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Sample records for influence carbon dissolution

  1. 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

  2. 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...

  3. 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...

  4. Measuring The Influence of Pearlite Dissolution on the Transient Dynamic Strength of Rapidly-Heated Plain Carbon Steels

    PubMed Central

    Mates, Steven; Stoudt, Mark; Gangireddy, Sindhura

    2016-01-01

    Carbon steels containing ferrite-pearlite microstructures weaken dramatically when pearlite dissolves into austenite on heating. The kinetics of this phase transformation, while fast, can play a role during dynamic, high temperature manufacturing processes, including high speed machining, when the time scale of this transformation is on the order of the manufacturing process itself. In such a regime, the mechanical strength of carbon steel can become time-dependent. The present work uses a rapidly-heated, high strain rate mechanical test to study the effect of temperature and time on the amount of pearlite dissolved and on the resulting transient effect on dynamic strength of a low and a high carbon (eutectoid) steel. Measurements indicate that the transient effect occurs for heating times less than about three seconds. The 1075 steel loses about twice the strength compared to the 1018 steel (85 MPa to 45 MPa) owing to its higher initial pearlite volume fraction. Pearlite dissolution is confirmed by metallographic examination of tested samples. Despite the different starting pearlite fractions, the kinetics of dissolution are comparable for the two steels, owing to the similarity in their initial pearlite morphology. PMID:28082822

  5. Measuring The Influence of Pearlite Dissolution on the Transient Dynamic Strength of Rapidly-Heated Plain Carbon Steels.

    PubMed

    Mates, Steven; Stoudt, Mark; Gangireddy, Sindhura

    2016-07-01

    Carbon steels containing ferrite-pearlite microstructures weaken dramatically when pearlite dissolves into austenite on heating. The kinetics of this phase transformation, while fast, can play a role during dynamic, high temperature manufacturing processes, including high speed machining, when the time scale of this transformation is on the order of the manufacturing process itself. In such a regime, the mechanical strength of carbon steel can become time-dependent. The present work uses a rapidly-heated, high strain rate mechanical test to study the effect of temperature and time on the amount of pearlite dissolved and on the resulting transient effect on dynamic strength of a low and a high carbon (eutectoid) steel. Measurements indicate that the transient effect occurs for heating times less than about three seconds. The 1075 steel loses about twice the strength compared to the 1018 steel (85 MPa to 45 MPa) owing to its higher initial pearlite volume fraction. Pearlite dissolution is confirmed by metallographic examination of tested samples. Despite the different starting pearlite fractions, the kinetics of dissolution are comparable for the two steels, owing to the similarity in their initial pearlite morphology.

  6. Dissolution Kinetics of Biogenic Carbonates in Seawater

    NASA Astrophysics Data System (ADS)

    Subhas, A.; Erez, J.; Rollins, N.; Adkins, J. F.; Berelson, W.; Ziveri, P. P. I.; Langer, G.

    2016-02-01

    We present here laboratory-based dissolution kinetic studies of inorganic, foraminiferal, and coccolith calcite, as well as high-Mg calcite from the soft coral Rhythismia fulvum. Dissolution rate measurements were conducted using a novel 13C-based tracer measurement, which traces mass loss via isotopic enrichment in a closed system of calcite and seawater. Inorganic calcite dissolution rates are highly nonlinear with respect to saturation state, and imply multiple dissolution mechanisms. Our work validates early characterizations of highly nonlinear dissolution rates, and also agrees with far-from-equilibrium rate determinations. Dissolution rates of biogenic materials are also highly nonlinear, although the relationship between undersaturation and dissolution rate often does not resemble that of inorganic calcite. Coccoliths dissolve slowly compared to inorganic calcite after surface area normalization, even when treated with bleach to remove their organic matter. High-Mg calcite from soft corals dissolves quickly, and the relationship between dissolution rate and undersaturation seems to be complicated by the presence of two (Mg-carbonate and Ca-carbonate) phases. These biogenic dissolution rates provide a new constraint on the sensitivities of these minerals to saturation state, both in the deep ocean water column and in the surface ocean as saturation state is decreasing due to ocean acidification.

  7. Foraminifer Shell Weight and Fragmentation: A Quantitative Study of the Influence of Temperature, [CO32-] and Dissolution on Proxies of the Marine Carbonate System

    NASA Astrophysics Data System (ADS)

    Mekik, F.; Pourmand, A.; Ward, B. M.

    2015-12-01

    Quantifying the various components of the marine carbonate system is important for understanding anthropogenic ocean acidification, and the rates and magnitudes of ocean acidification/ alkalization events in Earth's past. We performed multiple statistical analyses (factor analysis, partial correlations, multiple regression analysis and independent samples t -tests) on core top data using the Globorotalia menardii fragmentation index (MFI) in 89 core tops from across the tropical Pacific, Atlantic and Indian Oceans, the fragmentation trend of four species of foraminifers (Globorotalia truncatulinoides, G. menardii, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata) in the EEP, tropical Atlantic and tropical Indian Ocean core tops, and Globorotalia menardii shell weight in a suite of 25 core tops the EEP in order to isolate the effects of surface ocean parameters such as temperature and [CO32-] from dissolution in sediments. Surface ocean parameters showed no significant effect on the G. menardii fragmentation index. We found no statistically significant influence of habitat water temperature or [CO32-] on foraminifer fragmentation in any of four species. While we found a strong influence of habitat water [CO32-] on the size normalized shell weight proxy in N. dutertrei and Pulleniatina obliquiloculata in our previous work, we found a much reduced influence of [CO32-] on the shell weight of G. menardii, which is most influenced by shell dissolution.

  8. Carbonate ions and arsenic dissolution by groundwater

    USGS Publications Warehouse

    Kim, M.-J.; Nriagu, J.; Haack, S.

    2000-01-01

    solutions. The effects of pH and redox conditions on As dissolution were examined. Results showed that As was not leached significantly out of the Marshall Sandstone samples after 3 d using either deionized water or groundwater, but As was leached efficiently by sodium bicarbonate, potassium bicarbonate, and ferric chloride solutions. The leaching rate with sodium bicarbonate was about 25% higher than that with potassium bicarbonate. The data indicated that bicarbonate ion was involved primarily in As dissolution and that hydroxyl radical ion did not affect As dissolution to any significant degree. The amount of As leached was dependent upon the sodium bicarbonate concentration, increasing with reaction time for each concentration. Significant As leaching was found in the extreme pH ranges of <1.9 and 8.0-10.4. The resulting arseno-carbonate complexes formed were stable in groundwater.

  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. 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.

  11. 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.

  12. 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.

  13. Bisphosphonate binding affinity as assessed by inhibition of carbonated apatite dissolution in vitro

    PubMed Central

    Henneman, Zachary J.; Nancollas, George H.; Ebetino, F. Hal; Russell, R. Graham G.; Phipps, Roger J.

    2009-01-01

    Bisphosphonates (BPs), which display a high affinity for calcium phosphate surfaces, are able to selectively target bone mineral, where they are potent inhibitors of osteoclast-mediated bone resorption. The dissolution of synthetic hydroxyapatite (HAP) has been used previously as a model for BP effects on natural bone mineral. The present work examines the influence of BPs on carbonated apatite (CAP), which mimics natural bone more closely than does HAP. Constant composition dissolution experiments were performed at pH 5.50, physiological ionic strength (0.15M) and temperature (37°C). Selected BPs were added at (0.5 × 10−6) to (50.0 × 10−6)M, and adsorption affinity constants, KL, were calculated from the kinetics data. The BPs showed concentration-dependent inhibition of CAP dissolution, with significant differences in rank order zoledronate > alendronate > risedronate. In contrast, for HAP dissolution at pH 5.50, the differences between the individual BPs were considerably smaller. The extent of CAP dissolution was also dependent on the relative undersaturation, σ, and CAP dissolution rates increased with increasing carbonate content. These results demonstrate the importance of the presence of carbonate in mediating the dissolution of CAP, and the possible involvement of bone mineral carbonate in observed differences in bone affinities of BPs in clinical use. PMID:17907244

  14. 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

  15. Microscopic Effects of Carbonate, Manganese, and Strontium ions on Calcite Dissolution

    SciTech Connect

    Lea, Alan S.; Amonette, James E.; Baer, Donald R.; Liang, Yong; Colton, Nancy G.

    2001-02-01

    Aqueous dissolution of the (1014) surface of calcite was observed at pH near 9 using an atomic force microscope equipped with a fluid cell. The influence of carbonate, Sr, and Mn ion concentrations were observed. Carbonste ions were shown to have a step-specific effect on calcite dissolution. At ow levels (5 mu-M) of carbonate, the retreat rate of the more structually open [441]+steps was than the retreat rate of the structurally confined [441]-steps, leading to anisotropic dissolution. Increasing the carbonate level to 200 mu-M decreased the rate of retreat of both steps, but the [411]+step was slowed to a much greater extent making the dissolution nearly isotropic. At high levels (800 mu-M) of carbonate, the rate of retreat of the [441]+step was slower than that of the [441]-step making dissolution anisotropic in the opposite sense to that observed at low levels of carbonate. This decrease in step velocity at high carbonate levels was attributed to a corresponding increase in the reaction (i.e., precipitation) as the solution approached saturation with respect to calcite, and thus is related to the rate of incorporation of calcium cations into the structure. In addition to changing the rate, this back reaction also altered the shape of etch pits formed by dissolution. Strontium cations were also shown to have a step-specific effect on calcite dissolution similar to that of carbonate, suggesting that strontium is preferentially incorporated into the [441]-step to a greater extent than strontium. When the solution exceeded saturation with respect to rhodochrosite, calcite dissolution was nearly isotropic. These results suggest that the small manganese ion (r = 83 pm), is readily incorporated into both [441]+ and [441]-steps, in contrast to the larger Ca (r = 100 pm) and Sr (r = 131 pm) cations, which are preferentially incorporated into the [441]+step.

  16. Limestone dissolution induced by fungal mycelia, acidic materials, and carbonic anhydrase from fungi.

    PubMed

    Li, Wei; Zhou, Peng-Peng; Jia, Li-Ping; Yu, Long-Jiang; Li, Xue-Li; Zhu, Min

    2009-01-01

    Microorganisms influence the dissolution of a number of minerals. Limestone is one of the most abundant rock types in karst areas, and is predominantly calcium carbonate. Two types of experimental systems were designed in this paper, to make comparisons of limestone dissolution rate among the acidic materials and extracellular carbonic anhydrase (CA) excreted by fungi and the enwrapping effect of fungal mycelia. One was the simulated experimental system containing microorganisms. Another was the simulated experimental system without microorganisms. Results of previous experiment indicated that the acidic materials and CA like enzymatic materials excreted by fungi and the enwrapping effect of fungal mycelia were important factors influencing limestone dissolution. In the three factors mentioned above, the dissolution effect was mycelia enwraping effect>acidic dissolution effect>CA enzymatic effect. The results of the second experiment demonstrated further that the limestone dissolution effect of the acidic materials excreted by fungi was stronger than that of CA excreted by fungi. Nevertheless, CA still played an important role in promoting the dissolution of limestone.

  17. Dissolution Rates of Biogenic Carbonate Sediments from the Bermuda Platform

    NASA Astrophysics Data System (ADS)

    Finlay, A. J.; Andersson, A. J.

    2016-02-01

    The contribution of biogenic carbonate sediment dissolution rates to overall net reef accretion/erosion (under both present and future oceanic pCO2 levels) has been strikingly neglected, despite experimental results indicating that sediment dissolution might be more sensitive to ocean acidification (OA) than calcification. Dissolution of carbonate sediments could impact net reef accretion rates as well as the formation and preservation of valuable marine and terrestrial ecosystems. Bulk sediment dissolution rates of samples from the Bermuda carbonate platform were measured in natural seawater at pCO2 values ranging from approximately 3500 μatm to 9000 μatm. This range of pCO2 levels incorporates values currently observed in porewaters on the Bermuda carbonate platform as well as a potential future increase in porewater pCO2 levels due to OA. Sediment samples from two different stations on the reef platform were analyzed for grain size and mineralogy. Dissolution rates of sediments in the dominant grain size fraction of the platform (500-1000 μm) from both stations ranged between 16.25 and 47.19 (± 0.27 to 0.79) μmoles g-1 hr-1 and are comparable to rates previously obtained from laboratory experiments on other natural carbonate sediments. At a pCO2 of 3500 μatm, rates from both samples were similar, despite their differing mineralogy. However, at pCO2 levels above 3500 μatm, the sediment sample with a greater weight percent of Mg-calcite had slightly higher dissolution rates. Despite many laboratory studies on biogenic carbonate dissolution, a significant disparity still exists between laboratory measurements and field observations. Performing additional controlled, laboratory experiments on natural sediment may help to elucidate the reasons for this disparity.

  18. Impact of dissolution and carbonate precipitation on carbon storage in basalt

    NASA Astrophysics Data System (ADS)

    Wells, R. K.; Xiong, W.; Tadeoye, J.; Menefee, A.; Ellis, B. R.; Skemer, P. A.; Giammar, D.

    2016-12-01

    The spatial evolution of silicate mineral dissolution, carbonate precipitation, and the transport of fluids influence the viability of carbon storage in basalt reservoirs. Dissolution of natural basalt and subsequent carbonate precipitation in systems with different transport processes operating were characterized using static and flow-through (5 mL/hr) experiments at 50, 100, and 150 °C, and 100 bar CO2. Intact samples and cores with milled pathways that simulate fractures were tested. Spatial and mineralogical patterns in dissolution and precipitation were analyzed using optical and electron microscopy, microCT scanning, and surface roughness data. Precipitates and fluid chemistry were analyzed using Raman spectroscopy, SEM-EDS, and ICP-MS. Analysis of the bulk solution and surface topography suggests dissolution of olivine and pyroxene grains begins within hours of the start of the experiments. In flow-through experiments, total effluent cation concentrations reach a peak concentration within a few hours then drop towards a steady state within a few days. In static experiments, the initial rate of cation release is faster than it is after several weeks. In both cases Ca2+, Mg2+, and Fe2+ are the dominant cations in solution in the initial stages of reaction. Lower concentrations of Na2+, K+, and Al3+, and the preservation of feldspar and matrix grains after several weeks of reaction indicate the slow reactivity of these minerals. As the reaction progresses, the surface roughness increases steadily with cavities developing at the sites of olivine and pyroxene grains. Post-reaction analysis of basalt samples reacted at static conditions with milled pathways reveals that both siderite and amorphous silica precipitated within diffusion-limited zones as early as 4-6 weeks. Siderite abundance varies with distance along the pathway with the highest concentration of carbonates 1-2 cm below the fracture opening. Siderite precipitates are large enough to fill fracture

  19. The Influence of Chelating Agents on the Kinetics of Calcite Dissolution.

    PubMed

    Fredd; Fogler

    1998-08-01

    The kinetics of calcite dissolution in the presence of calcium chelating agents was investigated over the pH range of 3.3-12 using a rotating disk apparatus. The results show that the rate of dissolution is increased significantly by the presence of chelating agents such as CDTA, DTPA, and EDTA. The rate of dissolution is influenced by the kinetics of the chelation reactions and varies considerably with pH and type of chelating agent. A surface chelation mechanism was introduced to describe the dissolution. The mechanism involves the adsorption of the chelating agent onto the calcite surface and follows Langmuir-Hinshelwood kinetics. The dissolution is different from conventional hydrogen ion attack in that the chelating agent attacks the calcium component of the lattice rather than the carbonate component. Therefore, the rate of dissolution is enhanced by the influence of hydrogen ion attack at low pH. In addition, the various ionic forms of the chelating agents react with the calcite surface at different rates depending on the number of hydrogen ions associated with the species. In general, the rate of dissolution increases with increasing protonation. The surface complexation mechanism was shown to describe the rate of calcite dissolution in the presence of chelating agents over the pH range of 4-12. Copyright 1998 Academic Press.

  20. Dissolution of Spent Nuclear Fuel in Carbonate-Peroxide Solution

    SciTech Connect

    Soderquist, Chuck Z.; Hanson, Brady D.

    2010-01-31

    This study shows that spent UO2 fuel can be completely dissolved in a carbonate-peroxide solution apparently without attacking the metallic Mo-Tc-Ru-Rh-Pd fission product phase. Samples of spent nuclear fuel were pulverized and sieved to a uniform size, then duplicate aliquots were weighed into beakers for analysis. One set was dissolved in near-boiling 10M nitric acid, and the other set was dissolved in a solution of ammonium carbonate and hydrogen peroxide at room temperature. All the resulting fuel solutions were then analyzed for Sr-90, Tc-99, Cs-137, plutonium, and Am-241. For all the samples, the concentrations of Cs-137, Sr-90, plutonium, and Am-241 were the same for both the nitric acid dissolution and the ammonium carbonate-hydrogen peroxide dissolution, but the technetium concentration of the ammonium carbonate-hydrogen peroxide fuel solution was only about 25% of the same fuels dissolved in hot nitric acid.

  1. Late Pleistocene carbonate dissolution in the Venezuela Basin, Caribbean Sea

    SciTech Connect

    Cofer-Shabica, N.B.; Peterson, L.C.

    1985-01-01

    Piston cores from water depths greater than 4000 m in the Venezuela Basin (Caribbean Sea) provide continuous late Pleistocene records of carbonate dissolution and accumulation. The authors examination of multiple dissolution indices indicate that, at least for the last 150,000 years, dissolution of carbonate in the Venezuela Basin has been more intense during interglacial than glacial periods, a pattern opposite to more general observations from the deep Atlantic and Gulf of Mexico. By virtue of its shallow sill depth (1815 m), the Venezuela Basin is relatively isolated from the mainstream of Atlantic thermohaline circulation, and presently is filled with homogeneous, relatively warm (3.8/sup 0/C) waters primarily derived from Upper North Atlantic Deep Water. During the last glacial, the enhanced preservation of carbonate in the Venezuela Basin suggests the presence of a less corrosive, more oxygenated water mass in the Atlantic near sill depth. However, this simple interpretations is potentially complicated by past changes in the rain of biogenic materials from surface waters to the deep basin in what must be an essentially closed system below sill depth. Their observations of increased interglacial dissolution may help to explain previously noted discrepancies in the local glacial to interglacial amplitude of delta/sup 18/O variations recorded by coccoliths and planktonic foraminifera.

  2. CTAB-Influenced Electrochemical Dissolution of Silver Dendrites.

    PubMed

    O'Regan, Colm; Zhu, Xi; Zhong, Jun; Anand, Utkarsh; Lu, Jingyu; Su, Haibin; Mirsaidov, Utkur

    2016-04-19

    Dendrite formation on the electrodes of a rechargeable battery during the charge-discharge cycle limits its capacity and application due to short-circuits and potential ignition. However, understanding of the underlying dendrite growth and dissolution mechanisms is limited. Here, the electrochemical growth and dissolution of silver dendrites on platinum electrodes immersed in an aqueous silver nitrate (AgNO3) electrolyte solution was investigated using in situ liquid-cell transmission electron microscopy (TEM). The dissolution of Ag dendrites in an AgNO3 solution with added cetyltrimethylammonium bromide (CTAB) surfactant was compared to the dissolution of Ag dendrites in a pure aqueous AgNO3 solution. Significantly, when CTAB was added, dendrite dissolution proceeded in a step-by-step manner, resulting in nanoparticle formation and transient microgrowth stages due to Ostwald ripening. This resulted in complete dissolution of dendrites and "cleaning" of the cell of any silver metal. This is critical for practical battery applications because "dead" lithium is known to cause short circuits and high-discharge rates. In contrast to this, in a pure aqueous AgNO3 solution, without surfactant, dendrites dissolved incompletely back into solution, leaving behind minute traces of disconnected silver particles. Finally, a mechanism for the CTAB-influenced dissolution of silver dendrites was proposed based on electrical field dependent binding energy of CTA(+) to silver.

  3. Influence of dipalmitoylphosphatidylcholine on the dissolution of Brazilian chrysotile.

    PubMed

    Valentim, I B; Martins, M H; Joekes, I

    2008-10-01

    It is known that Brazilian chrysotile is rapidly removed from the lungs, but quantitative studies about the influence of lung surfactants on chrysotile dissolution have not been investigated. In this work, the chemical behavior of chrysotile and its dissolution in the presence of dipalmitoylphosphatidylcholine (DPPC) were investigated in physiological conditions. The dissolution was investigated through quantification of magnesium and silicon released by chrysotile. At 37 degrees C, the magnesium concentration is similar to control (without DPPC), which is about 2.0x10(-4)molL(-1), meaning that the dissolution process is not affected by the presence of this surfactant. The same was observed for silicon. The silicon concentration released by chrysotile is similar in all media tested. It is known that the dissolution mechanisms of brucite and tridymite layers are different. From our results, we propose that under physiological conditions, the mechanism of brucite dissolution is based on its interaction with hydrogen ions and that the mechanism of tridymite dissolution is based on a hydrolysis process.

  4. Influence of the Efavirenz Micronization on Tableting and Dissolution

    PubMed Central

    Pinto, Eduardo Costa; do Carmo, Flávia Almada; da Silva Honório, Thiago; da Silva Ascenção Barros, Rita de Cássia; Castro, Helena Carla Rangel; Rodrigues, Carlos Rangel; Esteves, Valéria Sant'Anna Dantas; Rocha, Helvécio Vinícius Antunes; de Sousa, Valeria Pereira; Cabral, Lucio Mendes

    2012-01-01

    The purpose of this study was to propose an analytical procedure that provides the effects of particle size and surface area on dissolution of efavirenz. Five different batches obtained by different micronization processes and with different particle size distribution and surface area were studied. The preformulation studies and dissolution curves were used to confirm the particle size distribution effect on drug solubility. No polymorphic variety or amorphization was observed in the tested batches and the particle size distribution was determined as directly responsible for the improvement of drug dissolution. The influence of the preparation process on the tablets derived from efavirenz was observed in the final dissolution result in which agglomeration, usually seen in non-lipophilic micronized material, was avoided through the use of an appropriate wet granulation method. For these reasons, micronization may represent one viable alternative for the formulation of brick dust drugs. PMID:24300301

  5. Comment on "On the influence of carbonate in mineral dissolution: 1. The thermodynamics and kinetics of hematite dissolution in bicarbonate solutions at T = 25°C" by J. Bruno, W. Stumm, P. Wersin, and F. Brandberg

    NASA Astrophysics Data System (ADS)

    Hummel, Wolfgang

    2000-06-01

    Within the scope of a planned update of the Nagra/PSI thermochemical database (Pearson and Berner, 1991; Pearson et al., 1992) we are currently reviewing data concerning the carbonate complexation of trace metals (Hummel et al., 2000). The investigation of Bruno et al. (1992) attracted our attention because it is to our present knowledge the only publication exploring the carbonate complexation of ferric iron. The lack of stability constants of Fe(III) carbonate complexes is regarded as a serious deficiency in our database, and therefore, the work of Bruno et al. (1992) has been carefully reviewed with the aim of including their results into the next version of the Nagra/PSI database. The important findings of Bruno et al. (1992) unfortunately are disguised by some inconsistencies in the treatment of their experimental data that, in turn, hide an unresolved ambiguity in their experiments: The stability constants of the complexes as reported by Bruno et al. (1992), and as already included into the IUPAC database (IUPAC, 1997), are such small numbers that Fe(III) carbonate complexes are predicted to be completely negligible in any aqueous system. On the other hand, their experimental findings point to the fact that Fe(III) carbonate complexes might be important in many groundwater systems. This comment aims at resolving this enigma and clarifying the importance of Fe(III) carbonate complexation.

  6. Boron isotope fractionation in magma via crustal carbonate dissolution

    PubMed Central

    Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

    2016-01-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle. PMID:27488228

  7. Boron isotope fractionation in magma via crustal carbonate dissolution.

    PubMed

    Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela

    2016-08-04

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  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. Determination of the carbonate dissolution mechanism of Lactococcus sp.

    NASA Astrophysics Data System (ADS)

    Yanmiş, Derya; Orhan, Furkan; Güllüce, Medine; Şahin, Fikrettin

    2017-04-01

    Magnesite, the main source for magnesium and magnesium derivatives, are also commonly used in the production of caustic, dead-burned and fused magnesia. World magnesite resources are estimated to be at 12 billion tonnes mostly located in China, Russia, North Korea, Australia and Turkey. Turkey is the second producer of the magnesite. Magnesite deposits in Turkey are sedimentary magnesite which have been formed in specific conditions as high concentrations of MgSO4 and CO2 and presence of certain organic salts or created by hot or cold dissolution connected with carbonate rocks mainly with dolomites. According to the genesis of magnesite deposits, they have some impurities as calcium, quartz, iron, etc. Impurities of magnesite, especially CaCO3, reduce its economic value and industrial usability. In our previous study, we have performed biotechnologically enrichment of magnesite by Lactococcus sp., which gave significantly important results. However, we had no information about carbonate dissolution mechanism of bacteria. Therefore, it is aimed to reveal the metabolites of Lactococcus sp. and mechanism leading to the carbonate dissolution (MgCO3 and CaCO3).

  10. 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

  11. Dissolution of Uranium(IV) Oxide in Solutions of Ammonium Carbonate and Hydrogen Peroxide

    SciTech Connect

    Smith, Steven C.; Peper, Shane M.; Douglas, Matthew; Ziegelgruber, Kate L.; Finn, Erin C.

    2009-09-12

    Understanding the dissolution characteristics of uranium oxides is of fundamental scientific interest. Bench scale experiments were conducted to determine the optimal dissolution parameters of uranium(IV) oxide (UO2) powder in solutions of ammonium carbonate [(NH4)2CO3] and hydrogen peroxide (H2O2). Experimental parameters included variable peroxide and carbonate concentrations, and temperature. Results indicate the dissolution rate of UO2 in 1 M (NH4)2CO3 increases linearly with peroxide concentration ranging from 0.05 – 2 M (1:1 to 40:1 mol ratio H2O2:U), with no apparent maximum rate reached under the limited conditions used in our study. Temperature ranging studies show the dissolution rate of UO2 in 1 M (NH4)2CO3 and 0.1 M H2O2 (2:1 mol ratio H2O2:U) increases linearly from 15 °C to 60 °C, again with no apparent maximum rate reached. Dissolution of UO2 in solutions with constant [H2O2] and [(NH4)2CO3] ranging from 0.5 to 2 M showed no difference in rate; however dissolution was significantly reduced in 0.05 M (NH4)2CO3 solution. The results of this study demonstrate the influence of [H2O2], [(NH4)2CO3], and temperature on the dissolution of UO2 in peroxide-containing (NH4)2CO3 solutions. Future studies are planned to elucidate the solution and solid state complexes in these systems.

  12. Rates of mineral dissolution and carbonation in peridotite and basalt

    NASA Astrophysics Data System (ADS)

    Kelemen, P. B.; Matter, J. M.

    2009-12-01

    We study natural rates and processes of mineral carbonation in peridotite (olivine-rich rock) in mantle rocks exposed to weathering in northern Oman to learn effective mechanisms from natural processes, and seek ways to accelerate them to achieve significant CO2 capture and storage via mineral carbonation at the lowest possible cost. In our first paper (1), we fit data on mantle olivine carbonation from the DOE Albany Research Center (2,3, ARC). These data, and data from Arizona State University (4, ASU) suggest that a peridotite rock volume heated to 185°C and infused with H2O+CO2 at PCO2 > 75 bars could consume ~ 1 ton CO2 per cubic meter of rock per year. Because it is more abundant than peridotite, other workers focus on carbonation of the most common type of lava on Earth, basalt, whose main mineral constituent is generally labradorite, part of the plagioclase feldspar solid solution series. Our intuition is that labradorite carbonation is much slower than mantle olivine carbonation. To quantify this, we compiled data on dissolution of mantle olivine, labradorite, crystalline basalt, and basaltic glass in aqueous fluids, as well as data on mantle olivine carbonation. The dissolution data are calibrated as a function of surface area (i.e., grain size and shape) and pH, as well as temperature, whereas most of the ARC and ASU experiments were done at a single pH and grain size. Thus, for comparison, we calculated dissolution rates for 70 micron spheres at pH 8, close to the ARC and ASU experimental conditions. At these conditions, olivine carbonation observed by ARC and ASU is 100 to 1000 times faster than labradorite and crystalline basalt, and faster than conventionally measured olivine dissolution rates. The ARC and ASU experiments were different from conventional dissolution experiments in several ways that could lead to an enhancement in olivine reaction rates: (a) they may have lower a(Mg) in fluid due to solid MgCO3 (magnesite) precipitation, (b) they

  13. Carbonate mineral dissolution kinetics in high pressure experiments

    NASA Astrophysics Data System (ADS)

    Dethlefsen, F.; Dörr, C.; Schäfer, D.; Ebert, M.

    2012-04-01

    The potential CO2 reservoirs in the North German Basin are overlain by a series of Mesozoic barrier rocks and aquifers and finally mostly by Tertiary and Quaternary close-to-surface aquifers. The unexpected rise of stored CO2 from its reservoir into close-to-surface aquifer systems, perhaps through a broken well casing, may pose a threat to groundwater quality because of the acidifying effect of CO2 dissolution in water. The consequences may be further worsening of the groundwater quality due to the mobilization of heavy metals. Buffer mechanisms counteracting the acidification are for instance the dissolution of carbonates. Carbonate dissolution kinetics is comparably fast and carbonates can be abundant in close-to-surface aquifers. The disadvantages of batch experiments compared to column experiments in order to determine rate constants are well known and have for instance been described by v. GRINSVEN and RIEMSDIJK (1992). Therefore, we have designed, developed, tested, and used a high-pressure laboratory column system to simulate aquifer conditions in a flow through setup within the CO2-MoPa project. The calcite dissolution kinetics was determined for CO2-pressures of 6, 10, and 50 bars. The results were evaluated by using the PHREEQC code with a 1-D reactive transport model, applying a LASAGA (1984) -type kinetic dissolution equation (PALANDRI and KHARAKA, 2004; eq. 7). While PALANDRI and KHARAKA (2004) gave calcite dissolution rate constants originating from batch experiments of log kacid = -0.3 and log kneutral = -5.81, the data of the column experiment were best fitted using log kacid = -2.3 and log kneutral = -7.81, so that the rate constants fitted using the lab experiment applying 50 bars pCO2 were approximately 100 times lower than according to the literature data. Rate constants of experiments performed at less CO2 pressure (pCO2 = 6 bars: log kacid = -1.78; log kneutral = -7.29) were only 30 times lower than literature data. These discrepancies in the

  14. Dissolution of carbon dioxide bubbles and microfluidic multiphase flows.

    PubMed

    Sun, Ruopeng; Cubaud, Thomas

    2011-09-07

    We experimentally study the dissolution of carbon dioxide bubbles into common liquids (water, ethanol, and methanol) using microfluidic devices. Elongated bubbles are individually produced using a hydrodynamic focusing section into a compact microchannel. The initial bubble size is determined based on the fluid volumetric flow rates of injection and the channel geometry. By contrast, the bubble dissolution rate is found to depend on the inlet gas pressure and the fluid pair composition. For short periods of time after the fluids initial contact, the bubble length decreases linearly with time. We show that the initial rate of bubble shrinkage is proportional to the ratio of the diffusion coefficient and the Henry's law constant associated with each fluid pair. Our study shows the possibility to rapidly impregnate liquids with CO(2) over short distances using microfluidic technology.

  15. Kinetics of carbonate dissolution in CO2-saturated aqueous system at reservoir conditions

    NASA Astrophysics Data System (ADS)

    Peng, Cheng; Crawshaw, John P.; Maitland, Geoffrey; Trusler, J. P. Martin

    2014-05-01

    In recent years, carbon capture and storage (CCS) has emerged as a key technology for limiting anthropogenic CO2 emissions while allowing the continued utilisation of fossil fuels. The most promising geological storage sites are deep saline aquifers because the capacity, integrity and injection economics are most favourable, and the environmental impact can be minimal. Many rock-fluid chemical reactions are known to occur both during and after CO2 injection in saline aquifers. The importance of rock-fluid reactions in the (CO2 + H2O) system can be understood in terms of their impact on the integrity and stability of both the formation rocks and cap rocks. The chemical interactions between CO2-acidified brines and the reservoir minerals can influence the porosity and permeability of the formations, resulting in changes in the transport processes occurring during CO2 storage. Since carbonate minerals are abundant in sedimentary rocks, one of the requirements to safely implement CO2 storage in saline aquifers is to characterise the reactivity of carbonate minerals in aqueous solutions at reservoir conditions. In this work, we reported measurements of the intrinsic rate of carbonate dissolution in CO2-saturated water under high-temperature high-pressure reservoir conditions extending up to 373 K and 14 MPa. The rate of carbonate dissolution in CO2-free HCl(aq) was also measured at ambient pressure at temperatures up to 353 K. Various pure minerals and reservoir rocks were investigated in this study, including single-crystals of calcite and magnesite, and samples of dolomite, chalks and sandstones. A specially-designed batch reactor system, implementing the rotating disc technique, was used to obtain the intrinsic reaction rate at the solid/liquid interface, free of mass transfer effects. The effective area and mineralogy of the exposed surface was determined by a combination of surface characterisation techniques including XRD, SEM, EDX and optical microscopy. The

  16. CaCO 3 dissolution in California continental margin sediments: The influence of organic matter remineralization

    NASA Astrophysics Data System (ADS)

    Jahnke, Richard A.; Craven, Deborah B.; McCorkle, Daniel C.; Reimers, Clare E.

    1997-09-01

    In situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of CaCO 3 on the continental rise adjacent to central California, USA. The porewater distributions and benthic fluxes of O 2, NO 3-, TA, Ca 2+, δ 13C, and TIC are interpreted using a numerical simulation of organic matter remineralization and CaCO 3 dissolution in marine sediments. The processes considered in the simulation include: organic matter oxidation by O 2, NO 3, and SO 42-; CaCO 3 dissolution and precipitation; HS - and NH 4+ oxidation; and sediment mixing and sediment accumulation. Calculated benthic fluxes of O 2, NO 3-, TA, TIC, δ 13C, and Ca 2+; porewater concentrations of O 2, NO 3-, and NH 4+; and sediment distributions of organic carbon, CaCO 3, excess 210Pb, and 14C agree well with the measurements. Benthic fluxes of alkalinity and inferred CaCO 3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation. If the influence of metabolically-produced CO 2 is included, benthic fluxes are fully reconciled, however. This is in agreement with benthic chamber Ca 2+ and δ 13C results that independently imply substantial CaCO 3 dissolution in these sediments. The above observations are in contrast to those reported by Jahnke et al. (1994) for the west African continental rise and the western equatorial Pacific where 1-G diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers. We conclude that the extent of metabolic CaCO 3 dissolution may vary regionally. Numerous factors, such as the depth of metabolic CO 2 production and CaCO 3 dissolution kinetics, are known or predicted to influence metabolic dissolution. Among the factors that should be considered in reconciling these observations are: (l) the extent to which sulfate reduction and reoxidation reactions may influence acid-base properties in surface sediments and (2) the total

  17. Heterogeneous alternation of fractured rock driven by preferential carbonate dissolution

    NASA Astrophysics Data System (ADS)

    Wen, H.; Zhi, W.; Li, L.

    2016-12-01

    Diffusivity Induced by Preferential Carbonate Dissolution. Energy & Fuels.

  18. Effect of trace lanthanum ion on dissolution and crystal growth of calcium carbonate

    NASA Astrophysics Data System (ADS)

    Kamiya, Natsumi; Kagi, Hiroyuki; Tsunomori, Fumiaki; Tsuno, Hiroshi; Notsu, Kenji

    2004-07-01

    Impurity effects of trace lanthanum ion (La 3+) on the dissolution and growth of calcium carbonate were studied with in situ observation techniques. Dissolution kinetics of two polymorphs of calcium carbonate, calcite and vaterite, were investigated by monitoring the pH in the solution with laser-induced fluorescence spectroscopy using a pH-sensitive reagent, seminaphthorhodafluors. No effect on dissolution of vaterite was observed with the spectroscopic observations, whereas calcite dissolution was significantly inhibited by lanthanum ion with concentrations higher than 1 μM. Crystal growth and dissolution processes of calcite under the lanthanum-doped condition were observed by means of atomic force microscopy. Step propagations during crystal growth and dissolution of calcite were inhibited by trace lanthanum ion (5 μM). An insoluble thin layer of lanthanum carbonate deposited on the step site of the calcite surface could be a possible cause of the inhibitions observed both for dissolution and growth.

  19. Reassessing the dissolution of marine carbonates: II. Reaction kinetics

    NASA Astrophysics Data System (ADS)

    Gehlen, M.; Bassinot, F. C.; Chou, L.; McCorkle, D.

    2005-08-01

    We studied dissolution kinetics of the carbonate fraction >150 μm of sediments sampled along two bathymetric transects in the eastern tropical Atlantic: the Sierra Leone Rise (SLR) and the Cape Verde Plateau (CVP). The reaction was followed by monitoring solution pH during freedrift experiments lasting between 46 and 50 h (20 °C, pCO 2≈3100 ppm and 1 atm pressure). The alkalinity reached at the end of the dissolution experiments ranged between 2.444 and 2.798 meq/kg sw. The dissolution time series was extrapolated to equilibrium by fitting an empirical relation to the data. The estimated asymptotic concentration products ([Ca 2+] ∞×[CO 32-] ∞, for t→∞ and dA/dt=0) range from 4.27×10 -7 to 6.77×10 -7 mol 2/kg sw2. These asymptotic concentration products are comparable with the stoichiometric concentration product of aragonite (6.56×10 -7 mol 2/kg sw2) and calcite (4.37 (±0.22)×10 -7 mol 2/kg sw2) derived for the same sediment material during long-term equilibration experiments. They are indicative of the presence of trace amounts of a higher solubility carbonate phase in sediments of the shallow stations (SLR station A, 2637 m; CVP station M, 3104 m). While it is likely that this phase is aragonite, the presence of authigenic carbonate precipitated in contact with supersaturated bottom waters cannot be excluded. Calcite is the main dissolving carbonate mineral in sediments from deeper stations. The order of reaction is always greater than unity. It varies between 1.4 (SLR station C) and 2.8 (CVP station M2), with an average n=2.3±0.4. The higher order reaction is explained in terms of a multiphase system. Specific rate constants range from 0.09 to 0.53 meq/m 2/d.

  20. Dissolution of a Carbon Dioxide Bubble in a Vertical Pipe

    NASA Astrophysics Data System (ADS)

    Abe, Satoru; Okawa, Hideaki; Hosokawa, Shigeo; Tomiyama, Akio

    Dissolution of single carbon dioxide (CO2) bubbles in a vertical pipe of 25 mm diameter is measured to examine the effects of the ratio λ of the sphere-volume equivalent bubble diameter to the pipe diameter, the liquid Reynolds number and surfactants on mass transfer. The bubble diameter and liquid Reynolds number are varied from 5.0 to 26 mm (0.20 < λ < 1.0) and from 0 to 3100, respectively. Millipore water, tap water or water contaminated with Triton X-100 are used for the liquid phase. Dissolution processes are measured at atmospheric pressure and room temperature. Mass transfer coefficients and Sherwood numbers are evaluated from measured bubble diameters. Complicated capillary waves are formed at the clean bubble surface, whereas there are no capillary waves at the contaminated bubble surface. The disappearance of capillary wave results in the retardation of surface renewal, and therefore, Sherwood number decreases with increasing surfactant concentration. Empirical correlations of Sherwood numbers for bubbles rising in clean and contaminated liquids in a vertical pipe are proposed. The correlations are applicable not only to bubbles in stagnant liquid but also to bubbles in pipe flow, provided that the liquid Reynolds number is not so high.

  1. Electrolytic dissolution characteristics of SIMFUEL in carbonate solutions of high concentration

    NASA Astrophysics Data System (ADS)

    Kim, Kwang-Wook; Hyun, Jun-Taek; Sung, Sae-Reum; Lee, Eil-Hee; Lee, Kune-Woo; Song, Kee-Chan

    2010-11-01

    This work studied anodic dissolution characteristics of a SIMFUEL electrode at several potentials in carbonate solutions of a high concentration at several pHs. The electrolytic uranium dissolution of SIMFUEL was much affected by a corrosion product of UO 2CO 3 generated at the electrode during the dissolution in carbonate solution. The corrosion product distorted the voltammogram of SIMFUEL in the potential region of oxygen evolution and increased the overpotential of oxygen evolution at the electrode. The effective dissolution of the SIMFUEL electrode in a carbonate solution could be obtained at an applied potential such as +4 V (vs SSE) or more which had an overpotential of oxygen evolution high enough to rupture the corrosion product on the electrode surface. The corrosion potential of SIMFUEL decreased with pH in the carbonate solution, and the dissolution rate and current efficiency of the SIMFUEL increased with a decrease of pH in the carbonate solution.

  2. Dissolution of Calcite in the Twilight Zone: Bacterial Control of Dissolution of Sinking Planktonic Carbonates Is Unlikely

    PubMed Central

    Bissett, Andrew; Neu, Thomas R.; de Beer, Dirk

    2011-01-01

    We investigated the ability of bacterial communities to colonize and dissolve two biogenic carbonates (Foraminifera and oyster shells). Bacterial carbonate dissolution in the upper water column is postulated to be driven by metabolic activity of bacteria directly colonising carbonate surfaces and the subsequent development of acidic microenvironments. We employed a combination of microsensor measurements, scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and image analysis and molecular documentation of colonising bacteria to monitor microbial processes and document changes in shell surface topography. Bacterial communities rapidly colonised shell surfaces, forming dense biofilms with extracellular polymeric substance (EPS) deposits. Despite this, we found no evidence of bacterially mediated carbonate dissolution. Dissolution was not indicated by Ca2+ microprofiles, nor was changes in shell surface structure related to the presence of colonizing bacteria. Given the short time (days) settling carbonate material is actually in the twilight zone (500–1000 m), it is highly unlikely that microbial metabolic activity on directly colonised shells plays a significant role in dissolving settling carbonates in the shallow ocean. PMID:22102861

  3. Fracture Dissolution of Carbonate Rock: An Innovative Process for Gas Storage

    SciTech Connect

    James W. Castle; Ronald W. Falta; David Bruce; Larry Murdoch; Scott E. Brame; Donald Brooks

    2006-10-31

    ) that allow for the easy removal of calcium waste from the well. Physical and chemical analysis of core samples taken from prospective geologic formations for the acid dissolution process confirmed that many of the limestone samples readily dissolved in concentrated hydrochloric acid. Further, some samples contained oily residues that may help to seal the walls of the final cavern structure. These results suggest that there exist carbonate rock formations well suited for the dissolution technology and that the presence of inert impurities had no noticeable effect on the dissolution rate for the carbonate rock. A sensitivity analysis was performed for characteristics of hydraulic fractures induced in carbonate formations to enhance the dissolution process. Multiple fracture simulations were conducted using modeling software that has a fully 3-D fracture geometry package. The simulations, which predict the distribution of fracture geometry and fracture conductivity, show that the stress difference between adjacent beds is the physical property of the formations that has the greatest influence on fracture characteristics by restricting vertical growth. The results indicate that by modifying the fracturing fluid, proppant type, or pumping rate, a fracture can be created with characteristics within a predictable range, which contributes to predicting the geometry of storage caverns created by acid dissolution of carbonate formations. A series of three-dimensional simulations of cavern formation were used to investigate three different configurations of the acid-dissolution process: (a) injection into an open borehole with production from that same borehole and no fracture; (b) injection into an open borehole with production from that same borehole, with an open fracture; and (c) injection into an open borehole connected by a fracture to an adjacent borehole from which the fluids are produced. The two-well configuration maximizes the overall mass transfer from the rock to the

  4. Reassessing the dissolution of marine carbonates: I. Solubility

    NASA Astrophysics Data System (ADS)

    Gehlen, M.; Bassinot, F. C.; Chou, L.; McCorkle, D.

    2005-08-01

    We studied the solubility of the [63-150 μm] and the greater than 150 μm size fractions of sediments from two bathymetric transects in the eastern tropical Atlantic (Sierra Leone rise and Cape Verde Plateau). Both fractions are made mainly of foraminiferal shells and fragments. We determined the calcite crystallinity (full width at half maximum of XRD (104) calcite peak) of the >150 μm size fraction. Equilibration experiments were carried out in artificial seawater (20 °C, pCO 2=3100 ppm) for up to 57 days starting from undersaturation with respect to calcite and supersaturation with respect to aragonite. Experiments starting from supersaturation yielded concentration products close to aragonite solubility for sediments from the shallowest stations, suggesting the presence of trace levels of aragonite in these samples. Concentration products computed for the deeper stations were intermediate between aragonite and calcite solubility. Our results indicate the formation of a high-Mg coating. The equilibration period was too short to allow the complete recrystallization of these Mg-rich overgrowths. Experiments initiated from undersaturation yield concentration products that are between 4% and 24% higher than the reported stoichiometric concentration product of synthetic calcite. These differences between estimates of calcite stoichiometric solubility products are explained in terms of variations in experimental conditions (artificial versus natural seawater) and related choices of carbonic acid dissociation constants. They do not reflect a true difference in solubility between biogenic and synthetic calcite. The thinning of the foraminiferal calcite (104) XRD peak from 0.168°( 2θ) to 0.148°( 2θ) along the depth transects is interpreted as reflecting an improvement in calcite crystallinity. This and the change in specific surface area are consistent with the progressive change of the carbonate assemblage. The evolution of the bulk composition of the carbonate

  5. Calcium isotope evidence for suppression of carbonate dissolution in carbonate-bearing organic-rich sediments

    NASA Astrophysics Data System (ADS)

    Turchyn, Alexandra V.; DePaolo, Donald J.

