear complexes with particulate organic matter in a naturally uranium-enriched peatland

DOE PAGES

Mikutta, Christian; Langner, Peggy; Bargar, John R.; ...

2016-09-16

Peatlands frequently serve as efficient biogeochemical traps for U. Mechanisms of U immobilization in these organic matter-dominated environments may encompass the precipitation of U-bearing mineral(oid)s and the complexation of U by a vast range of (in)organic surfaces. The objective of this work was to investigate the spatial distribution and molecular binding mechanisms of U in soils of an alpine minerotrophic peatland (pH 4.7–6.6, E h = –127 to 463 mV) using microfocused X-ray fluorescence spectrometry and bulk and microfocused U L 3-edge X-ray absorption spectroscopy. The soils contained 2.3–47.4 wt % organic C, 4.1–58.6 g/kg Fe, and up to 335 mg/kg geogenic U. Uranium was found to be heterogeneously distributed at the micrometer scale and enriched as both U(IV) and U(VI) on fibrous and woody plant debris (48 ± 10% U(IV),more » $$\\bar{x}$$ ± σ, n = 22). Bulk U X-ray absorption near edge structure (XANES) spectroscopy revealed that in all samples U(IV) comprised 35–68% of total U ($$\\bar{x}$$ = 50%, n = 15). Shell-fit analyses of bulk U L 3-edge extended X-ray absorption fine structure (EXAFS) spectra showed that U was coordinated to 1.3 ± 0.2 C atoms at a distance of 2.91 ± 0.01 Å ($$\\bar{x}$$ ± σ), which implies the formation of bidentate-mononuclear U(IV/VI) complexes with carboxyl groups. We neither found evidence for U shells at ~3.9 Å, indicative of mineral-associated U or multinuclear U(IV) species, nor for a substantial P/Fe coordination of U. As a result, our data indicates that U(IV/VI) complexation by natural organic matter prevents the precipitation of U minerals as well as U complexation by Fe/Mn phases at our field site, and suggests that organically complexed U(IV) is formed via reduction of organic matter-bound U(VI).« less

Characteristics of uranium biosorption from aqueous solutions on fungus Pleurotus ostreatus.

PubMed

Zhao, Changsong; Liu, Jun; Tu, Hong; Li, Feize; Li, Xiyang; Yang, Jijun; Liao, Jiali; Yang, Yuanyou; Liu, Ning; Sun, Qun

2016-12-01

Uranium(VI) biosorption from aqueous solutions was investigated in batch studies by using fungus Pleurotus ostreatus biomass. The optimal biosorption conditions were examined by investigating the reaction time, biomass dosage, pH, temperature, and uranium initial concentration. The interaction between fungus biomass and uranium was confirmed using Fourier transformed infrared (FT-IR), scanning electronic microscopy energy dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) analysis. Results exhibited that the maximum biosorption capacity of uranium on P. ostreatus was 19.95 ± 1.17 mg/g at pH 4.0. Carboxylic, amine, as well as hydroxyl groups were involved in uranium biosorption according to FT-IR analysis. The pseudo-second-order model properly evaluated the U(VI) biosorption on fungus P. ostreatus biomass. The Langmuir equation provided better fitting in comparison with Freundlich isotherm models. The obtained thermodynamic parameters suggested that biosorption is feasible, endothermic, and spontaneous. SEM-EDX and XPS were additionally conducted to comprehend the biosorption process that could be described as a complex process involving several mechanisms of physical adsorption, chemisorptions, and ion exchange. Results obtained from this work indicated that fungus P. ostreatus biomass can be used as potential biosorbent to eliminate uranium or other radionuclides from aqueous solutions.

The effect of humic acid on uranyl sorption onto bentonite at trace uranium levels.

PubMed

Ivanov, Peter; Griffiths, Tamara; Bryan, Nick D; Bozhikov, Gospodin; Dmitriev, Serguei

2012-11-01

The effect of humic acid (HA) on U(VI) sorption on bentonite was studied in batch experiments at room temperature and ambient atmosphere at a (237)U(VI) concentration of 8.4 × 10(-11) M and HA concentration of 100 mg L(-1). The distribution of U(VI) between the liquid and solid phases was studied as a function of pH and ionic strength both in the absence and presence of HA. It was shown that the uranyl sorption on bentonite is strongly dependent on pH and the presence of humics, and the effect of the addition order was negligible. In the absence of HA an enhancement in the uptake with increasing pH was observed and a sharp sorption edge was found to take place between pH 3.2 and 4.2. The presence of HA slightly increases uranium(VI) sorption at low pH and curtails it at moderate pH, compared to the absence of HA. In the basic pH range for both the presence and absence of HA the sorption of uranium is significantly reduced, which could be attributed to the formation of soluble uranyl carbonate complexes. The influence of ionic strength on U(VI) and HA uptake by bentonite were investigated in the range of 0.01-1.0 M, and while there was an enhancement in the sorption of humic acid with increasing ionic strength, no significant effect of the ionic strength on the U(VI) sorption was observed in both the absence and presence of HA.

Uranium Reduction by Fe(II) in the Presence of Montmorillonite and Nontronite.

PubMed

Tsarev, Sergey; Waite, T David; Collins, Richard N

2016-08-02

Uranium(VI) interactions with three smectites (one montmorillonite and two nontronites - NAu1 and NAu2) were examined with 0, 1, and 2 mM aqueous concentrations of Fe(II) over the pH range of 3-9.5 in a background electrolyte of 100 mM NaCl and 1 mM CaCl2 in equilibration with 400 ppmv CO2(g) ([U(VI)] = 4 μM and 0.5 g smectite/L). In the absence of Fe(II), no differences were observed in the U(VI) sorption curves for the three clay minerals. In the presence of 1 or 2 mM Fe(II), under anoxic conditions, U(VI) uptake by the smectites changed slightly between ∼pH 3 and 6; however, uranium uptake increased significantly above ∼pH 6 and was proportional to the concentration of Fe(II) added to the system, particularly at pH values >8. The uptake of Fe(II) showed a sharp edge starting from ∼pH 6.5 with 95%-100% uptake occurring at pH values >7.5, with no difference observed between the iron-rich nontronites and montmorillonite. After 3 days of reaction at pH 7.6 (i.e., above the Fe(II) "sorption" edge), U(VI) was transformed to a mixture of U(IV) and U(VI) sorption complexes, and after 14 days of reaction, 100% of the U was found to be reduced to U(IV) in the form of nanocrystalline uraninite. In contrast, U remained as sorbed species until 14 days of reaction at pH 6.5. Ferrihydrite (NAu1), lepidocrocite, and magnetite (NAu2) were detected as secondary mineralization products upon reaction of the nontronites with Fe(II) but appeared to have no effect on the partitioning or speciation of uranium.

Approaches to surface complexation modeling of Uranium(VI) adsorption on aquifer sediments

NASA Astrophysics Data System (ADS)

Davis, James A.; Meece, David E.; Kohler, Matthias; Curtis, Gary P.

2004-09-01

Uranium(VI) adsorption onto aquifer sediments was studied in batch experiments as a function of pH and U(VI) and dissolved carbonate concentrations in artificial groundwater solutions. The sediments were collected from an alluvial aquifer at a location upgradient of contamination from a former uranium mill operation at Naturita, Colorado (USA). The ranges of aqueous chemical conditions used in the U(VI) adsorption experiments (pH 6.9 to 7.9; U(VI) concentration 2.5 · 10 -8 to 1 · 10 -5 M; partial pressure of carbon dioxide gas 0.05 to 6.8%) were based on the spatial variation in chemical conditions observed in 1999-2000 in the Naturita alluvial aquifer. The major minerals in the sediments were quartz, feldspars, and calcite, with minor amounts of magnetite and clay minerals. Quartz grains commonly exhibited coatings that were greater than 10 nm in thickness and composed of an illite-smectite clay with occluded ferrihydrite and goethite nanoparticles. Chemical extractions of quartz grains removed from the sediments were used to estimate the masses of iron and aluminum present in the coatings. Various surface complexation modeling approaches were compared in terms of the ability to describe the U(VI) experimental data and the data requirements for model application to the sediments. Published models for U(VI) adsorption on reference minerals were applied to predict U(VI) adsorption based on assumptions about the sediment surface composition and physical properties (e.g., surface area and electrical double layer). Predictions from these models were highly variable, with results overpredicting or underpredicting the experimental data, depending on the assumptions used to apply the model. Although the models for reference minerals are supported by detailed experimental studies (and in ideal cases, surface spectroscopy), the results suggest that errors are caused in applying the models directly to the sediments by uncertain knowledge of: 1) the proportion and types of surface functional groups available for adsorption in the surface coatings; 2) the electric field at the mineral-water interface; and 3) surface reactions of major ions in the aqueous phase, such as Ca 2+, Mg 2+, HCO 3-, SO 42-, H 4SiO 4, and organic acids. In contrast, a semi-empirical surface complexation modeling approach can be used to describe the U(VI) experimental data more precisely as a function of aqueous chemical conditions. This approach is useful as a tool to describe the variation in U(VI) retardation as a function of chemical conditions in field-scale reactive transport simulations, and the approach can be used at other field sites. However, the semi-empirical approach is limited by the site-specific nature of the model parameters.

Approaches to surface complexation modeling of Uranium(VI) adsorption on aquifer sediments

USGS Publications Warehouse

Davis, J.A.; Meece, D.E.; Kohler, M.; Curtis, G.P.

2004-01-01

Uranium(VI) adsorption onto aquifer sediments was studied in batch experiments as a function of pH and U(VI) and dissolved carbonate concentrations in artificial groundwater solutions. The sediments were collected from an alluvial aquifer at a location upgradient of contamination from a former uranium mill operation at Naturita, Colorado (USA). The ranges of aqueous chemical conditions used in the U(VI) adsorption experiments (pH 6.9 to 7.9; U(VI) concentration 2.5 ?? 10-8 to 1 ?? 10-5 M; partial pressure of carbon dioxide gas 0.05 to 6.8%) were based on the spatial variation in chemical conditions observed in 1999-2000 in the Naturita alluvial aquifer. The major minerals in the sediments were quartz, feldspars, and calcite, with minor amounts of magnetite and clay minerals. Quartz grains commonly exhibited coatings that were greater than 10 nm in thickness and composed of an illite-smectite clay with occluded ferrihydrite and goethite nanoparticles. Chemical extractions of quartz grains removed from the sediments were used to estimate the masses of iron and aluminum present in the coatings. Various surface complexation modeling approaches were compared in terms of the ability to describe the U(VI) experimental data and the data requirements for model application to the sediments. Published models for U(VI) adsorption on reference minerals were applied to predict U(VI) adsorption based on assumptions about the sediment surface composition and physical properties (e.g., surface area and electrical double layer). Predictions from these models were highly variable, with results overpredicting or underpredicting the experimental data, depending on the assumptions used to apply the model. Although the models for reference minerals are supported by detailed experimental studies (and in ideal cases, surface spectroscopy), the results suggest that errors are caused in applying the models directly to the sediments by uncertain knowledge of: 1) the proportion and types of surface functional groups available for adsorption in the surface coatings; 2) the electric field at the mineral-water interface; and 3) surface reactions of major ions in the aqueous phase, such as Ca2+, Mg2+, HCO3-, SO42-, H4SiO4, and organic acids. In contrast, a semi-empirical surface complexation modeling approach can be used to describe the U(VI) experimental data more precisely as a function of aqueous chemical conditions. This approach is useful as a tool to describe the variation in U(VI) retardation as a function of chemical conditions in field-scale reactive transport simulations, and the approach can be used at other field sites. However, the semi-empirical approach is limited by the site-specific nature of the model parameters. ?? 2004 Elsevier Ltd.

Bioreduction of U(VI)-Phthalate to a Polymeric U(IV)-Phthalate Colloid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vazquez, G.; Dodge, C; Francis, A

2009-01-01

Phthalic acid, a ubiquitous organic ligand, formed soluble mono- and biligand complexes with a uranyl ion that was then reduced to a U(IV)-phthalate by a Clostridium species under anaerobic conditions. We confirmed the reduction of the hexavalent uranium to the tetravalent oxidation state by UV-vis absorption and X-ray absorption near edge structure spectroscopy. Sequential micro- and ultrafiltration of the solution revealed that the bioreduced uranium was present as a colloid with particles between 0.03 and 0.45 {mu}m. Analysis with extended X-ray absorption fine structure revealed the association of the reduced uranium with the phthalic acid as a repeating biligand 1:2more » U(IV):phthalic acid polymer. This is the first report of the formation of a U(IV) complexed to two phthalic acid molecules in the form of a polymeric colloid. Although it was proposed that the bioreduction and the precipitation of uranium might be an invaluable strategy to immobilize uranium in contaminated environments, our results suggest that the organic ligands present there might hinder the precipitation of the bioreduced uranium under anaerobic conditions and, thereby, enhance its environmental mobility as uranium organic complexes or colloids.« less

Using High Performance Computing to Understand Roles of Labile and Nonlabile U(VI) on Hanford 300 Area Plume Longevity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lichtner, Peter C.; Hammond, Glenn E.

Evolution of a hexavalent uranium [U(VI)] plume at the Hanford 300 Area bordering the Columbia River is investigated to evaluate the roles of labile and nonlabile forms of U(VI) on the longevity of the plume. A high fidelity, three-dimensional, field-scale, reactive flow and transport model is used to represent the system. Richards equation coupled to multicomponent reactive transport equations are solved for times up to 100 years taking into account rapid fluctuations in the Columbia River stage resulting in pulse releases of U(VI) into the river. The peta-scale computer code PFLOTRAN developed under a DOE SciDAC-2 project is employed inmore » the simulations and executed on ORNL's Cray XT5 supercomputer Jaguar. Labile U(VI) is represented in the model through surface complexation reactions and its nonlabile form through dissolution of metatorbernite used as a surrogate mineral. Initial conditions are constructed corresponding to the U(VI) plume already in place to avoid uncertainties associated with the lack of historical data for the waste stream. The cumulative U(VI) flux into the river is compared for cases of equilibrium and multirate sorption models and for no sorption. The sensitivity of the U(VI) flux into the river on the initial plume configuration is investigated. The presence of nonlabile U(VI) was found to be essential in explaining the longevity of the U(VI) plume and the prolonged high U(VI) concentrations at the site exceeding the EPA MCL for uranium.« less

Experimental and modeling study of the uranium (VI) sorption on goethite.

PubMed

Missana, Tiziana; García-Gutiérrez, Miguel; Maffiotte, Cesar

2003-04-15

Acicular goethite was synthesized in the laboratory and its main physicochemical properties (composition, microstructure, surface area, and surface charge) were analyzed as a previous step to sorption experiments. The stability of the oxide, under the conditions used in sorption studies, was also investigated. The sorption of U(VI) onto goethite was studied under O(2)- and CO(2)-free atmosphere and in a wide range of experimental conditions (pH, ionic strength, radionuclide, and solid concentration), in order to assess the validity of different surface complexation models available for the interpretation of sorption data. Three different models were used to fit the experimental data. The first two models were based on the diffuse double layer concept. The first one (Model 1) considered two different monodentate complexes with the goethite surface and the second (Model 2) a single binuclear bidentate complex. A nonelectrostatic (NE) approach was used as a third model and, in that case, the same species considered in Model 1 were used. The results showed that all the models are able to describe the sorption behavior fairly well as a function of pH, electrolyte concentration, and U(VI) concentration. However, Model 2 fails in the description of the uranium sorption behavior as a function of the sorbent concentration. This demonstrates the importance of checking the validity of any surface complexation model under the widest possible range of experimental conditions.

Persistence of uranium groundwater plumes: contrasting mechanisms at two DOE sites in the groundwater-river interaction zone.

PubMed

Zachara, John M; Long, Philip E; Bargar, John; Davis, James A; Fox, Patricia; Fredrickson, Jim K; Freshley, Mark D; Konopka, Allan E; Liu, Chongxuan; McKinley, James P; Rockhold, Mark L; Williams, Kenneth H; Yabusaki, Steve B

2013-04-01

We examine subsurface uranium (U) plumes at two U.S. Department of Energy sites that are located near large river systems and are influenced by groundwater-river hydrologic interaction. Following surface excavation of contaminated materials, both sites were projected to naturally flush remnant uranium contamination to levels below regulatory limits (e.g., 30 μg/L or 0.126 μmol/L; U.S. EPA drinking water standard), with 10 years projected for the Hanford 300 Area (Columbia River) and 12 years for the Rifle site (Colorado River). The rate of observed uranium decrease was much lower than expected at both sites. While uncertainty remains, a comparison of current understanding suggests that the two sites have common, but also different mechanisms controlling plume persistence. At the Hanford 300 A, the persistent source is adsorbed U(VI) in the vadose zone that is released to the aquifer during spring water table excursions. The release of U(VI) from the vadose zone and its transport within the oxic, coarse-textured aquifer sediments is dominated by kinetically-limited surface complexation. Modeling implies that annual plume discharge volumes to the Columbia River are small (

Persistence of uranium groundwater plumes: Contrasting mechanisms at two DOE sites in the groundwater-river interaction zone

NASA Astrophysics Data System (ADS)

Zachara, John M.; Long, Philip E.; Bargar, John; Davis, James A.; Fox, Patricia; Fredrickson, Jim K.; Freshley, Mark D.; Konopka, Allan E.; Liu, Chongxuan; McKinley, James P.; Rockhold, Mark L.; Williams, Kenneth H.; Yabusaki, Steve B.

2013-04-01

We examine subsurface uranium (U) plumes at two U.S. Department of Energy sites that are located near large river systems and are influenced by groundwater-river hydrologic interaction. Following surface excavation of contaminated materials, both sites were projected to naturally flush remnant uranium contamination to levels below regulatory limits (e.g., 30 μg/L or 0.126 μmol/L; U.S. EPA drinking water standard), with 10 years projected for the Hanford 300 Area (Columbia River) and 12 years for the Rifle site (Colorado River). The rate of observed uranium decrease was much lower than expected at both sites. While uncertainty remains, a comparison of current understanding suggests that the two sites have common, but also different mechanisms controlling plume persistence. At the Hanford 300 A, the persistent source is adsorbed U(VI) in the vadose zone that is released to the aquifer during spring water table excursions. The release of U(VI) from the vadose zone and its transport within the oxic, coarse-textured aquifer sediments is dominated by kinetically-limited surface complexation. Modeling implies that annual plume discharge volumes to the Columbia River are small (< one pore volume). At the Rifle site, slow oxidation of naturally reduced, contaminant U(IV) in the saturated zone and a continuous influx of U(VI) from natural, up-gradient sources influence plume persistence. Rate-limited mass transfer and surface complexation also control U(VI) migration velocity in the sub-oxic Rifle groundwater. Flux of U(VI) from the vadose zone at the Rifle site may be locally important, but it is not the dominant process that sustains the plume. A wide range in microbiologic functional diversity exists at both sites. Strains of Geobacter and other metal reducing bacteria are present at low natural abundance that are capable of enzymatic U(VI) reduction in localized zones of accumulated detrital organic carbon or after organic carbon amendment. Major differences between the sites include the geochemical nature of residual, contaminant U; the rates of current kinetic processes (both biotic and abiotic) influencing U(VI) solid-liquid distribution; the presence of detrital organic matter and the resulting spatial heterogeneity in microbially-driven redox properties; and the magnitude of groundwater hydrologic dynamics controlled by river-stage fluctuations, geologic structures, and aquifer hydraulic properties. The comparative analysis of these sites provides important guidance to the characterization, understanding, modeling, and remediation of groundwater contaminant plumes influenced by surface water interaction that are common world-wide.

Uranium redox transition pathways in acetate-amended sediments

USGS Publications Warehouse

Bargar, John R.; Williams, Kenneth H.; Campbell, Kate M.; Long, Philip E.; Stubbs, Joanne E.; Suvorova, Elenal I.; Lezama-Pacheco, Juan S.; Alessi, Daniel S.; Stylo, Malgorzata; Webb, Samuel M.; Davis, James A.; Giammar, Daniel E.; Blue, Lisa Y.; Bernier-Latmani, Rizlan

2013-01-01

Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobility of uranium in the environment and the accumulation of uranium in ore bodies, and inform our understanding of Earth’s geochemical history. The molecular-scale mechanistic pathways of these transitions determine the U(IV) products formed, thus influencing uranium isotope fractionation, reoxidation, and transport in sediments. Studies that improve our understanding of these pathways have the potential to substantially advance process understanding across a number of earth sciences disciplines. Detailed mechanistic information regarding uranium redox transitions in field sediments is largely nonexistent, owing to the difficulty of directly observing molecular-scale processes in the subsurface and the compositional/physical complexity of subsurface systems. Here, we present results from an in situ study of uranium redox transitions occurring in aquifer sediments under sulfate-reducing conditions. Based on molecular-scale spectroscopic, pore-scale geochemical, and macroscale aqueous evidence, we propose a biotic–abiotic transition pathway in which biomass-hosted mackinawite (FeS) is an electron source to reduce U(VI) to U(IV), which subsequently reacts with biomass to produce monomeric U(IV) species. A species resembling nanoscale uraninite is also present, implying the operation of at least two redox transition pathways. The presence of multiple pathways in low-temperature sediments unifies apparently contrasting prior observations and helps to explain sustained uranium reduction under disparate biogeochemical conditions. These findings have direct implications for our understanding of uranium bioremediation, ore formation, and global geochemical processes.

Role of U(VI) Adsorption in U(VI) Reduction by Geobacter Species.

DOE Office of Scientific and Technical Information (OSTI.GOV)

None, None

2009-03-09

Previous work had suggested that Acholeplasma palmae has a higher capacity for uranium sorption than other bacteria studied. Sorption studies were performed with cells in suspension in various solutions containing uranium and results were used to generate uranium-biosorption isotherms.

In Situ Immobilization of Uranium in Structured Porous Media (Invited)

NASA Astrophysics Data System (ADS)

Brooks, S. C.; Gu, B.; Wu, W.; Spalding, B. P.; Watson, D. B.; Jardine, P.

2009-12-01

Defense related activities have resulted in broad areas of uranium contaminated groundwater across the U. S. Department of Energy complex. For example, past waste disposal practices at the DOE’s Y-12 site generated a plume of uranium and nitrate contamination in the underlying vadose and saturated zones which extends more than 120 meters deep and thousands of meters along geologic strike. Several DOE sponsored research programs have enabled the study of multiple biotic and abiotic methods of immobilizing uranium in situ at the site. These include biostimulation of metal reducing bacteria to promote reduction of the more soluble U(VI) to the sparingly soluble U(IV) and pH manipulation to immobilize U(VI) through its interactions (e.g., sorption, coprecipitation) with incipient aluminum oxyhydroxide minerals. The application of laboratory based results to the field site must also account for (i) the structured media which can impose incomplete mixing conditions and (ii) steep geochemical gradients or transition zones which differ significantly from the typically well mixed laboratory conditions. In this presentation results of several of these studies will be reviewed and lessons learned summarized.

Behavior of Colorado Plateau uranium minerals during oxidation

USGS Publications Warehouse

Garrels, Robert Minard; Christ, C.L.

1956-01-01

Uranium occurs as U(VI) and U(IV) in minerals of the Colorado Plateau ores. The number of species containing U(VI) is large, but only two U(IV) minerals are known from the Plateau: uraninite, and oxide, and coffinite, a hydroxy-silicate. These oxidize to yield U(VI) before reacting significantly with other mineral constituents. Crystal-structure analysis has shown that U(VI) invariable occurs as uranyl ion, UO2+2. Uranyl ion may form complex carbonate or sulfate ions with resulting soluble compounds, but only in the absence of quinquevalent vanadium, arsenic, or phosphorous. In the presence of these elements in the +5 valence state, the uranyl ion is fixed in insoluble layer compounds formed by union of uranyl ion with orthovanadate, orthophosphate, or orthoarsenate. Under favorable conditions UO2+2 may react to form the relatively insoluble rutherfordine, UO2CO3, or hydrated uranyl hydroxides. These are rarely found on the Colorado Plateau as opposed to their excellent development in other uraniferous areas, a condition which is apparently related to the semiarid climate and low water table of the Plateau. Uranium may also be fixed as uranyl silicate, but little is known about minerals of this kind. In the present study emphasis has been placed on a detailing of the chemical and crystal structural changes which occur in the oxidation paragenetic sequence.

An experimental and modeling study of grain-scale uranium desorption from field-contaminated sediments and the potential influence of microporosity on mass-transfer

NASA Astrophysics Data System (ADS)

Stoliker, D.; Liu, C.; Kent, D. B.; Zachara, J. M.

2012-12-01

The aquifer below the 300-Area of the Hanford site (Richland, WA, USA) is plagued by a persistent plume of dissolved uranium (U(VI)) in excess of the Environmental Protection Agency drinking water maximum contamination level even after the removal of highly contaminated sediments. The aquifer sediments in the seasonally saturated lower vadose zone act as both a source and sink for uranium during stage changes in the nearby Columbia River. Diffusion limitation of uranium mass-transfer within these sediments has been cited as a potential cause of the plume's persistence. Equilibrium U(VI) sorption is a strong function of variable chemical conditions, especially carbonate, hydrogen, and uranyl ion activities. Field-contaminated sediments from the site require up to 1,000 hours to reach equilibrium in static batch reactors. Increases in U(VI) concentrations over longer time-scales result from changes in chemical conditions, which drive reactions with sediments that favor U(VI) desorption. Grain-scale U(VI) sorption/desorption rates are slow, likely owing to diffusion of U(VI) and other solutes through intra-granular pore domains. In order to improve understanding of the impact of intra-granular diffusion and chemical reactions controlling grain-scale U(VI) release, experiments were conducted on individual particle size fractions of a <8 mm composite of field-contaminated, lower vadose zone sediments. For each size fraction, equilibrium U(VI) sorption/desorption in static batch reactors was well-described by surface complexation models over a range of chemical conditions applicable to the field site. Desorption rates from individual size fractions in flow-through batch reactors, examined under a single set of constant chemical conditions with multiple stop-flow events, were similar for all size fractions <2 mm. Kinetic U(VI) desorption in flow-through batch reactors was modeled using a multi-rate surface complexation approach, where sorption/desorption rates were assumed to be proportional to the displacement from equilibrium and multiple diffusion domains were described with a two-parameter lognormal distribution of mass-transfer rate coefficients. Parameters describing mass transfer were the same for all size fractions <2 mm but differed for the largest (2-8 mm) size fraction. The evolution of pH, along with dissolved cation and carbonate concentrations, was modeled using equilibrium cation exchange, rate-limited calcite dissolution, aerobic respiration, and silica dissolution. Desorption and chemical reaction models calibrated with individual size fractions predicted U(VI) and chemical composition as a function of time for the bulk sediment sample. Volumes of pores less than 2.4 nm, quantified using nitrogen adsorption-desorption isotherms, were the same for all size fractions < 2 mm, nearly double that of the 2-8 mm size fraction. Similarity in the observed pore volumes and multi-rate mass-transfer parameters across all size fractions <2 mm suggest the importance of pores in this size class in controlling slow grain-scale U(VI) desorption rates. Models like these provide a means for testing the influence of grain-scale mass-transfer on the persistence of U(VI) plume at the site.

Fate and transport of uranium (VI) in weathered saprolite

DOE PAGES

Kim, Young-Jin; Brooks, Scott C.; Zhang, Fan; ...

2014-11-09

We conducted batch and column experiments to investigate sorption and transport of uranium (U) in the presence of saprolite derived from interbedded shale, limestone, and sandstone sequences. Sorption kinetics were measured at two initial concentrations (C0; 1, 10 mM) and three soil:solution ratios (Rs/w; 0.005, 0.25, 2 kg/L) at pH 4.5 (pH of the saprolite). The rate of U loss from solution (mmole/L/h) increased with increasing Rs/w. Uranium sorption exhibited a fast phase with 80% sorption in the first eight hours for all C0 and Rs/w values and a slow phase during which the reaction slowly approached (pseudo) equilibrium overmore » the next seven days. The pH-dependency of U sorption was apparent in pH sorption edges. U(VI) sorption increased over the pH range 4e6, then decreased sharply at pH > 7.5. U(VI) sorption edges were well described by a surface complexation model using calibrated parameters and the reaction network proposed by Waite et al. (1994). Sorption isotherms measured using the same Rs/w and pH values showed a solids concentration effect where U(VI) sorption capacity and affinity decreased with increasing solids concentration. Moreover, this effect may have been due to either particle aggregation or competition between U(VI) and exchangeable cations for sorption sites. The surface complexation model with calibrated parameters was able to predict the general sorption behavior relatively well, but failed to reproduce solid concentration effects, implying the importance of appropriate design if batch experiments are to be utilized for dynamic systems. Transport of U(VI) through the packed column was significantly retarded. We also conducted transport simulations using the reactive transport model HydroGeoChem (HGC) v5.0 that incorporated the surface complexation reaction network used to model the batch data. Model parameters reported by Waite et al. (1994) provided a better prediction of U transport than optimized parameters derived from our sorption edges. The results presented in this study highlight the challenges in defining appropriate conditions for batch-type experiments used to extrapolate parameters for transport models, and also underline a gap in our ability to transfer batch results to transport simulations.« less

Extracellular reduction of uranium via Geobacter conductive pili as a protective cellular mechanism.

PubMed

Cologgi, Dena L; Lampa-Pastirk, Sanela; Speers, Allison M; Kelly, Shelly D; Reguera, Gemma

2011-09-13

The in situ stimulation of Fe(III) oxide reduction by Geobacter bacteria leads to the concomitant precipitation of hexavalent uranium [U(VI)] from groundwater. Despite its promise for the bioremediation of uranium contaminants, the biological mechanism behind this reaction remains elusive. Because Fe(III) oxide reduction requires the expression of Geobacter's conductive pili, we evaluated their contribution to uranium reduction in Geobacter sulfurreducens grown under pili-inducing or noninducing conditions. A pilin-deficient mutant and a genetically complemented strain with reduced outer membrane c-cytochrome content were used as controls. Pili expression significantly enhanced the rate and extent of uranium immobilization per cell and prevented periplasmic mineralization. As a result, pili expression also preserved the vital respiratory activities of the cell envelope and the cell's viability. Uranium preferentially precipitated along the pili and, to a lesser extent, on outer membrane redox-active foci. In contrast, the pilus-defective strains had different degrees of periplasmic mineralization matching well with their outer membrane c-cytochrome content. X-ray absorption spectroscopy analyses demonstrated the extracellular reduction of U(VI) by the pili to mononuclear tetravalent uranium U(IV) complexed by carbon-containing ligands, consistent with a biological reduction. In contrast, the U(IV) in the pilin-deficient mutant cells also required an additional phosphorous ligand, in agreement with the predominantly periplasmic mineralization of uranium observed in this strain. These findings demonstrate a previously unrecognized role for Geobacter conductive pili in the extracellular reduction of uranium, and highlight its essential function as a catalytic and protective cellular mechanism that is of interest for the bioremediation of uranium-contaminated groundwater.

Characterization of the biochemical-pathway of uranium (VI) reduction in facultative anaerobic bacteria.

PubMed

Mtimunye, Phalazane J; Chirwa, Evans M N

2014-10-01

Cultures of U(VI) reducing bacteria sourced from abandoned uranium mine tailing dam were evaluated for their ability to reduce U(VI) to U(IV). The species in the cultures reduced U(VI) in solutions with initial U(VI) concentration up to 400mgL(-)(1) under a near neutral pH of 6.5. The electron flow pathway and fate of reduced species was also analysed in the individual species in order to evaluate the potential for control and optimisation of the reduction potential at the biochemical level. The results showed that U(VI) reduction in live cells was completely blocked by the NADH-dehydrogenase inhibitor, rotenone (C23H22O6), and thioredoxin inhibitor, cadmium chloride (CdCl2), showing that U(VI) reduction involves the electron flow through NADH-dehydrogenase, a primary electron donor to the electron transport respiratory (ETR) system. Mass balance analysis of uranium species aided by visual and electron microscopy suggest that most U(VI) reduction occurred on the cell surface of the isolated species. This finding indicates the possibility of easy uranium recovery for beneficial use through biological remediation. Should the U(VI) be reduced inside the cell, recovery would require complete disruption of the cells and therefore would be difficult. The study contributes new knowledge on the underlying mechanisms in the U(VI) reduction in facultative anaerobes. Copyright © 2014 Elsevier Ltd. All rights reserved.

Anaerobic bioremediation of hexavalent uranium in groundwater by reductive precipitation with methanogenic granular sludge.

PubMed

Tapia-Rodriguez, Aida; Luna-Velasco, Antonia; Field, Jim A; Sierra-Alvarez, Reyes

2010-04-01

Uranium has been responsible for extensive contamination of groundwater due to releases from mill tailings and other uranium processing waste. Past evidence has confirmed that certain bacteria can enzymatically reduce soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) under anaerobic conditions in the presence of appropriate electron donors. This paper focuses on the evaluation of anaerobic granular sludge as a source of inoculum for the bioremediation of uranium in water. Batch experiments were performed with several methanogenic anaerobic granular sludge samples and different electron donors. Abiotic controls consisting of heat-killed inoculum and non-inoculated treatments confirmed the biological removal process. In this study, unadapted anaerobic granular sludge immediately reduced U(VI), suggesting an intrinsic capacity of the sludge to support this process. The high biodiversity of anaerobic granular sludge most likely accounts for the presence of specific microorganisms capable of reducing U(VI). Oxidation by O(2) was shown to resolubilize the uranium. This observation combined with X-ray diffraction evidence of uraninite confirmed that the removal during anaerobic treatment was due to reductive precipitation. The anaerobic removal activity could be sustained after several respikes of U(VI). The U(VI) removal was feasible without addition of electron donors, indicating that the decay of endogenous biomass substrates was contributing electron equivalents to the process. Addition of electron donors, such as H(2) stimulated the removal of U(VI) to varying degrees. The stimulation was greater in sludge samples with lower endogenous substrate levels. The present work reveals the potential application of anaerobic granular sludge for continuous bioremediation schemes to treat uranium-contaminated water. Copyright (c) 2009 Elsevier Ltd. All rights reserved.

XAS and TRLIF spectroscopy of uranium and neptunium in seawater.

PubMed

Maloubier, Melody; Solari, Pier Lorenzo; Moisy, Philippe; Monfort, Marguerite; Den Auwer, Christophe; Moulin, Christophe

2015-03-28

Seawater contains radionuclides at environmental levels; some are naturally present and others come from anthropogenic nuclear activity. In this report, the molecular speciation in seawater of uranium(VI) and neptunium(V) at a concentration of 5 × 10(-5) M has been investigated for the first time using a combination of two spectroscopic techniques: Time-resolved laser-induced fluorescence (TRLIF) for U and extended X-ray absorption fine structure (EXAFS) for U and Np at the LIII edge. In parallel, the theoretical speciation of uranium and neptunium in seawater at the same concentration is also discussed and compared to spectroscopic data. The uranium complex was identified as the neutral carbonato calcic complex UO2(CO3)3Ca2, which has been previously described in other natural systems. In the case of neptunium, the complex identified is mainly a carbonato complex whose exact stoichiometry is more difficult to assess. The knowledge of the actinide molecular speciation and reactivity in seawater is of fundamental interest in the particular case of uranium recovery and more generally regarding the actinide life cycle within the biosphere in the case of accidental release. This is the first report of actinide direct speciation in seawater medium that can complement inventory data.

Supercritical Fluid Extraction and Separation of Uranium from Other Actinides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donna L. Quach; Bruce J. Mincher; Chien M. Wai

2014-06-01

This paper investigates the feasibility of separating uranium from other actinides by using supercritical fluid carbon dioxide (sc-CO2) as a solvent modified with tri-n-butylphosphate (TBP) for the development of an extraction and counter current stripping technique, which would be a more efficient and environmentally benign technology for used nuclear fuel reprocessing compared to traditional solvent extraction. Several actinides (U(VI), Np(VI), Pu(IV), and Am(III)) were extracted in sc-CO2 modified with TBP over a range of nitric acid concentrations and then the actinides were exposed to reducing and complexing agents to suppress their extractability. According to this study, the separation of uraniummore » from plutonium in sc-CO2 modified with TBP was successful at nitric acid concentrations of less than 3 M in the presence of acetohydroxamic acid or oxalic acid, and the separation of uranium from neptunium was successful at nitric acid concentrations of less than 1 M in the presence of acetohydroxamic acid, oxalic acid, or sodium nitrite.« less

Redox behavior of uranium at the nanoporous aluminum oxide-water interface: implications for uranium remediation.

PubMed

Jung, Hun Bok; Boyanov, Maxim I; Konishi, Hiromi; Sun, Yubing; Mishra, Bhoopesh; Kemner, Kenneth M; Roden, Eric E; Xu, Huifang

2012-07-03

Sorption-desorption experiments show that the majority (ca. 80-90%) of U(VI) presorbed to mesoporous and nanoporous alumina could not be released by extended (2 week) extraction with 50 mM NaHCO(3) in contrast with non-nanoporous α alumina. The extent of reduction of U(VI) presorbed to aluminum oxides was semiquantitatively estimated by comparing the percentages of uranium desorbed by anoxic sodium bicarbonate between AH(2)DS-reacted and unreacted control samples. X-ray absorption spectroscopy confirmed that U(VI) presorbed to non-nanoporous alumina was rapidly and completely reduced to nanoparticulate uraninite by AH(2)DS, whereas reduction of U(VI) presorbed to nanoporous alumina was slow and incomplete (<5% reduction after 1 week). The observed nanopore size-dependent redox behavior of U has important implications in developing efficient remediation techniques for the subsurface uranium contamination because the efficiency of in situ bioremediation depends on how effectively and rapidly U(VI) bound to sediment or soil can be converted to an immobile phase.

Non-enzymatic U(VI) interactions with biogenic mackinawite

NASA Astrophysics Data System (ADS)

Veeramani, H.; Qafoku, N. P.; Kukkadapu, R. K.; Murayama, M.; Hochella, M. F.

2011-12-01

Reductive immobilization of hexavalent uranium [U(VI)] by stimulation of dissimilatory metal and/or sulfate reducing bacteria (DMRB or DSRB) has been extensively researched as a remediation strategy for subsurface U(VI) contamination. These bacteria derive energy by reducing oxidized metals as terminal electron acceptors, often utilizing organic substrates as electron donors. Thus, when evaluating the potential for in-situ uranium remediation in heterogeneous subsurface media, it is important to understand how the presence of alternative electron acceptors such as Fe(III) and sulfate affect U(VI) remediation and the long term behavior and reactivity of reduced uranium. Iron, an abundant subsurface element, represents a substantial sink for electrons from DMRB, and the reduction of Fe(III) leads to the formation of dissolved Fe(II) or to reactive biogenic Fe(II)- and mixed Fe(II)/Fe(III)- mineral phases. Consequently, abiotic U(VI) reduction by reactive forms of biogenic Fe(II) minerals could be a potentially important process for uranium immobilization. In our study, the DMRB Shewanella putrefaciens CN32 was used to synthesize a biogenic Fe(II)-bearing sulfide mineral: mackinawite, that has been characterized by XRD, SEM, HRTEM and Mössbauer spectroscopy. Batch experiments involving treated biogenic mackinawite and uranium (50:1 molar ratio) were carried out at room temperature under strict anoxic conditions. Following complete removal of uranium from solution, the biogenic mackinawite was analyzed by a suite of analytical techniques including XAS, HRTEM and Mössbauer spectroscopy to determine the speciation of uranium and investigate concomitant Fe(II)-phase transformation. Determining the speciation of uranium is critical to success of a remediation strategy. The present work elucidates non-enzymatic/abiotic molecular scale redox interactions between biogenic mackinawite and uranium.

Extraction of U(VI) from oxalate solutions using tetradecylammonium oxalate (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuzina, M.G.; Lipovskii, A.A.

1973-07-01

The extraction of U(VI) from oxalate solutions at various pH values was studied. It was shown that, as a function of the extractant and uranium concentration ratios, the latter was extracted in the form of different acido and hydroxyacido complexes. With excess extractant, the compounds were (R/sub 4/N)/ sub 2/UO/sub 2/Ox/sub 2/ at lo w pH values of the aqueous solution and (R/sub 4/ N)/sub 2/UO/sub 2/Ox(OH)/sub 2/ at h igh values. When there was a deficit of the extractant, different hydroxyacido complexes were formed. (tr-auth)

Microbial reduction of uranium (VI) by Bacillus sp. dwc-2: A macroscopic and spectroscopic study.

PubMed

Li, Xiaolong; Ding, Congcong; Liao, Jiali; Du, Liang; Sun, Qun; Yang, Jijun; Yang, Yuanyou; Zhang, Dong; Tang, Jun; Liu, Ning

2017-03-01

The microbial reduction of U(VI) by Bacillus sp. dwc-2, isolated from soil in Southwest China, was explored using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). Our studies indicated that approximately 16.0% of U(VI) at an initial concentration of 100mg/L uranium nitrate could be reduced by Bacillus sp. dwc-2 at pH8.2 under anaerobic conditions at room temperature. Additionally, natural organic matter (NOM) played an important role in enhancing the bioreduction of U(VI) by Bacillus sp. dwc-2. XPS results demonstrated that the uranium presented mixed valence states (U(VI) and U(IV)) after bioreduction, which was subsequently confirmed by XANES. Furthermore, the TEM and high resolution transmission electron microscopy (HRTEM) analysis suggested that the reduced uranium was bioaccumulated mainly within the cell and as a crystalline structure on the cell wall. These observations implied that the reduction of uranium may have a significant effect on its fate in the soil environment in which these bacterial strains occur. Copyright © 2016. Published by Elsevier B.V.

Technical Basis for Assessing Uranium Bioremediation Performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

PE Long; SB Yabusaki; PD Meyer

2008-04-01

In situ bioremediation of uranium holds significant promise for effective stabilization of U(VI) from groundwater at reduced cost compared to conventional pump and treat. This promise is unlikely to be realized unless researchers and practitioners successfully predict and demonstrate the long-term effectiveness of uranium bioremediation protocols. Field research to date has focused on both proof of principle and a mechanistic level of understanding. Current practice typically involves an engineering approach using proprietary amendments that focuses mainly on monitoring U(VI) concentration for a limited time period. Given the complexity of uranium biogeochemistry and uranium secondary minerals, and the lack of documentedmore » case studies, a systematic monitoring approach using multiple performance indicators is needed. This document provides an overview of uranium bioremediation, summarizes design considerations, and identifies and prioritizes field performance indicators for the application of uranium bioremediation. The performance indicators provided as part of this document are based on current biogeochemical understanding of uranium and will enable practitioners to monitor the performance of their system and make a strong case to clients, regulators, and the public that the future performance of the system can be assured and changes in performance addressed as needed. The performance indicators established by this document and the information gained by using these indicators do add to the cost of uranium bioremediation. However, they are vital to the long-term success of the application of uranium bioremediation and provide a significant assurance that regulatory goals will be met. The document also emphasizes the need for systematic development of key information from bench scale tests and pilot scales tests prior to full-scale implementation.« less

In-situ evidence for uranium immobilization and remobilization

USGS Publications Warehouse

Senko, John M.; Istok, Jonathan D.; Suflita, Joseph M.; Krumholz, Lee R.

2002-01-01

The in-situ microbial reduction and immobilization of uranium was assessed as a means of preventing the migration of this element in the terrestrial subsurface. Uranium immobilization (putatively identified as reduction) and microbial respiratory activities were evaluated in the presence of exogenous electron donors and acceptors with field push−pull tests using wells installed in an anoxic aquifer contaminated with landfill leachate. Uranium(VI) amended at 1.5 μM was reduced to less than 1 nM in groundwater in less than 8 d during all field experiments. Amendments of 0.5 mM sulfate or 5 mM nitrate slowed U(VI) immobilization and allowed for the recovery of 10% and 54% of the injected element, respectively, as compared to 4% in the unamended treatment. Laboratory incubations confirmed the field tests and showed that the majority of the U(VI) immobilized was due to microbial reduction. In these tests, nitrate treatment (7.5 mM) inhibited U(VI) reduction, and nitrite was transiently produced. Further push−pull tests were performed in which either 1 or 5 mM nitrate was added with 1.0 μM U(VI) to sediments that already contained immobilized uranium. After an initial loss of the amendments, the concentration of soluble U(VI) increased and eventually exceeded the injected concentration, indicating that previously immobilized uranium was remobilized as nitrate was reduced. Laboratory experiments using heat-inactivated sediment slurries suggested that the intermediates of dissimilatory nitrate reduction (denitrification or dissimilatory nitrate reduction to ammonia), nitrite, nitrous oxide, and nitric oxide were all capable of oxidizing and mobilizing U(IV). These findings indicate that in-situ subsurface U(VI) immobilization can be expected to take place under anaerobic conditions, but the permanence of the approach can be impaired by disimilatory nitrate reduction intermediates that can mobilize previously reduced uranium.

Comparative study of uranyl(VI) and -(V) carbonato complexes in an aqueous solution.

PubMed

Ikeda, Atsushi; Hennig, Christoph; Tsushima, Satoru; Takao, Koichiro; Ikeda, Yasuhisa; Scheinost, Andreas C; Bernhard, Gert

2007-05-14

Electrochemical, complexation, and electronic properties of uranyl(VI) and -(V) carbonato complexes in an aqueous Na2CO3 solution have been investigated to define the appropriate conditions for preparing pure uranyl(V) samples and to understand the difference in coordination character between UO22+ and UO2+. Cyclic voltammetry using three different working electrodes of platinum, gold, and glassy carbon has suggested that the electrochemical reaction of uranyl(VI) carbonate species proceeds quasi-reversibly. Electrolysis of UO22+ has been performed in Na2CO3 solutions of more than 0.8 M with a limited pH range of 11.7 < pH < 12.0 using a platinum mesh electrode. It produces a high purity of the uranyl(V) carbonate solution, which has been confirmed to be stable for at least 2 weeks in a sealed glass cuvette. Extended X-ray absorption fine structure (EXAFS) measurements revealed the structural arrangement of uranyl(VI) and -(V) tricarbonato complexes, [UO2(CO3)3]n- [n = 4 for uranyl(VI), 5 for uranyl(V)]. The bond distances of U-Oax, U-Oeq, U-C, and U-Odist are determined to be 1.81, 2.44, 2.92, and 4.17 A for the uranyl(VI) complex and 1.91, 2.50, 2.93, and 4.23 A for the uranyl(V) complex, respectively. The validity of the structural parameters obtained from EXAFS has been supported by quantum chemical calculations for the uranyl(VI) complex. The uranium LI- and LIII-edge X-ray absorption near-edge structure spectra have been interpreted in terms of electron transitions and multiple-scattering features.

Biogenic formation and growth of uraninite (UO₂).

PubMed

Lee, Seung Yeop; Baik, Min Hoon; Choi, Jong Won

2010-11-15

Biogenic UO₂ (uraninite) nanocrystals may be formed as a product of a microbial reduction process in uranium-enriched environments near the Earth's surface. We investigated the size, nanometer-scale structure, and aggregation state of UO₂ formed by iron-reducing bacterium, Shewanella putrefaciens CN32, from a uranium-rich solution. Characterization of biogenic UO₂ precipitates by high-resolution transmission electron microscopy (HRTEM) revealed that the UO₂ nanoparticles formed were highly aggregated by organic polymers. Nearly all of the nanocrystals were networked in more or less 100 nm diameter spherical aggregates that displayed some concentric UO₂ accumulation with heterogeneity. Interestingly, pure UO₂ nanocrystals were piled on one another at several positions via UO₂-UO₂ interactions, which seem to be intimately related to a specific step in the process of growing large single crystals. In the process, calcium that was easily complexed with aqueous uranium(VI) appeared not to be combined with bioreduced uranium(IV), probably due to its lower binding energy. However, when phosphate was added to the system, calcium was found to be easily associated with uranium(IV), forming a new uranium phase, ningyoite. These results will extend the limited knowledge of microbial uraniferous mineralization and may provide new insights into the fate of aqueous uranium complexes.

Solid phase extraction of uranium(VI) onto benzoylthiourea-anchored activated carbon.

PubMed

Zhao, Yongsheng; Liu, Chunxia; Feng, Miao; Chen, Zhen; Li, Shuqiong; Tian, Gan; Wang, Li; Huang, Jingbo; Li, Shoujian

2010-04-15

A new solid phase extractant selective for uranium(VI) based on benzoylthiourea anchored to activated carbon was developed via hydroxylation, amidation and reaction with benzoyl isothiocyanate in sequence. Fourier transform infrared spectroscopy and total element analysis proved that benzoylthiourea had been successfully grafted to the surface of the activated carbon, with a loading capacity of 1.2 mmol benzoylthiourea per gram of activated carbon. The parameters that affect the uranium(VI) sorption, such as contact time, solution pH, initial uranium(VI) concentration, adsorbent dose and temperature, have been investigated. Results have been analyzed by Langmuir and Freundlich isotherm; the former was more suitable to describe the sorption process. The maximum sorption capacity (82 mg/g) for uranium(VI) was obtained at experimental conditions. The rate constant for the uranium sorption by the as-synthesized extractant was 0.441 min(-1) from the first order rate equation. Thermodynamic parameters (DeltaH(0)=-46.2 kJ/mol; DeltaS(0)=-98.0 J/mol K; DeltaG(0)=-17.5 kJ/mol) showed the adsorption of an exothermic process and spontaneous nature, respectively. Additional studies indicated that the benzoylthiourea-anchored activated carbon (BT-AC) selectively sorbed uranyl ions in the presence of competing ions, Na(+), Co(2+), Sr(2+), Cs(+) and La(3+). 2009 Elsevier B.V. All rights reserved.

Uranium Biominerals Precipitated by an Environmental Isolate of Serratia under Anaerobic Conditions.

PubMed

Newsome, Laura; Morris, Katherine; Lloyd, Jonathan R

2015-01-01

Stimulating the microbially-mediated precipitation of uranium biominerals may be used to treat groundwater contamination at nuclear sites. The majority of studies to date have focussed on the reductive precipitation of uranium as U(IV) by U(VI)- and Fe(III)-reducing bacteria such as Geobacter and Shewanella species, although other mechanisms of uranium removal from solution can occur, including the precipitation of uranyl phosphates via bacterial phosphatase activity. Here we present the results of uranium biomineralisation experiments using an isolate of Serratia obtained from a sediment sample representative of the Sellafield nuclear site, UK. When supplied with glycerol phosphate, this Serratia strain was able to precipitate 1 mM of soluble U(VI) as uranyl phosphate minerals from the autunite group, under anaerobic and fermentative conditions. Under phosphate-limited anaerobic conditions and with glycerol as the electron donor, non-growing Serratia cells could precipitate 0.5 mM of uranium supplied as soluble U(VI), via reduction to nano-crystalline U(IV) uraninite. Some evidence for the reduction of solid phase uranyl(VI) phosphate was also observed. This study highlights the potential for Serratia and related species to play a role in the bioremediation of uranium contamination, via a range of different metabolic pathways, dependent on culturing or in situ conditions.

Uranium Biominerals Precipitated by an Environmental Isolate of Serratia under Anaerobic Conditions

PubMed Central

Newsome, Laura; Morris, Katherine; Lloyd, Jonathan. R.

2015-01-01

Stimulating the microbially-mediated precipitation of uranium biominerals may be used to treat groundwater contamination at nuclear sites. The majority of studies to date have focussed on the reductive precipitation of uranium as U(IV) by U(VI)- and Fe(III)-reducing bacteria such as Geobacter and Shewanella species, although other mechanisms of uranium removal from solution can occur, including the precipitation of uranyl phosphates via bacterial phosphatase activity. Here we present the results of uranium biomineralisation experiments using an isolate of Serratia obtained from a sediment sample representative of the Sellafield nuclear site, UK. When supplied with glycerol phosphate, this Serratia strain was able to precipitate 1 mM of soluble U(VI) as uranyl phosphate minerals from the autunite group, under anaerobic and fermentative conditions. Under phosphate-limited anaerobic conditions and with glycerol as the electron donor, non-growing Serratia cells could precipitate 0.5 mM of uranium supplied as soluble U(VI), via reduction to nano-crystalline U(IV) uraninite. Some evidence for the reduction of solid phase uranyl(VI) phosphate was also observed. This study highlights the potential for Serratia and related species to play a role in the bioremediation of uranium contamination, via a range of different metabolic pathways, dependent on culturing or in situ conditions. PMID:26132209

Effect of phosphate on U(VI) sorption to montmorillonite: Ternary complexation and precipitation barriers

NASA Astrophysics Data System (ADS)

Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh S.; Giammar, Daniel E.; Catalano, Jeffrey G.

2016-02-01

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated. Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface.

Complexation of Uranium by Cells and S-Layer Sheets of Bacillus sphaericus JG-A12

PubMed Central

Merroun, Mohamed L.; Raff, Johannes; Rossberg, André; Hennig, Christoph; Reich, Tobias; Selenska-Pobell, Sonja

2005-01-01

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) possessing an ability to bind uranium and other heavy metals. Purified and recrystallized S-layer proteins were shown to be phosphorylated by phosphoprotein-specific staining, inductive coupled plasma mass spectrometry analysis, and a colorimetric method. We used extended X-ray absorption fine-structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-layer sheets of B. sphaericus JG-A12. In addition, we investigated the complexation of uranium by the vegetative bacterial cells. The EXAFS analysis demonstrated that in all samples studied, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.88 ± 0.02 Å and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.62 ± 0.02 Å. Transmission electron microscopy showed that the uranium accumulated by the cells of this strain is located in dense deposits at the cell surface. PMID:16151146

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits

NASA Astrophysics Data System (ADS)

Bhattacharyya, Amrita; Campbell, Kate M.; Kelly, Shelly D.; Roebbert, Yvonne; Weyer, Stefan; Bernier-Latmani, Rizlan; Borch, Thomas

2017-06-01

Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U(VI)) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U(IV) generated through biologically mediated U(VI) reduction is the predominant U(IV) species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (~58-89%) of U is bound as U(IV) to C-containing organic functional groups or inorganic carbonate, while uraninite and U(VI) represent only minor components. The uranium deposit exhibited mostly 238U-enriched isotope signatures, consistent with largely biotic reduction of U(VI) to U(IV). This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U(IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment.

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits

PubMed Central

Bhattacharyya, Amrita; Campbell, Kate M.; Kelly, Shelly D.; Roebbert, Yvonne; Weyer, Stefan; Bernier-Latmani, Rizlan; Borch, Thomas

2017-01-01

Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U(VI)) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U(IV) generated through biologically mediated U(VI) reduction is the predominant U(IV) species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (∼58-89%) of U is bound as U(IV) to C-containing organic functional groups or inorganic carbonate, while uraninite and U(VI) represent only minor components. The uranium deposit exhibited mostly 238U-enriched isotope signatures, consistent with largely biotic reduction of U(VI) to U(IV). This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U(IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment. PMID:28569759

Biogenic non-crystalline U (IV) revealed as major component in uranium ore deposits

DOE PAGES

Bhattacharyya, Amrita; Campbell, Kate M.; Kelly, Shelly D.; ...

2017-06-01

Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U (VI)) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U (IV) generated through biologically mediated U (VI) reduction is the predominant U (IV) species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (~58-89%) of U is bound as U (IV) to C-containing organic functional groups or inorganic carbonate, while uraninite and U (VI) represent only minor components. The uranium deposit exhibited mostly 238U-enriched isotopemore » signatures, consistent with largely biotic reduction of U (VI) to U (IV). This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U (IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment.« less

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits.

PubMed

Bhattacharyya, Amrita; Campbell, Kate M; Kelly, Shelly D; Roebbert, Yvonne; Weyer, Stefan; Bernier-Latmani, Rizlan; Borch, Thomas

2017-06-01

Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U (VI) ) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U (IV)  generated through biologically mediated U (VI)  reduction is the predominant U (IV)  species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (∼58-89%) of U is bound as U (IV) to C-containing organic functional groups or inorganic carbonate, while uraninite and U (VI) represent only minor components. The uranium deposit exhibited mostly 238 U-enriched isotope signatures, consistent with largely biotic reduction of U (VI) to U (IV) . This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U (IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment.

Biogenic non-crystalline U (IV) revealed as major component in uranium ore deposits

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharyya, Amrita; Campbell, Kate M.; Kelly, Shelly D.

Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U (VI)) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U (IV) generated through biologically mediated U (VI) reduction is the predominant U (IV) species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (~58-89%) of U is bound as U (IV) to C-containing organic functional groups or inorganic carbonate, while uraninite and U (VI) represent only minor components. The uranium deposit exhibited mostly 238U-enriched isotopemore » signatures, consistent with largely biotic reduction of U (VI) to U (IV). This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U (IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment.« less

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits

USGS Publications Warehouse

Bhattacharyya, Amrita; Campbell, Kate M.; Kelly, Shelly; Roebbert, Yvonne; Weyer, Stefan; Bernier-Latmani, Rizlan; Borch, Thomas

2017-01-01

Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U(VI)) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U(IV) generated through biologically mediated U(VI) reduction is the predominant U(IV) species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (∼58-89%) of U is bound as U(IV)to C-containing organic functional groups or inorganic carbonate, while uraninite and U(VI) represent only minor components. The uranium deposit exhibited mostly 238U-enriched isotope signatures, consistent with largely biotic reduction of U(VI) to U(IV). This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U(IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment.

Mechanism of uranium (VI) removal by two anaerobic bacterial communities.

PubMed

Martins, Mónica; Faleiro, Maria Leonor; da Costa, Ana M Rosa; Chaves, Sandra; Tenreiro, Rogério; Matos, António Pedro; Costa, Maria Clara

2010-12-15

The mechanism of uranium (VI) removal by two anaerobic bacterial consortia, recovered from an uncontaminated site (consortium A) and other from an uranium mine (consortium U), was investigated. The highest efficiency of U (VI) removal by both consortia (97%) occurred at room temperature and at pH 7.2. Furthermore, it was found that U (VI) removal by consortium A occurred by enzymatic reduction and bioaccumulation, while the enzymatic process was the only mechanism involved in metal removal by consortium U. FTIR analysis suggested that after U (VI) reduction, U (IV) could be bound to carboxyl, phosphate and amide groups of bacterial cells. Phylogenetic analysis of 16S rRNA showed that community A was mainly composed by bacteria closely related to Sporotalea genus and Rhodocyclaceae family, while community U was mainly composed by bacteria related to Clostridium genus and Rhodocyclaceae family. Copyright © 2010 Elsevier B.V. All rights reserved.

Highly Efficient Interception and Precipitation of Uranium(VI) from Aqueous Solution by Iron-Electrocoagulation Combined with Cooperative Chelation by Organic Ligands.

PubMed

Li, Peng; Zhun, Bao; Wang, Xuegang; Liao, PingPing; Wang, Guanghui; Wang, Lizhang; Guo, Yadan; Zhang, Weimin

2017-12-19

A new strategy combining iron-electrocoagulation and organic ligands (OGLs) cooperative chelation was proposed to screen and precipitate low concentrations (0-18.52 μmol/L) of uranium contaminant in aqueous solution. We hypothesized that OGLs with amino, hydroxyl, and carboxyl groups hydrophobically/hydrophilically would realize precuring of uranyl ion at pH < 3.0, and the following iron-electrocoagulation would achieve faster and more efficient uranium precipitation. Experimentally, the strategy demonstrated highly efficient uranium(VI) precipitation efficiency, especially with hydrophilic macromolecular OGLs. The uranium removal efficiency at optimized experimental condition reached 99.65%. The decrease of zeta potential and the lattice enwrapping between U-OGLs chelates and flocculation precursor were ascribed to the enhanced uranium precipitation activity. Uranium was precipitated as oxides of U(VI) or higher valences that were easily captured in aggregated micelles under low operation current potential. The actual uranium tailing wastewater was treated, and a satisfied uranium removal efficiency of 99.02% was discovered. After elution of the precipitated flocs, a concentrated uranium solution (up to 106.52 μmol/L) with very few other metallic impurities was obtained. Therefore, the proposed strategy could remove uranium and concentrate it concurrently. This work could provide new insights into the purification and recovery of uranium from aqueous solutions in a cost-effective and environmentally friendly process.

Spectroscopic Evidence of Uranium Immobilization in Acidic ...

EPA Pesticide Factsheets

Biogeochemistry of uranium in wetlands plays important roles in U immobilization in storage ponds of U mining and processing facilities but has not been well understood. The objective of this work was to study molecular mechanisms responsible for high U retention by Savannah River Site (SRS) wetland sediments under varying redox and acidic (pH = 2.6-5.8) conditions using U L3-edge X-ray absorption spectroscopy. Uranium in the SRS wetland sediments existed primarily as U(VI) bonded as a bidentate to carboxylic sites (U-C bond distance at ~2.88 Å), rather than phenolic or other sites of natural organic matter (NOM). In microcosms simulating the SRS wetland process, U immobilization on roots was 2 orders of magnitude higher than on the adjacent brown or more distant white sands in which U was U(VI). Uranium on the roots were both U(IV) and U(VI), which were bonded as a bidentate to carbon, but the U(VI) may also form a U phosphate mineral. After 140 days of air exposure, all U(IV) was reoxidized to U(VI) but remained as a bidentate bonding to carbon. This study demonstrated NOM and plant roots can highly immobilize U(VI) in the SRS acidic sediments, which has significant implication on the long-term stewardship of U-contaminated wetlands. There were several former U processing facilities at the Savannah River Site (SRS), Aiken, SC. As a result of their operations, uranium has entered the surrounding environments. For example, approximately 45,000 kg o

Sustained removal of uranium from contaminated groundwater following stimulation of dissimilatory metal reduction.

PubMed

N'Guessan, A Lucie; Vrionis, Helen A; Resch, Charles T; Long, Philip E; Lovley, Derek R

2008-04-15

Previous field studies on in situ bioremediation of uranium-contaminated groundwater in an aquifer in Rifle, Colorado identified two distinct phases following the addition of acetate to stimulate microbial respiration. In phase I, Geobacter species are the predominant organisms, Fe(III) is reduced, and microbial reduction of soluble U(VI) to insoluble U(IV) removes uranium from the groundwater. In phase II, Fe(III) is depleted, sulfate is reduced, and sulfate-reducing bacteria predominate. Long-term monitoring revealed an unexpected third phase during which U(VI) removal continues even after acetate additions are stopped. All three of these phases were successfully reproduced in flow-through sediment columns. When sediments from the third phase were heat sterilized, the capacity for U(VI) removal was lost. In the live sediments U(VI) removed from the groundwater was recovered as U(VI) in the sediments. This contrasts to the recovery of U(IV) in sediments resulting from the reduction of U(VI) to U(IV) during the Fe(III) reduction phase in acetate-amended sediments. Analysis of 16S rRNA gene sequences in the sediments in which U(VI) was being adsorbed indicated that members of the Firmicutes were the predominant organisms whereas no Firmicutes sequences were detected in background sediments which did not have the capacity to sorb U(VI), suggesting that the U(VI) adsorption might be due to the presence of these living organisms or at least their intact cell components. This unexpected enhanced adsorption of U(VI) onto sediments following the stimulation of microbial growth in the subsurface may potentially enhance the cost effectiveness of in situ uranium bioremediation.

Reduction of uranium by Desulfovibrio desulfuricans

USGS Publications Warehouse

Lovley, D.R.; Phillips, E.J.P.

1992-01-01

The possibility that sulfate-reducing microorganisms contribute to U(VI) reduction in sedimentary environments was investigated. U(VI) was reduced to U(IV) when washed cells of sulfate-grown Desulfovibrio desulfuricans were suspended in a bicarbonate buffer with lactate or H2 as the electron donor. There was no U(VI) reduction in the absence of an electron donor or when the cells were killed by heat prior to the incubation. The rates of U(VI) reduction were comparable to those in respiratory Fe(III)-reducing microorganisms. Azide or prior exposure of the cells to air did not affect the ability of D. desulfuricans to reduce U(VI). Attempts to grow D. desulfuricans with U(VI) as the electron acceptor were unsuccessful. U(VI) reduction resulted in the extracellular precipitation of the U(IV) mineral uraninite. The presence of sulfate had no effect on the rate of U(VI) reduction. Sulfate and U(VI) were reduced simultaneously. Enzymatic reduction of U(VI) by D. desulfuricans was much faster than nonenzymatic reduction of U(VI) by sulfide, even when cells of D. desulfuricans were added to provide a potential catalytic surface for the nonenzymatic reaction. The results indicate that enzymatic U(VI) reduction by sulfate-reducing microorganisms may be responsible for the accumulation of U(IV) in sulfidogenic environments. Furthermore, since the reduction of U(VI) to U(IV) precipitates uranium from solution, D. desulfuricans might be a useful organisms for recovering uranium from contaminated waters and waste streams.

Incorporation of Uranium into Hematite during Crystallization from Ferrihydrite

PubMed Central

2014-01-01

Ferrihydrite was exposed to U(VI)-containing cement leachate (pH 10.5) and aged to induce crystallization of hematite. A combination of chemical extractions, TEM, and XAS techniques provided the first evidence that adsorbed U(VI) (≈3000 ppm) was incorporated into hematite during ferrihydrite aggregation and the early stages of crystallization, with continued uptake occurring during hematite ripening. Analysis of EXAFS and XANES data indicated that the U(VI) was incorporated into a distorted, octahedrally coordinated site replacing Fe(III). Fitting of the EXAFS showed the uranyl bonds lengthened from 1.81 to 1.87 Å, in contrast to previous studies that have suggested that the uranyl bond is lost altogether upon incorporation into hematite. The results of this study both provide a new mechanistic understanding of uranium incorporation into hematite and define the nature of the bonding environment of uranium within the mineral structure. Immobilization of U(VI) by incorporation into hematite has clear and important implications for limiting uranium migration in natural and engineered environments. PMID:24580024

Investigation on Microbial Dissolution of Uranium (VI) from Autunite Mineral - 13421

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sepulveda, Paola; Katsenovich, Yelena; Lagos, Leonel

2013-07-01

Precipitating autunite minerals by polyphosphate injection was identified as a feasible remediation strategy for sequestering uranium in contaminated groundwater and soil in situ at the Hanford Site. Autunite stability under vadose and saturated zone environmental conditions can help to determine the long-term effectiveness of this remediation strategy. The Arthrobacter bacteria are one of the most common groups in soils and are found in large numbers in Hanford soil as well as other subsurface environments contaminated with radionuclides. Ubiquitous in subsurface microbial communities, these bacteria can play a significant role in the dissolution of minerals and the formation of secondary minerals.more » The main objective of this investigation was to study the bacterial interactions under oxidizing conditions with uranium (VI); study the potential role of bicarbonate, which is an integral complexing ligand for U(VI) and a major ion in groundwater compositions; and present data from autunite dissolution experiments using Arthrobacter strain G968, a less U(VI)-tolerant strain. Sterile 100 mL glass mixed reactors served as the major bioreactor for initial experimentation. These autunite-containing bioreactors were injected with bacterial cells after the autunite equilibrated with the media solution amended with 0 mM, 3 mM 5 mM and 10 mM concentrations of bicarbonate. G968 Arthrobacter cells in the amount of 10{sup 6} cells/mL were injected into the reactors after 27 days, giving time for the autunite to reach steady state. Abiotic non-carbonate controls were kept without bacterial inoculation to provide a control for the biotic samples. Samples of the solution were analyzed for dissolved U(VI) by means of kinetic phosphorescence analyzer KPA-11 (Chemcheck Instruments, Richland, WA). Analysis showed that as [HCO{sub 3}{sup -}] increases, a diminishing trend on the effect of bacteria on autunite leaching is observed. Viability of cells was conducted after 24 hours of cell incubation with the appropriate uranium and bicarbonate concentration treatment. As expected, the cells started to reduce after day 41 due to the nutritional exhaustion of the media. Moreover, viable bacteria accounted for more than 94% in the presence of 10 mM bicarbonate. Experiments showed that despite differences between the G975 and the G968 bacterial strains resistance to U(VI), in the presence of bicarbonate ions they are able to dissolute uranium from autunite mineral at the same capacity. The effect of both bacterial strains on autunite dissolution is reduced as the concentration of bicarbonate increases while the increase in soluble U(VI) concentration induced by G968 and G975 is dwarfed, for larger [HCO{sub 3}{sup -}]. (authors)« less

Simultaneous determination of uranium carbide dissolution products by capillary zone electrophoresis.

PubMed

Sladkov, Vladimir; Fourest, Blandine

2009-03-20

Separation and simultaneous determination of a number of organic acid anions (oxalate, mellitate, trimellitate and benzoate) and U(VI) with direct UV detection is developed for analysis of uranium carbide (UC) dissolution products by capillary zone electrophoresis (CZE). Reverse polarity mode is used. It is found that complex formation of U(VI) with carbonate, used as a carrier electrolyte, allows U(VI) to be determined, as negatively charged species, in a single run with organic acid anions. Some parameters such as pH value, composition of electrolyte and detection wavelength are optimized. Under the chosen conditions (carbonate buffer (ionic strength of 100 mM), pH 9.8, 0.15 mM tetradecyltrimethylammonium bromide (TTAB)) a complete separation is achieved. Calibration plots are linear in two ranges of concentration for U(VI) ( approximately 1 x 10(-5) to 1 x 10(-3)), mellitate and trimellitate ( approximately 5 x 10(-6) to 5 x 10(-4)), and about one range ( approximately 1 x 10(-4) to 5 x 10(-3)) for oxalate and benzoate. Accuracy of the procedure is checked by the "added-found" method in standard mixture solutions. Relative standard deviation is within the range of 2-10% and the recovery is in the range of 90-110%. This method is applied for the analysis of real UC dissolution samples.

Impact of uranyl-calcium-carbonato complexes on uranium(VI) adsorption to synthetic and natural sediments.

PubMed

Stewart, Brandy D; Mayes, Melanie A; Fendorf, Scott

2010-02-01

Adsorption on soil and sediment solids may decrease aqueous uranium concentrations and limit its propensity for migration in natural and contaminated settings. Uranium adsorption will be controlled in large part by its aqueous speciation, with a particular dependence on the presence of dissolved calcium and carbonate. Here we quantify the impact of uranyl speciation on adsorption to both goethite and sediments from the Hanford Clastic Dike and Oak Ridge Melton Branch Ridgetop formations. Hanford sediments were preconditioned with sodium acetate and acetic acid to remove carbonate grains, and Ca and carbonate were reintroduced at defined levels to provide a range of aqueous uranyl species. U(VI) adsorption is directly linked to UO(2)(2+) speciation, with the extent of retention decreasing with formation of ternary uranyl-calcium-carbonato species. Adsorption isotherms under the conditions studied are linear, and K(d) values decrease from 48 to 17 L kg(-1) for goethite, from 64 to 29 L kg (-1) for Hanford sediments, and from 95 to 51 L kg(-1) for Melton Branch sediments as the Ca concentration increases from 0 to 1 mM at pH 7. Our observations reveal that, in carbonate-bearing waters, neutral to slightly acidic pH values ( approximately 5) and limited dissolved calcium are optimal for uranium adsorption.

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

NASA Astrophysics Data System (ADS)

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.; Davis, J. A.

2018-01-01

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonite edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites ('spillover' effect). A series of U(VI) - Na-montmorillonite batch adsorption experiments was conducted as a function of pH, with variable U(VI), Ca, and dissolved carbonate concentrations. Based on the experimental data, a new type of surface complexation model (SCM) was developed for montmorillonite, that specifically accounts for the spillover effect using the edge surface speciation model by Tournassat et al. (2016a). The SCM allows for a prediction of U(VI) adsorption under varying chemical conditions with a minimum number of fitting parameters, not only for our own experimental results, but also for a number of published data sets. The model agreed well with many of these datasets without introducing a second site type or including the formation of ternary U(VI)-carbonato surface complexes. The model predictions were greatly impacted by utilizing analytical measurements of dissolved inorganic carbon (DIC) concentrations in individual sample solutions rather than assuming solution equilibration with a specific partial pressure of CO2, even when the gas phase was laboratory air. Because of strong aqueous U(VI)-carbonate solution complexes, the measurement of DIC concentrations was even important for systems set up in the 'absence' of CO2, due to low levels of CO2 contamination during the experiment.

Effect of Phosphate on U(VI) Sorption to Montmorillonite: Ternary Complexation and Precipitation Barriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated.more » Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface« less

Quantum mechanical calculation of aqueuous uranium complexes: carbonate, phosphate, organic and biomolecular species

PubMed Central

Kubicki, James D; Halada, Gary P; Jha, Prashant; Phillips, Brian L

2009-01-01

Background Quantum mechanical calculations were performed on a variety of uranium species representing U(VI), U(V), U(IV), U-carbonates, U-phosphates, U-oxalates, U-catecholates, U-phosphodiesters, U-phosphorylated N-acetyl-glucosamine (NAG), and U-2-Keto-3-doxyoctanoate (KDO) with explicit solvation by H2O molecules. These models represent major U species in natural waters and complexes on bacterial surfaces. The model results are compared to observed EXAFS, IR, Raman and NMR spectra. Results Agreement between experiment and theory is acceptable in most cases, and the reasons for discrepancies are discussed. Calculated Gibbs free energies are used to constrain which configurations are most likely to be stable under circumneutral pH conditions. Reduction of U(VI) to U(IV) is examined for the U-carbonate and U-catechol complexes. Conclusion Results on the potential energy differences between U(V)- and U(IV)-carbonate complexes suggest that the cause of slower disproportionation in this system is electrostatic repulsion between UO2 [CO3]35- ions that must approach one another to form U(VI) and U(IV) rather than a change in thermodynamic stability. Calculations on U-catechol species are consistent with the observation that UO22+ can oxidize catechol and form quinone-like species. In addition, outer-sphere complexation is predicted to be the most stable for U-catechol interactions based on calculated energies and comparison to 13C NMR spectra. Outer-sphere complexes (i.e., ion pairs bridged by water molecules) are predicted to be comparable in Gibbs free energy to inner-sphere complexes for a model carboxylic acid. Complexation of uranyl to phosphorus-containing groups in extracellular polymeric substances is predicted to favor phosphonate groups, such as that found in phosphorylated NAG, rather than phosphodiesters, such as those in nucleic acids. PMID:19689800

Spectroscopic evidence of uranium immobilization in acidic wetlands by natural organic matter and plant roots.

PubMed

Li, Dien; Kaplan, Daniel I; Chang, Hyun-Shik; Seaman, John C; Jaffé, Peter R; Koster van Groos, Paul; Scheckel, Kirk G; Segre, Carlo U; Chen, Ning; Jiang, De-Tong; Newville, Matthew; Lanzirotti, Antonio

2015-03-03

Biogeochemistry of uranium in wetlands plays important roles in U immobilization in storage ponds of U mining and processing facilities but has not been well understood. The objective of this work was to study molecular mechanisms responsible for high U retention by Savannah River Site (SRS) wetland sediments under varying redox and acidic (pH = 2.6-5.8) conditions using U L3-edge X-ray absorption spectroscopy. Uranium in the SRS wetland sediments existed primarily as U(VI) bonded as a bidentate to carboxylic sites (U-C bond distance at ∼2.88 Å), rather than phenolic or other sites of natural organic matter (NOM). In microcosms simulating the SRS wetland processes, U immobilization on roots was 2 orders of magnitude higher than on the adjacent brown or more distant white sands in which U was U(VI). Uranium on the roots were both U(IV) and U(VI), which were bonded as a bidentate to carbon, but the U(VI) may also form a U phosphate mineral. After 140 days of air exposure, all U(IV) was reoxidized to U(VI) but remained as a bidentate bonding to carbon. This study demonstrated NOM and plant roots can highly immobilize U(VI) in the SRS acidic sediments, which has significant implication for the long-term stewardship of U-contaminated wetlands.

The Effect of Si and Al Concentration Ratios on the Removal of U(VI) under Hanford Site 200 Area Conditions-12115

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsenovich, Yelena; Gonzalez, Nathan; Moreno-Pastor, Carol

2012-07-01

Injection of reactive gases, such as NH{sub 3}, is an innovative technique to mitigate uranium contamination in soil for a vadose zone (VZ) contaminated with radionuclides. A series of experiments were conducted to examine the effect of the concentration ratio of silicon to aluminum in the presence of various bicarbonate concentrations on the coprecipitation process of U(VI). The concentration of Al in all tests remained unchanged at 2.8 mM. Experiments showed that the removal efficiency of uranium was not significantly affected by the different bicarbonate and U(VI) concentrations tested. For the lower Si:Al molar ratios of 2:1 and 18:1, themore » removal efficiency of uranium was relatively low (≤ 8%). For the Si:Al molar ratio of 35:1, the removal efficiency of uranium was increased to an average of ∼82% for all bicarbonate concentrations tested. At higher Si:Al molar ratios (53:1 and above), a relatively high removal efficiency of U(VI), approximately 85% and higher, was observed. These results demonstrate that the U(VI) removal efficiency is more affected by the Si:Al molar ratio than by the bicarbonate concentration in solution. The results of this experiment are promising for the potential implementation of NH{sub 3} gas injection for the remediation of U(VI) -contaminated VZ. (authors)« less

Spectroscopic evidence of uranium immobilization in acidic wetlands by natural organic matter and plant roots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Dien; Kaplan, Daniel I.; Chang, Hyun-Shik

Biogeochemistry of uranium in wetlands plays important roles in U immobilization in storage ponds of U mining and processing facilities but has not been well understood. The objective of this work was to study molecular mechanisms responsible for high U retention by Savannah River Site (SRS) wetland sediments under varying redox and acidic (pH = 2.6–5.8) conditions using U L₃-edge X-ray absorption spectroscopy. Uranium in the SRS wetland sediments existed primarily as U(VI) bonded as a bidentate to carboxylic sites (U–C bond distance at ~2.88 Å), rather than phenolic or other sites of natural organic matter (NOM). In microcosms simulatingmore » the SRS wetland processes, U immobilization on roots was two orders of magnitude higher than on the adjacent brown or more distant white sands in which U was U(VI). Uranium on the roots were both U(IV) and U(VI), which were bonded as a bidentate to carbon, but the U(VI) may also form a U phosphate mineral. After 140 days of air exposure, all U(IV) was re-oxidized to U(VI) but remained as a bidentate bonding to carbon. This study demonstrated NOM and plant roots can highly immobilize U(VI) in the SRS acidic sediments, which has significant implication for the long-term stewardship of U-contaminated wetlands.« less

Spectroscopic evidence of uranium immobilization in acidic wetlands by natural organic matter and plant roots

DOE PAGES

Li, Dien; Kaplan, Daniel I.; Chang, Hyun-Shik; ...

