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Sample records for abiotic reductive dissolution

  1. Abiotic carbonate dissolution traps carbon in a semiarid desert

    PubMed Central

    Fa, Keyu; Liu, Zhen; Zhang, Yuqing; Qin, Shugao; Wu, Bin; Liu, Jiabin

    2016-01-01

    It is generally considered that desert ecosystems release CO2 to the atmosphere, but recent studies in drylands have shown that the soil can absorb CO2 abiotically. However, the mechanisms and exact location of abiotic carbon absorption remain unclear. Here, we used soil sterilization, 13CO2 addition, and detection methods to trace 13C in the soil of the Mu Us Desert, northern China. After 13CO2 addition, a large amount of 13CO2 was absorbed by the sterilised soil, and 13C was found enriched both in the soil gaseous phase and dissolved inorganic carbon (DIC). Further analysis indicated that about 79.45% of the total 13C absorbed by the soil was trapped in DIC, while the amount of 13C in the soil gaseous phase accounted for only 0.22% of the total absorbed 13C. However, about 20.33% of the total absorbed 13C remained undetected. Our results suggest that carbonate dissolution might occur predominately, and the soil liquid phase might trap the majority of abiotically absorbed carbon. It is possible that the trapped carbon in the soil liquid phase leaches into the groundwater; however, further studies are required to support this hypothesis. PMID:27020762

  2. A reductive dissolution study of magnetite

    SciTech Connect

    Hui-Jun Won; Jung-Soon Park; Chong-Hun Jung; Sang-Yoon Park; Wang-Kyu Choi; Jei-Kwon Moon

    2013-07-01

    Magnetite dissolution tests using a hydrazine base solution were performed at a temperature range of 90 to 150 deg. C. The dissolution rate of magnetite increased with [N{sub 2}H{sub 4}], time, and temperature. The optimum solution pH in the experimental range was 3. The addition of copper ion to the hydrazine base solution greatly increased the magnetite dissolution rate. This was explained by the complex formation between N{sub 2}H{sub 4} and Cu ions, and the reducing power of the hydrazine-Cu complex to the ferric ions of magnetite. The reductive decontamination solution can be applied below 100 deg. C by the addition of copper ions. The chemical decontamination of a Type 304 stainless steel specimen using a hydrazine base reductive decontamination solution was also performed. The contact dose rate was greatly decreased by the repetitive application of NP and the hydrazine base solution. (authors)

  3. Dissolution and reduction of magnetite by bacteria

    NASA Technical Reports Server (NTRS)

    Kostka, J. E.; Nealson, K. H.

    1995-01-01

    Magnetite (Fe3O4) is an iron oxide of mixed oxidation state [Fe(II), Fe(III)] that contributes largely to geomagnetism and plays a significant role in diagenesis in marine and freshwater sediments. Magnetic data are the primary evidence for ocean floor spreading and accurate interpretation of the sedimentary magnetic record depends on an understanding of the conditions under which magnetite is stable. Though chemical reduction of magnetite by dissolved sulfide is well known, biological reduction has not been considered likely based upon thermodynamic considerations. This study shows that marine and freshwater strains of the bacterium Shewanella putrefaciens are capable of the rapid dissolution and reduction of magnetite, converting millimolar amounts to soluble Fe(II)in a few days at room temperature. Conditions under which magnetite reduction is optimal (pH 5-6, 22-37 degrees C) are consistent with an enzymatic process and not with simple chemical reduction. Magnetite reduction requires viable cells and cell contact, and it appears to be coupled to electron transport and growth. In a minimal medium with formate or lactate as the electron donor, more than 10 times the amount of magnetite was reduced over no carbon controls. These data suggest that magnetite reduction is coupled to carbon metabolism in S. putrefaciens. Bacterial reduction rates of magnetite are of the same order of magnitude as those estimated for reduction by sulfide. If such remobilization of magnetite occurs in nature, it could have a major impact on sediment magnetism and diagenesis.

  4. Dissolution and reduction of magnetite by bacteria.

    PubMed

    Kostka, J E; Nealson, K H

    1995-10-01

    Magnetite (Fe3O4) is an iron oxide of mixed oxidation state [Fe(II), Fe(III)] that contributes largely to geomagnetism and plays a significant role in diagenesis in marine and freshwater sediments. Magnetic data are the primary evidence for ocean floor spreading and accurate interpretation of the sedimentary magnetic record depends on an understanding of the conditions under which magnetite is stable. Though chemical reduction of magnetite by dissolved sulfide is well known, biological reduction has not been considered likely based upon thermodynamic considerations. This study shows that marine and freshwater strains of the bacterium Shewanella putrefaciens are capable of the rapid dissolution and reduction of magnetite, converting millimolar amounts to soluble Fe(II)in a few days at room temperature. Conditions under which magnetite reduction is optimal (pH 5-6, 22-37 degrees C) are consistent with an enzymatic process and not with simple chemical reduction. Magnetite reduction requires viable cells and cell contact, and it appears to be coupled to electron transport and growth. In a minimal medium with formate or lactate as the electron donor, more than 10 times the amount of magnetite was reduced over no carbon controls. These data suggest that magnetite reduction is coupled to carbon metabolism in S. putrefaciens. Bacterial reduction rates of magnetite are of the same order of magnitude as those estimated for reduction by sulfide. If such remobilization of magnetite occurs in nature, it could have a major impact on sediment magnetism and diagenesis.

  5. Reductive Dissolution of Goethite and Hematite by Reduced Flavins

    SciTech Connect

    Shi, Zhi; Zachara, John M.; Wang, Zheming; Shi, Liang; Fredrickson, Jim K.

    2013-10-02

    The abiotic reductive dissolution of goethite and hematite by the reduced forms of flavin mononucleotide (FMNH2) and riboflavin (RBFH2), electron transfer mediators (ETM) secreted by the dissimilatory iron-reducing bacterium Shewanella, was investigated under stringent anaerobic conditions. In contrast to the rapid redox reaction rate observed for ferrihydrite and lepidocrocite (Shi et al., 2012), the reductive dissolution of crystalline goethite and hematite was slower, with the extent of reaction limited by the thermodynamic driving force at circumneutral pH. Both the initial reaction rate and reaction extent increased with decreasing pH. On a unit surface area basis, goethite was less reactive than hematite between pH 4.0 and 7.0. AH2DS, the reduced form of the well-studied synthetic ETM anthraquinone-2,6-disulfonate (AQDS), yielded higher rates than FMNH2 under most reaction conditions, despite the fact that FMNH2 was a more effective reductant than AH2DS for ferryhydrite and lepidocrocite. Two additional model compounds, methyl viologen and benzyl viologen, were investigated under similar reaction conditions to explore the relationship between reaction rate and thermodynamic properties. Relevant kinetic data from the literature were also included in the analysis to span a broad range of half-cell potentials. Other conditions being equal, the surface area normalized initial reaction rate (ra) increased as the redox potential of the reductant became more negative. A non-linear, parabolic relationship was observed between log ra and the redox potential for eight reducants at pH 7.0, as predicted by Marcus theory for electron transfer. When pH and reductant concentration were fixed, log ra was positively correlated to the redox potential of four Fe(III) oxides over a wide pH range, following a non-linear parabolic relationship as well.

  6. Abiotic nitrogen reduction on the early Earth.

    PubMed

    Brandes, J A; Boctor, N Z; Cody, G D; Cooper, B A; Hazen, R M; Yoder, H S

    1998-09-24

    The production of organic precursors to life depends critically on the form of the reactants. In particular, an environment dominated by N2 is far less efficient in synthesizing nitrogen-bearing organics than a reducing environment rich in ammonia. Relatively reducing lithospheric conditions on the early Earth have been presumed to favour the generation of an ammonia-rich atmosphere, but this hypothesis has not been studied experimentally. Here we demonstrate mineral-catalysed reduction of N2, NO2- and NO3- to ammonia at temperatures between 300 and 800 degrees C and pressures of 0.1-0.4 GPa-conditions typical of crustal and oceanic hydrothermal systems. We also show that only N2 is stable above 800 degrees C, thus precluding significant atmospheric ammonia formation during hot accretion. We conclude that mineral-catalysed N2 reduction might have provided a significant source of ammonia to the Hadean ocean. These results also suggest that, whereas nitrogen in the Earth's early atmosphere was present predominantly as N2, exchange with oceanic, hydrothermally derived ammonia could have provided a significant amount of the atmospheric ammonia necessary to resolve the early-faint-Sun paradox.

  7. Abiotic Reductive Immobilization of U(VI) by Biogenic Mackinawite

    SciTech Connect

    Veeramani, Harish; Scheinost, Andreas; Monsegue, Niven; Qafoku, Nikolla; Kukkadapu, Ravi K.; Newville, Mathew; Lanzirotti, Anthony; Pruden, Amy; Murayama, Mitsuhiro; Hochella, Michael F.

    2013-03-01

    During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in-situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze abiotic U6+ reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe1+xS, x = 0 to 0.11) to reduce U6+ abiotically was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U6+ indicate the formation of nanoparticulate UO2. This study suggests the relevance of Fe(II) and sulfide bearing biogenic minerals in mediating abiotic U6+ reduction, an alternative pathway in addition to direct enzymatic U6+ reduction.

  8. Abiotic reductive immobilization of U(VI) by biogenic mackinawite.

    PubMed

    Veeramani, Harish; Scheinost, Andreas C; Monsegue, Niven; Qafoku, Nikolla P; Kukkadapu, Ravi; Newville, Matt; Lanzirotti, Antonio; Pruden, Amy; Murayama, Mitsuhiro; Hochella, Michael F

    2013-03-05

    During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze abiotic U(VI) reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe 1+x S, x = 0 to 0.11) to reduce U(VI) abiotically was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS, and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U(VI) indicate the formation of nanoparticulate UO2. This study suggests the relevance of sulfide-bearing biogenic minerals in mediating abiotic U(VI) reduction, an alternative pathway in addition to direct enzymatic U(VI) reduction.

  9. Kinetics of Abiotic Uranium(VI) Reduction by Sulfide

    NASA Astrophysics Data System (ADS)

    Hyun, S.; Davis, J. A.; Hayes, K. F.

    2010-12-01

    Uranium(VI) reduction is an important process affecting the radionuclide’s fate under sulfate reducing conditions. In this work, kinetics of abiotic U(VI) reduction by dissolved sulfide was studied using a batch reactor. The effects of solution pH, dissolved carbonate, Ca(II), U(VI), and S(-II) concentration on the reduction kinetics were tested. The ranges of these experimental variables were designed to cover the variation in groundwater chemistry observed at the Old Rifle uranium mill tailings site (Colorado, USA). Dissolved U concentration was monitored as a function of time using inductively coupled plasma-mass spectrometry to measure the rate of U(VI) reduction. Solid phase reduction products were identified using X-ray diffraction, transmission electron microscopy, and X-ray absorption spectroscopy. The results showed that changes in the experimental variables significantly affected U(VI) reduction kinetics by dissolved sulfide. U(VI) reduction occurred under circumneutral pH while no reduction was observed under alkaline conditions. The reduction rate was slowed by increased dissolved carbonate concentration. One solid phase reduction product was identified as nanoscale uraninite (UO2+x(s)). Thermodynamic modeling showed that the dissolved U(VI) aqueous species changed as a function of solution conditions correlated with the change in the reduction rate. These results show that U(VI) aqueous speciation is important in determining abiotic U(VI) reduction kinetics by dissolved sulfide. This study also illustrates the potential importance of dissolved sulfide in field-scale modeling of U reactive transport, and is expected to contribute to the understanding of long-term effects of biostimulation on U transport at the Rifle site.

  10. Reduction of ferrihydrite with adsorbed and coprecipitated organic matter: microbial reduction by Geobacter bremensis vs. abiotic reduction by Na-dithionite

    NASA Astrophysics Data System (ADS)

    Eusterhues, K.; Hädrich, A.; Neidhardt, J.; Küsel, K.; Keller, T. F.; Jandt, K. D.; Totsche, K. U.

    2014-09-01

    Ferrihydrite is a widespread poorly crystalline Fe oxide which becomes easily coated by natural organic matter in the environment. This mineral-bound organic matter entirely changes the mineral surface properties and therefore the reactivity of the original mineral. Here, we investigated 2-line ferrihydrite, ferrihydrite with adsorbed organic matter, and ferrihydrite coprecipitated with organic matter for microbial and abiotic reduction of Fe(III). Ferrihydrite-organic matter associations with different organic matter loadings were reduced either by Geobacter bremensis or abiotically by Na-dithionite. Both types of experiments showed decreasing initial Fe-reduction rates and decreasing degrees of reduction with increasing amounts of mineral-bound organic matter. At similar organic matter loadings, coprecipitated ferrihydrites were more reactive than ferrihydrites with adsorbed organic matter. The difference can be explained by the smaller crystal size and poor crystallinity of such coprecipitates. At small organic matter loadings the poor crystallinity of coprecipitates led to even faster Fe-reduction rates than found for pure ferrihydrite. The amount of mineral-bound organic matter also affected the formation of secondary minerals: goethite was only found after reduction of organic matter-free ferrihydrite and siderite was only detected when ferrihydrites with relatively low amounts of mineral-bound organic matter were reduced. We conclude that direct contact of G. bremensis to the Fe oxide mineral surface was inhibited by attached organic matter. Consequently, mineral-bound organic matter shall be taken into account as a factor in slowing down reductive dissolution.

  11. Citrate influences microbial Fe hydroxide reduction via a dissolution-disaggregation mechanism

    NASA Astrophysics Data System (ADS)

    Braunschweig, Juliane; Klier, Christine; Schröder, Christian; Händel, Matthias; Bosch, Julian; Totsche, Kai U.; Meckenstock, Rainer U.

    2014-08-01

    abiotic dissolution kinetics revealed that colloid stabilization was most pronounced at citrate:Fe ratios of 0.1 - 0.5, whereas higher ratios led to enhanced dissolution of both colloidal and larger aggregated fractions. Mathematical simulation of the microbial reduction kinetics under consideration of partial dissolution and colloid stabilization showed that the bioaccessibility increases in the order large aggregates < stable colloids < Fe-citrate. These findings indicate that much of the organic acid driven mobilization of Fe oxy(hydr)oxides is most likely due to colloid formation and stabilization rather than solubilisation.

  12. Interactions between Biological and Abiotic Pathways in the Reduction of Chlorinated Solvents

    EPA Science Inventory

    While biologically mediated reductive dechlorination continues to be a significant focus of chlorinated solvent remediation, there has been an increased interest in abiotic reductive processes for the remediation of chlorinated solvents. In situ chemical reduction (ISCR) uses zer...

  13. The Use of Chemical Probes for the Characterization of the Predominant Abiotic Reductants in Anaerobic Sediments

    EPA Science Inventory

    Identifying the predominant chemical reductants and pathways for electron transfer in anaerobic systems is paramount to the development of environmental fate models that incorporate pathways for abiotic reductive transformations. Currently, such models do not exist. In this chapt...

  14. Reduction of ferrihydrite with adsorbed and coprecipitated organic matter: microbial reduction by Geobacter bremensis vs. abiotic reduction by Na-dithionite

    NASA Astrophysics Data System (ADS)

    Eusterhues, K.; Hädrich, A.; Neidhardt, J.; Küsel, K.; Keller, T. F.; Jandt, K. D.; Totsche, K. U.

    2014-04-01

    Ferrihydrite (Fh) is a widespread poorly crystalline Fe oxide which becomes easily coated by natural organic matter (OM) in the environment. This mineral-bound OM entirely changes the mineral surface properties and therefore the reactivity of the original mineral. Here, we investigated the reactivity of 2-line Fh, Fh with adsorbed OM and Fh coprecipitated with OM towards microbial and abiotic reduction of Fe(III). As a surrogate for dissolved soil OM we used a water extract of a Podzol forest floor. Fh-OM associations with different OM-loadings were reduced either by Geobacter bremensis or abiotically by Na-dithionite. Both types of experiments showed decreasing initial Fe reduction rates and decreasing degrees of reduction with increasing amounts of mineral-bound OM. At similar OM-loadings, coprecipitated Fhs were more reactive than Fhs with adsorbed OM. The difference can be explained by the smaller crystal size and poor crystallinity of such coprecipitates. At small OM loadings this led to even faster Fe reduction rates than found for pure Fh. The amount of mineral-bound OM also affected the formation of secondary minerals: goethite was only found after reduction of OM-free Fh and siderite was only detected when Fhs with relatively low amounts of mineral-bound OM were reduced. We conclude that direct contact of G. bremensis to the Fe oxide mineral surface was inhibited when blocked by OM. Consequently, mineral-bound OM shall be taken into account besides Fe(II) accumulation as a further widespread mechanism to slow down reductive dissolution.

  15. Biotic and abiotic interactions in aquatic microcosms determine fate and toxicity of Ag nanoparticles. Part 1. Aggregation and dissolution.

    PubMed

    Unrine, Jason M; Colman, Benjamin P; Bone, Audrey J; Gondikas, Andreas P; Matson, Cole W

    2012-07-03

    To better understand their fate and toxicity in aquatic environments, we compared the aggregation and dissolution behavior of gum arabic (GA) and polyvinylpyrrolidone (PVP) coated Ag nanoparticles (NPs) in aquatic microcosms. There were four microcosm types: surface water; water and sediment; water and aquatic plants; or water, sediment, and aquatic plants. Dissolution and aggregation behavior of AgNPs were examined using ultracentrifugation, ultrafiltration, and asymmetrical flow field flow fractionation coupled to ultraviolet-visible spectroscopy, dynamic and static laser light scattering, and inductively coupled plasma mass spectrometry. Plants released dissolved organic matter (DOM) into the water column either through active or passive processes in response to Ag exposure. This organic matter fraction readily bound Ag ions. The plant-derived DOM had the effect of stabilizing PVP-AgNPs as primary particles, but caused GA-AgNPs to be removed from the water column, likely by dissolution and binding of released Ag ions on sediment and plant surfaces. The destabilization of the GA-AgNPs also corresponded with X-ray absorption near edge spectroscopy results which suggest that 22-28% of the particulate Ag was associated with thiols and 5-14% was present as oxides. The results highlight the potential complexities of nanomaterial behavior in response to biotic and abiotic modifications in ecosystems, and may help to explain differences in toxicity of Ag observed in realistic exposure media compared to simplified laboratory exposures.

  16. Effect of abiotic factors on the mercury reduction process by humic acids in aqueous systems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Mercury (Hg) in the environment can have serious toxic effects on a variety of living organisms, and is a pollutant of concern worldwide. The reduction of mercury from the toxic Hg2+ form to Hg0 is especially important. One pathway for this reduction to occur is through an abiotic process with humic...

  17. Reductive dissolution and metal transport in lake coeur d alenesediments

    SciTech Connect

    Sengor, Sevinc.S.; Spycher, Nicolas.F.; Ginn, Timothy.R.; Moberly, James; Peyton, B.; Sani, Rajesh.K.

    2007-04-27

    The benthic sediments in Lake Coeur d Alene, northern Idaho,have been contaminated by metals (primarily Zn, Pb, and Cu) from decadesof upstream mining activities. As part of ongoing research on thebiogeo-chemical cycling of metals in this area, a diffusivereactive-transport model has been developed to simulate metal transportin the lake sediments. The model includes 1-D inorganic diffusivetransport coupled to a biotic reaction network with multiple terminalelectron acceptors under redox disequilibrium conditions. Here, the modelis applied to evaluate the competing effects of heavy-metal mobilizationthrough biotic reductive dissolution of Fe(III) (hydr)oxides, andimmobilization as biogenic sulfide minerals. Results indicate that therelative rates of Fe and sulfate reduction could play an important rolein metal transport through the envi-ronment, and that the formation of(bi)sulfide complexes could significantly enhance metal solubility, aswell as desorption from Fe hydroxides.

  18. The potential for metal release by reductive dissolution of weathered mine tailings

    NASA Astrophysics Data System (ADS)

    Ribeta, I.; Ptacek, C. J.; Blowes, D. W.; Jambor, J. L.

    1995-01-01

    Remediation programs proposed for decommissioned sulphide tailings may include the addition of a cover layer rich in organic-carbon material such as sewage sludge or composted municipal waste. These covers are designed to consume oxygen and prevent the oxidation of underlying sulphide minerals. The aerobic and anaerobic degradation of such organic-carbon-rich waste can release soluble organic compounds to infiltrating precipitation water. In laboratory experiments, and in natural settings, biotic and abiotic interactions between similar dissolved organic compounds and ferric-bearing secondary minerals have been observed to result in the reductive dissolution of ferric (oxy)hydroxides and the release of ferrous iron to pore waters. In weathered tailings, oxidation of sulphide minerals typically results in the formation of abundant ferric-bearing secondary precipitates near the tailings surface. These secondary precipitates may contain high concentrations of potentially toxic metals, either coprecipitated with or adsorbed onto ferric (oxy)hydroxides. Reductive dissolution reactions, resulting from the addition of the organic-carbon covers, may remobilize metals previously attenuated near the tailings surface. To assess the potential for metal release to tailings pore water by reductive dissolution reactions, a laboratory study was conducted on weathered tailings collected from the Nickel Rim mine tailings impoundment near Sudbury, Ontario, Canada. This site was selected for study because it is representative of many tailings sites. Mineralogical study indicates that sulphide minerals originally present in the vadose zone at the time of tailings deposition have been replaced by a series of secondary precipitates. The most abundant secondary minerals are goethite, gypsum and jarosite. Scanning electron microscopy, coupled with elemental analyses by X-ray energy dispersion analysis, and electron microprobe analysis indicate that trace metals including Ni, Cr and Cu are

  19. Linear free energy relationships for the biotic and abiotic reduction of nitroaromatic compounds.

    PubMed

    Luan, Fubo; Gorski, Christopher A; Burgos, William D

    2015-03-17

    Nitroaromatic compounds (NACs) are ubiquitous environmental contaminants that are susceptible to biological and abiotic reduction. Prior works have found that for the abiotic reduction of NACs, the logarithm of the NACs’ rate constants correlate with one-electron reduction potential values of the NACs (EH,NAC1) according to linear free energy relationships (LFERs). Here, we extend the application of LFERs to the bioreduction of NACs and to the abiotic reduction of NACs by bioreduced (and pasteurized) iron-bearing clay minerals. A linear correlation (R2=0.96) was found between the NACs’ bioreduction rate constants (kobs) and EH,NAC1 values. The LFER slope of log kobs versus EH,NAC1/(2.303RT/F) was close to one (0.97), which implied that the first electron transfer to the NAC was the rate-limiting step of bioreduction. LFERs were also established between NAC abiotic reduction rate constants by bioreduced iron-bearing clay minerals (montmorillonite SWy-2 and nontronite NAu-2). The second-order NAC reduction rate constants (k) by bioreduced SWy-2 and NAu-2 were well correlated to EH,NAC1 (R2=0.97 for both minerals), consistent with bioreduction results. However, the LFER slopes of log k versus EH,NAC1/(2.303RT/F) were significantly less than one (0.48–0.50) for both minerals, indicating that the first electron transfer to the NAC was not the rate-limiting step of abiotic reduction. Finally, we demonstrate that the rate of 4-acetylnitrobenzene reduction by bioreduced SWy-2 and NAu-2 correlated to the reduction potential of the clay (EH,clay, R2=0.95 for both minerals), indicating that the clay reduction potential also influences its reactivity.

  20. Electrical Signatures Associated with Abiotic and In Vitro Dissimilatory Iron Reduction

    NASA Astrophysics Data System (ADS)

    Regberg, A. B.; Brantley, S. L.; Singha, K.; Tien, M.

    2007-05-01

    Several researchers have described anomalous electrical signatures associated with bacterial activity in anoxic zones in aquifers containing organic contaminants. It is thought that these signals can be attributed to (bio)geochemical changes caused by the oxidation of organic contaminants and the reduction of associated species like iron oxides. We report laboratory observations of changes in electrical conductivity (EC) that can be attributed to specific (bio)geochemical reactions involving reductive dissolution of iron oxides enzymatically and nonenzymatically. Abiotic reduction of ferrihydrite by ascorbic acid in batch experiments causes a cumulative 20- 40% increase in measured conductivity, (EC increases by ~300 μ S/cm). This change can be attributed to a decrease in conductivity (Δ EC) from increasing proton activity (Δ pH = 3.25 --> 5.07, Δ EC = -200 μ S/cm) and an increase in dissolved Fe(II) (Δ [Fe] = 2.2 - 3.3 mM, Δ EC = 400 -700 μ S/cm). Conductivity is presumably unaffected by Fe(II) sorbed to the ferrihydrite. Rates calculated from this method are comparable to literature rates for similar experiments. In a similar in vitro system, total membrane fractions from Shewanella oneidensis MR-1 were used to reduce ferrihydrite in the presence of formate and HEPES buffer. A 10 - 15% increase in conductivity was observed in the batch experiment (Δ EC = ~280 μ S/cm). This Δ EC is attributed to an increase in the concentration of de-protonated HEPES as well as carbonate ion as formate is oxidized. Fe(II) released in this system is quickly sorbed onto the ferrihydrite surface and is not thought to change conductivity. Despite the sorption of iron in these in vitro experiments, conductivity changes measurably and documents the rate of the reaction. Accessory changes like buffer de- protonation play an important role in interpreting the electrical signals caused by dissimilatory iron reduction. In order to accurately interpret field data it is necessary

  1. Abiotic reduction reactions of anthropogenic organic chemicals in anaerobic systems: A critical review

    NASA Astrophysics Data System (ADS)

    Macalady, Donald L.; Tratnyek, Paul G.; Grundl, Timothy J.

    1986-02-01

    This review is predicated upon the need for a detailed process-level understanding of factors influencing the reduction of anthropogenic organic chemicals in natural aquatic systems. In particular, abiotic reductions of anthropogenic organic chemicals are reviewed. The most important reductive reaction is alkyl dehalogenation (replacement of chloride with hydrogen) which occurs in organisms, sediments, sewage sludge, and reduced iron porphyrin model systems. An abiotic mechanism involving a free radical intermediate has been proposed. The abstraction of vicinal dihalides (also termed dehalogenation) is another reduction that may have an abiotic component in natural systems. Reductive dehalogenation of aryl halides has recently been reported and further study of this reaction is needed. Several other degradation reactions of organohalides that occur in anaerobic environments are mentioned, the most important of which is dehydrohalogenation. The reduction of nitro groups to amines has also been thoroughly studied. The reactions can occur abiotically, and are affected by the redox conditions of the experimental system. However, a relationship between nitro-reduction rate and measured redox potential has not been clearly established. Reductive dealkylation of the N- and O-heteroatom of hydrocarbon pollutants has been observed but not investigated in detail. Azo compounds can be reduced to their hydrazo derivatives and a thorough study of this reaction indicates that it can be caused by extracellular electron transfer agents. Quinone-hydroquinone couples are important reactive groups in humic materials and similar structures in resazurin and indigo carmine make them useful as models for environmental redox conditions. The interconversion of sulfones, sulfoxides, and sulfides is a redox process and is implicated in the degradation of several pesticides though the reactions need more study. Two reductive heterocyclic cleavage reactions are also mentioned. Finally, several

  2. Reductive dissolution of As(V)-Fe oxyhydroxides: an experimental insight at biogeochemical interfaces in soil

    NASA Astrophysics Data System (ADS)

    Dia, A.; Davranche, M.; Fakih, M.; Nowack, B.; Morin, G.; Gruau, G.

    2009-04-01

    Iron (III) oxides are ubiquitous components of soils, sediments, aquifers and geological materials. Trace metals associate with Fe (III) oxides as adsorbed or co-precipitated species and, consequently the biogeochemical cycles of Fe and trace metals are closely linked. Using a new monitoring tool recently developed, this study was dedicated to understand how do interplay biological and mineralogical (crystallographic and specific surface area) controls in the Fe oxyhydroxide reductive dissolution within soils and which can be the consequences on associated trace metal release. For this purpose, polymer slides covered by synthetic As-spiked ferrihydrite (As-Fh) or As-spiked lepidocrocite (As-Lp) were inserted into an organic-rich wetland soil in non conventional columns system under anaerobic conditions. This technique was developed to allow the insertion of slides into a structured soil without significant disturbance and to avoid the mechanical abrasion of oxides from slides that would occur in an equilibrium batch system under stirring. Slides were recovered after different periods of time to evaluate (i) the impact of (bio)reduction on both Fe-oxide dissolution and secondary mineral precipitation and, (ii) the subsequent effects on As mobility. XRF analyses of the slides were conducted before and after contact with the soil to determine the amount of Fe and associated As remaining on the slides. Fe(II), acetate, nitrate, sulphate and total metals of the soil solution was followed through time by ion chromatography and ICP-MS measurements. The important bacterial colonization and occurrence of biofilm evidenced by SEM analyses of the slides suggested the presence of biologically mediated processes. As previously shown elsewhere the kinetics of the suspected occurring bacterial reduction differ significantly from abiotic reduction data from literature. The important point is that conversely to what has been observed in published experimental data, the dissolution

  3. Enhancement of carbon dioxide reduction and methane production by an obligate anaerobe and gas dissolution device.

    PubMed

    Kim, Seungjin; Choi, Kwangkeun; Kim, Jong-Oh; Chung, Jinwook

    2016-01-25

    The use of gas dissolution devices to improve the efficiency of H2 dissolution has enhanced CO2 reduction and CH4 production. In addition, the nutrients that initially existed in anaerobic sludge were exhausted over time, and the activities of anaerobic microorganisms declined. When nutrients were artificially injected, CO2 reduction and CH4 production rates climbed. Thus, assuming that the activity of the obligatory anaerobic microorganisms is maintained, a gas dissolution device will further enhance the efficiency of CO2 reduction and CH4 production.

  4. Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals. 2. Green rust.

    PubMed

    Lee, Woojin; Batchelor, Bill

    2002-12-15

    Abiotic reductive dechlorination of chlorinated ethylenes by the sulfate form of green rust (GR(SO4)) was examined in batch reactors. Dechlorination kinetics were described by a modified Langmuir-Hinshelwood model. The rate constant for reductive dechlorination of chlorinated ethylenes at reactive GR(SO4) surfaces was in the range of 0.592 (+/-4.4%) to 1.59 (+/-6.3%) day(-1). The specific reductive capacity of GR(SO4) for target organics was in the range of 9.86 (+/-10.1%) to 18.0 (+/-4.3%) microM/g and sorption coefficient was in the range of 0.53 (+/-2.4%) to 1.22 (+/-4.3%) mM(-1). Surface area-normalized pseudo-first-order initial rate constants for chlorinated ethylenes by GR(SO4) were 3.4 to 8.2 times greater than those by pyrite. Chlorinated ethylenes were mainly transformed to acetylene, and no detectable amounts of chlorinated intermediates were observed. The rate constants for the reductive dechlorination of trichloroethylene (TCE) increased as pH increased (6.8 to 10.1) but were independent of solid concentration and initial TCE concentration. Magnetite and/or maghemite were produced by the oxidation of GR(SO4) by TCE. These findings are relevant to the understanding of the role of abiotic reductive dechlorination during natural attenuation in environments that contain GR(SO4).

  5. Iron-mediated microbial oxidation and abiotic reduction of organic contaminants under anoxic conditions.

    PubMed

    Tobler, Nicole B; Hofstetter, Thomas B; Straub, Kristina L; Fontana, Daniela; Schwarzenbach, René P

    2007-11-15

    In anoxic environments, the oxidation of organic compounds, such as BTEX fuel components, by dissimilatory Fe(III) reduction can generate reactive mineral-bound Fe(II) species, which in turn are able to reduce other classes of organic and inorganic groundwater contaminants. In this study, we designed and evaluated an anaerobic batch reactor that mimicks iron-reducing conditions to investigate the factors that favor the coupling of microbial toluene oxidation and abiotic reduction of nitroaromatic contaminants. We investigated the influence of different Fe(III)-bearing minerals and combinations thereof on the coupling of these two processes. Results from laboratory model systems show that complete oxidation of toluene to CO2 by Geobacter metallireducens in the presence of Fe(III)-bearing minerals leads to the formation of mineral-bound Fe(II) species capable of the reduction of 4-nitroacetophenone. Whereas significant microbial toluene oxidation was only observed in the presence of amorphous Fe(III) phases, reduction of nitroaromatic compounds only proceeded with Fe(II) species bound to crystalline Fe(III) oxides. Our results suggest that in anoxic soils and sediments containing amorphous and crystalline iron phases simultaneously, coupling of microbial oxidation and abiotic reduction of organic compounds may allow for concurrent natural attenuation of different contaminant classes.

  6. Abiotic U(VI) Reduction by Sorbed Fe(II) on Natural Sediments

    SciTech Connect

    Fox, Patricia M.; Davis, James A.; Kukkadapu, Ravi K.; Singer, David M.; Bargar, John R.; Williams, Kenneth H.

    2013-09-15

    Laboratory experiments were performed as a function of aqueous Fe(II) concentration to determine the uptake and oxidation of Fe(II), and Fe(II)-mediated abiotic reduction of U(VI) by aquifer sediments from the Rifle IFRC field site in Colorado, USA. Mössbauer analysis of the sediments spiked with aqueous 57Fe(II) showed that 57Fe(II) was oxidized on the mineral surfaces to 57Fe(III) and most likely formed a nano-particulate Fe(III)-oxide or ferrihydrite-like phase. The extent of 57Fe oxidation decreased with increasing 57Fe(II) uptake, such that 100 % was oxidized at 7.3 μmol/g Fe and 52 % at 39.6 μmol/g Fe, indicating that the sediments had a finite capacity for oxidation of Fe(II). Abiotic U(VI) reduction was observed by XANES spectroscopy only when the Fe(II) uptake was greater than approximately 20 μmol/g and surface-bound Fe(II) was present. The level of U(VI) reduction increased with increasing Fe(II)- loading above this level to a maximum of 18 and 36 % U(IV) at pH 7.2 (40.7 μmol/g Fe) and 8.3 (56.1 μmol/g Fe), respectively in the presence of 400 ppm CO2. Greater U(VI) reduction was observed in CO2 free systems [up to 44 and 54 % at pH 7.2 (17.3 μmol/g Fe) and 8.3 (54.8 μmol/g Fe), respectively] compared to 400 ppm CO2 systems, presumably due to differences in aqueous U(VI) speciation. While pH affects the amount of Fe(II) uptake onto the solid phase, with greater Fe(II) uptake at higher pH, similar amounts of U(VI) reduction were observed at pH 7.2 and 8.3 for a similar Fe(II) uptake. Thus, it appears that abiotic U(VI) reduction is controlled primarily by Fe(II) concentration and aqueous U(VI) speciation. The range of Fe(II) loadings tested in this study are within the range observed in bioreduced sediments, suggesting that Fe(II)-mediated abiotic U(VI) reduction may indeed play a role in field settings.

  7. Mechanism of reductive dissolution of lepidocrocite by S(-II)

    NASA Astrophysics Data System (ADS)

    Behrends, Thilo; Hellige, Katrin; Peiffer, Stefan

    2010-05-01

    Reduction of ferric oxides by dissolved sufide species plays an important role in the redox dynamics of anaerobic subsurface environments. For example, S(-II) may be the dominant reductant for ferric oxides in sulfidic sediments and the reaction significantly contributes to the retention of reduced sulfur in these environments. The mechanism and rates of the reductive dissolution of ferric oxides by S(-II) have been frequently investigated and the reaction is generally considered to be a surface controlled process. The proposed mechanism includes the reduction of Fe(III) at the mineral surface upon S(-II) adsorption followed by the release of Fe(II) into solution, which is eventually followed by the precipitation of FeS at suitable conditions. However, several reported experimental observations, such as the remarkable high rate of lepidocrocite (g-FeOOH) reduction and the accumulation of surface bound Fe(II) (Poulton et al., 2004) are difficult to align with the proposed reaction mechanism. Here, we report experimental results which indicate that the prevailing idea about a surface controlled reaction between lepidocrocite and S(-II) has to be revised. We have studied the reaction of lepidocrocite and S(-II) in batch reactors at constant pH 8.0 by adding Na2S solution to the ferric oxide suspension. During the reaction, wide angle X-ray scattering (WAXS) and spectra from X-ray absorption (XANES and EXAFS) at the Fe K-edge (about 7.1 keV) were collected in situ by pumping suspension through a capillary, which was positioned inside the X-ray beam. These experiments were performed at the beamline BM26a (DUBBLE) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France (Nikitenko et al., 2008). Combining WAXS, XANES, and EXAFS allowed us to follow the change in the long-range periodic structure of the minerals simultaneously with changes in Fe redox state and local coordination environment. At pH 8.0 the reaction between lepidocrocite and S(-II) was

  8. Dissolution-Driven Permeability Reduction of a Fractured Carbonate Caprock

    SciTech Connect

    Ellis, Brian R.; Fitts, Jeffrey P.; Bromhal, Grant S.; McIntyre, Dustin L.; Tappero, Ryan; Peters, Catherine A.

    2013-04-01

    Geochemical reactions may alter the permeability of leakage pathways in caprocks, which serve a critical role in confining CO{sub 2} in geologic carbon sequestration. A caprock specimen from a carbonate formation in the Michigan sedimentary Basin was fractured and studied in a high-pressure core flow experiment. Inflowing brine was saturated with CO{sub 2} at 40°C and 10MPa, resulting in an initial pH of 4.6, and had a calcite saturation index of -0.8. Fracture permeability decreased during the experiment, but subsequent analyses did not reveal calcite precipitation. Instead, experimental observations indicate that calcite dissolution along the fracture pathway led to mobilization of less soluble mineral particles that clogged the flow path. Analyses of core sections via electron microscopy, synchrotron-based X-ray diffraction imaging, and the first application of microbeam Ca K-edge X-ray absorption near edge structure, provided evidence that these occlusions were fragments from the host rock rather than secondary precipitates. X-ray computed tomography showed a significant loss of rock mass within preferential flow paths, suggesting that dissolution also removed critical asperities and caused mechanical closure of the fracture. The decrease in fracture permeability despite a net removal of material along the fracture pathway demonstrates a nonintuitive, inverse relationship between dissolution and permeability evolution in a fractured carbonate caprock.

  9. Dissolution-Driven Permeability Reduction of a Fractured Carbonate Caprock

    PubMed Central

    Ellis, Brian R.; Fitts, Jeffrey P.; Bromhal, Grant S.; McIntyre, Dustin L.; Tappero, Ryan; Peters, Catherine A.

    2013-01-01

    Abstract Geochemical reactions may alter the permeability of leakage pathways in caprocks, which serve a critical role in confining CO2 in geologic carbon sequestration. A caprock specimen from a carbonate formation in the Michigan sedimentary Basin was fractured and studied in a high-pressure core flow experiment. Inflowing brine was saturated with CO2 at 40°C and 10 MPa, resulting in an initial pH of 4.6, and had a calcite saturation index of −0.8. Fracture permeability decreased during the experiment, but subsequent analyses did not reveal calcite precipitation. Instead, experimental observations indicate that calcite dissolution along the fracture pathway led to mobilization of less soluble mineral particles that clogged the flow path. Analyses of core sections via electron microscopy, synchrotron-based X-ray diffraction imaging, and the first application of microbeam Ca K-edge X-ray absorption near edge structure, provided evidence that these occlusions were fragments from the host rock rather than secondary precipitates. X-ray computed tomography showed a significant loss of rock mass within preferential flow paths, suggesting that dissolution also removed critical asperities and caused mechanical closure of the fracture. The decrease in fracture permeability despite a net removal of material along the fracture pathway demonstrates a nonintuitive, inverse relationship between dissolution and permeability evolution in a fractured carbonate caprock. PMID:23633894

  10. Interaction of abiotic and microbial processes in hexachloroethane reduction in groundwater

    USGS Publications Warehouse

    Roberts, A. Lynn; Gschwend, Philip M.

    1994-01-01

    In order to gain insight into mechanisms of hexachloroethane reduction, hexa- and pentachloroethane transformation rates were measured in anaerobic groundwater samples. For samples spiked with pentachloroethane, disappearance of pentachloroethane was accompanied by tetrachloroethylene production. Transformation rates were similar in unpoisoned and in HgCl2-poisoned samples, and rates were within ±20% of predictions based on measured pH and second-order dehydrochlorination rate constants determined in clean laboratory systems, indicating that the fate of pentachloroethane in this system is dominated by abiotic reactions. No hexachloroethane transformation was observed in HgCl2-poisoned samples, whereas in unpoisoned samples, hexachloroethane disappearance was accompanied by production of tetrachloroethylene as well as traces of pentachloroethane. Although only minor amounts of pentachloroethane accumulated, as much as 30% of the hexachloroethane transformation pathway proceeds via a pentachloroethane intermediate. This suggests that the microbial reduction of hexachloroethane proceeds at least in part through a free-radical mechanism. To the extent that hexachloroethane reduction to tetrachloroethylene occurs through a pentachloroethane intermediate, the first step in the sequence, the microbially-mediated step, is the slow step; the subsequent abiotic dehydrohalogenation step occurs much more rapidly.

  11. Archaeal (Per)Chlorate Reduction at High Temperature: An Interplay of Biotic and Abiotic Reactions

    NASA Astrophysics Data System (ADS)

    Liebensteiner, Martin G.; Pinkse, Martijn W. H.; Schaap, Peter J.; Stams, Alfons J. M.; Lomans, Bart P.

    2013-04-01

    Perchlorate and chlorate anions [(per)chlorate] exist in the environment from natural and anthropogenic sources, where they can serve as electron acceptors for bacteria. We performed growth experiments combined with genomic and proteomic analyses of the hyperthermophile Archaeoglobus fulgidus that show (per)chlorate reduction also extends into the archaeal domain of life. The (per)chlorate reduction pathway in A. fulgidus relies on molybdo-enzymes that have similarity with bacterial enzymes; however, chlorite is not enzymatically split into chloride and oxygen. Evidence suggests that it is eliminated by an interplay of abiotic and biotic redox reactions involving sulfur compounds. Biological (per)chlorate reduction by ancient archaea at high temperature may have prevented accumulation of perchlorate in early terrestrial environments and consequently given rise to oxidizing conditions on Earth before the rise of oxygenic photosynthesis.

  12. Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals. 1. Pyrite and magnetite.

    PubMed

    Lee, Woojin; Batchelor, Bill

    2002-12-01

    Abiotic reductive dechlorination of chlorinated ethylenes (tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cis-DCE), and vinyl chloride (VC)) by pyrite and magnetite was characterized in a batch reactor system. Dechlorination kinetics was adequately described by a modified Langmuir-Hinshelwood model that includes the effect of a decreasing reductive capacity of soil mineral. The kinetic rate constant for the reductive dechlorination of target organics at reactive sites of soil minerals was in the range of 0.185 (+/- 0.023) to 1.71 (+/- 0.06) day(-1). The calculated specific reductive capacity of soil minerals for target organics was in the range of 0.33 (+/- 0.02) to 2.26 (+/- 0.06) microM/g and sorption coefficient was in the range of 0.181 (+/- 0.006) to 0.7 (+/- 0.022) mM(-1). Surface area-normalized pseudo-first-order initial rate constants for target organics by pyrite were found to be 23.5 to 40.3 times greater than those by magnetite. Target organics were mainly transformed to acetylene and small amount of chlorinated intermediates, which suggests that beta-elimination was the main dechlorination pathway. The dechlorination of VC followed a hydrogenolysis pathway to produce ethylene and ethane. The addition of Fe(II) increased the dechlorination rate of cis-DCE and VC in magnetite suspension by nearly a factor of 10. The results obtained in this research provide basic knowledge to better predict the fate of chlorinated ethylenes and to understand the potential of abiotic processes in natural attenuation.

  13. Abiotic nitrogen fixation on terrestrial planets: reduction of NO to ammonia by FeS.

    PubMed

    Summers, David P; Basa, Ranor C B; Khare, Bishun; Rodoni, David

    2012-02-01

    Understanding the abiotic fixation of nitrogen and how such fixation can be a supply of prebiotic nitrogen is critical for understanding both the planetary evolution of, and the potential origin of life on, terrestrial planets. As nitrogen is a biochemically essential element, sources of biochemically accessible nitrogen, especially reduced nitrogen, are critical to prebiotic chemistry and the origin of life. Loss of atmospheric nitrogen can result in loss of the ability to sustain liquid water on a planetary surface, which would impact planetary habitability and hydrological processes that shape the surface. It is known that NO can be photochemically converted through a chain of reactions to form nitrate and nitrite, which can be subsequently reduced to ammonia. Here, we show that NO can also be directly reduced, by FeS, to ammonia. In addition to removing nitrogen from the atmosphere, this reaction is particularly important as a source of reduced nitrogen on an early terrestrial planet. By converting NO directly to ammonia in a single step, ammonia is formed with a higher product yield (~50%) than would be possible through the formation of nitrate/nitrite and subsequent conversion to ammonia. In conjunction with the reduction of NO, there is also a catalytic disproportionation at the mineral surface that converts NO to NO₂ and N₂O. The NO₂ is then converted to ammonia, while the N₂O is released back in the gas phase, which provides an abiotic source of nitrous oxide.

  14. Microbially Induced Reductive Dissolution of Trace Element-Rich Lacustrine Iron-Oxides

    NASA Astrophysics Data System (ADS)

    Crowe, S. A.; Kulczykci, E.; O'Neill, A. H.; Roberts, J. A.; Fowle, D. A.

    2004-12-01

    Iron (oxy)hydroxides are ubiquitous components of surfacial materials and are often the dominant redox buffering solid phases in soils and sediments. As a result, the geochemical behavior of these minerals has a profound influence on the global biogeochemical cycling of trace elements, including heavy metals and arsenic (As), in addition to nutrients such as, sulfur (S), carbon (C), nitrogen (N), and phosphorus (P). Understanding the behavior of trace elements and nutrients during biological and abiotic processes that effect iron (Fe) mineral phase transformations is paramount for predicting their distribution, mobility, and bioavailability in the environment. To evaluate the impact of dissimilatory Fe-reduction (DIR) on trace element mobility we have conducted batch incubations of Fe-rich lateritic lacustrine sediments. In contrast to mid-latitude lakes where Fe (oxy)hydroxides constitute only a small fraction of the total sediment, tropical lake sediments have been known to comprise up to 40-60 wt. % Fe-oxides. Under suboxic and nonsulphidogenic conditions it is likely that DIR plays a prominent role in early diagenesis and therefore may exert control on the fate and distribution of many trace elements in this environment (e.g. Crowe et al. 2004). In batch incubations conducted in a minimal media of similar composition to typical freshwater the lacustrine Fe-oxides were reductively dissolved at a rate very similar to pure synthetic goethite of similar surface area (measured by N2-BET). This is in contrast to the slower rates previously observed for trace element substituted Fe-oxides. These slower rates have been attributed to surface passivation by secondary Al and Cr mineral precipitation. We propose that these passivation effects may be offset in minimal media incubations by enhanced microbial metabolism due the presence of nutrients (P, Co and other metals) in the lacustrine Fe-oxides. These nutrients became available with progressive reduction as the

  15. A Review of Alumina Feeding and Dissolution Factors in Aluminum Reduction Cells

    NASA Astrophysics Data System (ADS)

    Lavoie, Pascal; Taylor, Mark P.; Metson, James B.

    2016-08-01

    Modern aluminum reduction cells use point feeding technology to replenish alumina as it is consumed by the electrolytic process. The dissolution of alumina has become increasingly difficult to control as the cell sizes and electrolysis intensity have increased. The mass of alumina added per unit time is now much higher than a decade ago, and must take place within a smaller electrolyte mixing volume. In order to replenish the alumina concentration evenly, the alumina needs to be delivered, dispersed, dissolved, and distributed throughout the reduction cell. The dissolution itself follows a 4-step process that can be limited by a multitude of factors. The status of the research on each of these factors is reviewed in the present paper. Although research in laboratory cells has been conducted many times, and the impact of many factors on dissolution has been measured, published observations of alumina feeding on industrial cells are very sparse, especially regarding the dissolution dynamics in the space-time domain and the impact of the feeder hole condition. The present paper therefore presents a qualitative model of the factors governing alumina dissolution in industrial cells and offers the hypothesis that maintenance of the feeder hole condition is central to ensuring alumina dissolution and prevention of sludging.

  16. Real-Time Manganese Phase Dynamics during Biological and Abiotic Manganese Oxide Reduction.

    PubMed

    Johnson, Jena E; Savalia, Pratixa; Davis, Ryan; Kocar, Benjamin D; Webb, Samuel M; Nealson, Kenneth H; Fischer, Woodward W

    2016-04-19

    Manganese oxides are often highly reactive and easily reduced, both abiotically, by a variety of inorganic chemical species, and biologically during anaerobic respiration by microbes. To evaluate the reaction mechanisms of these different reduction routes and their potential lasting products, we measured the sequence progression of microbial manganese(IV) oxide reduction mediated by chemical species (sulfide and ferrous iron) and the common metal-reducing microbe Shewanella oneidensis MR-1 under several endmember conditions, using synchrotron X-ray spectroscopic measurements complemented by X-ray diffraction and Raman spectroscopy on precipitates collected throughout the reaction. Crystalline or potentially long-lived phases produced in these experiments included manganese(II)-phosphate, manganese(II)-carbonate, and manganese(III)-oxyhydroxides. Major controls on the formation of these discrete phases were alkalinity production and solution conditions such as inorganic carbon and phosphate availability. The formation of a long-lived Mn(III) oxide appears to depend on aqueous Mn(2+) production and the relative proportion of electron donors and electron acceptors in the system. These real-time measurements identify mineralogical products during Mn(IV) oxide reduction, contribute to understanding the mechanism of various Mn(IV) oxide reduction pathways, and assist in interpreting the processes occurring actively in manganese-rich environments and recorded in the geologic record of manganese-rich strata.

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

    SciTech Connect

    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 direct 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.

  18. Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing phyllosilicates.

    PubMed

    Lee, Woojin; Batchelor, Bill

    2004-09-01

    Abiotic reductive dechlorination of chlorinated ethylenes (tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and vinylchloride (VC)) by iron-bearing phyllosilicates (biotite, vermiculite, and montmorillonite) was characterized to obtain better understanding of the behavior of these contaminants in systems undergoing remediation by natural attenuation and redox manipulation. Batch experiments were conducted to evaluate dechlorination kinetics and some experiments were conducted with addition of Fe(II) to simulate impact of microbial iron reduction. A modified Langmuir-Hinshelwood kinetic model adequately described reductive dechlorination kinetics of target organics by the iron-bearing phyllosilicates. The rate constants stayed between 0.08 (+/-10.4%) and 0.401 (+/-8.1%) day(-1) and the specific initial reductive capacity of iron-bearing phyllosilicates for chlorinated ethylenes stayed between 0.177 (+/-6.1%) and 1.06 (+/-7.1%) microM g(-1). The rate constants for the reductive dechlorination of TCE at reactive biotite surface increased as pH (5.5-8.5) and concentration of sorbed Fe(II) (0-0.15 mM g(-1)) increased. The appropriateness of the model is supported by the fact that the rate constants were independent of solid concentration (0.0085-0.17 g g(-1)) and initial TCE concentration (0.15-0.60 mM). Biotite had the greatest rate constant among the phyllosilicates both with and without Fe(II) addition. The rate constants were increased by a factor of 1.4-2.5 by Fe(II) addition. Between 1.8% and 36% of chlorinated ethylenes removed were partitioned to the phyllosilicates. Chloride was produced as a product of degradation and no chlorinated intermediates were observed throughout the experiment.

  19. Nature and Reactivity of Sediment-Associated Spiked Fe(II) Toward Abiotic Uranium Reduction

    NASA Astrophysics Data System (ADS)

    Kukkadapu, R.; Fox, P. M.; Davis, J.

    2011-12-01

    Uranium (U) is a priority contaminant at U.S. Department of Energy Uranium Mill Tailings Remedial Action (UMTRA) sites. Mobility of U in contaminated aquifers is governed by a complex assortment of site-specific biogeochemical and hydrological properties, sediment Fe-mineralogy, and redox status. There is a particular interest in understanding factors governing U attenuation to Fe-mineralogy under natural conditions. Thus, the goal of this work is to investigate geochemical effects of Fe redox state on U mobility under conditions relevant to the Rifle aquifer, an UMTRA site. Particularly, the focus is to gain insights into the degree and mechanism of Fe(II) uptake by Rifle sediments that exhibit complex Fe-mineralogy composed of various Fe-oxides and Fe-containing clays and on the possibility of abiotic U(VI) reduction by adsorbed Fe(II) and secondary Fe(II) minerals. Earlier field studies where Fe(II)-amended groundwater was injected into the Rifle aquifer indicated: a) Fe(II) uptake by Rifle sediments is extensive and b) abiotic U(VI) reduction by Fe(II) may be important at pH 8.3. Batch reactions between Rifle sediment and 57Fe(II) (57Fe isotope is a Mossbauer sensitive nuclide with a natural abundance of 2%) under conditions relevant to the Rifle aquifer indicated that, depending on the solution conditions: a) a large fraction of the spiked 57Fe(II) (55-100%) is oxidized to 57Fe(III) on sediment surfaces and, at pH 7.2, the degree of oxidation decreased as Fe(II) loading increased; b) the 57Fe(II)-oxidation is coupled to the transformation of an intrinsic ferrihydrite-like mineral to a nanoparticulate, Fe(II)/57Fe(III)-like mineral phase, and c) increasing pH from 7.2 to 8.3 and including carbonate in the medium has little or no effect on percent oxidation or mineral transformation. Preliminary X-ray absorption near edge structure (XANES) spectroscopy studies suggested that 20-30% of abiotic U(VI) reduction occurred, both at pH 7.2 and 8.3, in the sediments

  20. XPS study of reductive dissolution of birnessite by oxalate: Rates and mechanistic aspects of dissolution and redox processes

    SciTech Connect

    Banerjee, D.; Nesbitt, H.W.

    1999-10-01

    Reductive dissolution of synthetic 7{angstrom}-birnessite [MnO{sub 1.7}(OH){sub 0.25} or MnO{sub 1.95}] by Na-oxalate produces a Mn(III) intermediate reaction product (here represented as MnOOH) which subsequently reacts with sorbed (COO){sub 2}{sup {minus}2} to form an unreactive Mn(III)-oxalate surface complex at the solution-mineral interface. X-ray Photoelectron Spectroscopy (XPS) results from Mn2p{sub 3/2}, C1s and O1s spectra of reacted surfaces reveal that initially rapid production of CO{sub 2} results in accumulation of CO{sub 2} at the reaction interface. After about 15 min, the reaction rate decreases to the point where CO{sub 2} desorption keeps pace with accumulation. Surface concentrations of CO{sub 2} suggest that the rate of CO{sub 2} production decreases with time, until after 10 hr of reaction, it is undetectable. Reduction of Mn(IV) to Mn(III) suggests that the MnO{sub 2}-oxalate redox reaction proceeds as a transfer of one electron per metal center. There is no XPS evidence for reduction of Mn(III) from birnessite to Mn(II) in the presence of oxalate. Although this reaction proceeds in presence of arsenite, it is inhibited by oxalate, probably through formation of a strong Mn(III)-oxalate surface complex (either monodentate or bidentate). This hypothesis is consistent with Mn{sup 3+} (aq) stabilization by oxalate in aqueous solutions. Further study using X-ray absorption spectroscopy (XAS) is required for a better understanding of the structure of the surface complexes. Rate of release of soluble Mn(II) to dilute oxalate solutions (5 x 10{sup {minus}4} M) is lower by an order of magnitude than the rate of release to aerated, distilled water at similar pH. Apparently, the process of proton-promoted dissolution of the soluble Mn(II) component of birnessite in distilled water is impeded by the addition of oxalate, probably by formation of a binuclear, bidentate surface complex between Mn(II, III) and adsorbed oxalate ions.

  1. Biotic and a-biotic Mn and Fe cycling in deep sediments across a gradient of sulfate reduction rates along the California margin

    NASA Astrophysics Data System (ADS)

    Schneider-Mor, A.; Steefel, C.; Maher, K.

    2011-12-01

    The coupling between the biological and a-biotic processes controlling trace metals in deep marine sediments are not well understood, although the fluxes of elements and trace metals across the sediment-water interface can be a major contribution to ocean water. Four marine sediment profiles (ODP leg 167 sites 1011, 1017, 1018 and 1020)were examined to evaluate and quantify the biotic and abiotic reaction networks and fluxes that occur in deep marine sediments. We compared biogeochemical processes across a gradient of sulfate reduction (SR) rates with the objective of studying the processes that control these rates and how they affect major elements as well as trace metal redistribution. The rates of sulfate reduction, methanogenesis and anaerobic methane oxidation (AMO) were constrained using a multicomponent reactive transport model (CrunchFlow). Constraints for the model include: sediment and pore water concentrations, as well as %CaCO3, %biogenic silica, wt% carbon and δ13C of total organic carbon (TOC), particulate organic matter (POC) and mineral associated carbon (MAC). The sites are distinguished by the depth of AMO: a shallow zone is observed at sites 1018 (9 to 19 meters composite depth (mcd)) and 1017 (19 to 30 mcd), while deeper zones occur at sites 1011 (56 to 76 mcd) and 1020 (101 to 116 mcd). Sulfate reduction rates at the shallow AMO sites are on the order 1x10-16 mol/L/yr, much faster than rates in the deeper zone sulfate reduction (1-3x10-17 mol/L/yr), as expected. The dissolved metal ion concentrations varied between the sites, with Fe (0.01-7 μM) and Mn (0.01-57 μM) concentrations highest at Site 1020 and lowest at site 1017. The highest Fe and Mn concentrations occurred at various depths, and were not directly correlated with the rates of sulfate reduction and the maximum alkalinity values. The main processes that control cycling of Fe are the production of sulfide from sulfate reduction and the distribution of Fe-oxides. The Mn distribution

  2. Kinetics of Reductive Dissolution of Hematite by Bioreduced Anthraquinone-2,6-disulfate

    SciTech Connect

    Liu, Chongxuan; Zachara, John M; Foster, Nancy S; Strickland, Janae

    2007-11-15

    The reductive dissolution of hematite (α-Fe2O3) was investigated in a flow-through system using AH2DS, a reduced form of anthraquinone- 2,6 disulfonate (AQDS), which is often used as an electron shuttling compound in studies of dissimilatory microbial reduction of iron oxides. Influent flow-rate, pH, Fe(II) and phosphate concentrations were varied to investigate the redox reaction kinetics. The effluent AH2DS, AQDS, and Fe(II) concentrations changed significantly within the first half hour of AH2DS reaction with hematite and then gradually evolved toward steady-state. The steady-state rates decreased with increasing pH from 4.5 to 7.6 and decreased with decreasing flow-rate. The rates also decreased with increasing influent concentration of Fe(II) or phosphate that formed surface complexes at the experimental pH. Mineral surface properties, Fe(II) complexation reactions, and AQDS sorption on hematite surfaces were independently investigated for interpreting hematite reductive dissolution kinetics. AH2DS sorption to hematite was inferred from the parallel measurements of AQDS and AH2DS sorption to α-Al2O3, a redox stable analog of α-Fe2O3. Decreasing Fe(II) and increasing AH2DS sorption by controlling flow residence time, influent pH, Fe(II) and phosphate concentrations increased the rates of reductive dissolution. The rates were also affected by the redox reaction free energy when reductive dissolution approached equilibrium, as shown by the effect of increasing the influent concentration of Fe(II).

  3. Investigation of Dissolution Parameters for PbO2 Using Waste Cellulosic Reductants

    NASA Astrophysics Data System (ADS)

    Morcali, Mehmet Hakan; Zeytuncu, Bihter

    2016-08-01

    In this study, we aimed to establish the optimum reductive leaching process with diluted acetic acid for the lead dioxide recovery from lead-acid battery paste. The effects of various reducing agents, acid concentrations, pulp densities, reaction temperatures, and leaching times on the dissolution of lead dioxide were investigated. Lead dioxide dissolution by reductive acidic media is a chemically controlled process with activation energy of 44.51 ± 1.23 kJ/mol. After leaching, lead acetate ions were precipitated with chromic acid as the lead chromate (PbCrO4) compound. Lead acetate salt was also precipitated from the leaching solution using a crystallization method. These lead compounds can potentially be used in many industries ( e.g., pigment application to detect the poisonous gas hydrogen sulfide). Our findings indicate that this process could be effective in leaching lead dioxide.

  4. Micromodel investigation of transport effect on the kinetics of reductive dissolution of hematite.

    PubMed

    Zhang, Changyong; Liu, Chongxuan; Shi, Zhi

    2013-05-07

    Reductive dissolution of hematite in porous media was investigated using a micromodel (8.1 × 4.5 × 0.028 mm) with realistic pore network structures that include distinctive advection domain, macropores and micropores created in silicon substrate. The micromodel pore surface was sputter deposited with a thin layer (230 nm) of hematite. The hematite in the micromodel was reduced by injecting pH-varying solutions (pH 5.0, 6.0, 7.0) containing a reduced form of flavin mononucleotide (FMNH2, 100 μM), a biogenic soluble electron transfer mediator produced by Shewanella species. The reduction kinetics was determined by measuring effluent Fe(II) (aq) concentration and by spectroscopically monitoring the hematite dissolution front in the micromodel. Batch experiment was also performed to estimate the hematite reduction rate under the well-mixed condition. Results showed significant spatial variation in local redox reaction rate that was controlled by the coupled transport and reaction. The overall rate of the redox reaction in the micromodel required a three-domain numerical model to effectively describe reaction kinetics either with distinctive apparent rate parameters or mass transfer coefficients in different pore domains. Results from this study demonstrated the feasibility of a domain-based modeling approach for scaling reaction rates from batch to porous media systems where reactions may be significantly limited by transport.

  5. Micromodel Investigation of Transport Effect on the Kinetics of Reductive Dissolution of Hematite

    SciTech Connect

    Zhang, Changyong; Liu, Chongxuan; Shi, Zhi

    2013-03-13

    Reductive dissolution of hematite in porous media was investigated using a micromodel with realistic pore network structures that include distinctive advection domain, macro-pores and micro-pores created in silicon substrate. The micromodel pore surface was sputter deposited with a thin layer (230 nm) of hematite. The hematite in the micromodel was reduced by injecting pH-varying solutions containing a reduced form of flavin mononucleotide (FMNH2), a biogenic soluble electron transfer mediator produced by Shewanella species. The reduction kinetics was determined by measuring effluent Fe(II) concentration and by spectroscopically monitoring the hematite dissolution front in the micromodel. Batch experiment was also performed to estimate the hematite reduction rate under the well-mixed condition. The results showed a significant spatial variation in local redox reaction rate that was controlled by the coupled diffusion and reaction. The overall rate of the redox reaction in the micromodel required a three-domain numerical model to effectively describe with distinctive rate parameters in different pore domains. Results from this study demonstrated the important scaling effect when extrapolating geochemical or biogeochemical reaction rate from batch reactor to porous media and indicated a significant control of physical transport mechanisms on the reaction rate scaling.

  6. Reductive dissolution of Mn oxides in river-recharged aquifers: a laboratory column study

    NASA Astrophysics Data System (ADS)

    Petrunic, B. M.; MacQuarrie, K. T. B.; Al, T. A.

    2005-01-01

    River-recharged aquifers are developed for drinking water supplies in many parts of the world. Often, however, dissolved organic carbon (DOC) present in the infiltrating river water causes biogeochemical reactions to occur in the adjacent aquifer that create elevated Mn and Fe. Mn concentrations in groundwater from some of the production wells installed in the aquifer at Fredericton, New Brunswick exceed the Canadian Drinking Water Guideline of 9.1×10 -4 mmol/l by up to 5.5×10 -2 mmol/l. It has previously been hypothesized that the influx of DOC from the Saint John River is causing bacterially mediated reductive dissolution of Mn oxides in the aquifer system, leading to elevated aqueous Mn concentrations. Previous work was limited to the collection of water samples from production wells and several observation wells installed in the glacial outwash aquifer. The objective of this study was to investigate the biogeochemical controls on Mn concentrations using sand-filled columns. One column was inoculated with bacteria while a second column was treated with ethanol in order to decrease the microbial population initially present in the system. Both columns received the same influent solution that contained acetate as a source of DOC. The results of the experiments suggested that the two main controls on Mn concentrations in the columns were microbially mediated reductive dissolution of Mn oxides and cation exchange. The conceptual model that was developed based on the experimental data was supported by the results obtained using a one-dimensional reactive-transport model. The reductive dissolution of Mn oxides in the aquifer sands could be adequately simulated using dual-Monod kinetics. Similar trends are observed in the experimental data and field data collected from Production Well 5, located in the Fredericton Aquifer. From the experiments, it is evident that cation-exchange reactions may be an important geochemical control on Mn concentrations during the initial

  7. Theoretical evaluation of dissolution and biochemical reduction of TNT for phytoremediation of contaminated sediments

    NASA Astrophysics Data System (ADS)

    Voudrias, Evangelos A.; Assaf, Karim Shafe

    1996-07-01

    In this study the removal of 2,4,6-trinitrotoluene (TNT) in the subsurface was theoretically simulated using a steady-state one-dimensional form of the advection-dispersion-reaction (ADR) equation, also accounting for TNT dissolution. The system studied consists of equal-sized spherical TNT particles uniformly distributed in an anaerobic saturated sediment. Water is assumed to flow steadily and uniformly through the sediment. The TNT removal is accomplished by biochemical catalysts (enzymes) released by plants. A sensitivity analysis was performed by varying TNT particle diameter, soil TNT content, Darcy velocity and a first-order biochemical reduction rate constant, and studying their effect on the TNT aqueous-phase concentration and TNT removal rate from the exposure zone. With zero or low biochemical reduction rate constants, it was found that the rate of removal of TNT from the exposure zone improved with higher flushing rates. On the other hand, higher biochemical reduction rate constants resulted in significant reduction of the aqueous TNT concentration at all flushing rates and in higher TNT removal rates from the exposure zone. A biochemical reduction rate constant of 14.25 day -1 was measured for reduction of dissolved TNT by sediments containing biochemical catalysts under anaerobic conditions. A simulation using this rate constant suggested the feasibility of in situ phytoremediation of TNT-contaminated sediments.

  8. Simultaneous reductive dissolution of iron oxide and oxidation of iodide in ice.

    NASA Astrophysics Data System (ADS)

    Kim, Kitae; Choi, Wonyong

    2015-04-01

    Iron is an important trace element controlling the metabolism and growth of all kinds of living species. Especially, the bio-availability of iron has been regarded as the limiting factor for primary productivity in HNLC (High Nutrients Low Chlorophyll) regions including Southern ocean. The dissolution of iron oxide provides enhanced the bio-availability of iron for phytoplankton growth. The halogen chemistry in polar regions is related to various important environmental processes such as Antarctic Ozone Depletion Event(ODE), mercury depletion, oxidative processes in atmosphere, and the formation of CCN (Cloud Condensation Nuclei). In this study, we investigated the reductive dissolution of iron oxide particles to produce Fe(II)aq and simultaneous oxidation of I- (iodide) to I3- (tri-iodide) in ice phase under UV irradiation or dark condition. The reductive generation of Fe(II)aq from iron oxides and oxidation of iodide to I3- were negligible in water but significantly accelerated in frozen solution both in the presence and absence of light. The enhanced reductive generation of Fe(II)aq and oxidative formation of I3- in ice were observed regardless of the various types of iron oxides [hematite (α-Fe2O3) maghemite (γ- Fe2O3), goethite (α-FeOOH), lepidocrocite (γ-FeOOH) and, magnetite (Fe3O4)]. We explained that the enhanced redox production of Fe(II)aq and I3- in ice is contributed to the freeze concentration of iodides, protons, and dissolved oxygen in the unfrozen solution. When the concentration of both iodides and protons were raised by 10-fold each, the formation of Fe(II)aq in water under UV irradiation was approached to those in ice. The outdoor experiments were carried out under ambient solar radiation in winter season of mid-latitude (Pohang, Korea: 36°N latitude) and also confirmed that the production of Fe(II)aq via reductive dissolution of iron oxide and I3- generation via I- oxidation were enhanced in frozen solution. These results suggest that iron

  9. Role of microbial iron reduction in the dissolution of iron hydroxysulfate minerals

    NASA Astrophysics Data System (ADS)

    Jones, Elizabeth J. P.; Nadeau, Tracie-Lynn; Voytek, Mary A.; Landa, Edward R.

    2006-03-01

    Iron-hydroxysulfate minerals can be important hosts for metals such as lead, mercury, copper, zinc, silver, chromium, arsenic, and selenium and for radionuclides such as 226Ra. These mineral-bound contaminants are considered immobilized under oxic conditions. However, when anoxic conditions develop, the activities of sulfate- or iron-reducing bacteria could result in mineral dissolution, releasing these bound contaminants. Reduction of structural sulfate in the iron-hydroxysulfate mineral jarosite by sulfate-reducing bacteria has previously been demonstrated. The primary objective of this work was to evaluate the potential for anaerobic dissolution of the iron-hydroxysulfate minerals jarosite and schwertmannite at neutral pH by iron-reducing bacteria. Mineral dissolution was tested using a long-term cultivar, Geobacter metallireducens strain GS-15, and a fresh isolate Geobacter sp. strain ENN1, previously undescribed. ENN1 was isolated from the discharge site of Shadle Mine, in the southern anthracite coalfield of Pennsylvania, where schwertmannite was the predominant iron-hydroxysulfate mineral. When jarosite from Elizabeth Mine (Vermont) was provided as the sole terminal electron acceptor, resting cells of both G. metallireducens and ENN1 were able to reduce structural Fe(III), releasing Fe+2, SO4-2, and K+ ions. A lithified jarosite sample from Utah was more resistant to microbial attack, but slow release of Fe+2 was observed. Neither bacterium released Fe+2 from poorly crystalline synthetic schwertmannite. Our results indicate that exposure of jarosite to iron-reducing conditions at neutral pH is likely to promote the mobility of hazardous constituents and should therefore be considered in evaluating waste disposal and/or reclamation options involving jarosite-bearing materials.

  10. Role of microbial iron reduction in the dissolution of iron hydroxysulfate minerals

    USGS Publications Warehouse

    Jones, E.J.P.; Nadeau, T.-L.; Voytek, M.A.; Landa, E.R.