    2011-11-01

    Pore fluid calcium isotope, calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep-sea sediments containing abundant clay and organic material. This type of study of deep-sea sediment diagenesis provides unique information about the ultra-slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo-environmental information in carbonate fossils. For this study, calcium isotope ratios (δ 44/40Ca) of pore fluid calcium from Ocean Drilling Program (ODP) Sites 984 (North Atlantic) and 1082 (off the coast of West Africa) were measured to augment available pore fluid measurements of calcium and strontium concentration. Both study sites have high sedimentation rates and support quantitative sulfate reduction, methanogenesis and anaerobic methane oxidation. The pattern of change of δ 44/40Ca of pore fluid calcium versus depth at Sites 984 and 1082 differs markedly from that of previously studied deep-sea Sites like 590B and 807, which are composed of nearly pure carbonate sediment. In the 984 and 1082 pore fluids, δ 44/40Ca remains elevated near seawater values deep in the sediments, rather than shifting rapidly toward the δ 44/40Ca of carbonate solids. This observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate-rich sites. The data are fit using a numerical model, as well as more approximate analytical models, to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material. Our models give mutually consistent results and indicate that calcite dissolution rates at Sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate-rich sites, and the rate correlates with the abundance of clay. Our calculated rates are conservative for these

  6. Accelerating carbonate dissolution to sequester carbon dioxide in the ocean: Geochemical implications

    NASA Astrophysics Data System (ADS)

    Caldeira, Ken; Rau, Greg H.

    2000-01-01

    Various methods have been proposed for mitigating release of anthropogenic CO2 to the atmosphere, including deep-sea injection of CO2 captured from fossil-fuel fired power plants. Here, we use a schematic model of ocean chemistry and transport to analyze the geochemical consequences of a new method for separating carbon dioxide from a waste gas stream and sequestering it in the ocean. This method involves reacting CO2-rich power-plant gases with seawater to produce a carbonic acid solution which in turn is reacted on site with carbonate mineral (e.g., limestone) to form Ca2+ and bicarbonate in solution, which can then be released and diluted in the ocean. Such a process is similar to carbonate weathering and dissolution which would have otherwise occurred naturally, but over many millennia. Relative to atmospheric release or direct ocean CO2 injection, this method would greatly expand the capacity of the ocean to store anthropogenic carbon while minimizing environmental impacts of this carbon on ocean biota. This carbonate-dissolution technique may be more cost-effective and less environmentally harmful, and than previously proposed CO2 capture and sequestration techniques.

  7. Targeted Control of Permeability Using Carbonate Dissolution/Precipitation Reactions

    NASA Astrophysics Data System (ADS)

    Clarens, A. F.; Tao, Z.; Plattenberger, D.

    2016-12-01

    Targeted mineral precipitation reactions are a promising approach for controlling fluid flow in the deep subsurface. Here we studied the potential to use calcium and magnesium bearing silicates as cation donors that would react with aqueous phase CO2 under reservoir conditions to form solid carbonate precipitates. Preliminary experiments in high pressure and temperature columns suggest that these reactions can effectively lower the permeability of a porous media. Wollastonite (CaSiO3) was used as the model silicate, injected as solid particles into the pore space of a packed column, which was then subsequently flooded with CO2(aq). The reactions occur spontaneously, leveraging the favorable kinetics that occur at the high temperature and pressure conditions characteristic of the deep subsurface, to form solid phase calcium carbonate (CaCO3) and amorphous silica (SiO2) within the pore space. Both x-ray tomography imaging of reacted columns and electron microscopy imaging of thin sections were used to characterize where dissolution/precipitation occurred within the porous media. The spatial distribution of the products was closely tied to the flow rate and the duration of the experiment. The SiO2 product precipitated in close spatial proximity to the CaSiO3 reactant. The CaCO3 product, which is sensitive to the low pH and high pCO2 brine, precipitated out of solution further down the column as Ca2+ ions moved with the brine. The permeability of the columns decreased by several orders of magnitude after injecting the CaSiO3 particles. Following carbonation, the permeability decreased even further as precipitates filled flow paths within the pore network. A pore network model was developed to help understand the interplay between precipitation kinetics and flow in altering the permeability of the porous media. The effect of particle concentration and size, pore size, reaction time, and pCO2, are explored on pore/fracture aperture and reaction extent. To provide better

  8. The three steps of the carbonate biogenic dissolution process by microborers in coral reefs (New Caledonia).

    PubMed

    Grange, J S; Rybarczyk, H; Tribollet, A

    2015-09-01

    Biogenic dissolution of carbonates by microborers is one of the main destructive forces in coral reefs and is predicted to be enhanced by eutrophication and ocean acidification by 2100. The chlorophyte Ostreobium sp., the main agent of this process, has been reported to be one of the most responsive of all microboring species to those environmental factors. However, very little is known about its recruitment, how it develops over successions of microboring communities, and how that influences rates of biogenic dissolution. Thus, an experiment with dead coral blocks exposed to colonization by microborers was carried out on a reef in New Caledonia over a year period. Each month, a few blocks were collected to study microboring communities and the associated rates of biogenic dissolution. Our results showed a drastic shift in community species composition between the 4th and 5th months of exposure, i.e., pioneer communities dominated by large chlorophytes such as Phaeophila sp. were replaced by mature communities dominated by Ostreobium sp. Prior the 4th month of exposure, large chlorophytes were responsible for low rates of biogenic dissolution while during the community shift, rates increased exponentially (×10). After 6 months of exposure, rates slowed down and reached a "plateau" with a mean of 0.93 kg of CaCO3 dissolved per m(2) of reef after 12 months of exposure. Here, we show that (a) Ostreobium sp. settled down in new dead substrates as soon as the 3rd month of exposure but dominated communities only after 5 months of exposure and (b) microbioerosion dynamics comprise three distinct steps which fully depend on community development stage and grazing pressure.

  9. Effect of a new carbon dioxide laser treatment on dissolution profiles of dental enamel

    NASA Astrophysics Data System (ADS)

    Featherstone, John D. B.; Le, Charles Q.; Fried, Daniel

    2003-06-01

    Previous studies have shown that pretreatment of dental enamel by specific carbon dioxide laser conditions inhibited subsequent acid dissolution of the enamel surface. The aim of the present study was to examine the dissolution profiles following irradiation by a new short pulse carbon dioxide laser treatment. Bovine enamel blocks were irradiated at 9.6 μm with a 5-8 μs or a 20-30 μs pulse duration laser using overlapping spots, and a range of fluences. Dissolution profiles were measured in an acetate buffer. Higher fluences produced rapid initial dissolution followed by a plateau with a low dissolution rate. For caries inhibition purposes the high solubility decomposition phases need to be avoided or removed.

  10. Thermodynamic Simulation of Carbonate Cements-Water-Carbon Dioxide Equilibrium in Sandstone for Prediction of Precipitation/Dissolution of Carbonate Cements

    PubMed Central

    Zhong, Xinyan; Shang, Ruishu; Huang, Lihong

    2016-01-01

    Carbonate cements, such as calcite, dolomite, ferrocalcite and ankerite, play important roles in the formation of pores in sandstones: precipitation of carbonate cements modifies pores and inhibits compaction, while dissolution creates secondary pores. This work proposed a precipitation-dissolution model for carbonate cements-CO2-H2O system by means of ion equilibrium concentration ([M2+], M = Ca, Mg, Fe or Mn) with different factors, such as temperature, depth, pH, PCO2, variable rock composition and overpressure. Precipitation-dissolution reaction routes were also analyzed by minimization of the total Gibbs free energy (ΔG). Δ[M2+], the variation of [Ca2+], [Fe2+], [Mg2+] or [Mn2+] for every 100 m of burial depths, is used to predict precipitation or dissolution. The calculation results indicate that the increasing temperature results in decrease of equilibrium constant of reactions, while the increasing pressure results in a relatively smaller increase of equilibrium constant; As a result, with increasing burial depth, which brings about increase of both temperature and pressure, carbonate cements dissolve firstly and produces the maximal dissolved amounts, and then precipitation happens with further increasing depth; For example, calcite is dissolving from 0.0 km to 3.0 km with a maximal value of [Ca2+] at depth of 0.8 km, and then precipitates with depth deeper than 3.0 km. Meanwhile, with an increasing CO2 mole fraction in the gaseous phase from 0.1% to 10.0% in carbonate systems, the aqueous concentration of metal ions increases, e.g., dissolved amount of CaFe0.7Mg0.3(CO3)2 increases and reaches maximum of 1.78 mmol·L-1 and 8.26 mmol·L-1 at burial depth of 0.7 km with CO2 mole fraction of 0.1% and 10.0%, respectively. For the influence of overpressure in the calcite system, with overpressure ranging from 36 MPa to 83 MPa, pH reaches a minimum of 6.8 at overpressure of 51 MPa; meanwhile, Δ[Ca2+] increases slightly from -2.24 mmol·L-1 to -2.17 mmol·L-1

  11. Thermodynamic Simulation of Carbonate Cements-Water-Carbon Dioxide Equilibrium in Sandstone for Prediction of Precipitation/Dissolution of Carbonate Cements.

    PubMed

    Duan, Yiping; Feng, Mingshi; Zhong, Xinyan; Shang, Ruishu; Huang, Lihong

    2016-01-01

    Carbonate cements, such as calcite, dolomite, ferrocalcite and ankerite, play important roles in the formation of pores in sandstones: precipitation of carbonate cements modifies pores and inhibits compaction, while dissolution creates secondary pores. This work proposed a precipitation-dissolution model for carbonate cements-CO2-H2O system by means of ion equilibrium concentration ([M2+], M = Ca, Mg, Fe or Mn) with different factors, such as temperature, depth, pH, [Formula: see text], variable rock composition and overpressure. Precipitation-dissolution reaction routes were also analyzed by minimization of the total Gibbs free energy (ΔG). Δ[M2+], the variation of [Ca2+], [Fe2+], [Mg2+] or [Mn2+] for every 100 m of burial depths, is used to predict precipitation or dissolution. The calculation results indicate that the increasing temperature results in decrease of equilibrium constant of reactions, while the increasing pressure results in a relatively smaller increase of equilibrium constant; As a result, with increasing burial depth, which brings about increase of both temperature and pressure, carbonate cements dissolve firstly and produces the maximal dissolved amounts, and then precipitation happens with further increasing depth; For example, calcite is dissolving from 0.0 km to 3.0 km with a maximal value of [Ca2+] at depth of 0.8 km, and then precipitates with depth deeper than 3.0 km. Meanwhile, with an increasing CO2 mole fraction in the gaseous phase from 0.1% to 10.0% in carbonate systems, the aqueous concentration of metal ions increases, e.g., dissolved amount of CaFe0.7Mg0.3(CO3)2 increases and reaches maximum of 1.78 mmol·L-1 and 8.26 mmol·L-1 at burial depth of 0.7 km with CO2 mole fraction of 0.1% and 10.0%, respectively. For the influence of overpressure in the calcite system, with overpressure ranging from 36 MPa to 83 MPa, pH reaches a minimum of 6.8 at overpressure of 51 MPa; meanwhile, Δ[Ca2+] increases slightly from -2.24 mmol·L-1 to

  12. Direct nano-scale observations of carbon mineralization during brucite dissolution (Invited)

    NASA Astrophysics Data System (ADS)

    Hoevelmann, J.; Putnis, C. V.; Ruiz Agudo, E.; Austrheim, H.

    2013-12-01

    Aqueous mineral carbonation for ex situ CO2 sequestration involves coupled dissolution and precipitation processes occurring at the mineral-fluid interface. Critical insight into the reaction mechanisms is therefore gained from direct nano-scale observations of carbonation reactions using advanced analytical techniques such as Atomic Force Microscopy (AFM). Here we present a series of in situ an ex situ AFM experiments on the dissolution and carbonation of brucite [Mg(OH)2] at varying pH (2-12), temperature (23-40°C), aqueous NaHCO3 concentration (10-5-1 M), and PCO2 (0-1 atm). In all experiments, brucite dissolution proceeded by the formation and spreading of etch pits with equilateral triangular shapes. Dissolution rates increased with decreasing pH and increasing NaHCO3 concentration. Simultaneously with dissolution of brucite, the growth of a Mg-carbonate phase (probably dypingite) was directly observed. In NaHCO3 solutions (pH 7.2 - 9.3,), precipitation of Mg-carbonates was limited. Enhanced precipitation was, however, observed in acidified NaHCO3 solutions (pH 5, DIC ≈ 25.5 mM) and in solutions that were equilibrated under a CO2 atmosphere (pH 4, DIC ≈ 25.2 mM). Nucleation predominantly occurred in areas of high dissolution, such as deep step edges, suggesting that the carbonation reaction is locally diffusion-transport controlled within a fluid-mineral boundary layer and is the result of interface-coupled dissolution-precipitation. More extensive particle growth was also observed after ex situ experiments lasting for several hours. This AFM study contributes to an improved understanding of the mechanism of aqueous brucite carbonation at low temperature and PCO2 conditions and has implications for the development of mineral carbonation schemes involving brucite as well as silicates (e.g., serpentines) that contain 'brucite-layers' as structural components.

  13. Carbonate dissolution in nearshore terrigenous muds: the role of physical and biological reworking

    SciTech Connect

    Aller, R.C.

    1982-01-01

    Because shallow marine sediments generally underlie waters which are saturated with respect to aragonite and calcite, physical-chemical dissolution of carbonate in these environments is sometimes discounted. The present investigation, shows such an assumption to be unwarranted. In this case, study of terrigenous mud deposits for Long Island Sound, USA demonstrates extensive dissolution of molluscan shell debris near the sediment-water interface. Net buildup of carbonate varies significantly between different regions of the Sound despite fairly uniform production of shell debris and similar total sedimentation rates. Aside from this apparent discrepancy between rate of supply and net carbonate sedimentation, evidence for carbonate dissolution comes from the pitting of shells, elevated Ca/sup + +/ levels in pore water, and calculated undersaturation of pore waters with respect to carbonate minerals. Maximum shell preservation occurs in regions where physical disturbances cause poorly developed bottom communities, while only minimal preservation occurs where benthic communities are best developed and biogenic reworking is greatest.

  14. Influence of carbides and microstructure of CoCrMo alloys on their metallic dissolution resistance.

    PubMed

    Valero-Vidal, C; Casabán-Julián, L; Herraiz-Cardona, I; Igual-Muñoz, A

    2013-12-01

    CoCrMo alloys are passive and biocompatible materials widely used as joint replacements due to their good mechanical properties and corrosion resistance. Electrochemical behaviour of thermal treated CoCrMo alloys with different carbon content in their bulk alloy composition has been analysed. Both the amount of carbides in the CoCrMo alloys and the chemical composition of the simulated body fluid affect the electrochemical properties of these biomedical alloys, thus passive dissolution rate was influenced by the mentioned parameters. Lower percentage of carbon in the chemical composition of the bulk alloy and thermal treatments favour the homogenization of the surface (less amount of carbides), thus increasing the availability of Cr to form the oxide film and improving the corrosion resistance of the alloy.

  15. Influence of rapeseed phospholipids on ibuprofen dissolution from solid dispersions.

    PubMed

    Sosada, M; Gorecki, M; Pasker, B

    2006-08-01

    The dissolution profiles of ibuprofen (IB) from solid dispersions prepared by the solvent evaporation method, containing the rapeseed lecithin ethanol soluble fraction (LESF) or rapeseed phosphatidylcholine (RPC) have been determined. The effect of incorporation of PEG 4,000 or PEG 8,000 in the solid dispersions on the controlled-release of IB was also investigated. Dissolution studies conducted in double-distilled water using the paddle dissolution apparatus showed that the initial dissolution rate (IDR) within the first 5 min and the maximum percent of dissolved IB of IB/LESF were double of those of IB/RPC (both in ratio 4:1 w/w). The low amounts of LESF markedly increased dissolution of IB. Increasing of LESF concentration from 0 to 10 and 20% in solid dispersions produced 60 and 100% improvement of IB maximum dissolution level respectively, to compare with that of IB alone. PEG 4,000 caused the slightly decreasing in IB dissolution rate, while PEG 8,000 markedly improved the dissolution of IB in examined conditions.

  16. In situ measurements of calcium carbonate dissolution rates in deep-sea sediments

    NASA Astrophysics Data System (ADS)

    Berelson, W. M.; Hammond, D. E.; Cutter, G. A.

    1990-11-01

    Benthic fluxes of alkalinity, carbon dioxide, and oxygen have been measured using an in situ incubation chamber at three sites (MANOP Sites C and S and PACFLUX Site SC) in the central equatorial north Pacific. At two carbonate-rich sites (C and SC), a budget for oxygen, alkalinity, and TCO 2 fluxes indicate a net CaCO 3 dissolution rate of approximately 0.4 mmol m -2 day -1. This rate is only 20% of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deep-sea sediments and derived from in situ flux measurements in sediments of the southern California borderland. Organic matter oxidation in the sediment column provides the acid for 60-100% of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water. At a low-carbonate site (S), no carbonate dissolution in the sediment or on the sea floor is apparent, although sediment traps indicate a rain of CaCO 3 through 3400 m. The rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate, so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve, while organic carbon is largely oxidized before it can be physically removed.

  17. Calcium Carbonate Scale Dissolution in Water Stabilized by Carbon Dioxide Treatment

    DTIC Science & Technology

    1990-01-01

    in Aqueous Systems (E.A. Jenne, Ed.), ACS Symposium Series 93 (American Chemical Society, 1979); R. A. Bemer and J. W. Morse "Dissolution Kinetics of...Veyl. "A. J. Ellis, "The Solubility-of Calcite in Carbon Dioxide Solutions," American Journal of Science, Vol 257 (May 1959). "R. A. Bemer and J. W...Morse. "L. N. Plummer; T. M. L. Wigley, and D. L. Parkhurst. ISR. A. Bemer and J. W. Morse. 13 0.9 - 0.8 EXPLANATION 0 kja. = k2&,ca0.+ k%,o ! 0.7k ky

  18. The Influence of Various Process Parameters on Dissolution Kinetics and Mechanism of Struvite Seed Crystals

    NASA Astrophysics Data System (ADS)

    Ariyanto, Eko; Ang, Ha Ming; Sen, Tushar Kanti

    2017-07-01

    The basic understanding of struvite dissolution chemistry is essential to designers and operators for anticipating struvite problem and remediating existing struvite damage in a wastewater treatment. The dissolution kinetic of struvite seed crystals is very important parameters to determine a solid substance entering in solvent to yield a solution. In this study the dissolution kinetics of struvite crystals (MgNH4PO4·6H2O) in deionized water was investigated in a batch crystallizer. The effects of stirrer speeds, temperature and seed crystals size on the dissolution rate were determined. The results showed that an increase of struvite dissolution rate with increasing stirring speed. Struvite dissolution occurred via a diffusion-controlled mechanism in the range of stirrer speeds 120-400 rpm but became interfacial-reaction-controlling at over 400 rpm. The influence of temperature on dissolution kinetic of struvite crystals was also investigated at stirrer speeds of 200 and 500 rpm. The dissolution rates increased with an increase in the temperature for both stirrer speeds. The change in activation energies at different stirrer speeds confirmed that the change of dissolution mechanism from a diffusion-controlled mechanism at low stirrer speeds to an interfacial-reaction-controlled mechanism at higher stirrer speeds. The dissolution rate of struvite crystals increased with smaller crystal sizes.

  19. Dissolution and carbonation of Portlandite [Ca(OH)2] single crystals.

    PubMed

    Ruiz-Agudo, Encarnación; Kudłacz, Krzysztof; Putnis, Christine V; Putnis, Andrew; Rodriguez-Navarro, Carlos

    2013-10-01

    The dissolution and carbonation of portlandite (Ca(OH)2) single crystals was studied by a combination of in situ Atomic Force Microscopy, Scanning Electron Microscopy, and two-dimensional X-ray diffraction. The dissolution of portlandite {0001} surfaces in water proceeds by the formation and expansion of pseudohexagonal etch pits, with edges parallel to ⟨100⟩ directions. Etch pits on {010} surfaces are elongated along ⟨001⟩, with edges parallel to ⟨101⟩. The interaction between carbonate-bearing solutions and portlandite results in the dissolution of the substrate coupled with the precipitation of thick islands of CaCO3 that appear oriented on the portlandite substrate. Ex situ carbonation of portlandite in contact with air results in the formation of pseudomorphs that fully preserve the external shape of the original portlandite single crystals. Our observations suggest that portlandite carbonation in contact with air and carbonate-bearing solutions occurs by a similar mechanism, i.e. coupled dissolution-precipitation. Calcite grows epitaxially on {0001} portlandite surfaces with the following orientation: ⟨001⟩Cc∥ ⟨001⟩Port. Apparently, no porosity is generated during the reaction, which progresses through the formation of fractures. Our results are of relevance to many processes in which the carbonation of portlandite takes place, such as CO2 capture and storage or the carbonation of cementitious materials.

  20. Kinetics of carbonate mineral dissolution in CO2-acidified brines at storage reservoir conditions.

    PubMed

    Peng, Cheng; Anabaraonye, Benaiah U; Crawshaw, John P; Maitland, Geoffrey C; Trusler, J P Martin

    2016-10-20

    We report experimental measurements of the dissolution rate of several carbonate minerals in CO2-saturated water or brine at temperatures between 323 K and 373 K and at pressures up to 15 MPa. The dissolution kinetics of pure calcite were studied in CO2-saturated NaCl brines with molalities of up to 5 mol kg(-1). The results of these experiments were found to depend only weakly on the brine molality and to conform reasonably well with a kinetic model involving two parallel first-order reactions: one involving reactions with protons and the other involving reaction with carbonic acid. The dissolution rates of dolomite and magnesite were studied in both aqueous HCl solution and in CO2-saturated water. For these minerals, the dissolution rates could be explained by a simpler kinetic model involving only direct reaction between protons and the mineral surface. Finally, the rates of dissolution of two carbonate-reservoir analogue minerals (Ketton limestone and North-Sea chalk) in CO2-saturated water were found to follow the same kinetics as found for pure calcite. Vertical scanning interferometry was used to study the surface morphology of unreacted and reacted samples. The results of the present study may find application in reactive-flow simulations of CO2-injection into carbonate-mineral saline aquifers.

  1. Predicting carbonate mineral precipitation/dissolution events during progressive diagenesis of clastic rocks

    SciTech Connect

    Surdam, R.C.; MacGowan, D.B.; Dunn, T.L. ); Moraes, M. )

    1991-03-01

    There is an observable, regular progression of early and late carbonate cements that is separated by carbonate mineral dissolution in many sandstones during progressive burial and diagenesis. The distribution of early cements is a function of incipient hydration of framework grains, sulfate reduction, and bacterial methanogenesis. These early cements typically precipitate from the sediment water interace to burial depths corresponding to about 80C. The distribution of late carbonate cements is a function of the relationship of organic acid anions, aluminosilicate reactions and CO{sub 2} in formation waters. Elevated PCO{sub 2} in a fluid where the pH is buffered by organic acid anions or aluminosilicates results in precipitation of a late carbonate cement (typically ferroan); these late carbonate cements generally form over the temperature interval of 100-130C. The late and early carbonate cement events are separated in time by a period of carbonate mineral dissolution or nonprecipitation. This dissolution is related to the increase in concentration of carboxylic acid anions resulting from the thermocatalytic cracking of oxygen-bearing functional groups from kerogen and/or redox reactions involving kerogen. Examples of the importance of early carbonate cementation/decementation to hydrocarbon reservoirs include the Campos basin of Brazil and the U.S. Gulf Coast. An example of late carbonate cementation/decementation includes the Norphlet Formation. This observed sequence of cementation and decementation can be modeled, and the modeling results can be used to predict enhanced porosity in the subsurface.

  2. Experimental determination of natural carbonate rock dissolution rates with a focus on temperature dependency

    NASA Astrophysics Data System (ADS)

    Kirstein, Jens; Hellevang, Helge; Haile, Beyene G.; Gleixner, Gerd; Gaupp, Reinhard

    2016-05-01

    The denudation of carbonate rocks at landscape scale is controlled by factors like mineral composition, temperature, precipitation, runoff, fracture spacing and vegetation cover. Knowledge on carbonate denudation is important in order to understand landscape development and long-term terrestrial/marine carbon transport, but there are few laboratory studies done on weathering rates of natural carbonate rocks under the low temperatures relevant for glacial-interglacial periods. To enhance the understanding of carbonate dissolution kinetics we studied low-temperature dissolution reactions of various natural Triassic carbonate rocks belonging to the Lower Muschelkalk in Germany. We conducted batch and flow-through experiments investigating the direct correlation of dissolution rates with temperature, and to establish whether the fine-grained carbonate rocks (micrite) are more reactive than the coarser-grained sparitic limestones. By increasing the temperature from 5 to 26 °C far-from-equilibrium dissolution rates of micritic and sparitic limestone samples increased from 2.42 × 10- 07 to 10.88 × 10- 07 and 4.19 × 10- 07 to 7.74 × 10- 07 mol m- 2 s- 1, respectively (Specific Surface Areas (SSA) of about 0.006-0.01 m2/g). The dissolution rates of dolomite rock samples varied only slightly from 1.06 × 10- 07 to 2.02 × 10- 07 mol m- 2 s- 1 (SSA approximately 0.002 m2/g) in the temperature range 5-25 °C at circum-neutral pH. The obtained apparent activation energies are in the range of earlier experiments done at higher temperatures, but there is a distinct difference between the calcite in the micrite (~ 51 kJ/mol) and sparitic (~ 20-22 kJ/mol) lithologies, indicating that the dissolution mechanisms are not the same. Using these activation energies in modelling of natural carbonate denudation we see that there is a clear effect of changing temperature, but this is mostly through the increased solubility at lower temperatures and not through the increasing far

  3. Influence of cell culture medium composition on in vitro dissolution behavior of a fluoride-containing bioactive glass.

    PubMed

    Shah, Furqan A; Brauer, Delia S; Wilson, Rory M; Hill, Robert G; Hing, Karin A

    2014-03-01

    Bioactive glasses are used clinically for bone regeneration, and their bioactivity and cell compatibility are often characterized in vitro, using physiologically relevant test solutions. The aim of this study was to show the influence of varying medium characteristics (pH, composition, presence of proteins) on glass dissolution and apatite formation. The dissolution behavior of a fluoride-containing bioactive glass (BG) was investigated over a period of one week in Eagle's Minimal Essential Medium with Earle's Salts (MEM), supplemented with either, (a) acetate buffer, (b) 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer, (c) HEPES + carbonate, or (d) HEPES + carbonate + fetal bovine serum. Results show pronounced differences in pH, ion release, and apatite formation over 1 week: Despite its acidic pH (pH 5.8 after BG immersion, as compared to pH 7.4-8.3 for HEPES-containing media), apatite formation was fastest in acetate buffered (HEPES-free) MEM. Presence of carbonate resulted in formation of calcite (calcium carbonate). Presence of serum proteins, on the other hand, delayed apatite formation significantly. These results confirm that the composition and properties of a tissue culture medium are important factors during in vitro experiments and need to be taken into consideration when interpreting results from dissolution or cell culture studies.

  4. Comparison of Two Different Approaches to CO2 Dissolution Modeling in Geological Carbon Storage

    NASA Astrophysics Data System (ADS)

    van Nierop, E. A.; Saadatpoor, E.; Bryant, S. L.

    2011-12-01

    In geologic carbon sequestration there are three modes of storage that decrease the risk of leakage over a long period of time: residual, dissolution, and mineral trapping. Dissolution trapping is immobilization of CO2 as aqueous species are dissolved in previously uncontacted brine. The injected CO2 will dissolve in brine and the resulting brine-CO2 mixture will be slightly denser than the brine alone. Slow vertical flow of denser brine will cause further dissolution, as fresh brine is brought in contact with the CO2 phase. Hence, a compositional simulator that correctly models phase behavior is essential for geological CO2 storage simulation. The phase behavior model should predict the phase equilibrium compositions of the CO2-brine system and resulting densities of the phases in agreement with experimental data. In this work, we conduct a field study of CO2 storage in saline aquifers in Illinois and North Dakota. We compare two methods to model the phase behavior. First, a tuned Peng-Robinson equation of state (Kumar, 2004) is used. It is tuned using experimental data for solubility and density over the wide range of pressures, temperatures, and salinities that would be found in aquifer conditions. Second, an enhanced solubility model (Harvey, 1996) for CO2 Henry's constant is used. The Henry's constant is a function of pressure, temperature, and salinity. We study the effect of salinity, permeability heterogeneity, and vertical gridding on the two methods of dissolution modeling. The results of the two methods show good agreement in the amount of dissolution at higher salinities, which validates the consistency of each method in predicting the experimental data in that range, as reported in previously published studies. However, in lower salinities the tuned EOS method does not show a significant change in the solubility of CO2, which is inconsistent with the literature-reported increase in CO2 solubility as salinity decreases. Henry's method seems to give a

  5. Diurnal variation in rates of calcification and carbonate sediment dissolution in Florida Bay

    USGS Publications Warehouse

    Yates, K.K.; Halley, R.B.

    2006-01-01

    Water quality and circulation in Florida Bay (a shallow, subtropical estuary in south Florida) are highly dependent upon the development and evolution of carbonate mud banks distributed throughout the Bay. Predicting the effect of natural and anthropogenic perturbations on carbonate sedimentation requires an understanding of annual, seasonal, and daily variations in the biogenic and inorganic processes affecting carbonate sediment precipitation and dissolution. In this study, net calcification rates were measured over diurnal cycles on 27 d during summer and winter from 1999 to 2003 on mud banks and four representative substrate types located within basins between mud banks. Substrate types that were measured in basins include seagrass beds of sparse and intermediate density Thalassia sp., mud bottom, and hard bottom communities. Changes in total alkalinity were used as a proxy for calcification and dissolution. On 22 d (81%), diurnal variation in rates of net calcification was observed. The highest rates of net carbonate sediment production (or lowest rates of net dissolution) generally occurred during daylight hours and ranged from 2.900 to -0.410 g CaCO3 m-2 d-1. The lowest rates of carbonate sediment production (or net sediment dissolution) occurred at night and ranged from 0.210 to -1.900 g CaCO3 m -2 night-1. During typical diurnal cycles, dissolution during the night consumed an average of 29% of sediment produced during the day on banks and 68% of sediment produced during the day in basins. Net sediment dissolution also occurred during daylight, but only when there was total cloud cover, high turbidity, or hypersalinity. Diurnal variation in calcification and dissolution in surface waters and surface sediments of Florida Bay is linked to cycling of carbon dioxide through photosynthesis and respiration. Estimation of long-term sediment accumulation rates from diurnal rates of carbonate sediment production measured in this study indicates an overall average

  6. Bubble shrinkage and growth: A solution to carbon dioxide dissolution and solubility

    NASA Astrophysics Data System (ADS)

    Abolhasani, Milad; Kumacheva, Eugenia; Guenther, Axel

    2011-11-01

    Dynamic and equilibrium aspects of carbon dioxide transport across gas-liquid interfaces impact a wide range of technical, physiological and geological applications. We investigate carbon dioxide transport by continuously guiding a train of uniformly sized carbon dioxide bubbles and non-saturated liquid segments through a microchannel. The bubbles initially shrink and later expand. We quantitatively link the evolution of the bubble size to kinetic and equilibrium characteristics of carbon dioxide dissolution. While the initial velocity of carbon dioxide bubbles and the length of liquid segments significantly affect the dissolution of carbon dioxide, these parameters cannot be externally imposed, due to the dynamic nature of microscale gas-liquid flows. We use an automated microfluidic platform (gas impermeable) in combination with an image-based feedback control strategy to keep the dependent parameters constant and systematically determine the rate of carbon dioxide dissolution and the equilibrium solubility of carbon dioxide-liquid mixtures for a wide range of pressures, temperatures and liquids in a flowable format.

  7. 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

  8. Impact of pressure, salt concentration, and temperature on the convective dissolution of carbon dioxide in aqueous solutions.

    PubMed

    Loodts, V; Rongy, L; De Wit, A

    2014-12-01

    The convective dissolution of carbon dioxide (CO2) in salted water is theoretically studied to determine how parameters such as CO2 pressure, salt concentration, and temperature impact the short-time characteristics of the buoyancy-driven instability. On the basis of a parameter-free dimensionless model, we perform a linear stability analysis of the time-dependent concentration profiles of CO2 diffusing into the aqueous solution. We explicit the procedure to transform the predicted dimensionless growth rate and wavelength of the convective pattern into dimensional ones for typical laboratory-scale experiments in conditions close to room temperature and atmospheric pressure. This allows to investigate the implicit influence of the experimental parameters on the characteristic length and time scales of the instability. We predict that increasing CO2 pressure, or decreasing salt concentration or temperature destabilizes the system with regard to convection, leading to a faster dissolution of CO2 into salted water.

  9. CO2-induced dissolution of low permeability carbonates. Part II: Numerical modeling of experiments

    NASA Astrophysics Data System (ADS)

    Hao, Yue; Smith, Megan; Sholokhova, Yelena; Carroll, Susan

    2013-12-01

    We used the 3D continuum-scale reactive transport models to simulate eight core flood experiments for two different carbonate rocks. In these experiments the core samples were reacted with brines equilibrated with pCO2 = 3, 2, 1, 0.5 MPa (Smith et al., 2013 [27]). The carbonate rocks were from specific Marly dolostone and Vuggy limestone flow units at the IEAGHG Weyburn-Midale CO2 Monitoring and Storage Project in south-eastern Saskatchewan, Canada. Initial model porosity, permeability, mineral, and surface area distributions were constructed from micro tomography and microscopy characterization data. We constrained model reaction kinetics and porosity-permeability equations with the experimental data. The experimental data included time-dependent solution chemistry and differential pressure measured across the core, and the initial and final pore space and mineral distribution. Calibration of the model with the experimental data allowed investigation of effects of carbonate reactivity, flow velocity, effective permeability, and time on the development and consequences of stable and unstable dissolution fronts. The continuum scale model captured the evolution of distinct dissolution fronts that developed as a consequence of carbonate mineral dissolution and pore scale transport properties. The results show that initial heterogeneity and porosity contrast control the development of the dissolution fronts in these highly reactive systems. This finding is consistent with linear stability analysis and the known positive feedback between mineral dissolution and fluid flow in carbonate formations. Differences in the carbonate kinetic drivers resulting from the range of pCO2 used in the experiments and the different proportions of more reactive calcite and less reactive dolomite contributed to the development of new pore space, but not to the type of dissolution fronts observed for the two different rock types. The development of the dissolution front was much more

  10. Terraforming Mars: dissolution of carbonate rocks by cyanobacteria.

    PubMed

    Friedmann, E I; Hua, M; Ocampo-Friedmann, R

    1993-01-01

    One of the most difficult tasks in terraforming Mars is the release into the atmosphere of CO2 bound by the surface of Mars. Even if a sufficiently dense CO2 atmosphere can be created by appropriate technology, the maintenance of CO2 concentration remains a problem. As Mars lacks plate tectonics as well as active volcanism, an Earth-like carbon cycle cannot be reproduced there. We suggest that Matteia sp., a lime-boring cyanobacterium isolated from Negev desert rocks, be used to dissolve carbonate rocks both for initial release of CO2 and in design of a Martian carbon cycle.

  11. Experiment and Simulation Study of Hydrodynamic Dispersion and Finger Dynamics for Convective Dissolution of Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Liang, Y.; DiCarlo, D. A.; Hesse, M. A.

    2015-12-01

    Carbon capture and storage in deep geological formations has the potential to reduce anthropogenic CO2 emissions from industrial point sources. Dissolution of CO2 into the brine, resulting in stable stratification, has been identified as the key to long-term storage security. Here we present new analogue laboratory experiment method, advanced image processing method and optimized simulation method to characterize CO2 convective dissolution trapping process and gravitational finger behaviors, in order to study the effect of hydrodynamic dispersion on the CO2 convective dissolution process, as well as to study the effect of control physical parameters on the gravitational finger dynamics. Figure 1 shows the image processing method to analyze the finger dynamics. Understanding the effect of hydrodynamic dispersion and the finger dynamics are essential to evaluate whether convective dissolution occurs, as well as to predict how fast it occurs at the geological CO2 storage field scale. The effect of hydrodynamics dispersion and the finger dynamics can be applied to estimate the security of geological CO2 storage fields, in turn. Optimiezed simulation work is conducted to predict the CO2 dissolution rate at geological CO2 storage field. The large experimental assembly will allow us to quantify in detail for the first time the relationship between convective dissolution rate and the controlling factors of the system, including permeability and driven force, which could be essential to trapping process at Bravo Dome geological CO2 storage field. We complement the homogeneous experiments with a detailed study of the scaling law of the convective flux with dispersion effect. The advanced image processing method with Fourier's transform method allow us to understand the finger dynamics and corresponding control factors in porous media, for the first time. By applying the dispersion effect and finger dynamics we found from the experimental study, we optimize the simulation

  12. Ion-specific effects influencing the dissolution of tricalcium silicate

    SciTech Connect

    Nicoleau, L.; Schreiner, E.; Nonat, A.

    2014-05-01

    It has been recently demonstrated that the dissolution kinetics of tricalcium silicate (C{sub 3}S) is driven by the deviation from its solubility equilibrium. In this article, special attention is paid to ions relevant in cement chemistry likely to interact with C{sub 3}S. In order to determine whether specific effects occur at the interface C{sub 3}S–water, particular efforts have been made to model ion activities using Pitzer's model. It has been found that monovalent cations and monovalent anions interact very little with the surface of C{sub 3}S. On the other side, divalent anions like sulfate slow down the dissolution more strongly by modifying the surface charging of C{sub 3}S. Third, aluminate ions covalently bind to surface silicate monomers and inhibit the dissolution in mildly alkaline conditions. The formation and the breaking of these bonds depend on pH and on [Ca{sup 2+}]. Thermodynamic calculations performed using DFT combined with the COSMO-RS solvation method support the experimental findings.

  13. The Effect of Micrite on Velocity, Its Sensitivity to Pressure, and Dissolution of Carbonates

    NASA Astrophysics Data System (ADS)

    El Husseiny, A.; Vanorio, T.

    2014-12-01

    This study investigates the effect of micrite on the acoustic properties of well-controlled microstructures created in the laboratory to closely mimic carbonate rocks. In particular, we examine the effect of micrite content on the elastic stiffness rock, its sensitivity to pressure, and induced dissolution upon saturation with a reactive fluid. We followed Dunham's classification and fabricated the samples by mixing coarse (sand size) and very fine (micrite size) calcite grains in different ratios, with the addition of cement and then cold-compressing the mixture. The acoustic velocities were measured under bench-top conditions and as functions of confining pressure before and after the injection of a CO2aqueous solution. Our bench-top measurements indicated that micrite makes the frame of the carbonate samples stiffer. Since the sensitivity of the elastic stiffness to pressure decreases as the content of micrite increases (see figure 1), we hypothesize a stiffer pore structure (i.e., rounder pores) in micrite-richer fabrics. Furthermore, the presence of micrite makes the carbonate sample more reactive upon dissolution. The concentration of Ca+2 cations in the fluid measured at the outlet after the injection of the CO2 aqueous solution shows larger dissolution in the micrite-rich samples likely due to the higher surface area of the micrite aggregates. The content of micrite also seems to affect the evolution of stiffness as dissolution proceeds. As the content of micrite increases, the enhanced dissolution translates into a marked softening of the rock frame. We conclude that the content of micrite can play an important role in the complex rock-fluid interaction of carbonates as well as when comparing Gassmann's predictions to velocity measurements of saturated carbonates.

  14. Dissolution Trapping of Carbon Dioxide in Heterogeneous Aquifers.

    PubMed

    Soltanian, Mohamad Reza; Amooie, Mohammad Amin; Gershenzon, Naum; Dai, Zhenxue; Ritzi, Robert; Xiong, Fengyang; Cole, David; Moortgat, Joachim

    2017-07-05

    The geologic architecture in sedimentary reservoirs affects the behavior of density-driven flow and the dispersion of CO2-rich brine. The spatial organization and connectivity of facies types play an important role. Low-permeability facies may suppress fingering and reduce vertical spreading, but may also increase transverse mixing. This is more pronounced when geologic structures create preferential flow pathways through connected facies types. We perform high-resolution simulations of three-dimensional (3D) heterogeneous formations whose connectivity cannot be represented in two-dimensional models consistent with percolation theory. This work focuses on the importance of 3D facies-based heterogeneity and connectivity on advection-diffusion transport of dissolved CO2. Because the dissolution of CO2 and the subsequent density increase of brine are the driving force for gravitational instabilities, we model the phase behavior with the accurate cubic-plus-association equation-of-state, which accounts for the self-association of polar water molecules and the cross-association between CO2 and water. Our results elucidate how the spatial organization of facies affects the dynamics of CO2 convective mixing. Scaling relations for the evolution of a global dispersion-width provide insights that can be universally applied. The results suggest that the long-term evolution and scaling of dispersion are surprisingly similar for homogeneous and (binary and multiscale) heterogeneous porous media.

  15. Effect of Reservoir Anisotropy on Carbon Dioxide Dissolution-Induced Density-Driven Convection

    NASA Astrophysics Data System (ADS)

    Kneafsey, T. J.; Pruess, K.

    2011-12-01

    Sequestering carbon dioxide by injecting it into non-potable aquifers overlain by suitable cap rock is being widely considered and field tested to reduce greenhouse gas emissions to the atmosphere. Being less dense than local brine, supercritical carbon dioxide introduced into the aquifer will tend to spread beneath the cap rock. Numerical and experimental investigations have shown that beneath the buoyant carbon dioxide layer, carbon dioxide dissolution into the brine will increase the density of the brine, resulting in an unstable condition in which denser brine overlies less dense brine. This instability can lead to dissolution-induced density-driven convection of the carbon dioxide laden brine, enhancing dissolution and the permanence of the sequestration. We have performed a series of visualization and quantitative laboratory experiments with homogeneous, heterogeneous, and anisotropic media to examine this process. Our visualization experiments have shown dense finger formation and flow into the underlying brine. These experiments have led us to quantitative measurements of density-driven convection from carbon dioxide dissolution under a variety of conditions. These conditions include high and low permeability porous media, layered media, and fluids including pure water and various brines. Density-driven convection was quantified by measuring the carbon dioxide uptake rate for the systems, and comparing it to the predicted diffusive uptake rate. Uptake rates exceeding the diffusive uptake rate are indicative of convection. Our results show the effects of density-driven convection were smaller for lower permeability and higher salinity conditions, whereas strong convection occurred for pure water in a highly permeable medium. Quantitative tests investigating the effect of anisotropy were based on visualization test results and layered systems were used in the experiments. Detailed experimental results and interpretation of these tests will also be discussed.

  16. Macroscopic rates, microscopic observations, and molecular models of the dissolution of carbonate phases.

    SciTech Connect

    Duckworth, Owen W.; Cygan, Randall Timothy; Martin, Scot T.

    2004-05-01

    Bulk and surface energies are calculated for endmembers of the isostructural rhombohedral carbonate mineral family, including Ca, Cd, Co, Fe, Mg, Mn, Ni, and Zn compositions. The calculations for the bulk agree with the densities, bond distances, bond angles, and lattice enthalpies reported in the literature. The calculated energies also correlate with measured dissolution rates: the lattice energies show a log-linear relationship to the macroscopic dissolution rates at circumneutral pH. Moreover, the energies of ion pairs translated along surface steps are calculated and found to predict experimentally observed microscopic step retreat velocities. Finally, pit formation excess energies decrease with increasing pit size, which is consistent with the nonlinear dissolution kinetics hypothesized for the initial stages of pit formation.

  17. Influence of glyphosate on the copper dissolution in phosphate buffer

    NASA Astrophysics Data System (ADS)

    Coutinho, C. F. B.; Silva, M. O.; Machado, S. A. S.; Mazo, L. H.