2015-03-03

Biogeochemistry of uranium in wetlands plays important roles in U immobilization in storage ponds of U mining and processing facilities but has not been well understood. The objective of this work was to study molecular mechanisms responsible for high U retention by Savannah River Site (SRS) wetland sediments under varying redox and acidic (pH = 2.6–5.8) conditions using U L₃-edge X-ray absorption spectroscopy. Uranium in the SRS wetland sediments existed primarily as U(VI) bonded as a bidentate to carboxylic sites (U–C bond distance at ~2.88 Å), rather than phenolic or other sites of natural organic matter (NOM). In microcosms simulatingmore » the SRS wetland processes, U immobilization on roots was two orders of magnitude higher than on the adjacent brown or more distant white sands in which U was U(VI). Uranium on the roots were both U(IV) and U(VI), which were bonded as a bidentate to carbon, but the U(VI) may also form a U phosphate mineral. After 140 days of air exposure, all U(IV) was re-oxidized to U(VI) but remained as a bidentate bonding to carbon. This study demonstrated NOM and plant roots can highly immobilize U(VI) in the SRS acidic sediments, which has significant implication for the long-term stewardship of U-contaminated wetlands.« less

Synthesis and structural features of U VI and V IV chelate complexes with (hhmmbH)Cl·H 2O [hhmmb = {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide], a new Schiff base ligand derived from vitamin B6

NASA Astrophysics Data System (ADS)

Back, Davi Fernando; Ballin, Marco Aurélio; de Oliveira, Gelson Manzoni

2009-10-01

The Schiff base ligand {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide hydrochloride monohydrated {(hhmmbH)Cl·H 2O} ( 1) was prepared by reaction of pyridoxine hydrochloride with benzoic acid hydrazide. The reaction of 1 with [VO(acac) 2] and triethylamine yields the neutral vanadium IV complex [VO 2(hhmmb)]·Py ( 2), with a distorted quadratic pyramidal configuration. The Schiff base 1 reacts also with UO 2(NO 3) 2·6H 2O and triethylamine under deprotonation giving the uranium VI cationic complexes [UO 2(hhmmb)(H 2O)Cl] + ( 3) and [UO 2(hhmmb)(CH 3OH)Cl] + ( 4), both showing the classical pentagonal bipyrimidal geometry of UO22+ complexes. The structural features of all compounds are discussed.

HPLC separation post-column reaction, UV-visible and fluorescence detection of trace UO/sub 2//sup 2 +//U/sup 4 +/ species in aqueous solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karimi, A.R.

In this study a method for the measurement of uranium in natural waters at sub-ppB concentration levels by the separation and determination of U/sup 4 +/ and UO/sub 2//sup 2 +/ species is proposed. Reversed phase high performance liquid chromatography, followed by a post-column reaction and a sensitive UV-visible detection system was the method of choice to determine qualitatively and quantitatively the two uranium species. Also a cation-exchange and fluorescence detection system was studied for separation and determination of UO/sub 2//sup 2 +/ ions. Uranyl ion was selectively complexed with L-phenylalanine moetie in the sample solution containing U/sup 4 +/more » ions. Uranium (IV)/U(VI)-ligand was separated on a C/sub 18/ column with acetate buffer. Hexanesulfonate was found to be the choice for ion-pair reagent. The separation was best done with the acetate buffer at .01 M concentration and pH of 3.5. Absorption of the two species were measured after a post-column reaction with Arsenazo-III. Chromatographic parameters were calculated and a calibration curves were constructed. The detection limit for the procedure was 0.7 ..mu..g/mo and 1.2..mu..g/ml for U(IV) and U(VI) respectively. When U(VI) was separated on the cation-exchange column the limit of detection was calculated to be 1 ..mu..g/ml. The direct fluorometric method for U(VI) measurement results in a detection limit of 2 ppB and upper concentration limit of 2 ppM. The effect of interfering ions in the direct method of determination could be eliminated by dilution of sample solution.« less

Electrochemical and Spectroscopic Evidence on the One-Electron Reduction of U(VI) to U(V) on Magnetite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ke; Ilton, Eugene S.; Antonio, Mark R.

2015-05-19

Reduction of U(VI) to U(VI) on mineral surfaces is often considered a one-step two-electron process. However, stabilized U(V), with no evidence of U(IV), found in recent studies Indicates U(VI) can undergo a one-electron reduction to U(V) without further progression to U(VI),. We investigated reduction pathways of uranium by reducing U(VI) electrochemically on a, magnetite electrode at,pH 3.4. Cyclic voltammetry confirms the one-electron reduction of U(VI) . Formation of nanosize uranium precipitates on the magnetite surface at reducing potentials and dissolution of the solids at oxidizing potentials are observed by in situ electrochemical atomic force microscopy. XPS, analysis Of the magnetitemore » electrodes polarized in uranium solutions at voltages - from -0.1 to -0.9 V (E-U(VI)/U(V)(0)= -0.135 V vs Ag/AgCl) show the presence of, only U(V) and U(VI). The sample with the highest U(V)/U(VI) ratio was prepared at -0.7 V, where the longest average U-O-axial distance of 2.05 + 0.01 A was evident in the same sample revealed by extended X-ray absorption fine structure analysis. The results demonstrate that the electrochemical reduction of U(VI) On magnetite only yields,U(V), even at a potential of -0.9 V, which favors the one-electron reduction mechanism, U(V) does not disproportionate but stabilizes on magnetite through precipitation Of mixed-valence state -U(V)/U(VI) solids.« less

HNO3 modified biochars for uranium (VI) removal from aqueous solution.

PubMed

Jin, Jie; Li, Shiwei; Peng, Xianqiang; Liu, Wei; Zhang, Chenlu; Yang, Yan; Han, Lanfang; Du, Ziwen; Sun, Ke; Wang, Xiangke

2018-05-01

The HNO 3 treatment was used to chemically modify the biochars produced from wheat straw (WH) and cow manure for U(VI) removal from aqueous solution. Macroscopic experiments proved that the enrichment of U(VI) on the biochars was regulated by surface complexation and electrostatic interactions. FTIR and XPS analyses confirmed that the highly efficient adsorption of U(VI) was due to the carboxyl groups on the biochar surfaces. The reducing agents of the R-CH 2 OH groups facilitated U(VI) adsorption on the untreated biochars. Owing to the higher contents of surface COO groups and more negative surface charge, the modified biochars showed enhanced U(VI) adsorption ability than the untreated ones. The maximum adsorption capacity of U(VI) by the oxidized WH was calculated to be 355.6 mg/g at pH 4.5 and 298 K, which was an improvement of 40 times relative to the untreated WH and was higher than that of most carbon-based adsorbents. Copyright © 2018 Elsevier Ltd. All rights reserved.

Communication: Relativistic Fock-space coupled cluster study of small building blocks of larger uranium complexes.

PubMed

Tecmer, Paweł; Gomes, André Severo Pereira; Knecht, Stefan; Visscher, Lucas

2014-07-28

We present a study of the electronic structure of the [UO2](+), [UO2](2 +), [UO2](3 +), NUO, [NUO](+), [NUO](2 +), [NUN](-), NUN, and [NUN](+) molecules with the intermediate Hamiltonian Fock-space coupled cluster method. The accuracy of mean-field approaches based on the eXact-2-Component Hamiltonian to incorporate spin-orbit coupling and Gaunt interactions are compared to results obtained with the Dirac-Coulomb Hamiltonian. Furthermore, we assess the reliability of calculations employing approximate density functionals in describing electronic spectra and quantities useful in rationalizing Uranium (VI) species reactivity (hardness, electronegativity, and electrophilicity).

Communication: Relativistic Fock-space coupled cluster study of small building blocks of larger uranium complexes

NASA Astrophysics Data System (ADS)

Tecmer, Paweł; Severo Pereira Gomes, André; Knecht, Stefan; Visscher, Lucas

2014-07-01

We present a study of the electronic structure of the [UO2]+, [UO2]2 +, [UO2]3 +, NUO, [NUO]+, [NUO]2 +, [NUN]-, NUN, and [NUN]+ molecules with the intermediate Hamiltonian Fock-space coupled cluster method. The accuracy of mean-field approaches based on the eXact-2-Component Hamiltonian to incorporate spin-orbit coupling and Gaunt interactions are compared to results obtained with the Dirac-Coulomb Hamiltonian. Furthermore, we assess the reliability of calculations employing approximate density functionals in describing electronic spectra and quantities useful in rationalizing Uranium (VI) species reactivity (hardness, electronegativity, and electrophilicity).

Polyaniline (PANI) modified bentonite by plasma technique for U(VI) removal from aqueous solution

NASA Astrophysics Data System (ADS)

Liu, Xinghao; Cheng, Cheng; Xiao, Chengjian; Shao, Dadong; Xu, Zimu; Wang, Jiaquan; Hu, Shuheng; Li, Xiaolong; Wang, Weijuan

2017-07-01

Polyaniline (PANI) modified bentonite (PANI/bentonie) was synthesized by plasma induced polymerization of aniline on bentonite surface, and applied to uptake of uranium(VI) ions from aqueous solution. The as-synthesized PANI/bentonie was characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Batch adsorption technique was utilized to investigate the adsorption of U(VI) on bentonite and PANI/bentonite. The adsorption of U(VI) (10 mg/L) on PANI/bentonite surface is fairly depend on solution pH, ionic strength, and temperature in solution. The modified PANI on PANI/bentonite surface significantly enhances its adsorption capability for U(VI). The presence of humic acid (HA) can sound enhance U(VI) adsorption on PANI/bentonite at pH < 6.5 because of the strong complexation, and inhibits U(VI) adsorption at pH > 6.5. According to the thermodynamic parameters, the adsorption of U(VI) on PANI/bentonite surface is a spontaneous and endothermic process. The results highlight the application of PANI/bentonite composites as candidate material for the uptake of trace U(VI) from aqueous solution.

Selective separation of uranium using alizarin red S (ARS)-modified anion-exchange resin or by flotation of U-ARS chelate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khalifa, M.E.

An alizarin red S (ARS)-modified anion exchange resin was prepared by a simple reaction of ARS with the anion exchange Doulite A101 and used for the efficient sorption of uranium from aqueous media. The effect of various parameters on the sorption of U(VI) (pH effect, sorption kinetics, resin capacity and breakthrough curves) was investigated. The modified resin sorbs U(VI) over a wide range of pH (2.8--5) with a maximum sorption capacity of 0.68 mmol/g at pH 3.2 to 4.0. Iron(III), Zr(IV), Ti(IV), Cu(II), and Th(IV) ions are also sorbed to different extents, but Be(II), Bi(III), Ca(II), Mg(II), Pb(II), Hg(II), Zn(II),more » Cd(II), Al(III), Mn(II), Co(II) and Ni(II) are not sorbed; thus, conditions for separating U(VI) from these metal ions have been identified. For eluting U(VI) from the resin, 0.2 mol/L HCl was used and the recovery recorded was as high as 99.9%. The use of ARS is extended to float uranium quantitatively and selectively from aqueous media at pH {approx} 4 by using oleic acid as a surfactant. The different parameters affecting the flotation process have also been investigated. Uranium(VI) has been effectively separated from natural water samples and certified uranium ores using both procedures.« less

Identification of simultaneous U(VI) sorption complexes and U(IV) nanoprecipitates on the magnetite (111) surface.

PubMed

Singer, David M; Chatman, Shawn M; Ilton, Eugene S; Rosso, Kevin M; Banfield, Jillian F; Waychunas, Glenn A

2012-04-03

Sequestration of uranium (U) by magnetite is a potentially important sink for U in natural and contaminated environments. However, molecular-scale controls that favor U(VI) uptake including both adsorption of U(VI) and reduction to U(IV) by magnetite remain poorly understood, in particular, the role of U(VI)-CO(3)-Ca complexes in inhibiting U(VI) reduction. To investigate U uptake pathways on magnetite as a function of U(VI) aqueous speciation, we performed batch sorption experiments on (111) surfaces of natural single crystals under a range of solution conditions (pH 5 and 10; 0.1 mM U(VI); 1 mM NaNO(3); and with or without 0.5 mM CO(3) and 0.1 mM Ca) and characterized surface-associated U using grazing incidence extended X-ray absorption fine structure spectroscopy (GI-EXAFS), grazing incidence X-ray diffraction (GI-XRD), and scanning electron microscopy (SEM). In the absence of both carbonate ([CO(3)](T), denoted here as CO(3)) and calcium (Ca), or in the presence of CO(3) only, coexisting adsorption of U(VI) surface species and reduction to U(IV) occurs at both pH 5 and 10. In the presence of both Ca and CO(3), only U(VI) adsorption (VI) occurs. When U reduction occurs, nanoparticulate UO(2) forms only within and adjacent to surface microtopographic features such as crystal boundaries and cracks. This result suggests that U reduction is limited to defect-rich surface regions. Further, at both pH 5 and 10 in the presence of both CO(3) and Ca, U(VI)-CO(3)-Ca ternary surface species develop and U reduction is inhibited. These findings extend the range of conditions under which U(VI)-CO(3)-Ca complexes inhibit U reduction.

Uranium extremophily is an adaptive, rather than intrinsic, feature for extremely thermoacidophilic Metallosphaera species

PubMed Central

Mukherjee, Arpan; Wheaton, Garrett H.; Blum, Paul H.; Kelly, Robert M.

2012-01-01

Thermoacidophilic archaea are found in heavy metal-rich environments, and, in some cases, these microorganisms are causative agents of metal mobilization through cellular processes related to their bioenergetics. Given the nature of their habitats, these microorganisms must deal with the potentially toxic effect of heavy metals. Here, we show that two thermoacidophilic Metallosphaera species with nearly identical (99.99%) genomes differed significantly in their sensitivity and reactivity to uranium (U). Metallosphaera prunae, isolated from a smoldering heap on a uranium mine in Thüringen, Germany, could be viewed as a “spontaneous mutant” of Metallosphaera sedula, an isolate from Pisciarelli Solfatara near Naples. Metallosphaera prunae tolerated triuranium octaoxide (U3O8) and soluble uranium [U(VI)] to a much greater extent than M. sedula. Within 15 min following exposure to “U(VI) shock,” M. sedula, and not M. prunae, exhibited transcriptomic features associated with severe stress response. Furthermore, within 15 min post-U(VI) shock, M. prunae, and not M. sedula, showed evidence of substantial degradation of cellular RNA, suggesting that transcriptional and translational processes were aborted as a dynamic mechanism for resisting U toxicity; by 60 min post-U(VI) shock, RNA integrity in M. prunae recovered, and known modes for heavy metal resistance were activated. In addition, M. sedula rapidly oxidized solid U3O8 to soluble U(VI) for bioenergetic purposes, a chemolithoautotrophic feature not previously reported. M. prunae, however, did not solubilize solid U3O8 to any significant extent, thereby not exacerbating U(VI) toxicity. These results point to uranium extremophily as an adaptive, rather than intrinsic, feature for Metallosphaera species, driven by environmental factors. PMID:23010932

Influence of uranium on bacterial communities: a comparison of natural uranium-rich soils with controls.

PubMed

Mondani, Laure; Benzerara, Karim; Carrière, Marie; Christen, Richard; Mamindy-Pajany, Yannick; Février, Laureline; Marmier, Nicolas; Achouak, Wafa; Nardoux, Pascal; Berthomieu, Catherine; Chapon, Virginie

2011-01-01

This study investigated the influence of uranium on the indigenous bacterial community structure in natural soils with high uranium content. Radioactive soil samples exhibiting 0.26% - 25.5% U in mass were analyzed and compared with nearby control soils containing trace uranium. EXAFS and XRD analyses of soils revealed the presence of U(VI) and uranium-phosphate mineral phases, identified as sabugalite and meta-autunite. A comparative analysis of bacterial community fingerprints using denaturing gradient gel electrophoresis (DGGE) revealed the presence of a complex population in both control and uranium-rich samples. However, bacterial communities inhabiting uraniferous soils exhibited specific fingerprints that were remarkably stable over time, in contrast to populations from nearby control samples. Representatives of Acidobacteria, Proteobacteria, and seven others phyla were detected in DGGE bands specific to uraniferous samples. In particular, sequences related to iron-reducing bacteria such as Geobacter and Geothrix were identified concomitantly with iron-oxidizing species such as Gallionella and Sideroxydans. All together, our results demonstrate that uranium exerts a permanent high pressure on soil bacterial communities and suggest the existence of a uranium redox cycle mediated by bacteria in the soil.

Influence of Uranium on Bacterial Communities: A Comparison of Natural Uranium-Rich Soils with Controls

PubMed Central

Mondani, Laure; Benzerara, Karim; Carrière, Marie; Christen, Richard; Mamindy-Pajany, Yannick; Février, Laureline; Marmier, Nicolas; Achouak, Wafa; Nardoux, Pascal; Berthomieu, Catherine; Chapon, Virginie

2011-01-01

This study investigated the influence of uranium on the indigenous bacterial community structure in natural soils with high uranium content. Radioactive soil samples exhibiting 0.26% - 25.5% U in mass were analyzed and compared with nearby control soils containing trace uranium. EXAFS and XRD analyses of soils revealed the presence of U(VI) and uranium-phosphate mineral phases, identified as sabugalite and meta-autunite. A comparative analysis of bacterial community fingerprints using denaturing gradient gel electrophoresis (DGGE) revealed the presence of a complex population in both control and uranium-rich samples. However, bacterial communities inhabiting uraniferous soils exhibited specific fingerprints that were remarkably stable over time, in contrast to populations from nearby control samples. Representatives of Acidobacteria, Proteobacteria, and seven others phyla were detected in DGGE bands specific to uraniferous samples. In particular, sequences related to iron-reducing bacteria such as Geobacter and Geothrix were identified concomitantly with iron-oxidizing species such as Gallionella and Sideroxydans. All together, our results demonstrate that uranium exerts a permanent high pressure on soil bacterial communities and suggest the existence of a uranium redox cycle mediated by bacteria in the soil. PMID:21998695

In situ Bioreduction of Uranium (VI) in Groundwater and Sediments with Edible Oil as the Electron Donor

NASA Astrophysics Data System (ADS)

Wu, W.; Watson, D. B.; Mehlhorn, T.; Zhang, G.; Earles, J.; Lowe, K.; Phillips, J.; Boyanov, M.; Kemner, K. M.; Schadt, C. W.; Brooks, S. C.; Criddle, C.; Jardine, P.

2009-12-01

In situ bioremediation of a uranium-contaminated aquifer was conducted at the US DOE Environmental Remediation Sciences Program (ERSP) Integrated Field Research Challenge (IFRC) site, in Oak Ridge, TN. Edible oil was tested as a slow-release electron donor for microbially mediated U (VI) reduction. Uranium contaminated sediments from the site were used in laboratory microcosm tests to study the feasibility of using this electron donor under anaerobic, ambient temperature conditions. Parallel microcosms were established using ethanol as electron donor for comparison. The tests also examined the impact of sulfate concentrations on U (VI) reduction. The oil was degraded by indigenous microorganisms with acetate as a major product but at a much slower rate than ethanol. The rapid removal of U (VI) from the aqueous phase occurred concurrently with acetate production and sulfate reduction. Initial U(VI) concentration in the aqueous phase increased with increased sulfate concentration (1 vs. 5 mM), likely due to U(VI) desorption from the solid phase, but more U(VI) was reduced with higher initial sulfate level. Finally, the bioreaction in microcosms progressed to methanogenesis. Subsequently, a field test with the edible oil was conducted in a highly permeable gravelly layer (hydraulic conductivity 0.076 cm/sec). Groundwater at the site contained 5-6 μM U; 1.0-1.2 mM sulfate; 3-4 mM Ca; pH 6.8. Diluted emulsified oil (20% solution) was injected into three injection wells within 2 hrs. Geochemical analysis of site groundwater demonstrated the sequential reduction of nitrate, Mn, Fe(III) and sulfate. Transient accumulation of acetate was observed as an intermediate in the oil degradation. Reduction and removal of uranium from groundwater was observed in all wells connected to the injection wells after 2-4 weeks. Uranium concentrations in groundwater were reduced to below 0.126 μM (EPA drinking water standard), at some well locations. Rebound of U in groundwater was observed together with the rebound of sulfate concentrations as the oil was consumed. Uranium (VI) reduction to U (IV) in the microcosm and in situ field tests was confirmed by X-ray near-edge absorption spectroscopy analysis. Bacterial populations in microcosms and field samples were analyzed using 16S rRNA gene libraries and Geochip analysis.

Sorption characteristic of uranium(VI) ion onto K-feldspar.

PubMed

Gao, Xiaoqing; Bi, Mingliang; Shi, Keliang; Chai, Zhifang; Wu, Wangsuo

2017-10-01

The effect of pH, contact time, temperature, ionic strength and initial U(VI) concentration on U(VI) sorption onto K-feldspar was investigated using batch techniques. The sorption kinetics was evaluated and the activation energy was obtained based on the rate constants at different temperature. Graphical correlations of sorption isotherm models have been evaluated and applied for U(VI) uptake by K-feldspar. Various thermodynamic parameters, such as, Gibb's free energy, entropy and enthalpy of the on-going sorption process have been calculated and the possible sorption mechanism of U(VI) was deduced. The results are expected to help better understand the migration of uranium in the host materials of granite. Copyright © 2017 Elsevier Ltd. All rights reserved.

Visualizing different uranium oxidation states during the surface alteration of uraninite and uranium tetrachloride.

PubMed

Grossmann, Kay; Arnold, Thuro; Steudtner, Robin; Weiss, Stefan; Bernhard, Gert

2009-08-01

Low-temperature alteration reactions on uranium phases may lead to the mobilization of uranium and thereby poses a potential threat to humans living close to uranium-contaminated sites. In this study, the surface alteration of uraninite (UO(2)) and uranium tetrachloride (UCl(4)) in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy using an excitation wavelength of 408 nm. It was found that within minutes the oxidation state on the surface of the uraninite and the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride surface became stepwise oxidized by a one-electron step at first to U(V) and then further to U(VI). These observed changes in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on the basis of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415-475 nm was indicative for metastable uranium(V), and a fluorescence signal in the range of 480-560 nm was identified as uranium(VI). In addition, the oxidation process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically identified. The combination of microscopy and fluorescence spectroscopy provided a very convincing visualization of the brief presence of U(V) as a metastable reaction intermediate and of the simultaneous coexistence of the three states U(IV), U(V), and U(VI). These results have a significant importance for fundamental uranium redox chemistry and should contribute to a better understanding of the geochemical behavior of uranium in nature.

Impact of uranyl-calcium-carbonato complexes on uranium(VI) adsorption to synthetic and natural sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stewart, B.D.; Mayes, Melanie; Fendorf, Scott

2010-01-01

Adsorption on soil and sediment solids may decrease aqueous uranium concentrations and limit its propensity for migration in natural and contaminated settings. Uranium adsorption will be controlled in large part by its aqueous speciation, with a particular dependence on the presence of dissolved calcium and carbonate. Here we quantify the impact of uranyl speciation on adsorption to both goethite and sediments from the Hanford Clastic Dike and Oak Ridge Melton Branch Ridgetop formations. Hanford sediments were preconditioned with sodium acetate and acetic acid to remove carbonate grains, and Ca and carbonate were reintroduced at defined levels to provide a rangemore » of aqueous uranyl species. U(VI) adsorption is directly linked to UO{sub 2}{sup 2+} speciation, with the extent of retention decreasing with formation of ternary uranyl-calcium-carbonato species. Adsorption isotherms under the conditions studied are linear, and K{sub d} values decrease from 48 to 17 L kg{sup -1} for goethite, from 64 to 29 L kg{sup -1} for Hanford sediments, and from 95 to 51 L kg{sup -1} for Melton Branch sediments as the Ca concentration increases from 0 to 1 mM at pH 7. Our observations reveal that, in carbonate-bearing waters, neutral to slightly acidic pH values ({approx}5) and limited dissolved calcium are optimal for uranium adsorption.« less

Electrochemical and spectroscopic evidence on the one-electron reduction of U(VI) to U(V) on magnetite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ke; Ilton, Eugene S.; Antonio, Mark R.

2015-05-19

Reduction of U(VI) to U(IV) on mineral surfaces has been considered as a one-step two electron process. However, stabilized U(V), with no evidence of U(IV), found in recent studies indicates U(VI) can undergo a one electron reduction to U(V) without further progression to U(IV). We investigated the mechanisms of uranium reduction by reducing U(VI) electrochemically on a magnetite electrode at pH 3.4 . The one electron reduction of U(VI) was first confirmed using the cyclic voltammetry method. Formation of nano-size uranium precipitates on the surface of magnetite at reducing potentials and dissolution of the solids at oxidizing potentials were observedmore » by in situ electrochemical AFM. XPS analysis of the magnetite electrodes polarized in uranium solutions at voltages from 0.1 ~ 0.9 V (vs. Ag/AgCl) showed the presence of only U(V) and U(VI). The highest amount of U(V) relative to U(VI) was prepared at 0.7 V, where the longest average U–Oaxial distance of 2.05 ± 0.01 Å was evident in the same sample revealed by EXAFS analysis. The results demonstrate that the electrochemical reduction of U(VI) on magnetite only yields U(V), even at a potential of 0.9 V, which favors the one-electron reduction mechanism. U(V) did not disproportionate but stabilized on magnetite through precipitation of mixed-valence state U(VI)/U(V) solids.« less

Effect of natural uranium on the UMR-106 osteoblastic cell line: impairment of the autophagic process as an underlying mechanism of uranium toxicity.

PubMed

Pierrefite-Carle, Valérie; Santucci-Darmanin, Sabine; Breuil, Véronique; Gritsaenko, Tatiana; Vidaud, Claude; Creff, Gaelle; Solari, Pier Lorenzo; Pagnotta, Sophie; Al-Sahlanee, Rasha; Auwer, Christophe Den; Carle, Georges F

2017-04-01

Natural uranium (U), which is present in our environment, exerts a chemical toxicity, particularly in bone where it accumulates. Generally, U is found at oxidation state +VI in its oxocationic form [Formula: see text] in aqueous media. Although U(VI) has been reported to induce cell death in osteoblasts, the cells in charge of bone formation, the molecular mechanism for U(VI) effects in these cells remains poorly understood. The objective of our study was to explore U(VI) effect at doses ranging from 5 to 600 µM, on mineralization and autophagy induction in the UMR-106 model osteoblastic cell line and to determine U(VI) speciation after cellular uptake. Our results indicate that U(VI) affects mineralization function, even at subtoxic concentrations (<100 µM). The combination of thermodynamic modeling of U with EXAFS data in the culture medium and in the cells clearly indicates the biotransformation of U(VI) carbonate species into a meta-autunite phase upon uptake by osteoblasts. We next assessed U(VI) effect at 100 and 300 µM on autophagy, a survival process triggered by various stresses such as metal exposure. We observed that U(VI) was able to rapidly activate autophagy but an inhibition of the autophagic flux was observed after 24 h. Thus, our results indicate that U(VI) perturbs osteoblastic functions by reducing mineralization capacity. Our study identifies for the first time U(VI) in the form of meta-autunite in mammalian cells. In addition, U(VI)-mediated inhibition of the autophagic flux may be one of the underlying mechanisms leading to the decreased mineralization and the toxicity observed in osteoblasts.

A review of the high temperature oxidation of uranium oxides in molten salts and in the solid state to form alkali metal uranates, and their composition and properties

NASA Astrophysics Data System (ADS)

Griffiths, Trevor R.; Volkovich, Vladimir A.

An extensive review of the literature on the high temperature reactions (both in melts and in the solid state) of uranium oxides (UO 2, U 3O 8 and UO 3) resulting in the formation of insoluble alkali metal (Li to Cs) uranates is presented. Their uranate(VI) and uranate(V) compounds are examined, together with mixed and oxygen-deficient uranates. The reactions of uranium oxides with carbonates, oxides, per- and superoxides, chlorides, sulfates, nitrates and nitrites under both oxidising and non-oxidising conditions are critically examined and systematised, and the established compositions of a range of uranate(VI) and (V) compounds formed are discussed. Alkali metal uranates(VI) are examined in detail and their structural, physical, thermodynamic and spectroscopic properties considered. Chemical properties of alkali metal uranates(VI), including various methods for their reduction, are also reported. Errors in the current theoretical treatment of uranate(VI) spectra are identified and the need to develop routes for the preparation of single crystals is stressed.

Kinetics of triscarbonato uranyl reduction by aqueous ferrous iron: a theoretical study.

PubMed

Wander, Matthew C F; Kerisit, Sebastien; Rosso, Kevin M; Schoonen, Martin A A

2006-08-10

Uranium is a pollutant whose mobility is strongly dependent on its oxidation state. While U(VI) in the form of the uranyl cation is readily reduced by a range of natural reductants, by contrast complexation of uranyl by carbonate greatly reduces its reduction potential and imposes increased electron transfer (ET) distances. Very little is known about the elementary processes involved in uranium reduction from U(VI) to U(V) to U(IV) in general. In this study, we examine the theoretical kinetics of ET from ferrous iron to triscarbonato uranyl in aqueous solution. A combination of molecular dynamics (MD) simulations and density functional theory (DFT) electronic structure calculations is employed to compute the parameters that enter into Marcus' ET model, including the thermodynamic driving forces, reorganization energies, and electronic coupling matrix elements. MD simulations predict that two ferrous iron atoms will bind in an inner-sphere fashion to the three-membered carbonate ring of triscarbonato uranyl, forming the charge-neutral ternary Fe(2)UO(2)(CO(3))(3)(H(2)O)(8) complex. Through a sequential proton-coupled electron-transfer mechanism (PCET), the first ET step converting U(VI) to U(V) is predicted by DFT to occur with an electronic barrier that corresponds to a rate on the order of approximately 1 s(-1). The second ET step converting U(V) to U(IV) is predicted to be significantly endergonic. Therefore, U(V) is a stabilized end product in this ET system, in agreement with experiment.

Sensitivity of geological, geochemical and hydrologic parameters in complex reactive transport systems for in-situ uranium bioremediation

NASA Astrophysics Data System (ADS)

Yang, G.; Maher, K.; Caers, J.

2015-12-01

Groundwater contamination associated with remediated uranium mill tailings is a challenging environmental problem, particularly within the Colorado River Basin. To examine the effectiveness of in-situ bioremediation of U(VI), acetate injection has been proposed and tested at the Rifle pilot site. There have been several geologic modeling and simulated contaminant transport investigations, to evaluate the potential outcomes of the process and identify crucial factors for successful uranium reduction. Ultimately, findings from these studies would contribute to accurate predictions of the efficacy of uranium reduction. However, all these previous studies have considered limited model complexities, either because of the concern that data is too sparse to resolve such complex systems or because some parameters are assumed to be less important. Such simplified initial modeling, however, limits the predictive power of the model. Moreover, previous studies have not yet focused on spatial heterogeneity of various modeling components and its impact on the spatial distribution of the immobilized uranium (U(IV)). In this study, we study the impact of uncertainty on 21 parameters on model responses by means of recently developed distance-based global sensitivity analysis (DGSA), to study the main effects and interactions of parameters of various types. The 21 parameters include, for example, spatial variability of initial uranium concentration, mean hydraulic conductivity, and variogram structures of hydraulic conductivity. DGSA allows for studying multi-variate model responses based on spatial and non-spatial model parameters. When calculating the distances between model responses, in addition to the overall uranium reduction efficacy, we also considered the spatial profiles of the immobilized uranium concentration as target response. Results show that the mean hydraulic conductivity and the mineral reaction rate are the two most sensitive parameters with regard to the overall uranium reduction. But in terms of spatial distribution of immobilized uranium, initial conditions of uranium concentration and spatial uncertainty in hydraulic conductivity also become important. These analyses serve as the first step of further prediction practices of the complex uranium transport and reaction systems.

Influence of Calcium on Microbial Reduction of Solid Phase Uranium (VI)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M.

2007-06-27

The effect of calcium on microbial reduction of a solid phase U(VI), sodium boltwoodite (NaUO2SiO3OH ∙1.5H2O), was evaluated in a culture of a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1. Batch experiments were performed in a non-growth bicarbonate medium with lactate as electron donor at pH 7 buffered with PIPES. Calcium increased both the rate and extent of Na-boltwoodite dissolution by increasing its solubility through the formation of a ternary aqueous calcium-uranyl-carbonate species. The ternary species, however, decreased the rates of microbial reduction of aqueous U(VI). Laser-induced fluorescence spectroscopy (LIFS) and transmission electron microscopy (TEM) revealed that microbial reductionmore » of solid phase U(VI) is a sequentially coupled process of Na-boltwoodite dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) to U(IV) that accumulated on bacterial surfaces/periplasm. The overall rates of microbial reduction of solid phase U(VI) can be described by the coupled rates of dissolution and microbial reduction that were both influenced by calcium. The results demonstrated that dissolved U(VI) concentration during microbial reduction was a complex function of solid phase U(VI) dissolution kinetics, aqueous U(VI) speciation, and microbial activity.« less

Synthesis and characterization of UO(2)(2+)-ion imprinted polymer for selective extraction of UO(2)(2+).

PubMed

Singh, Dhruv K; Mishra, Shraddha

2009-06-30

Ion-imprinted polymers (IIPs) were prepared for uranyl ion (imprint ion) by formation of binary (salicylaldoxime (SALO) or 4-vinylpyridine (VP)) or ternary (salicylaldoxime and 4-vinylpyridine) complex in 2-methoxy ethanol (porogen) following copolymerization with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking monomer using 2,2'-azobisisobutyronitrile as initiator. Control polymers (CPs) were also prepared under identical experimental conditions without using imprint ion. The above synthesized polymers were characterized by surface area measurement, microanalysis and FT-IR analysis techniques. The imprinted polymer formed with ternary complex of UO(2)(2+)-SALO-VP (1:2:2, IIP3) showed quantitative enrichment of uranyl ion from dilute aqueous solution and hence was chosen for detailed studies. The optimal pH for quantitative enrichment is 3.5-6.5. The adsorbed UO(2)(2+) was completely eluted with 10 mL of 1.0 M HCl. The retention capacity of IIP3 was found to be 0.559 mmol g(-1). Further, the distribution ratio and selectivity coefficients of uranium and other selected inorganic ions were also evaluated. Five replicate determinations of 25 microg L(-1) of uranium(VI) gave a mean absorbance of 0.032 with a relative standard deviation of 2.20%. The detection limit corresponding to three times the standard deviation of the blank was found to be 5 microg L(-1). IIP3 was tested for preconcentration of uranium(VI) from ground, river and sea water samples.

Role of U(VI) Reduction by Geobacter species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lovely, Derrick

2008-12-23

Previous work had suggested that Acholeplasma palmae has a higher capacity for uranium sorption than other bacteria studied. Sorption studies were performed with cells in suspension in various solutions containing uranium, and results were used to generate uranium-biosorption isotherms. Results from this study showed that the U(VI) sorption capacity of G. uraniireducens was relatively similar in simple solutions, such as sodium chloride or bicarbonate. However, this ability to sorb uranium significantly decreased in groundwater. This suggested that certain chemicals present in the groundwater were inhibiting the ability of cell components of Geobacter to adsorb uranium. It was hypothesized that uraniummore » removal would also be diminished in the bicarbonate solution. However, this did not seem to be the case, as uranium was as easily removed in the bicarbonate solution as in the sodium chloride solution.« less

Multilinear analysis of Time-Resolved Laser-Induced Fluorescence Spectra of U(VI) containing natural water samples

NASA Astrophysics Data System (ADS)

Višňák, Jakub; Steudtner, Robin; Kassahun, Andrea; Hoth, Nils

2017-09-01

Natural waters' uranium level monitoring is of great importance for health and environmental protection. One possible detection method is the Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), which offers the possibility to distinguish different uranium species. The analytical identification of aqueous uranium species in natural water samples is of distinct importance since individual species differ significantly in sorption properties and mobility in the environment. Samples originate from former uranium mine sites and have been provided by Wismut GmbH, Germany. They have been characterized by total elemental concentrations and TRLFS spectra. Uranium in the samples is supposed to be in form of uranyl(VI) complexes mostly with carbonate (CO32- ) and bicarbonate (HCO3- ) and to lesser extend with sulphate (SO42- ), arsenate (AsO43- ), hydroxo (OH- ), nitrate (NO3- ) and other ligands. Presence of alkaline earth metal dications (M = Ca2+ , Mg2+ , Sr2+ ) will cause most of uranyl to prefer ternary complex species, e.g. Mn(UO2)(CO3)32n-4 (n ɛ {1; 2}). From species quenching the luminescence, Cl- and Fe2+ should be mentioned. Measurement has been done under cryogenic conditions to increase the luminescence signal. Data analysis has been based on Singular Value Decomposition and monoexponential fit of corresponding loadings (for separate TRLFS spectra, the "Factor analysis of Time Series" (FATS) method) and Parallel Factor Analysis (PARAFAC, all data analysed simultaneously). From individual component spectra, excitation energies T00, uranyl symmetric mode vibrational frequencies ωgs and excitation driven U-Oyl bond elongation ΔR have been determined and compared with quasirelativistic (TD)DFT/B3LYP theoretical predictions to cross -check experimental data interpretation. Note to the reader: Several errors have been produced in the initial version of this article. This new version published on 23 October 2017 contains all the corrections.

Sorption and bioreduction of hexavalent uranium at a military facility by the Chesapeake Bay.

PubMed

Dong, Wenming; Xie, Guibo; Miller, Todd R; Franklin, Mark P; Oxenberg, Tanya Palmateer; Bouwer, Edward J; Ball, William P; Halden, Rolf U

2006-07-01

Directly adjacent to the Chesapeake Bay lies the Aberdeen Proving Ground, a U.S. Army facility where testing of armor-piercing ammunitions has resulted in the deposition of >70,000 kg of depleted uranium (DU) to local soils and sediments. Results of previous environmental monitoring suggested limited mobilization in the impact area and no transport of DU into the nation's largest estuary. To determine if physical and biological reactions constitute mechanisms involved in limiting contaminant transport, the sorption and biotransformation behavior of the radionuclide was studied using geochemical modeling and laboratory microcosms (500 ppb U(VI) initially). An immediate decline in dissolved U(VI) concentrations was observed under both sterile and non-sterile conditions due to rapid association of U(VI) with natural organic matter in the sediment. Reduction of U(VI) to U(IV) occurred only in non-sterile microcosms. In the non-sterile samples, intrinsic bioreduction of uranium involved bacteria of the order Clostridiales and was only moderately enhanced by the addition of acetate (41% vs. 56% in 121 days). Overall, this study demonstrates that the migration of depleted uranium from the APG site into the Chesapeake Bay may be limited by a combination of processes that include rapid sorption of U(VI) species to natural organic matter, followed by slow, intrinsic bioreduction to U(IV).

Potential Aquifer Vulnerability in Regions Down-Gradient from ...

EPA Pesticide Factsheets

Sandstone-hosted roll-front uranium ore deposits originate when U(VI) dissolved in groundwater is reduced and precipitated as insoluble U(IV) minerals. Groundwater redox geochemistry, aqueous complexation, and solute migration are instrumental in leaching uranium from source rocks and transporting it in low concentrations to a chemical redox interface where it is deposited in an ore zone typically containing the uranium minerals uraninite, pitchblende, and/or coffinite; various iron sulfides; native selenium; clays; and calcite. In situ recovery (ISR) of these uranium ores is a process of contacting the uranium mineral deposit with leaching (lixiviant) fluids via injection of the lixiviant into wells drilled into the subsurface aquifer that hosts uranium ore, while other extraction wells pump the dissolved uranium after dissolution of the uranium minerals. Environmental concerns during and after ISR include water quality impacts from: 1) potential excursions of leaching solutions away from the injection zone into down-dip, underlying, or overlying aquifers; 2) potential migration of uranium and its decay products (e.g., Ra, Rn, Pb); and, 3) potential migration of redox-sensitive trace metals (e.g., Fe, Mn, Mo, Se, V), metalloids (e.g., As), and anions (e.g., sulfate). This review describes the geochemical processes that control roll-front uranium transport and fate in groundwater systems, identifies potential aquifer vulnerabilities to ISR operations, identifies

Predicting equilibrium uranium isotope fractionation in crystals and solution

NASA Astrophysics Data System (ADS)

Schauble, E. A.

2015-12-01

Despite the rapidly growing interest in using 238U/235U measurements as a proxy for changes in oxygen abundance in surface and near-surface environments, the present theoretical understanding of uranium isotope fractionation is limited to a few simple gas-phase molecules and analogues of dissolved species (e.g., 1,2,3). Understanding uranium isotope fractionation behavior in more complicated species, such as crystals and adsorption complexes, will help in the design and interpretation of experiments and field studies, and may suggest other uses for 38U/235U measurements. In this study, a recently developed first-principles method for estimating the nuclear volume component of field shift fractionation in crystals and complex molecular species (4) is combined with mass-dependent fractionation theory to predict equilibrium 38U/235U fractionations in aqueous and crystalline uranium compounds, including uraninite (UO2). The nuclear field shift effect, caused by the interaction of electrons with the finite volume of the positive charge distribution in uranium nuclei, is estimated using Density Functional Theory and the Projector Augmented Wave method (DFT-PAW). Tests against relativistic electronic structure calculations and Mössbauer isomer shift data indicate that the DFT-PAW method is reasonably accurate, while being much better suited to models of complex and crystalline species. Initial results confirm previous predictions that the nuclear volume effect overwhelms mass depdendent fractionation in U(VI)-U(IV) exchange reactions, leading to higher 238U/235U in U(IV) species (i.e., for UO2 xtal vs. UO22+aq, ln αNV ≈ +1.8‰ , ln αMD ≈ -0.8‰, ln αTotal ≈ +1.0‰ at 25ºC). UO2 and U(H2O)94+, are within ~0.4‰ of each other, while U(VI) species appear to be more variable. This suggests that speciation is likely to significantly affect natural uranium isotope fractionations, in addition to oxidation state. Tentatively, it appears that uranyl-type (UO22+-bearing) structures will tend to have higher 238U/235U than uranate-type structures that lack strong U=O bonds. References: 1. Bigeleisen (1996) JACS 118:3676; 2. Schauble (2006) Eos 87:V21B-0570; 3. Abe et al. (2008) J Chem Phys 128:144309, 129:164309, & Abe et al. (2010) J Chem Phys 133:044309; 4. Schauble (2013) PNAS 110:17714.

Réduction des nitrates et de l'uranium par les bactéries indigènes

NASA Astrophysics Data System (ADS)

Abdelouas, Abdesselam; Lutze, Werner; Nuttall, Eric

1998-07-01

A bioremediation concept has been developed to clean up ground water contaminated with nitrate (1200 mg·L -1) and uranium (0.25 mg·L -1). We studied the Tuba City mill tailings site, Arizona, USA. Indigenous bacteria capable of catalyzing the reduction of NO 3- and U(VI) were identified in the ground water and in the host rock, the Navajo sandstone. After complete reduction of O 2 and NO 3- within one week, U(VI) was reduced and precipitated as uraninite. Final uranium concentrations < 15 μg·L -1 were reached after a few weeks at 24 °C. Iron sulfide also precipitated as a result of reduction of Fe(III) on the sand surface and sulfate in the ground water. U(VI) was not reduced by sulfide. It was found that enzymatic reduction of U(VI) is faster than abiotic reduction under the conditions given by the composition of the ground water.

Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: the role of Fe(II) and Fe(III).

PubMed

Yan, Sen; Chen, Yongheng; Xiang, Wu; Bao, Zhengyu; Liu, Chongxuan; Deng, Baolin

2014-12-01

The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed that U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.9 to 9.0. For instance, at pH 6.9 the observed U(VI) reduction rates decreased by 81% and 82% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can be enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) possibly acted as an electron shuttle to ferry the electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 could facilitate U(VI) reductive immobilization in the contaminated groundwater.

Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: The role of Fe(II) and Fe(III)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Sen; Chen, Yongheng; Xiang, Wu

2014-12-01

The role of Fe(II) and Fe(III) on U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.92 to 9.03. For instance, at pH 6.92 the observed U(VI) reduction rates decreased by 80.7% and 82.3% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can bemore » enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) probably acted as an electron shuttle to mediate the transfer of electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 can facilitate the U(VI) reductive immobilization in the contaminated groundwater.« less

Long-term in situ oxidation of biogenic uraninite in an alluvial aquifer: impact of dissolved oxygen and calcium.

PubMed

Lezama-Pacheco, Juan S; Cerrato, José M; Veeramani, Harish; Alessi, Daniel S; Suvorova, Elena; Bernier-Latmani, Rizlan; Giammar, Daniel E; Long, Philip E; Williams, Kenneth H; Bargar, John R

2015-06-16

Oxidative dissolution controls uranium release to (sub)oxic pore waters from biogenic uraninite produced by natural or engineered processes, such as bioremediation. Laboratory studies show that uraninite dissolution is profoundly influenced by dissolved oxygen (DO), carbonate, and solutes such as Ca(2+). In complex and heterogeneous subsurface environments, the concentrations of these solutes vary in time and space. Knowledge of dissolution processes and kinetics occurring over the long-term under such conditions is needed to predict subsurface uranium behavior and optimize the selection and performance of uraninite-based remediation technologies over multiyear periods. We have assessed dissolution of biogenic uraninite deployed in wells at the Rifle, CO, DOE research site over a 22 month period. Uraninite loss rates were highly sensitive to DO, with near-complete loss at >0.6 mg/L over this period but no measurable loss at lower DO. We conclude that uraninite can be stable over decadal time scales in aquifers under low DO conditions. U(VI) solid products were absent over a wide range of DO values, suggesting that dissolution proceeded through complexation and removal of oxidized surface uranium atoms by carbonate. Moreover, under the groundwater conditions present, Ca(2+) binds strongly to uraninite surfaces at structural uranium sites, impacting uranium fate.

Comparative density functional study of the complexes [UO2(CO3)3]4- and [(UO2)3(CO3)6]6- in aqueous solution.

PubMed

Schlosser, Florian; Moskaleva, Lyudmila V; Kremleva, Alena; Krüger, Sven; Rösch, Notker

2010-06-28

With a relativistic all-electron density functional method, we studied two anionic uranium(VI) carbonate complexes that are important for uranium speciation and transport in aqueous medium, the mononuclear tris(carbonato) complex [UO(2)(CO(3))(3)](4-) and the trinuclear hexa(carbonato) complex [(UO(2))(3)(CO(3))(6)](6-). Focusing on the structures in solution, we applied for the first time a full solvation treatment to these complexes. We approximated short-range effects by explicit aqua ligands and described long-range electrostatic interactions via a polarizable continuum model. Structures and vibrational frequencies of "gas-phase" models with explicit aqua ligands agree best with experiment. This is accidental because the continuum model of the solvent to some extent overestimates the electrostatic interactions of these highly anionic systems with the bulk solvent. The calculated free energy change when three mono-nuclear complexes associate to the trinuclear complex, agrees well with experiment and supports the formation of the latter species upon acidification of a uranyl carbonate solution.

Rare-earth element fractionation in uranium ore and its U(VI) alteration minerals

DOE PAGES

Balboni, Enrica; Spano, T; Cook, N; ...

2017-10-20

We developed a cation exchange chromatography method employing sulfonated polysterene cation resin (DOWEX AG50-X8) in order to separate rare-earth elements (REEs) from uranium-rich materials. The chemical separation scheme is designed to reduce matrix effects and consequently yield enhanced ionization efficiencies for concentration determinations of REEs without significant fractionation using solution mode-inductively coupled plasma mass spectrometry (ICP-MS) analysis. This method was then applied to determine REE abundances in four uraninite (ideally UO 2) samples and their associated U(VI) alteration minerals. In three of the samples analyzed, the concentration of REEs for primary uraninite are higher than those for their corresponding secondarymore » uranium alteration phases. The results for U(VI) alteration minerals of two samples indicate enrichment of the light REEs (LREEs) over the heavy REEs (HREEs). This differential mobilization is attributed to differences in the mineralogical composition of the U(VI) alteration. There is a lack of fractionation of the LREEs in the uraninite alteration rind that is composed of U(VI) minerals containing Ca 2+ as the interlayer cation (uranophane and bequerelite); contrarily, U(VI) alteration minerals containing K + and Pb 2+ as interlayer cations (fourmarierite, dumontite) indicate fractionation (enrichment) of the LREEs. Our results have implications for nuclear forensic analyses since a comparison is reported between the REE abundances for the CUP-2 (processed uranium ore) certified reference material and previously determined values for uranium ore concentrate (UOC) produced from the same U deposit (Blind River/Elliott Lake, Canada). UOCs represent the most common form of interdicted nuclear material and consequently is material frequently targeted for forensic analysis. The comparison reveals similar chondrite normalized REE signatures but variable absolute abundances. Based on the results reported here, the latter may be attributed to the differing REE abundances between primary ore and associated alteration phases, and/or is related to varying fabrication processes adopted during production of UOC.« less

Rare-earth element fractionation in uranium ore and its U(VI) alteration minerals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balboni, Enrica; Spano, T; Cook, N

We developed a cation exchange chromatography method employing sulfonated polysterene cation resin (DOWEX AG50-X8) in order to separate rare-earth elements (REEs) from uranium-rich materials. The chemical separation scheme is designed to reduce matrix effects and consequently yield enhanced ionization efficiencies for concentration determinations of REEs without significant fractionation using solution mode-inductively coupled plasma mass spectrometry (ICP-MS) analysis. This method was then applied to determine REE abundances in four uraninite (ideally UO 2) samples and their associated U(VI) alteration minerals. In three of the samples analyzed, the concentration of REEs for primary uraninite are higher than those for their corresponding secondarymore » uranium alteration phases. The results for U(VI) alteration minerals of two samples indicate enrichment of the light REEs (LREEs) over the heavy REEs (HREEs). This differential mobilization is attributed to differences in the mineralogical composition of the U(VI) alteration. There is a lack of fractionation of the LREEs in the uraninite alteration rind that is composed of U(VI) minerals containing Ca 2+ as the interlayer cation (uranophane and bequerelite); contrarily, U(VI) alteration minerals containing K + and Pb 2+ as interlayer cations (fourmarierite, dumontite) indicate fractionation (enrichment) of the LREEs. Our results have implications for nuclear forensic analyses since a comparison is reported between the REE abundances for the CUP-2 (processed uranium ore) certified reference material and previously determined values for uranium ore concentrate (UOC) produced from the same U deposit (Blind River/Elliott Lake, Canada). UOCs represent the most common form of interdicted nuclear material and consequently is material frequently targeted for forensic analysis. The comparison reveals similar chondrite normalized REE signatures but variable absolute abundances. Based on the results reported here, the latter may be attributed to the differing REE abundances between primary ore and associated alteration phases, and/or is related to varying fabrication processes adopted during production of UOC.« less

Simultaneous reduction of arsenic(V) and uranium(VI) by mackinawite: role of uranyl arsenate precipitate formation.

PubMed

Troyer, Lyndsay D; Tang, Yuanzhi; Borch, Thomas

2014-12-16

Uranium (U) and arsenic (As) often occur together naturally and, as a result, can be co-contaminants at sites of uranium mining and processing, yet few studies have examined the simultaneous redox dynamics of U and As. This study examines the influence of arsenate (As(V)) on the reduction of uranyl (U(VI)) by the redox-active mineral mackinawite (FeS). As(V) was added to systems containing 47 or 470 μM U(VI) at concentrations ranging from 0 to 640 μM. In the absence of As(V), U was completely removed from solution and fully reduced to nano-uraninite (nano-UO2). While the addition of As(V) did not reduce U uptake, at As(V) concentrations above 320 μM, the reduction of U(VI) was limited due to the formation of a trögerite-like uranyl arsenate precipitate. The presence of U also significantly inhibited As(V) reduction. While less U(VI) reduction to nano-UO2 may take place in systems with high As(V) concentrations, formation of trögerite-like mineral phases may be an acceptable reclamation end point due to their high stability under oxic conditions.

U(VI) Reduction by Biogenic and Abiotic Hydroxycarbonate Green Rusts: Impacts on U(IV) Speciation and Stability Over Time

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Sen; Boyanov, Maxim I.; Mishra, Bhoopesh

Green rusts (GRs) are redox active Fe II-Fe III minerals that form in the environment via various biotic and abiotic processes. Although both biogenic (BioGR) and abiotic (ChemGR) GRs have been shown to reduce U VI, the dynamics of the transformations and the speciation and stability of the resulting U IV phases are poorly understood. We used carbonate extraction and XAFS spectroscopy to investigate the products of U VI reduction by BioGR and ChemGR. The results show that both GRs can rapidly remove U VI from synthetic groundwater via reduction to U IV. The initial products in the ChemGR systemmore » are solids-associated U IV-carbonate complexes that gradually transform to nanocrystalline uraninite over time, leading to a decrease in the proportion of carbonate-extractable U from ~95% to ~10%. In contrast, solid-phase U IV atoms in the BioGR system remain relatively extractable, non-uraninite U IV species over the same reaction period. The presence of calcium and carbonate in groundwater significantly increase the extractability of U IV in the BioGR system. Furthermore, these data provide new insights into the transformations of U under anoxic conditions in groundwater that contains calcium and carbonate, and have major implications for predicting uranium stability within redox dynamic environments and designing approaches for the remediation of uranium-contaminated groundwater.« less

U(VI) Reduction by Biogenic and Abiotic Hydroxycarbonate Green Rusts: Impacts on U(IV) Speciation and Stability Over Time

DOE PAGES

Yan, Sen; Boyanov, Maxim I.; Mishra, Bhoopesh; ...

2018-04-09

Green rusts (GRs) are redox active Fe II-Fe III minerals that form in the environment via various biotic and abiotic processes. Although both biogenic (BioGR) and abiotic (ChemGR) GRs have been shown to reduce U VI, the dynamics of the transformations and the speciation and stability of the resulting U IV phases are poorly understood. We used carbonate extraction and XAFS spectroscopy to investigate the products of U VI reduction by BioGR and ChemGR. The results show that both GRs can rapidly remove U VI from synthetic groundwater via reduction to U IV. The initial products in the ChemGR systemmore » are solids-associated U IV-carbonate complexes that gradually transform to nanocrystalline uraninite over time, leading to a decrease in the proportion of carbonate-extractable U from ~95% to ~10%. In contrast, solid-phase U IV atoms in the BioGR system remain relatively extractable, non-uraninite U IV species over the same reaction period. The presence of calcium and carbonate in groundwater significantly increase the extractability of U IV in the BioGR system. Furthermore, these data provide new insights into the transformations of U under anoxic conditions in groundwater that contains calcium and carbonate, and have major implications for predicting uranium stability within redox dynamic environments and designing approaches for the remediation of uranium-contaminated groundwater.« less

Simultaneous extraction and preconcentration of uranium and thorium in aqueous samples by new modified mesoporous silica prior to inductively coupled plasma optical emission spectrometry determination.

PubMed

Yousefi, Seyed Reza; Ahmadi, Seyed Javad; Shemirani, Farzaneh; Jamali, Mohammad Reza; Salavati-Niasari, Masoud

2009-11-15

A new synthesized modified mesoporous silica (MCM-41) using 5-nitro-2-furaldehyde (fural) was applied as an effective sorbent for the solid phase extraction of uranium(VI) and thorium(IV) ions from aqueous solution for the measurement by inductively coupled plasma optical emission spectrometry (ICP OES). The influences of some analytical parameters on the quantitative recoveries of the analyte ions were investigated in batch method. Under optimal conditions, the analyte ions were sorbed by the sorbent at pH 5.5 and then eluted with 1.0 mL of 1.0 mol L(-1) HNO(3). The preconcentration factor was 100 for a 100mL sample volume. The limits of detection (LOD) obtained for uranium(VI) and thorium(IV) were 0.3 microg L(-1). The maximum sorption capacity of the modified MCM-41 was found to be 47 and 49 mg g(-1) for uranium(VI) and thorium(IV), respectively. The sorbent exhibited good stability, reusability, high adsorption capacity and fast rate of equilibrium for sorption/desorption of uranium and thorium ions. The applicability of the synthesized sorbent was examined using CRM and real water samples.

Microbial Reduction of Fe(III) and U(VI) in Aquifers: Simulations Exploring Coupled Effects of Heterogeneity and Fe(II) Sorption

NASA Astrophysics Data System (ADS)

Scheibe, T. D.; Fang, Y.; Roden, E. E.; Brooks, S. C.; Chien, Y.; Murray, C. J.

2004-05-01

Uranium is a significant groundwater contaminant at many former mining and processing sites. In its oxidized state, U(VI) is soluble and mobile, although strongly retarded by sorption to natural iron oxide surfaces. It has been demonstrated that commonly occurring subsurface microorganisms can reduce uranium and other metals when provided sufficient carbon as an electron donor. Reduced U(IV) precipitates as a solid phase; therefore biostimulation provides a potential strategy for in situ removal from contaminated groundwater. However, these biogeochemical reactions occur in the context of a complex heterogeneous environment in which flow and transport dynamics and abiotic reactions can have significant impacts. We have constructed a high-resolution numerical model of groundwater flow and multicomponent reactive transport that incorporates heterogeneity in hydraulic conductivity and initial Fe(III) distribution, microbial growth and transport dynamics, and effects of sorption or precipitation of biogenic Fe(II) on availability of Fe(III) as an electron acceptor. The biogeochemical reaction models and their parameters are based on laboratory experiments; the heterogeneous field-scale property distributions are based on interpretations of geophysical and other observations at a highly characterized field site. The model is being run in Monte Carlo mode to examine the controls that these factors exert on 1) the initial distribution of sorbed uranium in an oxic environment and 2) the reduction and immobilization of uranium upon introduction of a soluble electron donor.

Model-based Analysis of Mixed Uranium(VI) Reduction by Biotic and Abiotic Pathways During in Situ Bioremediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Jiao; Scheibe, Timothy D.; Mahadevan, Radhakrishnan

2013-10-24

Uranium bioremediation has emerged as a potential strategy of cleanup of radionuclear contamination worldwide. An integrated geochemical & microbial community model is a promising approach to predict and provide insights into the bioremediation of a complicated natural subsurface. In this study, an integrated column-scale model of uranium bioremediation was developed, taking into account long-term interactions between biotic and abiotic processes. It is also combined with a comprehensive thermodynamic analysis to track the fate and cycling of biogenic species. As compared with other bioremediation models, the model increases the resolution of the connection of microbial community to geochemistry and establishes directmore » quantitative correlation between overall community evolution and geochemical variation, thereby accurately predicting the community dynamics under different sedimentary conditions. The thermodynamic analysis examined a recently identified homogeneous reduction of U(VI) by Fe(II) under dynamic sedimentary conditions across time and space. It shows that the biogenic Fe(II) from Geobacter metabolism can be removed rapidly by the biogenic sulphide from sulfate reducer metabolism, hence constituting one of the reasons that make the abiotic U(VI) reduction thermodynamically infeasible in the subsurface. Further analysis indicates that much higher influent concentrations of both Fe(II) and U(VI) than normal are required to for abiotic U(VI) reduction to be thermodynamically feasible, suggesting that the abiotic reduction cannot be an alternative to the biotic reduction in the remediation of uranium contaminated groundwater.« less

Uranium Redox Transformations after U(VI) Coprecipitation with Magnetite Nanoparticles.

PubMed

Pidchenko, Ivan; Kvashnina, Kristina O; Yokosawa, Tadahiro; Finck, Nicolas; Bahl, Sebastian; Schild, Dieter; Polly, Robert; Bohnert, Elke; Rossberg, André; Göttlicher, Jörg; Dardenne, Kathy; Rothe, Jörg; Schäfer, Thorsten; Geckeis, Horst; Vitova, Tonya

2017-02-21

Uranium redox states and speciation in magnetite nanoparticles coprecipitated with U(VI) for uranium loadings varying from 1000 to 10 000 ppm are investigated by X-ray absorption spectroscopy (XAS). It is demonstrated that the U M 4 high energy resolution X-ray absorption near edge structure (HR-XANES) method is capable to clearly characterize U(IV), U(V), and U(VI) existing simultaneously in the same sample. The contributions of the three different uranium redox states are quantified with the iterative transformation factor analysis (ITFA) method. U L 3 XAS and transmission electron microscopy (TEM) reveal that initially sorbed U(VI) species recrystallize to nonstoichiometric UO 2+x nanoparticles within 147 days when stored under anoxic conditions. These U(IV) species oxidize again when exposed to air. U M 4 HR-XANES data demonstrate strong contribution of U(V) at day 10 and that U(V) remains stable over 142 days under ambient conditions as shown for magnetite nanoparticles containing 1000 ppm U. U L 3 XAS indicates that this U(V) species is protected from oxidation likely incorporated into octahedral magnetite sites. XAS results are supported by density functional theory (DFT) calculations. Further characterization of the samples include powder X-ray diffraction (pXRD), scanning electron microscopy (SEM) and Fe 2p X-ray photoelectron spectroscopy (XPS).

In situ spectroscopy and spectroelectrochemistry of uranium in high-temperature alkali chloride molten salts.

PubMed

Polovov, Ilya B; Volkovich, Vladimir A; Charnock, John M; Kralj, Brett; Lewin, Robert G; Kinoshita, Hajime; May, Iain; Sharrad, Clint A

2008-09-01

Soluble uranium chloride species, in the oxidation states of III+, IV+, V+, and VI+, have been chemically generated in high-temperature alkali chloride melts. These reactions were monitored by in situ electronic absorption spectroscopy. In situ X-ray absorption spectroscopy of uranium(VI) in a molten LiCl-KCl eutectic was used to determine the immediate coordination environment about the uranium. The dominant species in the melt was [UO 2Cl 4] (2-). Further analysis of the extended X-ray absorption fine structure data and Raman spectroscopy of the melts quenched back to room temperature indicated the possibility of ordering beyond the first coordination sphere of [UO 2Cl 4] (2-). The electrolytic generation of uranium(III) in a molten LiCl-KCl eutectic was also investigated. Anodic dissolution of uranium metal was found to be more efficient at producing uranium(III) in high-temperature melts than the cathodic reduction of uranium(IV). These high-temperature electrolytic processes were studied by in situ electronic absorption spectroelectrochemistry, and we have also developed in situ X-ray absorption spectroelectrochemistry techniques to probe both the uranium oxidation state and the uranium coordination environment in these melts.

Biosorption characteristics of Uranium (VI) from aqueous solution by pollen pini.

PubMed

Wang, Feihong; Tan, Lichao; Liu, Qi; Li, Rumin; Li, Zhanshuang; Zhang, Hongsen; Hu, Songxia; Liu, Lianhe; Wang, Jun

2015-12-01

Uranium biosorption from aqueous solutions by pollen pini (Pinus massoniana pollen) was studied in a bath system. The biosorbent was characterized by Fourier-transform infrared spectroscopy and scanning electron microscope. The influences of pH, contact time and initial uranium concentration at room temperature were investigated and the experimental curves were obtained. The pollen pini exhibited the highest uranium sorption capacity at pH 5.0 after 2 h contact. At pH 2.5 pollen pini also exhibited a good uranium loading capacity (>15%). Therefore biosorption characteristics of uranium from aqueous solution onto pollen pini were examined at pH 2.5 as well. The kinetics followed a pseudo-second-order rate equation and adsorption process was well fitted with the Freundlich isotherm at both pH. The adsorption of uranium by the biosorbent was confirmed by energy dispersive spectroscopy. The present study suggested that pollen pini could be a suitable biosorbent for biosorption uranium (VI) from aqueous solution in a fast, low cost and convenient approach. Copyright © 2015 Elsevier Ltd. All rights reserved.

Influence of Bicarbonate, Sulfate, and Electron Donors on Biological reduction of Uranium and Microbial Community Composition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Wensui; Zhou, Jizhong; Wu, Weimin

2007-01-01

A microcosm study was performed to investigate the effect of ethanol and acetate on uranium(VI) biological reduction and microbial community changes under various geochemical conditions. Each microcosm contained an uranium-contaminated sediment (up to 2.8 g U/kg) suspended in buffer with bicarbonate at concentrations of either 1 mM or 40 mM and sulfate at either 1.1 or 3.2 mM. Ethanol or acetate was used as an electron donor. Results indicate that ethanol yielded in significantly higher U(VI) reduction rates than acetate. A low bicarbonate concentration (1 mM) was favored for U(VI) bioreduction to occur in sediments, but high concentrations of bicarbonatemore » (40 mM) and sulfate (3.2 mM) decreased the reduction rates of U(VI). Microbial communities were dominated by species from the Geothrix genus and Proteobacteria phylum in all microcosms. However, species in the Geobacteraceae family capable of reducing U(VI) were significantly enriched by ethanol and acetate in low bicarbonate buffer. Ethanol increased the population of unclassified Desulfuromonales, while acetate increased the population of Desulfovibrio. Additionally, species in the Geobacteraceae family were not enriched in high bicarbonate buffer, but the Geothrix and the unclassified Betaproteobacteria species were enriched. This study concludes that ethanol could be a better electron donor than acetate for reducing U(VI) under given experimental conditions, and electron donor and geoundwater geochemistry alter microbial communities responsible for U(VI) reduction.« less

Competing retention pathways of uranium upon reaction with Fe(II)

NASA Astrophysics Data System (ADS)

Massey, Michael S.; Lezama-Pacheco, Juan S.; Jones, Morris E.; Ilton, Eugene S.; Cerrato, José M.; Bargar, John R.; Fendorf, Scott

2014-10-01

Biogeochemical retention processes, including adsorption, reductive precipitation, and incorporation into host minerals, are important in contaminant transport, remediation, and geologic deposition of uranium. Recent work has shown that U can become incorporated into iron (hydr)oxide minerals, with a key pathway arising from Fe(II)-induced transformation of ferrihydrite, (Fe(OH)3·nH2O) to goethite (α-FeO(OH)); this is a possible U retention mechanism in soils and sediments. Several key questions, however, remain unanswered regarding U incorporation into iron (hydr)oxides and this pathway's contribution to U retention, including: (i) the competitiveness of U incorporation versus reduction to U(IV) and subsequent precipitation of UO2; (ii) the oxidation state of incorporated U; (iii) the effects of uranyl aqueous speciation on U incorporation; and, (iv) the mechanism of U incorporation. Here we use a series of batch reactions conducted at pH ∼7, [U(VI)] from 1 to 170 μM, [Fe(II)] from 0 to 3 mM, and [Ca] at 0 or 4 mM coupled with spectroscopic examination of reaction products of Fe(II)-induced ferrihydrite transformation to address these outstanding questions. Uranium retention pathways were identified and quantified using extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Analysis of EXAFS spectra showed that 14-89% of total U was incorporated into goethite, upon reaction with Fe(II) and ferrihydrite. Uranium incorporation was a particularly dominant retention pathway at U concentrations ⩽50 μM when either uranyl-carbonato or calcium-uranyl-carbonato complexes were dominant, accounting for 64-89% of total U. With increasing U(VI) and Fe(II) concentrations, U(VI) reduction to U(IV) became more prevalent, but U incorporation remained a functioning retention pathway. These findings highlight the potential importance of U(V) incorporation within iron oxides as a retention process of U across a wide range of biogeochemical environments and the sensitivity of uranium retention processes to operative (bio)geochemical conditions.

Pilot Study to Evaluate Hydrogen Injection for Stimulating Reduction and Immobilization of Uranium in Groundwater at an ISR Mining Site

NASA Astrophysics Data System (ADS)

Clapp, L. W.; Cabezas, J.; Gamboa, Y.; Fernandez, W.

2011-12-01

State and federal regulations require that groundwater at in-situ recovery (ISR) uranium mining operations be restored to pre-mining conditions. Reverse osmosis (RO) filtration of several pore volumes of the post-leached groundwater and reinjection of the clean permeate is the most common technology currently used for restoring groundwater at uranium ISR sites. However, this approach does not revert the formation back to its initial reducing conditions, which can potentially impede timely groundwater restoration. In-situ biostimulation of indigenous iron- and sulfate reducing bacteria by injection of organic electron donors (e.g., ethanol, acetate, and lactate) to promote soluble uranium reduction and immobilization has been the subject of previous studies. However, injection of organic substrates has been observed to cause aquifer clogging near the injection point. In addition, U(VI) solubility may be enhanced through complexation with carbonate generated by organic carbon oxidation. An alternative approach that may overcome these problems involves the use of hydrogen as a reductant to promote microbial reduction and immobilization of U(VI) in situ. To test this approach, approximately 100,000 scf of compressed hydrogen gas was injected into a leached unconsolidated sand zone over two months at an ISR mining site. During this time groundwater was recirculated between injection and extraction wells (separated by 130 ft) at a rate of about 40 gpm and bromide was coinjected as a conservative tracer. A well monitoring program has been executed since June 2009 to evaluate the performance of the hydrogen injection. Current results show that U(VI) has been reduced from 4.2 to 0.05 ppm in the area surrounding the injection well and to 2.0 ± 0.3 ppm in the area surrounding the extraction well and two intermediate monitoring wells. Other water quality changes near the injection well include significant decreases in concentrations of Mo, sulfate, Fe, Mn, bicarbonate, Ca, and Eh, and increases in pH, methane, and sulfide. No significant rebound of soluble uranium concentrations was observed, but significant rebounds in molybdenum and sulfate have been observed. Ongoing studies are evaluating the effective zone of influence of the hydrogen injection.

Competing retention pathways of uranium upon reaction with Fe(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Massey, Michael S.; Lezama Pacheco, Juan S.; Jones, Morris

Biogeochemical retention processes, including adsorption, reductive precipitation, and incorporation into host minerals, are important in contaminant transport, remediation, and geologic deposition of uranium. Recent work has shown that U can become incorporated into iron (hydr)oxide minerals, with a key pathway arising from Fe(II)-induced transformation of ferrihydrite, (Fe(OH)3•nH2O) to goethite (α-FeO(OH)); this is a possible U retention mechanism in soils and sediments. Several key questions, however, remain unanswered regarding U incorporation into iron (hydr)oxides and this pathway’s contribution to U retention, including: (i) the competitiveness of U incorporation versus reduction to U(IV) and subsequent precipitation of UO2; (ii) the oxidation statemore » of incorporated U; (iii) the effects of uranyl aqueous speciation on U incorporation; and, (iv) the mechanism of U incorporation. Here we use a series of batch reactions conducted at pH ~7, [U(VI)] from 1 to 170 μM, [Fe(II)] from 0 to 3 mM, and [Ca] at 0 or 4 mM) coupled with spectroscopic examination of reaction products of Fe(II)-induced ferrihydrite transformation to address these outstanding questions. Uranium retention pathways were identified and quantified using extended x-ray absorption fine structure (EXAFS) spectroscopy, x-ray powder diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy. Analysis of EXAFS spectra showed that 14 to 89% of total U was incorporated into goethite, upon reaction with Fe(II) and ferrihydrite. Uranium incorporation was a particularly dominant retention pathway at U concentrations ≤ 50 μM when either uranyl-carbonato or calcium-uranyl-carbonato complexes were dominant, accounting for 64 to 89% of total U. With increasing U(VI) and Fe(II) concentrations, U(VI) reduction to U(IV) became more prevalent, but U incorporation remained a functioning retention pathway. These findings highlight the potential importance of U(V) incorporation within iron oxides as a retention process of U across a wide range of biogeochemical environments and the sensitivity of uranium retention processes to operative (bio)geochemical conditions.« less

Formation of unprecedented actinidecarbon triple bonds in uranium methylidyne molecules

PubMed Central

Lyon, Jonathan T.; Hu, Han-Shi; Andrews, Lester; Li, Jun

2007-01-01

Chemistry of the actinide elements represents a challenging yet vital scientific frontier. Development of actinide chemistry requires fundamental understanding of the relative roles of actinide valence-region orbitals and the nature of their chemical bonding. We report here an experimental and theoretical investigation of the uranium methylidyne molecules X3UCH (X = F, Cl, Br), F2ClUCH, and F3UCF formed through reactions of laser-ablated uranium atoms and trihalomethanes or carbon tetrafluoride in excess argon. By using matrix infrared spectroscopy and relativistic quantum chemistry calculations, we have shown that these actinide complexes possess relatively strong UC triple bonds between the U 6d-5f hybrid orbitals and carbon 2s-2p orbitals. Electron-withdrawing ligands are critical in stabilizing the U(VI) oxidation state and sustaining the formation of uranium multiple bonds. These unique UC-bearing molecules are examples of the long-sought actinide-alkylidynes. This discovery opens the door to the rational synthesis of triple-bonded actinidecarbon compounds. PMID:18024591

Uranium reduction and resistance to reoxidation under iron-reducing and sulfate-reducing conditions.

PubMed

Boonchayaanant, Benjaporn; Nayak, Dipti; Du, Xin; Criddle, Craig S

2009-10-01

Oxidation and mobilization of microbially-generated U(IV) is of great concern for in situ uranium bioremediation. This study investigated the reoxidation of uranium by oxygen and nitrate in a sulfate-reducing enrichment and an iron-reducing enrichment derived from sediment and groundwater from the Field Research Center in Oak Ridge, Tennessee. Both enrichments were capable of reducing U(VI) rapidly. 16S rRNA gene clone libraries of the two enrichments revealed that Desulfovibrio spp. are dominant in the sulfate-reducing enrichment, and Clostridium spp. are dominant in the iron-reducing enrichment. In both the sulfate-reducing enrichment and the iron-reducing enrichment, oxygen reoxidized the previously reduced uranium but to a lesser extent in the iron-reducing enrichment. Moreover, in the iron-reducing enrichment, the reoxidized U(VI) was eventually re-reduced to its previous level. In both, the sulfate-reducing enrichment and the iron-reducing enrichment, uranium reoxidation did not occur in the presence of nitrate. The results indicate that the Clostridium-dominated iron-reducing communities created conditions that were more favorable for uranium stability with respect to reoxidation despite the fact that fewer electron equivalents were added to these systems. The likely reason is that more of the added electrons are present in a form that can reduce oxygen to water and U(VI) back to U(IV).

Efficacy of a novel chelator BPCBG for removing uranium and protecting against uranium-induced renal cell damage in rats and HK-2 cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bao, Yizhong; Wang, Dan; Li, Zhiming

2013-05-15

Chelation therapy is a known effective method to increase the excretion of U(VI) from the body. Until now, no any uranium chelator has been approved for emergency medical use worldwide. The present study aimed to evaluate the efficacy of new ligand BPCBG containing two catechol groups and two aminocarboxylic acid groups in decorporation of U(VI) and protection against acute U(VI) nephrotoxicity in rats, and further explored the detoxification mechanism of BPCBG for U(VI)-induced nephrotoxicity in HK-2 cells with comparison to DTPA-CaNa{sub 3}. Chelating agents were administered at various times before or after injections of U(VI) in rats. The U(VI) levelsmore » in urine, kidneys and femurs were measured 24 h after U(VI) injections. Histopathological changes in the kidney and serum urea and creatinine and urine protein were examined. After treatment of U(VI)-exposed HK-2 cells with chelating agent, the intracellular U(VI) contents, formation of micronuclei, lactate dehydrogenase (LDH) activity and production of reactive oxygen species (ROS) were assessed. It was found that prompt, advanced or delayed injections of BPCBG effectively increased 24 h-urinary U(VI) excretion and decreased the levels of U(VI) in kidney and bone. Meanwhile, BPCBG injection obviously reduced the severity of the U(VI)-induced histological alterations in the kidney, which was in parallel with the amelioration noted in serum indicators, urea and creatinine, and urine protein of U(VI) nephrotoxicity. In U(VI)-exposed HK-2 cells, immediate and delayed treatment with BPCBG significantly decreased the formation of micronuclei and LDH release by inhibiting the cellular U(VI) intake, promoting the intracellular U(VI) release and inhibiting the production of intracellular ROS. Our data suggest that BPCBG is a novel bi-functional U(VI) decorporation agent with a better efficacy than DTPA-CaNa{sub 3}. - Highlights: ► BPCBG accelerated the urine U(VI) excretion and reduced the tissues U(VI) in rats. ► BPCBG can effectively protect against the U(VI)-induced nephrotoxicity in rats. ► BPCBG increased the U(VI) release and reduced the U(VI) uptake in HK-2 cells. ► BPCBG decreased the U(VI)-induced MN formation and LDH release in HK-2 cells. ► BPCBG eliminated the U(VI)-induced intracellular ROS in HK-2 cells.« less

Bioreduction of U(VI) and stability of immobilized uranium under suboxic conditions.

PubMed

Hu, Nan; Ding, De-xin; Li, Shi-mi; Tan, Xiang; Li, Guang-yue; Wang, Yong-dong; Xu, Fei

2016-04-01

In order to study the bioreduction of U(VI) and stability of immobilized uranium under suboxic conditions, microcosm were amended with ethanol, lactate and glucose, and incubated under suboxic conditions. During the incubation, total dissolved U in amended microcosms decreased from 0.95 mg/L to 0.03 mg/L. Pyrosequencing results showed that, the proportion of anaerobic microorganisms capable of reducing U(VI) under suboxic conditions was small compared with that under anoxic conditions; the proportion of aerobic and facultative anaerobic microorganisms capable of consuming the dissolved oxygen was large; and some of the facultative anaerobic microorganisms could reduce U(VI). These results indicated that different microbial communities were responsible for the bioreduction of U(VI) under suboxic and anoxic conditions. After the electron donors were exhausted, total dissolved U in the amended microcosms remained unchanged, while the U(VI)/U(IV) ratio in the solid phase of sediments increased obviously. This implied that the performance of bioreduction of the U(VI) can be maintained under suboxic condition. Copyright © 2016 Elsevier Ltd. All rights reserved.

Comparison of in situ uranium KD values with a laboratory determined surface complexation model

USGS Publications Warehouse

Curtis, G.P.; Fox, P.; Kohler, M.; Davis, J.A.

2004-01-01

Reactive solute transport simulations in groundwater require a large number of parameters to describe hydrologic and chemical reaction processes. Appropriate methods for determining chemical reaction parameters required for reactive solute transport simulations are still under investigation. This work compares U(VI) distribution coefficients (i.e. KD values) measured under field conditions with KD values calculated from a surface complexation model developed in the laboratory. Field studies were conducted in an alluvial aquifer at a former U mill tailings site near the town of Naturita, CO, USA, by suspending approximately 10 g samples of Naturita aquifer background sediments (NABS) in 17-5.1-cm diameter wells for periods of 3 to 15 months. Adsorbed U(VI) on these samples was determined by extraction with a pH 9.45 NaHCO3/Na2CO3 solution. In wells where the chemical conditions in groundwater were nearly constant, adsorbed U concentrations for samples taken after 3 months of exposure to groundwater were indistinguishable from samples taken after 15 months. Measured in situ K D values calculated from the measurements of adsorbed and dissolved U(VI) ranged from 0.50 to 10.6 mL/g and the KD values decreased with increasing groundwater alkalinity, consistent with increased formation of soluble U(VI)-carbonate complexes at higher alkalinities. The in situ K D values were compared with KD values predicted from a surface complexation model (SCM) developed under laboratory conditions in a separate study. A good agreement between the predicted and measured in situ KD values was observed. The demonstration that the laboratory derived SCM can predict U(VI) adsorption in the field provides a critical independent test of a submodel used in a reactive transport model. ?? 2004 Elsevier Ltd. All rights reserved.