    2006-01-01

    Iron-hydroxysulfate minerals can be important hosts for metals such as lead, mercury, copper, zinc, silver, chromium, arsenic, and selenium and for radionuclides such as 226Ra. These mineral-bound contaminants are considered immobilized under oxic conditions. However, when anoxic conditions develop, the activities of sulfate- or iron-reducing bacteria could result in mineral dissolution, releasing these bound contaminants. Reduction of structural sulfate in the iron-hydroxysulfate mineral jarosite by sulfate-reducing bacteria has previously been demonstrated. The primary objective of this work was to evaluate the potential for anaerobic dissolution of the iron-hydroxysulfate minerals jarosite and schwertmannite at neutral PH by iron-reducing bacteria. Mineral dissolution was tested using a long-term cultivar, Geobacter metallireducens strain GS-15, and a fresh isolate Geobacter sp. strain ENN1, previously undescribed. ENN1 was isolated from the discharge site of Shadle Mine, in the southern anthracite coalfield of Pennsylvania, where schwertmannite was the predominant iron-hydroxysulfate mineral. When jarosite from Elizabeth Mine (Vermont) was provided as the sole terminal electron acceptor, resting cells of both G. metallireducens and ENN1 were able to reduce structural Fe(III), releasing Fe+2, SO4-2, and K+ ions. A lithified jarosite sample from Utah was more resistant to microbial attack, but slow release of Fe+2 was observed. Neither bacterium released Fe+2 from poorly crystalline synthetic schwertmannite. Our results indicate that exposure of jarosite to iron-reducing conditions at neutral pH is likely to promote the mobility of hazardous constituents and should therefore be considered in evaluating waste disposal and/or reclamation options involving jarosite-bearing materials.

  11. Role of microbial iron reduction in the dissolution of iron hydroxysulfate minerals - article no. G01012

    SciTech Connect

    Jones, E.J.P.; Nadeau, T.L.; Voytek, M.A.; Landa, E.R.

    2006-03-28

    Reduction of structural sulfate in the iron-hydroxysulfate mineral jarosite by sulfate-reducing bacteria has previously been demonstrated. The primary objective of this work was to evaluate the potential for anaerobic dissolution of the iron-hydroxysulfate minerals jarosite and schwertmannite at neutral pH by iron-reducing bacteria. Mineral dissolution was tested using a long-term cultivar, Geobacter metallireducens strain GS-15, and a fresh isolate Geobacter sp. strain ENN1, previously undescribed. ENN1 was isolated from the discharge site of Shadle Mine, in the southern anthracite coalfield of Pennsylvania, where schwertmannite was the predominant iron-hydroxysulfate mineral. When jarosite from Elizabeth Mine (Vermont) was provided as the sole terminal electron acceptor, resting cells of both G. metallireducens and ENN1 were able to reduce structural Fe(III), releasing Fe{sup +2}, SO{sub 4}{sup -2}, and K{sup +} ions. A lithified jarosite sample from Utah was more resistant to microbial attack, but slow release of Fe{sup +2} was observed. Neither bacterium released Fe{sup +2} from poorly crystalline synthetic schwertmannite. Our results indicate that exposure of jarosite to iron-reducing conditions at neutral pH is likely to promote the mobility of hazardous constituents and should therefore be considered in evaluating waste disposal and/or reclamation options involving jarosite-bearing materials.

  12. Dimensionality reduction, and function approximation of poly(lactic-co-glycolic acid) micro- and nanoparticle dissolution rate.

    PubMed

    Ojha, Varun Kumar; Jackowski, Konrad; Abraham, Ajith; Snášel, Václav

    2015-01-01

    Prediction of poly(lactic-co-glycolic acid) (PLGA) micro- and nanoparticles' dissolution rates plays a significant role in pharmaceutical and medical industries. The prediction of PLGA dissolution rate is crucial for drug manufacturing. Therefore, a model that predicts the PLGA dissolution rate could be beneficial. PLGA dissolution is influenced by numerous factors (features), and counting the known features leads to a dataset with 300 features. This large number of features and high redundancy within the dataset makes the prediction task very difficult and inaccurate. In this study, dimensionality reduction techniques were applied in order to simplify the task and eliminate irrelevant and redundant features. A heterogeneous pool of several regression algorithms were independently tested and evaluated. In addition, several ensemble methods were tested in order to improve the accuracy of prediction. The empirical results revealed that the proposed evolutionary weighted ensemble method offered the lowest margin of error and significantly outperformed the individual algorithms and the other ensemble techniques.

  13. Dimensionality reduction, and function approximation of poly(lactic-co-glycolic acid) micro- and nanoparticle dissolution rate

    PubMed Central

    Ojha, Varun Kumar; Jackowski, Konrad; Abraham, Ajith; Snášel, Václav

    2015-01-01

    Prediction of poly(lactic-co-glycolic acid) (PLGA) micro- and nanoparticles’ dissolution rates plays a significant role in pharmaceutical and medical industries. The prediction of PLGA dissolution rate is crucial for drug manufacturing. Therefore, a model that predicts the PLGA dissolution rate could be beneficial. PLGA dissolution is influenced by numerous factors (features), and counting the known features leads to a dataset with 300 features. This large number of features and high redundancy within the dataset makes the prediction task very difficult and inaccurate. In this study, dimensionality reduction techniques were applied in order to simplify the task and eliminate irrelevant and redundant features. A heterogeneous pool of several regression algorithms were independently tested and evaluated. In addition, several ensemble methods were tested in order to improve the accuracy of prediction. The empirical results revealed that the proposed evolutionary weighted ensemble method offered the lowest margin of error and significantly outperformed the individual algorithms and the other ensemble techniques. PMID:25709436

  14. Reductive diagenesis, magnetite dissolution, greigite growth and paleomagnetic smoothing in marine sediments: A new view

    NASA Astrophysics Data System (ADS)

    Rowan, Christopher J.; Roberts, Andrew P.; Broadbent, Thomas

    2009-01-01

    In many anoxic sedimentary environments, the onset of sulfate reduction, and pyritization of detrital iron-bearing minerals, leads to a precipitous decline in magnetic mineral concentration during early diagenesis. The usefulness of the surviving paleomagnetic record in such environments is usually argued to depend on how much of the primary detrital magnetic assemblage survives diagenetic dissolution. Detailed rock magnetic and electron microscope analyses of rapidly deposited (~ 7 cm/kyr) latest Pleistocene-Holocene sediments from the continental margins of Oman (22°22.4'N, 60°08.0'E) and northern California (38°24.8'N, 123°58.2'W) demonstrate that pyritization during early diagenesis also leads to the progressive down-core growth of the ferrimagnetic iron sulfide greigite. Greigite growth begins with nucleation of large concentrations of superparamagnetic (SP) nanoparticles at the inferred position of the sulfate-methane transition, which can explain the apparently paradoxical suggestion that diagenetically reduced sediments contain enhanced concentrations of SP particles. Looping of hysteresis parameters on a "Day" plot records the dissolution of single domain (SD) (titano-)magnetite and the formation of SP greigite, which then slowly and progressively grows through its SD blocking volume and acquires a stable paleomagnetic signal. This looping trend is also evident in data from several published records (Oregon margin, Korea Strait, Japan Sea, Niger Fan, Argentine margin, and the Ontong-Java Plateau), indicating that these processes may be widespread in reducing environments. Our observations have profound implications for paleomagnetic records from sulfate-reducing environments. The paleomagnetic signal recorded by greigite is offset from the age of the surrounding sediments by 10's of kyr, and ongoing growth of greigite at depth results in smoothing of the recorded signal over intervals of 10's to 100's of kyr. We therefore expect the presence of

  15. CHARACTERIZING THE ABIOTIC REDUCTANTS FOR NITROAROMATIC COMPOUNDS AS A FUNCTION OF REDOX ZONATION IN ANOXIC SEDIMENTS

    EPA Science Inventory

    Reductive transformation is the dominant reaction pathway for the degradation of nitroaromatic compounds in anaerobic environments (Larson and Weber, 1994). Proposed reductants cover a spectrum ranging from reduced rninerals and organic matter to microbial enzyme systems. Transfo...

  16. Extraction of copper from an oxidized (lateritic) ore using bacterially catalysed reductive dissolution.

    PubMed

    Nancucheo, Ivan; Grail, Barry M; Hilario, Felipe; du Plessis, Chris; Johnson, D Barrie

    2014-01-01

    An oxidized lateritic ore which contained 0.8 % (by weight) copper was bioleached in pH- and temperature-controlled stirred reactors under acidic reducing conditions using pure and mixed cultures of the acidophilic chemolithotrophic bacterium Acidithiobacillus ferrooxidans. Sulfur was provided as the electron donor for the bacteria, and ferric iron present in goethite (the major ferric iron mineral present in the ore) acted as electron acceptor. Significantly more copper was leached by bacterially catalysed reductive dissolution of the laterite than in aerobic cultures or in sterile anoxic reactors, with up to 78 % of the copper present in the ore being extracted. This included copper that was leached from acid-labile minerals (chiefly copper silicates) and that which was associated with ferric iron minerals in the lateritic ore. In the anaerobic bioreactors, soluble iron in the leach liquors was present as iron (II) and copper as copper (I), but both metals were rapidly oxidized (to iron (III) and copper (II)) when the reactors were aerated. The number of bacteria added to the reactors had a critical role in dictating the rate and yield of copper solubilised from the ore. This work has provided further evidence that reductive bioprocessing, a recently described approach for extracting base metals from oxidized deposits, has the potential to greatly extend the range of metal ores that can be biomined.

  17. Hydrous manganese oxide doped gel probe sampler for measuring in situ reductive dissolution rates. 1. Laboratory development.

    PubMed

    Farnsworth, Claire E; Hering, Janet G

    2010-01-01

    Reductive dissolution of redox-sensitive minerals such as manganese (Mn) oxides in natural sediments is an important mechanism for trace element mobilization into groundwater. A gel probe sampler has been constructed to study in situ reductive dissolution of Mn oxides. The gel consists of a polyacrylamide polymer matrix doped with hydrous Mn oxide (HMO). Gel slabs are mounted into a probe, which is designed to be inserted into the sediments. The amount of Mn released from the gel by reductive dissolution is determined by comparing the amount of Mn initially embedded into the gel with the amount remaining in the gel after exposure to conditions in the sediments or, in laboratory studies, to reducing agents. In this laboratory study, the performance of the gel probes was examined using the model reductant ascorbate and the Mn-reducing bacteria Shewanella oneidensis strain MR-1. In addition, a 1-D model was used to relate the reaction rates observed for HMO embedded in gels to those for HMO in suspension. One limitation of the HMO-doped gels for assessing microbial reduction rates is that the gels prevent direct contact between the microbes and the HMO and hence preclude enzymatic reduction at the cell surface. Nonetheless, the HMO-doped gel probes offer the possibility to establish a lower bound for Mn-reduction capacity in sediments.

  18. Technetium Reduction and Permanent Sequestration by Abiotic and Biotic Formation of Low-Solubility Sulfide Mineral Phases

    SciTech Connect

    Tratnyek, Paul G.; Tebo, Bradley M.; Fan, Dimin; Anitori, Roberto; Szecsody, Jim; Jansik, Danielle

    2015-11-14

    One way to minimize the mobility of the TcVII oxyanion pertechnetate (TcO4-) is to effect reduction under sulfidogenic conditions (generated abiotically by Fe0 or biotically) to form TcSx, which is significantly slower to oxidize than TcIVO2. In sediment systems, TcSx and other precipitates may oxidize more slowly due to oxygen diffusion limitations to these low permeability precipitate zones. In addition, the TcO4- reduction rate may be more rapid in the presence of sediment because of additional reductive surface phases. This project aims to provide a fundamental understanding of the feasibility of immobilization of TcO4- as TcSx in the vadose zone or groundwater by application nano zero-valent iron (nZVI), and sulfide or sulfate. Biotic batch experiments have used the sulfate-reducing bacterium (SRB) Desulfotomaculum reducens. The iron sulfide mineral mackinawite was generated under these conditions, while vivianite was formed in nZVI only controls. The sulfide/bacteria-containing system consistently reduced aqueous pertechnetate rapidly (> 95% in the first hour), a rate similar to that for the sulfide-free, nZVI only system. Reduced Tc (aged for 3 months) generated in both SRB/nZVI systems was highly resistant to reoxidation. In reduced samples, Tc was found associated with solid phases containing Fe and S (D. reducens/nZVI) or Fe (nZVI only). Experiments using D. reducens without nZVI provided some additional insights. Firstly, stationary phase cultures were able to slowly reduce pertechnetate. Secondly, addition of pertechnetate at the beginning of cell growth (lag phase) resulted in a faster rate of Tc reduction, possibly indicating a direct (e.g. enzymatic) role for D. reducens in Tc reduction. Abiotic batch experiments were conducted with Na2S as the sulfide source. Pertechnetate reduction was

  19. Nitrogen Assimilation, Abiotic Stress and Glucose 6-Phosphate Dehydrogenase: The Full Circle of Reductants.

    PubMed

    Esposito, Sergio

    2016-05-11

    Glucose 6 phosphate dehydrogenase (G6PDH; EC 1.1.1.49) is well-known as the main regulatory enzyme of the oxidative pentose phosphate pathway (OPPP) in living organisms. Namely, in Planta, different G6PDH isoforms may occur, generally localized in cytosol and plastids/chloroplasts. These enzymes are differently regulated by distinct mechanisms, still far from being defined in detail. In the last decades, a pivotal function for plant G6PDHs during the assimilation of nitrogen, providing reductants for enzymes involved in nitrate reduction and ammonium assimilation, has been described. More recently, several studies have suggested a main role of G6PDH to counteract different stress conditions, among these salinity and drought, with the involvement of an ABA depending signal. In the last few years, this recognized vision has been greatly widened, due to studies clearly showing the non-conventional subcellular localization of the different G6PDHs, and the peculiar regulation of the different isoforms. The whole body of these considerations suggests a central question: how do the plant cells distribute the reductants coming from G6PDH and balance their equilibrium? This review explores the present knowledge about these mechanisms, in order to propose a scheme of distribution of reductants produced by G6PDH during nitrogen assimilation and stress.

  20. Nitrogen Assimilation, Abiotic Stress and Glucose 6-Phosphate Dehydrogenase: The Full Circle of Reductants

    PubMed Central

    Esposito, Sergio

    2016-01-01

    Glucose 6 phosphate dehydrogenase (G6PDH; EC 1.1.1.49) is well-known as the main regulatory enzyme of the oxidative pentose phosphate pathway (OPPP) in living organisms. Namely, in Planta, different G6PDH isoforms may occur, generally localized in cytosol and plastids/chloroplasts. These enzymes are differently regulated by distinct mechanisms, still far from being defined in detail. In the last decades, a pivotal function for plant G6PDHs during the assimilation of nitrogen, providing reductants for enzymes involved in nitrate reduction and ammonium assimilation, has been described. More recently, several studies have suggested a main role of G6PDH to counteract different stress conditions, among these salinity and drought, with the involvement of an ABA depending signal. In the last few years, this recognized vision has been greatly widened, due to studies clearly showing the non-conventional subcellular localization of the different G6PDHs, and the peculiar regulation of the different isoforms. The whole body of these considerations suggests a central question: how do the plant cells distribute the reductants coming from G6PDH and balance their equilibrium? This review explores the present knowledge about these mechanisms, in order to propose a scheme of distribution of reductants produced by G6PDH during nitrogen assimilation and stress. PMID:27187489

  1. Abiotic reduction reactions of dichloroacetamide safeners: transformations of "inert" agrochemical constituents.

    PubMed

    Sivey, John D; Roberts, A Lynn

    2012-02-21

    Safeners are so-called "inert" constituents of herbicide formulations added to protect crops from the toxic effects of herbicides. We examined the reactivity of three dichloroacetamide safeners and 12 structural analogues [all neutral compounds of the form Cl(2)CXC(═O)NRR'; X = H, Cl; R-groups include alkyl, branched alkyl, n-allyl, and cyclic moieties] in one homogeneous and two heterogeneous reductant systems: solutions of Cr(H(2)O)(6)(2+), suspensions of Fe(II)-amended goethite, and suspensions of Fe(II)-amended hematite. Analyses of reaction products indicate each safener can undergo stepwise hydrogenolysis (replacement of chlorine by hydrogen) in each system at near-neutral pH. The first hydrogenolysis step generates compounds similar (in one case, identical) to herbicide active ingredients. Rates of product formation and (when reactions were sufficiently fast) parent loss were quantified; reaction rates in heterogeneous systems spanned 2 orders of magnitude and were strongly influenced by R-group structure. The length of n-alkyl R-groups exerted opposite effects on hydrogenolysis rates in homogeneous versus heterogeneous systems: as R-group size increased, reduction rates in heterogeneous systems increased, whereas reduction rates in the homogeneous system decreased. Branched alkyl R-groups decreased hydrogenolysis rates relative to their straight-chain homologues in both homogeneous and heterogeneous systems. Reaction rates in heterogeneous systems can be described via polyparameter linear free energy relationships employing molecular parameters likely to influence dichloroacetamide adsorption. The propensity of dichloroacetamide safeners to undergo reductive transformations into herbicide-like products challenges their classification as "inert" agrochemical ingredients.

  2. Abiotic reduction of nitroaromatic contaminants by iron(II) complexes with organothiol ligands.

    PubMed

    Naka, Daisuke; Kim, Dongwook; Carbonaro, Richard F; Strathmann, Timothy J

    2008-06-01

    Complexation of Fe(II) by dissolved and surface-bound ligands can significantly modify the metal's redox reactivity, and recent work reveals that Fe(II) complexes with selected classes of organic ligands are potent reductants that may contribute to the natural attenuation of subsurface contaminants. In the present study, we investigated the reactivity of Fe(II)-organothiol ligand complexes with nitroaromatic contaminants (NACs; ArNO(2)). Experimental results show that NACs are unreactive in Fe(2+)-only and ligand-only solutions but are reduced to the corresponding aniline compounds (ArNH(2)) in solutions containing both Fe(II) and a number of organothiol ligands. Observed reaction rates are highly dependent on the structure of the Fe(II)-complexing ligand, solution composition, Fe(II) speciation, and NAC structure. For two model ligands, cysteine and thioglycolic acid, observed pseudo-first order rate constants for 4-chloronitrobenzene reduction (k(obs); 1/s) are linearly correlated with the concentration of the respective 1:2 Fe(II)- organothiol complexes (FeL(2)(2-)), and k(obs) measurements are accurately predicted by k(obs) = k(FeL(2-)(2))[FeL(2-)(2)], where k(FeL(2-)(2)) = 1.70 (+/-0.59) 1/M/s and 26.0 (+/-4.8) 1/M/s for cysteine and thioglycolic acid, respectively. The high reactivity of these Fe(II) complexes is attributed to a lowering of the standard one-electron reduction potential of the Fe(III)/Fe(II) redox couple on complexation by organothiol ligands. The relative reactivity of a series of substituted NACs with individual Fe(II) complexes can be described by linear free-energy relationships with the apparent one-electron reduction potentials of the NACs. Tests also show that organothiol ligands can further promote NAC reduction indirectly by re-reducing the Fe(III) that forms when Fe(II) complexes are oxidized by reactions with the NACs.

  3. Stable Isotope Systematics of Abiotic Nitrite Reduction Coupled with Anaerobic Iron Oxidation: The Role of Reduced Clays and Fe-bearing Minerals

    NASA Astrophysics Data System (ADS)

    Grabb, K. C.; Buchwald, C.; Hansel, C. M.; Wankel, S. D.

    2014-12-01

    Under anaerobic conditions, it is widely assumed that nitrate (NO3-) and nitrite (NO2-) reduction is primarily the result of microbial respiration. However, it has also been shown that abiotic reduction of nitrate and nitrite by reduced iron (Fe(II)), whether mineral-bound or surface-associated, may also occur under certain environmentally relevant conditions. With a range of experimental conditions, we investigated the nitrogen and oxygen stable isotope systematics of abiotic nitrite reduction by Fe(II) in an effort to characterize biotic and abiotic processes in the environment. While homogenous reactions between NO2- and Fe(II) in artificial seawater showed little reduction, heterogeneous reactions involving Fe-containing minerals showed considerable nitrite loss. Specifically, rapid nitrite reduction was observed in experiments that included reduced clays (illite, Na-montmorillonite, and nontronite) and those that exhibited iron oxide formation (ferrihydrite, magnetite and/or green rust). While these iron oxides and clay minerals offer both a source of reduced iron in the mineral matrix as well as a surface for Fe(II) activation, control experiments with corundum as a non-Fe containing mineral surface showed little NO2- loss, implicating a more dominant role of structural Fe in the clays during nitrite reduction. The isotope effects for 15N and 18O (15ɛ and 18ɛ) ranged from 5 to 14‰ for 15ɛ and 5 to 17‰ for 18ɛ and were typically coupled such that 15ɛ ~ 18ɛ. Reactions below pH 7 were slower and the 18ɛ was affected by oxygen atom exchange with water. Although little data exist for comparison with the dual isotopes of microbial NO2- reduction, these data serve as a benchmark for evaluating the role of abiotic processes in N reduction, particularly in sediment systems low in organic carbon and high in iron.

  4. Reduction of photosynthetic sensitivity in response to abiotic stress in tomato is mediated by a new generation plant activator

    PubMed Central

    2013-01-01

    Background Yield losses as a result of abiotic stress factors present a significant challenge for the future of global food production. While breeding technologies provide potential to combat negative stress-mediated outcomes over time, interventions which act to prime plant tolerance to stress, via the use of phytohormone-based elicitors for example, could act as a valuable tool for crop protection. However, the translation of fundamental biology into functioning solution is often constrained by knowledge-gaps. Results Photosynthetic and transcriptomic responses were characterised in young tomato (Solanum lycopersicum L.) seedlings in response to pre-treatment with a new plant health activator technology, ‘Alethea’, followed by a subsequent 100 mM salinity stress. Alethea is a novel proprietary technology composed of three key constituent compounds; the hitherto unexplored compound potassium dihydrojasmonate, an analogue of jasmonic acid; sodium benzoate, a carboxylic acid precursor to salicylic acid, and the α-amino acid L-arginine. Salinity treatment led to a maximal 47% reduction in net photosynthetic rate 8 d following NaCl treatment, yet in Alethea pre-treated seedlings, sensitivity to salinity stress was markedly reduced during the experimental period. Microarray analysis of leaf transcriptional responses showed that while salinity stress and Alethea individually impacted on largely non-overlapping, distinct groups of genes, Alethea pre-treatment substantially modified the response to salinity. Alethea affected the expression of genes related to biotic stress, ethylene signalling, cell wall synthesis, redox signalling and photosynthetic processes. Since Alethea had clear effects on photosynthesis/chloroplastic function at the physiological and molecular levels, we also investigated the ability of Alethea to protect various crop species against methyl viologen, a potent generator of oxidative stress in chloroplasts. Alethea pre-treatment produced

  5. In situ spectroscopic and solution analyses of the reductive dissolution of Mn02 by Fe(II)

    USGS Publications Warehouse

    Villinski, John E.; O'Day, Peggy A.; Corley, Timothy L.; Conklin, Martha H.

    2001-01-01

    The reductive dissolution of MnO2 by Fe(II) under conditions simulating acid mine drainage (pH 3, 100 mM SO42-) was investigated by utilizing a flow-through reaction cell and synchrotron X-ray absorption spectroscopy. This configuration allows collection of in situ, real-time X-ray absorption near-edge structure (XANES) spectra and bulk solution samples. Analysis of the solution chemistry suggests that the reaction mechanism changed (decreased reaction rate) as MnO2 was reduced and Fe(III) precipitated, primarily as ferrihydrite. Simultaneously, we observed an additional phase, with the local structure of jacobsite (MnFe2O4), in the Mn XANES spectra of reactants and products. The X-ray absorbance of this intermediate phase increased during the experiment, implying an increase in concentration. The presence of this phase, which probably formed as a surface coating, helps to explain the reduced rate of dissolution of manganese(IV) oxide. In natural environments affected by acid mine drainage, the formation of complex intermediate solid phases on mineral surfaces undergoing reductive dissolution may likewise influence the rate of release of metals to solution.

  6. Microbially enhanced dissolution and reductive dechlorination of PCE by a mixed culture: Model validation and sensitivity analysis

    NASA Astrophysics Data System (ADS)

    Chen, Mingjie; Abriola, Linda M.; Amos, Benjamin K.; Suchomel, Eric J.; Pennell, Kurt D.; Löffler, Frank E.; Christ, John A.

    2013-08-01

    Reductive dechlorination catalyzed by organohalide-respiring bacteria is often considered for remediation of non-aqueous phase liquid (NAPL) source zones due to cost savings, ease of implementation, regulatory acceptance, and sustainability. Despite knowledge of the key dechlorinators, an understanding of the processes and factors that control NAPL dissolution rates and detoxification (i.e., ethene formation) is lacking. A recent column study demonstrated a 5-fold cumulative enhancement in tetrachloroethene (PCE) dissolution and ethene formation (Amos et al., 2009). Spatial and temporal monitoring of key geochemical and microbial (i.e., Geobacter lovleyi and Dehalococcoides mccartyi strains) parameters in the column generated a data set used herein as the basis for refinement and testing of a multiphase, compositional transport model. The refined model is capable of simulating the reactive transport of multiple chemical constituents produced and consumed by organohalide-respiring bacteria and accounts for substrate limitations and competitive inhibition. Parameter estimation techniques were used to optimize the values of sensitive microbial kinetic parameters, including maximum utilization rates, biomass yield coefficients, and endogenous decay rates. Comparison and calibration of model simulations with the experimental data demonstrate that the model is able to accurately reproduce measured effluent concentrations, while delineating trends in dechlorinator growth and reductive dechlorination kinetics along the column. Sensitivity analyses performed on the optimized model parameters indicate that the rates of PCE and cis-1,2-dichloroethene (cis-DCE) transformation and Dehalococcoides growth govern bioenhanced dissolution, as long as electron donor (i.e., hydrogen flux) is not limiting. Dissolution enhancements were shown to be independent of cis-DCE accumulation; however, accumulation of cis-DCE, as well as column length and flow rate (i.e., column residence time

  7. Evidence for ligand hydrolysis and Fe(III) reduction in the dissolution of goethite by desferrioxamine-B

    NASA Astrophysics Data System (ADS)

    Simanova, Anna A.; Persson, Per; Loring, John S.

    2010-12-01

    Desferrioxamine-B (DFOB) is a bacterial trihydroxamate siderophore and probably the most studied to date. However, the manner in which DFOB adsorbs at mineral surfaces and promotes dissolution is still under discussion. Here we investigated the adsorption and dissolution reactions in the goethite-DFOB system using both in situ infrared spectroscopic and quantitative analytical methods. Experiments were carried out at a total DFOB concentration of 1 μmol/m 2, at pH 6, and in the absence of visible light. Our infrared spectroscopic results indicated that the adsorption of DFOB was nearly complete after a 4-h reaction time. In an attempt to determine the coordination mode at the goethite surface, we compared the spectrum of adsorbed DFOB after a 4-h reaction time to the spectra of model aqueous species. However, this approach proved too simplistic in the case of such a complex ligand as DFOB, and we suggest that a more detailed investigation (IR in D 2O, EXAFS of adsorbed model complexes) is needed to elucidate the structure of the adsorbed siderophore. Between a 4-h and 4-day reaction time, we observed the growth of carboxylate stretching bands at 1548 and 1404 cm -1, which are indicators of DFOB hydrolysis. Acetate, a product of DFOB hydrolysis at its terminal hydroxamate group, was quantified by ion chromatography. Its rate of formation was linear and nearly the same as the rate of Fe(III) dissolution. The larger hydrolysis product, a hydroxylamine fragment, was not detected by LC-MS. However, a signal due to the oxidized form of this fragment, a nitroso compound, was found to increase linearly with time, which is an indirect indication for Fe(III) reduction. Based on these findings, we propose that DFOB undergoes metal-enhanced hydrolysis at the mineral surface followed by the reduction of surface Fe(III). While Fe(II) was not detected in solution, this is likely because it remains adsorbed at the goethite surface or becomes buried in the goethite crystal by

  8. Evidence for Ligand Hydrolysis and Fe(III) Reduction in the Dissolution of Goethite by Desferrioxamine-B

    SciTech Connect

    Simanova, Anna A.; Persson, Per; Loring, John S.

    2010-08-01

    Desferrioxamine-B (DFOB) is a bacterial trihydroxamate siderophore and probably the most studied to date. However, the manner in which DFOB adsorbs at mineral surfaces and promotes dissolution is still under discussion. Here we investigated the adsorption and dissolution reactions in the goethite DFOB system using both in situ infrared spectroscopic and quantitative analytical methods. Experiments were carried out at a total DFOB concentration of 1 lmol/m2, at pH 6, and in the absence of visible light. Our infrared spectroscopic results indicated that the adsorption of DFOB was nearly complete after a 4-h reaction time. In an attempt to determine the coordination mode at the goethite surface, we compared the spectrum of adsorbed DFOB after a 4-h reaction time to the spectra of model aqueous species. However, this approach proved too simplistic in the case of such a complex ligand as DFOB, and we suggest that a more detailed investigation (IR in D2O, EXAFS of adsorbed model complexes) is needed to elucidate the structure of the adsorbed siderophore. Between a 4-h and 4-day reaction time, we observed the growth of carboxylate stretching bands at 1548 and 1404 cm1, which are indicators of DFOB hydrolysis. Acetate, a product of DFOB hydrolysis at its terminal hydroxamate group, was quantified by ion chromatography. Its rate of formation was linear and nearly the same as the rate of Fe(III) dissolution. The larger hydrolysis product, a hydroxylamine fragment, was not detected by LC MS. However, a signal due to the oxidized form of this fragment, a nitroso compound, was found to increase linearly with time, which is an indirect indication for Fe(III) reduction. Based on these findings, we propose that DFOB undergoes metal-enhanced hydrolysis at the mineral surface followed by the reduction of surface Fe(III). While Fe(II) was not detected in solution, this is likely because it remains adsorbed at the goethite surface or becomes buried in the goethite crystal by electron

  9. Recovery of Nickel and Cobalt from Laterite Tailings by Reductive Dissolution under Aerobic Conditions Using Acidithiobacillus Species.

    PubMed

    Marrero, J; Coto, O; Goldmann, S; Graupner, T; Schippers, A

    2015-06-02

    Biomining of sulfidic ores has been applied for almost five decades. However, the bioprocessing of oxide ores such as laterites lags commercially behind. Recently, the Ferredox process was proposed to treat limonitic laterite ores by means of anaerobic reductive dissolution (AnRD), which was found to be more effective than aerobic bioleaching by fungi and other bacteria. We show here that the ferric iron reduction mediated by Acidithiobacillus thiooxidans can be applied to an aerobic reductive dissolution (AeRD) of nickel laterite tailings. AeRD using a consortium of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans extracted similar amounts of nickel (53-57%) and cobalt (55-60%) in only 7 days as AnRD using Acidithiobacillus ferrooxidans. The economic and environmental advantages of AeRD for processing of laterite tailings comprise no requirement for an anoxic atmosphere, 1.8-fold less acid consumption than for AnRD, as well as nickel and cobalt recovered in a ferrous-based pregnant leach solution (PLS), facilitating the subsequent metal recovery. In addition, an aerobic acid regeneration stage is proposed. Therefore, AeRD process development can be considered as environmentally friendly for treating laterites with low operational costs and as an attractive alternative to AnRD.

  10. Simultaneous Release of Fe and As during the Reductive Dissolution of Pb-As Jarosite by Shewanella putrefaciens CN32

    SciTech Connect

    Smeaton, Christina M; Walshe, Gillian E; Smith, Adrian M.L.; Hudson-Edwards, Karen A; Dubbin, William E; Wright, Kate; Beale, Andrew M; Fryer, Brian J; Weisener, Christopher G

    2012-11-05

    Jarosites are produced during metallurgical processing, on oxidized sulfide deposits, and in acid mine drainage environments. Despite the environmental relevance of jarosites, few studies have examined their biogeochemical stability. This study demonstrates the simultaneous reduction of structural Fe(III) and aqueous As(V) during the dissolution of synthetic Pb–As jarosite (PbFe3(SO4,AsO4)2(OH)6) by Shewanella putrefaciens using batch experiments under anaerobic circumneutral conditions. Fe(III) reduction occurred immediately in inoculated samples while As(V) reduction was observed after 72 h. XANES spectra showed As(III) (14.7%) in the solid phase at 168 h coincident with decreased aqueous As(V). At 336 h, XANES spectra and aqueous speciation analysis demonstrated 20.2% and 3.0% of total As was present as As(III) in the solid and aqueous phase, respectively. In contrast, 12.4% of total Fe was present as aqueous Fe(II) and was below the detection limits of XANES in the solid phase. TEM-EDS analysis at 336 h showed secondary precipitates enriched in Fe and O with minor amounts of As and Pb. Based on experimental data and thermodynamic modeling, we suggest that structural Fe(III) reduction was thermodynamically driven while aqueous As(V) reduction was triggered by detoxification induced to offset the high As(V) (328 μM) concentrations released during dissolution.

  11. Transition metal dissolution, ion migration, electrocatalytic reduction and capacity loss in Lithium-ion full cells

    DOE PAGES

    Gilbert, James A.; Shkrob, Ilya A.; Abraham, Daniel P.

    2017-01-05

    Continuous operation of full cells with layered transition metal (TM) oxide positive electrodes (NCM523) leads to dissolution of TM ions and their migration and incorporation into the solid electrolyte interphase (SEI) of the graphite-based negative electrode. These processes correlate with cell capacity fade and accelerate markedly as the upper cutoff voltage (UCV) exceeds 4.30 V. At voltages ≥ 4.4 V there is enhanced fracture of the oxide during cycling that creates new surfaces and causes increased solvent oxidation and TM dissolution. Despite this deterioration, cell capacity fade still mainly results from lithium loss in the negative electrode SEI. Among TMs,more » Mn content in the SEI shows a better correlation with cell capacity loss than Co and Ni contents. As Mn ions become incorporated into the SEI, the kinetics of lithium trapping change from power to linear at the higher UCVs, indicating a large effect of these ions on SEI growth and implicating (electro)catalytic reactions. Lastly, we estimate that each MnII ion deposited in the SEI causes trapping of ~102 additional Li+ ions thereby hastening the depletion of cyclable lithium ions. Using these results, we sketch a mechanism for cell capacity fade, emphasizing the conceptual picture over the chemical detail.« less

  12. Laboratory investigation of flux reduction from dense non-aqueous phase liquid (DNAPL) partial source zone remediation by enhanced dissolution

    NASA Astrophysics Data System (ADS)

    Kaye, Andrew J.; Cho, Jaehyun; Basu, Nandita B.; Chen, Xiaosong; Annable, Michael D.; Jawitz, James W.

    2008-11-01

    This study investigated the benefits of partial removal of dense nonaqueous phase liquid (DNAPL) source zones using enhanced dissolution in eight laboratory scale experiments. The benefits were assessed by characterizing the relationship between reductions in DNAPL mass and the corresponding reduction in contaminant mass flux. Four flushing agents were evaluated in eight controlled laboratory experiments to examine the effects of displacement fluid property contrasts and associated override and underride on contaminant flux reduction ( Rj) vs. mass reduction ( Rm) relationships ( Rj( Rm)): 1) 50% ethanol/50% water (less dense than water), 2) 40% ethyl-lactate/60% water (more dense than water), 3) 18% ethanol/26% ethyl-lactate/56% water (neutrally buoyant), and 4) 2% Tween-80 surfactant (also neutrally buoyant). For each DNAPL architecture evaluated, replicate experiments were conducted where source zone dissolution was conducted with a single flushing event to remove most of the DNAPL from the system, and with multiple shorter-duration floods to determine the path of the Rj( Rm) relationship. All of the single-flushing experiments exhibited similar Rj( Rm) relationships indicating that override and underride effects associated with cosolvents did not significantly affect the remediation performance of the agents. The Rj( Rm) relationship of the multiple injection experiments for the cosolvents with a density contrast with water tended to be less desirable in the sense that there was less Rj for a given Rm. UTCHEM simulations supported the observations from the laboratory experiments and demonstrated the capability of this model to predict Rj( Rm) relationships for non-uniformly distributed NAPL sources.

  13. Ultrasound-assisted reductive dissolution of CeO2 and PuO2 in the presence of Ti particles.

    PubMed

    Beaudoux, Xavier; Virot, Matthieu; Chave, Tony; Leturcq, Gilles; Jouan, Gauthier; Venault, Laurent; Moisy, Philippe; Nikitenko, Sergey I

    2016-06-07

    PuO2 is considered an important material for current and future nuclear fuel; however it is a very refractive compound towards dissolution. Among other techniques, its reprocessing can be performed via complexing dissolution in concentrated and boiling nitric acid containing hydrofluoric acid, or via oxidant dissolution in the presence of reagents with redox couples having high potentials such as Ce(iv)/Ce(iii), or Ag(ii)/Ag(i). Reductive dissolution can be performed under softer conditions and is considered an alternative to these methods which may suffer from several drawbacks (corrosion, effluent management, compatibility with nuclear waste disposal, etc.). In this study, a sonochemical and reductive approach is investigated for PuO2 dissolution under relatively mild conditions. At the first stage, the experiments are performed with CeO2 as an inactive surrogate for PuO2. The quantitative dissolution of both oxides can be achieved under ultrasound (20 kHz, 0.35-0.70 W mL(-1)) in 0.5 M HNO3/0.1 M [N2H5NO3]/2 M HCOOH sparged with Ar at 33-35 °C in the presence of Ti particles as a generating source of reductive species. Ultrasound enables the depassivation of the Ti surface (usually strongly passivated in nitric solutions) through acoustic cavitation which then allows further generation of the intermediate Ti(iii) reductive species. Dissolution rates and yields can be further increased with the injection of dilute fluoride aliquots (NH4F or HF) in the sonicated solution to favor Ti chemical depassivation. The rapid and complete dissolution of PuO2 under selected conditions is accompanied by Pu(iii) accumulation in solution.

  14. Observations of magnetite dissolution in poorly drained soils

    USGS Publications Warehouse

    Grimley, D.A.; Arruda, N.K.

    2007-01-01

    Dissolution of strongly magnetic minerals is a common and relatively rapid phenomenon in poorly drained soils of the central United States, resulting in low magnetic susceptibility (MS). Low Eh reducing conditions are primarily responsible for magnetic mineral dissolution; a process likely mediated by iron-reducing bacteria in the presence of soil organic matter. Based on transects across drainage sequences from nine sites, natural magnetic minerals (>5 ??m) extracted from surface soil consist of 54% ?? 18% magnetite, 21% ?? 11% titanomagnetite, and 17% ?? 14% ilmenite. Magnetite and titanomagnetite dissolution, assessed by scanning electron microscopy on a 0-to-3 scale, inversely correlates with surface soil MS (r = 0.53), a proxy for soil drainage at studied transects. Altered magnetite typically displays etch pits 5 ??m) include 26% ?? 18% anthropogenic fly ash that also exhibits greater dissolution in low MS soils (r = 0.38), indicating detectable alteration can occur within 150 years in low Eh soils. Laboratory induced reduction of magnetite, titanomagnetite, and magnetic fly ash, with a citrate-bicarbonate- dithionite solution, resulted in dissolution textures similar to those of in situ soil particles. Although experiments indicate that reductive dissolution of magnetite can occur abiotically under extreme conditions, bacteria likely play an important role in the natural environment. ?? 2007 Lippincott Williams & Wilkins, Inc.

  15. Combined abiotic and biotic in-situ reduction of hexavalent chromium in groundwater using nZVI and whey: A remedial pilot test.

    PubMed

    Němeček, Jan; Pokorný, Petr; Lacinová, Lenka; Černík, Miroslav; Masopustová, Zuzana; Lhotský, Ondřej; Filipová, Alena; Cajthaml, Tomáš

    2015-12-30

    The paper describes a pilot remediation test combining two Cr(VI) geofixation methods - chemical reduction by nanoscale zero-valent iron (nZVI) and subsequent biotic reduction supported by whey. Combination of the methods exploited the advantages of both - a rapid decrease in Cr(VI) concentrations by nZVI, which prevented further spreading of the contamination and facilitated subsequent use of the cheaper biological method. Successive application of whey as an organic substrate to promote biotic reduction of Cr(VI) after application of nZVI resulted in a further and long-term decrease in the Cr(VI) contents in the groundwater. The effect of biotic reduction was observed even in a monitoring well located at a distance of 22 m from the substrate injection wells after 10 months. The results indicated a reciprocal effect of both the phases - nZVI oxidized to Fe(III) during the abiotic phase was microbially reduced back to Fe(II) and acted as a reducing agent for Cr(VI) even when the microbial density was already low due to the consumed substrate. Community analysis with pyrosequencing of the 16S rRNA genes further confirmed partial recycling of nZVI in the form of Fe(II), where the results showed that the Cr(VI) reducing process was mediated mainly by iron-reducing and sulfate-reducing bacteria.

  16. Reduction of nitrogen compounds in oceanic basement and its implications for HCN formation and abiotic organic synthesis

    PubMed Central

    2009-01-01

    Hydrogen cyanide is an excellent organic reagent and is central to most of the reaction pathways leading to abiotic formation of simple organic compounds containing nitrogen, such as amino acids, purines and pyrimidines. Reduced carbon and nitrogen precursor compounds for the synthesis of HCN may be formed under off-axis hydrothermal conditions in oceanic lithosphere in the presence of native Fe and Ni and are adsorbed on authigenic layer silicates and zeolites. The native metals as well as the molecular hydrogen reducing CO2 to CO/CH4 and NO3-/NO2- to NH3/NH4+ are a result of serpentinization of mafic rocks. Oceanic plates are conveyor belts of reduced carbon and nitrogen compounds from the off-axis hydrothermal environments to the subduction zones, where compaction, dehydration, desiccation and diagenetic reactions affect the organic precursors. CO/CH4 and NH3/NH4+ in fluids distilled out of layer silicates and zeolites in the subducting plate at an early stage of subduction will react upon heating and form HCN, which is then available for further organic reactions to, for instance, carbohydrates, nucleosides or even nucleotides, under alkaline conditions in hydrated mantle rocks of the overriding plate. Convergent margins in the initial phase of subduction must, therefore, be considered the most potent sites for prebiotic reactions on Earth. This means that origin of life processes are, perhaps, only possible on planets where some kind of plate tectonics occur. PMID:19849830

  17. Reduction of nitrogen compounds in oceanic basement and its implications for HCN formation and abiotic organic synthesis.

    PubMed

    Holm, Nils G; Neubeck, Anna

    2009-10-22

    Hydrogen cyanide is an excellent organic reagent and is central to most of the reaction pathways leading to abiotic formation of simple organic compounds containing nitrogen, such as amino acids, purines and pyrimidines. Reduced carbon and nitrogen precursor compounds for the synthesis of HCN may be formed under off-axis hydrothermal conditions in oceanic lithosphere in the presence of native Fe and Ni and are adsorbed on authigenic layer silicates and zeolites. The native metals as well as the molecular hydrogen reducing CO2 to CO/CH4 and NO3-/NO2- to NH3/NH4+ are a result of serpentinization of mafic rocks. Oceanic plates are conveyor belts of reduced carbon and nitrogen compounds from the off-axis hydrothermal environments to the subduction zones, where compaction, dehydration, desiccation and diagenetic reactions affect the organic precursors. CO/CH4 and NH3/NH4+ in fluids distilled out of layer silicates and zeolites in the subducting plate at an early stage of subduction will react upon heating and form HCN, which is then available for further organic reactions to, for instance, carbohydrates, nucleosides or even nucleotides, under alkaline conditions in hydrated mantle rocks of the overriding plate. Convergent margins in the initial phase of subduction must, therefore, be considered the most potent sites for prebiotic reactions on Earth. This means that origin of life processes are, perhaps, only possible on planets where some kind of plate tectonics occur.

  18. Identification of abiotic and biotic reductive dechlorination in a chlorinated ethene plume after thermal source remediation by means of isotopic and molecular biology tools

    NASA Astrophysics Data System (ADS)

    Badin, Alice; Broholm, Mette M.; Jacobsen, Carsten S.; Palau, Jordi; Dennis, Philip; Hunkeler, Daniel

    2016-09-01

    Thermal tetrachloroethene (PCE) remediation by steam injection in a sandy aquifer led to the release of dissolved organic carbon (DOC) from aquifer sediments resulting in more reduced redox conditions, accelerated PCE biodegradation, and changes in microbial populations. These changes were documented by comparing data collected prior to the remediation event and eight years later. Based on the premise that dual C-Cl isotope slopes reflect ongoing degradation pathways, the slopes associated with PCE and TCE suggest the predominance of biotic reductive dechlorination near the source area. PCE was the predominant chlorinated ethene near the source area prior to thermal treatment. After thermal treatment, cDCE became predominant. The biotic contribution to these changes was supported by the presence of Dehalococcoides sp. DNA (Dhc) and Dhc targeted rRNA close to the source area. In contrast, dual C-Cl isotope analysis together with the almost absent VC 13C depletion in comparison to cDCE 13C depletion suggested that cDCE was subject to abiotic degradation due to the presence of pyrite, possible surface-bound iron (II) or reduced iron sulphides in the downgradient part of the plume. This interpretation is supported by the relative lack of Dhc in the downgradient part of the plume. The results of this study show that thermal remediation can enhance the biodegradation of chlorinated ethenes, and that this effect can be traced to the mobilisation of DOC due to steam injection. This, in turn, results in more reduced redox conditions which favor active reductive dechlorination and/or may lead to a series of redox reactions which may consecutively trigger biotically induced abiotic degradation. Finally, this study illustrates the valuable complementary application of compound-specific isotopic analysis combined with molecular biology tools to evaluate which biogeochemical processes are taking place in an aquifer contaminated with chlorinated ethenes.

  19. Constraining the role of iron in environmental nitrogen transformations: Dual stable isotope systematics of abiotic NO2- reduction by Fe(II) and its production of N2O

    NASA Astrophysics Data System (ADS)

    Buchwald, Carolyn; Grabb, Kalina; Hansel, Colleen M.; Wankel, Scott D.

    2016-08-01

    Despite mounting evidence for biogeochemical interactions between iron and nitrogen, our understanding of their environmental importance remains limited. Here we present an investigation of abiotic nitrite (NO2-) reduction by Fe(II) or 'chemodenitrification', and its relevance to the production of nitrous oxide (N2O), specifically focusing on dual (N and O) isotope systematics under a variety of environmental conditions. We observe a range of kinetic isotope effects that are regulated by reaction rates, with faster rates at higher pH (∼8), higher concentrations of Fe(II) and in the presence of mineral surfaces. A clear non-linear relationship between rate constant and kinetic isotope effects of NO2- reduction was evident (with larger isotope effects at slower rates) and is interpreted as reflecting the dynamics of Fe(II)-N reaction intermediates. N and O isotopic composition of product N2O also suggests a complex network of parallel and/or competing pathways. Our findings suggest that NO2- reduction by Fe(II) may represent an important abiotic source of environmental N2O, especially in iron-rich environments experiencing dynamic redox variations. This study provides a multi-compound, multi-isotope framework for evaluating the environmental occurrence of abiotic NO2- reduction and N2O formation, helping future studies constrain the relative roles of abiotic and biological N2O production pathways.

  20. A kinetic pressure effect on the experimental abiotic reduction of aqueous CO2 to methane from 1 to 3.5 kbar at 300 °C

    NASA Astrophysics Data System (ADS)

    Lazar, Codi; Cody, George D.; Davis, Jeffrey M.

    2015-02-01

    Aqueous abiotic methane concentrations in a range of geologic settings are below levels expected for equilibrium with coexisting CO2 and H2, indicating that kinetics can control the speciation of reduced carbon-bearing fluids. Previous studies have suggested that mineral catalysts or gas-phase reactions may increase the rate of methanogenesis. Here, we report on experiments that indicate pressure can also accelerate aqueous reduction of CO2 to CH4. Four series of cold-seal hydrothermal experiments were performed from 1 to 3.5 kbar at 300 °C for two weeks and analyzed using gas chromatography/mass spectrometry. The starting fluids were 10-20-μL solutions of 70-mmolal 13C-labeled formic acid (H13COOH) contained in welded gold capsules. Increasing pressure (P) resulted in a systematic, reproducible log-linear increase in 13CH4 yields. The pressure effect could be quantified the log-linear slope, Δlog[13CH4]/ΔP (log mmolal per kbar). The mean slope was 0.66 ± 0.05 (±1s.e.), indicating that 13CH4 yields increased by an average factor of 40-50 over a P range of 2.5 kbar. Pressure-independent variations in [13CH4] were observed as scatter about the log-linear regressions and as variations in the y-intercepts of the regressions. These variations were attributed to trace amounts of catalytic Fe along the inner capsule wall that remained despite cleaning the Au capsules in nitric acid prior to each experimental series. The mechanism for the pressure-dependent effect was interpreted to result from one or more of the following three processes: reduction of a metastable reaction intermediate such as methanol, formation of Fe-carbonyl complexes in the fluid, and/or heterogeneous catalysis by Fe. The results suggest that pressure may influence aqueous abiotic CH4 yields in certain geological environments, particularly when the relative effects of other kinetic factors such as temperature are diminished, e.g., in cool forearcs or other settings with a steep geothermal

  1. Final Report for "Toward Quantifying Kinetics of Biotic and Abiotic Metal Reduction with Electrical Geophysical Methods" DE-FG02-08ER64520

    SciTech Connect

    Singha, Kamini; Brantley, Susan

    2012-06-07

    Although changes in the bulk electrical conductivity in aquifers have been attributed to microbial activity, electrical conductivity has never been used to infer biogeochemical reaction rates quantitatively. To explore the use of electrical conductivity to measure reaction rates, we conducted iron oxide reduction experiments of increasing biological complexity. To quantify reaction rates, we proposed composite reactions that incorporated the stiochiometry of five different types of reactions: redox, acid-based, sorption, dissolution/precipitation, and biosynthesis. In batch and column experiments, such reaction stiochiometries inferred from a few chemical measurements allowed quantification of the Fe-oxide reduction rate based on changes in electrical conductivity. The relationship between electrical conductivity and fluid chemistry did not hold during the latter stages of the column experiment when electrical conductivity increased while fluid chemistry remained constant. Growth of an electrically conductive biofilm could explain this late stage electrical conductivity increase. This work demonstrates that measurements of electrical conductivity and flow rate, combined with a few direct chemical measurements, can be used to quantify biogeochemical reaction rates in controlled laboratory situations and may be able to detect the presence of biofilms.

  2. Constraining the role of iron in environmental nitrogen transformations. Dual stable isotope systematics of abiotic NO2- reduction by Fe(II) and its production of N2O

    SciTech Connect

    Johnston, David; Wankel, Scott David; Buchwald, Carolyn; Hansel, Colleen

    2015-09-16

    Redox reactions involving nitrogen and iron have been shown to have important implications for mobilization of priority contaminants. Thus, an understanding of the linkages between their biogeochemical cycling is critical for predicting subsurface mobilization of radionuclides such as uranium. Despite mounting evidence for biogeochemical interactions between iron and nitrogen, our understanding of their environmental importance remains limited. Here we present an investigation of abiotic nitrite (NO2-) reduction by Fe(II) or ‘chemodenitrification,’ and its relevance to the production of nitrous oxide (N2O), specifically focusing on dual (N and O) isotope systematics under a variety of environmentally relevant conditions. We observe a range of kinetic isotope effects that are regulated by reaction rates, with faster rates at higher pH (~8), higher concentrations of Fe(II) and in the presence of mineral surfaces. A clear non-linear relationship between rate constant and kinetic isotope effects of NO2- reduction was evident (with larger isotope effects at slower rates) and is interpreted as reflecting the dynamics of Fe(II)-N reaction intermediates. N and O isotopic composition of product N2O also suggests a complex network of parallel and/or competing pathways. Our findings suggest that NO2- reduction by Fe(II) may represent an important abiotic source of environmental N2O, especially in iron-rich environments experiencing dynamic redox variations. This study provides a multi-compound, multi-isotope framework for evaluating the environmental occurrence of abiotic NO2- reduction and N2O formation, helping future studies constrain the relative roles of abiotic and biological N2O production pathways.

  3. DOWNSTREAM IMPACTS OF SLUDGE MASS REDUCTION VIA ALUMINUM DISSOLUTION ON DWPF PROCESSING OF SAVANNAH RIVER SITE HIGH LEVEL WASTE - 9382

    SciTech Connect

    Pareizs, J; Cj Bannochie, C; Michael Hay, M; Daniel McCabe, D

    2009-01-14

    The SRS sludge that was to become a major fraction of Sludge Batch 5 (SB5) for the Defense Waste Processing Facility (DWPF) contained a large fraction of H-Modified PUREX (HM) sludge, containing a large fraction of aluminum compounds that could adversely impact the processing and increase the vitrified waste volume. It is beneficial to reduce the non-radioactive fraction of the sludge to minimize the number of glass waste canisters that must be sent to a Federal Repository. Removal of aluminum compounds, such as boehmite and gibbsite, from sludge can be performed with the addition of NaOH solution and heating the sludge for several days. Preparation of SB5 involved adding sodium hydroxide directly to the waste tank and heating the contents to a moderate temperature through slurry pump operation to remove a fraction of this aluminum. The Savannah River National Laboratory (SRNL) was tasked with demonstrating this process on actual tank waste sludge in our Shielded Cells Facility. This paper evaluates some of the impacts of aluminum dissolution on sludge washing and DWPF processing by comparing sludge processing with and without aluminum dissolution. It was necessary to demonstrate these steps to ensure that the aluminum removal process would not adversely impact the chemical and physical properties of the sludge which could result in slower processing or process upsets in the DWPF.

  4. Massive production of abiotic methane during subduction evidenced in metamorphosed ophicarbonates from the Italian Alps

    PubMed Central

    Vitale Brovarone, Alberto; Martinez, Isabelle; Elmaleh, Agnès; Compagnoni, Roberto; Chaduteau, Carine; Ferraris, Cristiano; Esteve, Imène

    2017-01-01

    Alteration of ultramafic rocks plays a major role in the production of hydrocarbons and organic compounds via abiotic processes on Earth and beyond and contributes to the redistribution of C between solid and fluid reservoirs over geological cycles. Abiotic methanogenesis in ultramafic rocks is well documented at shallow conditions, whereas natural evidence at greater depths is scarce. Here we provide evidence for intense high-pressure abiotic methanogenesis by reduction of subducted ophicarbonates. Protracted (≥0.5–1 Ma), probably episodic infiltration of reduced fluids in the ophicarbonates and methanogenesis occurred from at least ∼40 km depth to ∼15–20 km depth. Textural, petrological and isotopic data indicate that methane reached saturation triggering the precipitation of graphitic C accompanied by dissolution of the precursor antigorite. Continuous infiltration of external reducing fluids caused additional methane production by interaction with the newly formed graphite. Alteration of high-pressure carbonate-bearing ultramafic rocks may represent an important source of abiotic methane, with strong implications for the mobility of deep C reservoirs. PMID:28223715

  5. Massive production of abiotic methane during subduction evidenced in metamorphosed ophicarbonates from the Italian Alps

    NASA Astrophysics Data System (ADS)

    Vitale Brovarone, Alberto; Martinez, Isabelle; Elmaleh, Agnès; Compagnoni, Roberto; Chaduteau, Carine; Ferraris, Cristiano; Esteve, Imène

    2017-02-01

    Alteration of ultramafic rocks plays a major role in the production of hydrocarbons and organic compounds via abiotic processes on Earth and beyond and contributes to the redistribution of C between solid and fluid reservoirs over geological cycles. Abiotic methanogenesis in ultramafic rocks is well documented at shallow conditions, whereas natural evidence at greater depths is scarce. Here we provide evidence for intense high-pressure abiotic methanogenesis by reduction of subducted ophicarbonates. Protracted (>=0.5-1 Ma), probably episodic infiltration of reduced fluids in the ophicarbonates and methanogenesis occurred from at least ~40 km depth to ~15-20 km depth. Textural, petrological and isotopic data indicate that methane reached saturation triggering the precipitation of graphitic C accompanied by dissolution of the precursor antigorite. Continuous infiltration of external reducing fluids caused additional methane production by interaction with the newly formed graphite. Alteration of high-pressure carbonate-bearing ultramafic rocks may represent an important source of abiotic methane, with strong implications for the mobility of deep C reservoirs.

  6. Massive production of abiotic methane during subduction evidenced in metamorphosed ophicarbonates from the Italian Alps.

    PubMed

    Vitale Brovarone, Alberto; Martinez, Isabelle; Elmaleh, Agnès; Compagnoni, Roberto; Chaduteau, Carine; Ferraris, Cristiano; Esteve, Imène

    2017-02-22

    Alteration of ultramafic rocks plays a major role in the production of hydrocarbons and organic compounds via abiotic processes on Earth and beyond and contributes to the redistribution of C between solid and fluid reservoirs over geological cycles. Abiotic methanogenesis in ultramafic rocks is well documented at shallow conditions, whereas natural evidence at greater depths is scarce. Here we provide evidence for intense high-pressure abiotic methanogenesis by reduction of subducted ophicarbonates. Protracted (≥0.5-1 Ma), probably episodic infiltration of reduced fluids in the ophicarbonates and methanogenesis occurred from at least ∼40 km depth to ∼15-20 km depth. Textural, petrological and isotopic data indicate that methane reached saturation triggering the precipitation of graphitic C accompanied by dissolution of the precursor antigorite. Continuous infiltration of external reducing fluids caused additional methane production by interaction with the newly formed graphite. Alteration of high-pressure carbonate-bearing ultramafic rocks may represent an important source of abiotic methane, with strong implications for the mobility of deep C reservoirs.

  7. Solid dispersion of hydroxypropyl beta-cyclodextrin and ketorolac: enhancement of in-vitro dissolution rates, improvement in anti-inflammatory activity and reduction in ulcerogenicity in rats.

    PubMed

    Nagarsenker, M S; Meshram, R N; Ramprakash, G

    2000-08-01

    Ketorolac, is a non-steroidal anti-inflammatory drug, with strong analgesic activity. It is practically insoluble in water and has been implicated in causing gastrointestinal ulceration. This study describes the formulation of solid dispersions of ketorolac using hydroxypropyl beta-cyclodextrin (HPbeta-CyD) and beta-cyclodextin (beta-CyD) as carriers, to improve the aqueous solubility of the drug, thus enhancing its bioavailability. Also, reduction in ulcerogenicity was anticipated. Differential scanning calorimetry and X-ray diffraction studies indicated loss of crystalline nature of the drug, in the dispersions prepared with HPbeta-CyD. NMR studies revealed a strong interaction between drug and HPbeta-CyD. Solid dispersions of drug with beta-CyD retained the crystalline nature of the drug. All the solid dispersions showed a remarkable improvement in the rate and extent of dissolution of ketorolac. The kneaded dispersion with HPbeta-CyD prepared using a 1:1 alcohol-water mixture showed promise in reducing the ulcer-inducing effect of ketorolac in rats. Oral administration of this dispersion was found to inhibit carrageenan-induced paw oedema in rats to a significantly greater extent compared with ketorolac or its trometamol salt. Though beta-CyD as a carrier for ketorolac gave faster release of the poorly soluble drug, HPbeta-CyD proved to be superior to beta-CyD, as a carrier in the kneaded dispersion prepared using 1:1 alcohol-water mixture. These results suggest that solid dispersions of ketorolac with HPbeta-CyD aid in faster dissolution and better bioavailability of the drug. The higher solubility of the drug in the presence of HPbeta-CyD also reduces local gastrointestinal side-effects of the drug.

  8. Electrochemical studies on the oxygen reduction and NiO(Li) dissolution in molten carbonate fuel cells

    NASA Astrophysics Data System (ADS)

    Makkus, Robert Christiaan

    A study of the oxygen reduction in molten carbonate on a plane gold electrode submerged in a molten carbonate melt and on three different porous electrodes, made of NiO(Li), LiFeO2 (doped with either Mg or Co) and LiCoO2, is presented. From the impedance measurements made on plane gold electrode, two parallel reaction mechanisms are concluded to be involved in the oxygen reduction: in the first peroxycarbonate is reduced at a partly with oxide covered electrode surface; and in the second the steps could not be unraveled. Partial pressure dependencies of the diffusion arc observed in the impedance of the porous electrodes indicate that both oxygen and carbon dioxide are the diffusing species. From comparison of the ratios of the diffusion and kinetic arc, the catalytic activities of the three materials are concluded not to differ significantly, although this seems to be contradictory to the observation that the impedance for Co doped LiFeO2 is much Larger than for the other materials. This difference, however, is due to the large specific resistivity of Co doped LiFeO2 compared to the resistivity of the other materials.

  9. Evaluation of premeability-porosity relationships linked to mineral dissolution-precipitation using global implicit approach with a reduction scheme and operator splitting approach

    NASA Astrophysics Data System (ADS)

    Zolfaghari, R.; Shao, H.; Kolditz, O.

    2013-12-01

    Numerical simulation of reactive transport processes is essential in long term behavior assessment of hazardous materials. To simulate reactive transport processes global implicit approach (GIA) and operator splitting approach are commonly used. GIA has been getting more attentions due to advances in computational power and the lack of numerical accuracy and efficacy of operator splitting methods for simulating long term processes over the past few years. We have investigated the Efficiency and accuracy of these methods in handling slow reacting-processes in long term scenarios. GIA with reduction scheme proposed by Kräutel et al. (2010) and sequential non-iterative approach (SNIA) approach have been implemented into OpenGeoSys (OGS6) to solve reactive transport problems. The new reduction scheme in GIA uses a reformulation to reduce the number of coupled nonlinear partial differential equations by decoupling of equations and elimination of unknowns. The new reformulation divides components and species of the chemical system into decoupled linear reaction invariant components and coupled nonlinear reaction variant ones. A local chemical solver is used to handle the chemical problem in GIA and SNIA approaches. Equilibrium/ kinetic mineral reaction is treated as a complementarity problem in the local problem. In this context, a series of benchmarks have been adopted to assess the performance of GIA with reduction scheme and SNIA. The benchmarks objective is to simulate mineral dissolution-precipitation induced porosity changes and the resulting effects on the solute migration. The Carman-Kozeny relationship is used to describe changes in permeability as a function of porosity. The results produced by three codes of OGS6, OGS-PHREEQC and MIN3P have been compared and evaluated based on the benchmarks for the numerical accuracy and efficacy.

  10. Dissolution-and-reduction CVD synthesis of few-layer graphene on ultra-thin nickel film lifted off for mode-locking fiber lasers

    PubMed Central

    Peng, Kaung-Jay; Lin, Yung-Hsiang; Wu, Chung-Lun; Lin, Sheng-Fong; Yang, Chun-Yu; Lin, Shih-Meng; Tsai, Din-Ping; Lin, Gong-Ru

    2015-01-01

    The in-situ dissolution-and-reduction CVD synthesized few-layer graphene on ultra-thin nickel catalyst film is demonstrated at temperature as low as 550 °C, which can be employed to form transmission-type or reflection-type saturable absorber (SA) for mode-locking the erbium-doped fiber lasers (EDFLs). With transmission-type graphene SA, the EDFL shortens its pulsewidth from 483 to 441 fs and broadens its spectral linewidth from 4.2 to 6.1 nm with enlarging the pumping current from 200 to 900 mA. In contrast, the reflection-type SA only compresses the pulsewidth from 875 to 796 fs with corresponding spectral linewidth broadened from 2.2 to 3.3 nm. The reflection-type graphene mode-locker increases twice of its equivalent layer number to cause more insertion loss than the transmission-type one. Nevertheless, the reflection-type based saturable absorber system can generate stabilized soliton-like pulse easier than that of transmission-type system, because the nonlinearity induced self-amplitude modulation depth is simultaneously enlarged when passing through the graphene twice under the retro-reflector design. PMID:26328535

  11. Modeling intrinsic bioremediation for interpret observable biogeochemical footprints of BTEX biodegradation: the need for fermentation and abiotic chemical processes.

    PubMed

    Maurer, Max; Rittmann, Bruce E

    2004-12-01

    The intrinsic bioremediation of BTEX must be documented by the stoichiometric consumption and production of several other compounds, called 'footprints' of the biodegradation reaction. Although footprints of BTEX biodegradation are easy to identify from reaction stoichiometry, they can be confounded by the stepwise nature of the biodegradation reactions and by several abiotic chemical reactions that also produce or consume the footprints. In order to track the footprints for BTEX biodegradation, the following reactions need to be considered explicitly: (1) fermentation and methanogenesis as separate processes, (2) precipitation and dissolution of calcite, (3) precipitation and dissolution of amorphous iron monosulfide (FeS), (4) conversion of FeS into the thermodynamically stable pyrite (FeS2) with loss of sulfide and abiotic formation of H2, and (5) reductive dissolution of solid iron(III) by oxidation of sulfide. We critically review the research that underlies why these mechanisms must be included and how to describe them quantitatively. A companion manuscript develops and applies a mathematical model that includes these reactions.

  12. A novel determination of calcite dissolution kinetics in seawater

    NASA Astrophysics Data System (ADS)

    Subhas, Adam V.; Rollins, Nick E.; Berelson, William M.; Dong, Sijia; Erez, Jonathan; Adkins, Jess F.

    2015-12-01

    We present a novel determination of the dissolution kinetics of inorganic calcite in seawater. We dissolved 13 C -labeled calcite in unlabeled seawater, and traced the evolving δ13 C composition of the fluid over time to establish dissolution rates. This method provides sensitive determinations of dissolution rate, which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals. We have determined dissolution rates for two different abiotic calcite materials and three different grain sizes. Near-equilibrium dissolution rates are highly nonlinear, and are well normalized by geometric surface area, giving an empirical dissolution rate dependence on saturation state (Ω) of: This result substantiates the non-linear response of calcite dissolution to undersaturation. The bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments. Plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms, implying a criticality in the calcite-seawater system. Finally, our new rate determination has implications for modeling of pelagic and seafloor dissolution. Nonlinear dissolution kinetics in a simple 1-D lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth, and also confirm the importance of respiration-driven dissolution in setting the shape of the calcite lysocline.

  13. Biotic and Abiotic Reduction and Solubilization of Pu(IV)O2•xH2O(am) as Affected by Anthraquinone-2,6-disulfonate (AQDS) and Ethylenediaminetetraacetate (EDTA)

    SciTech Connect

    Plymale, Andrew E.; Bailey, Vanessa L.; Fredrickson, Jim K.; Heald, Steve M.; Buck, Edgar C.; Shi, Liang; Wang, Zheming; Resch, Charles T.; Moore, Dean A.; Bolton, Harvey

    2012-01-24

    In the presence of hydrogen (H{sub 2}), the synthetic chelating agent ethylenediaminetetraacetate (EDTA), and the electron shuttle anthraquinone-2,6-disulfonate (AQDS), the dissimilatory metal-reducing bacteria (DMRB) Shewanella oneidensis and Geobacter sulfurreducens both reductively solubilized 100% of added 0.5 mM plutonium (IV) hydrous oxide (Pu(IV)O{sub 2} {lg_bullet} xH{sub 2}O{sub (am)}) in {approx}24 h at pH 7 in a non-complexing buffer. In the absence of AQDS, bioreduction was much slower ({approx}22 days) and less extensive ({approx}83-94%). In the absence of DMRB but under comparable conditions, 89% (without AQDS) to 98% (with AQDS) of added 0.5 mM PuO{sub 2} {lg_bullet} xH{sub 2}O{sub (am)} was reductively solubilized over 418 days. Under comparable conditions but in the absence of EDTA, <0.001% of the 0.5 mM PuO{sub 2} {lg_bullet} xH{sub 2}O{sub (am)} was solubilized, with or without bacteria. However, Pu(aq) increased by as much as an order of magnitude in some EDTA-free treatments, both biotic and abiotic, and increases in solubility were associated with the production of both Pu(OH)3(am) and Pu(III)(aq). Incubation with DMRB in the absence of EDTA increased the polymeric and crystalline content of the PuO{sub 2} {lg_bullet} xH{sub 2}O{sub (am)} and also decreased Pu solubility in 6-N HCl. Results from an in vitro assay demonstrated electron transfer to PuO{sub 2} {lg_bullet} xH{sub 2}O{sub (am)} from the S. oneidensis outer-membrane c-type cytochrome MtrC, and EDTA increased the oxidation of MtrC by PuO{sub 2} {lg_bullet} xH{sub 2}O{sub (am)}. Our results suggest that PuO{sub 2} {lg_bullet} xH{sub 2}O{sub (am)} biotic and abiotic reduction and solubilization may be important in anoxic, reducing environments, especially where complexing ligands and electron shuttling compounds are present.

  14. Analysis of long-term bacterial vs. chemical Fe(III) oxide reduction kinetics

    NASA Astrophysics Data System (ADS)

    Roden, Eric E.

    2004-08-01

    Data from studies of dissimilatory bacterial (10 8 cells mL -1 of Shewanella putrefaciens strain CN32, pH 6.8) and ascorbate (10 mM, pH 3.0) reduction of two synthetic Fe(III) oxide coated sands and three natural Fe(III) oxide-bearing subsurface materials (all at ca. 10 mmol Fe(III) L -1) were analyzed in relation to a generalized rate law for mineral dissolution (J t/m 0 = k'(m/m 0) γ, where J t is the rate of dissolution and/or reduction at time t, m 0 is the initial mass of oxide, and m/m 0 is the unreduced or undissolved mineral fraction) in order to evaluate changes in the apparent reactivity of Fe(III) oxides during long-term biological vs. chemical reduction. The natural Fe(III) oxide assemblages demonstrated larger changes in reactivity (higher γ values in the generalized rate law) compared to the synthetic oxides during long-term abiotic reductive dissolution. No such relationship was evident in the bacterial reduction experiments, in which temporal changes in the apparent reactivity of the natural and synthetic oxides were far greater (5-10 fold higher γ values) than in the abiotic reduction experiments. Kinetic and thermodynamic considerations indicated that neither the abundance of electron donor (lactate) nor the accumulation of aqueous end-products of oxide reduction (Fe(II), acetate, dissolved inorganic carbon) are likely to have posed significant limitations on the long-term kinetics of oxide reduction. Rather, accumulation of biogenic Fe(II) on residual oxide surfaces appeared to play a dominant role in governing the long-term kinetics of bacterial crystalline Fe(III) oxide reduction. The experimental findings together with numerical simulations support a conceptual model of bacterial Fe(III) oxide reduction kinetics that differs fundamentally from established models of abiotic Fe(III) oxide reductive dissolution, and indicate that information on Fe(III) oxide reactivity gained through abiotic reductive dissolution techniques cannot be used to

  15. Diagnosing Abiotic Degradation

    EPA Science Inventory

    The abiotic degradation of chlorinated solvents in ground water can be difficult to diagnose. Under current practice, most of the “evidence” is negative; specifically the apparent disappearance of chlorinated solvents with an accumulation of vinyl chloride, ethane, ethylene, or ...

  16. Effects of Bacillus subtilis endospore surface reactivity on the rate of forsterite dissolution

    NASA Astrophysics Data System (ADS)

    Harrold, Z.; Gorman-Lewis, D.