    2007-01-01

    The electrochemical behavior of copper microelectrode in phosphate buffer in the presence of glyphosate was investigated by electrochemical techniques. It was observed that the additions of glyphosate in the phosphate buffer increased the anodic current of copper microelectrode and the electrochemical dissolution was observed. This phenomenon could be associated with the Cu(II) complexation by glyphosate forming a soluble complex. Physical characterization of the surface showed that, in absence of glyphosate, an insoluble layer covered the copper surface; on the other hand, in presence of glyphosate, it was observed a corroded copper surface with the formation of glyphosate complex in solution.

  18. A probabilistic assessment of calcium carbonate export and dissolution in the modern ocean

    NASA Astrophysics Data System (ADS)

    Battaglia, G.; Steinacher, M.; Joos, F.

    2015-12-01

    The marine cycle of calcium carbonate (CaCO3) is an important element of the carbon cycle and co-governs the distribution of carbon and alkalinity within the ocean. However, CaCO3 fluxes and mechanisms governing CaCO3 dissolution are highly uncertain. We present an observationally-constrained, probabilistic assessment of the global and regional CaCO3 budgets. Parameters governing pelagic CaCO3 export fluxes and dissolution rates are sampled using a Latin-Hypercube scheme to construct a 1000 member ensemble with the Bern3D ocean model. Ensemble results are constrained by comparing simulated and observation-based fields of excess dissolved calcium carbonate (TA*). The minerals calcite and aragonite are modelled explicitly and ocean-sediment fluxes are considered. For local dissolution rates either a strong, a weak or no dependency on CaCO3 saturation is assumed. Median (68 % confidence interval) global CaCO3 export is 0.82 (0.67-0.98) Gt PIC yr-1, within the lower half of previously published estimates (0.4-1.8 Gt PIC yr-1). The spatial pattern of CaCO3 export is broadly consistent with earlier assessments. Export is large in the Southern Ocean, the tropical Indo-Pacific, the northern Pacific and relatively small in the Atlantic. Dissolution within the 200 to 1500 m depth range (0.33; 0.26-0.40 Gt PIC yr-1) is substantially lower than inferred from the TA*-CFC age method (1 ± 0.5 Gt PIC yr-1). The latter estimate is likely biased high as the TA*-CFC method neglects transport. The constrained results are robust across a range of diapycnal mixing coefficients and, thus, ocean circulation strengths. Modelled ocean circulation and transport time scales for the different setups were further evaluated with CFC11 and radiocarbon observations. Parameters and mechanisms governing dissolution are hardly constrained by either the TA* data or the current compilation of CaCO3 flux measurements such that model realisations with and without saturation-dependent dissolution achieve

  19. A probabilistic assessment of calcium carbonate export and dissolution in the modern ocean

    NASA Astrophysics Data System (ADS)

    Battaglia, Gianna; Steinacher, Marco; Joos, Fortunat

    2016-05-01

    The marine cycle of calcium carbonate (CaCO3) is an important element of the carbon cycle and co-governs the distribution of carbon and alkalinity within the ocean. However, CaCO3 export fluxes and mechanisms governing CaCO3 dissolution are highly uncertain. We present an observationally constrained, probabilistic assessment of the global and regional CaCO3 budgets. Parameters governing pelagic CaCO3 export fluxes and dissolution rates are sampled using a Monte Carlo scheme to construct a 1000-member ensemble with the Bern3D ocean model. Ensemble results are constrained by comparing simulated and observation-based fields of excess dissolved calcium carbonate (TA*). The minerals calcite and aragonite are modelled explicitly and ocean-sediment fluxes are considered. For local dissolution rates, either a strong or a weak dependency on CaCO3 saturation is assumed. In addition, there is the option to have saturation-independent dissolution above the saturation horizon. The median (and 68 % confidence interval) of the constrained model ensemble for global biogenic CaCO3 export is 0.90 (0.72-1.05) Gt C yr-1, that is within the lower half of previously published estimates (0.4-1.8 Gt C yr-1). The spatial pattern of CaCO3 export is broadly consistent with earlier assessments. Export is large in the Southern Ocean, the tropical Indo-Pacific, the northern Pacific and relatively small in the Atlantic. The constrained results are robust across a range of diapycnal mixing coefficients and, thus, ocean circulation strengths. Modelled ocean circulation and transport timescales for the different set-ups were further evaluated with CFC11 and radiocarbon observations. Parameters and mechanisms governing dissolution are hardly constrained by either the TA* data or the current compilation of CaCO3 flux measurements such that model realisations with and without saturation-dependent dissolution achieve skill. We suggest applying saturation-independent dissolution rates in Earth system

  20. Eccentricity pacing of eastern equatorial Pacific carbonate dissolution cycles during the Miocene Climatic Optimum

    NASA Astrophysics Data System (ADS)

    Kochhann, Karlos G. D.; Holbourn, Ann; Kuhnt, Wolfgang; Channell, James E. T.; Lyle, Mitch; Shackford, Julia K.; Wilkens, Roy H.; Andersen, Nils

    2016-09-01

    The Miocene Climatic Optimum (MCO; ~16.9 to 14.7 Ma) provides an outstanding opportunity to investigate climate-carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (δ18O) and carbon (δ13C) isotope records (5-12 kyr time resolution) spanning the late early to middle Miocene interval (18 to 13 Ma) at Integrated Ocean Drilling Program (IODP) Site U1335 (eastern equatorial Pacific Ocean). The U1335 stable isotope series track the onset and development of the MCO as well as the transitional climatic phase culminating with global cooling and expansion of the East Antarctic Ice Sheet at ~13.8 Ma. We integrate these new data with published stable isotope, geomagnetic polarity, and X-ray fluorescence (XRF) scanner-derived carbonate records from IODP Sites U1335, U1336, U1337, and U1338 on a consistent, astronomically tuned timescale. Benthic isotope and XRF scanner-derived CaCO3 records depict prominent 100 kyr variability with 400 kyr cyclicity additionally imprinted on δ13C and CaCO3 records, pointing to a tight coupling between the marine carbon cycle and climate variations. Our intersite comparison further indicates that the lysocline behaved in highly dynamic manner throughout the MCO, with >75% carbonate loss occurring at paleodepths ranging from ~3.4 to ~4 km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (δ18O minima) and δ13C decreases, implying that climate-carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial-interglacial pattern, where dissolution maxima correspond to δ13C maxima and δ18O minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.

  1. HLW glass dissolution in the presence of magnesium carbonate: Diffusion cell experiment and coupled modeling of diffusion and geochemical interactions

    NASA Astrophysics Data System (ADS)

    Debure, Mathieu; De Windt, Laurent; Frugier, Pierre; Gin, Stéphane

    2013-11-01

    The influence of diffusion of reactive species in aqueous solutions on the alteration rate of borosilicate glass of nuclear interest in the presence of magnesium carbonate (hydromagnesite: 4MgCO3·Mg(OH)2·4H2O) is investigated together with the ability of coupled chemistry/transport models to simulate the processes involved. Diffusion cells in which the solids are separated by an inert stainless steel sintered filter were used to establish parameters for direct comparison with batch experiments in which solids are intimately mixed. The chemistry of the solution and solid phases was monitored over time by various analytical techniques including ICP-AES, XRD, and SEM. The primary mechanism controlling the geochemical evolution of the system remains the consumption of silicon from the glass by precipitation of magnesium silicates. The solution chemistry and the dissolution and precipitation of solid phases are correctly described by 2D modeling with the GRAAL model implemented in the HYTEC reactive transport code. The spatial symmetry of the boron concentrations in both compartments of the cells results from dissolution coupled with simple diffusion, whereas the spatial asymmetry of the silicon and magnesium concentrations is due to strong coupling between dissolution, diffusion, and precipitation of secondary phases. A sensitivity analysis on the modeling of glass alteration shows that the choice of these phases and their thermodynamic constants have only a moderate impact whereas the thickness of the filter has a greater barrier effect.

  2. Influence of Bacillus subtilis cell walls and EDTA on calcite dissolution rates and crystal surface features.

    PubMed

    Friis, A K; Davis, T A; Figueira, M M; Paquette, J; Mucci, A

    2003-06-01

    This study investigates the influence of EDTA and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological features on the calcite [1014] surface. The calcite dissolution rates are compared at equivalent saturation indicies (SI) and relative to its dissolution behavior in distilled water (DW). Results indicate that the presence of metabolically inactive B. subtilis does not affect the dissolution rates significantly. Apparent increases in dissolution rates in the presence of the dead bacterial cells can be accounted for by a decrease of the saturation state of the solution with respect to calcite resulting from bonding of dissolved Ca2+ by functional groups on the cell walls. In contrast, the addition of EDTA to the experimental solutions results in a distinct increase in dissolution rates relative to those measured in DW and the bacterial cell suspensions. These results are partly explained by the 6.5-8 orders of magnitude greater stability of the Ca-EDTA complex relative to the Ca-B. subtilis complexes as well as its free diffusion to and direct attack of the calcite surface. Atomic force microscopy images of the [1014] surface of calcite crystals exposed to our experimental solutions reveal the development of dissolution pits with different morphologies according to the nature and concentration of the ligand. Highly anisotropic dissolution pits develop in the early stages of the dissolution reaction at low B. subtilis concentrations (0.004 mM functional group sites) and in DW. In contrast, at high functional group concentrations (4.0 mM EDTA or equivalent B. subtilis functional group sites), dissolution pits are more isotropic. These results suggest that the mechanism of calcite dissolution is modified by the presence of high concentrations of organic ligands. Since all the pits that developed on the calcite surfaces display some degree of anisotropy and dissolution rates are strongly SI dependent, the rate

  3. Mineral dissolution and precipitation in carbonate dominated terranes assessed using Mg isotopes

    NASA Astrophysics Data System (ADS)

    Tipper, E.; Calmels, D.; Gaillardet, J.; Galy, A.

    2013-12-01

    Carbonate weathering by carbonic acid consumes atmospheric CO2 during mineral dissolution, fixing it as aqueous bicarbonate over millennial time-scales. Ocean acidification has increased the solubility of CO2 in seawater by changing the balance of pH to alkalinity (the oceanic reservoir of carbon). This has lengthened the time-scale for CO2 sequestration by carbonate weathering to tens of thousands of years. At a global scale, the net consumption of CO2 is at least equal to that from silicate weathering, but there is far less work on carbonate weathering compared to silicate weathering because it has generally been assumed to be CO2 neutral on geological time-scales. Carbonate rocks are more readily dissolved than silicate rocks, meaning that their dissolution will likely respond much more rapidly to global environmental change when compared with the dissolution of silicate minerals. Although far less concentrated than Ca in many carbonates, Mg substitutes for Ca and is more concentrated than any other metal ion. Tracing the behavior of Mg in river waters, using Mg stable isotopes (26Mg/24Mg ratio expressed as delta26Mg in per mil units) is therefore a novel way to understand the complex series of dissolution/precipitation reactions that govern solute concentrations of Ca and Mg, and hence CO2 transfer by carbonate weathering. We present new Mg isotope data on a series of river and spring waters from the Jura mountains in North-East France. The stratigraphic column is relatively uniform throughout the Jura mountains and is dominated by limestones. As the limestone of the Jura Mountains were deposited in high-energy shallow water environments (shore line, lagoon and coral reefs), they are usually clay and organic poor. The delta26Mg of the local rocks is very constant at circa -4permil. The delta26Mg of the river waters is also fairly constant, but offset from the rock at -2.5permil. This is an intriguing observation because the dissolution of limestones is expected

  4. Acid dissolution experiments - Carbonates and the 6.8-micrometer bands in interplanetary dust particles

    NASA Technical Reports Server (NTRS)

    Sandford, S. A.

    1986-01-01

    A chemical dissolution experiment on an interplanetary dust particle (IDP) showed that carbonates, not acid-insoluble organic compounds, were responsible for virtually all the absorption at 6.8 micrometers seen in the infrared spectra of this particle. The IDP examined had an infrared spectrum characteristic of layer-lattice silicates and belongs to a class of IDP's whose spectra resemble those of protostellar objects like W33 A, which also exhibit a band at 6.8 micrometers.

  5. Acid dissolution experiments - Carbonates and the 6.8-micrometer bands in interplanetary dust particles

    NASA Technical Reports Server (NTRS)

    Sandford, S. A.

    1986-01-01

    A chemical dissolution experiment on an interplanetary dust particle (IDP) showed that carbonates, not acid-insoluble organic compounds, were responsible for virtually all the absorption at 6.8 micrometers seen in the infrared spectra of this particle. The IDP examined had an infrared spectrum characteristic of layer-lattice silicates and belongs to a class of IDP's whose spectra resemble those of protostellar objects like W33 A, which also exhibit a band at 6.8 micrometers.

  6. Acid dissolution experiments - Carbonates and the 6.8-micrometer bands in interplanetary dust particles

    NASA Astrophysics Data System (ADS)

    Sandford, S. A.

    1986-03-01

    A chemical dissolution experiment on an interplanetary dust particle (IDP) showed that carbonates, not acid-insoluble organic compounds, were responsible for virtually all the absorption at 6.8 micrometers seen in the infrared spectra of this particle. The IDP examined had an infrared spectrum characteristic of layer-lattice silicates and belongs to a class of IDP's whose spectra resemble those of protostellar objects like W33 A, which also exhibit a band at 6.8 micrometers.

  7. Effect of iron on the dissolution of bovine enamel powder in vitro by carbonated beverages.

    PubMed

    Kato, Melissa Thiemi; Maria, Andrea Gutierrez; Sales-Peres, Sílvia Helena de Carvalho; Buzalaf, Marília Afonso Rabelo

    2007-07-01

    The aim of this study was to evaluate, in vitro, the effect of iron on the dissolution of bovine enamel powder, when added to two carbonated beverages. Powdered enamel was produced by griding enamel fragments of bovine incisor in a steel pestle and mortar. Particles between 75 and 106 microm were selected using appropriated meshes. At time zero, the carbonated beverage (Coke or Sprite Zero) was added to powdered enamel (1 mg enamel powder/10 microL of beverage) and vortexed for 30 s. The sample was immediately centrifuged (11,000 rpm) for 30 s and the supernatant was removed at 1 min 40 s. This procedure was repeated five times with the beverage containing increasing ferrous sulphate concentrations (1.25, 2.5, 5, 10, 15, 30 and 60 mmol/L). The phosphate released in the medium was analysed spectrophotometrically. Data were analysed using ANOVA and Tukey's test (p<0.05). When iron at 30 and 60 mmol/L was added to Coke, a significant reduction in the dissolution of powdered enamel was observed when compared to control (11 and 17%, respectively), while lower iron concentrations did not have any effect on enamel powder dissolution. Regarding Sprite Zero, iron concentrations up to 10 mmol/L had no significant effect, while higher concentrations significantly increased enamel powder dissolution. The results suggest that iron can interfere with the dissolution of dental enamel powder in the presence of acidic beverages and the type of acid in these beverages seems to modulate this effect.

  8. Evolution of permeability and microstructure of tight carbonates due to numerical simulation of calcite dissolution

    NASA Astrophysics Data System (ADS)

    Miller, K. J.; Vanorio, T.; Keehm, Y.

    2016-12-01

    The current study concerns fundamental controls on fluid flow in tight carbonate rocks during CO2 injection, which has implications for understanding carbonate diagenesis, enhanced hydrocarbon recovery, and CO2 sequestration. Experimental CO2-injection studies find that initial pore geometry is important to the trajectory of permeability-porosity trends. For example, Vanorio et al., [2014] observed over an order of magnitude increase in permeability over <1% increase in connected porosity. The focus of this study is to understand the microstructural origins for these changes and determine - if not porosity - the primary controls on permeability during CO2-injection. Given the grain-scale nature of chemical reactions, we took a digital rock physics approach. A 4.5-mm tight carbonate core was imaged using X-ray micro-computed tomography. Fluid flow was simulated using the Lattice-Boltzmann Method (LBM) [Keehm, 2003]. Dissolution was modeled using a simple, phenomenological approach that coupled the local surface area and velocity to the local reaction rate. Though our model does not include diffusion, it builds upon basic physicochemical principles that underpin transport-limited reaction behavior, namely: (a) the reaction in in non-percolating pathways is fully buffered and (b) the reaction is most rapid in regions where solvent flux is high. The results of our dissolution model mimic experimental CO2-injection: increasing permeability by 300 mD over <1% increase in connected porosity. An analysis of the fluid flux distribution showed that fluid flow tended to channelize, localizing dissolution to paths of least hydraulic resistance. These so-called percolation pathways [Martys and Garboczi, 1992; David, 1993] constituted less than half of the connected pore volume, yet accommodated 90% of the volumetric flux. Interestingly, the percolation porosity exhibited two stages of evolution: (1) decrease at the onset of dissolution until channels were established; (2

  9. The Impact of Mineral Dissolution on Multiphase Flow in Permeable Carbonates

    NASA Astrophysics Data System (ADS)

    Krevor, S. C.; Niu, B.

    2015-12-01

    Carbon dioxide injection into deep saline aquifers is governed by a number of physicochemical processes at a broad range of spatial scales including mineral dissolution and precipitation, fluid flow, and capillary trapping. Past efforts have mostly focused on measuring the multiphase flow properties, capillarity, relative permeability, and residual trapping. However, the impact of fluid-rock interaction on these properties is less well understood. In this work we have made a series of measurements characterizing the impact of rock mineral dissolution on multiphase flow in three carbonate rocks. We used core flooding techniques to mimic reactive conditions representative of the near the well bore and far field regions of a carbonate reservoir CO2 injection project. Tests sequentially induced mineral dissolution and characterized the impacts on multiphase flow properties. Temperature retarded acid was used to uniformly dissolve calcite in Ketton, Estaillades, and Edward Brown rock cores. A single dissolution stages removed approximately 0.5% of the mass of the rocks and measurements of relative permeability and residual trapping were made after each stage along with mercury injection capillary pressure (MICP) to quantify the variation of in the pore size distribution. Three Stages were performed on each of carbonates rocks. Imaging with x-ray micro-CT and medical CT were used to quantify the porosity variation and observe the changes in pore structure and multiphase flow properties at scales from the um to the cm. The pore size distribution of the rocks was observed to both increase and become less uniform with progressive dissolution, as shown in Figure 1. For Ketton, the micro-pores, with size range from 0.01 um to 0.1um, have less been involved in the reaction than the macro-pores (10 um to 100 um). A larger spread in capillary trapping was seen around a characteristic initial-residual curve. Relative permeability changes with progressive dissolution was not well

  10. Influence of polycarboxylic acid chelating agents on the kinetics of the dissolution of metal oxides

    SciTech Connect

    Dyatlova, N.M.; Gorichev, I.G.; Dukhanin, V.S.; Malov, L.V.

    1986-11-01

    The factors influencing the rate of dissolution of metal oxides in aqueous solutions of acids in the presence of polycarboxylic acid chelating agents and other complexing agents have been quantitatively compared in this review, and the decisive role of the gradient of protons and electrons in the realization of this process has been revealed. The main hypotheses of the proposed conceptions of the electron-proton theory for the dissolution of metal oxides have been stated: 1) The rate-limiting step is charge transfer (first hypothesis); 2) The rate limiting step is the desorption of the dissolution products (second hypothesis). The applicability of the proposed electron-proton theory to the theoretical substantiation of all the experimentally observed kinetic features of the influence of various factors has been demonstrated. Practical recommendations for the effective utilization of the chelating agents considered for removing iron oxide surface deposits have been given.

  11. Impact of geoengineering with olivine dissolution on the carbon cycle and marine biology

    NASA Astrophysics Data System (ADS)

    Köhler, P.; Abrams, J.; Völker, C.; Wolf-Gladrow, D. A.; Hartmann, J.

    2012-04-01

    We investigate the potential of a specific geoengineering technique: the carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification. If details of the marine chemistry are taken into consideration, a new mass ratio of CO2 sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. These upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2 in examples for the rivers Amazon and Congo (Köhler et al., 2010). The secondary effects of the input of silicic acid connected with this approach leads in an ecosystem model (ReCOM2.0 in MITgcm) to species shifts aways from the calcifying species towards diatoms, thus altering the biological carbon pumps. Open ocean dissolution of olivine would sequestrate about 1 Pg CO2 per Pg olivine from which about 8% are caused by changes in the biological pumps (increase export of organic matter, decreased export of CaCO3). The chemical impact of open ocean dissolution of olivine (the increased alkalinity input) is therefore less efficient than dissolution on land, but leads due to different chemical impacts to a higher surface ocean pH enhancement to counteract ocean acidification. We finally investigate open ocean dissolution rates of up to 10 Pg olivine per year corresponding to geoengineering rates which might be of interest in the light of expected future emission (e.g. A2 scenario with emissions rising to 30 PgC/yr in 2100 AD). Those rates would still sequestrate only less than 20% of the emission until 2100, but would require that the nowadays available

  12. Tertiary carbonate-dissolution cycles on the Sierra Leone Rise, eastern equatorial Atlantic Ocean

    USGS Publications Warehouse

    Dean, W.E.; Gardner, J.V.; Cepek, P.

    1981-01-01

    Most of the Tertiary section on Sierra Leone Rise off northwest Africa consists of chalk, marl, and limestone that show cyclic alterations of clay-rich and clay-poor beds about 20-60 cm thick. On the basis of biostratigraphic accumulation rates, the cycles in Oligocene and Miocene chalk have periods which average about 44,000 years, and those in Eocene siliceous limestone have periods of 4000-27,000 years. Several sections were sampled in detail to further define the cycles in terms of content of CaCO3, clay minerals, and relative abundances of calcareous nannofossils. Extending information gained by analyses of Pleistocene cores from the continental margin of northwest Africa to the Tertiary cycles on Sierra Leone Rise, both dilution by noncarbonate material and dissolution of CaCO3 could have contributed to the observed relative variations in clay and CaCO3. However, dissolution of CaCO3 as the main cause of the carbonate-clay cycles on the Sierra Leone Rise, rather than dilution by clay, is suggested by the large amount of change (several thousand percent) in terrigenous influx required to produce the observed variations in amount of clay and by the marked increase in abundance of dissolution-resistant discoasters relative to more easily dissolved coccoliths in low-carbonate parts of cycles. The main cause of dissolution of CaCO3 was shoaling of the carbonate compensation depth (CCD) during the early Neogene and climatically induced fluctuations in the thickness of Antarctic Bottom Water. ?? 1981.

  13. Proton-promoted dissolution of α-FeOOH nanorods and microrods: size dependence, anion effects (carbonate and phosphate), aggregation and surface adsorption.

    PubMed

    Rubasinghege, Gayan; Kyei, Patrick K; Scherer, Michelle M; Grassian, Vicki H

    2012-11-01

    Iron-containing oxide nanoparticles are of great interest from a number of technological perspectives and they are also present in the natural environment. Although recent evidence suggests that particle size plays an important role in the dissolution of metal oxides, a detailed fundamental understanding of the influence of particle size is just beginning to emerge. In the current study, we investigate whether nanoscale size-effects are observed for the dissolution of iron oxyhydroxide under different conditions. The dissolution of two particle sizes of goethite, α-FeOOH in the nanoscale and microscale size regimes (herein referred to as nanorods and microrods), in aqueous suspensions at pH 2 is investigated. It is shown here that in the presence of nitrate, nanorods shows greater dissolution on both a per mass and per surface area basis relative to microrods, in agreement with earlier studies. In the presence of carbonate and phosphate, however, dissolution of α-FeOOH nanorods at pH 2 is significantly inhibited, despite the fact that these anions result in a three- to fivefold enhancement of the dissolution of microrods relative to the nitrate anion. Light scattering techniques and electron microscopy show that nanorod suspensions are less stable compared to microrod suspensions resulting in nanorod aggregation under conditions where microrods stay more dispersed. Furthermore, spectroscopic studies using ATR-FTIR spectroscopy show distinct differences in phosphate and carbonate adsorption on nanorods compared to microrods. These results demonstrate that aggregation and the details of surface adsorption are important in the dissolution behavior of nanoscale materials. Copyright © 2012 Elsevier Inc. All rights reserved.

  14. Hydrogeomorphic and ecological control on carbonate dissolution in a patterned landscape in South Florida

    NASA Astrophysics Data System (ADS)

    Dong, X.; Heffernan, J. B.; Murray, A. B.; Cohen, M. J.; Martin, J. B.

    2016-12-01

    The evolution of the critical zone both shapes and reflects hydrologic, geochemical, and ecological processes. These interactions are poorly understood in karst landscapes with highly soluble bedrock. In this study, we used the regular-dispersed wetland basins of Big Cypress National Preserve in Florida as a focal case to model the hydrologic, geochemical, and biological mechanisms that affect soil development in karst landscapes. We addressed two questions: (1) What is the minimum timescale for wetland basin development, and (2) do changes in soil depth feed back on dissolution processes and if so by what mechanism? We developed an atmosphere-water-soil model with coupled water-solute transport, incorporating major ion equilibria and kinetic non-equilibrium chemistry, and biogenic acid production via roots distributed through the soil horizon. Under current Florida climate, weathering to a depth of 2 m (a typical depth of wetland basins) would take 4000 6000 yrs, suggesting that landscape pattern could have origins as recent as the most recent stabilization of sea level. Our model further illustrates that interactions between ecological and hydrologic processes influence the rate and depth-dependence of weathering. Absent inundation, dissolution rate decreased exponentially with distance from the bedrock to groundwater table. Inundation generally increased bedrock dissolution, but surface water chemistry and residence time produced complex and non-linear effects on dissolution rate. Biogenic acidity accelerated the dissolution rate by 50 and 1,000 times in inundated and exposed soils. Phase portrait analysis indicated that exponential decreases in bedrock dissolution rate with soil depth could produce stable basin depths. Negative feedback between hydro-period and total basin volume could stabilize the basin radius, but the lesser strength of this mechanism may explain the coalescence of wetland basins observed in some parts of the Big Cypress Landscape.

  15. Ab initio simulation of dissolution energy and carbon activity in fcc Fe

    NASA Astrophysics Data System (ADS)

    Ridnyi, Ya. M.; Mirzoev, A. A.; Mirzaev, D. A.

    2017-07-01

    The equilibrium structure and properties of fcc iron with a carbon impurity were simulated ab initio using the WIEN2k software package. A procedure is proposed that enables the simulation of the magnetically disordered state of a system within the density functional theory. In the framework of this procedure, the value of the dissolution energy of carbon was calculated, which was 0.25 eV. Interaction energies between carbon atoms in the first, second, and third coordination spheres of each other were also determined, which were E 1 = 0.06 eV, E 2 = 0.1 eV, and E 3 = 0.005 eV. To verify the reliability of the obtained energy values, the activity of carbon was calculated by the Monte Carlo method. A good qualitative agreement of the calculated activity with the experimental data indicates the reliability of the obtained energy parameters.

  16. Dissolution-rate enhancement of fenofibrate by adsorption onto silica using supercritical carbon dioxide.

    PubMed

    Sanganwar, Ganesh P; Gupta, Ram B

    2008-08-06

    Dissolution rate of a poorly water-soluble drug, fenofibrate, is increased by adsorbing the drug onto silica. The adsorption is achieved by first dissolving the drug in supercritical carbon dioxide and then depressurizing the solution onto silica. Loadings of up to 27.5 wt.% drug onto silica are obtained. Since solvents are not used in the loading process, the fenofibrate/silica formulation is free of any residual solvent, and carbon dioxide is freely removed upon depressurization. The formulation is characterized using infrared spectroscopy, ultraviolet spectroscopy, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. Based on in vitro dissolution study, a significant increase in the dissolution rate (approximately 80% drug release in 20 min) of drug-silica formulation is observed as compared to micronized fenofibrate (approximately 20% drug release in 20 min), which can be attributed to increase in the surface area and decrease in the crystallinity of drug after adsorption onto silica. Two different formulations are compared: (A) amorphous fenofibrate/silica and (B) slightly crystalline fenofibrate/silica. The second formulation is found to be more stable on storage.

  17. Pore-scale simulation of carbonate dissolution in micro-CT images

    NASA Astrophysics Data System (ADS)

    Pereira Nunes, J. P.; Blunt, M. J.; Bijeljic, B.

    2016-02-01

    We present a particle-based method to simulate carbonate dissolution at the pore scale directly on the voxels of three-dimensional micro-CT images. The flow field is computed on the images by solving the incompressible Navier-Stokes equations. Rock-fluid interaction is modeled using a three-step approach: solute advection, diffusion, and reaction. Advection is simulated with a semianalytical pore-scale streamline tracing algorithm, diffusion by random walk is superimposed, while the reaction rate is defined by the flux of particles through the pore-solid interface. We derive a relationship between the local particle flux and the independently measured batch calcite dissolution rate. We validate our method against a dynamic imaging experiment where a Ketton oolite is imaged during CO2-saturated brine injection at reservoir conditions. The image-calculated increases in porosity and permeability are predicted accurately, and the spatial distribution of the dissolution front is correctly replicated. The experiments and simulations are performed at a high flow rate, in the uniform dissolution regime - Pe ≫ 1 and PeDa ≪ 1—thus extending the reaction throughout the sample. Transport is advection dominated, and dissolution is limited to regions with significant inflow of solute. We show that the sample-averaged reaction rate is 1 order of magnitude lower than that measured in batch reactors. This decrease is the result of restrictions imposed on the flux of solute to the solid surface by the heterogeneous flow field, at the millimeter scale.

  18. Influence of pH, particle size and crystal form on dissolution behaviour of engineered nanomaterials.

    PubMed

    Avramescu, M-L; Rasmussen, P E; Chénier, M; Gardner, H D

    2017-01-01

    Solubility is a critical component of physicochemical characterisation of engineered nanomaterials (ENMs) and an important parameter in their risk assessments. Standard testing methodologies are needed to estimate the dissolution behaviour and biodurability (half-life) of ENMs in biological fluids. The effect of pH, particle size and crystal form on dissolution behaviour of zinc metal, ZnO and TiO2 was investigated using a simple 2 h solubility assay at body temperature (37 °C) and two pH conditions (1.5 and 7) to approximately frame the pH range found in human body fluids. Time series dissolution experiments were then conducted to determine rate constants and half-lives. Dissolution characteristics of investigated ENMs were compared with those of their bulk analogues for both pH conditions. Two crystal forms of TiO2 were considered: anatase and rutile. For all compounds studied, and at both pH conditions, the short solubility assays and the time series experiments consistently showed that biodurability of the bulk analogues was equal to or greater than biodurability of the corresponding nanomaterials. The results showed that particle size and crystal form of inorganic ENMs were important properties that influenced dissolution behaviour and biodurability. All ENMs and bulk analogues displayed significantly higher solubility at low pH than at neutral pH. In the context of classification and read-across approaches, the pH of the dissolution medium was the key parameter. The main implication is that pH and temperature should be specified in solubility testing when evaluating ENM dissolution in human body fluids, even for preliminary (tier 1) screening.

  19. Purification and Dissolution of Carbon Nanotube Fibers Spun from the Floating Catalyst Method.

    PubMed

    Tran, Thang Q; Headrick, Robert J; Bengio, E Amram; Myo Myint, Sandar; Khoshnevis, Hamed; Jamali, Vida; Duong, Hai M; Pasquali, Matteo

    2017-10-11

    In this study, we apply a simple but effective oxidative purification method to purify carbon nanotube (CNT) fibers synthesized via a floating catalyst technique. After the purification treatment, the resulting CNT fibers exhibited significant improvements in mechanical and electrical properties with an increase in strength, Young's modulus, and electrical conductivity by approximately 81, 230, and 100%, respectively. With the successful dissolution of the CNT fibers in superacid, an extensional viscosity method could be applied to measure the aspect ratio of the CNTs constituting the fibers, whereas high-purity CNT thin films could be produced with a low resistance of 720 Ω/sq at a transmittance of 85%. This work suggests that the oxidative purification approach and dissolution process are promising methods to improve the purity and performance of CNT macroscopic structures.

  20. Combined effect of carbonate and biotite dissolution in landslides biases silicate weathering proxies

    NASA Astrophysics Data System (ADS)

    Emberson, R.; Galy, A.; Hovius, N.

    2017-09-01

    Long-term estimates of the dissolution of silicate rock are generally derived from a range of isotopic proxies, such as the radiogenic strontium isotope ratio (87Sr/86Sr), which are preserved in sediment archives. For these systems to fairly represent silicate weathering, the changes in isotopic ratios in terrestrial surface waters should correspond to changes in the overall silicate dissolution. This assumes that the silicate mineral phases that act as sources of a given isotope dissolve at a rate that is proportional to the overall silicate weathering. Bedrock landsliding exhumes large quantities of fresh rock for weathering in transient storage, and rapid weathering in these deposits is controlled primarily by dissolution of the most reactive phases. In this study, we test the hypothesis that preferential weathering of these labile minerals can decouple the dissolution of strontium sources from the actual silicate weathering rates in the rapidly eroding Western Southern Alps (WSA) of New Zealand. We find that rapid dissolution of relatively radiogenic calcite and biotite in landslides leads to high local fluxes in strontium with isotopic ratios that offer no clear discrimination between sources. These higher fluxes of radiogenic strontium are in contrast to silicate weathering rates in landslides that are not systematically elevated. On a mountain belt scale, radiogenic strontium fluxes are not coupled to volumes of recent landslides in large (>100 km2) catchments, but silicate weathering fluxes are. Such decoupling is likely due first to the broad variability in the strontium content of carbonate minerals, and second to the combination of radiogenic strontium released from both biotite and carbonate in recent landslides. This study supports previous work suggesting the limited utility of strontium isotopes as a system to study silicate weathering in the WSA. Crucially however, in settings where bedrock landsliding is a dominant erosive process there is

  1. Effect of magnesium carbonate on the solubility, dissolution and oral bioavailability of fenofibric acid powder as an alkalising solubilizer.

    PubMed

    Kim, Kyeong Soo; Kim, Jeong Hyun; Jin, Sung Giu; Kim, Dong Wuk; Kim, Dong Shik; Kim, Jong Oh; Yong, Chul Soon; Cho, Kwan Hyung; Li, Dong Xun; Woo, Jong Soo; Choi, Han-Gon

    2016-04-01

    To investigate the possibility of developing a novel oral pharmaceutical product using fenofibric acid instead of choline fenofibrate, the powder properties, solubility, dissolution and pharmacokinetics in rats of fenofibrate, choline fenofibrate and fenofibric acid were compared. Furthermore, the effect of magnesium carbonate, an alkalising agent on the solubility, dissolution and oral bioavailability of fenofibric acid was assessed, a mixture of fenofibric acid and magnesium carbonate being prepared by simple blending at a weight ratio of 2/1. The three fenofibrate derivatives showed different particle sizes and melting points with similar crystalline shape. Fenofibric acid had a significantly higher aqueous solubility and dissolution than fenofibrate, but significantly lower solubility and dissolution than choline fenofibrate. However, the fenofibric acid/magnesium carbonate mixture greatly improved the solubility and dissolution of fenofibric acid with an enhancement to levels similar with those for choline fenofibrate. Fenofibric acid gave lower plasma concentrations, AUC and Cmax values compared to choline fenofibrate in rats. However, the mixture resulted in plasma concentrations, AUC and Cmax values levels not significantly different from those for choline fenofibrate. Specifically, magnesium carbonate increased the aqueous solubility, dissolution and bioavailability of fenofibric acid by about 7.5-, 4- and 1.6-fold, respectively. Thus, the mixture of fenofibric acid and magnesium carbonate at the weight ratio of 2/1 might be a candidate for an oral pharmaceutical product with improved oral bioavailability.

  2. Influence of Coformer Stoichiometric Ratio on Pharmaceutical Cocrystal Dissolution: Three Cocrystals of Carbamazepine/4-Aminobenzoic Acid

    PubMed Central

    Li, Zi; Matzger, Adam J.

    2016-01-01

    Cocrystallization is a technique to optimize solid forms that shows great potential to improve the solubility of active pharmaceutical ingredients (APIs). In some systems, an API can form cocrystals in multiple stoichiometries with the same coformer. However, it remains unclear how coformer stoichiometry influences solubility. This paper investigates the pharmaceutical:coformer pair carbamazepine (CBZ)/p-aminobenzoic acid (PABA); both CBZ/PABA 1:1 and 2:1 cocrystals are known, and a novel 4:1 CBZ/PABA cocrystal is reported here. The 4:1 cocrystal is structurally characterized, and phase stability data suggest that it is a thermodynamically unstable form. Dissolution experiments show that there is no correlation between the cocrystal stoichiometry and dissolution rate in this system. On the other hand, with the relatively weak intermolecular interactions, metastable forms can be beneficial to dissolution rate, which suggests that more effort should be devoted to cocrystal production with kinetic growth methods. PMID:26837376

  3. Permeability evolution due to dissolution and precipitation of carbonates using reactive transport modeling in pore networks

    NASA Astrophysics Data System (ADS)

    Nogues, Juan P.; Fitts, Jeffrey P.; Celia, Michael A.; Peters, Catherine A.

    2013-09-01

    A reactive transport model was developed to simulate reaction of carbonates within a pore network for the high-pressure CO2-acidified conditions relevant to geological carbon sequestration. The pore network was based on a synthetic oolithic dolostone. Simulation results produced insights that can inform continuum-scale models regarding reaction-induced changes in permeability and porosity. As expected, permeability increased extensively with dissolution caused by high concentrations of carbonic acid, but neither pH nor calcite saturation state alone was a good predictor of the effects, as may sometimes be the case. Complex temporal evolutions of interstitial brine chemistry and network structure led to the counterintuitive finding that a far-from-equilibrium solution produced less permeability change than a nearer-to-equilibrium solution at the same pH. This was explained by the pH buffering that increased carbonate ion concentration and inhibited further reaction. Simulations of different flow conditions produced a nonunique set of permeability-porosity relationships. Diffusive-dominated systems caused dissolution to be localized near the inlet, leading to substantial porosity change but relatively small permeability change. For the same extent of porosity change caused from advective transport, the domain changed uniformly, leading to a large permeability change. Regarding precipitation, permeability changes happen much slower compared to dissolution-induced changes and small amounts of precipitation, even if located only near the inlet, can lead to large changes in permeability. Exponent values for a power law that relates changes in permeability and porosity ranged from 2 to 10, but a value of 6 held constant when conditions led to uniform changes throughout the domain.

  4. Influence of EDTA and dentine in tissue dissolution ability of sodium hypochlorite.

    PubMed

    de Almeida, Luiza Helena Silva; Leonardo, Natália Gomes e Silva; Gomes, Ana Paula Neutzling; Souza, Erick Miranda; Pappen, Fernanda Geraldes

    2015-04-01

    This study verified whether ethylenediaminetetraacetic acid (EDTA) influences the pulp tissue dissolution capability of different concentrations of NaOCl, in the presence of dentine. NaOCl and EDTA solutions were simultaneously mixed in flasks either containing a dentine disc or those not containing a dentine disc. Previously weighed bovine pulp tissues were immersed in the solutions for 5, 15 and 30 min. The weight loss was measured. The dissolution tests were performed in triplicate. Univariate analysis of variance, along with further Tukey's honestly significant difference pairwise comparisons, was used to verify the effect of EDTA, different concentrations of NaOCl, dentine and time of incubation on the tissue dissolution. Higher concentrations of NaOCl increased the tissue dissolution. EDTA reduced the capacity of NaOCl to dissolve pulp tissue, even in presence of dentine. Dentine negatively affects the capacity of NaOCl to dissolve pulp tissue. In conclusion, the presence of EDTA and dentine negatively affects the tissue dissolution ability of NaOCl.

  5. Coarse fraction fluctuations in pelagic carbonate sediments from the tropical Indian Ocean: A 1500-kyr record of carbonate dissolution

    NASA Astrophysics Data System (ADS)

    Bassinot, Franck C.; Beaufort, Luc; Vincent, Edith; Labeyrie, Laurent D.; Rostek, Frauke; Müller, Peter J.; Quidelleur, Xavier; Lancelot, Yves

    1994-08-01

    Appendix Table Al Is available with entire article onmicrofiche. Order from the American Geophysical Union, 2000Florida Avenue, N.W., Washington, D.C. 20009. DocumentP94-001; $2.50. Payment must accompany order.We examined coarse fraction contents of pelagic carbonates deposited between 2000-and 3700-m water depth in the tropical Indian Ocean using Ocean Drilling Program (ODP) sites 722 (Owen Ridge, Arabian Sea) and 758 (Ninetyeast Ridge, eastern equatorial Indian Ocean), and four giant piston cores collected by the French R/V Marion Dufresne during the SEYMAMA expedition. Over the last 1500 kyr, coarse fraction records display high-amplitude oscillations with an irregular wavelength on the order of ˜500 kyr. These oscillations can be correlated throughout the entire equatorial Indian Ocean, from the Seychelles area eastward to the Ninetyeast Ridge, and into the Arabian Sea. Changes in grain size mainly result from changes in carbonate dissolution as evidenced by the positive relationship between coarse fraction content and a foraminiferal preservation index based on test fragmentation. The well-known "mid-Bruhes dissolution cycle"represents the last part of this irregular long-term dissolution oscillation. The origin of this long-term oscillation is still poorly understood. Our observations suggest that it is not a true cycle (it has an irregular wavelength) and we propose that it may result from long-term changes in Ca++flux to the ocean. Sites 722 and 758 δ18O records provide a high-resolution stratigraphy that allows a detailed intersite comparison of the two coarse fraction records over the last 1500 kyr. Site 722 (2030 m) lies above the present and late Pleistocene lysocline. The lysocline shoaled to the position of site 758 (2925 m) only during the interglacial intervals that occurred between about 300 and 500 ka (Peterson and Prell, 1985a). Despite these supralysoclinal positions of the two sites, short-term changes in coarse fraction contents are

  6. CO2-induced dissolution of low permeability carbonates. Part I: Characterization and experiments

    NASA Astrophysics Data System (ADS)

    Smith, Megan M.; Sholokhova, Yelena; Hao, Yue; Carroll, Susan A.

    2013-12-01

    The effect of elevated dissolved CO2 concentrations on compositionally and structurally distinct carbonate sample cores from the Weyburn-Midale CO2-enhanced oil recovery and storage site (Canada) was measured from analysis of 3-D sample characterization and fluid chemistry data from core-flood experiments. Experimental conditions (60 °C; 24.8 MPa confining pressure) and brine composition were chosen to mimic in situ reservoir conditions. Mineralogy and pore space distributions within the eight individual cores were characterized with X-ray computed microtomography and scanning electron microscopy both before and after exposure to brine with 0.5 ⩽ pCO2 ⩽ 3 MPa, while solution chemistry and differential fluid pressures were monitored during experiments. Our experimental study aimed to quantify the relationship between fluid flow, heterogeneity, and reaction specific to carbon storage at the Weyburn-Midale field by integrating characterization imaging, pressure data, and solution chemistry. Through the use of non-invasive microtomographic imaging, a variety of dissolution behaviors were observed, with variable effects on the evolution of solution chemistry and permeability as a result of heterogeneity within these two relatively low permeability carbonate samples. Similar-sized, evenly distributed pores, and steadily advancing dissolution fronts suggested that uniform flow velocities were maintained throughout the duration of the higher permeability “Marly” dolostone core experiments. The development of unstable dissolution fronts and fast pathways occurred in the “Vuggy” sample experiments when fluid velocities varied widely within the sample (as a result of increased pore structure heterogeneity). The overall effect of fast pathway development was to increase bulk permeability values by several orders of magnitude, allowing CO2-acidified fluids to travel through the cores largely unmodified by carbonate mineral reaction, as indicated by a lack of change

  7. 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

  8. Microfluidics experiments of dissolution in a fracture. Influence of Damköhler and Péclet numbers, and of the geometry on the dissolution pattern

    NASA Astrophysics Data System (ADS)

    Osselin, Florian; Budek, Agnieszka; Cybulski, Olgierd; Szymczak, Piotr

    2015-04-01

    Dissolution of natural rocks is an ever present phenomenon in nature. The shaping of natural landscapes by the dissolution of limestone gives for example birth to exceptional features like karsts. Currently dissolution is also at the heart of key research topics as Carbon Capture and Storage or Enhanced Oil Recovery. The basics principles of dissolution are well-known, however, the sheer amount of different patterns arising from these mechanisms and the strong dependency on parameters such as pore network, chemical composition and flow rate, make it particularly difficult to study theoretically and experimentally. In this study we present a microfluidic experiment simulating the behavior of a dissolving fluid in a fracture. The experiments consist of a chip of gyspum inserted between two polycarbonate plates and subjected to a constant flow rate of pure water. The point in using microfluidics is that it allows a complete control on the experimental parameters such as geometry and chemical composition of the porous medium, flow rate, fracture aperture, roughness of the fracture walls, and an in situ observation of the geometry evolution which is impossible with 3D natural rocks. Thanks to our experiments we have been able to cover the whole range of dissolution patterns, from wormholing or DLA fingering to homogeneous dissolution, by changing Péclet and Damköhler numbers. Moreover, we have been able to tweak the geometry of our artificial fracture, inserting finger seeds or non-dissolvable obstacles. The comparison of the experimental patterns with the numerical dissolution code dissol (Szymczak and Ladd 2011) has then shown a very good correlation of the patterns, giving confidence in both experiments and modeling.