In situ mobility of uranium in the presence of nitrate following sulfate-reducing conditions.

PubMed

Paradis, Charles J; Jagadamma, Sindhu; Watson, David B; McKay, Larry D; Hazen, Terry C; Park, Melora; Istok, Jonathan D

2016-04-01

Reoxidation and mobilization of previously reduced and immobilized uranium by dissolved-phase oxidants poses a significant challenge for remediating uranium-contaminated groundwater. Preferential oxidation of reduced sulfur-bearing species, as opposed to reduced uranium-bearing species, has been demonstrated to limit the mobility of uranium at the laboratory scale yet field-scale investigations are lacking. In this study, the mobility of uranium in the presence of nitrate oxidant was investigated in a shallow groundwater system after establishing conditions conducive to uranium reduction and the formation of reduced sulfur-bearing species. A series of three injections of groundwater (200 L) containing U(VI) (5 μM) and amended with ethanol (40 mM) and sulfate (20 mM) were conducted in ten test wells in order to stimulate microbial-mediated reduction of uranium and the formation of reduced sulfur-bearing species. Simultaneous push-pull tests were then conducted in triplicate well clusters to investigate the mobility of U(VI) under three conditions: 1) high nitrate (120 mM), 2) high nitrate (120 mM) with ethanol (30 mM), and 3) low nitrate (2 mM) with ethanol (30 mM). Dilution-adjusted breakthrough curves of ethanol, nitrate, nitrite, sulfate, and U(VI) suggested that nitrate reduction was predominantly coupled to the oxidation of reduced-sulfur bearing species, as opposed to the reoxidation of U(IV), under all three conditions for the duration of the 36-day tests. The amount of sulfate, but not U(VI), recovered during the push-pull tests was substantially more than injected, relative to bromide tracer, under all three conditions and further suggested that reduced sulfur-bearing species were preferentially oxidized under nitrate-reducing conditions. However, some reoxidation of U(IV) was observed under nitrate-reducing conditions and in the absence of detectable nitrate and/or nitrite. This suggested that reduced sulfur-bearing species may not be fully effective at limiting the mobility of uranium in the presence of dissolved and/or solid-phase oxidants. The results of this field study confirmed those of previous laboratory studies which suggested that reoxidation of uranium under nitrate-reducing conditions can be substantially limited by preferential oxidation of reduced sulfur-bearing species. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

In situ mobility of uranium in the presence of nitrate following sulfate-reducing conditions

DOE PAGES

Paradis, Charles J.; Jagadamma, Sindhu; Watson, David B.; ...

2016-02-11

Reoxidation and mobilization of previously reduced and immobilized uranium by dissolved phase oxidants poses a significant challenge for remediating uranium-contaminated groundwater. Preferential oxidation of reduced sulfur-bearing species, as opposed to reduced uranium bearing species, has been demonstrated to limit the mobility of uranium at the laboratory scale yet field-scale investigations are lacking. Here in this study, the mobility of uranium in the presence of nitrate oxidant was investigated in a shallow groundwater system after establishing conditions conducive to uranium reduction and the formation of reduced sulfur-bearing species. A series of three injections of groundwater (200 L) containing U(VI) (5 μM)more » and amended with ethanol (40 mM) and sulfate (20 mM) were conducted in ten test wells in order to stimulate microbial mediated reduction of uranium and the formation of reduced sulfur-bearing species. Simultaneous push-pull tests were then conducted in triplicate well clusters to investigate the mobility of U(VI) under three conditions: 1) high nitrate (120 mM), 2) high nitrate (120 mM) with ethanol (30 mM), and 3) low nitrate (2 mM) with ethanol (30 mM). Dilution-adjusted breakthrough curves of ethanol, nitrate, nitrite, sulfate, and U(VI) suggested that nitrate reduction was predominantly coupled to the oxidation of reduced-sulfur bearing species, as opposed to the reoxidation of U(IV), under all three conditions for the duration of the 36-day tests. The amount of sulfate, but not U(VI), recovered during the push-pull tests was substantially more than injected, relative to bromide tracer, under all three conditions and further suggested that reduced sulfur-bearing species were preferentially oxidized under nitrate-reducing conditions. However, some reoxidation of U(IV) was observed under nitrate-reducing conditions and in the absence of detectable nitrate and/or nitrite. This suggested that reduced sulfur-bearing species may not be fully effective at limiting the mobility of uranium in the presence of dissolved and/or solid-phase oxidants. Lastly, the results of this field study confirmed those of previous laboratory studies which suggested that reoxidation of uranium under nitrate-reducing conditions can be substantially limited by preferential oxidation of reduced sulfur-bearing species.« less

Approaches to modelling uranium (VI) adsorption on natural mineral assemblages

USGS Publications Warehouse

Waite, T.D.; Davis, J.A.; Fenton, B.R.; Payne, T.E.

2000-01-01

Component additivity (CA) and generalised composite (GC) approaches to deriving a suitable surface complexation model for description of U(VI) adsorption to natural mineral assemblages are pursued in this paper with good success. A single, ferrihydrite-like component is found to reasonably describe uranyl uptake to a number of kaolinitic iron-rich natural substrates at pH > 4 in the CA approach with previously published information on nature of surface complexes, acid-base properties of surface sites and electrostatic effects used in the model. The GC approach, in which little pre-knowledge about generic surface sites is assumed, gives even better fits and would appear to be a method of particular strength for application in areas such as performance assessment provided the model is developed in a careful, stepwise manner with simplicity and goodness of fit as the major criteria for acceptance.

Electron transfer at the cell-uranium interface in Geobacter spp.

PubMed

Reguera, Gemma

2012-12-01

The in situ stimulation of Fe(III) oxide reduction in the subsurface stimulates the growth of Geobacter spp. and the precipitation of U(VI) from groundwater. As with Fe(III) oxide reduction, the reduction of uranium by Geobacter spp. requires the expression of their conductive pili. The pili bind the soluble uranium and catalyse its extracellular reductive precipitation along the pili filaments as a mononuclear U(IV) complexed by carbon-containing ligands. Although most of the uranium is immobilized by the pili, some uranium deposits are also observed in discreet regions of the outer membrane, consistent with the participation of redox-active foci, presumably c-type cytochromes, in the extracellular reduction of uranium. It is unlikely that cytochromes released from the outer membrane could associate with the pili and contribute to the catalysis, because scanning tunnelling microscopy spectroscopy did not reveal any haem-specific electronic features in the pili, but, rather, showed topographic and electronic features intrinsic to the pilus shaft. Pili not only enhance the rate and extent of uranium reduction per cell, but also prevent the uranium from traversing the outer membrane and mineralizing the cell envelope. As a result, pili expression preserves the essential respiratory activities of the cell envelope and the cell's viability. Hence the results support a model in which the conductive pili function as the primary mechanism for the reduction of uranium and cellular protection in Geobacter spp.

Resistance, bioaccumulation and solid phase extraction of uranium (VI) by Bacillus vallismortis and its UV-vis spectrophotometric determination.

PubMed

Ozdemir, Sadin; Oduncu, M Kadir; Kilinc, Ersin; Soylak, Mustafa

2017-05-01

Bioaccumulation, resistance and preconcentration of uranium(VI) by thermotolerant Bacillus vallismortis were investigated in details. The minimum inhibition concentration of (MIC) value of U(VI) was found as 85 mg/L and 15 mg/L in liquid and solid medium, respectively. Furthermore, the effect of various U(VI) concentrations on the growth of bacteria and bioaccumulation on B. vallismortis was examined in the liquid culture media. The growth was not significantly affected in the presence of 1.0, 2.5 and 5.0 mg/L U(VI) up to 72 h. The highest bioaccumulation value at 1 mg/L U(VI) concentration was detected at the 72nd hour (10 mg/g metal/dry bacteria), while the maximum bioaccumulation value at 5 mg/L U(VI) concentration was determined at the 48th hour (50 mg metal/dry bacteria). In addition to these, various concentration of U(VI) on α-amylase production was studied. The α-amylase activities at 0, 1, 2.5 and 5 mg/L U(VI) were found as 3313.2, 3845.2, 3687.1 and 3060.8 U/mg, respectively at 48th. Besides, uranium (VI) ions were preconcentrated with immobilized B. vallismortis onto multiwalled carbon nanotube (MWCNT) and were determined by UV-vis spectrophotometry. The surface macro structure and functionalities of B. vallismortis immobilized onto multiwalled carbon nanotube with and without U(VI) were examined by FT-IR and SEM. The optimum pH and flow rate for the biosorption of U(VI) were 4.0-5.0 and 1.0 mL/min, respectively. The quantitative elution occurred with 5.0 mL of 1 mol/L HCl. The loading capacity of immobilized B. vallismortis was determined as 23.6 mg/g. The certified reference sample was employed for the validation of developed solid phase extraction method. The new validated method was applied to the determination of U(VI) in water samples from Van Lake-Turkey. Copyright © 2017 Elsevier Ltd. All rights reserved.

Complexation of uranium(VI) with glutarimidoxioxime: thermodynamic and computational studies.

PubMed

Endrizzi, Francesco; Melchior, Andrea; Tolazzi, Marilena; Rao, Linfeng

2015-08-21

The complex formation between a cyclic ligand glutarimidoxioxime (denoted as HL(III) in this paper) and UO2(2+) is studied by potentiometry and microcalorimetry. Glutarimidoxioxime (HL(III)), together with glutarimidedioxime (H2L(I)) and glutardiamidoxime (H2L(II)), belongs to a family of amidoxime derivatives with prospective applications as binding agents for the recovery of uranium from seawater. An optimized procedure of synthesis that leads to the preparation of glutarimidoxioxime in the absence of other amidoxime byproducts is described in this paper. Speciation models based on the thermodynamic results from this study indicate that, compared with H2L(I) and H2L(II), HL(III) forms a much weaker complex with UO2(2+), UO2(L(III))(+), and cannot effectively compete with the hydrolysis equilibria of UO2(2+) under neutral or alkaline conditions. DFT computations, taking into account the solvation by including discrete hydration water molecules and bulk solvent effects, were performed to evaluate the structures and energies of the possible isomers of UO2(L(III))(+). Differing from the tridentate or η(2)-coordination modes previously found in the U(vi) complexes with amidoxime-related ligands, a bidentate mode, involving the oxygen of the oxime group and the nitrogen of the imino group, is found to be the most probable mode in UO2(L(III))(+). The bidentate coordination mode seems to be stabilized by the formation of a hydrogen bond between the carbonyl group of HL(III) and a water molecule in the hydration sphere of UO2(2+).

Potential aquifer vulnerability in regions down-gradient from uranium in situ recovery (ISR) sites.

PubMed

Saunders, James A; Pivetz, Bruce E; Voorhies, Nathan; Wilkin, Richard T

2016-12-01

Sandstone-hosted roll-front uranium ore deposits originate when U(VI) dissolved in groundwater is reduced and precipitated as insoluble U(IV) minerals. Groundwater redox geochemistry, aqueous complexation, and solute migration are important in leaching uranium from source rocks and transporting it in low concentrations to a chemical redox interface where it is deposited in an ore zone typically containing the uranium minerals uraninite, pitchblende, and/or coffinite; various iron sulfides; native selenium; clays; and calcite. In situ recovery (ISR) of uranium ores is a process of contacting the uranium mineral deposit with leaching and oxidizing (lixiviant) fluids via injection of the lixiviant into wells drilled into the subsurface aquifer that hosts uranium ore, while other extraction wells pump the dissolved uranium after dissolution of the uranium minerals. Environmental concerns during and after ISR include water quality degradation from: 1) potential excursions of leaching solutions away from the injection zone into down-gradient, underlying, or overlying aquifers; 2) potential migration of uranium and its decay products (e.g., Ra, Rn, Pb); and, 3) potential mobilization and migration of redox-sensitive trace metals (e.g., Fe, Mn, Mo, Se, V), metalloids (e.g., As), and anions (e.g., sulfate). This review describes the geochemical processes that control roll-front uranium transport and fate in groundwater systems, identifies potential aquifer vulnerabilities to ISR operations, identifies data gaps in mitigating these vulnerabilities, and discusses the hydrogeological characterization involved in developing a monitoring program. Published by Elsevier Ltd.

Syntheses and structures of [UO2( L)5](ClO4)2 and [U( L')4(H2O)4](ClO4)4 ( L is dimethylformamide, L' is N,N-dimethylcarbamide)

NASA Astrophysics Data System (ADS)

Serezhkin, V. N.; Vologzhanina, A. V.; Pushkin, D. V.; Astashkina, D. A.; Savchenkov, A. V.; Serezhkina, L. B.

2017-09-01

The reaction of aqueous solutions of uranyl perchlorate with selected organic amides was studied in the dark and under the sunlight. The complexes [UVIO2(C3H7NO)5](ClO4)2 ( I) and [UIV(C3H8N2O)4(H2O)4](ClO4)4 ( II), where C3H7NO is N,N-dimethylformamide ( Dmfa) and C3H8N2O is N,N-dimethylcarbamide ( a-Dmur), were studied by X-ray diffraction. Complex II and the complex UIV( s-Dmur)4(H2O)4(ClO4)4 ( III), where s-Dmur is N,N'-dimethylcarbamide, were studied by IR spectroscopy. Crystals I and II are composed of mononuclear [UO2( Dmfa)5]2+ and [U( Dmur)4(H2O)4]4+ groups as uranium-containing structural units belonging to the crystal-chemical groups AM 7 1 ( A = UVI, M 1 = O2- and Dmfa) and AM 8 1 ( A = UIV, M 1 = Dmur and H2O) of uranium complexes, respectively. The mononuclear uranium- containing complexes in the crystals of U(IV) and U(VI) perchlorates were found to obey the 14 neighbors rule.

Rapid removal of uranium from aqueous solutions using magnetic Fe3O4@SiO2 composite particles.

PubMed

Fan, Fang-Li; Qin, Zhi; Bai, Jing; Rong, Wei-Dong; Fan, Fu-You; Tian, Wei; Wu, Xiao-Lei; Wang, Yang; Zhao, Liang

2012-04-01

Rapid removal of U(VI) from aqueous solutions was investigated using magnetic Fe(3)O(4)@SiO(2) composite particles as the novel adsorbent. Batch experiments were conducted to study the effects of initial pH, amount of adsorbent, shaking time and initial U(VI) concentrations on uranium sorption efficiency as well as the desorbing of U(VI). The sorption of uranium on Fe(3)O(4)@SiO(2) composite particles was pH-dependent, and the optimal pH was 6.0. In kinetics studies, the sorption equilibrium can be reached within 180 min, and the experimental data were well fitted by the pseudo-second-order model, and the equilibrium sorption capacities calculated by the model were almost the same as those determined by experiments. The Langmuir sorption isotherm model correlates well with the uranium sorption equilibrium data for the concentration range of 20-200 mg/L. The maximum uranium sorption capacity onto magnetic Fe(3)O(4)@SiO(2) composite particles was estimated to be about 52 mg/g at 25 °C. The highest values of uranium desorption (98%) was achieved using 0.01 M HCl as the desorbing agent. Fe(3)O(4)@SiO(2) composite particles showed a good selectivity for uranium from aqueous solution with other interfering cation ions. Present study suggested that magnetic Fe(3)O(4)@SiO(2) composite particles can be used as a potential adsorbent for sorption uranium and also provided a simple, fast separation method for removal of heavy metal ion from aqueous solution. Copyright © 2011 Elsevier Ltd. All rights reserved.

2,6-Diiminopiperidin-1-ol: an overlooked motif relevant to uranyl and transition metal binding on poly(amidoxime) adsorbents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kennedy, Zachary C.; Cardenas, Allan Jay P.; Corbey, Jordan F.

2016-01-01

Glutardiamidoxime, a structural motif on sorbents used in uranium extraction from seawater, was discovered to cyclize in situ at room temperature to 2,6-diimino-piperidin-1-ol in the presence of uranyl nitrate. The new diimino motif was also generated when exposed to competing transition metals Cu(II) and Ni(II). Multinuclear μ-O bridged U(VI), Cu(II), and Ni(II) complexes featuring bound diimino ligands were isolated. A Cu(II) complex with the historically relevant cyclic imide dioxime motif is also reported for structural comparison to the reported diimino complexes.

Biogeochemical controls of uranium bioavailability from the dissolved phase in natural freshwaters

USGS Publications Warehouse

Croteau, Marie-Noele; Fuller, Christopher C.; Cain, Daniel J.; Campbell, Kate M.; Aiken, George R.

2016-01-01

To gain insights into the risks associated with uranium (U) mining and processing, we investigated the biogeochemical controls of U bioavailability in the model freshwater speciesLymnaea stagnalis (Gastropoda). Bioavailability of dissolved U(VI) was characterized in controlled laboratory experiments over a range of water hardness, pH, and in the presence of complexing ligands in the form of dissolved natural organic matter (DOM). Results show that dissolved U is bioavailable under all the geochemical conditions tested. Uranium uptake rates follow first order kinetics over a range encompassing most environmental concentrations. Uranium uptake rates in L. stagnalis ultimately demonstrate saturation uptake kinetics when exposure concentrations exceed 100 nM, suggesting uptake via a finite number of carriers or ion channels. The lack of a relationship between U uptake rate constants and Ca uptake rates suggest that U does not exclusively use Ca membrane transporters. In general, U bioavailability decreases with increasing pH, increasing Ca and Mg concentrations, and when DOM is present. Competing ions did not affect U uptake rates. Speciation modeling that includes formation constants for U ternary complexes reveals that the aqueous concentration of dicarbonato U species (UO2(CO3)2–2) best predicts U bioavailability to L. stagnalis, challenging the free-ion activity model postulate.

Optimizing Metalloporphyrin-Catalyzed Reduction Reactions for In Situ Remediation of DOE Contaminants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schlautman, Mark A.

2013-07-14

Past activities have resulted in a legacy of contaminated soil and groundwater at Department of Energy facilities nationwide. Uranium and chromium are among the most frequently encountered and highest-priority metal and radionuclide contaminants at DOE installations. Abiotic chemical reduction of uranium and chromium at contaminated DOE sites can be beneficial because the reduced metal species are less soluble in water, less mobile in the environment, and less toxic to humans and ecosystems. Although direct biological reduction has been reported for U(VI) and Cr(VI) in laboratory studies and at some field sites, the reactions can sometimes be slow or even inhibitedmore » due to unfavorable environmental conditions. One promising approach for the in-situ remediation of DOE contaminants is to develop electron shuttle catalysts that can be delivered precisely to the specific subsurface locations where contaminants reside. Previous research has shown that reduction of oxidized organic and inorganic contaminants often can be catalyzed by electron shuttle systems. Metalloporphyrins and their derivatives are well known electron shuttles for many biogeochemical systems, and thus were selected to study their catalytic capabilities for the reduction of chromium and uranium in the presence of reducing agents. Zero valent iron (ZVI) was chosen as the primary electron donor in most experimental systems. Research proceeded in three phases and the key findings of each phase are reported here. Phase I examined Cr(VI) reduction and utilized micro- and nano-sized ZVI as the electron donors. Electron shuttle catalysts tested were cobalt- and iron-containing metalloporphyrins and Vitamin B12. To aid in the recycle and reuse of the nano-sized ZVI and soluble catalysts, sol-gels and calcium-alginate gel beads were tested as immobilization/support matrices. Although the nano-sized ZVI could be incorporated within the alginate gel beads, preliminary attempts to trap it in sol-gels were not successful. Conversely, the water-soluble catalysts could be trapped within sol-gel matrices but they tended to leach out of the alginate gel beads during use. In general, immobilization of the nano-sized ZVI in gel beads and of the catalysts in sol-gels tended to result in slower rates of Cr(VI) reduction, but these effects could be overcome to some extent by using higher reactant/catalyst concentrations. In addition, the lowering of their effectiveness would likely be offset by the benefits obtained when recycling and reusing the materials because they were immobilized. Addition of the catalytic electron shuttles will be most useful when the micro-sized or nano-sized ZVI becomes less reactive with reaction time. Continued work in Phase II in the area of nano-sized ZVI immobilization led to procedures that were successful in incorporating the iron particles in sol-gel matrices. The water-soluble reductants sodium dithionite and L-ascorbic acid were also tested, but their use appeared to lead to formation of complexes with the uranyl cation which limited their effectiveness. Also, although the sol-gel supported nano-sized ZVI showed some promise at reducing uranium, the fluoride used in the sol-gel synthesis protocol appeared to lead to formation of uranyl-fluoride complexes that were less reactive. Because hexavalent chromium is an anion which does not form complexes with fluoride, it was used to demonstrate the intrinsic reactivity of the sol-gel immobilized nano-sized ZVI. Consistent with our observations in Phase I, the sol-gel matrix once again slowed down the reduction reaction but the expected benefits of recycle/reuse should outweigh this adverse effect. The major emphasis in Phase III of this study was to simultaneously incorporate nano-sized ZVI and water-soluble catalysts in the same sol-gel matrix. The catalysts utilized were cobalt complexes of uroporphyrin and protoporphyrin and Cr(VI) reduction was used to test the efficacy of the combined "catalyst + reductant" sol-gel matrix. When enough catalyst was added to the sol-gels, enhancement of the Cr(VI) reduction reaction was observed. At the lowest levels of catalyst addition, however, the rates of Cr(VI) reduction were similar to those systems which only used sol-gel immobilized nano-sized ZVI without any catalyst present. These findings suggest future areas of research that should be pursued to further optimize abiotic reduction reactions of metals with combined "catalyst + reductant" matrices.« less

PRECIPITATION OF ZIRCONIUM AND FLUORIDE IONS FROM SOLUTIONS

DOEpatents

Newby, B.J.

1963-06-11

A process is given for removing zirconium and fluorine ions from aqueous solutions also containing uranium(VI). The precipitation is carried out with sodium formate, and the uranium remains in solution. (AEC)

Processes affecting transport of uranium in a suboxic aquifer

USGS Publications Warehouse

Davis, J.A.; Curtis, G.P.; Wilkins, M.J.; Kohler, M.; Fox, P.; Naftz, D.L.; Lloyd, J.R.

2006-01-01

At the Naturita site in Colorado, USA, groundwaters were sampled and analyzed for chemical composition and by culture and culture-independent microbiological techniques. In addition, sediments were extracted with a dilute sodium carbonate solution to determine quantities of labile uranium within the sediments. Samples from the upgradient portion of the contaminated aquifer, where very little dissolved Fe(II) is found in the groundwater, have uranium content that is controlled by U(VI) adsorption and few metal-reducing bacteria are observed. In the extreme downgradient portion of the aquifer, where dissolved Fe(II) is observed, uranium content of the sediments includes significant quantities of reduced U(IV) and diverse populations of Fe(III)-reducing bacteria were present in the subsurface with the potential of reducing U(VI) to U(IV). ?? 2006 Elsevier Ltd. All rights reserved.

Surface catalysis of uranium(VI) reduction by iron(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liger, E.; Charlet, L.; Van Cappellen, P.

1999-10-01

Colloidal hematite ({alpha}-Fe{sub 2}O{sub 3}) is used as model solid to investigate the kinetic effect of specific adsorption interactions on the chemical reduction of uranyl (U{sup VI}O{sub 2}{sup 2+}) by ferrous iron. Acid-base titrations and Fe(II) and uranyl adsorption experiments are performed on hematite suspensions, under O{sub 2}- and CO{sub 2}-free conditions. The results are explained in terms of a constant capacitance surface complexation model of the hematite-aqueous solution interface. Two distinct Fe(II) surface complexes are required to reproduce the data: ({equivalent{underscore}to}Fe{sup III}OFe{sup II}){sup +} (or {equivalent{underscore}to}Fe{sup III}OFe{sup II}(OH{sub 2}){sub n}{sup +}) and {equivalent{underscore}to}Fe{sup III}OFe{sup II}OH{sup 0} (or {equivalent{underscore}to}Fe{sup III}OFe{supmore » II}(OH{sub 2}){sub n{minus}1}OH{sup 0}). The latter complex represents a significant fraction of total adsorbed Fe(II) at pH {gt} 6.5. Uranyl binding to the hematite particles is characterized by a sharp adsorption edge between pH 4 and pH 5.5. Because of the absence of competing aqueous carbonate complexes, uranyl remains completely adsorbed at pH {gt} 7. A single mononuclear surface complex accounts for the adsorption of uranyl over the entire range of experimental conditions. Although thermodynamically feasible, no reaction between uranyl and Fe(II) is observed in homogeneous solution at pH 7.5, for periods of up to three days. In hematite suspensions, however, surface-bound uranyl reacts on a time scale of hours. Based on Fourier Transformed Infrared spectra, chemical reduction of U(VI) is inferred to be the mechanism responsible for the disappearance of uranyl. The kinetics of uranyl reduction are quantified by measuring the decrease with time of the concentration of U(VI) extractable from the hematite particles by NaHCO{sub 3}. In the presence of excess Fe(II), the initial rate of U(VI) reduction exhibits a first-order dependence on the concentration of adsorbed uranyl. The pseudo-first-order rate constant varies with pH (range, 6--7.5) and the total (dissolved + adsorbed) concentration of Fe(II) (range, 2--160 {micro}M). When analyzing the rate data in terms of the calculated surface speciation, the variability of the rate constant can be accounted for entirely by changes in the concentration of the Fe(II) monohydroxo surface complex {equivalent{underscore}to}Fe{sup III}OFe{sup II}OH{sup 0}. Therefore, the rate law is derived for the hematite-catalyzed reduction of uranyl by Fe(II), where the bimolecular rate constant {kappa} has a value of 399 {+-} 25 M{sup {minus}1} min{sup {minus}1} at 25 C. The hydroxo surface complex is the rate-controlling reductant species, because it provides the most favorable coordination environment in which electrons are removed from Fe(II). Natural particulate matter collected in the hypolimnion of a seasonally stratified lake also causes the rapid reduction of uranyl by Fe(II), Ferrihydrite, identified in the particulate matter by X-ray diffraction, is one possible mineral phase accelerating the reaction between U(VI) and Fe(II). At near-neutral pH and total Fe(II) levels less than 1 mM, the pseudo-first-order rate constants of chemical U(VI) reduction, measured in the presence of the hematite and lake particles, are of the same order of magnitude as the highest corresponding rate coefficients for enzymatic U(VI) reduction in bacterial cultures. Hence, based on the results of this study, surface-catalyzed U(VI) reduction by Fe(II) is expected to be a major pathway of uranium immobilization in a wide range of redox-stratified environments.« less

Effect of Reaction Pathway on the Extent and Mechanism of Uranium(VI) Immobilization with Calcium and Phosphate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehta, Vrajesh S.; Maillot, Fabien; Wang, Zheming

Phosphate addition to subsurface environments contaminated with uranium can be used as an in situ remediation approach. Batch experiments were conducted to evaluate the dependence of the extent and mechanism of uranium uptake on the pathway for reaction with calcium phosphates. At pH 4.0 and 6.0 uranium uptake occurred via autunite (Ca(UO2)(PO4)3) precipitation irrespective of the starting forms of calcium and phosphate. At pH 7.5, the uptake mechanism depended on the nature of the calcium and phosphate. When dissolved uranium, calcium, and phosphate were added simultaneously, uranium was structurally incorporated into a newly formed amorphous calcium phosphate solid. Adsorption wasmore » the dominant removal mechanism for uranium contacted with pre-formed amorphous calcium phosphate solids,. When U(VI) was added to a suspension containing amorphous calcium phosphate solids as well as dissolved calcium and phosphate, then removal occurred through precipitation (57±4 %) of autunite and adsorption (43±4 %) onto calcium phosphate. The solid phase speciation of the uranium was determined using X-ray absorption spectroscopy and laser induced fluorescence spectroscopy. Dissolved uranium, calcium, and phosphate concentrations with saturation index calculations helped identify removal mechanisms and determine thermodynamically favorable solid phases.« less

Miniaturizing and automation of free acidity measurements for uranium (VI)-HNO3 solutions: Development of a new sequential injection analysis for a sustainable radio-analytical chemistry.

PubMed

Néri-Quiroz, José; Canto, Fabrice; Guillerme, Laurent; Couston, Laurent; Magnaldo, Alastair; Dugas, Vincent

2016-10-01

A miniaturized and automated approach for the determination of free acidity in solutions containing uranium (VI) is presented. The measurement technique is based on the concept of sequential injection analysis with on-line spectroscopic detection. The proposed methodology relies on the complexation and alkalimetric titration of nitric acid using a pH 5.6 sodium oxalate solution. The titration process is followed by UV/VIS detection at 650nm thanks to addition of Congo red as universal pH indicator. Mixing sequence as well as method validity was investigated by numerical simulation. This new analytical design allows fast (2.3min), reliable and accurate free acidity determination of low volume samples (10µL) containing uranium/[H(+)] moles ratio of 1:3 with relative standard deviation of <7.0% (n=11). The linearity range of the free nitric acid measurement is excellent up to 2.77molL(-1) with a correlation coefficient (R(2)) of 0.995. The method is specific, presence of actinide ions up to 0.54molL(-1) does not interfere on the determination of free nitric acid. In addition to automation, the developed sequential injection analysis method greatly improves the standard off-line oxalate complexation and alkalimetric titration method by reducing thousand fold the required sample volume, forty times the nuclear waste per analysis as well as the analysis time by eight fold. These analytical parameters are important especially in nuclear-related applications to improve laboratory safety, personnel exposure to radioactive samples and to drastically reduce environmental impacts or analytical radioactive waste. Copyright © 2016 Elsevier B.V. All rights reserved.

The inverse-trans-influence in tetravalent lanthanide and actinide bis(carbene) complexes

NASA Astrophysics Data System (ADS)

Gregson, Matthew; Lu, Erli; Mills, David P.; Tuna, Floriana; McInnes, Eric J. L.; Hennig, Christoph; Scheinost, Andreas C.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Kerridge, Andrew; Liddle, Stephen T.

2017-02-01

Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal-ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle.

The inverse-trans-influence in tetravalent lanthanide and actinide bis(carbene) complexes.

PubMed

Gregson, Matthew; Lu, Erli; Mills, David P; Tuna, Floriana; McInnes, Eric J L; Hennig, Christoph; Scheinost, Andreas C; McMaster, Jonathan; Lewis, William; Blake, Alexander J; Kerridge, Andrew; Liddle, Stephen T

2017-02-03

Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal-ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle.

The inverse-trans-influence in tetravalent lanthanide and actinide bis(carbene) complexes

PubMed Central

Gregson, Matthew; Lu, Erli; Mills, David P.; Tuna, Floriana; McInnes, Eric J. L.; Hennig, Christoph; Scheinost, Andreas C.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Kerridge, Andrew; Liddle, Stephen T.

2017-01-01

Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal–ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle. PMID:28155857

Reactivity of Uranium and Ferrous Iron with Natural Iron Oxyhydroxides.

PubMed

Stewart, Brandy D; Cismasu, A Cristina; Williams, Kenneth H; Peyton, Brent M; Nico, Peter S

2015-09-01

Determining key reaction pathways involving uranium and iron oxyhydroxides under oxic and anoxic conditions is essential for understanding uranium mobility as well as other iron oxyhydroxide mediated processes, particularly near redox boundaries where redox conditions change rapidly in time and space. Here we examine the reactivity of a ferrihydrite-rich sediment from a surface seep adjacent to a redox boundary at the Rifle, Colorado field site. Iron(II)-sediment incubation experiments indicate that the natural ferrihydrite fraction of the sediment is not susceptible to reductive transformation under conditions that trigger significant mineralogical transformations of synthetic ferrihydrite. No measurable Fe(II)-promoted transformation was observed when the Rifle sediment was exposed to 30 mM Fe(II) for up to 2 weeks. Incubation of the Rifle sediment with 3 mM Fe(II) and 0.2 mM U(VI) for 15 days shows no measurable incorporation of U(VI) into the mineral structure or reduction of U(VI) to U(IV). Results indicate a significantly decreased reactivity of naturally occurring Fe oxyhydroxides as compared to synthetic minerals, likely due to the association of impurities (e.g., Si, organic matter), with implications for the mobility and bioavailability of uranium and other associated species in field environments.

XANES and EXAFS investigation of uranium incorporation on nZVI in the presence of phosphate.

PubMed

Qiu, Muqing; Wang, Min; Zhao, Qingzhou; Hu, Baowei; Zhu, Yuling

2018-06-01

Effect of phosphate on the reduction of U(VI) on nZVI was determined by batch, XPS, XANES and EXAFS techniques. The batch experiments showed that nZVI was quite effective for the removal of uranium under the anaerobic conditions, whereas the addition of phosphate enhanced uranium removal over wide pH range. At low pH, the reduction of U(VI) to U(IV) significantly decreased with increasing phosphate concentration by XPS and XANES analysis. According to EXAFS analysis, the occurrence of UU shell at 10 mg/L phosphate and pH 4.0 was similar to that of U (IV) O 2 (s), whereas the UP and UFe shells were observed at 50 mg/L phosphate, revealing that reductive co-precipitate (U (IV) O 2 (s)) and precipitation of uranyl-phosphate were observed at low and high phosphate, respectively. The findings are crucial for the prediction of the effect of phosphate on the speciation and binding of uranium by nZVI at low pH, which is significant in controlling the mobility of U(VI) in contaminated environments. Copyright © 2018 Elsevier Ltd. All rights reserved.

Response to the comment “Uranyl-chloride speciation and uranium transport in hydrothermal brines: Comment on Migdisov et al. (2018)” by Dargent et al.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Migdisov, A. A.; Runde, W.; Williams-Jones, A. E.

We welcome the comments provided by Dargent et al. (2018) and appreciate the effort they have made to evaluate our recently reported data on the stability of uranyl(VI) chloride complexes as function of temperature (Migdisov et al., 2018). We also appreciate the opportunity provided by the editor to clarify issues in our paper that were not clearly articulated or in error.

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes.

PubMed

Perez, Evan; Hanley, Cassandra; Koehler, Stephen; Pestok, Jordan; Polonsky, Nevo; Van Stipdonk, Michael

2016-12-01

The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e., free from influence of solvent and other condensed phase effects) of a wide range of metal ion complexes in a species-specific fashion. Here, electrospray ionization, collision-induced dissociation, and gas-phase ion-molecule reactions were used to create and characterize ions derived from precursors composed of uranyl cation (U VI O 2 2+ ) coordinated by formate or acetate ligands. Anionic complexes containing U VI O 2 2+ and formate ligands fragment by decarboxylation and elimination of CH 2 =O, ultimately to produce an oxo-hydride species [U VI O 2 (O)(H)] - . Cationic species ultimately dissociate to make [U VI O 2 (OH)] + . Anionic complexes containing acetate ligands exhibit an initial loss of acetyloxyl radical, CH 3 CO 2 •, with associated reduction of uranyl to U V O 2 + . Subsequent CID steps cause elimination of CO 2 and CH 4 , ultimately to produce [U V O 2 (O)] - . Loss of CH 4 occurs by an intra-complex H + transfer process that leaves U V O 2 + coordinated by acetate and acetate enolate ligands. A subsequent dissociation step causes elimination of CH 2 =C=O to leave [U V O 2 (O)] - . Elimination of CH 4 is also observed as a result of hydrolysis caused by ion-molecule reaction with H 2 O. The reactions of other anionic species with gas-phase H 2 O create hydroxyl products, presumably through the elimination of H 2 . Graphical Abstract ᅟ.

Study of polyethyleneimine- and amidoxime-functionalized hybrid biomass of Spirulina (Arthrospira) platensis for adsorption of uranium (VI) ion.

PubMed

Bayramoglu, Gulay; Akbulut, Aydin; Arica, M Yakup

2015-11-01

This study investigates the potential application of the polyethyleneimine- (PEI) and amidoxime-modified Spirulina (Arthrospira) platensis biomasses for the removal of uranium ion in batch mode using the native biomass as a control system. The uranium ion adsorption was also characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra, zeta potential analysis, and surface area measurement studies. The effects of pH, biomass amount, contact time, initial uranium ion concentration, and ionic strength were evaluated by using native and modified algal biomass preparations. The uranium ion removal was rapid, with more than 70% of total adsorption taking place in 40 min, and equilibrium was established within 60 min. From the experimental data, it was found that the amount of adsorption uranium ion on the algal preparations decreased in the following series: amidoxime-modified algal biomass > PEI-modified algal biomass > native algal biomass. Maximum adsorption capacities of amidoxime- and PEI-modified, and native algal biomasses were found to be 366.8, 279.5, and 194.6 mg/g, respectively, in batchwise studies. The adsorption rate of U(VI) ion by amidoxime-modified algal biomass was higher than those of the native and PEI-modified counterparts. The adsorption processes on all the algal biomass preparations followed by the Dubinin-Radushkevitch (D-R) and Temkin isotherms and pseudo-second-order kinetic models. The thermodynamic parameters were determined at four different temperatures (i.e., 15, 25, 35, and 45 °C) using the thermodynamics constant of the Temkin isotherm model. The ΔH° and ΔG° values of U(VI) ion adsorption on algal preparations show endothermic heat of adsorption; higher temperatures favor the process. The native and modified algal biomass preparations were regenerated using 10 mM HNO3. These results show that amidoxime-modified algal biomass can be a potential candidate for effective removal of U(VI) ion from aqueous solution.

Optimization of a bioremediation system of soluble uranium based on the biostimulation of an indigenous bacterial community.

PubMed

Maleke, Maleke; Williams, Peter; Castillo, Julio; Botes, Elsabe; Ojo, Abidemi; DeFlaun, Mary; van Heerden, Esta

2015-06-01

High concentrations of uranium(VI) in the Witwatersrand Basin, South Africa from mining leachate is a serious environmental concern. Treatment systems are often ineffective. Therefore, optimization of a bioremediation system that facilitates the bioreduction of U(VI) based on biostimulation of indigenous bacterial communities can be a viable alternative. Tolerance of the indigenous bacteria to high concentrations of U and the amount of citric acid required for U removal was optimized. Two bioreactor studies which showed effective U(VI) removal more than 99 % from low (0.0037 mg L(-1)) and high (10 mg L(-1)) concentrations of U to below the limit allowed by South African National Standards for drinking water (0.0015 mg L(-1)). The second bioreactor was able to successfully adapt even with increasing levels of U(VI) feed water up to 10 mg L(-1), provided that enough electron donor was available. Molecular biology analyses identified Desulfovibrio sp. and Geobacter sp. among known species, which are known to reduce U(VI). The mineralogical analysis determined that part of the uranium precipitated intracellularly, which meant that the remaining U(VI) was precipitated as U(IV) oxides and TEM-EDS also confirmed this analysis. This was predicted with the geochemical model from the chemical data, which demonstrated that the treated drainage was supersaturated with respect to uraninite > U4O9 > U3O8 > UO2(am). Therefore, the tolerance of the indigenous bacterial community could be optimized to remediate up to 10 mg L(-1), and the system can thus be upscaled and employed for remediation of U(VI) impacted sites.

Determination of trace uranium by resonance fluorescence method coupled with photo-catalytic technology and dual cloud point extraction

NASA Astrophysics Data System (ADS)

Li, Jiekang; Li, Guirong; Han, Qian

2016-12-01

In this paper, two kinds of salophens (Sal) with different solubilities, Sal1 and Sal2, have been respectively synthesized, and they all can combine with uranyl to form stable complexes: [UO22 +-Sal1] and [UO22 +-Sal2]. Among them, [UO22 +-Sal1] was used as ligand to extract uranium in complex samples by dual cloud point extraction (dCPE), and [UO22 +-Sal2] was used as catalyst for the determination of uranium by photocatalytic resonance fluorescence (RF) method. The photocatalytic characteristic of [UO22 +-Sal2] on the oxidized pyronine Y (PRY) by potassium bromate which leads to the decrease of RF intensity of PRY were studied. The reduced value of RF intensity of reaction system (ΔF) is in proportional to the concentration of uranium (c), and a novel photo-catalytic RF method was developed for the determination of trace uranium (VI) after dCPE. The combination of photo-catalytic RF techniques and dCPE procedure endows the presented methods with enhanced sensitivity and selectivity. Under optimal conditions, the linear calibration curves range for 0.067 to 6.57 ng mL- 1, the linear regression equation was ΔF = 438.0 c (ng mL- 1) + 175.6 with the correlation coefficient r = 0.9981. The limit of detection was 0.066 ng mL- 1. The proposed method was successfully applied for the separation and determination of uranium in real samples with the recoveries of 95.0-103.5%. The mechanisms of the indicator reaction and dCPE are discussed.

Mineral transformations during the dissolution of uranium ore minerals by dissimilatory metal-reducing bacteria

NASA Astrophysics Data System (ADS)

Glasauer, S.; Weidler, P.; Fakra, S.; Tyliszczak, T.; Shuh, D.

2011-12-01

Carnotite minerals [X2(UO2)2(VO4)2]; X = K, Ca, Ba, Mn, Na, Cu or Pb] form the major ore of uranium in the Colorado Plateau. These deposits are highly oxidized and contain U(VI) and V(IV). The biotransformation of U(VI) bound in carnotite by bacteria during dissimilatory metal reduction presents a complex puzzle in mineral chemistry. Both U(VI) and V(V) can be respired by metal reducing bacteria, and the mineral structure can change depending on the associated counterion. We incubated anaerobic cultures of S. putrefaciens CN32 with natural carnotite minerals from southeastern Utah in a nutrient-limited defined medium. Strain CN32 is a gram negative bacterium and a terrestrial isolate from New Mexico. The mineral and metal transformations were compared to a system that contained similar concentrations of soluble U(VI) and V(V). Electron (SEM, TEM) microscopies and x-ray spectromicroscopy (STXM) were used in conjunction with XRD to track mineral changes, and bacterial survival was monitored throughout the incubations. Slow rates of metal reduction over 10 months for the treatment with carnotite minerals revealed distinct biotic and abiotic processes, providing insight on mineral transformation and bacteria-metal interactions. The bacteria existed as small flocs or individual cells attached to the mineral phase, but did not adsorb soluble U or V, and accumulated very little of the biominerals. Reduction of mineral V(V) necessarily led to a dismantling of the carnotite structure. Bioreduction of V(V) by CN32 contributed small but profound changes to the mineral system, resulting in new minerals. Abiotic cation exchange within the carnotite group minerals induced the rearrangement of the mineral structures, leading to further mineral transformation. In contrast, bacteria survival was poor for treatments with soluble U(VI) and V(V), although both metals were reduced completely and formed solid UO2 and VO2; we also detected V(III). For these treatments, the bacteria formed extensive biofilms or flocs that contained U and V in the exopolymer, but excluded these metals from the bacteria. This suggests a specific mechanism to inhibit metal sorption to cell wall components. The example illustrates the interplay between bacteria and minerals under conditions that model oligotrophic survival, and provides insight on U mobilization from common uranium ore minerals.

Sequestration of U(VI) from Acidic, Alkaline, and High Ionic-Strength Aqueous Media by Functionalized Magnetic Mesoporous Silica Nanoparticles: Capacity and Binding Mechanisms

EPA Science Inventory

Uranium (VI) exhibits little adsorption onto sediment minerals in acidic, alkaline or high ionic-strength aqueous media that often occur in U mining or contaminated sites, which makes U(VI) very mobile and difficult to sequester. In this work, magnetic mesoporous silica nanoparti...

Acetate availability and its influence on sustainable bioremediation of Uranium-contaminated groundwater

USGS Publications Warehouse

Williams, K.H.; Long, P.E.; Davis, J.A.; Wilkins, M.J.; N'Guessan, A. L.; Steefel, Carl; Yang, L.; Newcomer, D.; Spane, F.A.; Kerkhof, L.J.; Mcguinness, L.; Dayvault, R.; Lovley, D.R.

2011-01-01

Field biostimulation experiments at the U.S. Department of Energy's Integrated Field Research Challenge (IFRC) site in Rifle, Colorado, have demonstrated that uranium concentrations in groundwater can be decreased to levels below the U.S. Environmental Protection Agency's (EPA) drinking water standard (0.126??M).During successive summer experiments - referred to as "Winchester" (2007) and "Big Rusty" (2008) - acetate was added to the aquifer to stimulate the activity of indigenous dissimilatory metal reducing bacteria capable of reductively immobilizing uranium. The two experiments differed in the length of injection (31 vs. 110 days), the maximum concentration of acetate (5 vs. 30 mM),and the extent to which iron reduction ("Winchester") or sulfate reduction("Big Rusty") was the predominant metabolic process. In both cases, rapid removal of U(VI) from groundwater occurred at calcium concentrations (6 mM) and carbonate alkalinities (8 meq/L) where Ca-UO2-CO3 ternary complexes constitute >90% of uranyl species in groundwater. Complete consumption of acetate and increased alkalinity (>30 meq/L) accompanying the onset of sulfate reduction corresponded to temporary increases in U(VI);however, by increasing acetate concentrations in excess of available sulfate (10 mM), low U(VI) concentrations (0.1-0.05 ??M) were achieved for extended periods of time (>140 days). Uniform delivery of acetate during "Big Rusty" was impeded due to decreases in injection well permeability, likely resulting from biomass accumulation and carbonate and sulfide mineral precipitation. Such decreases were not observed during the short-duration "Winchester" experiment. Terminal restriction fragment length polymorphism (TRFLP) analysis of 16S rRNA genes demonstrated that Geobacter sp. and Geobacter-like strains dominated the groundwater community profile during iron reduction, with 13C stable isotope probing (SIP) results confirming these strains were actively utilizing acetate to replicate their genome during the period of optimal U(VI) removal. Gene transcript levels during "Big Rusty" were quantified for Geobacter-specific citrate synthase (gltA), with ongoing transcription during sulfate reduction indicating that members of the Geobacteraceae were still active and likely contributing to U(VI) removal. The persistence of reducible Fe(III) in sediments recovered from an area of prolonged (110-day) sulfate reduction is consistent with this conclusion. These results indicate that acetate availability and its ability to sustain the activity of iron- and uranyl-respiring Geobacter strains during sulfate reduction exerts a primary control on optimized U(VI) removal from groundwater at the Rifle IFRC site over extended time scales (>50 days). ?? Taylor & Francis Group, LLC.

Total electron acceptor loading and composition affect hexavalent uranium reduction and microbial community structure in a membrane biofilm reactor.

PubMed

Ontiveros-Valencia, Aura; Zhou, Chen; Ilhan, Zehra Esra; de Saint Cyr, Louis Cornette; Krajmalnik-Brown, Rosa; Rittmann, Bruce E

2017-11-15

Molecular microbiology tools (i.e., 16S rDNA gene sequencing) were employed to elucidate changes in the microbial community structure according to the total electron acceptor loading (controlled by influent flow rate and/or medium composition) in a H 2 -based membrane biofilm reactor evaluated for removal of hexavalent uranium. Once nitrate, sulfate, and dissolved oxygen were replaced by U(VI) and bicarbonate and the total acceptor loading was lowered, slow-growing bacteria capable of reducing U(VI) to U(IV) dominated in the biofilm community: Replacing denitrifying bacteria Rhodocyclales and Burkholderiales were spore-producing Clostridiales and Natranaerobiales. Though potentially competing for electrons with U(VI) reducers, homo-acetogens helped attain steady U(VI) reduction, while methanogenesis inhibited U(VI) reduction. U(VI) reduction was reinstated through suppression of methanogenesis by addition of bromoethanesulfonate or by competition from SRB when sulfate was re-introduced. Predictive metagenome analysis further points out community changes in response to alterations in the electron-acceptor loading: Sporulation and homo-acetogenesis were critical factors for strengthening stable microbial U(VI) reduction. This study documents that sporulation was important to long-term U(VI) reduction, whether or not microorganisms that carry out U(VI) reduction mediated by cytochrome c 3 , such as SRB and ferric-iron-reducers, were inhibited. Copyright © 2017 Elsevier Ltd. All rights reserved.

A multi-instrumental geochemical study of anomalous uranium enrichment in coal.

PubMed

Havelcová, Martina; Machovič, Vladimír; Mizera, Jiří; Sýkorová, Ivana; Borecká, Lenka; Kopecký, Lubomír

2014-11-01

Contents of uranium in coals from Odeř in the northernmost part of the Sokolov Basin, Czech Republic, in the vicinity of the well known St. Joachimsthal uranium ore deposits, reach extremely high values. In the present work, coal samples with contents of uranium ranging from 0.02 to 6 wt.% were studied. The study employing a whole complex of analytical techniques has been aimed at identification of changes in the structure of coal organic matter, which are associated with the high contents of uranium in coal. The study includes proximate and ultimate analyses, multielement analysis by instrumental neutron and photon activation analyses, micropetrographic analysis by optical microscopy, ESEM/EDX analysis of mineral matter, infrared and Raman spectroscopies, solvent extraction followed by gas chromatography with mass spectroscopy (GC/MS), and analytical pyrolysis (Py-GC/MS). The study has confirmed previously proposed explanation of uraniferous mineralization in sedimentary carboniferous substances by the mechanism of reduction and fixation of soluble U(VI) (uranyl, UO2(2+)) species (e.g., humic, carbonate/hydroxo/phosphate complexes) by sedimentary organic matter under diagenetic or hydrothermal conditions, and formation of insoluble U(IV) species as phosphate minerals and uraninite. The process is accompanied with alteration and destruction of the coal organic matter. The changes in the structure of coal organic matter involve dehydrogenation and oxidation mainly in the aliphatic, aromatic and hydroxyl structures, and an increase in aromaticity, content of ether bonds, and the degree of coalification. Copyright © 2014 Elsevier Ltd. All rights reserved.

Subsurface Conditions Controlling Uranium Incorporation in Iron Oxides: A Redox Stable Sink

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fendorf, Scott

2016-04-05

Toxic metals and radionuclides throughout the U.S. Department of Energy Complex pose a serious threat to ecosystems and to human health. Of particular concern is the redox-sensitive radionuclide uranium, which is classified as a priority pollutant in soils and groundwaters at most DOE sites owing to its large inventory, its health risks, and its mobility with respect to primary waste sources. The goal of this research was to contribute to the long-term mission of the Subsurface Biogeochemistry Program by determining reactions of uranium with iron (hydr)oxides that lead to long-term stabilization of this pervasive contaminant. The research objectives of thismore » project were thus to (1) identify the (bio)geochemical conditions, including those of the solid-phase, promoting uranium incorporation in Fe (hydr)oxides, (2) determine the magnitude of uranium incorporation under a variety of relevant subsurface conditions in order to quantify the importance of this pathway when in competition with reduction or adsorption; (3) identify the mechanism(s) of U(VI/V) incorporation in Fe (hydr)oxides; and (4) determine the stability of these phases under different biogeochemical (inclusive of redox) conditions. Our research demonstrates that redox transformations are capable of achieving U incorporation into goethite at ambient temperatures, and that this transformation occurs within days at U and Fe(II) concentrations that are common in subsurface geochemical environments with natural ferrihydrites—inclusive of those with natural impurities. Increasing Fe(II) or U concentration, or initial pH, made U(VI) reduction to U(IV) a more competitive sequestration pathway in this system, presumably by increasing the relative rate of U reduction. Uranium concentrations commonly found in contaminated subsurface environments are often on the order of 1-10 μM, and groundwater Fe(II) concentrations can reach exceed 1 mM in reduced zones of the subsurface. The redox-driven U(V) incorporation mechanism may help to explain U retention in some geologic materials, improving our understanding of U-based geochronology and the redox status of ancient geochemical environments. Additionally, U(VI) may be incorporated within silicate minerals though encapsulation of U-bearing iron oxides, leading to a redox stable solid. Our research detailing previously unrecognized mechanism of U incorporation within sediment minerals may even lead to new approaches for in situ contamination remediation techniques, and will help refine models of U fate and transport in reduced subsurface zones.« less

Modulation of Medium pH by Caulobacter crescentus Facilitates Recovery from Uranium-Induced Growth Arrest

PubMed Central

Park, Dan M.

2014-01-01

The oxidized form of uranium [U(VI)] predominates in oxic environments and poses a major threat to ecosystems. Due to its ability to mineralize U(VI), the oligotroph Caulobacter crescentus is an attractive candidate for U(VI) bioremediation. However, the physiological basis for U(VI) tolerance is unclear. Here we demonstrated that U(VI) caused a temporary growth arrest in C. crescentus and three other bacterial species, although the duration of growth arrest was significantly shorter for C. crescentus. During the majority of the growth arrest period, cell morphology was unaltered and DNA replication initiation was inhibited. However, during the transition from growth arrest to exponential phase, cells with shorter stalks were observed, suggesting a decoupling between stalk development and the cell cycle. Upon recovery from growth arrest, C. crescentus proliferated with a growth rate comparable to that of a control without U(VI), although a fraction of these cells appeared filamentous with multiple replication start sites. Normal cell morphology was restored by the end of exponential phase. Cells did not accumulate U(VI) resistance mutations during the prolonged growth arrest, but rather, a reduction in U(VI) toxicity occurred concomitantly with an increase in medium pH. Together, these data suggest that C. crescentus recovers from U(VI)-induced growth arrest by reducing U(VI) toxicity through pH modulation. Our finding represents a unique U(VI) detoxification strategy and provides insight into how microbes cope with U(VI) under nongrowing conditions, a metabolic state that is prevalent in natural environments. PMID:25002429

Unprecedented reduction of the uranyl ion [UO2]2+ into a polyoxo uranium(IV) cluster: synthesis and crystal structure of the first f-element oxide with a M6(micro3-O)8 core.

PubMed

Berthet, Jean-Claude; Thuéry, Pierre; Ephritikhine, Michel

2005-07-21

The smooth comproportionation reaction of the U(VI) and U(III) complexes UO2(OTf)2 and U(OTf)3, afforded the hexanuclear U(IV) oxide cluster [U6(micro3-O)8(micro2-OTf)8(py)8], a rare example of a metal oxide with a M6(micro3-O)8 core.

Assessment of calcium addition on the removal of U(VI) in the alkaline conditions created by NH 3 gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsenovich, Yelena; Cardona, Claudia; Szecsody, Jim

Remediation of uranium (U) contamination in the deep vadose zone (VZ) sediments abundant in calcite mineral is a challenging task considering the formation of highly stable and mobile uranyl complexes with carbonate and calcium in pore water composition. There is a concern that uranium contamination in the VZ can serve as a continued source for groundwater pollution, creating a risk to human health and the environment through the groundwater pathway. This requires in-situ remediation of the radionuclide-contaminated VZ to convert soluble U species to low solubility precipitates that are stable in the natural environment. Injection of reactive gasses (e.g., NHmore » 3) is a promising technology to decrease U mobility in the unsaturated zone without the addition of liquid amendments. The NH 3 injection creates alkaline conditions that can alter the sediment pore water composition due to a release of elements from minerals (via desorption and dissolution) that are present in the sediment. However, it is not known how VZ pore water constituents (Si, Al 3+, HCO 3 -, and Ca 2 +) would affect U(VI) removal/precipitation in alkaline conditions. This study quantified the role of major pore water constituents typically present in the arid and semi-arid environments of the western regions of the U.S and identified solid uranium-bearing phases that could potentially precipitate from solutions approximating pore water compositions after pH manipulations via ammonia gas injections. Triplicate samples were prepared using six Si (5, 50 100, 150, 200, and 250 mM), six HCO 3 - (0, 3, 25, 50, 75, and 100 mM), and two Ca 2+ (5 and 10 mM) concentrations. The concentration of aluminum and uranium was kept constant at 5 mM and 0.0084 mM, respectively, in all synthetic formulations tested. Results showed that the percentage of U(VI) removal was controlled by the Si/Al molar ratios and Ca 2+ concentrations. Regardless of the bicarbonate concentration tested, the percentage of U(VI) removed increased as the Si/Al ratios were increased. However, higher Ca concentrations correlated with higher U(VI) removal, ranging between 96% and 99%, at low Si/Al ratios. The SEM images of dried precipitates displayed dense amorphous regions high in silica content, where EDS elemental analysis unveiled higher U atomic percentages. The formation of uranyl silicate and carbonate minerals was also predicted by the speciation modeling. XRD analysis revealed the presence of uranyl carbonate mineral phases (andersonite, grimselite); however, uranyl silicates predicted (Na-boltwoodite) were not identified experimentally, possibly due to the amorphous nature of the silica solid phases observed in our experiments.« less

Assessment of calcium addition on the removal of U(VI) in the alkaline conditions created by NH 3 gas

DOE PAGES

Katsenovich, Yelena; Cardona, Claudia; Szecsody, Jim; ...

2018-03-06

Remediation of uranium (U) contamination in the deep vadose zone (VZ) sediments abundant in calcite mineral is a challenging task considering the formation of highly stable and mobile uranyl complexes with carbonate and calcium in pore water composition. There is a concern that uranium contamination in the VZ can serve as a continued source for groundwater pollution, creating a risk to human health and the environment through the groundwater pathway. This requires in-situ remediation of the radionuclide-contaminated VZ to convert soluble U species to low solubility precipitates that are stable in the natural environment. Injection of reactive gasses (e.g., NHmore » 3) is a promising technology to decrease U mobility in the unsaturated zone without the addition of liquid amendments. The NH 3 injection creates alkaline conditions that can alter the sediment pore water composition due to a release of elements from minerals (via desorption and dissolution) that are present in the sediment. However, it is not known how VZ pore water constituents (Si, Al 3+, HCO 3 -, and Ca 2 +) would affect U(VI) removal/precipitation in alkaline conditions. This study quantified the role of major pore water constituents typically present in the arid and semi-arid environments of the western regions of the U.S and identified solid uranium-bearing phases that could potentially precipitate from solutions approximating pore water compositions after pH manipulations via ammonia gas injections. Triplicate samples were prepared using six Si (5, 50 100, 150, 200, and 250 mM), six HCO 3 - (0, 3, 25, 50, 75, and 100 mM), and two Ca 2+ (5 and 10 mM) concentrations. The concentration of aluminum and uranium was kept constant at 5 mM and 0.0084 mM, respectively, in all synthetic formulations tested. Results showed that the percentage of U(VI) removal was controlled by the Si/Al molar ratios and Ca 2+ concentrations. Regardless of the bicarbonate concentration tested, the percentage of U(VI) removed increased as the Si/Al ratios were increased. However, higher Ca concentrations correlated with higher U(VI) removal, ranging between 96% and 99%, at low Si/Al ratios. The SEM images of dried precipitates displayed dense amorphous regions high in silica content, where EDS elemental analysis unveiled higher U atomic percentages. The formation of uranyl silicate and carbonate minerals was also predicted by the speciation modeling. XRD analysis revealed the presence of uranyl carbonate mineral phases (andersonite, grimselite); however, uranyl silicates predicted (Na-boltwoodite) were not identified experimentally, possibly due to the amorphous nature of the silica solid phases observed in our experiments.« less

Uranium Bio-accumulation and Cycling as revealed by Uranium Isotopes in Naturally Reduced Sediments from the Upper Colorado River Basin

NASA Astrophysics Data System (ADS)

Lefebvre, Pierre; Noël, Vincent; Jemison, Noah; Weaver, Karrie; Bargar, John; Maher, Kate

2016-04-01

Uranium (U) groundwater contamination following oxidized U(VI) releases from weathering of mine tailings is a major concern at numerous sites across the Upper Colorado River Basin (CRB), USA. Uranium(IV)-bearing solids accumulated within naturally reduced zones (NRZs) characterized by elevated organic carbon and iron sulfide compounds. Subsequent re-oxidation of U(IV)solid to U(VI)aqueous then controls the release to groundwater and surface water, resulting in plume persistence and raising public health concerns. Thus, understanding the extent of uranium oxidation and reduction within NRZs is critical for assessing the persistence of the groundwater contamination. In this study, we measured solid-phase uranium isotope fractionation (δ238/235U) of sedimentary core samples from four study sites (Shiprock, NM, Grand Junction, Rifle and Naturita, CO) using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). We observe a strong correlation between U accumulation and the extent of isotopic fractionation, with Δ238U up to +1.8 ‰ between uranium-enriched and low concentration zones. The enrichment in the heavy isotopes within the NRZs appears to be especially important in the vadose zone, which is subject to variations in water table depth. According to previous studies, this isotopic signature is consistent with biotic reduction processes associated with metal-reducing bacteria. Positive correlations between the amount of iron sulfides and the accumulation of reduced uranium underline the importance of sulfate-reducing conditions for U(IV) retention. Furthermore, the positive fractionation associated with U reduction observed across all sites despite some variations in magnitude due to site characteristics, shows a regional trend across the Colorado River Basin. The maximum extent of 238U enrichment observed in the NRZ proximal to the water table further suggests that the redox cycling of uranium, with net release of U(VI) to the groundwater by non-fractionating oxidation, is occurring within this zone. Thus, release of uranium from the NRZs may play a critical role in the persistence of groundwater contamination at these sites.

Understanding Uranium Behavior in a Reduced Aquifer

NASA Astrophysics Data System (ADS)

Janot, N.; Lezama-Pacheco, J. S.; Williams, K. H.; Bernier-Latmani, R.; Long, P. E.; Davis, J. A.; Fox, P. M.; Yang, L.; Giammar, D.; Cerrato, J. M.; Bargar, J.

2012-12-01

Uranium contamination of groundwater is a concern at several US Department of Energy sites, such Old Rifle, CO. Uranium transport in the environment is mainly controlled by its oxidation state, since oxidized U(VI) is relatively mobile, whereas U(IV) is relatively insoluble. Bio-remediation of contaminated aquifers aims at immobilizing uranium in a reduced form. Previous laboratory and field studies have shown that adding electron donor (lactate, acetate, ethanol) to groundwater stimulates the activity of metal- and sulfate-reducing bacteria, which promotes U(VI) reduction in contaminated aquifers. However, obtaining information on chemical and physical forms of U, Fe and S species for sediments biostimulated in the field, as well as kinetic parameters such as U(VI) reduction rate, is challenging due to the low concentration of uranium in the aquifers (typically < 10 ppm) and the expense of collecting large number of cores. An in-situ technique has been developed for studying uranium, iron and sulfur reduction dynamics during such bioremediation episodes. This technique uses in-well columns to obtain direct access to chemical and physical forms of U(IV) produced in the aquifer, evolving microbial communities, and trace and major ion groundwater constituents. While several studies have explored bioreduction of uranium under sulfate-reducing conditions, less attention has been paid to the initial iron-reducing phase, noted as being of particular importance to uranium removal. The aim of this work was to assess the formation of U(IV) during the early stages of a bio-remediation experiment at the Old Rifle site, CO, from early iron-reducing conditions to the transition to sulfate-reducing conditions. Several in-well chromatographic columns packed with sediment were deployed and were sampled at different days after the start of bio-reduction. X-ray absorption spectroscopy and X-ray microscopy were used to obtain information on Fe, S and U speciation and distribution. Chemical extractions of the reduced sediments have also been performed, to determine the rate of Fe(II) and U(IV) accumulation.

Sorption behavior of uranium(VI) on a biotite mineral

DOE Office of Scientific and Technical Information (OSTI.GOV)

Idemitsu, K.; Obata, K.; Furuya, H.

1995-12-31

Biotite has the most important role for the sorption of radionuclides in granitic rocks. Experiments on the sorption of uranium(VI) on biotite were conducted to understand the fundamental controls on uranium sorption on biotite mineral, including the effects of pH and uranium concentration in solution. Biotite powder (mesh 32--60) were washed with 1N HCl for a week and were rinsed twice with deionized water for a week. This HCl treatment was necessary to avoid the effects by other minerals. The agreement between surface adsorption coefficient, Ka, of both biotites with and without HCl treatment was within one order of magnitude.more » The peak Ka value was in the range of 0.1 to 0.01 cm{sup 3}/cm{sup 2} around pH 6. A comparison of aqueous uranium speciations and sorption results indicates that neutral uranyl hydroxide could be an important species sorbed on the biotite. Sequential desorption experiments with KCl and HCl solutions were also carried out after sorption experiments to investigate sorption forms of uranium. Approximately 20% of uranium in solution were sorbed on the biotite as an exchangeable ion. The fraction of exchangeable uranium had a little dependence on pH. The other uranium could not be extracted even by 6N HCl solution. It is possible that most of the uranium could be precipitated as U(IV) via Fe(II) reduction on the biotite surface.« less

Effects of organic carbon supply rates on uranium mobility in a previously bioreduced contaminated sediment.

PubMed

Wan, Jiamin; Tokunaga, Tetsu K; Kim, Yongman; Brodie, Eoin; Daly, Rebecca; Hazen, Terry C; Firestone, Mary K

2008-10-15

Bioreduction-based strategies for remediating uranium (U)-contaminated sediments face the challenge of maintaining the reduced status of U for long times. Because groundwater influxes continuously bring in oxidizing terminal electron acceptors (O2, NO3(-)), it is necessary to continue supplying organic carbon (OC) to maintain the reducing environment after U bioreduction is achieved. We tested the influence of OC supply rates on mobility of previously microbial reduced uranium U(IV) in contaminated sediments. We found that high degrees of U mobilization occurred when OC supply rates were high, and when the sediment still contained abundant Fe(III). Although 900 days with low levels of OC supply minimized U mobilization, the sediment redox potential increased with time as did extractable U(VI) fractions. Molecular analyses of total microbial activity demonstrated a positive correlation with OC supply and analyses of Geobacteraceae activity (RT-qPCR of 16S rRNA) indicated continued activity even when the effluent Fe(II) became undetectable. These data support our hypothesis on the mechanisms responsible for remobilization of U under reducing conditions; that microbial respiration caused increased (bi)carbonate concentration and formation of stable uranyl carbonate complexes, thereby shifted U(IV)/U(VI) equilibrium to more reducing potentials. The data also suggested that low OC concentrations could not sustain the reducing condition of the sediment for much longer time. Bioreduced U(IV) is not sustainable in an oxidizing environment for a very long time.

Direct observation of pure pentavalent uranium in U2O5 thin films by high resolution photoemission spectroscopy.

PubMed

Gouder, T; Eloirdi, R; Caciuffo, R

2018-05-29

Thin films of the elusive intermediate uranium oxide U 2 O 5 have been prepared by exposing UO 3 precursor multilayers to atomic hydrogen. Electron photoemission spectra measured about the uranium 4f core-level doublet contain sharp satellites separated by 7.9(1) eV from the 4f main lines, whilst satellites characteristics of the U(IV) and U(VI) oxidation states, expected respectively at 6.9(1) and 9.7(1) eV from the main 4f lines, are absent. This shows that uranium ions in the films are in a pure pentavalent oxidation state, in contrast to previous investigations of binary oxides claiming that U(V) occurs only as a metastable intermediate state coexisting with U(IV) and U(VI) species. The ratio between the 5f valence band and 4f core-level uranium photoemission intensities decreases by about 50% from UO 2 to U 2 O 5 , which is consistent with the 5f  2 (UO 2 ) and 5f  1 (U 2 O 5 ) electronic configurations of the initial state. Our studies conclusively establish the stability of uranium pentoxide.

Decrease of U(VI) Immobilization Capability of the Facultative Anaerobic Strain Paenibacillus sp. JG-TB8 under Anoxic Conditions Due to Strongly Reduced Phosphatase Activity

PubMed Central

Reitz, Thomas; Rossberg, Andre; Barkleit, Astrid; Selenska-Pobell, Sonja; Merroun, Mohamed L.

2014-01-01

Interactions of a facultative anaerobic bacterial isolate named Paenibacillus sp. JG-TB8 with U(VI) were studied under oxic and anoxic conditions in order to assess the influence of the oxygen-dependent cell metabolism on microbial uranium mobilization and immobilization. We demonstrated that aerobically and anaerobically grown cells of Paenibacillus sp. JG-TB8 accumulate uranium from aqueous solutions under acidic conditions (pH 2 to 6), under oxic and anoxic conditions. A combination of spectroscopic and microscopic methods revealed that the speciation of U(VI) associated with the cells of the strain depend on the pH as well as on the aeration conditions. At pH 2 and pH 3, uranium was exclusively bound by organic phosphate groups provided by cellular components, independently on the aeration conditions. At higher pH values, a part (pH 4.5) or the total amount (pH 6) of the dissolved uranium was precipitated under oxic conditions in a meta-autunite-like uranyl phosphate mineral phase without supplying an additional organic phosphate substrate. In contrast to that, under anoxic conditions no mineral formation was observed at pH 4.5 and pH 6, which was clearly assigned to decreased orthophosphate release by the cells. This in turn was caused by a suppression of the indigenous phosphatase activity of the strain. The results demonstrate that changes in the metabolism of facultative anaerobic microorganisms caused by the presence or absence of oxygen can decisively influence U(VI) biomineralization. PMID:25157416

Methods for Estimating Adsorbed Uranium(VI) and Distribution Coefficients of Contaminated Sediments

USGS Publications Warehouse

Kohler, M.; Curtis, G.P.; Meece, D.E.; Davis, J.A.

2004-01-01

Assessing the quantity of U(VI) that participates in sorption/desorption processes in a contaminated aquifer is an important task when investigating U migration behavior. U-contaminated aquifer sediments were obtained from 16 different locations at a former U mill tailings site at Naturita, CO (U.S.A.) and were extracted with an artificial groundwater, a high pH sodium bicarbonate solution, hydroxylamine hydrochloride solution, and concentrated nitric acid. With an isotopic exchange method, both a KD value for the specific experimental conditions as well as the total exchangeable mass of U(VI) was determined. Except for one sample, KD values determined by isotopic exchange with U-contaminated sediments that were in equilibrium with atmospheric CO2 agreed within a factor of 2 with KD values predicted from a nonelectrostatic surface complexation model (NEM) developed from U(VI) adsorption experiments with uncontaminated sediments. The labile fraction of U(VI) and U extracted by the bicarbonate solution were highly correlated (r2 = 0.997), with a slope of 0.96 ?? 0.01. The proximity of the slope to one suggests that both methods likely access the same reservoir of U(VI) associated with the sediments. The results indicate that the bicarbonate extraction method is useful for estimating the mass of labile U(VI) in sediments that do not contain U(IV). In-situ KD values calculated from the measured labile U(VI) and the dissolved U(VI) in the Naturita alluvial aquifer agreed within a factor of 3 with in-situ K D values predicted with the NEM and groundwater chemistry at each well.

Kinetic and equilibrium characterization of uranium(VI) adsorption onto carboxylate-functionalized poly(hydroxyethylmethacrylate)-grafted lignocellulosics.

PubMed

Anirudhan, T S; Divya, L; Suchithra, P S

2009-01-01

This study investigated the feasibility of using a new adsorbent prepared from coconut coir pith, CP (a coir industry-based lignocellulosic residue), for the removal of uranium [U(VI)] from aqueous solutions. The adsorbent (PGCP-COOH) having a carboxylate functional group at the chain end was synthesized by grafting poly(hydroxyethylmethacrylate) onto CP using potassium peroxydisulphate-sodium thiosulphite as a redox initiator and in the presence of N,N'-methylenebisacrylamide as a crosslinking agent. IR spectroscopy results confirm the graft copolymer formation and carboxylate functionalization. XRD studies confirm the decrease of crystallinity in PGCP-COOH compared to CP, and it favors the protrusion of the functional group into the aqueous medium. The thermal stability of the samples was studied using thermogravimetry (TG). Surface charge density of the samples as a function of pH was determined using potentiometric titration. The ability of PGCP-COOH to remove U(VI) from aqueous solutions was assessed using a batch adsorption technique. The maximum adsorption capacity was observed at the pH range 4.0-6.0. Maximum removal of 99.2% was observed for an initial concentration of 25mg/L at pH 6.0 and an adsorbent dose of 2g/L. Equilibrium was achieved in approximately 3h. The experimental kinetic data were analyzed using a first-order kinetic model. The temperature dependence indicates an endothermic process. U(VI) adsorption was found to decrease with an increase in ionic strength due to the formation of outer-sphere surface complexes on PGCP-COOH. Equilibrium data were best modeled by the Langmuir isotherm. The thermodynamic parameters such as DeltaG(0), DeltaH(0) and DeltaS(0) were derived to predict the nature of adsorption. Adsorption experiments were also conducted using a commercial cation exchanger, Ceralite IRC-50, with carboxylate functionality for comparison. Utility of the adsorbent was tested by removing U(VI) from simulated nuclear industry wastewater. Adsorbed U(VI) ions were desorbed effectively (about 96.2+/-3.3%) by 0.1M HCl. The adsorbent was suitable for repeated use (more than four cycles) without any noticeable loss of capacity.

Chemistry of uranium in aluminophosphate glasses

NASA Technical Reports Server (NTRS)

Schreiber, H. D.; Balazs, G. B.; Williams, B. J.

1982-01-01

The U(VI)-U(V)-U(IV) redox equilibria are investigated in two sodium aluminophosphate base compositions at a variety of melt temperatures, imposed oxygen fugacities, and uranium contents. Results show that the higher redox states of uranium are quite soluble in the phosphate glasses, although U(IV) readily precipitates from the melts as UO2. In addition, comparisons of the uranium redox equilibria established in phosphate melts versus those in silicate melts shows that the coordination sites of the individual uranium species are generally the same in both solvent systems although they differ in detail.

Determination of trace uranium by resonance fluorescence method coupled with photo-catalytic technology and dual cloud point extraction.

PubMed

Li, Jiekang; Li, Guirong; Han, Qian

2016-12-05

In this paper, two kinds of salophens (Sal) with different solubilities, Sal1 and Sal2, have been respectively synthesized, and they all can combine with uranyl to form stable complexes: [UO2(2+)-Sal1] and [UO2(2+)-Sal2]. Among them, [UO2(2+)-Sal1] was used as ligand to extract uranium in complex samples by dual cloud point extraction (dCPE), and [UO2(2+)-Sal2] was used as catalyst for the determination of uranium by photocatalytic resonance fluorescence (RF) method. The photocatalytic characteristic of [UO2(2+)-Sal2] on the oxidized pyronine Y (PRY) by potassium bromate which leads to the decrease of RF intensity of PRY were studied. The reduced value of RF intensity of reaction system (ΔF) is in proportional to the concentration of uranium (c), and a novel photo-catalytic RF method was developed for the determination of trace uranium (VI) after dCPE. The combination of photo-catalytic RF techniques and dCPE procedure endows the presented methods with enhanced sensitivity and selectivity. Under optimal conditions, the linear calibration curves range for 0.067 to 6.57ngmL(-1), the linear regression equation was ΔF=438.0 c (ngmL(-1))+175.6 with the correlation coefficient r=0.9981. The limit of detection was 0.066ngmL(-1). The proposed method was successfully applied for the separation and determination of uranium in real samples with the recoveries of 95.0-103.5%. The mechanisms of the indicator reaction and dCPE are discussed. Copyright © 2016 Elsevier B.V. All rights reserved.

Diffusive parameters of tritiated water and uranium in chalk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Descostes, M.; UMR 8587 CEA, Universite d'Evry, CNRS,; Pili, E.

2012-07-15

The Cretaceous Chalk of North-western Europe exhibits a double porosity (matrix and fracture) providing pathways for both slow and rapid flow of water. The present study aims at understanding and predicting the contaminant transfer properties through a significant section of this formation, with a particular emphasis on diffusion. This requires to study the nature of porosity and to perform diffusion experiments in representative samples using uranium and tritiated water (HTO), respectively taken as a reactive tracer and an inert one. The diffusive parameters, i.e. the accessible porosity and the effective diffusion coefficient were determined. Additional information was obtained with mercurymore » porosimetry, gravimetric water content, textural and mineralogical characterization. The diffusion tests performed with HTO appear to be the best method to measure the total accessible porosity in any type of porous media, especially those having large pore size distributions. Our study demonstrates that classical gravimetric water content measurements are not sensitive to the reduction in pore size as opposed to HTO diffusion tests because capillary water is not extracted by conventional gravimetric method but can still be probed by diffusion experiments. We found effective diffusion coefficients D{sub e}(U(VI)) near 4 x 10{sup -10} m{sup 2}s{sup -1}). The slower migration of U(VI) compared to HTO indicates sorption, with R{sub d}(U(VI)) from 100 to 360 mL g{sup -1}. These values are one order of magnitude larger than other determinations of the U(VI) sorption coefficient because only the matrix porosity is concerned here. The migration of U(VI) in chalk is only limited by sorption on ancillary Fe-Pb-bearing minerals. Transport of HTO and U(VI) is independent of the porosity distribution. Uranium diffusion in the chalk matrix porosity is fast enough to allow the total invasion of the pore space within characteristic time scales of the order of 1000 years. This results in a partitioning of uranium velocities in fracture flow and matrix flow proportionally to the respective fracture and matrix porosities. (authors)« less

Biomineralization of Uranium by PhoY Phosphatase Activity Aids Cell Survival in Caulobacter crescentus

PubMed Central

Yung, Mimi C.

2014-01-01

Caulobacter crescentus is known to tolerate high levels of uranium [U(VI)], but its detoxification mechanism is poorly understood. Here we show that C. crescentus is able to facilitate U(VI) biomineralization through the formation of U-Pi precipitates via its native alkaline phosphatase activity. The U-Pi precipitates, deposited on the cell surface in the form of meta-autunite structures, have a lower U/Pi ratio than do chemically produced precipitates. The enzyme that is responsible for the phosphatase activity and thus the biomineralization process is identified as PhoY, a periplasmic alkaline phosphatase with broad substrate specificity. Furthermore, PhoY is shown to confer a survival advantage on C. crescentus toward U(VI) under both growth and nongrowth conditions. Results obtained in this study thus highlight U(VI) biomineralization as a resistance mechanism in microbes, which not only improves our understanding of bacterium-mineral interactions but also aids in defining potential ecological niches for metal-resistant bacteria. PMID:24878600

Biomineralization of Uranium by PhoY Phosphatase Activity Aids Cell Survival in Caulobacter crescentus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yung, M C; Jiao, Y

2014-07-22

Caulobacter crescentus is known to tolerate high levels of uranium [U(VI)], but its detoxification mechanism is poorly understood. Here we show that C. crescentus is able to facilitate U(VI) biomineralization through the formation of U-P i precipitates via its native alkaline phosphatase activity. The U-P i precipitates, deposited on the cell surface in the form of meta-autunite structures, have a lower U/P i ratio than do chemically produced precipitates. The enzyme that is responsible for the phosphatase activity and thus the biomineralization process is identified as PhoY, a periplasmic alkaline phosphatase with broad substrate specificity. Furthermore, PhoY is shown tomore » confer a survival advantage on C. crescentus toward U(VI) under both growth and nongrowth conditions. Results obtained in this study thus highlight U(VI) biomineralization as a resistance mechanism in microbes, which not only improves our understanding of bacterium-mineral interactions but also aids in defining potential ecological niches for metal-resistant bacteria.« less

The measurement of U(VI) and Np(IV) mass transfer in a single stage centrifugal contactor

NASA Astrophysics Data System (ADS)

May, I.; Birkett, E. J.; Denniss, I. S.; Gaubert, E. T.; Jobson, M.