    2013-12-01

    . Additional analyses including Mg concentrations, microprobe and BET analyses support mineral dissolution rate calculations and stoichiometry considerations. All experimental assays containing endospores show increased forsterite dissolution rates relative to abiotic controls. Forsterite dissolution rates increased by approximately one order of magnitude in dialysis bound, biotic experiments relative to abiotic assays. Homogenous biotic assays exhibited a more complex dissolution rate profile that changes over time. All microbially mediated forsterite dissolution rates returned to abiotic control rates after 10 to 15 days of incubation. This shift in dissolution rate likely corresponds to maximum endospore surface adsorption capacity. The Bacillus subtilis endospore surface serves as a first-order proxy for studying the effect of metabolizing microbe surfaces on silicate dissolution rates. Comparisons with published abiotic, microbial, and organic acid mediated forsterite dissolution rates will provide insight on the importance of bacterial surfaces in primary mineral dissolution processes.

  17. Reductive Sequestration Of Pertechnetate (99TcO4–) By Nano Zerovalent Iron (nZVI) Transformed By Abiotic Sulfide

    SciTech Connect

    Fan, Dimin; Anitori, Roberto; Tebo, Bradley M.; Tratnyek, Paul G.; Lezama Pacheco, Juan S.; Kukkadapu, Ravi K.; Engelhard, Mark H.; Bowden, Mark E.; Kovarik, Libor; Arey, Bruce W.

    2013-04-24

    Under anoxic conditions, soluble 99TcO4– can be reduced to less soluble TcO2•nH2O, but the oxide is highly susceptible to reoxidation. Here we investigate an alternative strategy for remediation of Tc-contaminated groundwater whereby sequestration as Tc sulfide is favored by sulfidic conditions stimulated by nano zero-valent iron (nZVI). nZVI was pre-exposed to increasing concentrations of sulfide in simulated Hanford groundwater for 24 hrs to mimic the stages of aquifer sulfate reduction and onset of biotic sulfidogenesis. Solid-phase characterizations of the sulfidated nZVI confirmed the formation of nanocrystalline FeS phases, but higher S/Fe ratios (>0.112) did not result in the formation of significantly more FeS. The kinetics of Tc sequestration by these materials showed faster Tc removal rates with increasing S/Fe between S/Fe = 0–0.056, but decreasing Tc removal rates with S/Fe > 0.224. The more favorable Tc removal kinetics at low S/Fe could be due to a higher affinity of TcO4– for FeS (over iron oxides), and electron microscopy confirmed that the majority of the Tc was associated with FeS phases. The inhibition of Tc removal at high S/Fe appears to have been caused by excess HS–. X-ray absorption spectroscopy revealed that as S/Fe increased, Tc speciation shifted from TcO2•nH2O to TcS2. The most substantial change of Tc speciation occurred at low S/Fe, coinciding with the rapid increase of Tc removal rate. This agreement further confirms the importance of FeS in Tc sequestration.

  18. Abiotic origin of biopolymers

    NASA Technical Reports Server (NTRS)

    Oro, J.; Stephen-Sherwood, E.

    1976-01-01

    A variety of methods have been investigated in different laboratories for the polymerization of amino acids and nucleotides under abiotic conditions. They include (1) thermal polymerization; (2) direct polymerization of certain amino acid nitriles, amides, or esters; (3) polymerization using polyphosphate esters; (4) polymerization under aqueous or drying conditions at moderate temperatures using a variety of simple catalysts or condensing agents like cyanamide, dicyandiamide, or imidazole; and (5) polymerization under similar mild conditions but employing activated monomers or abiotically synthesized high-energy compounds such as adenosine 5'-triphosphate (ATP). The role and significance of these methods for the synthesis of oligopeptides and oligonucleotides under possible primitive-earth conditions is evaluated. It is concluded that the more recent approach involving chemical processes similar to those used by contemporary living organisms appears to offer a reasonable solution to the prebiotic synthesis of these biopolymers.

  19. Formulations for iron oxides dissolution

    DOEpatents

    Horwitz, Earl P.; Chiarizia, Renato

    1992-01-01

    A mixture of a di- or polyphosphonic acid and a reductant wherein each is present in a sufficient amount to provide a synergistic effect with respect to the dissolution of metal oxides and optionally containing corrosion inhibitors and pH adjusting agents.

  20. Nanosizing of drugs: Effect on dissolution rate.

    PubMed

    Dizaj, S Maleki; Vazifehasl, Zh; Salatin, S; Adibkia, Kh; Javadzadeh, Y

    2015-01-01

    The solubility, bioavailability and dissolution rate of drugs are important parameters for achieving in vivo efficiency. The bioavailability of orally administered drugs depends on their ability to be absorbed via gastrointestinal tract. For drugs belonging to Class II of pharmaceutical classification, the absorption process is limited by drug dissolution rate in gastrointestinal media. Therefore, enhancement of the dissolution rate of these drugs will present improved bioavailability. So far several techniques such as physical and chemical modifications, changing in crystal habits, solid dispersion, complexation, solubilization and liquisolid method have been used to enhance the dissolution rate of poorly water soluble drugs. It seems that improvement of the solubility properties ofpoorly water soluble drugscan translate to an increase in their bioavailability. Nowadays nanotechnology offers various approaches in the area of dissolution enhancement of low aqueous soluble drugs. Nanosizing of drugs in the form of nanoparticles, nanocrystals or nanosuspensions not requiring expensive facilities and equipment or complicated processes may be applied as simple methods to increase the dissolution rate of poorly water soluble drugs. In this article, we attempted to review the effects of nanosizing on improving the dissolution rate of poorly aqueous soluble drugs. According to the reviewed literature, by reduction of drug particle size into nanometer size the total effective surface area is increased and thereby dissolution rate would be enhanced. Additionally, reduction of particle size leads to reduction of the diffusion layer thickness surrounding the drug particles resulting in the increment of the concentration gradient. Each of these process leads to improved bioavailability.

  1. Nanosizing of drugs: Effect on dissolution rate

    PubMed Central

    Dizaj, S. Maleki; Vazifehasl, Zh.; Salatin, S.; Adibkia, Kh.; Javadzadeh, Y.

    2015-01-01

    The solubility, bioavailability and dissolution rate of drugs are important parameters for achieving in vivo efficiency. The bioavailability of orally administered drugs depends on their ability to be absorbed via gastrointestinal tract. For drugs belonging to Class II of pharmaceutical classification, the absorption process is limited by drug dissolution rate in gastrointestinal media. Therefore, enhancement of the dissolution rate of these drugs will present improved bioavailability. So far several techniques such as physical and chemical modifications, changing in crystal habits, solid dispersion, complexation, solubilization and liquisolid method have been used to enhance the dissolution rate of poorly water soluble drugs. It seems that improvement of the solubility properties ofpoorly water soluble drugscan translate to an increase in their bioavailability. Nowadays nanotechnology offers various approaches in the area of dissolution enhancement of low aqueous soluble drugs. Nanosizing of drugs in the form of nanoparticles, nanocrystals or nanosuspensions not requiring expensive facilities and equipment or complicated processes may be applied as simple methods to increase the dissolution rate of poorly water soluble drugs. In this article, we attempted to review the effects of nanosizing on improving the dissolution rate of poorly aqueous soluble drugs. According to the reviewed literature, by reduction of drug particle size into nanometer size the total effective surface area is increased and thereby dissolution rate would be enhanced. Additionally, reduction of particle size leads to reduction of the diffusion layer thickness surrounding the drug particles resulting in the increment of the concentration gradient. Each of these process leads to improved bioavailability. PMID:26487886

  2. Dissolution enhancement of tadalafil by liquisolid technique.

    PubMed

    Lu, Mei; Xing, Haonan; Yang, Tianzhi; Yu, Jiankun; Yang, Zhen; Sun, Yanping; Ding, Pingtian

    2017-02-01

    This study aimed to enhance the dissolution of tadalafil, a poorly water-soluble drug by applying liquisolid technique. The effects of two critical formulation variables, namely drug concentration (17.5% and 35%, w/w) and excipients ratio (10, 15 and 20) on dissolution rates were investigated. Pre-compression tests, including particle size distribution, flowability determination, Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM), were carried out to investigate the mechanism of dissolution enhancement. Tadalafil liquisolid tablets were prepared and their quality control tests, dissolution study, contact angle measurement, Raman mapping, and storage stability test were performed. The results suggested that all the liquisolid tablets exhibited significantly higher dissolution rates than the conventional tablets and pure tadalafil. FT-IR spectrum reflected no drug-excipient interactions. DSC and XRD studies indicated reduction in crystallinity of tadalafil, which was further confirmed by SEM and Raman mapping outcomes. The contact angle measurement demonstrated obvious increase in wetting property. Taken together, the reduction of particle size and crystallinity, and the improvement of wettability were the main mechanisms for the enhanced dissolution rate. No significant changes were observed in drug crystallinity and dissolution behavior after storage based on XRD, SEM and dissolution results.

  3. Abiotic degradation of plastic films

    NASA Astrophysics Data System (ADS)

    Ángeles-López, Y. G.; Gutiérrez-Mayen, A. M.; Velasco-Pérez, M.; Beltrán-Villavicencio, M.; Vázquez-Morillas, A.; Cano-Blanco, M.

    2017-01-01

    Degradable plastics have been promoted as an option to mitigate the environmental impacts of plastic waste. However, there is no certainty about its degradability under different environmental conditions. The effect of accelerated weathering (AW), natural weathering (NW) and thermal oxidation (TO) on different plastics (high density polyethylene, HDPE; oxodegradable high density polyethylene, HDPE-oxo; compostable plastic, Ecovio ® metalized polypropylene, PP; and oxodegradable metalized polypropylene, PP-oxo) was studied. Plastics films were exposed to AW per 110 hours; to NW per 90 days; and to TO per 30 days. Plastic films exposed to AW and NW showed a general loss on mechanical properties. The highest reduction in elongation at break on AW occurred to HDPE-oxo (from 400.4% to 20.9%) and was higher than 90% for HDPE, HDPE-oxo, Ecovio ® and PP-oxo in NW. No substantial evidence of degradation was found on plastics exposed to TO. Oxo-plastics showed higher degradation rates than their conventional counterparts, and the compostable plastic was resistant to degradation in the studied abiotic conditions. This study shows that degradation of plastics in real life conditions will vary depending in both, their composition and the environment.

  4. Microbially mediated barite dissolution in anoxic brines

    USGS Publications Warehouse

    Ouyang, Bingjie; Akob, Denise M.; Dunlap, Darren S.; Renock, Devon

    2017-01-01

    Fluids injected into shale formations during hydraulic fracturing of black shale return with extraordinarily high total-dissolved-solids (TDS) and high concentrations of barium (Ba) and radium (Ra). Barite, BaSO4, has been implicated as a possible source of Ba as well as a problematic mineral scale that forms on internal well surfaces, often in close association with radiobarite, (Ba,Ra)SO4. The dissolution of barite by abiotic processes is well quantified. However, the identification of microbial communities in flowback and produced water necessitates the need to understand barite dissolution in the presence of bacteria. Therefore, we evaluated the rates and mechanisms of abiotic and microbially-mediated barite dissolution under anoxic and hypersaline conditions in the laboratory. Barite dissolution experiments were conducted with bacterial enrichment cultures established from produced water from Marcellus Shale wells located in northcentral Pennsylvania. These cultures were dominated by anaerobic halophilic bacteria from the genus Halanaerobium. Dissolved Ba was determined by ICP-OES and barite surfaces were investigated by SEM and AFM. Our results reveal that: 1) higher amounts of barium (up to ∼5 × ) are released from barite in the presence of Halanaerobium cultures compared to brine controls after 30 days of reaction, 2) etch pits that develop on the barite (001) surface in the presence of Halanaerobium exhibit a morphology that is distinct from those that form during control experiments without bacteria, 3) etch pits that develop in the presence of Halanaerobium exhibit a morphology that is similar to the morphology of etch pits formed in the presence of strong organic chelators, EDTA and DTPA, and 4) experiments using dialysis membranes to separate barite from bacteria suggest that direct contact between the two is not required in order to promote dissolution. These results suggest that Halanaerobium increase the rate of barite dissolution in anoxic and

  5. Boehmite Actual Waste Dissolutions Studies

    SciTech Connect

    Snow, Lanee A.; Lumetta, Gregg J.; Fiskum, Sandra K.; Peterson, Reid A.

    2008-07-15

    The U.S. Department of Energy plans to vitrify approximately 60,000 metric tons of high-level waste (HLW) sludge from underground storage tanks at the Hanford Nuclear Reservation. To reduce the volume of HLW requiring treatment, a goal has been set to remove a significant quantity of the aluminum, which comprises nearly 70 percent of the sludge. Aluminum is found in the form of gibbsite, sodium aluminate and boehmite. Gibbsite and sodium aluminate can be easily dissolved by washing the waste stream with caustic. Boehmite, which comprises nearly half of the total aluminum, is more resistant to caustic dissolution and requires higher treatment temperatures and hydroxide concentrations. Samples were taken from four Hanford tanks and homogenized in order to give a sample that is representative of REDOX (Reduction Oxidation process for Pu recovery) sludge solids. Bench scale testing was performed on the homogenized waste to study the dissolution of boehmite. Dissolution was studied at three different hydroxide concentrations, with each concentration being run at three different temperatures. Samples were taken periodically over the 170 hour runs in order to determine leaching kinetics. Results of the dissolution studies and implications for the proposed processing of these wastes will be discussed.

  6. INFLUENCE OF PH AND OXIDATION-REDUCTION POTENTIAL (EH) ON THE DISSOLUTION OF MERCURY-CONTAINING MINE WASTES FROM THE SULFUR BANK MERCURY MINE

    EPA Science Inventory

    This study was undertaken as a part of developing treatment alternatives for waste materials, primarily waste rock and roaster tailings, from sites contaminated with mercury (Hg) mining wastes. Leaching profiles of waste rock over a range of different pH and oxidation-reduction (...

  7. Abiotic stresses and endophyte effects

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Abiotic stresses consist of nonorganismal, nonpathogenic factors that inhibit plant function. Tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] is widely symbiotic with a naturally occurring endophytic fungus [Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin], which con...

  8. Abiotic tooth enamel

    NASA Astrophysics Data System (ADS)

    Yeom, Bongjun; Sain, Trisha; Lacevic, Naida; Bukharina, Daria; Cha, Sang-Ho; Waas, Anthony M.; Arruda, Ellen M.; Kotov, Nicholas A.

    2017-03-01

    Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix. This structural motif is unusually consistent across all species from all geological eras. Such invariability—especially when juxtaposed with the diversity of other tissues—suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels—we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that light-weight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth’s normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.

  9. Abiotic tooth enamel.

    PubMed

    Yeom, Bongjun; Sain, Trisha; Lacevic, Naida; Bukharina, Daria; Cha, Sang-Ho; Waas, Anthony M; Arruda, Ellen M; Kotov, Nicholas A

    2017-03-01

    Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix. This structural motif is unusually consistent across all species from all geological eras. Such invariability-especially when juxtaposed with the diversity of other tissues-suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels-we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that light-weight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth's normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.

  10. Accelerating Gallstone Dissolution

    PubMed Central

    Tao, J. C.; Cussler, E. L.; Evans, D. F.

    1974-01-01

    The dissolution rates of cholesterol in model bile salt solutions are controlled by diffusion in slowly flowing bile and by interfacial kinetics in rapidly flowing bile. At low flow, dissolution varies with the square root of bile flow and can be predicted, a priori, from existing correlations of mass transfer. At high bile flow, dissolution is independent of bile flow and is probably dominated by the rate of micelle adsorption. These results show that cholesterol gallstone dissolution, a potential nonsurgical therapy for cholelithiasis, can be accelerated little in slow bile, but more significantly in rapidly flowing bile. PMID:4530271

  11. Saltcake Dissolution Simulant Tests

    SciTech Connect

    Martino, C.J.

    2003-02-18

    Small-scale (15 to 50 mL) dissolution equilibrium tests were performed on surrogate waste representing typical saltcake at the Savannah River and Hanford Sites. The primary objectives of this study were to gain a better understanding of the solid-liquid equilibrium of simulated-waste saltcakes and chemistry of the dissolved salt solutions. These tests were performed in preparation for similar dissolution tests with actual-waste saltcakes. Two types of tests (single-wash and multiple-wash) were performed at two temperatures (25 degrees Celsius and 50 degrees Celsius) for each saltcake simulant. The compositions of the supernatant fluids are provided for both types of dissolution tests, and profiles of the elution of each salt component are provided for the multiple-wash tests. The conclusions from these tests follow: (1) For both salt waste surrogates, dissolution of the soluble components was achieved at less than a 2:1 mass ratio of inhibited water to saltcake during multiple-wash tests., (2) Dissolution of the Hanford S-112 simulant resulted in a relatively large weight percentage of residual insoluble material (4.2 wt. percent), which was identified as a mixture of Al(OH)3 phases (bayerite and gibbsite)., and (3) The profiles for the relative elution of anions from saltcake during dissolution exhibit distinctions that are dependent upon the dissolution temperature and the initial saltcake composition.

  12. Continuous plutonium dissolution apparatus

    DOEpatents

    Meyer, F.G.; Tesitor, C.N.

    1974-02-26

    This invention is concerned with continuous dissolution of metals such as plutonium. A high normality acid mixture is fed into a boiler vessel, vaporized, and subsequently condensed as a low normality acid mixture. The mixture is then conveyed to a dissolution vessel and contacted with the plutonium metal to dissolve the plutonium in the dissolution vessel, reacting therewith forming plutonium nitrate. The reaction products are then conveyed to the mixing vessel and maintained soluble by the high normality acid, with separation and removal of the desired constituent. (Official Gazette)

  13. ROS Regulation During Abiotic Stress Responses in Crop Plants.

    PubMed

    You, Jun; Chan, Zhulong

    2015-01-01

    Abiotic stresses such as drought, cold, salt and heat cause reduction of plant growth and loss of crop yield worldwide. Reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide anions (O2 (•-)), hydroxyl radical (OH•) and singlet oxygen ((1)O2) are by-products of physiological metabolisms, and are precisely controlled by enzymatic and non-enzymatic antioxidant defense systems. ROS are significantly accumulated under abiotic stress conditions, which cause oxidative damage and eventually resulting in cell death. Recently, ROS have been also recognized as key players in the complex signaling network of plants stress responses. The involvement of ROS in signal transduction implies that there must be coordinated function of regulation networks to maintain ROS at non-toxic levels in a delicate balancing act between ROS production, involving ROS generating enzymes and the unavoidable production of ROS during basic cellular metabolism, and ROS-scavenging pathways. Increasing evidence showed that ROS play crucial roles in abiotic stress responses of crop plants for the activation of stress-response and defense pathways. More importantly, manipulating ROS levels provides an opportunity to enhance stress tolerances of crop plants under a variety of unfavorable environmental conditions. This review presents an overview of current knowledge about homeostasis regulation of ROS in crop plants. In particular, we summarize the essential proteins that are involved in abiotic stress tolerance of crop plants through ROS regulation. Finally, the challenges toward the improvement of abiotic stress tolerance through ROS regulation in crops are discussed.

  14. ROS Regulation During Abiotic Stress Responses in Crop Plants

    PubMed Central

    You, Jun; Chan, Zhulong

    2015-01-01

    Abiotic stresses such as drought, cold, salt and heat cause reduction of plant growth and loss of crop yield worldwide. Reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide anions (O2•-), hydroxyl radical (OH•) and singlet oxygen (1O2) are by-products of physiological metabolisms, and are precisely controlled by enzymatic and non-enzymatic antioxidant defense systems. ROS are significantly accumulated under abiotic stress conditions, which cause oxidative damage and eventually resulting in cell death. Recently, ROS have been also recognized as key players in the complex signaling network of plants stress responses. The involvement of ROS in signal transduction implies that there must be coordinated function of regulation networks to maintain ROS at non-toxic levels in a delicate balancing act between ROS production, involving ROS generating enzymes and the unavoidable production of ROS during basic cellular metabolism, and ROS-scavenging pathways. Increasing evidence showed that ROS play crucial roles in abiotic stress responses of crop plants for the activation of stress-response and defense pathways. More importantly, manipulating ROS levels provides an opportunity to enhance stress tolerances of crop plants under a variety of unfavorable environmental conditions. This review presents an overview of current knowledge about homeostasis regulation of ROS in crop plants. In particular, we summarize the essential proteins that are involved in abiotic stress tolerance of crop plants through ROS regulation. Finally, the challenges toward the improvement of abiotic stress tolerance through ROS regulation in crops are discussed. PMID:26697045

  15. Abiotic methane formation during experimental serpentinization of olivine.

    PubMed

    McCollom, Thomas M

    2016-12-06

    Fluids circulating through actively serpentinizing systems are often highly enriched in methane (CH4). In many cases, the CH4 in these fluids is thought to derive from abiotic reduction of inorganic carbon, but the conditions under which this process can occur in natural systems remain unclear. In recent years, several studies have reported abiotic formation of CH4 during experimental serpentinization of olivine at temperatures at or below 200 °C. However, these results seem to contradict studies conducted at higher temperatures (300 °C to 400 °C), where substantial kinetic barriers to CH4 synthesis have been observed. Here, the potential for abiotic formation of CH4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 °C to 320 °C. A (13)C-labeled inorganic carbon source was used to unambiguously determine the origin of CH4 generated in the experiments. Consistent with previous high-temperature studies, the results indicate that abiotic formation of CH4 from reduction of dissolved inorganic carbon during the experiments is extremely limited, with nearly all of the observed CH4 derived from background sources. The results indicate that the potential for abiotic synthesis of CH4 in low-temperature serpentinizing environments may be much more limited than some recent studies have suggested. However, more extensive production of CH4 was observed in one experiment performed under conditions that allowed an H2-rich vapor phase to form, suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for abiotic synthesis of CH4.

  16. Abiotic methane formation during experimental serpentinization of olivine

    NASA Astrophysics Data System (ADS)

    McCollom, Thomas M.

    2016-12-01

    Fluids circulating through actively serpentinizing systems are often highly enriched in methane (CH4). In many cases, the CH4 in these fluids is thought to derive from abiotic reduction of inorganic carbon, but the conditions under which this process can occur in natural systems remain unclear. In recent years, several studies have reported abiotic formation of CH4 during experimental serpentinization of olivine at temperatures at or below 200 °C. However, these results seem to contradict studies conducted at higher temperatures (300 °C to 400 °C), where substantial kinetic barriers to CH4 synthesis have been observed. Here, the potential for abiotic formation of CH4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 °C to 320 °C. A 13C-labeled inorganic carbon source was used to unambiguously determine the origin of CH4 generated in the experiments. Consistent with previous high-temperature studies, the results indicate that abiotic formation of CH4 from reduction of dissolved inorganic carbon during the experiments is extremely limited, with nearly all of the observed CH4 derived from background sources. The results indicate that the potential for abiotic synthesis of CH4 in low-temperature serpentinizing environments may be much more limited than some recent studies have suggested. However, more extensive production of CH4 was observed in one experiment performed under conditions that allowed an H2-rich vapor phase to form, suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for abiotic synthesis of CH4.

  17. Abiotic Dissolved Organic Matter-Mineral Interaction in the Karstic Floridan Aquifer

    NASA Astrophysics Data System (ADS)

    Jin, J.; Zimmerman, A.

    2007-12-01

    Dissolved organic matter (DOM)-mineral interaction (e.g. adsorption, desorption, mineral dissolution) in groundwater is a significant factor controlling geochemical, environmental and microbial processes and may be helpful in efforts to track groundwater sources or contaminant fate. Despite its importance, the dynamics and consequences of these abiotic interactions remain poorly understood, largely due to the inaccessibility and heterogeneity of the subsurface, as well as the chemical complexity of DOM. This study models the OM-mineral interactions that takes place in the Floridan aquifer through laboratory adsorption-desorption experiments using DOM (groundwater, river water, soil extracts) and carbonate minerals (calcite, dolomite) collected in north Florida. High performance liquid chromatography-size exclusion chromatography (HPLC-SEC) and UV-fluorescence excitation-emission matrix (EEM) spectrophotometry was used to examine the organic compound types exhibiting preferential affinity for carbonate minerals. Our results show that the DOM-carbonate adsorption/desorption isotherms are well described by the Freundlich model. Freundlich exponents (average value: 0.6488) less than one indicated a filling of adsorption sites. Minerals from Ocala tend to have higher adsorption affinity as well as adsorption capacity than those from Suwannee River Basin; however, both were found to have mineral dissolution. Two fluorescent signals, indicative of a fulvic-like (at excitation wavelength 295-310 nm, emission 400-420 nm) and a protein-like (275/345nm) moiety, were detected in DOM. A reduction in the fulvic-like peak intensity occurred following carbonate adsorption while the protein-like peaks remain almost unchanged indicating the preferential adsorption of fulvic acids. HPLC-SEC results (DOM properties as a function of molecular weight) will be discussed. The chemical properties of DOM in environmental groundwater samples will also be presented and evaluated in light of

  18. Dissolution of Platinum in the Operational Range of Fuel Cells

    PubMed Central

    Keeley, Gareth P.; Geiger, Simon; Zeradjanin, Aleksandar R.; Hodnik, Nejc; Kulyk, Nadiia

    2015-01-01

    Abstract One of the most important practical issues in low‐temperature fuel‐cell catalyst degradation is platinum dissolution. According to the literature, it initiates at 0.6–0.9 VRHE, whereas previous time‐ and potential‐resolved inductively coupled plasma mass spectrometry (ICP–MS) experiments, however, revealed dissolution onset at only 1.05 VRHE. In this manuscript, the apparent discrepancy is addressed by investigating bulk and nanoparticulated catalysts. It is shown that, given enough time for accumulation, traces of platinum can be detected at potentials as low as 0.85 VRHE. At these low potentials, anodic dissolution is the dominant process, whereas, at more positive potentials, more platinum dissolves during the oxide reduction after accumulation. Interestingly, the potential and time dissolution dependence is similar for both types of electrode. Dissolution processes are discussed with relevance to fuel‐cell operation and plausible dissolution mechanisms are considered. PMID:27525206

  19. Modeling of the structure-specific kinetics of abiotic, dark reduction of Hg(II) complexed by O/N and S functional groups in humic acids while accounting for time-dependent structural rearrangement

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Redox transformations involving electron transfer from natural organic matter (NOM) are important for the mercury (Hg) biogeochemical cycle. In the water column light drives the reduction of Hg(II) to Hg(0), whereas in soils and sediments dark reduction of Hg(II) is of greater importance. The object...

  20. Calcination/dissolution residue treatment

    SciTech Connect

    Knight, R.C.; Creed, R.F.; Patello, G.K.; Hollenberg, G.W.; Buehler, M.F.; O`Rourke, S.M.; Visnapuu, A.; McLaughlin, D.F.

    1994-09-01

    Currently, high-level wastes are stored underground in steel-lined tanks at the Hanford site. Current plans call for the chemical pretreatment of these wastes before their immobilization in stable glass waste forms. One candidate pretreatment approach, calcination/dissolution, performs an alkaline fusion of the waste and creates a high-level/low-level partition based on the aqueous solubilities of the components of the product calcine. Literature and laboratory studies were conducted with the goal of finding a residue treatment technology that would decrease the quantity of high-level waste glass required following calcination/dissolution waste processing. Four elements, Fe, Ni, Bi, and U, postulated to be present in the high-level residue fraction were identified as being key to the quantity of high-level glass formed. Laboratory tests of the candidate technologies with simulant high-level residues showed reductive roasting followed by carbonyl volatilization to be successful in removing Fe, Ni, and Bi. Subsequent bench-scale tests on residues from calcination/dissolution processing of genuine Hanford Site tank waste showed Fe was separated with radioelement decontamination factors of 70 to 1,000 times with respect to total alpha activity. Thermodynamic analyses of the calcination of five typical Hanford Site tank waste compositions also were performed. The analyses showed sodium hydroxide to be the sole molten component in the waste calcine and emphasized the requirement for waste blending if fluid calcines are to be achieved. Other calcine phases identified in the thermodynamic analysis indicate the significant thermal reconstitution accomplished in calcination.

  1. Bioenhanced dissolution of dense non-aqueous phase of trichloroethylene as affected by iron reducing conditions: model systems and environmental samples.

    PubMed

    Paul, Laiby; Smolders, Erik

    2015-01-01

    The anaerobic biotransformation of trichloroethylene (TCE) can be affected by competing electron acceptors such as Fe (III). This study assessed the role of Fe (III) reduction on the bioenhanced dissolution of TCE dense non-aqueous phase liquid (DNAPL). Columns were set up as 1-D diffusion cells consisting of a lower DNAPL layer, a layer with an aquifer substratum and an upper water layer that is regularly refreshed. The substrata used were either inert sand or sand coated with 2-line ferrihydrite (HFO) or two environmental Fe (III) containing samples. The columns were inoculated with KB-1 and were repeatedly fed with formate. In none of the diffusion cells, vinyl chloride or ethene was detected while dissolved and extractable Fe (II) increased strongly during 60 d of incubation. The cis-DCE concentration peaked at 4.0 cm from the DNAPL (inert sand) while it was at 3.4 cm (sand+HFO), 1.7 cm and 2.5 cm (environmental samples). The TCE concentration gradients near the DNAPL indicate that the DNAPL dissolution rate was larger than that in an abiotic cell by factors 1.3 (inert sand), 1.0 (sand+HFO) and 2.2 (both environmental samples). This results show that high bioavailable Fe (III) in HFO reduces the TCE degradation by competitive Fe (III) reduction, yielding lower bioenhanced dissolution. However, Fe (III) reduction in environmental samples was not reducing TCE degradation and the dissolution factor was even larger than that of inert sand. It is speculated that physical factors, e.g. micro-niches in the environmental samples protect microorganisms from toxic concentrations of TCE.

  2. Biologically mediated dissolution of volcanic glass in seawater

    NASA Astrophysics Data System (ADS)

    Staudigel, H.; Yayanos, A.; Chastain, R.; Davies, G.; Verdurmen, E. A. Th; Schiffman, P.; Bourcier, R.; De Baar, H.

    1998-12-01

    We studied the effects of biological mediation on the dissolution of basaltic glass in seawater. Experiments with typical seawater microbial populations were contrasted with a sterile control, and reactions were monitored chemically and isotopically. Biologically mediated experiments produce twice the mass of authigenic phases than abiotic experiments and the phases are different. Abiotic alteration of glass dissolves basaltic Si and Ca and scavenges seawater Mg, while biotic alteration removes Ca from seawater. Such opposing behavior of Ca and Mg in biotic and abiotic alteration of basaltic glass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater. 87Sr/ 86Sr data of glass and alteration products suggest that biological mediation enhances both the diffusion of seawater Sr into glass by a factor of 3-4, and the dissolution of basaltic Sr into seawater by a factor of 20-40. The dependence of chemical exchange processes between seawater and glass on biological activity implies that chemical fluxes from water-rock interaction at low temperatures may change as life on Earth evolves.

  3. HEPA filter dissolution process

    DOEpatents

    Brewer, K.N.; Murphy, J.A.

    1994-02-22

    A process is described for dissolution of spent high efficiency particulate air (HEPA) filters and then combining the complexed filter solution with other radioactive wastes prior to calcining the mixed and blended waste feed. The process is an alternate to a prior method of acid leaching the spent filters which is an inefficient method of treating spent HEPA filters for disposal. 4 figures.

  4. Hepa filter dissolution process

    DOEpatents

    Brewer, Ken N.; Murphy, James A.

    1994-01-01

    A process for dissolution of spent high efficiency particulate air (HEPA) filters and then combining the complexed filter solution with other radioactive wastes prior to calcining the mixed and blended waste feed. The process is an alternate to a prior method of acid leaching the spent filters which is an inefficient method of treating spent HEPA filters for disposal.

  5. Mergers, Annexations, Dissolutions

    ERIC Educational Resources Information Center

    Russo, Alexander

    2006-01-01

    Consolidations come in all shapes and sizes, including mergers, annexations and dissolutions. They do not all take place under state mandate, however. A handful of districts consolidate every year in some states like Illinois that have large numbers of small districts, many of them dual districts that serve K-8 or 9-12 in the same geographic area.…

  6. HEPA filter dissolution process

    SciTech Connect

    Brewer, K.N.; Murphy, J.A.

    1992-12-31

    This invention is comprised of a process for dissolution of spent high efficiency particulate air (HEPA) filters and then combining the complexed filter solution with other radioactive wastes prior to calcining the mixed and blended waste feed. The process is an alternate to a prior method of acid leaching the spent filters which is an inefficient method of treating spent HEPA filters for disposal.

  7. Oxidative Dissolution of UO2 in a Simulated Groundwater Containing Synthetic Nanocrystalline Mackinawite

    SciTech Connect

    Bi, Yuqiang; Hyun, Sung Pil; Kukkadapu, Ravi K.; Hayes, Kim F.

    2013-02-01

    The long-term success of in situ reductive immobilization of uranium (U) depends on the stability of U(IV) precipitates (e.g., uraninite) under oxic conditions. Field and laboratory studies have implicated iron sulfide minerals as redox buffers or oxidant scavengers that may slow oxidation of reduced U(VI) solid phases by oxygen and Fe(III). Yet, the inhibition mechanism(s) and reaction rates of uraninite (UO2) oxidative dissolution by oxic species such as oxygen in FeS-bearing systems remain largely unresolved. To address this knowledge gap, abiotic batch experiments were conducted with synthetic UO2 in the presence and absence of synthetic mackinawite (FeS) under simulated groundwater conditions of pH = 7, PO2 = 0.02 atm, and PCO2 = 0.05 atm (equivalent to total dissolved carbonate of 0.01 M). The kinetic profiles of dissolved uranium indicate that FeS inhibited UO2 dissolution for 51 hr by effectively scavenging oxygen and keeping dissolved oxygen (DO) low. During this time period, oxidation of structural Fe(II) and S(-II) of FeS were found to control the DO levels, leading to the formation of iron oxyhydroxides and elemental sulfur, respectively, as verified by X-ray diffraction (XRD), Mössbauer and X-ray absorption spectroscopy (XAS). After FeS was depleted due to oxidation, DO levels increased and UO2 oxidative dissolution occurred at an initial rate of rm = 1.2 ± 0.4 ×10-8 mol•g-1•s-1, higher than rm = 5.4 ± 0.3 ×10-9 mol•g-1•s-1 in the control experiment where FeS was absent. Soluble U(VI) products were adsorbed by iron oxyhydroxides (i.e. nanogoethite and ferrihydrite) formed from FeS oxidation, which facilitated the detachment of U(VI) surface complexes and more rapid dissolution of UO2. XAS analysis confirmed the adsorption of U(VI) species, and also showed that U(VI) was not significantly incorporated into iron oxyhydroxide structure. This work reveals that both the oxygen scavenging by FeS and the adsorption of U(VI) to FeS oxidation

  8. Syntrophic Effects in a Subsurface Clostridial Consortium on Fe(III)-(Oxyhydr)oxide Reduction and Secondary Mineralization

    SciTech Connect

    Shah, Madhavi; Lin, Chu-Ching; Kukkadapu, Ravi K.; Engelhard, Mark H.; Zhao, Xiuhong; Wang, Yangping; Barkay, Tamar; Yee, Nathan

    2013-07-09

    In this study, we cultivated from subsurface sediments an anaerobic Clostridia 25 consortium that was composed of a fermentative Fe-reducer Clostridium species (designated as 26 strain FGH) and a novel sulfate-reducing bacterium belonging to the Clostridia family 27 Vellionellaceae (designated as strain RU4). In pure culture, Clostridium sp. strain FGH mediated 28 the reductive dissolution/transformation of iron oxides during growth on peptone. When 29 Clostridium sp. FGH was grown with strain RU4 on peptone, the rates of iron oxide reduction 30 were significantly higher. Iron reduction by the consortium was mediated by multiple 31 mechanisms, including biotic reduction by Clostridium sp. FGH and biotic/abiotic reactions 32 involving biogenic sulfide by strain RU4. The Clostridium sp. FGH produced hydrogen during 33 fermentation, and the presence of hydrogen inhibited growth and iron reduction activity. The 34 sulfate-reducing partner strain RU4 was stimulated by the presence of H2 gas and generated 35 reactive sulfide which promoted the chemical reduction of the iron oxides. Characterization of 36 Fe(II) mineral products showed the formation of magnetite during ferrihydrite reduction, and 37 the precipitation of iron sulfides during goethite and hematite reduction. The results suggest an 38 important pathway for iron reduction and secondary mineralization by fermentative sulfate-39 reducing microbial consortia is through syntrophy-driven biotic/abiotic reactions with biogenic 40 sulfide.

  9. Abiotic Organic Chemistry in Hydrothermal Systems.

    NASA Astrophysics Data System (ADS)

    Simoneit, B. R.; Rushdi, A. I.

    2004-12-01

    Abiotic organic chemistry in hydrothermal systems is of interest to biologists, geochemists and oceanographers. This chemistry consists of thermal alteration of organic matter and minor prebiotic synthesis of organic compounds. Thermal alteration has been extensively documented to yield petroleum and heavy bitumen products from contemporary organic detritus. Carbon dioxide, carbon monoxide, ammonia and sulfur species have been used as precursors in prebiotic synthesis experiments to organic compounds. These inorganic species are common components of hot spring gases and marine hydrothermal systems. It is of interest to further test their reactivities in reductive aqueous thermolysis. We have synthesized organic compounds (lipids) in aqueous solutions of oxalic acid, and with carbon disulfide or ammonium bicarbonate at temperatures from 175-400° C. The synthetic lipids from oxalic acid solutions consisted of n-alkanols, n-alkanoic acids, n-alkyl formates, n-alkanones, n-alkenes and n-alkanes, typically to C30 with no carbon number preferences. The products from CS2 in acidic aqueous solutions yielded cyclic thioalkanes, alkyl polysulfides, and thioesters with other numerous minor compounds. The synthesis products from oxalic acid and ammonium bicarbonate solutions were homologous series of n-alkyl amides, n-alkyl amines, n-alkanes and n-alkanoic acids, also to C30 with no carbon number predominance. Condensation (dehydration) reactions also occur under elevated temperatures in aqueous medium as tested by model reactions to form amide, ester and nitrile bonds. It is concluded that the abiotic formation of aliphatic lipids, condensation products (amides, esters, nitriles, and CS2 derivatives (alkyl polysulfides, cyclic polysulfides) is possible under hydrothermal conditions and warrants further studies.

  10. DISSOLUTION OF FISSILE MATERIALS CONTAINING TANTALUM METAL

    SciTech Connect

    Rudisill, T; Mark Crowder, M; Michael Bronikowski, M

    2007-05-29

    of fluoride by the Pu. The fluoride became unavailable to catalyze the dissolution of PuO{sub 2} as it formed on the surface of the metal. The mass of Pu dissolved is equivalent to the dissolution of 343 g of Pu in the HB-Line dissolvers. In the initial experiment with 0.175 M KF in the solution, we achieved complete dissolution of the Pu in 6 h. The mass of Pu dissolved scales to the dissolution of 358 g of Pu in the HB-Line dissolvers. The second experiment using 0.175 M KF was terminated after approximately 6 h following the dissolution of 92.7% of the Pu in the sample; however, dissolution of additional Pu was severely limited due to the slow dissolution rate observed beyond approximately 4 h. A small amount of PuO{sub 2} was also produced in the solution. The slow rate of dissolution was attributed to the diminishing surface area of the Pu and a reduction in the fluoride activity due to complexation with Pu. Given time (>4 h), the Pu metal may have dissolved using the original solution or a significant portion may have oxidized to PuO{sub 2}. If the metal oxidized to PuO{sub 2}, we expect little of the material would have dissolved due to the fluoride complexation and the low HNO{sub 3} concentration. The mass of Pu dissolved in the second experiment scales to the dissolution of 309 g of Pu in the HB-Line dissolvers. Based on the data from the Pu/Ta dissolution experiments we recommend the use of 4 M HNO{sub 3} containing 0.175 M KF for the dissolution of 300 g of Pu metal in the 15 L HB-Line dissolver. A dissolution temperature of nominally 95 C should allow for essentially complete dissolution of the metal in 6 h. Although the H{sub 2} concentration in the offgas from the experiments was at or below the detection limit of the gas chromatograph (GC) used in these experiments, small concentrations (<3 vol %) of H{sub 2} are typically produced in the offgas during Pu metal dissolutions. Therefore, appropriate controls must be established to address the small H

  11. Determinants of marriage dissolution

    NASA Astrophysics Data System (ADS)

    Rahim, Mohd Amirul Rafiq Abu; Shafie, Siti Aishah Mohd; Hadi, Az'lina Abdul; Razali, Nornadiah Mohd; Azid @ Maarof, Nur Niswah Naslina

    2015-10-01

    Nowadays, the number of divorce cases among Muslim couples is very worrisome whereby the total cases reported in 2013 increased by half of the total cases reported in the previous year. The questions on the true key factors of dissolution of marriage continue to arise. Thus, the objective of this study is to reveal the factors that contribute to the dissolution of marriage. A total of 181 cases and ten potential determinants were included in this study. The potential determinants considered were age at marriage of husband and wife, educational level of husband and wife, employment status of husband and wife, income of husband and wife, the number of children and the presence at a counseling session. Logistic regression analysis was used to analyze the data. The findings revealed that four determinants, namely the income of husband and wife, number of children and the presence at a counselling session were significant in predicting the likelihood of divorce among Muslim couples.

  12. Distinguishing Biotic from Abiotic Phosphate Oxygen Isotopic Signatures

    NASA Astrophysics Data System (ADS)

    Blake, R.; Moyer, C.; Colman, A.; Liang, Y.; Dogru, D.

    2006-05-01

    On earth, phosphate has a strong biological oxygen isotope signature due to its concentration and intense cycling by living organisms as an essential nutrient. Phosphate does not undergo oxygen isotope exchange with water at low temperature without enzymatic catalysis, making the oxygen isotope ratio (18O/16O) of phosphate, δ18OP, an attractive biosignature in the search for early and extraterrestrial life. Recent laboratory and field studies have demonstrated that the δ18OP value of dissolved inorganic phosphate (PO4) records specific microbial activity and enzymatic reaction pathways in both laboratory cultures and natural waters/sediments (Blake et al., 2005; Colman et al 2005; Liang and Blake, 2005). Phosphate oxygen isotope biosignatures may be distinguished from abiotic signatures by: (1) evaluating the degree of temperature-dependent PO4-water oxygen isotope exchange in aqueous systems and deviation from equilibrium; and (2) evolution from an abiotic P reservoir signature towards a biotic P reservoir signature. Important abiotic processes potentially affecting phosphate δ18OP values include dissolution/precipitation, adsorption/desorption, recrystallization of PO4 mineral phases, diagenesis and metamorphism. For most of these processes, the recording, retention and alteration of δ18OP biosignatures have not been evaluated. Deep-sea hydrothermal vent fields are an ideal system in which to study the preservation and alteration of δ18OP biosignatures, as well as potential look-alikes produced by heat-promoted PO4 -water oxygen isotope exchange. Results from recent studies of δ18OP biosignatures in hydrothermal deposits near 9 and 21 degrees N. EPR and at Loihi seamount will be presented.

  13. Abiotic pyrite formation produces a large Fe isotope fractionation.

    PubMed

    Guilbaud, Romain; Butler, Ian B; Ellam, Rob M

    2011-06-24

    The iron isotope composition of sedimentary pyrite has been proposed as a potential proxy to trace microbial metabolism and the redox evolution of the oceans. We demonstrate that Fe isotope fractionation accompanies abiotic pyrite formation in the absence of Fe(II) redox change. Combined fractionation factors between Fe(II)(aq), mackinawite, and pyrite permit the generation of pyrite with Fe isotope signatures that nearly encapsulate the full range of sedimentary δ(56)Fe(pyrite) recorded in Archean to modern sediments. We propose that Archean negative Fe isotope excursions reflect partial Fe(II)(aq) utilization during abiotic pyrite formation rather than microbial dissimilatory Fe(III) reduction. Late Proterozoic to modern sediments may reflect greater Fe(II)(aq) utilization and variations in source composition.

  14. Solubility limits on radionuclide dissolution

    SciTech Connect

    Kerrisk, J.F.

    1984-12-31

    This paper examines the effects of solubility in limiting dissolution rates of a number of important radionuclides from spent fuel and high-level waste. Two simple dissolution models were used for calculations that would be characteristics of a Yucca Mountain repository. A saturation-limited dissolution model, in which the water flowing through the repository is assumed to be saturated with each waste element, is very conservative in that it overestimates dissolution rates. A diffusion-limited dissolution model, in which element-dissolution rates are limited by diffusion of waste elements into water flowing past the waste, is more realistic, but it is subject to some uncertainty at this time. Dissolution rates of some elements (Pu, Am, Sn, Th, Zr, Sm) are always limited by solubility. Dissolution rates of other elements (Cs, Tc, Np, Sr, C, I) are never solubility limited; their release would be limited by dissolution of the bulk waste form. Still other elements (U, Cm, Ni, Ra) show solubility-limited dissolution under some conditions. 9 references, 3 tables.

  15. Understanding the dissolution of zeolites.

    PubMed

    Hartman, Ryan L; Fogler, H Scott

    2007-05-08

    Scientific knowledge of how zeolites, a unique classification of microporous aluminosilicates, undergo dissolution in aqueous hydrochloric acid solutions is limited. Understanding the dissolution of zeolites is fundamental to a number of processes occurring in nature and throughout industry. To better understand the dissolution process, experiments were carried out establishing that the Si-to-Al ratio controls zeolite framework dissolution, by which the selective removal of aluminum constrains the removal of silicon. Stoichiometric dissolution is observed for Type 4A zeolite in HCl where the Si-to-Al ratio is equal to 1.0. Framework silicon dissolves completely during Type 4A dissolution and is followed by silicate precipitation. However, for the zeolite analcime which has a Si-to-Al ratio of 2.0 dissolves non-stoichiometrically as the selective removal of aluminum results in partially dissolved silicate particles followed by silicate precipitation. In Type Y zeolite, exhibiting a Si-to-Al ratio of 3.0, there is insufficient aluminum to weaken the structure and cause silicon to dissolve in HCl. Thus, little or no precipitation is observed, and amorphous undissolvable silicate particles remain intact. The initial dissolution rates of Type Y and 4A zeolites demonstrate that dissolution is constrained by the number of available reaction sites, and a selective removal rate parameter is applied to delineate the mechanism of particle dissolution by demonstrating the kinetic influence of the Si-to-Al ratio. Zeolite framework models are constructed and used to undergird the basic dissolution mechanism. The framework models, scanning electron micrographs of partially dissolved crystals, and experimentally measured dissolution rates all demonstrate that a zeolite's Si-to-Al framework ratio plays a universal role in the dissolution mechanism, independent of framework type. Consequently, the unique mechanism of zeolite dissolution has general implications on how petroleum

  16. Abiotic Versus Biotic Weathering Of Olivine As Possible Biosignatures

    NASA Technical Reports Server (NTRS)

    Longazo, Teresa G.; Wentworth, Susan J.; Clemett, Simon J.; Southam, Gordon; McKay, David S.

    2001-01-01

    We are investigating the weathering of silicate minerals by both purely inorganic, and biologically mediated processes using field-emission scanning electron microscopy (FESEM) and energy dispersive x-ray spectroscopy (EDS). By resolving surface textures and chemical compositions of weathered surfaces at the sub-micron scale we hope to be able to distinguish abiotic from biotic weathering processes and so establish a new biosignature applicable to the study of astromaterials including but not limited to the Martian meteorites. Sterilized olivine grains (San Carlos, Arizona) no more than 1-2 mm in their longest dimension were optically assayed to be uniform in color and free of inclusions were selected as weathering subjects. Prior to all experiments surface morphologies and Fe/Mg ratios were determined for each grain using FE-SEM and EDS. Experiments were divided into two categories abiotic and biotic and were compared with "naturally" weathered samples. For the preliminary experiments, two trials (open and closed to the ambient laboratory environment) were performed under abiotic conditions, and three trials under biotic conditions (control, day 1 and day 2). The open system abiotic trials used sterile grains heated at 98 C and 200 C for both 24 and 48 hours in 1L double distilled de-ionized water. The closed system abiotic trials were conducted under the same conditions but in a sealed two layer steel/Teflon "bomb" apparatus. The biotic trials used sterile grains mounted in a flow-through device attached to a wellhead on the Columbia River aquifer. Several discolored, altered, grains were selected to document "natural" weathering surface textures for comparison with the experimental samples. Preliminary results indicate there are qualitative differences in weathered surface textures among all the designed experiments. The olivine grains in abiotic trials displayed etching, pitting, denticulate margins, dissolution and clay formation. The scale of the features

  17. Direct observation of microbial inhibition of calcite dissolution.

    PubMed

    Lüttge, Andreas; Conrad, Pamela G

    2004-03-01

    Vertical scanning interferometry (VSI) provides a method for quantification of surface topography at the angstrom to nanometer level. Time-dependent VSI measurements can be used to study the surface-normal retreat across crystal and other solid surfaces during dissolution or corrosion processes. Therefore, VSI can be used to directly and nondestructively measure mineral dissolution rates with high precision. We have used this method to compare the abiotic dissolution behavior of a representative calcite (CaCO(3)) cleavage face with that observed upon addition of an environmental microbe, Shewanella oneidensis MR-1, to the crystal surface. From our direct observations, we have concluded that the presence of the microbes results in a significant inhibition of the rate of calcite dissolution. This inhibition appears to be a 2nd-order effect that is related to the formation of etch pits. The opening of etch pits was greatly inhibited in the presence of added bacteria, suggesting that the bacterial cells exert their effect by inhibiting the formation of etch pits at high-energy sites at the crystal surface caused by lattice defects, e.g., screw or point dislocations. The experimental methodology thus provides a nondestructive, directly quantifiable, and easily visualized view of the interactions of microbes and minerals during weathering (or corrosion) processes or during mineral precipitation.

  18. Oxidative dissolution of UO2 in a simulated groundwater containing synthetic nanocrystalline mackinawite

    NASA Astrophysics Data System (ADS)

    Bi, Yuqiang; Hyun, Sung Pil; Kukkadapu, Ravi K.; Hayes, Kim F.

    2013-02-01

    The long-term success of in situ reductive immobilization of uranium (U) depends on the stability of U(IV) precipitates (e.g., uraninite) in the presence of natural oxidants, such as oxygen, Fe(III) hydroxides, and nitrite. Field and laboratory studies have implicated iron sulfide minerals as redox buffers or oxidant scavengers that may slow oxidation of reduced U(IV) solid phases. Yet, the inhibition mechanism(s) and reaction rates of uraninite (UO2) oxidative dissolution by oxic species such as oxygen in FeS-bearing systems remain largely unresolved. To address this knowledge gap, abiotic batch experiments were conducted with synthetic UO2 in the presence and absence of synthetic mackinawite (FeS) under simulated groundwater conditions of pH = 7, P = 0.02 atm, and P = 0.05 atm. The kinetic profiles of dissolved uranium indicate that FeS inhibited UO2 dissolution for about 51 h by effectively scavenging oxygen and keeping dissolved oxygen (DO) low. During this time period, oxidation of structural Fe(II) and S(-II) of FeS were found to control the DO levels, leading to the formation of iron oxyhydroxides and elemental sulfur, respectively, as verified by X-ray diffraction (XRD), Mössbauer, and X-ray absorption spectroscopy (XAS). After FeS was depleted due to oxidation, DO levels increased and UO2 oxidative dissolution occurred at an initial rate of rm = 1.2 ± 0.4 × 10-8 mol g-1 s-1, higher than rm = 5.4 ± 0.3 × 10-9 mol g-1 s-1 in the control experiment where FeS was absent. XAS analysis confirmed that soluble U(VI)-carbonato complexes were adsorbed by iron oxyhydroxides (i.e., nanogoethite and lepidocrocite) formed from FeS oxidation, which provided a sink for U(VI) retention. This work reveals that both the oxygen scavenging by FeS and the adsorption of U(VI) to FeS oxidation products may be important in U reductive immobilization systems subject to redox cycling events.

  19. Dissolution of Hausmannite (Mn(3)O(4)) in the Presence of the Trihydroxamate Siderophore Desferrioxamine B

    SciTech Connect

    Pena, J.; Duckworth, O.W.; Bargar, J.R.; Sposito, G.

    2009-06-02

    That microbial siderophores may be mediators of Mn(III) biogeochemistry is suggested by recent studies showing that these well known Fe(III)-chelating ligands form very stable Mn(III) aqueous complexes. In this study, we examine the influence of desferrioxamine B (DFOB), a trihydroxamate siderophore, on the dissolution of hausmannite, a mixed valence Mn(II,III) oxide found in soils and freshwater sediments. Batch dissolution experiments were conducted both in the absence (pH 4-9) and in the presence of 100 {mu}M DFOB (pH 5-9). In the absence of the ligand, there is a sharp decrease in the extent of proton-promoted dissolution above pH 5 and no appreciable dissolution above pH 8. The resulting aqueous Mn{sup 2+} activities were in good agreement with previous studies, indirectly supporting the accepted two-step mechanism involving the formation of manganite and reprecipitation of hausmannite. Desferrioxamine B enhanced hausmannite dissolution over the entire pH range investigated, both via the formation of a Mn(III) complex and through surface-catalyzed reductive dissolution. Above pH 8, non-reductive ligand-promoted dissolution dominated, whereas below pH 8, dissolution was non-stoichiometric with respect to DFOB. Concurrent proton-promoted, ligand-promoted, reductive, and induced dissolution was observed, with Mn release by either reductive or induced dissolution increasing linearly with decreasing pH. The fast kinetics of the DFOB-promoted dissolution of hausmannite, as compared to iron oxides, suggest that the siderophore-promoted dissolution of Mn(III)-bearing minerals may compete with the siderophore-promoted dissolution of Fe(III)-bearing minerals.

  20. Dissolution of hausmannite (Mn 3O 4) in the presence of the trihydroxamate siderophore desferrioxamine B

    NASA Astrophysics Data System (ADS)

    Peña, Jasquelin; Duckworth, Owen W.; Bargar, John R.; Sposito, Garrison

    2007-12-01

    That microbial siderophores may be mediators of Mn(III) biogeochemistry is suggested by recent studies showing that these well known Fe(III)-chelating ligands form very stable Mn(III) aqueous complexes. In this study, we examine the influence of desferrioxamine B (DFOB), a trihydroxamate siderophore, on the dissolution of hausmannite, a mixed valence Mn(II, III) oxide found in soils and freshwater sediments. Batch dissolution experiments were conducted both in the absence (pH 4-9) and in the presence of 100 μM DFOB (pH 5-9). In the absence of the ligand, there is a sharp decrease in the extent of proton-promoted dissolution above pH 5 and no appreciable dissolution above pH 8. The resulting aqueous Mn 2+ activities were in good agreement with previous studies, indirectly supporting the accepted two-step mechanism involving the formation of manganite and reprecipitation of hausmannite. Desferrioxamine B enhanced hausmannite dissolution over the entire pH range investigated, both via the formation of a Mn(III) complex and through surface-catalyzed reductive dissolution. Above pH 8, non-reductive ligand-promoted dissolution dominated, whereas below pH 8, dissolution was non-stoichiometric with respect to DFOB. Concurrent proton-promoted, ligand-promoted, reductive, and induced dissolution was observed, with Mn release by either reductive or induced dissolution increasing linearly with decreasing pH. The fast kinetics of the DFOB-promoted dissolution of hausmannite, as compared to iron oxides, suggest that the siderophore-promoted dissolution of Mn(III)-bearing minerals may compete with the siderophore-promoted dissolution of Fe(III)-bearing minerals.

  1. Plutonium dissolution process

    DOEpatents

    Vest, Michael A.; Fink, Samuel D.; Karraker, David G.; Moore, Edwin N.; Holcomb, H. Perry

    1996-01-01

    A two-step process for dissolving plutonium metal, which two steps can be carried out sequentially or simultaneously. Plutonium metal is exposed to a first mixture containing approximately 1.0M-1.67M sulfamic acid and 0.0025M-0.1M fluoride, the mixture having been heated to a temperature between 45.degree. C. and 70.degree. C. The mixture will dissolve a first portion of the plutonium metal but leave a portion of the plutonium in an oxide residue. Then, a mineral acid and additional fluoride are added to dissolve the residue. Alteratively, nitric acid in a concentration between approximately 0.05M and 0.067M is added to the first mixture to dissolve the residue as it is produced. Hydrogen released during the dissolution process is diluted with nitrogen.

  2. Plutonium dissolution process

    DOEpatents

    Vest, M.A.; Fink, S.D.; Karraker, D.G.; Moore, E.N.; Holcomb, H.P.

    1994-01-01

    A two-step process for dissolving Pu metal is disclosed in which two steps can be carried out sequentially or simultaneously. Pu metal is exposed to a first mixture of 1.0-1.67 M sulfamic acid and 0.0025-0.1 M fluoride, the mixture having been heated to 45-70 C. The mixture will dissolve a first portion of the Pu metal but leave a portion of the Pu in an oxide residue. Then, a mineral acid and additional fluoride are added to dissolve the residue. Alternatively, nitric acid between 0.05 and 0.067 M is added to the first mixture to dissolve the residue as it is produced. Hydrogen released during the dissolution is diluted with nitrogen.

  3. Siderophore-promoted Dissolution of Cobalt from Hydroxide Minerals

    SciTech Connect

    Bi, Y.; Hesterberg, D; Duckworth, O

    2010-01-01

    Recent research has revealed that siderophores, a class of biogenic ligands with high affinities for Fe(III), can also strongly complex Co(III), an element essential to the normal metabolic function of microbes and animals. This study was conducted to quantify the rates and identify the products and mechanisms of the siderophore-promoted dissolution of Co from synthetic Co-bearing minerals. The dissolution reactions of heterogenite (CoOOH) and four Co-substituted goethites (Co-FeOOH) containing different Co concentrations were investigated in the presence of a trihydroxamate siderophore, desferrioxamine B (DFOB), using batch and flow-through experiments. Results showed that DFOB-promoted dissolution of Co from Co-bearing minerals may occur via pH-dependent ligand-promoted or reductive dissolution mechanisms. For heterogenite, ligand-promoted dissolution was the dominant pathway at neutral to alkaline pH, while production of dissolved Co(II) for pH <6. It was not possible from our data to decouple the separate contributions of homogenous and heterogeneous reduction reactions to the aqueous Co(II) pool. Cobalt substitution in Co-substituted goethite, possibly caused by distortion of goethite structure and increased lattice strain, resulted in enhanced total dissolution rates of both Co and Fe. The DFOB-promoted dissolution rates of Co-bearing minerals, coupled with the high affinity of Co(III) for DFOB, suggest that siderophores may be effective for increasing Co solubility, and thus possibly Co bioavailability. The results also suggest that siderophores may contribute to the mobilization of radioactive {sup 60}Co from Co-bearing mineral phases through mineral weathering and dissolution processes.

  4. Siderophore-promoted dissolution of cobalt from hydroxide minerals

    NASA Astrophysics Data System (ADS)

    Bi, Yuqiang; Hesterberg, Dean L.; Duckworth, Owen W.

    2010-05-01

    Recent research has revealed that siderophores, a class of biogenic ligands with high affinities for Fe(III), can also strongly complex Co(III), an element essential to the normal metabolic function of microbes and animals. This study was conducted to quantify the rates and identify the products and mechanisms of the siderophore-promoted dissolution of Co from synthetic Co-bearing minerals. The dissolution reactions of heterogenite (CoOOH) and four Co-substituted goethites (Co-FeOOH) containing different Co concentrations were investigated in the presence of a trihydroxamate siderophore, desferrioxamine B (DFOB), using batch and flow-through experiments. Results showed that DFOB-promoted dissolution of Co from Co-bearing minerals may occur via pH-dependent ligand-promoted or reductive dissolution mechanisms. For heterogenite, ligand-promoted dissolution was the dominant pathway at neutral to alkaline pH, while production of dissolved Co(II) for pH <6. It was not possible from our data to decouple the separate contributions of homogenous and heterogeneous reduction reactions to the aqueous Co(II) pool. Cobalt substitution in Co-substituted goethite, possibly caused by distortion of goethite structure and increased lattice strain, resulted in enhanced total dissolution rates of both Co and Fe. The DFOB-promoted dissolution rates of Co-bearing minerals, coupled with the high affinity of Co(III) for DFOB, suggest that siderophores may be effective for increasing Co solubility, and thus possibly Co bioavailability. The results also suggest that siderophores may contribute to the mobilization of radioactive 60Co from Co-bearing mineral phases through mineral weathering and dissolution processes.

  5. Salicylic acid-induced abiotic stress tolerance and underlying mechanisms in plants

    PubMed Central

    Khan, M. Iqbal R.; Fatma, Mehar; Per, Tasir S.; Anjum, Naser A.; Khan, Nafees A.

    2015-01-01

    Abiotic stresses (such as metals/metalloids, salinity, ozone, UV-B radiation, extreme temperatures, and drought) are among the most challenging threats to agricultural system and economic yield of crop plants. These stresses (in isolation and/or combination) induce numerous adverse effects in plants, impair biochemical/physiological and molecular processes, and eventually cause severe reductions in plant growth, development and overall productivity. Phytohormones have been recognized as a strong tool for sustainably alleviating adverse effects of abiotic stresses in crop plants. In particular, the significance of salicylic acid (SA) has been increasingly recognized in improved plant abiotic stress-tolerance via SA-mediated control of major plant-metabolic processes. However, the basic biochemical/physiological and molecular mechanisms that potentially underpin SA-induced plant-tolerance to major abiotic stresses remain least discussed. Based on recent reports, this paper: (a) overviews historical background and biosynthesis of SA under both optimal and stressful environments in plants; (b) critically appraises the role of SA in plants exposed to major abiotic stresses; (c) cross-talks potential mechanisms potentially governing SA-induced plant abiotic stress-tolerance; and finally (d) briefly highlights major aspects so far unexplored in the current context. PMID:26175738

  6. One-dimensional model for biogeochemical interactions and permeability reduction in soils during leachate permeation.

    PubMed

    Singhal, Naresh; Islam, Jahangir

    2008-02-19

    This paper uses the findings from a column study to develop a reactive model for exploring the interactions occurring in leachate-contaminated soils. The changes occurring in the concentrations of acetic acid, sulphate, suspended and attached biomass, Fe(II), Mn(II), calcium, carbonate ions, and pH in the column are assessed. The mathematical model considers geochemical equilibrium, kinetic biodegradation, precipitation-dissolution reactions, bacterial and substrate transport, and permeability reduction arising from bacterial growth and gas production. A two-step sequential operator splitting method is used to solve the coupled transport and biogeochemical reaction equations. The model gives satisfactory fits to experimental data and the simulations show that the transport of metals in soil is controlled by multiple competing biotic and abiotic reactions. These findings suggest that bioaccumulation and gas formation, compared to chemical precipitation, have a larger influence on hydraulic conductivity reduction.

  7. Abiotic Reductive Dechlorination of Tetrachloroethylene and Trichloroethylene in Anaerobic Environments

    DTIC Science & Technology

    2009-01-15

    the Presence of Chloride Green Rust (GR- Cl), pyrite , Sulfate Green Rust (GR-SO4), and Magnetite at pH 8. Lines Represent a Pseudo first-order Model...Rust (GR- Cl), Pyrite , Sulfate Green Rust (GR-SO4), and Magnetite at pH 8. Lines Represent a Pseudo first-order Model fit. The Insets Show Reaction...Rust (GR-Cl) and Pyrite at pH 8. Lines Represent a Rayleigh Model Fit. Uncertainties are 95% Confidence Intervals Calculated by Nonlinear Regression

  8. ABIOTIC REDUCTION AND DETOXIFICATION OF CHROMATE PRESENT IN SOILS

    EPA Science Inventory

    Theoretical and experimental research has supported the assertion that Cr(III) species are the most stable, immobile, and nontoxic forms of chromium and that they may form rapidly when adequate reducing agents are introduced in an oxidized soil environment. The objective of this ...

  9. DEMONSTRATION BULLETIN: METAL-ENHANCED ABIOTIC DEGRADATION TECHNOLOGY - ENVIROMETAL TECHNOLOGIES, INC.

    EPA Science Inventory

    EnviroMetal Technologies, Inc. (ETI), of Guelph, ON, Canada, has developed the metal-enhanced abiotic degradation technology to treat halogenated volatile organic compounds (VOC) in water. A reactive, zero-valent, granular iron medium causes reductive dehalogenation of VOCs yield...

  10. Interactions between gravity currents and convective dissolution

    NASA Astrophysics Data System (ADS)

    Elenius, M. T.; Voskov, D. V.; Tchelepi, H. A.

    2015-09-01

    Geological storage of carbon dioxide (CO2) is a promising technology for reducing atmospheric emissions. The large discrepancy in the time- and length-scales between up-dip migration of buoyant supercritical CO2 and the sinking fingers of dissolved CO2 poses a challenge for numerical simulations aimed at describing the fate of the plume. Hence, several investigators have suggested methods to simplify the problem, but to date there has been no reference solution with which these simplified models can be compared. We investigate the full problem of Darcy-based two-phase flow with gravity-current propagation and miscible convective mixing, using high-resolution numerical simulations. We build on recent developments of the Automatic Differentiation - General Purpose Research Simulator (AD-GPRS) at Stanford. The results show a CO2 plume that travels for 5000 years reaching a final distance of 14 km up-dip from the injection site. It takes another 2000 years before the CO2 is completely trapped as residual (40%) and dissolved (60%) CO2. Dissolution causes a significant reduction of the plume speed. While fingers of dissolved CO2 appear under the propagating gravity current, the resident brine does not become fully saturated with CO2 anywhere under the plume. The overall mass transfer of CO2 into the brine under the plume remains practically constant for several thousands of years. These results can be used as a benchmark for verification, or improvements, of simplified (reduced-dimensionality, upscaled) models. Our results indicate that simplified models need to account for: (i) reduced dissolution due to interaction with the plume, and (ii) gradual reduction of the local dissolution rate after the fingers begin to interact with the bottom of the aquifer.

  11. 12 CFR 146.4 - Voluntary dissolution.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 12 Banks and Banking 1 2014-01-01 2014-01-01 false Voluntary dissolution. 146.4 Section 146.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 146.4 Voluntary dissolution. (a) A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  12. 12 CFR 146.4 - Voluntary dissolution.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 12 Banks and Banking 1 2012-01-01 2012-01-01 false Voluntary dissolution. 146.4 Section 146.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 146.4 Voluntary dissolution. (a) A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  13. 12 CFR 146.4 - Voluntary dissolution.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 12 Banks and Banking 1 2013-01-01 2013-01-01 false Voluntary dissolution. 146.4 Section 146.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 146.4 Voluntary dissolution. (a) A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  14. 12 CFR 546.4 - Voluntary dissolution.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 12 Banks and Banking 5 2010-01-01 2010-01-01 false Voluntary dissolution. 546.4 Section 546.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  15. 12 CFR 546.4 - Voluntary dissolution.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 12 Banks and Banking 6 2014-01-01 2012-01-01 true Voluntary dissolution. 546.4 Section 546.4 Banks... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  16. 12 CFR 546.4 - Voluntary dissolution.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 12 Banks and Banking 6 2013-01-01 2012-01-01 true Voluntary dissolution. 546.4 Section 546.4 Banks... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  17. 12 CFR 546.4 - Voluntary dissolution.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 12 Banks and Banking 5 2011-01-01 2011-01-01 false Voluntary dissolution. 546.4 Section 546.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  18. 12 CFR 546.4 - Voluntary dissolution.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 12 Banks and Banking 6 2012-01-01 2012-01-01 false Voluntary dissolution. 546.4 Section 546.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The...

  19. Pathways for abiotic organic synthesis at submarine hydrothermal fields

    PubMed Central

    McDermott, Jill M.; Seewald, Jeffrey S.; German, Christopher R.; Sylva, Sean P.

    2015-01-01

    Arguments for an abiotic origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H2-rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the abiotic generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for abiotic organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H2 generation during active serpentinization. Rather, our results indicate that CH4 found in vent fluids is formed in H2-rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond. PMID:26056279

  20. Pathways for abiotic organic synthesis at submarine hydrothermal fields.

    PubMed

    McDermott, Jill M; Seewald, Jeffrey S; German, Christopher R; Sylva, Sean P

    2015-06-23

    Arguments for an abiotic origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H2-rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the abiotic generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for abiotic organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H2 generation during active serpentinization. Rather, our results indicate that CH4 found in vent fluids is formed in H2-rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond.

  1. Bacterial dissolution of fluorapatite as a possible source of elevated dissolved phosphate in the environment

    NASA Astrophysics Data System (ADS)

    Feng, Mu-hua; Ngwenya, Bryne T.; Wang, Lin; Li, Wenchao; Olive, Valerie; Ellam, Robert M.

    2011-10-01

    In order to understand the contribution of geogenic phosphorus to lake eutrophication, we have investigated the rate and extent of fluorapatite dissolution in the presence of two common soil bacteria ( Pantoea agglomerans and Bacillus megaterium) at T = 25 °C for 26 days. The release of calcium (Ca), phosphorus (P), and rare earth elements (REE) under biotic and abiotic conditions was compared to investigate the effect of microorganism on apatite dissolution. The release of Ca and P was enhanced under the influence of bacteria. Apatite dissolution rates obtained from solution Ca concentration in the biotic reactors increased above error compared with abiotic controls. Chemical analysis of biomass showed that bacteria scavenged Ca, P, and REE during their growth, which lowered their fluid concentrations, leading to apparent lower release rates. The temporal evolution of pH in the reactors reflected the balance of apatite weathering, solution reactions, bacterial metabolism, and potentially secondary precipitation, which was implied in the variety of REE patterns in the biotic and abiotic reactors. Light rare earth elements (LREE) were preferentially adsorbed to cell surfaces, whereas heavy rare earth elements (HREE) were retained in the fluid phase. Decoupling of LREE and HREE could possibly be due to preferential release of HREE from apatite or selective secondary precipitation of LREE enriched phosphates, especially in the presence of bacteria. When corrected for intracellular concentrations, both biotic reactors showed high P and REE release compared with the abiotic control. We speculate that lack of this correction explains the conflicting findings about the role of bacteria in mineral weathering rates. The observation that bacteria enhance the release rates of P and REE from apatite could account for some of the phosphorus burden and metal pollution in aquatic environments.

  2. Low Temperature Aluminum Dissolution Of Sludge Waste

    SciTech Connect

    Keefer, M.T.; Hamm, B.A.; Pike, J.A.