  9. 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

    Microbial reduction of ferric iron is partly dependent on Fe hydroxide particle size: nanosized Fe hydroxides greatly exceed the bioavailability of their counterparts larger than 1 μm. Citrate as a low molecular weight organic acid can likewise stabilize colloidal suspensions against aggregation by electrostatic repulsion but also increase Fe bioavailability by enhancing Fe hydroxide solubility. The aim of this study was to see whether adsorption of citrate onto surfaces of large ferrihydrite aggregates results in the formation of a stable colloidal suspension by electrostatic repulsion and how this effect influences microbial Fe reduction. Furthermore, we wanted to discriminate between citrate-mediated colloid stabilization out of larger aggregates and ferrihydrite dissolution and their influence on microbial Fe hydroxide reduction. Dissolution kinetics of ferrihydrite aggregates induced by different concentrations of citrate and humic acids were compared to microbial reduction kinetics with Geobacter sulfurreducens. Dynamic light scattering results showed the formation of a stable colloidal suspension and colloids with hydrodynamic diameters of 69 (±37) to 165 (± 65) nm for molar citrate:Fe ratios of 0.1 to 0.5 and partial dissolution of ferrihydrite at citrate:Fe ratios ⩾ 0.1. No dissolution or colloid stabilization was detected in the presence of humic acids. Adsorption of citrate, necessary for dissolution, reversed the surface charge and led to electrostatic repulsion between sub-aggregates of ferrihydrite and colloid stabilization when the citrate:Fe ratio was above a critical value (⩽ 0.1). Lower ratios resulted in stronger ferrihydrite aggregation instead of formation of a stable colloidal suspension, owing to neutralization of the positive surface charge. At the same time, microbial ferrihydrite reduction increased from 0.029 to 0.184 mM h-1 indicating that colloids stabilized by citrate addition enhanced microbial Fe reduction. Modelling of

  10. Experimental Study of Convective Dissolution of Carbon Dioxide in Heterogeneous Media

    NASA Astrophysics Data System (ADS)

    Liang, Y.; DiCarlo, D. A.; Hesse, M. A.

    2013-12-01

    Carbon capture and storage in deep geological formations has the potential to reduce anthropogenic carbon dioxide (CO2) emissions from industrial point sources. The technology is only viable, if the long-term security of the geological CO2 storage can be demonstrated. Dissolution of CO2 into the brine, resulting in stable stratification, has been identified as the key to long-term storage security. Here we present new analogue laboratory experiments to characterize convective dissolution and to study the effect of porosity and permeability heterogeneity on the CO2 dissolution rate. Understanding the effect of heterogeneity is essential to evaluate if convective dissolution occurs in the field and, in turn, to estimate the security of geological CO2 storage fields. In particular we want to test if the strong heterogeneity observed at the Bravo Dome natural CO2 field can prevent convective currents, which may explain the persistence of free phase CO2 over millennia. Initial laboratory experiments in homogeneous media confirm that the non-classical scaling of the convective flux scales with the 4/5 power of the Rayleigh number that has recently been reported. The large experimental assembly will allow us to quantify for the first time the relationship between wavenumber of the convective motion and the Rayleigh number of the system, which could be essential to trapping process at Bravo Dome. Figure 1 shows the number of fingers that we can observe in our new experimental setup. Figure 2 shows the same photograph that has been processed to enhance the visibility of the dense plumes descending from the interface. Also we plan to complement the homogeneous experiments with a detailed study of the scaling law of the convective flux in heterogeneous, layered media; in particular. Low permeability layers are ubiquitous in geological storage formations and have been observed at Bravo Dome. We plan to measure the reduction in the convective flux due to these barriers compared

  11. Dissolution of CO2 in Brines and Mineral Reactions during Geological Carbon Storage: AN Eor Experiment

    NASA Astrophysics Data System (ADS)

    Bickle, M. J.; Chapman, H.; Galy, A.; Kampman, N.; Dubacq, B.; Ballentine, C. J.; Zhou, Z.

    2015-12-01

    Dissolution of CO2 in formation brines is likely to be a major process which stabilises stored CO2 on longer time scales and mitigates CO2 migrating through storage complexes. However very little is known about the likely rates of CO2 dissolution as CO2 flows through natural heterogeneous brine filled reservoirs. Here we report the results of sampling fluids over 6 months after a phase of CO2 injection commenced for enhanced oil recovery coupled with injection of isotopically enriched 3He and 129Xe. Modelling of the changes in fluid chemistry has previously been interpreted to indicate significant dissolution of silicate minerals where fluids remained close to saturation with calcite. These calculations, which are based on modal decomposition of changes in cation concentrations, are supported by changes in the isotopic compositions of Sr, Li and Mg. Analysis of Sr-isotopic compositions of samples from outcrops of the Frontier Formation, which forms the reservoir sampled by the EOR experiment, reveals substantial heterogeneity. Silicate mineral compositions have 87Sr/86Sr ratios between 0.709 and 0.719 whereas carbonate cements have values around 0.7076. Calculation of CO2 dissolution based on simplified 2-D flow models shows that fluids likely sample reservoir heterogeneities present on a finer scale with CO2 fingers occupying the most permeable horizons and most water flow in the adjacent slightly less permeable zones. Smaller time scale variations in 87Sr/86Sr ratios are interpreted to reflect variations in flow paths on small length scales driven by invading CO2.

  12. Evolution of permeability and microstructure of tight carbonates due to numerical simulation of calcite dissolution

    NASA Astrophysics Data System (ADS)

    Miller, Kevin; Vanorio, Tiziana; Keehm, Youngseuk

    2017-06-01

    The current study concerns fundamental controls on fluid flow in tight carbonate rocks undergoing CO2 injection. Tight carbonates exposed to weak carbonic acid exhibit order of magnitude changes in permeability while maintaining a nearly constant porosity with respect to the porosity of the unreacted sample. This study aims to determine—if not porosity—what are the microstructural changes that control permeability evolution in these rocks? Given the pore-scale nature of chemical reactions, we took a digital rock physics approach. Tight carbonate mudstone was imaged using X-ray microcomputed tomography. We simulated calcite dissolution using a phenomenological numerical model that stands from experimental and microstructural observations under transport-limited reaction conditions. Fluid flow was simulated using the lattice-Boltzmann method, and the pore wall was adaptively eroded at a rate determined by the local surface area and velocity magnitude, which we use in place of solvent flux. We identified preexisting, high-conductivity fluid pathways imprinted in the initial microstructure. Though these pathways comprise a subset of the total connected porosity, they accommodated 80 to 99% of the volumetric flux through the digital sample and localized dissolution. Porosity-permeability evolution exhibited two stages: selective widening of narrow pore throats that comprised preferential pathways and development and widening of channels. We quantitatively monitored attributes of the pore geometry, namely, porosity, specific surface area, tortuosity, and average hydraulic diameter, which we qualitatively linked to permeability. This study gives a pore-scale perspective on the microstructural origins of laboratory permeability-porosity trends of tight carbonates undergoing transport-limited reaction with CO2-rich fluid.

  13. Dissolution of hematite nanoparticle aggregates: influence of primary particle size, dissolution mechanism, and solution pH.

    PubMed

    Lanzl, Caylyn A; Baltrusaitis, Jonas; Cwiertny, David M

    2012-11-13

    The size-dependent dissolution of nanoscale hematite (8 and 40 nm α-Fe(2)O(3)) was examined across a broad range of pH (pH 1-7) and mechanisms including proton- and ligand- (oxalate-) promoted dissolution and dark (ascorbic acid) and photochemical (oxalate) reductive dissolution. Empirical relationships between dissolution rate and pH revealed that suspensions of 8 nm hematite exhibit between 3.3- and 10-fold greater reactivity per unit mass than suspensions of 40 nm particles across all dissolution modes and pH, including circumneutral. Complementary suspension characterization (i.e., sedimentation studies and dynamic light scattering) indicated extensive aggregation, with steady-state aggregate sizes increasing with pH but being roughly equivalent for both primary particles. Thus, while the reactivity difference between 8 and 40 nm suspensions is generally greater than expected from specific surface areas measured via N(2)-BET or estimated from primary particle geometry, loss of reactive surface area during aggregation limits the certainty of such comparisons. We propose that the relative reactivity of 8 and 40 nm hematite suspensions is best explained by differences in the fraction of aggregate surface area that is reactive. This scenario is consistent with TEM images revealing uniform dissolution of aggregated 8 nm particles, whereas 40 nm particles within aggregates undergo preferential etching at edges and structural defects. Ultimately, we show that comparably sized hematite aggregates can exhibit vastly different dissolution activity depending on the nature of the primary nanoparticles from which they are constructed, a result with wide-ranging implications for iron redox cycling.

  14. 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.

  15. Evolving Spatial Heterogeneity Induced by Preferential Carbonate Dissolution in Fractured Media

    NASA Astrophysics Data System (ADS)

    Wen, H.; Li, L.; Crandall, D.; Hakala, A.

    2014-12-01

    Spatial heterogeneity plays a key role in determining physical and geochemical processes in geological systems. In reactive fractures, mineral reactions also can alter fracture properties locally, therefore leading to evolving spatial heterogeneity. Here we use two-dimensional (2D) reactive transport modeling to 1) understand the evolving spatial heterogeneity due to the preferential dissolution of carbonate and 2) quantify the dependence of calcite dissolution on characteristics of spatial heterogeneity, including fracture roughness (i.e., aperture standard derivation, surface parameter and fractal dimension), flow connectivity (i.e., ratio of effective permeability keff over geometric mean of local permeability kG), and transport connectivity indicators (e.g., ratio of late 5% arrival time tlate5% over average arrival time tave). The fractured core samples from Brady's Hot Springs geothermal field are composed of primarily carbonate, clay, and quartz. The computational domains were set up using fracture images obtained from CT scanning at the resolution of 31.6 μm. The two samples have similar initial average aperture, porosity, permeability, and mineralogical composition. They differ in the spatial patterns: one has narrow large-aperture zones distributed widely (AD sample); the other has a major large-aperture zone in the middle of the sample (AC sample). Simulation results show that highly connected flow path forms quickly in the AD sample, leading to an increase of average chemical aperture, effective permeability, and flow velocity by five times after 75 days of injecting salt water. In contrast, these properties remain constant in the AC sample. Other parameters that quantitatively characterize the spatial heterogeneity, including connectivity and the tail slope of the breakthrough curves, also change dramatically, indicating major alteration in fracture properties due to calcite dissolution.

  16. Influence of Experimental Conditions on Electronic Tongue Results—Case of Valsartan Minitablets Dissolution

    PubMed Central

    Wesoły, Małgorzata; Kluk, Anna; Sznitowska, Małgorzata; Ciosek, Patrycja; Wróblewski, Wojciech

    2016-01-01

    A potentiometric electronic tongue was applied to study the release of valsartan from pharmaceutical formulations, i.e., minitablets uncoated and coated with Eudragit E. Special attention was paid to evaluate the influence of medium temperature and composition, as well as to compare the performances of the sensor arrays working in various hydrodynamic conditions. The drug dissolution profiles registered with the ion-sensitive electrodes were compared with standard dissolution tests performed with USP Apparatus 2 (paddle). Moreover, the signal changes of all sensors were processed by principal component analysis to visualize the release modifications, related to the presence of the coating agent. Finally, the importance and influence of the experimental conditions on the results obtained using potentiometric sensor arrays were discussed. PMID:27563904

  17. Influence of essential onion oil on tin and chromium dissolution from tinplate.

    PubMed

    Nincević Grassino, A; Grabarić, Z; Pezzani, A; Fasanaro, G; Lo Voi, A

    2009-07-01

    During food and beverage packaging in tinplate cans the dissolution of tin and chromium into food content may occur. To protect metallic surface different corrosion inhibitors are recommended, nowadays particularly a new group of natural products is of interest. In this work the influence of essential onion oil (EOO) on metals dissolution (tin and chromium) from tinplate sheets before food canning was investigated. The analyses were performed by galvanostatic method and atomic absorption spectroscopy. The values of tin obtained for the internal surface of tinplate covered with EOO (7.31-9.76 gm(-2)) are lower than the values when dioctyl sebacate oil (DOS), as a protective tinplate surface layer for food caning, was used (9.24-11.03 gm(-2)). Obviously, the presence of EOO diminished more efficiently then DOS oil the dissolution of tin in electrolyte during galvanostatic analyses. The efficiency of EOO as corrosion inhibitor was even more pronounced in the case of chromium where the dissolution from 1.8-2.5 mgm(-2) (DOS oil) was lowered to 1.0-1.3 mgm(-2) (EOO). Correlation of results obtained with two different physico-chemical methods was satisfying.

  18. Influence of oxygen, albumin and pH on copper dissolution in a simulated uterine fluid.

    PubMed

    Bastidas, D M; Cano, E; Mora, E M

    2005-06-01

    The aim of this paper is to study the influence of albumin content, from 5 to 45 g/L, on copper dissolution and compounds composition in a simulated uterine solution. Experiments were performed in atmospheric pressure conditions and with an additional oxygen pressure of 0.2 atmospheres, at 6.3 and 8.0 pH values, and at a temperature of 37 +/- 0.1 degrees C for 1, 3, 7, and 30 days experimentation time. The copper dissolution rate has been determined using absorbance measurements, finding the highest value for pH 8.0, 35 g/L albumin, and with an additional oxygen pressure of 0.2 atmospheres: 674 microg/day for 1 day, and 301 microg/day for 30 days. X-ray photoelectron spectroscopy (XPS) results show copper(II) as the main copper oxidation state at pH 8.0; and copper(I) and metallic copper at pH 6.3. The presence of albumin up to 35 g/L, accelerates copper dissolution. For high albumin content a stabilisation on the copper dissolution takes place. Corrosion product layer morphology is poorly protective, showing paths through which copper ions can release.

  19. Fabrication of carbonate apatite blocks from set gypsum based on dissolution-precipitation reaction in phosphate-carbonate mixed solution.

    PubMed

    Nomura, Shunsuke; Tsuru, Kanji; Maruta, Michito; Matsuya, Shigeki; Takahashi, Ichiro; Ishikawa, Kunio

    2014-01-01

    Carbonate apatite (CO3Ap), fabricated by dissolution-precipitation reaction based on an appropriate precursor, is expected to be replaced by bone according to bone remodeling cycle. One of the precursor candidates is gypsum because it shows self-setting ability, which then enables it to be shaped and molded. The aim of this study, therefore, was to fabricate CO3Ap blocks from set gypsum. Set gypsum was immersed in a mixed solution of 0.4 mol/L disodium hydrogen phosphate (Na2HPO4) and 0.4 mol/L sodium hydrogen carbonate (NaHCO3) at 80-200°C for 6-48 h. Powder X-ray diffraction patterns and Fourier transform infrared spectra showed that CO3Ap block was fabricated by dissolution-precipitation reaction in Na2HPO4-NaHCO3 solution using set gypsum in 48 h when the temperature was 100°C or higher. Conversion rate to CO3Ap increased with treatment temperature. CO3Ap block containing a larger amount of carbonate was obtained when treated at lower temperature.

  20. Constant-distance mode scanning potentiometry. 1. Visualization of calcium carbonate dissolution in aqueous solution.

    PubMed

    Etienne, Mathieu; Schulte, Albert; Mann, Stefan; Jordan, Guntram; Dietzel, Irmgard D; Schuhmann, Wolfgang

    2004-07-01

    Constant-distance mode scanning potentiometry was established by integrating potentiometric microsensors as ion-selective scanning probes into a SECM setup that was equipped with a piezoelectric shear force-based tip-to-sample distance control. The combination of specially designed micrometer-sized potentiometric tips with an advanced system for tip positioning allowed simultaneous acquisition of both topographic and potentiometric information at solid/liquid interfaces with high spatial resolution. The performance of the approach was evaluated by applying Ca(2+)-selective constant-distance mode potentiometry to monitor the dissolution of calcium carbonate occurring either at the (104) surface of calcite crystals or in proximity to the more complex surface of cross sections of a calcium carbonate shell of Mya arenaria exposed to slightly acidic aqueous solutions. Micrometer-scale heterogeneities in the apparent calcium activity profiles have successfully been resolved for both samples.

  1. Influence of pH and temperature on alunite dissolution rates and products

    NASA Astrophysics Data System (ADS)

    Acero, Patricia; Hudson-Edwards, Karen

    2015-04-01

    Aluminium is one of the main elements in most mining-affected environments, where it may influence the mobility of other elements and play a key role on pH buffering. Moreover, high concentrations of Al can have severe effects on ecosystems and humans; Al intake, for example, has been implicated in neurological pathologies (e.g., Alzheimer's disease; Flaten, 2001). The behaviour of Al in mining-affected environments is commonly determined, at least partially, by the dissolution of Al sulphate minerals and particularly by the dissolution of alunite (KAl3(SO4)2(OH)6), which is one of the most important and ubiquitous Al sulphates in mining-affected environments (Nordstrom, 2011). The presence of alunite has been described in other acid sulphate environments, including some soils (Prietzel & Hirsch, 1998) and on the surface of Mars (Swayze et al., 2008). Despite the important role of alunite, its dissolution rates and products, and their controlling factors under conditions similar to those found in these environments, remain largely unknown. In this work, batch dissolution experiments have been carried out in order to shed light on the rates, products and controlling factors of alunite dissolution under different pH conditions (between 3 and 8) and temperatures (between 279 and 313K) similar to those encountered in natural systems. The obtained initial dissolution rates using synthetic alunite, based on the evolution of K concentrations, are between 10-9.7 and 10-10.9 mol-m-2-s-1, with the lowest rates obtained at around pH 4.8, and increases in the rates recorded with both increases and decreases in pH. Increases of temperature in the studied range also cause increases in the dissolution rates. The dissolution of alunite dissolution is incongruent, as has been reported for jarosite (isostructural with alunite) by Welch et al. (2008). Compared with the stoichiometric ratio in the bulk alunite (Al/K=3), K tends to be released to the solution preferentially over Al

  2. Anomalous electrochemical dissolution and passivation of iron growth catalysts in carbon nanotubes.

    PubMed

    Lyon, Jennifer L; Stevenson, Keith J

    2007-10-23

    Catalytically synthesized carbon nanotubes (CNTs) such as those prepared via chemical vapor deposition (CVD) contain metallic impurities including Fe, Ni, Co, and Mo. Transition metal contaminants such as Fe can participate in redox cycling reactions that catalyze the generation of reactive oxygen species and other products. Through the nature of the CVD growth process, metallic nanoparticles become encased within the CNT graphene lattice and may still be chemically accessible and participate in redox chemistry, especially when these materials are utilized as electrodes in electrochemical applications. We demonstrate that metallic impurities can be selectively dissolved and/or passivated during electrochemical potential cycling. Anomalous Fe dissolution and passivation behavior is observed in neutral (pH=6.40+/-0.03) aqueous solutions when using multiwalled CNTs prepared from CVD. Fe particles contained within these CNTs display intriguing, potential-dependent Fe redox activity that varies with supporting electrolyte composition. In neutral solutions containing dibasic sodium phosphate, sodium acetate, and sodium citrate, FeII dissolution and surface confined FeII/III redox activity are significant despite Fe being encapsulated within CNT graphene layers. However, no apparent Fe dissolution is observed in 1 M potassium nitrate solutions, suggesting that the electrolyte composition plays an important role in observing FeII dissolution, passivation, and surface confined FeII/III redox activity. Between potentials of 0 and -1.1 V versus Hg/Hg2SO4, the primary redox-active Fe species are surface FeII/III oxides/oxyhydroxides. This FeII/III surface oxide redox chemistry can be completely suppressed by passivating Fe through repeated cycling of the CNTs in supporting electrolyte. By increasing the potential to more negative values (>-1.3 V), FeII dissolution may be induced in electrolyte solutions containing acetate and phosphate and inhibited by addition of sodium

  3. Accelerated Carbonate Dissolution as a CO2 Separation and Sequestration Strategy

    SciTech Connect

    Caldeira, K G; Knauss, K G; Rau, G H

    2004-02-18

    process is geochemically equivalent to continental and marine carbonate weathering which will otherwise naturally consume anthropogenic CO{sub 2}, but over many millennia (e.g. [7,8,9]). We identify the enhanced form of this process as Accelerated Weathering of Limestone or accelerated carbonate dissolution. Previously, it has been shown that accelerated carbonate dissolution can effectively convert a significant fraction of US CO{sub 2} emissions to long-term storage as bicarbonate in the ocean, while avoiding or possibly reversing environmental impacts associated with either the ongoing passive or the proposed active injection of CO{sub 2} into the ocean [6,10]. Being analogous to the widespread use of wet limestone to desulfurize flue gas, accelerated carbonate dissolution reactors could be retrofitted to many existing coastal power plants at a typical cost estimated to be $20-$30/tonne CO{sub 2} mitigated [5,11]. This paper further explores limestone availability, cost, transportation, and reaction kinetics as well as ocean and environmental impacts, and the overall economics and practicality of accelerated carbonate dissolution CO{sub 2} mitigation.

  4. Influence of Sodium Lauryl Sulfate and Tween 80 on Carbamazepine–Nicotinamide Cocrystal Solubility and Dissolution Behaviour

    PubMed Central

    Li, Mingzhong; Qiao, Ning; Wang, Ke

    2013-01-01

    The influence of the surfactants of sodium lauryl sulfate (SLS) and Tween 80 on carbamazepine–nicotinamide (CBZ–NIC) cocrystal solubility and dissolution behaviour has been studied in this work. The solubility of the CBZ–NIC cocrystal was determined by measuring the eutectic concentrations of the drug and the coformer. Evolution of the intrinsic dissolution rate (IDR) of the CBZ–NIC cocrystal was monitored by the UV imaging dissolution system during dissolution. Experimental results indicated that SLS and Tween 80 had little influence upon the solubility of the CBZ–NIC cocrystal but they had totally opposite effects on the IDR of the CBZ–NIC cocrystal during dissolution. SLS significantly increased the IDR of the CBZ–NIC cocrystal while Tween 80 decreased its IDR. PMID:24300560

  5. Influence of sodium lauryl sulfate and tween 80 on carbamazepine-nicotinamide cocrystal solubility and dissolution behaviour.

    PubMed

    Li, Mingzhong; Qiao, Ning; Wang, Ke

    2013-10-11

    The influence of the surfactants of sodium lauryl sulfate (SLS) and Tween 80 on carbamazepine-nicotinamide (CBZ-NIC) cocrystal solubility and dissolution behaviour has been studied in this work. The solubility of the CBZ-NIC cocrystal was determined by measuring the eutectic concentrations of the drug and the coformer. Evolution of the intrinsic dissolution rate (IDR) of the CBZ-NIC cocrystal was monitored by the UV imaging dissolution system during dissolution. Experimental results indicated that SLS and Tween 80 had little influence upon the solubility of the CBZ-NIC cocrystal but they had totally opposite effects on the IDR of the CBZ-NIC cocrystal during dissolution. SLS significantly increased the IDR of the CBZ-NIC cocrystal while Tween 80 decreased its IDR.

  6. Carbon dioxide sequestration using NaHSO4 and NaOH: A dissolution and carbonation optimisation study.

    PubMed

    Sanna, Aimaro; Steel, Luc; Maroto-Valer, M Mercedes

    2017-03-15

    The use of NaHSO4 to leach out Mg fromlizardite-rich serpentinite (in form of MgSO4) and the carbonation of CO2 (captured in form of Na2CO3 using NaOH) to form MgCO3 and Na2SO4 was investigated. Unlike ammonium sulphate, sodium sulphate can be separated via precipitation during the recycling step avoiding energy intensive evaporation process required in NH4-based processes. To determine the effectiveness of the NaHSO4/NaOH process when applied to lizardite, the optimisation of the dissolution and carbonation steps were performed using a UK lizardite-rich serpentine. Temperature, solid/liquid ratio, particle size, concentration and molar ratio were evaluated. An optimal dissolution efficiency of 69.6% was achieved over 3 h at 100 °C using 1.4 M sodium bisulphate and 50 g/l serpentine with particle size 75-150 μm. An optimal carbonation efficiency of 95.4% was achieved over 30 min at 90 °C and 1:1 magnesium:sodium carbonate molar ratio using non-synthesised solution. The CO2 sequestration capacity was 223.6 g carbon dioxide/kg serpentine (66.4% in terms of Mg bonded to hydromagnesite), which is comparable with those obtained using ammonium based processes. Therefore, lizardite-rich serpentinites represent a valuable resource for the NaHSO4/NaOH based pH swing mineralisation process.

  7. Lab-Scale Study of the Calcium Carbonate Dissolution and Deposition by Marine Cyanobacterium Phormidium subcapitatum

    NASA Technical Reports Server (NTRS)

    Karakis, S. G.; Dragoeva, E. G.; Lavrenyuk, T. I.; Rogochiy, A.; Gerasimenko, L. M.; McKay, D. S.; Brown, I. I.

    2006-01-01

    Suggestions that calcification in marine organisms changes in response to global variations in seawater chemistry continue to be advanced (Wilkinson, 1979; Degens et al. 1985; Kazmierczak et al. 1986; R. Riding 1992). However, the effect of [Na+] on calcification in marine cyanobacteria has not been discussed in detail although [Na+] fluctuations reflect both temperature and sea-level fluctuations. The goal of these lab-scale studies therefore was to study the effect of environmental pH and [Na+] on CaCO3 deposition and dissolution by marine cyanobacterium Phormidium subcapitatum. Marine cyanobacterium P. subcapitatum has been cultivated in ASN-III medium. [Ca2+] fluctuations were monitored with Ca(2+) probe. Na(+) concentrations were determined by the initial solution chemistry. It was found that the balance between CaCO3 dissolution and precipitation induced by P. subcapitatum grown in neutral ASN III medium is very close to zero. No CaCO3 precipitation induced by cyanobacterial growth occurred. Growth of P. subcapitatum in alkaline ASN III medium, however, was accompanied by significant oscillations in free Ca(2+) concentration within a Na(+) concentration range of 50-400 mM. Calcium carbonate precipitation occurred during the log phase of P. subcapitatum growth while carbonate dissolution was typical for the stationary phase of P. subcapitatum growth. The highest CaCO3 deposition was observed in the range of Na(+) concentrations between 200-400 mM. Alkaline pH also induced the clamping of P. subcapitatum filaments, which appeared to have a strong affinity to envelop particles of chemically deposited CaCO3 followed by enlargement of those particles size. EDS analysis revealed the presence of Mg-rich carbonate (or magnesium calcite) in the solution containing 10-100 mM Na(+); calcite in the solution containing 200 mM Na(+); and aragonite in the solution containing with 400 mM Na(+). Typical present-day seawater contains xxmM Na(+). Early (Archean) seawater was

  8. Influence of Heterogamy by Religion on Risk of Marital Dissolution: A Cohort Study of 20,000 Couples.

    PubMed

    Wright, David M; Rosato, Michael; O'Reilly, Dermot

    2017-01-01

    Heterogamous marriages, in which partners have dissimilar attributes (e.g. by socio-economic status or ethnicity), are often at elevated risk of dissolution. We investigated the influences of heterogamy by religion and area of residence on risk of marital dissolution in Northern Ireland, a country with a history of conflict and residential segregation along Catholic-Protestant lines. We expected Catholic-Protestant marriages to have elevated risks of dissolution, especially in areas with high concentrations of a single religious group where opposition to intermarriage was expected to be high. We estimated risks of marital dissolution from 2001 to 2011 for 19,791 couples drawn from the Northern Ireland Longitudinal Study (a record linkage study), adjusting for a range of compositional and contextual factors using multilevel logistic regression. Dissolution risk decreased with increasing age and higher socio-economic status. Catholic-Protestant marriages were rare (5.9 % of the sample) and were at increased risk of dissolution relative to homogamous marriages. We found no association between local population composition and dissolution risk for Catholic-Protestant couples, indicating that partner and household characteristics may have a greater influence on dissolution risk than the wider community.

  9. Comparative solubilisation of potassium carbonate, sodium bicarbonate and sodium carbonate in hot dimethylformamide: application of cylindrical particle surface-controlled dissolution theory.

    PubMed

    Forryan, Claire L; Compton, Richard G; Klymenko, Oleksiy V; Brennan, Colin M; Taylor, Catherine L; Lennon, Martin

    2006-02-07

    A surface-controlled dissolution of cylindrical solid particles model is applied to potassium carbonate, sodium bicarbonate and sodium carbonate in dimethylformamide at elevated temperatures. Previously published data for the dissolution of potassium carbonate is interpreted assuming a cylindrical rather than a spherical shape of the particles, the former representing a closer approximation to the true shape of the particles as revealed by scanning electron microscopy. The dissolution kinetics of sodium carbonate and sodium bicarbonate in dimethylformamide at 100 degrees C were investigated via monitoring of the deprotonation of 2-cyanophenol with dissolved solid to form the 2-cyanophenolate anion that was detected with UV-visible spectroscopy. From fitting of experimental results to theory, the dissolution rate constant, k, for the dissolutions of potassium carbonate, sodium bicarbonate and sodium carbonate in dimethylformamide at 100 degrees C were found to have the values of (1.0 +/- 0.1) x 10(-7) mol cm(-2) s(-1), (5.5 +/- 0.3) x 10(-9) mol cm(-2) s(-1) and (9.7 +/- 0.8) x 10(-9) mol cm(-2) s(-1), respectively.

  10. Chemomechanical evolution of pore space in carbonate microstructures upon dissolution: Linking pore geometry to bulk elasticity

    NASA Astrophysics Data System (ADS)

    Arson, C.; Vanorio, T.

    2015-10-01

    One of the challenges faced today in a variety of geophysical applications is the need to understand the changes of elastic properties due to time-variant chemomechanical processes. The objective of this work is to model carbonate rock elastic properties as functions of pore geometry changes that occur when the solid matrix is dissolved by carbon dioxide. We compared two carbonate microstructures: porous micrite ("mudstone") and grain-supported carbonate ("packstone"). We formulated a mathematical model that distinguishes the effects of microporosity and macroporosity on stiffness changes. We used measures of mechanical and chemical porosity changes recorded during injection tests to compute elastic moduli and compare them to moduli obtained from wave velocity measurements. In mudstones, both experimental and numerical results indicate that bulk moduli change by less than 5%. The evolution of elastic moduli is controlled by macropore enlargement. In packstones, model predictions underestimate changes of elastic moduli with total porosity by 10% to 80%. The total porosity variation is 60% to 75% smaller than the chemical porosity variation, which indicates that pore expansion due to dissolution is counterbalanced by pore shrinkage due to compaction. Packstone elastic properties are controlled by grain sliding. The methodology presented in this paper can be generalized to other chemomechanical processes studied in rocks, such as dislocations, glide, diffusive mass transfer, recrystallization, and precipitation.

  11. 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.

  12. Coupled dissolution-precipitation as a mechanism for amorphous-to-crystalline calcium carbonate phase transition

    NASA Astrophysics Data System (ADS)

    Rodriguez-Navarro, Carlos Manuel; Kudłacz, Krzysztof; Ruiz-Agudo, Encarnacion

    2014-05-01

    Growing evidence shows that several calcium carbonate biominerals form via an amorphous precursor phase. Such a biomineralization strategy could also be applicable for the biomimetic synthesis of novel functional materials. A crucial step in this process is the transformation of amorphous calcium carbonate (ACC) into calcite. However, controversy exists as to what is the actual mechanism of this transformation: Is it a solid-solid (solid state) or a dissolution/precipitation mechanism? Determining the transition mechanism is critical for example in interpreting the formation of oriented crystalline structures in biominerals (e.g., echinoderm spicles). We studied calcium carbonate precipitation and phase transitions according to the overall reaction Ca(OH)2 + CO2 = CaCO3+ H2O. Mineral phase transformations during this reaction were studied using transmission electron microscopy (TEM). Our TEM analysis showed that two different types of ACC are sequentially formed during this reaction. Type I ACC shows no well-defined short-range order, while Type II ACC shows a short-range order corresponding to calcite. Following e-beam irradiation, Type I ACC particles transform into randomly oriented CaO nanocrystals, while irradiation of Type II ACC leads to the formation of pseudomorphs made up of perfectly oriented aggregates of calcite nanocrystals. Moreover, calcite crystals formed in solution or in air (85 % relative humidity) after Type II ACC are also pseudomorphs made up of porous aggregates of preferentially oriented calcite nanocrystals. Our results give experimental evidence showing that the ACC to calcite transformation under relevant biomineralization conditions (low T and P), also applicable in the biomimetic synthesis of calcite, is a pseudomorphic dissolution-precipitation process. This mechanism involves the tightly interface-coupled dissolution of the precursor amorphous phase (with the crystalline phase protostructure) and concomitant deposition of the

  13. Detection and projection of carbonate dissolution in the water column and deep-sea sediments due to ocean acidification

    NASA Astrophysics Data System (ADS)

    Ilyina, Tatiana; Zeebe, Richard E.

    2012-03-01

    Dissolution of fossil fuel CO2 in seawater results in decreasing carbonate ion concentration and lowering of seawater pH with likely negative impacts for many marine organisms. We project detectable changes in carbonate dissolution and evaluate their potential to mitigate atmospheric CO2 and ocean acidification with a global biogeochemistry model HAMOCC forced by different CO2 emission scenarios. Our results suggest that as the anthropogenic CO2 signal penetrates into ocean interior, the saturation state of carbonate minerals will drop drastically - with undersaturation extending from the ocean floor up to 100-150 m depth in the next century. This will induce massive dissolution of CaCO3 in the water column as well as the sediment, increasing the Total Alkalinity (TA) by up to 180 μmol kg-1 at the surface and in the ocean interior over the next 2500 years. Model results indicate an inhomogeneous response among different ocean basins: Atlantic carbonate chemistry responds faster and starts recovering two millennia after CO2 emissions cease, which is not the case in the Pacific. CaCO3 rain stops in the Pacific Ocean around 2230. Using an observation-derived detection threshold for TA, we project detectable dissolution-driven changes only by the year 2070 in the surface ocean and after 2230 and 2500 in the deep Atlantic and Pacific respectively. We show that different model assumptions regarding dissolution and calcification rates have little impact on future projections. Instead, anthropogenic CO2 emissions overwhelmingly control the degree of perturbation in ocean chemistry. In conclusion, ocean carbonate dissolution has insignificant potential in mitigating atmospheric CO2 and ocean acidification in the next millennia.

  14. Modeling and simulation of NiO dissolution and Ni deposition in molten carbonate fuel cells

    SciTech Connect

    Nam, Suk Woo; Choi, Hyung-Joon; Lim, Tae Hoon

    1996-12-31

    Dissolution of NiO cathode into the electrolyte matrix is an important phenomena limiting the lifetime of molten carbonate fuel cell (MCFC). The dissolved nickel diffuses into the matrix and is reduced by dissolved hydrogen leading to the formation of metallic nickel films in the pores of the matrix. The growth of Ni films in the electrolyte matrix during the continuous cell operation results eventually in shorting between cathode and anode. Various mathematical and empirical models have been developed to describe the NiO dissolution and Ni deposition processes, and these models have some success in estimating the lifetime of MCFC by correlating the amount of Ni deposited in the matrix with shorting time. Since the exact mechanism of Ni deposition was not well understood, deposition reaction was assumed to be very fast in most of the models and the Ni deposition region was limited around a point in the matrix. In fact, formation of Ni films takes place in a rather broad region in the matrix, the location and thickness of the film depending on operating conditions as well as matrix properties. In this study, we assumed simple reaction kinetics for Ni deposition and developed a mathematical model to get the distribution of nickel in the matrix.

  15. Controlled release based on the dissolution of a calcium carbonate layer deposited on hydrogels.

    PubMed

    Ogomi, Daisuke; Serizawa, Takeshi; Akashi, Mitsuru

    2005-03-21

    It is possible that inorganic materials conjugated to suitable organic materials may induce unique mechanical, optical and other functional properties. Therefore, artificial conjugation of organic and inorganic components is attractive for preparing novel functional materials. Recently, we developed an alternate soaking process for calcium salt formation on/in polymer materials. In this study, a poly(vinyl alcohol) (PVA) hydrogel-calcium carbonate (CaCO(3)) composite was prepared by the aforementioned process as a controlled release support. Brilliant blue FCF (Mw = 794), FITC labeled BSA (Mw = 6.6 x 10(4)), FITC labeled dextran-10 k (Mw = 9.5 x 10(3)) and FITC labeled dextran-40 k (Mw = 4.3 x 10(4)) were loaded into the composite as model drugs. CaCO(3) dissolution and model drug release rates increased with a decrease in buffer pH. In addition, model drug release rates increased with a decrease in model drug molecular weight. These results show that CaCO(3) layers on hydrogels behave as capping layers for model drug release; the release rate of model drugs can be controlled by the dissolution rate of CaCO(3) and the molecular weight of the drug.

  16. Dissolution along faults-fractures and hypogenic karst in carbonates: examples from Brazil

    NASA Astrophysics Data System (ADS)

    Ennes-Silva, Renata; Cazarin, Caroline; Bezerra, Francisco; Auler, Augusto; Klimchouk, Alexander

    2015-04-01

    Dissolution along faults-fractures and hypogenic karst in carbonates: examples from Brazil Ennes-Silva, R.A; Cazarin, C.L.; Bezerra, F.H.; Auler, A.S.; Klimchouk, A.B. Dissolution along zones of preferential flow enhances anisotropy in geological media and increases its complexity. Changes in parameters such as porosity and permeability due to diagenesis and presence of ascendant fluids along fractures and faults can be responsible for hypogenic karstic system. The present study investigates the relationship between lithofacies, tectonics and karstification in the Neoproterozoic Salitre Formation, located in the central-eastern Brazil. This unit comprises several systems of caves including the Toca da Boa Vista and da Barriguda hypogenic caves, the largests in South America, and focus of this study. We focused on cave mapping and morphogenetic analysis, determination of petrophysical properties, thin-section description, micro-tomography, and isotopic analysis. The Salitre Formation, deposited in an epicontinental sea, comprises mud/wakestones, grainstones, microbial facies, and fine siliciclastic rocks. Passages occur in several levels within ca. 60 m thick cave-forming section, limited at the top by lithofacies with low permeability and fractures. Cave development occurred in phreatic sluggish-flow environment with overall upwelling flow. Fluids rise via cross-formational fractures and were distributed laterally within the cave-forming section using geological heterogeneities to eventually discharge up through outlets breaching across the upper confining beds. Maps of conduits show preferred directions for development of conduits: NNE-SSW and E-W. These two directions represents a relation between structures and hypogenic morphology. Joints, axis fold and fractures allowed pathways to the fluid rises, and then development of channels of entrance (feeders), outputs (outlets) and some cupolas, which are clearly aligned to fractures. Our data indicate several events

  17. Enhanced olivine carbonation within a basalt as compared to single-phase experiments: the impact of redox and bulk composition on the dissolution kinetics of olivine

    NASA Astrophysics Data System (ADS)

    Sissmann, O.; Brunet, F.; Martinez, I.; Guyot, F. J.; Verlaguet, A.; Pinquier, Y.; Garcia, B.; Chardin, M.; Kohler, E.; Daval, D.

    2014-12-01

    Olivine (Mg,Fe)2SiO4, which is one of the major mineral constituents of mafic and ultramafic rocks, has an attractive potential for CO2 mineral sequestration, as it possesses a high content of carbonate-forming divalent cations and exhibits one of the highest dissolution rate amongst rock-forming minerals. This study reports drastic differences in carbonation yields between experiments performed on olivine-rich basalt samples and on olivine separates (a more restricted chemical system). Batch experiments were conducted in water at 150°C and pCO2 = 280 bars on a Mg-rich tholeiitic basalt (9.3 wt.% MgO and 12.2 wt.% CaO), composed of olivine, Ti-magnetite, plagioclase and clinopyroxene. After 45 days of reaction, 56 wt.% of the initial MgO has reacted with CO2 to form Fe-bearing magnesite (Mg0.8Fe0.2)CO3 along with minor calcium carbonates. The substantial decrease of olivine content upon carbonation supports the idea that ferroan magnesite formation mainly follows from olivine dissolution. In contrast, in experiments performed under similar run durations and P/T conditions with a San Carlos olivine separate (47.8 wt.% MgO) of similar grain size, only 5 wt.% of the initial MgO content reacted to form Fe-bearing magnesite. The overall carbonation kinetics of the basalt is enhanced by a factor of 40. It could be accounted for by differences in chemical and textural properties of the secondary-silica layer which covers reacted olivine grains in both types of sample. A TEM inspection of mineral surfaces shows that the thin amorphous silica layer (~100 nm) is porous in the case of the basalt sample and that it contains significant amounts of iron and aluminum. Thus, we propose that the composition of the olivine environment itself can strongly influence the olivine dissolution-carbonation process. Consequently, laboratory data obtained on olivine separates might yield a conservative estimate of the true carbonation potential of olivine-bearing basaltic rocks. More

  18. The influence of pH on biotite dissolution and alteration kinetics at low temperature

    USGS Publications Warehouse

    Acker, James G.; Bricker, O.P.

    1992-01-01

    Biotite dissolution rates in acidic solutions were determined in fluidized-bed reactors and flowthrough columns. Biotite dissolution rates increased inversely as a linear function of pH in the pH range 3-7, where the rate order n = -0.34. Biotite dissolved incongruently over this pH range, with preferential release of magnesium and iron from the octahedral layer. Release of tetrahedral silicon was much greater at pH 3 than at higher pH. Iron release was significantly enhanced by low pH conditions. Solution compositions from a continuous exposure flow-through column of biotite indicated biotite dissolves incongruently at pH 4, consistent with alteration to a vermiculite-type product. Solution compositions from a second intermittent-flow column exhibited elevated cation release rates upon the initiation of each exposure to solution. The presence of strong oxidizing agents, the mineral surface area, and sample preparation methodology also influenced the dissolution or alteration kinetics of biotite. ?? 1992.

  19. Tuning the dissolution kinetics of wollastonite via chelating agents for CO2 sequestration with integrated synthesis of precipitated calcium carbonates.

    PubMed

    Zhao, Huangjing; Park, Youngjune; Lee, Dong Hyun; Park, Ah-Hyung Alissa

    2013-09-28

    Carbon mineralization has recently received much attention as one of the most promising options for CO2 sequestration. The engineered weathering of silicate minerals as a means of permanent carbon storage has unique advantages such as the abundance of naturally occurring calcium and magnesium-bearing minerals and the formation of environmentally-benign and geologically stable solids via a thermodynamically favored carbonation reaction. However, several challenges need to be overcome to successfully deploy carbon mineralization on a large scale. In particular, the acceleration of the rate-limiting mineral dissolution step along with process optimization is essential to ensure the economic feasibility of the proposed carbon storage technology. In this study, the effect of various types of chelating agents on the dissolution rate of calcium-bearing silicate mineral, wollastonite, was explored to accelerate its weathering rate. It was found that chelating agents such as acetic acid and gluconic acid significantly improved the dissolution kinetics of wollastonite even at a much diluted concentration of 0.006 M by complexing with calcium in the mineral matrix. Calcium extracted from wollastonite was then reacted with a carbonate solution to form precipitated calcium carbonate (PCC), while tuning the particle size and the morphological structure of PCC to mimic commercially available PCC-based filler materials.

  20. The effect of the carbon dissolution on the crystal structure of a-quartz

    NASA Astrophysics Data System (ADS)

    Mitani, S.; Kyono, A.

    2015-12-01

    Silicon is one of the major and important element that constitutes the Earth's crust and mantle. An enormous amount of carbon is also contained in the Earth's interior, which suggests that silicate could be closely interacted with carbon under high-pressure and high-temperature (Sen et al. 2013, PNAS). It is suggested that carbon dioxide is dissolved in cristobalite and the average composition of CO2-SiO2 solid solution is C0.6(1)Si0.4(1)O2 High-pressure experiment (Santoro et al. 2014, Nat. Commun.). Furthermore, the first-principles calculations suggested the possibility of successive CO2 dissolution in cristobalite at ambient pressure (Aravindh et al. 2007, Solid State Commun.). However, CO2-SiO2 solid solution at ambient pressure has not confirmed in laboratory experiment. In this study, we mixed amorphous silica and amorphous carbon and synthesized CO2-SiO2 solid solution at high-temperature under ambient pressure. Powder amorphous silica and graphite was mixed together in the agate mill in order to be homogenized mixture. They were heated for 1300 ˚C, 3 days under ambient pressure. Then, the samples were quenched at room temperature. The samples of CO2-SiO2 solid solution were carefully examined by powder XRD, EPMA measurement, and so on. From the result of the powder XRD, the products were a-quartz. In this lecture, we report the quantity of carbon dissolved in a-quartz and its effect for the crystal structure of a-quartz in detail.