2000-07-01

BNFL currently operates two reprocessing plants for the conversion of spent nuclear fuel into uranium and plutonium products for fabrication into uranium oxide and mixed uranium and plutonium oxide (MOX) fuels. To safeguard the future commercial viability of this process, BNFL is developing novel single cycle flowsheets that can be operated in conjunction with intensified centrifugal contactors.

Evaluating chemical extraction techniques for the determination of uranium oxidation state in reduced aquifer sediments.

PubMed

Stoliker, Deborah L; Campbell, Kate M; Fox, Patricia M; Singer, David M; Kaviani, Nazila; Carey, Minna; Peck, Nicole E; Bargar, John R; Kent, Douglas B; Davis, James A

2013-08-20

Extraction techniques utilizing high pH and (bi)carbonate concentrations were evaluated for their efficacy in determining the oxidation state of uranium (U) in reduced sediments collected from Rifle, CO. Differences in dissolved concentrations between oxic and anoxic extractions have been proposed as a means to quantify the U(VI) and U(IV) content of sediments. An additional step was added to anoxic extractions using a strong anion exchange resin to separate dissolved U(IV) and U(VI). X-ray spectroscopy showed that U(IV) in the sediments was present as polymerized precipitates similar to uraninite and/or less ordered U(IV), referred to as non-uraninite U(IV) species associated with biomass (NUSAB). Extractions of sediment containing both uraninite and NUSAB displayed higher dissolved uranium concentrations under oxic than anoxic conditions while extractions of sediment dominated by NUSAB resulted in identical dissolved U concentrations. Dissolved U(IV) was rapidly oxidized under anoxic conditions in all experiments. Uraninite reacted minimally under anoxic conditions but thermodynamic calculations show that its propensity to oxidize is sensitive to solution chemistry and sediment mineralogy. A universal method for quantification of U(IV) and U(VI) in sediments has not yet been developed but the chemical extractions, when combined with solid-phase characterization, have a narrow range of applicability for sediments without U(VI).

Evaluating chemical extraction techniques for the determination of uranium oxidation state in reduced aquifer sediments

USGS Publications Warehouse

Stoliker, Deborah L.; Campbell, Kate M.; Fox, Patricia M.; Singer, David M.; Kaviani, Nazila; Carey, Minna; Peck, Nicole E.; Barger, John R.; Kent, Douglas B.; Davis, James A.

2013-01-01

Extraction techniques utilizing high pH and (bi)carbonate concentrations were evaluated for their efficacy in determining the oxidation state of uranium (U) in reduced sediments collected from Rifle, CO. Differences in dissolved concentrations between oxic and anoxic extractions have been proposed as a means to quantify the U(VI) and U(IV) content of sediments. An additional step was added to anoxic extractions using a strong anion exchange resin to separate dissolved U(IV) and U(VI). X-ray spectroscopy showed that U(IV) in the sediments was present as polymerized precipitates similar to uraninite and/or less ordered U(IV), referred to as non-uraninite U(IV) species associated with biomass (NUSAB). Extractions of sediment containing both uraninite and NUSAB displayed higher dissolved uranium concentrations under oxic than anoxic conditions while extractions of sediment dominated by NUSAB resulted in identical dissolved U concentrations. Dissolved U(IV) was rapidly oxidized under anoxic conditions in all experiments. Uraninite reacted minimally under anoxic conditions but thermodynamic calculations show that its propensity to oxidize is sensitive to solution chemistry and sediment mineralogy. A universal method for quantification of U(IV) and U(VI) in sediments has not yet been developed but the chemical extractions, when combined with solid-phase characterization, have a narrow range of applicability for sediments without U(VI).

Quantifying differences in the impact of variable chemistry on equilibrium uranium(VI) adsorption properties of aquifer sediments

USGS Publications Warehouse

Stoliker, Deborah L.; Kent, Douglas B.; Zachara, John M.

2011-01-01

Uranium adsorption-desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500-1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO22+ + 2CO32- = >SOUO2(CO3HCO3)2-, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logKc) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logKc values. Using this approach, logKc values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (Kc uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors.

Uranium bioreduction rates across scales: biogeochemical hot moments and hot spots during a biostimulation experiment at Rifle, Colorado.

PubMed

Bao, Chen; Wu, Hongfei; Li, Li; Newcomer, Darrell; Long, Philip E; Williams, Kenneth H

2014-09-02

We aim to understand the scale-dependent evolution of uranium bioreduction during a field experiment at a former uranium mill site near Rifle, Colorado. Acetate was injected to stimulate Fe-reducing bacteria (FeRB) and to immobilize aqueous U(VI) to insoluble U(IV). Bicarbonate was coinjected in half of the domain to mobilize sorbed U(VI). We used reactive transport modeling to integrate hydraulic and geochemical data and to quantify rates at the grid block (0.25 m) and experimental field scale (tens of meters). Although local rates varied by orders of magnitude in conjunction with biostimulation fronts propagating downstream, field-scale rates were dominated by those orders of magnitude higher rates at a few selected hot spots where Fe(III), U(VI), and FeRB were at their maxima in the vicinity of the injection wells. At particular locations, the hot moments with maximum rates negatively corresponded to their distance from the injection wells. Although bicarbonate injection enhanced local rates near the injection wells by a maximum of 39.4%, its effect at the field scale was limited to a maximum of 10.0%. We propose a rate-versus-measurement-length relationship (log R' = -0.63 log L - 2.20, with R' in μmol/mg cell protein/day and L in meters) for orders-of-magnitude estimation of uranium bioreduction rates across scales.

A novel benzimidazole-functionalized 2-D COF material: synthesis and application as a selective solid-phase extractant for separation of uranium.

PubMed

Li, Juan; Yang, Xiaodan; Bai, Chiyao; Tian, Yin; Li, Bo; Zhang, Shuang; Yang, Xiaoyu; Ding, Songdong; Xia, Chuanqin; Tan, Xinyu; Ma, Lijian; Li, Shoujian

2015-01-01

A novel COF-based material (COF-COOH) containing large amounts of carboxylic groups was prepared for the first time by using a simple and effective one-step synthetic method, in which the cheap and commercially available raw materials, trimesoyl chloride and p-phenylenediamine, were used. The as-synthesized COF-COOH was modified with previously synthesized 2-(2,4-dihydroxyphenyl)-benzimidazole (HBI) by "grafting to" method, and a new solid-phase extractant (COF-HBI) with highly efficient sorption performance for uranium(VI) was consequently obtained. A series of characterizations demonstrated that COF-COOH and COF-HBI exhibited great thermostabilities and irradiation stabilities. Sorption behavior of the COF-based materials toward U(VI) was compared in simulated nuclear industrial effluent containing UO2(2+) and 11 undesired ions, and the UO2(2+) sorption amount of COF-HBI was 81 mg g(-1), accounting for approximately 58% of the total sorption amount, which was much higher than the sorption selectivity of COF-COOH to UO2(2+) (39%). Batch sorption experiment results indicated that the uranium(VI) sorption on COF-HBI was a pH dependent, rapid (sorption equilibrium was reached in 30 min), endothermic and spontaneous process. In the most favorable conditions, the equilibrium sorption capacity of the adsorbent for uranium could reach 211 mg g(-1). Copyright © 2014 Elsevier Inc. All rights reserved.

Uranium Biomineralization By Natural Microbial Phosphatase Activities in the Subsurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taillefert, Martial

This project investigated the geochemical and microbial processes associated with the biomineralization of radionuclides in subsurface soils. During this study, it was determined that microbial communities from the Oak Ridge Field Research subsurface are able to express phosphatase activities that hydrolyze exogenous organophosphate compounds and result in the non-reductive bioimmobilization of U(VI) phosphate minerals in both aerobic and anaerobic conditions. The changes of the microbial community structure associated with the biomineralization of U(VI) was determined to identify the main organisms involved in the biomineralization process, and the complete genome of two isolates was sequenced. In addition, it was determined thatmore » both phytate, the main source of natural organophosphate compounds in natural environments, and polyphosphate accumulated in cells could also be hydrolyzed by native microbial population to liberate enough orthophosphate and precipitate uranium phosphate minerals. Finally, the minerals produced during this process are stable in low pH conditions or environments where the production of dissolved inorganic carbon is moderate. These findings suggest that the biomineralization of U(VI) phosphate minerals is an attractive bioremediation strategy to uranium bioreduction in low pH uranium-contaminated environments. These efforts support the goals of the SBR long-term performance measure by providing key information on "biological processes influencing the form and mobility of DOE contaminants in the subsurface".« less

Significant Association between Sulfate-Reducing Bacteria and Uranium-Reducing Microbial Communities as Revealed by a Combined Massively Parallel Sequencing-Indicator Species Approach▿ †

PubMed Central

Cardenas, Erick; Wu, Wei-Min; Leigh, Mary Beth; Carley, Jack; Carroll, Sue; Gentry, Terry; Luo, Jian; Watson, David; Gu, Baohua; Ginder-Vogel, Matthew; Kitanidis, Peter K.; Jardine, Philip M.; Zhou, Jizhong; Criddle, Craig S.; Marsh, Terence L.; Tiedje, James M.

2010-01-01

Massively parallel sequencing has provided a more affordable and high-throughput method to study microbial communities, although it has mostly been used in an exploratory fashion. We combined pyrosequencing with a strict indicator species statistical analysis to test if bacteria specifically responded to ethanol injection that successfully promoted dissimilatory uranium(VI) reduction in the subsurface of a uranium contamination plume at the Oak Ridge Field Research Center in Tennessee. Remediation was achieved with a hydraulic flow control consisting of an inner loop, where ethanol was injected, and an outer loop for flow-field protection. This strategy reduced uranium concentrations in groundwater to levels below 0.126 μM and created geochemical gradients in electron donors from the inner-loop injection well toward the outer loop and downgradient flow path. Our analysis with 15 sediment samples from the entire test area found significant indicator species that showed a high degree of adaptation to the three different hydrochemical-created conditions. Castellaniella and Rhodanobacter characterized areas with low pH, heavy metals, and low bioactivity, while sulfate-, Fe(III)-, and U(VI)-reducing bacteria (Desulfovibrio, Anaeromyxobacter, and Desulfosporosinus) were indicators of areas where U(VI) reduction occurred. The abundance of these bacteria, as well as the Fe(III) and U(VI) reducer Geobacter, correlated with the hydraulic connectivity to the substrate injection site, suggesting that the selected populations were a direct response to electron donor addition by the groundwater flow path. A false-discovery-rate approach was implemented to discard false-positive results by chance, given the large amount of data compared. PMID:20729318

Significant association between sulfate-reducing bacteria and uranium-reducing microbial communities as revealed by a combined massively parallel sequencing-indicator species approach.

PubMed

Cardenas, Erick; Wu, Wei-Min; Leigh, Mary Beth; Carley, Jack; Carroll, Sue; Gentry, Terry; Luo, Jian; Watson, David; Gu, Baohua; Ginder-Vogel, Matthew; Kitanidis, Peter K; Jardine, Philip M; Zhou, Jizhong; Criddle, Craig S; Marsh, Terence L; Tiedje, James M

2010-10-01

Massively parallel sequencing has provided a more affordable and high-throughput method to study microbial communities, although it has mostly been used in an exploratory fashion. We combined pyrosequencing with a strict indicator species statistical analysis to test if bacteria specifically responded to ethanol injection that successfully promoted dissimilatory uranium(VI) reduction in the subsurface of a uranium contamination plume at the Oak Ridge Field Research Center in Tennessee. Remediation was achieved with a hydraulic flow control consisting of an inner loop, where ethanol was injected, and an outer loop for flow-field protection. This strategy reduced uranium concentrations in groundwater to levels below 0.126 μM and created geochemical gradients in electron donors from the inner-loop injection well toward the outer loop and downgradient flow path. Our analysis with 15 sediment samples from the entire test area found significant indicator species that showed a high degree of adaptation to the three different hydrochemical-created conditions. Castellaniella and Rhodanobacter characterized areas with low pH, heavy metals, and low bioactivity, while sulfate-, Fe(III)-, and U(VI)-reducing bacteria (Desulfovibrio, Anaeromyxobacter, and Desulfosporosinus) were indicators of areas where U(VI) reduction occurred. The abundance of these bacteria, as well as the Fe(III) and U(VI) reducer Geobacter, correlated with the hydraulic connectivity to the substrate injection site, suggesting that the selected populations were a direct response to electron donor addition by the groundwater flow path. A false-discovery-rate approach was implemented to discard false-positive results by chance, given the large amount of data compared.

Uranium Biomineralization by Natural Microbial Phosphatase Activities in the Subsurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sobecky, Patricia A.

2015-04-06

In this project, inter-disciplinary research activities were conducted in collaboration among investigators at The University of Alabama (UA), Georgia Institute of Technology (GT), Lawrence Berkeley National Laboratory (LBNL), Brookhaven National Laboratory (BNL), the DOE Joint Genome Institute (JGI), and the Stanford Synchrotron Radiation Light source (SSRL) to: (i) confirm that phosphatase activities of subsurface bacteria in Area 2 and 3 from the Oak Ridge Field Research Center result in solid U-phosphate precipitation in aerobic and anaerobic conditions; (ii) investigate the eventual competition between uranium biomineralization via U-phosphate precipitation and uranium bioreduction; (iii) determine subsurface microbial community structure changes of Areamore » 2 soils following organophosphate amendments; (iv) obtain the complete genome sequences of the Rahnella sp. Y9-602 and the type-strain Rahnella aquatilis ATCC 33071 isolated from these soils; (v) determine if polyphosphate accumulation and phytate hydrolysis can be used to promote U(VI) biomineralization in subsurface sediments; (vi) characterize the effect of uranium on phytate hydrolysis by a new microorganism isolated from uranium-contaminated sediments; (vii) utilize positron-emission tomography to label and track metabolically-active bacteria in soil columns, and (viii) study the stability of the uranium phosphate mineral product. Microarray analyses and mineral precipitation characterizations were conducted in collaboration with DOE SBR-funded investigators at LBNL. Thus, microbial phosphorus metabolism has been shown to have a contributing role to uranium immobilization in the subsurface.« less

Performance and Mechanism of Uranium Adsorption from Seawater to Poly(dopamine)-Inspired Sorbents.

PubMed

Wu, Fengcheng; Pu, Ning; Ye, Gang; Sun, Taoxiang; Wang, Zhe; Song, Yang; Wang, Wenqing; Huo, Xiaomei; Lu, Yuexiang; Chen, Jing

2017-04-18

Developing facile and robust technologies for effective enrichment of uranium from seawater is of great significance for resource sustainability and environmental safety. By exploiting mussel-inspired polydopamine (PDA) chemistry, diverse types of PDA-functionalized sorbents including magnetic nanoparticle (MNP), ordered mesoporous carbon (OMC), and glass fiber carpet (GFC) were synthesized. The PDA functional layers with abundant catechol and amine/imine groups provided an excellent platform for binding to uranium. Due to the distinctive structure of PDA, the sorbents exhibited multistage kinetics which was simultaneously controlled by chemisorption and intralayer diffusion. Applying the diverse PDA-modified sorbents for enrichment of low concentration (parts per billion) uranium in laboratory-prepared solutions and unpurified seawater was fully evaluated under different scenarios: that is, by batch adsorption for MNP and OMC and by selective filtration for GFC. Moreover, high-resolution X-ray photoelectron spectroscopic and extended X-ray absorption fine structure studies were performed for probing the underlying coordination mechanism between PDA and U(VI). The catechol hydroxyls of PDA were identified as the main bidentate ligands to coordinate U(VI) at the equatorial plane. This study assessed the potential of versatile PDA chemistry for development of efficient uranium sorbents and provided new insights into the interaction mechanism between PDA and uranium.

Pore-scale characterization of biogeochemical controls on iron and uranium speciation under flow conditions.

PubMed

Pearce, Carolyn I; Wilkins, Michael J; Zhang, Changyong; Heald, Steve M; Fredrickson, Jim K; Zachara, John M

2012-08-07

Etched silicon microfluidic pore network models (micromodels) with controlled chemical and redox gradients, mineralogy, and microbiology under continuous flow conditions are used for the incremental development of complex microenvironments that simulate subsurface conditions. We demonstrate the colonization of micromodel pore spaces by an anaerobic Fe(III)-reducing bacterial species (Geobacter sulfurreducens) and the enzymatic reduction of a bioavailable Fe(III) phase within this environment. Using both X-ray microprobe and X-ray absorption spectroscopy, we investigate the combined effects of the precipitated Fe(III) phases and the microbial population on uranium biogeochemistry under flow conditions. Precipitated Fe(III) phases within the micromodel were most effectively reduced in the presence of an electron shuttle (AQDS), and Fe(II) ions adsorbed onto the precipitated mineral surface without inducing any structural change. In the absence of Fe(III), U(VI) was effectively reduced by the microbial population to insoluble U(IV), which was precipitated in discrete regions associated with biomass. In the presence of Fe(III) phases, however, both U(IV) and U(VI) could be detected associated with biomass, suggesting reoxidation of U(IV) by localized Fe(III) phases. These results demonstrate the importance of the spatial localization of biomass and redox active metals, and illustrate the key effects of pore-scale processes on contaminant fate and reactive transport.

The Model VI transmission fluorimeter for the determination of uranium

USGS Publications Warehouse

Kinser, Charles Alvin

1954-01-01

An improved transmission fluorimeter (Model VI) for use in the determination of uranium consists of a line-operated, low-voltage d-c supply, powering a small 3-watt ultraviolet lamp as a source of long wavelength ultraviolet radiation; a Model V phototube housing and. fluorimeter head containing the sample holder, shutter, and primary and secondary filters; an end-window multiplier phototube powered by a stable, commercially available high-voltage supply; and an electronic microammeter for measuring the output current from the photomultiplier tube. The instrument has excellent electrical stability and operates over a wide range of sensitivity. Its versatility makes it useful for both routine and research work.

Microbial Community Changes in Response to Ethanol or Methanol Amendments for U(VI) Reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vishnivetskaya, Tatiana A; Brandt, Craig C; Madden, Andrew

2010-01-01

Microbial community responses to ethanol, methanol and methanol + humics amendments in relationship to uranium bioremediation were studied in laboratory microcosm experiments using sediments and ground water from a uranium-contaminated site in Oak Ridge, Tennessee. Ethanol addition always resulted in uranium reduction at rate of 0.8-1.0 mol l-1 d-1 while methanol addition did so occasionally at rate 0.95 mol l-1 d-1. The type of carbon source added, the duration of incubation, and the sampling site influenced the bacterial community structure upon incubation. Analysis of 16S rRNA gene clone libraries indicated (1) bacterial communities found in ethanol- and methanol-amended samples withmore » U(VI) reduction were similar due to presence of -Proteobacteria, and -Proteobacteria (members of the families Burkholderiaceae, Comamonadaceae, Oxalobacteraceae, and Rhodocyclaceae); (2) methanol-amended samples without U(VI) reduction exhibited the lowest diversity and the bacterial community contained 69.2-92.8% of the family Methylophilaceae; and (3) the addition of humics resulted in an increase of phylogenetic diversity of -Proteobacteria (Rodoferax, Polaromonas, Janthinobacterium, Methylophilales, unclassified) and Firmicutes (Desulfosporosinus, Clostridium).« less

Bioremediation of uranium-contaminated groundwater: a systems approach to subsurface biogeochemistry.

PubMed

Williams, Kenneth H; Bargar, John R; Lloyd, Jonathan R; Lovley, Derek R

2013-06-01

Adding organic electron donors to stimulate microbial reduction of highly soluble U(VI) to less soluble U(IV) is a promising strategy for immobilizing uranium in contaminated subsurface environments. Studies suggest that diagnosing the in situ physiological status of the subsurface community during uranium bioremediation with environmental transcriptomic and proteomic techniques can identify factors potentially limiting U(VI) reduction activity. Models which couple genome-scale in silico representations of the metabolism of key microbial populations with geochemical and hydrological models may be able to predict the outcome of bioremediation strategies and aid in the development of new approaches. Concerns remain about the long-term stability of sequestered U(IV) minerals and the release of co-contaminants associated with Fe(III) oxides, which might be overcome through targeted delivery of electrons to select microorganisms using in situ electrodes. Copyright © 2012 Elsevier Ltd. All rights reserved.

Unexpected Actinyl Cation-Directed Structural Variation in Neptunyl(VI) A-Type Tri-lacunary Heteropolyoxotungstate Complexes

DOE PAGES

Berg, John M.; Gaunt, Andrew J.; May, Iain; ...

2015-04-22

A-type tri-lacunary heteropolyoxotungstate anions (e.g., [PW 9O 34] 9-, [AsW 9O 34] 9-, [SiW 9O 34] 10- and [GeW 9O 34] 10-) are multi-dentate oxygen donor ligands that readily form sandwich complexes with actinyl cations ({UO 2} 2+, {NpO 2} +, {NpO 2} 2+ & {PuO 2} 2+) in near neutral/slightly alkaline aqueous solutions. Two or three actinyl cations are sandwiched between two trilacunary anions, with additional cations (Na +, K + or NH 4 +) also often held within the cluster. Studies thus far have indicated that it is these additional +I cations, rather than the specific actinylmore » cation, that direct the structural variation in the complexes formed. We now report the structural characterization of the neptunyl (VI) cluster complex (NH 4) 13 [Na(NpO 2) 2(A-α- PW 9O 34) 2]·12H 2O. The anion in this complex, [Na(NpO 2) 2(PW 9O 34) 2] 13-, contains one Na + cation and two {NpO 2} 2+ cations held between two [PW 9O 34] 9- anions – with an additional partial occupancy NH 4 + or {NpO 2} 2+ cation also present. In the analogous uranium (VI) system, under similar reaction conditions that includes an excess of NH 4Cl in the parent solution, it was previously shown that [(NH 4) 2(U VIO 2) 2(A-PW 9O 34) 2] 12- is the dominant species in both solution and the crystallized salt. Spectroscopic studies provide further proof of differences in the observed chemistry for the {NpO 2} 2+/[PW 9O 34] 9- and {UO 2} 2+/[PW 9O 34] 9- systems, both in solution and in solid state complexes crystallized from comparable salt solutions. The work revealed that varying the actinide element (Np vs. U) can indeed measurably impact structure and complex stability in the cluster chemistry of actinyl (VI) cations with A-type tri-lacunary heteropolyoxotungstate anions.« less

Comparative analysis of uranium bioassociation with halophilic bacteria and archaea

PubMed Central

Bader, Miriam; Müller, Katharina; Foerstendorf, Harald; Schmidt, Matthias; Simmons, Karen; Swanson, Juliet S.; Reed, Donald T.; Stumpf, Thorsten

2018-01-01

Rock salt represents a potential host rock formation for the final disposal of radioactive waste. The interactions between indigenous microorganisms and radionuclides, e.g. uranium, need to be investigated to better predict the influence of microorganisms on the safety assessment of the repository. Hence, the association process of uranium with two microorganisms isolated from rock salt was comparatively studied. Brachybacterium sp. G1, which was isolated from the German salt dome Gorleben, and Halobacterium noricense DSM15987T, were selected as examples of a moderately halophilic bacterium and an extremely halophilic archaeon, respectively. The microorganisms exhibited completely different association behaviors with uranium. While a pure biosorption process took place with Brachybacterium sp. G1 cells, a multistage association process occurred with the archaeon. In addition to batch experiments, in situ attenuated total reflection Fourier-transform infrared spectroscopy was applied to characterize the U(VI) interaction process. Biosorption was identified as the dominating process for Brachybacterium sp. G1 with this method. Carboxylic functionalities are the dominant interacting groups for the bacterium, whereas phosphoryl groups are also involved in U(VI) association by the archaeon H. noricense. PMID:29329319

Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer

PubMed Central

Suzuki, Yohey; Mukai, Hiroki; Ishimura, Toyoho; Yokoyama, Takaomi D.; Sakata, Shuhei; Hirata, Takafumi; Iwatsuki, Teruki; Mizuno, Takashi

2016-01-01

The stimulation of bacterial activities that convert hexavalent uranium, U(VI), to tetravalent uranium, U(IV), appears to be feasible for cost-effective remediation of contaminated aquifers. However, U(VI) reduction typically results in the precipitation of U(IV) particles less than 5 nanometers in diameter, except for environmental conditions enriched with iron. Because these tiny particles are mobile and susceptible to oxidative dissolution after the termination of nutrient injection, in situ bioremediation remains to be impractical. Here we show that U(IV) nanoparticles of coffinite (U(SiO4)1−x(OH)4x) formed in fracture-filling calcium carbonate in a granitic aquifer. In situ U-Pb isotope dating demonstrates that U(IV) nanoparticles have been sequestered in the calcium carbonate for at least 1 million years. As the microbiologically induced precipitation of calcium carbonate in aquifer systems worldwide is extremely common, we anticipate simultaneous stimulation of microbial activities for precipitation reactions of calcium carbonate and U(IV) nanoparticles, which leads to long-term sequestration of uranium and other radionuclides in contaminated aquifers and deep geological repositories. PMID:26948389

Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer.

PubMed

Suzuki, Yohey; Mukai, Hiroki; Ishimura, Toyoho; Yokoyama, Takaomi D; Sakata, Shuhei; Hirata, Takafumi; Iwatsuki, Teruki; Mizuno, Takashi

2016-03-07

The stimulation of bacterial activities that convert hexavalent uranium, U(VI), to tetravalent uranium, U(IV), appears to be feasible for cost-effective remediation of contaminated aquifers. However, U(VI) reduction typically results in the precipitation of U(IV) particles less than 5 nanometers in diameter, except for environmental conditions enriched with iron. Because these tiny particles are mobile and susceptible to oxidative dissolution after the termination of nutrient injection, in situ bioremediation remains to be impractical. Here we show that U(IV) nanoparticles of coffinite (U(SiO4)1-x(OH)4x) formed in fracture-filling calcium carbonate in a granitic aquifer. In situ U-Pb isotope dating demonstrates that U(IV) nanoparticles have been sequestered in the calcium carbonate for at least 1 million years. As the microbiologically induced precipitation of calcium carbonate in aquifer systems worldwide is extremely common, we anticipate simultaneous stimulation of microbial activities for precipitation reactions of calcium carbonate and U(IV) nanoparticles, which leads to long-term sequestration of uranium and other radionuclides in contaminated aquifers and deep geological repositories.

Performance Indicators for Uranium Bioremediation in the Subsurface: Basis and Assessment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, Philip E.; Yabusaki, Steven B.

2006-12-29

The purpose of this letter report is to identify performance indicators for in situ engineered bioremediation of subsurface uranium (U) contamination. This report focuses on in situ treatment of groundwater by biostimulation of extant in situ microbial populations (see http://128.3.7.51/NABIR/generalinfo/primers_guides/03_NABIR_primer.pdf for background information on bioremediation of metals and radionuclides). The treatment process involves amendment of the subsurface with an electron donor such as acetate, lactate, ethanol or other organic compound such that in situ microorganisms mediate the reduction of U(VI) to U(IV). U(VI) precipitates as uraninite or other insoluble U phase. Uranium is thus immobilized in place by such processesmore » and is subject to reoxidation that may remobilize the reduced uranium. Related processes include augmenting the extant subsurface microbial populations, addition of electron acceptors, and introduction of chemically reducing materials such as zero-valent Fe. While metrics for such processes may be similar to those for in situ biostimulation, these related processes are not directly in the scope of this letter report.« less

Uranium delivery and uptake in a montane wetland, north-central Colorado, USA

USGS Publications Warehouse

Schumann, R. Randall; Zielinski, Robert A.; Otton, James K.; Pantea, Michael P.; Orem, William H.

2017-01-01

Comprehensive sampling of peat, underlying lakebed sediments, and coexisting waters of a naturally uraniferous montane wetland are combined with hydrologic measurements to define the important controls on uranium (U) supply and uptake. The major source of U to the wetland is groundwater flowing through locally fractured and faulted granite gneiss of Proterozoic age. Dissolved U concentrations in four springs and one seep ranged from 20 to 83 ppb (μg/l). Maximum U concentrations are ∼300 ppm (mg/kg) in lakebed sediments and >3000 ppm in peat. Uranium in lakebed sediments is primarily stratabound in the more organic-rich layers, but samples of similar organic content display variable U concentrations. Post-depositional modifications include variable additions of U delivered by groundwater. Uranium distribution in peat is heterogeneous and primarily controlled by proximity to groundwater-fed springs and seeps that act as local point sources of U, and by proximity to groundwater directed along the peat/lakebeds contact. Uranium is initially sorbed on various organic components of peat as oxidized U(VI) present in groundwater. Selective extractions indicate that the majority of sorbed U remains as the oxidized species despite reducing conditions that should favor formation of U(IV). Possible explanations are kinetic hindrances related to strong complex formation between uranyl and humic substances, inhibition of anaerobic bacterial activity by low supply of dissolved iron and sulfate, and by cold temperatures.

Thiocyanate complexes of uranium in multiple oxidation states: a combined structural, magnetic, spectroscopic, spectroelectrochemical, and theoretical study.

PubMed

Hashem, Emtithal; Platts, James A; Hartl, František; Lorusso, Giulia; Evangelisti, Marco; Schulzke, Carola; Baker, Robert J

2014-08-18

A comprehensive study of the complexes A4[U(NCS)8] (A = Cs, Et4N, (n)Bu4N) and A3[UO2(NCS)5] (A = Cs, Et4N) is described, with the crystal structures of [(n)Bu4N]4[U(NCS)8]·2MeCN and Cs3[UO2(NCS)5]·O0.5 reported. The magnetic properties of square antiprismatic Cs4[U(NCS)8] and cubic [Et4N]4[U(NCS)8] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, μeff = 1.21 μB and 0.53 μB, respectively. Electronic absorption and photoluminescence spectra of the uranium(IV) compounds have been measured. The redox chemistry of [Et4N]4[U(NCS)8] has been explored using IR and UV-vis spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc(+), followed by an irreversible oxidation to form dithiocyanogen (NCS)2 which upon back reduction regenerates thiocyanate anions coordinating to UO2(2+). NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U(NCS)8](4-) is delocalized over all NCS(-) ligands. Reduction of the uranyl(VI) complex [Et4N]3[UO2(NCS)5] to uranyl(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An(NCS)8](4-) (An = Th, U) and [UO2(NCS)5](3-) has been explored by a combination of DFT and QTAIM analysis, and the U-N bonds are predominantly ionic, with the uranyl(V) species more ionic that the uranyl(VI) ion. Additionally, the U(IV)-NCS ion is more ionic than what was found for U(IV)-Cl complexes.

Adsorption property of Br-PADAP-impregnated multiwall carbon nanotubes towards uranium and its performance in the selective separation and determination of uranium in different environmental samples.

PubMed

Khamirchi, Ramzanali; Hosseini-Bandegharaei, Ahmad; Alahabadi, Ahmad; Sivamani, Selvaraju; Rahmani-Sani, Abolfazl; Shahryari, Taher; Anastopoulos, Ioannis; Miri, Mohammad; Tran, Hai Nguyen

2018-04-15

A newer efficient U(VI) ion adsorbent was synthesized by impregnating Br-PADAP [2-(5-Bromo-2-pyridylazo)-5-(diethylamino)phenol] onto multiwall carbon nanotubes (MWCNTs). The effects of various operation conditions on uranium adsorption (i.e., pH contact time, temperature, and initial uranium concentration) were systematically evaluated using batch experiments. The results indicated that the uranium adsorption on modified MWNCTs (5.571 × 10 -3 g/mg × min) reached faster equilibrium than that on pristine MWNCTs (4.832 × 10 -3 g/mg × min), reflecting the involvement of appropriate functional groups of Br-PADAP on the chelating ion-exchange mechanism of U(VI) adsorption. Modified MWNCTs (83.4mg/g) exhibited significantly higher maximum Langmuir adsorption capacity than pristine MWNCTs (15.1mg/g). Approximately 99% of uranium adsorbed onto modified MWNCTs can be desorbed by 2.5mL of 1M HNO 3 solution. Therefore, Br-PADAP-modified MWNCTs can server as a promising adsorbent for efficient uranium adsorption applications in water treatment. Subsequently, the proposed solid-phase extraction (using a mini-column packed with Br-PADAP/MWCNT) was successfully utilized for analysing trace uranium levels by the ICP-AES method in different environmental samples with a pre-concentration factor of 300-fold. The coexistence of other ions demonstrated an insignificant interference on the separative pre-concentration of uranium. the detection limit was recognized as 0.14μg/L, and the relative standard deviation was approximately 3.3% (n = 7). Copyright © 2017 Elsevier Inc. All rights reserved.

Influence of Reactive Transport on the Reduction of U(VI) in the Presence of Fe(III) and Nitrate: Implications for U(VI) Immobilization by Bioremediation / Biobarriers- Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

B.D. Wood

2007-01-01

Subsurface contamination by metals and radionuclides represent some of the most challenging remediation problems confronting the Department of Energy (DOE) complex. In situ remediation of these contaminants by dissimilatory metal reducing bacteria (DMRB) has been proposed as a potential cost effective remediation strategy. The primary focus of this research is to determine the mechanisms by which the fluxes of electron acceptors, electron donors, and other species can be controlled to maximize the transfer of reductive equivalents to the aqueous and solid phases. The proposed research is unique in the NABIR portfolio in that it focuses on (i) the role ofmore » flow and transport in the initiation of biostimulation and the successful sequestration of metals and radionuclides [specifically U(VI)], (ii) the subsequent reductive capacity and stability of the reduced sediments produced by the biostimulation process, and (iii) the potential for altering the growth of biomass in the subsurface by the addition of specific metabolic uncoupling compounds. A scientifically-based understanding of these phenomena are critical to the ability to design successful bioremediation schemes. The laboratory research will employ Shewanella putrefaciens (CN32), a facultative DMRB that can use Fe(III) oxides as a terminal electron acceptor. Sediment-packed columns will be inoculated with this organism, and the reduction of U(VI) by the DMRB will be stimulated by the addition of a carbon and energy source in the presence of Fe(III). Separate column experiments will be conducted to independently examine: (1) the importance of the abiotic reduction of U(VI) by biogenic Fe(II); (2) the influence of the transport process on Fe(III) reduction and U(VI) immobilization, with emphasis on methods for controlling the fluxes of aqueous species to maximize uranium reduction; (3) the reductive capacity of biologically-reduced sediments (with respect to re-oxidation by convective fluxes of O2 and NO3-) and the long-term stability of immobilized uranium mineral phases after bioremediation processes are complete, and (4) the ability for metabolic uncoupling compounds to maintain microbial growth while limiting biomass production. The results of the laboratory experiments will be used to develop mathematical descriptive models for the coupled transport and reduction processes.« less

Using 238U/235U ratios to understand the formation and oxidation of reduced uranium solids in naturally reduced zones

NASA Astrophysics Data System (ADS)

Jemison, N.; Johnson, T. M.; Druhan, J. L.; Davis, J. A.

2016-12-01

Uranium occurs in groundwater primarily as soluble and mobile U(VI), which can be reduced to immobile U(IV), often observed in sediments as uraninite. Numerous U(VI)-contaminated sites, such as the DOE field site in Rifle, CO, contain naturally reduced zones (NRZ's) that have relatively high concentrations of organic matter. Reduction of heavy metals occurs within NRZ's, producing elevated concentrations of iron sulfides and U(IV). Slow, natural oxidation of U(IV) from NRZ's may prolong U(VI) contamination of groundwater. The reduction of U(VI) produces U(IV) with a higher 238U/235U ratio. Samples from two NRZ sediment cores recovered from the Rifle site revealed that the outer fringes of the NRZ contain U(IV) with a high 238U/235U ratio, while lower values are observed in the center . We suggest that as aqueous U(VI) was reduced in the NRZ, it was driven to lower 238U/235U values, such that U(IV) formed in the core of the NRZ reflects a lower 238U/235U. Two oxidation experiments were conducted by injecting groundwater containing between 14.9 and 21.2 mg/L dissolved O2 as an oxidant into the NRZ. The oxidation of U(IV) from this NRZ increased aqueous U(VI) concentrations and caused a shift to higher 238U/235U in groundwater as U(IV) was oxidized primarily on the outer fringes of the NRZ. In total these observations suggest that the stability of solid phase uranium is governed by coupled reaction and transport processes. To better understand various reactive transport scenarios we developed a model for the formation and oxidation of NRZ's utilizing the reactive transport software CrunchTope. These simulations suggest that the development of isotopically heterogeneous U(IV) within NRZ's is largely controlled by permeability of the NRZ and the U(VI) reduction rate. Oxidation of U(IV) from the NRZ's is constrained by the oxidation rate of U(IV) as well as iron sulfides, which can prevent oxidation of U(IV) by scavenging dissolved oxygen.

How to Make Data a Blessing to Parametric Uncertainty Quantification and Reduction?

NASA Astrophysics Data System (ADS)

Ye, M.; Shi, X.; Curtis, G. P.; Kohler, M.; Wu, J.

2013-12-01

In a Bayesian point of view, probability of model parameters and predictions are conditioned on data used for parameter inference and prediction analysis. It is critical to use appropriate data for quantifying parametric uncertainty and its propagation to model predictions. However, data are always limited and imperfect. When a dataset cannot properly constrain model parameters, it may lead to inaccurate uncertainty quantification. While in this case data appears to be a curse to uncertainty quantification, a comprehensive modeling analysis may help understand the cause and characteristics of parametric uncertainty and thus turns data into a blessing. In this study, we illustrate impacts of data on uncertainty quantification and reduction using an example of surface complexation model (SCM) developed to simulate uranyl (U(VI)) adsorption. The model includes two adsorption sites, referred to as strong and weak sites. The amount of uranium adsorption on these sites determines both the mean arrival time and the long tail of the breakthrough curves. There is one reaction on the weak site but two reactions on the strong site. The unknown parameters include fractions of the total surface site density of the two sites and surface complex formation constants of the three reactions. A total of seven experiments were conducted with different geochemical conditions to estimate these parameters. The experiments with low initial concentration of U(VI) result in a large amount of parametric uncertainty. A modeling analysis shows that it is because the experiments cannot distinguish the relative adsorption affinity of the strong and weak sites on uranium adsorption. Therefore, the experiments with high initial concentration of U(VI) are needed, because in the experiments the strong site is nearly saturated and the weak site can be determined. The experiments with high initial concentration of U(VI) are a blessing to uncertainty quantification, and the experiments with low initial concentration help modelers turn a curse into a blessing. The data impacts on uncertainty quantification and reduction are quantified using probability density functions of model parameters obtained from Markov Chain Monte Carlo simulation using the DREAM algorithm. This study provides insights to model calibration, uncertainty quantification, experiment design, and data collection in groundwater reactive transport modeling and other environmental modeling.

Precipitation and Dissolution of Uranyl Phosphates in a Microfluidic Pore Structure

NASA Astrophysics Data System (ADS)

Werth, C. J.; Fanizza, M.; Strathmann, T.; Finneran, K.; Oostrom, M.; Zhang, C.; Wietsma, T. W.; Hess, N. J.

2011-12-01

The abiotic precipitation of uranium (U(VI)) was evaluated in a microfluidic pore structure (i.e. micromodel) to assess the efficacy of using a phosphate amendment to immobilize uranium in groundwater and mitigate the risk of this contaminant to potential down-gradient receptor sites. U(VI) was mixed transverse to the direction of flow with hydrogen phosphate (HPO42-), in the presence or absence of calcium (Ca2+) or sulfate (SO42-), in order to identify precipitation rates, the morphology and types of minerals formed, and the stability of these minerals to dissolution with and without bicarbonate (HCO3-) present. Raman backscattering spectroscopy and micro X-ray diffraction (μ-XRD) results both showed that the only mineral precipitated was chernikovite (also known as hydrogen uranyl phosphate; UO2HPO4), even though the formation of other minerals were thermodynamically favored depending on the experimental conditions. Precipitation and dissolution rates varied with influent conditions. Relative to when only U(VI) and HPO42- were present, precipitation rates were 2.3 times slower when SO42- was present, and 1.4 times faster when Ca2+ was present. These rates were inversely related to the size of crystals formed during precipitation. Dissolution rates for chernikovite increased with increasing HCO3- concentrations, consistent with formation of uranyl carbonate complexes in aqueous solution, and they were the fastest for chernikovite formed in the presence of SO42-, and slowest for the chernikovite formed in the presence of Ca2+. These rates are related to the ratios of mineral-water interfacial area to mineral volume. Fluorescent tracer studies and laser confocal microscopy images showed that densely aggregated precipitates blocked pores and reduced permeability. The results suggest that changes in the solute conditions evaluated affect precipitation rates, crystal morphology, and crystal stability, but not mineral type.

Uranium Bioreduction Rates across Scales: Biogeochemical Hot Moments and Hot Spots during a Biostimulation Experiment at Rifle, Colorado

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bao, Chen; Wu, Hongfei; Li, Li

2014-09-02

We aim to understand the scale-dependent evolution of uranium bioreduction during a field experiment at a former uranium mill site near Rifle, Colorado. Acetate was injected to stimulate Fe-reducing bacteria (FeRB) and to immobilize aqueous U(VI) to insoluble U(IV). Bicarbonate was coinjected in half of the domain to mobilize sorbed U(VI). We used reactive transport modeling to integrate hydraulic and geochemical data and to quantify rates at the grid block (0.25 m) and experimental field scale (tens of meters). Although local rates varied by orders of magnitude in conjunction with biostimulation fronts propagating downstream, field-scale rates were dominated by thosemore » orders of magnitude higher rates at a few selected hot spots where Fe(III), U(VI), and FeRB were at their maxima in the vicinity of the injection wells. At particular locations, the hot moments with maximum rates negatively corresponded to their distance from the injection wells. Although bicarbonate injection enhanced local rates near the injection wells by a maximum of 39.4%, its effect at the field scale was limited to a maximum of 10.0%. We propose a rate-versus-measurement-length relationship (log R' = -0.63« less

Fractionation of 238U/235U by reduction during low temperature uranium mineralisation processes

NASA Astrophysics Data System (ADS)

Murphy, Melissa J.; Stirling, Claudine H.; Kaltenbach, Angela; Turner, Simon P.; Schaefer, Bruce F.

2014-02-01

Investigations of ‘stable’ uranium isotope fractionation during low temperature, redox transformations may provide new insights into the usefulness of the 238U/235U isotope system as a tracer of palaeoredox processes. Sandstone-hosted uranium deposits accumulate at an oxidation/reduction interface within an aquifer from the low temperature reduction of soluble U(VI) complexes in groundwaters, forming insoluble U(IV) minerals. This setting provides an ideal environment in which to investigate the effects of redox transformations on 238U/235U fractionation. Here we present the first coupled measurements of 238U/235U isotopic compositions and U concentrations for groundwaters and mineralised sediment samples from the same redox system in the vicinity of the high-grade Pepegoona sandstone-hosted uranium deposit, Australia. The mineralised sediment samples display extremely variable 238U/235U ratios (herein expressed as δUCRM145238, the per-mil deviation from the international NBL standard CRM145). The majority of mineralised sediment samples have δUCRM145238 values between -1.30±0.05 and 0.55±0.12‰, spanning a ca. 2‰ range. However, one sample has an unusually light isotopic composition of -4.13±0.05‰, which suggests a total range of U isotopic variability of up to ca. 5‰, the largest variation found thus far in a single natural redox system. The 238U/235U isotopic signature of the mineralised sediments becomes progressively heavier (enriched in 238U) along the groundwater flow path. The groundwaters show a greater than 2‰ variation in their 238U/235U ratios, ranging from δUCRM145238 values of -2.39±0.07 to -0.71±0.05‰. The majority of the groundwater data exhibit a clear systematic relationship between 238U/235U isotopic composition and U concentration; samples with the lowest U concentrations have the lowest 238U/235U ratios. The preferential incorporation of 238U during reduction of U(VI) to U(IV) and precipitation of uranium minerals leaves the groundwaters enriched in 235U, resulting in a progressive shift in 238U/235U towards lighter values in the aqueous phase as U is removed. These data can be modelled by a closed system Rayleigh fractionation model, with a fractionation factor (α, representing the 238U/235U composition of the groundwater relative to the solid uranium minerals) ranging from ∼0.9996 to 1.0000, with the majority of datapoints ranging from α values of 0.9998 to 0.9999. The sense and magnitude of the results of this study imply that 238U/235U fractionation is likely to be controlled by volume-dependent nuclear field shift effects during the reduction of U(VI) to U(IV) during mineralisation processes. These findings support the use of the 238U/235U isotopic system as a tracer to constrain the nature and timing of palaeoredox conditions.

Characterization of U(VI) reduction in contaminated sediments with slow-degrading electron donor source

NASA Astrophysics Data System (ADS)

Wu, W.; Watson, D. B.; Zhang, G.; Mehlhorn, T.; Lowe, K.; Earles, J.; Phillips, J.; Kelly, S. D.; Boyanov, M.; Kemner, K. M.; Schadt, C.; Criddle, C. S.; Jardine, P. M.; Brooks, S. C.

2011-12-01

In order to select sustainable, high efficiency and cost effective electron donor source, oleate and emulsified vegetable oil (EVO) were tested uranium (VI) reduction in comparison with ethanol in microcosms using uranium contaminated sediments and groundwater from the US DOE Oak Ridge Integrated Field Research Challenge (ORIFRC) site. The effect of initial sulfate concentration on U(VI) reduction was also tested. Both oleate and EVO were effective electron donor sources for U(VI) reduction. Accumulation of acetate as a major product and the removal of aqueous U(VI) were observed and were associated with sulfate reduction. Both oleate and EVO supported U(VI) reduction but at slower rates with a comparable but slightly lower extent of reduction than ethanol. X-ray absorption near-edge spectroscopy (XANES) analysis confirmed reduction of U(VI) to U(IV). The extent of U(VI) reduction in solid phase was negatively influenced by aqueous calcium concentration. The majority of electrons of the three substrates were consumed by sulfate reduction, Fe(III) reduction, and methanogenesis. Initial U(VI) concentration in the aqueous phase increased with increased sulfate concentration (1 versus 5 mM), likely due to U(VI) desorption from the solid phase. At the higher initial sulfate concentration more U(VI) was reduced and fewer electrons were used in methanogenesis. Analysis of bacterial and archeal populations using 16S rRNA gene libraries showed a significant increase in Deltaproteobacteria after biostimulation. The microbial community structures developed with oleate and EVO were significantly distinct from those developed with ethanol. Bacteria similar to Desulforegula spp. was predominant for oleate and EVO degradation but were not observed in ethanol-amended microcosms. Known U(VI)-reducing bacteria in the microcosms amended with the three electron donor sources included iron(III) reducing Geobacter spp. but in lower abundances than sulfate-reducing Desulfovibrio spp. The test results were used for the design a field test by one-time injection of EVO to the subsurface for U(VI) reduction in Area 2 of the ORIFRC site.

Pore-Scale Characterization of Biogeochemical Controls on Iron and Uranium Speciation under Flow Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pearce, Carolyn I.; Wilkins, Michael J.; Zhang, Changyong

2012-09-17

Etched silicon microfluidic pore network models (micromodels) with controlled chemical and redox gradients, mineralogy, and microbiology under continuous flow conditions are used for the incremental development of complex microenvironments that simulate subsurface conditions. We demonstrate the colonization of micromodel pore spaces by an anaerobic Fe(III)-reducing bacterial species (Geobacter sulfurreducens) and the enzymatic reduction of a bioavailable Fe(III) phase within this environment. Using both X-ray Microprobe and X-ray Absorption Spectroscopy, we investigate the combined effects of the precipitated Fe(III) phases and the microbial population on uranium biogeochemistry under flow conditions. Precipitated Fe(III) phases within the micromodel were most effectively reduced inmore » the presence of an electron shuttle (AQDS), and Fe(II) ions adsorbed onto the precipitated mineral surface without inducing any structural change. In the absence of Fe(III), U(VI) was effectively reduced by the microbial population to insoluble U(IV), which was precipitated in discrete regions associated with biomass. In the presence of Fe(III) phases, however, both U(IV) and U(VI) could be detected associated with biomass, suggesting re-oxidation of U(IV) by localized Fe(III) phases. These results demonstrate the importance of the spatial localization of biomass and redox active metals, and illustrate the key effects of pore-scale processes on contaminant fate and reactive transport.« less

Model-Based Analysis of the Role of Biological, Hydrological and Geochemical Factors Affecting Uranium Bioremediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Jiao; Scheibe, Timothy D.; Mahadevan, Radhakrishnan

2011-01-24

Uranium contamination is a serious concern at several sites motivating the development of novel treatment strategies such as the Geobacter-mediated reductive immobilization of uranium. However, this bioremediation strategy has not yet been optimized for the sustained uranium removal. While several reactive-transport models have been developed to represent Geobacter-mediated bioremediation of uranium, these models often lack the detailed quantitative description of the microbial process (e.g., biomass build-up in both groundwater and sediments, electron transport system, etc.) and the interaction between biogeochemical and hydrological process. In this study, a novel multi-scale model was developed by integrating our recent model on electron capacitancemore » of Geobacter (Zhao et al., 2010) with a comprehensive simulator of coupled fluid flow, hydrologic transport, heat transfer, and biogeochemical reactions. This mechanistic reactive-transport model accurately reproduces the experimental data for the bioremediation of uranium with acetate amendment. We subsequently performed global sensitivity analysis with the reactive-transport model in order to identify the main sources of prediction uncertainty caused by synergistic effects of biological, geochemical, and hydrological processes. The proposed approach successfully captured significant contributing factors across time and space, thereby improving the structure and parameterization of the comprehensive reactive-transport model. The global sensitivity analysis also provides a potentially useful tool to evaluate uranium bioremediation strategy. The simulations suggest that under difficult environments (e.g., highly contaminated with U(VI) at a high migration rate of solutes), the efficiency of uranium removal can be improved by adding Geobacter species to the contaminated site (bioaugmentation) in conjunction with the addition of electron donor (biostimulation). The simulations also highlight the interactive effect of initial cell concentration and flow rate on U(VI) reduction.« less

Simultaneous spectrophotometric determination of trace amounts of uranium, thorium, and zirconium using the partial least squares method after their preconcentration by alpha-benzoin oxime modified Amberlite XAD-2000 resin.

PubMed

Ghasemi, Jahan B; Zolfonoun, E

2010-01-15

A new solid phase extraction method for separation and preconcentration of trace amounts of uranium, thorium, and zirconium in water samples is proposed. The procedure is based on the adsorption of U(VI), Th(IV) and Zr(IV) ions on a column of Amberlite XAD-2000 resin loaded with alpha-benzoin oxime prior to their simultaneous spectrophotometric determination with Arsenazo III using orthogonal signal correction partial least squares method. The enrichment factor for preconcentration of uranium, thorium, and zirconium was found to be 100. The detection limits for U(VI), Th(IV) and Zr(IV) were 0.50, 0.54, and 0.48microgL(-1), respectively. The precision of the method, evaluated as the relative standard deviation obtained by analyzing a series of 10 replicates, was below 4% for all elements. The practical applicability of the developed sorbent was examined using synthetic seawater, natural waters and ceramic samples.

Effect of pH on uranium(VI) biosorption and biomineralization by Saccharomyces cerevisiae.

PubMed

Zheng, X Y; Shen, Y H; Wang, X Y; Wang, T S

2018-07-01

Biosorption of radionuclides by microorganisms is a promising and effective method for the remediation of contaminated areas. pH is the most important factor during uranium biosorption by Saccharomyces cerevisiae because the pH value not only affects the biosorption rate but also affects the precipitation structure. This study investigated the effect of pH on uranium (VI) biosorption and biomineralization by S. cerevisiae. Cells have the ability to buffer the solution to neutral, allowing the biosorption system to reach an optimal level regardless of the initial pH value. This occurs because there is a release of phosphate and ammonium ions during the interaction between cells and uranium. The uranyl and phosphate ions formed nano-particles, which is chernikovite H 2 (UO 2 ) 2 (PO 4 ) 2 ·8H 2 O (PDF #08-0296), on cell surface under the initial acidic conditions. However, under the initial alkaline conditions, the uranyl, phosphate and ammonium ions formed a large amount of scale-like precipitation, which is uramphite (NH 4 )(UO 2 )PO 4 ·3H 2 O (PDF #42-0384), evenly over on cell surface. Copyright © 2018 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehta, Vrajesh; Maillot, Fabien; Wang, Zheming

Uranyl phosphate solids are often found with uranium ores, and their low solubility makes them promising target phases for in situ remediation of uranium-contaminated subsurface environments. The products and solubility of uranium(VI) precipitated with phosphate can be affected by the pH, dissolved inorganic carbon (DIC) concentration, and co-solute composition (e.g. Na+/Ca2+) of the groundwater. Batch experiments were performed to study the effect of these parameters on the products and extent of uranium precipitation induced by phosphate addition. In the absence of co-solute cations, chernikovite [H3O(UO2)(PO4)•3H2O] precipitated despite uranyl orthophosphate [(UO2)3(PO4)2•4H2O] being thermodynamically more favorable under certain conditions. As determined usingmore » X-ray diffraction, electron microscopy, and laser induced fluorescence spectroscopy, the presence of Na+ or Ca2+ as a co-solute led to the precipitation of sodium autunite ([Na2(UO2)2(PO4)2] and autunite [Ca(UO2)2(PO4)2]), which are structurally similar to chernikovite. In the presence of sodium, the dissolved U(VI) concentrations were generally in agreement with equilibrium predictions of sodium autunite solubility. However, in the calcium-containing systems, the observed concentrations were below the predicted solubility of autunite, suggesting the possibility of uranium adsorption to or incorporation in a calcium phosphate precipitate in addition to the precipitation of autunite.« less

Uranium Isotope Ratios in Modern and Precambrian Soils

NASA Astrophysics Data System (ADS)

DeCorte, B.; Planavsky, N.; Wang, X.; Auerbach, D. J.; Knudsen, A. C.

2015-12-01

Uranium isotopes (δ238U values) are an emerging paleoredox proxy that can help to better understand the redox evolution of Earth's surface environment. Recently, uranium isotopes have been used to reconstruct ocean and atmospheric redox conditions (Montoya-Pino et al., 2010; Brennecka et al., 2011; Kendall et al., 2013; Dahl et al., 2014). However, to date, there have not been studies on paleosols, despite that paleosols are, arguably better suited to directly tracking the redox conditions of the atmosphere. Sedimentary δ238U variability requires the formation of the soluble, oxidized form of U, U(VI). The formation of U(VI) is generally thought to require oxygen levels orders of magnitude higher than prebiotic levels. Without significant U mobility, it would have been impossible to develop isotopically distinct pools of uranium in ancient Earth environments. Conversely, an active U redox cycle leads to significant variability in δ238U values. Here we present a temporally and geographically expansive uranium isotope record from paleosols and modern soils to better constrain atmospheric oxygen levels during the Precambrian. Preliminary U isotope measurements of paleosols are unfractionated (relative to igneous rocks), possibly because of limited fractionation during oxidation (e.g., {Wang, 2015 #478}) or insufficient atmospheric oxygen levels to oxidize U(IV)-bearing minerals in the bedrock. Further U isotope measurements of paleosols with comparison to modern soils will resolve this issue.

Formation of stable uranium(VI) colloidal nanoparticles in conditions relevant to radioactive waste disposal.

PubMed

Bots, Pieter; Morris, Katherine; Hibberd, Rosemary; Law, Gareth T W; Mosselmans, J Frederick W; Brown, Andy P; Doutch, James; Smith, Andrew J; Shaw, Samuel

2014-12-09

The favored pathway for disposal of higher activity radioactive wastes is via deep geological disposal. Many geological disposal facility designs include cement in their engineering design. Over the long term, interaction of groundwater with the cement and waste will form a plume of a hyperalkaline leachate (pH 10-13), and the behavior of radionuclides needs to be constrained under these extreme conditions to minimize the environmental hazard from the wastes. For uranium, a key component of many radioactive wastes, thermodynamic modeling predicts that, at high pH, U(VI) solubility will be very low (nM or lower) and controlled by equilibrium with solid phase alkali and alkaline-earth uranates. However, the formation of U(VI) colloids could potentially enhance the mobility of U(VI) under these conditions, and characterizing the potential for formation and medium-term stability of U(VI) colloids is important in underpinning our understanding of U behavior in waste disposal. Reflecting this, we applied conventional geochemical and microscopy techniques combined with synchrotron based in situ and ex situ X-ray techniques (small-angle X-ray scattering and X-ray adsorption spectroscopy (XAS)) to characterize colloidal U(VI) nanoparticles in a synthetic cement leachate (pH > 13) containing 4.2-252 μM U(VI). The results show that in cement leachates with 42 μM U(VI), colloids formed within hours and remained stable for several years. The colloids consisted of 1.5-1.8 nm nanoparticles with a proportion forming 20-60 nm aggregates. Using XAS and electron microscopy, we were able to determine that the colloidal nanoparticles had a clarkeite (sodium-uranate)-type crystallographic structure. The presented results have clear and hitherto unrecognized implications for the mobility of U(VI) in cementitious environments, in particular those associated with the geological disposal of nuclear waste.

Uncertainty analysis of multi-rate kinetics of uranium desorption from sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaoying; Liu, Chongxuan; Hu, Bill X.

2014-01-01

A multi-rate expression for uranyl [U(VI)] surface complexation reactions has been proposed to describe diffusion-limited U(VI) sorption/desorption in heterogeneous subsurface sediments. An important assumption in the rate expression is that its rate constants follow a certain type probability distribution. In this paper, a Bayes-based, Differential Evolution Markov Chain method was used to assess the distribution assumption and to analyze parameter and model structure uncertainties. U(VI) desorption from a contaminated sediment at the US Hanford 300 Area, Washington was used as an example for detail analysis. The results indicated that: 1) the rate constants in the multi-rate expression contain uneven uncertaintiesmore » with slower rate constants having relative larger uncertainties; 2) the lognormal distribution is an effective assumption for the rate constants in the multi-rate model to simualte U(VI) desorption; 3) however, long-term prediction and its uncertainty may be significantly biased by the lognormal assumption for the smaller rate constants; and 4) both parameter and model structure uncertainties can affect the extrapolation of the multi-rate model with a larger uncertainty from the model structure. The results provide important insights into the factors contributing to the uncertainties of the multi-rate expression commonly used to describe the diffusion or mixing-limited sorption/desorption of both organic and inorganic contaminants in subsurface sediments.« less

Functionalized Sugarcane Bagasse for U(VI) Adsorption from Acid and Alkaline Conditions.

PubMed

Su, Shouzheng; Liu, Qi; Liu, Jingyuan; Zhang, Hongsen; Li, Rumin; Jing, Xiaoyan; Wang, Jun

2018-01-15

The highly efficient removal of uranium from mine tailings effluent, radioactive wastewater and enrichment from seawater is of great significance for the development of nuclear industry. In this work, we prepared an efficient U(VI) adsorbent by EDTA modified sugarcane bagasse (MESB) with a simple process. The prepared adsorbent preserves high adsorptive capacity for UO 2 2+ (pH 3.0) and uranyl complexes, such as UO 2 (OH) + , (UO 2 ) 2 (OH) 2 2+ and (UO 2 ) 3 (OH) 5 + (pH 4.0 and pH 5.0) and good repeatability in acidic environment. The maximum adsorption capacity for U(VI) at pH 3.0, 4.0 and 5.0 is 578.0, 925.9 and 1394.1 mg/g and the adsorption capacity loss is only 7% after five cycles. With the pH from 3.0 to 5.0, the inhibitive effects of Na + and K + decreased but increased of Mg 2+ and Ca 2+ . MESB also exhibits good adsorption for [UO 2 (CO 3 ) 3 ] 4- at pH 8.3 from 10 mg/L to 3.3 μg/L. Moreover, MESB could effectively extract U(VI) from simulated seawater in the presence of other metals ions. This work provided a general and efficient uranyl enriched material for nuclear industry.

Enzymatic iron and uranium reduction by sulfate-reducing bacteria

USGS Publications Warehouse

Lovley, D.R.; Roden, E.E.; Phillips, E.J.P.; Woodward, J.C.

1993-01-01

The potential for sulfate-reducing bacteria (SRB) to enzymatically reduce Fe(III) and U(VI) was investigated. Five species of Desulfovibrio as well as Desulfobacterium autotrophicum and Desulfobulbus propionicus reduced Fe(III) chelated with nitrilotriacetic acid as well as insoluble Fe(III) oxide. Fe(III) oxide reduction resulted in the accumulation of magnetite and siderite. Desulfobacter postgatei reduced the chelated Fe(III) but not Fe(III) oxide. Desulfobacter curvatus, Desulfomonile tiedjei, and Desulfotomaculum acetoxidans did not reduce Fe(III). Only Desulfovibrio species reduced U(VI). U(VI) reduction resulted in the precipitation of uraninite. None of the SRB that reduced Fe(III) or U(VI) appeared to conserve enough energy to support growth from this reaction. However, Desulfovibrio desulfuricans metabolized H2 down to lower concentrations with Fe(III) or U(VI) as the electron acceptor than with sulfate, suggesting that these metals may be preferred electron acceptors at the low H2 concentrations present in most marine sediments. Molybdate did not inhibit Fe(III) reduction by D. desulfuricans. This indicates that the inability of molybdate to inhibit Fe(III) reduction in marine sediments does not rule out the possibility that SRB are important catalysts for Fe(III) reduction. The results demonstrate that although SRB were previously considered to reduce Fe(III) and U(VI) indirectly through the production of sulfide, they may also directly reduce Fe(III) and U(VI) through enzymatic mechanisms. These findings, as well as our recent discovery that the So-reducing microorganism Desulfuromonas acetoxidans can reduce Fe(III), demonstrate that there are close links between the microbial sulfur, iron, and uranium cycles in anaerobic marine sediments. ?? 1993.

Adsorption of Fe(II) and U(VI) to carboxyl-functionalized microspheres: The influence of speciation on uranyl reduction studied by titration and XAFS

NASA Astrophysics Data System (ADS)

Boyanov, Maxim I.; O'Loughlin, Edward J.; Roden, Eric E.; Fein, Jeremy B.; Kemner, Kenneth M.

2007-04-01

The chemical reduction of U(VI) by Fe(II) is a potentially important pathway for immobilization of uranium in subsurface environments. Although the presence of surfaces has been shown to catalyze the reaction between Fe(II) and U(VI) aqueous species, the mechanism(s) responsible for the enhanced reactivity remain ambiguous. To gain further insight into the U-Fe redox process at a complexing, non-conducting surface that is relevant to common organic phases in the environment, we studied suspensions containing combinations of 0.1 mM U(VI), 1.0 mM Fe(II), and 4.2 g/L carboxyl-functionalized polystyrene microspheres. Acid-base titrations were used to monitor protolytic reactions, and Fe K-edge and U L-edge X-ray absorption fine structure spectroscopy was used to determine the valence and atomic environment of the adsorbed Fe and U species. In the Fe + surface carboxyl system, a transition from monomeric to oligomeric Fe(II) surface species was observed between pH 7.5 and pH 8.4. In the U + surface carboxyl system, the U(VI) cation was adsorbed as a mononuclear uranyl-carboxyl complex at both pH 7.5 and 8.4. In the ternary U + Fe + surface carboxyl system, U(VI) was not reduced by the solvated or adsorbed Fe(II) at pH 7.5 over a 4-month period, whereas complete and rapid reduction to U(IV) nanoparticles occurred at pH 8.4. The U(IV) product reoxidized rapidly upon exposure to air, but it was stable over a 4-month period under anoxic conditions. Fe atoms were found in the local environment of the reduced U(IV) atoms at a distance of 3.56 Å. The U(IV)-Fe coordination is consistent with an inner-sphere electron transfer mechanism between the redox centers and involvement of Fe(II) atoms in both steps of the reduction from U(VI) to U(IV). The inability of Fe(II) to reduce U(VI) in solution and at pH 7.5 in the U + Fe + carboxyl system is explained by the formation of a transient, "dead-end" U(V)-Fe(III) complex that blocks the U(V) disproportionation pathway after the first electron transfer. The increased reactivity at pH 8.4 relative to pH 7.5 is explained by the reaction of U(VI) with an Fe(II) oligomer, whereby the bonds between Fe atoms facilitate the transfer of a second electron to the hypothetical U(V)-Fe(III) intermediate. We discuss how this mechanism may explain the commonly observed higher efficiency of uranyl reduction by adsorbed or structural Fe(II) relative to aqueous Fe(II).

Fate of Uranium During Transport Across the Groundwater-Surface Water Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaffe, Peter R.; Kaplan, Daniel I.

Discharge of contaminated groundwater to surface waters is of concern at many DOE facilities. For example, at F-Area and TNX-Area on the Savannah River Site, contaminated groundwater, including uranium, is already discharging into natural wetlands. It is at this interface where contaminants come into contact with the biosphere. These this research addressed a critical knowledge gap focusing on the geochemistry of uranium (or for that matter, any redox-active contaminant) in wetland systems. Understanding the interactions between hydrological, microbial, and chemical processes will make it possible to provide a more accurate conceptual and quantitative understanding of radionuclide fate and transport undermore » these unique conditions. Understanding these processes will permit better long-term management and the necessary technical justification for invoking Monitored Natural Attenuation of contaminated wetland areas. Specifically, this research did provide new insights on how plant-induced alterations to the sediment biogeochemical processes affect the key uranium reducing microorganisms, the uranium reduction, its spatial distribution, the speciation of the immobilized uranium, and its long-term stability. This was achieved by conducting laboratory mesocosm wetland experiments as well as field measurements at the SRNL. Results have shown that uranium can be immobilized in wetland systems. To a degree some of the soluble U(VI) was reduced to insoluble U(IV), but the majority of the immobilized U was incorporated into iron oxyhydroxides that precipitated onto the root surfaces of wetland plants. This U was immobilized mostly as U(VI). Because it was immobilized in its oxidized form, results showed that dry spells, resulting in the lowering of the water table and the exposure of the U to oxic conditions, did not result in U remobilization.« less

Quantifying Differences in the Impact of Variable Chemistry on Equilibrium Uranium(VI) Adsorption Properties of Aquifer Sediments

PubMed Central

2011-01-01

Uranium adsorption–desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500–1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO22+ + 2CO32- = >SOUO2(CO3HCO3)2–, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logKc) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logKc values. Using this approach, logKc values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (<0.063 mm) of another could be demonstrated despite the fines requiring a different reaction stoichiometry. Estimates of logKc uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors. PMID:21923109

Quantifying differences in the impact of variable chemistry on equilibrium Uranium(VI) adsorption properties of aquifer sediments.

PubMed

Stoliker, Deborah L; Kent, Douglas B; Zachara, John M

2011-10-15

Uranium adsorption-desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500-1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO₂²⁺ + 2CO₃²⁻ = >SOUO₂(CO₃HCO₃)²⁻, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logK(c)) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logK(c) values. Using this approach, logK(c) values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (< 0.063 mm) of another could be demonstrated despite the fines requiring a different reaction stoichiometry. Estimates of logK(c) uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors.

Quantitative Analysis of Uranium Accumulation on Sediments during Field-scale Biostimulation under Variable Bicarbonate Concentrations at the Rifle IFRC Site

NASA Astrophysics Data System (ADS)

Fox, P. M.; Davis, J. A.; Bargar, J.; Williams, K. H.; Singer, D. M.; Long, P.

2011-12-01

Bioremediation of uranium in subsurface environments is an approach that has been used at numerous field sites throughout the U.S in an attempt to lower dissolved U(VI) concentrations in groundwater. At the Rifle IFRC research site in Colorado, biostimulation of the native microbial population through acetate amendment for various periods of time has been tested in order to immobilize uranium through reduction U(VI) to U(IV). While this approach has successfully decreased U(VI) concentrations in the dissolved phase, often to levels below the EPA's maximum contaminant level of 0.13 μM, little work has examined the solid-phase accumulation of U during field-scale biostimulation. The lack of information on solid-phase U accumulation is due in large part to the difficulty of obtaining comparable pre- and post-biostimulation field sediment samples. In addition, the relatively low (<10 ppm) U concentrations present in most sediments preclude the use of spectroscopic techniques such as XAS for examining solid-phase U speciation. However, a recently developed technique of performing column experiments in situ has allowed us to overcome both of these problems, obtaining sediment samples which were exposed to the same biogeochemical conditions as subsurface sediments during the course of biostimulation. During the 2010 Rifle IFRC field experiment (dubbed "Super 8"), a number of in situ columns were deployed in various wells representing regions of the aquifer affected by acetate amendment (ambient bicarbonate) and concomitant acetate and bicarbonate amendment (elevated bicarbonate). Elevated levels of bicarbonate have been shown to cause desorption of U(VI) from the solid phase at the Rifle site under non-stimulated conditions, resulting in higher dissolved U(VI) concentrations in the aquifer. The Super 8 field experiment was designed in part to test the effect of elevated bicarbonate concentrations on U sequestration during biostimulation. Results from this experiment provide a comparison of temporal aqueous and solid-phase U concentrations under ambient and elevated bicarbonate conditions during field-scale biostimulation. Additionally, a subset of in situ columns amended with 20 μM U(VI) were analyzed by XANES in order to determine the relative importance of U(VI) and U(IV) in the solid phase. While the elevated bicarbonate concentrations did not impede reduction and sequestration of U, differences in the behavior of dissolved U(VI) after acetate amendment was stopped demonstrate the importance of U adsorption-desorption reactions in controlling dissolved U concentrations post-biostimulation.

Uranium XAFS analysis of kidney from rats exposed to uranium

PubMed Central

Kitahara, Keisuke; Numako, Chiya; Terada, Yasuko; Nitta, Kiyohumi; Homma-Takeda, Shino

2017-01-01

The kidney is the critical target of uranium exposure because uranium accumulates in the proximal tubules and causes tubular damage, but the chemical nature of uranium in kidney, such as its chemical status in the toxic target site, is poorly understood. Micro-X-ray absorption fine-structure (µXAFS) analysis was used to examine renal thin sections of rats exposed to uranyl acetate. The U L III-edge X-ray absorption near-edge structure spectra of bulk renal specimens obtained at various toxicological phases were similar to that of uranyl acetate: their edge position did not shift compared with that of uranyl acetate (17.175 keV) although the peak widths for some kidney specimens were slightly narrowed. µXAFS measurements of spots of concentrated uranium in the micro-regions of the proximal tubules showed that the edge jump slightly shifted to lower energy. The results suggest that most uranium accumulated in kidney was uranium (VI) but a portion might have been biotransformed in rats exposed to uranyl acetate. PMID:28244440

Uranium XAFS analysis of kidney from rats exposed to uranium.

PubMed

Kitahara, Keisuke; Numako, Chiya; Terada, Yasuko; Nitta, Kiyohumi; Shimada, Yoshiya; Homma-Takeda, Shino

2017-03-01

The kidney is the critical target of uranium exposure because uranium accumulates in the proximal tubules and causes tubular damage, but the chemical nature of uranium in kidney, such as its chemical status in the toxic target site, is poorly understood. Micro-X-ray absorption fine-structure (µXAFS) analysis was used to examine renal thin sections of rats exposed to uranyl acetate. The U L III -edge X-ray absorption near-edge structure spectra of bulk renal specimens obtained at various toxicological phases were similar to that of uranyl acetate: their edge position did not shift compared with that of uranyl acetate (17.175 keV) although the peak widths for some kidney specimens were slightly narrowed. µXAFS measurements of spots of concentrated uranium in the micro-regions of the proximal tubules showed that the edge jump slightly shifted to lower energy. The results suggest that most uranium accumulated in kidney was uranium (VI) but a portion might have been biotransformed in rats exposed to uranyl acetate.

Volumetric determination of uranium titanous sulfate as reductant before oxidimetric titration

USGS Publications Warehouse

Wahlberg, J.S.; Skinner, D.L.; Rader, L.F.

1957-01-01

Need for a more rapid volumetric method for the routine determination of uranium in uranium-rich materials has led to the development of a method that uses titanous sulfate as a reductant before oxidimetric titration. Separation of the hydrogen sulfide group is not necessary. Interfering elements precipitated by cupferron are removed by automatic filtrations made simultaneously rather than by the longer chloroform extraction method. Uranium is reduced from VI to IV by addition of an excess of titanous sulfate solution, cupric ion serving as an indicator by forming red metallic copper when reduction is complete. The copper is reoxidized by addition of mercuric perchlorate. The reduced uranium is then determined by addition of excess ferric sulfate and titration with ceric sulfate. The method has proved to be rapid, accurate, and economical.

Bioprospecting of gum kondagogu (Cochlospermum gossypium) for bioremediation of uranium (VI) from aqueous solution and synthetic nuclear power reactor effluents.

PubMed

Sashidhar, R B; Selvi, S Kalaignana; Vinod, V T P; Kosuri, Tanuja; Raju, D; Karuna, R

2015-10-01

An ecofriendly green chemistry method using a natural biopolymer, Gum Kondagogu (GK) for the removal of U (VI) from aqueous, simulated nuclear effluents was studied. The adsorption characteristic of GK towards U (VI) from aqueous solution was studied at varied pH, contact time, adsorbent dose, initial U (VI) concentration and temperature using UV-Visible spectroscopy and ICP-MS. Maximum adsorption was seen at pH 4, 0.1% GK with 60 min contact time at room temperature. The GK- U (VI) composite was characterized by FT-IR, zeta potential, TEM and SEM-EDAX. The Langmuir isotherm was found to be 487 mg of U (VI) g(-1) of GK. The adsorption capacity and (%) of U (VI) was found to be 490 ± 5.4 mg g(-1) and 98.5%. Moreover adsorption of U (VI) by GK was not influenced by other cations present in the simulated effluents. The adsorbed U (VI) was efficiently stripped from composite using 1 M HCl. Copyright © 2015 Elsevier Ltd. All rights reserved.

Redox properties of biscyclopentadienyl uranium(V) imido-halide complexes: a relativistic DFT study.

PubMed

Elkechai, Aziz; Kias, Farida; Talbi, Fazia; Boucekkine, Abdou

2014-06-01

Calculations of ionization energies (IE) and electron affinities (EA) of a series of biscyclopentadienyl imido-halide uranium(V) complexes Cp*2U(=N-2,6-(i)Pr2-C6H3)(X) with X =  F, Cl, Br, and I, related to the U(IV)/U(V) and U(V)/U(VI) redox systems, were carried out, for the first time, using density functional theory (DFT) in the framework of the relativistic zeroth order regular approximation (ZORA) coupled with the conductor-like screening model (COSMO) solvation approach. A very good linear correlation (R(2) =  0.993) was obtained, between calculated ionization energies at the ZORA/BP86/TZP level, and the experimental half-wave oxidation potentials E1/2. A similar linear correlation between the computed electron affinities and the electrochemical reduction U(IV)/U(III) potentials (R(2) =  0.996) is obtained. The importance of solvent effects and of spin-orbit coupling is definitively confirmed. The molecular orbital analysis underlines the crucial role played by the 5f orbitals of the central metal whereas the Nalewajski-Mrozek (N-M) bond indices explain well the bond distances variations following the redox processes. The IE variation of the complexes, i.e., IE(F) < IE(Cl) < IE(Br) < IE(I) is also well rationalized considering the frontier MO diagrams of these species. Finally, this work confirms the relevance of the Hirshfeld charges analysis which bring to light an excellent linear correlation (R(2) =  0.999) between the variations of the uranium charges and E1/2 in the reduction process of the U(V) species.

Uranium in granitic magmas: Part 1. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H 2O-Na 2CO 3 system at 720-770°C, 2 kbar

NASA Astrophysics Data System (ADS)

Peiffert, Chantal; Cuney, Michel; Nguyen-Trung, Chinh

1994-06-01

The solubility of uranium was investigated in both carbonated aqueous fluid and granitic melt in equilibrium in the system haplogranite-uranium oxide-H 2O-Na 2CO 3 (0.5-1 molal) at 720-770°C, 2 kbar, andƒo 2 fixed by Ni-NiO, Fe 3O 4-Fe 2O 3, and Cu 2O-CuO buffers. As complete solid solution exists between UO 2.00 and UO 2.25 (i.e., 75 mol% UO 2 + 25 mol% UO 3), three distinct uranium oxides: UO (2.01 ± 0.01), UO (2.1.0 ± 0.02), and UO (2.25 ± 0.02) were, respectively, obtained at equilibrium, under the three ƒo 2 conditions cited above. Thus, the percentage of U (VI) in uranium oxide increased with increasing log ƒo 2. The thermal decomposition of Na 2CO 3 to CO 2 and Na 2O led to the decrease of the sodium carbonate concentration from 0.5-1 molal to ~10 -2 molal in all aqueous fluids and to the dissolution of Na in the silicate melts. Crystal-free silicate glasses with four agpaitic coefficients, α = ( (Na+K)/Al) = 1.1, 1.3, 1.5, and 1.7 were obtained. The uranium solubility in 10 -2 m aqueous carbonated fluid ((8.1 ± 0.1) ≤ quench pH ≤ (8.9 ± 0.1)) was in the range 1-17 ppm and increased linearly with increasing ƒo 2 according to the expression: log (U) (ppm) = 0.09 ·log ƒo 2 (bar) + 1.47 . This equation is valid for the temperature range 720-770°C and 2 kbar. U(IV) carbonate possibly were major species in aqueous solutions under reducing conditions (Ni-NiO buffer) whereas U(VI) carbonate complexes dominated under higher oxidation conditions (Fe 3O 4-Fe 2O 3, Cu 2O-CuO buffers). The uranium content in silicate glasses varied in a large range (10 2-2 × 10 5 ppm) and log (U) (ppm) increases linearly with both ƒo 2, and α in the range 1.1-1.5 according to the equation log (U) (ppm) = 0.04 log ƒo 2 (bar) + 3.80α -1.34 . This equation is valid for (1)ƒ o 2 ranging from Ni-NiO to Cu 2O-CuO, and (2) the temperature range 720-770°C at 2 kbar. The effect of ƒo 2 on the uranium solubility in silicate melt slightly decreased with increasing α from 1.1 to 1.5. For α in the range 1.5-1.7, the effect of both ƒo 2 and agpaicity index on the uranium solubility was considerably reduced. The temperature variation in the range 720-770°C had no significant effect on the uranium solubility in either aqueous fluid or silicate melt. The partition coefficient (D fluid/melt) of uranium was in the range 10 -4.0-10 -1.5 and depended on both ƒo 2 and α according to the equation log D fluid/melt = 0.05 log ƒo 2 (bar) - 3.78α + 2.84 . The validity conditions of this equation are similar to those of the preceding one. Results obtained in the present study could be used to predict the geochemical behaviour of uranium during magma fractionation and to further understanding of the formation of uranium ore deposits related to partial melting or fractional crystallization of felsic magmas. The genesis of the Kvanefjeld (Ilimaussaq, Greenland) uranium deposit is discussed.