    2008-07-01

    High Level Waste (HLW) at the Savannah River Site (SRS) is currently stored in aging underground storage tanks. This waste is a complex mixture of insoluble solids, referred to as sludge, and soluble salts. Continued long-term storage of these radioactive wastes poses an environmental risk. The sludge is currently being stabilized in the Defense Waste Processing Facility (DWPF) through a vitrification process immobilizing the waste in a borosilicate glass matrix for long-term storage in a federal repository. Without additional treatment, the existing volume of sludge would produce nearly 8000 canisters of vitrified waste. Aluminum compounds, along with other non-radioactive components, represent a significant portion of the sludge mass currently planned for vitrification processing in DWPF. Removing the aluminum from the waste stream reduces the volume of sludge requiring vitrification and improves production rates. Treating the sludge with a concentrated sodium hydroxide (caustic) solution at elevated temperatures (>90 deg. C) to remove aluminum is part of an overall sludge mass reduction effort to reduce the number of vitrified canisters, shorten the life cycle for the HLW system, and reduce the risk associated with the long term storage of radioactive wastes at SRS. A projected reduction of nearly 900 canisters will be achieved by performing aluminum dissolution on six targeted sludge batches; however, a project to develop and install equipment will not be ready for operation until 2013. The associated upgrades necessary to implement a high temperature process in existing facilities are costly and present many technical challenges. Efforts to better understand the characteristics of the sludge mass and dissolution kinetics are warranted to overcome these challenges. Opportunities to further reduce the amount of vitrified waste and increase production rates should also be pursued. Sludge staged in Tank 51 as the next sludge batch for feed to DWPF consisted

  3. Alginic Acid Accelerates Calcite Dissolution

    NASA Astrophysics Data System (ADS)

    Perry, T. D.; Duckworth, O. W.; McNamara, C. J.; Martin, S. T.; Mitchell, R.

    2003-12-01

    Accelerated carbonate weathering through biological activity affects both geochemical cycling and the local pH and alkalinity of terrestrial and marine waters. Microbes affect carbonate dissolution through metabolic activity, production of acidic or chelating exudates, and cation binding by cell walls. Dissolution occurs within microbial biofilms - communities of microorganisms attached to stone in an exopolymer matrix. We investigated the effect of alginic acid, a common biological polymer produced by bacteria and algae, on calcite dissolution using a paired atomic force microscopy/flow-through reactor apparatus. The alginic acid caused up to an order of magnitude increase in dissolution rate at 3 < pH < 12. Additionally, the polymer preferentially binds to the obtuse pit steps and increases step velocity. We propose that the polymer is actively chelating surficial cations reducing the activation energy and increasing dissolution rate. The role of biologically produced polymers in mineral weathering is important in the protection of cultural heritage materials and understanding of marine and terrestrial systems.

  4. Abiotic Bromination of Soil Organic Matter.

    PubMed

    Leri, Alessandra C; Ravel, Bruce

    2015-11-17

    Biogeochemical transformations of plant-derived soil organic matter (SOM) involve complex abiotic and microbially mediated reactions. One such reaction is halogenation, which occurs naturally in the soil environment and has been associated with enzymatic activity of decomposer organisms. Building on a recent finding that naturally produced organobromine is ubiquitous in SOM, we hypothesized that inorganic bromide could be subject to abiotic oxidations resulting in bromination of SOM. Through lab-based degradation treatments of plant material and soil humus, we have shown that abiotic bromination of particulate organic matter occurs in the presence of a range of inorganic oxidants, including hydrogen peroxide and assorted forms of ferric iron, producing both aliphatic and aromatic forms of organobromine. Bromination of oak and pine litter is limited primarily by bromide concentration. Fresh plant material is more susceptible to bromination than decayed litter and soil humus, due to a labile pool of mainly aliphatic compounds that break down during early stages of SOM formation. As the first evidence of abiotic bromination of particulate SOM, this study identifies a mechanistic source of the natural organobromine in humic substances and the soil organic horizon. Formation of organobromine through oxidative treatments of plant material also provides insights into the relative stability of aromatic and aliphatic components of SOM.

  5. RBM25 Mediates Abiotic Responses in Plants

    PubMed Central

    Cheng, Chunhong; Wang, Zhijuan; Yuan, Bingjian; Li, Xia

    2017-01-01

    Alternative splicing (AS) of pre-mRNAs is one of the most important post-transcriptional regulations that enable a single gene to code for multiple proteins resulting in the biodiversity of proteins in eukaryotes. Recently, we have shown that an Arabidopsis thaliana RNA recognition motif-containing protein RBM25 is a novel splicing factor to modulate plant response to ABA during seed germination and post-germination through regulating HAB1 pre-mRNA AS. Here, we show that RBM25 is preferentially expressed in stomata and vascular tissues in Arabidopsis and is induced by ABA and abiotic stresses. Loss-of-function mutant is highly tolerant to drought and sensitive to salt stress. Bioinformatic analysis and expression assays reveal that Arabidopsis RBM25 is induced by multiple abiotic stresses, suggesting a crucial role of RBM25 in Arabidopsis responses to adverse environmental conditions. Furthermore, we provide a comprehensive characterization of the homologous genes of Arabidopsis RBM25 based on the latest plant genome sequences and public microarray databases. Fourteen homologous genes are identified in different plant species which show similar structure in gene and protein. Notably, the promoter analysis reveals that RBM25 homologs are likely controlled by the regulators involved in multiple plant growth and abiotic stresses, such as drought and unfavorable temperature. The comparative analysis of general and unique cis regulatory elements of the RBM25 homologs highlights the conserved and unique molecular processes that modulate plant response to abiotic stresses through RBM25-mediated alternative splicing. PMID:28344583

  6. RBM25 Mediates Abiotic Responses in Plants.

    PubMed

    Cheng, Chunhong; Wang, Zhijuan; Yuan, Bingjian; Li, Xia

    2017-01-01

    Alternative splicing (AS) of pre-mRNAs is one of the most important post-transcriptional regulations that enable a single gene to code for multiple proteins resulting in the biodiversity of proteins in eukaryotes. Recently, we have shown that an Arabidopsis thaliana RNA recognition motif-containing protein RBM25 is a novel splicing factor to modulate plant response to ABA during seed germination and post-germination through regulating HAB1 pre-mRNA AS. Here, we show that RBM25 is preferentially expressed in stomata and vascular tissues in Arabidopsis and is induced by ABA and abiotic stresses. Loss-of-function mutant is highly tolerant to drought and sensitive to salt stress. Bioinformatic analysis and expression assays reveal that Arabidopsis RBM25 is induced by multiple abiotic stresses, suggesting a crucial role of RBM25 in Arabidopsis responses to adverse environmental conditions. Furthermore, we provide a comprehensive characterization of the homologous genes of Arabidopsis RBM25 based on the latest plant genome sequences and public microarray databases. Fourteen homologous genes are identified in different plant species which show similar structure in gene and protein. Notably, the promoter analysis reveals that RBM25 homologs are likely controlled by the regulators involved in multiple plant growth and abiotic stresses, such as drought and unfavorable temperature. The comparative analysis of general and unique cis regulatory elements of the RBM25 homologs highlights the conserved and unique molecular processes that modulate plant response to abiotic stresses through RBM25-mediated alternative splicing.

  7. Evaluation of abiotic fate mechanisms in soil slurry bioreactor treatment

    SciTech Connect

    Glaser, J.A.; McCauley, P.T.; Dosani, M.A.

    1995-10-01

    Biological treatment of contaminated soil slurries may offer a viable technology for soil bioremediation. Slurry bioreactor treatment of soils, however, has not sufficiently progressed to be a durable, reliable, and cost-effective treatment option. Critical to the evaluation of slurry bioreactors is a better description of pollutant mass transfer during the treatment phase. Losses attributable to abiotic means are generally overlooked in field application of the technology. Discussions with EPA regional personnel and inspection of active soil slurry bioreactor operations have identified operational problems such as foaming which could result in possible abiotic loss. Field bioslurry operations have adopted various approaches to reduce foaming: (1) the addition of defoaming agents, (2) the reduction of rotational speed of the agitator, and (3) the reduction of gas flow through the bioreactor system. We have conducted two bench-scale slurry bioreactor treatability studies, at the U.S. EPA Testing & Evaluation Facility in Cincinnati, Ohio, which were designed to investigate some of the operating factors leading to foam formation and identify the most advantageous means to deal with foaming. The initial study has been previously presented as a general treatability study for treatment of creosote contamination in a soil. During this study, foaming became a major problem for operation. The foaming conditions were mitigated by use of defoamer and, in the more extreme cases, through reduction of the mixer rotational speed and gas flow. A subsequent study which was devoted specifically to investigating the causes and conditions of foaming using a different batch of soil from the same site as the earlier study showed little foaming at the very beginning of the study.

  8. Influence of abiotic factors on the antimicrobial activity of chitosan.

    PubMed

    Tavaria, Freni K; Costa, Eduardo M; Gens, Eduardo J; Malcata, Francisco Xavier; Pintado, Manuela E

    2013-12-01

    In an effort to bypass the adverse secondary effects attributed to the traditional therapeutic approaches used to treat skin disorders (such as atopic dermatitis), alternative antimicrobials have recently been suggested. One such antimicrobial is chitosan, owing to the already proved biological properties associated with its use. However, the influence of abiotic factors on such activities warrants evaluation. This research effort assessed the antimicrobial activity of chitosan upon skin microorganisms (Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli) in vitro when subject to a combination of different abiotic factors such as pH, ionic strength, organic acids and free fatty acids. Free fatty acids, ionic strength and pH significantly affected chitosan's capability of reducing the viable numbers of S. aureus. This antimicrobial action was potentiated in the presence of palmitic acid and a lower ionic strength (0.2% NaCl), while a higher ionic strength (0.4% NaCl) favored chitosan's action upon the reduction of viable numbers of S. epidermidis and E. coli. Although further studies are needed, these preliminary results advocate that chitosan can in the future be potentially considered as an antimicrobial of choice when handling symptoms associated with atopic dermatitis.

  9. Selective dissolution in binary alloys

    NASA Astrophysics Data System (ADS)

    McCall, Carol Rene

    Corrosion is an important issue in the design of engineering alloys. De-alloying is an aspect of alloy corrosion related to the selective dissolution of one or more of the components in an alloy. The work reported herein focuses on the topic of de-alloying specific to single-phase binary noble metal alloy systems. The alloy systems investigated were gold-silver and gold-copper. The onset of a bulk selective dissolution process is typically marked by a critical potential whereby the more reactive component in the alloy begins dissolving from the bulk, leading to the formation of a bi-continuous solid-void morphology. The critical potential was investigated for the entire composition range of gold-silver alloys. The results presented herein include the formulation of an expression for critical potential as a function of both alloy and electrolyte composition. Results of the first investigation of underpotential deposition (UPD) on alloys are also presented herein. These results were implemented as an analytical tool to provide quantitative measurements of the surface evolution of gold during de-alloying. The region below the critical potential was investigated in terms of the compositional evolution of the alloy surface. Below the critical potential, there is a competition between the dissolution of the more reactive alloying constituent (either silver or copper) and surface diffusion of gold that serves to cover dissolution sites and prevent bulk dissolution. By holding the potential at a prescribed value below the critical potential, a time-dependent gold enrichment occurs on the alloy surface leading to passivation. A theoretical model was developed to predict the surface enrichment of gold based on the assumption of layer-by-layer dissolution of the more reactive alloy constituent. The UPD measurements were used to measure the time-dependent surface gold concentration and the results agreed with the predictions of the theoretical model.

  10. Principles of Calcite Dissolution in Human and Artificial Otoconia

    PubMed Central

    Walther, Leif Erik; Blödow, Alexander; Buder, Jana; Kniep, Rüdiger

    2014-01-01

    Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (calcite gelatin nanocomposits) and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV. PMID:25048115

  11. Chemical Reactivity Probes for Assessing Abiotic Natural Attenuation by Reducing Iron Minerals.

    PubMed

    Fan, Dimin; Bradley, Miranda J; Hinkle, Adrian W; Johnson, Richard L; Tratnyek, Paul G

    2016-02-16

    Increasing recognition that abiotic natural attenuation (NA) of chlorinated solvents can be important has created demand for improved methods to characterize the redox properties of the aquifer materials that are responsible for abiotic NA. This study explores one promising approach: using chemical reactivity probes (CRPs) to characterize the thermodynamic and kinetic aspects of contaminant reduction by reducing iron minerals. Assays of thermodynamic CRPs were developed to determine the reduction potentials (ECRP) of suspended minerals by spectrophotometric determination of equilibrium CRP speciation and calculations using the Nernst equation. ECRP varied as expected with mineral type, mineral loading, and Fe(II) concentration. Comparison of ECRP with reduction potentials measured potentiometrically using a Pt electrode (EPt) showed that ECRP was 100-150 mV more negative than EPt. When EPt was measured with small additions of CRPs, the systematic difference between EPt and ECRP was eliminated, suggesting that these CRPs are effective mediators of electron transfer between mineral and electrode surfaces. Model contaminants (4-chloronitrobenzene, 2-chloroacetophenone, and carbon tetrachloride) were used as kinetic CRPs. The reduction rate constants of kinetic CRPs correlated well with the ECRP for mineral suspensions. Using the rate constants compiled from literature for contaminants and relative mineral reduction potentials based on ECRP measurements, qualitatively consistent trends were obtained, suggesting that CRP-based assays may be useful for estimating abiotic NA rates of contaminants in groundwater.

  12. In vitro dissolution methodology, mini-Gastrointestinal Simulator (mGIS), predicts better in vivo dissolution of a weak base drug, dasatinib.

    PubMed

    Tsume, Yasuhiro; Takeuchi, Susumu; Matsui, Kazuki; Amidon, Gregory E; Amidon, Gordon L

    2015-08-30

    USP apparatus I and II are gold standard methodologies for determining the in vitro dissolution profiles of test drugs. However, it is difficult to use in vitro dissolution results to predict in vivo dissolution, particularly the pH-dependent solubility of weak acid and base drugs, because the USP apparatus contains one vessel with a fixed pH for the test drug, limiting insight into in vivo drug dissolution of weak acid and weak base drugs. This discrepancy underscores the need to develop new in vitro dissolution methodology that better predicts in vivo response to assure the therapeutic efficacy and safety of oral drug products. Thus, the development of the in vivo predictive dissolution (IPD) methodology is necessitated. The major goals of in vitro dissolution are to ensure the performance of oral drug products and the support of drug formulation design, including bioequivalence (BE). Orally administered anticancer drugs, such as dasatinib and erlotinib (tyrosine kinase inhibitors), are used to treat various types of cancer. These drugs are weak bases that exhibit pH-dependent and high solubility in the acidic stomach and low solubility in the small intestine (>pH 6.0). Therefore, these drugs supersaturate and/or precipitate when they move from the stomach to the small intestine. Also of importance, gastric acidity for cancer patients may be altered with aging (reduction of gastric fluid secretion) and/or co-administration of acid-reducing agents. These may result in changes to the dissolution profiles of weak base and the reduction of drug absorption and efficacy. In vitro dissolution methodologies that assess the impact of these physiological changes in the GI condition are expected to better predict in vivo dissolution of oral medications for patients and, hence, better assess efficacy, toxicity and safety concerns. The objective of this present study is to determine the initial conditions for a mini-Gastrointestinal Simulator (mGIS) to assess in vivo

  13. Enzymatic activity in the presence of surfactants commonly used in dissolution media, Part 1: Pepsin.

    PubMed

    Guzman, Maria L; Marques, Margareth R; Olivera Me, Maria E; Stippler, Erika S

    2016-01-01

    The United States Pharmacopeia (USP) General Chapters Dissolution 〈711〉 and Disintegration and Dissolution of Dietary Supplements 〈2040〉 allows the use of enzymes in dissolution media when gelatin capsules do not conform to dissolution specifications due to cross linking. Possible interactions between enzymes and surfactants when used together in dissolution media could result in loss of the enzymatic activity. Pepsin is an enzyme commonly used in dissolution media, and in this work, the activity of pepsin was determined in the presence of different surfactants as usually found in case of dissolution tests of certain gelatin capsule formulations. Pepsin enzymatic activity was determined according to the Ninth Edition of the Food Chemicals Codex (FCC) 9 method, in dissolution conditions: simulated gastric fluid, 37 °C and 50 rpm. Sodium dodecyl sulfate (SDS), cetyltrimethyl ammonium bromide (CTAB), polysorbate 80 (Tween 80) and octoxynol 9 (Triton X100) in concentrations above and below their critical micellar concentrations were selected. Results showed a significant reduction in the activity of pepsin at all the concentrations of SDS assayed. On the contrary, CTAB, Tween 80, and Triton X100 did not alter the enzymatic activity at of pepsin any of the concentration assayed. This data demonstrates a rational selection of the surfactant to be used when pepsin is required in dissolution test.

  14. High temperature dissolution of chromium substituted nickel ferrite in nitrilotriacetic acid medium

    NASA Astrophysics Data System (ADS)

    Sathyaseelan, V. S.; Chandramohan, P.; Velmurugan, S.

    2016-12-01

    High temperature (HT) dissolution of chromium substituted nickel ferrite was carried out with relevance to the decontamination of nuclear reactors by way of chemical dissolution of contaminated corrosion product oxides present on stainless steel coolant circuit surfaces. Chromium substituted nickel ferrites of composition, NiFe(2-x)CrxO4 (x ≤ 1), was synthetically prepared and characterized. HT dissolution of these oxides was carried out in nitrilotriacetic acid medium at 160 °C. Dissolution was remarkably increased at 160 °C when compared to at 85 °C in a reducing decontamination formulation. Complete dissolution could be achieved for the oxides with chromium content 0 and 0.2. Increasing the chromium content brought about a marked reduction in the dissolution rate. About 40 fold decrease in rate of dissolution was observed when chromium was increased from 0 to 1. The rate of dissolution was not very significantly reduced in the presence of N2H4. Dissolution of oxide was found to be stoichiometric.

  15. Dissolution of biogenic and synthetic UO2 under varied reducing conditions.

    PubMed

    Ulrich, Kai-Uwe; Singh, Abhas; Schofield, Eleanor J; Bargar, John R; Veeramani, Harish; Sharp, Jonathan O; Bernier-Latmani, Rizlan; Giammar, Daniel E

    2008-08-01

    The chemical stability of biogenic UO2, a nanoparticulate product of environmental bioremediation, may be impacted by the particles' surface free energy, structural defects, and compositional variability in analogy to abiotic UO(2+x) (0 < or = x < or = 0.25). This study quantifies and compares intrinsic solubility and dissolution rate constants of biogenic nano-UO2 and synthetic bulk UO2.00, taking molecular-scale structure into account. Rates were determined under anoxic conditions as a function of pH and dissolved inorganic carbon in continuous-flow experiments. The dissolution rates of biogenic and synthetic UO2 solids were lowest at near neutral pH and increased with decreasing pH. Similar surface area-normalized rates of biogenic and synthetic UO2 suggest comparable reactive surface site densities. This finding is consistent with the identified structural homology of biogenic UO2 and stoichiometric UO2.00 Compared to carbonate-free anoxic conditions, dissolved inorganic carbon accelerated the dissolution rate of biogenic UO2 by 3 orders of magnitude. This phenomenon suggests continuous surface oxidation of U(IV) to U(VI), with detachment of U(VI) as the rate-determining step in dissolution. Although reducing conditions were maintained throughout the experiments, the UO2 surface can be oxidized by water and radiogenic oxidants. Even in anoxic aquifers, UO2 dissolution may be controlled by surface U(VI) rather than U(IV) phases.

  16. Bacterially enhanced dissolution of meta-autunite

    SciTech Connect

    Smeaton, C.M.; Weisener, C.G.; Burns, P.C.; Fryer, B.J.; Fowle, D.A.

    2008-12-15

    The release of U from the mineral meta-autunite {l_brace}Ca[(UO{sub 2})(PO{sub 2})](H{sub 2}O){sub 6}{r_brace} was evaluated using spectroscopy, aqueous geochemistry, and electron microscopy in a minimal media with the dissimilatory metal-reducing bacterium Shewanella putrefaciens 200R. The onset of anaerobic conditions resulted in the rapid release of U and phosphate to solution followed by the reprecipitation of meta-autinite. Spectroscopy measurements (XANES) indicated that the U was not released via reduction during the bacterial incubations, but instead dissolution was promoted by uptake and immobilization of P by the bacterial cells. Our results suggest that U(VI) in 'refractory' P mineral phases may be mobilized from U mill tailings and/or U disposal sites and that the nutrient status (P) of the geologic setting may be a predictor for the lability of U in these environments.

  17. Siderophore-manganese(lll) Interactions. II. Manganite dissolution promoted by desferrioxamine B.

    PubMed

    Duckworth, Owen W; Sposito, Garrison

    2005-08-15

    Recent laboratory and field studies suggest that Mn(lll) forms persistent aqueous complexes with high-affinity ligands. Aqueous Mn(lll) species thus may play a significant but largely unexplored role in biogeochemical processes. One formation mechanism for these species is the dissolution of Mn(lll)-bearing minerals. To investigate this mechanism, we measured the steady-state dissolution rates of manganite (gamma-MnOOH) in the presence of desferrioxamine B (DFOB), a common trihydroxamate siderophore. We find that DFOB dissolves manganite by both reductive and nonreductive reaction pathways. For pH > 6.5, a nonreductive ligand-promoted reaction is the dominant dissolution pathway, with a steady-state dissolution rate proportional to the surface concentration of DFOB. In the absence of reductants, the aqueous Mn(lIl)HDFOB+ complex resulting from dissolution is stable for at least several weeks at circumneutral to alkaline pH and at 25 degrees C. For pH < 6.5, Mn2+ is the dominant aqueous species resulting from manganite dissolution, implicating a reductive dissolution pathway. These results have important implications for the biogeochemical cycling of both manganese and siderophores--as well as Fe(lll)--in natural waters and soils.

  18. 12 CFR 239.16 - Voluntary dissolution.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 12 Banks and Banking 4 2012-01-01 2012-01-01 false Voluntary dissolution. 239.16 Section 239.16... (CONTINUED) MUTUAL HOLDING COMPANIES (REGULATION MM) Mutual Holding Companies § 239.16 Voluntary dissolution. (a) A mutual holding company's board of directors may propose a plan for dissolution of the...

  19. 12 CFR 239.16 - Voluntary dissolution.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 12 Banks and Banking 4 2014-01-01 2014-01-01 false Voluntary dissolution. 239.16 Section 239.16... (CONTINUED) MUTUAL HOLDING COMPANIES (REGULATION MM) Mutual Holding Companies § 239.16 Voluntary dissolution. (a) A mutual holding company's board of directors may propose a plan for dissolution of the...

  20. 12 CFR 239.16 - Voluntary dissolution.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 12 Banks and Banking 4 2013-01-01 2013-01-01 false Voluntary dissolution. 239.16 Section 239.16... (CONTINUED) MUTUAL HOLDING COMPANIES (REGULATION MM) Mutual Holding Companies § 239.16 Voluntary dissolution. (a) A mutual holding company's board of directors may propose a plan for dissolution of the...

  1. 5 CFR 2634.410 - Dissolution.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 5 Administrative Personnel 3 2013-01-01 2013-01-01 false Dissolution. 2634.410 Section 2634.410..., QUALIFIED TRUSTS, AND CERTIFICATES OF DIVESTITURE Qualified Trusts § 2634.410 Dissolution. Within thirty days of dissolution of a qualified trust, the interested party shall file a report of the...

  2. 5 CFR 2634.410 - Dissolution.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 5 Administrative Personnel 3 2014-01-01 2014-01-01 false Dissolution. 2634.410 Section 2634.410..., QUALIFIED TRUSTS, AND CERTIFICATES OF DIVESTITURE Qualified Trusts § 2634.410 Dissolution. Within thirty days of dissolution of a qualified trust, the interested party shall file a report of the...

  3. Comparison on Response and Dissolution Rates Between Ursodeoxycholic Acid Alone or in Combination With Chenodeoxycholic Acid for Gallstone Dissolution According to Stone Density on CT Scan

    PubMed Central

    Lee, Jae Min; Hyun, Jong Jin; Choi, In Young; Yeom, Suk Keu; Kim, Seung Young; Jung, Sung Woo; Jung, Young Kul; Koo, Ja Seol; Yim, Hyung Joon; Lee, Hong Sik; Lee, Sang Woo; Kim, Chang Duck

    2015-01-01

    Abstract Medical dissolution of gallstone is usually performed on radiolucent gallstones in a functioning gallbladder. However, absence of visible gallstone on plain abdominal x-ray does not always preclude calcification. This study aims to compare the response and dissolution rates between ursodeoxycholic acid (UDCA) alone or in combination with chenodeoxycholic acid (CDCA) according to stone density on computed tomography (CT) scan. A total of 126 patients underwent dissolution therapy with either UDCA alone or combination of CDCA and UDCA (CNU) from December 2010 to March 2014 at Korea University Ansan Hospital. In the end, 81 patients (CNU group = 44, UDCA group = 37) completed dissolution therapy for 6 months. Dissolution rate (percentage reduction in the gallstone volume) and response to therapy (complete dissolution or partial dissolution defined as reduction in stone volume of >50%) were compared between the 2 groups. Dissolution and response rates of sludge was also compared between the 2 groups. The overall response rate was 50.6% (CNU group 43.2% vs UDCA group 59.5%, P = 0.14), and the overall dissolution rate was 48.34% (CNU group 41.5% vs UDCA group 56.5%, P = 0.13). When analyzed according to stone density, response rate was 33.3%, 87.1%, 30.0%, and 6.2% for hypodense, isodense, hyperdense, and calcified stones, respectively. Response rate (85.7% vs 88.2%, P = 0.83) and dissolution rate (81.01% vs 85.38%, P = 0.17) of isodense stones were similar between CNU and UDCA group. When only sludge was considered, the overall response rate was 87.5% (CNU group 71.4% vs UDCA group 94.1%, P = 0.19), and the overall dissolution rate was 85.42% (CNU group 67.9% vs UDCA group 92.7%, P = 0.23). Patients with isodense gallstones and sludge showed much better response to dissolution therapy with CNU and UDCA showing comparable efficacy. Therefore, CT scan should be performed before medication therapy if stone dissolution is intended

  4. Modeling dissolution in aluminum alloys

    NASA Astrophysics Data System (ADS)

    Durbin, Tracie Lee

    2005-07-01

    Aluminum and its alloys are used in many aspects of modern life, from soda cans and household foil to the automobiles and aircraft in which we travel. Aluminum alloy systems are characterized by good workability that enables these alloys to be economically rolled, extruded, or forged into useful shapes. Mechanical properties such as strength are altered significantly with cold working, annealing, precipitation-hardening, and/or heat-treatments. Heat-treatable aluminum alloys contain one or more soluble constituents such as copper, lithium, magnesium, silicon and zinc that individually, or with other elements, can form phases that strengthen the alloy. Microstructure development is highly dependent on all of the processing steps the alloy experiences. Ultimately, the macroscopic properties of the alloy depend strongly on the microstructure. Therefore, a quantitative understanding of the microstructural changes that occur during thermal and mechanical processing is fundamental to predicting alloy properties. In particular, the microstructure becomes more homogeneous and secondary phases are dissolved during thermal treatments. Robust physical models for the kinetics of particle dissolution are necessary to predict the most efficient thermal treatment. A general dissolution model for multi-component alloys has been developed using the front-tracking method to study the dissolution of precipitates in an aluminum alloy matrix. This technique is applicable to any alloy system, provided thermodynamic and diffusion data are available. Treatment of the precipitate interface is explored using two techniques: the immersed-boundary method and a new technique, termed here the "sharp-interface" method. The sharp-interface technique is based on a variation of the ghost fluid method and eliminates the need for corrective source terms in the characteristic equations. In addition, the sharp-interface method is shown to predict the dissolution behavior of precipitates in aluminum

  5. Dissolution Kinetics of Alumina Calcine

    SciTech Connect

    Batcheller, Thomas Aquinas

    2001-09-01

    Dissolution kinetics of alumina type non-radioactive calcine was investigated as part of ongoing research that addresses permanent disposal of Idaho High Level Waste (HLW). Calcine waste was produced from the processing of nuclear fuel at the Idaho Nuclear Technology and Engineering Center (INTEC). Acidic radioactive raffinates were solidified at ~500°C in a fluidized bed reactor to form the dry granular calcine material. Several Waste Management alternatives for the calcine are presented in the Idaho High Level Waste Draft EIS. The Separations Alternative addresses the processing of the calcine so that the HLW is ready for removal to a national geological repository by the year 2035. Calcine dissolution is the key front-end unit operation for the separations alternative.

  6. Dissolution of HFIR control plates

    SciTech Connect

    Posey, J.C.

    1984-03-01

    A process was developed for the dissolution of High Flux Isotope Reactor (HFIR) control plates. These plates consist of aluminum metal, intensely radioactive europium oxide, and a small amount of tantalum metal. The radioactive solution will be diluted, mixed with grout, and disposed of by shale fracture. The plates are dissolved in nitric acid using a mercury catalyst. Conditions were determined that would produce a reaction rate compatible with existing equipment. 3 references, 1 figure, 3 tables.

  7. After adoption: dissolution or permanence?

    PubMed

    Festinger, Trudy

    2002-01-01

    Results are presented on the whereabouts of 516 adopted children, based on a random sample of children adopted from placement in New York City in 1996. Data from interviews with adoptive parents were augmented by information from adoption subsidy records and state child tracking files, as well as interviews with caregivers of children whose adoptive parents were deceased. There were few dissolutions, but postadoption service needs were many.

  8. Mass exchange during simultaneous grinding and dissolution

    SciTech Connect

    Aksel'rud, G.A.; Semenishin, E.M.; Kopyt, S.Ya.; Trotskii, V.I.

    1988-03-20

    Extraction of ore components of interest has a number of disadvantages, one of which being low efficiency. Combining the grinding and dissolution steps in one apparatus makes the process more efficient. Adoption of this technology, however, requires theoretical and mathematical studies. This paper reports the kinetics of simultaneous grinding and dissolution of copper-containing minerals. Simultaneous grinding and dissolution accelerated several fold the mass transfer of components of interest in the interaction of malachite and azurite with sulfuric acid solutions. The complete dissolution time was determined by adding the experimental rates of dissolution and abrasion.

  9. Abiotic Immobilization of Nitrate in Forest Soils: a Double Label Approach

    NASA Astrophysics Data System (ADS)

    Maclean, R. W.; Ollinger, S. V.; Hobbie, E. A.; Frey, S. D.; Dail, D. B.

    2007-12-01

    Mechanisms of soil nitrogen (N) retention remain a key uncertainty in the terrestrial N cycle. During recent work at the Harvard Forest Chronic N Experiment, 15N added to soils as ammonia nitrate was observed to be rapidly immobilized after addition to soil on a time scale of minutes. In published results it was hypothesized that the rapid time of immobilization could be explained by abiotic immobilization of both ammonia and nitrate. The possibility of abiotic immobilization of nitrate has been studied since the first half of the 20th century, mainly using ideal compounds and soil sterilization techniques. However, critics of these studies have argued that while in vitro studies may indicate the possibility of an abiotic reaction, they cannot demonstrate its plausibility in soils. Soil sterilization methods have been criticized, because they are not effective enough to eliminate biotic interactions within an experimental treatment. Isotopic tracer studies have also been used but also have problems differentiating biotic and abiotic reactions. This study is an attempt to demonstrate abiotic immobilization of nitrate in soil samples through the use of double labeled nitrate (15N18O3- ). The resolution of this method depends on the biochemistry of microbial immobilization of nitrate; reduction of nitrate to nitrite, then ammonia and glutamine before incorporation into microbial biomass. Reduction of 15N18O3- before microbial utilization of the 15N implies that retention of both heavy isotopes in the soil can only occur through abiotic reaction of 15N18Ox species. In biotic immobilization the 18O is lost to the system in water. While nitrate has proven unreactive in soils, its reduced product, nitrite, is known to be readily reactive with various soil compounds. Nitrite can be introduced into the soil environment naturally by both 'leakiness' in nitrification and denitrification and may possibly be generated abiotically through methods such as the proposed Ferrous

  10. Oxylipins and plant abiotic stress resistance.

    PubMed

    Savchenko, T V; Zastrijnaja, O M; Klimov, V V

    2014-04-01

    Oxylipins are signaling molecules formed enzymatically or spontaneously from unsaturated fatty acids in all aerobic organisms. Oxylipins regulate growth, development, and responses to environmental stimuli of organisms. The oxylipin biosynthesis pathway in plants includes a few parallel branches named after first enzyme of the corresponding branch as allene oxide synthase, hydroperoxide lyase, divinyl ether synthase, peroxygenase, epoxy alcohol synthase, and others in which various biologically active metabolites are produced. Oxylipins can be formed non-enzymatically as a result of oxygenation of fatty acids by free radicals and reactive oxygen species. Spontaneously formed oxylipins are called phytoprostanes. The role of oxylipins in biotic stress responses has been described in many published works. The role of oxylipins in plant adaptation to abiotic stress conditions is less studied; there is also obvious lack of available data compilation and analysis in this area of research. In this work we analyze data on oxylipins functions in plant adaptation to abiotic stress conditions, such as wounding, suboptimal light and temperature, dehydration and osmotic stress, and effects of ozone and heavy metals. Modern research articles elucidating the molecular mechanisms of oxylipins action by the methods of biochemistry, molecular biology, and genetics are reviewed here. Data on the role of oxylipins in stress signal transduction, stress-inducible gene expression regulation, and interaction of these metabolites with other signal transduction pathways in cells are described. In this review the general oxylipin-mediated mechanisms that help plants to adjust to a broad spectrum of stress factors are considered, followed by analysis of more specific responses regulated by oxylipins only under certain stress conditions. New approaches to improvement of plant resistance to abiotic stresses based on the induction of oxylipin-mediated processes are discussed.

  11. Effects of particle size distribution on limestone dissolution in wet FGD process applications

    SciTech Connect

    Ukawa, Naohiko; Takashina, Toru; Shinoda, Naoharu ); Shimizu, Taku )

    1993-08-01

    The kinetics of limestone dissolution in the wet type flue gas desulfurization (FGD) processes has been studied. The rates of dissolution and particle size reduction were measured in both batch and continuous reaction systems for limestone of different size distributions. A predictive model was developed based on mass transfer mechanisms. It was in good agreement with experimental data. Moreover, the rate of dissolution for 25 limestones of different compositions and size distributions were measured in apparatus with a sulfur dioxide absorber which simulated FGD processes. The model was also in good agreement with these results. 11 refs., 8 figs., 2 tabs.

  12. DISSOLUTION OF NEPTUNIUM OXIDE RESIDUES

    SciTech Connect

    Kyser, E

    2009-01-12

    This report describes the development of a dissolution flowsheet for neptunium (Np) oxide (NpO{sub 2}) residues (i.e., various NpO{sub 2} sources, HB-Line glovebox sweepings, and Savannah River National Laboratory (SRNL) thermogravimetric analysis samples). Samples of each type of materials proposed for processing were dissolved in a closed laboratory apparatus and the rate and total quantity of off-gas were measured. Samples of the off-gas were also analyzed. The quantity and type of solids remaining (when visible) were determined after post-dissolution filtration of the solution. Recommended conditions for dissolution of the NpO{sub 2} residues are: Solution Matrix and Loading: {approx}50 g Np/L (750 g Np in 15 L of dissolver solution), using 8 M nitric acid (HNO{sub 3}), 0.025 M potassium fluoride (KF) at greater than 100 C for at least 3 hours. Off-gas: Analysis of the off-gas indicated nitric oxide (NO), nitrogen dioxide (NO{sub 2}) and nitrous oxide (N{sub 2}O) as the only identified components. No hydrogen (H{sub 2}) was detected. The molar ratio of off-gas produced per mole of Np dissolved ranged from 0.25 to 0.4 moles of gas per mole of Np dissolved. A peak off-gas rate of {approx}0.1 scfm/kg bulk oxide was observed. Residual Solids: Pure NpO{sub 2} dissolved with little or no residue with the proposed flowsheet but the NpCo and both sweepings samples left visible solid residue after dissolution. For the NpCo and Part II Sweepings samples the residue amounted to {approx}1% of the initial material, but for the Part I Sweepings sample, the residue amounted to {approx}8 % of the initial material. These residues contained primarily aluminum (Al) and silicon (Si) compounds that did not completely dissolve under the flowsheet conditions. The residues from both sweepings samples contained minor amounts of plutonium (Pu) particles. Overall, the undissolved Np and Pu particles in the residues were a very small fraction of the total solids.

  13. SERDP ER-1421 Abiotic and Biotic Mechanisms Controlling In Situ Remediation of NDMA: Final Report

    SciTech Connect

    Szecsody, James E.; McKinley, James P.; Crocker, Fiona H.; Breshears, Andrew T.; Devary, Brooks J.; Fredrickson, Herbert L.; Thompson, Karen T.

    2009-09-30

    This laboratory-scale project was initiated to investigate in situ abiotic/biotic mineralization of NDMA. Under iron-reducing conditions, aquifer sediments showed rapid abiotic NDMA degradation to dimethylamine (DMA), nitrate, formate, and finally, CO2. These are the first reported experiments of abiotic NDMA mineralization. The NDMA reactivity of these different iron phases showed that adsorbed ferrous iron was the dominant reactive phase that promoted NDMA reduction, and other ferrous phases present (siderite, iron sulfide, magnetite, structural ferrous iron in 2:1 clays) did not promote NDMA degradation. In contrast, oxic sediments that were biostimulated with propane promoted biomineralization of NDMA by a cometabolic monooxygenase enzyme process. Other monooxygenase enzyme processes were not stimulated with methane or toluene additions, and acetylene addition did not block mineralization. Although NDMA mineralization extent was the highest in oxic, biostimulated sediments (30 to 82%, compared to 10 to 26% for abiotic mineralization in reduced sediments), large 1-D column studies (high sediment/water ratio of aquifers) showed 5.6 times higher NDMA mineralization rates in reduced sediment (half-life 410 ± 147 h) than oxic biomineralization (half life 2293 ± 1866 h). Sequential reduced/oxic biostimulated sediment mineralization (half-life 3180 ± 1094 h) was also inefficient compared to reduced sediment. These promising laboratory-scale results for NDMA mineralization should be investigated at field scale. Future studies of NDMA remediation should focus on the comparison of this in situ abiotic NDMA mineralization (iron-reducing environments) to ex situ biomineralization, which has been shown successful in other studies.

  14. Assessment of solvents for cellulose dissolution.

    PubMed

    Ghasemi, Mohammad; Tsianou, Marina; Alexandridis, Paschalis

    2017-03-01

    A necessary step in the processing of biomass is the pretreatment and dissolution of cellulose. A good solvent for cellulose involves high diffusivity, aggressiveness in decrystallization, and capability of disassociating the cellulose chains. However, it is not clear which of these factors and under what conditions should be improved in order to obtain a more effective solvent. To this end, a newly-developed phenomenological model has been applied to assess the controlling mechanism of cellulose dissolution. Among the findings, the cellulose fibers remain crystalline almost to the end of the dissolution process for decrystallization-controlled kinetics. In such solvents, decreasing the fiber crystallinity, e.g., via pretreatment, would result in a considerable increase in the dissolution rate. Such insights improve the understanding of cellulose dissolution and facilitate the selection of more efficient solvents and processing conditions for biomass. Specific examples of solvents are provided where dissolution is limited due to decrystallization or disentanglement.

  15. Effects of pH and carbonate concentration on dissolution rates of the lead corrosion product PbO(2).

    PubMed

    Xie, Yanjiao; Wang, Yin; Singhal, Vidhi; Giammar, Daniel E

    2010-02-01

    Lead(IV) oxide is a corrosion product that can develop on lead pipes and affect lead concentrations in drinking water. Continuously stirred flow-though reactors were used to quantify the dissolution rates of plattnerite (beta-PbO(2)) at different pH values and dissolved inorganic carbon (DIC) concentrations. Organic pH buffers were not used, because several were found to be reductants for PbO(2) that accelerated its dissolution. Most plattnerite dissolution rates were on the order of 10(-10) mol/min-m(2). The rate of dissolution increased with decreasing pH and with increasing DIC. The effect of DIC is consistent with a reductive dissolution mechanism that involves the reduction of Pb(IV) to Pb(II) at the plattnerite surface followed by the formation of soluble Pb(II)-carbonate complexes that accelerate Pb(II) release from the surface. Under the experimental conditions, dissolved lead concentrations were controlled by the dissolution rate of plattnerite and not by its equilibrium solubility. A dissolution rate model was developed and can be used to predict dissolution rates of plattnerite as a function of pH and DIC.

  16. Dissolution of cinnabar (HgS) in the presence of natural organic matter

    USGS Publications Warehouse

    Waples, J.S.; Nagy, K.L.; Aiken, G.R.; Ryan, J.N.

    2005-01-01

    Cinnabar (HgS) dissolution rates were measured in the presence of 12 different natural dissolved organic matter (DOM) isolates including humic, fulvic, and hydrophobic acid fractions. Initial dissolution rates varied by 1.3 orders of magnitude, from 2.31 ?? 10-13 to 7.16 ?? 10-12 mol Hg (mg C)-1 m-2 s-1. Rates correlate positively with three DOM characteristics: specific ultraviolet absorbance (R2 = 0.88), aromaticity (R2 = 0.80), and molecular weight (R2 = 0.76). Three experimental observations demonstrate that dissolution was controlled by the interaction of DOM with the cinnabar surface: (1) linear rates of Hg release with time, (2) significantly reduced rates when DOM was physically separated from the surface by dialysis membranes, and (3) rates that approached constant values at a specific ratio of DOM concentration to cinnabar surface area, suggesting a maximum surface coverage by dissolution-reactive DOM. Dissolution rates for the hydrophobic acid fractions correlate negatively with sorbed DOM concentrations, indicating the presence of a DOM component that reduced the surface area of cinnabar that can be dissolved. When two hydrophobic acid isolates that enhanced dissolution to different extents were mixed equally, a 20% reduction in rate occurred compared to the rate with the more dissolution-enhancing isolate alone. Rates in the presence of the more dissolution-enhancing isolate were reduced by as much as 60% when cinnabar was prereacted with the isolate that enhanced dissolution to a lesser extent. The data, taken together, imply that the property of DOM that enhances cinnabar dissolution is distinct from the property that causes it to sorb irreversibly to the cinnabar surface. Copyright ?? 2005 Elsevier Ltd.

  17. Dissolution of cinnabar (HgS) in the presence of natural organic matter

    NASA Astrophysics Data System (ADS)

    Waples, Jacob S.; Nagy, Kathryn L.; Aiken, George R.; Ryan, Joseph N.

    2005-03-01

    Cinnabar (HgS) dissolution rates were measured in the presence of 12 different natural dissolved organic matter (DOM) isolates including humic, fulvic, and hydrophobic acid fractions. Initial dissolution rates varied by 1.3 orders of magnitude, from 2.31 × 10 -13 to 7.16 × 10 -12 mol Hg (mg C) -1 m -2s -1. Rates correlate positively with three DOM characteristics: specific ultraviolet absorbance (R 2 = 0.88), aromaticity (R 2 = 0.80), and molecular weight (R 2 = 0.76). Three experimental observations demonstrate that dissolution was controlled by the interaction of DOM with the cinnabar surface: (1) linear rates of Hg release with time, (2) significantly reduced rates when DOM was physically separated from the surface by dialysis membranes, and (3) rates that approached constant values at a specific ratio of DOM concentration to cinnabar surface area, suggesting a maximum surface coverage by dissolution-reactive DOM. Dissolution rates for the hydrophobic acid fractions correlate negatively with sorbed DOM concentrations, indicating the presence of a DOM component that reduced the surface area of cinnabar that can be dissolved. When two hydrophobic acid isolates that enhanced dissolution to different extents were mixed equally, a 20% reduction in rate occurred compared to the rate with the more dissolution-enhancing isolate alone. Rates in the presence of the more dissolution-enhancing isolate were reduced by as much as 60% when cinnabar was prereacted with the isolate that enhanced dissolution to a lesser extent. The data, taken together, imply that the property of DOM that enhances cinnabar dissolution is distinct from the property that causes it to sorb irreversibly to the cinnabar surface.

  18. Abiotic Methane Synthesis: Caveats and New Results

    NASA Astrophysics Data System (ADS)

    Zou, R.; Sharma, A.

    2005-12-01

    The role of mineral interaction with geochemical fluids under hydrothermal conditions has invoked models of geochemical synthesis of organic molecules at deep crustal conditions. Since Thomas Gold's (1992) hypothesis of the possibility of an abiotic organic synthesis, there have been several reports of hydrocarbon formation under high pressure and temperature conditions. Several previous experimental studies have recognized that small amounts of methane (and other light HC compounds) can be synthesized via catalysis by transition metals: Fe, Ni (Horita and Berndt, 1999 Science) and Cr (Foustavous and Seyfried, 2004 Science). In light of these pioneering experiments, an investigation of the feasibility of abiotic methane synthesis at higher pressure conditions in deep geological setting and the possible role of catalysis warrants a closer look. We conducted three sets of experiments in hydrothermal diamond anvil cell using FeO nanopowder, CaCO 3 and water at 300° - 600° C and 0.5 - 5 GPa : (a) with stainless steel gasket, (b) gold-lined gasket, and (c) gold-lined gasket with added Fe and Ni nanopowder. The reactions were monitored in-situ using micro-Raman spectroscopy with 532nm and 632nm lasers. The solids phases were characterized in-situ using synchrotron X-ray diffraction at CHESS-Cornell and quenched products with an electron microprobe. Interestingly, a variable amount of hydrocarbon was observed only in runs with stainless steel gasket and with Fe, Ni nanoparticles. Experiments with gold-lined reactors did not show any hydrocarbon formation. Added high resolution microscopy of the products and their textural relationship within the diamond cell with Raman spectroscopy data show that the hydrocarbon (methane and other light fractions) synthesis is a direct result of transition metal catalysis, rather than wustite - calcium carbonate reaction as recently reported by Scott et al (2004, PNAS). The author will further present new results highlighting abiotic

  19. Generation of RNA in abiotic conditions.

    NASA Astrophysics Data System (ADS)

    di Mauro, Ernesto

    Generation of RNA in abiotic conditions. Ernesto Di Mauro Dipartimento di Genetica Bi-ologia Molecolare, Universit` "Sapienza" Roma, Italy. a At least four conditions must be satisfied for the spontaneous generation of (pre)-genetic poly-mers: 1) availability of precursors that are activated enough to spontaneously polymerize. Preliminary studies showed that (a) nucleic bases and acyclonucleosides can be synthesized from formamide H2NCOH by simply heating with prebiotically available mineral catalysts [last reviewed in (1)], and that b) nucleic bases can be phosphorylated in every possible posi-tion [2'; 3'; 5'; cyclic 2',3'; cyclic 3',5' (2)]. The higher stability of the cyclic forms allows their accumulation. 2) A polymerization mechanism. A reaction showing the formation of RNA polymers starting from prebiotically plausible precursors (3',5' cyclic GMP and 3', 5'cyclic AMP) was recently reported (3). Polymerization in these conditions is thermodynamically up-hill and an equilibrium is attained that limits the maximum length of the polymer produced to about 40 nucleotides for polyG and 100 nucleotides for polyA. 3) Ligation of the synthesized oligomers. If this type of reaction could occur according to a terminal-joining mechanism and could generate canonical 3',5' phosphodiester bonds, exponential growth would be obtained of the generated oligomers. This type of reaction has been reported (4) , limited to homogeneous polyA sequences and leading to the production of polyA dimers and tetramers. What is still missing are: 4) mechanisms that provide the proof of principle for the generation of sequence complexity. We will show evidence for two mechanisms providing this proof of principle for simple complementary sequences. Namely: abiotic sequence complementary-driven terminal ligation and sequence-complementary terminal growth. In conclusion: all the steps leading to the generation of RNA in abiotic conditions are satisfied. (1) R Saladino, C Crestini, F

  20. MICROSCALE METABOLIC, REDOX AND ABIOTIC REACTIONS IN HANFORD 300 AREA SUBSURFACE SEDIMENTS

    SciTech Connect

    Beyenal, Haluk; McLEan, Jeff; Majors, Paul; Fredrickson, Jim

    2013-11-14

    The Hanford 300 Area is a unique site due to periodic hydrologic influence of river water resulting in changes in groundwater elevation and flow direction. This area is also highly subject to uranium remobilization, the source of which is currently believed to be the region at the base of the vadose zone that is subject to period saturation due to the changes in the water levels in the Columbia River. We found that microbial processes and redox and abiotic reactions which operate at the microscale were critical to understanding factors controlling the macroscopic fate and transport of contaminants in the subsurface. The combined laboratory and field research showed how microscale conditions control uranium mobility and how biotic, abiotic and redox reactions relate to each other. Our findings extended the current knowledge to examine U(VI) reduction and immobilization using natural 300 Area communities as well as selected model organisms on redox-sensitive and redox-insensitive minerals. Using innovative techniques developed specifically to probe biogeochemical processes at the microscale, our research expanded our current understanding of the roles played by mineral surfaces, bacterial competition, and local biotic, abiotic and redox reaction rates on the reduction and immobilization of uranium.

  1. The Influence of Milling on the Dissolution Performance of Simvastatin.

    PubMed

    Zimper, Ulrike; Aaltonen, Jaakko; Krauel-Goellner, Karen; Gordon, Keith C; Strachan, Clare J; Rades, Thomas

    2010-12-17

    Particle size reduction is a simple means to enhance the dissolution rate of poorly water soluble BCS-class II and IV drugs. However, the major drawback of this process is the possible introduction of process induced disorder. Drugs with different molecular arrangements may exhibit altered properties such as solubility and dissolution rate and, therefore, process induced solid state modifications need to be monitored. The aim of this study was two-fold: firstly, to investigate the dissolution rates of milled and unmilled simvastatin; and secondly, to screen for the main milling factors, as well as factor interactions in a dry ball milling process using simvastatin as model drug, and to optimize the milling procedure with regard to the opposing responses particle size and process induced disorder by application of a central composite face centered design. Particle size was assessed by scanning electron microscopy (SEM) and image analysis. Process induced disorder was determined by partial least squares (PLS) regression modeling of respective X-ray powder diffractograms (XRPD) and Raman spectra. Valid and significant quadratic models were built. The investigated milling factors were milling frequency, milling time and ball quantity at a set drug load, out of which milling frequency was found to be the most important factor for particle size as well as process induced disorder. Milling frequency and milling time exhibited an interaction effect on the responses. The optimum milling settings using the maximum number of milling balls (60 balls with 4 mm diameter) was determined to be at a milling frequency of 21 Hz and a milling time of 36 min with a resulting primary particle size of 1.4 μm and a process induced disorder of 6.1% (assessed by Raman spectroscopy) and 8.4% (assessed by XRPD), at a set optimization limit of < 2 μm for particle size and < 10% for process induced disorder. This optimum was tested experimentally and the process induced disorder was

  2. Cell wall remodeling under abiotic stress

    PubMed Central

    Tenhaken, Raimund

    2015-01-01

    Plants exposed to abiotic stress respond to unfavorable conditions on multiple levels. One challenge under drought stress is to reduce shoot growth while maintaining root growth, a process requiring differential cell wall synthesis and remodeling. Key players in this process are the formation of reactive oxygen species (ROS) and peroxidases, which initially cross-link phenolic compounds and glycoproteins of the cell walls causing stiffening. The function of ROS shifts after having converted all the peroxidase substrates in the cell wall. If ROS-levels remain high during prolonged stress, OH°-radicals are formed which lead to polymer cleavage. In concert with xyloglucan modifying enzymes and expansins, the resulting cell wall loosening allows further growth of stressed organs. PMID:25709610

  3. Abiotic formation of oligonucleotides on basalt surfaces

    NASA Astrophysics Data System (ADS)

    Otroshchenko, V. A.; Vasilyeva, N. V.; Kopilov, A. M.

    1985-06-01

    The complication and further evolution of abiotic syntheses products occurred under environmental influences at the prebiological stage. From this point of view, the influence of some types of irradiation on the organic molecules adsorbed on the surfaces of volcanic rocks, appeared to be of great importance. In this connection, the effect of gamma rays on the AMP molecules adsorbed on mineral surfaces such as cinders and ashes has been studied. It has been shown that they can polymerize with the formation of oligonucleotides. The treatment of oligomers obtained by venom phosphodiesterase has shown that a polymeric product has mainly 3' 5' and 2' 5' bonds between nucleotides. The results obtained have been discussed from the evolutionary aspect.

  4. Effects of crossover hydrogen on platinum dissolution and agglomeration

    NASA Astrophysics Data System (ADS)

    Cheng, Tommy T. H.; Rogers, Erin; Young, Alan P.; Ye, Siyu; Colbow, Vesna; Wessel, Silvia

    2011-10-01

    The durability of catalysts in the polymer-electrolyte membrane fuel cell (PEMFC) is identified as a critical limiting factor for wide commercialization of fuel cells. Even though much progress has been made in understanding the degradation mechanisms, the phenomena of Pt dissolution and agglomeration and their contributing factors are not fully understood. In the present investigation, the effects of crossover hydrogen on Pt degradation are studied using an accelerated stress test (AST). The end-of-test (EOT) membrane-electrode-assemblies (MEAs) were characterized by X-ray diffraction (XRD), scanning-electron microscopy (SEM), and energy-dispersive X-ray (EDX). The results provided mechanistic understanding of Pt dissolution and agglomeration: Pt growth and agglomeration were found to be less severe with more crossover hydrogen due likely to the chemical reduction of Pt oxides by crossover hydrogen and the subsequently decrease in the amount of Pt ions formed via the oxide pathway.

  5. Economic incentives for additional critical experimentation applicable to fuel dissolution

    SciTech Connect

    Mincey, J.F.; Primm, R.T. III; Waltz, W.R.

    1981-01-01

    Fuel dissolution operations involving soluble absorbers for criticality control are among the most difficult to establish economical subcritical limits. The paucity of applicable experimental data can significantly hinder a precise determination of a bias in the method chosen for calculation of the required soluble absorber concentration. Resorting to overly conservative bias estimates can result in excessive concentrations of soluble absorbers. Such conservatism can be costly, especially if soluble absorbers are used in a throw-away fashion. An economic scoping study is presented which demonstrates that additional critical experimentation will likely lead to reductions in the soluble absorber (i.e., gadolinium) purchase costs for dissolution operations. The results indicate that anticipated savings maybe more than enough to pay for the experimental costs.

  6. ABIOTIC IN SITU TECHNOLOGIES FOR GROUNDWATER REMEDIATION CONFERENCE: PROCEEDINGS

    EPA Science Inventory

    The USEPA conference on Abiotic In Situ Technologies for Groundwater Remediation was held in Dallas, TX, 8/31-9/2/99. The goal of the meeting was to disseminate current information on abiotic in situ groundwater treatment echnologies. Although much information is being provided a...

  7. The Stable Isotope Fractionation of Abiotic Reactions: A Benchmark in the Detection of Life

    NASA Technical Reports Server (NTRS)

    Summers, David P.

    2003-01-01

    mil to as low as -60 % (potentially comparable to that which accompanies the biosynthesis of organic matter). We need to understand what kind of fractionations are observed with reactions under the non-reducing or mildly reducing conditions now thought to be present on the early Earth. While nitrogen is receiving increased attention as a tool for these kinds of analyses, almost nothing is known about the isotope fractionation that one would expect for abiotic sources of fixed/reduced nitrogen. This project will measure the fixation from a series of abiotic reactions that may have been present on the early Earth (and other terrestrial planets) and produced organic material that could have ended up in the rock record. The work will look at a number of reactions, under a non- reducing, or mildly reducing, atmosphere, covering sources of prebiotic organic C & N from shock heating, to photochemistry, to hydrothermal reactions. Some reactions that we plan to study are; Shock heating of a non-reducing atmosphere to produce CO and NO (in collaboration with Chris McKay), formation of formaldehyde (and related compounds) from COY the formation of ammonia from nitrogen oxides (ultimately from NO) by ferrous iron reduction, and the hydrothermal synthesis of compounds including the hydrocarboxylation/hydrocarbonylation reaction (in collaboration with George Cody), reactions of oxalate to form hydrocarbons and other oxygenated compounds and the formation of lipids from oxalic/formic acid (in collaboration with Tom McCollom), and reactions of carbon monoxide & carbon dioxide with N2, ammonia or nitritehitrate to form hydrogen cyanide, nitriles, ammonia/amines and nitrous

  8. Microbial- and thiosulfate-mediated dissolution of mercury sulfide minerals and transformation to gaseous mercury

    PubMed Central

    Vázquez-Rodríguez, Adiari I.; Hansel, Colleen M.; Zhang, Tong; Lamborg, Carl H.; Santelli, Cara M.; Webb, Samuel M.; Brooks, Scott C.

    2015-01-01

    Mercury (Hg) is a toxic heavy metal that poses significant environmental and human health risks. Soils and sediments, where Hg can exist as the Hg sulfide mineral metacinnabar (β-HgS), represent major Hg reservoirs in aquatic environments. Metacinnabar has historically been considered a sink for Hg in all but severely acidic environments, and thus disregarded as a potential source of Hg back to aqueous or gaseous pools. Here, we conducted a combination of field and laboratory incubations to identify the potential for metacinnabar as a source of dissolved Hg within near neutral pH environments and the underpinning (a)biotic mechanisms at play. We show that the abundant and widespread sulfur-oxidizing bacteria of the genus Thiobacillus extensively colonized metacinnabar chips incubated within aerobic, near neutral pH creek sediments. Laboratory incubations of axenic Thiobacillus thioparus cultures led to the release of metacinnabar-hosted Hg(II) and subsequent volatilization to Hg(0). This dissolution and volatilization was greatly enhanced in the presence of thiosulfate, which served a dual role by enhancing HgS dissolution through Hg complexation and providing an additional metabolic substrate for Thiobacillus. These findings reveal a new coupled abiotic-biotic pathway for the transformation of metacinnabar-bound Hg(II) to Hg(0), while expanding the sulfide substrates available for neutrophilic chemosynthetic bacteria to Hg-laden sulfides. They also point to mineral-hosted Hg as an underappreciated source of gaseous elemental Hg to the environment. PMID:26157421

  9. Improved abiotic stress tolerance of bermudagrass by exogenous small molecules.

    PubMed

    Chan, Zhulong; Shi, Haitao

    2015-01-01

    As a widely used warm-season turfgrass in landscapes and golf courses, bermudagrass encounters multiple abiotic stresses during the growth and development. Physiology analysis indicated that abiotic stresses induced the accumulation of ROS and decline of photosynthesis, resulting in increased cell damage and inhibited growth. Proteomic and metabolomic approaches showed that antioxidant enzymes and osmoprotectant contents (sugar, sucrose, dehydrin, proline) were extensively changed under abiotic stress conditions. Exogenous application of small molecules, such as ABA, NO, CaCl2, H2S, polyamine and melatonin, could effectively alleviate damages caused by multiple abiotic stresses, including drought, salt, heat and cold. Based on high through-put RNA seq analysis, genes involved in ROS, transcription factors, hormones, and carbohydrate metabolisms were largely enriched. The data indicated that small molecules induced the accumulation of osmoprotectants and antioxidants, kept cell membrane integrity, increased photosynthesis and kept ion homeostasis, which protected bermudagrass from damages caused by abiotic stresses.

  10. Abiotic stresses induce different localizations of anthocyanins in Arabidopsis

    PubMed Central

    Kovinich, Nik; Kayanja, Gilbert; Chanoca, Alexandra; Otegui, Marisa S; Grotewold, Erich

    2015-01-01

    Anthocyanins are induced in plants in response to abiotic stresses such as drought, high salinity, excess light, and cold, where they often correlate with enhanced stress tolerance. Numerous roles have been proposed for anthocyanins induced during abiotic stresses including functioning as ROS scavengers, photoprotectants, and stress signals. We have recently found different profiles of anthocyanins in Arabidopsis (Arabidopsis thaliana) plants exposed to different abiotic stresses, suggesting that not all anthocyanins have the same function. Here, we discuss these findings in the context of other studies and show that anthocyanins induced in Arabidopsis in response to various abiotic stresses have different localizations at the organ and tissue levels. These studies provide a basis to clarify the role of particular anthocyanin species during abiotic stress. PMID:26179363

  11. DISSOLUTION OF LANTHANUM FLUORIDE PRECIPITATES

    DOEpatents

    Fries, B.A.

    1959-11-10

    A plutonium separatory ore concentration procedure involving the use of a fluoride type of carrier is presented. An improvement is given in the derivation step in the process for plutonium recovery by carrier precipitation of plutonium values from solution with a lanthanum fluoride carrier precipitate and subsequent derivation from the resulting plutonium bearing carrier precipitate of an aqueous acidic plutonium-containing solution. The carrier precipitate is contacted with a concentrated aqueous solution of potassium carbonate to effect dissolution therein of at least a part of the precipitate, including the plutonium values. Any remaining precipitate is separated from the resulting solution and dissolves in an aqueous solution containing at least 20% by weight of potassium carbonate. The reacting solutions are combined, and an alkali metal hydroxide added to a concentration of at least 2N to precipitate lanthanum hydroxide concomitantly carrying plutonium values.

  12. Characterization of Thin Film Dissolution in Water with in Situ Monitoring of Film Thickness Using Reflectometry.

    PubMed

    Yersak, Alexander S; Lewis, Ryan J; Tran, Jenny; Lee, Yung C

    2016-07-13

    Reflectometry was implemented as an in situ thickness measurement technique for rapid characterization of the dissolution dynamics of thin film protective barriers in elevated water temperatures above 100 °C. Using this technique, multiple types of coatings were simultaneously evaluated in days rather than years. This technique enabled the uninterrupted characterization of dissolution rates for different coating deposition temperatures, postdeposition annealing conditions, and locations on the coating surfaces. Atomic layer deposition (ALD) SiO2 and wet thermally grown SiO2 (wtg-SiO2) thin films were demonstrated to be dissolution-predictable barriers for the protection of metals such as copper. A ∼49% reduction in dissolution rate was achieved for ALD SiO2 films by increasing the deposition temperatures from 150 to 300 °C. ALD SiO2 deposited at 300 °C and followed by annealing in an inert N2 environment at 1065 °C resulted in a further ∼51% reduction in dissolution rate compared with the nonannealed sample. ALD SiO2 dissolution rates were thus lowered to values of wtg-SiO2 in water by the combination of increasing the deposition temperature and postdeposition annealing. Thin metal films, such as copper, without a SiO2 barrier corroded at an expected ∼1-2 nm/day rate when immersed in room temperature water. This measurement technique can be applied to any optically transparent coating.

  13. 25 CFR 11.606 - Dissolution proceedings.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the... proceeding for dissolution of marriage or legal separation shall allege that the marriage is irretrievably... under the jurisdiction of the court of each party; (2) The date of the marriage and the place at...

  14. 25 CFR 11.606 - Dissolution proceedings.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the... proceeding for dissolution of marriage or legal separation shall allege that the marriage is irretrievably... under the jurisdiction of the court of each party; (2) The date of the marriage and the place at...

  15. 25 CFR 11.606 - Dissolution proceedings.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the... proceeding for dissolution of marriage or legal separation shall allege that the marriage is irretrievably... under the jurisdiction of the court of each party; (2) The date of the marriage and the place at...

  16. 25 CFR 11.606 - Dissolution proceedings.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the... proceeding for dissolution of marriage or legal separation shall allege that the marriage is irretrievably... under the jurisdiction of the court of each party; (2) The date of the marriage and the place at...

  17. 25 CFR 11.606 - Dissolution proceedings.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the... proceeding for dissolution of marriage or legal separation shall allege that the marriage is irretrievably... under the jurisdiction of the court of each party; (2) The date of the marriage and the place at...

  18. Stirring effect on kaolinite dissolution rate

    NASA Astrophysics Data System (ADS)

    Metz, Volker; Ganor, Jiwchar

    2001-10-01

    Experiments were carried out measuring kaolinite dissolution rates using stirred and nonstirred flow-through reactors at pHs 2 to 4 and temperatures of 25°C, 50°C, and 70°C. The results show an increase of kaolinite dissolution rate with increasing stirring speed. The stirring effect is reversible, i.e., as the stirring slows down the dissolution rate decreases. The effect of stirring speed on kaolinite dissolution rate is higher at 25°C than at 50°C and 70°C and at pH 4 than at pHs 2 and 3. It is suggested that fine kaolinite particles are formed as a result of stirring-induced spalling or abrasion of kaolinite. These very fine particles have an increased ratio of reactive surface area to specific surface area, which results in enhancement of kaolinite dissolution rate. A balance between production and dissolution of the fine particles explains both the reversibility and the temperature and pH dependence of the stirring effect. Since the stirring effect on kaolinite dissolution rate varies with temperature and pH, measurement of kinetic parameters such as activation energy may be influenced by stirring. Therefore, standard use of nonagitated reaction vessels for kinetic experiments of mineral dissolution and precipitation is recommended, at least for slow reactions that are surface controlled.

  19. Thermal dissolution of solid fossil fuels

    SciTech Connect

    E.G. Gorlov

    2007-10-15

    The use of oil shales and coals in the processes of thermal dissolution is considered. It is shown that thermal dissolution is a mode of liquefaction of solid fossil fuels and can be used both independently and in combination with liquefaction of coals and processing of heavy petroleum residues.

  20. CALCIUM CARBONATE DISSOLUTION RATE IN LIMESTONE CONTACTORS

    EPA Science Inventory

    The rate of carbonate mineral dissolution from limestone was studied using a rotating disk apparatus and samples of limestone of varied composition. The purpose of this study was to determine the effect of limestone composition on the kinetics of carbonate mineral dissolution. Th...

  1. Emotional and Cognitive Coping in Relationship Dissolution

    ERIC Educational Resources Information Center

    Wrape, Elizabeth R.; Jenkins, Sharon Rae; Callahan, Jennifer L.; Nowlin, Rachel B.

    2016-01-01

    Dissolution of a romantic relationship can adversely affect functioning among college students and represents one primary reason for seeking campus counseling. This study examined the associations among common coping strategies and distress following relationship dissolution. Avoidance and repetitive negative thinking (RNT) were significantly…

  2. 25 CFR 11.605 - Dissolution.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... Domestic Relations § 11.605 Dissolution. (a) The Court of Indian Offenses shall enter a decree of... these matters. (b) If a party requests a decree of legal separation rather than a decree of dissolution of marriage, the Court of Indian Offenses shall grant the decree in that form unless the other...

  3. Dissolution enthalpies of cellulose in ionic liquids.

    PubMed

    Parviainen, Helena; Parviainen, Arno; Virtanen, Tommi; Kilpeläinen, Ilkka; Ahvenainen, Patrik; Serimaa, Ritva; Grönqvist, Stina; Maloney, Thaddeus; Maunu, Sirkka Liisa

    2014-11-26

    In this work, interactions between cellulose and ionic liquids were studied calorimetrically and by optical microscopy. Two novel ionic liquids (1,5-Diazabicyclo[4.3.0]non-5-enium propionate and N-methyl-1,5-diazabicyclo[4.3.0]non-5-enium dimethyl phosphate) and 1-ethyl-3-methylimidazolium acetate-water mixtures were used as solvents. Optical microscopy served in finding the extent of dissolution and identifying the dissolution pattern of the cellulose sample. Calorimetric studies identified a peak relating to dissolution of cellulose in solvent. The transition did, however, not indicate complete dissolution, but rather dissolution inside fibre or fibrils. This method was used to study differences between four cellulose samples with different pretreatment or origins.

  4. Synthetic coprecipitates of exopolysaccharides and ferrihydrite. Part II: Siderophore-promoted dissolution

    NASA Astrophysics Data System (ADS)

    Mikutta, Christian; Kretzschmar, Ruben

    2008-02-01

    Ferrihydrite (Fh) coprecipitated with exopolymers of plants and microbes may differ in its geochemical reactivity from its abiotic counterpart. We synthesized Fh in the presence and absence of acid polysaccharides (polygalacturonic acid (PGA), alginate, xanthan) and characterized the physical and structural properties of the precipitates formed [Mikutta C., Mikutta R., Bonneville S., Wagner F., Voegelin A., Christl I. and Kretzschmar R. (2008) Synthetic coprecipitates of exopolysaccharides and ferrihydrite. Part I: Characterization. Geochim. Cosmochim. Acta]. In this paper, we focus on the reactivity of PGA and alginate coprecipitates and pure Fh, and studied their interaction with the microbial siderophore desferrioxamine B (DFOB) in the presence and absence of low molecular weight organic (LMWO) acid anions (malate, citrate). Batch adsorption and dissolution experiments were performed in the dark at pH 7 in 10 mM NaClO 4 background electrolyte. In the dissolution experiments, different modes of ligand addition were applied (single, simultaneous, stepwise). With an estimated Langmuir sorption maximum of 15 mmol/mol Fe, a PGA coprecipitate with 11% C org sorbed about four times as much DFOB as pure Fh, and the amount of DFOB sorbed was ˜4-fold larger than estimated from the sum of DFOB sorption to pure Fh and PGA alone. The apparent initial dissolution rates, Rapp-initial, and pseudo-first order rate coefficients, k, of the coprecipitates exceeded those of pure Fh by up to two orders of magnitude. Citrate and malate exerted a strong synergistic effect on the DFOB-promoted dissolution of pure Fh, whereas synergistic effects of both anions were absent or negligible for the coprecipitates. Rapp-initial of the citrate and DFOB-promoted dissolution of PGA coprecipitates increased with increasing molar C/Fe ratio of the coprecipitates, independent of the charge of the LMWO ligand. Our results indicate that polyuronates stabilize Fh particles sterically and /or

  5. Hydrogen production from the dissolution of nano zero valent iron and its effect on anaerobic digestion.

    PubMed

    Huang, Yu-Xi; Guo, Jialiang; Zhang, Chunyang; Hu, Zhiqiang

    2016-01-01

    Nano zero valent iron (NZVI) has shown inhibition on methanogenesis in anaerobic digestion due to its reductive decomposition of cell membrane. The inhibition was accompanied by the accumulation of hydrogen gas due to rapid NZVI dissolution. It is not clear whether and how rapid hydrogen release from NZVI dissolution directly affects anaerobic digestion. In this study, the hydrogen release kinetics from NZVI (average size = 55 ± 11 nm) dissolution in deionized water under anaerobic conditions was first evaluated. The first-order NZVI dissolution rate constant was 2.62 ± 0.26 h(-1) with its half-life of 0.26 ± 0.03 h. Two sets of anaerobic digestion experiments (i.e., in the presence of glucose or without any substrate but at different anaerobic sludge concentrations) were performed to study the impact of H2 release from rapid NZVI dissolution, in which H2 was generated in a separate water bottle containing NZVI (i.e., ex situ H2 or externally supplied from NZVI dissolution) before hydrogen gas was introduced to anaerobic digestion. The results showed that the H2 partial pressure in the headspace of the digestion bottle reached as high as 0.27 atm due to rapid NZVI dissolution, resulting in temporary inhibition of methane production. Nevertheless, the 5-d cumulative methane volume in the group with ex situ H2 production due to NZVI dissolution was actually higher than that of control, suggesting NZVI inhibition on methanogenesis is solely due to the reductive decomposition of cell membrane after direct contact with NZVI.