  1. The influence of parents' martial dissolutions on children's attitudes toward family formation.

    PubMed

    Axinn, W G; Thornton, A

    1996-02-01

    We investigate the influence of parents' martial dissolutions on their children's attitudes toward several dimensions of family formation. Hypotheses focus on the role of patients' attitudes as a mechanism linking parents' behavior to their children's attitudes. We test these hypotheses using intergenerational panel data that include measures of children's attitudes taken directly from children. Results demonstrate strong effects of parental divorce, remarriage, and widowhood on children's attitudes toward premarital sex, cohabitation, marriage, childbearing, and divorce. The results also show that parents' own attitudes link their behavior to their children's attitudes, although substantial effects of parental behavior remain after controlling for parents' attitudes.

  2. Porous calcium carbonate as a carrier material to increase the dissolution rate of poorly soluble flavouring compounds.

    PubMed

    Lundin Johnson, Maria; Noreland, David; Gane, Patrick; Schoelkopf, Joachim; Ridgway, Cathy; Millqvist Fureby, Anna

    2017-03-15

    Two different food grade functionalised porous calcium carbonates (FCC), with different pore size and pore size distributions, were characterised and used as carrier materials to increase the dissolution rate of poorly soluble flavouring compounds in aqueous solution. The loading level was varied between 1.3% by weight (wt%) and 35 wt%, where the upper limit of 35 wt% was the total maximum loading capacity of flavouring compound in FCC based on the fraction of the total weight of FCC plus flavouring compound. Flavouring compounds (l-carvone, vanillin, and curcumin) were selected based on their difference in hydrophilicity and capacity to crystallise. Release kinetic studies revealed that all flavouring compounds showed an accelerated release when loaded in FCC compared to dissolution of the flavouring compound itself in aqueous medium. The amorphous state and/or surface enlargement of the flavouring compound inside or on FCC explains the faster release. The flavouring compounds capable of crystallising (vanillin and curcumin) were almost exclusively amorphous within the porous FCC material as determined by X-ray powder diffraction one week after loading and after storing the loaded FCC material for up to 9 months at room temperature. A small amount of crystalline vanillin and curcumin was detected in the FCC material with large pores and high flavouring compound loading (≥30 wt%). Additionally, two different loading strategies were evaluated, loading by dissolving the flavouring compound in acetone or loading by a hot melt method. Porosimetry data showed that the melt method was more efficient in filling the smallest pores (<100 nm). The main factor influencing the release rate appears to be the amorphous state of the flavouring compound and the increase in exposed surface area. The confinement in small pores prevents crystallisation of the flavouring compounds during storage, providing a stable amorphous form retaining high release rate also after storage.

  3. High energy ball milling and supercritical carbon dioxide impregnation as co-processing methods to improve dissolution of tadalafil.

    PubMed

    Krupa, Anna; Descamps, Marc; Willart, Jean-François; Jachowicz, Renata; Danède, Florence

    2016-12-01

    Tadalafil (TD) is a crystalline drug of a high melting point (Tm=299°C) and limited solubility in water (<5μg/mL). These properties may result in reduced and variable bioavailability after oral administration. Since the melting of TD is followed by its decomposition, the drug processing at high temperatures is limited. The aim of the research is, therefore, to improve the dissolution of TD by its co-processing with the hydrophilic polymer Soluplus® (SL) at temperatures below 40°C. In this study, two methods, i.e. high energy ball-milling and supercritical carbon dioxide impregnation (scCO2) are compared, with the aim to predict their suitability for the vitrification of TD. The influence of the amount of SL and the kind of co-processing method on TD thermal properties is analyzed. The results show that only the high energy ball milling process makes it possible to obtain a completely amorphous form of TD, with the characteristic X-ray 'halo' pattern. The intensity of the Bragg peaks diminishes for all the formulations treated with scCO2, but these samples remain crystalline. The MDSC results show that high energy ball milling is capable of forcing the mixing of TD and SL at a molecular level, providing a homogeneous amorphous solid solution. The glass transition temperatures (Tg), determined for the co-milled formulations, range from 79°C to 139°C and they are higher than Tg of pure SL (ca. 70°C) and lower than Tg of pure TD (ca. 149°C). In contrast to the co-milled formulations which are in the form of powder, all the formulations after scCO2 impregnation form a hard residue, sticking to the reaction vessel, which needs to be ground before analysis or further processing. Finally, the dissolution studies show that not only has SL a beneficial effect on the amount of TD dissolved, but also both co-processing methods make the dissolution enhancement of TD possible. After co-processing by scCO2, the amount of TD dissolved increases with the decreasing amount

  4. Influence of type and neutralisation capacity of antacids on dissolution rate of ciprofloxacin and moxifloxacin from tablets.

    PubMed

    Uzunović, Alija; Vranić, Edina

    2009-02-01

    Dissolution rate of two fluoroquinolone antibiotics (ciprofloxacin and moxifloxacin) was analysed in presence/absence of three antacid formulations. Disintegration time and neutralisation capacity of antacid tablets were also checked. Variation in disintegration time indicated the importance of this parameter, and allowed evaluation of the influence of postponed antacid-fluoroquinolone contact. The results obtained in this study showed decreased dissolution rate of fluoroquinolone antibiotics from tablets in simultaneous presence of antacids, regardless of their type and neutralisation capacity.

  5. Dissolution and secondary mineral precipitation in basalts due to reactions with carbonic acid

    NASA Astrophysics Data System (ADS)

    Kanakiya, Shreya; Adam, Ludmila; Esteban, Lionel; Rowe, Michael C.; Shane, Phil

    2017-06-01

    One of the leading hydrothermal alteration processes in volcanic environments is when rock-forming minerals with high concentrations of iron, magnesium, and calcium react with CO2 and water to form carbonate minerals. This is used to the advantage of geologic sequestration of anthropogenic CO2. Here we experimentally investigate how mineral carbonation processes alter the rock microstructure due to CO2-water-rock interactions. In order to characterize these changes, CO2-water-rock alteration in Auckland Volcanic Field young basalts (less than 0.3 Ma) is studied before and after a 140 day reaction period. We investigate how whole core basalts with similar geochemistry but different porosity, permeability, pore geometry, and volcanic glass content alter due to CO2-water-rock reactions. Ankerite and aluminosilicate minerals precipitate as secondary phases in the pore space. However, rock dissolution mechanisms are found to dominate this secondary mineral precipitation resulting in an increase in porosity and decrease in rigidity of all samples. The basalt with the highest initial porosity and volcanic glass volume shows the most secondary mineral precipitation. At the same time, this sample exhibits the greatest increase in porosity and permeability, and a decrease in rock rigidity post reaction. For the measured samples, we observe a correlation between volcanic glass volume and rock porosity increase due to rock-fluid reactions. We believe this study can help understand the dynamic rock-fluid interactions when monitoring field scale CO2 sequestration projects in basalts.

  6. Prevalence of Ca2+-ATPase-Mediated Carbonate Dissolution among Cyanobacterial Euendoliths

    PubMed Central

    Ramírez-Reinat, E. L.

    2012-01-01

    Recent physiological work has shown that the filamentous euendolithic cyanobacterium Mastigocoleus testarum (strain BC008) is able to bore into solid carbonates using Ca2+-ATPases to take up Ca2+ from the medium at the excavation front, promoting dissolution of CaCO3 there. It is not known, however, if this is a widespread mechanism or, rather, a unique capability of this model strain. To test this, we undertook a survey of multispecies euendolithic microbial assemblages infesting natural carbonate substrates in marine coastal waters of the Caribbean, Mediterranean, South Pacific, and Sea of Cortez. Microscopic examination revealed the presence of complex assemblages of euendoliths, encompassing 3 out of the 5 major cyanobacterial orders. 16S rRNA gene clone libraries detected even greater diversity, particularly among the thin-filamentous forms, and allowed us to categorize the endoliths in our samples into 8 distinct phylogenetic clades. Using real-time Ca2+ imaging under a confocal laser scanning microscope, we could show that all communities displayed light-dependent formation of Ca2+-supersaturated zones in and around boreholes, a staple of actively boring phototrophs. In 3 out of 4 samples, boring activity was sensitive to at least one of two inhibitors of Ca2+-ATPase transporters (thapsigargin or tert-butylhydroquinone), indicating that the Ca2+-ATPase mechanism is widespread among cyanobacterial euendoliths but perhaps not universal. Function-community structure correlations point to one particular clade of baeocyte-forming euendoliths as the potential exception. PMID:22038600

  7. Dissolution and storage stability of nanostructured calcium carbonates and phosphates for nutrition

    NASA Astrophysics Data System (ADS)

    Posavec, Lidija; Knijnenburg, Jesper T. N.; Hilty, Florentine M.; Krumeich, Frank; Pratsinis, Sotiris E.; Zimmermann, Michael B.

    2016-10-01

    Rapid calcium (Ca) dissolution from nanostructured Ca phosphate and carbonate (CaCO3) powders may allow them to be absorbed in much higher fraction in humans. Nanosized Ca phosphate and CaCO3 made by flame-assisted spray pyrolysis were characterized by nitrogen adsorption, X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. As-prepared nanopowders contained both CaCO3 and CaO, but storing them under ambient conditions over 130 days resulted in a complete transformation into CaCO3, with an increase in both crystal and particle sizes. The small particle size could be stabilized against such aging by cation (Mg, Zn, Sr) and anion (P) doping, with P and Mg being most effective. Calcium phosphate nanopowders made at Ca:P ≤ 1.5 were XRD amorphous and contained γ-Ca2P2O7 with increasing hydroxyapatite content at higher Ca:P. Aging of powders with Ca:P = 1.0 and 1.5 for over 500 days gradually increased particle size (but less than for CaCO3) without a change in phase composition or crystallinity. In 0.01 M H3PO4 calcium phosphate nanopowders dissolved ≈4 times more Ca than micronsized compounds and about twice more Ca than CaCO3 nanopowders, confirming that nanosizing and/or amorphous structuring sharply increases Ca powder dissolution. Because higher Ca solubility in vitro generally leads to greater absorption in vivo, these novel FASP-made Ca nanostructured compounds may prove useful for nutrition applications, including supplementation and/or food fortification.

  8. Influence of Permian salt dissolution on Cretaceous oil and gas entrapment and reserve potential, Denver basin, Western Nebraska

    SciTech Connect

    Oldham, D.W.; Smosna, R.A.

    1996-06-01

    Location and trap type of Cretaceous oil and gas fields in the D-J Fairway of Nebraska are related to the occurrence of 12 Permian salt zones. Salt distribution is controlled by the configuration of evaporate basins, truncation at a sub-Jurassic unconformity, and post-Jurassic subsurface dissolution. The Sidney Trough, which marks the eastern (regionally updip) limit of Cretaceous oil production in western Nebraska, is a rootless salt-dissolution collapse feature, whose location and origin is controlled by an abrupt linear facies change from thick, porous Lyons Sandstone to Leonardian salt. Eastward gravity-driven groundwater flow within the Lyons occurred in response to hydraulic gradient and recharge along the Front Range Uplift following Laramide orogeny. Dissolution of salt at the facies change caused collapse of overlying strata, producing fractures through which cross-formational flow occurred. Younger salts were dissolved, enhancing relief across the regional depression and subsidiary synclines. Timing of post-Jurassic dissolution influenced entrapment within D and J sandstone reservoirs. Where Early Cretaceous (pre-reservoir) dissolution occurred, structure at the D and J sandstone level is relatively simple, and stratigraphic traps predominate. Where Late Cretaceous - Tertiary (post-reservoir) dissolution occurred, structure is more complex, formation waters are more saline, oil and gas are localized on dissolution-induced anticlines, and per-well reserves are significantly higher.

  9. Gravitational instability due to the dissolution of carbon dioxide in a Hele-Shaw cell

    NASA Astrophysics Data System (ADS)

    Vreme, A.; Nadal, F.; Pouligny, B.; Jeandet, P.; Liger-Belair, G.; Meunier, P.

    2016-10-01

    We present an experimental study of the gravitational instability triggered by dissolution of carbon dioxide through a water-gas interface. We restrict the study to vertical parallelepipedic Hele-Shaw geometries, for which the thickness is smaller than the other dimensions. The partial pressure of carbon dioxide is quickly increased, leading to a denser layer of CO2-enriched water underneath the surface. This initially one-dimensional diffusive layer destabilizes through a convection-diffusion process. The concentration field of carbon dioxide, which is visualized by means of a pH-sensitive dye, shows a fingering pattern whose characteristics (wavelength and amplitude growth rate) are functions of the Rayleigh (Ra) and the Darcy (Da) numbers. At low Rayleigh numbers, the growth rate and the wave numbers are independent of the Rayleigh number and in excellent agreement with the classical results obtained numerically and theoretically in the Darcy regime. However, above a threshold of Ra√{Da} of the order of 10, the growth rate and the wave number strongly decrease due to the Brinkman term associated with the viscous diffusion in the vertical and longitudinal directions. In this Darcy-Brinkman regime, the growth rate and the wave number depend only on the thickness-based Rayleigh number Ra√{Da} . The classical Rayleigh-Taylor theory including the Brinkman term has been extended to this diffusive gravitational instability and gives an excellent prediction of the growth rate over four decades of Rayleigh numbers. However, the Brinkman regime seems to be valid only until Ra√{Da}=1000 . Above this threshold, the transverse velocity profile is no longer parabolic, which leads to an overestimation of the wave number by the theory.

  10. Numerical ages of Holocene tributary debris fans inferred from dissolution pitting on carbonate boulders in the Grand Canyon of Arizona

    USGS Publications Warehouse

    Hereford, R.; Thompson, K.S.; Burke, K.J.

    1998-01-01

    Carbonate boulders transported down steep tributary channels by debris flow came to rest on Holocene debris fans beside the Colorado River in Grand Canyon National Park. Weakly acidic rainfall and the metabolic activity of blue-green algae have produced roughly hemispheric dissolution pits as much as 2-cm deep on the initially smooth surfaces of the boulders. The average depth of dissolution pits increases with relative age of fan surfaces. The deepening rate averages 2.4 mm/1000 yr (standard error = 0.2 mm/1000 yr), as calculated from several radiometrically dated surfaces and an archeological structure. This linear rate, which appears constant over at least the past 3000 yr, is consistent with field relations limiting the maximum age of the fans and with the physical chemistry of limestone dissolution. Dissolution-pit measurements (n = 6973) were made on 617 boulders on 71 fan surfaces at the 26 largest debris fans in Grand Canyon. Among these fan surfaces, the average pit depth ranges from 1.2 to 17.4 mm, and the resulting pit dissolution ages range from 500 to 7300 cal yr B.P. Most (75%) surfaces are younger than 3000 yr, probably because of removal of older debris fans by the Colorado River. Many of the ages are close to 800, 1600, 2300, 3100, or 4300 cal yr B.P. If not the result of differential preservation of fan surfaces, this clustering implies periods of heightened debris-flow activity and increased precipitation.

  11. Numerical Ages of Holocene Tributary Debris Fans Inferred from Dissolution Pitting on Carbonate Boulders in the Grand Canyon of Arizona

    NASA Astrophysics Data System (ADS)

    Hereford, Richard; Thompson, Kathryn S.; Burke, Kelly J.

    1998-09-01

    Carbonate boulders transported down steep tributary channels by debris flow came to rest on Holocene debris fans beside the Colorado River in Grand Canyon National Park. Weakly acidic rainfall and the metabolic activity of blue-green algae have produced roughly hemispheric dissolution pits as much as 2-cm deep on the initially smooth surfaces of the boulders. The average depth of dissolution pits increases with relative age of fan surfaces. The deepening rate averages 2.4 mm/1000 yr (standard error = 0.2 mm/1000 yr), as calculated from several radiometrically dated surfaces and an archeological structure. This linear rate, which appears constant over at least the past 3000 yr, is consistent with field relations limiting the maximum age of the fans and with the physical chemistry of limestone dissolution. Dissolution-pit measurements ( n= 6973) were made on 617 boulders on 71 fan surfaces at the 26 largest debris fans in Grand Canyon. Among these fan surfaces, the average pit depth ranges from 1.2 to 17.4 mm, and the resulting pit dissolution ages range from 500 to 7300 cal yr B.P. Most (75%) surfaces are younger than 3000 yr, probably because of removal of older debris fans by the Colorado River. Many of the ages are close to 800, 1600, 2300, 3100, or 4300 cal yr B.P. If not the result of differential preservation of fan surfaces, this clustering implies periods of heightened debris-flow activity and increased precipitation.

  12. Solution-state polymer assemblies influence BCS class II drug dissolution and supersaturation maintenance.

    PubMed

    Dalsin, Molly C; Tale, Swapnil; Reineke, Theresa M

    2014-02-10

    Spray dried dispersions (SDDs), solid dispersions of polymer excipients and active pharmaceuticals, are important to the field of oral drug delivery for improving active stability, bioavailability, and efficacy. Herein, we examine the influence of solution-state polymer assemblies on amorphous spray-dried dispersion (SDD) performance with two BCS II model drugs, phenytoin and probucol. These drugs were spray dried with 4 model polymer excipients consisting of poly(ethylene-alt-propylene) (PEP), N,N,-dimethylacrylamide (DMA), or 2-methacrylamido glucopyranose (MAG): amphiphilic diblock ter- and copolymers, PEP-P(DMA-grad-MAG) and PEP-PDMA, and their respective hydrophilic analogues, P(DMA-grad-MAG) and PDMA. Selective and nonselective solvents for the hydrophilic block of the diblock ter- and copolymers were used to induce or repress solution-state assemblies prior to spray drying. Prespray dried solution-state assemblies of these four polymers were probed with dynamic light scattering (DLS) and showed differences in solution assembly size and structure (free polymer versus aggregates versus micelles). Solid-state structures of spray dried dispersions (SDDs) showed a single glass transition event implying a homogeneous mixture of drug/polymer. Crystallization temperatures and enthalpies indicated that the drugs interact mostly with the DMA-containing portions of the polymers. Scanning electron microscopy was used to determine SDD particle size and morphology for the various polymer-drug pairings. In vitro dissolution tests showed excellent performance for one system, spray-dried PEP-PDMA micelles with probucol. Dissolution structures were investigated through DLS to determine drug-polymer aggregates that lead to enhanced SDD performance. Forced aggregation of the polymer into regular micelle structures was found to be a critical factor to increase the dissolution rate and supersaturation maintenance of SDDs, and may be an attractive platform to exploit in excipient

  13. Observations, Measurements, and Simulations of Convectively Enhanced Carbon Dioxide Dissolution (Invited)

    NASA Astrophysics Data System (ADS)

    Kneafsey, T. J.; Pruess, K.

    2010-12-01

    Carbon dioxide injected into a porous, permeable rock stratum overlain by low-permeability caprock will flow in response to applied pressures and buoyant, viscous, and capillary forces. Four modes of CO2 storage will occur upon injection, which are (in order of increased security and permanence): 1) free-phase supercritical CO2, 2) capillary-trapped CO2, 3) CO2 dissolved into the brine, and 4) CO2 that has chemically reacted with aqueous species and host rock resulting in precipitation. In the target formation, the injected supercritical CO2 will tend to rise due to buoyancy, and accumulate beneath the caprock. At some distance from the injection well, the CO2/brine interface will be roughly horizontal. In the absence of fluid motion, CO2 dissolution into the brine will be dominated by the slow process of molecular diffusion of the CO2 away from the CO2-brine interface, and the rate of dissolution will decrease with time. As CO2 dissolves into the brine, the density of the brine increases by a small amount, on the order of 0.1 to 1%. This results in a fluid dynamics instability because denser fluid overlies less dense fluid, which induces convective flow of the denser fluid downward. The downward convection of the CO2-bearing denser fluid causes less dense brine to flow upwards and contact the CO2. This is a desirable process because it significantly increases the dissolution of CO2 into the brine. We have performed laboratory visualization tests, quantitative measurements at elevated pressures, and numerical simulations to examine this phenomenon. In our visualization tests, we introduce CO2 into the headspace above water containing a pH sensitive indicator contained in a transparent Hele-Shaw cell. When CO2 dissolves into the water, the pH is lowered and the indicator changes color. Upon introduction of CO2 into the cell, a fairly uniform layer of low pH fluid containing dissolved CO2 slowly enlarges downward from the gas-water interface. At some point, many

  14. EVALUATION OF ARG-1 SAMPLES PREPARED BY CESIUM CARBONATE DISSOLUTION DURING THE ISOLOK SME ACCEPTABILITY TESTING

    SciTech Connect

    Edwards, T.; Hera, K.; Coleman, C.

    2011-12-05

    Evaluation of Defense Waste Processing Facility (DWPF) Chemical Process Cell (CPC) cycle time identified several opportunities to improve the CPC processing time. The Mechanical Systems & Custom Equipment Development (MS&CED) Section of the Savannah River National Laboratory (SRNL) recently completed the evaluation of one of these opportunities - the possibility of using an Isolok sampling valve as an alternative to the Hydragard valve for taking DWPF process samples at the Slurry Mix Evaporator (SME). The use of an Isolok for SME sampling has the potential to improve operability, reduce maintenance time, and decrease CPC cycle time. The SME acceptability testing for the Isolok was requested in Task Technical Request (TTR) HLW-DWPF-TTR-2010-0036 and was conducted as outlined in Task Technical and Quality Assurance Plan (TTQAP) SRNLRP-2011-00145. RW-0333P QA requirements applied to the task, and the results from the investigation were documented in SRNL-STI-2011-00693. Measurement of the chemical composition of study samples was a critical component of the SME acceptability testing of the Isolok. A sampling and analytical plan supported the investigation with the analytical plan directing that the study samples be prepared by a cesium carbonate (Cs{sub 2}CO{sub 3}) fusion dissolution method and analyzed by Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES). The use of the cesium carbonate preparation method for the Isolok testing provided an opportunity for an additional assessment of this dissolution method, which is being investigated as a potential replacement for the two methods (i.e., sodium peroxide fusion and mixed acid dissolution) that have been used at the DWPF for the analysis of SME samples. Earlier testing of the Cs{sub 2}CO{sub 3} method yielded promising results which led to a TTR from Savannah River Remediation, LLC (SRR) to SRNL for additional support and an associated TTQAP to direct the SRNL efforts. A technical report resulting

  15. Dissolution kinetics of {delta} phase and its influence on the notch sensitivity of Inconel 718

    SciTech Connect

    Cai Dayong . E-mail: dayongcai@sina.com.cn; Zhang Weihong; Nie Pulin; Liu Wenchang; Yao Mei

    2007-03-15

    The dissolution kinetics of {delta} phase in Inconel 718 at 980 deg. C, 1000 deg. C and 1020 deg. C and its influence on high temperature notch sensitivity have been studied using a quantitative X-ray diffraction (XRD) method and high temperature stress rupture life tests of notched specimens. The amount of {delta} phase decreases gradually during holding time at 980 deg. C, 1000 deg. C and 1020 deg. C. The {delta} phase will be fully dissolved in the austenitic matrix at 1020 deg. C for more than 2 h. A certain amount of {delta} phase still exists after holding at 980 deg. C and 1000 deg. C for times up to 6 h; the amount remaining are 3 wt.% and 0.6 wt.%, respectively. The dissolution rate remains at a high level at the beginning, and then decreases gradually with an increase of holding time. A dynamic equilibrium state can be approached after holding at 980 deg. C for more than 30 min and at 1000 deg. C for more than 2 h. The alloy with {delta} phase amounts higher than 0.62 wt.% does not exhibit notch sensitivity, whereas serious notch sensitivity exists if the concentration is below 0.43 wt.%.

  16. The Dissolution of Synthetic Na-Boltwoodite in Sodium Carbonate Solutions

    SciTech Connect

    Ilton, Eugene S.; Liu, Chongxuan; Yantasee, Wassana; Wang, Zheming; Moore, Dean A.; Felmy, Andrew R.; Zachara, John M.

    2006-09-01

    Uranyl silicates such as uranophane and Na-boltwoodite appear to control the solubility of uranium in the contaminated sediments at the US Department of Energy Hanford site (Liu et al., 2004). Consequently, the solubility of synthetic Na-boltwoodite was determined over a wide range of bicarbonate concentrations, from circumneutral to alkaline pH, that are representative of porewater and groundwater compositions at the Hanford site. Results show that Na-boltwoodite dissolution was nearly congruent and its solubility increased with increasing bicarbonate concentration. Calculated solubility constants varied by nearly 2 log units from low bicarbonate (no added NaCO3) to 50 mmol/L bicarbonate. However, the solubility constants only vary by 0.5 log units from 0 added bicarbonate to 1.2 mmol/L bicarbonate, where logKsp = 5.39-5.92 and the average logKsp = 5.63. No systematic trend in logKsp was apparent over this range in bicarbonate concentrations. LogKsp values trended down with increasing bicarbonate concentration, where logKsp = 4.06 at 50 mmol/L bicarbonate. We conclude that the calculated solubility constants at high bicarbonate are compromised by an incomplete or inaccurate uranyl-carbonate speciation model.

  17. Reactive Transport at the Pore Scale with Applications to the Dissolution of Carbonate Rocks for CO2 Sequestration Operations

    NASA Astrophysics Data System (ADS)

    Boek, E.; Gray, F.; Welch, N.; Shah, S.; Crawshaw, J.

    2014-12-01

    In CO2 sequestration operations, CO2 injected into a brine aquifer dissolves in the liquid to create an acidic solution. This may result in dissolution of the mineral grains in the porous medium. Experimentally, it is hard to investigate this process at the pore scale. Therefore we develop a new hybrid particle simulation algorithm to study the dissolution of solid objects in a laminar flow field, as encountered in porous media flow situations. First, we calculate the flow field using a multi-relaxation-time lattice Boltzmann (LB) algorithm implemented on GPUs, which demonstrates a very efficient use of the GPU device and a considerable performance increase over CPU calculations. Second, using a stochastic particle approach, we solve the advection-diffusion equation for a single reactive species and dissolve solid voxels according to our reaction model. To validate our simulation, we first calculate the dissolution of a solid sphere as a function of time under quiescent conditions. We compare with the analytical solution for this problem [1] and find good agreement. Then we consider the dissolution of a solid sphere in a laminar flow field and observe a significant change in the sphericity with time due to the coupled dissolution - flow process. Second, we calculate the dissolution of a cylinder in channel flow in direct comparison with corresponding dissolution experiments. We discuss the evolution of the shape and dissolution rate. Finally, we calculate the dissolution of carbonate rock samples at the pore scale in direct comparison with micro-CT experiments. This work builds on our recent research on calculation of multi-phase flow [2], [3] and hydrodynamic dispersion and molecular propagator distributions for solute transport in homogeneous and heterogeneous porous media using LB simulations [4]. It turns out that the hybrid simulation model is a suitable tool to study reactive flow processes at the pore scale. This is of great importance for CO2 storage and

  18. Stalagmite carbon isotopes and dead carbon proportion (DCP) in a near-closed-system situation: An interplay between sulphuric and carbonic acid dissolution

    NASA Astrophysics Data System (ADS)

    Bajo, Petra; Borsato, Andrea; Drysdale, Russell; Hua, Quan; Frisia, Silvia; Zanchetta, Giovanni; Hellstrom, John; Woodhead, Jon

    2017-08-01

    In this study, the 'dead carbon proportion' (DCP) calculated from combined U-Th and radiocarbon analyses was used to explore the carbon isotope systematics in Corchia Cave (Italy) speleothems, using the example of stalagmite CC26 which grew during the last ∼12 ka. The DCP values in CC26 are among the highest ever recorded in a stalagmite, spanning the range 44.8-68.8%. A combination of almost closed-system conditions and sulphuric acid dissolution (SAD) are proposed as major drivers in producing such a high DCP with minor contribution from old organic matter from the deep vadose zone. The long-term decrease in both DCP and δ13C most likely reflects post-glacial soil recovery above the cave, with a progressive increase of soil CO2 contribution to the total dissolved inorganic carbon (DIC). Pronounced millennial-scale shifts in DCP and relatively small coeval but antipathetic changes in δ13C are modulated by the effects of hydrological variability on open and closed-system dissolution, SAD and prior calcite precipitation. Hence, the DCP in Corchia Cave speleothems represents an additional proxy for rainfall amount.

  19. Use of carbon paste electrodes for the voltammetric detection of silver leached from the oxidative dissolution of silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Mullaugh, Katherine M.; Pearce, Olivia M.

    2017-04-01

    The widespread use of silver nanoparticles (Ag NPs) in consumer goods has raised concerns about the release of silver in environmental waters. Of particular concern is the oxidative dissolution of Ag NPs to release Ag+ ions, which are highly toxic to many aquatic organisms. Here, we have investigated the application of differential pulse stripping voltammetry (DPSV) with carbon paste electrodes (CPEs) in monitoring the oxidation of Ag NPs. Using a commercially available, unmodified carbon paste and 60-s deposition times, a detection limit of 3 nM Ag+ could be achieved. We demonstrate its selectivity for free Ag+ ions over Ag nanoparticles, allowing for analysis of the oxidation of Ag NPs without the need for separation of ions and nanoparticles prior to analysis. We applied this approach to investigate the effect of pH in the oxidative dissolution of Ag NPs, demonstrating the usefulness of CPEs in studies of this type.

  20. Mesoporous carbon as a novel drug carrier of fenofibrate for enhancement of the dissolution and oral bioavailability.

    PubMed

    Niu, Xia; Wan, Long; Hou, Zhong; Wang, Tianyi; Sun, Changshan; Sun, Jin; Zhao, Peng; Jiang, Tongying; Wang, Siling

    2013-08-16

    The purpose of this study was to develop mesoporous carbon loaded with a poorly watersoluble drug to enhance the drug dissolution and improve the oral bioavailability. Mesoporous carbon was synthesized using Pluronic 127 triblock polymer (F127), TEOS and phenolic resins. Fenofibrate (FFB) was chosen as a model drug and loaded onto mesoporous carbon using three different loading methods involving incipient wetness impregnation, and the solvent and melting methods. The effect of the physical state and the specific surface area were investigated using nitrogen adsorption, transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was found that the physicochemical properties of the drug as well as the drug loading methods had critical effects on the drug release rate. In vitro drug release studies showed that incorporation of FFB in mesoporous carbon greatly enhanced the dissolution rate in comparison with that of the pure crystalline drug. Moreover, the oral bioavailability of the drug from mesoporous carbon was higher than that of FFB commercial capsules. Furthermore, mesoporous carbon produced no irritation of the mucosa of the gastrointestinal tract as shown by gastric mucosa irritation test. Copyright © 2013 Elsevier B.V. All rights reserved.

  1. Dissolution rates of pure methane hydrate and carbon-dioxide hydrate in undersaturated seawater at 1000-m depth

    USGS Publications Warehouse

    Rehder, G.; Kirby, S.H.; Durham, W.B.; Stern, L.A.; Peltzer, E.T.; Pinkston, J.; Brewer, P.G.

    2004-01-01

    To help constrain models involving the chemical stability and lifetime of gas clathrate hydrates exposed at the seafloor, dissolution rates of pure methane and carbon-dioxide hydrates were measured directly on the seafloor within the nominal pressure-temperature (P/T) range of the gas hydrate stability zone. Other natural boundary conditions included variable flow velocity and undersaturation of seawater with respect to the hydrate-forming species. Four cylindrical test specimens of pure, polycrystalline CH4 and CO2 hydrate were grown and fully compacted in the laboratory, then transferred by pressure vessel to the seafloor (1028 m depth), exposed to the deep ocean environment, and monitored for 27 hours using time-lapse and HDTV cameras. Video analysis showed diameter reductions at rates between 0.94 and 1.20 ??m/s and between 9.0 and 10.6 ?? 10-2 ??m/s for the CO2 and CH4 hydrates, respectively, corresponding to dissolution rates of 4.15 ?? 0.5 mmol CO2/m2s and 0.37 ?? 0.03 mmol CH4/m2s. The ratio of the dissolution rates fits a diffusive boundary layer model that incorporates relative gas solubilities appropriate to the field site, which implies that the kinetics of the dissolution of both hydrates is diffusion-controlled. The observed dissolution of several mm (CH4) or tens of mm (CO2) of hydrate from the sample surfaces per day has major implications for estimating the longevity of natural gas hydrate outcrops as well as for the possible roles of CO2 hydrates in marine carbon sequestration strategies. ?? 2003 Elsevier Ltd.

  2. Mesoporous carbon with spherical pores as a carrier for celecoxib with needle-like crystallinity: improve dissolution rate and bioavailability.

    PubMed

    Zhu, Wenquan; Zhao, Qinfu; Sun, Changshan; Zhang, Zhiwen; Jiang, Tongying; Sun, Jin; Li, Yaping; Wang, Siling

    2014-06-01

    The purposes of this investigation are to design mesoporous carbon (MC) with spherical pore channels and incorporate CEL to it for changing its needlelike crystal form and improving its dissolution and bioavailability. A series of solid-state characterization methods, such as SEM, TEM, DSC and XRD, were employed to systematically investigate the existing status of celecoxib (CEL) within the pore channels of MC. The pore size, pore volume and surface area of samples were characterized by nitrogen physical absorption. Gastric mucosa irritation test was carried out to evaluate the safety of mesoporous carbon as a drug carrier. Dissolution tests and in vivo pharmacokinetic studies were conducted to confirm the improvement in drug dissolution kinetics and oral bioavailability. Uptake experiments were conducted to investigate the mechanism of the improved oral bioavailability. The results of solid state characterization showed that MC was prepared successfully and CEL was incorporated into the mesoporous channels of the MC. The crystallinity of CEL in MC was affected by different loading methods, which involve evaporation method and melting method. The dissolution rate of CEL from MC was found to be significantly higher than that of pure CEL, which attributed to reduced crystallinity of CEL. The gastric mucosa irritation test indicated that the MC caused no harm to the stomach and produced a protective effect on the gastric mucosa. Uptake experiments indicated that MC enhanced the amount of CEL absorbed by Caco-2 cells. Moreover, oral bioavailability of CEL loaded within the MC was approximately 1.59-fold greater than that of commercial CEL. In conclusion, MC was a safe carrier to load water insoluble drug by controlling the crystallinity or crystal form with improvement in drug dissolution kinetics and oral bioavailability.

  3. Isotopic evidence of enhanced carbonate dissolution at a coal mine drainage site in Allegheny County, Pennsylvania, USA

    SciTech Connect

    Sharma, Shikha; Sack, Andrea; Adams, James P.; Vesper, Dorothy; J Capo, Rosemary C.; Hartsock, Angela; Edenborn, Harry M.

    2013-01-01

    Stable isotopes were used to determine the sources and fate of dissolved inorganic C (DIC) in the circumneutral pH drainage from an abandoned bituminous coal mine in western Pennsylvania. The C isotope signatures of DIC (δ{sup 13}C{sub DIC}) were intermediate between local carbonate and organic C sources, but were higher than those of contemporaneous Pennsylvanian age groundwaters in the region. This suggests a significant contribution of C enriched in {sup 13}C due to enhanced carbonate dissolution associated with the release of H{sub 2}SO{sub 4} from pyrite oxidation. The Sr isotopic signature of the drainage was similar to other regional mine waters associated with the same coal seam and reflected contributions from limestone dissolution and cation exchange with clay minerals. The relatively high δ{sup 34}S{sub SO4} and δ{sup 18}O{sub SO4} isotopic signatures of the mine drainage and the presence of presumptive SO{sub 4}-reducing bacteria suggest that SO{sub 4} reduction activity also contributes C depleted in {sup 13}C isotope to the total DIC pool. With distance downstream from the mine portal, C isotope signatures in the drainage increased, accompanied by decreased total DIC concentrations and increased pH. These data are consistent with H{sub 2}SO{sub 4} dissolution of carbonate rocks, enhanced by cation exchange, and C release to the atmosphere via CO{sub 2} outgassing.

  4. Rapid Assessment of the Influence of Solution pH, Anion Concentration and Temperature on the Dissolution of Alloy 22

    SciTech Connect

    Gray, J J; Hayes, J R; Gdowski, G E; Viani, B E; Orme, C A

    2005-05-19

    We introduce an acid titration technique for the rapid characterization of the influence of solution pH, anion (such as chloride) concentration and temperature on the dissolution of metals. We demonstrate the technique with the characterization of the dissolution of alloy 22 (Ni-22Cr-13Mo-3W-3Fe) exposed to chloride-containing hydrochloric, sulfuric and nitric acid environments as a function of pH (from pH 5 to pH -1) and temperature (25-90 C). A combination of electrochemical techniques (electrochemical impedance spectroscopy and linear polarization resistance) and atomic force microscopy are used to characterize the influence of the various solutions on the dissolution of alloy 22. In solutions containing hydrochloric and sulfuric acids, a critical temperature exists for passive film breakdown on alloy 22 for all environments tested. Below the critical temperature, corrosion rates are less than 1 {micro}m/year. Above the critical temperature, the effect of temperature on dissolution rates is a function of both the pH and chloride content of the solution. In nitric acid containing solutions, the presence of nitrates promotes a stable passive oxide film that inhibits dissolution in all environments tested.

  5. Effect of Mineral Dissolution/Precipitation and CO2 Exsolution on CO2 transport in Geological Carbon Storage.

    PubMed

    Xu, Ruina; Li, Rong; Ma, Jin; He, Di; Jiang, Peixue

    2017-09-19

    Geological carbon sequestration (GCS) in deep saline aquifers is an effective means for storing carbon dioxide to address global climate change. As the time after injection increases, the safety of storage increases as the CO2 transforms from a separate phase to CO2(aq) and HCO3(-) by dissolution and then to carbonates by mineral dissolution. However, subsequent depressurization could lead to dissolved CO2(aq) escaping from the formation water and creating a new separate phase which may reduce the GCS system safety. The mineral dissolution and the CO2 exsolution and mineral precipitation during depressurization change the morphology, porosity, and permeability of the porous rock medium, which then affects the two-phase flow of the CO2 and formation water. A better understanding of these effects on the CO2-water two-phase flow will improve predictions of the long-term CO2 storage reliability, especially the impact of depressurization on the long-term stability. In this Account, we summarize our recent work on the effect of CO2 exsolution and mineral dissolution/precipitation on CO2 transport in GCS reservoirs. We place emphasis on understanding the behavior and transformation of the carbon components in the reservoir, including CO2(sc/g), CO2(aq), HCO3(-), and carbonate minerals (calcite and dolomite), highlight their transport and mobility by coupled geochemical and two-phase flow processes, and consider the implications of these transport mechanisms on estimates of the long-term safety of GCS. We describe experimental and numerical pore- and core-scale methods used in our lab in conjunction with industrial and international partners to investigate these effects. Experimental results show how mineral dissolution affects permeability, capillary pressure, and relative permeability, which are important phenomena affecting the input parameters for reservoir flow modeling. The porosity and the absolute permeability increase when CO2 dissolved water is continuously

  6. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  7. Modeling the Influence of Transport on Chemical Reactivity in Microbial Membranes: Mineral Precipitation/Dissolution Reactions.

    NASA Astrophysics Data System (ADS)

    Felmy, A. R.; Liu, C.; Clark, S.; Straatsma, T.; Rustad, J.

    2003-12-01

    It has long been known that microorganisms can alter the chemical composition of their immediate surroundings and influence such processes as ion uptake or adsorption and mineral precipitation dissolution. However, only recently have molecular imaging and molecular modeling capabilities been developed that begin to shed light on the nature of these processes at the nm to um scale at the surface of bacterial membranes. In this presentation we will show the results of recent molecular simulations of microbial surface reactions and describe our efforts to develop accurate non-equilibrium thermodynamic models for the microbial surface that can describe ion uptake and surface induced mineral precipitation. The thermodynamic models include the influence of the bacterial electrical double layer on the uptake of ions from solution and the removal, or exclusion, of ions from the surface of the cell, non-equilibrium diffusion and chemical reaction within the membrane, as well as a new thermodynamic approach to representing ion activities within the microbial membrane. In the latter case, the variability in the water content within the microbial membrane has a significant influence on the calculated mineral saturation indices. In such cases, we will propose the use of recently developed mixed solvent-electrolyte formalisms. Recent experimental data for mixed-solvent electrolyte systems will also be presented to demonstrate the potential impact of the variable water content on calculated ion activities within the membrane.

  8. On the Spheroidized Carbide Dissolution and Elemental Partitioning in High Carbon Bearing Steel 100Cr6

    NASA Astrophysics Data System (ADS)

    Song, Wenwen; Choi, Pyuck-Pa; Inden, Gerhard; Prahl, Ulrich; Raabe, Dierk; Bleck, Wolfgang

    2014-02-01

    We report on the characterization of high carbon bearing steel 100Cr6 using electron microscopy and atom probe tomography in combination with multi-component diffusion simulations. Scanning electron micrographs show that around 14 vol pct spheroidized carbides are formed during soft annealing and only 3 vol pct remain after dissolution into the austenitic matrix through austenitization at 1123 K (850 °C) for 300 seconds. The spheroidized particles are identified as (Fe, Cr)3C by transmission electron microscopy. Atom probe analysis reveals the redistribution and partitioning of the elements involved, i.e., C, Si, Mn, Cr, Fe, in both, the spheroidized carbides and the bainitic matrix in the sample isothermally heat-treated at 773 K (500 °C) after austenitization. Homogeneous distribution of C and a Cr gradient were detected within the spheroidized carbides. Due to its limited diffusivity in (Fe, Cr)3C, Cr exhibits a maximum concentration at the surface of spheroidized carbides (16 at. pct) and decreases gradually from the surface towards the core down to about 2 at. pct. The atom probe results also indicate that the partially dissolved spheroidized carbides during austenitization may serve as nucleation sites for intermediate temperature cementite within bainite, which results in a relatively softer surface and harder core in spheroidized particles. This microstructure may contribute to the good wear resistance and fatigue properties of the steel. Good agreement between DICTRA simulations and experimental composition profiles is obtained by an increase of mobility of the substitutional elements in cementite by a factor of five, compared to the mobility in the database MOBFE2.

  9. Dissolution kinetics of granular calcium carbonate in concentrated aqueous sodium dichromate solution at pH 6.0-7.0 and 110-130 degrees C.

    PubMed

    Wang, Tiangui; Li, Zuohu

    2005-01-01

    An understanding of the factors controlling calcite dissolution is important for modeling geochemical cycles and impacts of greenhouse gases on climate, diagenesis of sediments, and sedimentary rocks. It also has practical significance in the investigation of behavior of carbonates in petroleum and natural gas reservoirs and in the preservation of buildings and monuments constructed from limestone and marble. A large number of papers have been published on dissolution kinetics of calcium carbonate in aqueous solutions. But few involved the near-equilibrium region, especially at elevated temperatures and in concentrated solutions. In this paper, the dissolution kinetics of calcium carbonate in concentrated aqueous sodium dichromate solutions at pH 6.0-7.0 and 110-130 degrees C were studied in a 2-L autoclave. The results indicate that the dissolution reaction is mix-controlled, with surface reaction as the prevailing factor. The concentration of calcium ions in solution hardly affects the dissolution rate, but carbon dioxide in the vapor phase inhibits the dissolution reaction. The dissolution rate can be expressed by R = k(1)a(2)(H+) + k(2), and the apparent activation energy is 55-84 kJ mol(-1).

  10. Study of dolomite dissolution at various temperatures - Evidence for the formation of nanocrystalline secondary phases at dolomite surface and influence on dolomite interactions with other minerals

    NASA Astrophysics Data System (ADS)

    Debure, M.; Andreazza, P.; Grangeon, S.; Lerouge, C.; Montes-Hernandez, G.; MADE, B.; Tournassat, C.

    2015-12-01

    In most clay-rock geological formation studied for the storage of nuclear waste, pore water compositions are expected to be at equilibrium with carbonate minerals, which are always included in predictive models for pore water composition calculations [1]. Among the carbonates known to be present, dolomite may be problematic in the pore water composition calculation because its solubility spans a large range of values as a function of its crystallinity in thermodynamic databases. In addition, the composition of dolomite minerals observed in clay-rock formations such as Callovian-Oxfordian or Opalinus clay formation differs from this of a pure dolomite: the Ca/Mg stoichiometry is not ideal, and the minerals contain minor amounts of Fe and traces of many other elements [2]. To understand the influence of secondary phases precipitation during dolomite dissolution on pore water chemistry, the dissolution of monocrystals of dolomite were investigated at 25 °C and at 80 °C in a pH range 3 to 8 for various time periods (30 minutes to 21 days) in sealed PTFE reactors. Solution analyses evidenced a stoichiometric release of Ca and Mg in solution during dolomite dissolution. Scanning Electron Microscopy (SEM), Raman and X-Ray Diffraction (XRD) analyses did not evidence secondary Mg-bearing minerals precipitation, but revealed the formation of Fe-bearing particles on the dolomite surface. Morphological characterizations performed with Small-angle X-ray scattering (SAXS) evidenced that the precipitation occurs along a specific crystallographic plane of the dolomite monocrystal. Thus, the precipitated nanoparticles clustered on specific surface sites, and are made of Fe-rich phases poorly crystallized (carbonates, oxides and hydroxides). [1] Tournassat et al. 2015. Ch. 3: Chemical Conditions in Clay-Rocks. Natural and Engineered Clay Barriers, Elsevier. [2] Lerouge et al. 2011. Geochim. et Cosmoch. Acta, 2011, 75, 2633-2663.