Geology, geochemistry, and geophysics of the Fry Canyon uranium/copper project site, southeastern Utah - Indications of contaminant migration

USGS Publications Warehouse

Otton, James K.; Zielinski, Robert A.; Horton, Robert J.

2010-01-01

The Fry Canyon uranium/copper project site in San Juan County, southeastern Utah, was affected by the historical (1957-68) processing of uranium and copper-uranium ores. Relict uranium tailings and related ponds, and a large copper heap-leach pile at the site represent point sources of uranium and copper to local soils, surface water, and groundwater. This study was designed to establish the nature, extent, and pathways of contaminant dispersion. The methods used in this study are applicable at other sites of uranium mining, milling, or processing. The uranium tailings and associated ponds sit on a bench that is as much as 4.25 meters above the level of the adjacent modern channel of Fry Creek. The copper heap leach pile sits on bedrock just south of this bench. Contaminated groundwater from the ponds and other nearby sites moves downvalley and enters the modern alluvium of adjacent Fry Creek, its surface water, and also a broader, deeper paleochannel that underlies the modern creek channel and adjacent benches and stream terraces. The northern extent of contaminated groundwater is uncertain from geochemical data beyond an area of monitoring wells about 300 meters north of the site. Contaminated surface water extends to the State highway bridge. Some uranium-contaminated groundwater may also enter underlying bedrock of the Permian Cedar Mesa Sandstone along fracture zones. Four dc-resistivity surveys perpendicular to the valley trend were run across the channel and its adjacent stream terraces north of the heap-leach pile and ponds. Two surveys were done in a small field of monitoring wells and two in areas untested by borings to the north of the well field. Bedrock intercepts, salt distribution, and lithologic information from the wells and surface observations in the well field aided interpretation of the geophysical profiles there and allowed interpretation of the two profiles not tested by wells. The geophysical data for the two profiles to the north of the well field suggest that the paleochannel persists at least 900 m to the north of the heap leach and pond sites. Contamination of groundwater beneath the stream terraces may extend at least that far. Fry Creek surface water (six samples), seeps and springs (six samples), and wells (eight samples) were collected during a dry period of April 16-19, 2007. The most uranium-rich (18.7 milligrams per liter) well water on the site displays distinctive Ca-Mg-SO4-dominant chemistry indicating the legacy of heap leaching copper-uranium ores with sulfuric acid. This same water has strongly negative d34S of sulfate (-13.3 per mil) compared to most local waters of -2.4 to -5.4 per mil. Dissolved uranium species in all sampled waters are dominantly U(VI)-carbonate complexes. All waters are undersaturated with respect to U(VI) minerals. The average 234U/238U activity ratio (AR) in four well waters from the site (0.939 + or ? 0.011) is different from that of seven upstream waters (1.235 + or ? 0.069). This isotopic contrast permits quantitative estimates of mixing of site-derived uranium with natural uranium in waters collected downstream. At the time of sampling, uranium in downstream surface water was mostly (about 67 percent) site-derived and subject to further concentration by evaporation. Three monitoring wells located approximately 0.4 kilometer downstream contained dominantly (78-87 percent) site-derived uranium. Distinctive particles of chalcopyrite (CuFeS) and variably weathered pyrite (FeS2) are present in tailings at the stream edge on the site and are identified in stream sediments 1.3 kilometers downstream, based on inspection of polished grain mounts of magnetic mineral separates.

Microbiological, Geochemical and Hydrologic Processes Controlling Uranium Mobility: An Integrated Field-Scale Subsurface Research Challenge Site at Rifle, Colorado, Quality Assurance Project Plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fix, N. J.

The U.S. Department of Energy (DOE) is cleaning up and/or monitoring large, dilute plumes contaminated by metals, such as uranium and chromium, whose mobility and solubility change with redox status. Field-scale experiments with acetate as the electron donor have stimulated metal-reducing bacteria to effectively remove uranium [U(VI)] from groundwater at the Uranium Mill Tailings Site in Rifle, Colorado. The Pacific Northwest National Laboratory and a multidisciplinary team of national laboratory and academic collaborators has embarked on a research proposed for the Rifle site, the object of which is to gain a comprehensive and mechanistic understanding of the microbial factors andmore » associated geochemistry controlling uranium mobility so that DOE can confidently remediate uranium plumes as well as support stewardship of uranium-contaminated sites. This Quality Assurance Project Plan provides the quality assurance requirements and processes that will be followed by the Rifle Integrated Field-Scale Subsurface Research Challenge Project.« less

U(VI) bioreduction with emulsified vegetable oil as the electron donor--model application to a field test.

PubMed

Tang, Guoping; Watson, David B; Wu, Wei-Min; Schadt, Christopher W; Parker, Jack C; Brooks, Scott C

2013-04-02

We amended a shallow fast-flowing uranium (U) contaminated aquifer with emulsified vegetable oil (EVO) and subsequently monitored the biogeochemical responses for over a year. Using a biogeochemical model developed in a companion article (Tang et al., Environ. Sci. Technol.2013, doi: 10.1021/es304641b) based on microcosm tests, we simulated geochemical and microbial dynamics in the field test during and after the 2-h EVO injection. When the lab-determined parameters were applied in the field-scale simulation, the estimated rate coefficient for EVO hydrolysis in the field was about 1 order of magnitude greater than that in the microcosms. Model results suggested that precipitation of long-chain fatty acids, produced from EVO hydrolysis, with Ca in the aquifer created a secondary long-term electron donor source. The model predicted substantial accumulation of denitrifying and sulfate-reducing bacteria, and U(IV) precipitates. The accumulation was greatest near the injection wells and along the lateral boundaries of the treatment zone where electron donors mixed with electron acceptors in the groundwater. While electron acceptors such as sulfate were generally considered to compete with U(VI) for electrons, this work highlighted their role in providing electron acceptors for microorganisms to degrade complex substrates thereby enhancing U(VI) reduction and immobilization.

Development of Modeling Methods and Tools for Predicting Coupled Reactive Transport Processes in Porous Media at Multiple Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clement, T. Prabhakar; Barnett, Mark O.; Zheng, Chunmiao

DE-FG02-06ER64213: Development of Modeling Methods and Tools for Predicting Coupled Reactive Transport Processes in Porous Media at Multiple Scales Investigators: T. Prabhakar Clement (PD/PI) and Mark O. Barnett (Auburn), Chunmiao Zheng (Univ. of Alabama), and Norman L. Jones (BYU). The objective of this project was to develop scalable modeling approaches for predicting the reactive transport of metal contaminants. We studied two contaminants, a radioactive cation [U(VI)] and a metal(loid) oxyanion system [As(III/V)], and investigated their interactions with two types of subsurface materials, iron and manganese oxyhydroxides. We also developed modeling methods for describing the experimental results. Overall, the project supportedmore » 25 researchers at three universities. Produced 15 journal articles, 3 book chapters, 6 PhD dissertations and 6 MS theses. Three key journal articles are: 1) Jeppu et al., A scalable surface complexation modeling framework for predicting arsenate adsorption on goethite-coated sands, Environ. Eng. Sci., 27(2): 147-158, 2010. 2) Loganathan et al., Scaling of adsorption reactions: U(VI) experiments and modeling, Applied Geochemistry, 24 (11), 2051-2060, 2009. 3) Phillippi, et al., Theoretical solid/solution ratio effects on adsorption and transport: uranium (VI) and carbonate, Soil Sci. Soci. of America, 71:329-335, 2007« less

Extractive separation of uranium and zirconium sulfates by amines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schroetterova, D.; Nekovar, P.; Mrnka, M.

1992-04-01

This paper describes an amine extraction process for zirconium and uranium separation. The behaviour of an extraction system containing uranium (VI) sulfate, zirconium (IV) sulfate, 0.2 and 0.5 M sulfuric acid (as the original aqueous phase), tertiary amine tri-n-lauryl- amine or primary amine Primene JMT in benzene (as the original organic phase) is discussed on the basis of equilibrium data. The measured dependences show that the degree of extraction of zirconium at the sulfuric acid concentration of 0.5 M and above is only slightly affected by a presence of uranium in solution. From this surprising behaviour it follows that zirconiummore » may be employed for the displacement of uranium from the organic phase. This effect is more pronounced with the primary amine Primene JMT than with TLA. 29 refs., 4 figs., 1 tab.« less

Method of preparation of uranium nitride

DOEpatents

Kiplinger, Jaqueline Loetsch; Thomson, Robert Kenneth James

2013-07-09

Method for producing terminal uranium nitride complexes comprising providing a suitable starting material comprising uranium; oxidizing the starting material with a suitable oxidant to produce one or more uranium(IV)-azide complexes; and, sufficiently irradiating the uranium(IV)-azide complexes to produce the terminal uranium nitride complexes.

Detection and characterization of uranium-humic complexes during 1D transport studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lesher, Emily K.; Honeyman, Bruce D.; Ranville, James F.

2013-05-01

The speciation and transport of uranium (VI) through porous media is highly dependent on solution conditions, the presence of complexing ligands, and the nature of the porous media. The dependency on many variables makes prediction of U transport in bench-scale experiments and in the field difficult. In particular, the identification of colloidal U phases poses a technical challenge. Transport of U in the presence and absence of natural organic matter (Suwannee River humic acid, SRHA) through silica sand and hematite coated silica sand was tested at pH 4 and 5 using static columns, where flow is controlled by gravity andmore » residence time between advective pore volume exchanges can be strictly controlled. The column effluents were characterized by traditional techniques including ICPMS quantification of total [U] and [Fe], TOC analysis of [DOC], and pH analysis, and also by non-traditional techniques: flow field flow fractionation with online ICPMS detection (FlFFF-ICPMS) and specific UV absorbance (SUVA) characterization of effluent fractions. Key results include that the transport of U through the columns was enhanced by pre-equilibration with SRHA, and previously deposited U was remobilized by the addition of SRHA. The advanced techniques yielded important insights on the mechanisms of transport: FlFFF-ICPMS identified a U-SRHA complex as the mobile U species and directly quantified relative amounts of the complex, while specific UV absorbance (SUVA) measurements indicated a composition-based fractionation onto the porous media.« less

Solid state speciation of uranium and its local structure in Sr2CeO4 using photoluminescence spectroscopy.

PubMed

Sahu, M; Gupta, Santosh K; Jain, D; Saxena, M K; Kadam, R M

2018-04-15

An effort was taken to carry our speciation study of uranium ion in technologically important cerate host Sr 2 CeO 4 using time resolved photoluminescence spectroscopy. Such studies are not relevant only to nuclear industry but can give rich insight into fundamentals of 5f electron chemistry in solid state systems. In this work both undoped and varied amount of uranium doped Sr 2 CeO 4 compound is synthesized using complex polymerization method and is characterized systematically using X-ray diffraction (XRD), Raman spectroscopy, impedance spectroscopy and scanning electron microscopy (SEM). Both XRD and Raman spectroscopy confirmed the formation of pure Sr 2 CeO 4 which has tendency to decompose peritectically to SrCeO 3 and SrO at higher temperature. Uranium doping is confirmed by XRD. Uranium exhibits a rich chemistry owing to its variable oxidation state from +3 to +6. Each of them exhibits distinct luminescence properties either due to f-f transitions or ligand to metal charge transfer (LMCT). We have taken Sr 2 CeO 4 as a model host lattice to understand the photophysical characteristics of uranium ion in it. Emission spectroscopy revealed the stabilization of uranium as U (VI) in the form of UO 6 6- (octahedral uranate) in Sr 2 CeO 4 . Emission kinetics study reflects that uranate ions are not homogeneously distributed in Sr 2 CeO 4 and it has two different environments due to its stabilization at both Sr 2+ as well as Ce 4+ site. The lifetime population analysis interestingly pinpointed that majority of uranate ion resided at Ce 4+ site. The critical energy-transfer distance between the uranate ion was determined based on which the concentration quenching mechanism was attributed to electric multipolar interaction. These studies are very important in designing Sr 2 CeO 4 based optoelectronic material as well exploring it for actinides studies. Copyright © 2018 Elsevier B.V. All rights reserved.

Solid state speciation of uranium and its local structure in Sr2CeO4 using photoluminescence spectroscopy

NASA Astrophysics Data System (ADS)

Sahu, M.; Gupta, Santosh K.; Jain, D.; Saxena, M. K.; Kadam, R. M.

2018-04-01

An effort was taken to carry our speciation study of uranium ion in technologically important cerate host Sr2CeO4 using time resolved photoluminescence spectroscopy. Such studies are not relevant only to nuclear industry but can give rich insight into fundamentals of 5f electron chemistry in solid state systems. In this work both undoped and varied amount of uranium doped Sr2CeO4 compound is synthesized using complex polymerization method and is characterized systematically using X-ray diffraction (XRD), Raman spectroscopy, photoluminescence spectroscopy and scanning electron microscopy (SEM). Both XRD and Raman spectroscopy confirmed the formation of pure Sr2CeO4 which has tendency to decompose peritectically to SrCeO3 and SrO at higher temperature. Uranium doping is confirmed by XRD. Uranium exhibits a rich chemistry owing to its variable oxidation state from +3 to +6. Each of them exhibits distinct luminescence properties either due to f-f transitions or ligand to metal charge transfer (LMCT). We have taken Sr2CeO4 as a model host lattice to understand the photophysical characteristics of uranium ion in it. Emission spectroscopy revealed the stabilization of uranium as U (VI) in the form of UO66- (octahedral uranate) in Sr2CeO4. Emission kinetics study reflects that uranate ions are not homogeneously distributed in Sr2CeO4 and it has two different environments due to its stabilization at both Sr2+ as well as Ce4+ site. The lifetime population analysis interestingly pinpointed that majority of uranate ion resided at Ce4+ site. The critical energy-transfer distance between the uranate ion was determined based on which the concentration quenching mechanism was attributed to electric multipolar interaction. These studies are very important in designing Sr2CeO4 based optoelectronic material as well exploring it for actinides studies.

Analysis of benchmark critical experiments with ENDF/B-VI data sets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardy, J. Jr.; Kahler, A.C.

1991-12-31

Several clean critical experiments were analyzed with ENDF/B-VI data to assess the adequacy of the data for U{sup 235}, U{sup 238} and oxygen. These experiments were (1) a set of homogeneous U{sup 235}-H{sub 2}O assemblies spanning a wide range of hydrogen/uranium ratio, and (2) TRX-1, a simple, H{sub 2}O-moderated Bettis lattice of slightly-enriched uranium metal rods. The analyses used the Monte Carlo program RCP01, with explicit three-dimensional geometry and detailed representation of cross sections. For the homogeneous criticals, calculated k{sub crit} values for large, thermal assemblies show good agreement with experiment. This supports the evaluated thermal criticality parameters for U{supmore » 235}. However, for assemblies with smaller H/U ratios, k{sub crit} values increase significantly with increasing leakage and flux-spectrum hardness. These trends suggest that leakage is underpredicted and that the resonance eta of the ENDF/B-VI U{sup 235} is too large. For TRX-1, reasonably good agreement is found with measured lattice parameters (reaction-rate ratios). Of primary interest is rho28, the ratio of above-thermal to thermal U{sup 238} capture. Calculated rho28 is 2.3 ({+-} 1.7) % above measurement, suggesting that U{sup 238} resonance capture remains slightly overpredicted with ENDF/B-VI. However, agreement is better than observed with earlier versions of ENDF/B.« less

Bacterial Community Shift and Coexisting/Coexcluding Patterns Revealed by Network Analysis in a Uranium-Contaminated Site after Bioreduction Followed by Reoxidation.

PubMed

Li, Bing; Wu, Wei-Min; Watson, David B; Cardenas, Erick; Chao, Yuanqing; Phillips, D H; Mehlhorn, Tonia; Lowe, Kenneth; Kelly, Shelly D; Li, Pengsong; Tao, Huchun; Tiedje, James M; Criddle, Craig S; Zhang, Tong

2018-05-01

A site in Oak Ridge, TN, USA, has sediments that contain >3% iron oxides and is contaminated with uranium (U). The U(VI) was bioreduced to U(IV) and immobilized in situ through intermittent injections of ethanol. It then was allowed to reoxidize via the invasion of low-pH (3.6 to 4.0), high-nitrate (up to 200 mM) groundwater back into the reduced zone for 1,383 days. To examine the biogeochemical response, high-throughput sequencing and network analysis were applied to characterize bacterial population shifts, as well as cooccurrence and coexclusion patterns among microbial communities. A paired t test indicated no significant changes of α-diversity for the bioactive wells. However, both nonmetric multidimensional scaling and analysis of similarity confirmed a significant distinction in the overall composition of the bacterial communities between the bioreduced and the reoxidized sediments. The top 20 major genera accounted for >70% of the cumulative contribution to the dissimilarity in the bacterial communities before and after the groundwater invasion. Castellaniella had the largest dissimilarity contribution (17.7%). For the bioactive wells, the abundance of the U(VI)-reducing genera Geothrix , Desulfovibrio , Ferribacterium , and Geobacter decreased significantly, whereas the denitrifying Acidovorax abundance increased significantly after groundwater invasion. Additionally, seven genera, i.e., Castellaniella , Ignavibacterium , Simplicispira , Rhizomicrobium , Acidobacteria Gp1, Acidobacteria Gp14, and Acidobacteria Gp23, were significant indicators of bioactive wells in the reoxidation stage. Canonical correspondence analysis indicated that nitrate, manganese, and pH affected mostly the U(VI)-reducing genera and indicator genera. Cooccurrence patterns among microbial taxa suggested the presence of taxa sharing similar ecological niches or mutualism/commensalism/synergism interactions. IMPORTANCE High-throughput sequencing technology in combination with a network analysis approach were used to investigate the stabilization of uranium and the corresponding dynamics of bacterial communities under field conditions with regard to the heterogeneity and complexity of the subsurface over the long term. The study also examined diversity and microbial community composition shift, the common genera, and indicator genera before and after long-term contaminated-groundwater invasion and the relationship between the target functional community structure and environmental factors. Additionally, deciphering cooccurrence and coexclusion patterns among microbial taxa and environmental parameters could help predict potential biotic interactions (cooperation/competition), shared physiologies, or habitat affinities, thus, improving our understanding of ecological niches occupied by certain specific species. These findings offer new insights into compositions of and associations among bacterial communities and serve as a foundation for future bioreduction implementation and monitoring efforts applied to uranium-contaminated sites. Copyright © 2018 American Society for Microbiology.

Microbacterium lemovicicum sp. nov., a bacterium isolated from a natural uranium-rich soil.

PubMed

Mondani, Laure; Piette, Laurie; Christen, Richard; Bachar, Dipankar; Berthomieu, Catherine; Chapon, Virginie

2013-07-01

An actinobacterial strain, designated ViU22(T), was isolated from a natural uranium-rich soil and was studied using a polyphasic approach. Cells formed orange-pigmented colonies, were rod-shaped, Gram-positive (non-staining method), non-motile and non-spore-forming. This organism grew in 0-4.5 % (w/v) NaCl and at 15-37 °C, with optimal growth occurring in 0.5 % (w/v) NaCl and at 30 °C. Comparative 16S rRNA gene sequence analysis revealed that the strain ViU22(T) belonged to the genus Microbacterium. It exhibited highest 16S rRNA gene sequence similarity with the type strains of Microbacterium testaceum (98.14 %) and Microbacterium binotii (98.02 %). The DNA-DNA relatedness of strains ViU22(T) with the most closely related type strains Microbacterium testaceum and Microbacterium binotii DSM 19164(T) was 20.10 % (± 0.70) and 28.05 % (± 0.35), respectively. Strain ViU22(T) possessed a type B2β peptidoglycan with partial substitution of glutamic acid by 3-hydroxy glutamic acid. The major menaquinones were MK-11 and MK-12. Major polar lipids detected in the strain ViU22(T) were diphosphatidylglycerol, phosphatidylglycerol, an unknown phospholipid and unknown glycolipids. The predominant fatty acids were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0, a pattern reported for other Microbacterium species. The major cell-wall sugars were galactose, xylose and mannose and the DNA G+C content was 71 mol%. Together, the DNA-DNA hybridization results and the differentiating phenotypic characteristics, showed that strain ViU22(T) should be classified as the type strain of a novel species within the genus Microbacterium, for which the name Microbacterium lemovicicum sp. nov. is proposed. The type strain is ViU22(T) ( = ATCC BAA-2396(T) = CCUG 62198(T) = DSM 25044(T)).

Unusual Versatility of the Filamentous, Diazotrophic Cyanobacterium Anabaena torulosa Revealed for Its Survival during Prolonged Uranium Exposure

PubMed Central

Chandwadkar, Pallavi; Nayak, Chandrani

2017-01-01

ABSTRACT Reports on interactions between cyanobacteria and uranyl carbonate are rare. Here, we present an interesting succession of the metabolic responses employed by a marine, filamentous, diazotrophic cyanobacterium, Anabaena torulosa for its survival following prolonged exposure to uranyl carbonate extending up to 384 h at pH 7.8 under phosphate-limited conditions. The cells sequestered uranium (U) within polyphosphates on initial exposure to 100 μM uranyl carbonate for 24 to 28 h. Further incubation until 120 h resulted in (i) significant degradation of cellular polyphosphates causing extensive chlorosis and cell lysis, (ii) akinete differentiation followed by (iii) extracellular uranyl precipitation. X-ray diffraction (XRD) analysis, fluorescence spectroscopy, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy established the identity of the bioprecipitated uranium as a U(VI) autunite-type mineral, which settled at the bottom of the vessel. Surprisingly, A. torulosa cells resurfaced as small green flakes typical of actively growing colonies on top of the test solutions within 192 to 240 h of U exposure. A consolidated investigation using kinetics, microscopy, and physiological and biochemical analyses suggested a role of inducible alkaline phosphatase activity of cell aggregates/akinetes in facilitating the germination of akinetes leading to substantial regeneration of A. torulosa by 384 h of uranyl incubation. The biomineralized uranium appeared to be stable following cell regeneration. Altogether, our results reveal novel insights into the survival mechanism adopted by A. torulosa to resist sustained uranium toxicity under phosphate-limited oxic conditions. IMPORTANCE Long-term effects of uranyl exposure in cyanobacteria under oxic phosphate-limited conditions have been inadequately explored. We conducted a comprehensive examination of the metabolic responses displayed by a marine cyanobacterium, Anabaena torulosa, to cope with prolonged exposure to uranyl carbonate at pH 7.8 under phosphate limitation. Our results highlight distinct adaptive mechanisms harbored by this cyanobacterium that enabled its natural regeneration following extensive cell lysis and uranium biomineralization under sustained uranium exposure. Such complex interactions between environmental microbes such as Anabaena torulosa and uranium over a broader time range advance our understanding on the impact of microbial processes on uranium biogeochemistry. PMID:28258135

Linking Specific Heterotrophic Bacterial Populations to Bioreduction of Uranium and Nitrate in Contaminated Subsurface Sediments by Using Stable Isotope Probing▿†

PubMed Central

Akob, Denise M.; Kerkhof, Lee; Küsel, Kirsten; Watson, David B.; Palumbo, Anthony V.; Kostka, Joel E.

2011-01-01

Shifts in terminal electron-accepting processes during biostimulation of uranium-contaminated sediments were linked to the composition of stimulated microbial populations using DNA-based stable isotope probing. Nitrate reduction preceded U(VI) and Fe(III) reduction in [13C]ethanol-amended microcosms. The predominant, active denitrifying microbial groups were identified as members of the Betaproteobacteria, whereas Actinobacteria dominated under metal-reducing conditions. PMID:21948831

High-Quality Draft Genome Sequence of Desulfovibrio carbinoliphilus FW-101-2B, an Organic Acid-Oxidizing Sulfate-Reducing Bacterium Isolated from Uranium(VI)-Contaminated Groundwater

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramsay, Bradley D.; Hwang, Chiachi; Woo, Hannah L.

2015-03-12

Desulfovibrio carbinoliphilus subsp. oakridgensis FW-101-2B is an anaerobic, organic acid/alcohol-oxidizing, sulfate-reducing δ-proteobacterium. FW-101-2B was isolated from contaminated groundwater at The Field Research Center at Oak Ridge National Lab after in situ stimulation for heavy metal-reducing conditions. The genome will help elucidate the metabolic potential of sulfate-reducing bacteria during uranium reduction.

Bacterial population dynamics during uranium reduction andre-oxidation: Application of a novel high density oligonucleotidemicroarray approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brodie, Eoin L.; DeSantis, Todd Z.; Joyner, Dominique C.

2006-01-30

Reduction of soluble uranium U(VI) to less-soluble uraniumU(IV) is a promising approach to minimize migration from contaminatedaquifers. It is generally assumed that, under constant reducingconditions, U(IV) is stable and immobile; however, in a previous study,we documented reoxidation of U(IV) under continuous reducing conditions(Wan et al., Environ. Sci. Technol. 2005, 39:6162 6169). To determine ifchanges in microbial community composition were a factor in U(IV)reoxidation, we employed a high-density phylogenetic DNA microarray (16Smicroarray) containing 500,000 probes to monitor changes in bacterialpopulations during this remediation process. Comparison of the 16Smicroarray with clone libraries demonstrated successful detection andclassification of most clone groups. Analysis ofmore » the most dynamic groupsof 16S rRNA gene amplicons detected by the 16S microarray identified fiveclusters of bacterial subfamilies responding in a similar manner. Thisapproach demonstrated that amplicons of known metal-reducing bacteriasuch as Geothrix fermentans (confirmed by quantitative PCR) and thosewithin the Geobacteraceae were abundant during U(VI) reduction and didnot decline during the U(IV) reoxidation phase. Significantly, it appearsthat the observed reoxidation of uranium under reducing conditionsoccurred despite elevated microbial activity and the consistent presenceof metal-reducing bacteria. High-density phylogenetic microarraysconstitute a powerful tool, enabling the detection and monitoring of asubstantial portion of the microbial population in a routine, accurate,and reproducible manner.« less

Upscaling of U (VI) desorption and transport from decimeter‐scale heterogeneity to plume‐scale modeling

USGS Publications Warehouse

Curtis, Gary P.; Kohler, Matthias; Kannappan, Ramakrishnan; Briggs, Martin A.; Day-Lewis, Frederick D.

2015-01-01

Scientifically defensible predictions of field scale U(VI) transport in groundwater requires an understanding of key processes at multiple scales. These scales range from smaller than the sediment grain scale (less than 10 μm) to as large as the field scale which can extend over several kilometers. The key processes that need to be considered include both geochemical reactions in solution and at sediment surfaces as well as physical transport processes including advection, dispersion, and pore-scale diffusion. The research summarized in this report includes both experimental and modeling results in batch, column and tracer tests. The objectives of this research were to: (1) quantify the rates of U(VI) desorption from sediments acquired from a uranium contaminated aquifer in batch experiments;(2) quantify rates of U(VI) desorption in column experiments with variable chemical conditions, and(3) quantify nonreactive tracer and U(VI) transport in field tests.

c-Type Cytochrome-Dependent Formation of U(IV) Nanoparticles by Shewanella oneidensis

PubMed Central

Marshall, Matthew J; Dohnalkova, Alice C; Kennedy, David W; Shi, Liang; Wang, Zheming; Boyanov, Maxim I; Lai, Barry; Kemner, Kenneth M; McLean, Jeffrey S; Reed, Samantha B; Culley, David E; Bailey, Vanessa L; Simonson, Cody J; Saffarini, Daad A; Romine, Margaret F; Zachara, John M

2006-01-01

Modern approaches for bioremediation of radionuclide contaminated environments are based on the ability of microorganisms to effectively catalyze changes in the oxidation states of metals that in turn influence their solubility. Although microbial metal reduction has been identified as an effective means for immobilizing highly-soluble uranium(VI) complexes in situ, the biomolecular mechanisms of U(VI) reduction are not well understood. Here, we show that c-type cytochromes of a dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1, are essential for the reduction of U(VI) and formation of extracelluar UO 2 nanoparticles. In particular, the outer membrane (OM) decaheme cytochrome MtrC (metal reduction), previously implicated in Mn(IV) and Fe(III) reduction, directly transferred electrons to U(VI). Additionally, deletions of mtrC and/or omcA significantly affected the in vivo U(VI) reduction rate relative to wild-type MR-1. Similar to the wild-type, the mutants accumulated UO 2 nanoparticles extracellularly to high densities in association with an extracellular polymeric substance (EPS). In wild-type cells, this UO 2-EPS matrix exhibited glycocalyx-like properties and contained multiple elements of the OM, polysaccharide, and heme-containing proteins. Using a novel combination of methods including synchrotron-based X-ray fluorescence microscopy and high-resolution immune-electron microscopy, we demonstrate a close association of the extracellular UO 2 nanoparticles with MtrC and OmcA (outer membrane cytochrome). This is the first study to our knowledge to directly localize the OM-associated cytochromes with EPS, which contains biogenic UO 2 nanoparticles. In the environment, such association of UO 2 nanoparticles with biopolymers may exert a strong influence on subsequent behavior including susceptibility to oxidation by O 2 or transport in soils and sediments. PMID:16875436

Aqueous suspensions of carbon nanotubes: surface oxidation, colloidal stability and uranium sorption.

PubMed

Schierz, A; Zänker, H

2009-04-01

The objective of this study is to obtain information on the behaviour of carbon nanotubes (CNTs) as potential carriers of pollutants in the case of accidental CNT release to the environment and on the properties of CNTs as a potential adsorbent material in water purification. The effects of acid treatment of CNTs on (i) the surface properties, (ii) the colloidal stability and (iii) heavy metal sorption are investigated, the latter being exemplified by uranium(VI) sorption. There is a pronounced influence of surface treatment on the behaviour of the CNTs in aqueous suspension. Results showed that acid treatment increases the amount of acidic surface groups on the CNTs. Therefore, acid treatment has an increasing effect on the colloidal stability of the CNTs and on their adsorption capacity for U(VI). Another way to stabilise colloids of pristine CNTs in aqueous suspension is the addition of humic acid.

Elucidating bonding preferences in tetrakis(imido)uranate(VI) dianions

NASA Astrophysics Data System (ADS)

Anderson, Nickolas H.; Xie, Jing; Ray, Debmalya; Zeller, Matthias; Gagliardi, Laura; Bart, Suzanne C.

2017-09-01

Actinyl species, [AnO2]2+, are well-known derivatives of the f-block because of their natural occurrence and essential roles in the nuclear fuel cycle. Along with their nitrogen analogues, [An(NR)2]2+, actinyls are characterized by their two strong trans-An-element multiple bonds, a consequence of the inverse trans influence. We report that these robust bonds can be weakened significantly by increasing the number of multiple bonds to uranium, as demonstrated by a family of uranium(VI) dianions bearing four U-N multiple bonds, [M]2[U(NR)4] (M = Li, Na, K, Rb, Cs). Their geometry is dictated by cation coordination and sterics rather than by electronic factors. Multiple bond weakening by the addition of strong π donors has the potential for applications in the processing of high-valent actinyls, commonly found in environmental pollutants and spent nuclear fuels.

238U and 235U isotope fractionation upon oxidation of uranium-bearing rocks by fracture waters

NASA Astrophysics Data System (ADS)

Chernyshev, I. V.; Golubev, V. N.; Chugaev, A. V.; Mandzhieva, G. V.

2016-10-01

The variations in 238U/235U values accompanying mobilization of U by fracture waters from uranium-bearing rocks, in which U occurs as a fine impregnation of oxides and silicates, were studied by the high-precision (±0.07‰) MC-ICP-MS method. Transition of U into the aqueous phase in the oxidized state U(VI) is accompanied by its isotope fractionation with enrichment of dissolved U(VI) in the heavy isotope 238U up to 0.32‰ in relation to the composition of the solid phases. According to the sign, this effect is consistent with the tendency of the behavior of 238U and 235U upon interaction of river waters with rocks of the catchment areas [11] and with the effect observed during oxidation of uraninite by the oxygen-bearing NaHCO3 solution [12].

Nano-Scale Hydroxyapatite: Synthesis, Two-Dimensional Transport Experiments, and Application for Uranium Remediation

DOE PAGES

Kanel, S. R.; Clement, T. P.; Barnett, M. O.; ...

2011-01-01

Synthetic nano-scale hydroxyapatite (NHA) was prepared and characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The XRD data confirmed that the crystalline structure and chemical composition of NHA correspond to Ca 5 OH(PO 4 ) 3 . The SEM data confirmed the size of NHA to be less than 50 nm. A two-dimensional physical model packed with saturated porous media was used to study the transport characteristics of NHA under constant flow conditions. The data show that the transport patterns of NHA were almost identical to tracer transport patterns. This result indicates that the NHA material can movemore » with water like a tracer, and its movement was neither retarded nor influenced by any physicochemical interactions and/or density effects. We have also tested the reactivity of NHA with 1 mg/L hexavalent uranium (U(VI)) and found that complete removal of U(VI) is possible using 0.5 g/L NHA at pH 5 to 6. Our results demonstrate that NHA has the potential to be injected as a dilute slurry for in situ treatment of U(VI)-contaminated groundwater systems.« less

Comparison of heavy metals and uranium removal using adsorbent in soil

NASA Astrophysics Data System (ADS)

Choi, Jaeyoung; Yun, Hunsik

2017-04-01

This study investigates heavy metals (As, Ni, Zn, Cd, and Pb) and uranium removal onto geomaterials (limestone, black shale, and concrete) and biosorbents (Pseudomonas putida and starfish) from waste in soil. Geomaterials or biosorbents with a high capacity for heavy metals and uranium can be obtained and employed of with little cost. For investigating the neutralization capacity, the change in pH, Eh, and EC as a function of time was quantified. The adsorption of heavy metals and uranium by the samples was influenced by pH, and increased with increasing heavy metals and uranium concentrations. Dead cells adsorbed the largest quantity of all heavy metals than lother sorbents. The adsorption capacity followed the order: U(VI) > Pb > Cd > Ni. The results also suggest that bacterial membrane cells can be used successfully in the treatment of high strength metal-contaminated soil.

Mineral solubility and free energy controls on microbial reaction kinetics: Application to contaminant transport in the subsurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taillefert, Martial; Van Cappellen, Philippe

Recent developments in the theoretical treatment of geomicrobial reaction processes have resulted in the formulation of kinetic models that directly link the rates of microbial respiration and growth to the corresponding thermodynamic driving forces. The overall objective of this project was to verify and calibrate these kinetic models for the microbial reduction of uranium(VI) in geochemical conditions that mimic as much as possible field conditions. The approach combined modeling of bacterial processes using new bioenergetic rate laws, laboratory experiments to determine the bioavailability of uranium during uranium bioreduction, evaluation of microbial growth yield under energy-limited conditions using bioreactor experiments, competitionmore » experiments between metabolic processes in environmentally relevant conditions, and model applications at the field scale. The new kinetic descriptions of microbial U(VI) and Fe(III) reduction should replace those currently used in reactive transport models that couple catabolic energy generation and growth of microbial populations to the rates of biogeochemical redox processes. The above work was carried out in collaboration between the groups of Taillefert (batch reactor experiments and reaction modeling) at Georgia Tech and Van Cappellen (retentostat experiments and reactive transport modeling) at University of Waterloo (Canada).« less

Oxidative dissolution of biogenic uraninite in groundwater at Old Rifle, CO

USGS Publications Warehouse

Campbell, Kate M.; Veeramani, Harish; Ulrich, Kai-Uwe; Blue, Lisa Y.; Giammar, Dianiel E.; Bernier-Latmani, Rizlan; Stubbs, Joanne E.; Suvorova, Elena; Yabusaki, Steve; Lezama-Pacheco, Juan S.; Mehta, Apurva; Long, Philip E.; Bargar, John R.

2011-01-01

Reductive bioremediation is currently being explored as a possible strategy for uranium-contaminated aquifers such as the Old Rifle site (Colorado). The stability of U(IV) phases under oxidizing conditions is key to the performance of this procedure. An in situ method was developed to study oxidative dissolution of biogenic uraninite (UO2), a desirable U(VI) bioreduction product, in the Old Rifle, CO, aquifer under different variable oxygen conditions. Overall uranium loss rates were 50–100 times slower than laboratory rates. After accounting for molecular diffusion through the sample holders, a reactive transport model using laboratory dissolution rates was able to predict overall uranium loss. The presence of biomass further retarded diffusion and oxidation rates. These results confirm the importance of diffusion in controlling in-aquifer U(IV) oxidation rates. Upon retrieval, uraninite was found to be free of U(VI), indicating dissolution occurred via oxidation and removal of surface atoms. Interaction of groundwater solutes such as Ca2+ or silicate with uraninite surfaces also may retard in-aquifer U loss rates. These results indicate that the prolonged stability of U(IV) species in aquifers is strongly influenced by permeability, the presence of bacterial cells and cell exudates, and groundwater geochemistry.

Modeling Reduction of Uranium U(VI) under Variable Sulfate Concentrations by Sulfate-Reducing Bacteria

PubMed Central

Spear, John R.; Figueroa, Linda A.; Honeyman, Bruce D.

2000-01-01

The kinetics for the reduction of sulfate alone and for concurrent uranium [U(VI)] and sulfate reduction, by mixed and pure cultures of sulfate-reducing bacteria (SRB) at 21 ± 3°C were studied. The mixed culture contained the SRB Desulfovibrio vulgaris along with a Clostridium sp. determined via 16S ribosomal DNA analysis. The pure culture was Desulfovibrio desulfuricans (ATCC 7757). A zero-order model best fit the data for the reduction of sulfate from 0.1 to 10 mM. A lag time occurred below cell concentrations of 0.1 mg (dry weight) of cells/ml. For the mixed culture, average values for the maximum specific reaction rate, Vmax, ranged from 2.4 ± 0.2 μmol of sulfate/mg (dry weight) of SRB · h−1) at 0.25 mM sulfate to 5.0 ± 1.1 μmol of sulfate/mg (dry weight) of SRB · h−1 at 10 mM sulfate (average cell concentration, 0.52 mg [dry weight]/ml). For the pure culture, Vmax was 1.6 ± 0.2 μmol of sulfate/mg (dry weight) of SRB · h−1 at 1 mM sulfate (0.29 mg [dry weight] of cells/ml). When both electron acceptors were present, sulfate reduction remained zero order for both cultures, while uranium reduction was first order, with rate constants of 0.071 ± 0.003 mg (dry weight) of cells/ml · min−1 for the mixed culture and 0.137 ± 0.016 mg (dry weight) of cells/ml · min−1 (U0 = 1 mM) for the D. desulfuricans culture. Both cultures exhibited a faster rate of uranium reduction in the presence of sulfate and no lag time until the onset of U reduction in contrast to U alone. This kinetics information can be used to design an SRB-dominated biotreatment scheme for the removal of U(VI) from an aqueous source. PMID:10966381

Measurement and modelling of reactive transport in geological barriers for nuclear waste containment

DOE PAGES

Xiong, Qingrong; Joseph, Claudia; Schmeide, Katja; ...

2015-10-26

Compacted clays are considered as excellent candidates for barriers to radionuclide transport in future repositories for nuclear waste due to their very low hydraulic permeability. Diffusion is the dominant transport mechanism, controlled by a nano-scale pore system. Assessment of the clays' long-term containment function requires adequate modelling of such pore systems and their evolution. Existing characterisation techniques do not provide complete pore space information for effective modelling, such as pore and throat size distributions and connectivity. Special network models for reactive transport are proposed here using the complimentary character of the pore space and the solid phase. Here, this balancesmore » the insufficient characterisation information and provides the means for future mechanical–physical–chemical coupling. The anisotropy and heterogeneity of clays is represented using different length parameters and percentage of pores in different directions. Resulting networks are described as mathematical graphs with efficient discrete calculus formulation of transport. Opalinus Clay (OPA) is chosen as an example. Experimental data for the tritiated water (HTO) and U(VI) diffusion through OPA are presented. Calculated diffusion coefficients of HTO and uranium species are within the ranges of the experimentally determined data in different clay directions. This verifies the proposed pore network model and validates that uranium complexes are diffusing as neutral species in OPA. In the case of U(VI) diffusion the method is extended to account for sorption and convection. Finally, rather than changing pore radii by coarse grained mathematical formula, physical sorption is simulated in each pore, which is more accurate and realistic.« less

Measurement and modelling of reactive transport in geological barriers for nuclear waste containment.

PubMed

Xiong, Qingrong; Joseph, Claudia; Schmeide, Katja; Jivkov, Andrey P

2015-11-11

Compacted clays are considered as excellent candidates for barriers to radionuclide transport in future repositories for nuclear waste due to their very low hydraulic permeability. Diffusion is the dominant transport mechanism, controlled by a nano-scale pore system. Assessment of the clays' long-term containment function requires adequate modelling of such pore systems and their evolution. Existing characterisation techniques do not provide complete pore space information for effective modelling, such as pore and throat size distributions and connectivity. Special network models for reactive transport are proposed here using the complimentary character of the pore space and the solid phase. This balances the insufficient characterisation information and provides the means for future mechanical-physical-chemical coupling. The anisotropy and heterogeneity of clays is represented using different length parameters and percentage of pores in different directions. Resulting networks are described as mathematical graphs with efficient discrete calculus formulation of transport. Opalinus Clay (OPA) is chosen as an example. Experimental data for the tritiated water (HTO) and U(vi) diffusion through OPA are presented. Calculated diffusion coefficients of HTO and uranium species are within the ranges of the experimentally determined data in different clay directions. This verifies the proposed pore network model and validates that uranium complexes are diffusing as neutral species in OPA. In the case of U(vi) diffusion the method is extended to account for sorption and convection. Rather than changing pore radii by coarse grained mathematical formula, physical sorption is simulated in each pore, which is more accurate and realistic.

Removal of uranium (VI) from aqueous systems by nanoscale zero-valent iron particles suspended in carboxy-methyl cellulose

NASA Astrophysics Data System (ADS)

Popescu (Hoştuc), Ioana-Carmen; Filip, Petru; Humelnicu, Doina; Humelnicu, Ionel; Scott, Thomas Bligh; Crane, Richard Andrew

2013-11-01

Carboxy-methyl-cellulose (CMC), a common "delivery vehicle" for the subsurface deployment of iron nanoparticles (INP) has been tested in the current work for the removal of aqueous uranium from synthetic water samples. A comparison of the removal of aqueous uranium from solutions using carboxy-methyl-cellulose with and without iron nanoparticles (CMC-INP and CMC, respectively) was tested over a 48 h reaction period. Analysis of liquid samples using spectrophotometry determined a maximum sorption capacity of uranium, Qmax, of 185.18 mg/g and 322.58 mg/g for CMC and CMC-INP respectively, providing strong evidence of an independent aqueous uranium removal ability exhibited by CMC. The results point out that CMC provides an additional capacity for aqueous uranium removal. Further tests are required to determine whether similar behaviour will be observed for other aqueous contaminant species and if the presence of CMC within a INP slurry inhibits or aids the reactivity, reductive capacity and affinity of INP for aqueous contaminant removal.

Study of uranium oxidation states in geological material.

PubMed

Pidchenko, I; Salminen-Paatero, S; Rothe, J; Suksi, J

2013-10-01

A wet chemical method to determine uranium (U) oxidation states in geological material has been developed and tested. The problem faced in oxidation state determinations with wet chemical methods is that U redox state may change when extracted from the sample material, thereby leading to erroneous results. In order to quantify and monitor U redox behavior during the acidic extraction in the procedure, an analysis of added isotopic redox tracers, (236)U(VI) and (232)U(IV), and of variations in natural uranium isotope ratio ((234)U/(238)U) of indigenous U(IV) and U(VI) fractions was performed. Two sample materials with varying redox activity, U bearing rock and U-rich clayey lignite sediment, were used for the tests. The Fe(II)/Fe(III) redox-pair of the mineral phases was postulated as a potentially disturbing redox agent. The impact of Fe(III) on U was studied by reducing Fe(III) with ascorbic acid, which was added to the extraction solution. We observed that ascorbic acid protected most of the U from oxidation. The measured (234)U/(238)U ratio in U(IV) and U(VI) fractions in the sediment samples provided a unique tool to quantify U oxidation caused by Fe(III). Annealing (sample heating) to temperatures above 500 °C was supposed to heal ionizing radiation induced defects in the material that can disturb U redox state during extraction. Good agreement between two independent methods was obtained for DL-1a material: an average 38% of U(IV) determined by redox tracer corrected wet chemistry and 45% for XANES. Copyright © 2013 Elsevier Ltd. All rights reserved.

Immobilization of uranium into magnetite from aqueous solution by electrodepositing approach.

PubMed

Lu, Bing-Qing; Li, Mi; Zhang, Xiao-Wen; Huang, Chun-Mei; Wu, Xiao-Yan; Fang, Qi

2018-02-05

Immobilization of uranium into magnetite (Fe 3 O 4 ), which was generated from metallic iron by electrochemical method, was proposed to rapidly remove uranium from aqueous solution. The effects of electrochemical parameters such as electrode materials, voltage, electrode gap, reaction time and pH value on the crystallization of Fe 3 O 4 and uranium removal efficiencies were investigated. More than 90% uranium in the solution was precipitated with Fe 3 O 4 under laboratory conditions when uranium concentration range from 0.5mg/L to 10mg/L. The Fe 3 O 4 crystallization mechanism and immobilization of uranium was proved by XPS, XRD, TEM, FTIR and VSM methods. The results indicated that the cationic (including Fe 2+ , Fe 3+ and U(VI)) migrate to cathode side under the electric field and the uranium was incorporated or adsorbed by Fe 3 O 4 which was generated at cathode while the pH ranges between 2-7. The uranium-containing precipitate of Fe 3 O 4 can exist stably at the acid concentration below 60g/L. Furthermore, the precipitate may be used as valuable resources for uranium or iron recycling, which resulted in no secondary pollution in the removal of uranium from aqueous solution. Copyright © 2017. Published by Elsevier B.V.

Mechanisms and Rates of U(VI) Reduction by Fe(II) in Homogeneous Aqueous Solution and the Role of U(V) Disproportionation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, Richard N.; Rosso, Kevin M.

Molecular-level pathways in the aqueous redox transformation of uranium by iron remain unclear, despite the importance of this knowledge for predicting uranium transport and distribution in natural and engineered environments. As the relative importance of homogeneous versus heterogeneous pathways is difficult to probe experimentally, here we apply computational molecular simulation to isolate rates of key one electron transfer reactions in the homogeneous pathway. By comparison to experimental observations the role of the heterogeneous pathway also becomes clear. Density functional theory (DFT) and Marcus theory calculations for all primary monomeric species at pH values ≤7 show for UO22+ and its hydrolysismore » species UO2OH+ and UO2(OH)20 that reduction by Fe2+ is thermodynamically favorable, though kinetically limited for UO22+. An inner-sphere encounter complex between UO2OH+ and Fe2+ was the most stable for the first hydrolysis species and displayed an electron transfer rate constant ket = 4.3 × 103 s-1. Three stable inner- and outer-sphere encounter complexes between UO2(OH)20 and Fe2+ were found, with electron transfer rate constants ranging from ket = 7.6 × 102 to 7.2 × 104 s-1. Homogeneous reduction of these U(VI) hydrolysis species to U(V) is, therefore, predicted to be facile. In contrast, homogeneous reduction of UO2+ by Fe2+ was found to be thermodynamically unfavorable, suggesting the possible importance of U(V)-U(V) disproportionation as a route to U(IV). Calculations on homogeneous disproportionation, however, while yielding a stable outer-sphere U(V)-U(V) encounter complex, indicate that this electron transfer reaction is not feasible at circumneutral pH. Protonation of both axial O atoms of acceptor U(V) (i.e., by H3O+) was found to be a prerequisite to stabilize U(IV), consistent with the experimental observation that the rate of this reaction is inversely correlated with pH. Thus, despite prevailing notions that U(V) is rapidly eliminated by homogeneous disproportionation, this pathway is irrelevant at environmental conditions.« less

Lithological and hydrochemical controls on distribution and speciation of uranium in groundwaters of hard-rock granitic aquifers of Madurai District, Tamil Nadu (India).

PubMed

Thivya, C; Chidambaram, S; Keesari, Tirumalesh; Prasanna, M V; Thilagavathi, R; Adithya, V S; Singaraja, C

2016-04-01

Uranium is a radioactive element normally present in hexavalent form as U(VI) in solution and elevated levels in drinking water cause health hazards. Representative groundwater samples were collected from different litho-units in this region and were analyzed for total U and major and minor ions. Results indicate that the highest U concentration (113 µg l(-1)) was found in granitic terrains of this region and about 10 % of the samples exceed the permissible limit for drinking water. Among different species of U in aqueous media, carbonate complexes [UO2(CO3)(2)(2-)] are found to be dominant. Groundwater with higher U has higher pCO2 values, indicating weathering by bicarbonate ions resulting in preferential mobilization of U in groundwater. The major minerals uraninite and coffinite were found to be supersaturated and are likely to control the distribution of U in the study area. Nature of U in groundwater, the effects of lithology on hydrochemistry and factors controlling its distribution in hard rock aquifers of Madurai district are highlighted in this paper.

Determination of Plutonium Isotope Ratios at Very Low Levels by ICP-MS using On-Line Electrochemically Modulated Separations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liezers, Martin; Lehn, Scott A; Olsen, Khris B

2009-10-01

Electrochemically modulated separations (EMS) are shown to be a rapid and selective means of extracting and concentrating Pu from complex solutions prior to isotopic analysis by inductively coupled plasma mass spectrometry (ICP-MS). This separation is performed in a flow injection mode, on-line with the ICP-MS. A three-electrode, flow-by electrochemical cell is used to accumulate Pu at an anodized glassy carbon electrode by redox conversion of Pu(III) to Pu (IV&VI). The entire process takes place in 2% v/v (0.46M) HNO 3. No redox chemicals or acid concentration changes are required. Plutonium accumulation and release is redox dependent and controlled by themore » applied cell potential. Thus large transient volumetric concentration enhancements can be achieved. Based on more negative U(IV) potentials relative to Pu(IV), separation of Pu from uranium is efficient, thereby eliminating uranium hydride interferences. EMS-ICP-MS isotope ratio measurement performance will be presented for femtogram to attogram level plutonium concentrations.« less

New Technique for Speciation of Uranium in Sediments Following Acetate-Stimulated Bioremediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

2011-06-22

Acetate-stimulated bioremediation is a promising new technique for sequestering toxic uranium contamination from groundwater. The speciation of uranium in sediments after such bioremediation attempts remains unknown as a result of low uranium concentration, and is important to analyzing the stability of sequestered uranium. A new technique was developed for investigating the oxidation state and local molecular structure of uranium from field site sediments using X-Ray Absorption Spectroscopy (XAS), and was implemented at the site of a former uranium mill in Rifle, CO. Glass columns filled with bioactive Rifle sediments were deployed in wells in the contaminated Rifle aquifer and amendedmore » with a hexavalent uranium (U(VI)) stock solution to increase uranium concentration while maintaining field conditions. This sediment was harvested and XAS was utilized to analyze the oxidation state and local molecular structure of the uranium in sediment samples. Extended X-Ray Absorption Fine Structure (EXAFS) data was collected and compared to known uranium spectra to determine the local molecular structure of the uranium in the sediment. Fitting was used to determine that the field site sediments did not contain uraninite (UO{sub 2}), indicating that models based on bioreduction using pure bacterial cultures are not accurate for bioremediation in the field. Stability tests on the monomeric tetravalent uranium (U(IV)) produced by bioremediation are needed in order to assess the efficacy of acetate-stimulation bioremediation.« less

Uranium(III)-carbon multiple bonding supported by arene δ-bonding in mixed-valence hexauranium nanometre-scale rings.

PubMed

Wooles, Ashley J; Mills, David P; Tuna, Floriana; McInnes, Eric J L; Law, Gareth T W; Fuller, Adam J; Kremer, Felipe; Ridgway, Mark; Lewis, William; Gagliardi, Laura; Vlaisavljevich, Bess; Liddle, Stephen T

2018-05-29

Despite the fact that non-aqueous uranium chemistry is over 60 years old, most polarised-covalent uranium-element multiple bonds involve formal uranium oxidation states IV, V, and VI. The paucity of uranium(III) congeners is because, in common with metal-ligand multiple bonding generally, such linkages involve strongly donating, charge-loaded ligands that bind best to electron-poor metals and inherently promote disproportionation of uranium(III). Here, we report the synthesis of hexauranium-methanediide nanometre-scale rings. Combined experimental and computational studies suggest overall the presence of formal uranium(III) and (IV) ions, though electron delocalisation in this Kramers system cannot be definitively ruled out, and the resulting polarised-covalent U = C bonds are supported by iodide and δ-bonded arene bridges. The arenes provide reservoirs that accommodate charge, thus avoiding inter-electronic repulsion that would destabilise these low oxidation state metal-ligand multiple bonds. Using arenes as electronic buffers could constitute a general synthetic strategy by which to stabilise otherwise inherently unstable metal-ligand linkages.

Identification of bacteria synthesizing ribosomal RNA in response to uranium addition during biostimulation at the Rifle, CO Integrated Field Research site

DOE PAGES

McGuinness, Lora R.; Wilkins, Michael J.; Williams, Kenneth H.; ...

2015-09-18

Understanding which organisms are capable of reducing uranium at historically contaminated sites provides crucial information needed to evaluate treatment options and outcomes. One approach is determination of the bacteria which directly respond to uranium addition. In this research, uranium amendments were made to groundwater samples from a site of ongoing biostimulation with acetate. The active microbes in the planktonic phase were deduced by monitoring ribosomes production via RT-PCR. The results indicated several microorganisms were synthesizing ribosomes in proportion with uranium amendment up to 2 μM. Concentrations of U (VI) >2 μM were generally found to inhibit ribosome synthesis. Two activemore » bacteria responding to uranium addition in the field were close relatives of Desulfobacter postgateii and Geobacter bemidjiensis. Since RNA content often increases with growth rate, our findings suggest it is possible to rapidly elucidate active bacteria responding to the addition of uranium in field samples and provides a more targeted approach to stimulate specific populations to enhance radionuclide reduction in contaminated sites.« less

Identification of Bacteria Synthesizing Ribosomal RNA in Response to Uranium Addition During Biostimulation at the Rifle, CO Integrated Field Research Site

PubMed Central

McGuinness, Lora R.; Wilkins, Michael J.; Williams, Kenneth H.; Long, Philip E.; Kerkhof, Lee J.

2015-01-01

Understanding which organisms are capable of reducing uranium at historically contaminated sites provides crucial information needed to evaluate treatment options and outcomes. One approach is determination of the bacteria which directly respond to uranium addition. In this study, uranium amendments were made to groundwater samples from a site of ongoing biostimulation with acetate. The active microbes in the planktonic phase were deduced by monitoring ribosomes production via RT-PCR. The results indicated several microorganisms were synthesizing ribosomes in proportion with uranium amendment up to 2 μM. Concentrations of U (VI) >2 μM were generally found to inhibit ribosome synthesis. Two active bacteria responding to uranium addition in the field were close relatives of Desulfobacter postgateii and Geobacter bemidjiensis. Since RNA content often increases with growth rate, our findings suggest it is possible to rapidly elucidate active bacteria responding to the addition of uranium in field samples and provides a more targeted approach to stimulate specific populations to enhance radionuclide reduction in contaminated sites. PMID:26382047

Structural determination of individual chemical species in a mixed system by iterative transformation factor analysis-based X-ray absorption spectroscopy combined with UV-visible absorption and quantum chemical calculation.

PubMed

Ikeda, Atsushi; Hennig, Christoph; Rossberg, André; Tsushima, Satoru; Scheinost, Andreas C; Bernhard, Gert

2008-02-15

A multitechnique approach using extended X-ray absorption fine structure (EXAFS) spectroscopy based on iterative transformation factor analysis (ITFA), UV-visible absorption spectroscopy, and density functional theory (DFT) calculations has been performed in order to investigate the speciation of uranium(VI) nitrate species in acetonitrile and to identify the complex structure of individual species in the system. UV-visible spectral titration suggests that there are four different species in the system, that is, pure solvated species, mono-, di-, and trinitrate species. The pure EXAFS spectra of these individual species are extracted by ITFA from the measured spectral mixtures on the basis of the speciation distribution profile calculated from the UV-visible data. Data analysis of the extracted EXAFS spectra, with the help of DFT calculations, reveals the most probable complex structures of the individual species. The pure solvated species corresponds to a uranyl hydrate complex with an equatorial coordination number (CNeq) of 5, [UO2(H2O)5]2+. Nitrate ions tend to coordinate to the uranyl(VI) ion in a bidentate fashion rather than a unidentate one in acetonitrile for all the nitrate species. The mononitrate species forms the complex of [UO2(H2O)3NO3]+ with a CNeq value of 5, while the di- and trinitrate species have a CNeq value of 6, corresponding to [UO2(H2O)2(NO3)2]0 (D2h) and [UO2(NO3)3]- (D3h), respectively.

The effect of bicarbonate on the microbial dissolution of autunite mineral in the presence of gram-positive bacteria.

PubMed

Sepulveda-Medina, Paola M; Katsenovich, Yelena P; Wellman, Dawn M; Lagos, Leonel E

2015-06-01

Bacteria are key players in the processes that govern fate and transport of contaminants. The uranium release from Na and Ca-autunite by Arthrobacter oxydans strain G968 was evaluated in the presence of bicarbonate ions. This bacterium was previously isolated from Hanford Site soil and in earlier prescreening tests demonstrated low tolerance to U(VI) toxicity compared to other A. oxydans isolates. Experiments were conducted using glass serum bottles as mixed bioreactors and sterile 6-well cell culture plates with inserts separating bacteria cells from mineral solids. Reactors containing phosphorus-limiting media were amended with bicarbonate ranging between 0 and 10 mM and meta-autunite solids to provide a U(VI) concentration of 4.4 mmol/L. Results showed that in the presence of bicarbonate, A. oxydans G968 was able to enhance the release of U(VI) from Na and Ca autunite at the same capacity as other A. oxydans isolates with relatively high tolerance to U(VI). The effect of bacterial strains on autunite dissolution decreases as the concentration of bicarbonate increases. The results illustrate that direct interaction between the bacteria and the mineral is not necessary to result in U(VI) biorelease from autunite. The formation of secondary calcium-phosphate mineral phases on the surface of the mineral during the dissolution can ultimately reduce the natural autunite mineral contact area, which bacterial cells can access. This thereby reduces the concentration of uranium released into the solution. This study provides a better understanding of the interactions between meta-autunite and microbes in conditions mimicking arid and semiarid subsurface environments of western U.S. Copyright © 2015 Elsevier Ltd. All rights reserved.

The Effect of Bicarbonate on the Microbial Dissolution of Autunite Mineral in the Presence of Gram-Positive Bacteria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sepulveda-Medina, Paola; Katsenovich, Yelena; Wellman, Dawn M.

Bacteria are key players in the processes that govern fate and transport of contaminants. The uranium release from Na and Ca-autunite by Arthrobacter oxydans strain G968 was evaluated in the presence of bicarbonate ions. This bacterium was previously isolated from Hanford Site soil and in earlier prescreening tests demonstrated low tolerance to U(VI) toxicity compared to other A.oxydans isolates. Experiments were conducted using glass serum bottles as mixed bioreactors and sterile 6-well cell culture plates with inserts separating bacteria cells from mineral solids. Reactors containing phosphorus-limiting media were amended with bicarbonate ranging between 0-10 mM and metaautunite solids to providemore » a U(VI) concentration of 4.4 mmol/L. Results showed that in the presence of bicarbonate, A.oxydans G968 was able to enhance the release of U(VI) from Na and Ca autunite at the same capacity as other A.oxydans isolates with relatively high tolerance to U(VI). The effect of bacterial strains on autunite dissolution decreases as the concentration of bicarbonate increases. The results illustrate that direct interaction between the bacteria and the mineral is not necessary to result in U (VI) biorelease from autunite. The formation of secondary calcium-phosphate mineral phases on the surface of the mineral during the dissolution can ultimately reduce the natural autunite mineral contact area, which bacterial cells can access. This thereby reduces the concentration of uranium released into the solution. This study provides a better understanding of the interactions between meta-autunite and microbes in conditions mimicking arid and semiarid subsurface environments of western U.S.« less

Raoultella sp. SM1, a novel iron-reducing and uranium-precipitating strain.

PubMed

Sklodowska, Aleksandra; Mielnicki, Sebastian; Drewniak, Lukasz

2018-03-01

The main aim of this study was the characterisation of novel Raoutella isolate, an iron-reducing and uranium-precipitating strain, originating from microbial mats occurring in the sediments of a closed down uranium mine in Kowary (SW Poland). Characterisation was done in the context of its potential role in the functioning of these mats and the possibility to use them in uranium removal/recovery processes. In our experiment, we observed the biological precipitation of iron and uranium's secondary minerals containing oxygen, potassium, sodium and phosphor, which were identified as ningyoite-like minerals. The isolated strain, Raoultella sp. SM1, was also able to dissimilatory reduce iron (III) and uranium (VI) in the presence of citrate as an electron donor. Our studies allowed us to characterise a new strain which may be used as a model microorganism in the study of Fe and U respiratory processes and which may be useful in the bioremediation of uranium-contaminated waters and sediments. During this process, uranium may be immobilised in ningyoite-like minerals and can then be recovered in nano/micro-particle form, which may be easily transformed to uraninite. Copyright © 2017 Elsevier Ltd. All rights reserved.

Efficient sorption and reduction of U(VI) on zero-valent iron-polyaniline-graphene aerogel ternary composite.

PubMed

Chen, Lili; Feng, Shaojie; Zhao, Donglin; Chen, Shaohua; Li, Feifei; Chen, Changlun

2017-03-15

In this work, zero-valent iron-polyaniline-graphene aerogel composite (Fe-PANI-GA) was prepared and applied in the removal of U(VI) from aqueous solutions by batch sorption experiments. The experimental results showed that the Fe-PANI-GA composite had an excellent removal capacity for the removal of U(VI) in acidic solutions. The results also showed that the maximum removal capacity of the Fe-PANI-GA toward U(VI) was 350.47mg/g at pH 5.5. The sorption kinetics data were well-described by pseudo-second-order. The sorption isotherms of U(VI) fitted well with Langmuir isotherm and exhibited better removal efficiency with the increase of temperature. The thermodynamic parameters (ΔG, ΔS, ΔH) indicated that the sorption of U(VI) on the Fe-PANI-GA was an endothermic and spontaneous process. Moreover, removal mechanisms were studied based on the results of XRD, FTIR and XPS. Both U(VI) sorption and partially reductive precipitation of U(VI) to U(IV) contributed to the removal of U(VI) on Fe-PANI-GA. Therefore, Fe-PANI-GA was an economic and effective material for the removal of uranium from nuclear waste in practical application. Copyright © 2016 Elsevier Inc. All rights reserved.

Uranium(iii) complexes supported by hydrobis(mercaptoimidazolyl)borates: synthesis and oxidation chemistry.

PubMed

Maria, Leonor; Santos, Isabel C; Santos, Isabel

2018-05-23

The reaction of [UI3(thf)4] with the sodium or lithium salts of hydrobis(2-mercapto-1-methylimidazolyl)borate ligands ([H(R)B(timMe)2]-) in a 1 : 2 ratio, in tetrahydrofuran, gave the U(iii) complexes [UI{κ3-H,S,S'-H(R)B(timMe)2}2(thf)2] (R = H (1), Ph (2)) in good yields. Crystals of [UI{κ3-H,S,S'-H(Ph)B(timMe)2}2(thf)2] (2) were obtained by recrystallization from a tetrahydrofuran/acetonitrile solution, and the ion-separated uranium complex [U{κ3-H,S,S'-H(Ph)B(timMe)2}2(CH3CN)3][I] (3-I) was obtained by dissolution of 2 in acetonitrile followed by recrystallization. One-electron oxidation of 2 with AgBPh4 or I2 resulted in the formation of the cationic U(iv) complexes [U{κ3-H,S,S'-H(Ph)B(timMe)2}3][X] (X = BPh4 (6-BPh4), I (6-I)), due to a ligand redistribution process. These complexes are the first examples of homoleptic poly(azolyl)borate U(iv) complexes. Treatment of complex 2 with azobenzene led to the isolation of crystals of the U(iv) compound [UI{κ3-H(Ph)B(timMe)2}2(κ2-timMe)] (7). Treatment of 2 with pyridine-N oxide (pyNO) led to the formation of the uranyl complex [UO2{κ2-S,S'-H(Ph)B(timMe)2}2] (8) and of complex 6-I, while from the reaction of [U{κ3-H(Ph)B(timMe)2}2(thf)3][BPh4] (5) with pyNO, the oxo-bridged U(iv) complex [{U{κ3-H(Ph)B(timMe)2}2(pyNO)}2(μ-O)][BPh4]2 (9) was also obtained. In the U(iii) and U(iv) complexes, the bis(azolyl)borate ligands bind to the uranium center in a κ3-H,S,S' coordination mode, while in the U(vi) complex the ligands bind to the metal in a κ2-S,S' mode. The presence of UH-B interactions in the solid-state, for the nine-coordinate complexes 1, 2, 3, 6 and 7 and for the eight-coordinate complex 9, was supported by IR spectroscopy and/or X-ray diffraction analysis.

The application of zero-valent iron nanoparticles for the remediation of a uranium-contaminated waste effluent.

PubMed

Dickinson, Michelle; Scott, Thomas B

2010-06-15

Zero-valent iron nanoparticles (INP) were investigated as a remediation strategy for a uranium-contaminated waste effluent from AWE, Aldermaston. Nanoparticles were introduced to the effluent, under both oxic and anoxic conditions, and allowed to react for a 28-d period during which the liquid and nanoparticle solids were periodically sampled. Analysis of the solution indicated that under both conditions U was removed to <1.5% of its initial concentration within 1h of introduction and remained at similar concentrations until approximately 48 h. A rapid release of Fe into solution was also recorded during this initial period; attributed to the limited partial dissolution of the INP. XPS analyses of the reacted nanoparticulate solids between 1 and 48 h showed an increased Fe(III):Fe(II) ratio, consistent with the detection of iron oxidation products (akaganeite and magnetite) by XRD and FIB. XPS analysis also recorded uranium on the recovered particulates indicating the chemical reduction of U(VI) to U(IV) within 1h. Following the initial retention period U-dissolution of U was recorded from 48 h, and attributed to reoxidation. The efficient uptake and retention of U on the INP for periods up to 48 h provide proof that INP may be effectively used for the remediation of complex U-contaminated effluents. Copyright 2010 Elsevier B.V. All rights reserved.

Stochastic simulation of uranium migration at the Hanford 300 Area.

PubMed

Hammond, Glenn E; Lichtner, Peter C; Rockhold, Mark L

2011-03-01

This work focuses on the quantification of groundwater flow and subsequent U(VI) transport uncertainty due to heterogeneity in the sediment permeability at the Hanford 300 Area. U(VI) migration at the site is simulated with multiple realizations of stochastically-generated high resolution permeability fields and comparisons are made of cumulative water and U(VI) flux to the Columbia River. The massively parallel reactive flow and transport code PFLOTRAN is employed utilizing 40,960 processor cores on DOE's petascale Jaguar supercomputer to simultaneously execute 10 transient, variably-saturated groundwater flow and U(VI) transport simulations within 3D heterogeneous permeability fields using the code's multi-realization simulation capability. Simulation results demonstrate that the cumulative U(VI) flux to the Columbia River is less responsive to fine scale heterogeneity in permeability and more sensitive to the distribution of permeability within the river hyporheic zone and mean permeability of larger-scale geologic structures at the site. Copyright © 2010 Elsevier B.V. All rights reserved.

Upscaling of U(VI) Desorption and Transport from Decimeter-Scale Heterogeneity to Plume-Scale Modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Curtis, Gary P.; Kohler, Matthias; Kannappan, Ramakrishnan

2015-02-24

Scientifically defensible predictions of field scale U(VI) transport in groundwater requires an understanding of key processes at multiple scales. These scales range from smaller than the sediment grain scale (less than 10 μm) to as large as the field scale which can extend over several kilometers. The key processes that need to be considered include both geochemical reactions in solution and at sediment surfaces as well as physical transport processes including advection, dispersion, and pore-scale diffusion. The research summarized in this report includes both experimental and modeling results in batch, column and tracer tests. The objectives of this research weremore » to: (1) quantify the rates of U(VI) desorption from sediments acquired from a uranium contaminated aquifer in batch experiments;(2) quantify rates of U(VI) desorption in column experiments with variable chemical conditions, and(3) quantify nonreactive tracer and U(VI) transport in field tests.« less

Innovative Approach to Prevent Acid Drainage from Uranium Mill Tailings Based on the Application of Na-Ferrate (VI)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fernandes, H.M.; Reinhart, D.; Lettie, L.

2006-07-01

The operation of uranium mining and milling plants gives rise to huge amounts of wastes from both mining and milling operations. When pyrite is present in these materials, the generation of acid drainage can take place and result in the contamination of underground and surface waters through the leaching of heavy metals and radionuclides. To solve this problem, many studies have been conducted to find cost-effective solutions to manage acid mine drainage; however, no adequate strategy to deal with sulfide-ric h wastes is currently available. Ferrate (VI) is a powerful oxidizing agent in aqueous media. Under acidic conditions, the redoxmore » potential of the Ferrate (VI) ion is the highest of any other oxidant used in wastewater treatment processes. The standard half cell reduction potential of ferrate (VI) has been determined as +2.20 V to + 0.72 V in acidic and basic solutions, respectively. Ferrate (VI) exhibits a multitude of advantageous properties, including higher reactivity and selectivity than traditional oxidant alternatives, as well as disinfectant, flocculating, and coagulant properties. Despite numerous beneficial properties in environmental applications, ferrate (VI) has remained commercially unavailable. Starting in 1953, different methods for producing a high purity, powdered ferrate (VI) product were developed. However, producing this dry, stabilized ferrate (VI) product required numerous process steps which led to excessive synthesis costs (over $20/lb) thereby preventing bulk industrial use. Recently a novel synthesis method for the production of a liquid ferrate (VI) based on hypochlorite oxidation of ferric ion in strongly alkaline solutions has been discovered (USPTO 6,790,428; September 14, 2004). This on-site synthesis process dramatically reduces manufacturing cost for the production of ferrate (VI) by utilizing common commodity feedstocks. This breakthrough means that for the first time ferrate (VI) can be an economical alternative to treating acid mining drainage generating materials. The objective of the present study was to investigate a methodology of preventing the generation of acid drainage by applying ferrate (VI) to acid generating materials prior to the disposal in impoundments or piles. Oxidizing the pyritic material in mining waste could diminish the potential for acid generation and its related environmental risks and long-term costs at disposal sites. The effectiveness of toxic metals removal from acid mine drainage by applying ferrate (VI) is also examined. Preliminary results presented in this paper show that the oxidation of pyrite by ferrate is a first-order rate reaction in Fe(VI) with a half-life of about six hours. The stability of Fe(VI) in water solutions will not influence the reaction rate in a significant manner. New low-cost production methods for making liquid ferrate on-site makes this technology a very attractive option to mitigate one of the most pressing environmental problems in the mining industry. (authors)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yingjie, E-mail: yzx@ansto.gov.au; Bhadbhade, Mohan; Karatchevtseva, Inna

Three new coordination polymers of uranium(VI) with pyromellitic acid (H{sub 4}btca) have been synthesized and structurally characterized. (ED)[(UO{sub 2})(btca)]·(DMSO)·3H{sub 2}O (1) (ED=ethylenediammonium; DMSO=dimethylsulfoxide) has a lamellar structure with intercalation of ED and DMSO. (NH{sub 4}){sub 2}[(UO{sub 2}){sub 6}O{sub 2}(OH){sub 6}(btca)]·~6H{sub 2}O (2) has a 3D framework built from 7-fold coordinated uranyl trinuclear units and btca ligands with 1D diamond-shaped channels (~8.5 Å×~8.6 Å). [(UO{sub 2}){sub 2}(H{sub 2}O)(btca)]·4H{sub 2}O (3) has a 3D network constructed by two types of 7-fold coordinated uranium polyhedron. The unique μ{sub 5}-coordination mode of btca in 3 enables the formation of 1D olive-shaped large channels (~4.5more » Å×~19 Å). Vibrational modes, thermal stabilities and fluorescence properties have been investigated. - Graphical abstract: Table of content: three new uranium(VI) coordination polymers with pyromellitic acid (H{sub 4}btca) have been synthesized via room temperature and hydrothermal synthesis methods, and structurally characterized. Two to three dimensional (3D) frameworks are revealed. All 3D frameworks have unique 1D large channels. Their vibrational modes, thermal stabilities and photoluminescence properties have been investigated. - Highlights: • Three new coordination polymers of U(VI) with pyromellitic acid (H{sub 4}btca). • Structures from a 2D layer to 3D frameworks with unique 1D channels. • Unusual µ{sub 5}-(η{sub 1}:η{sub 2}:η{sub 1}:η{sub 2:}η{sub 1}) coordination mode of btca ligand. • Vibrational modes, thermal stabilities and luminescent properties reported.« less

Influence of calcium on microbial reduction of solid phase uranium(VI).

PubMed

Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M; Wang, Zheming

2007-08-15

The effect of calcium on the dissolution and microbial reduction of a representative solid phase uranyl [U(VI)], sodium boltwoodite (NaUO(2)SiO(3)OH . 1.5H(2)O), was investigated to evaluate the rate-limiting step of microbial reduction of the solid phase U(VI). Microbial reduction experiments were performed in a culture of a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1, in a bicarbonate medium with lactate as electron donor at pH 6.8 buffered with PIPES. Calcium increased the rate of Na-boltwoodite dissolution and U(VI) bioavailability by increasing its solubility through the formation of a ternary aqueous calcium-uranyl-carbonate species. The ternary species, however, decreased the rates of microbial reduction of aqueous U(VI). Laser-induced fluorescence spectroscopy (LIFS) and transmission electron microscopy (TEM) collectively revealed that microbial reduction of solid phase U(VI) was a sequentially coupled process of Na-boltwoodite dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) to U(IV) that accumulated on bacterial surfaces/periplasm. Under studied experimental conditions, the overall rate of microbial reduction of solid phase U(VI) was limited by U(VI) dissolution reactions in solutions without calcium and limited by microbial reduction in solutions with calcium. Generally, the overall rate of microbial reduction of solid phase U(VI) was determined by the coupling of solid phase U(VI) dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) that were all affected by calcium. (c) 2007 Wiley Periodicals, Inc.

Uranium immobilization and nanofilm formation on magnesium-rich minerals

DOE PAGES

van Veelen, Arjen; Bargar, John R.; Law, Gareth T. W.; ...

2016-03-18

Polarization-dependent grazing incidence X-ray absorption spectroscopy (XAS) measurements were completed on oriented single crystals of magnesite [MgCO 3] and brucite [Mg(OH) 2] reacted with aqueous uranyl chloride above and below the solubility boundaries of schoepite (500, 50, and 5 ppm) at pH 8.3 and at ambient (P CO2 = 10 –3.5) or reduced partial pressures of carbon dioxide (P CO2 = 10 –4.5). X-ray absorption near edge structure (XANES) spectra show a striking polarization dependence (χ = 0° and 90° relative to the polarization plane of the incident beam) and consistently demonstrated that the uranyl molecule was preferentially oriented withmore » its O axial = U(VI) = O axial linkage at high angles (60–80°) to both magnesite (101¯4) and brucite (0001). Extended X-ray absorption fine structure (EXAFS) analysis shows that the “effective” number of U(VI) axial oxygens is the most strongly affected fitting parameter as a function of polarization. Furthermore, axial tilt in the surface thin films (thickness ~ 21 Å) is correlated with surface roughness [σ]. Our results show that hydrated uranyl(-carbonate) complexes polymerize on all of our experimental surfaces and that this process is controlled by surface hydroxylation. Lastly, these results provide new insights into the bonding configuration expected for uranyl complexes on the environmentally significant carbonate and hydroxide mineral surfaces.« less

Uranium Immobilization and Nanofilm Formation on Magnesium-Rich Minerals.

PubMed

van Veelen, Arjen; Bargar, John R; Law, Gareth T W; Brown, Gordon E; Wogelius, Roy A

2016-04-05

Polarization-dependent grazing incidence X-ray absorption spectroscopy (XAS) measurements were completed on oriented single crystals of magnesite [MgCO3] and brucite [Mg(OH)2] reacted with aqueous uranyl chloride above and below the solubility boundaries of schoepite (500, 50, and 5 ppm) at pH 8.3 and at ambient (PCO2 = 10(-3.5)) or reduced partial pressures of carbon dioxide (PCO2 = 10(-4.5)). X-ray absorption near edge structure (XANES) spectra show a striking polarization dependence (χ = 0° and 90° relative to the polarization plane of the incident beam) and consistently demonstrated that the uranyl molecule was preferentially oriented with its Oaxial═U(VI)═Oaxial linkage at high angles (60-80°) to both magnesite (101̅4) and brucite (0001). Extended X-ray absorption fine structure (EXAFS) analysis shows that the "effective" number of U(VI) axial oxygens is the most strongly affected fitting parameter as a function of polarization. Furthermore, axial tilt in the surface thin films (thickness ∼ 21 Å) is correlated with surface roughness [σ]. Our results show that hydrated uranyl(-carbonate) complexes polymerize on all of our experimental surfaces and that this process is controlled by surface hydroxylation. These results provide new insights into the bonding configuration expected for uranyl complexes on the environmentally significant carbonate and hydroxide mineral surfaces.

Thermodynamic parameters of U (VI) sorption onto soils in aquatic systems.

PubMed

Kumar, Ajay; Rout, Sabyasachi; Ghosh, Malay; Singhal, Rakesh Kumar; Ravi, Pazhayath Mana

2013-01-01

The thermodynamic parameters viz. the standard free energy (∆Gº), Standard enthalpy change (∆Hº) and standard entropy change (∆Sº) were determined using the obtained values of distribution coefficient (kd) of U (VI) in two different types of soils (agricultural and undisturbed) by conducting a batch equilibrium experiment with aqueous media (groundwater and deionised water) at two different temperatures 25°C and 50°C. The obtained distribution coefficients (kd) values of U for undisturbed soil in groundwater showed about 75% higher than in agricultural soil at 25°C while in deionised water, these values were highly insignificant for both soils indicating that groundwater was observed to be more favorable for high surface sorption. At 50°C, the increased kd values in both soils revealed that solubility of U decreased with increasing temperature. Batch adsorption results indicated that U sorption onto soils was promoted at higher temperature and an endothermic and spontaneous interfacial process. The high positive values of ∆Sº for agricultural soil suggested a decrease in sorption capacity of U in that soil due to increased randomness at solid-solution interface. The low sorption onto agricultural soil may be due to presence of high amount of coarse particles in the form of sand (56%). Geochemical modeling predicted that mixed hydroxo-carbonato complexes of uranium were the most stable and abundant complexes in equilibrium solution during experimental.