  6. Coupled biotic-abiotic oxidation of organic matter by biogenic MnO_{2}

    NASA Astrophysics Data System (ADS)

    Gonzalez, Julia; Peña, Jasquelin

    2016-04-01

    Some reactive soil minerals are strongly implicated in stabilising organic matter. However, others can play an active role in the oxidation of organic molecules. In natural systems, layer-type manganese oxide minerals (MnO2) typically occur as biomineral assemblages consisting of mineral particles and microbial biomass. Both the mineral and biological fractions of the assemblage can be powerful oxidants of organic C. The biological compartment relies on a set of enzymes to drive oxidative transformations of reduced C-substrates, whereas MnO2 minerals are strong, less specific abiotic oxidants that are assumed to rely on interfacial interactions between C-substrates and the mineral surface. This project aims to understand the coupling between microbial C mineralization and abiotic C oxidation mediated by MnO2 in bacterial-MnO2 assemblages. Specifically, under conditions of high C turnover, microbial respiration can significantly alter local pH, dissolved oxygen and pool of available reductants, which may modify rates and mechanism of C oxidation by biotic and abiotic components. We first investigated changes in the solution chemistry of Pseudomonas putida suspensions exposed to varying concentrations of glucose, chosen to represent readily bioavailable substrates in soils. Glucose concentrations tested ranged between 0 and 5.5mM and changes in pH, dissolved oxygen and dissolved organic and inorganic carbon were tracked over 48h. We then combined literature review and wet-chemical experiments to compile the pH dependence of rates of organic substrate oxidation by MnO2, including glucose. Our results demonstrate a strong pH dependence for these abiotic reactions. In assemblages of P. putida - MnO2, kinetic limitations for abiotic C oxidation by MnO2 are overcome by changes in biogeochemical conditions that result from bacterial C metabolism. When extrapolated to a soil solution confronted to an input of fresh dissolved organic matter, bacterial C metabolism of the

  7. Abiotic and biotic factors influencing the mobility of arsenic in groundwater of a through-flow island in the Okavango Delta, Botswana

    NASA Astrophysics Data System (ADS)

    Mladenov, Natalie; Wolski, Piotr; Hettiarachchi, Ganga M.; Murray-Hudson, Michael; Enriquez, Hersy; Damaraju, Sivaramakrishna; Galkaduwa, Madhubhashini B.; McKnight, Diane M.; Masamba, Wellington

    2014-10-01

    The Okavango Delta of Botswana is a large arid-zone wetland comprising 20,000 km2 of permanent and seasonal floodplains and over 100,000 islands. It has been shown that island groundwater can have very high dissolved arsenic (As) concentration, but the abiotic and biotic controls on As mobility are not well understood in this setting. At New Island, an island located in the seasonal swamp, dissolved As concentration increased from below detection limits in the surface water to 180 μg/L in groundwater, present as As(III) species. We investigated the relative importance of hydrologic, geochemical, and geomicrobial processes, as well as influences of recent extreme flooding events, in mobilizing and sequestering As in the shallow groundwater system under this island. Our results suggest that evapotranspiration and through-flow conditions control the location of the high arsenic zone. A combination of processes is hypothesized to control elevated As in the concentration zone of New Island: high evapotranspiration rates concentrate As and other solutes, more alkaline pH leads to desorption of arsenic or dissolution of arsenic sulfides, and formation of thioarsenic complexes acts to keep arsenic in solution. Evidence from X-ray absorption near-edge structure spectroscopy (XANES) and sulfate reducing bacteria (SRB) measurements further suggests that SRBs influence arsenic sequestration as orpiment (As2S3). Although dissolved organic matter (DOM) was not significantly correlated to dissolved As in the groundwater, our results suggest that DOM may serve as an electron donor for sulfate reduction or other microbial reactions that influence redox state and As mobility. These results have important implications for water management in the region and in other large wetland environments. The processes evaluated in this study are also relevant for arsenic removal in subsurface constructed wetland systems that may exhibit rapidly changing processes over small spatial scales.

  8. The abiotic degradation of soil organic matter to oxalic acid

    NASA Astrophysics Data System (ADS)

    Studenroth, Sabine; Huber, Stefan; Schöler, H. F.

    2010-05-01

    The abiotic degradation of soil organic matter to volatile organic compounds was studied intensely over the last years (Keppler et al., 2000; Huber et al., 2009). It was shown that soil organic matter is oxidised due to the presence of iron (III), hydrogen peroxide and chloride and thereby produces diverse alkyl halides, which are emitted into the atmosphere. The formation of polar halogenated compounds like chlorinated acetic acids which are relevant toxic environmental substances was also found in soils and sediments (Kilian et al., 2002). The investigation of the formation of other polar halogenated and non-halogenated compounds like diverse mono- and dicarboxylic acids is going to attain more and more importance. Due to its high acidity oxalic acid might have impacts on the environment e.g., nutrient leaching, plant diseases and negative influence on microbial growth. In this study, the abiotic formation of oxalic acid in soil is examined. For a better understanding of natural degradation processes mechanistic studies were conducted using the model compound catechol as representative for structural elements of the humic substances and its reaction with iron (III) and hydrogen peroxide. Iron is one of the most abundant elements on earth and hydrogen peroxide is produced by bacteria or through incomplete reduction of oxygen. To find suitable parameters for an optimal reaction and a qualitative and quantitative analysis method the following reaction parameters are varied: concentration of iron (III) and hydrogen peroxide, time dependence, pH-value and influence of chloride. Analysis of oxalic acid was performed employing an ion chromatograph equipped with a conductivity detector. The time dependent reaction shows a relatively fast formation of oxalic acid, the optimum yield is achieved after 60 minutes. Compared to the concentration of catechol an excess of hydrogen peroxide as well as a low concentration of iron (III) are required. In absence of chloride the

  9. Recent Molecular Advances on Downstream Plant Responses to Abiotic Stress

    PubMed Central

    dos Reis, Sávio Pinho; Lima, Aline Medeiros; de Souza, Cláudia Regina Batista

    2012-01-01

    Abiotic stresses such as extremes of temperature and pH, high salinity and drought, comprise some of the major factors causing extensive losses to crop production worldwide. Understanding how plants respond and adapt at cellular and molecular levels to continuous environmental changes is a pre-requisite for the generation of resistant or tolerant plants to abiotic stresses. In this review we aimed to present the recent advances on mechanisms of downstream plant responses to abiotic stresses and the use of stress-related genes in the development of genetically engineered crops. PMID:22942725

  10. Polyamines and abiotic stress tolerance in plants

    PubMed Central

    Gill, Sarvajeet Singh

    2010-01-01

    Environmental stresses including climate change, especially global warming, are severely affecting plant growth and productivity worldwide. It has been estimated that two-thirds of the yield potential of major crops are routinely lost due to the unfavorable environmental factors. On the other hand, the world population is estimated to reach about 10 billion by 2050, which will witness serious food shortages. Therefore, crops with enhanced vigour and high tolerance to various environmental factors should be developed to feed the increasing world population. Maintaining crop yields under adverse environmental stresses is probably the major challenge facing modern agriculture where polyamines can play important role. Polyamines (PAs)(putrescine, spermidine and spermine) are group of phytohormone-like aliphatic amine natural compounds with aliphatic nitrogen structure and present in almost all living organisms including plants. Evidences showed that polyamines are involved in many physiological processes, such as cell growth and development and respond to stress tolerance to various environmental factors. In many cases the relationship of plant stress tolerance was noted with the production of conjugated and bound polyamines as well as stimulation of polyamine oxidation. Therefore, genetic manipulation of crop plants with genes encoding enzymes of polyamine biosynthetic pathways may provide better stress tolerance to crop plants. Furthermore, the exogenous application of PAs is also another option for increasing the stress tolerance potential in plants. Here, we have described the synthesis and role of various polyamines in abiotic stress tolerance in plants. PMID:20592804

  11. Abiotic stress and the plant circadian clock

    PubMed Central

    Sanchez, Alfredo; Shin, Jieun

    2011-01-01

    In this review, we focus on the interaction between the circadian clock of higher plants to that of metabolic and physiological processes that coordinate growth and performance under a predictable, albeit changing environment. In this, the phytochrome and cryptochrome photoreceptors have shown to be important, but not essential for oscillator control under diurnal cycles of light and dark. From this foundation, we will examine how emerging findings have firmly linked the circadian clock, as a central mediator in the coordination of metabolism, to maintain homeostasis. This occurs by oscillator synchronization of global transcription, which leads to a dynamic control of a host of physiological processes. These include the determination of the levels of primary and secondary metabolites, and the anticipation of future environmental stresses, such as mid-day drought and midnight coldness. Interestingly, metabolic and stress cues themselves appear to feedback on oscillator function. In such a way, the circadian clock of plants and abiotic-stress tolerance appear to be firmly interconnected processes. PMID:21325898

  12. Molecular dynamic simulations of ocular tablet dissolution.

    PubMed

    Ru, Qian; Fadda, Hala M; Li, Chung; Paul, Daniel; Khaw, Peng T; Brocchini, Steve; Zloh, Mire

    2013-11-25

    Small tablets for implantation into the subconjunctival space in the eye are being developed to inhibit scarring after glaucoma filtration surgery (GFS). There is a need to evaluate drug dissolution at the molecular level to determine how the chemical structure of the active may correlate with dissolution in the nonsink conditions of the conjunctival space. We conducted molecular dynamics simulations to study the dissolution process of tablets derived from two drugs that can inhibit fibrosis after GFS, 5-fluorouracil (5-FU) and the matrix metalloprotease inhibitor (MMPi), ilomastat. The dissolution was simulated in the presence of simple point charge (SPC) water molecules, and the liquid turnover of the aqueous humor in the subconjunctival space was simulated by removal of the dissolved drug molecules at regular intervals and replacement by new water molecules. At the end of the simulation, the total molecular solvent accessible surface area of 5-FU tablets increased by 60 times more than that of ilomastat as a result of tablet swelling and release of molecules into solution. The tablet dissolution pattern shown in our molecular dynamic simulations tends to correlate with experimental release profiles. This work indicates that a series of molecular dynamic simulations can be used to predict the influence of the molecular properties of a drug on its dissolution profile and could be useful during preformulation where sufficient amounts of the drug are not always available to perform dissolution studies.

  13. Distinct iron isotopic signatures and supply from marine sediment dissolution.

    PubMed

    Homoky, William B; John, Seth G; Conway, Tim M; Mills, Rachel A

    2013-01-01

    Oceanic iron inputs must be traced and quantified to learn how they affect primary productivity and climate. Chemical reduction of iron in continental margin sediments provides a substantial dissolved flux to the oceans, which is isotopically lighter than the crust, and so may be distinguished in seawater from other sources, such as wind-blown dust. However, heavy iron isotopes measured in seawater have recently led to the proposition of another source of dissolved iron from 'non-reductive' dissolution of continental margins. Here we present the first pore water iron isotope data from a passive-tectonic and semi-arid ocean margin (South Africa), which reveals a smaller and isotopically heavier flux of dissolved iron to seawater than active-tectonic and dysoxic continental margins. These data provide in situ evidence of non-reductive iron dissolution from a continental margin, and further show that geological and hydro-climatic factors may affect the amount and isotopic composition of iron entering the ocean.

  14. Mechanism of Uranium Reduction and Immobilization in Desulfovibrio vulgaris Biofilms.

    PubMed

    Stylo, Malgorzata; Neubert, Nadja; Roebbert, Yvonne; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-09-01

    The prevalent formation of noncrystalline U(IV) species in the subsurface and their enhanced susceptibility to reoxidation and remobilization, as compared to crystalline uraninite, raise concerns about the long-term sustainability of the bioremediation of U-contaminated sites. The main goal of this study was to resolve the remaining uncertainty concerning the formation mechanism of noncrystalline U(IV) in the environment. Controlled laboratory biofilm systems (biotic, abiotic, and mixed biotic-abiotic) were probed using a combination of U isotope fractionation and X-ray absorption spectroscopy (XAS). Regardless of the mechanism of U reduction, the presence of a biofilm resulted in the formation of noncrystalline U(IV). Our results also show that biotic U reduction is the most effective way to immobilize and reduce U. However, the mixed biotic-abiotic system resembled more closely an abiotic system: (i) the U(IV) solid phase lacked a typically biotic isotope signature and (ii) elemental sulfur was detected, which indicates the oxidation of sulfide coupled to U(VI) reduction. The predominance of abiotic U reduction in our systems is due to the lack of available aqueous U(VI) species for direct enzymatic reduction. In contrast, in cases where bicarbonate is present at a higher concentration, aqueous U(VI) species dominate, allowing biotic U reduction to outcompete the abiotic processes.

  15. Microbial extracellular polysaccharides and plagioclase dissolution

    SciTech Connect

    Welch, S.A.; Barker, W.W.; Banfield, J.F.

    1999-05-01

    Bytownite feldspar was dissolved in batch reactors in solutions of starch (glucose polymer), gum xanthan (glucose, mannose, glucuronic acid), pectin (poly-galacturonic acid), and four alginates (mannuronic and guluronic acid) with a range of molecular weights (low, medium, high and uncharacterized) to evaluate the effect of extracellular microbial polymers on mineral dissolution rates. Solutions were analyzed for dissolved Si and Al as an indicator of feldspar dissolution. At neutral pH, feldspar dissolution was inhibited by five of the acid polysaccharides, gum xanthan, pectin, alginate low, alginate medium, alginate high, compared to an organic-free control. An uncharacterized alginate substantially enhanced both Si and Al release from the feldspar. Starch, a neutral polysaccharide, had no apparent effect. Under mildly acidic conditions, initial pH {approx} 4, all of the polymers enhanced feldspar dissolution compared to the inorganic controls. Si release from feldspar in starch solution exceeded the control by a factor of three. Pectin and gum xanthan increased feldspar dissolution by a factor of 10, and the alginates enhanced feldspar dissolution by a factor of 50 to 100. Si and Al concentrations increased with time, even though solutions were supersaturated with respect to several possible secondary phases. Under acidic conditions, initial pH {approx} 3, below the pK{sub a} of the carboxylic acid groups, dissolution rates increased, but the relative increase due to the polysaccharides is lower, approximately a factor of two to ten. Microbial extracellular polymers play a complex role in mineral weathering. Polymers appear to inhibit dissolution under some conditions, possibly by irreversibly binding to the mineral surfaces. The extracellular polysaccharides can also enhance dissolution by providing protons and complexing with ions in solution.

  16. Oxidative UO2 dissolution induced by soluble Mn(III).

    PubMed

    Wang, Zimeng; Xiong, Wei; Tebo, Bradley M; Giammar, Daniel E

    2014-01-01

    The stability of UO2 is critical to the success of reductive bioremediation of uranium. When reducing conditions are no longer maintained, Mn redox cycling may catalytically mediate the oxidation of UO2 and remobilization of uranium. Ligand-stabilized soluble Mn(III) was recently recognized as an important redox-active intermediate in Mn biogeochemical cycling. This study evaluated the kinetics of oxidative UO2 dissolution by soluble Mn(III) stabilized by pyrophosphate (PP) and desferrioxamine B (DFOB). The Mn(III)-PP complex was a potent oxidant that induced rapid UO2 dissolution at a rate higher than that by a comparable concentration of dissolved O2. However, the Mn(III)-DFOB complex was not able to induce oxidative dissolution of UO2. The ability of Mn(III) complexes to oxidize UO2 was probably determined by whether the coordination of Mn(III) with ligands allowed the attachment of the complexes to the UO2 surface to facilitate electron transfer. Systematic investigation into the kinetics of UO2 oxidative dissolution by the Mn(III)-PP complex suggested that Mn(III) could directly oxidize UO2 without involving particulate Mn species (e.g., MnO2). The expected 2:1 reaction stoichiometry between Mn(III) and UO2 was observed. The reactivity of soluble Mn(III) in oxidizing UO2 was higher at lower ratios of pyrophosphate to Mn(III) and lower pH, which is probably related to differences in the ligand-to-metal ratio and/or protonation states of the Mn(III)-pyrophosphate complexes. Disproportionation of Mn(III)-PP occurred at pH 9.0, and the oxidation of UO2 was then driven by both MnO2 and soluble Mn(III). Kinetic models were derived that provided excellent fits of the experimental results.

  17. In silico dissolution rates of pharmaceutical ingredients

    NASA Astrophysics Data System (ADS)

    Dogan, Berna; Schneider, Julian; Reuter, Karsten

    2016-10-01

    The correlation between in vitro dissolution rates and the efficiency of drug formulations establishes an opportunity for accelerated drug development. Using in silico methods to predict the dissolution rates bears the prospect of further efficiency gains by avoiding the actual synthesis of candidate formulations. Here, we present a computational protocol that achieves such prediction for molecular crystals at low undersaturation. The protocol exploits the classic spiral dissolution model to minimize the number of material parameters that require explicit molecular simulations. Comparison to available data for acetylsalicylic acid and alpha lactose monohydrate indicates a tunable accuracy within one order of magnitude.

  18. Circadian regulation of abiotic stress tolerance in plants

    PubMed Central

    Grundy, Jack; Stoker, Claire; Carré, Isabelle A.

    2015-01-01

    Extremes of temperatures, drought and salinity cause widespread crop losses throughout the world and impose severe limitations on the amount of land that can be used for agricultural purposes. Hence, there is an urgent need to develop crops that perform better under such abiotic stress conditions. Here, we discuss intriguing, recent evidence that circadian clock contributes to plants’ ability to tolerate different types of environmental stress, and to acclimate to them. The clock controls expression of a large fraction of abiotic stress-responsive genes, as well as biosynthesis and signaling downstream of stress response hormones. Conversely, abiotic stress results in altered expression and differential splicing of the clock genes, leading to altered oscillations of downstream stress-response pathways. We propose a range of mechanisms by which this intimate coupling between the circadian clock and environmental stress-response pathways may contribute to plant growth and survival under abiotic stress. PMID:26379680

  19. Abiotic stress responses in plant roots: a proteomics perspective

    PubMed Central

    Ghosh, Dipanjana; Xu, Jian

    2014-01-01

    Abiotic stress conditions adversely affect plant growth, resulting in significant decline in crop productivity. To mitigate and recover from the damaging effects of such adverse environmental conditions, plants have evolved various adaptive strategies at cellular and metabolic levels. Most of these strategies involve dynamic changes in protein abundance that can be best explored through proteomics. This review summarizes comparative proteomic studies conducted with roots of various plant species subjected to different abiotic stresses especially drought, salinity, flood, and cold. The main purpose of this article is to highlight and classify the protein level changes in abiotic stress response pathways specifically in plant roots. Shared as well as stressor-specific proteome signatures and adaptive mechanism(s) are simultaneously described. Such a comprehensive account will facilitate the design of genetic engineering strategies that enable the development of broad-spectrum abiotic stress-tolerant crops. PMID:24478786

  20. EVALUATION OF LOW TEMPERATURE ALUMINUM DISSOLUTION IN TANK 51

    SciTech Connect

    Pike, J

    2008-09-04

    Tank 41 that was stored and sampled in Tank 49 was determined to be supersaturated relative to aluminum. Supersaturation in Tank 49 is not a risk to LTAD. However, storing and processing of this supernate carries a risk of solids precipitation, primarily in the form of gibbsite or boehmite. Blending with the supernate in Tank 11 neither increases nor decreases this risk. LTAD was initiated as an opportunity to substantially mitigate the planned increase in canister production and DWPF lifecycle after the realization of more sludge solids stored in the HLW tanks. As determined from the preliminary evaluation of LTAD, the direct benefit of the decanted liquid stored in Tank 11 represents 45 canisters at 34% waste loading with potential indirect benefits for much larger reductions. Application of an aluminum dissolution process to the remaining high aluminum content sludge will potentially reduce the planned canister production by several hundred canisters at 34%-38% waste loading.

  1. Contributions of Fe Minerals to Abiotic Dechlorination

    EPA Science Inventory

    Most applications of enhanced in situ bioremediation are based on biological reductive dechlorination. Anaerobic metabolism can also produce reactive minerals that allow for in situ biogeochemical transformation of chlorinated organic contaminants such as PCE, TCE, and cis-DCE. ...

  2. Nucleotide Selectivity in Abiotic RNA Polymerization Reactions.

    PubMed

    Coari, Kristin M; Martin, Rebecca C; Jain, Kopal; McGown, Linda B

    2017-02-03

    In order to establish an RNA world on early Earth, the nucleotides must form polymers through chemical rather than biochemical reactions. The polymerization products must be long enough to perform catalytic functions, including self-replication, and to preserve genetic information. These functions depend not only on the length of the polymers, but also on their sequences. To date, studies of abiotic RNA polymerization generally have focused on routes to polymerization of a single nucleotide and lengths of the homopolymer products. Less work has been done the selectivity of the reaction toward incorporation of some nucleotides over others in nucleotide mixtures. Such information is an essential step toward understanding the chemical evolution of RNA. To address this question, in the present work RNA polymerization reactions were performed in the presence of montmorillonite clay catalyst. The nucleotides included the monophosphates of adenosine, cytosine, guanosine, uridine and inosine. Experiments included reactions of mixtures of an imidazole-activated nucleotide (ImpX) with one or more unactivated nucleotides (XMP), of two or more ImpX, and of XMP that were activated in situ in the polymerization reaction itself. The reaction products were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the lengths and nucleotide compositions of the polymerization products. The results show that the extent of polymerization, the degree of heteropolymerization vs. homopolymerization, and the composition of the polymeric products all vary among the different nucleotides and depend upon which nucleotides and how many different nucleotides are present in the mixture.

  3. Nucleotide Selectivity in Abiotic RNA Polymerization Reactions

    NASA Astrophysics Data System (ADS)

    Coari, Kristin M.; Martin, Rebecca C.; Jain, Kopal; McGown, Linda B.

    2017-02-01

    In order to establish an RNA world on early Earth, the nucleotides must form polymers through chemical rather than biochemical reactions. The polymerization products must be long enough to perform catalytic functions, including self-replication, and to preserve genetic information. These functions depend not only on the length of the polymers, but also on their sequences. To date, studies of abiotic RNA polymerization generally have focused on routes to polymerization of a single nucleotide and lengths of the homopolymer products. Less work has been done the selectivity of the reaction toward incorporation of some nucleotides over others in nucleotide mixtures. Such information is an essential step toward understanding the chemical evolution of RNA. To address this question, in the present work RNA polymerization reactions were performed in the presence of montmorillonite clay catalyst. The nucleotides included the monophosphates of adenosine, cytosine, guanosine, uridine and inosine. Experiments included reactions of mixtures of an imidazole-activated nucleotide (ImpX) with one or more unactivated nucleotides (XMP), of two or more ImpX, and of XMP that were activated in situ in the polymerization reaction itself. The reaction products were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the lengths and nucleotide compositions of the polymerization products. The results show that the extent of polymerization, the degree of heteropolymerization vs. homopolymerization, and the composition of the polymeric products all vary among the different nucleotides and depend upon which nucleotides and how many different nucleotides are present in the mixture.

  4. Detection of Abiotic Methane in Terrestrial Continental Hydrothermal Systems: Implications for Methane on Mars

    NASA Technical Reports Server (NTRS)

    Socki, Richard A.; Niles, Paul B.; Gibson, Everett K., Jr.; Romanek, Christopher S.; Zhang, Chuanlun L.; Bissada, Kadry K.

    2008-01-01

    The recent detection of methane in the Martian atmosphere and the possibility that its origin could be attributed to biological activity, have highlighted the importance of understanding the mechanisms of methane formation and its usefulness as a biomarker. Much debate has centered on the source of the methane in hydrothermal fluids, whether it is formed biologically by microorganisms, diagenetically through the decomposition of sedimentary organic matter, or inorganically via reduction of CO2 at high temperatures. Ongoing research has now shown that much of the methane present in sea-floor hydrothermal systems is probably formed through inorganic CO2 reduction processes at very high temperatures (greater than 400 C). Experimental results have indicated that methane might form inorganically at temperatures lower still, however these results remain controversial. Currently, methane in continental hydrothermal systems is thought to be formed mainly through the breakdown of sedimentary organic matter and carbon isotope equilibrium between CO2 and CH4 is thought to be rarely present if at all. Based on isotopic measurements of CO2 and CH4 in two continental hydrothermal systems, we suggest that carbon isotope equilibration exists at temperatures as low as 155 C. This would indicate that methane is forming through abiotic CO2 reduction at lower temperatures than previously thought and could bolster arguments for an abiotic origin of the methane detected in the martian atmosphere.

  5. An omics approach to understand the plant abiotic stress.

    PubMed

    Debnath, Mousumi; Pandey, Mukeshwar; Bisen, P S

    2011-11-01

    Abiotic stress can lead to changes in development, productivity, and severe stress and may even threaten survival of plants. Several environmental stresses cause drastic changes in the growth, physiology, and metabolism of plants leading to the increased accumulation of secondary metabolites. As medicinal plants are important sources of drugs, steps are taken to understand the effect of stress on the physiology, biochemistry, genomic, proteomic, and metabolic levels. The molecular responses of plants to abiotic stress are often considered as a complex process. They are mainly based on the modulation of transcriptional activity of stress-related genes. Many genes have been induced under stress conditions. The products of stress-inducible genes protecting against these stresses includes the enzymes responsible for the synthesis of various osmoprotectants. Genetic engineering of tolerance to abiotic stresses help in molecular understanding of pathways induced in response to one or more of the abiotic stresses. Systems biology and virtual experiments allow visualizing and understanding how plants work to overcome abiotic stress. This review discusses the omic approach to understand the plant response to abiotic stress with special emphasis on medicinal plant.

  6. Dissolution and Separation of Aluminum and Aluminosilicates

    SciTech Connect

    McFarlane, Joanna; Benker, Dennis; DePaoli, David W.; Felker, Leslie Kevin; Mattus, Catherine H.

    2015-12-19

    The selection of an aluminum alloy for target irradiation affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in the dissolver, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. Aluminosilicate dissolution presents challenges in a number of different areas, metals extraction from minerals, flyash treatment, and separations from aluminum alloys. We present experimental work that attempts to maximize dissolution of aluminum metal, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as a function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. Our data have been compared with published calculations of aluminum phase diagrams. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.

  7. Low temperature dissolution flowsheet for plutonium metal

    SciTech Connect

    Daniel, W. E.; Almond, P. M.; Rudisill, T. S.

    2016-05-01

    The H-Canyon flowsheet used to dissolve Pu metal for PuO2 production utilizes boiling HNO3. SRNL was requested to develop a complementary dissolution flowsheet at two reduced temperature ranges. The dissolution and H2 generation rates of Pu metal were investigated using a dissolving solution at ambient temperature (20-30 °C) and for an intermediate temperature of 50-60 °C. Additionally, the testing included an investigation of the dissolution rates and characterization of the off-gas generated from the ambient temperature dissolution of carbon steel cans and the nylon bags that contain the Pu metal when charged to the dissolver.

  8. [Phytobezoar dissolution with Coca-Cola].

    PubMed

    Martínez de Juan, F; Martínez-Lapiedra, C; Picazo, V

    2006-05-01

    The treatment of phytobezoar is empiric. The various therapeutic choices include dietary modifications, prokinetic drugs, gastric lavage, enzymatic dissolution, endoscopic treatment, and surgery. We present two cases of phytobezoar with successful outcome after Coca-Cola administration.

  9. Dissolution and Separation of Aluminum and Aluminosilicates

    DOE PAGES

    McFarlane, Joanna; Benker, Dennis; DePaoli, David W.; ...

    2015-12-19

    The selection of an aluminum alloy for target irradiation affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in the dissolver, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. Aluminosilicate dissolution presents challenges in a number of different areas, metals extraction from minerals, flyash treatment, and separations from aluminum alloys. We present experimental work that attempts to maximize dissolution of aluminum metal, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as amore » function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. Our data have been compared with published calculations of aluminum phase diagrams. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.« less

  10. The Alkaline Dissolution Rate of Calcite.

    PubMed

    Colombani, Jean

    2016-07-07

    Due to the widespread presence of calcium carbonate on Earth, several geochemical systems, among which is the global CO2 cycle, are controlled to a large extent by the dissolution and precipitation of this mineral. For this reason, the dissolution of calcite has been thoroughly investigated for decades. Despite this intense activity, a consensual value of the dissolution rate of calcite has not been found yet. We show here that the inconsistency between the reported values stems mainly from the variability of the chemical and hydrodynamic conditions of measurement. The spreading of the values, when compared in identical conditions, is much less than expected and is interpreted in terms of sample surface topography. This analysis leads us to propose benchmark values of the alkaline dissolution rate of calcite compatible with all the published values, and a method to use them in various chemical and hydrodynamic contexts.

  11. Impact of chlorine disinfectants on dissolution of the lead corrosion product PbO2.

    PubMed

    Xie, Yanjiao; Wang, Yin; Giammar, Daniel E

    2010-09-15

    Plattnerite (β-PbO(2)) is a corrosion product that develops on lead pipes that have been in contact with free chlorine present as a residual disinfectant. The reductive dissolution of PbO(2) can cause elevated lead concentrations in tap water when the residual disinfectant is switched from free chlorine to monochloramine. The objectives of this study were to quantify plattnerite dissolution rates in the presence of chlorine disinfectants, gain insights into dissolution mechanisms, and measure plattnerite's equilibrium solubility in the presence of free chlorine. The effects of free chlorine and monochloramine on the dissolution rates of plattnerite were quantified in completely mixed continuous-flow reactors at relevant pH and dissolved inorganic carbon conditions. Plattnerite dissolution rates decreased in the following order: no disinfectant > monochloramine > chlorine, which was consistent with the trend in the redox potential. Compared with experiments without disinfectant, monochloramine inhibited plattnerite dissolution in continuous-flow experiments. Although free chlorine maintained steady-state lead concentrations below the action level of 15 μg/L in flow-through experiments, in batch experiments lead concentrations exceeded the action level for longer residence times and approached an equilibrium value that was several orders of magnitude higher than that predicted from available thermodynamic data.

  12. Development and characterization of solid dispersion of piroxicam for improvement of dissolution rate using hydrophilic carriers

    PubMed Central

    Barzegar-Jalali, Mohammad; Ghanbarzadeh, Saeed; Adibkia, Khosro; Valizadeh, Hadi; Bibak, Siamak; Mohammadi, Ghobad; Siahi-Shadbad, Mohammad Reza

    2014-01-01

    Introduction: The main objective of this study was preparation and characterization of solid dispersion of piroxicam to enhance its dissolution rate. Methods: Solid dispersion formulations with different carriers including crospovidone, microcrystalline cellulose, Elaeagnus angustifolia fruit powder, with different drug to carrier ratios were prepared employing cogrinding method. Dissolution study of the piroxicam powders, physical mixtures and solid dispersions was performed in simulated gastric fluid and simulated intestinal fluid using USP Apparatus type II. The physical characterization of formulations were analyzed using powder X ray diffraction (PXRD), particle size analyzer and differential scanning calorimetry (DSC). Interactions between the drug and carriers were evaluated by Fourier transform infrared (FT-IR) spectroscopic method. Results: It was revealed that all of three carriers increase the dissolution rate of piroxicam from physical mixtures and especially in solid dispersions compared to piroxicam pure and treated powders. PXRD and DSC results confirmed the reduction of crystalline form of piroxicam. FT-IR analysis did not show any physicochemical interaction between drug and carriers in the solid dispersion formulations. Conclusion: Dissolution rate was dependent on the type and ratio of drug to carrier as well as pH of dissolution medium. Dissolution data of formulations were fitted well into the linear Weibull as well as non-linear logistic and suggested models. PMID:25337467

  13. Dissolution rates of prehnite, epidote, and albite

    SciTech Connect

    Rosemary, N.M. )

    1991-11-01

    Dissolution rates of prehnite and epidote in aqueous solutions were measured in the temperature range 25 to 90C, and as a function of pH. The dissolution rate of albite was measured at pH 1.4 at temperatures between 25 and 90C. Batch experiments using low ionic strength pH buffers in constant temperature water batch or ovens provided data on cumulative element release as a function of time. Steady state Si, Ca, Na, and Al release data obtained from these experiments were used to obtain limiting dissolution rates, where the term limiting rate denotes dissolution of a bulk mineral under conditions where it is far from equilibrium with the fluid. At 90C and at pH 1.4 to 6, prehnite and epidote dissolution rates decrease and are proportional to approximately {minus}0.3 pH for prehnite and {minus}0.2 pH for epidote. Above pH 6, prehnite dissolution becomes pH independent, by epidote dissolution increases with rates that are proportional to between +0.3 and +0.6 pH. Prehnite and epidote dissolution is linear and stoichiometric at low pH. At pH greater than 7, both minerals initially display preferential release of Si and Al relative to Ca; however, with increasing reaction dissolution becomes stoichiometric. This suggests that a Ca-enriched layer forms but reaches a steady state thickness which does not impede subsequent linear stoichiometric release. At pH 1.4, the limiting dissolution rate for albite is linear and stoichiometric. At pH 1.4, the activation energies are 18.12 {plus minus} 0.81 kcal mol{sup {minus}1} for prehnite, 19.76 {plus minus} 1.2 kcal mol{sup {minus}1} for epidote and 17.07 {plus minus} 1.6 kcal mol{sup {minus}1} for albite. At pH 6.5, the activation energy for prehnite dissolution is 20.73 {plus minus} 3.2 kcal mol{sup {minus}1}.

  14. Evaluating the role of re-adsorption of dissolved Hg(2+) during cinnabar dissolution using isotope tracer technique.

    PubMed

    Jiang, Ping; Li, Yanbin; Liu, Guangliang; Yang, Guidi; Lagos, Leonel; Yin, Yongguang; Gu, Baohua; Jiang, Guibin; Cai, Yong

    2016-11-05

    Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbed Hg on cinnabar surface via the reduction in spiked (202)Hg(2+). By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred μgL(-1), while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. These results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.

  15. Evaluating the role of re-adsorption of dissolved Hg2+ during cinnabar dissolution using isotope tracer technique

    DOE PAGES

    Jiang, Ping; Li, Yanbin; Liu, Guangliang; ...

    2016-06-02

    Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbedmore » Hg on cinnabar surface via the reduction in spiked 202Hg2+. By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred g L–1, while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. Lastly, these results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.« less

  16. Kinetics of anorthite dissolution in basaltic melt

    NASA Astrophysics Data System (ADS)

    Yu, Yi; Zhang, Youxue; Chen, Yang; Xu, Zhengjiu

    2016-04-01

    We report convection-free anorthite dissolution experiments in a basaltic melt at 1280-1500 °C and 0.5 GPa on two different crystallographic surfaces, (1 2 1 bar) and (3 bar 0 2) to investigate dissolution kinetics. The anisotropy of the anorthite dissolution rate along these two surfaces is negligible. Time series experiments at ∼1280 °C show that anorthite dissolution is mainly controlled by diffusion in the melt within experimental uncertainty. Analytical solutions were used to model the dissolution and diffusion processes, and to obtain the diffusivities and the saturation concentrations of the equilibrium-determining component (Al2O3) for anorthite dissolution into the basaltic melt. For the first time, we are able to show the physical and chemical characteristics of quench growth effect on the near-interface melt using high spatial resolution (0.3 μm) EDS analyses. For anorthite (An# ⩾ 90) saturation in a melt with 39-53 wt% SiO2 and ⩽0.4 wt% H2O, the concentration of Al2O3 in wt% depends on temperature as follows:

  17. Oxidative dissolution of uraninite precipitated on Navajo sandstone

    NASA Astrophysics Data System (ADS)

    Abdelouas, A.; Lutze, W.; Nuttall, H. E.

    1999-03-01

    Column and batch experiments were conducted with sandstone and ground water samples to investigate oxidation of uraninite precipitated by microbially mediated reduction of U(VI), a contaminant in ground water beneath a uranium mill tailings site near Tuba City, AZ, USA. Uraninite precipitated together with mackinawite (FeS 0.9) because Fe(III) from the sandstone and sulfate, another contaminant in the water were reduced together with U(VI). After completion of U(VI) reduction, experiments were conducted to find out whether uraninite is protected by mackinawite against reoxidation. Uncontaminated ground water from the same site, containing 7 mg/l of dissolved oxygen, was passed through the columns or mixed with sandstone in batch experiments. The results showed that small masses of uraninite, 0.1 μg/g of sandstone, are protected by mackinawite from reoxidation. Uraninite masses on the order of 0.1 μg/g correspond to U(VI) concentrations of 0.5 mg/l, typically encountered in uranium contaminated ground waters. Mackinawite is an effective buffer and is formed in sufficient quantity to provide long-term protection of uraninite. Uranium concentrations in ground water passed through the columns are too low (4 μg/l) to distinguish between dissolution and oxidative dissolution of uraninite. However, batch experiments showed that uraninite oxidation takes place.

  18. Polyamines and abiotic stress in plants: a complex relationship1

    PubMed Central

    Minocha, Rakesh; Majumdar, Rajtilak; Minocha, Subhash C.

    2014-01-01

    The physiological relationship between abiotic stress in plants and polyamines was reported more than 40 years ago. Ever since there has been a debate as to whether increased polyamines protect plants against abiotic stress (e.g., due to their ability to deal with oxidative radicals) or cause damage to them (perhaps due to hydrogen peroxide produced by their catabolism). The observation that cellular polyamines are typically elevated in plants under both short-term as well as long-term abiotic stress conditions is consistent with the possibility of their dual effects, i.e., being protectors from as well as perpetrators of stress damage to the cells. The observed increase in tolerance of plants to abiotic stress when their cellular contents are elevated by either exogenous treatment with polyamines or through genetic engineering with genes encoding polyamine biosynthetic enzymes is indicative of a protective role for them. However, through their catabolic production of hydrogen peroxide and acrolein, both strong oxidizers, they can potentially be the cause of cellular harm during stress. In fact, somewhat enigmatic but strong positive relationship between abiotic stress and foliar polyamines has been proposed as a potential biochemical marker of persistent environmental stress in forest trees in which phenotypic symptoms of stress are not yet visible. Such markers may help forewarn forest managers to undertake amelioration strategies before the appearance of visual symptoms of stress and damage at which stage it is often too late for implementing strategies for stress remediation and reversal of damage. This review provides a comprehensive and critical evaluation of the published literature on interactions between abiotic stress and polyamines in plants, and examines the experimental strategies used to understand the functional significance of this relationship with the aim of improving plant productivity, especially under conditions of abiotic stress. PMID:24847338

  19. Coupling microbial catabolic actions with abiotic redox processes: a new recipe for persistent organic pollutant (POP) removal.

    PubMed

    Jeon, Jong-Rok; Murugesan, Kumarasamy; Nam, In-Hyun; Chang, Yoon-Seok

    2013-01-01

    The continuous release of toxic persistent organic pollutants (POPs) into the environment has raised a need for effective cleanup methods. The tremendous natural diversity of microbial catabolic mechanisms suggests that catabolic routes may be applied to the remediation of POP-contaminated fields. A large number of the recalcitrant xenobiotics have been shown to be removable via the natural catabolic mechanisms of microbes, and detailed biochemical studies of the catabolic methods, together with the development of sophisticated genetic engineering, have led to the use of synthetic microbes for the bioremediation of POPs. However, the steric effects of substituted halogen moieties, microbe toxicity, and the low bioavailability of POPs still deteriorate the efficiency of removal strategies based on natural and synthetic catabolic mechanisms. Recently, abiotic redox processes that induce rapid reductive dehalogenation, hydroxyl radical-based oxidation, or electron shuttling have been reasonably coupled with microbial catabolic actions, thereby compensating for the drawbacks of biotic processes in POP removal. In this review, we first compare the pros and cons of individual methodologies (i.e., the natural and synthetic catabolism of microbes and the abiotic processes involving zero-valent irons, advanced oxidation processes, and small organic stimulants) for POP removal. We then highlight recent trends in coupling the biotic-abiotic methodologies and discuss how the processes are both feasible and superior to individual methodologies for POP cleanup. Cost-effective and environmentally sustainable abiotic redox actions could enhance the microbial bioremediation potential for POPs.

  20. Discriminative Dissolution Method for Benzoyl Metronidazole Oral Suspension.

    PubMed

    da Silva, Aline Santos; da Rosa Silva, Carlos Eduardo; Paula, Fávero Reisdorfer; da Silva, Fabiana Ernestina Barcellos

    2016-06-01

    A dissolution method for benzoyl metronidazole (BMZ) oral suspensions was developed and validated using a high-performance liquid chromatography (HPLC) method. After determination of sink conditions, dissolution profiles were evaluated using different dissolution media and agitation speeds. The sample insertion mode in dissolution media was also evaluated. The best conditions were obtained using a paddle, 50 rpm stirring speed, simulated gastric fluid (without pepsin) as the dissolution medium, and sample insertion by a syringe. These conditions were suitable for providing sink conditions and discriminatory power between different formulations. Through the tested conditions, the results can be considered specific, linear, precise, accurate, and robust. The dissolution profiles of five samples were compared using the similarity factor (f 2) and dissolution efficiency. The dissolution kinetics were evaluated and described by the Weibull model. Whereas there is no monograph for this pharmaceutical formulation, the dissolution method proposed can be considered suitable for quality control and dissolution profile comparison of different commercial formulations.

  1. Siderophore-Mediated Iron Dissolution from Nontronites Is Controlled by Mineral Cristallochemistry.

    PubMed

    Parrello, Damien; Zegeye, Asfaw; Mustin, Christian; Billard, Patrick

    2016-01-01

    Bacteria living in oxic environments experience iron deficiency due to limited solubility and slow dissolution kinetics of iron-bearing minerals. To cope with iron deprivation, aerobic bacteria have evolved various strategies, including release of siderophores or other organic acids that scavenge external Fe(III) and deliver it to the cells. This research investigated the role of siderophores produced by Pseudomonas aeruginosa in the acquisition of Fe(III) from two iron-bearing colloidal nontronites (NAu-1 and NAu-2), comparing differences in bioavailability related with site occupancy and distribution of Fe(III) in the two lattices. To avoid both the direct contact of the mineral colloids with the bacterial cells and the uncontrolled particle aggregation, nontronite suspensions were homogenously dispersed in a porous silica gel before the dissolution experiments. A multiparametric approach coupling UV-vis spectroscopy and spectral decomposition algorithm was implemented to monitor simultaneously the solubilisation of Fe and the production of pyoverdine in microplate-based batch experiments. Both nontronites released Fe in a particle concentration-dependent manner when incubated with the wild-type P. aeruginosa strain, however iron released from NAu-2 was substantially greater than from NAu-1. The profile of organic acids produced in both cases was similar and may not account for the difference in the iron dissolution efficiency. In contrast, a pyoverdine-deficient mutant was unable to mobilize Fe(III) from either nontronite, whereas iron dissolution occurred in abiotic experiments conducted with purified pyoverdine. Overall, our data provide evidence that P. aeruginosa indirectly mobilize Fe from nontronites primarily through the production of pyoverdine. The structural Fe present on the edges of NAu-2 rather than NAu-1 particles appears to be more bio-accessible, indicating that the distribution of Fe, in the tetrahedron and/or in the octahedron sites, governs

  2. Abiotic Stresses Downregulate Key Genes Involved in Nitrogen Uptake and Assimilation in Brassica juncea L.

    PubMed Central

    Goel, Parul; Singh, Anil Kumar

    2015-01-01

    Abiotic stresses such as salinity, drought and extreme temperatures affect nitrogen (N) uptake and assimilation in plants. However, little is known about the regulation of N pathway genes at transcriptional level under abiotic stress conditions in Brassica juncea. In the present work, genes encoding nitrate transporters (NRT), ammonium transporters (AMT), nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), asparagines synthetase (ASN) were cloned from Brassica juncea L. var. Varuna. The deduced protein sequences were analyzed to predict their subcellular localization, which confirmed localization of all the proteins in their respective cellular organelles. The protein sequences were also subjected to conserved domain identification, which confirmed presence of characteristic domains in all the proteins, indicating their putative functions. Moreover, expression of these genes was studied after 1h and 24h of salt (150 mM NaCl), osmotic (250 mM Mannitol), cold (4°C) and heat (42°C) stresses. Most of the genes encoding nitrate transporters and enzymes responsible for N assimilation and remobilization were found to be downregulated under abiotic stresses. The expression of BjAMT1.2, BjAMT2, BjGS1.1, BjGDH1 and BjASN2 was downregulated after 1hr, while expression of BjNRT1.1, BjNRT2.1, BjNiR1, BjAMT2, BjGDH1 and BjASN2 was downregulated after 24h of all the stress treatments. However, expression of BjNRT1.1, BjNRT1.5 and BjGDH2 was upregulated after 1h of all stress treatments, while no gene was found to be upregulated after 24h of stress treatments, commonly. These observations indicate that expression of most of the genes is adversely affected under abiotic stress conditions, particularly under prolonged stress exposure (24h), which may be one of the reasons of reduction in plant growth and development under abiotic stresses. PMID:26605918

  3. Exploring biotic vs. abiotic controls on syngenetic carbonate and clay mineral precipitation

    NASA Astrophysics Data System (ADS)

    Nascimento, Gabriela S.; McKenzie, Judith A.; Martinez Ruiz, Francisca; Bontognali, Tomaso R. R.; Vasconcelos, Crisogono

    2016-04-01

    A possible syngenetic relationship between carbonate and clay mineral precipitation has been reported for sedimentary rocks deposited in both lacustrine and marine sedimentary environments throughout the geological record. In particular, the mineral dolomite is often found associated with Mg-rich clays, such as stevensite. It is notable that this carbonate/clay association has been recorded in numerous samples taken from modern dolomite precipitating environments; for example, the Coorong lakes, South Australia, coastal sabkhas, Abu Dhabi, UAE and coastal hypersaline lagoons (Lagoa Vermelha and Brejo do Espinho) east of Rio de Janeiro, Brazil. An HRTEM study of samples from these three locations indicates a possible physical/chemical association between the Ca-dolomite and Mg-rich clays, demonstrating a probable co-precipitation. To test this hypothesis, we have conducted a series of biotic and abiotic laboratory experiments. If this syngenesis actually occurs in nature, what, if any, are the biogeochemical processes controlling these precipitation reactions? Our experiments were designed to determine the extent of the biotic versus abiotic component influencing the mineral precipitation and, in the case of a biotic influence, to understand the mechanism through which microorganisms might mediate the formation of clay minerals. The experiments were carried out in the Geomicrobiology Laboratory of ETH Zürich using cultures of living microbes and artificial organic compounds that simulate functional groups present in natural biofilms formed under both aerobic and anaerobic conditions. In addition, pure inorganic experiments were designed to understand possible physico-chemical conditions for diagenetic processes that could induce dissolution of Mg-carbonates and precipitation of Mg-rich clays. Our results show a remarkable biotic influence during the formation of clay minerals. Specifically, extracellular polymeric substances (EPS), released by microbes in their

  4. Dissolution behavior of a miscible polymer blend

    SciTech Connect

    Rodriguez, F.

    1996-12-31

    The orderly dissolution process with minimal swelling exhibited by poly(methyl methacrylate), PMMA, also is preserved in some blends of PMMA with other polymers. In the present work, dissolution rates for blends with up to 30 % poly(epichlorohydrin), PECH, have been measured in 4-methyl-2-pentanone at temperatures of 20 to 40{degrees}C. For films in the thickness range of 0.5 to 1 {mu}m, a laser interferometer yielded both the rate and the presence or absence of a transition layer at the polymer-solvent interface. The dissolution rate increases monotonically as the amount of PECH is increased. Beyond about 40% PECH, the dissolution process becomes less orderly. When a laser beam is reflected from a flat polymer film on a reflecting substrate like silicon, the reflected light intensity takes the form of a sinusoidal (or nearly sinusoidal) oscillation. The period of the oscillation can be related to the rate of dissolution. The amplitude of the oscillations gives a direct measure of refractive index of the polymer film. Changes in the amplitude (and, sometimes, the rate) give information about swelling. The offset between the maximum in the oscillations during dissolution compared to the reflectance of the bare wafer can be converted into a transition layer thickness although it is necessary to interpose a mathematical model for the concentration gradient in the layer. The most investigated {open_quotes}well-ordered{close_quotes} polymer is poly(methylmethacrylate), PMMA. Although primarily limited to lithography using electron beams or x-rays, PMMA continues to be a valuable reference polymer for dissolution studies.

  5. Comparison on Response and Dissolution Rates Between Ursodeoxycholic Acid Alone or in Combination With Chenodeoxycholic Acid for Gallstone Dissolution According to Stone Density on CT Scan: Strobe Compliant Observation Study.

    PubMed

    Lee, Jae Min; Hyun, Jong Jin; Choi, In Young; Yeom, Suk Keu; Kim, Seung Young; Jung, Sung Woo; Jung, Young Kul; Koo, Ja Seol; Yim, Hyung Joon; Lee, Hong Sik; Lee, Sang Woo; Kim, Chang Duck

    2015-12-01

    Medical dissolution of gallstone is usually performed on radiolucent gallstones in a functioning gallbladder. However, absence of visible gallstone on plain abdominal x-ray does not always preclude calcification. This study aims to compare the response and dissolution rates between ursodeoxycholic acid (UDCA) alone or in combination with chenodeoxycholic acid (CDCA) according to stone density on computed tomography (CT) scan. A total of 126 patients underwent dissolution therapy with either UDCA alone or combination of CDCA and UDCA (CNU) from December 2010 to March 2014 at Korea University Ansan Hospital. In the end, 81 patients (CNU group = 44, UDCA group = 37) completed dissolution therapy for 6 months. Dissolution rate (percentage reduction in the gallstone volume) and response to therapy (complete dissolution or partial dissolution defined as reduction in stone volume of >50%) were compared between the 2 groups. Dissolution and response rates of sludge was also compared between the 2 groups. The overall response rate was 50.6% (CNU group 43.2% vs UDCA group 59.5%, P = 0.14), and the overall dissolution rate was 48.34% (CNU group 41.5% vs UDCA group 56.5%, P = 0.13). When analyzed according to stone density, response rate was 33.3%, 87.1%, 30.0%, and 6.2% for hypodense, isodense, hyperdense, and calcified stones, respectively. Response rate (85.7% vs 88.2%, P = 0.83) and dissolution rate (81.01% vs 85.38%, P = 0.17) of isodense stones were similar between CNU and UDCA group. When only sludge was considered, the overall response rate was 87.5% (CNU group 71.4% vs UDCA group 94.1%, P = 0.19), and the overall dissolution rate was 85.42% (CNU group 67.9% vs UDCA group 92.7%, P = 0.23). Patients with isodense gallstones and sludge showed much better response to dissolution therapy with CNU and UDCA showing comparable efficacy. Therefore, CT scan should be performed before medication therapy if stone dissolution is intended.

  6. The interactive biotic and abiotic processes of DDT transformation under dissimilatory iron-reducing conditions.

    PubMed

    Jin, Xin; Wang, Fang; Gu, Chenggang; Yang, Xinglun; Kengara, Fredrick O; Bian, Yongrong; Song, Yang; Jiang, Xin

    2015-11-01

    The objective of the study was to elucidate the biotic and abiotic processes under dissimilatory iron reducing conditions involved in reductive dechlorination and iron reduction. DDT transformation was investigated in cultures of Shewanella putrefaciens 200 with/without α-FeOOH. A modified first-order kinetics model was developed and described DDT transformation well. Both the α-FeOOH reduction rate and the dechlorination rate of DDT were positively correlated to the biomass. Addition of α-FeOOH enhanced reductive dechlorination of DDT by favoring the cell survival and generating Fe(II) which was absorbed on the surface of bacteria and iron oxide. 92% of the absorbed Fe(II) was Na-acetate (1M) extractable. However, α-FeOOH also played a negative role of competing for electrons as reflected by the dechlorination rate of DDT was inhibited when increasing the α-FeOOH from 1 g L(-1) to 5 g L(-1). DDT was measured to be toxic to S. putrefaciens 200. The metabolites DDD, DDE and DDMU were recalcitrant to S. putrefaciens 200. The results suggested that iron oxide was not the key factor to promote the dissipation of DDX (DDT and the metabolites), whereas the one-electron reduction potential (E1) of certain organochlorines is the main factor and that the E1 higher than the threshold of the reductive driving forces of DIRB probably ensures the occur of reductive dechlorination.

  7. I Situ Laser Interferometry and Fluorescence Quenching Measurements of Poly(methyl Methacrylate) Thin Film Dissolution.

    NASA Astrophysics Data System (ADS)

    Wang, Fei

    The dissolution mechanisms of poly(methyl methacrylate) (PMMA) thin films in selected organic solvents was investigated. The dissolution was monitored using an in situ laser interferometry and fluorescence quenching (LIFQ) technique. Phenanthrene -labeled PMMA (Phe-PMMA) was used as a probe. Solutions of PMMA in toluene were spin-coated onto sapphire substrate to form films approximately 1 μm thick. The LIFQ results show that for PMMA film dissolution the transition layer thickness increases until the dissolution reaches its steady state. Then this final transition layer thickness (FTL) does not change until solvent vanguard molecules reach the surface of the substrate. Thermal history effects on PMMA film dissolution were examined. The dissolution rate decreases with increasing baking temperature and reaches a constant value for annealing at 150^circC. The results show that the thermal history has negligible effect on the factor of reduction f obtained from interferometry measurements. Fluorescence quenching measurements, by contrast, suggest that transition layer thickness decreases with increasing baking temperature. This suggests that the fluorescence quenching part of the LIFQ experiment is sensitive to the Fickian precursor portion of the solvent concentration profile in the film. The dissolution of PMMA films in acetone, 2-butanone, and 2-pentanone was studied. The results show that the dissolution rate decreases significantly with increasing solvent molecular size. Significant differences are found for FTL values calculated from LIFQ experiments and those calculated from f obtained by laser interferometry. Values of f are essentially identical in three solvents used. The effect of non-solvent on PMMA dissolution was studied by using 2-propanol and 2-butanone mixtures as solvents. The dissolution rate decreases with increasing non-solvent content. This indicates a strong thermodynamic effect, especially at high concentration of non-solvent. Molecular weight

  8. Evaluation of hydrodynamics in the basket dissolution apparatus using computational fluid dynamics--dissolution rate implications.

    PubMed

    D'Arcy, Deirdre M; Corrigan, Owen I; Healy, Anne Marie

    2006-02-01

    The aim of this work was to simulate the fluid flow in the basket dissolution apparatus using computational fluid dynamics (CFD) and to use the resulting velocity data (in combination with velocity data from simulated flow fields of the paddle dissolution apparatus) to relate velocities in the vicinity of a dissolving surface to dissolution rate. A further objective of the work was to compare fluid velocities between the basket and paddle dissolution apparatuses. CFD simulations of the basket apparatus were carried out using Fluent software. Flow field solutions were compared with results from flow visualisation techniques and with published ultrasound-pulse-echo velocity data. Velocity data from the flow field solution revealed velocities within the basket to be of the same order as those at the base of the paddle apparatus at the same rotation speed, supporting equivalent dissolution rate data from these locations. Dissolution rates were obtained for compacts of benzoic acid dissolved in 0.1 M HCl at 37 degrees C in the basket apparatus at 50 rpm. The relationship between maximum velocity in the vicinity of a dissolving surface and dissolution rate data from both the paddle and basket apparatuses was in good agreement with theoretical predictions. Analysis of the dissolution rates suggests a significant contribution from free convection in regions of low velocity at the base of the vessel of the basket apparatus.

  9. Plant cell organelle proteomics in response to abiotic stress.

    PubMed

    Hossain, Zahed; Nouri, Mohammad-Zaman; Komatsu, Setsuko

    2012-01-01

    Proteomics is one of the finest molecular techniques extensively being used for the study of protein profiling of a given plant species experiencing stressed conditions. Plants respond to a stress by alteration in the pattern of protein expression, either by up-regulating of the existing protein pool or by the synthesizing novel proteins primarily associated with plants antioxidative defense mechanism. Improved protein extraction protocols and advance techniques for identification of novel proteins have been standardized in different plant species at both cellular and whole plant level for better understanding of abiotic stress sensing and intracellular stress signal transduction mechanisms. In contrast, an in-depth proteome study of subcellular organelles could generate much detail information about the intrinsic mechanism of stress response as it correlates the possible relationship between the protein abundance and plant stress tolerance. Although a wealth of reviews devoted to plant proteomics are available, review articles dedicated to plant cell organelle proteins response under abiotic stress are very scanty. In the present review, an attempt has been made to summarize all significant contributions related to abiotic stresses and their impacts on organelle proteomes for better understanding of plants abiotic stress tolerance mechanism at protein level. This review will not only provide new insights into the plants stress response mechanisms, which are necessary for future development of genetically engineered stress tolerant crop plants for the benefit of humankind, but will also highlight the importance of studying changes in protein abundance within the cell organelles in response to abiotic stress.

  10. Dissolution of Fe(III)(hydr)oxides by an Aerobic Bacterium

    SciTech Connect

    Maurice, P.

    2004-12-13

    This project investigated the effects of an aerobic Pseudomonas mendocina bacterium on the dissolution of Fe(III)(hydr)oxides. The research is important because metals and radionuclides that adsorb to Fe(III)(hydr)oxides could potentially be remobilized by dissolving bacteria. We showed that P. mendocina is capable of dissolving Fe-bearing minerals by a variety of mechanisms, including production of siderophores, pH changes, and formation of reductants. The production of siderophores by P. mendocina was quantified under a variety of growth conditions. Finally, we demonstrated that microbial siderophores may adsorb to and enhance dissolution of clay minerals.

  11. Can the dissolution rates of individual minerals be used to describe whole rock dissolution?

    NASA Astrophysics Data System (ADS)

    Critelli, Teresa; Marini, Luigi; Schott, Jacques; Mavromatis, Vasileios; Apollaro, Carmine; Rinder, Thomas; De Rosa, Rosanna; Oelkers, Eric H.

    2014-05-01

    There have been an exhaustive number of laboratory studies determining the dissolution rates of individual minerals, but few have focused on the dissolution rates of minerals in multi-mineralic rocks. As a result, geochemical modeling of the temporal evolution of water-rock interaction is generally based on the assumption that the dissolution rate of minerals within a rock is equal to that measured in the laboratory on individual minerals. To verify this hypothesis, we have determined experimentally the dissolution rates of a well characterized metabasalt rock (Apollaro et al., 2011; Bloise et al., 2012) from the Mt. Reventino area (Southern Italy) at 25°C in mixed flow reactors. From these experiments and rock modal analysis we have deduced the dissolution rates of the minerals present in the rock (actinolite, albite, chlorite, epidote, and phengite). The major observation of this effort include: (i) only small differences in the dissolution rates of the individual minerals were observed; these rates are close to the whole-rock dissolution rate and (ii) the dissolution rates of albite and chlorite are in close agreement with laboratory rates obtained from individual mineral dissolution experiments, whereas those of actinolite, phengite, and epidote are not consistent with those reported in literature by 1-2 orders of magnitude. These results demonstrate that the dissolution rate of a given mineral in a multi-phase rock can be affected by the presence of the other minerals. Rock dissolution kinetics are likely constrained by the dissolution rates of the more abundant, lesser reactive mineral or minerals in the rock. These unreactive minerals can prevent the dissolution of the more rapidly dissolving mineral grains by keeping them out of contact with the aqueous phase. This implies that the overall weathering rate of rocks cannot be modelled from the measured dissolution rates of its individual minerals. If confirmed through further studies, this conclusion may

  12. Use of Silicate Minerals for pH Control during Reductive Dechlorination of Chloroethenes in Batch Cultures of Different Microbial Consortia

    PubMed Central

    Lacroix, Elsa; Brovelli, Alessandro; Barry, D. A.

    2014-01-01

    In chloroethene-contaminated sites undergoing in situ bioremediation, groundwater acidification is a frequent problem in the source zone, and buffering strategies have to be implemented to maintain the pH in the neutral range. An alternative to conventional soluble buffers is silicate mineral particles as a long-term source of alkalinity. In previous studies, the buffering potentials of these minerals have been evaluated based on abiotic dissolution tests and geochemical modeling. In the present study, the buffering potentials of four silicate minerals (andradite, diopside, fayalite, and forsterite) were tested in batch cultures amended with tetrachloroethene (PCE) and inoculated with different organohalide-respiring consortia. Another objective of this study was to determine the influence of pH on the different steps of PCE dechlorination. The consortia showed significant differences in sensitivities toward acidic pH for the different dechlorination steps. Molecular analysis indicated that Dehalococcoides spp. that were present in all consortia were the most pH-sensitive organohalide-respiring guild members compared to Sulfurospirillum spp. and Dehalobacter spp. In batch cultures with silicate mineral particles as pH-buffering agents, all four minerals tested were able to maintain the pH in the appropriate range for reductive dechlorination of chloroethenes. However, complete dechlorination to ethene was observed only with forsterite, diopside, and fayalite. Dissolution of andradite increased the redox potential and did not allow dechlorination. With forsterite, diopside, and fayalite, dechlorination to ethene was observed but at much lower rates for the last two dechlorination steps than with the positive control. This indicated an inhibition effect of silicate minerals and/or their dissolution products on reductive dechlorination of cis-dichloroethene and vinyl chloride. Hence, despite the proven pH-buffering potential of silicate minerals, compatibility with

  13. The impact of abiotic factors on cellulose synthesis.

    PubMed

    Wang, Ting; McFarlane, Heather E; Persson, Staffan

    2016-01-01

    As sessile organisms, plants require mechanisms to sense and respond to changes in their environment, including both biotic and abiotic factors. One of the most common plant adaptations to environmental changes is differential regulation of growth, which results in growth either away from adverse conditions or towards more favorable conditions. As cell walls shape plant growth, this differential growth response must be accompanied by alterations to the plant cell wall. Here, we review the impact of four abiotic factors (osmotic conditions, ionic stress, light, and temperature) on the synthesis of cellulose, an important component of the plant cell wall. Understanding how different abiotic factors influence cellulose production and addressing key questions that remain in this field can provide crucial information to cope with the need for increased crop production under the mounting pressures of a growing world population and global climate change.

  14. Integrated metabolomics for abiotic stress responses in plants.

    PubMed

    Nakabayashi, Ryo; Saito, Kazuki

    2015-04-01

    Plants are considered to biosynthesize specialized (traditionally called secondary) metabolites to adapt to environmental stresses such as biotic and abiotic stresses. The majority of specialized metabolites induced by abiotic stress characteristically exhibit antioxidative activity in vitro, but their function in vivo is largely yet to be experimentally confirmed. In this review, we highlight recent advances in the identification of the role of abiotic stress-responsive specialized metabolites with an emphasis on flavonoids. Integrated 'omics' analysis, centered on metabolomics with a series of plant resources differing in their flavonoid accumulation, showed experimentally that flavonoids play a major role in antioxidation in vivo. In addition, the results also suggest the role of flavonoids in the vacuole. To obtain more in-depth insights, chemical and biological challenges need to be addressed for the identification of unknown specialized metabolites and their in vivo functions.

  15. Criticality safety in high explosives dissolution

    SciTech Connect

    Troyer, S.D.

    1997-06-01

    In 1992, an incident occurred at the Pantex Plant in which the cladding around a fissile material component (pit) cracked during dismantlement of the high explosives portion of a nuclear weapon. Although the event did not result in any significant contamination or personnel exposures, concerns about the incident led to the conclusion that the current dismantlement process was unacceptable. Options considered for redesign, dissolution tooling design considerations, dissolution tooling design features, and the analysis of the new dissolution tooling are summarized. The final tooling design developed incorporated a number of safety features and provides a simple, self-contained, low-maintenance method of high explosives removal for nuclear explosive dismantlement. Analyses demonstrate that the tooling design will remain subcritical under normal, abnormal, and credible accident scenarios. 1 fig.

  16. Sodium sulfate - Deposition and dissolution of silica

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.

    1989-01-01

    The hot-corrosion process for SiO2-protected materials involves deposition of Na2SO4 and dissolution of the protective SiO2 scale. Dew points for Na2SO4 deposition are calculated as a function of pressure, sodium content, and sulfur content. Expected dissolution regimes for SiO2 are calculated as a function of Na2SO4 basicity. Controlled-condition burner-rig tests on quartz verify some of these predicted dissolution regimes. The basicity of Na2SO4 is not always a simple function of P(SO3). Electrochemical measurements of an (Na2O) show that carbon creates basic conditions in Na2SO4, which explains the extensive corrosion of SiO2-protected materials containing carbon, such as SiC.

  17. Formation and dissolution of bacterial colonies.

    PubMed

    Weber, Christoph A; Lin, Yen Ting; Biais, Nicolas; Zaburdaev, Vasily

    2015-09-01

    Many organisms form colonies for a transient period of time to withstand environmental pressure. Bacterial biofilms are a prototypical example of such behavior. Despite significant interest across disciplines, physical mechanisms governing the formation and dissolution of bacterial colonies are still poorly understood. Starting from a kinetic description of motile and interacting cells we derive a hydrodynamic equation for their density on a surface, where most of the kinetic coefficients are estimated from experimental data for N. gonorrhoeae bacteria. We use it to describe the formation of multiple colonies with sizes consistent with experimental observations. Finally, we show how the changes in the cell-to-cell interactions lead to the dissolution of the bacterial colonies. The successful application of kinetic theory to a complex far from equilibrium system such as formation and dissolution of living bacterial colonies potentially paves the way for the physical quantification of the initial stages of biofilm formation.

  18. Formation and dissolution of bacterial colonies

    NASA Astrophysics Data System (ADS)

    Weber, Christoph A.; Lin, Yen Ting; Biais, Nicolas; Zaburdaev, Vasily

    2015-09-01

    Many organisms form colonies for a transient period of time to withstand environmental pressure. Bacterial biofilms are a prototypical example of such behavior. Despite significant interest across disciplines, physical mechanisms governing the formation and dissolution of bacterial colonies are still poorly understood. Starting from a kinetic description of motile and interacting cells we derive a hydrodynamic equation for their density on a surface, where most of the kinetic coefficients are estimated from experimental data for N. gonorrhoeae bacteria. We use it to describe the formation of multiple colonies with sizes consistent with experimental observations. Finally, we show how the changes in the cell-to-cell interactions lead to the dissolution of the bacterial colonies. The successful application of kinetic theory to a complex far from equilibrium system such as formation and dissolution of living bacterial colonies potentially paves the way for the physical quantification of the initial stages of biofilm formation.

  19. Environmental Selenium Transformations: Distinguishing Abiotic and Biotic Factors Influencing Se Redox Transformations

    NASA Astrophysics Data System (ADS)

    Rosenfeld, C.; Kenyon, J.; James, B. R.; Santelli, C. M.

    2014-12-01

    Worldwide, selenium (Se) is proving to be a significant environmental concern, with many anthropogenic activities (e.g. coal mining and combustion, phosphate mining and agricultural irrigation) releasing potentially hazardous concentrations into surface and subsurface ecosystems. The US EPA is currently considering aquatic Se regulations, however no guidelines exist for excess soil Se, despite its ability to act as a persistent Se source. Various abiotic and biological processes mediate Se oxidation/reduction (redox) transformations in soils, thus influencing its solubility and bioavailability. In this research we assess (1) the ability of metal-transforming fungal species to aerobically reduce Se (Se (IV and/or VI) to Se(0)), and (2) the relative contribution of biotic and abiotic pathways for aerobic Se transformation. The primary objective of this research is to determine what abiotic and biotic factors enhance or restrict Se bioavailability. Results indicate that fungal-mediated Se reduction may be quite widespread, with at least 7 out of 10 species of known Mn(II)-oxidizing fungi isolated from metal impacted environments also identified as capable of aerobically reducing Se(IV) and/or Se(VI) to Se(0). Increasing concentrations of selenite (SeO32-; Se(IV)) and selenate (SeO42-; Se(VI)) generally reduced fungal growth rates, although selenate was more likely to inhibit fungal growth than selenite. To study oxidation, Se(0) was combined with Mn(III/IV) (hydr)oxides (henceforth referred to as Mn oxides), Se-transforming fungi (Alternaria alternata), and oxalic acid to mimic Se biogeochemistry at the plant-soil interface. Increased pH in the presence of fungi (7.2 with fungi, 6.8 without fungi after 24 days) was observed. Additionally, a slight decrease in redox potential was measured for incubations without Mn oxides (236 mV with Mn oxides, 205 mV without Mn oxides after 24 days), indicating that Mn oxides may enhance Se oxidation. Elemental Se oxidation rates to

  20. Abiotic systems for the catalytic treatment of solvent-contaminated water

    SciTech Connect

    Betterton, E.A.; Arnold, R.G.; Liu, Zhijie; Hollan, N.

    1996-12-31

    Three abiotic systems are described that catalyze the reductive dehalogenation of heavily halogenated environmental pollutants, including carbon tetrachloride, trichloroethene, and perchloroethene. These systems include (a) an electrolytic reactor in which the potential on the working electrode (cathode) is fixed by using a potentiostat, (b) a light-driven system consisting of a semiconductor and (covalently attached) macrocycle that can accept light transmitted via an optical fiber, and a light-driven, two-solvent (isopropanol/acetone) system that promotes dehalogenation reactions via an unknown mechanism. Each is capable of accelerating reductive dehalogenation reactions to very high rates under laboratory conditions. Typically, millimolar concentrations of aqueous-phase targets can be dehalogenated in minutes to hours. The description of each system includes the elements of reaction mechanism (to the extent known), typical kinetic data, and a discussion of the feasibility of applying this technology for the in situ destruction of hazardous compounds. 14 refs., 11 figs., 2 tabs.

  1. Dissolution Kinetics of Hausmannite in the Presence of the Siderophore, DFO-B

    NASA Astrophysics Data System (ADS)

    Pena, J.; Duckworth, O. W.; Sposito, G.