  11. Cellulose Dissolution and In Situ Grafting in a Reversible System using an Organocatalyst and Carbon Dioxide.

    PubMed

    Song, Longchu; Yang, Yunlong; Xie, Haibo; Liu, Enhui

    2015-10-12

    Cellulose is a promising renewable material, but cannot easily be processed homogeneously owing to the stiffness of the molecules and the dense packing of its chains, due to intermolecular hydrogen bonds. Cellulose processability can be improved by chemical modification. The reversible reaction of cellulose with carbon dioxide in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) allows dissolution of cellulose in dimethyl sulfoxide (DMSO). This DMSO solution is an effective medium for grafting L-lactide (LLA) from cellulose by ring-opening polymerization (ROP) under mild conditions, allowing to prepare cellulose-graft-poly(L-lactide) co-polymers with a molar substitution (MSPLLA ) of poly(L-lactide) in the range of 0.37-5.32, at 80 °C. This makes DBU not only an important reagent to achieve cellulose dissolution, but it also acts as organocatalyst for the subsequent ring-opening polymerization process. Characterization of the structure and thermal properties of the co-polymers by a variety of techniques reveals that they have a single glass-transition temperature (Tg ), which decreases with increasing MSPLLA . Thus, the modification results in a transformation of the originally semirigid cellulose into a thermoplastic material with tunable Tg . The carbon dioxide dissolution strategy is an efficient platform for cellulose derivatization by homogeneous organocatalysis.

  12. Spectroscopic investigation confirms retaining the pristine nature of single-walled carbon nanotubes on dissolution in aniline

    NASA Astrophysics Data System (ADS)

    Singha, Somdutta; Ghosh, Swapankumar

    2017-09-01

    Carbon nanotubes in all forms are very much insoluble in both organic and inorganic solvents due to its high agglomeration and entangled morphology. General methods for dissolution of single-walled carbon nanotubes (SWNTs) are mostly associated with complexation or polymerization or addition of macromolecules which change the physical or chemical properties of SWNTs and the pristine nature of SWNTs is lost. Dissolution of SWNTs in a solvent like aniline is practiced here which is a very simple reaction method. Here aniline is capable to form a SWNT-aniline charge transfer complex without attachment of macromolecules or polymer which is also soluble in other organic solvents. Solvation of SWNTs by this method is also capable of maintaining the similarity between the structure of SWNTs before and after the dissolution, which means that the pristine nature of SWNTs is preserved. Formation of charge transfer complex in this reaction has been proven by UV-Vis/NIR absorption and photoluminescence spectroscopy. Raman spectroscopy and electron microscopy (FESEM and TEM) are the evidences for protection of the pristine nature of SWNTs even after high-temperature complexation reaction with aniline and also after solubilization in organic solvents.

  13. Geometry of modified release formulations during dissolution--influence on performance of dosage forms with diclofenac sodium.

    PubMed

    Dorożyński, Przemysław; Kulinowski, Piotr; Jamróz, Witold; Juszczyk, Ewelina

    2014-12-30

    The objectives of the work included: presentation of magnetic resonance imaging (MRI) and fractal analysis based approach to comparison of dosage forms of different composition, structure, and assessment of the influence of the compositional factors i.e., matrix type, excipients etc., on properties and performance of the dosage form during drug dissolution. The work presents the first attempt to compare MRI data obtained for tablet formulations of different composition and characterized by distinct differences in hydration and drug dissolution mechanisms. The main difficulty, in such a case stems from differences in hydration behavior and tablet's geometry i.e., swelling, cracking, capping etc. A novel approach to characterization of matrix systems i.e., quantification of changes of geometrical complexity of the matrix shape during drug dissolution has been developed. Using three chosen commercial modified release tablet formulations with diclofenac sodium we present the method of parameterization of their geometrical complexity on the base of fractal analysis. The main result of the study is the correlation between the hydrating tablet behavior and drug dissolution - the increase of geometrical complexity expressed as fractal dimension relates to the increased variability of drug dissolution results.

  14. Influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steels

    NASA Astrophysics Data System (ADS)

    Li, Junru; Liu, Jianjun; Jiang, Bo; Zhang, Chaolei; Liu, Yazheng

    2017-03-01

    The dissolution process of delta ferrites and the influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steel 10Cr12Ni3Mo2VN were studied by isothermal heating and thermal simulation experiments. The precipitation temperature of delta ferrites in experimental steel is about 1195 °C. M23C6-type carbides incline to precipitate and coarsen at the boundaries of delta ferrites below 930 °C, and can be rapidly dissolved by heating at 1180 °C. The percentage of delta ferrites gradually decreases with heating time. And a Kolmogorov-Johnson-Mehl-Avrami equation was established to describe the dissolution process of delta ferrites at 1180 °C. High temperature pre-deformation can markedly increase the dissolution rate of delta ferrites. Pre-deformation can largely increase the interface area between delta ferrite and matrix and thus increase the unit-time diffusing quantities of alloying elements between delta ferrites and matrix. In addition, high temperature pre-deformation leads to dynamic recrystallization and increases the number of internal grain boundaries in the delta ferrites. This can also greatly increase the diffusing rate of alloying elements. In these cases, the dissolution of delta ferrites can be promoted.

  15. Influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steels

    NASA Astrophysics Data System (ADS)

    Li, Junru; Liu, Jianjun; Jiang, Bo; Zhang, Chaolei; Liu, Yazheng

    2017-02-01

    The dissolution process of delta ferrites and the influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steel 10Cr12Ni3Mo2VN were studied by isothermal heating and thermal simulation experiments. The precipitation temperature of delta ferrites in experimental steel is about 1195 °C. M23C6-type carbides incline to precipitate and coarsen at the boundaries of delta ferrites below 930 °C, and can be rapidly dissolved by heating at 1180 °C. The percentage of delta ferrites gradually decreases with heating time. And a Kolmogorov-Johnson-Mehl-Avrami equation was established to describe the dissolution process of delta ferrites at 1180 °C. High temperature pre-deformation can markedly increase the dissolution rate of delta ferrites. Pre-deformation can largely increase the interface area between delta ferrite and matrix and thus increase the unit-time diffusing quantities of alloying elements between delta ferrites and matrix. In addition, high temperature pre-deformation leads to dynamic recrystallization and increases the number of internal grain boundaries in the delta ferrites. This can also greatly increase the diffusing rate of alloying elements. In these cases, the dissolution of delta ferrites can be promoted.

  16. Storm-generated bedforms and relict dissolution pits and channels on the Yucatan carbonate platform

    NASA Astrophysics Data System (ADS)

    Gulick, S. P.; Goff, J. A.; Stewart, H. A.; Perez-Cruz, L. L.; Davis, M. B.; Duncan, D.; Saustrup, S.; Sanford, J. C.; Fucugauchi, J. U.

    2013-12-01

    The Yucatan 2013 (cruise number 2013/4_ECORD) geophysical and geotechnical hazard site survey took place aboard the R/V Justo Sierra in April 2013. Our study was conducted within the Chicxulub impact crater, encompassing three potential IODP drilling sites. The survey was located ~32 km northwest of Progreso, Mexico; data acquired included ~15.6 km2 of complete multibeam bathymetry coverage, ~435 line km of side scan sonar and CHIRP data, 204 line kilometers of magnetometer data, and 194 line kilometers of surface tow boomer profiles. Based on these data, this portion of the Yucatan Shelf consists of flat-lying, hard limestone rock overlain by isolated ribbons of carbonate sand <1.0 m thick. These ribbons are oriented along NE-SW trends and have smaller scale orthogonal sand-waves (~20-100 m wavelengths and relief of ~0.2-0.6 m) on them. The sand waves are anisotropic with steeper slopes facing the NE. The larger scale morphology can be classified as longitudinal bedforms (ribbons), and the smaller scale transverse bedforms formed in response to a NE-directed flow. This flow direction is inconsistent with the ambient west-directed current conditions, and may therefore be indicative of storm-driven currents. Numerous dissolution pits, ~5-50m in diameter, ~0.2-0.5 m deep with steep (0.1-0.5 gradient) walls, are present in the bare rock regions of most of the study area. These occasionally are floored by rippled, highly reflective (coarse) sediments. We interpret these pits as representing karstic morphology formed during the last sub-aerial exposure of the study area interpreted to have occurred during Holocene times given the present day ~17 m average water depth. A sub-surface reflector imaged on the surface tow boomer data lies 1-3 m below the hard seafloor reflection (sand ribbons are below the vertical resolution of the surface tow boomer), which we interpret as a layer within the limestone bedrock. This reflector is flat-lying and undisturbed throughout the

  17. [Influence of different auxiliary materials on the dissolution of carbamazepine from solid dosage forms].

    PubMed

    Jeköné, B Z

    1998-03-01

    Results of the development of a solid dosage form containing 200 mg Carbamazepine (CBZ) are presented. Citric acid and low substituted Hydroxypropyl-cellulose (L-HPC) were used as dissolution enhancers of the active ingredient. Granulation the CBZ and citric acid with water has no effect on the dissolution of CBZ, but the granulation with absolute alcohol increases the dissolution rate. This enhancement could be explained with a molecular interaction between the CBZ and citric acid in water-free media. This interaction is indicated by the melting points, IR-spectra and scanning electron microscopy of the materials and granules. Further dissolution enhancement can be reached with L-HPC because of its disintegrating effect on the granules. Application of citric acid and L-HPC together results in extremely fast dissolution of the CBZ.

  18. Mesoporous silica sub-micron spheres as drug dissolution enhancers: Influence of drug and matrix chemistry on functionality and stability.

    PubMed

    Brigo, Laura; Scomparin, Elisa; Galuppo, Marco; Capurso, Giovanni; Ferlin, Maria Grazia; Bello, Valentina; Realdon, Nicola; Brusatin, Giovanna; Morpurgo, Margherita

    2016-02-01

    Mesoporous silica particles prepared through a simplified Stöber method and low temperature solvent promoted surfactant removal are evaluated as dissolution enhancers for poorly soluble compounds, using a powerful anticancer agent belonging to pyrroloquinolinones as a model for anticancer oral therapy, and anti-inflammatory ibuprofen as a reference compound. Mesoporous powders composed of either pure silica or silica modified with aminopropyl residues are produced. The influence of material composition and drug chemical properties on drug loading capability and dissolution enhancement are studied. The two types of particles display similar size, surface area, porosity, erodibility, drug loading capability and stability. An up to 50% w/w drug loading is reached, showing correlation between drug concentration in adsorption medium and content in the final powder. Upon immersion in simulating body fluids, immediate drug dissolution occurred, allowing acceptor solutions to reach concentrations equal to or greater than drug saturation limits. The matrix composition influenced drug solution maximal concentration, complementing the dissolution enhancement generated by a mesoporous structure. This effect was found to depend on both matrix and drug chemical properties allowing us to hypothesise general prediction behaviour rules.

  19. Electrolytic recycling of a carbonate salt in a process with a dissolution of spent nuclear fuel in a strong alkaline carbonate media

    SciTech Connect

    Kwang-Wook Kim; In-Tae Kim; Seong-Min Kim; Yeon-Hwa Kim; Eil-Hee Lee; Kwang-Yong Jee

    2007-07-01

    A removal of only uranium from spent nuclear fuel with the concepts of a high proliferation-resistance and a minimal generation of waste is helpful for a spent fuel management in view of a volume reduction of the high level radioactive waste generated from the spent fuel treatment. That can be accomplished by a process using a selective oxidative dissolution of the spent fuel in a carbonate solution of high alkalinity. In this work, an electrolytic method for a de-carbonation and a recovery of CO{sub 2} for recycling the used carbonate solution contaminated with some impurity metal ions generated in such a process with a concept of zero-release of waste solution was studied. A carbonate solution generated from such a system was confirmed to be completely recycled within the system, while the impurity ions being separated from the carbonate solution. (authors)

  20. Fabrication of Carbonate Apatite Block through a Dissolution-Precipitation Reaction Using Calcium Hydrogen Phosphate Dihydrate Block as a Precursor.

    PubMed

    Tsuru, Kanji; Yoshimoto, Ayami; Kanazawa, Masayuki; Sugiura, Yuki; Nakashima, Yasuharu; Ishikawa, Kunio

    2017-03-31

    Carbonate apatite (CO₃Ap) block, which is a bone replacement used to repair defects, was fabricated through a dissolution-precipitation reaction using a calcium hydrogen phosphate dihydrate (DCPD) block as a precursor. When the DCPD block was immersed in NaHCO₃ or Na₂CO₃ solution at 80 °C, DCPD converted to CO₃Ap within 3 days. β-Tricalcium phosphate was formed as an intermediate phase, and it was completely converted to CO₃Ap within 2 weeks when the DCPD block was immersed in Na₂CO₃ solution. Although the crystal structures of the DCPD and CO₃Ap blocks were different, the macroscopic structure was maintained during the compositional transformation through the dissolution-precipitation reaction. CO₃Ap block fabricated in NaHCO₃ or Na₂CO₃ solution contained 12.9 and 15.8 wt % carbonate, respectively. The diametral tensile strength of the CO₃Ap block was 2 MPa, and the porosity was approximately 57% regardless of the carbonate solution. DCPD is a useful precursor for the fabrication of CO₃Ap block.

  1. From slots to tubes: The influence of dimensionality on fracture dissolution models

    NASA Astrophysics Data System (ADS)

    Szymczak, Piotr

    2013-12-01

    We briefly review the models of fracture dissolution process, discussing the experimental and numerical evidence showing that this phenomenon is inherently two-dimensional and hence cannot be accurately described by one-dimensional models. The physical reason for this incompatibility is that a dissolution front in a single rock fracture is potentially unstable to small variations in local permeability, leading to spontaneous formation of dissolution channels in the rock. This leads to a dramatic increase of fissure opening rates, which must be taken into account not only in the estimation of karstification times but also in the assessment of ground subsidence, dam collapse or toxic seepage risks.

  2. The Combination Therapy of Dissolution Using Carbonated Liquid and Endoscopic Procedure for Bezoars: Pragmatical and Clinical Review

    PubMed Central

    Ogawa, Kohei; Mizuno, Ken-ichi; Shinagawa, Yoko; Kobayashi, Yuji; Abe, Hiroyuki; Watanabe, Yukari; Takahashi, Shunsaku; Hayashi, Kazunao; Yokoyama, Junji; Takeuchi, Manabu; Yamagiwa, Satoshi; Sato, Yuichi; Terai, Shuji

    2016-01-01

    Bezoars are relatively rare foreign bodies of gastrointestinal tract and often cause ileus and ulcerative lesions in the stomach and subsequent bleeding and perforation due to their size and stiffness. Therefore, the removal of bezoars is essential and recent development of devices, the endoscopic removal procedure, is often applied. However, due to their stiffness, simple endoscopic removal failed in not a few cases, and surgical removal has also been used. Recently, the efficacy of a combination therapy of endoscopic procedure and dissolution using carbonated liquid has been reported. To develop the safe and effective removal procedure, we carefully reviewed a total of 55 reported cases in this study including our 3 additional cases, successfully treated with dissolution with endoscopic fragmentation. In summary, the data showed the efficiency in the combination therapy, treating the larger size of bezoar and reducing the length of hospital stay. To the best of our knowledge, this is the largest pragmatical and clinical review for the combination therapy of dissolution and endoscopic treatment for bezoars. This review should help physicians to manage bezoars more efficiently. PMID:27642293

  3. Precipitation and dissolution of calcium carbonate: key processes bridging the bio- and geosciences (Vladimir Ivanovich Vernadsky Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Gattuso, J.-P.

    2012-04-01

    In this Vladimir Ivanovich Vernadsky medal lecture, I will focus on the biogeochemical cycle of calcium carbonate (CaCO3) which is arguably one of the best example of a set processes that bridge the bio- and geosciences. The main reactions involved are calcification and dissolution that, respectively, manufacture and destroy calcium carbonate. Biology is intimately involved in these two processes which are key controls of the Earth's climate and leave remains that are of great use to human societies (as building materials) and geoscientists. I will illustrate the bridge between the bio- and geosciences by providing brief examples for each of the following four issues. (1) The marine cycle of CaCO3 and its relationship with climate. The release of CO2 by the precipitation of calcium carbonate and the uptake of CO2 by its dissolution are important controls of atmospheric CO2 and climate. The vertical distribution of Ψ, the ratio of CO2 released/used per CaCO3 precipitated/dissolved in the ocean will be shown to be consistent with the Högbom-Urey reactions. (2) The use of CaCO3 in paleooceanography. The remains of calcium carbonate shells and skeletons are wonderful archives of past environmental changes. Their isotopic composition and the concen-tration of trace elements are invaluable in the reconstruction of past climate. I will address the challenge of calibrating one of the proxies used to reconstruct past ocean pH. (3) The challenge of understanding calcification. Despite having been investigated for decades, many aspects of the physiological and molecular processes involved in calcification by marine organisms remain obscure. Recent breakthroughs, mostly on reef-building corals, will be briefly reviewed. (4) The response of calcification and dissolution to environmental change. The critical importance of CaCO3 precipitation and dissolution as climate controls makes it vital to understand their response to global environmental changes such as ocean warming and

  4. Karst Lands: The dissolution of carbonate rock produces unique landscapes and poses significant hydrological and environmental concerns

    SciTech Connect

    White, W.B.; Culver, D.C.; Herman, J.S.

    1995-09-01

    Karst lands are produced by the action of water on soluble rocks, a process among the most dynamic of all erosive forces that counterbalance the uplifting forces of tectonics. The dissolution of carbonate rock, primarily limestone and dolomite, produces unique landscapes and poses significant hydrological and environmental concerns. The major topic areas discussed in this article include the following: processes that form karst; karst drainage basins; discharge from karst aquifers; caves as paleoclimatic recorders; caves as ecosystems; water issues in karst regions; and sinkholes, soil piping and subsidence. 20 refs., 9 figs.

  5. Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics

    SciTech Connect

    Ostfeld, Aminy E.; Arias, Ana Claudia; Catheline, Amélie; Ligsay, Kathleen; Kim, Kee-Chan; Fogden, Siân; Chen, Zhihua; Facchetti, Antonio

    2014-12-22

    Solutions of unbundled and unbroken single-walled carbon nanotubes have been prepared using a reductive dissolution process. Transparent conductive films spray-coated from these solutions show a nearly twofold improvement in the ratio of electrical conductivity to optical absorptivity versus those deposited from conventional aqueous dispersions, due to substantial de-aggregation and sizable nanotube lengths. These transparent electrodes have been utilized to fabricate P3HT-PCBM organic solar cells achieving power conversion efficiencies up to 2.3%, comparable to those of solar cells using indium tin oxide transparent electrodes.

  6. A silica-supported solid dispersion of bifendate using supercritical carbon dioxide method with enhanced dissolution rate and oral bioavailability.

    PubMed

    Cai, Cuifang; Liu, Muhua; Li, Yun; Guo, Bei; Chang, Hui; Zhang, Xiangrong; Yang, Xiaoxu; Zhang, Tianhong

    2016-01-01

    In this study, to enhance the dissolution rate and oral bioavailability of bifendate, a silica-supported solid dispersion (SD) of bifendate was prepared using supercritical carbon dioxide (ScCO2) technology. The properties of bifendate-silica SD were characterized by differential scanning calorimetry (DSC), X-ray diffraction (X-RD) and scanning electron microscopy. The pharmacokinetic study was carried out in beagle dogs using commercial bifendate dropping pills as a reference which is a conventional SD formulation of bifendate and PEG6000. A novel method of Ultra Performance Convergence Chromatography-tandem mass spectrometry (UPC(2)™-MS/MS) method was applied to determine bifendate concentration in plasma. The amorphous state of bifendate in bifendate-silica SD was revealed in X-RD and DSC when the ratios of bifendate and silica were 1:15 and 1:19, respectively. In vitro dissolution rate was significantly improved with cumulative release of 67% within 20 min relative to 8% for the physical mixture of bifendate and silica, and which was also higher than the commercial dropping pill of 52%. After storage at 75% relative humidity (RH) for 10 d, no recrystallization was found and reduced dissolution rate was obtained due to the absorption of moisture. In pharmacokinetic study, Cmax and AUC0-t for bifendate-silica SD were 153.1 ng/ml and 979.8 ng h/ml, respectively. AUC0-t of bifendate-silica SDs was ∼1.6-fold higher than that of the commercial dropping pills. These results suggest that adsorbing bifendate onto porous silica via ScCO2 technique could be a feasible method to enhance oral bioavailability together with a higher dissolution rate.

  7. Pore-scale study of the effect of secondary carbonate precipitation on the dissolution of primary minerals using the lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Kang, Q.; Chen, L.; Carey, J. W.

    2013-12-01

    Reactive transport processes involving dissolution and/or precipitation are pervasive in Earth, energy, and environmental systems. One typical example is geologic sequestration of carbon dioxide. Among these reactive processes, it is commonly encountered that a second phase precipitates while the primary phase dissolves, and the precipitation and dissolution reactions are fully coupled with each other. In the case of mineral trapping of CO2, the primary silicate mineral dissolves due to a decrease of pH caused by the dissolution of CO2 into the solution; meanwhile the dissolved CO2 can react with cations to form a secondary precipitate of carbonate mineral. Although the effect of precipitation of secondary solid phase on the dissolution of the primary solid phase has been studied extensively, the results reported in the literature are often inconclusive and sometimes even contradict one another. The reason is that the coupled dissolution and precipitation processes are controlled by several factors whose contribution is difficult to ascertain, including the dissolution and precipitation reaction kinetics, temperature and pressure, pH and species concentration of the solution, physicochemical properties of the primary and secondary minerals, as well as the nucleation and crystal mechanisms of the precipitates, etc. In this study, a pore-scale (mesoscopic) model based on the lattice Boltzmann method (LBM) is developed to investigate the effects of secondary precipitation on the dissolution of the primary mineral. The model can predict coupled multiple physicochemical processes including fluid flow, mass transport, chemical reaction, dissolution, precipitation consisting of nucleation and crystal growth, as well as dynamical evolution of pore geometries. Effects of dissolution and precipitation reaction kinetics, molar volumes of primary and secondary minerals, initial powder size and surface roughness of the primary mineral, as well as nucleation and crystal growth

  8. Influence of variable rates of neritic carbonate deposition on atmospheric carbon dioxide and pelagic sediments

    NASA Technical Reports Server (NTRS)

    Walker, J. C.; Opdyke, B. C.

    1995-01-01

    Short-term imbalances in the global cycle of shallow water calcium carbonate deposition and dissolution may be responsible for much of the observed Pleistocene change in atmospheric carbon dioxide content. However, any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep-sea carbonates. The possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle. Boundary conditions can be defined by using extant shallow water carbonate accumulation data and pelagic carbonate deposition/dissolution data. On timescales of thousands of years carbonate deposition versus dissolution is rarely out of equilibrium by more than 1.5 x 10(13) mole yr-1. Results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on timescales less than 10 ka. This disequilibrium is probably due to sea level-induced changes in shallow water calcium carbonate deposition/dissolution, an interpretation that does not conflict with pelagic sedimentary data from the central Pacific.

  9. Influence of variable rates of neritic carbonate deposition on atmospheric carbon dioxide and pelagic sediments

    NASA Technical Reports Server (NTRS)

    Walker, J. C.; Opdyke, B. C.

    1995-01-01

    Short-term imbalances in the global cycle of shallow water calcium carbonate deposition and dissolution may be responsible for much of the observed Pleistocene change in atmospheric carbon dioxide content. However, any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep-sea carbonates. The possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle. Boundary conditions can be defined by using extant shallow water carbonate accumulation data and pelagic carbonate deposition/dissolution data. On timescales of thousands of years carbonate deposition versus dissolution is rarely out of equilibrium by more than 1.5 x 10(13) mole yr-1. Results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on timescales less than 10 ka. This disequilibrium is probably due to sea level-induced changes in shallow water calcium carbonate deposition/dissolution, an interpretation that does not conflict with pelagic sedimentary data from the central Pacific.

  10. Influence of variable rates of neritic carbonate deposition on atmospheric carbon dioxide and pelagic sediments.

    PubMed

    Walker, J C; Opdyke, B C

    1995-06-01

    Short-term imbalances in the global cycle of shallow water calcium carbonate deposition and dissolution may be responsible for much of the observed Pleistocene change in atmospheric carbon dioxide content. However, any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep-sea carbonates. The possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle. Boundary conditions can be defined by using extant shallow water carbonate accumulation data and pelagic carbonate deposition/dissolution data. On timescales of thousands of years carbonate deposition versus dissolution is rarely out of equilibrium by more than 1.5 x 10(13) mole yr-1. Results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on timescales less than 10 ka. This disequilibrium is probably due to sea level-induced changes in shallow water calcium carbonate deposition/dissolution, an interpretation that does not conflict with pelagic sedimentary data from the central Pacific.

  11. Calcite Dissolution Kinetics

    NASA Astrophysics Data System (ADS)

    Berelson, W.; Subhas, A.; Dong, S.; Naviaux, J.; Adkins, J. F.

    2016-12-01

    A geological buffer for high atmospheric CO2 concentrations is neutralization via reaction with CaCO3. We have been studying the dissolution kinetics of carbonate minerals using labeled 13C calcite and Picarro-based measurements of 13C enrichments in solution DIC. This methodology has greatly facilitated our investigation of dissolution kinetics as a function of water carbonate chemistry, temperature and pressure. One can adjust the saturation state Omega by changing the ion activity product (e.g. adjusting carbonate ion concentration), or by changing the solubility product (e.g. adjusting temperature or pressure). The canonical formulation of dissolution rate vs. omega has been refined (Subhas et al. 2015) and shows distinct non-linear behavior near equilibrium and rates in sea water of 1-3 e-6 g/cm2day at omega = 0.8. Carbonic anhydrase (CA), an enzyme that catalyzes the hydration of dissolved CO2 to carbonic acid, was shown (in concentrations <=0.04 g/L) to enhance the dissolution rate at low degrees of undersaturation by >500x. This result points to the importance of carbonic acid in enhancing dissolution at low degrees of undersaturation. CA activity and abundance in nature must be considered regarding the role it plays in catalyzing dissolution. We also have been investigating the role of temperature on dissolution kinetics. An increase of 16C yields an order of magnitude increase in dissolution rate. Temperature (and P) also change Omega critical, the saturation state where dissolution rates change substantially. Increasing pressure (achieved in a pressure reaction chamber we built) also shifts Omega critical closer to equilibrium and small pressure increases have large impact on dissolution kinetics. Dissolution rates are enhanced by an order of magnitude for a change in pressure of 1500 psi relative to the dissolution rate achieved by water chemistry effects alone for an omega of 0.8. We've shown that the thermodynamic determination of saturation state

  12. Dynamics of carbonate chemistry, production, and calcification of the Florida Reef Tract (2009-2010): Evidence for seasonal dissolution

    NASA Astrophysics Data System (ADS)

    Muehllehner, Nancy; Langdon, Chris; Venti, Alyson; Kadko, David

    2016-05-01

    Ocean acidification is projected to lower the Ωar of reefal waters by 0.3-0.4 units by the end of century, making it more difficult for calcifying organisms to secrete calcium carbonate while at the same time making the environment more favorable for abiotic and biotic dissolution of the reefal framework. There is great interest in being able to project the point in time when coral reefs will cross the tipping point between being net depositional to net erosional in terms of their carbonate budgets. Periodic in situ assessments of the balance between carbonate production and dissolution that spans seasonal time scales may prove useful in monitoring and formulating projections of the impact of ocean acidification on reefal carbonate production. This study represents the first broad-scale geochemical survey of the rates of net community production (NCP) and net community calcification (NCC) across the Florida Reef Tract (FRT). Surveys were performed at approximately quarterly intervals in 2009-2010 across seven onshore-offshore transects spanning the upper, middle, and lower Florida Keys. Averaged across the FRT, the rates of NCP and NCC were positive during the spring/summer at 62 ± 7 and 17 ± 2 mmol m-2 d-1, respectively, and negative during the fall/winter at -33 ± 6 and -7 ± 2 mmol m-2 d-1. The most significant finding of the study was that the northernmost reef is already net erosional (-1.1 ± 0.4 kg CaCO3 m-2 yr-1) and midreefs to the south were net depositional on an annual basis (0.4 ± 0.1 kg CaCO3 m-2 yr-1) but erosional during the fall and winter. Only the two southernmost reefs were net depositional year-round. These results indicate that parts of the FRT have already crossed the tipping point for carbonate production and other parts are getting close.

  13. Characterization of carbonate reservoir property changes due to dissolution for far-field conditions of CO2 storage

    NASA Astrophysics Data System (ADS)

    Mangane, P. O.; Gouze, P.; Luquot, L.

    2012-12-01

    Geological storage of CO2 in reservoir pore fluid (e.g. deep saline aquifers), is one of the diverse technologies being explored for deacreasing atmospheric CO2 concentration. After injecting the CO2 as a supercritical fluid at depth, it will slowly dissolve into the pore water producing low pH fluids with a high capacity for dissolving carbonates and consequently changing irreversibly the hydrodynamical properties of the reservoir. Characterizing these changes is essential for modelling flow and CO2 transport during and after the CO2 injection. Here we report experimental results from the injection of the CO2-saturated brine into two distinct limestone cores (a bioclastic carbonate and an oolitic carbonate) of 9 mm diameter, 18 mm length. 3D high-resolution X-ray microtomography (XRMT) of the rock sample have been performed before and after the experiments. The experiments were performed using in-situ sequestration conditions (P = 12MPa and T = 100°C), and notably, under chemical conditions given at the position far away from the well injection site (i.e area where the volume of dissolved CO2 into the brine is low, due to CO2 consumption by the dissolution processes occured during its transport from the well injection site). Permeability k is calculated from the pressure drop across the sample and porosity Φ is deduced from chemical concentration of the outlet fluid. The change of the pore structure is analysed in terms of connectivity, tortuosity and fluid-rock interface from processing the XRMT images. These experiments show that far from the well injection site, dissolution processes are characterized by slow mass tranfer including, in the case of carbonate rock, transport of fine particles, which locally clog the porous space. Then, that leads to the damage of the carbonate reservoir both in terms of connectivity of the porous space and CO2 hydrodynamical storage capacity. In fact, the results of the two experiments show that the porosity decreased locally

  14. Influence of layering on the formation and growth of dissolution pipes in karst systems

    NASA Astrophysics Data System (ADS)

    Petrus, Karine; Pecelerowicz, Michal; Szymczak, Piotr

    2015-04-01

    In karst systems, hydraulic conduits called dissolution pipes (a.k.a. wormholes) are formed as a result of the dissolution of limestone rocks by the water surcharged with CO2. The dissolution pipes are the end result of a positive feedback between spatial variations in porosity in the initial matrix and the local dissolution rate. A small enhancement in porosity at some point in the reaction front increases the fluid flow in that region, which convects reactant further downstream. By this means any local variation in porosity is amplified as the reaction front passes through and propagates downstream with the front, eventually developing into dissolution pipes. As dissolution proceeds the growing pipes interact, competing for the available flow, and eventually the growth of the shorter ones ceases. Here, we investigate numerically the effect of rock stratification on the dissolution pipe growth, using a simple model system with a number of horizontal bedding planes, which are less porous than the rest of the matrix. Stratification is shown to affect the resulting piping patterns in a variety of ways. First of all, it enhances the competition between the pipes, impeding the growth of the shorter ones and enhancing the flow in the longer ones, which therefore grow longer. Next, it affects the shapes of individual dissolution pipes, with characteristic widening of the profiles in between the layers and narrowing within the layers. These results are in qualitative agreement with the piping morphologies observed in nature. Importantly, measuring the ratio between the pipe diameters in different layers can provide one with information on the conditions prevailing during the formation of the pattern as well as on the physical characteristics of the layers in a given natural system. Additionally, we have investigated the model with layers of the same porosity but a smaller dissolution rate. Interestingly, in this case, the stratification is shown to weaken the competition

  15. Fabrication of calcite blocks from gypsum blocks by compositional transformation based on dissolution-precipitation reactions in sodium carbonate solution.

    PubMed

    Ishikawa, Kunio; Kawachi, Giichiro; Tsuru, Kanji; Yoshimoto, Ayami

    2017-03-01

    Calcium carbonate (CaCO3) has been used as a bone substitute, and is a precursor for carbonate apatite, which is also a promising bone substitute. However, limited studies have been reported on the fabrication of artificial calcite blocks. In the present study, cylindrical calcite blocks (ϕ6×3mm) were fabricated by compositional transformation based on dissolution-precipitation reactions using different calcium sulfate blocks as a precursor. In the dissolution-precipitation reactions, both CaSO4·2H2O and CaSO4 transformed into calcite, a polymorph of CaCO3, while maintaining their macroscopic structure when immersed in 1mol/L Na2CO3 solution at 80°C for 1week. The diametral tensile strengths of the calcite blocks formed using CaSO4·2H2O and CaSO4 were 1.0±0.3 and 2.3±0.7MPa, respectively. The fabrication of calcite blocks using CaSO4·2H2O and CaSO4 proposed in this investigation may be a useful method to produce calcite blocks because of the self-setting ability and high temperature stability of gypsum precursors. Copyright © 2016 Elsevier B.V. All rights reserved.

  16. Study of dissolution hydrodynamic conditions versus drug release from hypromellose matrices: the influence of agitation sequence.

    PubMed

    Asare-Addo, Kofi; Levina, Marina; Rajabi-Siahboomi, Ali R; Nokhodchi, Ali

    2010-12-01

    In this article, the influence of agitation in descending and ascending sequences as a systematic method development process for potentially discriminating fed and fasted states and evaluation of its effects on the drug release from swelling gel-forming hydrophilic matrix tablets were investigated. Theophylline extended release (ER) matrices containing hypromellose (hydroxypropyl methylcellulose (HPMC)) were evaluated in media with a pH range of 1.2-7.5, using an automated USP type III, Bio-Dis dissolution apparatus at 5, 10, 15, 20, 25 and 30 dips per minute (dpm). Agitation had a profound effect on the drug release from the HPMC K100LV matrices. Drug release in pH 1.2 changed from about 40% at 5 dpm to about 80% at 30 dpm over a 60 min period alone. The matrices containing HPMC K4M, K15M and K100M however were not significantly affected by the agitation rate. The similarity factor f2 was calculated using drug release at 10 dpm as a reference. The ascending agitations of 5-30 dpm and the descending order of agitation 30-5 dpm were also evaluated. Anomalous transport was the only kinetic of release for the K4M, K15M and K100M tablet matrices. The lower viscous polymer of K100LV had some matrices exhibiting Fickian diffusion as its kinetics of release. The use of systematic change of agitation method may indicate potential fed and fasted effects on drug release from hydrophilic matrices.

  17. Pressurized laboratory experiments show no stable carbon isotope fractionation of methane during gas hydrate dissolution and dissociation.

    PubMed

    Lapham, Laura L; Wilson, Rachel M; Chanton, Jeffrey P

    2012-01-15

    The stable carbon isotopic ratio of methane (δ(13)C-CH(4)) recovered from marine sediments containing gas hydrate is often used to infer the gas source and associated microbial processes. This is a powerful approach because of distinct isotopic fractionation patterns associated with methane production by biogenic and thermogenic pathways and microbial oxidation. However, isotope fractionations due to physical processes, such as hydrate dissolution, have not been fully evaluated. We have conducted experiments to determine if hydrate dissolution or dissociation (two distinct physical processes) results in isotopic fractionation. In a pressure chamber, hydrate was formed from a methane gas source at 2.5 MPa and 4 °C, well within the hydrate stability field. Following formation, the methane source was removed while maintaining the hydrate at the same pressure and temperature which stimulated hydrate dissolution. Over the duration of two dissolution experiments (each ~20-30 days), water and headspace samples were periodically collected and measured for methane concentrations and δ(13)C-CH(4) while the hydrate dissolved. For both experiments, the methane concentrations in the pressure chamber water and headspace increased over time, indicating that the hydrate was dissolving, but the δ(13)C-CH(4) values showed no significant trend and remained constant, within 0.5‰. This lack of isotope change over time indicates that there is no fractionation during hydrate dissolution. We also investigated previous findings that little isotopic fractionation occurs when the gas hydrate dissociates into gas bubbles and water due to the release of pressure. Over a 2.5 MPa pressure drop, the difference in the δ(13)C-CH(4) was <0.3‰. We have therefore confirmed that there is no isotope fractionation when the gas hydrate dissociates and demonstrated that there is no fractionation when the hydrate dissolves. Therefore, measured δ(13)C-CH(4) values near gas hydrates are not affected

  18. Prediction and inhibition of molten carbonate fuel cell shorting by NiO cathode dissolution

    SciTech Connect

    Ogawa, Takashi; Nirasawa, Hitoshi; Murata, Kenji

    1995-12-31

    A model of time until shorting begins due to NiO dissolution/precipitation in MCFC was developed on the assumption that electronic conduction in the cell would happen when the concentration of dispersed nickel particles exceeded a critical value at the anode/electrolyte interface. The equation for the estimation of time-to-short-beginning (TTS) was derived as: TTS{sup 0.5}/t = A + B/K{sub Ni} pCO{sub 2} (t: matrix thickness, K{sub Ni}: NiO solubility at pCO{sub 2} = 1 atm., and A, B: constant). Life tests under different conditions on several single cells proved the usability of this equation. For the purpose of retarding MCFC shorting, a cell with a low rate of NiO dissolution, with a LiFeO{sub 2} layer, an out-of-cell oxidized NiO cathode, and a Li{sub 2}CO{sub 3}-Na{sub 2}CO{sub 3} eutectic electrolyte was made. The life test results showed that the nickel dissolution rate in the cell was less than 1/5 slower than that in the ordinary cells with an in situ oxidized NiO cathode and high Li{sub 2}CO{sub 3}-K{sub 2}CO{sub 3} eutectic electrolyte.

  19. A porous silica rock ("tripoli") in the footwall of the Jurassic Úrkút manganese deposit, Hungary: composition, and origin through carbonate dissolution

    USGS Publications Warehouse

    Polgari, Marta; Szabo, Zoltan; Szabo-Drubina, Magda; Hein, James R.; Yeh, Hsueh-Wen

    2005-01-01

    The mineralogical, chemical, and isotopic compositions were determined for a white tripoli from the footwall of the Jurassic Úrkút Mn-oxide ore deposit in the Bakony Mountains, Hungary. The tripoli consists of quartz and chalcedony, with SiO2 contents up to 100 wt.%; consequently, trace-element contents are very low. Oxygen isotopes and quartz crystallinity indicate a low-temperature diagenetic origin for this deposit. The tripoli was formed by dissolution of the carbonate portion of the siliceous (sponge spicules) Isztimér Limestone. Dissolution of the carbonate was promoted by inorganic and organic acids generated during diagensis and left a framework composed of diagenetic silica that preserved the original volume of the limestone layer. The relative enrichment of silica and high porosity is the result of that carbonate dissolution. The silty texture of this highly friable rock is due to the structurally weak silica framework.

  20. Effects of acid deposition on dissolution of carbonate stone during summer storms in the Adirondack Mountains, New York, 1987-89

    USGS Publications Warehouse

    Schuster, Paul F.; Reddy, Michael M.; Sherwood, S.I.

    1994-01-01

    This study is part of a long-term research program designed to identify and quantify acid rain damage to carbonate stone. Acidic deposition accelerates the dissolution of carbonate-stone monuments and building materials. Sequential sampling of runoff from carbonate-stone (marble) and glass (reference) microcatchments in the Adirondack Mountains in New York State provided a detailed record of the episodic fluctuations in rain rate and runoff chemistry during individual summer storms. Rain rate and chemical concentrations from carbonate-stone and glass runoff fluctuated three to tenfold during storms. Net calcium-ion concentrations from the carbonatestone runoff, a measure of stone dissolution, typically fluctuated twofold during these storms. High net sulfate and net calcium concentrations in the first effective runoff at the start of a storm indicated that atmospheric pollutants deposited on the stone surface during dry periods formed calcium sulfate minerals, an important process in carbonate stone dissolution. Dissolution of the carbonate stone generally increased up to twofold during coincident episodes of low rain rate (less than 5 millimeters per hour) and decreased rainfall (glass runoff) pH (less than 4.0); episodes of high rain rate (cloudbursts) were coincident with a rapid increase in rainfall pH and also a rapid decrease in the dissolution of carbonate-stone. During a storm, it seems the most important factors causing increased dissolution of carbonate stone are coincident periods of low rain rate and decreased rainfall pH. Dissolution of the carbonate stone decreased slightly as the rain rate exceeded about 5 millimeters per hour, probably in response to rapidly increasing rainfall pH during episodes of high rain rate and shorter contact time between the runoff and the stone surface. High runoff rates resulting from cloudbursts remove calcium sulfate minerals formed during dry periods prior to storms and also remove dissolution products formed in large

  1. Influence of Non-homogeneous Particle Distributions on Drug Release in a Couette in vitro Dissolution Device

    NASA Astrophysics Data System (ADS)

    Jayaraman, Balaji; Brasseur, James; Wang, Yanxing

    2015-11-01

    Drug dissolution rates from powdered formulations are commonly measured in in vitro devices. Both measurements and models commonly assume perfect mixing of drug and particle within the device. In this study we analyze the potential importance of heterogeneity in particle concentration and distribution using CFD that incorporates physically accurate mathematical representations of hydrodynamic enhancement of mass transport from shear as applicable to drug dissolution in vivo as well as in vitro. We have developed a high-fidelity computational formulation using the Lattice Boltzmann Method (LBM) with the parallel particle tracking for a polydisperse collection transported by the flow. Drug release from the small (<100 μm) Lagrangian `point' particles is modeled using a mathematical framework that is built on a validated first principles `quasi-steady state' approximation with correlations for shear enhancement and integrated with the coarser Eulerian LBM flow field using a subgrid formulation Our Eulerian-Lagrangian formulation takes into account spatial variations in particle `bulk' concentration from polydisperse particle distributions with specified particle distribution heterogeneities. We shall discuss the primary influences of heterogeneous bulk concentrations surrounding individual particles and non-homogeneous particle distributions in an in vitro Couette flow device to quantify the relative influences of shear enhancement on drug dissolution in vivo vs. in vitro

  2. Solutal convection induced by dissolution. Influence on erosion dynamics and interface shaping.

    NASA Astrophysics Data System (ADS)

    Berhanu, Michael; Philippi, Julien; Cohen, Caroline; Derr, Julien; Courrech du Pont, Sylvain

    2017-04-01

    Rock fractures invaded by a water flow, are often subjected to dissolution, which let grow and evolve the initial fracture network, by evacuating the eroded minerals under a solute form. In the case of fast kinetic of dissolution, local erosion rate is set by the advection of the solute. The erosion velocity decreases indeed with the solute concentration at the interface and vanishes when this concentration reaches the saturation value. Even in absence of an imposed or external flow, advection can drive the dissolution, when buoyancy effects due to gravity induce a solutal convection flow, which controls the erosive dynamics and modifies the shape of the dissolving interface. Here, we investigate using model experiments with fast dissolving materials and numerical simulations in simplified situations, solutal convection induced by dissolution. Results are interpreted regarding a linear stability analysis of the corresponding solutal Rayleigh-Benard instability. A dissolving surface is suspended above a water height, initially at rest. In a first step, solute flux is transported through a growing diffusion layer. Then after an onset time, once the layer exceeds critical width, convection flow starts under the form of falling plumes. A dynamic equilibrium results in average from births and deaths of intermittent plumes, setting the size of the solute concentration boundary layer at the interface and thus the erosion velocity. Solutal convection can also induce a pattern on the dissolving interface. We show experimentally with suspended and inclined blocks of salt and sugar, that in a linear stage, the first wavelength of the dissolution pattern corresponds to the wavelength of the convection instability. Then pattern evolves to more complex shapes due to non-linear interactions between the flow and the eroded interface. More generally, we inquire what are the conditions to observe a such solutal convection instability in geological situations and if the properties of

  3. Influence of surfactant-treated starch on the disintegration and dissolution of sulphadiazine tablets.

    PubMed

    Nasipuri, R N; Omotosho, J A

    1985-03-01

    The effects of treating cassava starch with sodium lauryl sulphate and Polysorbate 80 and the method of incorporating the treated and plain starch as disintegrant on the physical properties of sulphadiazine tablets were investigated. Disintegration and dissolution rates were faster with starch in which surfactant was incorporated in dry state than with starch treated with solution of surfactant. A direct correlation was observed between the Hardness-Friability Index and T90 values. Polysorbate 80-treated starch exhibited a better dissolution profile than SLS-treated starch.