Speciation and reactivity of uranium products formed during in situ bioremediation in a shallow alluvial aquifer.

PubMed

Alessi, Daniel S; Lezama-Pacheco, Juan S; Janot, Noémie; Suvorova, Elena I; Cerrato, José M; Giammar, Daniel E; Davis, James A; Fox, Patricia M; Williams, Kenneth H; Long, Philip E; Handley, Kim M; Bernier-Latmani, Rizlan; Bargar, John R

2014-11-04

In this study, we report the results of in situ U(VI) bioreduction experiments at the Integrated Field Research Challenge site in Rifle, Colorado, USA. Columns filled with sediments were deployed into a groundwater well at the site and, after a period of conditioning with groundwater, were amended with a mixture of groundwater, soluble U(VI), and acetate to stimulate the growth of indigenous microorganisms. Individual reactors were collected as various redox regimes in the column sediments were achieved: (i) during iron reduction, (ii) just after the onset of sulfate reduction, and (iii) later into sulfate reduction. The speciation of U retained in the sediments was studied using X-ray absorption spectroscopy, electron microscopy, and chemical extractions. Circa 90% of the total uranium was reduced to U(IV) in each reactor. Noncrystalline U(IV) comprised about two-thirds of the U(IV) pool, across large changes in microbial community structure, redox regime, total uranium accumulation, and reaction time. A significant body of recent research has demonstrated that noncrystalline U(IV) species are more suceptible to remobilization and reoxidation than crystalline U(IV) phases such as uraninite. Our results highlight the importance of considering noncrystalline U(IV) formation across a wide range of aquifer parameters when designing in situ remediation plans.

Speciation and Reactivity of Uranium Products Formed during in Situ Bioremediation in a Shallow Alluvial Aquifer

PubMed Central

2015-01-01

In this study, we report the results of in situ U(VI) bioreduction experiments at the Integrated Field Research Challenge site in Rifle, Colorado, USA. Columns filled with sediments were deployed into a groundwater well at the site and, after a period of conditioning with groundwater, were amended with a mixture of groundwater, soluble U(VI), and acetate to stimulate the growth of indigenous microorganisms. Individual reactors were collected as various redox regimes in the column sediments were achieved: (i) during iron reduction, (ii) just after the onset of sulfate reduction, and (iii) later into sulfate reduction. The speciation of U retained in the sediments was studied using X-ray absorption spectroscopy, electron microscopy, and chemical extractions. Circa 90% of the total uranium was reduced to U(IV) in each reactor. Noncrystalline U(IV) comprised about two-thirds of the U(IV) pool, across large changes in microbial community structure, redox regime, total uranium accumulation, and reaction time. A significant body of recent research has demonstrated that noncrystalline U(IV) species are more suceptible to remobilization and reoxidation than crystalline U(IV) phases such as uraninite. Our results highlight the importance of considering noncrystalline U(IV) formation across a wide range of aquifer parameters when designing in situ remediation plans. PMID:25265543

Release of U(VI) from spent biosorbent immobilized in cement concrete blocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venkobachar, C.; Iyengar, L.; Mishra, U.K.

1995-12-01

This paper deals with cementation as the method for the disposal of spent biosorbent, Ganoderma lucidum (a wood rotting macrofungi) after it is used for the removal of Uranium. Results on the uranium release during the curing of cement-concrete (CC) blocks indicated that placing the spent sorbent at the center of the blocks during their casting yields better immobilization of uranium as compared to the homogeneous mixing of the spent sorbent with the cement. Short term leach tests indicated that the uranium release was negligible in simulated seawater, 1.8% in 0.2 N sodium carbonate and 6.0% in 0.2 N HCl.more » The latter two leachates were used to represent the extreme environmental conditions. It was observed that the presence of the spent biosorbent up to 5% by weight did not affect the compressive strength of CC blocks. Thus cementation technique is suitable for the immobilization of uranium loaded biosorbent for its ultimate disposal.« less

Influence of mineral colloids and humic substances on uranium(VI) transport in water-saturated geologic porous media

NASA Astrophysics Data System (ADS)

Wang, Qing; Cheng, Tao; Wu, Yang

2014-12-01

Mineral colloids and humic substances often co-exist in subsurface environment and substantially influence uranium (U) transport. However, the combined effects of mineral colloids and humic substances on U transport are not clear. This study is aimed at quantifying U transport and elucidating geochemical processes that control U transport when both mineral colloids and humic acid (HA) are present. U-spiked solutions/suspensions were injected into water-saturated sand columns, and U and colloid concentrations in column effluent were monitored. We found that HA promoted U transport via (i) formation of aqueous U-HA complexes, and (ii) competition against aqueous U for surface sites on transport media. Illite colloids had no influence on U transport at pH 5 in the absence of HA due to low mobility of the colloids. At pH 9, U desorbed from mobile illite and the presence of illite decreased U transport. At pH 5, high U transport occurred when both illite colloids and HA were present, which was attributed to enhanced U adsorption to illite colloids via formation of ternary illite-HA-U surface complexes, and enhanced illite transport due to HA attachment to illite and transport media. This study demonstrates that the combined effects of mineral colloids and HA on contaminant transport is different from simple addition of the individual effect.

Unusual Versatility of the Filamentous, Diazotrophic Cyanobacterium Anabaena torulosa Revealed for Its Survival during Prolonged Uranium Exposure.

PubMed

Acharya, Celin; Chandwadkar, Pallavi; Nayak, Chandrani

2017-05-01

Reports on interactions between cyanobacteria and uranyl carbonate are rare. Here, we present an interesting succession of the metabolic responses employed by a marine, filamentous, diazotrophic cyanobacterium, Anabaena torulosa for its survival following prolonged exposure to uranyl carbonate extending up to 384 h at pH 7.8 under phosphate-limited conditions. The cells sequestered uranium (U) within polyphosphates on initial exposure to 100 μM uranyl carbonate for 24 to 28 h. Further incubation until 120 h resulted in (i) significant degradation of cellular polyphosphates causing extensive chlorosis and cell lysis, (ii) akinete differentiation followed by (iii) extracellular uranyl precipitation. X-ray diffraction (XRD) analysis, fluorescence spectroscopy, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy established the identity of the bioprecipitated uranium as a U(VI) autunite-type mineral, which settled at the bottom of the vessel. Surprisingly, A. torulosa cells resurfaced as small green flakes typical of actively growing colonies on top of the test solutions within 192 to 240 h of U exposure. A consolidated investigation using kinetics, microscopy, and physiological and biochemical analyses suggested a role of inducible alkaline phosphatase activity of cell aggregates/akinetes in facilitating the germination of akinetes leading to substantial regeneration of A. torulosa by 384 h of uranyl incubation. The biomineralized uranium appeared to be stable following cell regeneration. Altogether, our results reveal novel insights into the survival mechanism adopted by A. torulosa to resist sustained uranium toxicity under phosphate-limited oxic conditions. IMPORTANCE Long-term effects of uranyl exposure in cyanobacteria under oxic phosphate-limited conditions have been inadequately explored. We conducted a comprehensive examination of the metabolic responses displayed by a marine cyanobacterium, Anabaena torulosa , to cope with prolonged exposure to uranyl carbonate at pH 7.8 under phosphate limitation. Our results highlight distinct adaptive mechanisms harbored by this cyanobacterium that enabled its natural regeneration following extensive cell lysis and uranium biomineralization under sustained uranium exposure. Such complex interactions between environmental microbes such as Anabaena torulosa and uranium over a broader time range advance our understanding on the impact of microbial processes on uranium biogeochemistry. Copyright © 2017 American Society for Microbiology.

Variably Saturated Flow and Multicomponent Biogeochemical Reactive Transport Modeling of a Uranium Bioremediation Field Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yabusaki, Steven B.; Fang, Yilin; Williams, Kenneth H.

2011-11-01

Field experiments at a former uranium mill tailings site have identified the potential for stimulating indigenous bacteria to catalyze the conversion of aqueous uranium in the +6 oxidation state to immobile solid-associated uranium in the +4 oxidation state. This effectively removes uranium from solution resulting in groundwater concentrations below actionable standards. Three-dimensional, coupled variably-saturated flow and biogeochemical reactive transport modeling of a 2008 in situ uranium bioremediation field experiment is used to better understand the interplay of transport rates and biogeochemical reaction rates that determine the location and magnitude of key reaction products. A comprehensive reaction network, developed largely throughmore » previous 1-D modeling studies, was used to simulate the impacts on uranium behavior of pulsed acetate amendment, seasonal water table variation, spatially-variable physical (hydraulic conductivity, porosity) and geochemical (reactive surface area) material properties. A principal challenge is the mechanistic representation of biologically-mediated terminal electron acceptor process (TEAP) reactions whose products significantly alter geochemical controls on uranium mobility through increases in pH, alkalinity, exchangeable cations, and highly reactive reduction products. In general, these simulations of the 2008 Big Rusty acetate biostimulation field experiment in Rifle, Colorado confirmed previously identified behaviors including (1) initial dominance by iron reducing bacteria that concomitantly reduce aqueous U(VI), (2) sulfate reducing bacteria that become dominant after {approx}30 days and outcompete iron reducers for the acetate electron donor, (3) continuing iron-reducer activity and U(VI) bioreduction during dominantly sulfate reducing conditions, and (4) lower apparent U(VI) removal from groundwater during dominantly sulfate reducing conditions. New knowledge on simultaneously active metal and sulfate reducers has been incorporated into the modeling. In this case, an initially small population of slow growing sulfate reducers is active from the initiation of biostimulation. Three-dimensional, variably saturated flow modeling was used to address impacts of a falling water table during acetate injection. These impacts included a significant reduction in aquifer saturated thickness and isolation of residual reactants and products, as well as unmitigated uranium, in the newly unsaturated vadose zone. High permeability sandy gravel structures resulted in locally high flow rates in the vicinity of injection wells that increased acetate dilution. In downgradient locations, these structures created preferential flow paths for acetate delivery that enhanced local zones of TEAP reactivity and subsidiary reactions. Conversely, smaller transport rates associated with the lower permeability lithofacies (e.g., fine) and vadose zone were shown to limit acetate access and reaction. Once accessed by acetate, however, these same zones limited subsequent acetate dilution and provided longer residence times that resulted in higher concentrations of TEAP products when terminal electron donors and acceptors were not limiting. Finally, facies-based porosity and reactive surface area variations were shown to affect aqueous uranium concentration distributions; however, the ranges were sufficiently small to preserve general trends. Large computer memory and high computational performance were required to simulate the detailed coupled process models for multiple biogeochemical components in highly resolved heterogeneous materials for the 110-day field experiment and 50 days of post-biostimulation behavior. In this case, a highly-scalable subsurface simulator operating on 128 processor cores for 12 hours was used to simulate each realization. An equivalent simulation without parallel processing would have taken 60 days, assuming sufficient memory was available.« less

Maximum likelihood Bayesian model averaging and its predictive analysis for groundwater reactive transport models

USGS Publications Warehouse

Curtis, Gary P.; Lu, Dan; Ye, Ming

2015-01-01

While Bayesian model averaging (BMA) has been widely used in groundwater modeling, it is infrequently applied to groundwater reactive transport modeling because of multiple sources of uncertainty in the coupled hydrogeochemical processes and because of the long execution time of each model run. To resolve these problems, this study analyzed different levels of uncertainty in a hierarchical way, and used the maximum likelihood version of BMA, i.e., MLBMA, to improve the computational efficiency. This study demonstrates the applicability of MLBMA to groundwater reactive transport modeling in a synthetic case in which twenty-seven reactive transport models were designed to predict the reactive transport of hexavalent uranium (U(VI)) based on observations at a former uranium mill site near Naturita, CO. These reactive transport models contain three uncertain model components, i.e., parameterization of hydraulic conductivity, configuration of model boundary, and surface complexation reactions that simulate U(VI) adsorption. These uncertain model components were aggregated into the alternative models by integrating a hierarchical structure into MLBMA. The modeling results of the individual models and MLBMA were analyzed to investigate their predictive performance. The predictive logscore results show that MLBMA generally outperforms the best model, suggesting that using MLBMA is a sound strategy to achieve more robust model predictions relative to a single model. MLBMA works best when the alternative models are structurally distinct and have diverse model predictions. When correlation in model structure exists, two strategies were used to improve predictive performance by retaining structurally distinct models or assigning smaller prior model probabilities to correlated models. Since the synthetic models were designed using data from the Naturita site, the results of this study are expected to provide guidance for real-world modeling. Limitations of applying MLBMA to the synthetic study and future real-world modeling are discussed.

Enhanced uranium immobilization and reduction by Geobacter sulfurreducens biofilms.

PubMed

Cologgi, Dena L; Speers, Allison M; Bullard, Blair A; Kelly, Shelly D; Reguera, Gemma

2014-11-01

Biofilms formed by dissimilatory metal reducers are of interest to develop permeable biobarriers for the immobilization of soluble contaminants such as uranium. Here we show that biofilms of the model uranium-reducing bacterium Geobacter sulfurreducens immobilized substantially more U(VI) than planktonic cells and did so for longer periods of time, reductively precipitating it to a mononuclear U(IV) phase involving carbon ligands. The biofilms also tolerated high and otherwise toxic concentrations (up to 5 mM) of uranium, consistent with a respiratory strategy that also protected the cells from uranium toxicity. The enhanced ability of the biofilms to immobilize uranium correlated only partially with the biofilm biomass and thickness and depended greatly on the area of the biofilm exposed to the soluble contaminant. In contrast, uranium reduction depended on the expression of Geobacter conductive pili and, to a lesser extent, on the presence of the c cytochrome OmcZ in the biofilm matrix. The results support a model in which the electroactive biofilm matrix immobilizes and reduces the uranium in the top stratum. This mechanism prevents the permeation and mineralization of uranium in the cell envelope, thereby preserving essential cellular functions and enhancing the catalytic capacity of Geobacter cells to reduce uranium. Hence, the biofilms provide cells with a physically and chemically protected environment for the sustained immobilization and reduction of uranium that is of interest for the development of improved strategies for the in situ bioremediation of environments impacted by uranium contamination. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

Enhanced Uranium Immobilization and Reduction by Geobacter sulfurreducens Biofilms

PubMed Central

Cologgi, Dena L.; Speers, Allison M.; Bullard, Blair A.; Kelly, Shelly D.

2014-01-01

Biofilms formed by dissimilatory metal reducers are of interest to develop permeable biobarriers for the immobilization of soluble contaminants such as uranium. Here we show that biofilms of the model uranium-reducing bacterium Geobacter sulfurreducens immobilized substantially more U(VI) than planktonic cells and did so for longer periods of time, reductively precipitating it to a mononuclear U(IV) phase involving carbon ligands. The biofilms also tolerated high and otherwise toxic concentrations (up to 5 mM) of uranium, consistent with a respiratory strategy that also protected the cells from uranium toxicity. The enhanced ability of the biofilms to immobilize uranium correlated only partially with the biofilm biomass and thickness and depended greatly on the area of the biofilm exposed to the soluble contaminant. In contrast, uranium reduction depended on the expression of Geobacter conductive pili and, to a lesser extent, on the presence of the c cytochrome OmcZ in the biofilm matrix. The results support a model in which the electroactive biofilm matrix immobilizes and reduces the uranium in the top stratum. This mechanism prevents the permeation and mineralization of uranium in the cell envelope, thereby preserving essential cellular functions and enhancing the catalytic capacity of Geobacter cells to reduce uranium. Hence, the biofilms provide cells with a physically and chemically protected environment for the sustained immobilization and reduction of uranium that is of interest for the development of improved strategies for the in situ bioremediation of environments impacted by uranium contamination. PMID:25128347

The effect of uranium on bacterial viability and cell surface morphology using atomic force microscopy in the presence of bicarbonate ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sepulveda-Medina, Paola; Katsenovich, Yelena; Musaramthota, Vishal

Nuclear production facilities during the Cold War have caused liquid waste to leak and soak into the ground creating multiple radionuclide plumes. The Arthrobacter bacteria are one of the most common groups in soils and are found in large numbers in subsurface environments contaminated with radionuclides. This study experimentally analyzed changes on the bacteria surface after uranium exposure and evaluated the effect of bicarbonate ions on U(VI) toxicity of a less uranium tolerant Arthrobacter strain, G968, by investigating changes in adhesion forces and cells dimensions via atomic force microscopy (AFM). AFM and viability studies showed that samples containing bicarbonate aremore » able to acclimate and withstand uranium toxicity. Samples containing no bicarbonate exhibited deformed surfaces and a low height profile, which might be an indication that the cells are not alive.« less

Biosorption and biomineralization of uranium(VI) by Saccharomyces cerevisiae-Crystal formation of chernikovite.

PubMed

Zheng, Xin-Yan; Wang, Xiao-Yu; Shen, Yang-Hao; Lu, Xia; Wang, Tie-Shan

2017-05-01

Biosorption of heavy metal elements including radionuclides by microorganisms is a promising and effective method for the remediation of the contaminated places. The responses of live Saccharomyces cerevisiae in the toxic uranium solutions during the biosorption process and the mechanism of uranium biomineralization by cells were investigated in the present study. A novel experimental phenomenon that uranium concentrations have negative correlation with pH values and positive correlation with phosphate concentrations in the supernatant was observed, indicating that hydrogen ions, phosphate ions and uranyl ions were involved in the chernikovite precipitation actively. During the biosorption process, live cells desorb deposited uranium within the equilibrium state of biosorption system was reached and the phosphorus concentration increased gradually in the supernatant. These metabolic detoxification behaviours could significantly alleviate uranium toxicity and protect the survival of the cells better in the environment. The results of microscopic and spectroscopic analysis demonstrated that the precipitate on the cell surface was a type of uranium-phosphate compound in the form of a scale-like substance, and S. cerevisiae could transform the uranium precipitate into crystalline state-tetragonal chernikovite [H 2 (UO 2 ) 2 (PO 4 ) 2 ·8H 2 O]. Copyright © 2017 Elsevier Ltd. All rights reserved.

Oxidation of naturally reduced uranium in aquifer sediments by dissolved oxygen and its potential significance to uranium plume persistence

NASA Astrophysics Data System (ADS)

Davis, J. A.; Smith, R. L.; Bohlke, J. K.; Jemison, N.; Xiang, H.; Repert, D. A.; Yuan, X.; Williams, K. H.

2015-12-01

The occurrence of naturally reduced zones is common in alluvial aquifers in the western U.S.A. due to the burial of woody debris in flood plains. Such reduced zones are usually heterogeneously dispersed in these aquifers and characterized by high concentrations of organic carbon, reduced mineral phases, and reduced forms of metals, including uranium(IV). The persistence of high concentrations of dissolved uranium(VI) at uranium-contaminated aquifers on the Colorado Plateau has been attributed to slow oxidation of insoluble uranium(IV) mineral phases found in association with these reducing zones, although there is little understanding of the relative importance of various potential oxidants. Four field experiments were conducted within an alluvial aquifer adjacent to the Colorado River near Rifle, CO, wherein groundwater associated with the naturally reduced zones was pumped into a gas-impermeable tank, mixed with a conservative tracer (Br-), bubbled with a gas phase composed of 97% O2 and 3% CO2, and then returned to the subsurface in the same well from which it was withdrawn. Within minutes of re-injection of the oxygenated groundwater, dissolved uranium(VI) concentrations increased from less than 1 μM to greater than 2.5 μM, demonstrating that oxygen can be an important oxidant for uranium in such field systems if supplied to the naturally reduced zones. Dissolved Fe(II) concentrations decreased to the detection limit, but increases in sulfate could not be detected due to high background concentrations. Changes in nitrogen species concentrations were variable. The results contrast with other laboratory and field results in which oxygen was introduced to systems containing high concentrations of mackinawite (FeS), rather than the more crystalline iron sulfides found in aged, naturally reduced zones. The flux of oxygen to the naturally reduced zones in the alluvial aquifers occurs mainly through interactions between groundwater and gas phases at the water table. Seasonal variations of the water table at the Rifle, CO site may play an important role in introducing oxygen into the system. Although oxygen was introduced directly to the naturally reduced zones in these experiments, delivery of oxidants to the system may also be controlled by other oxidative pathways in which oxygen plays an indirect role.

Effect of pH and Fe/U ratio on the U(VI) removal rate by the synergistic effect of Fe(II) and O2

NASA Astrophysics Data System (ADS)

Fu, Yukui; Luo, Yingfeng; Fang, Qi; Xie, Yanpei; Wang, Zhihong; Zhu, Xiangyu

2018-02-01

As for the decommissioned uranium deposits of acid in-situ leaching, both of the concentrations of U(VI) and Fe(II) are relatively high in groundwater. In the presence of O2, the oxidation of Fe(II) into Fe(III) that forms Fe-hydroxides could effectively remove U(VI) in the forms of sorption or co-precipitation. In this process, pH condition and Fe content will have a significant effect on the U(VI) removal rate by the synergistic effect of Fe(II) and O2. In the present work, a series of batch experiments were carried out to investigate the effect of pH values and Fe/U mass ratio on the U(VI) removal rate by the synergistic effect of Fe(II) and O2. Experiment results show that the removal rate of U(VI) is mainly controlled by pH and secondly by Fe/U mass ratio. In the neutral conditions with pH at 7 and 8, the removal rate of U(VI) reaches up to 90% for all solutions with different initial Fe(II) concentrations. The optimal pH for the removal rate of U(VI) is above 7. In the acidic conditions with pH below 6, the effect of Fe/U mass ratio on the removal rate of U(VI) becomes more obvious and the optimal Fe/U mass ratio for U(VI) removal is 1:2.

Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry.

PubMed

Janot, Noémie; Lezama Pacheco, Juan S; Pham, Don Q; O'Brien, Timothy M; Hausladen, Debra; Noël, Vincent; Lallier, Florent; Maher, Kate; Fendorf, Scott; Williams, Kenneth H; Long, Philip E; Bargar, John R

2016-01-05

The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. We show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence.

Ultraviolet-B radiation mobilizes uranium from uranium-dissolved organic carbon complexes in aquatic systems, demonstrated by asymmetrical flow field-flow fractionation.

PubMed

Nehete, Sachin Vilas; Christensen, Terje; Salbu, Brit; Teien, Hans-Christian

2017-05-05

Humic substances have a tendency to form complexes with metal ions in aquatic medium, impacting the metal mobility, decreasing bioavailability and toxicity. Ultraviolet-B (UV-B) radiation exposure degrades the humic substance, changes their molecular weight distribution and their metal binding capacity in aquatic medium. In this study, we experimented the effect of UV-B radiation on the uranium complexed with fulvic acids and humic acids in a soft water system at different pH, uranium concentrations and radiant exposure. The concentration and distribution of uranium in a complexed form were investigated by asymmetrical flow field-flow fractionation coupled to multi detection technique (AsFlFFF-UV-ICP-MS). The major concentration of uranium present in complexes was primarily associated with average and higher molecular weight fulvic and humic acids components. The concentration of uranium in a complexed form increased with increasing fulvic and humic acid concentrations as well as pH of the solution. The higher molecular weight fraction of uranium was degraded due to the UV-B exposure, transforming about 50% of the uranium-dissolved organic carbon complexes into low molecular weight uranium species in complex form with organic ligands and/or free form. The result also suggests AsFlFFF-UV-ICP-MS to be an important separation and detection technique for understanding the interaction of radionuclides with dissolved organic matter, tracking size distribution changes during degradation of organic complexes for understanding mobility, bioavailability and ecosystem transfer of radionuclides as well as metals. Copyright © 2017 Elsevier B.V. All rights reserved.

Spectrophotometric study of the thorium-morin mixed-color system

USGS Publications Warehouse

Fletcher, M.H.; Milkey, R.G.

1956-01-01

A spectrophotometric study was made of the thoriummorin reaction to evaluate the suitability of morin as a reagent for the determination of trace amounts of thorium. At pH 2, the equilibrium constant for the reaction is 1 ?? 106, and a single complex having a thorium-morin ratio of 1 to 2 is formed. The complex shows maximum absorbance at a wave length of 410 m??, and its absorbance obeys Beer's law. The absorbance readings are highly reproducible, and the sensitivity is relatively high, an absorbance difference of 0.001 being equivalent to 0.007 ?? of ThO2 per sq. cm. The effects of acid, alcohol, and morin concentration, time, temperature, and age of the morin reagent as well as the behavior of morin with zirconium(IV), iron(III), aluminum(III), ytterbium(III), yttrium(III), uranium(VI), praseodymium(III), lead(II), lanthanum(III), and calcium(II) ions are discussed. A method is presented for the determination of thorium in pure solutions. Appropriate separations for the isolation of thorium may extend the usefulness of the method and permit the determination of trace amounts of thorium in complex materials.

Novel Sensor for the In Situ Measurement of Uranium Fluxes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hatfield, Kirk

2015-02-10

The goal of this project was to develop a sensor that incorporates the field-tested concepts of the passive flux meter to provide direct in situ measures of flux for uranium and groundwater in porous media. Measurable contaminant fluxes [J] are essentially the product of concentration [C] and groundwater flux or specific discharge [q ]. The sensor measures [J] and [q] by changes in contaminant and tracer amounts respectively on a sorbent. By using measurement rather than inference from static parameters, the sensor can directly advance conceptual and computational models for field scale simulations. The sensor was deployed in conjunction withmore » DOE in obtaining field-scale quantification of subsurface processes affecting uranium transport (e.g., advection) and transformation (e.g., uranium attenuation) at the Rifle IFRC Site in Rifle, Colorado. Project results have expanded our current understanding of how field-scale spatial variations in fluxes of uranium, groundwater and salient electron donor/acceptors are coupled to spatial variations in measured microbial biomass/community composition, effective field-scale uranium mass balances, attenuation, and stability. The coupling between uranium, various nutrients and micro flora can be used to estimate field-scale rates of uranium attenuation and field-scale transitions in microbial communities. This research focuses on uranium (VI), but the sensor principles and design are applicable to field-scale fate and transport of other radionuclides. Laboratory studies focused on sorbent selection and calibration, along with sensor development and validation under controlled conditions. Field studies were conducted at the Rifle IFRC Site in Rifle, Colorado. These studies were closely coordinated with existing SBR (formerly ERSP) projects to complement data collection. Small field tests were conducted during the first two years that focused on evaluating field-scale deployment procedures and validating sensor performance under controlled field conditions. In the third and fourth year a suite of larger field studies were conducted. For these studies, the uranium flux sensor was used with uranium speciation measurements and molecular-biological tools to characterize microbial community and active biomass at synonymous wells distributed in a large grid. These field efforts quantified spatial changes in uranium flux and field-scale rates of uranium attenuation (ambient and stimulated), uranium stability, and quantitatively assessed how fluxes and effective reaction rates were coupled to spatial variations in microbial community and active biomass. Analyses of data from these field experiments were used to generate estimates of Monod kinetic parameters that are ‘effective’ in nature and optimal for modeling uranium fate and transport at the field-scale. This project provided the opportunity to develop the first sensor that provides direct measures of both uranium (VI) and groundwater flux. A multidisciplinary team was assembled to include two geochemists, a microbiologist, and two quantitative contaminant hydrologists. Now that the project is complete, the sensor can be deployed at DOE sites to evaluate field-scale uranium attenuation, source behavior, the efficacy of remediation, and off-site risk. Because the sensor requires no power, it can be deployed at remote sites for periods of days to months. The fundamental science derived from this project can be used to advance the development of predictive models for various transport and attenuation processes in aquifers. Proper development of these models is critical for long-term stewardship of contaminated sites in the context of predicting uranium source behavior, remediation performance, and off-site risk.« less

Plasma-induced grafting of acrylic acid on bentonite for the removal of U(VI) from aqueous solution

NASA Astrophysics Data System (ADS)

Hongshan, ZHU; Shengxia, DUAN; Lei, CHEN; Ahmed, ALSAEDI; Tasawar, HAYAT; Jiaxing, LI

2017-11-01

Fabrication of reusable adsorbents with satisfactory adsorption capacity and using environment-friendly preparation processes is required for the environment-related applications. In this study, acrylic acid (AA) was grafted onto bentonite (BT) to generate an AA-graft-BT (AA-g-BT) composite using a plasma-induced grafting technique considered to be an environment-friendly method. The as-prepared composite was characterized by scanning electron microscopy, x-ray powder diffraction, thermal gravity analysis, Fourier transform infrared spectroscopy and Barrett-Emmett-Teller analysis, demonstrating the successful grafting of AA onto BT. In addition, the removal of uranium(VI) (U(VI)) from contaminated aqueous solutions was examined using the as-prepared composite. The influencing factors, including contact time, pH value, ionic strength, temperature, and initial concentration, for the removal of U(VI) were investigated by batch experiments. The experimental process fitted best with the pseudo-second-order kinetic and the Langmuir models. Moreover, thermodynamic investigation revealed a spontaneous and endothermic process. Compared with previous adsorbents, AA-g-BT has potential practical applications in treating U(VI)-contaminated solutions.

Influence of calcite and dissolved calcium on uranium(VI) sorption to a hanford subsurface sediment.

PubMed

Dong, Wenming; Ball, William P; Liu, Chongxuan; Wang, Zheming; Stone, Alan T; Bai, Jing; Zachara, John M

2005-10-15

The influence of calcite and dissolved calcium on U(VI) adsorption was investigated using a calcite-containing sandy silt/clay sediment from the U. S. Department of Energy Hanford site. U(VI) adsorption to sediment, treated sediment, and sediment size fractions was studied in solutions that both had and had not been preequilibrated with calcite, at initial [U(VI)] = 10(-7)-10(-5) mol/L and final pH = 6.0-10.0. Kinetic and reversibility studies (pH 8.4) showed rapid sorption (30 min), with reasonable reversibility in the 3-day reaction time. Sorption from solutions equilibrated with calcite showed maximum U(VI) adsorption at pH 8.4 +/- 0.1. In contrast, calcium-free systems showed the greatest adsorption at pH 6.0-7.2. At pH > 8.4, U(VI) adsorption was identical from calcium-free and calcium-containing solutions. For calcite-presaturated systems, both speciation calculations and laser-induced fluorescence spectroscopic analyses indicated that aqueous U(VI) was increasingly dominated by Ca2UO2(CO3)3(0)(aq) at pH < 8.4 and thatformation of Ca2UO2(CO3)3(0)(aq) is what suppresses U(VI) adsorption. Above pH 8.4, aqueous U(VI) speciation was dominated by UO2(CO3)3(4-) in all solutions. Finally, results also showed that U(VI) adsorption was additive in regard to size fraction but not in regard to mineral mass: Carbonate minerals may have blocked U(VI) access to surfaces of higher sorption affinity.

Phosphate-Induced Immobilization of Uranium in Hanford Sediments.

PubMed

Pan, Zezhen; Giammar, Daniel E; Mehta, Vrajesh; Troyer, Lyndsay D; Catalano, Jeffrey G; Wang, Zheming

2016-12-20

Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred only at high initial U(VI) (>25 μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.

Phosphate-Induced Immobilization of Uranium in Hanford Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Zezhen; Giammar, Daniel E.; Mehta, Vrajesh

2016-12-20

Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred onlymore » at high initial U(VI) (>25 μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.« less

Phosphate-Induced Immobilization of Uranium in Hanford Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Zezhen; Giammar, Daniel E.; Mehta, Vrajesh

2016-12-20

Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred onlymore » at high initial U(VI) (>25μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.« less

Bacterial community succession during in situ uranium bioremediation: spatial similarities along controlled flow paths.

PubMed

Hwang, Chiachi; Wu, Weimin; Gentry, Terry J; Carley, Jack; Corbin, Gail A; Carroll, Sue L; Watson, David B; Jardine, Phil M; Zhou, Jizhong; Criddle, Craig S; Fields, Matthew W

2009-01-01

Bacterial community succession was investigated in a field-scale subsurface reactor formed by a series of wells that received weekly ethanol additions to re-circulating groundwater. Ethanol additions stimulated denitrification, metal reduction, sulfate reduction and U(VI) reduction to sparingly soluble U(IV). Clone libraries of SSU rRNA gene sequences from groundwater samples enabled tracking of spatial and temporal changes over a 1.5-year period. Analyses showed that the communities changed in a manner consistent with geochemical variations that occurred along temporal and spatial scales. Canonical correspondence analysis revealed that the levels of nitrate, uranium, sulfide, sulfate and ethanol were strongly correlated with particular bacterial populations. As sulfate and U(VI) levels declined, sequences representative of sulfate reducers and metal reducers were detected at high levels. Ultimately, sequences associated with sulfate-reducing populations predominated, and sulfate levels declined as U(VI) remained at low levels. When engineering controls were compared with the population variation through canonical ordination, changes could be related to dissolved oxygen control and ethanol addition. The data also indicated that the indigenous populations responded differently to stimulation for bioreduction; however, the two biostimulated communities became more similar after different transitions in an idiosyncratic manner. The strong associations between particular environmental variables and certain populations provide insight into the establishment of practical and successful remediation strategies in radionuclide-contaminated environments with respect to engineering controls and microbial ecology.

Removal of uranium from aqueous solution by a low cost and high-efficient adsorbent

NASA Astrophysics Data System (ADS)

Liu, Yun-Hai; Wang, You-Qun; Zhang, Zhi-Bin; Cao, Xiao-Hong; Nie, Wen-Bin; Li, Qin; Hua, Rong

2013-05-01

In this study, a low-cost and high-efficient carbonaceous adsorbent (HTC-COOH) with carboxylic groups was developed for U(VI) removal from aqueous solution compared with the pristine hydrothermal carbon (HTC). The structure and chemical properties of resultant adsorbents were characterized by Scanning electron microscope (SEM), N2 adsorption-desorption, Fourier transform-infrared spectra (FT-IR) and acid-base titration. The key factors (solution pH, contact time, initial U(VI) concentrations and temperature) affected the adsorption of U(VI) on adsorbents were investigated using batch experiments. The adsorption of U(VI) on HTC and HTC-COOH was pH-dependent, and increased with temperature and initial ion concentration. The adsorption equilibrium of U(VI) on adsorbents was well defined by the Langmuir isothermal equation, and the monolayer adsorption capacity of HTC-COOH was found to be 205.8 mg/g. The kinetics of adsorption was very in accordance with the pseudo-second-order rate model. The adsorption processes of U(VI) on HTC and HTC-COOH were endothermic and spontaneous in nature according to the thermodynamics of adsorption. Furthermore, HTC-COOH could selectively adsorption of U(VI) in aqueous solution containing co-existing ions (Mg2+, Co2+, Ni2+, Zn2+ and Mn2+). From the results of the experiments, it is found that the HTC-COOH is a potential adsorbent for effective removal of U(VI) from polluted water.

Preparation of graphene oxide-manganese dioxide for highly efficient adsorption and separation of Th(IV)/U(VI).

PubMed

Pan, Ning; Li, Long; Ding, Jie; Li, Shengke; Wang, Ruibing; Jin, Yongdong; Wang, Xiangke; Xia, Chuanqin

2016-05-15

Manganese dioxide decorated graphene oxide (GOM) was prepared via fixation of crystallographic MnO2 (α, γ) on the surface of graphene oxide (GO) and was explored as an adsorbent material for simultaneous removal of thorium/uranium ions from aqueous solutions. In single component systems (Th(IV) or U(VI)), the α-GOM2 (the weight ratio of GO/α-MnO2 of 2) exhibited higher maximum adsorption capacities toward both Th(IV) (497.5mg/g) and U(VI) (185.2 mg/g) than those of GO. In the binary component system (Th(IV)/U(VI)), the saturated adsorption capacity of Th(IV) (408.8 mg/g)/U(VI) (66.8 mg/g) on α-GOM2 was also higher than those on GO. Based on the analysis of various data, it was proposed that the adsorption process may involve four types of molecular interactions including coordination, electrostatic interaction, cation-pi interaction, and Lewis acid-base interaction between Th(IV)/U(VI) and α-GOM2. Finally, the Th(IV)/U(VI) ions on α-GOM2 can be separated by a two-stage desorption process with Na2CO3/EDTA. Those results displayed that the α-GOM2 may be utilized as an potential adsorbent for removing and separating Th(IV)/U(VI) ions from aqueous solutions. Copyright © 2016 Elsevier B.V. All rights reserved.

Structure, equilibrium and ligand exchange dynamics in the binary and ternary dioxouranium(VI)-ethylenediamine-N,N'-diacetic acid-fluoride system: A potentiometric, NMR and X-ray crystallographic study.

PubMed

Palladino, Giuseppe; Szabó, Zoltán; Fischer, Andreas; Grenthe, Ingmar

2006-11-21

The structure, thermodynamics and kinetics of the binary and ternary uranium(VI)-ethylenediamine-N,N'-diacetate (in the following denoted EDDA) fluoride systems have been studied using potentiometry, 1H, 19F NMR spectroscopy and X-ray diffraction. The UO2(2+)-EDDA system could be studied up to -log[H3O+] = 3.4 where the formation of two binary complexes UO2(EDDA)(aq) and UO2(H3EDDA)3+ were identified, with equilibrium constants logbeta(UO2EDDA) = 11.63 +/- 0.02 and logbeta(UO2H3EDDA3+) = 1.77 +/- 0.04, respectively. In the ternary system the complexes UO2(EDDA)F-, UO2(EDDA)(OH)- and (UO2)2(mu-OH)2(HEDDA)2F2(aq) were identified; the latter through 19F NMR. 1H NMR spectra indicate that the EDDA ligand is chelate bonded in UO2(EDDA)(aq), UO2(EDDA)F- and UO2(EDDA)(OH)- while only one carboxylate group is coordinated in UO2(H3EDDA)3+. The rate and mechanism of the fluoride exchange between UO2(EDDA)F- and free fluoride was studied by 19F NMR spectroscopy. Three reactions contribute to the exchange; (i) site exchange between UO2(EDDA)F- and free fluoride without any net chemical exchange, (ii) replacement of the coordinated fluoride with OH- and (iii) the self dissociation of the coordinated fluoride forming UO2(EDDA)(aq); these reactions seem to follow associative mechanisms. (1)H NMR spectra show that the exchange between the free and chelate bonded EDDA is slow and consists of several steps, protonation/deprotonation and chelate ring opening/ring closure, the mechanism cannot be elucidated from the available data. The structure (UO2)2(EDDA)2(mu-H2EDDA) was determined by single crystal X-ray diffraction and contains two UO2(EDDA) units with tetracoordinated EDDA linked by H2EDDA in the "zwitterion" form, coordinated through a single carboxylate oxygen from each end to the two uranium atoms. The geometry of the complexes indicates that there is no geometric constraint for an associative ligand substitution mechanism.

Uranium fate in wetland mesocosms: Effects of plants at two ...

EPA Pesticide Factsheets

Small-scale continuous flow wetland mesocosms (~0.8 L) were used to evaluate how plant roots under different iron loadings affect uranium (U) mobility. When significant concentrations of ferrous iron (Fe) were present at circumneutral pH values, U concentrations in root exposed sediments were an order of magnitude greater than concentrations in root excluded sediments. Micro X-ray absorption near-edge structure (µ-XANES) spectroscopy indicated that U was associated with the plant roots primarily as U(VI) or U(V), with limited evidence of U(IV). Micro X-ray fluorescence (µ-XRF) of plant roots suggested that for high iron loading at circumneutral pH, U was co-located with Fe, perhaps co-precipitated with root Fe plaques, while for low iron loading at a pH of ~4 the correlation between U and Fe was not significant, consistent with previous observations of U associated with organic matter. Quantitative PCR analyses indicated that the root exposed sediments also contained elevated numbers of Geobacter spp., which are likely associated with enhanced iron cycling, but may also reduce mobile U(VI) to less mobile U(IV) species. There are significant uncertainties regarding the environmental fate of uranium (U) and efforts to minimize U exposures require understanding of its mobility in environmental systems. Much research has focused on sequestering U as solids within groundwater aquifers, where localized risks can be controlled.1 Subsurface sequestration limits t

A Comparison of Naturally-Occurring and Artificially Stimulated Uranium(VI) Bioreduction in Sediment from a Field-scale Experiment in Rifle, CO

NASA Astrophysics Data System (ADS)

Campbell, K. M.; Williams, K. H.; Lesher, E.; Davis, J. A.; Long, P. E.

2007-12-01

Long-term remediation of uranium (U)-contaminated groundwater poses one of the greatest challenges in the clean-up of impacted sites. One solution is to reduce dissolved U(VI) to insoluble U(IV) precipitates by stimulating indigenous metal reducing bacterial populations in situ. Contamination from a former U mine tailings repository (Rifle, CO) provides a research site to study the efficacy of biostimulated U(VI) reduction at the field scale. Several cores were drilled in June 2007 across a region of naturally-occurring U(VI) bioreduction. The cores represent a cross section of sediment that ranges from minimally reducing to highly reducing. Anaerobic sediment samples from the cores were analyzed for labile U(VI) content by carbonate extraction in anoxic conditions (pH 9.4, 14 mM NaHCO3, 2.8 mM Na2CO¬3). A subset of the same core sections were dried and oxidized by exposure to air for 2 weeks. The carbonate extraction was repeated, and the amount of U(IV) present in the anaerobic sample was calculated by difference between the anoxic and oxidized extractions. An acid extraction was also performed on the oxidized sediments to compare the carbonate extractable and the acid extractable U fractions. The highest U concentrations were found in the highly bioreduced sediment, with the majority of U present as U(IV) (66-92%). The regions of highest bioreduction also correspond to elevated concentrations of solid phase organic carbon, suggesting that natural bioreduction is stimulated by zones of increased organic carbon content. The same field site was then used for an artificially stimulated bioreduction experiment, where the indigenous bacterial community was stimulated by injecting acetate upgradient of the core collection location. Carbonate and acid extractions were performed on core samples taken after the completion of the acetate injection. This work evaluates the composition of the sediment before and after biostimulation as a way of directly comparing the extent of natural U(VI) bioreduction to acetate-stimulated bioreduction in order to facilitate the design of a more effective bioremediation strategy for this site.

Subcellular distribution of uranium in the roots of Spirodela punctata and surface interactions

NASA Astrophysics Data System (ADS)

Nie, Xiaoqin; Dong, Faqin; Liu, Ning; Liu, Mingxue; Zhang, Dong; Kang, Wu; Sun, Shiyong; Zhang, Wei; Yang, Jie

2015-08-01

The subcellular distribution of uranium in roots of Spirodela punctata (duckweed) and the process of surface interaction were studied upon exposure to U (0, 5-200 mg/L) at pH 5. The concentration of uranium in each subcelluar fraction increased significantly with increasing solution U level, after 200 mg/L uranium solution treatment 120 h, the proportion of uranium concentration approximate as 8:2:1 in the cell wall organelle and cytosol fractions of roots of S. punctata. OM SEM and EDS showed after 5-200 mg/L U treatment 4-24 h, some intracellular fluid released from the root cells, after 100 mg/L U treatment 48 h, the particles including 35% Fe (wt%) and other organic matters such as EPS released from the cells, most of the uranium bound onto the root surface and contacted with phosphorus ligands and formed as nano-scales U-P lamellar crystal, similar crystal has been found in the cell wall and organelle fractions after 50 mg/L U treatment 120 h. FTIR and XPS analyses result indicates the uranium changed the band position and shapes of phosphate group, and the region of characteristic peak belongs to U(VI) and U(IV) were also observed.

Bioreduction and immobilization of uranium in situ: a case study at a USA Department of Energy radioactive waste site, Oak Ridge, Tennessee

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Weimin; Carley, Jack M; Watson, David B

Bioremediation of uranium contaminated groundwater was tested by delivery of ethanol as an electron donor source to stimulate indigenous microbial bioactivity for reduction and immobilization of uranium in situ, followed by tests of stability of uranium sequestration in the bioreduced area via delivery of dissolved oxygen or nitrate at the US Department of energy's Integrated Field Research Challenge site located at Oak Ridge, Tennessee, USA. After long term treatment that spanned years, uranium in groundwater was reduced from 40-60 mg {center_dot} L{sup -1} to <0.03 mg {center_dot} L{sup -1}, below the USA EPA standard for drinking water. The bioreduced uraniummore » was stable under anaerobic or anoxic conditions, but addition of DO and nitrate to the bioreduced zone caused U remobilization. The change in the microbial community and functional microorganisms related to uranium reduction and oxidation were characterized. The delivery of ethanol as electron donor stimulated the activities of indigenous microorganisms for reduction of U(VI) to U(IV). Results indicated that the immobilized U could be partially remobilized by D0 and nitrate via microbial activity. An anoxic environmental condition without nitrate is essential to maintain the stability of bioreduced uranium.« less

DISSOLUTION OF ZIRCONIUM-CONTAINING FUEL ELEMENTS

DOEpatents

Horn, F.L.

1961-12-12

Uranium is recovered from spent uranium fuel elements containing or clad with zirconium. These fuel elements are placed in an anhydrous solution of hydrogen fluoride and nitrogen dioxide. Within this system uranium forms a soluble complex and zirconium forms an insoluble complex. The uranium can then be separated, treated, and removed from solution as uranium hexafluoride. (AEC)

Anion-exchange high-performance liquid chromatography of water-soluble chromium (VI) and chromium (III) complexes in biological materials.

PubMed

Suzuki, Y

1987-04-10

A high-performance anion-exchange liquid chromatograph coupled to visible-range (370 nm) and UV (280 nm) detectors and an atomic-absorption spectrometer allowed the rapid determination of CrVI and/or complexes of CrIII in rat plasma, erythrocyte lysate and liver supernatant treated with CrVI or CrIII in vitro. CrVI in the eluates was determined using both the visible-range detector and atomic-absorption spectrometer (AAS). The detection limits of CrVI in standard solutions using these methods were 2 and 5 ng (signal-to-noise ratio = 2), respectively. Separations of the biological components and of CrIII complexes were monitored by UV and AAS analyses, respectively. Time-related decreases of CrVI accompanied by increases in CrIII complexes were observed, indicating the reduction of CrVI by some of the biological components. The reduction rates were considerably higher in the liver supernatant and erythrocyte lysate than in the plasma. These results indicate that the anion-exchange high-performance liquid chromatographic system is useful for simultaneous determination of CrVI and CrIII complexes in biological materials.

Reaction-Based Reactive Transport Modeling of Iron Reduction and Uranium Immobilization at Area 2 of the NABIR Field Research Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burgos, W.D.

2009-09-02

This report summarizes research conducted in conjunction with a project entitled “Reaction-Based Reactive Transport Modeling of Iron Reduction and Uranium Immobilization at Area 2 of the NABIR Field Research Center”, which was funded through the Integrative Studies Element of the former NABIR Program (now the Environmental Remediation Sciences Program) within the Office of Biological and Environmental Research. Dr. William Burgos (The Pennsylvania State University) was the overall PI/PD for the project, which included Brian Dempsey (Penn State), Gour-Tsyh (George) Yeh (Central Florida University), and Eric Roden (formerly at The University of Alabama, now at the University of Wisconsin) as separately-fundedmore » co-PIs. The project focused on development of a mechanistic understanding and quantitative models of coupled Fe(III)/U(VI) reduction in FRC Area 2 sediments. The work builds on our previous studies of microbial Fe(III) and U(VI) reduction, and was directly aligned with the Scheibe et al. ORNL FRC Field Project at Area 2.« less

Emergence of Uranium as a Distinct Metal Center for Building Intrinsic X-ray Scintillators.

PubMed

Wang, Yaxing; Yin, Xuemiao; Liu, Wei; Xie, Jian; Chen, Junfeng; Silver, Mark A; Sheng, Daopeng; Chen, Lanhua; Diwu, Juan; Liu, Ning; Chai, Zhifang; Albrecht-Schmitt, Thomas E; Wang, Shuao

2018-06-25

The combination of high atomic number and high oxidation state in U VI materials gives rise to both high X-ray attenuation efficiency and intense green luminescence originating from ligand-to-metal charge transfer. These two features suggest that U VI materials might act as superior X-ray scintillators, but this postulate has remained substantially untested. Now the first observation of intense X-ray scintillation in a uranyl-organic framework (SCU-9) that is observable by the naked eye is reported. Combining the advantage in minimizing the non-radiative relaxation during the X-ray excitation process over those of inorganic salts of uranium, SCU-9 exhibits a very efficient X-ray to green light luminescence conversion. The luminescence intensity shows an essentially linear correlation with the received X-ray intensity, and is comparable with that of commercially available CsI:Tl. SCU-9 possesses an improved X-ray attenuation efficiency (E>20 keV) as well as enhanced radiation resistance and decreased hygroscopy compared to CsI:Tl. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Izbicki, John A.; Wright, Michael T.; Seymour, Whitney A.

Hexavalent chromium, Cr(VI), in 918 wells sampled throughout California between 2004 and 2012 by the Groundwater Ambient Monitoring and Assessment Program—Priority Basin Project (GAMA—PBP) ranged from less than the study reporting limit (SRL) of 1 microgram per liter (μg/L) to 32 μg/L. Statewide, Cr(VI) was reported in 31 percent of sampled wells and equaled or exceeded the recently established (2014) California Maximum Contaminant Level (MCL) for Cr(VI) of 10 μg/L in 4 percent of sampled wells. Cr(VI) data collected for regulatory purposes overestimate Cr(VI) occurrence. Ninety percent of chromium was present as Cr(VI), which was detected more frequently and atmore » higher concentrations in alkaline (pH > 8), oxic water, and more frequently in agricultural and urban land uses compared to native land uses. Chemical, isotopic (tritium and carbon-14), and noble-gas data show high Cr(VI) in water from wells in alluvial aquifers in the southern California deserts result from long groundwater-residence times and geochemical reactions such as silicate weathering that increase pH, while oxic conditions persist. High Cr(VI) in water from wells in alluvial aquifers along the west-side of the Central Valley results from high-chromium abundance in source rock eroded to form those aquifers, and areal recharge processes (including irrigation return) that mobilize chromium from the unsaturated zone. Cr(VI) co-occurred with oxyanions having similar chemistry, including vanadium, selenium, and uranium. Cr(VI) was positively correlated with nitrate, consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return.« less

Thermodynamic Insight into the Solvation and Complexation Behavior of U(VI) in Ionic Liquid: Binding of CMPO with U(VI) Studied by Optical Spectroscopy and Calorimetry.

PubMed

Wu, Qi; Sun, Taoxiang; Meng, Xianghai; Chen, Jing; Xu, Chao

2017-03-06

The complexation of U(VI) with octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, denoted as L) in ionic liquid (IL) C 4 mimNTf 2 was investigated by UV-vis absorption spectrophotometry and isothermal titration calorimetry. Spectro-photometric titration suggests that three successive complexes, UO 2 L j 2+ (j = 1-3), formed both in "dry" (water content < 250 ppm) and "wet" (water content ≈ 12 500 ppm) ionic liquid. However, the thermodynamic parameters are distinctly different in the two ILs. In dry IL, the complexation strength between CMPO and U(VI) is much stronger, with stability constants of the respective complexes more than 1 order of magnitude higher than that in wet IL. Energetically, the complexation of U(VI) with CMPO in dry IL is mainly driven by negative enthalpies. In contrast, the complexation in wet IL is overwhelmingly driven by highly positive entropies as a result of the release of a large amount of water molecules from the solvation sphere of U(VI). Moreover, comparisons between the fitted absorption spectra of complexes in wet IL and that of extractive samples from solvent extraction have identified the speciation involved in the extraction of U(VI) by CMPO in ionic liquid. The results from this study not only offer a thermodynamic insight into the complexation behavior of U(VI) with CMPO in IL but also provide valuable information for understanding the extraction behavior in the corresponding solvent extraction system.

Cr(VI) Occurrence and Geochemistry in Water From Public-Supply Wells in California

DOE PAGES

Izbicki, John A.; Wright, Michael T.; Seymour, Whitney A.; ...

2015-08-18

Hexavalent chromium, Cr(VI), in 918 wells sampled throughout California between 2004 and 2012 by the Groundwater Ambient Monitoring and Assessment Program—Priority Basin Project (GAMA—PBP) ranged from less than the study reporting limit (SRL) of 1 microgram per liter (μg/L) to 32 μg/L. Statewide, Cr(VI) was reported in 31 percent of sampled wells and equaled or exceeded the recently established (2014) California Maximum Contaminant Level (MCL) for Cr(VI) of 10 μg/L in 4 percent of sampled wells. Cr(VI) data collected for regulatory purposes overestimate Cr(VI) occurrence. Ninety percent of chromium was present as Cr(VI), which was detected more frequently and atmore » higher concentrations in alkaline (pH > 8), oxic water, and more frequently in agricultural and urban land uses compared to native land uses. Chemical, isotopic (tritium and carbon-14), and noble-gas data show high Cr(VI) in water from wells in alluvial aquifers in the southern California deserts result from long groundwater-residence times and geochemical reactions such as silicate weathering that increase pH, while oxic conditions persist. High Cr(VI) in water from wells in alluvial aquifers along the west-side of the Central Valley results from high-chromium abundance in source rock eroded to form those aquifers, and areal recharge processes (including irrigation return) that mobilize chromium from the unsaturated zone. Cr(VI) co-occurred with oxyanions having similar chemistry, including vanadium, selenium, and uranium. Cr(VI) was positively correlated with nitrate, consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return.« less

Cr(VI) occurrence and geochemistry in water from public-supply wells in California

USGS Publications Warehouse

Izbicki, John; Wright, Michael; Seymour, Whitney A.; McCleskey, R. Blaine; Fram, Miranda S.; Belitz, Kenneth; Esser, Bradley K.

2015-01-01

Hexavalent chromium, Cr(VI), in 918 wells sampled throughout California between 2004 and 2012 by the Groundwater Ambient Monitoring and Assessment-Priority Basin Project (GAMA-PBP) ranged from less than the study reporting limit of 1 microgram per liter (μg/L) to 32 μg/L. Statewide, Cr(VI) was reported in 31 percent of wells and equaled or exceeded the recently established (2014) California Maximum Contaminant Level (MCL) for Cr(VI) of 10 μg/L in 4 percent of wells. Cr(VI) data collected for regulatory purposes overestimated Cr(VI) occurrence compared to spatially-distributed GAMA-PBP data. Ninety percent of chromium was present as Cr(VI), which was detected more frequently and at higher concentrations in alkaline (pH ≥ 8), oxic water; and more frequently in agricultural and urban land uses compared to native land uses. Chemical, isotopic (tritium and carbon-14), and noble-gas data show high Cr(VI) in water from wells in alluvial aquifers in the southern California deserts result from long groundwater-residence times and geochemical reactions such as silicate weathering that increase pH, while oxic conditions persist. High Cr(VI) in water from wells in alluvial aquifers along the west-side of the Central Valley results from high-chromium in source rock eroded to form those aquifers, and areal recharge processes (including irrigation return) that can mobilize chromium from the unsaturated zone. Cr(VI) co-occurred with oxyanions having similar chemistry, including vanadium, selenium, and uranium. Cr(VI) was positively correlated with nitrate, consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return.

Reactivity of nitrido complexes of ruthenium(VI), osmium(VI), and manganese(V) bearing Schiff base and simple anionic ligands.

PubMed

Man, Wai-Lun; Lam, William W Y; Lau, Tai-Chu

2014-02-18

Nitrido complexes (M≡N) may be key intermediates in chemical and biological nitrogen fixation and serve as useful reagents for nitrogenation of organic compounds. Osmium(VI) nitrido complexes bearing 2,2':6',2″-terpyridine (terpy), 2,2'-bipyridine (bpy), or hydrotris(1-pyrazolyl)borate anion (Tp) ligands are highly electrophilic: they can react with a variety of nucleophiles to generate novel osmium(IV)/(V) complexes. This Account describes our recent results studying the reactivity of nitridocomplexes of ruthenium(VI), osmium(VI), and manganese(V) that bear Schiff bases and other simple anionic ligands. We demonstrate that these nitrido complexes exhibit rich chemical reactivity. They react with various nucleophiles, activate C-H bonds, undergo N···N coupling, catalyze the oxidation of organic compounds, and show anticancer activities. Ruthenium(VI) nitrido complexes bearing Schiff base ligands, such as [Ru(VI)(N)(salchda)(CH3OH)](+) (salchda = N,N'-bis(salicylidene)o-cyclohexyldiamine dianion), are highly electrophilic. This complex reacts readily at ambient conditions with a variety of nucleophiles at rates that are much faster than similar reactions using Os(VI)≡N. This complex also carries out unique reactions, including the direct aziridination of alkenes, C-H bond activation of alkanes and C-N bond cleavage of anilines. The addition of ligands such as pyridine can enhance the reactivity of [Ru(VI)(N)(salchda)(CH3OH)](+). Therefore researchers can tune the reactivity of Ru≡N by adding a ligand L trans to nitride: L-Ru≡N. Moreover, the addition of various nucleophiles (Nu) to Ru(VI)≡N initially generate the ruthenium(IV) imido species Ru(IV)-N(Nu), a new class of hydrogen-atom transfer (HAT) reagents. Nucleophiles also readily add to coordinated Schiff base ligands in Os(VI)≡N and Ru(VI)≡N complexes. These additions are often stereospecific, suggesting that the nitrido ligand has a directing effect on the incoming nucleophile. M≡N is also a potential platform for the design of new oxidation catalysts. For example, [Os(VI)(N)Cl4](-) catalyzes the oxidation of alkanes by a variety of oxidants, and the addition of Lewis acids greatly accelerates these reactions. [Mn(V)(N)(CN)4]2(-) is another highly efficient oxidation catalyst, which facilitates the epoxidation of alkenes and the oxidation of alcohols to carbonyl compounds using H2O2. Finally, M≡N can potentially bind to and exert various effects on biomolecules. For example, a number of Os(VI)≡N complexes exhibit novel anticancer properties, which may be related to their ability to bind to DNA or other biomolecules.

Selective Extraction of Uranium from Liquid or Supercritical Carbon Dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farawila, Anne F.; O'Hara, Matthew J.; Wai, Chien M.

2012-07-31

Current liquid-liquid extraction processes used in recycling irradiated nuclear fuel rely on (1) strong nitric acid to dissolve uranium oxide fuel, and (2) the use of aliphatic hydrocarbons as a diluent in formulating the solvent used to extract uranium. The nitric acid dissolution process is not selective. It dissolves virtually the entire fuel meat which complicates the uranium extraction process. In addition, a solvent washing process is used to remove TBP degradation products, which adds complexity to the recycling plant and increases the overall plant footprint and cost. A liquid or supercritical carbon dioxide (l/sc -CO2) system was designed tomore » mitigate these problems. Indeed, TBP nitric acid complexes are highly soluble in l/sc -CO2 and are capable of extracting uranium directly from UO2, UO3 and U3O8 powders. This eliminates the need for total acid dissolution of the irradiated fuel. Furthermore, since CO2 is easily recycled by evaporation at room temperature and pressure, it eliminates the complex solvent washing process. In this report, we demonstrate: (1) A reprocessing scheme starting with the selective extraction of uranium from solid uranium oxides into a TBP-HNO3 loaded Sc-CO2 phase, (2) Back extraction of uranium into an aqueous phase, and (3) Conversion of recovered purified uranium into uranium oxide. The purified uranium product from step 3 can be disposed of as low level waste, or mixed with enriched uranium for use in a reactor for another fuel cycle. After an introduction on the concept and properties of supercritical fluids, we first report the characterization of the different oxides used for this project. Our extraction system and our online monitoring capability using UV-Vis absorbance spectroscopy directly in sc-CO2 is then presented. Next, the uranium extraction efficiencies and kinetics is demonstrated for different oxides and under different physical and chemical conditions: l/sc -CO2 pressure and temperature, TBP/HNO3 complex used, reductant or complexant used for selectivity, and ionic liquids used as supportive media. To complete the extraction and recovery cycle, we then demonstrate uranium back extraction from the TBP loaded sc-CO2 phase into an aqueous phase and the characterization of the uranium complex formed at the end of this process. Another aspect of this project was to limit proliferation risks by either co-extracting uranium and plutonium, or by leaving plutonium behind by selectively extracting uranium. We report that the former is easily achieved, since plutonium is in the tetravalent or hexavalent oxidation state in the oxidizing environment created by the TBP-nitric acid complex, and is therefore co-extracted. The latter is more challenging, as a reductant or complexant to plutonium has to be used to selectively extract uranium. After undertaking experiments on different reducing or complexing systems (e.g., AcetoHydroxamic Acid (AHA), Fe(II), ascorbic acid), oxalic acid was chosen as it can complex tetravalent actinides (Pu, Np, Th) in the aqueous phase while allowing the extraction of hexavalent uranium in the sc-CO2 phase. Finally, we show results using an alternative media to commonly used aqueous phases: ionic liquids. We show the dissolution of uranium in ionic liquids and its extraction using sc-CO2 with and without the presence of AHA. The possible separation of trivalent actinides from uranium is also demonstrated in ionic liquids using neodymium as a surrogate and diglycolamides as the extractant.« less

RECOVERY OF URANIUM FROM PITCHBLENDE

DOEpatents

Ruehle, A.E.

1958-06-24

The decontamination of uranium from molybdenum is described. When acid solutions containing uranyl nitrate are contacted with ether for the purpose of extracting the uranium values, complex molybdenum compounds are coextracted with the uranium and also again back-extracted from the ether with the uranium. This invention provides a process for extracting uranium in which coextraction of molybdenum is avoided. It has been found that polyhydric alcohols form complexes with molybdenum which are preferentially water-soluble are taken up by the ether extractant to only a very minor degree. The preferred embodiment of the process uses mannitol, sorbitol or a mixture of the two as the complexing agent.

Anaerobic U(IV) Bio-oxidation and the Resultant Remobilization of Uranium in Contaminated Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coates, John D.

2005-06-01

A proposed strategy for the remediation of uranium (U) contaminated sites is based on immobilizing U by reducing the oxidized soluble U, U(VI), to form a reduced insoluble end product, U(IV). Due to the use of nitric acid in the processing of nuclear fuels, nitrate is often a co-contaminant found in many of the environments contaminated with uranium. Recent studies indicate that nitrate inhibits U(VI) reduction in sediment slurries. However, the mechanism responsible for the apparent inhibition of U(VI) reduction is unknown, i.e. preferential utilization of nitrate as an electron acceptor, direct biological oxidation of U(IV) coupled to nitrate reduction,more » and/or abiotic oxidation by intermediates of nitrate reduction. Recent studies indicates that direct biological oxidation of U(IV) coupled to nitrate reduction may exist in situ, however, to date no organisms have been identified that can grow by this metabolism. In an effort to evaluate the potential for nitrate-dependent bio-oxidation of U(IV) in anaerobic sedimentary environments, we have initiated the enumeration of nitrate-dependent U(IV) oxidizing bacteria. Sediments, soils, and groundwater from uranium (U) contaminated sites, including subsurface sediments from the NABIR Field Research Center (FRC), as well as uncontaminated sites, including subsurface sediments from the NABIR FRC and Longhorn Army Ammunition Plant, Texas, lake sediments, and agricultural field soil, sites served as the inoculum source. Enumeration of the nitrate-dependent U(IV) oxidizing microbial population in sedimentary environments by most probable number technique have revealed sedimentary microbial populations ranging from 9.3 x 101 - 2.4 x 103 cells (g sediment)-1 in both contaminated and uncontaminated sites. Interestingly uncontaminated subsurface sediments (NABIR FRC Background core FB618 and Longhorn Texas Core BH2-18) both harbored the most numerous nitrate-dependent U(IV) oxidizing population 2.4 x 103 cells (g sediment)-1. The nitrate-dependent U(IV) oxidizing microbial population in groundwaters is less numerous ranging from 0 cells mL-1 (Well FW300, Uncontaminated Background NABIR FRC) to 4.3 x 102 cells mL-1 (Well TPB16, Contaminated Area 2 NABIR FRC). The presence of nitrate-dependent U(IV) oxidizing bacteria supports our hypothesis that bacteria capable of anaerobic U(IV) oxidation are ubiquitous and indigenous to sedimentary and groundwater environments.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mouser, Paula J.; N'Guessan, A. Lucie; Qafoku, Nikolla

The capacity for subsurface sediments to sequester metal contaminants, such as uranium (U), and retain them after bioremediation efforts are completed is critical to site stewardship. Sediments enriched in natural organic matter are capable of sequestering significant quantities of U, but may also serve as sources to the aquifer, contributing to plume persistence. Two types of sediments were compared to better understand the mechanisms contributing to the sequestration and release of U in the presence of organic matter. Artificially bioreduced sediments were retrieved from a field experimental plot previously stimulated with acetate while naturally bioreduced sediments were collected from amore » location enriched in organic matter but never subject to acetate amendment. Batch incubations demonstrated that the artificially bioreduced sediments were primed to rapidly remove uranium from the groundwater whereas naturally bioreduced sediments initially released a sizeable portion of sediment U before U(VI)-removal commenced. Column experiments confirmed that U release persisted for 65 pore volumes in naturally bioreduced sediments, demonstrating the sink-source behavior of this sediment. Acetate addition to artificially bioreduced sediments shifted the microbial community from one dominated by sulfate-reducing bacteria within Desulfobacteraceae to the iron-reducing family Geobacteraceae and Firmicutes during U(VI) reduction. In contrast, initial Geobacteraceae communities innaturally reduced sediments were replaced by clone sequences with similarity to opportunistic Pseudomonas spp. during U release, while U(VI) removal occurred concurrent with enrichment of Firmicutes. These investigations stress the importance of characterizing zones with heterogeneous carbon pools at U contaminated sites prior to the determination of a remedial strategy.« less

Bacterial Community Succession During in situ Uranium Bioremediation: Spatial Similarities Along Controlled Flow Paths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, Chiachi; Wu, Weimin; Gentry, Terry J.

2009-05-22

Bacterial community succession was investigated in a field-scale subsurface reactor formed by a series of wells that received weekly ethanol additions to re-circulating groundwater. Ethanol additions stimulated denitrification, metal reduction, sulfate reduction, and U(VI) reduction to sparingly soluble U(IV). Clone libraries of SSU rRNA gene sequences from groundwater samples enabled tracking of spatial and temporal changes over a 1.5 y period. Analyses showed that the communities changed in a manner consistent with geochemical variations that occurred along temporal and spatial scales. Canonical correspondence analysis revealed that the levels of nitrate, uranium, sulfide, sulfate, and ethanol strongly correlated with particular bacterialmore » populations. As sulfate and U(VI) levels declined, sequences representative of sulfate-reducers and metal-reducers were detected at high levels. Ultimately, sequences associated with sulfate-reducing populations predominated, and sulfate levels declined as U(VI) remained at low levels. When engineering controls were compared to the population variation via canonical ordination, changes could be related to dissolved oxygen control and ethanol addition. The data also indicated that the indigenous populations responded differently to stimulation for bio-reduction; however, the two bio-stimulated communities became more similar after different transitions in an idiosyncratic manner. The strong associations between particular environmental variables and certain populations provide insight into the establishment of practical and successful remediation strategies in radionuclide-contaminated environments with respect to engineering controls and microbial ecology.« less

Retardation of uranium and thorium by a cementitious backfill developed for radioactive waste disposal.

PubMed

Felipe-Sotelo, M; Hinchliff, J; Field, L P; Milodowski, A E; Preedy, O; Read, D

2017-07-01

The solubility of uranium and thorium has been measured under the conditions anticipated in a cementitious, geological disposal facility for low and intermediate level radioactive waste. Similar solubilities were obtained for thorium in all media, comprising NaOH, Ca(OH) 2 and water equilibrated with a cement designed as repository backfill (NRVB, Nirex Reference Vault Backfill). In contrast, the solubility of U(VI) was one order of magnitude higher in NaOH than in the remaining solutions. The presence of cellulose degradation products (CDP) results in a comparable solubility increase for both elements. Extended X-ray Absorption Fine Structure (EXAFS) data suggest that the solubility-limiting phase for uranium corresponds to a becquerelite-type solid whereas thermodynamic modelling predicts a poorly crystalline, hydrated calcium uranate phase. The solubility-limiting phase for thorium was ThO 2 of intermediate crystallinity. No breakthrough of either uranium or thorium was observed in diffusion experiments involving NRVB after three years. Nevertheless, backscattering electron microscopy and microfocus X-ray fluorescence confirmed that uranium had penetrated about 40 μm into the cement, implying active diffusion governed by slow dissolution-precipitation kinetics. Precise identification of the uranium solid proved difficult, displaying characteristics of both calcium uranate and becquerelite. Copyright © 2017 Elsevier Ltd. All rights reserved.

Spatial Distribution of an Uranium-Respiring Betaproteobacterium at the Rifle, CO Field Research Site

PubMed Central

Koribanics, Nicole M.; Tuorto, Steven J.; Lopez-Chiaffarelli, Nora; McGuinness, Lora R.; Häggblom, Max M.; Williams, Kenneth H.; Long, Philip E.; Kerkhof, Lee J.

2015-01-01

The Department of Energy’s Integrated Field-Scale Subsurface Research Challenge Site (IFRC) at Rifle, Colorado was created to address the gaps in knowledge on the mechanisms and rates of U(VI) bioreduction in alluvial sediments. Previous studies at the Rifle IFRC have linked microbial processes to uranium immobilization during acetate amendment. Several key bacteria believed to be involved in radionuclide containment have been described; however, most of the evidence implicating uranium reduction with specific microbiota has been indirect. Here, we report on the cultivation of a microorganism from the Rifle IFRC that reduces uranium and appears to utilize it as a terminal electron acceptor for respiration with acetate as electron donor. Furthermore, this bacterium constitutes a significant proportion of the subsurface sediment community prior to biostimulation based on TRFLP profiling of 16S rRNA genes. 16S rRNA gene sequence analysis indicates that the microorganism is a betaproteobacterium with a high similarity to Burkholderia fungorum. This is, to our knowledge, the first report of a betaproteobacterium capable of uranium respiration. Our results indicate that this microorganism occurs commonly in alluvial sediments located between 3-6 m below ground surface at Rifle and may play a role in the initial reduction of uranium at the site. PMID:25874721

Rapid and efficient uranium(VI) capture by phytic acid/polyaniline/FeOOH composites.

PubMed

Wei, Xintao; Liu, Qi; Zhang, Hongsen; Liu, Jingyuan; Chen, Rongrong; Li, Rumin; Li, Zhangshuang; Liu, Peili; Wang, Jun

2018-02-01

Uranium plays an indispensable role in nuclear energy, but there are limited land resources to meet the ever growing demand; therefore, a need exists to develop efficient materials for capturing uranium from water. Herein, we synthesize a promising adsorbent of phytic acid/polyaniline/FeOOH composites (PA/PANI/FeOOH) by oxidative polymerization. Phytic acid, acting asa gelator and dopant, plays an important role in the formation of polyaniline (PANI). The PA/PANI/FeOOH exhibites high adsorption capacity (q m =555.8mgg -1 , T=298K), rapid adsorption rate (within 5min), excellent selectivity and cyclic stability. In addition, the results show that the adsorption isotherm is well fitted to the Langmuir isotherm model, and the adsorption kinetics agree with a pseudo-second order model. XPS analysis indicates that the removal of uranium is mainly attributed to abundant amine and imine groups on the surface of PA/PANI/FeOOH. Importantly, the removal of uranium from low concentrations of simulated seawater is highly efficient with a removal rate exceeding 92%. From our study, superior adsorption capacities, along with a low-cost, environmentally friendly and facile synthesis, reveal PA/PANI/FeOOH asa promising material for uranium capture. Copyright © 2017. Published by Elsevier Inc.

Spatial distribution of an uranium-respiring betaproteobacterium at the Rifle, CO field research site

DOE PAGES

Koribanics, Nicole M.; Tuorto, Steven J.; Lopez-Chiaffarelli, Nora; ...

2015-04-13

The Department of Energy’s Integrated Field-Scale Subsurface Research Challenge Site (IFRC) at Rifle, Colorado was created to address the gaps in knowledge on the mechanisms and rates of U(VI) bioreduction in alluvial sediments. Previous studies at the Rifle IFRC have linked microbial processes to uranium immobilization during acetate amendment. Several key bacteria believed to be involved in radionuclide containment have been described; however, most of the evidence implicating uranium reduction with specific microbiota has been indirect. Here, we report on the cultivation of a microorganism from the Rifle IFRC that reduces uranium and appears to utilize it as a terminalmore » electron acceptor for respiration with acetate as electron donor. Furthermore, this bacterium constitutes a significant proportion of the subsurface sediment community prior to biostimulation based on TRFLP profiling of 16S rRNA genes. 16S rRNA gene sequence analysis indicates that the microorganism is a betaproteobacterium with a high similarity to Burkholderia fungorum. This is, to our knowledge, the first report of a betaproteobacterium capable of uranium respiration. Our results indicate that this microorganism occurs commonly in alluvial sediments located between 3-6 m below ground surface at Rifle and may play a role in the initial reduction of uranium at the site.« less

The adsorption behavior of U(VI) on granite.

PubMed

Fan, Q H; Hao, L M; Wang, C L; Zheng, Z; Liu, C L; Wu, W S

2014-03-01

The effects of pH, counter ions and temperature on the adsorption of U(VI) on Beishan granite (BsG) were investigated in the presence and absence of fulvic acid (FA) and humic acid (HA). The adsorption edge of U(VI) on BsG suggested that U(VI) adsorption was mainly controlled by ion exchange and outer-sphere complexation at low pH, whereas inner-sphere complex was the dominant adsorption species in the pH range of 4.0-9.0. Above pH 9.0, Na2U2O7 might play an important role in the rise of U(VI) adsorption again. Counter ions such as Cl(-), SO4(2-) and PO4(3-) can provoke U(VI) adsorption on BsG to some extent, which was directly correlated to the complexing ability of U(VI)-ligand. More noticeably, the large enhancement of U(VI) adsorption in the presence of phosphate can be attributed to the ternary complex formation (BsG-PO4-UO2), precipitation ((UO2)3(PO4)2(s)) and secondary phase (Na-autunite). Both FA and HA can slightly increase U(VI) adsorption at low pH, whereas they strongly inhibited U(VI) adsorption at high pH range. Artificial synthesized granite (AsG) prepared in the laboratory is impossible to use as an analogue of natural granite because of the large difference in the adsorption and surface properties.

Hydrothermal synthesis of (C6N2H14)2(UVI2UIVO4F12), a mixed-valent one-dimensional uranium oxyfluoride.

PubMed

Allen, S; Barlow, S; Halasyamani, P S; Mosselmans, J F; O'Hare, D; Walker, S M; Walton, R I

2000-08-21

A new hybrid organic-inorganic mixed-valent uranium oxyfluoride, (C6N2H14)2(U3O4F12), UFO-17, has been synthesized under hydrothermal conditions using uranium dioxide as the uranium source, hydrofluoric acid as mineralizer, and 1,4-diazabicyclo[2.2.2]octane as template. The single-crystal X-ray structure was determined. Crystals of UFO-17 belonged to the orthorhombic space group Cmcm (no. 63), with a = 14.2660(15) A, b = 24.5130(10) A, c = 7.201(2) A, and Z = 4. The structure reveals parallel uranium-containing chains of two types: one type is composed of edge-sharing UO2F5 units; the other has a backbone of edge-sharing UF8 units, each sharing an edge with a pendant UO2F5 unit. Bond-valence calculations suggest the UF8 groups contain UIV, while the UO2F5 groups contain UVI. EXAFS data give results consistent with the single-crystal X-ray structure determination, while comparison of the uranium LIII-edge XANES of UFO-17 with that of related UIV and UVI compounds supports the oxidation-state assignment. Variable-temperature magnetic susceptibility measurements on UFO-17 and a range of related hybrid organic-inorganic uranium(IV) and uranium(VI) fluorides and oxyfluorides further support the formulation of UFO-17 as a mixed-valent UIV/UVI compound.

Advective removal of intraparticle uranium from contaminated vadose zone sediments, Hanford, U.S.

PubMed

Ilton, Eugene S; Qafoku, Nikolla P; Liu, Chongxuan; Moore, Dean A; Zachara, John M

2008-03-01

A column study on U(VI)-contaminated vadose zone sediments from the Hanford Site, WA, was performed to investigate U(VI) release kinetics with water advection and variable geochemical conditions. The sediments were collected from an area adjacent to and below tank BX-102 that was contaminated as a result of a radioactive tank waste overfill event. The primary reservoir for U(VI) in the sediments are micrometer-size precipitates composed of nanocrystallite aggregates of a Na-U-Silicate phase, most likely Na-boltwoodite, that nucleated and grew within microfractures of the plagioclase component of sand-sized granitic clasts. Two sediment samples, with different U(VI) concentrations and intraparticle mass transfer properties, were leached with advective flows of three different solutions. The influent solutions were all calcite-saturated and in equilibrium with atmospheric CO2. One solution was prepared from DI water, the second was a synthetic groundwater (SGW) with elevated Na that mimicked groundwater at the Hanford site, and the third was the same SGW but with both elevated Na and Si. The latter two solutions were employed, in part, to test the effect of saturation state on U(VI) release. For both sediments, and all three electrolytes, there was an initial rapid release of U(VI) to the advecting solution followed by slower near steady-state release. U(VI)aq concentrations increased during subsequent stop-flow events. The electrolytes with elevated Na and Si depressed U(VL)aq concentrations in effluent solutions. Effluent U(VI)aq concentrations for both sediments and all three electrolytes were simulated reasonably well by a three domain model (the advecting fluid, fractures, and matrix) that coupled U(VI) dissolution, intraparticle U(VI)aq diffusion, and interparticle advection, where diffusion and dissolution properties were parameterized in a previous batch study.

Long-term diffusion of U(VI) in bentonite: Dependence on density

DOE PAGES

Joseph, Claudia; Mibus, Jens; Trepte, Paul; ...