    2004-12-01

    Siderophores are organic ligands with a very high affinity for Fe(III) that have been shown to dissolve iron-(III) bearing minerals, thus increasing the bioavailability of this nutrient. Recent work also has shown that siderophores are capable of forming stable Mn (III) complexes in aqueous environments and that they can promote the dissolution of Mn (III)-bearing minerals such as manganite (γ -MnOOH). The goal of this study was to investigate the dissolution kinetics of the mineral, hausmannite, in the presence of desferrioxamine B (DFO-B), a common trihydroxamate siderophore, synthesized by fungi and bacteria, which may play a role in the reduction of soluble Mn (III) to Mn2^+. Hausmannite, a mixed-valence Mn (II, III) oxide mineral with the formula Mn3O4, is a proposed intermediate in the oxidation of Mn2^+ to thermodynamically stable MnO2. Hausmannite particles were synthesized and characterized by X-ray diffraction, BET specific surface area, and SEM imaging. The extent and rate of dissolution were measured as a function of pH and ligand concentration in batch reactors at 25 ± 3 ° C. Total Mn concentrations were measured by ICP-AES, while complexed-Mn (III) was measured using UV-Vis spectrophotometry. In the absence of the ligand, the greatest amount of total Mn in solution was observed at pH ≈ 5. There was a sharp decrease in the extent of dissolution at pH > 5, however, and no appreciable dissolution occurred at pH > 8. In the presence of DFO-B, ligand-promoted dissolution dominated at pH > 8, with more than 90 % of the ligand complexed within 1 hour after addition. Below pH ≈ 8, a complex combination of reductive, ligand-promoted, and proton-promoted dissolution was observed. Our study revealed that complex mechanisms are involved in the DFOB-promoted dissolution of hausmannite, with several dissolution pathways occurring simultaneously. The results presented herein may have implications for mineral weathering, the biogeochemical cycling of Fe and Mn

  2. Strategies to ameliorate abiotic stress-induced plant senescence.

    PubMed

    Gepstein, Shimon; Glick, Bernard R

    2013-08-01

    The plant senescence syndrome resembles, in many molecular and phenotypic aspects, plant responses to abiotic stresses. Both processes have an enormous negative global agro-economic impact and endanger food security worldwide. Premature plant senescence is the main cause of losses in grain filling and biomass yield due to leaf yellowing and deteriorated photosynthesis, and is also responsible for the losses resulting from the short shelf life of many vegetables and fruits. Under abiotic stress conditions the yield losses are often even greater. The primary challenge in agricultural sciences today is to develop technologies that will increase food production and sustainability of agriculture especially under environmentally limiting conditions. In this chapter, some of the mechanisms involved in abiotic stress-induced plant senescence are discussed. Recent studies have shown that crop yield and nutritional values can be altered as well as plant stress tolerance through manipulating the timing of senescence. It is often difficult to separate the effects of age-dependent senescence from stress-induced senescence since both share many biochemical processes and ultimately result in plant death. The focus of this review is on abiotic stress-induced senescence. Here, a number of the major approaches that have been developed to ameliorate some of the effects of abiotic stress-induced plant senescence are considered and discussed. Some approaches mimic the mechanisms already used by some plants and soil bacteria whereas others are based on development of new improved transgenic plants. While there may not be one simple strategy that can effectively decrease all losses of crop yield that accrue as a consequence of abiotic stress-induced plant senescence, some of the strategies that are discussed already show great promise.

  3. Microbial- and thiosulfate-mediated dissolution of mercury sulfide minerals and transformation to gaseous mercury

    SciTech Connect

    Vázquez-Rodríguez, Adiari I.; Hansel, Colleen M.; Zhang, Tong; Lamborg, Carl H.; Santelli, Cara M.; Webb, Samuel M.; Brooks, Scott C.

    2015-06-23

    Mercury (Hg) is a toxic heavy metal that poses significant environmental and human health risks. Soils and sediments, where Hg can exist as the Hg sulfide mineral metacinnabar (β-HgS), represent major Hg reservoirs in aquatic environments. Metacinnabar has historically been considered a sink for Hg in all but severely acidic environments, and thus disregarded as a potential source of Hg back to aqueous or gaseous pools. In this study, we conducted a combination of field and laboratory incubations to identify the potential for metacinnabar as a source of dissolved Hg within near neutral pH environments and the underpinning (a)biotic mechanisms at play. We show that the abundant and widespread sulfur-oxidizing bacteria of the genus Thiobacillus extensively colonized metacinnabar chips incubated within aerobic, near neutral pH creek sediments. Laboratory incubations of axenic Thiobacillus thioparus cultures led to the release of metacinnabar-hosted Hg(II) and subsequent volatilization to Hg(0). This dissolution and volatilization was greatly enhanced in the presence of thiosulfate, which served a dual role by enhancing HgS dissolution through Hg complexation and providing an additional metabolic substrate for Thiobacillus. These findings reveal a new coupled abiotic-biotic pathway for the transformation of metacinnabar-bound Hg(II) to Hg(0), while expanding the sulfide substrates available for neutrophilic chemosynthetic bacteria to Hg-laden sulfides. Lastly, they also point to mineral-hosted Hg as an underappreciated source of gaseous elemental Hg to the environment.

  4. Microbial- and thiosulfate-mediated dissolution of mercury sulfide minerals and transformation to gaseous mercury

    DOE PAGES

    Vázquez-Rodríguez, Adiari I.; Hansel, Colleen M.; Zhang, Tong; ...

    2015-06-23

    Mercury (Hg) is a toxic heavy metal that poses significant environmental and human health risks. Soils and sediments, where Hg can exist as the Hg sulfide mineral metacinnabar (β-HgS), represent major Hg reservoirs in aquatic environments. Metacinnabar has historically been considered a sink for Hg in all but severely acidic environments, and thus disregarded as a potential source of Hg back to aqueous or gaseous pools. In this study, we conducted a combination of field and laboratory incubations to identify the potential for metacinnabar as a source of dissolved Hg within near neutral pH environments and the underpinning (a)biotic mechanismsmore » at play. We show that the abundant and widespread sulfur-oxidizing bacteria of the genus Thiobacillus extensively colonized metacinnabar chips incubated within aerobic, near neutral pH creek sediments. Laboratory incubations of axenic Thiobacillus thioparus cultures led to the release of metacinnabar-hosted Hg(II) and subsequent volatilization to Hg(0). This dissolution and volatilization was greatly enhanced in the presence of thiosulfate, which served a dual role by enhancing HgS dissolution through Hg complexation and providing an additional metabolic substrate for Thiobacillus. These findings reveal a new coupled abiotic-biotic pathway for the transformation of metacinnabar-bound Hg(II) to Hg(0), while expanding the sulfide substrates available for neutrophilic chemosynthetic bacteria to Hg-laden sulfides. Lastly, they also point to mineral-hosted Hg as an underappreciated source of gaseous elemental Hg to the environment.« less

  5. DISSOLUTION OF IRRADIATED MURR FUEL ASSEMBLIES

    SciTech Connect

    Kyser, E.

    2010-06-17

    A literature survey on the dissolution of spent nuclear fuel from the University of Missouri Research Reactor (MURR) has been performed. This survey encompassed both internal and external literature sources for the dissolution of aluminum-clad uranium alloy fuels. The most limiting aspect of dissolution in the current facility configuration involves issues related to the control of the flammability of the off-gas from this process. The primary conclusion of this work is that based on past dissolution of this fuel in H-Canyon, four bundles of this fuel (initial charge) may be safely dissolved in a nitric acid flowsheet catalyzed with 0.002 M mercuric nitrate using a 40 scfm purge to control off-gas flammability. The initial charge may be followed by a second charge of up to five bundles to the same dissolver batch depending on volume and concentration constraints. The safety of this flowsheet relies on composite lower flammability limits (LFL) estimated from prior literature, pilot-scale work on the dissolution of site fuels, and the proposed processing flowsheet. Equipment modifications or improved LFL data offer the potential for improved processing rates. The fuel charging sequence, as well as the acid and catalyst concentrations, will control the dissolution rate during the initial portion of the cycle. These parameters directly impact the hydrogen and off-gas generation and, along with the purge flowrate determine the number of bundles that may be charged. The calculation approach within provides Engineering a means to determine optimal charging patterns. Downstream processing of this material should be similar to that of recent processing of site fuels requiring only minor adjustments of the existing flowsheet parameters.

  6. Do organic ligands affect calcite dissolution rates?

    NASA Astrophysics Data System (ADS)

    Oelkers, Eric H.; Golubev, Sergey V.; Pokrovsky, Oleg S.; Bénézeth, Pascale

    2011-04-01

    Steady state Iceland-spar calcite dissolution rates were measured at 25 °C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO 2 sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA 4-, succinate, D-glucosaminate, L-glutamate, D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of <0.05 mol/kg of these organic anions changes calcite dissolution rates by less than a factor of 2.5 with the exception of citrate and EDTA 4-. The presence of 0.05 mol/kg citrate and EDTA 4- increases calcite dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further calcite dissolution experiments were performed in the presence of organic polymers similar to bacterial exudates, cell exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change calcite dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.

  7. Dissolution enhancement of atorvastatin calcium by co-grinding technique.

    PubMed

    Prabhu, Priyanka; Patravale, Vandana

    2016-08-01

    Atorvastatin calcium (AC) is a BCS class II drug which shows poor bioavailability due to inadequate dissolution. Solid dispersions present a promising option to enhance the solubility of poorly soluble drugs. Co-grinding with hydrophilic excipients is an easy and economical technique to improve the solubility of poorly soluble drugs and is free from usage of organic solvents. The aim of the present study was to explore novel carrier VBP-1 (organosulphur compound) for formulating a solid dispersion by using a simple, commercially viable co-grinding technique to enhance the dissolution of AC and to develop an oral formulation of the same. Composition of the solid dispersion was optimized based on the release profile in pH 1.2 buffer. The optimized solid dispersion was further characterized for flow properties, DSC, FTIR spectroscopy, XRD, contact angle, SEM studies and release profile in phosphate buffer pH 6.8. The developed solid dispersion gave similar release profile as the innovator formulation (Lipitor® tablets) in both pH 1.2 buffer and phosphate buffer pH 6.8. The developed solid dispersion was formulated into hard gelatin capsules (size 3). The developed capsules were found to give similar release as the innovator formulation in both pH 1.2 buffer and phosphate buffer pH 6.8. The developed capsules were found to be stable for a period of 6 months. Anti-hyperlipidemic efficacy studies in rats showed higher reduction in cholesterol and triglyceride levels by the developed capsules in comparison to pure AC. In conclusion, novel carrier VBP-1 was successfully employed to enhance the dissolution of AC using co-grinding technique.

  8. Comparison of three preservation techniques for slowing dissolution of calcareous nannofossils in organic rich sediments

    USGS Publications Warehouse

    Seefelt, Ellen L.; Self-Trail, Jean; Schultz, Arthur P.

    2015-01-01

    In an attempt to halt or reduce dissolution of calcareous nannofossils in organic and/or pyrite-rich sediments, three different methods of short-term storage preservation were tested for efficacy: vacuum packing, argon gas replacement, and buffered water. Abundance counts of calcareous nannofossil assemblages over a six month period showed that none of the three preservation methods were consistently effective in reducing assemblage loss due to dissolution. In most cases, the control slides made at the drill site had more abundant calcareous nannofossil assemblages than those slides made from sediments stored via vacuum packing, argon gas replacement, or buffered water. Thin section and XRD analyses showed that in most cases, <1% pyrite was needed to drive the oxidation-reduction reaction that resulted in dissolution, even in carbonate-rich sediments.

  9. Nitric oxide signaling in plant responses to abiotic stresses.

    PubMed

    Qiao, Weihua; Fan, Liu-Min

    2008-10-01

    Nitric oxide (NO) plays important roles in diverse physiological processes in plants. NO can provoke both beneficial and harmful effects, which depend on the concentration and location of NO in plant cells. This review is focused on NO synthesis and the functions of NO in plant responses to abiotic environmental stresses. Abiotic stresses mostly induce NO production in plants. NO alleviates the harmfulness of reactive oxygen species, and reacts with other target molecules, and regulates the expression of stress responsive genes under various stress conditions.

  10. Starch as a determinant of plant fitness under abiotic stress.

    PubMed

    Thalmann, Matthias; Santelia, Diana

    2017-03-09

    I. II. III. IV. V. VI. References SUMMARY: Abiotic stresses, such as drought, high salinity and extreme temperatures, pose one of the most important constraints to plant growth and productivity in many regions of the world. A number of investigations have shown that plants, including several important crops, remobilize their starch reserve to release energy, sugars and derived metabolites to help mitigate the stress. This is an essential process for plant fitness with important implications for plant productivity under challenging environmental conditions. In this Tansley insight, we evaluate the current literature on starch metabolism in response to abiotic stresses, and discuss the key enzymes involved and how they are regulated.

  11. SIMFUEL dissolution studies in granitic groundwater

    NASA Astrophysics Data System (ADS)

    Ollila, K.

    1992-08-01

    The dissolution behaviour of an unirradiated chemical analogue of spent nuclear fuel, SIMFUEL, has been studied in synthetic, granitic groundwater under anoxic conditions. The release of U and the minor components Mo, Ru, Sr, Ba, La, Zr, Ce, Y, Rh, Pd and Nd was monitored during static (batch) leaching experiments. For molybdenum, ruthenium, strontium and barium, the leaching results (the total experimental time of 300 days) show a trend to congruent dissolution with the UO 2 matrix. The release rates of lanthanum, zirconium and cerium are higher relative to uranium. Sorption, colloidal and/or precipitation phenomena appear to play an important role under these experimental conditions.

  12. Microbial dissolution of silicate materials. Final report

    SciTech Connect

    Schwartzman, D.

    1996-03-26

    The objective of this research was to better understand the role of selected thermophilic bacteria in the colonization and dissolution of silicate minerals, with potential applications to the HDR Project. The demonstration of enhanced dissolution from microbial effects is critically dependent on providing a mineral bait within a media deficient in the critical nutrient found in the mineral (e.g., Fe). Reproducible experimental conditions in batch experiments require agitation to expose mineral powders, as well as nearly similar initial conditions for both inoculated cultures and controls. It is difficult, but not impossible to ensure reproducible conditions with microbes favoring filamentous growth habits.

  13. Improving the API dissolution rate during pharmaceutical hot-melt extrusion I: Effect of the API particle size, and the co-rotating, twin-screw extruder screw configuration on the API dissolution rate.

    PubMed

    Li, Meng; Gogos, Costas G; Ioannidis, Nicolas

    2015-01-15

    The dissolution rate of the active pharmaceutical ingredients in pharmaceutical hot-melt extrusion is the most critical elementary step during the extrusion of amorphous solid solutions - total dissolution has to be achieved within the short residence time in the extruder. Dissolution and dissolution rates are affected by process, material and equipment variables. In this work, we examine the effect of one of the material variables and one of the equipment variables, namely, the API particle size and extruder screw configuration on the API dissolution rate, in a co-rotating, twin-screw extruder. By rapidly removing the extruder screws from the barrel after achieving a steady state, we collected samples along the length of the extruder screws that were characterized by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) to determine the amount of undissolved API. Analyses of samples indicate that reduction of particle size of the API and appropriate selection of screw design can markedly improve the dissolution rate of the API during extrusion. In addition, angle of repose measurements and light microscopy images show that the reduction of particle size of the API can improve the flowability of the physical mixture feed and the adhesiveness between its components, respectively, through dry coating of the polymer particles by the API particles.

  14. Giant radiolytic dissolution rates of aqueous ceria observed in-situ by liquid-cell TEM.

    PubMed

    Asghar, Muhammad Sajid Ali; Inkson, Beverley J; Moebus, Guenter

    2017-03-09

    Dynamics of cerium oxide nanoparticle aqueous corrosion are revealed in-situ. We use innovative liquid-cell transmission electron microscopy (TEM) combined with deliberate high-intensity electron-beam irradiation of nanoparticle suspensions. This enables life video-recording of materials reactions in liquid, with nm-resolution. We introduce image-quantification to measure detailed rates of dissolution as a function of time and particle size to be compared with literature data. Giant dissolution rates, exceeding any previous reports for chemical dissolution rates at room temperature by many orders of magnitude, are discovered. Reasons for accelerated dissolution are outlined, including the importance of radiolysis of water preceding ceria-attack. Electron-water interaction generates radicals, ions and hydrated electrons, which assist in hydration and reductive dissolution of oxide minerals. The presented methodology has the potential to become a novel accelerated testing procedure to compare multiple nanoscale materials for relative aqueous durability. The ceria-water system is of crucial importance for the fields of catalysis, abrasive polishing, environmental remediation, and as simulant for actinide-oxide behaviour in contact with liquid for nuclear engineering.

  15. Evaluating reaction pathways of hydrothermal abiotic organic synthesis at elevated temperatures and pressures using carbon isotopes

    NASA Astrophysics Data System (ADS)

    Fu, Qi; Socki, Richard A.; Niles, Paul B.

    2015-04-01

    Experiments were performed to better understand the role of environmental factors on reaction pathways and corresponding carbon isotope fractionations during abiotic hydrothermal synthesis of organic compounds using piston cylinder apparatus at 750 °C and 5.5 kbars. Chemical compositions of experimental products and corresponding carbon isotopic values were obtained by a Pyrolysis-GC-MS-IRMS system. Alkanes (methane and ethane), straight-chain saturated alcohols (ethanol and n-butanol) and monocarboxylic acids (formic and acetic acids) were generated with ethanol being the only organic compound with higher δ13C than CO2. CO was not detected in experimental products owing to the favorable water-gas shift reaction under high water pressure conditions. The pattern of δ13C values of CO2, carboxylic acids and alkanes are consistent with their equilibrium isotope relationships: CO2 > carboxylic acids > alkanes, but the magnitude of the fractionation among them is higher than predicted isotope equilibrium values. In particular, the isotopic fractionation between CO2 and CH4 remained constant at ∼31‰, indicating a kinetic effect during CO2 reduction processes. No "isotope reversal" of δ13C values for alkanes or carboxylic acids was observed, which indicates a different reaction pathway than what is typically observed during Fischer-Tropsch synthesis under gas phase conditions. Under constraints imposed in experiments, the anomalous 13C isotope enrichment in ethanol suggests that hydroxymethylene is the organic intermediate, and that the generation of other organic compounds enriched in 12C were facilitated by subsequent Rayleigh fractionation of hydroxymethylene reacting with H2 and/or H2O. Carbon isotope fractionation data obtained in this study are instrumental in assessing the controlling factors on abiotic formation of organic compounds in hydrothermal systems. Knowledge on how environmental conditions affect reaction pathways of abiotic synthesis of organic

  16. A proposed abiotic reaction scheme for hydroxylamine and monochloramine under chloramination relevant drinking water conditions.

    PubMed

    Wahman, David G; Speitel, Gerald E; Machavaram, Madhav V

    2014-09-01

    Drinking water monochloramine (NH2Cl) use may promote ammonia-oxidizing bacteria (AOB). AOB use (i) ammonia monooxygenase for biological ammonia (NH3) oxidation to hydroxylamine (NH2OH) and (ii) hydroxylamine oxidoreductase for NH2OH oxidation to nitrite. NH2Cl and NH2OH may react, providing AOB potential benefits and detriments. The NH2Cl/NH2OH reaction would benefit AOB by removing the disinfectant (NH2Cl) and releasing their growth substrate (NH3), but the NH2Cl/NH2OH reaction would also provide a possible additional inactivation mechanism besides direct NH2Cl reaction with cells. Because biological NH2OH oxidation supplies the electrons required for biological NH3 oxidation, the NH2Cl/NH2OH reaction provides a direct mechanism for NH2Cl to inhibit NH3 oxidation, starving the cell of reductant by preventing biological NH2OH oxidation. To investigate possible NH2Cl/NH2OH reaction implications on AOB, an understanding of the underlying abiotic reaction is first required. The present study conducted a detailed literature review and proposed an abiotic NH2Cl/NH2OH reaction scheme (RS) for chloramination relevant drinking water conditions (μM concentrations, air saturation, and pH 7-9). Next, RS literature based kinetics and end-products were evaluated experimentally between pHs 7.7 and 8.3, representing (i) the pH range for future experiments with AOB and (ii) mid-range pHs typically found in chloraminated drinking water. In addition, a (15)N stable isotope experiment was conducted to verify nitrous oxide and nitrogen gas production and their nitrogen source. Finally, the RS was slightly refined using the experimental data and an AQUASIM implemented kinetic model. A chloraminated drinking water relevant RS is proposed and provides the abiotic reaction foundation for future AOB biotic experiments.

  17. Microbial exudate promoted dissolution and transformation of chromium containing minerals

    NASA Astrophysics Data System (ADS)

    Saad, E. M.; Sun, J.; Tang, Y.

    2015-12-01

    Because of its utility in many industrial processes, chromium has become the second most common metal contaminant in the United States. The two most common oxidation states of chromium in nature are Cr(III), which is highly immobile, and Cr(VI), which is highly mobile and toxic. In both natural and engineered environments, the most common remediation of Cr(VI) is through reduction, which results in chromium sequestration in the low solubility mixed Cr(III)-Fe(III) (oxy)hydroxide phases. Consequently, the stability of these minerals must be examined to assess the fate of chromium in the subsurface. We examined the dissolution of mixed Cr(III)-Fe(III) (oxy)hydroxides in the presence of common microbial exudates, including the siderophore desferrioxamine B (DFOB; a common organic ligand secreted by most microbes with high affinity for ferric iron and other trivalent metal ions) and oxalate (a common organic acid produced by microbes). The solids exhibited incongruent dissolution with preferential leaching of Fe from the solid phase. Over time, this leads to a more Cr rich mineral, which is known to be more soluble than the corresponding mixed mineral phase. We are currently investigating the structure of the reacted mineral phases and soluble Cr(III) species, as well as the potential oxidation and remobilization of the soluble Cr species. Results from this study will provide insights regarding the long term transport and fate of chromium in the natural environment in the presence of microbial activities.

  18. 25 CFR 11.605 - Dissolution.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is... affecting the attitude of one or both of the parties towards the marriage; (2) The court finds that either... of marriage, the Court of Indian Offenses shall grant the decree in that form unless the other...

  19. 25 CFR 11.605 - Dissolution.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is... affecting the attitude of one or both of the parties towards the marriage; (2) The court finds that either... of marriage, the Court of Indian Offenses shall grant the decree in that form unless the other...

  20. 25 CFR 11.605 - Dissolution.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is... affecting the attitude of one or both of the parties towards the marriage; (2) The court finds that either... of marriage, the Court of Indian Offenses shall grant the decree in that form unless the other...

  1. 25 CFR 11.605 - Dissolution.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is... affecting the attitude of one or both of the parties towards the marriage; (2) The court finds that either... of marriage, the Court of Indian Offenses shall grant the decree in that form unless the other...

  2. Dissolution Treatment of Depleted Uranium Waste

    SciTech Connect

    Gates-Anderson, D D; Laue, C A; Fitch, T E

    2004-02-09

    Researchers at LLNL have developed a 3-stage process that converts pyrophoric depleted uranium metal turnings to a solidified final product that can be transported to and buried at a permitted land disposal site. The three process stages are: (1) pretreatment; (2) dissolution; and (3) solidification. Each stage was developed following extensive experimentation. This report presents the results of their experimental studies.

  3. Spousal Dissimilarity, Race, and Marital Dissolution

    ERIC Educational Resources Information Center

    Clarkwest, Andrew

    2007-01-01

    I test the claims that spousal differences in ideational, behavioral, and other traits contribute to elevated rates of marital dissolution among African Americans. Using data from 3 waves of the National Survey of Families and Households (N = 5,424), I find that African American spouses experience high levels of dissimilarity in traits that may…

  4. Dissolution enhancement of chlorzoxazone using cogrinding technique

    PubMed Central

    Raval, Mihir K.; Patel, Jaydeep M.; Parikh, Rajesh K.; Sheth, Navin R.

    2015-01-01

    Purpose: The aim of the present work was to improve rate of dissolution and processing parameters of BCS class II drug, chlorzoxazone using cogrinding technique in the presence of different excipients as a carrier. Materials and Methods: The drug was coground with various carriers like polyethylene glycol (PEG 4000), hydroxypropyl methylcellulose (HPMC) E50LV, polyvinylpyrrolidone (PVP)K30, Kaolin and Neusilin US2 using ball mill, where only PEG 4000 improved dissolution rate of drug by bringing amorphization in 1:3 ratio. The coground mixture after 3 and 6 h was evaluated for various analytical, physicochemical and mechanical parameters. Results: The analysis showed conversion of Chlorzoxazone from its crystalline to amorphization form upon grinding with PEG 4000. Coground mixture as well as its directly compressed tablet showed 2.5-fold increment in the dissolution rate compared with pure drug. Directly compressible tablets prepared from pure drug required a large quantity of microcrystalline cellulose (MCC) during compression. The coground mixture and formulation was found stable in nature even after storage (40°C/75% relative humidity). Conclusions: Cogrinding can be successfully utilized to improve the rate of dissolution of poorly water soluble drugs and hence bioavailability. PMID:26682195

  5. On the dissolution of iridium by aluminum.

    SciTech Connect

    Hewson, John C.

    2009-08-01

    The potential for liquid aluminum to dissolve an iridium solid is examined. Substantial uncertainties exist in material properties, and the available data for the iridium solubility and iridium diffusivity are discussed. The dissolution rate is expressed in terms of the regression velocity of the solid iridium when exposed to the solvent (aluminum). The temperature has the strongest influence in the dissolution rate. This dependence comes primarily from the solubility of iridium in aluminum and secondarily from the temperature dependence of the diffusion coefficient. This dissolution mass flux is geometry dependent and results are provided for simplified geometries at constant temperatures. For situations where there is negligible convective flow, simple time-dependent diffusion solutions are provided. Correlations for mass transfer are also given for natural convection and forced convection. These estimates suggest that dissolution of iridium can be significant for temperatures well below the melting temperature of iridium, but the uncertainties in actual rates are large because of uncertainties in the physical parameters and in the details of the relevant geometries.

  6. Dilution physics modeling: Dissolution/precipitation chemistry

    SciTech Connect

    Onishi, Y.; Reid, H.C.; Trent, D.S.

    1995-09-01

    This report documents progress made to date on integrating dilution/precipitation chemistry and new physical models into the TEMPEST thermal-hydraulics computer code. Implementation of dissolution/precipitation chemistry models is necessary for predicting nonhomogeneous, time-dependent, physical/chemical behavior of tank wastes with and without a variety of possible engineered remediation and mitigation activities. Such behavior includes chemical reactions, gas retention, solids resuspension, solids dissolution and generation, solids settling/rising, and convective motion of physical and chemical species. Thus this model development is important from the standpoint of predicting the consequences of various engineered activities, such as mitigation by dilution, retrieval, or pretreatment, that can affect safe operations. The integration of a dissolution/precipitation chemistry module allows the various phase species concentrations to enter into the physical calculations that affect the TEMPEST hydrodynamic flow calculations. The yield strength model of non-Newtonian sludge correlates yield to a power function of solids concentration. Likewise, shear stress is concentration-dependent, and the dissolution/precipitation chemistry calculations develop the species concentration evolution that produces fluid flow resistance changes. Dilution of waste with pure water, molar concentrations of sodium hydroxide, and other chemical streams can be analyzed for the reactive species changes and hydrodynamic flow characteristics.

  7. Genetic mapping of abiotic stress responses in sorghum

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Due to rich genetic diversity for tolerance to various abiotic stress conditions, sorghum is an ideal system for genetic mapping and elucidation of genome regions that confer such response among cereal crops. Coupled with the development of DNA marker technologies and most recently the sequencing o...

  8. ABIOTIC DEGRADATION OF TRICHLOROETHYLENE UNDER THERMAL REMEDIATION CONDITIONS

    EPA Science Inventory

    The degradation of TCE (C2HCl3) to carbon dioxide (CO2) and chloride (Cl-) has been reported to occur during thermal remediation of subsurface environments. The overall goal of this study was to evaluate abiotic degradation of TCE at el...

  9. Effect of background electrolytes on gypsum dissolution

    NASA Astrophysics Data System (ADS)

    Burgos-Cara, Alejandro; Putnis, Christine; Ruiz-Agudo, Encarnacion

    2015-04-01

    Knowledge of the dissolution behaviour of gypsum (CaSO4· 2H2O) in aqueous solutions is of primary importance in many natural and technological processes (Pachon-Rodriguez and Colombani, 2007), including the weathering of rocks and gypsum karst formations, deformation of gypsum-bearing rocks, the quality of drinking water, amelioration of soil acidity, scale formation in the oil and gas industry or measurement of water motion in oceanography. Specific ions in aqueous solutions can play important but very different roles on mineral dissolution. For example, the dissolution rates and the morphology of dissolution features may be considerably modified by the presence of the foreign ions in the solution, which adsorb at the surface and hinder the detachment of the ions building the crystal. Dissolution processes in the aqueous environment are closely related to the rearrangement of water molecules around solute ions and the interaction between the solvent molecules themselves. The rearrangement of water molecules with respect to solute species has been recognized as the main kinetic barrier for crystal dissolution in many systems (Davis, 2000; De Yoreo and Dove 2004; Wasylenki et al. 2005). Current research suggest that the control that electrolytes exert on water structure is limited to the local environment surrounding the ions and is not related to long-range electric fields emanating from the ions but results from effects associated with the hydration shell(s) of the ions (Collins et al. 2007) and the ions' capacity to break or structure water (i.e. chaotropic and kosmotropic ions, respectively). These effects will ultimately affect the kinetics of crystal dissolution, and could be correlated with the water affinity of the respective background ions following a trend known as the lyotropic or Hofmeister series (Kunz et al. 2004; Dove and Craven, 2005). In situ macroscopic and Atomic Force Microscopy (AFM) flow-through dissolution experiments were conducted at a

  10. Weathering-associated bacteria from the Damma glacier forefield: physiological capabilities and impact on granite dissolution.

    PubMed

    Frey, Beat; Rieder, Stefan R; Brunner, Ivano; Plötze, Michael; Koetzsch, Stefan; Lapanje, Ales; Brandl, Helmut; Furrer, Gerhard

    2010-07-01

    Several bacterial strains isolated from granitic rock material in front of the Damma glacier (Central Swiss Alps) were shown (i) to grow in the presence of granite powder and a glucose-NH(4)Cl minimal medium without additional macro- or micronutrients and (ii) to produce weathering-associated agents. In particular, four bacterial isolates (one isolate each of Arthrobacter sp., Janthinobacterium sp., Leifsonia sp., and Polaromonas sp.) were weathering associated. In comparison to what was observed in abiotic experiments, the presence of these strains caused a significant increase of granite dissolution (as measured by the release of Fe, Ca, K, Mg, and Mn). These most promising weathering-associated bacterial species exhibited four main features rendering them more efficient in mineral dissolution than the other investigated isolates: (i) a major part of their bacterial cells was attached to the granite surfaces and not suspended in solution, (ii) they secreted the largest amounts of oxalic acid, (iii) they lowered the pH of the solution, and (iv) they formed significant amounts of HCN. As far as we know, this is the first report showing that the combined action of oxalic acid and HCN appears to be associated with enhanced elemental release from granite, in particular of Fe. This suggests that extensive microbial colonization of the granite surfaces could play a crucial role in the initial soil formation in previously glaciated mountain areas.

  11. Natural organic matter influences the dissolution and stability of reduced technetium(IV) and uranium(IV)

    NASA Astrophysics Data System (ADS)

    Gu, B.; Dong, W.; Liang, L.; Wall, N.

    2010-12-01

    Reductive precipitation and immobilization of soluble technetium (as pertechnetate, Tc(VII)O4-) and uranium (as uranyl, U(VI)O22+) to sparingly soluble Tc(IV) and U(IV) species have been proposed as one of the promising remediation technologies to immobilize uranium and technetium in situ in the subsurface. However, the dissolution and long-term stability of reduced Tc(IV) and U(IV) species are poorly understood, particularly in the presence of natural and synthetic organic ligands, which are known to form complexes with these metals or radionuclides and thus cause their mobilization. In this study, the kinetics of both ligand-promoted and oxidative dissolution of Tc(IV) and U(IV) solids are determined, and their mobility is evaluated in the presence of natural organic matter (e.g.,humic acid and fulvic acid) and synthetic ethylenediaminetetraacetate (EDTA). We found that EDTA and the humic acid are among the most effective in promoting the ligand-induced dissolution of Tc(IV) and U(IV) by complexation. However, EDTA is found to suppress the oxidative dissoltuion of Tc(IV) and U(IV), whereas the humic acid enhances the oxidative dissolution due to its redox reactive functional properties. Furthermore, the oxidative dissolution is found to be much quicker than the ligand-promoted dissolution by humic substances. Studies of the dissolution and stability of reduced U(IV) in a contaminated sediment column confirms that both the synthetic and natural organic ligands can cause the mobilization of U(IV) although the dissolution rate is relatively slow. Because these organic ligands commonly co-exit at comtaminated sites, our results suggest that their presence can potentially impact the long-term stability and mobility of reduced Tc(IV) or U(IV) and should be considered in designing remediation strategies using the reductive precipitation approach.

  12. Integrating omic approaches for abiotic stress tolerance in soybean

    PubMed Central

    Deshmukh, Rupesh; Sonah, Humira; Patil, Gunvant; Chen, Wei; Prince, Silvas; Mutava, Raymond; Vuong, Tri; Valliyodan, Babu; Nguyen, Henry T.

    2014-01-01

    Soybean production is greatly influenced by abiotic stresses imposed by environmental factors such as drought, water submergence, salt, and heavy metals. A thorough understanding of plant response to abiotic stress at the molecular level is a prerequisite for its effective management. The molecular mechanism of stress tolerance is complex and requires information at the omic level to understand it effectively. In this regard, enormous progress has been made in the omics field in the areas of genomics, transcriptomics, and proteomics. The emerging field of ionomics is also being employed for investigating abiotic stress tolerance in soybean. Omic approaches generate a huge amount of data, and adequate advancements in computational tools have been achieved for effective analysis. However, the integration of omic-scale information to address complex genetics and physiological questions is still a challenge. In this review, we have described advances in omic tools in the view of conventional and modern approaches being used to dissect abiotic stress tolerance in soybean. Emphasis was given to approaches such as quantitative trait loci (QTL) mapping, genome-wide association studies (GWAS), and genomic selection (GS). Comparative genomics and candidate gene approaches are also discussed considering identification of potential genomic loci, genes, and biochemical pathways involved in stress tolerance mechanism in soybean. This review also provides a comprehensive catalog of available online omic resources for soybean and its effective utilization. We have also addressed the significance of phenomics in the integrated approaches and recognized high-throughput multi-dimensional phenotyping as a major limiting factor for the improvement of abiotic stress tolerance in soybean. PMID:24917870

  13. Reactive oxygen species signaling in plants under abiotic stress.

    PubMed

    Choudhury, Shuvasish; Panda, Piyalee; Sahoo, Lingaraj; Panda, Sanjib Kumar

    2013-04-01

    Abiotic stresses like heavy metals, drought, salt, low temperature, etc. are the major factors that limit crop productivity and yield. These stresses are associated with production of certain deleterious chemical entities called reactive oxygen species (ROS), which include hydrogen peroxide (H₂O₂), superoxide radical (O₂(-)), hydroxyl radical (OH(-)), etc. ROS are capable of inducing cellular damage by degradation of proteins, inactivation of enzymes, alterations in the gene and interfere in various pathways of metabolic importance. Our understanding on ROS in response to abiotic stress is revolutionized with the advancements in plant molecular biology, where the basic understanding on chemical behavior of ROS is better understood. Understanding the molecular mechanisms involved in ROS generation and its potential role during abiotic stress is important to identify means by which plant growth and metabolism can be regulated under acute stress conditions. ROS mediated oxidative stress, which is the key to understand stress related toxicity have been widely studied in many plants and the results in those studies clearly revealed that oxidative stress is the main symptom of toxicity. Plants have their own antioxidant defense mechanisms to encounter ROS that is of enzymic and non-enzymic nature . Coordinated activities of these antioxidants regulate ROS detoxification and reduces oxidative load in plants. Though ROS are always regarded to impart negative impact on plants, some reports consider them to be important in regulating key cellular functions; however, such reports in plant are limited. Molecular approaches to understand ROS metabolism and signaling have opened new avenues to comprehend its critical role in abiotic stress. ROS also acts as secondary messenger that signals key cellular functions like cell proliferation, apoptosis and necrosis. In higher eukaryotes, ROS signaling is not fully understood. In this review we summarize our understanding on ROS

  14. Abiotic ozone and oxygen in atmospheres similar to prebiotic Earth

    SciTech Connect

    Domagal-Goldman, Shawn D.; Segura, Antígona; Claire, Mark W.; Robinson, Tyler D.; Meadows, Victoria S.

    2014-09-10

    The search for life on planets outside our solar system will use spectroscopic identification of atmospheric biosignatures. The most robust remotely detectable potential biosignature is considered to be the detection of oxygen (O{sub 2}) or ozone (O{sub 3}) simultaneous to methane (CH{sub 4}) at levels indicating fluxes from the planetary surface in excess of those that could be produced abiotically. Here we use an altitude-dependent photochemical model with the enhanced lower boundary conditions necessary to carefully explore abiotic O{sub 2} and O{sub 3} production on lifeless planets with a wide variety of volcanic gas fluxes and stellar energy distributions. On some of these worlds, we predict limited O{sub 2} and O{sub 3} buildup, caused by fast chemical production of these gases. This results in detectable abiotic O{sub 3} and CH{sub 4} features in the UV-visible, but no detectable abiotic O{sub 2} features. Thus, simultaneous detection of O{sub 3} and CH{sub 4} by a UV-visible mission is not a strong biosignature without proper contextual information. Discrimination between biological and abiotic sources of O{sub 2} and O{sub 3} is possible through analysis of the stellar and atmospheric context—particularly redox state and O atom inventory—of the planet in question. Specifically, understanding the spectral characteristics of the star and obtaining a broad wavelength range for planetary spectra should allow more robust identification of false positives for life. This highlights the importance of wide spectral coverage for future exoplanet characterization missions. Specifically, discrimination between true and false positives may require spectral observations that extend into infrared wavelengths and provide contextual information on the planet's atmospheric chemistry.

  15. Dissolution of two NWCF calcines: Extent of dissolution and characterization of undissolved solids

    SciTech Connect

    Brewer, K.N.; Herbst, R.S.; Tranter, T.J.

    1995-01-01

    A study was undertaken to determine the dissolution characteristics of two NWCF calcine types. A two-way blended calcine made from 4 parts nonradioactive aluminum nitrate and one part WM-102 was studied to determine the extent of dissolution for aluminum-type calcines. A two-way blend of 3.5 parts fluorinel waste from WM-187 and 1 part sodium waste from WM-185 was used to determine the extent of dissolution for zirconium-type calcines. This study was necessary to develop suitable aqueous separation flowsheets for the partitioning of actinides and fission products from ICPP calcines and to determine the disposition of the resulting undissolved solids (UDS). The dissolution flowsheet developed by Herbst was used to dissolve these two NWCF calcine types. Results show that greater than 95 wt% of aluminum and zirconium calcine types were dissolved after a single batch contact with 5 M HNO{sub 3}. A characterization of the UDS indicates that the weight percent of TRU elements in the UDS resulting from both calcine type dissolutions increases by approximately an order of magnitude from their concentrations prior to dissolution. Substantial activities of cesium and strontium are also present in the UDS resulting from the dissolution of both calcine types. Multiple TRU, Cs, and Sr analyses of both UDS types show that these solids are relatively homogeneous. From this study, it is estimated that between 63.5 and 635 cubic meters of UDS will be generated from the dissolution of 3800 M{sub 3} of calcine. The significant actinide and fission product activities in these UDS will preclude their disposal as low-level waste. If the actinide and fission activity resulting from the UDS is the only considered source in the dissolved calcine solutions, an estimated 99.9 to 99.99 percent of the solids must be removed from this solution for it to meet non-TRU Class A low-level waste.

  16. Microbiological and abiotic processes in modelling longer-term marine corrosion of steel.

    PubMed

    Melchers, Robert E

    2014-06-01

    Longer term exposure of mild steel in natural (biotic) waters progresses as a bimodal function of time, both for corrosion mass loss and for pit depth. Recent test results, however, found this also for immersion in clean fresh, almost pure and triply distilled waters. This shows chlorides or microbiological activity is not essential for the electrochemical processes producing bimodal behaviour. It is proposed that the first mode is aerobic corrosion that eventually produces a non-homogeneous corroded surface and rust coverage sufficient to allow formation of anoxic niches. Within these, aggressive autocatalytic reduction then occurs under anoxic abiotic conditions, caused by sulfide species originating from the MnS inclusions typical in steels. This is consistent with Wranglen's model for abiotic anoxic crevice and pitting corrosion without external aggressive ions. In biotic conditions, metabolites from anaerobic bacterial activity within and near the anoxic niches provides additional (sulfide) species to contribute to the severity of corrosion. Limited observational evidence that supports this hypothesis is given but further investigation is required to determine all contributor(s) to the cathodic current for the electrochemical reaction. The results are important for estimating the contribution of microbiological corrosion in infrastructure applications.

  17. Chemical structure influence on NAPL mixture nonideality evolution, rate-limited dissolution, and contaminant mass flux.

    PubMed

    Padgett, Mark C; Tick, Geoffrey R; Carroll, Kenneth C; Burke, William R

    2017-03-01

    The influence of chemical structure on NAPL mixture nonideality evolution, rate-limited dissolution, and contaminant mass flux was examined. The variability of measured and UNIFAC modeled NAPL activity coefficients as a function of mole fraction was compared for two NAPL mixtures containing structurally-different contaminants of concern including toluene (TOL) or trichloroethene (TCE) within a hexadecane (HEXDEC) matrix. The results showed that dissolution from the NAPL mixtures transitioned from ideality for mole fractions >0.05 to nonideality as mole fractions decreased. In particular, the TCE generally exhibited more ideal dissolution behavior except at lower mole fractions, and may indicate greater structural/polarity similarity between the two compounds. Raoult's Law and UNIFAC generally under-predicted the batch experiment results for TOL:HEXDEC mixtures especially for mole fractions ≤0.05. The dissolution rate coefficients were similar for both TOL and TCE over all mole fractions tested. Mass flux reduction (MFR) analysis showed that more efficient removal behavior occurred for TOL and TCE with larger mole fractions compared to the lower initial mole fraction mixtures (i.e. <0.2). However, compared to TOL, TCE generally exhibited more efficient removal behavior over all mole fractions tested and may have been the result of structural and molecular property differences between the compounds. Activity coefficient variability as a function of mole fraction was quantified through regression analysis and incorporated into dissolution modeling analyses for the dynamic flushing experiments. TOL elution concentrations were modeled (predicted) reasonable well using ideal and equilibrium assumptions, but the TCE elution concentrations could not be predicted using the ideal model. Rather, the dissolution modeling demonstrated that TCE elution was better described by the nonideal model whereby NAPL-phase activity coefficient varied as a function of COC mole fraction

  18. DISSOLUTION OF PLUTONIUM METAL USING NITRIC ACID SOLUTIONS CONTAINING POTASSIUM FLUORIDE

    SciTech Connect

    Rudisill, T.; Crowder, M.; Bronikowski, M.

    2007-10-15

    The deinventory and deactivation of the Savannah River Site's (SRS's) FB-Line facility required the disposition of approximately 2000 items from the facility's vaults. Plutonium (Pu) scraps and residues which do not meet criteria for conversion to a mixed oxide fuel will be dissolved and the solution stored for subsequent disposition. Some of the items scheduled for dissolution are composite materials containing Pu and tantalum (Ta) metals. The preferred approach for handling this material is to dissolve the Pu metal, rinse the Ta metal with water to remove residual acid, and burn the Ta metal. The use of a 4 M nitric acid (HNO{sub 3}) solution containing 0.2 M potassium fluoride (KF) was initially recommended for the dissolution of approximately 500 g of Pu metal. However, prior to the use of the flowsheet in the SRS facility, a new processing plan was proposed in which the feed to the dissolver could contain up to 1250 g of Pu metal. To evaluate the use of a larger batch size and subsequent issues associated with the precipitation of plutonium-containing solids from the dissolving solution, scaled experiments were performed using Pu metal and samples of the composite material. In the initial experiment, incomplete dissolution of a Pu metal sample demonstrated that a 1250 g batch size was not feasible in the HB-Line dissolver. Approximately 45% of the Pu was solubilized in 4 h. The remaining Pu metal was converted to plutonium oxide (PuO{sub 2}). Based on this work, the dissolution of 500 g of Pu metal using a 4-6 h cycle time was recommended for the HB-Line facility. Three dissolution experiments were subsequently performed using samples of the Pu/Ta composite material to demonstrate conditions which reduced the risk of precipitating a double fluoride salt containing Pu and K from the dissolving solution. In these experiments, the KF concentration was reduced from 0.2 M to either 0.15 or 0.175 M. With the use of 4 M HNO{sub 3} and a reduction in the KF

  19. Metal oxyhydroxide dissolution as promoted by structurally diverse siderophores and oxalate

    NASA Astrophysics Data System (ADS)

    Akafia, Martin M.; Harrington, James M.; Bargar, John R.; Duckworth, Owen W.

    2014-09-01

    Siderophores, a class of biogenic ligands with high affinities for Fe(III), promote the dissolution of metal ions from sparingly soluble mineral phases. However, most geochemical studies have focused on quantifying the reactivity of DFOB, a model trishydroxamate siderophore. This study utilized three different siderophores, desferrioxamine B, rhizoferrin, and protochelin, with structures that contain the most commonly observed binding moieties of microbial siderophores to examine the siderophore-promoted dissolution rates of FeOOH, CoOOH, and MnOOH in the absence and presence of the ubiquitous low molecular mass organic acid oxalate by utilizing batch dissolution experiments at pH = 5-9. Metal-siderophore complex and total dissolved metal concentrations were monitored for durations of one hour to fourteen days, depending on the metal oxyhydroxide identity and solution pH. The results demonstrate that MnOOH and CoOOH generally dissolve more quickly in the presence of siderophores than FeOOH. Whereas FeOOH dissolved exclusively by a ligand-promoted dissolution mechanism, MnOOH and CoOOH dissolved predominantly by a reductive dissolution mechanism under most experimental conditions. For FeOOH, siderophore-promoted dissolution rates trended with the stability constant of the corresponding aqueous Fe(III) complex. In the presence of oxalate, measured siderophore-promoted dissolution rates were found to increase, decrease, or remain unchanged as compared to the observed rates in single-ligand systems, depending on the pH of the system, the siderophore present, and the identity of the metal oxyhydroxide. Increases in observed dissolution rates in the presence of oxalate were generally greater for FeOOH than for MnOOH or CoOOH. These results elucidate potential dissolution mechanisms of both ferric and non-ferric oxyhydroxide minerals by siderophores in the environment, and may provide further insights into the biological strategies of metal acquisition facilitated by

  20. Mg-calcite dissolution in carbonate sediments: role in ocean acidification

    NASA Astrophysics Data System (ADS)

    Drupp, P. S.; De Carlo, E. H.; Mackenzie, F. T.

    2014-12-01

    An array of porewater wells at two locations on Hawaiian reefs have been utilized to obtain interstitial pore fluid from various depths in permeable sandy sediments. The total alkalinity (AT) and pH (total scale) were measured for each sample (depths 0, 2, 4, 6, 8, 12, 16, 20, 30, 40, and 60 cm) as well as calcium, magnesium, and strontium concentrations. Ca2+ and Mg2+ concentrations co-vary and appear to be directly related to AT and pH. The ratio of the change in calcium and magnesium (ΔCa, ΔMg) between the overlying water column and the porewater indicates that an 18 mol % Mg-calcite phase is dissolving within the sediment column. This could represent the dissolution of coralline algae such as Porolithon or Lithothamnion both of which produce ~18% Mg-calcite skeletons and are present on Hawaiian reefs. The small changes in Mg concentrations from dissolution/precipitation of high Mg-calcites is typically difficult to measure against the high background matrix of seawater and to our knowledge these data represent some of the first magnesium concentrations measured in permeable sediments. Saturation state (Ω) for Mg-calcites was calculated using both sets of stoichiometric solubility products (K) widely accepted in the literature. Depending on the K used, most of the porewater was undersaturated with respect to the high Mg calcites (>12%). Saturation states were determined using an ion activity product (IAP) calculated from the measured values of calcium and magnesium. This produces a more accurate Ω than assuming calcium and magnesium concentrations based on salinity, as is typically done in surface waters. As surface water becomes more corrosive to carbonate minerals due to enhanced ocean acidification through the next century, it is expected that dissolution of both biogenic high Mg-calcites and abiotic Mg-calcite cements will increase, potentially destabilizing reef framework and altering the biogeochemical cycling of carbon in these environments.

  1. Impact of iron chelators on short-term dissolution of basaltic glass

    NASA Astrophysics Data System (ADS)

    Perez, Anne; Rossano, Stéphanie; Trcera, Nicolas; Verney-Carron, Aurélie; Huguenot, David; van Hullebusch, Eric D.; Catillon, Gilles; Razafitianamaharavo, Angelina; Guyot, François

    2015-08-01

    Although microorganisms seem to play an important role in the alteration processes of basaltic glasses in solution, the elementary mechanisms involved remain unclear in particular with regard to the role of organic ligands excreted by the cells. Two glasses, one with Fe and one without Fe were synthesized to model basaltic glass compositions. Fe in the glass was mostly Fe(III) for enhancing interaction with siderophores, yet with small but significant amounts of Fe(II) (between 10% and 30% of iron). The prepared samples were submitted to abiotic alteration experiments in buffered (pH 6.4) diluted solutions of metal-specific ligands, namely oxalic acid (OA, 10 mM), desferrioxamine (DFA, 1 mM) or 2,2‧-bipyridyl (BPI, 1 mM). Element release from the glass into the solution after short term alteration (maximum 1 week) was measured by ICP-OES, and normalized mass losses and relative release ratios (with respect to Si) were evaluated for each element in each experimental condition. The presence of organic ligands had a significant effect on the dissolution of both glasses. Trivalent metals chelators (OA, DFA) impacted on the release of Fe3+ and Al3+, and thus on the global dissolution of both glasses, enhancing all release rates and dissolution stoichiometry (release rates were increased up to 7 times for Al or Fe). As expected, the mostly divalent metal chelator BPI interacted preferentially with Ca2+, Mg2+ and Fe2+. This study thus allows to highlight the central roles of iron and aluminium in interaction with some organic ligands in the alteration processes of basaltic glasses. It thus provides a step toward understanding the biological contribution of this fundamental geological process.

  2. 20 CFR 404.1219 - Dissolution of political subdivision.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 20 Employees' Benefits 2 2010-04-01 2010-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is...

  3. 32 CFR 202.10 - RAB adjournment and dissolution.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 32 National Defense 2 2013-07-01 2013-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution....

  4. 12 CFR 710.8 - Certificate of dissolution and liquidation.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 12 Banks and Banking 7 2012-01-01 2012-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution...

  5. 12 CFR 710.8 - Certificate of dissolution and liquidation.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 12 Banks and Banking 7 2013-01-01 2013-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution...

  6. 20 CFR 404.1219 - Dissolution of political subdivision.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 20 Employees' Benefits 2 2011-04-01 2011-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is...

  7. 20 CFR 404.1219 - Dissolution of political subdivision.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 20 Employees' Benefits 2 2012-04-01 2012-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is...

  8. 32 CFR 202.10 - RAB adjournment and dissolution.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 32 National Defense 2 2012-07-01 2012-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution....

  9. 32 CFR 202.10 - RAB adjournment and dissolution.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 32 National Defense 2 2011-07-01 2011-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution....

  10. Examining Two Types of Best Friendship Dissolution during Early Adolescence

    ERIC Educational Resources Information Center

    Bowker, Julie C.

    2011-01-01

    This study examined young adolescents' experiences with best friendship dissolution. Participants were 77 sixth-grade students (M age = 11.63 years, SD = 0.36; 11.00-12.69 age range) who reported on past experiences with (1) "complete dissolutions" (when friendship ties are completely severed), and (2) "downgrade dissolutions"…

  11. 12 CFR 710.8 - Certificate of dissolution and liquidation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 12 Banks and Banking 7 2014-01-01 2014-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution...

  12. 12 CFR 710.8 - Certificate of dissolution and liquidation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 12 Banks and Banking 6 2010-01-01 2010-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution...

  13. 20 CFR 404.1219 - Dissolution of political subdivision.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 20 Employees' Benefits 2 2013-04-01 2013-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is...

  14. 12 CFR 710.8 - Certificate of dissolution and liquidation.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 12 Banks and Banking 6 2011-01-01 2011-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution...

  15. 32 CFR 202.10 - RAB adjournment and dissolution.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 32 National Defense 2 2014-07-01 2014-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution....

  16. 20 CFR 404.1219 - Dissolution of political subdivision.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 20 Employees' Benefits 2 2014-04-01 2014-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is...

  17. 32 CFR 202.10 - RAB adjournment and dissolution.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 2 2010-07-01 2010-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution....

  18. RELATIVE DISSOLUTION RATES OF RADIOACTIVE MATERIALS USED AT AWE.

    PubMed

    Miller, T J; Bingham, D; Cockerill, R; Waldren, S; Moth, N

    2016-09-01

    A simple in vitro dissolution test was used to provide a semi-quantitative comparison of the relative dissolution rates of samples of radioactive materials used at Atomic Weapons Establishment in a lung fluid surrogate (Ringer's solution). A wide range of dissolution rates were observed for aged legacy actinides, freshly produced actinide alloys and actinides from waste management operations.

  19. Dissolution Kinetics of Biogenic Magnesian Calcites

    NASA Astrophysics Data System (ADS)

    Thompson, R.; Guidry, M.; Mackenzie, F. T.; De Carlo, E. H.

    2014-12-01

    Ocean acidification (OA) is a serious concern for the health of calcifying ecosystems in the near future. During the past century, surface ocean pH has decreased by ~0.1 pH units, and is expected to decrease further by 0.3-0.4 pH units by the end of this century. The process of OA will likely result in both decreased calcification rates and increased rates of carbonate mineral dissolution, particularly involving the magnesian calcite (Mg-calcite) calcifiers found in shallow-water reef and other carbonate environments. Many Mg-calcite compositions are the most soluble of the carbonate phases commonly found in reef environments (often comprising much of the cementation and structure within a reef), and are therefore potentially the most susceptible to dissolution processes associated with OA. However, the dissolution kinetics of these phases is poorly known, limiting our ability to understand their behavior in nature. Laboratory experiments designed to investigate the mechanisms and dissolution rates of biogenic Mg-calcite mineral phases in distilled water and seawater over a range of CO2 and T conditions were conducted employing both batch and fluidized-bed reactor systems and using a variety of cleaned and annealed biogenic Mg-calcite phases. Our initial results have shown that the dissolution rate at 298 K and a pCO2 of ~350 ppm of the crustose coralline alga Amphiroa rigida (~20 mol% MgCO3) in seawater undersaturated with respect to this phase is 3.6 μmol g-1 hr-1, nearly 50% greater than that under similar conditions for aragonite. This rate and the derived experimental rate law are consistent with the preliminary findings of Walter and Morse (1985). Additional kinetic (and also solubility) data will be presented for the following species: Chiton tuberculatus (~0-4 mol% MgCO3); Echinometra mathei and/or Lytechinus variegatus (~8-12 mol% MgCO3); Homotrema rubrum (12-16 mol% MgCO3); and Lithothamnion sp. (~18-24 mol% MgCO3). Quantification of the rates of

  20. Montmorillonite Dissolution in Simulated Lung Fluids

    NASA Astrophysics Data System (ADS)

    Schmidt, M.; Wendlandt, R. F.

    2008-12-01

    Because lung fluids" first interaction is with the surface of inhaled grains, the surface properties of inhaled mineral dusts may have a generally mitigating effect on cytotoxicity and carcinogenicity. Wendlandt et al. (Appl. Geochem. 22, 2007) investigated the surface properties of respirable-sized quartz grains in bentonites and recognized pervasive montmorillonite surface coatings on silica grains. The purpose of this study was to determine the dissolution rate and biodurability of montmorillonite in simulated lung fluids and to assess its potential to mitigate silica cytotoxicity. Modified batch reaction experiments were conducted on purified and size fractionated calcic (SAz-2; 0.4-5 μm) and sodic (DC-2; 0.4-2 μm) montmorillonites for 120 to 160 days of reaction time at 37°C in both simulated extracellular lung fluid (Lu) and simulated lysosomal fluid (Ly). Modified batch experiments simulated a flow-through setup and minimized sample handling difficulties. Reacted Lu and Ly fluid was analyzed for Mg, Al, and Si on an ICP-OE spectrometer. Steady state dissolution was reached 90-100 days after the start of the experiment and maintained for 40-60 days. Measured montmorillonite dissolution rates based on BET surface areas and Si steady state release range from 4.1x10-15 mol/m2/s at the slowest to 1.0x10-14 mol/m2/s at the fastest with relative uncertainties of less than 10%. Samples reacting in Ly (pH = 4.55) dissolved faster than those in Lu (pH = 7.40), and DC-2 dissolved faster than SAz-2. The measured range of biodurabilities was 1,300 to 3,400 years for a 1 μm grain assuming a spherical volume and a molar volume equal to that of illite. The difference in salinities of the two fluids was too slight to draw conclusions about the relationship of ionic strength to dissolution rate. Results indicate that montmorillonite dissolution is incongruent and edge controlled. Dissolution rates for DC- 2 and SAz-2 clays were comparable to those reported in the

  1. Ego-Dissolution and Psychedelics: Validation of the Ego-Dissolution Inventory (EDI)

    PubMed Central

    Nour, Matthew M.; Evans, Lisa; Nutt, David; Carhart-Harris, Robin L.

    2016-01-01

    Aims: The experience of a compromised sense of “self”, termed ego-dissolution, is a key feature of the psychedelic experience. This study aimed to validate the Ego-Dissolution Inventory (EDI), a new 8-item self-report scale designed to measure ego-dissolution. Additionally, we aimed to investigate the specificity of the relationship between psychedelics and ego-dissolution. Method: Sixteen items relating to altered ego-consciousness were included in an internet questionnaire; eight relating to the experience of ego-dissolution (comprising the EDI), and eight relating to the antithetical experience of increased self-assuredness, termed ego-inflation. Items were rated using a visual analog scale. Participants answered the questionnaire for experiences with classical psychedelic drugs, cocaine and/or alcohol. They also answered the seven questions from the Mystical Experiences Questionnaire (MEQ) relating to the experience of unity with one’s surroundings. Results: Six hundred and ninety-one participants completed the questionnaire, providing data for 1828 drug experiences (1043 psychedelics, 377 cocaine, 408 alcohol). Exploratory factor analysis demonstrated that the eight EDI items loaded exclusively onto a single common factor, which was orthogonal to a second factor comprised of the items relating to ego-inflation (rho = −0.110), demonstrating discriminant validity. The EDI correlated strongly with the MEQ-derived measure of unitive experience (rho = 0.735), demonstrating convergent validity. EDI internal consistency was excellent (Cronbach’s alpha 0.93). Three analyses confirmed the specificity of ego-dissolution for experiences occasioned by psychedelic drugs. Firstly, EDI score correlated with drug-dose for psychedelic drugs (rho = 0.371), but not for cocaine (rho = 0.115) or alcohol (rho = −0.055). Secondly, the linear regression line relating the subjective intensity of the experience to ego-dissolution was significantly steeper for psychedelics

  2. Mechanisms of plant-plant interactions: concealment from herbivores is more important than abiotic-stress mediation in an African savannah.

    PubMed

    Louthan, Allison M; Doak, Daniel F; Goheen, Jacob R; Palmer, Todd M; Pringle, Robert M

    2014-04-07

    Recent work on facilitative plant-plant interactions has emphasized the importance of neighbours' amelioration of abiotic stress, but the facilitative effects of neighbours in reducing plant apparency to herbivores have received less attention. Whereas theory on stress reduction predicts that competition should be more important in less stressful conditions, with facilitation becoming more important in harsh environments, apparency theory suggests that facilitation should be greater in the presence of herbivores, where it is disadvantageous to be conspicuous regardless of abiotic stress level. We tested the relative strength of neighbours' stress reduction versus apparency reduction on survival, growth, reproduction and lifetime fitness of Hibiscus meyeri, a common forb in central Kenya, using neighbour removals conducted inside and outside large-herbivore exclosures replicated in arid and mesic sites. In the absence of herbivores, neighbours competed with H. meyeri in mesic areas and facilitated H. meyeri in arid areas, as predicted by stress-reduction mechanisms. By contrast, neighbours facilitated H. meyeri in the presence of herbivory, regardless of aridity level, consistent with plant apparency. Our results show that the facilitative effects arising from plant apparency are stronger than the effects arising from abiotic stress reduction in this system, suggesting that plant-apparency effects may be particularly important in systems with extant large-herbivore communities.

  3. Utilization of spray drying technique for improvement of dissolution and anti-inflammatory effect of Meloxicam.

    PubMed

    Shazly, Gamal; Badran, Mohamed; Zoheir, Khairy; Alomrani, Abdullah

    2015-01-01

    Meloxicam (MLX) is a poorly water-soluble non steroidal anti-inflammatory drug (NSAID). The main objective of the present work was to enhance the dissolution of MLX and thus its bioavailability by the aid of additives. The novelty of this work rises from the utilization of spray drying technology to produce micro particulates solid dispersion systems containing MLX in the presence of small amount of additives. Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and Scan Electron Microscope (SEM) were used for studying the physico-chemical and morphological properties of MLX samples. The dissolution of MLX samples was investigated in two different pH media. The morphology of MLX solid dispersion micro-particles was spherical in shape according to SEM. FT-IR profiles indicated that a complex was formed between MLX and the additives. DSC patterns of the MLX micro-particles suggested a reduction in the crystallinity of MLX and probability of presence of an interaction between MLX and the additives. The rate of dissolution of the spray-dried MLX enhanced as compared with the unprocessed MLX in both acidic and neutral media. It was found that 100% of the added MLX released within 5 min in phosphate buffer dissolution medium (pH 7.4) compared to that of the unprocessed MLX (15% in 60 min). Such increase rate in the dissolution of the spray dried MLX could be attributed to the increase in wettability of MLX particles and the hydrophilic nature of the additives. The anti-inflammatory effect of the spray dried MLX was explored using formalin induced rat paw edema model. The spray-dried samples showed an increase in the anti-inflammatory activity of MLX as compared to the unprocessed MLX. This work reveals that the spray drying technique is suitable for preparation of micro-particles with improved dissolution and anti-inflammatory effect of MLX.

  4. The Dissolution of an Interfween Miscible Liquids

    NASA Technical Reports Server (NTRS)

    Vlad, D.H.; Maher, J.V.

    1999-01-01

    The disappearance of the surface tension of the interface of a binary mixture, measured using the dynamic surface light scattering technique, is slower for a binary mixture of higher density contrast. A comparison with a naive diffusion model, expected to provide a lower limit for the speed of dissolution in the absence of gravity shows that the interfacial surface tension disappears much slower than even by diffusion with the effect becoming much more pronounced when density contrast between the liquid phases is increased. Thus, the factor most likely to be responsible for this anomalously slow dissolution is gravity. A mechanism could be based on the competition between diffusive relaxation and sedimentation at the dissolving interface.

  5. The Dissolution of Double Holliday Junctions

    PubMed Central

    Bizard, Anna H.; Hickson, Ian D.

    2014-01-01

    Double Holliday junctions (dHJS) are important intermediates of homologous recombination. The separate junctions can each be cleaved by DNA structure-selective endonucleases known as Holliday junction resolvases. Alternatively, double Holliday junctions can be processed by a reaction known as “double Holliday junction dissolution.” This reaction requires the cooperative action of a so-called “dissolvasome” comprising a Holliday junction branch migration enzyme (Sgs1/BLM RecQ helicase) and a type IA topoisomerase (Top3/TopoIIIα) in complex with its OB (oligonucleotide/oligosaccharide binding) fold containing accessory factor (Rmi1). This review details our current knowledge of the dissolution process and the players involved in catalyzing this mechanistically complex means of completing homologous recombination reactions. PMID:24984776

  6. Uranium-Molybdenum Dissolution Flowsheet Studies

    SciTech Connect

    Pierce, R. A.

    2007-03-01

    The Super Kukla (SK) Prompt Burst Reactor operated at the Nevada Test Site from 1964 to 1978. The SK material is a uranium-molybdenum (U-Mo) alloy material of 90% U/10% Mo by weight at approximately 20% 235U enrichment. H-Canyon Engineering (HCE) requested that the Savannah River National Lab (SRNL) define a flowsheet for safely and efficiently dissolving the SK material. The objective is to dissolve the material in nitric acid (HNO3) in the H-Canyon dissolvers to a U concentration of 15-20 g/L (3-4 g/L 235U) without the formation of precipitates or the generation of a flammable gas mixture. Testing with SK material validated the applicability of dissolution and solubility data reported in the literature for various U and U-Mo metals. Based on the data, the SK material can be dissolved in boiling 3.0-6.0 M HNO3 to a U concentration of 15-20 g/L and a corresponding Mo concentration of 1.7-2.2 g/L. The optimum flowsheet will use 4.0-5.0 M HNO3 for the starting acid. Any nickel (Ni) cladding associated with the material will dissolve readily. After dissolution is complete, traditional solvent extraction flowsheets can be used to recover and purify the U. Dissolution rates for the SK material are consistent with those reported in the literature and are adequate for H-Canyon processing. When the SK material dissolved at 70-100 o C in 1-6 M HNO3, the reaction bubbled vigorously and released nitrogen oxide (NO) and nitrogen dioxide (NO2) gas. Gas generation tests in 1 M and 2 M HNO3 at 100 o C generated less than 0.1 volume percent hydrogen (H2) gas. It is known that higher HNO3 concentrations are less favorable for H2 production. All tests at 70-100 o C produced sufficient gas to mix the solutions without external agitation. At room temperature in 5 M HNO3, the U-Mo dissolved slowly and the U-laden solution sank to the bottom of the dissolution vessel because of its greater density. The effect of the density difference insures that the SK material cannot dissolve and

  7. A morpholinium ionic liquid for cellulose dissolution.

    PubMed

    Raut, Dilip G; Sundman, Ola; Su, Weiqing; Virtanen, Pasi; Sugano, Yasuhito; Kordas, Krisztian; Mikkola, Jyri-Pekka

    2015-10-05

    A series of substituted morpholinium ionic salts and allyl ammonium acetates were prepared. Amongst those, N-allyl-N-methylmorpholinium acetate ([AMMorp][OAc]) was found to dissolve cellulose readily without any pre-processing of native cellulose. At 120°C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of cellulose with degree of polymerization (DPn) - 789, 1644 and 2082 respectively, in 20 min. Importantly, SEC analysis indicated that no discernible changes occurred in terms of the degree of polymerization of the different celluloses after regeneration. Furthermore, when comparing the cellulose dissolution capability of these newly synthesized ionic liquids, it is evident that the combination of all three constituents - the morpholinium cation, the existence of an allyl group and choosing the acetate anion are essential for efficient cellulose dissolution. The structure and morphology of the regenerated cellulosic materials were characterized by SEM, XRD, TGA, CP/MAS (13)C NMR and FTIR, respectively.

  8. Growth and dissolution kinetics of tetragonal lysozyme

    NASA Technical Reports Server (NTRS)

    Monaco, L. A.; Rosenberger, F.

    1993-01-01

    The growth and dissolution kinetics of lysozyme in a 25 ml solution bridge inside a closed growth cell was investigated. It was found that, under all growth conditions, the growth habit forming (110) and (101) faces grew through layer spreading with different growth rate dependence on supersaturation/temperature. On the other hand, (100) faces which formed only at low temperatures underwent a thermal roughening transition around 12 C.

  9. Calcite dissolution in two deep eutrophic lakes

    SciTech Connect

    Ramisch, F.; Dittrich, M.; Mattenberger, C.; Wehrli, B.; Wueest, A.

    1999-10-01

    The calcium cycle, in particular carbonate dissolution, was analyzed in two deep eutrophic lakes, Lago di Lugano (288 m maximum depth) and Sempachersee (87 m) located in Switzerland. A box model approach was used to calculate calcite dissolution in the water column and at the sediment-water interface based on various lake monitoring data such as sediment traps, sediment cores, water and pore-water interface based on various lake monitoring data such as sediment traps, sediment cores, water and pore-water analysis. A model for stationary conditions allowing the calculation of calcite dissolution in the water column for a given particle size distribution was developed. The relative values of the simulated flux were consistent with sediment trap observations. The best fit of the dissolution rate constant of sinking calcite in Lago di Lugano was on the same order of magnitude (3 {center{underscore}dot} 10{sup {minus}10} kg{sup 1/3} s{sup {minus}1}) as published laboratory values for this surface controlled process. Both lakes show a similar specific calcite precipitation rate of 170 g Ca m{sup {minus}2} a{sup {minus}1}. The diffusive flux across the sediment-water interface amounts to about 15 and 10% of total calcite precipitation in Sempachersee and Lago di Lugano, respectively. However, 61% of the precipitated calcite is dissolved in the water column of Lago di Lugano compared to only 13% in Sempachersee. These results point towards the importance of grain size distributions and settling times in stratified deep waters as the two most important factors determining calcite retention in sediments of hard water lakes.

  10. Effects of sinker shapes on dissolution profiles.

    PubMed

    Soltero, R A; Hoover, J M; Jones, T F; Standish, M

    1989-01-01

    In dissolution testing, according to the U.S. Pharmacopeia, a nonreactive stainless steel wire helix is typically used to sink dosage forms that would otherwise float. The objective of this investigation was to determine if other sinker shapes will influence the rate, extent, or variability of dissolution. Criteria for the optimal sinker were defined. Various new sinker designs were fabricated, tested, and classified. Four classes of sinker shapes were defined: longitudinal, lateral, screen enclosures, and internal weights. Longitudinal sinkers contact the dosage forms on the long axis. Lateral sinkers either wrap around or contact capsule dosage forms in the middle, such as the line where the top and bottom halves of a capsule shell come together. Screen enclosures are of two types: either a wire cage, which holds the entire capsule, or a circular piece of wire screen placed on top of the capsule. Internal weights consist of two steel ball bearings, one inserted into each end of the capsule. The investigation consisted of four studies: (1) visual observation of the dissolution performance using 12 different sinkers; (2) the effect on drug release from nine classified sinkers on two different capsule formulations; (3) side-by-side comparison between the selected optimal longitudinal U clip and the wire helix lateral type sinkers; and (4) hydrodynamic effects caused by the use of the longitudinal U clip and the wire helix lateral type sinkers in the absence of capsule shells. We concluded that capsules sunk with either of the two longitudinal sinkers, the U clip or the paper clip, have faster, more complete dissolution and less variable results than did lateral type sinkers.(ABSTRACT TRUNCATED AT 250 WORDS)

  11. Aggregation, sedimentation, dissolution and bioavailability of ...

    EPA Pesticide Factsheets

    To understand their fate and transport in estuarine systems, the aggregation, sedimentation, and dissolution of CdSe quantum dots (QDs) in seawater were investigated. Hydrodynamic size increased from 40 to 60 nm to >1 mm within 1 h in seawater, and the aggregates were highly polydispersed. Their sedimentation rates in seawater were measured to be 4–10 mm/day. Humic acid (HA), further increased their size and polydispersity, and slowed sedimentation. Light increased their dissolution and release of dissolved Cd. The ZnS shell also slowed release of Cd ions. With sufficient light, HA increased the dissolution of QDs, while with low light, HA alone did not change their dissolution. The benthic zone in estuarine systems is the most probable long-term destination of QDs due to aggregation and sedimentation. The bioavailability of was evaluated using the mysid Americamysis bahia. The 7-day LC50s of particulate and dissolved QDs were 290 and 23 μg (total Cd)/L, respectively. For mysids, the acute toxicity appears to be from Cd ions; however, research on the effects of QDs should be conducted with other organisms where QDs may be lodged in critical tissues such as gills or filtering apparatus and Cd ions may be released and delivered directly to those tissues. Because of their increasing use and value to society, cadmium-based quantum dots (QDs) will inevitably find their way into marine systems. In an effort to understand the fate and transport of CdSe QDs in estuar

  12. DISSOLUTION OF ZIRCONIUM AND ALLOYS THEREFOR

    DOEpatents

    Swanson, J.L.