  4. Swelling and erosion properties of hydroxypropylmethylcellulose (Hypromellose) matrices--influence of agitation rate and dissolution medium composition.

    PubMed

    Kavanagh, Nicole; Corrigan, Owen I

    2004-07-26

    The effect of dissolution medium variables, such as medium composition, ionic strength and agitation rate, on the swelling and erosion of Hypromellose (hydroxypropylmethylcellulose, HPMC) matrices of different molecular weights was examined. Swelling and erosion of HPMC polymers was determined by measuring the wet and subsequent dry weights of matrices. It was possible to describe the rate of dissolution medium uptake in terms of a square root relationship and the erosion of the polymer in terms of the cube root law. The extent of swelling increased with increasing molecular weight, and decreased with increasing agitation rate. The erosion rate was seen to increase with decrease in polymer molecular weight, with a decrease in ionic strength and with increasing agitation rate. The sensitivity of polymer erosion to the degree of agitation may influence the ability of these polymers to give reproducible, agitation-independent release, compared to more rigid non-eroding matrix materials, in the complex hydrodynamic environment of the gastrointestinal tract.

  5. Carbide Formation and Dissolution in Biomedical Co-Cr-Mo Alloys with Different Carbon Contents during Solution Treatment

    NASA Astrophysics Data System (ADS)

    Mineta, Shingo; Namba, Shigenobu; Yoneda, Takashi; Ueda, Kyosuke; Narushima, Takayuki

    2010-08-01

    The microstructures of as-cast and heat-treated biomedical Co-Cr-Mo (ASTM F75) alloys with four different carbon contents were investigated. The as-cast alloys were solution treated at 1473 to 1548 K for 0 to 43.2 ks. The precipitates in the matrix were electrolytically extracted from the as-cast and heat-treated alloys. An M23C6 type carbide and an intermetallic σ phase (Co(Cr,Mo)) were detected as precipitates in the as-cast Co-28Cr-6Mo-0.12C alloy; an M23C6 type carbide, a σ phase, an η phase (M6C-M12C type carbide), and a π phase (M2T3X type carbide with a β-manganese structure) were detected in the as-cast Co-28Cr-6Mo-0.15C alloy; and an M23C6 type carbide and an η phase were detected in the as-cast Co-28Cr-6Mo-0.25C and Co-28Cr-6Mo-0.35C alloys. After solution treatment, complete precipitate dissolution occurred in all four alloys. Under incomplete precipitate dissolution conditions, the phase and shape of precipitates depended on the heat-treatment conditions and the carbon content in the alloys. The π phase was detected in the alloys with carbon contents of 0.15, 0.25, and 0.35 mass pct after heat treatment at high temperature such as 1548 K for a short holding time of less than 1.8 ks. The presence of the π phase in the Co-Cr-Mo alloys has been revealed in this study for the first time.

  6. The dissolution of synthetic Na-boltwoodite in sodium carbonate solutions

    NASA Astrophysics Data System (ADS)

    Ilton, Eugene S.; Liu, Chongxuan; Yantasee, Wassana; Wang, Zheming; Moore, Dean A.; Felmy, Andrew R.; Zachara, John M.

    2006-10-01

    Uranyl silicates such as uranophane and Na-boltwoodite appear to control the solubility of uranium in certain contaminated sediments at the US Department of Energy Hanford site [Liu, C., Zachara, J.M., Qafoku, O., McKinley, J.P., Heald, S.M., Wang, Z. 2004. Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA. Geochim. Cosmochim. Acta68, 4519-4537.]. Consequently, the solubility of synthetic Na-boltwoodite, Na(UO 2)(SiO 3OH) · 1.5H 2O, was determined over a wide range of bicarbonate concentrations, from circumneutral to alkaline pH, that are representative of porewater and groundwater compositions at the Hanford site and calcareous environments generally. Experiments were open to air. Results show that Na-boltwoodite dissolution was nearly congruent and its solubility and dissolution kinetics increased with increasing bicarbonate concentration and pH. A consistent set of solubility constants were determined from circumneutral pH (0 added bicarbonate) to alkaline pH (50 mM added bicarbonate). Average logKspo=5.86±0.24 or 5.85 ± 0.0.26; using the Pitzer ion-interaction model or Davies equation, respectively. These values are close to the one determined by [Nguyen, S.N., Silva, R.J., Weed, H.C., Andrews, Jr., J.E., 1992. Standard Gibbs free energies of formation at the temperature 303.15 K of four uranyl silicates: soddyite, uranophane, sodium boltwoodite, and sodium weeksite. J. Chem. Thermodynamics24, 359-376.] under very different conditions (pH 4.5, Ar atmosphere).

  7. Influence of ammonia on silver nanoparticle dissolution and toxicity to Nitrosomonas europaea.

    PubMed

    Kostigen Mumper, Cameron; Ostermeyer, Ann-Kathrin; Semprini, Lewis; Radniecki, Tyler S

    2013-11-01

    Nitrosomonas europaea, a model ammonia oxidizing bacterium, was sensitive to both ionic silver (Ag(+)) and 20 nm citrate capped silver nanoparticles (AgNPs). AgNP toxicity has been previously shown to be primarily due to the dissolution of Ag(+). The rate of AgNP dissolution dramatically increased in test medium containing ammonium sulfate ((NH4)2SO4) and HEPES buffer compared to test medium containing either deionized water or HEPES buffer alone. The AgNP dissolution rates accelerated with increases in ammonia (NH3) concentrations either through increases in pH or through higher (NH4)2SO4 concentrations. Ammonia likely participated in the oxidation of the AgNP to form [Formula: see text] in solution leading to the observed increase in AgNP dissolution rates. AgNP toxicity was enhanced as NH3 concentrations increased. However, Ag(+) toxicity was constant at all NH3 concentrations tested. Therefore, it can be concluded that the increased AgNP toxicity was due to increased Ag(+) release and not due to a synergistic effect between NH3 and Ag(+). The results of this study may provide insights in the fate and toxicity of AgNPs in high NH3 environments including wastewater treatment plants, eutrophic waterways and alkaline environments.

  8. Influence of bovine serum albumin and alginate on silver nanoparticle dissolution and toxicity to Nitrosomonas europaea.

    PubMed

    Ostermeyer, Ann-Kathrin; Kostigen Mumuper, Cameron; Semprini, Lewis; Radniecki, Tyler

    2013-12-17

    Bovine serum albumin (BSA), a model protein, reduced the toxicity of 20 nm citrate silver nanoparticles (AgNP) toward Nitrosomonas europaea, a model ammonia oxidizing bacteria, through a dual-mode protection mechanism. BSA reduced AgNP toxicity by chelating the silver ions (Ag(+)) released from the AgNPs. BSA further reduced AgNP toxicity by binding to the AgNP surface thus preventing NH3-dependent dissolution from occurring. Due to BSA's affinity toward Ag(+) chemisorbed on the AgNP surface, increased concentrations of BSA lead to increased AgNP dissolution rates. This, however, did not increase AgNP toxicity as the dissolved Ag(+) were adsorbed onto the BSA molecules. Alginate, a model extracellular polysaccharide (EPS), lacks strong Ag(+) ligands and was unable to protect N. europaea from Ag(+) toxicity. However, at high concentrations, alginate reduced AgNP toxicity by binding to the AgNP surface and reducing AgNP dissolution rates. Unlike BSA, alginate only weakly interacted with the AgNP surface and was unable to completely prevent NH3-dependent AgNP dissolution from occurring. Based on these results, AgNP toxicity in high protein environments (e.g., wastewater) is expected to be muted while the EPS layers of wastewater biofilms may provide additional protection from AgNPs, but not from Ag(+) that have already been released.

  9. The dissolution of calcite in aqueous acid: The influence of humic species

    SciTech Connect

    Compton, R.G.; Sanders, G.H.W. )

    1993-07-01

    The kinetics of proton-induced calcite dissolution in aqueous solution in the presence of humic acids and their sodium salts are reported. In equilibrated acid solutions (pH <4) there is no inhibition by humic material and dissolution proceeds at a rate simply determined by the solution pH. Contrastingly the sodium salts of humic acids were found to have a significant inhibitory effect on the acid catalyzed dissolution. This was quantified using a novel channel flow cell experiment which employed two electrodes, the upstream of which was used to inject protons into a neutral solution, which also contained sodium salts of humic acid, via electrolytic oxidation of dissolved hydroquinone. The two electrodes were located immediately upstream and downstream of a calcite crystal so that the proton injection served to dissolve the calcite in the (inhibiting) presence of humic salts unequilibrated with the solution pH. The amount of H[sup +] which survived passage to the downstream detector'' electrode was used to quantify the rate of dissolution and hence the inhibitory effects of the humic acid. The latter were found to operate in a manner not inconsistent with Langmuirian adsorption.

  10. Oxidative dissolution of unirradiated Mimas MOX fuel (U/Pu oxides) in carbonated water under oxic and anoxic conditions

    NASA Astrophysics Data System (ADS)

    Odorowski, Mélina; Jégou, Christophe; De Windt, Laurent; Broudic, Véronique; Peuget, Sylvain; Magnin, Magali; Tribet, Magaly; Martin, Christelle

    2016-01-01

    Few studies exist concerning the alteration of Mimas Mixed-OXide (MOX) fuel, a mixed plutonium and uranium oxide, and data is needed to better understand its behavior under leaching, especially for radioactive waste disposal. In this study, two leaching experiments were conducted on unirradiated MOX fuel with a strong alpha activity (1.3 × 109 Bq.gMOX-1 reproducing the alpha activity of spent MOX fuel with a burnup of 47 GWd·tHM-1 after 60 years of decay), one under air (oxic conditions) for 5 months and the other under argon (anoxic conditions with [O2] < 1 ppm) for one year in carbonated water (10-2 mol L-1). For each experiment, solution samples were taken over time and Eh and pH were monitored. The uranium in solution was assayed using a kinetic phosphorescence analyzer (KPA), plutonium and americium were analyzed by a radiochemical route, and H2O2 generated by the water radiolysis was quantified by chemiluminescence. Surface characterizations were performed before and after leaching using Scanning Electron Microscopy (SEM), Electron Probe Microanalyzer (EPMA) and Raman spectroscopy. Solubility diagrams were calculated to support data discussion. The uranium releases from MOX pellets under both oxic and anoxic conditions were similar, demonstrating the predominant effect of alpha radiolysis on the oxidative dissolution of the pellets. The uranium released was found to be mostly in solution as carbonate species according to modeling, whereas the Am and Pu released were significantly sorbed or precipitated onto the TiO2 reactor. An intermediate fraction of Am (12%) was also present as colloids. SEM and EPMA results indicated a preferential dissolution of the UO2 matrix compared to the Pu-enriched agglomerates, and Raman spectroscopy showed the Pu-enriched agglomerates were slightly oxidized during leaching. Unlike Pu-enriched zones, the UO2 grains were much more sensitive to oxidative dissolution, but the presence of carbonates did not enable observation of an

  11. The influence of deposited films on the anodic dissolution of uranium dioxide

    NASA Astrophysics Data System (ADS)

    Ofori, Derrick; Keech, Peter G.; Noël, James J.; Shoesmith, David W.

    2010-05-01

    Corrosion product deposits formed over long periods of time could exert a considerable influence on the corrosion rate of used nuclear fuel under permanent disposal conditions. To simulate the build up of such deposits, the oxidative dissolution of UO 2 (nuclear fuel) has been studied under constant current conditions in sodium chloride (pH = 9.5) solutions containing silicate. Currents in the range 1-300 nA cm -2 (normalized to the geometric area of the electrode surface) were applied in an attempt to simulate rates as close as experimentally feasible to those anticipated under disposal conditions. The deposits were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. At high currents (⩾20 nA cm -2) very high potentials (˜0.5 V vs. SCE) were achieved and surface deposits were formed at localized sites on the electrode surface. Raman analyses indicated that these deposits were hydrated uranyl silicates. Their localization was shown to be due to the formation of acidified sites on an otherwise passive surface as a consequence of uranyl ion hydrolysis underneath the deposit. At these sites the local current density was considerably higher than the nominally applied current density. The fraction of the surface covered by a deposit increased as the applied current decreased, leading to a decrease in the extent of acidification. Measurements as a function of applied current density established a potential of ˜0.25 V (vs. SCE) as a threshold below which acidification did not occur despite the formation of a deposit. When the current was reduced to 1-2 nA cm -2, the potential (˜0.11 V (vs. SCE)) approached the range of corrosion potentials measured in aerated solutions. These values are well below the threshold potential. Since the maximum corrosion current densities anticipated under actual disposal conditions are <1 nA cm -2, the prospects for acidification leading to enhanced corrosion and radionuclide

  12. Dissolved inorganic carbon (DIC) and its δ13C in the Ganga (Hooghly) River estuary, India: Evidence of DIC generation via organic carbon degradation and carbonate dissolution

    NASA Astrophysics Data System (ADS)

    Samanta, Saumik; Dalai, Tarun K.; Pattanaik, Jitendra K.; Rai, Santosh K.; Mazumdar, Aninda

    2015-09-01

    In this study, we present comprehensive data on dissolved Ca, dissolved inorganic carbon (DIC) and its carbon isotope composition (δ13CDIC) of (i) the Ganga (Hooghly) River estuary water sampled during six seasons of contrasting water discharge over 2 years (2012 and 2013), (ii) shallow groundwater from areas adjacent to the estuary and (iii) industrial effluent water and urban wastewater draining into the estuary. Mass balance calculations indicate that processes other than the conservative mixing of seawater and river water are needed to explain the measured DIC and δ13CDIC. Results of mixing calculations in conjunction with the estimated undersaturated levels of dissolved O2 suggest that biological respiration and organic carbon degradation dominate over biological production in the estuary. An important outcome of this study is that a significant amount of DIC and dissolved Ca is produced within the estuary at salinity ⩾10, particularly during the monsoon period. Based on consideration of mass balance and a strong positive correlation observed between the "excess" DIC and "excess" Ca, we contend that the dominant source of DIC generated within the estuary is carbonate dissolution that is inferred to be operating in conjunction with degradation of organic carbon. Calculations show that groundwater cannot account for the observed "excess" Ca in the high salinity zone. Estimated DIC contributions from anthropogenic activity are minor, and they constitute ca. 2-3% of the river water DIC concentrations. The estimated annual DIC flux from the estuary to the Bay of Bengal is ca. (3-4) × 1012 g, of which ca. 40-50% is generated within the estuary. The monsoon periods account for the majority (ca. 70%) of the annual DIC generation in the estuary. The annual DIC flux from the Hooghly estuary accounts for ca. 1% of the global river DIC flux to the oceans. This is disproportionately higher than the water contribution from the Hooghly River to the oceans, which

  13. Dissolution kinetics of polycrystalline calcium sulfate-based materials: influence of chemical modification.

    PubMed

    Fisher, Robin D; Mbogoro, Michael M; Snowden, Michael E; Joseph, Maxim B; Covington, James A; Unwin, Patrick R; Walton, Richard I

    2011-09-01

    Using a channel flow cell (CFC) system, the dissolution kinetics of polycrystalline gypsum-based materials have been examined with the aim of understanding their interaction with water, a property that limits the applications of the material in many situations. ICP (inductively coupled plasma) analysis of elemental concentrations in solution as a function of time yields surface fluxes by using a finite element modeling approach to simulate the hydrodynamic behavior within the CFC. After correction for surface roughness, a value for the intrinsic dissolution flux into water of pure polycrystalline gypsum, CaSO(4).2H(2)O, of 1.1 (±0.4) × 10(-8) mol cm(-2) s(-1) has been obtained. The addition of known humid creep inhibitors to the gypsum samples, including boric acid, tartaric acid and 3,4,5-trihydroxybenzoic acid (gallic acid), was found to have little measurable effect on the dissolution kinetics of gypsum: all yielded dissolution fluxes of 1.4 (±0.6) × 10(-8) mol cm(-2) s(-1). However, trisodium trimetaphosphate (STMP) was found to have a small detectable inhibitory effect relative to pure gypsum yielding a flux of 7.4 (±2.0) × 10(-9) mol cm(-2) s(-1). The data strongly suggest that models for humid creep inhibition that involve dissolution-crystallization of gypsum crystallites are less likely than those that involve a hindered ingress of water into the gypsum matrix. For comparison, composite materials that comprised of calcium sulfate anhydrite (CaSO(4)) crystallites bound by a polyphosphate matrix were also studied. For some of these samples, Ca(2+) surface fluxes were observed to be ∼1 order of magnitude lower than values for polycrystalline gypsum control substrates, suggesting a useful way to impart water resistance to gypsum-based materials.

  14. Influence of Concentration and Agitation of Sodium Hypochlorite and Peracetic Acid Solutions on Tissue Dissolution.

    PubMed

    Tanomaru-Filho, Mário; Silveira, Bruna Ramos Franco; Martelo, Roberta Bosso; Guerreiro-Tanomaru, Juliane Maria

    2015-11-01

    To evaluated the tissue dissolution of sodium hypochlorite (NaOCl) and peracetic acid (PA) solutions at different concentrations, with or without ultrasonic agitation. The following solutions were analyzed: 2.5% NaOCl, 0.5, 1 and 2% PA, 1% PA associated with 6.5% hydrogen peroxide (HP) and saline. Fragments of bovine pulp tissue with 25 ± 2g mg were immersed into test tubes containing 4 mL of the solutions for 10 minutes. In the groups with agitation, pulp tissues were submitted to 2 cycles of 1 minute of ultrasonic agitation. The specimens were weighed after the removal from the solutions. The percentage of mass loss was calculated according to the difference of mass before and after exposure to solutions. Data were submitted to ANOVA and Tukey tests (p < 0.05). A total of 2.5% NaOCl with or without agitation showed the higher tissue dissolution (between 64.5 and 67% of mass reduction) (p < 0.005). By comparing the PA solutions, the concentrations of 1 and 2% with or without agitation and the concentration of 0.5% with agitation showed similar dissolution activity (between 35.4 and 44% of mass reduction). The use of the ultrasonic agitation promoted an increase of the dissolution ability only for 0.5% PA. Peracetic acid solution has pulp tissue dissolution. However, this ability is lower than 2.5% NaOCl solution. The sodium hypochlorite solution shows higher ability to dissolve tissue than PA.

  15. Theoretical study of the influence of chemical reactions and physical parameters on the convective dissolution of CO2 in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Loodts, Vanessa; Rongy, Laurence; De Wit, Anne

    2014-05-01

    Subsurface carbon sequestration has emerged as a promising solution to the problem of increasing atmospheric carbon dioxide (CO2) levels. How does the efficiency of such a sequestration process depend on the physical and chemical characteristics of the storage site? This question is emblematic of the need to better understand the dynamics of CO2 in subsurface formations, and in particular, the properties of the convective dissolution of CO2 in the salt water of aquifers. This dissolution is known to improve the safety of the sequestration by reducing the risks of leaks of CO2 to the atmosphere. Buoyancy-driven convection makes this dissolution faster by transporting dissolved CO2 further away from the interface. Indeed, upon injection, the less dense CO2 phase rises above the aqueous layer where it starts to dissolve. The dissolved CO2 increases the density of the aqueous solution, thereby creating a layer of denser CO2-rich solution above less dense solution. This unstable density gradient in the gravity field is at the origin of convection. In this framework, we theoretically investigate the effect of CO2 pressure, salt concentration, temperature, and chemical reactions on the dissolution-driven convection of CO2 in aqueous solutions. On the basis of a linear stability analysis, we assess the stability of the time-dependent density profiles developing when CO2 dissolves in an aqueous layer below it. We predict that increasing CO2 pressure destabilizes the system with regard to buoyancy-driven convection, because it increases the density gradient at the origin of the instability. By contrast, increasing salt concentration or temperature stabilizes the system via effects on CO2 solubility, solutal expansion coefficient, diffusion coefficient and on the viscosity and density of the solution. We also show that a reaction of CO2 with chemical species dissolved in the aqueous solution can either enhance or decrease the amplitude of the convective dissolution compared

  16. Influence of Permian salt dissolution on distribution of shallow Niobrara gas fields, eastern Colorado

    SciTech Connect

    Oldham, D.W.; Smosna, R.A.

    1996-06-01

    Subsurface analysis of Permian salt and related strata in the shallow Niobrara gas area on the eastern flank of the Denver basin reveals that the location of faulted anticlines which produce gas from porous chalk is related to the occurrence of six Nippewalla Group (Leonardian) salt zones. Salt distribution is controlled by the configuration of evaporate basins during the Leonardian, truncation at a sub-Jurassic unconformity (which has completely removed Guadalupian salts), and post-Jurassic subsurface dissolution. Significant dissolution took place in response to Laramide orogeny and subsequent eastward regional groundwater flow within the Lyons (Cedar Hills) Sandstone aquifer. Initially, dissolution occurred along a regional facies change from sandstone to salt. Solution collapse allowed for cross-formational flow and removal of younger salts. Shallow Niobrara gas fields are situated above salt outliers or along regionally updip salt edges. No significant Niobrara production exists in areas where salt is absent. Structural relief across fields is related to Leonardian thickness variations, rather than subsalt offset. Seismic data reveal abrupt Leonardian thinning at the regionally updip limit of Eckley field, which has produced over 33 BCFG. Thickness of residual salt may be important in controlling the amount of gas trapped within the Niobrara. Where thick salts are preserved, structural relief is greater, the gas-water transition zone is thicker, and gas saturation is higher at the crests of faulted anticlines.

  17. Influence of coating material on the flowability and dissolution of dry-coated fine ibuprofen powders.

    PubMed

    Qu, Li; Zhou, Qi Tony; Denman, John A; Stewart, Peter J; Hapgood, Karen P; Morton, David A V

    2015-10-12

    This study investigates the effects of a variety of coating materials on the flowability and dissolution of dry-coated cohesive ibuprofen powders, with the ultimate aim to use these in oral dosage forms. A mechanofusion approach was employed to apply a 1% (w/w) dry coating onto ibuprofen powder with coating materials including magnesium stearate (MgSt), L-leucine, sodium stearyl fumarate (SSF) and silica-R972. No significant difference in particle size or shape was measured following mechanofusion with any material. Powder flow behaviours characterised by the Freeman FT4 system indicated coatings of MgSt, L-leucine and silica-R972 produced a notable surface modification and substantially improved flow compared to the unprocessed and SSF-mechanofused powders. ToF-SIMS provided a qualitative measure of coating extent, and indicated a near-complete layer on the drug particle surface after dry coating with MgSt or silica-R972. Of particular note, the dissolution rates of all mechanofused powders were enhanced even with a coating of a highly hydrophobic material such as magnesium stearate. This surprising increase in dissolution rate of the mechanofused powders was attributed to the lower cohesion and the reduced agglomeration after mechanical coating. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. The Influence of Dissolution on Bedrock Channel Evolution: Insights from Modelling and Field Observations

    NASA Astrophysics Data System (ADS)

    Thaler, E.; Myre, J. M.; Covington, M. D.

    2015-12-01

    Despite the large global distribution of soluble bedrock, fluvial geomorphological studies typically regard dissolution as a negligible erosion mechanism in bedrock channels when compared to rates of mechanical erosion. Limited prior field observations have suggested that at the transition from insoluble to soluble substrate bedrock channels become wider, less steep, or both. By extending the Fastscape landscape evolution model to include dissolution as an erosion mechanism, we repeatedly produce landscapes with trunk streams consistent with field observations. However, in small tributaries, channel steepening occurs at the contact of the insoluble and soluble lithologies. Furthermore, as the main channel in a basin encounters the soluble layer, the increased erosion due to dissolution acts produces a local increase in the rate of base level lowering, resulting in steepening of channels upstream of the lithologic contact. The increased erosion at the lithological contact in the main stem also causes hillsope steepening in the soluble reaches. Independent field observations in the Buffalo National River Basin agree with the model results. Knickpoints and slot canyons are common at the lithologic contact in small tributaries, and channel widening occurs in soluble reaches in the main stem.

  19. Facilitating Conceptual Understanding of Gas-Liquid Mass Transfer Coefficient through a Simple Experiment Involving Dissolution of Carbon Dioxide in Water in a Surface Aeration Reactor

    ERIC Educational Resources Information Center

    Utgikar, Vivek P.; MacPherson, David

    2016-01-01

    Students in the undergraduate "transport phenomena" courses typically have a greater difficulty in understanding the theoretical concepts underlying the mass transport phenomena as compared to the concepts of momentum and energy transport. An experiment based on dissolution of carbon dioxide in water was added to the course syllabus to…

  20. Facilitating Conceptual Understanding of Gas-Liquid Mass Transfer Coefficient through a Simple Experiment Involving Dissolution of Carbon Dioxide in Water in a Surface Aeration Reactor

    ERIC Educational Resources Information Center

    Utgikar, Vivek P.; MacPherson, David

    2016-01-01

    Students in the undergraduate "transport phenomena" courses typically have a greater difficulty in understanding the theoretical concepts underlying the mass transport phenomena as compared to the concepts of momentum and energy transport. An experiment based on dissolution of carbon dioxide in water was added to the course syllabus to…

  1. A dynamic system for the simulation of fasting luminal pH-gradients using hydrogen carbonate buffers for dissolution testing of ionisable compounds.

    PubMed

    Garbacz, Grzegorz; Kołodziej, Bartosz; Koziolek, Mirko; Weitschies, Werner; Klein, Sandra

    2014-01-23

    The hydrogen carbonate buffer is considered as the most biorelevant buffer system for the simulation of intestinal conditions and covers the physiological pH range of the luminal fluids from pH 5.5 to about pH 8.4. The pH value of a hydrogen carbonate buffer is the result of a complex and dynamic interplay of the concentration of hydrogen carbonate ions, carbonic acid, the concentration of dissolved and solvated carbon dioxide and its partial pressure above the solution. The complex equilibrium between the different ions results in a thermodynamic instability of hydrogen carbonate solutions. In order to use hydrogen carbonate buffers with pH gradients in the physiological range and with the dynamics observed in vivo without changing the ionic strength of the solution, we developed a device (pHysio-grad®) that provides both acidification of the dissolution medium by microcomputer controlled carbon dioxide influx and alkalisation by degassing. This enables a continuous pH control and adjustment during dissolution of ionisable compounds. The results of the pH adjustment indicate that the system can compensate even rapid pH changes after addition of a basic or acidic moiety in amounts corresponding up to 90% of the overall buffer capacity. The results of the dissolution tests performed for a model formulation containing ionizable compounds (Nexium 20mg mups) indicate that both the simulated fasting intraluminal pH-profiles and the buffer species can significantly affect the dissolution process by changing the lag time prior to initial drug release and the release rate of the model compound. A prediction of the in vivo release behaviour of this formulation is thus most likely strongly related to the test conditions such as pH and buffer species. Copyright © 2013 Elsevier B.V. All rights reserved.

  2. Submarine Dissolution During the Late-Miocene Carbonate Crash and Subsequent Mega-Pockmark Formation on the Cocos Ridge

    NASA Astrophysics Data System (ADS)

    Kluesner, J.; Silver, E. A.; Bangs, N. L.; McIntosh, K. D.

    2014-12-01

    A large field (245km2) seabed mega-pockmarks (~1 km to 4 km in diameter) was recently imaged on the western edge of the Cocos Ridge near the Middle American Trench. The pockmarks are part of a vast mega-pockmark field (~10x150 km) and were imaged using high-resolution multibeam bathymetry and backscatter and 3D seismic reflection data. On the seafloor, multiple pockmarks exhibit a two-tiered geomorphology, some of which contain small high-backscatter mounds, possibly indicating recent seafloor seepage. 3D seismic data reveal that the two-tiered morphology is caused by collapse structures at depth with large pockmarks above the walls of the former. Observed collapse structures are characterized by steep walls that truncate surrounding strata, apparent normal "ring" faults, chaotic internal reflections interpreted as infill, and circular morphologies. Younger pockmarks located above the walls of the collapse structures are larger in diameter, have gently dipping walls that do not truncate surrounding strata, and typically show elliptical morphologies. Physical properties results at IODP Site U1414 that intersects the 3D seismic volume suggest that observed reverse polarity lens-shaped zones, which are truncated by the deeper collapse structures, represent anomalous regions of high porosity and low density. In addition, a rapid drop in Ca concentrations observed within this interval at Site U1414 suggests a relationship with possible carbonate dissolution. Correlation of the collapse structures stratigraphic timing with nanno-fossil data at Site U1414 suggests formation occurred ~8-10 Ma, approximately during the Late Miocene eastern Pacific carbonate crash. Based on 3D seismic analysis and recent drilling results, we propose a two-stage formation process that consists of initial collapse caused by carbonate dissolution during the late Miocene, followed by sustained fluid-flow along the walls of established collapse features, resulting in pockmark formation. This

  3. An ecological mechanism to create regular patterns of surface dissolution in a low-relief carbonate landscape

    NASA Astrophysics Data System (ADS)

    Cohen, M. J.; Martin, J. B.; Mclaughlin, D. L.; Osborne, T.; Murray, A.; Watts, A. C.; Watts, D.; Heffernan, J. B.

    2012-12-01

    Development of karst landscapes is controlled by focused delivery of water undersaturated with respect to the soluble rock minerals. As that water comes to equilibrium with the rock, secondary porosity is incrementally reinforced creating a positive feedback that acts to augment the drainage network and subsequent water delivery. In most self-organizing systems, spatial positive feedbacks create features (in landscapes: patches; in karst aquifers: conduits) whose size-frequency relationship follows a power function, indicating a higher probability of large features than would occur with a random or Gaussian genesis process. Power functions describe several aspects of secondary porosity in the Upper Floridan Aquifer in north Florida. In contrast, a different pattern arises in the karst landscape in southwest Florida (Big Cypress National Preserve; BICY), where low-relief and a shallow aquiclude govern regional hydrology. There, the landscape pattern is highly regular (Fig. 1), with circular cypress-dominated wetlands occupying depressions that are hydrologically isolated and distributed evenly in a matrix of pine uplands. Regular landscape patterning results from spatially coupled feedbacks, one positive operating locally that expands patches coupled to another negative that operates at distance, eventually inhibiting patch expansion. The positive feedback in BICY is thought to derive from the presence of surface depressions, which sustain prolonged inundation in this low-relief setting, and facilitate wetland development that greatly augments dissolution potential of infiltrating water in response to ecosystem metabolic processes. In short, wetlands "drill" into the carbonate leading to both vertical and lateral basin expansion. Wetland expansion occurs at the expense of surrounding upland area, which is the local catchment that subsidizes water availability. A distal inhibitory feedback on basin expansion thus occurs as the water necessary to sustain prolonged

  4. Size and composition of synthetic calcium sulfate beads influence dissolution and elution rates in vitro.

    PubMed

    Roberts, Randy; McConoughey, Stephen J; Calhoun, Jason H

    2014-05-01

    Treatments of osteomyelitis lag behind bacterial resistance to antibiotics. We tested different-sized calcium sulfate beads and their ability to elute multiple antibiotics in vitro as a possible method to improve the therapeutic delivery in patients. Two sizes of calcium sulfate beads (4.8 and 3.0 mm diameter) that contained vancomycin, tobramycin, or both were dissolved in phosphate-buffered saline, and the rate of dissolution by weight and antibiotic elution by the disc diffusion assay and high-pressure liquid chromatography were measured. The 4.8 mm beads showed significantly higher dissolution rates relative to the 3.0 mm beads (2.3 mg/day vs. 1.3 mg/day). While the vancomycin-loaded 4.8 mm beads eluted for a longer time relative to the 3.0 mm beads (20 days vs. 10 days), the smaller beads had threefold higher elution for the first 2 days, before dropping to near zero elution by day 4. The presence of tobramycin extended the elution of the vancomycin to day 40, which closely matches the recommended 6 weeks to treat orthopedic staphylococcus infections. These data suggest that size and content of the bead are variables that could affect their clinical success, and both could be exploited to tailor treatments of specific infections and injuries.

  5. The influence of amorphization methods on the apparent solubility and dissolution rate of tadalafil.

    PubMed

    Wlodarski, K; Sawicki, W; Paluch, K J; Tajber, L; Grembecka, M; Hawelek, L; Wojnarowska, Z; Grzybowska, K; Talik, E; Paluch, M

    2014-10-01

    This study for the first time investigates the solubility and dissolution rate of amorphous tadalafil (Td)--a poorly water soluble chemical compound which is commonly used for treating the erectile dysfunction. To convert the crystalline form of Td drug to its amorphous counterpart we have employed most of the commercially available amorphization techniques i.e. vitrification, cryogenic grinding, ball milling, spray drying, freeze drying and antisolvent precipitation. Among the mentioned methods only quenched cooling of the molten sample was found to be an inappropriate method of Td amorphization. This is due to the thermal decomposition of Td above 200°C, as proved by the thermogravimetric analysis (TGA). Disordered character of all examined samples was confirmed using differential scanning calorimetry (DSC) and X-ray powder diffraction (PXRD). In the case of most amorphous powders, the largest 3-fold increase of apparent solubility was observed after 5 min, indicating their fast recrystallization in water. On the other hand, the partially amorphous precipitate of Td and hypromellose enhanced the solubility of Td approximately 14 times, as compared with a crystalline substance, which remained constant for half an hour. Finally, disk intrinsic dissolution rate (DIDR) of amorphous forms of Td was also examined. Copyright © 2014 Elsevier B.V. All rights reserved.

  6. Fabrication of carbonate apatite block based on internal dissolution-precipitation reaction of dicalcium phosphate and calcium carbonate.

    PubMed

    Daitou, Fumikazu; Maruta, Michito; Kawachi, Giichiro; Tsuru, Kanji; Matsuya, Shigeki; Terada, Yoshihiro; Ishikawa, Kunio

    2010-05-01

    In this study, we investigated a novel method for fabrication of carbonate apatite block without ionic movement between precursor and solution by using precursor that includes all constituent ions of carbonate apatite. A powder mixture prepared from dicalcium phosphate anhydrous and calcite at appropriate Ca/P ratios (1.5, 1.67, and 1.8) was used as starting material. For preparation of specimens, the slurry made from the powder mixture and distilled water was packed in a split stainless steel mold and heat - treated, ranging from 60 degrees C to 100 degrees C up to 48 hours at 100% humidity. It appeared that carbonate apatite could be obtained above 70 degrees C and monophasic carbonate apatite could be obtained from the powder mixture at Ca/P ratio of 1.67. Carbonate content of the specimen was about 5-7%. Diametral tensile strength of the carbonate apatite blocks slightly decreased with increasing treatment temperature. The decrease in diametral tensile strength is thought to be related to the crystal size of the carbonate apatite formed.

  7. Elevated pCO2 effects on the geochemistry of carbonate aquifers: calcite dissolution as a driver of elevated metal concentrations

    NASA Astrophysics Data System (ADS)

    Wunsch, A.; Navarre-Sitchler, A. K.; Moore, J.; McCray, J. E.

    2012-12-01

    Geological carbon capture, utilization and storage has gained momentum in the last decade as a viable option of reducing anthropogenic emissions of CO2, with several demonstration projects completed, in progress or planned for upcoming years. However, large-scale CO2-injection operations are accompanied by concerns of CO2 leakage from deep geological repositories and subsequent contact with shallower aquifers, such as underground sources of drinking water. Direct toxicity of CO2 is of lesser concern; rather, it is the acidification of aquifers from increased CO2 partial-pressures (pCO2), which may lead to release of metals into groundwater through mineral dissolution and metal desorption. Previous geochemical studies have suggested that the presence of calcite in aquifer material would reduce the hazard of metal release by effectively buffering acidity via calcite dissolution at elevated pCO2, thus placing carbonate aquifers at lesser risk in case of CO2 leakage. Yet calcite is rarely found in pure form, and often contains a wide range of impurities, including metals such as As, Cr, and Pb, in solid-solution. Dissolution of calcite during acidity buffering is accompanied by release of these impurities from the calcite lattice. We show through experimental work that dissolution of calcite is the primary mechanism responsible for elevated concentrations of metals in carbonate aquifers at high pCO2. It is also evident that the mechanism responsible for metal release, i.e. dissolution or desorption, is metal-specific and pCO2-specific. Modeling work based on our experimental results suggests that in reducing aquifers calcite can contribute more to release of metals than sulfides, which are generally viewed as likely sources of metals in aquifers, during a hypothetical 30-year CO2 leak. In addition, modeling work suggests that when sulfide minerals are present in a carbonate aquifer, metals release would be more sensitive to pO2 than to pCO2.

  8. Is there a component of Pleistocene CO2 change associated with carbonate dissolution cycles?

    NASA Astrophysics Data System (ADS)

    Keir, Robin S.

    1995-10-01

    The only processes which could have decreased atmospheric CO2 during glacial climates without appreciably changing the carbon isotope distribution in the sea appear to be (1) dissolved calcium carbonate input to the ocean, e.g., coral reef buildup and erosion, (2) the ocean solubility pump, due to changes in surface temperature or air-sea exchange, or (3) decreased biological production of calcium carbonate. It is assumed here that one of these mechanisms caused part of the atmospheric CO2 changes recorded in the 200-kyr-long Vostok ice core. Two residual CO2 records are generated by scaling the δ13C difference between planktonic and benthic foraminifera in marine sediment cores to -82 ppm CO2 per 1‰ increase in Δδ13C and subtracting from this the measured CO2 concentration in the ice core. Both residual CO2 records exhibit two broad maximums between about 20-50 ka and 140-200 ka, indicating that during these times, about 40 ppm of the CO2 decrease from interglacial levels cannot be explained by the interaction of the ocean's biological and vertical mixing cycles. The shape of the residual CO2 curve is similar qualitatively to the variation of calcium carbonate in central equatorial Pacific sediments during this time period, which would imply that changes in dissolved carbonate input to the ocean contributed the added component of CO2 change. However, recent models of atmospheric CO2 change in response to changing alkaline input to the ocean exhibit about a 25 to 35 ppm decrease per 1013 mol yr-1 increase in dissolved CaCO3 input. If compensation for the changing input is occurring mostly within an area of about 40 × 106 km² below the lysocline in the Indo-Pacific, the change in carbonate accumulation rate corresponding to a -40 ppm CO2 change would be a minimum of 3 mg cm-2 yr-1. This can be compared to glacial increases of 0.5 to 1.0 mg cm-2 yr-1 during the last 200 kyr in central equatorial Pacific sediments. Thus, the added glacial accumulation of

  9. Identification of formulation and manufacturing variables that influence in vitro dissolution and in vivo bioavailability of propranolol hydrochloride tablets.

    PubMed

    Eddington, N D; Ashraf, M; Augsburger, L L; Leslie, J L; Fossler, M J; Lesko, L J; Shah, V P; Rekhi, G S

    1998-11-01

    The purpose of this study was to evaluate the effect of formulation and processing changes on the dissolution and bioavailability of propranolol hydrochloride tablets. Directly compressed blends of 6 kg (20,000 units) were prepared by mixing in a 16-qt V blender and tablets were compressed on an instrumented Manesty D3B tablet press. A half-factorial (2(5-1), Resolution V) design was used to study the following variables: filler ratio (lactose/dicalcium phosphate), sodium starch glycolate level, magnesium stearate level, lubricant blend time, and compression force. The levels and ranges of the excipients and processing changes studied represented level 2 or greater changes as indicated by the Scale-up and Post Approval Changes (SUPAC-IR) Guidance. Changes in filler ratio, disintegrant level, and compression force were significant in affecting percent drug released (Q) in 5 min (Q5) and Q10. However, changes in magnesium stearate level and lubricant blend time did not influence Q5 and Q10. Hardness was found to be affected by changes in all of the variables studied. Some interaction effects between the variables studied were also found to be significant. To examine the impact of formulation and processing variables on in vivo absorption, three batches were selected for a bioavailability study based on their dissolution profiles. Thirteen subjects received four propranolol treatments (slow-, medium-, and fast-dissolving formulations and Inderal 80 mg) separated by 1 week washout according to a randomized crossover design. The formulations were found to be bioequivalent with respect to the log Cmax and log AUC0-infinity. The results of this study suggest that (i) bioavailability/bioequivalency studies may not be necessary for propranolol and perhaps other class 1 drugs after level 2 type changes, and (ii) in vitro dissolution tests may be used to show bioequivalence of propranolol formulations with processing or formulation changes within the specified level 2 ranges

  10. Characterization of excipient and tableting factors that influence folic acid dissolution, friability, and breaking strength of oil- and water-soluble multivitamin with minerals tablets.

    PubMed

    Du, Jianping; Hoag, Stephen W

    2003-11-01

    The goal of this study is to characterize the formulation and processing factors that influence folic acid dissolution from oil- and water-soluble multivitamin with minerals tablet formulations for direct compression. The following parameters were studied: bulk filler solubility, soluble to insoluble bulk filler ratio, triturating agent (preblending carrier) solubility, disintegrant usage, compression pressure, and folic acid particle size. Folic acid particle size was determined by using light microscopy, and surface area was measured by using BET adsorption. The tablets were compressed on an instrumented Stokes B2 tablet press, and the friability, weight variation, and dissolution were measured according to USP methods, along with tablet breaking strength. In summary, we found the following factors to be critical to folic acid dissolution: bulk filler solubility (soluble fillers, such as maltose, increase folic acid dissolution); disintegrant amount (levels less than 0.4% (w/w) are ineffectual, whereas levels greater than 1.2% (w/w) did not further increase dissolution); and compression force (generally, maltose produce harder tablets). In addition, folic acid dissolution was less affected by changes in compaction pressure when a "super" disintegrant and maltose, as a bulk filler, were used. It was determined that the trituration agent did not play a significant role in folic acid dissolution. In the range of parameters studied, statistical analysis found no significant interactions between the parameters studied, which means they act independently in an additive manner. The results also show that no one factor is completely responsible for dissolution failure. Thus, it is the combination of formulation factors and processing conditions that collectively add up to produce dissolution failure; however, the use of a disintegrant and a soluble filler such as maltose can make a formulation more robust to the inevitable changes that can occur during commercial

  11. Influence of drug load on dissolution behavior of tablets containing a poorly water-soluble drug: estimation of the percolation threshold.

    PubMed

    Wenzel, Tim; Stillhart, Cordula; Kleinebudde, Peter; Szepes, Anikó

    2017-08-01

    Drug load plays an important role in the development of solid dosage forms, since it can significantly influence both processability and final product properties. The percolation threshold of the active pharmaceutical ingredient (API) corresponds to a critical concentration, above which an abrupt change in drug product characteristics can occur. The objective of this study was to identify the percolation threshold of a poorly water-soluble drug with regard to the dissolution behavior from immediate release tablets. The influence of the API particle size on the percolation threshold was also studied. Formulations with increasing drug loads were manufactured via roll compaction using constant process parameters and subsequent tableting. Drug dissolution was investigated in biorelevant medium. The percolation threshold was estimated via a model dependent and a model independent method based on the dissolution data. The intragranular concentration of mefenamic acid had a significant effect on granules and tablet characteristics, such as particle size distribution, compactibility and tablet disintegration. Increasing the intragranular drug concentration of the tablets resulted in lower dissolution rates. A percolation threshold of approximately 20% v/v could be determined for both particle sizes of the API above which an abrupt decrease of the dissolution rate occurred. However, the increasing drug load had a more pronounced effect on dissolution rate of tablets containing the micronized API, which can be attributed to the high agglomeration tendency of micronized substances during manufacturing steps, such as roll compaction and tableting. Both methods that were applied for the estimation of percolation threshold provided comparable values.

  12. Direct electrolytic dissolution of silicate minerals for air CO2 mitigation and carbon-negative H2 production.

    PubMed

    Rau, Greg H; Carroll, Susan A; Bourcier, William L; Singleton, Michael J; Smith, Megan M; Aines, Roger D

    2013-06-18

    We experimentally demonstrate the direct coupling of silicate mineral dissolution with saline water electrolysis and H2 production to effect significant air CO2 absorption, chemical conversion, and storage in solution. In particular, we observed as much as a 10(5)-fold increase in OH(-) concentration (pH increase of up to 5.3 units) relative to experimental controls following the electrolysis of 0.25 M Na2SO4 solutions when the anode was encased in powdered silicate mineral, either wollastonite or an ultramafic mineral. After electrolysis, full equilibration of the alkalized solution with air led to a significant pH reduction and as much as a 45-fold increase in dissolved inorganic carbon concentration. This demonstrated significant spontaneous air CO2 capture, chemical conversion, and storage as a bicarbonate, predominantly as NaHCO3. The excess OH(-) initially formed in these experiments apparently resulted via neutralization of the anolyte acid, H2SO4, by reaction with the base mineral silicate at the anode, producing mineral sulfate and silica. This allowed the NaOH, normally generated at the cathode, to go unneutralized and to accumulate in the bulk electrolyte, ultimately reacting with atmospheric CO2 to form dissolved bicarbonate. Using nongrid or nonpeak renewable electricity, optimized systems at large scale might allow relatively high-capacity, energy-efficient (<300 kJ/mol of CO2 captured), and inexpensive (<$100 per tonne of CO2 mitigated) removal of excess air CO2 with production of carbon-negative H2. Furthermore, when added to the ocean, the produced hydroxide and/or (bi)carbonate could be useful in reducing sea-to-air CO2 emissions and in neutralizing or offsetting the effects of ongoing ocean acidification.