2016-10-12

As a contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over six years. Synthetic MX-80 model pore water was used as background electrolyte. Speciation calculations showed that Ca 2UO 2(CO 3) 3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3 mm, 1.5 mm, and 1 mm into the clay plug at ρ = 1.3, 1.6, and 1.9 g/cm 3, respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uraniummore » contained in the clay occurred and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficients, D e and D a, decreased with increasing dry density. The D a values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, D a values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. Some potential reasons for this behavior that were evaluated are changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time. By applying Archie's law and the extended Archie's law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). Finally, the results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joel E. Kostka

This project represented a joint effort between Oak Ridge National Laboratory (ORNL), the University of Tennessee (UT), and Florida State University (FSU). ORNL served as the lead in-stitution with Dr. A.V. Palumbo responsible for project coordination, integration, and deliver-ables. In situ uranium bioremediation is focused on biostimulating indigenous microorganisms through a combination of pH neutralization and the addition of large amounts of electron donor. Successful biostimulation of U(VI) reduction has been demonstrated in the field and in the laboratory. However, little data is available on the dynamics of microbial populations capable of U(VI) reduction, and the differences in the microbialmore » community dynamics between proposed electron donors have not been explored. In order to elucidate the potential mechanisms of U(VI) reduction for optimization of bioremediation strategies, structure-function relationships of microbial populations were investigated in microcosms of subsurface materials cocontaminated with radionuclides and nitrate from the Oak Ridge Field Research Center (ORFRC), Oak Ridge, Tennessee.« less

Uranium(IV) adsorption by natural organic matter in anoxic sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bone, Sharon E.; Dynes, James J.; Cliff, John

2017-01-09

Uranium is an important fuel source and a global environmental contaminant. It accumulates in the tetravalent state, U(IV), in anoxic sediments, including ore deposits, marine basins, and contaminated aquifers. However, very little is known about the speciation of U(IV) in low temperature geochemical environments, inhibiting the development of a conceptual model of U behavior. Until recently, U(IV) was assumed to exist predominantly as the sparingly soluble mineral uraninite (UO 2) in anoxic sediments; yet studies now show that UO 2 is not often dominant in these environments. However, a model of U(IV) speciation under environmentally relevant conditions has not yetmore » been developed. Here we show that complexes of U(IV) adsorb on organic carbon and organic carbon-coated clays in an organic-rich natural substrate under field-relevant conditions. Whereas previous research assumed that the U(IV) product depended on the reduction pathway, our results demonstrate that UO 2 formation can be inhibited simply by decreasing the U:solid ratio. Thus, it is the number and type of surface ligands that controls U(IV) speciation subsequent to U(VI) reduction. Projections of U transport and bioavailability, and thus its threat to human and ecosystem health, must consider retention of U(IV) ions within the local sediment environment.« less

Effects of nitrate on the stability of uranium in a bioreduced region of the subsurface.

PubMed

Wu, Wei-Min; Carley, Jack; Green, Stefan J; Luo, Jian; Kelly, Shelly D; Van Nostrand, Joy; Lowe, Kenneth; Mehlhorn, Tonia; Carroll, Sue; Boonchayanant, Benjaporn; Löfller, Frank E; Watson, David; Kemner, Kenneth M; Zhou, Jizhong; Kitanidis, Peter K; Kostka, Joel E; Jardine, Philip M; Criddle, Craig S

2010-07-01

The effects of nitrate on the stability of reduced, immobilized uranium were evaluated in field experiments at a U.S. Department of Energy site in Oak Ridge, TN. Nitrate (2.0 mM) was injected into a reduced region of the subsurface containing high levels of previously immobilized U(IV). The nitrate was reduced to nitrite, ammonium, and nitrogen gas; sulfide levels decreased; and Fe(II) levels increased then deceased. Uranium remobilization occurred concomitant with nitrite formation, suggesting nitrate-dependent, iron-accelerated oxidation of U(IV). Bromide tracer results indicated changes in subsurface flowpaths likely due to gas formation and/or precipitate. Desorption-adsorption of uranium by the iron-rich sediment impacted uranium mobilization and sequestration. After rereduction of the subsurface through ethanol additions, background groundwater containing high levels of nitrate was allowed to enter the reduced test zone. Aqueous uranium concentrations increased then decreased. Clone library analyses of sediment samples revealed the presence of denitrifying bacteria that can oxidize elemental sulfur, H(2)S, Fe(II), and U(IV) (e.g., Thiobacillus spp.), and a decrease in relative abundance of bacteria that can reduce Fe(III) and sulfate. XANES analyses of sediment samples confirmed changes in uranium oxidation state. Addition of ethanol restored reduced conditions and triggered a short-term increase in Fe(II) and aqueous uranium, likely due to reductive dissolution of Fe(III) oxides and release of sorbed U(VI). After two months of intermittent ethanol addition, sulfide levels increased, and aqueous uranium concentrations gradually decreased to <0.1 microM.

Ferrate(VI) oxidation of cyanide in water.

PubMed

Costarramone, N; Kneip, A; Castetbon, A

2004-08-01

Experiments were conducted to test removal of cyanide (free cyanide and several cyanide complexes) in water, under alkaline medium (pH > or = 11), by a new potassium ferrate salt. The removal rate of free cyanide by oxidation with Fe(VI) was greater at pH 11.0 than at pH 12.0. A complete oxidation was obtained with a 2.67 Fe(VI)/CN ratio at pH 11.0. In these conditions, the rate of cyanide oxidation by Fe(VI) was slow, with a reaction rate constant estimated at 0.95 +/- 0.10 s(-1) l mol(-1) at pH 11.0 and 19.6 degrees C in this study. This study revealed that Fe(VI) did not decompose all cyanide complexes. Copper, cadmium and zinc complexes were removed efficiently by Fe(VI). Moreover, these metals were also removed from the solution by coagulation effect of Fe(OH)3, the Fe(VI) product of reaction. A particular behaviour was reported with copper, as a rapid oxidation of cyanide was observed in the presence of this metal. On the contrary, oxidation of nickel and silver complexes was incomplete.

Mechanism study of humic acid functional groups for Cr(VI) retention: Two-dimensional FTIR and 13C CP/MAS NMR correlation spectroscopic analysis.

PubMed

Zhang, Jia; Chen, Linpeng; Yin, Huilin; Jin, Song; Liu, Fei; Chen, Honghan

2017-06-01

Undissolved humic acid (HA) is known to substantially effect the migration and transformation of hexavalent chromium [Cr(VI)] in soils. The mechanisms of Cr(VI) retention in soils by undissolved HA have been reported; however, past studies are inconclusive about the types of HA functional groups that are involved in Cr(VI) retention and the retention mechanisms. Utilizing a two-dimensional correlation spectroscopy (2DCOS) analysis for FTIR and 13 C CP/MAS NMR, this study investigated the variations of HA function groups and molecular structures after reactions with aqueous Cr(VI) under different pH conditions. Based on the changing sequence of functional groups interpreted from the 2DCOS results, a four-step mechanism for Cr(VI) retention was determined as follows: (1) electrostatic adsorption of Cr(VI) to HA surface, (2) complexation of adsorbed Cr(VI) by carboxyl and ester, (3) reduction of complexed Cr(VI) to Cr(III) by phenol and polysaccharide, and (4) complexation of reduced Cr(III) by carboxylic groups. These functional groups that are involved in Cr(VI) retention were determined to occur in aromatic domains. Copyright © 2017 Elsevier Ltd. All rights reserved.

Maximum likelihood Bayesian model averaging and its predictive analysis for groundwater reactive transport models

DOE PAGES

Lu, Dan; Ye, Ming; Curtis, Gary P.

2015-08-01

While Bayesian model averaging (BMA) has been widely used in groundwater modeling, it is infrequently applied to groundwater reactive transport modeling because of multiple sources of uncertainty in the coupled hydrogeochemical processes and because of the long execution time of each model run. To resolve these problems, this study analyzed different levels of uncertainty in a hierarchical way, and used the maximum likelihood version of BMA, i.e., MLBMA, to improve the computational efficiency. Our study demonstrates the applicability of MLBMA to groundwater reactive transport modeling in a synthetic case in which twenty-seven reactive transport models were designed to predict themore » reactive transport of hexavalent uranium (U(VI)) based on observations at a former uranium mill site near Naturita, CO. Moreover, these reactive transport models contain three uncertain model components, i.e., parameterization of hydraulic conductivity, configuration of model boundary, and surface complexation reactions that simulate U(VI) adsorption. These uncertain model components were aggregated into the alternative models by integrating a hierarchical structure into MLBMA. The modeling results of the individual models and MLBMA were analyzed to investigate their predictive performance. The predictive logscore results show that MLBMA generally outperforms the best model, suggesting that using MLBMA is a sound strategy to achieve more robust model predictions relative to a single model. MLBMA works best when the alternative models are structurally distinct and have diverse model predictions. When correlation in model structure exists, two strategies were used to improve predictive performance by retaining structurally distinct models or assigning smaller prior model probabilities to correlated models. Since the synthetic models were designed using data from the Naturita site, the results of this study are expected to provide guidance for real-world modeling. Finally, limitations of applying MLBMA to the synthetic study and future real-world modeling are discussed.« less

Use of Sodium Dithionite as Part of a More Efficient Groundwater Restoration Method Following In-situ Recovery of Uranium at the Smith-Ranch Highland Site in Wyoming

NASA Astrophysics Data System (ADS)

Harris, R.; Reimus, P. W.; Ware, D.; Williams, K.; Chu, D.; Perkins, G.; Migdissov, A. A.; Bonwell, C.

2017-12-01

Uranium is primarily mined for nuclear power production using an aqueous extraction technique called in-situ recovery (ISR). ISR can pollute groundwater with residual uranium and other heavy metals. Reverse osmosis and groundwater sweep are currently used to restore groundwater after ISR mining, but are not permanent solutions. Sodium dithionite is being tested as part of a method to more permanently restore groundwater after ISR mining at the Smith-Ranch Highland site in Wyoming. Sodium dithionite is a chemical reductant that can reduce sediments that were oxidized during ISR. The reduced sediments can reduce soluble uranium (VI) in the groundwater to insoluble uranium (IV). Laboratory studies that use sodium dithionite to treat sediments and waters from the site may help predict how it will behave during a field deployment. An aqueous batch experiment showed that sodium dithionite reduced uranium in post-mined untreated groundwater from 38 ppm to less than 1 ppm after 1 day. A sediment reduction batch experiment showed that sodium dithionite-treated sediments were capable of reducing uranium in post-mined untreated groundwater from 38 ppm to 2 ppm after 7 days. One column experiment is showing post-mined sodium dithionite-treated sediments are capable of reducing uranium in post-mined groundwater for over 30 pore volumes past the initial injection. While these results are promising for field deployments of sodium dithionite, another column experiment with sodium dithionite-treated sediments containing uranium rich organic matter is showing net production of uranium instead of uranium uptake. Sodium dithionite appears to liberate uranium from the organic matter. Another sediment reduction experiment is being conducted to further investigate this hypothesis. These experiments are helping guide plans for field deployments of sodium dithionite at uranium ISR mining sites.

Ferrate(VI) oxidation of zinc-cyanide complex.

PubMed

Yngard, Ria; Damrongsiri, Seelawut; Osathaphan, Khemarath; Sharma, Virender K

2007-10-01

Zinc-cyanide complexes are found in gold mining effluents and in metal finishing rinse water. The effect of Zn(II) on the oxidation of cyanide by ferrate(VI) (Fe(VI)O(4)(2-), Fe(VI)) was thus investigated by studying the kinetics of the reaction of Fe(VI) with cyanide present in a potassium salt of a zinc cyanide complex (K(2)Zn(CN)(4)) and in a mixture of Zn(II) and cyanide solutions as a function of pH (9.0-11.0). The rate-law for the oxidation of Zn(CN)(4)(2-) by Fe(VI) was found to be -d[Fe(VI)]/dt=k[Fe(VI)][Zn(CN)(4)(2-)](0.5). The rate constant, k, decreased with an increase in pH. The effect of temperature (15-45 degrees C) on the oxidation was studied at pH 9.0, which gave an activation energy of 45.7+/-1.5kJmol(-1). The cyanide oxidation rate decreased in the presence of the Zn(II) ions. However, Zn(II) ions had no effect on the cyanide removal efficiency by Fe(VI) and the stoichiometry of Fe(VI) to cyanide was approximately 1:1; similar to the stoichiometry in absence of Zn(II) ions. The destruction of cyanide by Fe(VI) resulted in cyanate. The experiments on removal of cyanide from rinse water using Fe(VI) demonstrated complete conversion of cyanide to cyanate.

Dynamics of microbial community composition and function during in-situ bioremediation of a uranium-contaminated aquifer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nostrand, J.D. Van; Wu, L.; Wu, W.M.

2010-08-15

A pilot-scale system was established to examine the feasibility of in situ U(VI) immobilization at a highly contaminated aquifer (U.S. DOE Integrated Field Research Challenge site, Oak Ridge, TN). Ethanol was injected intermittently as an electron donor to stimulate microbial U(VI) reduction, and U(VI) concentrations fell to below the Environmental Protection Agency drinking water standard (0.03 mg liter{sup -1}). Microbial communities from three monitoring wells were examined during active U(VI) reduction and maintenance phases with GeoChip, a high-density, comprehensive functional gene array. The overall microbial community structure exhibited a considerable shift over the remediation phases examined. GeoChip-based analysis revealed thatmore » Fe(III)-reducing bacterial (FeRB), nitrate-reducing bacterial (NRB), and sulfate-reducing bacterial (SRB) functional populations reached their highest levels during the active U(VI) reduction phase (days 137 to 370), in which denitrification and Fe(III) and sulfate reduction occurred sequentially. A gradual decrease in these functional populations occurred when reduction reactions stabilized, suggesting that these functional populations could play an important role in both active U(VI) reduction and maintenance of the stability of reduced U(IV). These results suggest that addition of electron donors stimulated the microbial community to create biogeochemical conditions favorable to U(VI) reduction and prevent the reduced U(IV) from reoxidation and that functional FeRB, SRB, and NRB populations within this system played key roles in this process.« less

Dynamics of Microbial Community Composition and Function during In Situ Bioremediation of a Uranium-Contaminated Aquifer▿‡

PubMed Central

Van Nostrand, Joy D.; Wu, Liyou; Wu, Wei-Min; Huang, Zhijian; Gentry, Terry J.; Deng, Ye; Carley, Jack; Carroll, Sue; He, Zhili; Gu, Baohua; Luo, Jian; Criddle, Craig S.; Watson, David B.; Jardine, Philip M.; Marsh, Terence L.; Tiedje, James M.; Hazen, Terry C.; Zhou, Jizhong

2011-01-01

A pilot-scale system was established to examine the feasibility of in situ U(VI) immobilization at a highly contaminated aquifer (U.S. DOE Integrated Field Research Challenge site, Oak Ridge, TN). Ethanol was injected intermittently as an electron donor to stimulate microbial U(VI) reduction, and U(VI) concentrations fell to below the Environmental Protection Agency drinking water standard (0.03 mg liter−1). Microbial communities from three monitoring wells were examined during active U(VI) reduction and maintenance phases with GeoChip, a high-density, comprehensive functional gene array. The overall microbial community structure exhibited a considerable shift over the remediation phases examined. GeoChip-based analysis revealed that Fe(III)-reducing bacterial (FeRB), nitrate-reducing bacterial (NRB), and sulfate-reducing bacterial (SRB) functional populations reached their highest levels during the active U(VI) reduction phase (days 137 to 370), in which denitrification and Fe(III) and sulfate reduction occurred sequentially. A gradual decrease in these functional populations occurred when reduction reactions stabilized, suggesting that these functional populations could play an important role in both active U(VI) reduction and maintenance of the stability of reduced U(IV). These results suggest that addition of electron donors stimulated the microbial community to create biogeochemical conditions favorable to U(VI) reduction and prevent the reduced U(IV) from reoxidation and that functional FeRB, SRB, and NRB populations within this system played key roles in this process. PMID:21498771

Uranium and Cesium sorption to bentonite colloids in high salinity and carbonate-rich environments: Implications for radionuclide transport

NASA Astrophysics Data System (ADS)

Tran, E. L.; Teutsch, N.; Klein-BenDavid, O.; Weisbrod, N.

2017-12-01

When radionuclides are leaked into the subsurface due to engineered waste disposal container failure, the ultimate barrier to migration of radionuclides into local aquifers is sorption to the surrounding rock matrix and sediments, which often includes a bentonite backfill. The extent of this sorption is dependent on pH, ionic strength, surface area availability, radionuclide concentration, surface mineral composition, and solution chemistry. Colloidal-sized bentonite particles eroded from the backfill have been shown to facilitate the transport of radionuclides sorbed to them away from their source. Thus, sorption of radionuclides such as uranium and cesium to bentonite surfaces can be both a mobilization or retardation factor. Though numerous studies have been conducted to-date on sorption of radionuclides under low ionic strength and carbonate-poor conditions, there has been little research conducted on the behavior of radionuclides in high salinities and carbonate rich conditions typical of aquifers in the vicinity of some potential nuclear repositories. This study attempts to characterize the sorption properties of U(VI) and Cs to bentonite colloids under these conditions using controlled batch experiments. Results indicated that U(VI) undergoes little to no sorption to bentonite colloids in a high-salinity (TDS= 9000 mg/L) artificial groundwater. This lack of sorption was attributed to the formation of CaUO2(CO3)22- and Ca2UO2(CO3)3 aqueous ions which stabilize the UO22+ ions in solution. In contrast, Cs exhibited greater sorption, the extent to which was influenced greatly by the matrix water's ionic strength and the colloid concentration used. Surprisingly, when both U and Cs were together, the presence of U(VI) in solution decreased Cs sorption, possibly due to the formation of stabilizing CaUO2(CO3)22- anions. The implications of this research are that rather than undergoing colloid-facilitated transport, U(VI) is expected to migrate similarly to a conservative dissolved species under these conditions, and little retardation through sorption onto the surrounding rock matrix is predicted. Cs is expected to undergo more sorption, though U(VI) presence may have a mobilizing effect.

Formic acid interaction with the uranyl(VI) ion: structural and photochemical characterization.

PubMed

Lucks, Christian; Rossberg, André; Tsushima, Satoru; Foerstendorf, Harald; Fahmy, Karim; Bernhard, Gert

2013-10-07

Complex formation between the uranyl(VI) ion and formic acid was studied by infrared absorption (IR) and X-ray absorption (EXAFS) spectroscopy as well as density functional theory (DFT) calculations. In contrast to the acetate ion which forms exclusively a bidentate complex with uranyl(VI), the formate ion binds to uranyl(VI) in a unidentate fashion. The photochemistry of the uranyl(VI)-formic acid system was explored by DFT calculations and photoreduction of uranyl(VI) in the presence of formic acid was found to occur via an intermolecular process, that is, hydrogen abstraction from hydrogenformate by the photo-excited uranyl(VI). There is no photo-induced decarboxylation of uranyl(VI) formate via an intramolecular process, presumably due to lack of a C=C double bond.

Characterization of Uranium Tolerance and Biomineralization Potential of Caulobacter crescentus

NASA Astrophysics Data System (ADS)

Park, D.

2015-12-01

Due to its high toxicity and mobility, U(VI) poses a major environmental threat to ecosystems. The ubiquitous aerobic bacterium Caulobacter cresecentus is an attractive candidate for U(VI) bioremediation because of its ability to survive in low-nutrient environments (5, 6), tolerate high U concentrations and mineralize U(VI) aerobically through the formation of uranyl phosphate (U-Pi) precipitates. Despite these attractive environmental properties, both a systems level understanding of the adaptive response pathways involved in U tolerance and the environmental conditions affecting the biomineralization process and stability of biogenic U-Pi minerals remain limited. By measuring changes in both mRNA and protein expression during exposure to high U levels, we have identified the core stress response pathways involved in U tolerance. Pathways associated with heat shock, lipospolysaccharide biosynthesis and transport, outer membrane lipoprotein transport and outermembrane assembly were highly induced at both the RNA and protein levels. Correspondingly, removal of integral components of proteolysis pathways including clpA, clpS and degP significantly reduced U tolerance under biomineralization conditions. Surprisingly, in contrast to many other heavy metals, U did not cause oxidative stress or DNA damage. Together, these analyses indicate that U predominately targets the outermembrane and causes mis-folding of both cytoplasmic and extracytoplasmic proteins. Efforts are currently underway to characterize the morphological and structural properties of biogenic U-Pi minerals and the environmental factors that influence their production and stability. Preliminary AFM studies suggest that U-Pi minerals formed under biomineralization conditions appear morphologically distinct from those formed abiotically between U(VI) and inorganic phosphate. Additionally, we observed that biomineralization tolerates a wide pH range (pH 6-9). Our long-range goal is the development of a conceptual model of the role of microbes in U cycling under oxidizing conditions across the DOE complex, and ultimately, provide DOE with the scientific basis to support decisions for the remediation of legacy sites.

Characterizing particle-scale equilibrium adsorption and kinetics of uranium(VI) desorption from U-contaminated sediments

USGS Publications Warehouse

Stoliker, Deborah L.; Liu, Chongxuan; Kent, Douglas B.; Zachara, John M.

2013-01-01

Rates of U(VI) release from individual dry-sieved size fractions of a field-aggregated, field-contaminated composite sediment from the seasonally saturated lower vadose zone of the Hanford 300-Area were examined in flow-through reactors to maintain quasi-constant chemical conditions. The principal source of variability in equilibrium U(VI) adsorption properties of the various size fractions was the impact of variable chemistry on adsorption. This source of variability was represented using surface complexation models (SCMs) with different stoichiometric coefficients with respect to hydrogen ion and carbonate concentrations for the different size fractions. A reactive transport model incorporating equilibrium expressions for cation exchange and calcite dissolution, along with rate expressions for aerobic respiration and silica dissolution, described the temporal evolution of solute concentrations observed during the flow-through reactor experiments. Kinetic U(VI) desorption was well described using a multirate SCM with an assumed lognormal distribution for the mass-transfer rate coefficients. The estimated mean and standard deviation of the rate coefficients were the same for all <2 mm size fractions but differed for the 2–8 mm size fraction. Micropore volumes, assessed using t-plots to analyze N2 desorption data, were also the same for all dry-sieved <2 mm size fractions, indicating a link between micropore volumes and mass-transfer rate properties. Pore volumes for dry-sieved size fractions exceeded values for the corresponding wet-sieved fractions. We hypothesize that repeated field wetting and drying cycles lead to the formation of aggregates and/or coatings containing (micro)pore networks which provided an additional mass-transfer resistance over that associated with individual particles. The 2–8 mm fraction exhibited a larger average and standard deviation in the distribution of mass-transfer rate coefficients, possibly caused by the abundance of microporous basaltic rock fragments.

Uranium fate in wetland mesocosms: Effects of plants at two iron loadings with different pH values.

PubMed

Koster van Groos, Paul G; Kaplan, Daniel I; Chang, Hyun-Shik; Seaman, John C; Li, Dien; Peacock, Aaron D; Scheckel, Kirk G; Jaffé, Peter R

2016-11-01

Small-scale continuous flow wetland mesocosms (∼0.8 L) were used to evaluate how plant roots under different iron loadings affect uranium (U) mobility. When significant concentrations of ferrous iron (Fe) were present at circumneutral pH values, U concentrations in root exposed sediments were an order of magnitude greater than concentrations in root excluded sediments. Micro X-ray absorption near-edge structure (μ-XANES) spectroscopy indicated that U was associated with the plant roots primarily as U(VI) or U(V), with limited evidence of U(IV). Micro X-ray fluorescence (μ-XRF) of plant roots suggested that for high iron loading at circumneutral pH, U was co-located with Fe, perhaps co-precipitated with root Fe plaques, while for low iron loading at a pH of ∼4 the correlation between U and Fe was not significant, consistent with previous observations of U associated with organic matter. Quantitative PCR analyses indicated that the root exposed sediments also contained elevated numbers of Geobacter spp., which are likely associated with enhanced iron cycling, but may also reduce mobile U(VI) to less mobile U(IV) species. Copyright © 2016 Elsevier Ltd. All rights reserved.

Thermal expansion of the nuclear fuel-sodium reaction product Na3(U0.84(2),Na0.16(2))O4 - Structural mechanism and comparison with related sodium-metal ternary oxides

NASA Astrophysics Data System (ADS)

Illy, Marie-Claire; Smith, Anna L.; Wallez, Gilles; Raison, Philippe E.; Caciuffo, Roberto; Konings, Rudy J. M.

2017-07-01

Na3.16(2)UV,VI0.84(2)O4 is obtained from the reaction of sodium with uranium dioxide under oxygen potential conditions typical of a sodium-cooled fast nuclear reactor. In the event of a breach of the steel cladding, it would be the dominant reaction product forming at the rim of the mixed (U,Pu)O2 fuel pellets. High-temperature X-ray diffraction measurements show that a distortion of the uranium environment in Na3.16(2)UV,VI0.84(2)O4 results in a strongly anisotropic thermal expansion. A comparison with several related sodium metallates Nan-2Mn+On-1 - including Na3SbO4 and Na3TaO4, whose crystal structures are reported for the first time - has allowed us to assess the role played in the lattice expansion by the Mn+ cation radius and the Na/M ratio. On this basis, the thermomechanical behavior of the title compound is discussed, along with those of several related double oxides of sodium and actinide elements, surrogate elements, or fission products.

High-resolution mineralogical characterization and biogeochemical modeling of uranium reaction pathways at the FRC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Zhu

2006-06-15

High-Resolution Mineralogical Characterization and Biogeochemical Modeling of Uranium Reduction Pathways at the Oak Ridge Field-Research Center (FRC) Chen Zhu, Indiana University, David R. Veblen, Johns Hopkins University We have successfully completed a proof-of-concept, one-year grant on a three-year proposal from the former NABIR program, and here we seek additional two-year funding to complete and publish the research. Using a state-of-the-art 300-kV, atomic resolution, Field Emission Gun Transmission Electron Microscope (TEM), we have successfully identified three categories of mineral hosts for uranium in contaminated soils: (1) iron oxides; (2) mixed manganese-iron oxides; and (3) uranium phosphates. Method development using parallel electronmore » energy loss spectroscopy (EELS) associated with the TEM shows great promise for characterizing the valence states of immobilized U during bioremediation. We have also collected 27 groundwater samples from two push-pull field biostimulation tests, which form two time series from zero to approximately 600 hours. The temporal evolution in major cations, anions, trace elements, and the stable isotopes 34S, 18O in sulfate, 15N in nitrate, and 13C in dissolved inorganic carbon (DIC) clearly show that biostimulation resulted in reduction of nitrate, Mn(IV), Fe(III), U(VI), sulfate, and Tc(VII), and these reduction reactions were intimately coupled with a complex network of inorganic reactions evident from alkalinity, pH, Na, K, Mg, and Ca concentrations. From these temporal trends, apparent zero order rates were regressed. However, our extensive suite of chemical and isotopic data sets, perhaps the first and only comprehensive data set available at the FRC, show that the derived rates from these field biostimulation experiments are composite and lump-sum rates. There were several reactions that were occurring at the same time but were masked by these pseudo-zero order rates. A reaction-path model comprising a total of nine redox couples (NO3–/NH4+, MnO2(s)/Mn2+, Fe(OH)3(s) /Fe2+, TcO4–/TcO2(s), UO22+/UO2(s), SO42–/HS–, CO2/CH4, ethanol/acetate, and H+/H2.) is used to simulate the temporal biogeochemical evolution observed in the field tests. Preliminary results show that the models based on thermodynamics and more complex rate laws can generate the apparent zero order rates when several concurrent or competing reactions occur. Professor Alex Halliday of Oxford University, UK, and his postdoctoral associates are measuring the uranium isotopes in our groundwater samples. Newly developed state-of-the-art analytical techniques in measuring variability in 235U/238U offer the potential to distinguish biotic and abiotic uranium reductive mechanisms.« less

Uranium(VI) Complexes with a Calix[4]arene‐Based 8‐Hydroxyquinoline Ligand: Thermodynamic and Structural Characterization Based on Calorimetry, Spectroscopy, and Liquid–Liquid Extraction

PubMed Central

Bauer, Anne; Jäschke, Astrid; Schöne, Sebastian; Barthen, Robert; März, Juliane; Patzschke, Michael; Kersting, Berthold; Fahmy, Karim; Oertel, Jana; Brendler, Vinzenz; Stumpf, Thorsten

2018-01-01

Abstract The environmental aspects of ore processing and waste treatment call for an optimization of applied technologies. There, understanding of the structure and complexation mechanism on a molecular scale is indispensable. Here, the complexation of UVI with a calix[4]arene‐based 8‐hydroxyquinoline ligand was investigated by applying a wide range of complementary methods. In solution, the formation of two complex species was proven with stability constants of log ß 1:1=5.94±0.02 and log ß 2:1=6.33±0.01, respectively. The formation of the 1:1 complex was found to be enthalpy driven [ΔH 1:1=(−71.5±10.0) kJ mol−1; TΔS 1:1=(−37.57±10.0) kJ mol−1], whereas the second complexation step was found to be endothermic and entropy driven [ΔH 2:1=(32.8±4.0) kJ mol−1; TΔS 2:1=(68.97±4.0) kJ mol−1]. Moreover, the molecular structure of [UO2(H6L)(NO3)](NO3) (1) was determined by single‐crystal X‐ray diffraction. Concluding, radiotoxic UVI was separated from a EuIII‐containing solution by the calix[4]arene‐based ligand in solvent extractions. PMID:29930893

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joseph, Claudia; Mibus, Jens; Trepte, Paul

As a contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over six years. Synthetic MX-80 model pore water was used as background electrolyte. Speciation calculations showed that Ca 2UO 2(CO 3) 3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3 mm, 1.5 mm, and 1 mm into the clay plug at ρ = 1.3, 1.6, and 1.9 g/cm 3, respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uraniummore » contained in the clay occurred and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficients, D e and D a, decreased with increasing dry density. The D a values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, D a values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. Some potential reasons for this behavior that were evaluated are changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time. By applying Archie's law and the extended Archie's law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). Finally, the results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.« less

Fast Oxidation Processes in a Naturally Reduced Aquifer Zone Caused by Dissolved Oxygen

NASA Astrophysics Data System (ADS)

Davis, J. A.; Jemison, N. E.; Williams, K. H.; Hobson, C.; Bush, R. P.

2014-12-01

The occurrence of naturally reduced zones is quite common in alluvial aquifers in the western U.S.A. due to the burial of woody debris in flood plains. The naturally reduced zones are heterogeneously dispersed in such aquifers and are characterized by high concentrations of organic carbon and reduced phases, including iron sulfides and reduced forms of metals, including uranium(IV). The persistence of high concentrations of dissolved uranium(VI) at uranium-contaminated aquifers on the Colorado Plateau has been attributed to slow oxidation of insoluble uranium(IV) mineral phases that are found in association with these natural reducing zones, although there is little understanding of the relative importance of various potential oxidants. Three field experiments were conducted within an alluvial aquifer adjacent to the Colorado River near Rifle, CO wherein groundwater associated with naturally reduced zones was pumped into a gas-impermeable tank, mixed with a conservative tracer (Br-), bubbled with a gas phase composed of 97% O2 and 3% CO2, and then returned to the subsurface in the same well from which it was withdrawn. Within minutes of re-injection of the oxygenated groundwater, dissolved uranium(VI) concentrations increased from less than 1 μM to greater than 2.5 μM, demonstrating that oxygen can be an important oxidant for uranium in these field systems if supplied to the naturally reduced zones. Small concentrations of nitrate were also observed in the previously nitrate-free groundwater, and Fe(II) decreased to the detection limit. These results contrast with other laboratory and field results in which oxygen was introduced to systems containing high concentrations of mackinawite (FeS) rather than the more crystalline iron sulfides found in aged, naturally reduced zones. The flux of oxygen to the naturally reduced zones in the alluvial aquifers occurs mainly through interactions between groundwater and gas phases at the water table, and seasonal variations of the water table at the Rifle, CO site may play an important role in introducing oxygen into the system. Although oxygen was introduced directly to the naturally reduced zones in these experiments, delivery of oxidants to the system may normally be controlled by other oxidative pathways in which oxygen plays an indirect role.

Preparation and characterization of porous reduced graphene oxide based inverse spinel nickel ferrite nanocomposite for adsorption removal of radionuclides.

PubMed

Lingamdinne, Lakshmi Prasanna; Choi, Yu-Lim; Kim, Im-Soon; Yang, Jae-Kyu; Koduru, Janardhan Reddy; Chang, Yoon-Young

2017-03-15

For the removal of uranium(VI) (U(VI)) and thorium(IV) (Th(IV)), graphene oxide based inverse spinel nickel ferrite (GONF) nanocomposite and reduced graphene oxide based inverse spinel nickel ferrite (rGONF) nanocomposite were prepared by co-precipitation of GO with nickel and iron salts in one pot. The spectral characterization analyses revealed that GONF and rGONF have a porous surface morphology with an average particle size of 41.41nm and 32.16nm, respectively. The magnetic property measurement system (MPMS) studies confirmed the formation of ferromagnetic GONF and superparamagnetic rGONF. The adsorption kinetics studies found that the pseudo-second-order kinetics was well tune to the U(VI) and Th(IV) adsorption. The results of adsorption isotherms showed that the adsorption of U(VI) and Th(IV) were due to the monolayer on homogeneous surface of the GONF and rGONF. The adsorptions of both U(VI) and Th(IV) were increased with increasing system temperature from 293 to 333±2K. The thermodynamic studies reveal that the U(VI) and Th(IV) adsorption onto GONF and rGONF was endothermic. GONF and rGONF, which could be separated by external magnetic field, were recycled and re-used for up to five cycles without any significant loss of adsorption capacity. Copyright © 2016 Elsevier B.V. All rights reserved.

PROCESS OF RECOVERING URANIUM

DOEpatents

Kilner, S.B.

1959-12-29

A method is presented for separating and recovering uranium from a complex mixure of impurities. The uranium is dissolved to produce an aqueous acidic solution including various impurities. In accordance with one method, with the uranium in the uranyl state, hydrogen cyanide is introduced into the solution to complex the impurities. Subsequently, ammonia is added to the solution to precipitate the uraniunn as ammonium diuranate away from the impurities in the solution. Alternatively, the uranium is precipitated by adding an alkaline metal hydroxide. In accordance with the second method, the uranium is reduced to the uranous state in the solution. The reduced solution is then treated with solid alkali metal cyanide sufficient to render the solution about 0.1 to 1.0 N in cyanide ions whereat cyanide complex ions of the metal impurities are produced and the uranium is simultaneously precipituted as uranous hydroxide. Alternatively, hydrogen cyanide may be added to the reduced solution and the uranium precipitated subsequently by adding ammonium hydroxide or an alkali metal hydroxide. Other refinements of the method are also disclosed.

Inherently safe in situ uranium recovery

DOEpatents

Krumhansl, James L; Brady, Patrick V

2014-04-29

An in situ recovery of uranium operation involves circulating reactive fluids through an underground uranium deposit. These fluids contain chemicals that dissolve the uranium ore. Uranium is recovered from the fluids after they are pumped back to the surface. Chemicals used to accomplish this include complexing agents that are organic, readily degradable, and/or have a predictable lifetime in an aquifer. Efficiency is increased through development of organic agents targeted to complexing tetravalent uranium rather than hexavalent uranium. The operation provides for in situ immobilization of some oxy-anion pollutants under oxidizing conditions as well as reducing conditions. The operation also artificially reestablishes reducing conditions on the aquifer after uranium recovery is completed. With the ability to have the impacted aquifer reliably remediated, the uranium recovery operation can be considered inherently safe.

Osmium(VI) complexes as a new class of potential anti-cancer agents.

PubMed

Ni, Wen-Xiu; Man, Wai-Lun; Cheung, Myra Ting-Wai; Sun, Raymond Wai-Yin; Shu, Yuan-Lan; Lam, Yun-Wah; Che, Chi-Ming; Lau, Tai-Chu

2011-02-21

A nitridoosmium(VI) complex [Os(VI)(N)(sap)(OH(2))Cl] (H(2)sap = N-salicylidene-2-aminophenol) displays prominent in vitro and in vivo anti-cancer properties, induces S- and G2/M-phase arrest and forms a stable adduct with dianionic 5'-guanosine monophosphate.

Uranium extraction by complexation with siderophores

NASA Astrophysics Data System (ADS)

Bahamonde Castro, Cristina

One of the major concerns of energy production is the environmental impact associated with the extraction of natural resources. Nuclear energy fuel is obtained from uranium, an abundant and naturally occurring element in the environment, but the currently used techniques for uranium extraction leave either a significant fingerprint (open pit mines) or a chemical residue that alters the pH of the environment (acid or alkali leaching). It is therefore clear that a new and greener approach to uranium extraction is needed. Bioleaching is one potential alternative. In bioleaching, complexants naturally produced from fungi or bacteria may be used to extract the uranium. In the following research, the siderophore enterobactin, which is naturally produced by bacteria to extract and solubilize iron from the environment, is evaluated to determine its potential for complexing with uranium. To determine whether enterobactin could be used for uranium extraction, its acid dissociation and its binding strength with the metal of interest must be determined. Due to the complexity of working with radioactive materials, lanthanides were used as analogs for uranium. In addition, polyprotic acids were used as structural and chemical analogs for the siderophore during method development. To evaluate the acid dissociation of enterobactin and the subsequent binding constants with lanthanides, three different analytical techniques were studied including: potentiometric titration, UltraViolet Visible (UV-Vis) spectrophotometry and Isothermal Titration Calorimetry (ITC). After evaluation of three techniques, a combination of ITC and potentiometric titrations was deemed to be the most viable way for studying the siderophore of interest. The results obtained from these studies corroborate the ideal pH range for enterobactin complexation to the lanthanide of interest and pave the way for determining the strength of complexation relative to other naturally occurring metals. Ultimately, this fundamental research enhances our current understanding of heavy metal complexation to naturally occurring complexants, which may enhance the metals mobility in the environment or potentially be used as a greener alternative in uranium extraction or remediation.

Interactions between Silicon Oxide Nanoparticles (SONPs) and U(VI) Contaminations: Effects of pH, Temperature and Natural Organic Matters

PubMed Central

Wu, Hanyu; Li, Ping; Pan, Duoqiang; Yin, Zhuoxin; Fan, Qiaohui; Wu, Wangsuo

2016-01-01

The interactions between contaminations of U(VI) and silicon oxide nanoparticles (SONPs), both of which have been widely used in modern industry and induced serious environmental challenge due to their high mobility, bioavailability, and toxicity, were studied under different environmental conditions such as pH, temperature, and natural organic matters (NOMs) by using both batch and spectroscopic approaches. The results showed that the accumulation process, i.e., sorption, of U(VI) on SONPs was strongly dependent on pH and ionic strength, demonstrating that possible outer- and/or inner-sphere complexes were controlling the sorption process of U(VI) on SONPs in the observed pH range. Humic acid (HA), one dominated component of NOMs, bounded SONPs can enhance U(VI) sorption below pH~4.5, whereas restrain at high pH range. The reversible sorption of U(VI) on SONPs possibly indicated that the outer-sphere complexes were prevalent at pH 5. However, an irreversible interaction of U(VI) was observed in the presence of HA (Fig 1). It was mainly due to the ternary SONPs-HA-U(VI) complexes (Type A Complexes). After SONPs adsorbed U(VI), the particle size in suspension was apparently increased from ~240 nm to ~350 nm. These results showed that toxicity of both SONPs and U(VI) will decrease to some extent after the interaction in the environment. These findings are key for providing useful information on the possible mutual interactions among different contaminants in the environment. PMID:26930197

Injection of Emulsified Vegetable Oil for Long-Term Bioreduction of Uranium

NASA Astrophysics Data System (ADS)

Brooks, S. C.; Watson, D. B.; Schadt, C. W.; Jardine, P. M.; Gihring, T. M.; Zhang, G.; Mehlhorn, T.; Lowe, K.; Phillips, J.; Earles, J.; Wu, W.; Criddle, C. S.; Kemner, K. M.; Boyanov, M.

2011-12-01

In situ bioremediation of a uranium and nitrate-contaminated aquifer with the slow-release electron donor, emulsified vegetable oil (EVO), was tested at the US DOE Subsurface Biogeochemical Research Program (SBR) Integrated Field Research Challenge (IFRC) site, in Oak Ridge, TN. The EVO injection took place in Area 2 of the IFRC located about 300 m downgradient of the former S-3 disposal ponds. Liquid wastes, disposed in the ponds from 1951 to 1983, were primarily composed of nitric acid, plating wastes containing various metals (Cr, Ni) radionuclides (U, Tc), inorganics (nitrate, sulfate) and organic contaminants (tetrachloroethylene, acetone). Prior pond closure in 1987, large volumes of waste fluids migrated into the subsurface, down Bear Creek Valley and into Bear Creek. Contaminants detected at Area 2 were transported through a high permeability gravelly fill that is considered a preferred transport pathway for U to Bear Creek. Groundwater in the gravelly fill is contaminated with U (1-3 mg/L), sulfate (95-130 mg/L), and nitrate (20-40 mg/L) and 500 mg/kg or higher U has been detected on the solid phase of the fill material. The objective of this study is to investigate the feasibility and long-term sustainability of U(VI) reduction and immobilization, and nitrate degradation in the high permeability, high flow gravel fill using EVO as the electron donor. A one-time EVO injection was conducted over a 2 hour period in the highly permeable gravel (hydraulic conductivity 0.08 cm/sec) in the well instrumented IFRC Area 2 field plot. Extensive monitoring of geochemical parameters, dissolved gases and microbial populations were conducted during the test. A bromide tracer test was conducted prior to the injection of the EVO to assess transport pathways and rates. Geochemical analysis of site groundwater demonstrated the sequential bioreduction of oxygen, nitrate, Mn(IV), Fe(III) and sulfate. Transient accumulation of acetate was observed as an intermediate in the oil degradation. Reduction and removal of U and nitrate from groundwater was observed in all wells in hydraulic connection to the injection wells after 2-4 weeks. U concentrations in groundwater were reduced to below 30 ppb (US EPA drinking water standard) at some well locations and nitrate was reduced to below detectable levels. Rebound of U in groundwater was observed together with the rebound of sulfate concentrations as the EVO was consumed. The flux of U and nitrate contamination from groundwater to the surface water receptor (Bear Creek) was significantly reduced by the EVO injection over a one year period. Uranium (VI) reduction to U(IV) in the field tests was confirmed by X-ray absorption near-edge spectroscopy (XANES) analysis. The reduced U(IV) was determined by X-ray absorption fine structure (XAFS) to be in an Fe-U complex, not uraninite. The activities of major Fe(III)- and sulfate-reducing bacteria with U(VI)-reducing capability as well as methanogens was stimulated after injection of the oil.

Variations of uranium concentrations in a multi-aquifer system under the impact of surface water-groundwater interaction

NASA Astrophysics Data System (ADS)

Wu, Ya; Li, Junxia; Wang, Yanxin; Xie, Xianjun

2018-04-01

Understanding uranium (U) mobility is vital to minimizing its concentrations in potential drinking water sources. In this study, we report spatial-seasonal variations in U speciation and concentrations in a multi-aquifer system under the impact of Sanggan River in Datong basin, northern China. Hydrochemical and H, O, Sr isotopic data, thermodynamic calculations, and geochemical modeling are used to investigate the mechanisms of surface water-groundwater mixing-induced mobilization and natural attenuation of U. In the study site, groundwater U concentrations are up to 30.2 μg/L, and exhibit strong spatial-seasonal variations that are related to pH and Eh values, as well as dissolved Ca2+, HCO3-, and Fe(III) concentrations. For the alkaline aquifers of this site (pH 7.02-8.44), U mobilization is due to the formation and desorption of Ca2UO2(CO3)30 and CaUO2(CO3)32- caused by groundwater Ca2+ elevation via mineral weathering and Na-Ca exchange, incorporated U(VI) release from calcite, and U(IV) oxidation by Fe(OH)3. U immobilization is linked to the adsorption of CaUO2(CO3)32- and UO2(CO3)34- shifted from Ca2UO2(CO3)30 because of HCO3- elevation and Ca2+ depletion, U(VI) co-precipitation with calcite, and U(VI) reduction by adsorbed Fe2+ and FeS. Those results are of great significance for the groundwater resource management of this and similar other surface water-groundwater interaction zones.

Responses of microbial community functional structures to pilot-scale uranium in situ bioremediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, M.; Wu, W.-M.; Wu, L.

2010-02-15

A pilot-scale field test system with an inner loop nested within an outer loop was constructed for in situ U(VI) bioremediation at a US Department of Energy site, Oak Ridge, TN. The outer loop was used for hydrological protection of the inner loop where ethanol was injected for biostimulation of microorganisms for U(VI) reduction/immobilization. After 2 years of biostimulation with ethanol, U(VI) levels were reduced to below drinking water standard (<30 {micro}gl{sup -1}) in the inner loop monitoring wells. To elucidate the microbial community structure and functions under in situ uranium bioremediation conditions, we used a comprehensive functional gene arraymore » (GeoChip) to examine the microbial functional gene composition of the sediment samples collected from both inner and outer loop wells. Our study results showed that distinct microbial communities were established in the inner loop wells. Also, higher microbial functional gene number, diversity and abundance were observed in the inner loop wells than the outer loop wells. In addition, metal-reducing bacteria, such as Desulfovibrio, Geobacter, Anaeromyxobacter and Shewanella, and other bacteria, for example, Rhodopseudomonas and Pseudomonas, are highly abundant in the inner loop wells. Finally, the richness and abundance of microbial functional genes were highly correlated with the mean travel time of groundwater from the inner loop injection well, pH and sulfate concentration in groundwater. These results suggest that the indigenous microbial communities can be successfully stimulated for U bioremediation in the groundwater ecosystem, and their structure and performance can be manipulated or optimized by adjusting geochemical and hydrological conditions.« less

Redox-Active vs Redox-Innocent: A Comparison of Uranium Complexes Containing Diamine Ligands.

PubMed

Pattenaude, Scott A; Mullane, Kimberly C; Schelter, Eric J; Ferrier, Maryline G; Stein, Benjamin W; Bone, Sharon E; Lezama Pacheco, Juan S; Kozimor, Stosh A; Fanwick, Phillip E; Zeller, Matthias; Bart, Suzanne C

2018-05-11

Uranium complexes ( Mes DAE) 2 U(THF) (1-DAE) and Cp 2 U( Mes DAE) (2-DAE) ( Mes DAE = [ArN-CH 2 CH 2 -NAr]; Ar = 2,4,6-trimethylphenyl (Mes)), bearing redox-innocent diamide ligands, have been synthesized and characterized for a full comparison with previously published, redox-active diimine complexes, ( Mes DAB Me ) 2 U(THF) (1-DAB) and Cp 2 U( Mes DAB Me ) (2-DAB) ( Mes DAB Me = [ArN═C(Me)C(Me)═NAr]; Ar = Mes). These redox-innocent analogues maintain an analogous steric environment to their redox-active ligand counterparts to facilitate a study aimed at determining the differing electronic behavior around the uranium center. Structural analysis by X-ray crystallography showed 1-DAE and 2-DAE have a structural environment very similar to 1-DAB and 2-DAB, respectively. The main difference occurs with coordination of the ene-backbone to the uranium center in the latter species. Electronic absorption spectroscopy reveals these new DAE complexes are nearly identical to each other. X-ray absorption spectroscopy suggests all four species contain +4 uranium ions. The data also indicates that there is an electronic difference between the bis(diamide)-THF uranium complexes as opposed to those that only contain one diamide and two cyclopentadienyl rings. Finally, magnetic measurements reveal that all complexes display temperature-dependent behavior consistent with uranium(IV) ions that do not include ligand radicals. Overall, this study determines that there is no significant bonding difference between the redox-innocent and redox-active ligand frameworks on uranium. Furthermore, there are no data to suggest covalent bonding character using the latter ligand framework on uranium, despite what is known for transition metals.

Microbial Communities in Contaminated Sediments, Associated with Bioremediation of Uranium to Submicromolar Levels▿

PubMed Central

Cardenas, Erick; Wu, Wei-Min; Leigh, Mary Beth; Carley, Jack; Carroll, Sue; Gentry, Terry; Luo, Jian; Watson, David; Gu, Baohua; Ginder-Vogel, Matthew; Kitanidis, Peter K.; Jardine, Philip M.; Zhou, Jizhong; Criddle, Craig S.; Marsh, Terence L.; Tiedje, James M.

2008-01-01

Microbial enumeration, 16S rRNA gene clone libraries, and chemical analysis were used to evaluate the in situ biological reduction and immobilization of uranium(VI) in a long-term experiment (more than 2 years) conducted at a highly uranium-contaminated site (up to 60 mg/liter and 800 mg/kg solids) of the U.S. Department of Energy in Oak Ridge, TN. Bioreduction was achieved by conditioning groundwater above ground and then stimulating growth of denitrifying, Fe(III)-reducing, and sulfate-reducing bacteria in situ through weekly injection of ethanol into the subsurface. After nearly 2 years of intermittent injection of ethanol, aqueous U levels fell below the U.S. Environmental Protection Agency maximum contaminant level for drinking water and groundwater (<30 μg/liter or 0.126 μM). Sediment microbial communities from the treatment zone were compared with those from a control well without biostimulation. Most-probable-number estimations indicated that microorganisms implicated in bioremediation accumulated in the sediments of the treatment zone but were either absent or in very low numbers in an untreated control area. Organisms belonging to genera known to include U(VI) reducers were detected, including Desulfovibrio, Geobacter, Anaeromyxobacter, Desulfosporosinus, and Acidovorax spp. The predominant sulfate-reducing bacterial species were Desulfovibrio spp., while the iron reducers were represented by Ferribacterium spp. and Geothrix spp. Diversity-based clustering revealed differences between treated and untreated zones and also within samples of the treated area. Spatial differences in community structure within the treatment zone were likely related to the hydraulic pathway and to electron donor metabolism during biostimulation. PMID:18456853

Uranium-mediated electrocatalytic dihydrogen production from water.

PubMed

Halter, Dominik P; Heinemann, Frank W; Bachmann, Julien; Meyer, Karsten

2016-02-18

Depleted uranium is a mildly radioactive waste product that is stockpiled worldwide. The chemical reactivity of uranium complexes is well documented, including the stoichiometric activation of small molecules of biological and industrial interest such as H2O, CO2, CO, or N2 (refs 1 - 11), but catalytic transformations with actinides remain underexplored in comparison to transition-metal catalysis. For reduction of water to H2, complexes of low-valent uranium show the highest potential, but are known to react violently and uncontrollably forming stable bridging oxo or uranyl species. As a result, only a few oxidations of uranium with water have been reported so far; all stoichiometric. Catalytic H2 production, however, requires the reductive recovery of the catalyst via a challenging cleavage of the uranium-bound oxygen-containing ligand. Here we report the electrocatalytic water reduction observed with a trisaryloxide U(III) complex [(((Ad,Me)ArO)3mes)U] (refs 18 and 19)--the first homogeneous uranium catalyst for H2 production from H2O. The catalytic cycle involves rare terminal U(IV)-OH and U(V)=O complexes, which have been isolated, characterized, and proven to be integral parts of the catalytic mechanism. The recognition of uranium compounds as potentially useful catalysts suggests new applications for such light actinides. The development of uranium-based catalysts provides new perspectives on nuclear waste management strategies, by suggesting that mildly radioactive depleted uranium--an abundant waste product of the nuclear power industry--could be a valuable resource.

RECOVERY OF URANIUM BY SECONDARY XANTHATE COMPLEXING

DOEpatents

Neville, O.K.

1959-09-01

A method is described for separating and recovering uranium values contained in an acidic aqueous solution together with thorium or protactinium values. In accordance with the invention, the acidic solution containing uranium in the uranyl form is contacted with an organic xanthate. The xanthate forms a urano-xanthate complex but is substantially non-reactive with thorium and protactinium. The urano-xanthate complex is recovered by organic solvent extraction.

The effect of uranium on bacterial viability and cell surface morphology using atomic force microscopy in the presence of bicarbonate ions.

PubMed

Sepulveda-Medina, Paola; Katsenovich, Yelena; Musaramthota, Vishal; Lee, Michelle; Lee, Brady; Dua, Rupak; Lagos, Leonel

2015-06-01

Past disposal practices at nuclear production facilities have led to the release of liquid waste into the environment creating multiple radionuclide plumes. Microorganisms are known for the ability to interact with radionuclides and impact their mobility in soils and sediments. Gram-positive Arthrobacter sp. are one of the most common bacterial groups in soils and are found in large numbers in subsurface environments contaminated with radionuclides. This study experimentally analyzed changes on the bacteria surface at the nanoscale level after uranium exposure and evaluated the effect of aqueous bicarbonate ions on U(VI) toxicity of a low uranium-tolerant Arthrobacter oxydans strain G968 by investigating changes in adhesion forces and cell dimensions via atomic force microscopy (AFM). Experiments were extended to assess cell viability by the Live/Dead BacLight Bacterial Viability Kit (Molecular Probes) and quantitatively illustrate the effect of uranium exposure in the presence of varying concentrations of bicarbonate ions. AFM and viability studies showed that samples containing bicarbonate were able to withstand uranium toxicity and remained viable. Samples containing no bicarbonate exhibited deformed surfaces and a low height profile, which, in conjunction with viability studies, indicated that the cells were not viable. Copyright © 2015 Institut Pasteur. All rights reserved.

The geometric structures, vibrational frequencies and redox properties of the actinyl coordination complexes ([AnO2(L)n](m); An = U, Pu, Np; L = H2O, Cl-, CO3(2-), CH3CO2(-), OH-) in aqueous solution, studied by density functional theory methods.

PubMed

Austin, Jonathan P; Sundararajan, Mahesh; Vincent, Mark A; Hillier, Ian H

2009-08-14

The geometric and electronic structures of the aqua, chloro, acetato, hydroxo and carbonato complexes of U, Np and Pu in both their (VI) and (V) oxidation states, and in an aqueous environment, have been studied using density functional theory methods. We have obtained micro-solvated structures derived from molecular dynamics simulations and included the bulk solvent using a continuum model. We find that two different hydrogen bonding patterns involving the axial actinyl oxygen atoms are sometimes possible, and may give rise to different An-O bond lengths and vibrational frequencies. These alternative structures are reflected in the experimental An-O bond lengths of the aqua and carbonato complexes. The variation of the redox potential of the uranyl complexes with the different ligands has been studied using both BP86 and B3LYP functionals. The relative values for the four uranium complexes having anionic ligands are in surprisingly good agreement with experiment, although the absolute values are in error by approximately 1 eV. The absolute error for the aqua species is much less, leading to an incorrect order of the redox potentials of the aqua and chloro species.

Probing the interaction of U (VI) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy

DOE PAGES

Uribe, Eva C.; Mason, Harris E.; Shusterman, Jennifer A.; ...

2016-05-30

The fundamental interaction of U (VI) with diethylphosphatoethyl triethoxysilane functionalized SBA-15 mesoporous silica is studied by macroscopic batch experiments and solid-state NMR spectroscopy. DPTS-functionalized silica has been shown to extract U (VI) from nitric acid solutions at or above pH 3. Extraction is dependent on pH and ionic strength. Single-pulse 31P NMR on U (VI) contacted samples revealed that U (VI)only interacts with a fraction of the ligands present on the surface. At pH 4 the U (VI) extraction capacity of the material is limited to 27–37% of the theoretical capacity, based on ligand loading. We combined single pulse 31Pmore » NMR on U (VI)-contacted samples with batch studies to measure a ligand-to-metal ratio of approximately 2 : 1 at pH 3 and 4. Batch studies and cross-polarization NMR measurements reveal that U (VI) binds to deprotonated phosphonate and/or silanol sites. We use 31P– 31P DQ-DRENAR NMR studies to compare the average dipolar coupling between phosphorus spins for both U (VI)-complexed and non-complexed ligand environments. Furthermore, these measurements reveal that U (VI) extraction is not limited by inadequate surface distribution of ligands, but rather by low stability of the surface phosphonate complex.« less

Probing the interaction of U (VI) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uribe, Eva C.; Mason, Harris E.; Shusterman, Jennifer A.

The fundamental interaction of U (VI) with diethylphosphatoethyl triethoxysilane functionalized SBA-15 mesoporous silica is studied by macroscopic batch experiments and solid-state NMR spectroscopy. DPTS-functionalized silica has been shown to extract U (VI) from nitric acid solutions at or above pH 3. Extraction is dependent on pH and ionic strength. Single-pulse 31P NMR on U (VI) contacted samples revealed that U (VI)only interacts with a fraction of the ligands present on the surface. At pH 4 the U (VI) extraction capacity of the material is limited to 27–37% of the theoretical capacity, based on ligand loading. We combined single pulse 31Pmore » NMR on U (VI)-contacted samples with batch studies to measure a ligand-to-metal ratio of approximately 2 : 1 at pH 3 and 4. Batch studies and cross-polarization NMR measurements reveal that U (VI) binds to deprotonated phosphonate and/or silanol sites. We use 31P– 31P DQ-DRENAR NMR studies to compare the average dipolar coupling between phosphorus spins for both U (VI)-complexed and non-complexed ligand environments. Furthermore, these measurements reveal that U (VI) extraction is not limited by inadequate surface distribution of ligands, but rather by low stability of the surface phosphonate complex.« less

COORDINATION COMPOUND-SOLVENT EXTRACTION PROCESS FOR URANIUM RECOVERY

DOEpatents

Reas, W.H.

1959-03-10

A method is presented for the separation of uranium from aqueous solutions containing a uranyl salt and thorium. Thc separation is effected by adding to such solutions an organic complexing agent, and then contacting the solution with an organic solvent in which the organic complexing agent is soluble. By use of the proper complexing agent in the proper concentrations uranium will be complexed and subsequently removed in the organic solvent phase, while the thorium remains in the aqueous phase. Mentioned as suitable organic complexing agents are antipyrine, bromoantipyrine, and pyramidon.

Effects of sulfate ligand on uranyl carbonato surface species on ferrihydrite surfaces

USGS Publications Warehouse

Arai, Yuji; Fuller, C.C.

2012-01-01

Understanding uranium (U) sorption processes in permeable reactive barriers (PRB) are critical in modeling reactive transport for evaluating PRB performance at the Fry Canyon demonstration site in Utah, USA. To gain insight into the U sequestration mechanism in the amorphous ferric oxyhydroxide (AFO)-coated gravel PRB, U(VI) sorption processes on ferrihydrite surfaces were studied in 0.01 M Na2SO4 solutions to simulate the major chemical composition of U-contaminatedgroundwater (i.e., [SO42-]~13 mM L-1) at the site. Uranyl sorption was greater at pH 7.5 than that at pH 4 in both air- and 2% pCO2-equilibrated systems. While there were negligible effects of sulfate ligands on the pH-dependent U(VI) sorption (<24 h) in both systems, X-ray absorption spectroscopy (XAS) analysis showed sulfate ligand associated U(VI) surface species at the ferrihydrite–water interface. In air-equilibrated systems, binary and mono-sulfate U(VI) ternary surface species co-existed at pH 5.43. At pH 6.55–7.83, a mixture of mono-sulfate and bis-carbonato U(VI) ternary surface species became more important. At 2% pCO2, there was no contribution of sulfate ligands on the U(VI) ternary surface species. Instead, a mixture of bis-carbonato inner-sphere (38%) and tris-carbonato outer-sphere U(VI) ternary surface species (62%) was found at pH 7.62. The study suggests that the competitive ligand (bicarbonate and sulfate) coordination on U(VI) surface species might be important in evaluating the U solid-state speciation in the AFO PRB at the study site where pCO2 fluctuates between 1 and 2 pCO2%.

Effects of sulfate ligand on uranyl carbonato surface species on ferrihydrite surfaces.

PubMed

Arai, Yuji; Fuller, C C

2012-01-01

Understanding uranium (U) sorption processes in permeable reactive barriers (PRB) are critical in modeling reactive transport for evaluating PRB performance at the Fry Canyon demonstration site in Utah, USA. To gain insight into the U sequestration mechanism in the amorphous ferric oxyhydroxide (AFO)-coated gravel PRB, U(VI) sorption processes on ferrihydrite surfaces were studied in 0.01 M Na(2)SO(4) solutions to simulate the major chemical composition of U-contaminated groundwater (i.e., [SO(4)(2-)] ~13 mM L(-1)) at the site. Uranyl sorption was greater at pH 7.5 than that at pH 4 in both air- and 2% pCO(2)-equilibrated systems. While there were negligible effects of sulfate ligands on the pH-dependent U(VI) sorption (<24 h) in both systems, X-ray absorption spectroscopy (XAS) analysis showed sulfate ligand associated U(VI) surface species at the ferrihydrite-water interface. In air-equilibrated systems, binary and mono-sulfate U(VI) ternary surface species co-existed at pH 5.43. At pH 6.55-7.83, a mixture of mono-sulfate and bis-carbonato U(VI) ternary surface species became more important. At 2% pCO(2), there was no contribution of sulfate ligands on the U(VI) ternary surface species. Instead, a mixture of bis-carbonato inner-sphere (38%) and tris-carbonato outer-sphere U(VI) ternary surface species (62%) was found at pH 7.62. The study suggests that the competitive ligand (bicarbonate and sulfate) coordination on U(VI) surface species might be important in evaluating the U solid-state speciation in the AFO PRB at the study site where pCO(2) fluctuates between 1 and 2 pCO(2)%. Copyright © 2011 Elsevier Inc. All rights reserved.

Chemical and mineralogical composition of the Mongolian rural soils and their uranium sorption behavior.

PubMed

Tserenpil, Sh; Maslov, O D; Norov, N; Liu, Q C; Fillipov, M F; Theng, Benny K G; Belov, A G

2013-04-01

Distribution of uranium (VI) between soil solids and solutions is a key parameter in assessing the risk to the biosphere of disposing uranium-rich waste products from nuclear plants as well as uranium (U) ore mining. Both of these topics have recently been brought to public attention in Mongolia. Regional background levels of soil elements are an important dataset for accessing the actual environmental situation and monitoring pollution levels. Little information, however, is available on background concentrations of various elements in Mongolian soils. Thirteen rural soils were sampled from six provinces in Mongolia, and the concentrations of macro-, micro- and trace elements were measured. The values obtained served as a reference (baseline) for uncontaminated soils. The soils were characterized with slightly acidic to strongly alkaline pH values. With the exception of the sample from a western province, all the soils investigated contained little organic matter. The content of soil elements did not vary widely among geographical regions. The concentration of most micro elements was within the range of worldwide soil values but the value for Zn tended to be moderately higher. The U (VI) sorption into the soils was investigated using the batch technique and the (237)U radionuclide tracer, produced by the photo fission reaction (238)U(γ, n) (237)U at an electron accelerator. The (237)U distribution coefficient (K(d)), derived from the sorption isotherms, was related to solution pH and varying from 9 to 2547 mL g(-1) when the pH ranged between 3 and 7.7. The sorption process was interpreted in terms of the formation of different U (VI) species at given concentrations, calculated using the Speciation program with and without carbonate in the system. The U sorption isotherm displayed two general patterns: one where sorption decreased as solution pH increased, showing a maximum at pH 3, and another pattern revealed an adsorption maximum at pH 5 and then decreased up to pH 7.7 (the final solution pH). The observed decrease in K(d) when solution pH increased from 6 to 8 was consistent with the increased formation of soluble UO(2)(OH)(2) species. A linear negative correlation between lgK(d) and the solution pH was observed similarly to that reported for the soils with a pH ≥ 6. Copyright © 2012 Elsevier Ltd. All rights reserved.

Surface Complexation Modeling of Eu(III) and U(VI) Interactions with Graphene Oxide.

PubMed

Xie, Yu; Helvenston, Edward M; Shuller-Nickles, Lindsay C; Powell, Brian A

2016-02-16

Graphene oxide (GO) has great potential for actinide removal due to its extremely high sorption capacity, but the mechanism of sorption remains unclear. In this study, the carboxylic functional group and an unexpected sulfonate functional group on GO were characterized as the reactive surface sites and quantified via diffuse layer modeling of the GO acid/base titrations. The presence of sulfonate functional group on GO was confirmed using elemental analysis and X-ray photoelectron spectroscopy. Batch experiments of Eu(III) and U(VI) sorption to GO as the function of pH (1-8) and as the function of analyte concentration (10-100, 000 ppb) at a constant pH ≈ 5 were conducted; the batch sorption results were modeled simultaneously using surface complexation modeling (SCM). The SCM indicated that Eu(III) and U(VI) complexation to carboxylate functional group is the main mechanism for their sorption to GO; their complexation to the sulfonate site occurred at the lower pH range and the complexation of Eu(III) to sulfonate site are more significant than that of U(VI). Eu(III) and U(VI) facilitated GO aggregation was observed with high Eu(III) and U(VI) concentration and may be caused by surface charge neutralization of GO after sorption.

77 FR 51579 - Application for a License To Export High-Enriched Uranium

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-24

... NUCLEAR REGULATORY COMMISSION Application for a License To Export High-Enriched Uranium Pursuant.... Complex, July 30, 2012, August Uranium (93.35%). uranium-235 high-enriched 1, 2012, XSNM3726, 11006037. contained in 7.5 uranium in the kilograms uranium. form of broken metal to the Atomic Energy of Canada...

[Effect of the chelator BPCBG on the decorporation of uranium in vivo and uranium-induced damage of human renal tubular epithelial cells in vitro].

PubMed

Bao, Yi-zhong; Wang, Dan; Hu, Yu-xing; Xu, Ai-hong; Sun, Mei-zhen; Chen, Hong-hong

2011-11-01

This study is to assess the efficacy of BPCBG on the decorporation of uranium (VI) and protecting human renal proximal tubular epithelial cells (HK-2) against uranium-induced damage. BPCBG at different doses was injected intramuscularly to male SD rats immediately after a single intraperitoneal injection of UO2(CH3COO)2. Twenty-four hours later uranium contents in urine, kidneys and femurs were measured by ICP-MS. After HK-2 cells were exposed to UO2(CH3COO)2 immediately or for 24 h followed by BPCBG treatment at different doses for another 24 or 48 h, the uranium contents in HK-2 cells were measured by ICP-MS, the cell survival was assayed by cell counting kit-8 assay, formation of micronuclei was determined by the cytokinesis-block (CB) micronucleus assay and the production of intracellular reactive oxygen species (ROS) was detected by 2',7'-dichlorofluorescin diacetate (DCFH-DA) oxidation. DTPA-CaNa3 was used as control. It was found that BPCBG at dosages of 60, 120, and 600 micromol kg(-1) resulted in 37%-61% increase in 24 h-urinary uranium excretion, and significantly decreased the amount of uranium retention in kidney and bone to 41%-31% and 86%-42% of uranium-treated group, respectively. After HK-2 cells that had been pre-treated with UO2(CH3COO)2 for 24 h were treated with the chelators for another 24 h, 55%-60% of the intracellular uranium was removed by 10-250 micromol L(-1) of BPCBG. Treatment of uranium-treated HK-2 cells with BPCBG significantly enhanced the cell survival, decreased the formation of micronuclei and inhibited the production of intracellular ROS. Although DTPA-CaNa3 markedly reduced the uranium retention in kidney of rats and HK-2 cells, its efficacy of uranium removal from body was significantly lower than that of BPCBG and it could not protect uranium-induced cell damage. It can be concluded that BPCBG effectively decorporated the uranium from UO2(CH3COO)2-treated rats and HK-2 cells, which was better than DTPA-CaNa3. It could also scavenge the uranium-induced intracellular ROS and protect against the uranium-induced cell damage. BPCBG is worth further investigation.

GeoChip-based analysis of functional microbial communities in a bioreduced uranium-contaminated aquifer during reoxidation by oxygen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Nostrand, J.D.; Wu, W.-M.; Wu, L.

2009-07-15

A pilot-scale system was established for in situ biostimulation of U(VI) reduction by ethanol addition at the US Department of Energy's (DOE's) Field Research Center (Oak Ridge, TN). After achieving U(VI) reduction, stability of the bioreduced U(IV) was evaluated under conditions of (i) resting (no ethanol injection), (ii) reoxidation by introducing dissolved oxygen (DO), and (iii) reinjection of ethanol. GeoChip, a functional gene array with probes for N, S and C cycling, metal resistance and contaminant degradation genes, was used for monitoring groundwater microbial communities. High diversity of all major functional groups was observed during all experimental phases. The microbialmore » community was extremely responsive to ethanol, showing a substantial change in community structure with increased gene number and diversity after ethanol injections resumed. While gene numbers showed considerable variations, the relative abundance (i.e. percentage of each gene category) of most gene groups changed little. During the reoxidation period, U(VI) increased, suggesting reoxidation of reduced U(IV). However, when introduction of DO was stopped, U(VI) reduction resumed and returned to pre-reoxidation levels. These findings suggest that the community in this system can be stimulated and that the ability to reduce U(VI) can be maintained by the addition of electron donors. This biostimulation approach may potentially offer an effective means for the bioremediation of U(VI)-contaminated sites.« less

Incorporation of oxidized uranium into Fe (hydr)oxides during Fe(II) catalyzed remineralization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nico, Peter S.; Stewart, Brandy D.; Fendorf, Scott

2009-07-01

The form of solid phase U after Fe(II) induced anaerobic remineralization of ferrihydrite in the presence of aqueous and absorbed U(VI) was investigated under both abiotic batch and biotic flow conditions. Experiments were conducted with synthetic ground waters containing 0.168 mM U(VI), 3.8 mM carbonate, and 3.0 mM Ca{sup 2+}. In spite of the high solubility of U(VI) under these conditions, appreciable removal of U(VI) from solution was observed in both the abiotic and biotic systems. The majority of the removed U was determined to be substituted as oxidized U (U(VI) or U(V)) into the octahedral position of the goethitemore » and magnetite formed during ferrihydrite remineralization. It is estimated that between 3% and 6% of octahedral Fe(III) centers in the new Fe minerals were occupied by U(VI). This site specific substitution is distinct from the non-specific U co-precipitation processes in which uranyl compounds, e.g. uranyl hydroxide or carbonate, are entrapped with newly formed Fe oxides. The prevalence of site specific U incorporation under both abiotic and biotic conditions and the fact that the produced solids were shown to be resistant to both extraction (30 mM KHCO{sub 3}) and oxidation (air for 5 days) suggest the potential importance of sequestration in Fe oxides as a stable and immobile form of U in the environment.« less

Removal of Cr(VI) from Aqueous Environments Using Micelle-Clay Adsorption

PubMed Central

Qurie, Mohannad; Khamis, Mustafa; Manassra, Adnan; Ayyad, Ibrahim; Nir, Shlomo; Scrano, Laura; Bufo, Sabino A.; Karaman, Rafik

2013-01-01

Removal of Cr(VI) from aqueous solutions under different conditions was investigated using either clay (montmorillonite) or micelle-clay complex, the last obtained by adsorbing critical micelle concentration of octadecyltrimethylammonium ions onto montmorillonite. Batch experiments showed the effects of contact time, adsorbent dosage, and pH on the removal efficiency of Cr(VI) from aqueous solutions. Langmuir adsorption isotherm fitted the experimental data giving significant results. Filtration experiments using columns filled with micelle-clay complex mixed with sand were performed to assess Cr(VI) removal efficiency under continuous flow at different pH values. The micelle-clay complex used in this study was capable of removing Cr(VI) from aqueous solutions without any prior acidification of the sample. Results demonstrated that the removal effectiveness reached nearly 100% when using optimal conditions for both batch and continuous flow techniques. PMID:24222757

Diversity and Characterization of Sulfate-Reducing Bacteria in Groundwater at a Uranium Mill Tailings Site

PubMed Central

Chang, Yun-Juan; Peacock, Aaron D.; Long, Philip E.; Stephen, John R.; McKinley, James P.; Macnaughton, Sarah J.; Hussain, A. K. M. Anwar; Saxton, Arnold M.; White, David C.

2001-01-01

Microbially mediated reduction and immobilization of U(VI) to U(IV) plays a role in both natural attenuation and accelerated bioremediation of uranium-contaminated sites. To realize bioremediation potential and accurately predict natural attenuation, it is important to first understand the microbial diversity of such sites. In this paper, the distribution of sulfate-reducing bacteria (SRB) in contaminated groundwater associated with a uranium mill tailings disposal site at Shiprock, N.Mex., was investigated. Two culture-independent analyses were employed: sequencing of clone libraries of PCR-amplified dissimilatory sulfite reductase (DSR) gene fragments and phospholipid fatty acid (PLFA) biomarker analysis. A remarkable diversity among the DSR sequences was revealed, including sequences from δ-Proteobacteria, gram-positive organisms, and the Nitrospira division. PLFA analysis detected at least 52 different mid-chain-branched saturate PLFA and included a high proportion of 10me16:0. Desulfotomaculum and Desulfotomaculum-like sequences were the most dominant DSR genes detected. Those belonging to SRB within δ-Proteobacteria were mainly recovered from low-uranium (≤302 ppb) samples. One Desulfotomaculum-like sequence cluster overwhelmingly dominated high-U (>1,500 ppb) sites. Logistic regression showed a significant influence of uranium concentration over the dominance of this cluster of sequences (P = 0.0001). This strong association indicates that Desulfotomaculum has remarkable tolerance and adaptation to high levels of uranium and suggests the organism's possible involvement in natural attenuation of uranium. The in situ activity level of Desulfotomaculum in uranium-contaminated environments and its comparison to the activities of other SRB and other functional groups should be an important area for future research. PMID:11425735

Uranium speciation in Fernald soils. Progress report, January 1--May 31, 1992

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morris, D.E.; Conradson, S.D.; Tait, C.D.

1992-05-31

This report details progress made from January 1 to May 31, 1992 in this analytical support task to determine the speciation of uranium in contaminated soil samples from the Fernald Environmental Management Project site under the auspices of the Uranium in Soils Integrated Demonstration funded through the US DOE`s Office of Technology Development. The authors` efforts have focused on characterization of soil samples collected by S.Y. Lee (Oak Ridge National Laboratory) from five locales at the Fernald site. These were chosen to sample a broad range of uranium source terms. On the basis of x-ray absorption spectroscopy data, they havemore » determined that the majority of uranium (> 80--90%) exists in the hexavalent oxidation state for all samples examined. This is a beneficial finding from the perspective of remediation, because U(VI) species are more soluble in general than uranium species in other oxidation states. Optical luminescence data from many of the samples show the characteristic structured yellow-green emission from the uranyl (UO{sub 2}{sup 2+}) moiety. The luminescence data also suggest that much of the uranium in these soils is present as well-crystallized UO{sub 2}{sup 2+} species. Some clear spectroscopic distinctions have been noted for several samples that illustrate significant differences in the speciation (1) from site to site, (2) within different horizons at the same site, and (3) within different size fractions of the soils in the same horizon at the same site. This marked heterogeneity in uranyl speciation suggests that several soil washing strategies may be necessary to reduce the total uranium concentrations within these soils to regulatory limits.« less

Temperature Dependence of Uranium and Vanadium Adsorption on Amidoxime-Based Adsorbents in Natural Seawater

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuo, Li-Jung; Gill, Gary A.; Tsouris, Costas

Recent advances in the development of amidoxime-based adsorbents have made it highly promising for seawater uranium extraction. However, there is a great need to understand the influence of temperature on the uranium sequestration performance of the adsorbents in natural seawater. Here in this work, the apparent enthalpy and entropy of the sorption of uranium (VI) and vanadium (V) with amidoxime-based adsorbents were determined in natural seawater tests at 8, 20, and 31 °C that cover a broad range of ambient seawater temperature. The sorption of U was highly endothermic, producing apparent enthalpies of 57 ± 6.0 and 59 ± 11more » kJ mol -1 and apparent entropies of 314 ± 21 and 320 ± 36 J K-1 mol -1, respectively, for two adsorbent formulations. In contrast, the sorption of V showed a much smaller temperature sensitivity, producing apparent enthalpies of 6.1 ± 5.9 and -11 ± 5.7 kJ mol -1 and apparent entropies of 164 ± 20 and 103 ± 19 J K -1 mol -1, respectively. This new thermodynamic information suggests that amidoxime-based adsorbents will deliver significantly increased U adsorption capacities and improved selectivity in warmer waters. A separate field study of seawater uranium adsorption conducted in a warm seawater site (Miami, FL, USA) confirm the observed strong temperature effect on seawater uranium mining. Lastly, this strong temperature dependence demonstrates that the warmer the seawater where the amidoxime-based adsorbents are deployed the greater the yield for seawater uranium extraction.« less

Temperature Dependence of Uranium and Vanadium Adsorption on Amidoxime-Based Adsorbents in Natural Seawater

DOE PAGES

Kuo, Li-Jung; Gill, Gary A.; Tsouris, Costas; ...

2018-01-16

Recent advances in the development of amidoxime-based adsorbents have made it highly promising for seawater uranium extraction. However, there is a great need to understand the influence of temperature on the uranium sequestration performance of the adsorbents in natural seawater. Here in this work, the apparent enthalpy and entropy of the sorption of uranium (VI) and vanadium (V) with amidoxime-based adsorbents were determined in natural seawater tests at 8, 20, and 31 °C that cover a broad range of ambient seawater temperature. The sorption of U was highly endothermic, producing apparent enthalpies of 57 ± 6.0 and 59 ± 11more » kJ mol -1 and apparent entropies of 314 ± 21 and 320 ± 36 J K-1 mol -1, respectively, for two adsorbent formulations. In contrast, the sorption of V showed a much smaller temperature sensitivity, producing apparent enthalpies of 6.1 ± 5.9 and -11 ± 5.7 kJ mol -1 and apparent entropies of 164 ± 20 and 103 ± 19 J K -1 mol -1, respectively. This new thermodynamic information suggests that amidoxime-based adsorbents will deliver significantly increased U adsorption capacities and improved selectivity in warmer waters. A separate field study of seawater uranium adsorption conducted in a warm seawater site (Miami, FL, USA) confirm the observed strong temperature effect on seawater uranium mining. Lastly, this strong temperature dependence demonstrates that the warmer the seawater where the amidoxime-based adsorbents are deployed the greater the yield for seawater uranium extraction.« less

SEPARATION OF URANIUM FROM OTHER METALS

DOEpatents

Hyman, H.H.

1959-07-01

The separation of uranium from other elements, such as ruthenium, zirconium, niobium, cerium, and other rare earth metals is described. According to the invention, this is accomplished by adding hydrazine to an acid aqueous solution containing salts of uranium, preferably hexavalent uranium, and then treating the mixture with a substantially water immiscible ketone, such as hexone. A reaction takes place between the ketone and the hydrazine whereby a complex, a ketazine, is formed; this complex has a greater power of extraction for uranium than the ketone by itself. When contaminating elements are present, they substantially remain in ihe aqueous solution.

URANIUM RECOVERY AND PURIFICATION PROCESS AND PRODUCTION OF HIGH PURITY URANIUM TETRAFLUORIDE

DOEpatents

Bailes, R.H.; Long, R.S.; Grinstead, R.R.

1957-09-17

A process is described wherein an anionic exchange technique is employed to separate uramium from a large variety of impurities. Very efficient and economical purification of contamimated uranium can be achieved by treatment of the contaminated uranium to produce a solution containing a high concentration of chloride. Under these conditions the uranium exists as an aniomic chloride complex. Then the uranium chloride complex is adsorbed from the solution on an aniomic exchange resin, whereby a portion of the impurities remain in the solution and others are retained with the uramium by the resin. The adsorbed impurities are then removed by washing the resin with pure concentrated hydrochloric acid, after which operation the uranium is eluted with pure water yielding an acidic uranyl chloride solution of high purity.