    1961-07-11

    The dissolution of zirconium cladding in a water solution of ammonium fluoride and ammonium nitrate is described. The method finds particular utility in processing spent fuel elements for nuclear reactors. The zirconium cladding is first dissolved in a water solution of ammonium fluoride and ammonium nitrate; insoluble uranium and plutonium fiuorides formed by attack of the solvent on the fuel materiai of the fuel element are then separated from the solution, and the fuel materiai is dissolved in another solution.

  13. Alloy dissolution in argon stirred steel

    NASA Astrophysics Data System (ADS)

    Webber, Darryl Scott

    Alloying is required for the production of all steel products from small castings to large beams. Addition of large quantities of bulk alloys can result in alloy segregation and inconsistent alloy recovery. The objective of this research was to better understand alloy dissolution in liquid steel especially as it relates to Missouri S&Ts' patented continuous steelmaking process. A 45-kilogram capacity ladle with a single porous plug was used to evaluate the effect of four experimental factors on alloy dissolution: alloy species, alloy size or form, argon flow rate, and furnace tap temperature. Four alloys were tested experimentally including Class I low carbon ferromanganese, nickel and tin (as a surrogate for low melting alloys) and Class II ferroniobium. The alloys ranged in size and form from granular to 30 mm diameter lumps. Experimental results were evaluated using a theoretically based numerical model for the steel shell period, alloy mixing (Class I) and alloy dissolution (Class II). A CFD model of the experimental ladle was used to understand steel motion in the ladle and to provide steel velocity magnitudes for the numerical steel shell model. Experiments and modeling confirmed that smaller sized alloys have shorter steel shell periods and homogenize faster than larger particles. Increasing the argon flow rate shortened mixing times and reduced the delay between alloy addition and the first appearance of alloy in the melt. In addition, for every five degree increase in steel bath temperature the steel shell period was shortened by approximately four percent. Class II ferroniobium alloy dissolution was an order of magnitude slower than Class I alloy mixing.

  14. Biotic and abiotic controls on co-occurring nitrogen cycling processes in shallow Arctic shelf sediments

    NASA Astrophysics Data System (ADS)

    McTigue, N. D.; Gardner, W. S.; Dunton, K. H.; Hardison, A. K.

    2016-10-01

    The processes that convert bioavailable inorganic nitrogen to inert nitrogen gas are prominent in continental shelf sediments and represent a critical global sink, yet little is known of these pathways in the Arctic where 18% of the world's continental shelves are located. Moreover, few data from the Arctic exist that separate loss processes like denitrification and anaerobic ammonium oxidation (anammox) from recycling pathways like dissimilatory nitrate reduction to ammonium (DNRA) or source pathways like nitrogen fixation. Here we present measurements of these co-occurring processes using 15N tracers. Denitrification was heterogeneous among stations and an order of magnitude greater than anammox and DNRA, while nitrogen fixation was undetectable. No abiotic factors correlated with interstation variability in biogeochemical rates; however, bioturbation potential explained most of the variation. Fauna-enhanced denitrification is a potentially important but overlooked process on Arctic shelves and highlights the role of the Arctic as a significant global nitrogen sink.

  15. Biotic and abiotic controls on co-occurring nitrogen cycling processes in shallow Arctic shelf sediments

    PubMed Central

    McTigue, N. D.; Gardner, W. S.; Dunton, K. H.; Hardison, A. K.

    2016-01-01

    The processes that convert bioavailable inorganic nitrogen to inert nitrogen gas are prominent in continental shelf sediments and represent a critical global sink, yet little is known of these pathways in the Arctic where 18% of the world's continental shelves are located. Moreover, few data from the Arctic exist that separate loss processes like denitrification and anaerobic ammonium oxidation (anammox) from recycling pathways like dissimilatory nitrate reduction to ammonium (DNRA) or source pathways like nitrogen fixation. Here we present measurements of these co-occurring processes using 15N tracers. Denitrification was heterogeneous among stations and an order of magnitude greater than anammox and DNRA, while nitrogen fixation was undetectable. No abiotic factors correlated with interstation variability in biogeochemical rates; however, bioturbation potential explained most of the variation. Fauna-enhanced denitrification is a potentially important but overlooked process on Arctic shelves and highlights the role of the Arctic as a significant global nitrogen sink. PMID:27782213

  16. Three-dimensional simulations of fracture dissolution

    NASA Astrophysics Data System (ADS)

    Starchenko, Vitaliy; Marra, Cameron J.; Ladd, Anthony J. C.

    2016-09-01

    Numerical studies of fracture dissolution are frequently based on two-dimensional models, where the fracture geometry is represented by an aperture field h(x,y). However, it is known that such models can break down when the spatial variations in aperture are rapid or large in amplitude; for example, in a rough fracture or when instabilities in the dissolution front develop into pronounced channels (or wormholes). Here we report a finite-volume implementation of a three-dimensional reactive transport model using the OpenFOAM® toolkit. Extensions to the OpenFOAM source code have been developed which displace and then relax the mesh in response to variations in the surface concentration; up to 100-fold increases in fracture aperture are possible without remeshing. Our code has simulated field-scale fractures with physical dimensions of about 10 m. We report simulations of smooth fractures, with small, well-controlled perturbations in fracture aperture introduced at the inlet. This allows for systematic convergence studies and for detailed comparisons with results from a two-dimensional model. Initially, the fracture aperture develops similarly in both models, but as local inhomogeneities develop the results start to diverge. We investigate numerically the onset of instabilities in the dissolution of fractures with small random variations in the initial aperture field. Our results show that elliptical cross sections, which are characteristic of karstic conduits, can develop very rapidly, on time scales of 10-20 years in calcite rocks.

  17. SERDP ER-1376 Enhancement of In Situ Bioremediation of Energetic Compounds by Coupled Abiotic/Biotic Processes:Final Report for 2004 - 2006

    SciTech Connect

    Szecsody, James E.; Comfort, Steve; Fredrickson, Herbert L.; Boparai, Hardiljeet K.; Devary, Brooks J.; Thompson, Karen T.; Phillips, Jerry L.; Crocker, Fiona H.; Girvin, Donald C.; Resch, Charles T.; Shea, Patrick; Fischer, Ashley E.; Durkin, Lisa M.

    2007-08-07

    This project was initiated by SERDP to quantify processes and determine the effectiveness of abiotic/biotic mineralization of energetics (RDX, HMX, TNT) in aquifer sediments by combinations of biostimulation (carbon, trace nutrient additions) and chemical reduction of sediment to create a reducing environment. Initially it was hypothesized that a balance of chemical reduction of sediment and biostimulation would increase the RDX, HMX, and TNT mineralization rate significantly (by a combination of abiotic and biotic processes) so that this abiotic/biotic treatment may be a more efficient for remediation than biotic treatment alone in some cases. Because both abiotic and biotic processes are involved in energetic mineralization in sediments, it was further hypothesized that consideration for both abiotic reduction and microbial growth was need to optimize the sediment system for the most rapid mineralization rate. Results show that there are separate optimal abiotic/biostimulation aquifer sediment treatments for RDX/HMX and for TNT. Optimal sediment treatment for RDX and HMX (which have chemical similarities and similar degradation pathways) is mainly chemical reduction of sediment, which increased the RDX/HMX mineralization rate 100 to150 times (relative to untreated sediment), with additional carbon or trace nutrient addition, which increased the RDX/HMX mineralization rate an additional 3 to 4 times. In contrast, the optimal aquifer sediment treatment for TNT involves mainly biostimulation (glucose addition), which stimulates a TNT/glucose cometabolic degradation pathway (6.8 times more rapid than untreated sediment), degrading TNT to amino-intermediates that irreversibly sorb (i.e., end product is not CO2). The TNT mass migration risk is minimized by these transformation reactions, as the triaminotoluene and 2,4- and 2,6-diaminonitrotoluene products that irreversibly sorb are no longer mobile in the subsurface environment. These transformation rates are increased

  18. Hormone balance and abiotic stress tolerance in crop plants.

    PubMed

    Peleg, Zvi; Blumwald, Eduardo

    2011-06-01

    Plant hormones play central roles in the ability of plants to adapt to changing environments, by mediating growth, development, nutrient allocation, and source/sink transitions. Although ABA is the most studied stress-responsive hormone, the role of cytokinins, brassinosteroids, and auxins during environmental stress is emerging. Recent evidence indicated that plant hormones are involved in multiple processes. Cross-talk between the different plant hormones results in synergetic or antagonic interactions that play crucial roles in response of plants to abiotic stress. The characterization of the molecular mechanisms regulating hormone synthesis, signaling, and action are facilitating the modification of hormone biosynthetic pathways for the generation of transgenic crop plants with enhanced abiotic stress tolerance.

  19. An abiotic analogue of the nuclear pore complex hydrogel.

    PubMed

    Bird, Sean P; Baker, Lane A

    2011-09-12

    We describe an abiotic hydrogel that mimics selectivity of the nuclear pore complex. Copolymerization of peptide tetramers (phenylalanine-serine-phenylalanine-glycine, FSFG) with acrylamide results in hydrophobic interactions significant enough to allow the formation of freestanding hydrogel structures. Incorporation of FSFG motifs also renders the hydrogels selective. Selective binding of importins and nuclear transport receptor-cargo complexes is qualitatively demonstrated and compared with polyacrylamide, hydrogels prepared from a control peptide, and hydrogels prepared from the nuclear pore complex protein Nsp1. These abiotic hydrogels will enable further studies of the unique transport mechanisms of the nuclear pore complex and provide an interesting paradigm for the future development of synthetic platforms for separations and selective interfaces.

  20. Abiotic mediation of a mutualism drives herbivore abundance.

    PubMed

    Mooney, Emily H; Phillips, Joseph S; Tillberg, Chadwick V; Sandrow, Cheryl; Nelson, Annika S; Mooney, Kailen A

    2016-01-01

    Species abundance is typically determined by the abiotic environment, but the extent to which such effects occur through the mediation of biotic interactions, including mutualisms, is unknown. We explored how light environment (open meadow vs. shaded understory) mediates the abundance and ant tending of the aphid Aphis helianthi feeding on the herb Ligusticum porteri. Yearly surveys consistently found aphids to be more than 17-fold more abundant on open meadow plants than on shaded understory plants. Manipulations demonstrated that this abundance pattern was not due to the direct effects of light environment on aphid performance, or indirectly through host plant quality or the effects of predators. Instead, open meadows had higher ant abundance and per capita rates of aphid tending and, accordingly, ants increased aphid population growth in meadow but not understory environments. The abiotic environment thus drives the abundance of this herbivore exclusively through the mediation of a protection mutualism.

  1. Experiments on the abiotic amplification of optical activity

    NASA Technical Reports Server (NTRS)

    Bonner, W. A.; Blair, N. E.; Dirbas, F. M.

    1981-01-01

    Experiments concerning the physical mechanisms for the abiotic generation and chemical mechanisms for the amplification of optical activity in biological compounds are reviewed. Attention is given to experiments involving the determination of the differential adsorption of racemic amino acids on d- and l-quartz, the asymmetric photolysis of racemic amino acids by circularly polarized light, and the asymmetric radiolysis of solid amino acids by longitudinally polarized electrons, and the enantiomeric enrichments thus obtained are noted. Further experiments on the amplification of the chirality in the polymerization of D, L-amino acid mixtures and the hydrolysis of D-, L-, and D, L-polypeptides are discussed. It is suggested that a repetitive cycle of partial polymerization-hydrolyses may account for the abiotic genesis of optically enriched polypeptides on the primitive earth.

  2. Transcriptional networks-crops, clocks, and abiotic stress.

    PubMed

    Gehan, Malia A; Greenham, Kathleen; Mockler, Todd C; McClung, C Robertson

    2015-04-01

    Several factors affect the yield potential and geographical range of crops including the circadian clock, water availability, and seasonal temperature changes. In order to sustain and increase plant productivity on marginal land in the face of both biotic and abiotic stresses, we need to more efficiently generate stress-resistant crops through marker-assisted breeding, genetic modification, and new genome-editing technologies. To leverage these strategies for producing the next generation of crops, future transcriptomic data acquisition should be pursued with an appropriate temporal design and analyzed with a network-centric approach. The following review focuses on recent developments in abiotic stress transcriptional networks in economically important crops and will highlight the utility of correlation-based network analysis and applications.

  3. SUMO, a heavyweight player in plant abiotic stress responses.

    PubMed

    Castro, Pedro Humberto; Tavares, Rui Manuel; Bejarano, Eduardo R; Azevedo, Herlânder

    2012-10-01

    Protein post-translational modifications diversify the proteome and install new regulatory levels that are crucial for the maintenance of cellular homeostasis. Over the last decade, the ubiquitin-like modifying peptide small ubiquitin-like modifier (SUMO) has been shown to regulate various nuclear processes, including transcriptional control. In plants, the sumoylation pathway has been significantly implicated in the response to environmental stimuli, including heat, cold, drought, and salt stresses, modulation of abscisic acid and other hormones, and nutrient homeostasis. This review focuses on the emerging importance of SUMO in the abiotic stress response, summarizing the molecular implications of sumoylation and emphasizing how high-throughput approaches aimed at identifying the full set of SUMO targets will greatly enhance our understanding of the SUMO-abiotic stress association.

  4. Arbuscular mycorrhizal fungal responses to abiotic stresses: A review.

    PubMed

    Lenoir, Ingrid; Fontaine, Joël; Lounès-Hadj Sahraoui, Anissa

    2016-03-01

    The majority of plants live in close collaboration with a diversity of soil organisms among which arbuscular mycorrhizal fungi (AMF) play an essential role. Mycorrhizal symbioses contribute to plant growth and plant protection against various environmental stresses. Whereas the resistance mechanisms induced in mycorrhizal plants after exposure to abiotic stresses, such as drought, salinity and pollution, are well documented, the knowledge about the stress tolerance mechanisms implemented by the AMF themselves is limited. This review provides an overview of the impacts of various abiotic stresses (pollution, salinity, drought, extreme temperatures, CO2, calcareous, acidity) on biodiversity, abundance and development of AMF and examines the morphological, biochemical and molecular mechanisms implemented by AMF to survive in the presence of these stresses.

  5. The dynamics of household dissolution and change in socio-economic position: A survival model in a rural South Africa

    PubMed Central

    Sartorius, Kurt; Sartorius, Benn KD; Collinson, Mark A; Tollman, Stephen M

    2014-01-01

    This paper investigates household dissolution and changes in asset wealth (socio-economic position) in a rural South African community containing settled refugees. Survival analysis applied to a longitudinal dataset indicated that the covariates increasing the risk of forced household dissolution were a reduction in socio-economic position (asset wealth), adult deaths and the permanent outmigration of more than 40% of the household. Conversely, the risk of dissolution was reduced by bigger households, state grants and older household heads. Significant spatial clusters of former refugee villages also showed a higher risk of dissolution after 20 years of permanent residence. A discussion of the dynamics of dissolution showed how an outflow/inflow of household assets (socio-economic position) was precipitated by each of the selected covariates. The paper shows how an understanding of the dynamics of forced household dissolution, combined with the use of geo-spatial mapping, can inform inter-disciplinary policy in a rural community. PMID:25937697

  6. Dissolution of glass wool, rock wool and alkaline earth silicate wool: morphological and chemical changes in fibers.

    PubMed

    Campopiano, Antonella; Cannizzaro, Annapaola; Angelosanto, Federica; Astolfi, Maria Luisa; Ramires, Deborah; Olori, Angelo; Canepari, Silvia; Iavicoli, Sergio

    2014-10-01

    The behavior of alkaline earth silicate (AES) wool and of other biosoluble wools in saline solution simulating physiological fluids was compared with that of a traditional wool belonging to synthetic vitreous fibers. Morphological and size changes of fibers were studied by scanning electron microscopy (SEM). The elements extracted from fibers were analyzed by inductively coupled plasma atomic emission spectrometry. SEM analysis showed a larger reduction of length-weighted geometric mean fiber diameter at 4.5 pH than at 7.4 pH. At the 7.4 pH, AES wool showed a higher dissolution rate and a dissolution time less than a few days. Their dissolution was highly non-congruent with rapid leaching of calcium. Unlike rock wool, glass wool dissolved more rapidly at physiological pH than at acid pH. Dissolution of AES and biosoluble rock wool is accompanied by a noticeable change in morphology while by no change for glass wool. Biosoluble rock wool developed a leached surface with porous honeycomb structure. SEM analysis showed the dissolution for glass wool is mainly due to breakage transverse of fiber at pH 7.4. AES dissolution constant (Kdis) was the highest at pH 7.4, while at pH 4.5 only biosoluble rockwool 1 showed a higher Kdis.

  7. Sustainability of Long-Term Abiotic Attenuation of Chlorinated Ethenes

    DTIC Science & Technology

    2007-09-28

    that contribute to abiotic transformations is critical to assess the feasibility of natural attenuation and promote the rationale design of...anaerobic glovebox. The resulting slurry was mixed for three days and then decanted into polypropylene centrifuge bottles. These bottles were...tightly sealed and centrifuged at 8000 rpm for 10 minutes. The supernatant in the bottles was discarded, and fresh nitrogen-purged deionized water was

  8. Biotic-Abiotic Nanoscale Interactions in Biological Fuel Cells

    DTIC Science & Technology

    2014-03-28

    Force Office of Scientific Research 875 North Randolph Street 4027 Arlington VA 22203 email: Patrick.Bradshaw@afosr.af.mil phone : 703-588-8492...Science Center 215C Los Angeles, CA 90089-0484 email: mnaggar@usc.edu phone : 213-740-2394 2 Biotic-Abiotic Nanoscale Interactions in...aggregation – collaboration with Naval Research Lab. 2.4 As part of an international collaboration, we reported on filamentous bacteria mediating centimeter

  9. Changes in biotic and abiotic processes following mangrove clearing

    NASA Astrophysics Data System (ADS)

    Granek, Elise; Ruttenberg, Benjamin I.

    2008-12-01

    Mangrove forests, important tropical coastal habitats, are in decline worldwide primarily due to removal by humans. Changes to mangrove systems can alter ecosystem properties through direct effects on abiotic factors such as temperature, light and nutrient supply or through changes in biotic factors such as primary productivity or species composition. Despite the importance of mangroves as transitional habitats between land and sea, little research has examined changes that occur when they are cleared. We examined changes in a number of biotic and abiotic factors following the anthropogenic removal of red mangroves ( Rhizophora mangle) in the Panamanian Caribbean, including algal biomass, algal diversity, algal grazing rates, light penetration, temperature, sedimentation rates and sediment organic content. In this first study examining multiple ecosystem-level effects of mangrove disturbance, we found that areas cleared of mangroves had higher algal biomass and richness than intact mangrove areas. This increase in algal biomass and richness was likely due to changes in abiotic factors (e.g. light intensity, temperature), but not biotic factors (fish herbivory). Additionally the algal and cyanobacterial genera dominating mangrove-cleared areas were rare in intact mangroves and included a number of genera that compete with coral for space on reefs. Interestingly, sedimentation rates did not differ between intact and cleared areas, but the sediments that accumulated in intact mangroves had higher organic content. These findings are the first to demonstrate that anthropogenic clearing of mangroves changes multiple biotic and abiotic processes in mangrove forests and that some of these changes may influence adjacent habitats such as coral reefs and seagrass beds. Additional research is needed to further explore the community and ecosystem-level effects of mangrove clearing and their influence on adjacent habitats, but it is clear that mangrove conservation is an

  10. Wheat EST resources for functional genomics of abiotic stress

    PubMed Central

    Houde, Mario; Belcaid, Mahdi; Ouellet, François; Danyluk, Jean; Monroy, Antonio F; Dryanova, Ani; Gulick, Patrick; Bergeron, Anne; Laroche, André; Links, Matthew G; MacCarthy, Luke; Crosby, William L; Sarhan, Fathey

    2006-01-01

    Background Wheat is an excellent species to study freezing tolerance and other abiotic stresses. However, the sequence of the wheat genome has not been completely characterized due to its complexity and large size. To circumvent this obstacle and identify genes involved in cold acclimation and associated stresses, a large scale EST sequencing approach was undertaken by the Functional Genomics of Abiotic Stress (FGAS) project. Results We generated 73,521 quality-filtered ESTs from eleven cDNA libraries constructed from wheat plants exposed to various abiotic stresses and at different developmental stages. In addition, 196,041 ESTs for which tracefiles were available from the National Science Foundation wheat EST sequencing program and DuPont were also quality-filtered and used in the analysis. Clustering of the combined ESTs with d2_cluster and TGICL yielded a few large clusters containing several thousand ESTs that were refractory to routine clustering techniques. To resolve this problem, the sequence proximity and "bridges" were identified by an e-value distance graph to manually break clusters into smaller groups. Assembly of the resolved ESTs generated a 75,488 unique sequence set (31,580 contigs and 43,908 singletons/singlets). Digital expression analyses indicated that the FGAS dataset is enriched in stress-regulated genes compared to the other public datasets. Over 43% of the unique sequence set was annotated and classified into functional categories according to Gene Ontology. Conclusion We have annotated 29,556 different sequences, an almost 5-fold increase in annotated sequences compared to the available wheat public databases. Digital expression analysis combined with gene annotation helped in the identification of several pathways associated with abiotic stress. The genomic resources and knowledge developed by this project will contribute to a better understanding of the different mechanisms that govern stress tolerance in wheat and other cereals. PMID

  11. Theoretical Analysis of Drug Dissolution: I. Solubility and Intrinsic Dissolution Rate.

    PubMed

    Shekunov, Boris; Montgomery, Eda Ross

    2016-09-01

    The first-principles approach presented in this work combines surface kinetics and convective diffusion modeling applied to compounds with pH-dependent solubility and in different dissolution media. This analysis is based on experimental data available for approximately 100 compounds of pharmaceutical interest. Overall, there is a linear relationship between the drug solubility and intrinsic dissolution rate expressed through the total kinetic coefficient of dissolution and dimensionless numbers defining the mass transfer regime. The contribution of surface kinetics appears to be significant constituting on average ∼20% resistance to the dissolution flux in the compendial rotating disk apparatus at 100 rpm. The surface kinetics contribution becomes more dominant under conditions of fast laminar or turbulent flows or in cases when the surface kinetic coefficient may decrease as a function of solution composition or pH. Limitations of the well-known convective diffusion equation for rotating disk by Levich are examined using direct computational modeling with simultaneous dissociation and acid-base reactions in which intrinsic dissolution rate is strongly dependent on pH profile and solution ionic strength. It is shown that concept of diffusion boundary layer does not strictly apply for reacting/interacting species and that thin-film diffusion models cannot be used quantitatively in general case.

  12. Titania may produce abiotic oxygen atmospheres on habitable exoplanets

    NASA Astrophysics Data System (ADS)

    Narita, Norio; Enomoto, Takafumi; Masaoka, Shigeyuki; Kusakabe, Nobuhiko

    2015-12-01

    The search for habitable exoplanets in the Universe is actively ongoing in the field of astronomy. The biggest future milestone is to determine whether life exists on such habitable exoplanets. In that context, oxygen in the atmosphere has been considered strong evidence for the presence of photosynthetic organisms. In this paper, we show that a previously unconsidered photochemical mechanism by titanium (IV) oxide (titania) can produce abiotic oxygen from liquid water under near ultraviolet (NUV) lights on the surface of exoplanets. Titania works as a photocatalyst to dissociate liquid water in this process. This mechanism offers a different source of a possibility of abiotic oxygen in atmospheres of exoplanets from previously considered photodissociation of water vapor in upper atmospheres by extreme ultraviolet (XUV) light. Our order-of-magnitude estimation shows that possible amounts of oxygen produced by this abiotic mechanism can be comparable with or even more than that in the atmosphere of the current Earth, depending on the amount of active surface area for this mechanism. We conclude that titania may act as a potential source of false signs of life on habitable exoplanets.Reference:Narita N. et al.,Scientific Reports 5, Article number: 13977 (2015)http://www.nature.com/articles/srep13977

  13. Titania may produce abiotic oxygen atmospheres on habitable exoplanets.

    PubMed

    Narita, Norio; Enomoto, Takafumi; Masaoka, Shigeyuki; Kusakabe, Nobuhiko

    2015-09-10

    The search for habitable exoplanets in the Universe is actively ongoing in the field of astronomy. The biggest future milestone is to determine whether life exists on such habitable exoplanets. In that context, oxygen in the atmosphere has been considered strong evidence for the presence of photosynthetic organisms. In this paper, we show that a previously unconsidered photochemical mechanism by titanium (IV) oxide (titania) can produce abiotic oxygen from liquid water under near ultraviolet (NUV) lights on the surface of exoplanets. Titania works as a photocatalyst to dissociate liquid water in this process. This mechanism offers a different source of a possibility of abiotic oxygen in atmospheres of exoplanets from previously considered photodissociation of water vapor in upper atmospheres by extreme ultraviolet (XUV) light. Our order-of-magnitude estimation shows that possible amounts of oxygen produced by this abiotic mechanism can be comparable with or even more than that in the atmosphere of the current Earth, depending on the amount of active surface area for this mechanism. We conclude that titania may act as a potential source of false signs of life on habitable exoplanets.

  14. Abiotic Deposition of Fe Complexes onto Leptothrix Sheaths.

    PubMed

    Kunoh, Tatsuki; Hashimoto, Hideki; McFarlane, Ian R; Hayashi, Naoaki; Suzuki, Tomoko; Taketa, Eisuke; Tamura, Katsunori; Takano, Mikio; El-Naggar, Mohamed Y; Kunoh, Hitoshi; Takada, Jun

    2016-06-03

    Bacteria classified in species of the genus Leptothrix produce extracellular, microtubular, Fe-encrusted sheaths. The encrustation has been previously linked to bacterial Fe oxidases, which oxidize Fe(II) to Fe(III) and/or active groups of bacterial exopolymers within sheaths to attract and bind aqueous-phase inorganics. When L. cholodnii SP-6 cells were cultured in media amended with high Fe(II) concentrations, Fe(III) precipitates visibly formed immediately after addition of Fe(II) to the medium, suggesting prompt abiotic oxidation of Fe(II) to Fe(III). Intriguingly, these precipitates were deposited onto the sheath surface of bacterial cells as the population was actively growing. When Fe(III) was added to the medium, similar precipitates formed in the medium first and were abiotically deposited onto the sheath surfaces. The precipitates in the Fe(II) medium were composed of assemblies of globular, amorphous particles (ca. 50 nm diameter), while those in the Fe(III) medium were composed of large, aggregated particles (≥3 µm diameter) with a similar amorphous structure. These precipitates also adhered to cell-free sheaths. We thus concluded that direct abiotic deposition of Fe complexes onto the sheath surface occurs independently of cellular activity in liquid media containing Fe salts, although it remains unclear how this deposition is associated with the previously proposed mechanisms (oxidation enzyme- and/or active group of organic components-involved) of Fe encrustation of the Leptothrix sheaths.

  15. Titania may produce abiotic oxygen atmospheres on habitable exoplanets

    PubMed Central

    Narita, Norio; Enomoto, Takafumi; Masaoka, Shigeyuki; Kusakabe, Nobuhiko

    2015-01-01

    The search for habitable exoplanets in the Universe is actively ongoing in the field of astronomy. The biggest future milestone is to determine whether life exists on such habitable exoplanets. In that context, oxygen in the atmosphere has been considered strong evidence for the presence of photosynthetic organisms. In this paper, we show that a previously unconsidered photochemical mechanism by titanium (IV) oxide (titania) can produce abiotic oxygen from liquid water under near ultraviolet (NUV) lights on the surface of exoplanets. Titania works as a photocatalyst to dissociate liquid water in this process. This mechanism offers a different source of a possibility of abiotic oxygen in atmospheres of exoplanets from previously considered photodissociation of water vapor in upper atmospheres by extreme ultraviolet (XUV) light. Our order-of-magnitude estimation shows that possible amounts of oxygen produced by this abiotic mechanism can be comparable with or even more than that in the atmosphere of the current Earth, depending on the amount of active surface area for this mechanism. We conclude that titania may act as a potential source of false signs of life on habitable exoplanets. PMID:26354078

  16. Cell Wall Metabolism in Response to Abiotic Stress.

    PubMed

    Le Gall, Hyacinthe; Philippe, Florian; Domon, Jean-Marc; Gillet, Françoise; Pelloux, Jérôme; Rayon, Catherine

    2015-02-16

    This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions.

  17. Abiotic Deposition of Fe Complexes onto Leptothrix Sheaths

    PubMed Central

    Kunoh, Tatsuki; Hashimoto, Hideki; McFarlane, Ian R.; Hayashi, Naoaki; Suzuki, Tomoko; Taketa, Eisuke; Tamura, Katsunori; Takano, Mikio; El-Naggar, Mohamed Y.; Kunoh, Hitoshi; Takada, Jun

    2016-01-01

    Bacteria classified in species of the genus Leptothrix produce extracellular, microtubular, Fe-encrusted sheaths. The encrustation has been previously linked to bacterial Fe oxidases, which oxidize Fe(II) to Fe(III) and/or active groups of bacterial exopolymers within sheaths to attract and bind aqueous-phase inorganics. When L. cholodnii SP-6 cells were cultured in media amended with high Fe(II) concentrations, Fe(III) precipitates visibly formed immediately after addition of Fe(II) to the medium, suggesting prompt abiotic oxidation of Fe(II) to Fe(III). Intriguingly, these precipitates were deposited onto the sheath surface of bacterial cells as the population was actively growing. When Fe(III) was added to the medium, similar precipitates formed in the medium first and were abiotically deposited onto the sheath surfaces. The precipitates in the Fe(II) medium were composed of assemblies of globular, amorphous particles (ca. 50 nm diameter), while those in the Fe(III) medium were composed of large, aggregated particles (≥3 µm diameter) with a similar amorphous structure. These precipitates also adhered to cell-free sheaths. We thus concluded that direct abiotic deposition of Fe complexes onto the sheath surface occurs independently of cellular activity in liquid media containing Fe salts, although it remains unclear how this deposition is associated with the previously proposed mechanisms (oxidation enzyme- and/or active group of organic components-involved) of Fe encrustation of the Leptothrix sheaths. PMID:27271677

  18. Abscisic Acid and Abiotic Stress Tolerance in Crop Plants

    PubMed Central

    Sah, Saroj K.; Reddy, Kambham R.; Li, Jiaxu

    2016-01-01

    Abiotic stress is a primary threat to fulfill the demand of agricultural production to feed the world in coming decades. Plants reduce growth and development process during stress conditions, which ultimately affect the yield. In stress conditions, plants develop various stress mechanism to face the magnitude of stress challenges, although that is not enough to protect them. Therefore, many strategies have been used to produce abiotic stress tolerance crop plants, among them, abscisic acid (ABA) phytohormone engineering could be one of the methods of choice. ABA is an isoprenoid phytohormone, which regulates various physiological processes ranging from stomatal opening to protein storage and provides adaptation to many stresses like drought, salt, and cold stresses. ABA is also called an important messenger that acts as the signaling mediator for regulating the adaptive response of plants to different environmental stress conditions. In this review, we will discuss the role of ABA in response to abiotic stress at the molecular level and ABA signaling. The review also deals with the effect of ABA in respect to gene expression. PMID:27200044

  19. Cell Wall Metabolism in Response to Abiotic Stress

    PubMed Central

    Gall, Hyacinthe Le; Philippe, Florian; Domon, Jean-Marc; Gillet, Françoise; Pelloux, Jérôme; Rayon, Catherine

    2015-01-01

    This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions. PMID:27135320

  20. Mineral dissolution kinetics at the pore scale

    SciTech Connect

    Li, L.; Steefel, C.I.; Yang, L.

    2007-05-24

    Mineral dissolution rates in the field have been reported to be orders of magnitude slower than those measured in the laboratory, an unresolved discrepancy that severely limits our ability to develop scientifically defensible predictive or even interpretive models for many geochemical processes in the earth and environmental sciences. One suggestion links this discrepancy to the role of physical and chemical heterogeneities typically found in subsurface soils and aquifers in producing scale-dependent rates where concentration gradients develop. In this paper, we examine the possibility that scale-dependent mineral dissolution rates can develop even at the single pore and fracture scale, the smallest and most fundamental building block of porous media. To do so, we develop two models to analyze mineral dissolution kinetics at the single pore scale: (1) a Poiseuille Flow model that applies laboratory-measured dissolution kinetics at the pore or fracture wall and couples this to a rigorous treatment of both advective and diffusive transport, and (2) a Well-Mixed Reactor model that assumes complete mixing within the pore, while maintaining the same reactive surface area, average flow rate, and geometry as the Poiseuille Flow model. For a fracture, a 1D Plug Flow Reactor model is considered in addition to quantify the effects of longitudinal versus transverse mixing. The comparison of averaged dissolution rates under various conditions of flow, pore size, and fracture length from the three models is used as a means to quantify the extent to which concentration gradients at the single pore and fracture scale can develop and render rates scale-dependent. Three important minerals that dissolve at widely different rates, calcite, plagioclase, and iron hydroxide, are considered. The modeling indicates that rate discrepancies arise primarily where concentration gradients develop due to comparable rates of reaction and advective transport, and incomplete mixing via molecular

  1. Evaluating the role of re-adsorption of dissolved Hg2+ during cinnabar dissolution using isotope tracer technique

    SciTech Connect

    Jiang, Ping; Li, Yanbin; Liu, Guangliang; Yang, Guidi; Lagos, Leonel; Yin, Yongguang; Gu, Baohua; Jiang, Guibin; Cai, Yong

    2016-06-02

    Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbed Hg on cinnabar surface via the reduction in spiked 202Hg2+. By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred g L–1, while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. Lastly, these results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.

  2. Kinetic dissolution of carbonates and Mn oxides in acidic water: Measurement of in situ field rates and reactive transport modeling

    USGS Publications Warehouse

    Brown, J.G.; Glynn, P.D.

    2003-01-01

    The kinetics of carbonate and Mn oxide dissolution under acidic conditions were examined through the in situ exposure of pure phase samples to acidic ground water in Pinal Creek Basin, Arizona. The average long-term calculated in situ dissolution rates for calcite and dolomite were 1.65??10-7 and 3.64??10-10 mmol/(cm2 s), respectively, which were about 3 orders of magnitude slower than rates derived in laboratory experiments by other investigators. Application of both in situ and lab-derived calcite and dolomite dissolution rates to equilibrium reactive transport simulations of a column experiment did not improve the fit to measured outflow chemistry: at the spatial and temporal scales of the column experiment, the use of an equilibrium model adequately simulated carbonate dissolution in the column. Pyrolusite (MnO2) exposed to acidic ground water for 595 days increased slightly in weight despite thermodynamic conditions that favored dissolution. This result might be related to a recent finding by another investigator that the reductive dissolution of pyrolusite is accompanied by the precipitation of a mixed Mn-Fe oxide species. In PHREEQC reactive transport simulations, the incorporation of Mn kinetics improved the fit between observed and simulated behavior at the column and field scales, although the column-fitted rate for Mn-oxide dissolution was about 4 orders of magnitude greater than the field-fitted rate. Remaining differences between observed and simulated contaminant transport trends at the Pinal Creek site were likely related to factors other than the Mn oxide dissolution rate, such as the concentration of Fe oxide surface sites available for adsorption, the effects of competition among dissolved species for available surface sites, or reactions not included in the model.

  3. Direct imaging of nanoscale dissolution of dicalcium phosphate dihydrate by an organic ligand: concentration matters.

    PubMed

    Qin, Lihong; Zhang, Wenjun; Lu, Jianwei; Stack, Andrew G; Wang, Lijun

    2013-01-01

    Unraveling the kinetics and mechanisms of sparingly soluble calcium orthophosphate (Ca-P) dissolution in the presence of organic acids at microscopic levels is important for an improved understanding in determining the effectiveness of organic acids present in most rhizosphere environments. Herein, we use in situ atomic force microscopy (AFM) coupled with a fluid reaction cell to image dissolution on the (010) face of brushite, CaHPO4 · 2H2O, in citrate-bearing solutions over a broad concentration range. We directly measure the dependence of molecular step retreat rate on citrate concentration at various pH values and ionic strengths, relevant to soil solution conditions. We find that low concentrations of citrate (10-100 μM) induced a reduction in step retreat rates along both the [100]Cc and [101]Cc directions. However, at higher concentrations (exceeding 0.1 mM), this inhibitory effect was reversed with step retreat speeds increasing rapidly. These results demonstrate that the concentration-dependent modulation of nanoscale Ca-P phase dissolution by citrate may be applied to analyze the controversial role of organic acids in enhancing Ca-P mineral dissolution in a more complex rhizosphere environment. These in situ observations may contribute to resolving the previously unrecognized interactions of root exudates (low molecular weight organic acids) and sparingly soluble Ca-P minerals.

  4. Preparation and Characterization of Liquisolid Compacts for Improved Dissolution of Telmisartan

    PubMed Central

    Narra, Nataraj; Rama Rao, Tadikonda

    2014-01-01

    The objective of the present work was to obtain pH independent and improved dissolution profile for a poorly soluble drug, telmisartan using liquisolid compacts. Liquisolid compacts were prepared using Transcutol HP as vehicle, Avicel PH102 as carrier, and Aerosil 200 as a coating material. The formulations were evaluated for drug excipient interactions, change in crystallinity of drug, flow properties, and general quality control tests of tablets using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), angle of repose, and various pharmacopoeial tests. In vitro dissolution studies were performed at three pH conditions (1.2, 4.5 and 7.4). Stability studies were performed at 40°C and 75% RH for three months. The formulation was found to comply with Indian pharmacopoeial limits for tablets. FTIR studies confirmed no interaction between drug and excipients. XRD and DSC studies indicate change/reduction in crystallinity of drug. Dissolution media were selected based on the solubility studies. The optimized formulation showed pH independent release profile with significant improvement (P < 0.005) in dissolution compared to plain drug and conventional marketed formulation. No significant difference was seen in the tablet properties, and drug release profile after storage for 3 months. PMID:25371826

  5. Probing ganglia dissolution and mobilization in a water-saturated porous medium using MRI

    SciTech Connect

    Johns, M.L.; Gladden, L.F.

    2000-05-01

    Magnetic resonance imaging (MRI) is used to probe the evolution of geometric characteristics such as the volume, shape, surface area, and cluster size of octanol ganglia trapped in a model porous medium, in this case a packing of spheres, as they dissolve into a mobile aqueous phase. The resulting pore-scale information is used to assess various assumptions used in existing models of the dissolution process. Dissolution of the ganglia was characterized by a reduction in the overall number of ganglia with little effect on the shape and mean of the volume distribution of the ganglia. This apparently anomalous result is explained by dissolution of the ganglia until they reach a critical size, which is dependent on the structure of the pore space, at which point they are mobilized and subsequently removed from the porous medium. The shape of the entrapped ganglia is characterized by a fractal dimension in the range 2.2--2.3, suggesting that models which assume a Euclidean geometry for the entrapped ganglia are appropriate. No significant change in the shape of entrapped ganglia is observed during dissolution. In agreement with the results of earlier workers, most hydrocarbon ganglia exist as singlets within the pore structure.

  6. Enhanced dissolution and bioavailability of raloxifene hydrochloride by co-grinding with different superdisintegrants.

    PubMed

    Jagadish, Balasubramaniam; Yelchuri, Rajesh; K, Bindu; Tangi, Hemalatha; Maroju, Swetha; Rao, Vinay Umesh

    2010-03-01

    The present study investigated the effect of co-grinding raloxifene HCL (RHCL) with different superdisintegrants, namely crospovidone (CP), croscarmellose sodium (CCS) and sodium starch glycolate (SSG), using a ball mill, in order to determine the potential effect on dissolution rate and bioavailability of raloxifene hydrochloride (RHCL). The dissolution studies of the co-ground compositions and the corresponding physical mixtures were carried out in U.S. Pharmacopeia (USP) Type II apparatus. The solid state interactions of the co-ground and the physical mixtures were evaluated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The pharmacokinetics of co-ground mixture (1 : 5 RHCL : CP) and milled RHCL was evaluated following oral administration (25 mg/kg) in healthy female Sprague-Dawley rats. DSC studies showed that the crystalline nature of RHCL was reduced after co-grinding with superdisintegrants, while co-grinding with CP resulted in significant particle-size reduction of the mixture. Significant enhancement in dissolution rate was observed with co-ground mixture of RHCL with CP (1 : 5). The extent of the mean plasma exposures of RHCL was 7-fold higher in animals treated with co-ground mixture of RHCL, CP (1 : 5) compared to animals treated with milled RHCL. Co-grinding of RHCL with CP, reduced drug crystallinity, increased the rate and extent of dissolution, and improved bioavailability.

  7. Dissolution-induced preferential flow in a limestone fracture.

    PubMed

    Liu, Jishan; Polak, Amir; Elsworth, Derek; Grader, Avrami

    2005-06-01

    Flow in a rock fracture is surprisingly sensitive to the evolution of flow paths that develop as a result of dissolution. Net dissolution may either increase or decrease permeability uniformly within the fracture, or may form a preferential flow path through which most of the injected fluid flows, depending on the prevailing ambient mechanical and chemical conditions. A flow-through test was completed on an artificial fracture in limestone at room temperature under ambient confining stress of 3.5 MPa. The sample was sequentially circulated by water of two different compositions through the 1500 h duration of the experiment; the first 935 h by tap groundwater, followed by 555 h of distilled water. Measurements of differential pressures between the inlet and the outlet, fluid and dissolved mass fluxes, and concurrent X-ray CT imaging and sectioning were used to characterize the evolution of flow paths within the limestone fracture. During the initial circulation of groundwater, the differential pressure increased almost threefold, and was interpreted as a net reduction in permeability as the contacting asperities across the fracture are removed, and the fracture closes. With the circulation of distilled water, permeability initially reduces threefold, and ultimately increases by two orders of magnitude. This spontaneous switch from net decrease in permeability, to net increase occurred with no change in flow rate or applied effective stress, and is attributed to the evolving localization of flow path as evidenced by CT images. Based on the X-ray CT characterizations, a flow path-dependent flow model was developed to simulate the evolution of flow paths within the fracture and its influence on the overall flow behaviors of the injected fluid in the fracture.

  8. Dissolution testing of acetylsalicylic acid by a channel flow method-correlation to USP basket and intrinsic dissolution methods.

    PubMed

    Peltonen, Leena; Liljeroth, Peter; Heikkilä, Tiina; Kontturi, Kyösti; Hirvonen, Jouni

    2003-08-01

    A new modification of the channel flow dissolution method is introduced together with the theoretical basis to extract the solubility and mass transfer parameters from the dissolution experiments. Correlation of drug dissolution profiles in the channel flow apparatus was evaluated with respect to USP basket and intrinsic dissolution methods at pH 1.2 or 6.8. Acetylsalicylic acid (ASA) was studied as a pure drug substance and as three simple tablet compositions with microcrystalline cellulose (MCC) and/or lactose as excipients. The channel flow measurements of 100% ASA tablets correlated well with the results of intrinsic dissolution tests. In the channel flow method as well as in the USP basket method the release of ASA was fastest from the tablet compositions containing lactose, while the slowest dissolution rate was observed with the composition containing MCC as the only excipient. As presumed, the dissolution rate of the weak acid was decreased as the pH of the medium was lowered, which was clearly confirmed also by the three dissolution methods. MCC forms matrix tablets and in the USP basket method the dissolution profiles followed square root of time kinetics indicating that diffusion was the rate-controlling step of ASA dissolution. Also the channel flow results indicated that the dissolution of ASA was controlled by mass transfer. The swelling behaviour of the tablets is different in the channel flow method as compared to the basket method: only one tablet surface is exposed to the dissolution medium in the channel flow system. The contact between the tablet surface and the dissolution medium is more similar between the channel flow and intrinsic dissolution methods.

  9. The unique mechanism of analcime dissolution by hydrogen ion attack.

    PubMed

    Hartman, Ryan L; Fogler, H Scott

    2006-12-19

    Acidization is the process of injecting acid into porous oil bearing formations to dissolve minerals in the pore space and is a common technique to increase oil production. Analcime is a zeolite which is one of the minerals found in oil reservoirs in the Gulf of Mexico. This mineral is particularly troublesome during the injection of hydrochloric acid during stimulation of the well reservoir because of the precipitation of silicate and analcime dissolution products. To better understand the dissolution/precipitation process, a fundamental investigation of dissolution of analcime was carried out. Experiments establish that silicate precipitates completely from solution during analcime dissolution in hydrochloric acid and that the precipitation does not influence the dissolution kinetics. Comparison of Si and Al initial dissolution rates demonstrates that Al is selectively removed from the zeolite. The selective removal rate parameter is defined as the ratio of the measured Si dissolution rate to the stoichiometric Si dissolution rate. A new concept is introduced of using the selective removal rate parameter to delineate the mechanism of particle dissolution by demonstrating the influence of the Si-to-Al ratio. The mechanism comprises the removal of Si facilitated by the selective removal of Al, leading to the formation of undissolvable silicate particles. Consequently, the unique mechanism of analcime dissolution has general implications pertaining to how microporous materials dissolve.

  10. Siderophore-Mediated Iron Dissolution from Nontronites Is Controlled by Mineral Cristallochemistry

    PubMed Central

    Parrello, Damien; Zegeye, Asfaw; Mustin, Christian; Billard, Patrick

    2016-01-01

    Bacteria living in oxic environments experience iron deficiency due to limited solubility and slow dissolution kinetics of iron-bearing minerals. To cope with iron deprivation, aerobic bacteria have evolved various strategies, including release of siderophores or other organic acids that scavenge external Fe(III) and deliver it to the cells. This research investigated the role of siderophores produced by Pseudomonas aeruginosa in the acquisition of Fe(III) from two iron-bearing colloidal nontronites (NAu-1 and NAu-2), comparing differences in bioavailability related with site occupancy and distribution of Fe(III) in the two lattices. To avoid both the direct contact of the mineral colloids with the bacterial cells and the uncontrolled particle aggregation, nontronite suspensions were homogenously dispersed in a porous silica gel before the dissolution experiments. A multiparametric approach coupling UV-vis spectroscopy and spectral decomposition algorithm was implemented to monitor simultaneously the solubilisation of Fe and the production of pyoverdine in microplate-based batch experiments. Both nontronites released Fe in a particle concentration-dependent manner when incubated with the wild-type P. aeruginosa strain, however iron released from NAu-2 was substantially greater than from NAu-1. The profile of organic acids produced in both cases was similar and may not account for the difference in the iron dissolution efficiency. In contrast, a pyoverdine-deficient mutant was unable to mobilize Fe(III) from either nontronite, whereas iron dissolution occurred in abiotic experiments conducted with purified pyoverdine. Overall, our data provide evidence that P. aeruginosa indirectly mobilize Fe from nontronites primarily through the production of pyoverdine. The structural Fe present on the edges of NAu-2 rather than NAu-1 particles appears to be more bio-accessible, indicating that the distribution of Fe, in the tetrahedron and/or in the octahedron sites, governs

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

    SciTech Connect

    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. 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

  12. Mesoscale Approach to Feldspar Dissolution: Quantification of Dissolution Incongruency Based on Al/Si Ordering State

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Min, Y.; Jun, Y.

    2012-12-01

    Dissolution mechanism of aluminosilicates is important for understanding natural and anthropogenic carbon cycles. The total mass of atmospheric CO2 is regulated by the weathering of silicate minerals, and the fate of geologically sequestered CO2 is affected by the interactions between brine, sandstone, caprock, and CO2, which is initiated by mineral dissolution. It has been shown through both experimental and ab initio studies that the dissolution/weathering reactivities of Al and Si in the matrix of an aluminosilicate can be different under many conditions. A subsequent observation is that the release rates of Al and Si, both from the same mineral, may not be stoichiometric when compared to the bulk chemistry of the mineral. For a very long time, the relationship between mineral dissolution incongruency and mineral crystallographic properties remain largely qualitative and descriptive. Here we study the dissolution incongruency of feldspars, the most abundant aluminosilicate on earth. Mineral dissolution experiments for a series of alkali feldspars (albite, anorthoclase, sanidine, and microcline) and plagioclases (oligoclase, andesine, labradorite, bytownite, and anorthite) were conducted at pH 1.68 under ambient conditions. Synchrotron-based X-ray diffraction (HR-XRD), Fourier transform infrared spectroscopy (FTIR), and water chemistry analysis (ICP-MS) are combined to examine the effect of Al/Si ordering on mineral dissolution. Our analysis based on a C1 structure model shows that the incongruency, stemming from the different reactivities of Al-O-Si and Si-O-Si linkages in feldspar's framework, is quantifiable and closely related to the Al/Si ordering state of a feldspar. Our results also suggest that the more random the Al/Si distribution of a mineral, the greater the dissolution incongruency. Our results have significant implications for understanding water-rock interactions. First, when studying the effect of water chemistry on water-rock interaction, smaller

  13. Dissolution of FB-Line Cabinet Sweepings

    SciTech Connect

    Crowder, Mark L.

    2005-06-14

    Three FB-Line samples were received by the Savannah River National Laboratory (SRNL) for characterization and evaluation for suitability for HB-Line dissolution. These samples are part of a larger sampling/evaluation program in support of FB-Line deinventory efforts. The samples studied were identified as MC04-147- HBL, MC04-148-HBL, and FBL-SWP-04-016-HBL (N). The first sample, MC04-147-HBL, is a portion of FB-Line Packaging and Stabilization (P&S) materials. The second sample, MC04-148-HBL, is a sweeping from Cabinet 6-8, which is not representative of the mechanical line. The third sample, FBL-SWP-04-016-HBL (N), is an FB-Line North cabinet sweeping. The samples were described by FB-Line personnel as containing plutonium oxide (PuO{sub 2}) which had not been high-fired. This description was generally confirmed by solids analysis and off gas measurements. All three samples were dissolved in 8 M HNO{sub 3}/0.1 M KF at 90-100 C leaving minor amounts of solid residue. During dissolution, sample MC04-147 did not generate hydrogen gas. Sample MC04-148 generated modest amounts of gas, which contained 4.0 to 4.7 volume percent (vol %) hydrogen (H{sub 2}) at a ratio of up to 8.4 x 10{sup -5} mol H{sub 2}/g sample. Sample FBL-SWP-04-016-HBL (N) was nearly completely soluble in 8 M HNO{sub 3}and produced a very small amount of gas. Apparently, the CaF{sub 2} in that sample dissolves and provides sufficient fluoride to support the dissolution of other components.

  14. The dissolution or growth of a sphere

    NASA Technical Reports Server (NTRS)

    Shankar, N.; Wiltshire, Timothy J.; Subramanian, R. Shankar

    1984-01-01

    The problem of the dissolution or growth of an isolated stationary sphere in a large fluid body is analyzed. The motion of the boundary as well as the the resulting motion in the liquid are properly taken into account. The governing equations are solved using a recently developed technique (Subramanian and Weinberg, 1981) which employs an asymptotic expansion in time. Results for the radius of the sphere as a function of time are calculated. The range of utility of the present solution is established by comparison with a numerical solution of the governing equations obtained by the method of finite differences.

  15. Dissolution of premarital cohabitation in Canada.

    PubMed

    Wu, Z; Balakrishnan, T R

    1995-11-01

    The rapid increase in the number of unmarried cohabiting couples, indicated by recent evidence, is crucial to our understanding of changing marriage patterns. The levels and patterns of entry into cohabitation have been well documented over the last two decades, but little is known about the outcomes of nonmarital cohabitation. In this study we examine two competing outcomes of cohabitation relationships: union separation and legalization of the union through marriage. Our results show that the hazard rate of union dissolution is affected particularly by gender, fertility status, partner's marital status, religion, age at start of cohabitation, year cohabitation commenced, and region.

  16. New mixing system in dissolution isoperibol microcalorimeter.

    PubMed

    Moreno-Piraján, Juan Carlos; Giraldo-Gutierréz, Liliana

    2007-04-01

    In order to determine dissolution enthalpies of small amounts of easily or slightly soluble solids, a new cell for batch isoperibolic microcalorimetry was developed at the Universities of the Andes and the National of Colombia. An innovative mixing system for avoiding error due to the common effect of the brittle point breakage has been designed for this cell. The cell has a capacity of 40 ml and the sample holder can bear solid samples between 10.0 and 30.0 mg. The high stability of the base line allows solution experiments to be extended over several hours. All measurements reported were conducted at 298.15 K using water as solvent.

  17. Dissolution of Uranium Oxides Under Alkaline Oxidizing Conditions

    SciTech Connect

    Smith, Steven C.; Peper, Shane M.; Douglas, Matthew; Ziegelgruber, Kate L.; Finn, Erin C.

    2009-11-01

    Bench scale experiments were conducted to determine the dissolution characteristics of uranium oxide powders (UO2, U3O8, and UO3) in aqueous peroxide-carbonate solutions. Experimental parameters included H2O2 concentration, carbonate counter cation (NH4+, Na+, K+, and Rb+), and pH. Results indicate the dissolution rate of UO2 in 1 M (NH4)2CO3 increases linearly with peroxide concentration ranging from 0.05 – 2 M. The three uranium oxide powders exhibited different dissolution patterns however, UO3 exhibited prompt complete dissolution. Carbonate counter cation affected the dissolution kinetics. There is minimal impact of solution pH, over the range 8.8 to 10.6, on initial dissolution rate.

  18. Influence of Dissolved Organic Matter and Fe (II) on the Abiotic Reduction of Pentachloronitrobenzene

    EPA Science Inventory

    Nitroaromatic pesticides (NAPs) are hydrophobic contaminants that can accumulate in sediments by the deposition of suspended solids from surface waters. Fe(II) and dissolved organic matter (DOM), present in suboxic and anoxic zones of freshwater sediments, can transform NAPs in n...

  19. On the dissolution properties of GaAs in Ga

    NASA Technical Reports Server (NTRS)

    Davidson, M. C.; Moynahan, A. H.

    1977-01-01

    The dissolution of GaAs in Ga was studied to determine the nature and cause of faceting effects. Ga was allowed to dissolve single crystalline faces under isothermal conditions. Of the crystalline planes with low number indices, only the (100) surface showed a direct correlation of dissolution sites to dislocations. The type of dissolution experienced depended on temperature, and there were three distinct types of behavior.

  20. The di- and tricalcium silicate dissolutions

    SciTech Connect

    Nicoleau, L.; Nonat, A.; Perrey, D.

    2013-05-15

    In this study, a specially designed reactor connected to an ICP spectrometer enabled the careful determination of the dissolution rates of C{sub 3}S, C{sub 2}S and CaO, respectively, over a broad range of concentration of calcium and silicates under conditions devoid of C–S–H. The kinetic laws, bridging the dissolution rates and the undersaturations, were obtained after extrapolation of rate zero allowing the estimation of the true experimental solubility products of C{sub 3}S (K{sub sp} = 9.6 · 10{sup −23}), C{sub 2}S (K{sub sp} = 4.3 · 10{sup −18}) and CaO (K{sub sp} = 9.17 · 10{sup −6}). The latter are then compared to the solubilities calculated from the enthalpies of formation. We propose that the observed deviations result from the protonation of the unsaturated oxygen atoms present at the surface of these minerals. Hydration rates measured in cement pastes or in C{sub 3}S pastes are in excellent agreement with the kinetic law found in this study for C{sub 3}S under conditions undersaturated with respect to C–S–H.

  1. Bench Scale Saltcake Dissolution Test Report

    SciTech Connect

    BECHTOLD, D.B.; PACQUET, E.A.

    2000-12-06

    A potential scenario for retrieving saltcake from single shell tanks is the ''Rainbird{reg_sign} sprinkler'' method. Water is distributed evenly across the surface of the saltcake and allowed to percolate by gravity through the waste. The salt dissolves in the water, forming a saturated solution. The saturated liquid is removed by a saltwell pump situated near the bottom of the tank. By this method, there is never a large inventory of liquid in the tank that could pose a threat of leakage. There are many variables or factors that can influence the hydrodynamics of this retrieval process. They include saltcake porosity; saltwell pumping rate; salt dissolution chemistry; factors that could promote flow channeling (e.g. tank walls, dry wells, inclusions or discontinuities in the saltcake); method of water distribution; plug formation due to crystal formations or accumulation of insoluble solids. A brief literature search indicates that very little experimental data exist on these aspects of saltcake dissolution (Wiersma 1996, 1997). The tests reported here were planned (Herting, 2000) to provide preliminary data and information for planning future, scaled-up tests of the sprinkler method.

  2. Dissolution and crystallization of calcium sulfite platelets

    SciTech Connect

    Gleason, C.L.; Rochelle, G.T.

    1987-01-01

    The rates of calcium sulfite dissolution and crystallization are important in slurry scrubbing processes for flue gas desulfurization. The rates affect the scrubber solution composition, SO/sub 2/ absorption, sulfite oxidation and limestone utilization. The dissolution and crystallization rates of platelet shaped calcium sulfite crystals were measured in the pH state apparatus. The solution pH was varied from 3.0 to 6.0. The effects of sulfate content in the solids and solution were also investigated. The measured rates for the platelets were compared to the rates previously determined for agglomerates. It was determined that there are subtle differences between platelet and agglomerated calcium sulfite. The platelet sample with a low solid sulfate content dissolved and crystallized slower than the sample with a high solid sulfate content and the agglomerated samples. The inhibiting effect of dissolved sulfate was also greater for the low solid sulfate sample. The sample with a high solid sulfate content dissolved and crystallized at approximately the same rate as the agglomerates.

  3. Magnesium inhibition of calcite dissolution kinetics

    SciTech Connect

    Arvidson, Rolf S.; Collier, Martin; Davis, Kevin J.; Vinson, Michael D.; Amonette, James E.; Luttge, Andreas

    2006-02-01

    We present evidence of inhibition of calcite dissolution by dissolved magnesium through direct observations of the (104) surface using atomic force microscopy (AFM) and vertical scanning interferometry (VSI). Far from equilibrium, the pattern of magnesium inhibition is dependent on solution composition and specific to surface step geometry. In CO2-free solutions (pH 8.8), dissolved magnesium brings about little inhibition even at concentrations of 0.8 x 10-3 molal. At the same pH, magnesium concentrations of less than 0.05 x 10-3 molal in carbonate-buffered solutions generate significant inhibition, although no changes in surface and etch pit morphology are observed. As concentrations exceed magnesite saturation, the dissolution rate shows little additional decrease; however, selective pinning of step edges results in unique etch-pit profiles, seen in both AFM and VSI datasets. Despite the decreases in step velocity, magnesium addition in carbonated solutions also appears to activate the surface by increasing the nucleation rate of new defects. These relationships suggest that the modest depression of the bulk rate measured by VSI reflects a balance between competing reaction mechanisms that simultaneously depress the rate through selective inhibition of step movement, but also enhance reactivity on terraces by lowering the energy barrier to new etch-pit formation.

  4. Buffering children from marital conflict and dissolution.

    PubMed

    Katz, L F; Gottman, J M

    1997-06-01

    Examined several protective mechanisms that may reduce deleterious correlates of marital conflict and marital dissolution in young children. One set of potential buffers focused on parent-child interaction: parental warmth, parental scaffolding/praise, and inhibition of parental rejection. As a second set of potential buffers, each parent was interviewed about their "meta-emotion philosophy"--that is, their feelings about their own emotions, and their attitudes and responses to their children's anger and sadness. The third set of potential buffers concerned intraindividual characteristics of the child, including the child's intelligence and regulatory physiology (basal vagal tone and vagal suppression). Fifty-six families with a preschool child were studied at two time points: when the children were 5 years old (Time 1) and again when the children were 8 years old (Time 2). At Time 1, naturalistic observations of marital and parent-child interaction were conducted and assessment of child regulatory physiology was obtained through measures of basal vagal tone and suppression of vagal tone. Parents were also interviewed individually about their feelings about their own and their children's emotions, and children's intelligence was assessed. At Time 2, assessment of child outcomes were obtained, including observations of peer interaction, mother ratings of behavior problems and mother and teacher ratings of peer aggression, mother ratings of child physical illness, and measures of achievement. Results indicated that all Time 1 buffering factors protected children in face of marital conflict and dissolution.

  5. Coupled Abiotic-Biotic Degradation of Bisphenol A

    NASA Astrophysics Data System (ADS)

    Im, J.; Prevatte, C.; Campagna, S. R.; Loeffler, F.

    2014-12-01

    Bisphenol A (BPA) is a ubiquitous environmental contaminant with weak estrogenic activity. BPA is readily biodegradable with oxygen available, but is recalcitrant to microbial degradation under anoxic conditions. However, BPA is susceptible to abiotic transformation under anoxic conditions. To better understand the fate of BPA in anoxic environments, the kinetics of BPA transformation by manganese oxide (d-MnO2) were investigated. BPA was rapidly transformed by MnO2 with a pseudo-first-order rate constant of 0.413 min-1. NMR and LC-MS analyses identified 4-hydroxycumyl alcohol (HCA) as a major intermediate. Up to 64% of the initial amount of BPA was recovered as HCA within 5 min, but the conversion efficiency decreased with time, suggesting that HCA was further degraded by MnO2. Further experiments confirmed that HCA was also susceptible to transformation by MnO2, albeit at 5-fold lower rates than BPA transformation. Mass balance approaches suggested that HCA was the major BPA transformation intermediate, but other compounds may also be formed. The abiotic transformation of BPA by MnO2 was affected by pH, and 10-fold higher transformation rates were observed at pH 4.5 than at pH 10. Compared to BPA, HCA has a lower octanol-water partitioning coefficient (Log Kow) of 0.76 vs 2.76 for BPA and a higher aqueous solubility of 2.65 g L-1 vs 0.31 g L-1 for BPA, suggesting higher mobility of HCA in the environment. Microcosms established with freshwater sediment materials collected from four geographically distinct locations and amended with HCA demonstrated rapid HCA biodegradation under oxic, but not under anoxic conditions. These findings suggest that BPA is not inert under anoxic conditions and abiotic reactions with MnO2 generate HCA, which has increased mobility and is susceptible to aerobic degradation. Therefore, coupled abiotic-biotic processes can affect the fate and longevity of BPA in terrestrial environments.

  6. Abiotic gas formation drives nitrogen loss from a desert ecosystem.

    PubMed

    McCalley, Carmody K; Sparks, Jed P

    2009-11-06

    In arid environments such as deserts, nitrogen is often the most limiting nutrient for biological activity. The majority of the ecosystem nitrogen flux is typically thought to be driven by production and loss of reactive nitrogen species by microorganisms in the soil. We found that high soil-surface temperatures (greater than 50 degrees C), driven by solar radiation, are the primary cause of nitrogen loss in Mojave Desert soils. This abiotic pathway not only enables the balancing of arid ecosystem nitrogen budgets, but also changes our view of global nitrogen cycling and the predicted impact of climate change and increased temperatures on nitrogen bioavailability.

  7. Carbon and chlorine isotope analysis to identify abiotic degradation pathways of 1,1,1-trichloroethane.

    PubMed

    Palau, Jordi; Shouakar-Stash, Orfan; Hunkeler, Daniel

    2014-12-16

    This study investigates dual C-Cl isotope fractionation during 1,1,1-TCA transformation by heat-activated persulfate (PS), hydrolysis/dehydrohalogenation (HY/DH) and Fe(0). Compound-specific chlorine isotope analysis of 1,1,1-TCA was performed for the first time, and transformation-associated isotope fractionation ε bulk C and ε bulk Cl values were -4.0 ± 0.2‰ and no chlorine isotope fractionation with PS, -1.6 ± 0.2‰ and -4.7 ± 0.1‰ for HY/DH, -7.8 ± 0.4‰ and -5.2 ± 0.2‰ with Fe(0). Distinctly different dual isotope slopes (Δδ13C/Δδ37Cl): ∞ with PS, 0.33 ± 0.04 for HY/DH and 1.5 ± 0.1 with Fe(0) highlight the potential of this approach to identify abiotic degradation pathways of 1,1,1-TCA in the field. The trend observed with PS agreed with a C-H bond oxidation mechanism in the first reaction step. For HY/DH and Fe(0) pathways, different slopes were obtained although both pathways involve cleavage of a C-Cl bond in their initial reaction step. In contrast to the expected larger primary carbon isotope effects relative to chlorine for C-Cl bond cleavage, ε bulk C < ε bulk Cl was observed for HY/DH and in a similar range for reduction by Fe(0), suggesting the contribution of secondary chlorine isotope effects. Therefore, different magnitude of secondary chlorine isotope effects could at least be partly responsible for the distinct slopes between HY/DH and Fe(0) pathways. Following this dual isotope approach, abiotic transformation processes can unambiguously be identified and quantified.

  8. Biotic and Abiotic Transformation of a Volatile Organics Plume in a Semi-Arid Vadose Zone

    SciTech Connect

    Studer, J.E.; Singletary, M.A.; Miller, D.R.

    1999-04-08

    An evaluation of biotic and abiotic attenuation processes potentially important to chlorinated and non-chlorinated volatile organic compound (VOC) fate and transport in the 148 meter thick vadose zone beneath the Chemical Waste Landfill (CWL) was conducted. A unique feature of this evaluation is the comparison of two estimates of VOC mass present in the soil gas, pore-water, and solid phases (but not including mass as non-aqueous phase liquid [NAPL]) of the vadose zone in 1993. One estimate, 1,800 kg, was obtained from vadose zone transport modeling that incorporated molecular diffusion and volatilization to the atmosphere, but not biotic or chemical processes. The other estimate, 2,120 kg, was obtained from the sum of VOC mass physically removed during soil vapor extraction and an estimate of VOC mass remaining in the vadose zone in 1998, both adjusted to exclude NAPL mass. This comparison indicates that biogeochemical processes were at best slightly important to historical VOC plume development. Some evidence of aerobic degradation of non-chlorinated VOCs and abiotic transformation of 1,1,1-Trichloroethane was identified. Despite potentially amenable site conditions, no evidence was found of cometabolic and anaerobic transformation pathways. Relying principally on soil-gas analytical results, an upper-bound estimate of 21% mass reduction due to natural biogeochemical processes was developed. Although available information for the CWL indicates that natural attenuation processes other than volatilization to the atmosphere did not effective y enhance groundwater protection, these processes could be important in significantly reducing groundwater contamination and exposure risks at other sites. More laboratory and field research is required to improve our collective ability to characterize and exploit natural VOC attenuation processes, especially with respect to the combination of relatively thick and dry vadose zones and chlorinated VOCs.

  9. Dissolution kinetics of calcium carbonate in equatorial Pacific sediments

    NASA Astrophysics Data System (ADS)

    Berelson, William M.; Hammond, Douglas E.; McManus, James; Kilgore, Tammy E.

    1994-06-01

    Benthic chambers were deployed in the equatorial eastern Pacific Ocean on a transect along the equator between 103°W and 140°W and on a transect across the equator at 140°W in order to establish the rate of calcium carbonate dissolution on the seafloor. Dissolution was determined from the rate of alkalinity increase within an incubation chamber, measured over an 80-120 hour incubation period. Dissolution rates were lowest at eastern Pacific sites (0.2-0.4 mmol CaCO3/m2/d) and highest at the equatorial, 140°W sites (0.5-0.7 mmol/m2/d). Both oxygen consumption rates and the degree of bottom water saturation govern dissolution rates. Measured dissolution and oxygen consumption rates are used with a numerical model to constrain the value of the dissolution rate constant k, formulated according to the equation developed by Keir [1980]: dissolution rate = kγ(1-Ω)n. The observed dissolution fluxes are predicted by the model when k = 5 to 100%/d and n = 4.5. This range of k values has important implications regarding the type of carbonate dissolving and its location within the sediment column. At low values of k, organic carbon rain rates to the seafloor become the dominant driving force of carbonate dissolution. At higher values of k, the degree of bottom water undersaturation becomes more important. Dissolution of carbonate within equatorial Pacific sediments can be adequately described with k = 20 ± 10%/d, a rate constant much lower than some previously used values. Dissolution rates do not vary significantly over chamber boundary layer thicknesses between 200 and 800 μm, indicating that dissolution is not controlled by hydrodynamic conditions. Chambers acidified with HCl yield very large dissolution rates, but for a given degree of acidification the dissolution rate was constant for sites ranging from water depths of 3300-4400 m. This implies that there are not more and less easily dissolved forms of CaCO3 arriving on the seafloor between these depths. A budget

  10. Dissolution of beryllium in artificial lung alveolar macrophage phagolysosomal fluid.

    PubMed

    Stefaniak, Aleksandr B; Virji, M Abbas; Day, Gregory A

    2011-05-01

    Dissolution of a lung burden of poorly soluble beryllium particles is hypothesized to be necessary for development of chronic beryllium lung disease (CBD) in humans. As such, particle dissolution rate must be sufficient to activate the lung immune response and dissolution lifetime sufficient to maintain chronic inflammation for months to years to support development of disease. The purpose of this research was to investigate the hypothesis that poorly soluble beryllium compounds release ions via dissolution in lung fluid. Dissolution kinetics of 17 poorly soluble particulate beryllium materials that span extraction through ceramics machining (ores, hydroxide, metal, copper-beryllium [CuBe] fume, oxides) and three CuBe alloy reference materials (chips, solid block) were measured over 31 d using artificial lung alveolar macrophage phagolysosomal fluid (pH 4.5). Differences in beryllium-containing particle physicochemical properties translated into differences in dissolution rates and lifetimes in artificial phagolysosomal fluid. Among all materials, dissolution rate constant values ranged from 10(-5) to 10(-10)gcm(-2)d(-1) and half-times ranged from tens to thousands of days. The presence of magnesium trisilicate in some beryllium oxide materials may have slowed dissolution rates. Materials associated with elevated prevalence of CBD had faster beryllium dissolution rates [10(-7)-10(-8)gcm(-2)d(-1)] than materials not associated with elevated prevalence (p<0.05).

  11. Effect of thermal gelation on dissolution from coated tablets.

    PubMed

    Schwartz, J B; Alvino, T P

    1976-04-01

    Tablets with a methylcellulose coating were found to exhibit lower dissolution profiles than those coated with a hydroxypropyl methylcellulose coating at 37 degrees, and the cause was investigated. The differences are attributed to thermal gelation of the methylcellulose at temperatures near 37 degrees, which creates a barrier to the dissolution process and essentially changes the dissolution mechanism. This mechanism is substantiated by the fact that at temperatures below the gel point and at increased agitation, the effect disappears. The retarded dissolution effect is not peculiar to the drug involved.

  12. Dissolution studies with pilot plant and actual INTEC calcines

    SciTech Connect

    Herbst, R.S.; Garn, T.G.

    1999-04-01

    The dissolution of Idaho Nuclear Technology and Engineering Center (INTEC) pilot plant calcines was examined to determine solubility of calcine matrix components in acidic media. Two representatives pilot plant calcine types were studied: Zirconia calcine and Zirconia/Sodium calcine. Dissolution of these calcines was evaluated using lower initial concentrations of nitric acid than used in previous tests to decrease the [H+] concentration in the final solutions. Lower [H+] concentrations contribute to more favorable TRUEX/SREX solvent extraction flowsheet performance. Dissolution and analytical results were also obtained for radioactive calcines produced using high sodium feeds blended with non-radioactive Al(NO{sub 3}){sub 3} solutions to dilute the sodium concentration and prevent bed agglomeration during the calcination process. Dissolution tests indicated {gt}95 wt.% of the initial calcine mass can be dissolved using the baseline dissolution procedure, with the exception that higher initial nitric acid concentrations are required. The higher initial acid concentration is required for stoichiometric dissolution of the oxides, primarily aluminum oxide. Statistically designed experiments using pilot plant calcine were performed to determine the effect of mixing rate on dissolution efficiency. Mixing rate was determined to provide minimal effects on wt.% dissolution. The acid/calcine ratio and temperature were the predominate variables affecting the wt.% dissolution, a result consistent with previous studies using other similar types of pilot plant calcines.

  13. Dissolution Studies With Pilot Plant and Actual INTEC Calcines

    SciTech Connect

    Herbst, Ronald Scott; Garn, Troy Gerry

    1999-04-01

    The dissolution of Idaho Nuclear Technology and Engineering Center (INTEC) pilot plant calcines was examined to determine solubility of calcine matrix components in acidic media. Two representatives pilot plant calcine types were studied: Zirconia calcine and Zirconia/ Sodium calcine. Dissolution of these calcines was evaluated using lower initial concentrations of nitric acid than used in previous tests to decrease the [H+] concentration in the final solutions. Lower [H+] concentrations contribute to more favorable TRUEX/SREX solvent extraction flowsheet performance. Dissolution and analytical results were also obtained for radioactive calcines produced using high sodium feeds blended with non-radioactive A1(NO3)3 solutions to dilute the sodium concentration and prevent bed agglomeration during the calcination process. Dissolution tests indicated >95 wt. % of the initial calcine mass can be dissolved using the baseline dissolution procedure, with the exception that higher initial nitric acid concentrations are required. The higher initial acid concentration is required for stoichiometric dissolution of the oxides, primarily aluminum oxide. Statistically designed experiments using pilot plant calcine were performed to determine the effect of mixing rate on dissolution efficiency. Mixing rate was determined to provide minimal effects on wt. % dissolution. The acid/calcine ratio and temperature were the predominate variables affecting the wt. % dissolution, a result consistent with previous studies using other similar types of pilot plant calcines.

  14. Dissolution of sodium chlorate crystals in supersaturated solutions

    NASA Astrophysics Data System (ADS)

    Malivuk, Dragana A.; Žekić, Andrijana A.; Mitrović, Mićo M.; Misailović, Branislava M.

    2013-08-01

    The results of the investigations regarding the growth and the dissolution behavior of small sodium chlorate crystals at temperatures near saturation temperature of (31.00±0.02)°C are presented. Above this temperature all the observed crystals dissolved, as was expected. At temperatures between 30.5°C and 31.0°C coexistence of growing, non-growing and dissolving crystals was occurred. At temperatures below 30.5°C dissolution of the crystals did not occur. A significant growth/dissolution rate dispersion existed at all temperatures. Possible reasons for simultaneous growth and dissolution are discussed.

  15. 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.

  16. 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

  17. Uranium isotopes fingerprint biotic reduction

    SciTech Connect

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J.; Weyer, Stefan; Bernier-Latmani, Rizlan

    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), 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.

  18. Uranium isotopes fingerprint biotic reduction

    PubMed Central

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J.; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-01-01

    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. PMID:25902522

  19. Dissolution of carbon from alumina-carbon mixtures into liquid iron: Influence of carbonaceous materials

    NASA Astrophysics Data System (ADS)

    Khanna, Rita; Sahajwalla, Veena; Rodgers, Brenton; McCarthy, Fiona

    2006-08-01

    Due to their excellent thermal shock and wear resistance at high temperatures, alumina-carbon based refractories are used extensively in the steel industry. A clear understanding of factors affecting the dissolution of carbon from refractories is of crucial importance, as carbon depletion from the refractory can significantly deteriorate refractory performance and metal quality. Atomistic simulations on the alumina-graphite/liquid iron system have shown that nonwetting between alumina and liquid iron is an important factor inhibiting the penetration of liquid metal in the refractory matrix and limiting carbon dissolution. This study investigates the role played by the carbonaceous material in the dissolution of carbon from the refractory composite. Two carbonaceous materials, namely, petroleum coke and natural graphite, respectively, containing 0.35 and 5.26 pct ash, were used in this study. Substrates were prepared from mixtures of alumina and carbon over a wide concentration range. Using a sessile drop arrangement, carbon pickup by liquid iron from alumina-carbon mixtures was measured at 1550 °C and was compared with the carbon pickup from alumina-synthetic graphite mixtures. These studies were supplemented with wettability measurements and microscopic investigations on the interfacial region. For high alumina concentrations (>40 wt pct), carbon dissolution from refractory mixtures was found to be negligible for all carbonaceous materials under investigation. Significant differences however were observed at lower alumina concentrations. Carbon dissolution from alumina-petroleum coke mixtures was much lower than the corresponding dissolution from alumina synthetic graphite-mixtures and was attributed to poor wettability of petroleum coke with liquid iron, its structural disorder, and the presence of sulfur. Very high levels of carbon dissolution, however, were observed from alumina-natural graphite mixtures, with carbon pickup by liquid iron from mixtures with up

  20. Method for improving dissolution efficiency in gas-absorption and liquid extraction processes

    DOEpatents

    Kanak, Brant E.; Stephenson, Michael J.

    1981-01-01

    This invention is a method for improving dissolution efficiency in processes in which a feed fluid is introduced to a zone where it is contacted with a liquid solvent for preferentially removing a component of the feed and where part of the solvent so contacted undergoes transfer into the feed fluid to saturate the same. It has been found that such transfer significantly impairs dissolution efficiency. In accordance with the invention, an amount of the above-mentioned solvent is added to the feed fluid being introduced to the contact zone, the solvent being added in an amount sufficient to effect reduction or elimination of the above-mentioned transfer. Preferably, the solvent is added to the feed fluid in an amount saturating or supersaturating the feed fluid under the conditions prevailing in the contact zone.

  1. Method for improving dissolution efficiency in gas-absorption and liquid extraction processes. [Patent application

    DOEpatents

    Kanak, B.E.; Stephenson, M.J.

    1980-01-11

    A method is described for improving dissolution efficiency in processes in which a feed fluid is introduced to a zone where it is contacted with a liquid solvent for preferentially removing a component of the feed and where part of the solvent so contacted undergoes transfer into the feed fluid to saturate the same. It has been found that such transfer significantly impairs dissolution efficiency. In accordance with the invention, an amount of the above-mentioned solvent is added to the feed fluid being introduced to the contact zone, the solvent being added in an amount sufficient to effect reduction or elimination of the above-mentioned transfer. Preferably, the solvent is added to the feed fluid in an amount saturating or supersaturating the feed fluid under the conditions prevailing in the contact zone.

  2. Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution.

    PubMed

    Hodnik, Nejc; Baldizzone, Claudio; Polymeros, George; Geiger, Simon; Grote, Jan-Philipp; Cherevko, Serhiy; Mingers, Andrea; Zeradjanin, Aleksandar; Mayrhofer, Karl J J

    2016-10-21

    The recycling of precious metals, for example, platinum, is an essential aspect of sustainability for the modern industry and energy sectors. However, due to its resistance to corrosion, platinum-leaching techniques rely on high reagent consumption and hazardous processes, for example, boiling aqua regia; a mixture of concentrated nitric and hydrochloric acid. Here we demonstrate that complete dissolution of metallic platinum can be achieved by induced surface potential alteration, an 'electrode-less' process utilizing alternatively oxidative and reductive gases. This concept for platinum recycling exploits the so-called transient dissolution mechanism, triggered by a repetitive change in platinum surface oxidation state, without using any external electric current or electrodes. The effective performance in non-toxic low-concentrated acid and at room temperature is a strong benefit of this approach, potentially rendering recycling of industrial catalysts, including but not limited to platinum-based systems, more sustainable.

  3. Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution

    PubMed Central

    Hodnik, Nejc; Baldizzone, Claudio; Polymeros, George; Geiger, Simon; Grote, Jan-Philipp; Cherevko, Serhiy; Mingers, Andrea; Zeradjanin, Aleksandar; Mayrhofer, Karl J. J.

    2016-01-01

    The recycling of precious metals, for example, platinum, is an essential aspect of sustainability for the modern industry and energy sectors. However, due to its resistance to corrosion, platinum-leaching techniques rely on high reagent consumption and hazardous processes, for example, boiling aqua regia; a mixture of concentrated nitric and hydrochloric acid. Here we demonstrate that complete dissolution of metallic platinum can be achieved by induced surface potential alteration, an ‘electrode-less' process utilizing alternatively oxidative and reductive gases. This concept for platinum recycling exploits the so-called transient dissolution mechanism, triggered by a repetitive change in platinum surface oxidation state, without using any external electric current or electrodes. The effective performance in non-toxic low-concentrated acid and at room temperature is a strong benefit of this approach, potentially rendering recycling of industrial catalysts, including but not limited to platinum-based systems, more sustainable. PMID:27767178

  4. Early microfluidic dissolution regime of CO2 bubbles in viscous oils

    NASA Astrophysics Data System (ADS)

    Sauzade, Martin; Cubaud, Thomas

    2013-11-01

    We investigate the initial dynamical behavior of dissolving micro-bubbles composed of carbon dioxide gas in highly viscous silicone oils over a range of flow rates and pressure conditions. Microfluidic periodic trains of monodisperse CO2 bubbles are used to probe the interrelation between bubble dissolution and high-viscosity multiphase flows in microgeometries. The effective mass diffusion flux across the interface is measured by tracking individual bubbles and monitoring their shape as they experience a size reduction. The initial steady mass flux is characterized using a dissolution coefficient that depends on the fluids physicochemical properties. Our findings show the possibility to control and exploit the interplay between capillary and mass transfer phenomena with highly viscous fluids in small-scale systems. This work is supported by NSF (CBET- 1150389).

  5. Preparation, characterization and dissolution of passive oxide film on the 400 series stainless steel surfaces

    NASA Astrophysics Data System (ADS)

    Sathyaseelan, V. S.; Rufus, A. L.; Chandramohan, P.; Subramanian, H.; Velmurugan, S.

    2015-12-01

    Full system decontamination of Primary Heat Transport (PHT) system of Pressurised Heavy Water Reactors (PHWRs) resulted in low decontamination factors (DF) on stainless steel (SS) surfaces. Hence, studies were carried out with 403 SS and 410 SS that are the material of construction of "End-Fitting body" and "End-Fitting Liner tubes". Three formulations were evaluated for the dissolution of passive films formed over these alloys viz., i) Two-step process consisting of oxidation and reduction reactions, ii) Dilute Chemical Decontamination (DCD) and iii) High Temperature Process. The two-step and high temperature processes could dissolve the oxide completely while the DCD process could remove only 60%. Various techniques like XRD, Raman spectroscopy and SEM-EDX were used for assessing the dissolution process. The two-step process is time consuming, laborious while the high temperature process is less time consuming and is recommended for SS decontamination.

  6. Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution

    NASA Astrophysics Data System (ADS)

    Hodnik, Nejc; Baldizzone, Claudio; Polymeros, George; Geiger, Simon; Grote, Jan-Philipp; Cherevko, Serhiy; Mingers, Andrea; Zeradjanin, Aleksandar; Mayrhofer, Karl J. J.

    2016-10-01

    The recycling of precious metals, for example, platinum, is an essential aspect of sustainability for the modern industry and energy sectors. However, due to its resistance to corrosion, platinum-leaching techniques rely on high reagent consumption and hazardous processes, for example, boiling aqua regia; a mixture of concentrated nitric and hydrochloric acid. Here we demonstrate that complete dissolution of metallic platinum can be achieved by induced surface potential alteration, an `electrode-less' process utilizing alternatively oxidative and reductive gases. This concept for platinum recycling exploits the so-called transient dissolution mechanism, triggered by a repetitive change in platinum surface oxidation state, without using any external electric current or electrodes. The effective performance in non-toxic low-concentrated acid and at room temperature is a strong benefit of this approach, potentially rendering recycling of industrial catalysts, including but not limited to platinum-based systems, more sustainable.

  7. The relative abundances of resolved l2CH2D2 and 13CH3D and mechanisms controlling isotopic bond ordering in abiotic and biotic methane gases

    NASA Astrophysics Data System (ADS)

    Young, E. D.; Kohl, I. E.; Lollar, B. Sherwood; Etiope, G.; Rumble, D.; Li (李姝宁), S.; Haghnegahdar, M. A.; Schauble, E. A.; McCain, K. A.; Foustoukos, D. I.; Sutclife, C.; Warr, O.; Ballentine, C. J.; Onstott, T. C.; Hosgormez, H.; Neubeck, A.; Marques, J. M.; Pérez-Rodríguez, I.; Rowe, A. R.; LaRowe, D. E.; Magnabosco, C.; Yeung, L. Y.; Ash, J. L.; Bryndzia, L. T.

    2017-04-01

    We report measurements of resolved 12CH2D2 and 13CH3D at natural abundances in a variety of methane gases produced naturally and in the laboratory. The ability to resolve 12CH2D2 from 13CH3D provides unprecedented insights into the origin and evolution of CH4. The results identify conditions under which either isotopic bond order disequilibrium or equilibrium are expected. Where equilibrium obtains, concordant Δ12CH2D2 and Δ13CH3D temperatures can be used reliably for thermometry. We find that concordant temperatures do not always match previous hypotheses based on indirect estimates of temperature of formation nor temperatures derived from CH4/H2 D/H exchange, underscoring the importance of reliable thermometry based on the CH4 molecules themselves. Where Δ12CH2D2 and Δ13CH3D values are inconsistent with thermodynamic equilibrium, temperatures of formation derived from these species are spurious. In such situations, while formation temperatures are unavailable, disequilibrium isotopologue ratios nonetheless provide novel information about the formation mechanism of the gas and the presence or absence of multiple sources or sinks. In particular, disequilibrium isotopologue ratios may provide the means for differentiating between methane produced by abiotic synthesis vs. biological processes. Deficits in 12CH2D2 compared with equilibrium values in CH4 gas made by surface-catalyzed abiotic reactions are so large as to point towards a quantum tunneling origin. Tunneling also accounts for the more moderate depletions in 13CH3D that accompany the low 12CH2D2 abundances produced by abiotic reactions. The tunneling signature may prove to be an important tracer of abiotic methane formation, especially where it is preserved by dissolution of gas in cool hydrothermal systems (e.g., Mars). Isotopologue signatures of abiotic methane production can be erased by infiltration of microbial communities, and Δ12CH2D2 values are a key tracer of microbial recycling.

  8. Small RNAs in Plant Responses to Abiotic Stresses: Regulatory Roles and Study Methods

    PubMed Central

    Ku, Yee-Shan; Wong, Johanna Wing-Hang; Mui, Zeta; Liu, Xuan; Hui, Jerome Ho-Lam; Chan, Ting-Fung; Lam, Hon-Ming

    2015-01-01

    To survive under abiotic stresses in the environment, plants trigger a reprogramming of gene expression, by transcriptional regulation or translational regulation, to turn on protective mechanisms. The current focus of research on how plants cope with abiotic stresses has transitioned from transcriptomic analyses to small RNA investigations. In this review, we have summarized and evaluated the current methodologies used in the identification and validation of small RNAs and their targets, in the context of plant responses to abiotic stresses. PMID:26501263

  9. Dissolution of Technetium(IV) Oxide by Natural and Synthetic Organic Ligands Under both Reducing and Oxidizing Conditions

    SciTech Connect

    Gu, Baohua; Dong, W.; Liang, Liyuan; Wall, Nathalie

    2011-01-01

    Technetium-99 (Tc) in nuclear waste is a significant environmental concern due to its long half-life and high mobility in the subsurface. Reductive precipitation of Tc(IV) oxides [TcO2(s)] is an effective means of immobilizing Tc, thereby impeding its migration in groundwater. However, TcO2(s) is subject to dissolution by oxidants and/or complexing agents. In this study we ascertain the effects of a synthetic organic ligand, ethylenediaminetetraacetate (EDTA), and two natural humic isolates on the dissolution and solubility of Tc(IV) oxides. Pure synthetic TcO2(s) (0.23 mM) was used in batch experiments to determine dissolution kinetics at pH ~6 under both reducing and oxidizing conditions. All organic ligands were found to enhance the dissolution of Tc(IV) oxides, increasing their solubility from ~10-8 M (without ligands) to 4 10-7 M under strictly anoxic conditions. Reduced Tc(IV) was also found to re-oxidize rapidly under oxic conditions, with an observed oxidative dissolution rate approximately an order of magnitude higher than that of ligand-promoted dissolution under reducing conditions. Significantly, oxidative dissolution was inhibited by EDTA but enhanced by humic acid compared with experiments without any complexing agents. The redox functional properties of humics, capable of facilitating intra-molecular electron transfer, may account for this increased oxidation rate under oxic conditions. Our results highlight the importance of complex interactions for the stability and mobility of Tc, and thus for the long-term fate of Tc in contaminated environments.

  10. Dolomite Dissolution in Alkaline Cementious Media

    NASA Astrophysics Data System (ADS)

    Mittermayr, Florian; Klammer, Dietmar; Köhler, Stephan; Dietzel, Martin

    2010-05-01

    Chemical alteration of concrete has gained much attention over the past years as many cases of deterioration due to sulphate attack, thaumasite formation (TSA) or alkali silica reactions (ASR) have been reported in various constructions (Schmidt et al, 2009). Much less is known about the so called alkali carbonate reaction (ACR). It is believed that dolomite aggregates can react with the alkalis from the cement, dissolve and form calcite and brucite (Katayama, 2004). Due to very low solubility of dolomite in alkaline solutions this reaction seems doubtful. In this study we are trying to gain new insides about the conditions that can lead to the dissolution of dolomite in concrete. Therefore we investigated concrete samples from Austrian tunnels that show partially dissolved dolomite aggregates. Petrological analysis such as microprobe, SEM and Raman spectroscopy as well as a hydrochemical analysis of interstitial solutions and ground water and modelling with PhreeqC (Parkhurst and Appelo, 1999) are carried out. In addition a series of batch experiments is set up. Modelling approaches by PhreeqC show a thermodynamically possibility in the alkaline range when additional Ca2+ in solution causes dolomite to become more and more undersaturated as calcite gets supersaturated. Interacting ground water is enriched in Ca2+and saturated with respect to gypsum as marine evaporites are found in situ rocks. Furthermore it is more likely that Portlandite (Ca(OH)2) plays a more important role than Na and K in the cement. Portlandite acts as an additional Ca2+ source and is much more abundant than the alkalies. Some interstitial solutions are dominated mainly by Na+ and SO42- and reach concentrations up to 30 g/l TDS. It is believed that solutions can even reach thenardite saturation as efflorescences are found on the tunnel walls. In consequence dolomite solubility increases with increasing ionic strength. pH > 11 further accelerate the process of dedolomitization by the removal

  11. Development and application of a screening model for evaluating bioenhanced dissolution in DNAPL source zones

    NASA Astrophysics Data System (ADS)

    Phelan, Thomas J.; Abriola, Linda M.; Gibson, Jenny L.; Smits, Kathleen M.; Christ, John A.

    2015-12-01

    In-situ bioremediation, a widely applied treatment technology for source zones contaminated with dense non-aqueous phase liquids (DNAPLs), has proven economical and reasonably efficient for long-term management of contaminated sites. Successful application of this remedial technology, however, requires an understanding of the complex interaction of transport, mass transfer, and biotransformation processes. The bioenhancement factor, which represents the ratio of DNAPL mass transfer under microbially active conditions to that which would occur under abiotic conditions, is commonly used to quantify the effectiveness of a particular bioremediation remedy. To date, little research has been directed towards the development and validation of methods to predict bioenhancement factors under conditions representative of real sites. This work extends an existing, first-order, bioenhancement factor expression to systems with zero-order and Monod kinetics, representative of many source-zone scenarios. The utility of this model for predicting the bioenhancement factor for previously published laboratory and field experiments is evaluated. This evaluation demonstrates the applicability of these simple bioenhancement factors for preliminary experimental design and analysis, and for assessment of dissolution enhancement in ganglia-contaminated source zones. For ease of application, a set of nomographs is presented that graphically depicts the dependence of bioenhancement factor on physicochemical properties. Application of these nomographs is illustrated using data from a well-documented field site. Results suggest that this approach can successfully capture field-scale, as well as column-scale, behavior. Sensitivity analyses reveal that bioenhanced dissolution will critically depend on in-situ biomass concentrations.

  12. Calcium-Mediated Abiotic Stress Signaling in Roots

    PubMed Central

    Wilkins, Katie A.; Matthus, Elsa; Swarbreck, Stéphanie M.; Davies, Julia M.

    2016-01-01

    Roots are subjected to a range of abiotic stresses as they forage for water and nutrients. Cytosolic free calcium is a common second messenger in the signaling of abiotic stress. In addition, roots take up calcium both as a nutrient and to stimulate exocytosis in growth. For calcium to fulfill its multiple roles must require strict spatio-temporal regulation of its uptake and efflux across the plasma membrane, its buffering in the cytosol and its sequestration or release from internal stores. This prompts the question of how specificity of signaling output can be achieved against the background of calcium’s other uses. Threats to agriculture such as salinity, water availability and hypoxia are signaled through calcium. Nutrient deficiency is also emerging as a stress that is signaled through cytosolic free calcium, with progress in potassium, nitrate and boron deficiency signaling now being made. Heavy metals have the capacity to trigger or modulate root calcium signaling depending on their dose and their capacity to catalyze production of hydroxyl radicals. Mechanical stress and cold stress can both trigger an increase in root cytosolic free calcium, with the possibility of membrane deformation playing a part in initiating the calcium signal. This review addresses progress in identifying the calcium transporting proteins (particularly channels such as annexins and cyclic nucleotide-gated channels) that effect stress-induced calcium increases in roots and explores links to reactive oxygen species, lipid signaling, and the unfolded protein response. PMID:27621742

  13. Abiotic factors influence plant storage lipid accumulation and composition.

    PubMed

    Singer, Stacy D; Zou, Jitao; Weselake, Randall J

    2016-02-01

    The demand for plant-derived oils has increased substantially over the last decade, and is sure to keep growing. While there has been a surge in research efforts to produce plants with improved oil content and quality, in most cases the enhancements have been small. To add further complexity to this situation, substantial differences in seed oil traits among years and field locations have indicated that plant lipid biosynthesis is also influenced to a large extent by multiple environmental factors such as temperature, drought, light availability and soil nutrients. On the molecular and biochemical levels, the expression and/or activities of fatty acid desaturases, as well as diacylglycerol acyltransferase 1, have been found to be affected by abiotic factors, suggesting that they play a role in the lipid content and compositional changes seen under abiotic stress conditions. Unfortunately, while only a very small number of strategies have been developed as of yet to minimize these environmental effects on the production of storage lipids, it is clear that this feat will be of the utmost importance for developing superior oil crops with the capability to perform in a consistent manner in field conditions in the future.

  14. RNA helicases: diverse roles in prokaryotic response to abiotic stress.

    PubMed

    Owttrim, George W

    2013-01-01

    Similar to proteins, RNA molecules must fold into the correct conformation and associate with protein complexes in order to be functional within a cell. RNA helicases rearrange RNA secondary structure and RNA-protein interactions in an ATP-dependent reaction, performing crucial functions in all aspects of RNA metabolism. In prokaryotes, RNA helicase activity is associated with roles in housekeeping functions including RNA turnover, ribosome biogenesis, translation and small RNA metabolism. In addition, RNA helicase expression and/or activity are frequently altered during cellular response to abiotic stress, implying they perform defined roles during cellular adaptation to changes in the growth environment. Specifically, RNA helicases contribute to the formation of cold-adapted ribosomes and RNA degradosomes, implying a role in alleviation of RNA secondary structure stabilization at low temperature. A common emerging theme involves RNA helicases acting as scaffolds for protein-protein interaction and functioning as molecular clamps, holding RNA-protein complexes in specific conformations. This review highlights recent advances in DEAD-box RNA helicase association with cellular response to abiotic stress in prokaryotes.

  15. Influence of abiotic stress signals on secondary metabolites in plants

    PubMed Central

    Ramakrishna, Akula; Ravishankar, Gokare Aswathanarayana

    2011-01-01

    Plant secondary metabolites are unique sources for pharmaceuticals, food additives, flavors, and industrially important biochemicals. Accumulation of such metabolites often occurs in plants subjected to stresses including various elicitors or signal molecules. Secondary metabolites play a major role in the adaptation of plants to the environment and in overcoming stress conditions. Environmental factors viz. temperature, humidity, light intensity, the supply of water, minerals, and CO2 influence the growth of a plant and secondary metabolite production. Drought, high salinity, and freezing temperatures are environmental conditions that cause adverse effects on the growth of plants and the productivity of crops. Plant cell culture technologies have been effective tools for both studying and producing plant secondary metabolites under in vitro conditions and for plant improvement. This brief review summarizes the influence of different abiotic factors include salt, drought, light, heavy metals, frost etc. on secondary metabolites in plants. The focus of the present review is the influence of abiotic factors on secondary metabolite production and some of important plant pharmaceuticals. Also, we describe the results of in vitro cultures and production of some important secondary metabolites obtained in our laboratory. PMID:22041989

  16. Abiotic stress and control of grain number in cereals.

    PubMed

    Dolferus, Rudy; Ji, Xuemei; Richards, Richard A

    2011-10-01

    Grain number is the only yield component that is directly associated with increased grain yield in important cereal crops like wheat. Historical yield studies show that increases in grain yield are always accompanied by an increase in grain number. Adverse weather conditions can cause severe fluctuations in grain yield and substantial yield losses in cereal crops. The problem is global and despite its impact on world food production breeding and selection approaches have only met with limited success. A specific period during early reproductive development, the young microspore stage of pollen development, is extremely vulnerable to abiotic stress in self-fertilising cereals (wheat, rice, barley, sorghum). A better understanding of the physiological and molecular processes that lead to stress-induced pollen abortion may provide us with the key to finding solutions for maintaining grain number under abiotic stress conditions. Due to the complexity of the problem, stress-proofing our main cereal crops will be a challenging task and will require joint input from different research disciplines.

  17. Abiotic Racemization Kinetics of Amino Acids in Marine Sediments

    PubMed Central

    Steen, Andrew D.; Jørgensen, Bo Barker; Lomstein, Bente Aa.

    2013-01-01

    The ratios of d- versus l-amino acids can be used to infer the sources and composition of sedimentary organic matter. Such inferences, however, rely on knowing the rates at which amino acids in sedimentary organic matter racemize abiotically between the d- and the l-forms. Based on a heating experiment, we report kinetic parameters for racemization of aspartic acid, glutamic acid, serine, and alanine in bulk sediment from Aarhus Bay, Denmark, taken from the surface, 30 cm, and 340 cm depth below seafloor. Extrapolation to a typical cold deep sea sediment temperature of 3°C suggests racemization rate constants of 0.50×10−5–11×10−5 yr−1. These results can be used in conjunction with measurements of sediment age to predict the ratio of d:l amino acids due solely to abiotic racemization of the source material, deviations from which can indicate the abundance and turnover of active microbial populations. PMID:23951211

  18. Dissolution of Arsenic Minerals Mediated by Dissimilatory Arsenate Reducing Bacteria: Estimation of the Physiological Potential for Arsenic Mobilization

    PubMed Central

    Lukasz, Drewniak; Liwia, Rajpert; Aleksandra, Mantur; Aleksandra, Sklodowska

    2014-01-01

    The aim of this study was characterization of the isolated dissimilatory arsenate reducing bacteria in the context of their potential for arsenic removal from primary arsenic minerals through reductive dissolution. Four strains, Shewanella sp. OM1, Pseudomonas sp. OM2, Aeromonas sp. OM4, and Serratia sp. OM17, capable of anaerobic growth with As (V) reduction, were isolated from microbial mats from an ancient gold mine. All of the isolated strains: (i) produced siderophores that promote dissolution of minerals, (ii) were resistant to dissolved arsenic compounds, (iii) were able to use the dissolved arsenates as the terminal electron acceptor, and (iii) were able to use copper minerals containing arsenic minerals (e.g., enargite) as a respiratory substrate. Based on the results obtained in this study, we postulate that arsenic can be released from some As-bearing polymetallic minerals (such as copper ore concentrates or middlings) under reductive conditions by dissimilatory arsenate reducers in indirect processes. PMID:24724102

  19. Dissolution of arsenic minerals mediated by dissimilatory arsenate reducing bacteria: estimation of the physiological potential for arsenic mobilization.

    PubMed

    Lukasz, Drewniak; Liwia, Rajpert; Aleksandra, Mantur; Aleksandra, Sklodowska

    2014-01-01

    The aim of this study was characterization of the isolated dissimilatory arsenate reducing bacteria in the context of their potential for arsenic removal from primary arsenic minerals through reductive dissolution. Four strains, Shewanella sp. OM1, Pseudomonas sp. OM2, Aeromonas sp. OM4, and Serratia sp. OM17, capable of anaerobic growth with As (V) reduction, were isolated from microbial mats from an ancient gold mine. All of the isolated strains: (i) produced siderophores that promote dissolution of minerals, (ii) were resistant to dissolved arsenic compounds, (iii) were able to use the dissolved arsenates as the terminal electron acceptor, and (iii) were able to use copper minerals containing arsenic minerals (e.g., enargite) as a respiratory substrate. Based on the results obtained in this study, we postulate that arsenic can be released from some As-bearing polymetallic minerals (such as copper ore concentrates or middlings) under reductive conditions by dissimilatory arsenate reducers in indirect processes.

  20. Dissolution of FB-Line Residues Containing Beryllium Metal

    SciTech Connect

    TRACY, RUDISILL

    2005-02-11

    Scrap materials containing plutonium (Pu) metal are currently being transferred from the FB Line vault to HB Line for dissolution and subsequent disposition through the H-Canyon facility. Some of the items scheduled for dissolution contain both Pu and beryllium (Be) metal as a composite material. The Pu and Be metals were physically separated to minimize the amount of Be associated with the Pu; however, the dissolution flowsheet was required to dissolve small amounts of Be combined with the Pu metal using a dissolving solution containing nitric acid (HNO3) and potassium fluoride (KF). Since the dissolution of Pu metal in HNO3/fluoride (F-) solutions is well understood, the primary focus of the experimental program was the dissolution of Be metal. Initially, small-scale experiments were used to measure the dissolution rate of Be metal foils using conditions effective for the dissolution of Pu metal. The experiments demonstrated that the dissolution rate was nearly independent of the HNO3 concentration over the limited range of investigation and only a moderate to weak function of the F- concentration. The effect of temperature was more pronounced, significantly increasing the dissolution rate between 40 and 105 degrees C. The offgas from three Be metal foil dissolutions was collected and characterized. The production of hydrogen (H2) was found to be sensitive to the HNO3 concentration, decreasing by a factor of approximately two when the HNO3 was increased from 4 to 8 M. This result is consistent with the dissolution mechanism shifting away from a typical metal/acid reaction toward increased production of nitrogen oxides by nitrate (NO3-) oxidation.

  1. Reductive leaching of low-grade manganese ore with pre-processed cornstalk

    NASA Astrophysics Data System (ADS)

    Yi, Ai-fei; Wu, Meng-ni; Liu, Peng-wei; Feng, Ya-li; Li, Hao-ran

    2015-12-01

    Cornstalk is usually directly used as a reductant in reductive leaching manganese. However, low utilization of cornstalk makes low manganese dissolution ratio. In the research, pretreatment for cornstalk was proposed to improve manganese dissolution ratio. Cornstalk was preprocessed by a heated sulfuric acid solution (1.2 M of sulfuric acid concentration) for 10 min at 80°C. Thereafter, both the pretreated solution and the residue were used as a reductant for manganese leaching. This method not only exhibited superior activity for hydrolyzing cornstalk but also enhanced manganese dissolution. These effects were attributed to an increase in the amount of reductive sugars resulting from lignin hydrolysis. Through acid pretreatment for cornstalk, the manganese dissolution ratio was improved from 50.14% to 83.46%. The present work demonstrates for the first time the effective acid pretreatment of cornstalk to provide a cost-effective reductant for manganese leaching.

  2. The Influence of CaCO3 Dissolution on Core Top Radiocarbon Ages for Deep-Sea Sediments

    NASA Astrophysics Data System (ADS)

    Broecker, Wallace S.; Klas, Mieczyslawa; Clark, Elizabeth; Bonani, Georges; Ivy, Susan; Wolfli, Willy

    1991-10-01

    Radiocarbon ages on CaCO3 from deep-sea cores offer constraints on the nature of the CaCO3 dissolution process. The idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone. If so, dissolution would shift the mass distribution in favor of younger grains, thereby reducing the mean radiocarbon age for the grain ensemble. We have searched in vain for evidence supporting the existence of such an age reduction. Instead, we find that for water depths of more than 4 km in the tropical Pacific the radiocarbon age increases with the extent of dissolution. We can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion. The idea is that during the Holocene the rate of dissolution of CaCO3 has exceeded the rain rate of CaCO3. In this circumstance, bioturbation exhumes CaCO3 from the underlying glacial sediment and mixes it with CaCO3 raining from the sea surface.

  3. Calcite Dissolution by Brevibacterium sp. SOTI06: A Futuristic Approach for the Reclamation of Calcareous Sodic Soils

    PubMed Central

    Tamilselvi, S. M.; Thiyagarajan, Chitdeshwari; Uthandi, Sivakumar

    2016-01-01

    Assessing the ability of soil microorganisms to dissolute poorly soluble native calcite to supply Ca2+ is a new area to be explored in reclaiming sodic soils by supplying adequate Ca2+ and reducing the recurrent sodicity. Hence, the present study aimed to isolate a calcite dissolving bacteria (CDB) from calcareous sodic soils and to understand the mechanism of calcite dissolution. Of the 33 CDB isolates recovered from the calcareous sodic soils of Tamil Nadu (Coimbatore, Ramnad, and Trichy), 11 isolates were screened for calcite dissolution based on titratable acidity. 16S rRNA gene sequence analysis of the three best isolates viz., SORI09, SOTI05, and SOTI06 revealed 99% similarity to Bacillus aryabhattai, 100% to B. megaterium, and 93% to Brevibacterium sp., respectively. Among them, Brevibacterium sp. SOTI06 released more Ca2+ (3.6 g.l−1) by dissolving 18.6% of the native calcite. The spectral data of FTIR also showed reduction in the intensity of calcite (55.36–41.27) by the isolate at a wave number of 1636 cm−1 which confirmed the dissolution. Besides producing organic acids (gluconic acid and acetic acid), Brevibacterium sp. SOTI06 also produced siderophore (91.6%) and extracellular polysaccharides (EPS, 13.3 μg. ml−1) which might have enhanced the calcite dissolution. PMID:28008333

  4. Dissolution of bulk specimens of silicon nitride

    NASA Technical Reports Server (NTRS)

    Davis, W. F.; Merkle, E. J.

    1981-01-01

    An accurate chemical characterization of silicon nitride has become important in connection with current efforts to incorporate components of this material into advanced heat engines. However, there are problems concerning a chemical analysis of bulk silicon nitride. Current analytical methods require the pulverization of bulk specimens. A pulverization procedure making use of grinding media, on the other hand, will introduce contaminants. A description is given of a dissolution procedure which overcomes these difficulties. It has been found that up to at least 0.6 g solid pieces of various samples of hot pressed and reaction bonded silicon nitride can be decomposed in a mixture of 3 mL hydrofluoric acid and 1 mL nitric acid overnight at 150 C in a Parr bomb. High-purity silicon nitride is completely soluble in nitric acid after treatment in the bomb. Following decomposition, silicon and hydrofluoric acid are volatilized and insoluble fluorides are converted to a soluble form.

  5. Solvent effects on starch dissolution and gelatinization.

    PubMed

    Koganti, Nagamani; Mitchell, John R; Ibbett, Roger N; Foster, Tim J

    2011-08-08

    The disruption of starch granular structure during dissolution in varying concentrations of N-methyl morpholine N-oxide (NMMO) has been studied using three maize starches with varying ratios of amylose and amylopectin. Behavior in NMMO has been characterized by differential scanning calorimetry (DSC), microscopy, rapid viscosity analysis (RVA), and rheometry. Exothermic transitions were observed for the three starches in both 78 and 70% NMMO; the transition changed to an endotherm at 60 and 50% NMMO. Consistent with DSC, hot stage microscopy showed that starch granules dissolved at NMMO concentrations of 78 and 70%, whereas in 60 and 50% NMMO, gelatinization behavior similar to that found for starch in water was observed. Mechanical spectroscopy revealed the dominant viscous behavior (G″ > G') of starch at NMMO concentrations of 70 and 78% and more elastic behavior (G' > G″) at lower concentrations. Starch solutions in 78% NMMO obey the Cox-Merz rule, suggesting that the solutions are homogeneous on a molecular level.

  6. Dissolution test for silymarin tablets and capsules.

    PubMed

    Campodónico, A; Collado, E; Ricci, R; Pappa, H; Segall, A; Pizzorno, M T

    2001-01-01

    Silybine (SBN), isosilybine (ISBN), silycristine (SCN), silydianine (SDN), and taxifoline (TXF) are the main active flavonoids commonly found in the dried fruits of Silybum marianum, Gaertner (Compositae). Concentrations of these compounds, except TXF, are usually expressed together as silymarin content. This paper describes a simple dissolution test developed to estimate silymarin (Sl) in pharmaceutical formulations. Five commercial products were tested using this new method (including tablets, sugar tablets, and capsules): two from Argentina, one from Brazil, one from Spain, and one from Italy. Results demonstrated that, provided the dosage form disintegrates, amounts dissolved range from 50 to 90% of the labeled value. Products were analyzed by high performance liquid chromatography (HPLC) and UV spectrophotometry.

  7. Dissolution chemistry of Minnesota Lunar Simulant

    NASA Astrophysics Data System (ADS)

    Oglesby, James P.; Lindsay, Willard L.; Sadeh, Willy Z.

    1993-07-01

    Dissolution studies of Minnesota Lunar Simulant (MLS), a prepared finely ground basalt, were conducted to measure solution species, to assess the levels of plant nutrients and toxic elements, and to identify minerals controlling these levels. Many of the plant nutrients in the MLS solution (Mg, S, K, Ca, Cl, Mo, P, B, Ni, and Cu) are found to be in concentrations acceptable for plant growth. Nitrogen and manganese, however, are found to be deficient, and extractable iron and zinc are marginal after 150 d. The solution concentrations of metals are several orders of magnitude below levels that are toxic to plants. Aluminum hydroxide, calcite, and clinoenstatite are found to be the most likely mineral controls for aluminum, calcium, and magnesium, respectively. Many of the methods employed can be used to study actual lunar regolith.

  8. Uranium Metal Analysis via Selective Dissolution

    SciTech Connect

    Delegard, Calvin H.; Sinkov, Sergey I.; Schmidt, Andrew J.; Chenault, Jeffrey W.

    2008-09-10

    Uranium metal, which is present in sludge held in the Hanford Site K West Basin, can create hazardous hydrogen atmospheres during sludge handling, immobilization, or subsequent transport and storage operations by its oxidation/corrosion in water. A thorough knowledge of the uranium metal concentration in sludge therefore is essential to successful sludge management and waste process design. The goal of this work was to establish a rapid routine analytical method to determine uranium metal concentrations as low as 0.03 wt% in sludge even in the presence of up to 1000-fold higher total uranium concentrations (i.e., up to 30 wt% and more uranium) for samples to be taken during the upcoming sludge characterization campaign and in future analyses for sludge handling and processing. This report describes the experiments and results obtained in developing the selective dissolution technique to determine uranium metal concentration in K Basin sludge.

  9. Aggregation, sedimentation, dissolution and bioavailability of ...

    EPA Pesticide Factsheets

    Due to increasing use in flat screen applications, solar cells, ink–jet printing, and medical devices, cadmium-based quantum dots (QDs) are among the fastest growing classes of engineered nanomaterial. These wide-ranging consumer product applications and end of use disposal issues assure that QDs will eventually enter the marine environment. In an effort to understand the fate and transport of CdSe QDs in estuarine systems, the aggregation, sedimentation, dissolution, and bioavailability of CdSe QDs in seawater was investigated. The size of CdSe QDs increased from 40-60 nm to >1 mm within one hour once introduced to seawater, and the diffusion-limited aggregation led to highly polydispersed aggregates with loose structures. As a result, the sedimentation rate of CdSe QD aggregates in seawater was measured to be 4-10 mm/day, which was slow considering their relatively large size. Humic acid (HA), as a model natural organic matter, further increased the size and polydispersity of CdSe QDs, and slowed their sedimentation accordingly. Given the effect of light on CdSe QDs, natural sunlight and light filters were employed to simulate the photic conditions at different water depths in an estuarine system. It was observed that light played a vital role in promoting the dissolution of CdSe QDs and the release of dissolved Cd. The ZnS shell surrounding the CdSe core also significantly hindered the degradation of CdSe QDs into their ionic components. With sufficient

  10. Glass dissolution rate measurement and calculation revisited

    NASA Astrophysics Data System (ADS)

    Fournier, Maxime; Ull, Aurélien; Nicoleau, Elodie; Inagaki, Yaohiro; Odorico, Michaël; Frugier, Pierre; Gin, Stéphane

    2016-08-01

    Aqueous dissolution rate measurements of nuclear glasses are a key step in the long-term behavior study of such waste forms. These rates are routinely normalized to the glass surface area in contact with solution, and experiments are very often carried out using crushed materials. Various methods have been implemented to determine the surface area of such glass powders, leading to differing values, with the notion of the reactive surface area of crushed glass remaining vague. In this study, around forty initial dissolution rate measurements were conducted following static and flow rate (SPFT, MCFT) measurement protocols at 90 °C, pH 10. The international reference glass (ISG), in the forms of powders with different particle sizes and polished monoliths, and soda-lime glass beads were examined. Although crushed glass grains clearly cannot be assimilated with spheres, it is when using the samples geometric surface (Sgeo) that the rates measured on powders are closest to those found for monoliths. Overestimation of the reactive surface when using the BET model (SBET) may be due to small physical features at the atomic scale-contributing to BET surface area but not to AFM surface area. Such features are very small compared with the thickness of water ingress in glass (a few hundred nanometers) and should not be considered in rate calculations. With a SBET/Sgeo ratio of 2.5 ± 0.2 for ISG powders, it is shown here that rates measured on powders and normalized to Sgeo should be divided by 1.3 and rates normalized to SBET should be multiplied by 1.9 in order to be compared with rates measured on a monolith. The use of glass beads indicates that the geometric surface gives a good estimation of glass reactive surface if sample geometry can be precisely described. Although data clearly shows the repeatability of measurements, results must be given with a high uncertainty of approximately ±25%.

  11. 50 CFR 270.23 - Dissolution of Councils.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 11 2012-10-01 2012-10-01 false Dissolution of Councils. 270.23 Section 270.23 Wildlife and Fisheries NATIONAL MARINE FISHERIES SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC... § 270.23 Dissolution of Councils. (a) Petition for termination. (1) A petition to terminate a...

  12. 29 CFR 511.5 - Vacancies and dissolution of committees.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 3 2010-07-01 2010-07-01 false Vacancies and dissolution of committees. 511.5 Section 511.5 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR REGULATIONS WAGE ORDER PROCEDURE FOR AMERICAN SAMOA § 511.5 Vacancies and dissolution of committees....

  13. 29 CFR 511.5 - Vacancies and dissolution of committees.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 3 2014-07-01 2014-07-01 false Vacancies and dissolution of committees. 511.5 Section 511.5 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR REGULATIONS WAGE ORDER PROCEDURE FOR AMERICAN SAMOA § 511.5 Vacancies and dissolution of committees....

  14. 50 CFR 270.23 - Dissolution of Councils.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 9 2011-10-01 2011-10-01 false Dissolution of Councils. 270.23 Section 270.23 Wildlife and Fisheries NATIONAL MARINE FISHERIES SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC... § 270.23 Dissolution of Councils. (a) Petition for termination. (1) A petition to terminate a...

  15. 29 CFR 511.5 - Vacancies and dissolution of committees.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 3 2012-07-01 2012-07-01 false Vacancies and dissolution of committees. 511.5 Section 511.5 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR REGULATIONS WAGE ORDER PROCEDURE FOR AMERICAN SAMOA § 511.5 Vacancies and dissolution of committees....

  16. 29 CFR 511.5 - Vacancies and dissolution of committees.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 3 2013-07-01 2013-07-01 false Vacancies and dissolution of committees. 511.5 Section 511.5 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR REGULATIONS WAGE ORDER PROCEDURE FOR AMERICAN SAMOA § 511.5 Vacancies and dissolution of committees....

  17. 50 CFR 270.23 - Dissolution of Councils.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 11 2014-10-01 2014-10-01 false Dissolution of Councils. 270.23 Section 270.23 Wildlife and Fisheries NATIONAL MARINE FISHERIES SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC... § 270.23 Dissolution of Councils. (a) Petition for termination. (1) A petition to terminate a...

  18. 50 CFR 270.23 - Dissolution of Councils.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 11 2013-10-01 2013-10-01 false Dissolution of Councils. 270.23 Section 270.23 Wildlife and Fisheries NATIONAL MARINE FISHERIES SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC... § 270.23 Dissolution of Councils. (a) Petition for termination. (1) A petition to terminate a...

  19. 29 CFR 511.5 - Vacancies and dissolution of committees.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 3 2011-07-01 2011-07-01 false Vacancies and dissolution of committees. 511.5 Section 511.5 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR REGULATIONS WAGE ORDER PROCEDURE FOR AMERICAN SAMOA § 511.5 Vacancies and dissolution of committees....

  20. Kinetic study of asphaltene dissolution in amphiphile/alkane solutions

    SciTech Connect

    Permsukarome, P.; Chang, C.; Fogler, H.S.

    1997-09-01

    The kinetics of dissolution of pentane-insoluble solid asphaltene precipitates by amphiphile/alkane solutions were investigated using a differential reactor flow system. Two amphiphiles, dodecylbenzenesulfonic acid and nonylphenol, and five alkane solvents, ranging from hexane to hexadecane, were used. Results showed that the rate of asphaltene dissolution in amphiphile/alkane fluids could be approximated with a first-order kinetics with respect to the undissolved asphaltene mass in solution. The specific dissolution rate constant, k, varied with the concentration of amphiphiles, the type of alkane solvents, the temperature, and the fluid flow rate. The rate of asphaltene dissolution displayed a Langmuir-Hinshelwood kinetics with respect to the concentration of amphiphiles. Increasing the temperature of amphiphile/alkane fluids also enhanced the rate of asphaltene dissolution. The apparent activation energy for asphaltene dissolution was approximated to be 4--7 kcal/mol. The rate of asphaltene dissolution was also greater in amphiphile solutions containing lighter alkanes, such as hexane, with lower viscosities. These trends suggest that both surface reaction and mass transfer processes are important to the rate of asphaltene dissolution in amphiphile/alkane fluids.

  1. Frogging It: A Poetic Analysis of Relationship Dissolution

    ERIC Educational Resources Information Center

    Faulkner, Sandra L.

    2012-01-01

    Often, themes in work and life intertwine; the author recognized that a cadre of poems she had written during the past several years were about relationship dissolution. The poems concerned romantic and friendship dissolution and the aspects of identity creation and loss this entails. The author presents the poems and makes an explicit connection…

  2. Constant composition kinetics study of carbonated apatite dissolution

    NASA Astrophysics Data System (ADS)

    Tang, Ruikang; Henneman, Zachary J.; Nancollas, George H.

    2003-03-01

    The carbonated apatites (CAP) may be more suitable models for biominerals such as bone and dental hard tissues than is pure hydroxyapatite (HAP) since they have similar chemical compositions. Although they contain only a relatively small amount of carbonate, the solubility and dissolution properties are different. The solubility product of the CAP particles used in this dissolution study, 2.88×10 -112 mol 18 l -18, was significantly greater than that of HAP, 5.52×10 -118 mol 18 l -18. The kinetics of dissolution of CAP has been studied using the constant composition (CC) method. At low undersaturations, the dissolution reaction appeared to be controlled mainly by surface diffusion with an effective reaction order of 1.9±0.1 with respect to the relative undersaturation. These results together with those obtained by scanning electron microscopy (SEM) suggest a dissolution model. Based on the surface diffusion theory of Burton, Cabrera and Frank (BCF). The interfacial tension between CAP and the aqueous phase calculated from this dissolution model, 9.0 m J m -2, was consistent with its relatively low solubility. An abnormal but interesting dissolution behavior is that the CAP dissolution rate was relatively insensitive to changes in calcium and phosphate concentrations at higher undersaturations, suggesting the importance of the carbonate component under these conditions.

  3. Thermal dissolution of maize starches in aqueous medium

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Starches are not soluble in neutral water at room temperature. However, if they are heated in a closed container beyond the boiling point of water, they eventually dissolve. The dissolution temperature depends on the type of starch. The dissolution process was monitored in real time by measuring ...

  4. Dissolution Profile of Nimesulide from Pharmaceutical Preparations for Oral Use.

    PubMed

    Tubić, Biljana; Uzunović, Alija; Pilipović, Saša; Gagić, Žarko

    2016-01-01

    Nimesulide belongs to the group of semi-selective COX-2 inhibitors, widely used in solid oral formulations. In the present work the influence of surfactants among other drug excipients, as well as particle size of the active substance and the effects of medium pH on the dissolution rate of nimesulide from solid pharmaceutical forms. For that purpose, four different preparations containing 100 mg nimesulide per tablet and available in the market of Bosnia and Herzegovina (labeled here as A, B, C and D) were studied. The test for the assessment of dissolution profiles of the formulations was performed in surfactant-free dissolution medium pH 7.5. The dissolution profiles were compared by calculating difference (f1), and similarity (f2) factors. The increasing dissolution medium pH value from 7.5 to 7.75 resulted in a significant increase of nimesulide dissolution rate from the examined formulations. Also, the results showed that particle size affects to a great extent the dissolution rate and the best results were achieved with micronized nimesulide. The presence of the surfactants among the other excipients expressed a negligible effect on the dissolution profile.

  5. Dissolution of populations of ultrafine grains with applications to feldspars

    SciTech Connect

    Talman, S.J.; Nesbitt, H.W. )

    1988-06-01

    Mineral dissolution studies are difficult to interpret when the solid reactant displays a wide range in grain sizes, since the rate of dissolution of the finest grains may not be simply related to their surface area. The transient apparent rate of dissolution of a population of fine-grained reactants is modeled to predict changes to the solution composition, as well as changes in the size distribution of ultra-fine particles as functions of time. The model is applies to the experimental data on Amelia albite of Hodlren and Berner (1979) from which both solution composition and grain size distribution have been obtained. The observed size distribution cannot be duplicated if the dissolution rate is proportional to surface area (i.e. dV/dt=Kr{sup 2}); other contributions to the rate, such as dependence on grain size and the specific contributions from edges and corners, must be invoked. The observed grain size distribution and pseudo-parabolic rate can be reproduced when the rate of dissolution of the fine grains is proportional to its radius (i.e. dV/dt=Kr). The rate constant, K, is consistent with a rate limited by dissolution at the edges of the grains. The possibility of predicting both the contributions of ultrafine particles to the observed dissolution rate and the time evolution of the grain size distribution makes the model a useful tool for interpreting mineral dissolution data.

  6. 10 CFR 960.4-2-6 - Dissolution.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 4 2011-01-01 2011-01-01 false Dissolution. 960.4-2-6 Section 960.4-2-6 Energy DEPARTMENT OF ENERGY GENERAL GUIDELINES FOR THE PRELIMINARY SCREENING OF POTENTIAL SITES FOR A NUCLEAR WASTE REPOSITORY Postclosure Guidelines § 960.4-2-6 Dissolution. (a) Qualifying condition. The site shall...

  7. 10 CFR 960.4-2-6 - Dissolution.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 4 2010-01-01 2010-01-01 false Dissolution. 960.4-2-6 Section 960.4-2-6 Energy DEPARTMENT OF ENERGY GENERAL GUIDELINES FOR THE PRELIMINARY SCREENING OF POTENTIAL SITES FOR A NUCLEAR WASTE REPOSITORY Postclosure Guidelines § 960.4-2-6 Dissolution. (a) Qualifying condition. The site shall...

  8. 10 CFR 960.4-2-6 - Dissolution.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 4 2012-01-01 2012-01-01 false Dissolution. 960.4-2-6 Section 960.4-2-6 Energy DEPARTMENT OF ENERGY GENERAL GUIDELINES FOR THE PRELIMINARY SCREENING OF POTENTIAL SITES FOR A NUCLEAR WASTE REPOSITORY Postclosure Guidelines § 960.4-2-6 Dissolution. (a) Qualifying condition. The site shall...

  9. 10 CFR 960.4-2-6 - Dissolution.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 4 2013-01-01 2013-01-01 false Dissolution. 960.4-2-6 Section 960.4-2-6 Energy DEPARTMENT OF ENERGY GENERAL GUIDELINES FOR THE PRELIMINARY SCREENING OF POTENTIAL SITES FOR A NUCLEAR WASTE REPOSITORY Postclosure Guidelines § 960.4-2-6 Dissolution. (a) Qualifying condition. The site shall...

  10. 10 CFR 960.4-2-6 - Dissolution.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 4 2014-01-01 2014-01-01 false Dissolution. 960.4-2-6 Section 960.4-2-6 Energy DEPARTMENT OF ENERGY GENERAL GUIDELINES FOR THE PRELIMINARY SCREENING OF POTENTIAL SITES FOR A NUCLEAR WASTE REPOSITORY Postclosure Guidelines § 960.4-2-6 Dissolution. (a) Qualifying condition. The site shall...

  11. The effect of fuel chemistry on UO2 dissolution

    SciTech Connect

    Casella, Amanda; Hanson, Brady; Miller, William

    2016-08-01

    The dissolution rate of both unirradiated UO2 and used nuclear fuel has been studied by numerous countries as part of the performance assessment of proposed geologic repositories. In the scenario of waste package failure and groundwater infiltration into the fuel, the effects of variables such as temperature, dissolved oxygen, and water and fuel chemistry on the dissolution rates of the fuel are necessary to provide a quantitative estimate of the potential release over geologic time frames. The primary objective of this research was to determine the influence these parameters have on the dissolution rate of unirradiated UO2 under repository conditions and compare them to the rates predicted by current dissolution models. Both unirradiated UO2 and UO2 doped with varying concentrations of Gd2O3, to simulate used fuel composition after long time periods where radiolysis has minor contributions to dissolution, were examined. In general, a rise in temperature increased the dissolution rate of UO2 and had a larger effect on pure UO2 than on those doped with Gd2O3. Oxygen dependence was observed in the UO2 samples with no dopant and increased as the temperature rose; in the doped fuels less dependence was observed. The addition of gadolinia into the UO2 matrix showed a significant decrease in the dissolution rate. The matrix stabilization effect resulting from the dopant proved even more beneficial in lowering the dissolution rate at higher temperatures and dissolved O2 concentrations in the leachate where the rates would typically be elevated.

  12. Fibrin formation and dissolution in women receiving oral contraceptive drugs.

    PubMed

    Ball, A P; McKee, P A

    1977-04-01

    Factors affecting fibrin formation and dissolution were compared for 15 women taking combined oral contraceptives and 15 women using nonpharmacological methods of birth control. The two groups were matched for age, body weight, time of blood collection, and day in menstrual cycle; none of the women was receiving other drugs known to affect the blood coagulation or fibrinolytic parameters measured in this study. Fibrinogen concentrations tended to be higher in the experimental group; the degree of fibrinogen degradation, number of fibrin cross-links, and levels of factor XIII and plasminogen were the same for both group. There were significant reductions in antithrombin activity, the euglobulin lysis time, and fibrinolytic inhibitor level in women using oral contraceptives. An estrogen dose effect was suggested for fibrinogen concentration and the degree of antithrombin activity. The increased fibrinolytic activity and decreased fibrinolytic inhibitor levels are consistent with in vitro observations that antithrombin also inhibits plasmin activity. Thus while oral contraceptive-induced depression of antithrombin III could possibly predispose to thrombosis by diminishing the inhibition of the serine protease clotting factors, the concomitant decreased level of plasmin inhibition might balance the system by favoring thrombolysis as well as the digestion and inactivation of certain clotting factors by plasmin.

  13. Kinetics of pyrite, pyrrhotite, and chalcopyrite dissolution by Acidithiobacillus ferrooxidans.

    PubMed

    Kocaman, Ayse Tuba; Cemek, Mustafa; Edwards, Katrina Jane

    2016-08-01

    The main objective of this study was to investigate the dissolution kinetics of pyrite, pyrrhotite, and chalcopyrite. Crushed minerals were reacted with Acidithiobacillus ferrooxidans (25 °C). The kinetics of dissolution was investigated by monitoring pH and Fe(2+) and Fe(3+) ion concentrations in the leaching solutions. Pyrite, pyrrhotite, and chalcopyrite dissolution by A. ferrooxidans was found to be a chemically controlled process. With bacteria, the dissolution rates of the minerals increased in the order of pyrrhotite, pyrite, and chalcopyrite. The number of cells attached to mineral surfaces increased in the same order. Acidithiobacillus ferrooxidans was found to enhance the dissolution rates of the minerals. The acid-insoluble trait of pyrite and acid-soluble trait of the other 2 minerals affected the pH changes in the leaching solutions.

  14. Carbon in oxides and silicates - Dissolution versus exsolution

    NASA Technical Reports Server (NTRS)

    Freund, F.

    1986-01-01

    A theory of CO2 dissolution in the solid state is developed, using the idea proposed by Freund (1983) concerning dissolution of CO/CO2 in MgO on the basis of their experimental results obtained with an MgO-containing carbon impurity. It is shown that the dissolution mechanism may be linked to an internal redox reaction by which a certain number of lattice oxygens change their formal oxidation state from -2 to -1, while the carbon becomes reduced. The similarities between the mechanisms of CO and/or CO2 dissolution and that of H2O dissolution are pointed out. A hypothesis is proposed concerning the exsolution of reduced carbon from supersaturated solid solutions under conditions which permit C-C bond formation.

  15. Effect of nonionic surfactants on naphthalene dissolution and biodegradation.

    PubMed

    Mulder, H; Wassink, G R; Breure, A M; van Andel, J G; Rulkens, W H

    1998-11-20

    The effect of six nonionic surfactants, Igepal CA-720, Tergitol NPX, Triton X-100, PLE4, PLE10, and PLE23, on the dissolution rate of solid naphthalene was studied in stirred batch reactors. Results showed increased mass-transfer rates with increased surfactant concentrations up to 10 kg m-3. Dissolution experiments were adequatly described by a mechanistic mass-transfer model. Partitioning of naphthalene into the micelles and the diffusion coefficients of the micelles affected the dissolution rate most significantly. Combined dissolution and biodegradation experiments with Triton X-100 or PLE10 with naphthalene showed that the biomass-formation rate of Pseudomonas 8909N (DSM No. 11634) increased concomitantly with the mass-transfer rate under naphthalene-dissolution limited conditions up to surfactant concentrations of 6 kg m-3.

  16. Dissolution Model of Multiple Species: Leaching of Highly Soluble Minerals

    NASA Astrophysics Data System (ADS)

    Moreno, Luis; Ordóñez, Javier I.; Cisternas, Luis A.

    2017-03-01

    Dissolution of multi-species from a solid matrix is widely extended in different processes such as leaching of minerals; however, its modeling is often focused on a single species. A model for the simultaneous dissolution of soluble species was developed, which considers different solubilities and dissolution rates and considers that particle collapses when the rapidly soluble species is depleted. The collapsed matter is formed by inert material and a fraction of the soluble species with lower dissolution rate that has not dissolved yet. The model is applied to the leaching of a water-soluble mineral (caliche) with two soluble species dissolving simultaneously with different rates. Measured outlet concentrations of nitrate and magnesium were used to validate the model. Results showed that the model reproduced adequately the leaching of species with rapid and intermediate dissolution rate. Effect of the operating and kinetic parameters on the leaching process is also shown using the actual conditions of heap leaching for caliche mineral.

  17. Aluminum Target Dissolution in Support of the Pu-238 Program

    SciTech Connect

    McFarlane, Joanna; Benker, Dennis; DePaoli, David W; Felker, Leslie Kevin; Mattus, Catherine H

    2014-09-01

    Selection of an aluminum alloy for target cladding affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in the caustic dissolution step, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. We present a study to maximize dissolution of aluminum metal alloy, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as a function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. These data have been compared with published calculations of aluminum phase diagrams. Temperature logging during the transients has been investigated as a means to generate kinetic and mass transport data on the dissolution process. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.

  18. Factors associated with relationship dissolution and post-dissolution adjustment among lesbian adoptive couples.

    PubMed

    Farr, Rachel H

    2017-01-02

    Same-sex adoptive couples are increasingly visible, yet few studies have addressed relationship stability and dissolution among these couples. In this study, using a theoretical framework based on Investment Models and Vulnerability-Stress-Adaptation Theory, factors associated with dissolution and post-dissolution adjustment among 27 lesbian adoptive couples were examined across two points. At Wave 1, all 27 couples were together; children were on average 3 years old. Results revealed that nearly one third broke up over 5 years (between Waves 1 and 2). Factors related to shorter relationship length and undermining coparenting at Wave 1 distinguished women who later broke up versus stayed together. Worse mental health at Wave 2 characterized women in dissolved rather than sustained relationships, even with comparable individual adjustment at Wave 1. Weaker parenting alliance and greater dissatisfaction with childcare divisions were reported by women no longer with their partners at Wave 2 as compared with those in enduring partnerships. This research has implications for understanding lesbian relationship dynamics and associations with individual adjustment.

  19. Abiotic Formation of Methyl Halides in the Terrestrial Environment

    NASA Astrophysics Data System (ADS)

    Keppler, F.

    2011-12-01

    Methyl chloride and methyl bromide are the most abundant chlorine and bromine containing organic compounds in the atmosphere. Since both compounds have relatively long tropospheric lifetimes they can effectively transport halogen atoms from the Earth's surface, where they are released, to the stratosphere and following photolytic oxidation form reactive halogen gases that lead to the chemical destruction of ozone. Methyl chloride and methyl bromide account for more than 20% of the ozone-depleting halogens delivered to the stratosphere and are predicted to grow in importance as the chlorine contribution to the stratosphere from anthropogenic CFCs decline. Today methyl chloride and methyl bromide originate mainly from natural sources with only a minor fraction considered to be of anthropogenic origin. However, until as recently as 2000 most of the methyl chloride and methyl bromide input to the atmosphere was considered to originate from the oceans, but investigations in recent years have clearly demonstrated that terrestrial sources such as biomass burning, wood-rotting fungi, coastal salt marshes, tropical vegetation and organic matter degradation must dominate the atmospheric budgets of these trace gases. However, many uncertainties still exist regarding strengths of both sources and sinks, as well as the mechanisms of formation of these naturally occurring halogenated gases. A better understanding of the atmospheric budget of both methyl chloride and methyl bromide is therefore required for reliable prediction of future ozone depletion. Biotic and abiotic methylation processes of chloride and bromide ion are considered to be the dominant pathways of formation of these methyl halides in nature. In this presentation I will focus on abiotic formation processes in the terrestrial environment and the potential parameters that control their emissions. Recent advances in our understanding of the abiotic formation pathway of methyl halides will be discussed. This will

  20. Microbial reduction of iodate

    USGS Publications Warehouse

    Councell, T.B.; Landa, E.R.; Lovley, D.R.

    1997-01-01

    The different oxidation species of iodine have markedly different sorption properties. Hence, changes in iodine redox states can greatly affect the mobility of iodine in the environment. Although a major microbial role has been suggested in the past to account for these redox changes, little has been done to elucidate the responsible microorganisms or the mechanisms involved. In the work presented here, direct microbial reduction of iodate was demonstrated with anaerobic cell suspensions of the sulfate reducing bacterium Desulfovibrio desulfuricans which reduced 96% of an initial 100 ??M iodate to iodide at pH 7 in 30 mM NaHCO3 buffer, whereas anaerobic cell suspensions of the dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens were unable to reduce iodate in 30 mM NaHCO3 buffer (pH 7). Both D. desulfuricans and S. putrefaciens were able to reduce iodate at pH 7 in 10 mM HEPES buffer. Both soluble ferrous iron and sulfide, as well as iron monosulfide (FeS) were shown to abiologically reduce iodate to iodide. These results indicate that ferric iron and/or sulfate reducing bacteria are capable of mediating both direct, enzymatic, as well as abiotic reduction of iodate in natural anaerobic environments. These microbially mediated reactions may be important factors in the fate and transport of 129I in natural systems.

  1. Dissolution of two-phase microsystems: Gas and liquid microparticle dissolution and dehydration of biomaterials

    NASA Astrophysics Data System (ADS)

    Duncan, Phillip Brent

    A main focus of this research is to develop techniques to study the dissolution process of two-phase microsystems on a single microparticle basis. This dissertation introduces a systematic approach to investigate the formation of microparticles to fulfill the need for rational design of microspheres for a range of applications. This novel method is based on the micropipet manipulation technique and can essentially test any system, where the continuous phase is a liquid and the dispersed phase is practically any phase, a gas (foam), a liquid (emulsion), or a solid (suspension). It is possible to study single microparticle volumes in the picoliter to nanoliter scale, which is on the same size-scale as particles created in bulk suspensions, microsphere processes, and applications. The ability to create, isolate, observe, and manipulate individual gas, liquid or solid microparticles in a well-defined and controlled liquid environment was found to be ideal to study gas microbubbles and microparticles, liquid microdroplets, and the dehydration of dissolved solutes. Subsequently, one can directly measure the dissolution rate and, when a solute is present, calculate its concentration during the dissolution process. Microbubble or microdroplet dissolution in a second phase is driven by two independent factors, a concentration gradient (undersaturation of the dispersed phase in the continuous phase) and a pressure gradient (due to the Laplace-overpressure inside the microparticle created by the surface tension). Experimentally, each of these driving forces can be independently tested. Both the gas microparticle and pure liquid microdroplet dissolution can be predicted by a simple theory based on the diffusion coefficient and solubility limit of the dispersed phase in the continuous phase. The dehydration of a salt ion solution microdroplet results in the nucleation and growth of a crystal, while the dehydration of proteins leads to glassification of the protein. The water

  2. The abiotic degradation of methyl parathion in anoxic sulfur-containing system mediated by natural organic matter.

    PubMed

    Liao, Xiaoping; Zhang, Caixiang; Wang, Yanxin; Tang, Mi

    2017-06-01

    Although the kinetics and transformation of methyl parathion have been investigated extensively, its abiotic degradation mechanism in anoxic sulfur-containing groundwater system is still not clear. In this work, the abiotic degradation of methyl parathion in anoxic sulfur-containing system mediated by natural organic matter (NOM) was investigated in batch experiments. It was found that the removal of methyl parathion (up to 80.7%) was greatly improved in sulfide containing NOM compared to those in sulfide alone (with 15.5%) and in NOM alone (almost negligible). Various sulfur species presented significant differences in behaviors methyl parathion degradation, but followed by the pseudo-first-order model well. No facilitated degradation of methyl parathion was observed in sulfite (SO3(2-)) or thiosulfate (S2O3(2-)) containing NOM such as anthraquinone. Although elemental sulfur (S(0)) and cysteine could further improve the degradation rate of methyl parahtion, their impacts was very limited. The removal efficiency of methyl parathion in anoxic sulfur-containing system were related remarkably with NOM concentration and solution pH. Based on the transformation products identified by gas chromatography-mass spectrometer (GC/MS) and liquid chromatography high resolution mass spectrometer (LC/HRMS), both the nitro group reduction and hydrolysis (SN@C) processes by sulfide (HS(-)) were further proved to be two predominant reaction mechanisms for the abiotic degradation of methyl parathion in anoxic sulfur-containing system. The results of this study help to understand the natural attenuation of methyl parathion under anoxic sulfide-containing groundwater system mediated by NOM.

  3. Endophytic fungi: resource for gibberellins and crop abiotic stress resistance.

    PubMed

    Khan, Abdul Latif; Hussain, Javid; Al-Harrasi, Ahmed; Al-Rawahi, Ahmed; Lee, In-Jung

    2015-03-01

    The beneficial effects of endophytes on plant growth are important for agricultural ecosystems because they reduce the need for fertilizers and decrease soil and water pollution while compensating for environmental perturbations. Endophytic fungi are a novel source of bioactive secondary metabolites; moreover, recently they have been found to produce physiologically active gibberellins as well. The symbiosis of gibberellins producing endophytic fungi with crops can be a promising strategy to overcome the adverse effects of abiotic stresses. The association of such endophytes has not only increased plant biomass but also ameliorated plant-growth during extreme environmental conditions. Endophytic fungi represent a trove of unexplored biodiversity and a frequently overlooked component of crop ecology. The present review describes the role of gibberellins producing endophytic fungi, suggests putative mechanisms involved in plant endophyte stress interactions and discusses future prospects in this field.

  4. Histone variants and chromatin assembly in plant abiotic stress responses.

    PubMed

    Zhu, Yan; Dong, Aiwu; Shen, Wen-Hui

    2013-01-01

    Genome organization into nucleosomes and higher-order chromatin structures has profound implications for the regulation of gene expression, DNA replication and repair. The structure of chromatin can be remodeled by several mechanisms; among others, nucleosome assembly/disassembly and replacement of canonical histones with histone variants constitute important ones. In this review, we provide a brief description on the current knowledge about histone chaperones involved in nucleosome assembly/disassembly and histone variants in Arabidopsis thaliana. We discuss recent advances in revealing crucial functions of histone chaperones, nucleosome assembly/disassembly and histone variants in plant response to abiotic stresses. It appears that chromatin structure remodeling may provide a flexible, global and stable means for the regulation of gene transcription to help plants more effectively cope with environmental stresses. This article is part of a Special Issue entitled: Histone chaperones and chromatin assembly.

  5. An Abiotic Glass-Bead Collector Exhibiting Active Transport

    NASA Astrophysics Data System (ADS)

    Goto, Youhei; Kanda, Masato; Yamamoto, Daigo; Shioi, Akihisa

    2015-09-01

    Animals relocate ob