Draft Genome Sequences for Two Metal-Reducing Pelosinus fermentans Strains Isolated from a Cr(VI)-Contaminated Site and for Type Strain R7

PubMed Central

Brown, Steven D.; Podar, Mircea; Klingeman, Dawn M.; Johnson, Courtney M.; Yang, Zamin K.; Utturkar, Sagar M.; Land, Miriam L.; Mosher, Jennifer J.; Hurt, Richard A.; Phelps, Tommy J.; Palumbo, Anthony V.; Arkin, Adam P.; Hazen, Terry C.

2012-01-01

Pelosinus fermentans 16S rRNA gene sequences have been reported from diverse geographical sites since the recent isolation of the type strain. We present the genome sequence of the P. fermentans type strain R7 (DSM 17108) and genome sequences for two new strains with different abilities to reduce iron, chromate, and uranium. PMID:22933770

Uranium (VI) transport in saturated heterogeneous media: Influence of kaolinite and humic acid.

PubMed

Chen, Chong; Zhao, Kang; Shang, Jianying; Liu, Chongxuan; Wang, Jin; Yan, Zhifeng; Liu, Kesi; Wu, Wenliang

2018-05-07

Natural aquifers typically exhibit a variety of structural heterogeneities. However, the effect of mineral colloids and natural organic matter on the transport behavior of uranium (U) in saturated heterogeneous media are not totally understood. In this study, heterogeneous column experiments were conducted, and the constructed columns contained a fast-flow domain (FFD) and a slow-flow domain (SFD). The effect of kaolinite, humic acid (HA), and kaolinite/HA mixture on U(VI) retention and release in saturated heterogeneous media was examined. Media heterogeneity significantly influenced U fate and transport behavior in saturated subsurface environment. The presence of kaolinite, HA, and kaolinite/HA enhanced the mobility of U in heterogeneous media, and the mobility of U was the highest in the presence of kaolinite/HA and the lowest in the presence of kaolinite. In the presence of kaolinite, there was no difference in the amount of U released from the FFD and SFD. However, in the presence of HA and kaolinite/HA, a higher amount of U was released from the FFD. The findings in this study showed that medium structure and mineral colloids, as well as natural organic matter in the aqueous phase had significant effects on U transport and fate in subsurface environment. Copyright © 2018 Elsevier Ltd. All rights reserved.

Physicochemical heterogeneity controls on uranium bioreduction rates at the field scale.

PubMed

Li, Li; Gawande, Nitin; Kowalsky, Michael B; Steefel, Carl I; Hubbard, Susan S

2011-12-01

It has been demonstrated in laboratory systems that U(VI) can be reduced to immobile U(IV) by bacteria in natural environments. The ultimate efficacy of bioreduction at the field scale, however, is often challenging to quantify and depends on site characteristics. In this work, uranium bioreduction rates at the field scale are quantified, for the first time, using an integrated approach. The approach combines field data, inverse and forward hydrological and reactive transport modeling, and quantification of reduction rates at different spatial scales. The approach is used to explore the impact of local scale (tens of centimeters) parameters and processes on field scale (tens of meters) system responses to biostimulation treatments and the controls of physicochemical heterogeneity on bioreduction rates. Using the biostimulation experiments at the Department of Energy Old Rifle site, our results show that the spatial distribution of hydraulic conductivity and solid phase mineral (Fe(III)) play a critical role in determining the field-scale bioreduction rates. Due to the dependence on Fe-reducing bacteria, field-scale U(VI) bioreduction rates were found to be largely controlled by the abundance of Fe(III) minerals at the vicinity of the injection wells and by the presence of preferential flow paths connecting injection wells to down gradient Fe(III) abundant areas.

Uranium isotopes fingerprint biotic reduction.

PubMed

Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J; Weyer, Stefan; Bernier-Latmani, Rizlan

2015-05-05

Knowledge of paleo-redox conditions in the Earth's history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth's crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

Uranium: A Dentist's perspective

PubMed Central

Toor, R. S. S.; Brar, G. S.

2012-01-01

Uranium is a naturally occurring radionuclide found in granite and other mineral deposits. In its natural state, it consists of three isotopes (U-234, U-235 and U-238). On an average, 1% – 2% of ingested uranium is absorbed in the gastrointestinal tract in adults. The absorbed uranium rapidly enters the bloodstream and forms a diffusible ionic uranyl hydrogen carbonate complex (UO2HCO3+) which is in equilibrium with a nondiffusible uranyl albumin complex. In the skeleton, the uranyl ion replaces calcium in the hydroxyapatite complex of the bone crystal. Although in North India, there is a risk of radiological toxicity from orally ingested natural uranium, the principal health effects are chemical toxicity. The skeleton and kidney are the primary sites of uranium accumulation. Acute high dose of uranyl nitrate delays tooth eruption, and mandibular growth and development, probably due to its effect on target cells. Based on all previous research and recommendations, the role of a dentist is to educate the masses about the adverse effects of uranium on the overall as well as the dental health. The authors recommended that apart from the discontinuation of the addition of uranium to porcelain, the Public community water supplies must also comply with the Environmental Protection Agency (EPA) standards of uranium levels being not more than 30 ppb (parts per billion). PMID:24478959

Decontamination of TCE- and U-rich waters by granular iron: Role of sorbed Fe(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Charlet, L.; Liger, E.; Gerasimo, P.

1998-01-01

Uranium (UO{sub 2}{sup 2+}) and chlorinated aliphatics [tetrachloroethane (PCE) and trichloroethane (TCE)] can be reduced and thus immobilized or degraded, respectively, by the same abiotic mechanism. In this mechanism the reduction reaction is coupled to the oxidation of Fe(II) sorbed on iron corrosion products such as hematite. This is indicated by the equilibrium E{sub h} values measured during uranium immobilization and PCE degradation reactions of zerovalent iron. These values fit closely with those measured in the Fe(II)-{alpha}Fe{sub 2}O{sub 3}-H{sub 2}O system (in the absence of U or PCE), not those of the Fe(o)/Fe(II) or H{sub 2}(g)/H{sub 2}O couples. Because ironmore » (II) is very unstable in environments that are not strictly anaerobic, Fe(o) serves as a source of Fe(II). The reduction kinetic rate, analyzed in detail for the reduction of U(VI), is found to be a function of the concentration of OH{sup {minus}}, Fe{sup 2+} and reactive surface sites, and is given in terms of sorbed species concentrations by {l_brace}d[U(VI)]{sub ads}{r_brace}/dt = {l_brace}{minus}k{prime}[{triple_bond}FeOFeOH{sup 0}][U(VI)]{sub ads}{r_brace}. This rate law applies to organic pollutants as well, as long as they can be reduced by surface Fe(II): {l_brace}d[Pollutant]{r_brace}/dt = {l_brace}{minus}k{prime}[{triple_bond}FeOFeOH{sup 0}][Pollutant]{r_brace}. This mechanism suggests new possibilities for the improvement of low-cost decontamination techniques for U- and chlorinated aliphatic-rich waters.« less

Microscale geochemical gradients in Hanford 300 Area sediment biofilms and influence of uranium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Hung D.; Cao, Bin; Mishra, Bhoopesh

2012-01-01

The presence and importance of microenvironments in the subsurface at contaminated sites were suggested by previous geochemical studies. However, no direct quantitative characterization of the geochemical microenvironments had been reported. We quantitatively characterized microscale geochemical gradients (dissolved oxygen (DO), H(2), pH, and redox potential) in Hanford 300A subsurface sediment biofilms. Our results revealed significant differences in geochemical parameters across the sediment biofilm/water interface in the presence and absence of U(VI) under oxic and anoxic conditions. While the pH was relatively constant within the sediment biofilm, the redox potential and the DO and H(2) concentrations were heterogeneous at the microscale (<500-1000more » μm). We found microenvironments with high DO levels (DO hotspots) when the sediment biofilm was exposed to U(VI). On the other hand, we found hotspots (high concentrations) of H(2) under anoxic conditions both in the presence and in the absence of U(VI). The presence of anoxic microenvironments inside the sediment biofilms suggests that U(VI) reduction proceeds under bulk oxic conditions. To test this, we operated our biofilm reactor under air-saturated conditions in the presence of U(VI) and characterized U speciation in the sediment biofilm. U L(III)-edge X-ray absorption spectroscopy (XANES and EXAFS) showed that 80-85% of the U was in the U(IV) valence state.« less

Microscale geochemical gradients in Hanford 300 Area sediment biofilms and influence of uranium.

PubMed

Nguyen, Hung Duc; Cao, Bin; Mishra, Bhoopesh; Boyanov, Maxim I; Kemner, Kenneth M; Fredrickson, Jim K; Beyenal, Haluk

2012-01-01

The presence and importance of microenvironments in the subsurface at contaminated sites were suggested by previous geochemical studies. However, no direct quantitative characterization of the geochemical microenvironments had been reported. We quantitatively characterized microscale geochemical gradients (dissolved oxygen (DO), H(2), pH, and redox potential) in Hanford 300A subsurface sediment biofilms. Our results revealed significant differences in geochemical parameters across the sediment biofilm/water interface in the presence and absence of U(VI) under oxic and anoxic conditions. While the pH was relatively constant within the sediment biofilm, the redox potential and the DO and H(2) concentrations were heterogeneous at the microscale (<500-1000 μm). We found microenvironments with high DO levels (DO hotspots) when the sediment biofilm was exposed to U(VI). On the other hand, we found hotspots (high concentrations) of H(2) under anoxic conditions both in the presence and in the absence of U(VI). The presence of anoxic microenvironments inside the sediment biofilms suggests that U(VI) reduction proceeds under bulk oxic conditions. To test this, we operated our biofilm reactor under air-saturated conditions in the presence of U(VI) and characterized U speciation in the sediment biofilm. U L(III)-edge X-ray absorption spectroscopy (XANES and EXAFS) showed that 80-85% of the U was in the U(IV) valence state. Copyright © 2011 Elsevier Ltd. All rights reserved.

Se Isotopes as groundwater redox indicators: Detecting natural attenuation of Se at an in situ recovery U mine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anirban, Basu; Schilling, Kathrin; Brown, Shaun T.

One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. Here in this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradientmore » wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ 82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ 82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of $-$2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Moreover, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.« less

Se Isotopes as groundwater redox indicators: Detecting natural attenuation of Se at an in situ recovery U mine

DOE PAGES

Anirban, Basu; Schilling, Kathrin; Brown, Shaun T.; ...

2016-08-22

One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. Here in this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradientmore » wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ 82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ 82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of $-$2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Moreover, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.« less

Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.

Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on themore » temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.« less

Regeneration of pilot-scale ion exchange columns for hexavalent chromium removal.

PubMed

Korak, Julie A; Huggins, Richard; Arias-Paic, Miguel

2017-07-01

Due to stricter regulations, some drinking water utilities must implement additional treatment processes to meet potable water standards for hexavalent chromium (Cr(VI)), such as the California limit of 10 μg/L. Strong base anion exchange is effective for Cr(VI) removal, but efficient resin regeneration and waste minimization are important for operational, economic and environmental considerations. This study compared multiple regeneration methods on pilot-scale columns on the basis of regeneration efficiency, waste production and salt usage. A conventional 1-Stage regeneration using 2 N sodium chloride (NaCl) was compared to 1) a 2-Stage process with 0.2 N NaCl followed by 2 N NaCl and 2) a mixed regenerant solution with 2 N NaCl and 0.2 N sodium bicarbonate. All methods eluted similar cumulative amounts of chromium with 2 N NaCl. The 2-Stage process eluted an additional 20-30% of chromium in the 0.2 N fraction, but total resin capacity is unaffected if this fraction is recycled to the ion exchange headworks. The 2-Stage approach selectively eluted bicarbonate and sulfate with 0.2 N NaCl before regeneration using 2 N NaCl. Regeneration approach impacted the elution efficiency of both uranium and vanadium. Regeneration without co-eluting sulfate and bicarbonate led to incomplete uranium elution and potential formation of insoluble uranium hydroxides that could lead to long-term resin fouling, decreased capacity and render the resin a low-level radioactive solid waste. Partial vanadium elution occurred during regeneration due to co-eluting sulfate suppressing vanadium release. Waste production and salt usage were comparable for the 1- and 2-Stage regeneration processes with similar operational setpoints with respect to chromium or nitrate elution. Published by Elsevier Ltd.

Removal of Radioactive Materials from Groundwater Using Porous Iron Composite Media

NASA Astrophysics Data System (ADS)

Dorward, E.; Thomas, R.; Cochran, J. P.; Chang, H. S.; Tandukar, M.; Coutelot, F.; Seaman, J. C.

2017-12-01

Uranium (U) is a concern in aqueous environments because of its toxicity. Reducing the mobile U(VI) to the relatively immobile U(IV) can decrease soluble U concentrations. Zero valent iron (ZVI) has been demonstrated as an effective reducing agent for U(VI) as well as other frequently occurring co-contaminants, such as nitrate (NO3-). However, the ability of ZVI to chemically reduce and immobilize U and other associated contaminants in more complex systems containing many alternate electron acceptors and non-ideal chemical conditions remains a concern. Porous iron composite (PIC) materials were evaluated for their ability to address these concerns in both batch and column experiments. We created an artificial groundwater surrogate containing ≈ 100 mg L-1 NO3-, 200 mg L-1 alkalinity, 100 µg L-1 U(VI) as uranyl (UO2+2), 100 µg L-1 rhenium (Re) as perrhenate (ReO4-), and 50 µg L-1 arsenic (As). In batch, we reacted 5 grams of PIC material with 200 mL groundwater surrogate under two different atmospheric conditions to evaluate the impact of O2. At specific time intervals, 5 mL aliquots from each batch treatment were removed for chemical analysis (i.e., U, Re, As, Fe, NO3, etc.) and the pH and ORP of the remaining suspension was measured. The PIC was effective at fully reducing NO3- levels over the extended reaction time despite rapid pH increase (> 8) during equilibration. Soluble levels of U and Re, a chemical surrogate for 99Tc, decreased in a similar fashion to NO3- in both the presence and absence of O2. Soluble As levels decreased more rapidly than other contaminants, but remained at ≈ 1 µg L-1. Very little nitrite (NO2-) was detected in the batch tests, with NH4+ levels consistent with the amount of NO3- reduced. Similar rates of immobilization for U, Re, and As were observed in the presence and absence of NO3-. Subsequent leaching tests corresponding to residence times ranging from 120 to 7.5 minutes demonstrated the ability of the PIC to reduce NO3- to NH4+, with no persistence of NO2-. Uranium and As were readily immobilized regardless of flow velocity. A strong kinetic component was observed for Re leaching behavior in the column tests. These results indicate the strong ability of PIC material to reduce U, NO3-, and other species under conditions that frequently inhibit conventional ZVI effectiveness.

Separation of uranium from technetium in recovery of spent nuclear fuel

NASA Astrophysics Data System (ADS)

Friedman, H. A.

1984-06-01

A method for decontaminating uranium product from the Purex 5 process is described. Hydrazine is added to the product uranyl nitrate stream from the Purex process, which contains hexavalent (UO2(2+)) uranium and heptavalent technetius (TcO4-). Technetium in the product stream is reduced and then complexed by the addition of oxalic acid (H2O2O4), and the Tc-oxalate complex is readily separated from the 10 uranium by solvent extraction with 30 vol % tributyl phosphate in n-dodecane.

Can we predict uranium bioavailability based on soil parameters? Part 2: soil solution uranium concentration is not a good bioavailability index.

PubMed

Vandenhove, H; Van Hees, M; Wannijn, J; Wouters, K; Wang, L

2007-01-01

The present study aimed to quantify the influence of soil parameters on uranium uptake by ryegrass. Ryegrass was established on eighteen distinct soils, spiked with (238)U. Uranium soil-to-plant transfer factors (TF) ranged from 0.0003 to 0.0340kgkg(-1). There was no significant relation between the U soil-to-plant transfer (or total U uptake or flux) and the uranium concentration in the soil solution or any other soil factor measured, nor with the U recovered following selective soil extractions. Multiple linear regression analysis resulted in a significant though complex model explaining up to 99% of variation in TF. The influence of uranium speciation on uranium uptake observed was featured: UO(2)(+2), uranyl carbonate complexes and UO(2)PO(4)(-) seem the U species being preferentially taken up by the roots and transferred to the shoots. Improved correlations were obtained when relating the uranium TF with the summed soil solution concentrations of mentioned uranium species.

Tolerance and bioaccumulation of U(VI) by Bacillus mojavensis and its solid phase preconcentration by Bacillus mojavensis immobilized multiwalled carbon nanotube.

PubMed

Özdemir, Sadin; Oduncu, M Kadir; Kilinc, Ersin; Soylak, Mustafa

2017-02-01

In this study, uranium(VI) tolerance and bioaccumulation were investigated by using thermo -tolerant Bacillus mojavensis. The level of U(VI) was measured by UV-VIS spectrophotometry. The minimum inhibition concentration (MIC) value of U(VI) was experimented. Bacterial growth was not affected in the presence of 1.0 and 2.5 mg/L U(VI) at 36 h and the growth was partially affected in the presence of 5 mg/L U(VI) at 24 h. What was obtained from this study is that there was diversity in the various periods of the growth phases of metal bioaccumulation capacity, which was shown by B. mojavensis. The maximum bioaccumulation capacities were found to be 12.8, 22.7, and 48.2 mg/g dried bacteria, at 24th hours at concentration of 1.0, 2.5 and 5 mg/L U(VI), respectively. In addition to these, U(VI) has been preconcentrated on B. mojavensis immobilized MWCNT. Several factors such as pH, flow rate of solution, amount of biosorbent and support materials, eluent type, concentration and volume, the matrix interference effect on retention have been studied, and extraction conditions were optimized. Preconcentration factor was achieved as 60. Under the optimized conditions, the limit of detection (LOD) and quantification (LOQ) were calculated as 0.74 and 2.47 μg/L. The biosorption capacity of immobilized B. mojavensis was calculated for U(VI) as 25.8 mg/g. The results demonstrated that the immobilized biosorbent column could be reused at least 30 cycles of biosorption and desorption with the higher than 95% recovery. FT-IR and SEM analysis were performed to understand the surface properties of B. mojavensis. Copyright © 2016 Elsevier Ltd. All rights reserved.

Uranium speciation as a function of depth in contaminated hanford sediments--a micro-XRF, micro-XRD, and micro- and bulk-XAFS study.

PubMed

Singer, David M; Zachara, John M; Brown, Gordon E

2009-02-01

The distribution and speciation of U and Cu in contaminated vadose zone and aquifer sediments from the U.S. DOE Hanford site (300 Area) were determined using a combination of synchrotron-based micro-X-ray fluorescence (microXRF) imaging, micro-X-ray absorption near edge structure (microXANES) spectroscopy, and micro-X-ray diffraction (microXRD) techniques combined with bulk U LIII-edge X-ray absorption fine structure (XAFS) spectroscopy. Samples were collected from within the inactive North Process Pond (NPP2) at 8 ft (2.4 m, NPP2-8) depth and 12 ft (3.7 m, NPP2-12) depth in the vadose zone, and fines were isolated from turbid groundwater just below the water Table (12-14 ft, approximately 4 m, NPP2-GW). microXRF imaging, microXRD, and microXANES spectroscopy revealed two major U occurrences within the vadose and groundwater zones: (1) low to moderate concentrations of U(VI) associated with fine-textured grain coatings that were consistently found to contain clinochlore (referred to here as chlorite) observed in all three samples, and (2) U(VI)-Cu(II) hotspots consisting of micrometer-sized particles associated with surface coatings on grains of muscovite and chlorite observed in samples NPP2-8' and NPP2-GW. In the aquifer fines (NPP2-GW), these particles were identified as cuprosklodowskite (cps: Cu[(UO2)(SiO2OH)]2 x 6H2O) and metatorbernite (mtb: Cu(UO2)2(PO4)2 x 8H2O). In contrast, the U-Cu-containing particles in the vadose zone were X-ray amorphous. Analyses of U LIII-edge XAFS spectra by linear-combination fitting indicated that U speciation consisted of (1) approximately 75% uranyl sorbed to chlorite and approximately 25% mtb-like X-ray amorphous U-Cu-phosphates (8 ft depth), (2) nearly 100% sorbed uranyl (12 ft depth), and (3) approximately 70% uranyl sorbed to chlorite and approximately 30% cps/mtb (groundwater zone). These findings suggest that dissolution of U(VI)-Cu(II)-bearing solids as well as desorption of U(VI), mainly from phyllosilicates, are important persistent sources of U(VI) to the associated uranium groundwater plume in Hanford Area 300.

Characterization and treatment of water used for human consumption from six sources located in the Cameron/Tuba City abandoned uranium mining area.

PubMed

Orescanin, Visnja; Kollar, Robert; Nad, Karlo; Mikelic, Ivanka Lovrencic; Kollar, Iris

2011-01-01

The purpose of this research was the characterization and improvement of the quality of water used for human consumption of unregulated/regulated water sources located in the Cameron/Tuba City abandoned uranium mining area (NE Arizona, western edge of the Navajo Nation). Samples were collected at six water sources which included regulated sources: Wind Mill (Tank 3T-538), Badger Springs and Paddock Well as well as unregulated sources: Willy Spring, Water Wall and Water Hole. Samples taken from Wind Mill, Water Wall and Water Hole were characterized with high turbidity and color as well as high level of manganese, iron and nickel and elevated value of molybdenum. High level of iron was also found in Badger Spring, Willy Spring, and Paddock Well. These three water sources were also characterized with elevated values of fluoride and vanadium. Significant amounts of zinc were found in Water Wall and Water Hole samples. Water Wall sample was also characterized with high level of Cr(VI). Compared to primary or secondary Navajo Nation Environmental Protection Agency (NNEPA) water quality standard the highest enrichment was found for turbidity (50.000 times), color (up to 1.796 times) and manganese (71 times), Cr(VI) (17.5 times), iron (7.4 times) and arsenic (5.2 times). Activities of (226)Ra and (238)U in water samples were still in agreement with the maximum contaminant levels. In order to comply with NNEPA water quality standard water samples were subjected to electrochemical treatment. This method was selected due to its high removal efficiency for heavy metals and uranium, lower settlement time, production of smaller volume of waste mud and higher stability of waste mud compared to physico-chemical treatment. Following the treatment, concentrations of heavy metals and activities of radionuclides in all samples were significantly lower compared to NNEPA or WHO regulated values. The maximum removal efficiencies for color, turbidity, arsenic, manganese, molybdenum and nickel were 100.0%. Maximum removal percentage of Cu, F(-), V, Zn, (137)Cs, (226)Ra, (232)Th, (238)U were as follows: 98.0%; 82.7%; 99.9%; 95.6%; 75.0%; 76.9%; 80.0% and 99.2%. From the results presented it could be concluded that electrochemical treatment is a suitable approach for the purification of drinking water with complex mixture of contaminants, especially those with high turbidity and color.

Uranium-mediated electrocatalytic dihydrogen production from water

NASA Astrophysics Data System (ADS)

Halter, Dominik P.; Heinemann, Frank W.; Bachmann, Julien; Meyer, Karsten

2016-02-01

Depleted uranium is a mildly radioactive waste product that is stockpiled worldwide. The chemical reactivity of uranium complexes is well documented, including the stoichiometric activation of small molecules of biological and industrial interest such as H2O, CO2, CO, or N2 (refs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11), but catalytic transformations with actinides remain underexplored in comparison to transition-metal catalysis. For reduction of water to H2, complexes of low-valent uranium show the highest potential, but are known to react violently and uncontrollably forming stable bridging oxo or uranyl species. As a result, only a few oxidations of uranium with water have been reported so far; all stoichiometric. Catalytic H2 production, however, requires the reductive recovery of the catalyst via a challenging cleavage of the uranium-bound oxygen-containing ligand. Here we report the electrocatalytic water reduction observed with a trisaryloxide U(III) complex [((Ad,MeArO)3mes)U] (refs 18 and 19)—the first homogeneous uranium catalyst for H2 production from H2O. The catalytic cycle involves rare terminal U(IV)-OH and U(V)=O complexes, which have been isolated, characterized, and proven to be integral parts of the catalytic mechanism. The recognition of uranium compounds as potentially useful catalysts suggests new applications for such light actinides. The development of uranium-based catalysts provides new perspectives on nuclear waste management strategies, by suggesting that mildly radioactive depleted uranium—an abundant waste product of the nuclear power industry—could be a valuable resource.

Behavior of anionic molybdenum(IV, VI) and tungsten(IV, VI) complexes containing bulky hydrophobic dithiolate ligands and intramolecular NH···S hydrogen bonds in nonpolar solvents.

PubMed

Hasenaka, Yuki; Okamura, Taka-aki; Tatsumi, Miki; Inazumi, Naoya; Onitsuka, Kiyotaka

2014-11-07

Molybdenum(IV, VI) and tungsten(IV, VI) complexes, (Et4N)2[M(IV)O{1,2-S2-3,6-(RCONH)2C6H2}2] and (Et4N)2[M(VI)O2{1,2-S2-3,6-(RCONH)2C6H2}2] (M = Mo, W; R = (4-(t)BuC6H4)3C), with bulky hydrophobic dithiolate ligands containing NH···S hydrogen bonds were synthesized. These complexes are soluble in nonpolar solvents like toluene, which allows the detection of unsymmetrical coordination structures and elusive intermolecular interactions in solution. The (1)H NMR spectra of the complexes in toluene-d8 revealed an unsymmetrical coordination structure, and proximity of the counterions to the anion moiety was suggested at low temperatures. The oxygen-atom-transfer reaction between the molybdenum(IV) complex and Me3NO in toluene was considerably accelerated in nonpolar solvents, and this increase was attributed to the favorable access of the substrate to the active center in the hydrophobic environment.

Apoptosis of lymphocytes in the presence of Cr(V) complexes: role in Cr(VI)-induced toxicity.

PubMed

Vasant, C; Balamurugan, K; Rajaram, R; Ramasami, T

2001-08-03

Cr(VI) compounds have been declared as a potent occupational carcinogen by IARC (1990) through epidemiological studies among workers in chrome plating, stainless-steel, and pigment industries. Studies relating to the role of intermediate oxidation states such as Cr(V) and Cr(IV) in Cr(VI)-induced carcinogenicity are gaining importance. In this study, issues relating to toxicity elicited by Cr(V) have been addressed and comparisons made with those relating to Cr(VI) employing human peripheral blood lymphocytes. Lymphocytes have been isolated from heparinized blood by Ficoll-Hypaque density gradient centrifugation and exposed to Cr(V) complexes viz. sodium bis(2-ethyl-2-hydroxybutyrato)oxochromate(V), Na[Cr(V)O(ehba)(2)], 1 and sodium bis(2-hydroxy-2-methylbutyrato)oxochromate(V), Na[Cr(V)O(hmba)(2)], 2 and Cr(VI). The phytohemagglutinin (PHA)-induced proliferation of lymphocytes has been found to be inhibited by the two complexes of Cr(V) and chromate Cr(VI) in a time- and concentration-dependent manner. Viability of cells decreases in the presence of Cr(V). Apoptosis appears to be the mode of cell death in the presence of both Cr(V) and Cr(VI). Pretreatment of cells with antioxidants before exposure to chromium(V) complexes reverse apoptosis partially. Possibility for the formation and implication of reactive oxygen species in Cr(V)-induced apoptosis of human lymphocyte cells has been indicated in this investigation. The intermediates of Cr(V) and radical species in the biotoxic pathways elicited by Cr(VI) seems feasible. Copyright 2001 Academic Press.

Water-soluble Schiff base-actinyl complexes and their effect on the solvent extraction of f-elements

DOE PAGES

Hawkins, Cory A.; Bustillos, Christian G.; May, Iain; ...

2016-09-07

Conventional solvent extraction of selected f-element cations by bis(2-ethylhexyl)phosphoric acid (HDEHP) yields increased extraction from aqueous to organic solution along the series Np(V) < Cm(III) < Eu(III) < U(VI), with distribution ratios all within two orders of magnitude. However, in the presence of the water-soluble tetradentate Schiff base (N,N'-bis(5-sulfonatosalicylidene)-ethylenediamine or H 2salenSO 3), selective complexation of the two actinyl cations (Np(V) and U(VI)) resulted in an extraction order of Np(V) < U(VI) << Eu(III) < Cm(III). The extraction of neither Cm(III) or Eu(III) by HDEHP are significantly impacted by the presence of the aqueous phase Schiff base. Despite observed hydrolyticmore » decomposition of H 2salenSO 3 in aqueous solutions, the calculated high conditional stability constant (β 11 = 26) for the complex [UO 2(salenSO 3)] 2- demonstrates its capacity for aqueous hold-back of U(VI). UV-visible-NIR spectroscopy of solutions prepared with a Np(VI) stock and H 2salenSO 3 suggest that reduction of Np(VI) to Np(V) by the ligand was rapid, resulting in a pentavalent Np complex that was substantially retained in the aqueous phase. Lastly, results from 1H NMR of aqueous solutions of H 2salenSO 3 with U(VI) and La(III), Eu(III), and Lu(III) provides additional evidence that the ligand readily chelates U(VI), but has only weak interactions with trivalent lanthanide ions.« less

Isotopic and geochemical tracers for U(VI) reduction and U mobility at an in situ recovery U mine

DOE PAGES

Basu, Anirban; Brown, Shaun T.; Christensen, John N.; ...

2015-05-19

In situ recovery (ISR) uranium (U) mining mobilizes U in its oxidized hexavalent form (U(VI)) by oxidative dissolution of U from the roll-front U deposits. Post-mining natural attenuation of residual U(VI) at ISR mines is a potential remediation strategy. Detection and monitoring of naturally occurring reducing subsurface environments are important for successful implementation of this remediation scheme. We used the isotopic tracers ²³⁸U/²³⁵U (δ²³⁸U), ²³⁴U/²³⁸U activity ratio, and ³⁴S/³²S (δ³⁴S), and geochemical measurements of U ore and groundwater collected from 32 wells located within, upgradient, and downgradient of a roll-front U deposit to detect U(VI) reduction and U mobility atmore » an ISR mining site at Rosita, TX, USA. The δ²³⁸U in Rosita groundwater varies from 0.61‰ to -2.49‰, with a trend toward lower δ²³⁸U in downgradient wells. The concurrent decrease in U(VI) concentration and δ²³⁸U with an ε of 0.48‰ ± 0.08‰ is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic ²³⁴U/²³⁸U activity ratio and δ³⁴S values may also be used to trace the mobility of the ore zone groundwater after mining has ended. These results support the use of U isotope-based detection of natural attenuation of U(VI) at Rosita and other similar ISR mining sites.« less

Isotopic and geochemical tracers for U(VI) reduction and U mobility at an in situ recovery U mine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basu, Anirban; Brown, Shaun T.; Christensen, John N.

In situ recovery (ISR) uranium (U) mining mobilizes U in its oxidized hexavalent form (U(VI)) by oxidative dissolution of U from the roll-front U deposits. Post-mining natural attenuation of residual U(VI) at ISR mines is a potential remediation strategy. Detection and monitoring of naturally occurring reducing subsurface environments are important for successful implementation of this remediation scheme. We used the isotopic tracers ²³⁸U/²³⁵U (δ²³⁸U), ²³⁴U/²³⁸U activity ratio, and ³⁴S/³²S (δ³⁴S), and geochemical measurements of U ore and groundwater collected from 32 wells located within, upgradient, and downgradient of a roll-front U deposit to detect U(VI) reduction and U mobility atmore » an ISR mining site at Rosita, TX, USA. The δ²³⁸U in Rosita groundwater varies from 0.61‰ to -2.49‰, with a trend toward lower δ²³⁸U in downgradient wells. The concurrent decrease in U(VI) concentration and δ²³⁸U with an ε of 0.48‰ ± 0.08‰ is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic ²³⁴U/²³⁸U activity ratio and δ³⁴S values may also be used to trace the mobility of the ore zone groundwater after mining has ended. These results support the use of U isotope-based detection of natural attenuation of U(VI) at Rosita and other similar ISR mining sites.« less

The role of uranium-arene bonding in H2O reduction catalysis

NASA Astrophysics Data System (ADS)

Halter, Dominik P.; Heinemann, Frank W.; Maron, Laurent; Meyer, Karsten

2018-03-01

The reactivity of uranium compounds towards small molecules typically occurs through stoichiometric rather than catalytic processes. Examples of uranium catalysts reacting with water are particularly scarce, because stable uranyl groups form that preclude the recovery of the uranium compound. Recently, however, an arene-anchored, electron-rich uranium complex has been shown to facilitate the electrocatalytic formation of H2 from H2O. Here, we present the precise role of uranium-arene δ bonding in intermediates of the catalytic cycle, as well as details of the atypical two-electron oxidative addition of H2O to the trivalent uranium catalyst. Both aspects were explored by synthesizing mid- and high-valent uranium-oxo intermediates and by performing comparative studies with a structurally related complex that cannot engage in δ bonding. The redox activity of the arene anchor and a covalent δ-bonding interaction with the uranium ion during H2 formation were supported by density functional theory analysis. Detailed insight into this catalytic system may inspire the design of ligands for new uranium catalysts.

Formation of ternary CaUO2(CO3)3(2-) and Ca2UO2(CO3)3(aq) complexes under neutral to weakly alkaline conditions.

PubMed

Lee, Jun-Yeop; Yun, Jong-Il

2013-07-21

The chemical behavior of ternary Ca-UO2-CO3 complexes was investigated by using time-resolved laser fluorescence spectroscopy (TRLFS) in combination with EDTA complexation at pH 7-9. A novel TRLFS revealed two distinct fluorescence lifetimes of 12.7 ± 0.2 ns and 29.2 ± 0.4 ns for uranyl complexes which were formed increasingly dependent upon the calcium ion concentration, even though nearly indistinguishable fluorescence peak shapes and positions were measured for both Ca-UO2-CO3 complexes. For identifying the stoichiometric number of complexed calcium ions, slope analysis in terms of relative fluorescence intensity versus calcium concentration was employed in a combination with the complexation reaction of CaEDTA(2-) by adding EDTA. The formation of CaUO2(CO3)3(2-) and Ca2UO2(CO3)3(aq) was identified under given conditions and their formation constants were determined at I = 0.1 M Na/HClO4 medium, and extrapolated to infinitely dilute solution using specific ion interaction theory (SIT). As a result, the formation constants for CaUO2(CO3)3(2-) and Ca2UO2(CO3)3(aq) were found to be log β113(0) = 27.27 ± 0.14 and log β213(0) = 29.81 ± 0.19, respectively, providing that the ternary Ca-UO2-CO3 complexes were predominant uranium(vi) species at neutral to weakly alkaline pH in the presence of Ca(2+) and CO3(2-) ions.

Colorimetric detection of uranium in water

DOEpatents

DeVol, Timothy A [Clemson, SC; Hixon, Amy E [Piedmont, SC; DiPrete, David P [Evans, GA

2012-03-13

Disclosed are methods, materials and systems that can be used to determine qualitatively or quantitatively the level of uranium contamination in water samples. Beneficially, disclosed systems are relatively simple and cost-effective. For example, disclosed systems can be utilized by consumers having little or no training in chemical analysis techniques. Methods generally include a concentration step and a complexation step. Uranium concentration can be carried out according to an extraction chromatographic process and complexation can chemically bind uranium with a detectable substance such that the formed substance is visually detectable. Methods can detect uranium contamination down to levels even below the MCL as established by the EPA.

The application of N,N-dimethyl-3-oxa-glutaramic acid (DOGA) in the PUREX process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jianchen, Wang; Jing, Chen

2007-07-01

The new salt-free complexant, DOGA for separating trace Pu(IV) and Np(IV) from U(VI) nitric acid solution was studied. DOGA has stronger complexing abilities to Pu(IV) and Np(IV), but complexing ability of DOGA to U(VI) was weaker. The DOGA can be used in the PUREX process to separate Pu(IV) and Np(IV) from U(VI) nitric solution. On one hand, U(IV) in the nitric acid solution containing trace Pu(IV) and Np(IV) was extracted by 30%TBP - kerosene(v/v) in the presence of DOGA, but Pu(IV) and Np(IV) were kept in the aqueous phase. On the other hand, Pu(IV) and Np(IV) loading in 30% TBPmore » - kerosene were effectively stripped by DOGA into the aqueous phase, but U(VI) loading in 30% TBP - kerosene was remained in 30% TBP - kerosene. DOGA is a promising complexant to separate Pu(IV) and Np(IV) from U(VI) solution in the U-cycle of the PUREX process. (authors)« less

Kinetics and Mechanism of the Reaction of a Ruthenium(VI) Nitrido Complex with HSO3 (-) and SO3 (2-) in Aqueous Solution.

PubMed

Wang, Qian; Zhao, Hong Yan; Man, Wai-Lun; Lam, William W Y; Lau, Kai-Chung; Lau, Tai-Chu

2016-07-25

The kinetics and mechanism of the reaction of S(IV) (SO3 (2-) +HSO3 (-) ) with a ruthenium(VI) nitrido complex, [(L)Ru(VI) (N)(OH2 )](+) (Ru(VI) N, L=N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion), in aqueous acidic solutions are reported. The kinetic results are consistent with parallel pathways involving oxidation of HSO3 (-) and SO3 (2-) by Ru(VI) N. A deuterium isotope effect of 4.7 is observed in the HSO3 (-) pathway. Based on experimental results and DFT calculations the proposed mechanism involves concerted N-S bond formation (partial N-atom transfer) between Ru(VI) N and HSO3 (-) and H(+) transfer from HSO3 (-) to a H2 O molecule. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Density functional theory study of defects in unalloyed δ-Pu

DOE PAGES

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

2017-03-19

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Density functional theory study of defects in unalloyed δ-Pu

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Determination of hexavalent chromium in exhaled breath condensate and environmental air among chrome plating workers.

PubMed

Goldoni, Matteo; Caglieri, Andrea; Poli, Diana; Vettori, Maria Vittoria; Corradi, Massimo; Apostoli, Pietro; Mutti, Antonio

2006-03-15

Chromium speciation has attracted attention because of the different toxicity of Cr(III), which is considered relatively non-toxic, and Cr(VI), which can cross cell membranes mainly as a chromate anion and has been classified as a class I human carcinogen. The aims of the present study were to measure soluble Cr(VI) levels in environmental samples, to develop a simple method of quantifying Cr(VI) in exhaled breath condensate (EBC), and to follow the kinetics of EBC Cr(VI) in chrome plating workers.Personal air samples were collected from 10 chrome platers; EBC was collected from the same workers immediately after the work shift on Tuesday and before the work shift on the following Wednesday. Environmental and EBC Cr(VI) levels were determined by means of colorimetry and electrothermal absorption atomic spectrometry, respectively.The method of detecting Cr(VI) in environmental air was based on the extraction of the Cr(VI)-diphenylcarbazide (Cr(VI)-DPC) complex in 1-butanol, whereas EBC Cr(VI) was determined using a solvent extraction of Cr(VI) as an ion pair with tetrabutylammonium ion, and subsequent direct determination of the complex (Cr(VI)-DPC) in EBC.Kinetic data showed that airborne Cr(VI) was reduced by 50% in airway lining fluid sampled at the end of exposure and that there was a further 50% reduction after about 15 h. The persistence of Cr(VI) in EBC supports the use of EBC in assessing target tissue levels of Cr(VI).

Semimicrodetermination of combined tantalum and niobium with selenous acid

USGS Publications Warehouse

Grimaldi, F.S.; Schnepfe, M.

1959-01-01

Tantalum and niobium are separated and determined gravimetrically by precipitation with selenous acid from highly acidic solutions in the absence of complexing agents. Hydrogen peroxide is used in the preparation of the solution and later catalytically destroyed during digestion of the precipitate. From 0.2 to 30 mg., separately or in mixtures, of niobium or tantalum pentoxide can be separated from mixtures containing 100 mg. each of the oxides of scandium, yttrium, cerium, vanadium, molybdenum, iron, aluminum, tin, lead, and bismuth with a single precipitation; and from 30 mg. of titanium dioxide, and 50 mg. each of the oxides of antimony and thorium, when present separately, with three precipitations. At least 50 mg. of uranium(VI) oxide can be separated with a single precipitation when present alone; otherwise, three precipitations may be needed. Zirconium does not interfere when the tantalum and niobium contents of the sample are small, but in general, zirconium as well as tungsten interfere. The method is applied to the determination of the earth acids in tantaloniobate ores.

Natural uranium and thorium isotopes in sediment cores off Malaysian ports

NASA Astrophysics Data System (ADS)

Yusoff, Abdul Hafidz; Sabuti, Asnor Azrin; Mohamed, Che Abd Rahim

2015-06-01

Sediment cores collected from three Malaysian marine ports, namely, Kota Kinabalu, Labuan and Klang were analyzed to determine the radioactivities of 234U, 238U, 230Th, 232Th and total organic carbon (TOC) content. The objectives of this study were to determine the factors that control the activity of uranium isotopes and identify the possible origin of uranium and thorium in these areas. The activities of 234U and 238U show high positive correlation with TOC at the middle of sediment core from Kota Kinabalu port. This result suggests that activity of uranium at Kota Kinabalu port was influenced by organic carbon. The 234U/238U value at the upper layer of Kota Kinabalu port was ≥1.14 while the ratio value at Labuan and Klang port was ≤ 1.14. These results suggest a reduction process occurred at Kota Kinabalu port where mobile U(VI) was converted to immobile U(IV) by organic carbon. Therefore, it can be concluded that the major input of uranium at Kota Kinabalu port is by sorptive uptake of authigenic uranium from the water column whereas the major inputs of uranium to Labuan and Klang port are of detrital origin. The ratio of 230Th/232Th was used to estimate the origin of thorium. Low ratio value (lt; 1.5) at Labuan and Klang ports support the suggestion that thorium from both areas were come from detrital input while the high ratio (> 1.5) of 230Th/232Th at Kota Kinabalu port suggest the anthropogenic input of 230Th to this area. The source of 230Th is probably from phosphate fertilizers used in the oil-palm cultivation in Kota Kinabalu that is adjacent to the Kota Kinabalu port.

Uranium bioprecipitation mediated by yeasts utilizing organic phosphorus substrates.

PubMed

Liang, Xinjin; Csetenyi, Laszlo; Gadd, Geoffrey Michael

2016-06-01

In this research, we have demonstrated the ability of several yeast species to mediate U(VI) biomineralization through uranium phosphate biomineral formation when utilizing an organic source of phosphorus (glycerol 2-phosphate disodium salt hydrate (C3H7Na2O6P·xH2O (G2P)) or phytic acid sodium salt hydrate (C6H18O24P6·xNa(+)·yH2O (PyA))) in the presence of soluble UO2(NO3)2. The formation of meta-ankoleite (K2(UO2)2(PO4)2·6(H2O)), chernikovite ((H3O)2(UO2)2(PO4)2·6(H2O)), bassetite (Fe(++)(UO2)2(PO4)2·8(H2O)), and uramphite ((NH4)(UO2)(PO4)·3(H2O)) on cell surfaces was confirmed by X-ray diffraction in yeasts grown in a defined liquid medium amended with uranium and an organic phosphorus source, as well as in yeasts pre-grown in organic phosphorus-containing media and then subsequently exposed to UO2(NO3)2. The resulting minerals depended on the yeast species as well as physico-chemical conditions. The results obtained in this study demonstrate that phosphatase-mediated uranium biomineralization can occur in yeasts supplied with an organic phosphate substrate as sole source of phosphorus. Further understanding of yeast interactions with uranium may be relevant to development of potential treatment methods for uranium waste and utilization of organic phosphate sources and for prediction of microbial impacts on the fate of uranium in the environment.

Separation of uranium from technetium in recovery of spent nuclear fuel

DOEpatents

Friedman, H.A.

1984-06-13

A method for decontaminating uranium product from the Purex 5 process comprises addition of hydrazine to the product uranyl nitrate stream from the Purex process, which contains hexavalent (UO/sub 2//sup 2 +/) uranium and heptavalent technetium (TcO/sub 4/-). Technetium in the product stream is reduced and then complexed by the addition of oxalic acid (H/sub 2/C/sub 2/O/sub 4/), and the Tc-oxalate complex is readily separated from the 10 uranium by solvent extraction with 30 vol % tributyl phosphate in n-dodecane.

Separation of uranium from technetium in recovery of spent nuclear fuel

DOEpatents

Friedman, Horace A.

1985-01-01

A method for decontaminating uranium product from the Purex process comprises addition of hydrazine to the product uranyl nitrate stream from the Purex process, which contains hexavalent (UO.sub.2.sup.2+) uranium and heptavalent technetium (TcO.sub.4 -). Technetium in the product stream is reduced and then complexed by the addition of oxalic acid (H.sub.2 C.sub.2 O.sub.4), and the Tc-oxalate complex is readily separated from the uranium by solvent extraction with 30 vol. % tributyl phosphate in n-dodecane.

DOE/SC0001389 Final technical report: Investigation of uranium attenuation and release at column and pore scales in response to advective geochemical gradients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Savage, Kaye S.; Zhu, Wenyi; Barnett, Mark O.

2013-05-13

Experimental approach Column experiments were devised to investigate the role of changing fluid composition on mobility of uranium through a sequence of geologic media. Fluids and media were chosen to be relevant to the ground water plume emanating from the former S-3 ponds at the Oak Ridge Integrated Field Research Challenge (ORIFC) site. Synthetic ground waters were pumped upwards at 0.05 mL/minute for 21 days through layers of quartz sand alternating with layers of uncontaminated soil, quartz sand mixed with illite, quartz sand coated with iron oxides, and another soil layer. Increases in pH or concentration of phosphate, bicarbonate, ormore » acetate were imposed on the influent solutions after each 7 pore volumes while uranium (as uranyl) remained constant at 0.1mM. A control column maintained the original synthetic groundwater composition with 0.1mM U. Pore water solutions were extracted to assess U retention and release in relation to the advective ligand or pH gradients. Following the column experiments, subsamples from each layer were characterized using microbeam X-ray absorption spectroscopy (XANES) in conjunction with X-ray fluorescence mapping and compared to sediment core samples from the ORIFC, at SSRL Beam Line 2-3. Results U retention of 55-67mg occurred in phosphate >pH >control >acetate >carbonate columns. The mass of U retained in the first-encountered quartz layer in all columns was highest and increased throughout the experiment. The rate of increase in acetate- and bicarbonate-bearing columns declined after ligand concentrations were raised. U also accumulated in the first soil layer; the pH-varied column retained most, followed by the increasing-bicarbonate column. The mass of U retained in the upper layers was far lower. Speciation of U, interpreted from microbeam XANES spectra and XRF maps, varied within and among the columns. Evidence of minor reduction to U(IV) was observed in the first-encountered quartz layer in the phosphate, bicarbonate, and pH columns while only U(VI) was observed in the control and acetate columns. In the soil layer, the acetate and bicarbonate columns both indicate minor reduction to U(IV), but U(VI) predominated in all columns. In the ORIFC soils, U was consistently present as U(VI); sorption appears to be the main mechanism of association for U present with Fe and/or Mn, while U occurring with P appears in discrete particles consistent with a U mineral phase. U in soil locations with no other elemental associations shown by XRF are likely uranium oxide phases.« less

Uranium isotopes fingerprint biotic reduction

DOE PAGES

Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; ...

2015-04-20

Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U),more » i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. In addition, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.« less

Final Project Report, DE-SC0001280, Characterizing the Combined Roles of Iron and Transverse Mixing on Uranium Bioremediation in Groundwater using Microfluidic Devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finneran, Kevin; Werth, Charles; Strathmann, Timothy

2015-01-10

In situ bioremediation of U(VI) involves amending groundwater with an appropriate electron donor and limiting nutrients to promote biological reduction to the less soluble and mobile U(IV) oxidation state. Groundwater flow is laminar; mixing is controlled by hydrodynamic dispersion. Recent studies indicate that transverse dispersion along plume margins can limit mixing of the amended electron donor and accepter (such as U(VI) in remediation applications). As a result, microbial growth, and subsequently contaminant reaction, may be limited to these transverse mixing zones during bioremediation. The primary objective of this work was to characterize the combined effects of hydrology, geochemistry, and biologymore » on the (bio)remediation of U(VI). Our underlying hypothesis was that U(VI) reaction in groundwater is controlled by transverse mixing with an electron donor along plume margins, and that iron bioavailability in these zones affects U(VI) reduction kinetics and U(IV) re-oxidation. Our specific objectives were to a) quantify reaction kinetics mediated by biological versus geochemical reactions leading to U(VI) reduction and U(IV) re-oxidation, b) understand the influence of bioavailable iron on U(VI) reduction and U(IV) re-oxidation along the transverse mixing zones, c) determine how transverse mixing limitations and the presence of biomass in pores affects these reactions, and d) identify how microbial populations that develop along transverse mixing zones are influenced by the presence of iron and the concentration of electron donor. In the completed work, transverse mixing zones along plume margins were re-created in microfluidic pore networks, referred to as micromodels. We conducted a series of experiments that allowed us to distinguish among the hydraulic, biological, and geochemical mechanisms that contribute to U(VI) reduction, U(IV) re-oxidation, and U(VI) abiotic reaction with the limiting biological nutrient HP042-. This systematic approach may lead to a better understanding of U(VI) remediation, and better strategies for groundwater amendments to maximize remediation efficiency.« less

RECOVERY OF URANIUM BY AROMATIC DITHIOCARBAMATE COMPLEXING

DOEpatents

Neville, O.K.

1959-08-11

A selective complexing organic solvent extraction process is presented for the separation of uranium values from an aqueous nitric acid solution of neutron irradiated thorium. The process comprises contacting the solution with an organic aromatic dithiccarbamaie and recovering the resulting urancdithiccarbamate complex with an organic solvent such as ethyl acetate.

Gas-Phase Coordination Complexes of UVIO{2/2+}, NpVIO{2/2+}, and PuVIO{2/2+} with Dimethylformamide

NASA Astrophysics Data System (ADS)

Rutkowski, Philip X.; Rios, Daniel; Gibson, John K.; van Stipdonk, Michael J.

2011-11-01

Electrospray ionization of actinyl perchlorate solutions in H2O with 5% by volume of dimethylformamide (DMF) produced the isolatable gas-phase complexes, [AnVIO2(DMF)3(H2O)]2+ and [AnVIO2(DMF)4]2+, where An = U, Np, and Pu. Collision-induced dissociation confirmed the composition of the dipositive coordination complexes, and produced doubly- and singly-charged fragment ions. The fragmentation products reveal differences in underlying chemistries of uranyl, neptunyl, and plutonyl, including the lower stability of Np(VI) and Pu(VI) compared with U(VI).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kanel, S. R.; Clement, T. P.; Barnett, M. O.

Synthetic nano-scale hydroxyapatite (NHA) was prepared and characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The XRD data confirmed that the crystalline structure and chemical composition of NHA correspond to Ca 5 OH(PO 4 ) 3 . The SEM data confirmed the size of NHA to be less than 50 nm. A two-dimensional physical model packed with saturated porous media was used to study the transport characteristics of NHA under constant flow conditions. The data show that the transport patterns of NHA were almost identical to tracer transport patterns. This result indicates that the NHA material can movemore » with water like a tracer, and its movement was neither retarded nor influenced by any physicochemical interactions and/or density effects. We have also tested the reactivity of NHA with 1 mg/L hexavalent uranium (U(VI)) and found that complete removal of U(VI) is possible using 0.5 g/L NHA at pH 5 to 6. Our results demonstrate that NHA has the potential to be injected as a dilute slurry for in situ treatment of U(VI)-contaminated groundwater systems.« less

Determination of hexavalent chromium in exhaled breath condensate and environmental air among chrome plating workers

PubMed Central

Goldoni, Matteo; Caglieri, Andrea; Poli, Diana; Vettori, Maria Vittoria; Corradi, Massimo; Apostoli, Pietro; Mutti, Antonio

2006-01-01

Chromium speciation has attracted attention because of the different toxicity of Cr(III), which is considered relatively non-toxic, and Cr(VI), which can cross cell membranes mainly as a chromate anion and has been classified as a class I human carcinogen. The aims of the present study were to measure soluble Cr(VI) levels in environmental samples, to develop a simple method of quantifying Cr(VI) in exhaled breath condensate (EBC), and to follow the kinetics of EBC Cr(VI) in chrome plating workers. Personal air samples were collected from 10 chrome platers; EBC was collected from the same workers immediately after the work shift on Tuesday and before the work shift on the following Wednesday. Environmental and EBC Cr(VI) levels were determined by means of colorimetry and electrothermal absorption atomic spectrometry, respectively. The method of detecting Cr(VI) in environmental air was based on the extraction of the Cr(VI)-diphenylcarbazide (Cr(VI)–DPC) complex in 1-butanol, whereas EBC Cr(VI) was determined using a solvent extraction of Cr(VI) as an ion pair with tetrabutylammonium ion, and subsequent direct determination of the complex (Cr(VI)–DPC) in EBC. Kinetic data showed that airborne Cr(VI) was reduced by 50% in airway lining fluid sampled at the end of exposure and that there was a further 50% reduction after about 15 h. The persistence of Cr(VI) in EBC supports the use of EBC in assessing target tissue levels of Cr(VI). PMID:17047732

Ship-in-a-bottle CMPO in MIL-101(Cr) for selective uranium recovery from aqueous streams through adsorption.

PubMed

De Decker, Jeroen; Folens, Karel; De Clercq, Jeriffa; Meledina, Maria; Van Tendeloo, Gustaaf; Du Laing, Gijs; Van Der Voort, Pascal

2017-08-05

Mesoporous MIL-101(Cr) is used as host for a ship-in-a-bottle type adsorbent for selective U(VI) recovery from aqueous environments. The acid-resistant cage-type MOF is built in-situ around N,N-Diisobutyl-2-(octylphenylphosphoryl)acetamide (CMPO), a sterically demanding ligand with high U(VI) affinity. This one-step procedure yields an adsorbent which is an ideal compromise between homogeneous and heterogeneous systems, where the ligand can act freely within the pores of MIL-101, without leaching, while the adsorbent is easy separable and reusable. The adsorbent was characterized by XRD, FTIR spectroscopy, nitrogen adsorption, XRF, ADF-STEM and EDX, to confirm and quantify the successful encapsulation of the CMPO in MIL-101, and the preservation of the host. Adsorption experiments with a central focus on U(VI) recovery were performed. Very high selectivity for U(VI) was observed, while competitive metal adsorption (rare earths, transition metals...) was almost negligible. The adsorption capacity was calculated at 5.32mg U/g (pH 3) and 27.99mg U/g (pH 4), by fitting equilibrium data to the Langmuir model. Adsorption kinetics correlated to the pseudo-second-order model, where more than 95% of maximum uptake is achieved within 375min. The adsorbed U(VI) is easily recovered by desorption in 0.1M HNO 3 . Three adsorption/desorption cycles were performed. Copyright © 2017 Elsevier B.V. All rights reserved.

Homologation and functionalization of carbon monoxide by a recyclable uranium complex.

PubMed

Gardner, Benedict M; Stewart, John C; Davis, Adrienne L; McMaster, Jonathan; Lewis, William; Blake, Alexander J; Liddle, Stephen T

2012-06-12

Carbon monoxide (CO) is in principle an excellent resource from which to produce industrial hydrocarbon feedstocks as alternatives to crude oil; however, CO has proven remarkably resistant to selective homologation, and the few complexes that can effect this transformation cannot be recycled because liberation of the homologated product destroys the complexes or they are substitutionally inert. Here, we show that under mild conditions a simple triamidoamine uranium(III) complex can reductively homologate CO and be recycled for reuse. Following treatment with organosilyl halides, bis(organosiloxy)acetylenes, which readily convert to furanones, are produced, and this was confirmed by the use of isotopically (13)C-labeled CO. The precursor to the triamido uranium(III) complex is formed concomitantly. These findings establish that, under appropriate conditions, uranium(III) can mediate a complete synthetic cycle for the homologation of CO to higher derivatives. This work may prove useful in spurring wider efforts in CO homologation, and the simplicity of this system suggests that catalytic CO functionalization may soon be within reach.

Homologation and functionalization of carbon monoxide by a recyclable uranium complex

PubMed Central

Gardner, Benedict M.; Stewart, John C.; Davis, Adrienne L.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Liddle, Stephen T.

2012-01-01

Carbon monoxide (CO) is in principle an excellent resource from which to produce industrial hydrocarbon feedstocks as alternatives to crude oil; however, CO has proven remarkably resistant to selective homologation, and the few complexes that can effect this transformation cannot be recycled because liberation of the homologated product destroys the complexes or they are substitutionally inert. Here, we show that under mild conditions a simple triamidoamine uranium(III) complex can reductively homologate CO and be recycled for reuse. Following treatment with organosilyl halides, bis(organosiloxy)acetylenes, which readily convert to furanones, are produced, and this was confirmed by the use of isotopically 13C-labeled CO. The precursor to the triamido uranium(III) complex is formed concomitantly. These findings establish that, under appropriate conditions, uranium(III) can mediate a complete synthetic cycle for the homologation of CO to higher derivatives. This work may prove useful in spurring wider efforts in CO homologation, and the simplicity of this system suggests that catalytic CO functionalization may soon be within reach. PMID:22652572

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hawkins, Cory A.; Bustillos, Christian G.; May, Iain

Conventional solvent extraction of selected f-element cations by bis(2-ethylhexyl)phosphoric acid (HDEHP) yields increased extraction from aqueous to organic solution along the series Np(V) < Cm(III) < Eu(III) < U(VI), with distribution ratios all within two orders of magnitude. However, in the presence of the water-soluble tetradentate Schiff base (N,N'-bis(5-sulfonatosalicylidene)-ethylenediamine or H 2salenSO 3), selective complexation of the two actinyl cations (Np(V) and U(VI)) resulted in an extraction order of Np(V) < U(VI) << Eu(III) < Cm(III). The extraction of neither Cm(III) or Eu(III) by HDEHP are significantly impacted by the presence of the aqueous phase Schiff base. Despite observed hydrolyticmore » decomposition of H 2salenSO 3 in aqueous solutions, the calculated high conditional stability constant (β 11 = 26) for the complex [UO 2(salenSO 3)] 2- demonstrates its capacity for aqueous hold-back of U(VI). UV-visible-NIR spectroscopy of solutions prepared with a Np(VI) stock and H 2salenSO 3 suggest that reduction of Np(VI) to Np(V) by the ligand was rapid, resulting in a pentavalent Np complex that was substantially retained in the aqueous phase. Lastly, results from 1H NMR of aqueous solutions of H 2salenSO 3 with U(VI) and La(III), Eu(III), and Lu(III) provides additional evidence that the ligand readily chelates U(VI), but has only weak interactions with trivalent lanthanide ions.« less

Kinetic, equilibrium and thermodynamic studies on sorption of uranium and thorium from aqueous solutions by a selective impregnated resin containing carminic acid.

PubMed

Rahmani-Sani, Abolfazl; Hosseini-Bandegharaei, Ahmad; Hosseini, Seyyed-Hossein; Kharghani, Keivan; Zarei, Hossein; Rastegar, Ayoob

2015-04-09

In this work, the removal of uranium and thorium ions from aqueous solutions was studied by solid-liquid extraction using an advantageous extractant-impregnated resin (EIR) prepared by loading carminic acid (CA) onto Amberlite XAD-16 resin beads. Batch sorption experiments using CA/XAD-16 beads for the removal of U(VI) and Th(IV) ions were carried out as a function of several parameters, like equilibration time, metal ion concentration, etc. The equilibrium data obtained from the sorption experiments were adjusted to the Langmuir isotherm model and the calculated maximum sorption capacities in terms of monolayer sorption were in agreement with those obtained from the experiments. The experimental data on the sorption behavior of both metal ions onto the EIR beads fitted well in both Bangham and intra-particle diffusion kinetic models, indicating that the intra-particle diffusion is the rate-controlling step. The thermodynamic studies at different temperatures revealed the feasibility and the spontaneous nature of the sorption process for both uranium and thorium ions. Copyright © 2014 Elsevier B.V. All rights reserved.

Facile Reductive Silylation of UO22+ to Uranium(IV) Chloride.

PubMed

Kiernicki, John J; Zeller, Matthias; Bart, Suzanne C

2017-01-19

General reductive silylation of the UO 2 2+ cation occurs readily in a one-pot, two-step stoichiometric reaction at room temperature to form uranium(IV) siloxides. Addition of two equivalents of an alkylating reagent to UO 2 X 2 (L) 2 (X=Cl, Br, I, OTf; L=triphenylphosphine oxide, 2,2'-bipyridyl) followed by two equivalents of a silyl (pseudo)halide, R 3 Si-X (R=aryl, alkyl, H; X=Cl, Br, I, OTf, SPh), cleanly affords (R 3 SiO) 2 UX 2 (L) 2 in high yields. Support is included for the key step in the process, reduction of U VI to U V . This procedure is applicable to a wide range of commercially available uranyl salts, silyl halides, and alkylating reagents. Under this protocol, one equivalent of SiCl 4 or two equivalents of Me 2 SiCl 2 results in direct conversion of the uranyl to uranium(IV) tetrachloride. Full spectroscopic and structural characterization of the siloxide products is reported. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Linking Chaotic Advection with Subsurface Biogeochemical Processes

NASA Astrophysics Data System (ADS)

Mays, D. C.; Freedman, V. L.; White, S. K.; Fang, Y.; Neupauer, R.

2017-12-01

This work investigates the extent to which groundwater flow kinematics drive subsurface biogeochemical processes. In terms of groundwater flow kinematics, we consider chaotic advection, whose essential ingredient is stretching and folding of plumes. Chaotic advection is appealing within the context of groundwater remediation because it has been shown to optimize plume spreading in the laminar flows characteristic of aquifers. In terms of subsurface biogeochemical processes, we consider an existing model for microbially-mediated reduction of relatively mobile uranium(VI) to relatively immobile uranium(IV) following injection of acetate into a floodplain aquifer beneath a former uranium mill in Rifle, Colorado. This model has been implemented in the reactive transport code eSTOMP, the massively parallel version of STOMP (Subsurface Transport Over Multiple Phases). This presentation will report preliminary numerical simulations in which the hydraulic boundary conditions in the eSTOMP model are manipulated to simulate chaotic advection resulting from engineered injection and extraction of water through a manifold of wells surrounding the plume of injected acetate. This approach provides an avenue to simulate the impact of chaotic advection within the existing framework of the eSTOMP code.

DOE Office of Scientific and Technical Information (OSTI.GOV)

MIchael A. Pope

Six early cores of the MASURCA R-Z program were modeled using ERANOS 2.1. These cores were designed such that their neutron spectra would be similar to that of an oxide-fueled sodium-cooled fast reactor, some containing enriched uranium and others containing depleted uranium and plutonium. Effects of modeling assumptions and solution methods both in ECCO lattice calculations and in BISTRO Sn flux solutions were evaluated using JEFF-3.1 cross-section libraries. Reactivity effects of differences between JEFF-3.1 and ENDF/B-VI.8 were also quantified using perturbation theory analysis. The most important nuclide with respect to reactivity differences between cross-section libraries was 23Na, primarily a resultmore » of differences in the angular dependence of elastic scattering which is more forward-peaked in ENDF/B-VI.8 than in JEFF-3.1. Differences in 23Na inelastic scattering cross-sections between libraries also generated significant differences in reactivity, more due to the differences in magnitude of the cross-sections than the angular dependence. The nuclide 238U was also found to be important with regard to reactivity differences between the two libraries mostly due to a large effect of inelastic scattering differences and two smaller effects of elastic scattering and fission cross-sections. In the cores which contained plutonium, 239Pu fission cross-section differences contributed significantly to the reactivity differences between libraries.« less

Reduced Uranium Phases Produced from Anaerobic Reaction with Nanoscale Zerovalent Iron.

PubMed

Tsarev, Sergey; Collins, Richard N; Fahy, Adam; Waite, T David

2016-03-01

Nanoscale zerovalent iron (nZVI) has shown potential to be an effective remediation agent for uranium-contaminated subsurface environments, however, the nature of the reaction products and their formation kinetics have not been fully elucidated over a range of environmentally relevant conditions. In this study, the oxygen-free reaction of U(VI) with varying quantities of nZVI was examined at pH 7 in the presence of both calcium and carbonate using a combination of X-ray absorption spectroscopy, X-ray diffraction and transmission electron microscopy. It was observed that the structure of the reduced U solid phases was time dependent and largely influenced by the ratio of nZVI to U in the system. At the highest U:Fe molar ratio examined (1:4), nanoscale uraninite (UO2) was predominantly formed within 1 day of reaction. At lower U:Fe molar ratios (1:21), evidence was obtained for the formation of sorbed U(IV) and U(V) surface complexes which slowly transformed to UO2 nanoparticles that were stable for up to 1 year of anaerobic incubation. After 8 days of reaction at the lowest U:Fe molar ratio examined (1:110), sorbed U(IV) was still the major form of U associated with the solid phase. Regardless of the U:Fe molar ratio, the anaerobic corrosion of nZVI resulted in the slow formation of micron-sized fibrous chukanovite (Fe2(OH)2CO3) particles.

Theoretical investigations of geometry, electronic structure and stability of UO(6): octahedral uranium hexoxide and its isomers.

PubMed

Xiao, Hai; Hu, Han-Shi; Schwarz, W H Eugen; Li, Jun

2010-08-26

The existence of a novel octahedral UO(6) complex had been suggested by Pyykko et al. [Pyykko, P.; Runeberg, N.; Straka, M.; Dyall, K. G. Chem. Phys. Lett. 2000, 328, 415]. We have now investigated the stability, the geometric and electronic structures, and the vibrations of various UO(6) molecules, using spin-orbit density functional and scalar-relativistic coupled-cluster approaches. We find four different (meta-)stable species, namely (3)D(2h)-UO(2)(eta(2)-O(2)(*))(2) at lowest energy, (3)C(2v)-UO(4)(*)(eta(2)-O(2)(*)) and (1)D(3)-U(eta(2)-O(2))(3) at medium energies, and (1)O(h)-UO(6) at highest energy. The decay of O(h)-UO(6) occurs via an activated spin-flip mechanism. The UO(6) species correspond to local minima on singlet and triplet energy surfaces and might be trapped in noble gas matrices. Experimentally, the four species might be identified through their vibrational spectra. Uranium is best described as coordinated by oxygen atoms in various oxidation states as oxo O(2-), oxido(1) O(*-), peroxido O(2)(2-), and superoxido O(2)(*-) ligands. The occurrence of monovalent oxygen is remarkable. The resulting characterization of the central ion as U(VI) in all four cases does not fully reflect the electronic differences, nor the "valence-activity" of the U-6p(6) semicore shell.

ViSEN: methodology and software for visualization of statistical epistasis networks

PubMed Central

Hu, Ting; Chen, Yuanzhu; Kiralis, Jeff W.; Moore, Jason H.

2013-01-01

The non-linear interaction effect among multiple genetic factors, i.e. epistasis, has been recognized as a key component in understanding the underlying genetic basis of complex human diseases and phenotypic traits. Due to the statistical and computational complexity, most epistasis studies are limited to interactions with an order of two. We developed ViSEN to analyze and visualize epistatic interactions of both two-way and three-way. ViSEN not only identifies strong interactions among pairs or trios of genetic attributes, but also provides a global interaction map that shows neighborhood and clustering structures. This visualized information could be very helpful to infer the underlying genetic architecture of complex diseases and to generate plausible hypotheses for further biological validations. ViSEN is implemented in Java and freely available at https://sourceforge.net/projects/visen/. PMID:23468157

Cell metal interactions: A comparison of natural uranium to other common metals in renal cells and bone osteoblasts

NASA Astrophysics Data System (ADS)

Milgram, S.; Carrière, M.; Thiebault, C.; Berger, P.; Khodja, H.; Gouget, B.

2007-07-01

Uranium acute intoxication has been documented to induce nephrotoxicity. Kidneys are the main target organs after short term exposures to high concentrations of the toxic, while chronic exposures lead to its accumulation in the skeleton. In this paper, chemical toxicity of uranium is investigated for rat osteoblastic bone cells and compared to results previously obtained on renal cells. We show that bone cells are less sensitive to uranium than renal cells. The influence of the chemical form on U cytotoxicity is demonstrated. For both cell types, a comparison of uranium toxicity with other metals or metalloids toxicities (Mn, Ni, Co, Cu, Zn, Se and Cd) permits classification of Cd, Zn, Se IV and Cu as the most toxic and Ni, Se VI, Mn and U as the least toxic. Chemical toxicity of natural uranium proves to be far less than that of cadmium. To try to explain the differences in sensitivities observed between metals and different cell types, cellular accumulations in cell monolayers are quantified by inductively coupled plasma-mass spectroscopy (ICP-MS), function of time or function of dose: lethal doses which simulate acute intoxications and sub-lethal doses which are more realistic with regard to environmentally metals concentrations. In addition to being more resistant, bone cells accumulated much more uranium than did renal cells. Moreover, for both cell models, Mn, U-citrate and U-bicarbonate are strongly accumulated whereas Cu, Zn and Ni are weakly accumulated. On the other hand, a strong difference in Cd behaviour between the two cell types is shown: whereas Cd is very weakly accumulated in bone cells, it is very strongly accumulated in renal cells. Finally, elemental distribution of the toxics is determined on a cellular scale using nuclear microprobe analysis. For both renal and osteoblastic cells, uranium was accumulated in as intracellular precipitates similar to those observed previously by SEM/EDS.

Bioremediation of Uranium-Contaminated Groundwater using Engineered Injection and Extraction

NASA Astrophysics Data System (ADS)

Greene, J. A.; Neupauer, R.; Ye, M.; Kasprzyk, J. R.; Mays, D. C.; Curtis, G. P.

2017-12-01

During in-situ remediation of contaminated groundwater, a treatment chemical is injected into the contaminated groundwater to react with and degrade the contaminant, with reactions occurring where the treatment chemical contacts the contaminant. Traditional in-situ groundwater remediation relies on background groundwater flow for spreading of treatment chemicals into contaminant plumes. Engineered Injection and Extraction (EIE), in which time-varying induced flow fields are used to actively spread the treatment chemical into the contaminant plume, has been developed to increase contact between the contaminant and treatment chemical, thereby enhancing contaminant degradation. EIE has been investigated for contaminants that degrade through irreversible bimolecular reaction with a treatment chemical, but has not been investigated for a contaminant governed by reversible reactions. Uranium primarily occurs in its aqueous, mobile form, U(VI), in the environment but can be bioreduced to its sparingly soluble, immobile form, U(IV), by iron reducing bacteria stimulated by an acetate amendment. In this study, we investigate the ability of EIE to facilitate and sustain favorable conditions to immobilize uranium during remediation, and to prevent re-mobilization of uranium into the aqueous phase after active remediation has ended. Simulations in this investigation are conducted using a semi-synthetic model based on physical and chemical conditions at the Naturita Uranium Mill Tailings Remedial Action (UMTRA) site in southwestern Colorado and the Old Rifle UMTRA site in western Colorado. The EIE design is optimized for the synthetic model using the Borg multi-objective evolutionary algorithm.

In situ bioremediation of uranium with emulsified vegetable oil as the electron donor.

PubMed

Watson, David B; Wu, Wei-Min; Mehlhorn, Tonia; Tang, Guoping; Earles, Jennifer; Lowe, Kenneth; Gihring, Thomas M; Zhang, Gengxin; Phillips, Jana; Boyanov, Maxim I; Spalding, Brian P; Schadt, Christopher; Kemner, Kenneth M; Criddle, Craig S; Jardine, Philip M; Brooks, Scott C

2013-06-18

A field test with a one-time emulsified vegetable oil (EVO) injection was conducted to assess the capacity of EVO to sustain uranium bioreduction in a high-permeability gravel layer with groundwater concentrations of (mM) U, 0.0055; Ca, 2.98; NO3(-), 0.11; HCO3(-), 5.07; and SO4(2-), 1.23. Comparison of bromide and EVO migration and distribution indicated that a majority of the injected EVO was retained in the subsurface from the injection wells to 50 m downgradient. Nitrate, uranium, and sulfate were sequentially removed from the groundwater within 1-2 weeks, accompanied by an increase in acetate, Mn, Fe, and methane concentrations. Due to the slow release and degradation of EVO with time, reducing conditions were sustained for approximately one year, and daily U discharge to a creek, located approximately 50 m from the injection wells, decreased by 80% within 100 days. Total U discharge was reduced by 50% over the one-year period. Reduction of U(VI) to U(IV) was confirmed by synchrotron analysis of recovered aquifer solids. Oxidants (e.g., dissolved oxygen, nitrate) flowing in from upgradient appeared to reoxidize and remobilize uranium after the EVO was exhausted as evidenced by a transient increase of U concentration above ambient values. Occasional (e.g., annual) EVO injection into a permeable Ca and bicarbonate-containing aquifer can sustain uranium bioreduction/immobilization and decrease U migration/discharge.

Surface reactions kinetics between nanocrystalline magnetite and uranyl.

PubMed

Missana, Tiziana; Maffiotte, César; García-Gutiérrez, Miguel

2003-05-01

Magnetite is the most important end member of iron corrosion products under reducing environment, which is the condition expected in a deep geological high level radioactive waste disposal. Nanocrystalline magnetite was synthesized in the laboratory and its physicochemical properties were analyzed in detail. The kinetics of the adsorption of U(VI) and the kinetics of the actinide reduction to a lower oxidation state, in presence of the oxide, were studied by means of batch sorption techniques and X-ray photoelectron spectroscopy (XPS) analysis. The results showed that the uranium sorption and reduction processes on the magnetite surface have very fast kinetics (hours), the reduction process being triggered by sorption. XPS measurements showed that the speciation of uranium at the surface does not show significant changes with time (from 1 day to 3 months), as well as the quantity of uranium detected at the surface. The surface speciation depended on the initial pH of the contact solution. Considering that the Eh of equilibrium between magnetite and the solution, under our experimental conditions, is slightly positive (50-100 mV), the uranium reduction would also be thermodynamically possible within the liquid phase. However, the kinetics of reduction in the liquid occur at a much slower rate which, in turn, has to depend on the attainment of the magnetite/solution equilibrium. The decrease of uranium in solution, observed after the uranyl adsorption stage, and particularly at acidic pH, is most probably due to the precipitation of U(IV) formed in the solution.

New Synthesis of nZVI/C Composites as an Efficient Adsorbent for the Uptake of U(VI) from Aqueous Solutions.

PubMed

Liu, Haibo; Li, Mengxue; Chen, Tianhu; Chen, Changlun; Alharbi, Njud S; Hayat, Tasawar; Chen, Dong; Zhang, Qiang; Sun, Yubing

2017-08-15

New nanoscale zerovalent iron/carbon (nZVI/C) composites were successfully prepared via heating natural hematite and pine sawdust at 800 °C under nitrogen conditions. Characterization by SEM, XRD, FTIR, and XPS analyses indicated that the as-prepared nZVI/C composites contained a large number of reactive sites. The lack of influence of the ionic strength revealed inner-sphere complexation dominated U(VI) uptake by the nZVI/C composites. Simultaneous adsorption and reduction were involved in the uptake process of U(VI) according to the results of XPS and XANES analyses. The presence of U-C/U-U shells demonstrated that innersphere complexation and surface coprecipitation dominated the U(VI) uptake at low and high pH conditions, respectively. The uptake behaviors of U(VI) by the nZVI/C composites were fitted well by surface complexation modeling with two weak and two strong sites. The maximum uptake capacity of U(VI) by the nZVI/C composites was 186.92 mg/g at pH 4.0 and 328 K. Additionally, the nZVI/C composites presented good recyclability and recoverability for U(VI) uptake in regeneration experiments. These observations indicated that the nZVI/C composites can be considered as potential adsorbents to remove radionuclides for environmental remediation.

Nitrogen reduction and functionalization by a multimetallic uranium nitride complex

NASA Astrophysics Data System (ADS)

Falcone, Marta; Chatelain, Lucile; Scopelliti, Rosario; Živković, Ivica; Mazzanti, Marinella

2017-07-01

Molecular nitrogen (N2) is cheap and widely available, but its unreactive nature is a challenge when attempting to functionalize it under mild conditions with other widely available substrates (such as carbon monoxide, CO) to produce value-added compounds. Biological N2 fixation can do this, but the industrial Haber-Bosch process for ammonia production operates under harsh conditions (450 degrees Celsius and 300 bar), even though both processes are thought to involve multimetallic catalytic sites. And although molecular complexes capable of binding and even reducing N2 under mild conditions are known, with co-operativity between metal centres considered crucial for the N2 reduction step, the multimetallic species involved are usually not well defined, and further transformation of N2-binding complexes to achieve N-H or N-C bond formation is rare. Haber noted, before an iron-based catalyst was adopted for the industrial Haber-Bosch process, that uranium and uranium nitride materials are very effective heterogeneous catalysts for ammonia production from N2. However, few examples of uranium complexes binding N2 are known, and soluble uranium complexes capable of transforming N2 into ammonia or organonitrogen compounds have not yet been identified. Here we report the four-electron reduction of N2 under ambient conditions by a fully characterized complex with two UIII ions and three K+ centres held together by a nitride group and a flexible metalloligand framework. The addition of H2 and/or protons, or CO to the resulting complex results in the complete cleavage of N2 with concomitant N2 functionalization through N-H or N-C bond-forming reactions. These observations establish that a molecular uranium complex can promote the stoichiometric transformation of N2 into NH3 or cyanate, and that a flexible, electron-rich, multimetallic, nitride-bridged core unit is a promising starting point for the design of molecular complexes capable of cleaving and functionalizing N2 under mild conditions.

Functionalization of carbon dioxide and carbon disulfide using a stable uranium(III) alkyl complex.

PubMed

Matson, Ellen M; Forrest, William P; Fanwick, Phillip E; Bart, Suzanne C

2011-04-06

A rare uranium(III) alkyl complex, Tp*(2)U(CH(2)Ph) (2) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate), was synthesized by salt metathesis from Tp*(2)UI (1) and KCH(2)Ph and fully characterized using (1)H NMR, infrared, and electronic absorption spectroscopies as well as X-ray crystallography. This complex has a uranium-carbon distance of 2.57(2) Å, which is comparable to other uranium alkyls reported. Treating this compound with either carbon dioxide or carbon disulfide results in insertion into the uranium-carbon bond to generate Tp*(2)U(κ(2)-O(2)CCH(2)Ph) (3) and Tp*(2)U(SC(S)CH(2)Ph) (4), respectively. These species, characterized spectroscopically and by X-ray crystallography, feature new carboxylate and dithiocarboxylate ligands. Analysis by electronic absorption spectroscopy supports the trivalent oxidation state of the uranium center in both of these derivatives. Addition of trimethylsilylhalides (Me(3)SiX; X = Cl, I) to 3 results in the release of the free silyl ester, Me(3)SiOC(O)CH(2)Ph, forming the initial uranium monohalide species, Tp*(2)UX, which can then be used over multiple cycles for the functionalization of carbon dioxide. © 2011 American Chemical Society