  13. Direct electrolytic dissolution of silicate minerals for air CO2 mitigation and carbon-negative H2 production

    PubMed Central

    Rau, Greg H.; Carroll, Susan A.; Bourcier, William L.; Singleton, Michael J.; Smith, Megan M.; Aines, Roger D.

    2013-01-01

    We experimentally demonstrate the direct coupling of silicate mineral dissolution with saline water electrolysis and H2 production to effect significant air CO2 absorption, chemical conversion, and storage in solution. In particular, we observed as much as a 105-fold increase in OH− concentration (pH increase of up to 5.3 units) relative to experimental controls following the electrolysis of 0.25 M Na2SO4 solutions when the anode was encased in powdered silicate mineral, either wollastonite or an ultramafic mineral. After electrolysis, full equilibration of the alkalized solution with air led to a significant pH reduction and as much as a 45-fold increase in dissolved inorganic carbon concentration. This demonstrated significant spontaneous air CO2 capture, chemical conversion, and storage as a bicarbonate, predominantly as NaHCO3. The excess OH− initially formed in these experiments apparently resulted via neutralization of the anolyte acid, H2SO4, by reaction with the base mineral silicate at the anode, producing mineral sulfate and silica. This allowed the NaOH, normally generated at the cathode, to go unneutralized and to accumulate in the bulk electrolyte, ultimately reacting with atmospheric CO2 to form dissolved bicarbonate. Using nongrid or nonpeak renewable electricity, optimized systems at large scale might allow relatively high-capacity, energy-efficient (<300 kJ/mol of CO2 captured), and inexpensive (<$100 per tonne of CO2 mitigated) removal of excess air CO2 with production of carbon-negative H2. Furthermore, when added to the ocean, the produced hydroxide and/or (bi)carbonate could be useful in reducing sea-to-air CO2 emissions and in neutralizing or offsetting the effects of ongoing ocean acidification. PMID:23729814

  14. The influence of surface state and saturation state on the dissolution kinetics of biogenic aragonite in seawater

    USGS Publications Warehouse

    Acker, James G.; Byrne, R.H.

    1989-01-01

    Uses several realistic partial molar volume changes (??V) for aragonite dissolution in seawater. Indicates that the molar volume change for aragonite dissolution is within the bounds -37 cm 3/mole ?????V ??? -39.5 cm3/mole. -from Authors

  15. Glacial magnetite dissolution in abyssal NW Pacific sediments - evidence for carbon trapping?

    NASA Astrophysics Data System (ADS)

    Korff, Lucia; von Dobeneck, Tilo; Frederichs, Thomas; Kasten, Sabine; Kuhn, Gerhard; Gersonde, Rainer; Diekmann, Bernhard

    2016-04-01

    The abyssal North Pacific Ocean's large volume, depth, and terminal position on the deep oceanic conveyor make it a candidate site for deep carbon trapping as postulated by climate theory to explain the massive glacial drawdown of atmospheric CO2. As the major basins of the North Pacific have depths of 5500-6500m, far below the modern and glacial Calcite Compensation Depths (CCD), these abyssal sediments are carbonate-free and therefore not suitable for carbonate-based paleoceanographic proxy reconstructions. Instead, paleo-, rock and environmental magnetic methods are generally well applicable to hololytic abyssal muds and clays. In 2009, the international paleoceanographic research cruise SO 202 INOPEX ('Innovative North Pacific Experiment') of the German RV SONNE collected two ocean-spanning EW sediment core transects of the North Pacific and Bering Sea recovering a total of 50 piston and gravity cores from 45 sites. Out of seven here considered abyssal Northwest Pacific piston cores collected at water depths of 5100 to 5700m with mostly coherent shipboard susceptibility logs, the 20.23m long SO202-39-3, retrieved from 5102 m water depth east of northern Shatsky Rise (38°00.70'N, 164°26.78'E), was rated as the stratigraphically most promising record of the entire core transect and selected for detailed paleo- and environmental magnetic, geochemical and sedimentological investigations. This core was dated by correlating its RPI and Ba/Ti records to well-dated reference records and obviously provides a continuous sequence of the past 940 kyrs. The most striking orck magnetic features are coherent magnetite-depleted zones corresponding to glacial periods. In the interglacial sections, detrital, volcanic and even submicron bacterial magnetite fractions are excellently preserved. These alternating magnetite preservation states seem to reflect dramatic oxygenation changes in the deep North Pacific Ocean and hint at large-scale benthic glacial carbon trapping

  16. Arsenic incorporation into FeS 2 pyrite and its influence on dissolution: A DFT study

    NASA Astrophysics Data System (ADS)

    Blanchard, Marc; Alfredsson, Maria; Brodholt, John; Wright, Kate; Catlow, C. Richard A.

    2007-02-01

    FeS 2 pyrite can incorporate large amounts of arsenic (up to ca. 10 wt%) and hence has a strong impact on the mobility of this toxic metalloid. Focussing on the lowest arsenic concentrations for which the incorporation occurs in solid solution, the substitution mechanisms involved have been investigated by assuming simple incorporation reactions in both oxidising and reducing conditions. The solution energies were calculated by Density Functional Theory (DFT) calculations and we predict that the formation of AsS dianion groups is the most energetically favourable mechanism. The results also suggest that the presence of arsenic will accelerate the dissolution and thus the generation of acid drainage, when the crystal dissolves in oxidising conditions.

  17. Bovine Serum Albumin binding to CoCrMo nanoparticles and the influence on dissolution

    NASA Astrophysics Data System (ADS)

    Simoes, T. A.; Brown, A. P.; Milne, S. J.; Brydson, R. M. D.

    2015-10-01

    CoCrMo alloys exhibit good mechanical properties, excellent biocompatibility and are widely utilised in orthopaedic joint replacements. Metal-on-metal hip implant degradation leads to the release of metal ions and nanoparticles, which persist through the implant's life and could be a possible cause of health complications. This study correlates preferential binding between proteins and metal alloy nanoparticles to the alloy's corrosion behaviour and the release of metal ions. TEM images show the formation of a protein corona in all particles immersed in albumin containing solutions. Only molybdenum release was significant in these tests, suggesting high dissolution of this element when CoCrMo alloy nanoparticles are produced as wear debris in the presence of serum albumin. The same trend was observed during extended exposure of molybdenum reference nanoparticles to albumin.

  18. Influence of Common Bean (Phaseolus vulgaris) Grown in Elevated CO2 on Apatite Dissolution

    NASA Astrophysics Data System (ADS)

    Olsen, A. A.; Morra, B.

    2016-12-01

    We ran a series of experiments to test the hypothesis that release of plant nutrients contained in apatite will be accelerated by the growth of Langstrath Stringless green bean in the presence of atmospheric CO2 meant to simulate possible future atmospheric conditions due a higher demand of nutrients and growth rate caused by elevated CO2. We hypothesize that elevated atmospheric CO2 will lead to both increased root growth and organic acid exudation. These two traits will lead to improved acquisition of P derived from apatite. Experiments were designed to investigate the effect of these changes on soil mineral weathering using plants grown under two conditions, ambient CO2 (400ppm) and elevated CO2 (1000ppm). Plants were grown in flow-through microcosms consisting of a mixture of quartz and apatite sands. Mini-greenhouses were utilized to control CO2 levels. Plant growth was sustained by a nutrient solution lacking in Ca and P. Calcium and P content of the leachate and plant tissue served as a proxy for apatite dissolution. Plants were harvested biweekly during the eight-week experiment and analyzed for Ca and P to calculate apatite dissolution kinetics. Preliminary results suggest that approximately four times more P and Ca are present in the leachate from experiments containing plants under both ambient and elevated CO2 levels than in abiotic experiments; however, the amounts of both P and Ca released in experiments conducted under both ambient and elevated CO2 levels are similar. Additionally, the amount of P in plant tissue grown under ambient and elevated CO2 conditions is similar. Plants grown in elevated CO2 had a greater root to shoot ratio. The planted microcosms were found to have a lower pH than abiotic controls most likely due to root respiration and exudation of organic acids.

  19. Evaluation of Influence of Various Polymers on Dissolution and Phase Behavior of Carbamazepine-Succinic Acid Cocrystal in Matrix Tablets.

    PubMed

    Ullah, Majeed; Ullah, Hanif; Murtaza, Ghulam; Mahmood, Qaisar; Hussain, Izhar

    2015-01-01

    The aim of current study was to explore the influence of three commonly used polymers, that is, cellulosics and noncellulosics, for example, Methocel K4M, Kollidon VA/64, and Soluplus, on the phase disproportionation and drug release profile of carbamazepine-succinic acid (CBZ-SUC) cocrystal at varying drug to polymer ratios (1 : 1 to 1 : 0.25) in matrix tablets. The polymorphic phase disproportionation during in-depth dissolution studies of CBZ-SUC cocrystals and its crystalline properties were scrutinized by X-ray powder diffractrometry and Raman spectroscopy. The percent drug release from HPMC formulations (CSH) showed inverse relation with the concentration of polymer; that is, drug release increased with decrease in polymer concentration. On contrary, direct relation was observed between percent drug release and polymer concentrations of Kollidon VA 64/Soluplus (CSK, CSS). At similar polymer concentration, drug release from pure carbamazepine was slightly lower with HPMC formulations than that of cocrystal; however, opposite trend in release rate was observed with Kollidon VA/64 and Soluplus. The significant increase in dissolution rate of cocrystal occurred with Kollidon VA/64 and Soluplus at higher polymer concentration. Moreover, no phase change took place in Methocel and Kollidon formulations. No tablet residue was left for Soluplus formulation so the impact of polymer on cocrystal integrity cannot be predicted.

  20. Kinetics of Inorganic Calcite Dissolution in Seawater under Pressure

    NASA Astrophysics Data System (ADS)

    Dong, S.; Subhas, A.; Rollins, N.; Berelson, W.; Adkins, J. F.

    2016-02-01

    While understanding calcium carbonate dissolution is vital in constructing global carbon cycles and predicting the effect of seawater acidification as a result of increasing atmospheric CO2, there is still a major debate over the basic formulation of a dissolution rate law. The kinetics of calcium carbonate dissolution are typically described by the equation: Rate=k(1-Ω)n, while Ω=[Ca2+][CO32-]/Ksp. In this study, 13C-labeled calcite is dissolved in unlabeled seawater and the evolving d13C composition of the fluid is traced over time to establish dissolution rate. Instead of changing ion concentration to obtain varying Ω (as in our previous study; Subhas et al. 2015), we changed Ksp by conducting experiments under different pressures (described in theory as ∂lnKsp/∂P=-ΔV/RT, where ΔV is partial molal volume). This involved the construction of a pressure vessel that could hold our sample bag and provide aliquots while remaining pressurized. Pressure experiments were conducted between 0-2000PSI. Results support the conclusion in our previous study that near-equilibrium dissolution rates are highly nonlinear, but give a disparate relationship between undersaturation and dissolution rate if Ω is calculated assuming the specific ΔV embedded in CO2SYS. A revised ΔV from -37cm3 to -65cm3 would make the dissolution formulation equation agree, but clearly appears unreasonable. Our results are explained by a pressure effect on carbonate dissolution kinetics over and above the influence of pressure on Ω. If this is a phenomenon that occurs in nature, then we would predict that dissolution should be occurring shallower in the water column (as sometimes observed) than indicated by standard Ω calculations.

  1. The Role of Sulfur Oxidation in Carbonate Precipitation and Dissolution Within Sulfidic Hot Springs

    NASA Astrophysics Data System (ADS)

    Alford, S. E.; Kapitulčinová, D.; Kotrc, B.; Langerhuus, A. T.; Berelson, W.; Dawson, S.; Corsetti, F.; Hanselmann, K.; Johnson, H.; Spear, J.; Stevenson, B. S.; de La Torre, J.; 2008, G.

    2008-12-01

    Geothermal waters that have interacted with subsurface limestones often precipitate aragonite and calcite (travertine) upon cooling and degassing of CO2, forming terraced travertine deposits like those at Mammoth Hot Springs (MHS) in Yellowstone National Park. It has been shown that surfaces of filamentous microbial "Aquificales-dominated streamer communities" comprising the Apron and Channel Facies in these systems can act as nucleation sites for carbonate precipitation leading to the fine-scale tubular micro-structures consistently observed in travertine terraces, modern and ancient. The expected carbonate precipitates were found on streamer communities on the proximal Slope facies, however, ESEM imaging and EDX analysis revealed sulfur crystals, rather than carbonate precipitates, in association with Aquificales-dominated communities collected near the mouth of Narrow Gauge (pH 6.43, T 73.5°C), a sulfidic bicarbonate spring within the MHS system. Thermodynamic analysis of geochemical spring water datasets (data from Angel Terrace Spring applied to the Narrow Gauge site) demonstrates that lowering of the acid-neutralizing capacity (ANC) of spring waters can be achieved by sulfur oxidation. Although the first step of oxidation from H2S to S° cannot account for the lack of aragonite on the streamer biofilms, oxidation of even small amounts of S° to S2O32- and further to SO42- markedly decreases ANC. This microbially mediated reaction may lead to a shift in the local pH and a shift in the ion activity product (IAP) for Ca2+ x CO32- to below the solubility product (Ksp) of CaCO3. Our calculations suggest that this reaction, sulfur oxidation with oxygen to sulfate, can liberate sufficient protons to drive aragonite to undersaturation, if the initial sulfur concentration is 5 mM, and the [Ca] and [CO3] concentrations are initially 0.01 M and 1-10 uM, respectively. The potential importance of sulfur oxidation in hot springs, the molecular signatures of this process

  2. Reactive-convective dissolution in a porous medium: the storage of carbon dioxide in saline aquifers.

    PubMed

    Ghoshal, Parama; Kim, Min Chan; Cardoso, Silvana S S

    2016-12-21

    We quantify the destabilising effect of a first-order chemical reaction on the fingering instability of a diffusive boundary layer in a porous medium. Using scaling, we show that the dynamics of such a reactive boundary layer is fully determined by two dimensionless groups: Da/Ra(2), which measures the timescale for convection compared to those for reaction and diffusion; and βC/βA, which reflects the density change induced by the product relative to that of the diffusing solute. Linear stability and numerical results for βC/βA in the range 0-10 and Da/Ra(2) in the range 0-0.01 are presented. It is shown that the chemical reaction increases the growth rate of a transverse perturbation and favours large wavenumbers compared to the inert system. Higher βC/βA and Da/Ra(2) not only accelerate the onset of convection, but crucially also double the transport of the solute compared to the inert system. Application of our findings to the storage of carbon dioxide in carbonate saline aquifers reveals that chemical equilibrium curtails this increase of CO2 flux to 50%.

  3. Debundling and dissolution of single-walled carbon nanotubes in amide solvents.

    PubMed

    Furtado, C A; Kim, U J; Gutierrez, H R; Pan, Ling; Dickey, E C; Eklund, Peter C

    2004-05-19

    Wet chemical methods involving ultrasound and amide solvents were used to purify and separate large bundles of single-walled carbon nanotubes (SWNTs) into individual nanotubes that could then be transported to silicon or mica substrates. The SWNTs studied were produced by the arc-discharge process. Dry oxidation was used in an initial step to remove amorphous carbon. Subsequently, two acid purification schemes were investigated (HCl- and HNO(3)-reflux) to remove the metal growth catalyst (Ni-Y). Finally, ultrasonic dispersion of isolated tubes into either N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) was carried out. Raman scattering, atomic force microscopy (AFM), and electron microscopy were used to study the evolution of the products. Raman scattering was used to probe possible wall damage during the chemical processing. We found that both HCl and HNO(3) could be used to successfully remove the Ni-Y below approximately 1 wt %. However, the HNO(3)-reflux produced significant wall damage (that could be reversed by vacuum annealing at 1000 degrees C). In the dispersion step, both amide solvents (DMF and NMP) produced a high degree of isolated tubes in the final product, and no damage during this dispersion step was observed. HNO(3)-refluxed tubes were found to disperse the best into the amide solvents, perhaps because of significant wall functionalization. AFM was used to study the filament diameter and length distributions in the final product, and interesting differences in these distributions were observed, depending on the chemical processing route.

  4. Dissolution-Induced Nanowire Synthesis on Hot-Dip Galvanized Surface in Supercritical Carbon Dioxide.

    PubMed

    Kaleva, Aaretti; Saarimaa, Ville; Heinonen, Saara; Nikkanen, Juha-Pekka; Markkula, Antti; Väisänen, Pasi; Levänen, Erkki

    2017-07-11

    In this study, we demonstrate a rapid treatment method for producing a needle-like nanowire structure on a hot-dip galvanized sheet at a temperature of 50 °C. The processing method involved only supercritical carbon dioxide and water to induce a reaction on the zinc surface, which resulted in growth of zinc hydroxycarbonate nanowires into flower-like shapes. This artificial patina nanostructure predicts high surface area and offers interesting opportunities for its use in industrial high-end applications. The nanowires can significantly improve paint adhesion and promote electrochemical stability for organic coatings, or be converted to ZnO nanostructures by calcining to be used in various semiconductor applications.

  5. Dissolution-Induced Nanowire Synthesis on Hot-Dip Galvanized Surface in Supercritical Carbon Dioxide

    PubMed Central

    Saarimaa, Ville; Heinonen, Saara; Nikkanen, Juha-Pekka; Markkula, Antti; Väisänen, Pasi; Levänen, Erkki

    2017-01-01

    In this study, we demonstrate a rapid treatment method for producing a needle-like nanowire structure on a hot-dip galvanized sheet at a temperature of 50 °C. The processing method involved only supercritical carbon dioxide and water to induce a reaction on the zinc surface, which resulted in growth of zinc hydroxycarbonate nanowires into flower-like shapes. This artificial patina nanostructure predicts high surface area and offers interesting opportunities for its use in industrial high-end applications. The nanowires can significantly improve paint adhesion and promote electrochemical stability for organic coatings, or be converted to ZnO nanostructures by calcining to be used in various semiconductor applications. PMID:28696374

  6. [Influence of specification on chemical composition of dissolution and hepatocytes toxicity of Polygonum multiflorum].

    PubMed

    lI, Yu-Meng; Li, Rui-Yu; Niu, Ming; Li, Chun-Yu; Bai, Zhao-Fang; Feng, Wu-Wen; Zhang, Cong-En; Tan, Peng; Huang, Zhi-Pu; Ma, Wei-Guang; Wang, Jia-Bo; Xiao, Xiao-He

    2016-03-01

    According to different toxicities of various aqueous extracts of Polygonum multiflorum on hepatocyte, the impacts of chemical composition on the safety of P. multiforum was studied. In this study, 8 main chemical compositions in aqueous extracts of P. multiflorum were determined by the established HPLC method; at the same time, the inhibition ratios of different aqueous extracts of P. multiflorum on L02 cell were determined. Afterwards, the potential compounds related to the toxicity of P. multiforum were tentatively found through a multiple correlation analysis. The results showed that P. multiforum with different chemical compositions exhibited great differences in dissolution. The hepatocyte toxicity of P. multiflorum powder was much greater than P. multiflorum lumps. In addition, three constituents closely related to toxicity of P. multiflorum were found by multiple correlation analysis. The study revealed that chemical composition of P. multiflorum is closely related to the hepatotoxicity, and the hepatotoxicity of P. multiflorum powder is greater than that of other dosage forms. This study indicates that P. multiflorum with different chemical compositions show varying toxicity, which therefore shall be given high attention. Copyright© by the Chinese Pharmaceutical Association.

  7. Nonequilibrium NAPL dissolution and solute transport: Influence on aquifer remediation and post remedial contaminant rebound

    SciTech Connect

    1995-03-01

    The rate of ground-water pumping can affect the efficiency of contaminant transport. High pore-water velocities affect remedial pumping efficiency by limiting the solute concentration in the extracted ground water. The two separate processes potentially involved are solute transport and residual NAPL dissolution. In both cases, the contact time between mobile ground water and immobile contaminant phases (i.e., sorbed contaminants or residual NAPL) is reduced by a higher pore-water velocity. The relative chemical equilibrium established can result in a reduced solute concentration due to mass transfer limitations. This effect is often described as nonequilibrium contaminant transport and is thought to be due to a molecular diffusion rate-limited effect. Several methods are described to apply the nonequilibrium concepts of both contaminant transport processes to zero-dimensional and one-dimensional models. Two spreadsheet-based analytical computer programs are provided and application of the models are demonstrated by simulating several case examples. The two computer models are practical management tools which cannot only estimate the volume of extracted water and remedial pumping times required, but they also have the unique capability to simulate solute contaminant rebound resulting from a drop in the ground-water velocity.

  8. A new influence on iron dissolution in Bangladesh aquifers: electron shuttling by groundwater fulvic acids

    NASA Astrophysics Data System (ADS)

    Mladenov, N.; Kulkarni, H. V.; McKnight, D. M.; Zheng, Y.; Kirk, M. F.

    2016-12-01

    It was demonstrated more than two decades ago that the electron shuttling ability of fulvic acids (FA) accelerates iron (Fe) reduction. However, the environmental relevance of this mechanism for arsenic-laden groundwater environments has thus far only been hypothesized. Here we show that FAs isolated from high and low arsenic groundwater aquifers in the Bengal Basin can act to shuttle electrons between bacteria and Fe(III). Bangladesh groundwater FAs were reduced by Geobacter metallireducens and were subsequently capable of abiotically reducing Fe(III) to Fe(II). Moreover, all four Bangladesh groundwater FAs investigated in the study had higher Fe(III) to Fe(II) conversion rates compared to anthraquinone disulfonate, an oxidized quinone, and Suwannee River Fulvic Acid, a commercially-available FA isolated from a terrestrially-dominated surface water source. Until now, microbially-mediated reductive dissolution of Fe (oxy)hydroxides, driven by the availability of labile organic matter, was widely accepted as the main control on arsenic mobilization in reducing aquifers. Our evidence for the electron shuttling ability of Bangladesh FAs implicates electron shuttling as another important control on elevated As concentrations in groundwater of the Bengal Basin.

  9. A mechanistic understanding of plagioclase dissolution based on Al occupancy and T-O bond length: from geologic carbon sequestration to ambient conditions.

    PubMed

    Yang, Yi; Min, Yujia; Jun, Young-Shin

    2013-11-14

    A quantitative description of how the bulk properties of aluminosilicates affect their dissolution kinetics is important in helping people understand the regulation of atmospheric CO2 concentration by silicate weathering and predict the fate and transport of geologically sequestered CO2 through brine-rock interactions. In this study, we employed a structure model based on the C1 space group to illustrate how differences in crystallographic properties of aluminosilicates, such as T-O (Tetrahedral site-Oxygen) bond length and Al/Si ordering, can result in quantifiable variations in mineral dissolution rates. The dissolution rates of plagioclases were measured under representative geologic carbon sequestration (GCS) conditions (90 °C, 100 atm of CO2, 1.0 M NaCl, and pH ∼ 3.1), and used to validate the model. We found that the logarithm of the characteristic time of the breakdown of Al-O-Si linkages in plagioclases follows a good linear relation with the mineral's aluminum content (nAl). The Si release rates of plagioclases can be calculated based on an assumption of dissolution congruency or on the regularity of Al/Si distribution in the constituent tetrahedra of the mineral. We further extended the application of our approach to scenarios where dissolution incongruency arises because of different linkage reactivities in the solid matrix, and compared the model predictions with published data. The application of our results enables a significant reduction of experimental work for determining the dissolution rates of structurally related aluminosilicates, given a reaction environment.

  10. DISSOLUTION OF METAL OXIDES AND SEPARATION OF URANIUM FROM LANTHANIDES AND ACTINIDES IN SUPERCRITICAL CARBON DIOXIDE

    SciTech Connect

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

    2013-10-01

    This paper investigates the feasibility of extracting and separating uranium from lanthanides and other actinides by using supercritical fluid carbon dioxide (sc-CO2) as a solvent modified with tri-n-butylphosphate (TBP) for the development of a counter current stripping technique, which would be a more efficient and environmentally benign technology for spent nuclear fuel reprocessing compared to traditional solvent extraction. Several actinides (U, Pu, and Np) and europium were extracted in sc-CO2 modified with TBP over a range of nitric acid concentrations and then the actinides were exposed to reducing and complexing agents to suppress their extractability. According to this study, uranium/europium and uranium/plutonium extraction and separation in sc-CO2 modified with TBP is successful at nitric acid concentrations of less than 6 M and at nitric acid concentrations of less than 3 M with acetohydroxamic acid or oxalic acid, respectively. A scheme for recycling uranium from spent nuclear fuel by using sc-CO2 and counter current stripping columns is presented.

  11. Dissolution of metal oxides and separation of uranium from lanthanides and actinides in supercritical carbon dioxide

    SciTech Connect

    Quach, D.L.; Wai, C.M.; Mincher, B.J.

    2013-07-01

    This paper investigates the feasibility of extracting and separating uranium from lanthanides and other actinides by using supercritical fluid carbon dioxide (sc-CO{sub 2}) as a solvent modified with tri-n-butylphosphate (TBP) for the development of a counter current stripping technique, which would be a more efficient and environmentally benign technology for spent nuclear fuel reprocessing compared to traditional solvent extraction. Several actinides (U, Pu, and Np) and europium were extracted in sc-CO{sub 2} modified with TBP over a range of nitric acid concentrations and then the actinides were exposed to reducing and complexing agents to suppress their extractability. According to this study, uranium/europium and uranium/plutonium extraction and separation in sc-CO{sub 2} modified with TBP is successful at nitric acid concentrations of less than 6 M and at nitric acid concentrations of less than 3 M with acetohydroxamic acid or oxalic acid, respectively. A scheme for recycling uranium from spent nuclear fuel by using sc-CO{sub 2} and counter current stripping columns is presented. (authors)

  12. Dissolution of Columbia River Basalt Under Mildly Acidic Conditions as a Function of Temperature: Experimental Results Relevant to the Geological Sequestration of Carbon Dioxide

    SciTech Connect

    Schaef, Herbert T.; McGrail, B. Peter

    2009-05-01

    Increasing attention is being focused on the rapid rise of carbon dioxide levels in the atmosphere, which many believe to be the major contributing factor to global climate change. Sequestering CO2 in deep geological formations has been proposed as a long-term solution to help stabilize CO2 levels. However, before such technology can be developed and implemented, a basic understanding of H2O-CO2 systems and the chemical interactions of these fluids with the host formation must be obtained. Important issues concerning mineral stability, reaction rates, and carbonate formation are all controlled or at least significantly impacted by the kinetics of rock-water reactions in mildly acidic, CO2-saturated solutions. Basalt has recently been identified as a potentially important host formation for geological sequestration. Dissolution kinetics of the Columbia River Basalt (CRB) were measured for a range of temperatures (25° to 90°C) under mildly acidic to neutral pH conditions using the single-pass flow-through test method. Under anaerobic conditions, the normalized dissolution rates for CRB decrease with increasing pH (3≤pH≤7) with a slope, η, of -0.12 ± 0.02. An activation energy, Ea, has been estimated at 30.3 ± 2.4 kJ mol-1. Dissolution kinetics measurements like these are essential for modeling the rate at which the CO2 reacts with basalt and ultimately converted to carbonate minerals in situ.

  13. Dissolution effect and cytotoxicity of diamond-like carbon coatings on orthodontic archwires.

    PubMed

    Kobayashi, Shinya; Ohgoe, Yasuharu; Ozeki, Kazuhide; Hirakuri, Kenji; Aoki, Hideki

    2007-12-01

    Nickel-titanium (NiTi) has been used for implants in orthodontics due to the unique properties such as shape memory effect and superelasticity. However, NiTi alloys are eroded in the oral cavity because they are immersed by saliva with enzymolysis. Their reactions lead corrosion and nickel release into the body. The higher concentrations of Ni release may generate harmful reactions. Ni release causes allergenic, toxic and carcinogenic reactions. It is well known that diamond-like carbon (DLC) films have excellent properties, such as extreme hardness, low friction coefficients, high wear resistance. In addition, DLC film has many other superior properties as a protective coating for biomedical applications such as biocompatibility and chemical inertness. Therefore, DLC film has received enormous attention as a biocompatible coating. In this study, DLC film coated NiTi orthodontic archwires to protect Ni release into the oral cavity. Each wire was immersed in physiological saline at the temperature 37 degrees C for 6 months. The release concentration of Ni ions was detected using microwave induced plasma mass spectrometry (MIP-MS) with the resolution of ppb level. The toxic effect of Ni release was studied the cell growth using squamous carcinoma cells. These cells were seeded in 24 well culture plates and materials were immersed in each well directly. The concentration of Ni ions in the solutions had been reduced one-sixth by DLC films when compared with non-coated wire. This study indicated that DLC films have the protective effect of the diffusion and the non-cytotoxicity in corrosive environment.

  14. Determination of dissolution rates of spent fuel in carbonate solutions under different redox conditions with a flow-through experiment

    NASA Astrophysics Data System (ADS)

    Röllin, S.; Spahiu, K.; Eklund, U.-B.

    2001-09-01

    Dissolution rates of spent UO 2 fuel have been investigated using flow-through experiments under oxidizing, anoxic and reducing conditions. For oxidizing conditions, approximately congruent dissolution rates were obtained in the pH range 3-9.3 for U, Np, Ba, Tc, Cs, Sr and Rb. For these elements, steady-state conditions were obtained in the flow rate range 0.02-0.3 ml min -1. The dissolution rates were about 3 mg d -1 m-2 for pH>6. For pH<6, dissolution rates were strongly increasing for decreasing pH. Incongruent dissolution was found for Zr, Mo, Ru, Rh, Pd, Am and the lanthanides. The dissolution rates with H 2(g) saturated solutions dropped by up to four orders of magnitude as compared to oxidizing conditions. Because of the very low concentrations, only U, Pu, Am, Mo, Tc and Cs could be measured. For anoxic conditions, both the redox potential and dissolution rates increased approaching the same values as under oxidizing conditions.

  15. The difference between surface ocean carbonate chemistry and calcite dissolution in deep sea sediments as observed in tests of Globorotalia menardii

    NASA Astrophysics Data System (ADS)

    Russo, M.; Mekik, F.

    2010-12-01

    The Globorotalia menardii Fragmentation Index (MFI) was developed to trace deep sea calcite dissolution within sediments. While this proxy has a multi-basin core top calibration ranging the tropical and subtropical world ocean, the effect of the surface ocean [CO32-] on thickness of whole G. menardii shells has not been previously tested. If the size-normalized shell weight (SNSW) of G. menardii tests were affected by the [CO32-] of ambient habitat waters, this would put constraints on the applicability of MFI as a reliable bulk sediment calcite dissolution proxy. We present new SNSW data from G. menardii shells within core tops in the eastern equatorial Pacific where there is both a strong gradient to surface ocean [CO32-] and calcite dissolution in the sediments. We compare our G.menardii SNSW data with that of other species in the region, such as Neogloboquadrina dutertrei and Pulleniatina obliquiloculata. While SNSW of both N. dutertrei and P. obliquiloculata have clear relationships with surface ocean [CO32-], we do not find a similar relationship between G. menardii SNSW and surface ocean parameters, particularly [CO32-]. This bolsters our confidence in the reliability of MFI as a deep sea carbonate dissolution tracer.

  16. Coupled alkai fieldspar dissolution and secondary mineral precipatation in batch systems-2: New experiments with supercritical CO2 and implications for carbon sequestration

    SciTech Connect

    Lu, Peng; Fu, Qi; Seyfried, William E. Jr.; Hedges, Sheila W.; Soong, Yee; Jones, Kyle; Zhua, Chen

    2013-01-01

    In order to evaluate the extent of CO{sub 2}–water–rock interactions in geological formations for C sequestration, three batch experiments were conducted on alkali feldspars–CO{sub 2}–brine interactions at 150–200 °C and 300 bars. The elevated temperatures were necessary to accelerate the reactions to facilitate attainable laboratory measurements. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. SEM, TEM and XRD analysis of reaction products showed extensive dissolution features (etch pits, channels, kinks and steps) on feldspars and precipitation of secondary minerals (boehmite, kaolinite, muscovite and paragonite) on feldspar surfaces. Therefore, these experiments have generated both solution chemistry and secondary mineral identity. The experimental results show that partial equilibrium was not attained between secondary minerals and aqueous solutions for the feldspar hydrolysis batch systems. Evidence came from both solution chemistry (supersaturation of the secondary minerals during the entire experimental duration) and metastable co-existence of secondary minerals. The slow precipitation of secondary minerals results in a negative feedback in the dissolution–precipitation loop, reducing the overall feldspar dissolution rates by orders of magnitude. Furthermore, the experimental data indicate the form of rate laws greatly influence the steady state rates under which feldspar dissolution took place. Negligence of both the mitigating effects of secondary mineral precipitation and the sigmoidal shape of rate–ΔG{sub r} relationship can overestimate the extent of feldspar dissolution during CO{sub 2} storage. Finally, the literature on feldspar dissolution in CO{sub 2}-charged systems has been reviewed. The data available are insufficient and new experiments are urgently needed to establish a database on feldspar dissolution mechanism, rates and rate laws, as well as secondary mineral

  17. Interactions between ciprofloxacin and antacids--dissolution and adsorption studies.

    PubMed

    Arayne, M Saeed; Sultana, Najma; Hussain, Fida

    2005-01-01

    Ciprofloxacin is a fluorinated quinolone antibacterial agent extensively used against both Gram-positive and Gram-negative microorganisms. In certain polytherapy programs, ciprofloxacin can be administered with some antacids that could modify its dissolution rate and reduce its absorption leading to therapeutic failure. The aim of this study was to evaluate the influence of some antacids on the availability of ciprofloxacin. The release of ciprofloxacin from tablets in the presence of antacids, such as sodium bicarbonate, calcium hydroxide, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, magnesium trisilicate and magaldrate was studied on BP 2002 dissolution test apparatus. These studies were carried out in simulated gastric and intestinal juices for 3 hours at 37 degrees C. The results confirmed that the dissolution rate of tablets was markedly retarded in the presence of all the antacids studied. Magaldrate and calcium carbonate in simulated gastric juice exhibited relatively higher adsorption capacities, as did magnesium trisilicate and calcium hydroxide in simulated intestinal juice.

  18. Influence of the physiological variability of fasted gastric pH and tablet retention time on the variability of in vitro dissolution and simulated plasma profiles.

    PubMed

    Kovačič, Nataša Nagelj; Pišlar, Mitja; Ilić, Ilija; Mrhar, Aleš; Bogataj, Marija

    2014-10-01

    The aim of the present study was to show that the physiological variability of fasted gastric pH and tablet gastric retention time contributes to the overall variability of simulated plasma profiles of diclofenac. Those two parameters were implemented into dissolution study and plasma profiles were simulated under assumptions that in vitro dissolution well represents that occurring in vivo, and that absorption profiles are identical to dissolution profiles, as diclofenac is a highly permeable drug. Dissolution experiments were performed using USP 2 apparatus and two consecutive dissolution media, namely, an acidic medium of various pH (ranging from 1-3), where tablets were kept for a certain time (10-200 min), and phosphate buffer (pH 6.8). It was shown that the acid pH value and acid retention time of tablets affect in vitro drug release, and consequently also influence the simulated plasma profiles. Lower acid pH resulted in lower plasma peaks at each studied acid retention time. Longer acid retention time caused lower plasma concentrations at lower acid pH values, whereas at pH 3 higher plasma concentrations were noted. Additionally, it was demonstrated that the variability of both parameters represents an important contribution to the overall variability of plasma profiles.

  19. CO2 sequestration by mineral carbonation of steel slags under ambient temperature: parameters influence, and optimization.

    PubMed

    Ghacham, Alia Ben; Pasquier, Louis-César; Cecchi, Emmanuelle; Blais, Jean-François; Mercier, Guy

    2016-09-01

    This work focuses on the influence of different parameters on the efficiency of steel slag carbonation in slurry phase under ambient temperature. In the first part, a response surface methodology was used to identify the effect and the interactions of the gas pressure, liquid/solid (L/S) ratio, gas/liquid ratio (G/L), and reaction time on the CO2 removed/sample and to optimize the parameters. In the second part, the parameters' effect on the dissolution of CO2 and its conversion into carbonates were studied more in detail. The results show that the pressure and the G/L ratio have a positive effect on both the dissolution and the conversion of CO2. These results have been correlated with the higher CO2 mass introduced in the reactor. On the other hand, an important effect of the L/S ratio on the overall CO2 removal and more specifically on the carbonate precipitation has been identified. The best results were obtained L/S ratios of 4:1 and 10:1 with respectively 0.046 and 0.052 gCO2 carbonated/g sample. These yields were achieved after 10 min reaction, at ambient temperature, and 10.68 bar of total gas pressure following direct gas treatment.

  20. The influence of co-formers on the dissolution rates of co-amorphous sulfamerazine/excipient systems.

    PubMed

    Gniado, Katarzyna; Löbmann, Korbinian; Rades, Thomas; Erxleben, Andrea

    2016-05-17

    A comprehensive study on the dissolution properties of three co-amorphous sulfamerazine/excipient systems, namely sulfamerazine/deoxycholic acid, sulfamerazine/citric acid and sulfamerazine/sodium taurocholate (SMZ/DA, SMZ/CA and SMZ/NaTC; 1:1 molar ratio), is reported. While all three co-formers stabilize the amorphous state during storage, only co-amorphization with NaTC provides a dissolution advantage over crystalline SMZ and the reasons for this were analyzed. In the case of SMZ/DA extensive gelation of DA protects the amorphous phase from crystallization upon contact with buffer, but at the same time prevents the release of SMZ into solution. Disk dissolution studies showed an improved dissolution behavior of SMZ/CA compared to crystalline SMZ. However, enhanced dissolution properties were not seen in powder dissolution testing due to poor dispersibility. Co-amorphization of SMZ and NaTC resulted in a significant increase in dissolution rate, both in powder and disk dissolution studies.

  1. Stable carbon isotope budget of CO 2 in a wet, modern soil as inferred from Fe(CO 3)OH in pedogenic goethite: possible role of calcite dissolution

    NASA Astrophysics Data System (ADS)

    Hsieh, Jean C. C.; Yapp, Crayton J.

    1999-07-01

    δ 13C values of the Fe(CO 3)OH component in pedogenic goethites from a young soil developed on the Eocene Weches formation in east Texas increase from approximately -13 or -14‰ at depths of 31-64 cm to values around -6 to -4‰ at depths greater than 122 cm. This spatial distribution of δ 13C values suggests that dissolution of precursor fossiliferous marine calcite (still present at deeper levels in the soil) has contributed significantly to the isotopic budget of CO 2 in this soil. A local isotopic material balance was calculated for the soil CO 2 at each sample depth using a calcite δ 13C value of -1‰, an organic matter δ 13C value of -25‰, and the measured δ 13C value of the Fe(CO 3)OH component in each sample. Although there is presently no calcite in the upper 120 cm of the profile, the calculated apparent contribution of CO 2 from a calcite source ranges from 16% to 45% at these shallow depths. Below 120 cm, dissolution of calcite appears to contribute more than 50% of the CO 2 in the soil gas. Similar results might be expected in other wet, goethite-bearing soils that contain relict calcite and thus have not achieved the highly leached characteristics of laterites (such as those in the Amazon basin). Models of the soil CO 2 budget in such systems may need to consider both oxidation of organic matter and dissolution of carbonate minerals as in situ sources of carbon isotope variation in CO 2. The variation with depth of the δ 13C values of the Fe(CO 3)OH component suggests an ongoing process of goethite dissolution and reprecipitation in the active, aerobic soil zone. If so, the extremely low solubility of goethite in oxidizing environments suggests that this dissolution process is probably biologically mediated. Dissolution and reprecipitation of goethite in an aerobic soil would favor the recording of steady-state soil CO 2 δ 13C patterns. Preservation of such information in ancient soils would probably depend upon burial and consequent

  2. Impact of sulfuric and nitric acids on carbonate dissolution, and the associated deficit of CO2 uptake in the upper-middle reaches of the Wujiang River, China.

    PubMed

    Huang, Qi-Bo; Qin, Xiao-Qun; Liu, Peng-Yu; Zhang, Lian-Kai; Su, Chun-Tian

    2017-08-01

    Carbonate weathering and the CO2 consumption in karstic area are extensive affected by anthropogenic activities, especially sulfuric and nitric acids usage in the upper-middle reaches of Wujiang River, China. The carbonic acid would be substituted by protons from sulfuric and nitric acids which can be reduce CO2 absorption. Therefore, The goal of this study was to highlight the impacts of sulfuric and nitric acids on carbonate dissolution and the associated deficit of CO2 uptaking during carbonate weathering. The hydrochemistries and carbon isotopic signatures of dissolved inorganic carbon from groundwater were measured during the rainy season (July; 41 samples) and post-rainy season (October; 26 samples). Our results show that Ca(2+) and Mg(2+) were the dominant cations (55.87-98.52%), and HCO3(-) was the dominant anion (63.63-92.87%). The combined concentrations of Ca(2+) and Mg(2+) commonly exceeded the equivalent concentration of HCO3(-), with calculated [Ca(2+)+Mg(2+)]/[HCO3(-)] equivalent ratios of 1.09-2.12. The mean measured groundwater δ(13)CDIC value (-11.38‰) was higher than that expected for carbonate dissolution mediated solely by carbonic acid (-11.5‰), and the strong positive correlation of these values with [SO4(2-)+NO3(-)]/HCO3(-) showed that additional SO4(2-) and NO3(-) were required to compensate for this cation excess. Nitric and sulfuric acids are, therefore, suggested to have acted as the additional proton-promoted weathering agents of carbonate in the region, alongside carbonic acid. The mean contribution of atmospheric/pedospheric CO2 to the total aquatic HCO3(-) decreased by 15.67% (rainy season) and 14.17% (post-rainy season) due to the contributions made by these acids. The annual mean deficit of soil CO2 uptake by carbonate weathering across the study area was 14.92%, which suggests that previous workers may have overestimated the absorption of CO2 by carbonate weathering in other karstic areas worldwide. Copyright © 2017 Elsevier

  3. Impact of sulfuric and nitric acids on carbonate dissolution, and the associated deficit of CO2 uptake in the upper-middle reaches of the Wujiang River, China

    NASA Astrophysics Data System (ADS)

    Huang, Qi-bo; Qin, Xiao-qun; Liu, Peng-yu; Zhang, Lian-kai; Su, Chun-tian

    2017-08-01

    Carbonate weathering and the CO2 consumption in karstic area are extensive affected by anthropogenic activities, especially sulfuric and nitric acids usage in the upper-middle reaches of Wujiang River, China. The carbonic acid would be substituted by protons from sulfuric and nitric acids which can be reduce CO2 absorption. Therefore, The goal of this study was to highlight the impacts of sulfuric and nitric acids on carbonate dissolution and the associated deficit of CO2 uptaking during carbonate weathering. The hydrochemistries and carbon isotopic signatures of dissolved inorganic carbon from groundwater were measured during the rainy season (July; 41 samples) and post-rainy season (October; 26 samples). Our results show that Ca2 + and Mg2 + were the dominant cations (55.87-98.52%), and HCO3- was the dominant anion (63.63-92.87%). The combined concentrations of Ca2 + and Mg2 + commonly exceeded the equivalent concentration of HCO3-, with calculated [Ca2 + + Mg2 +]/[HCO3-] equivalent ratios of 1.09-2.12. The mean measured groundwater δ13CDIC value (- 11.38‰) was higher than that expected for carbonate dissolution mediated solely by carbonic acid (- 11.5‰), and the strong positive correlation of these values with [SO42 - + NO3-]/HCO3- showed that additional SO42 - and NO3- were required to compensate for this cation excess. Nitric and sulfuric acids are, therefore, suggested to have acted as the additional proton-promoted weathering agents of carbonate in the region, alongside carbonic acid. The mean contribution of atmospheric/pedospheric CO2 to the total aquatic HCO3- decreased by 15.67% (rainy season) and 14.17% (post-rainy season) due to the contributions made by these acids. The annual mean deficit of soil CO2 uptake by carbonate weathering across the study area was 14.92%, which suggests that previous workers may have overestimated the absorption of CO2 by carbonate weathering in other karstic areas worldwide.

  4. Forsterite dissolution in saline water at elevated temperature and high CO2 pressure.

    PubMed

    Wang, Fei; Giammar, Daniel E

    2013-01-02

    The rates and mechanisms of magnesium silicate dissolution can control the aqueous chemistry in ways that influence carbonate mineral precipitation during geologic carbon sequestration (GCS). A series of batch experiments was performed with forsterite (Mg(1.81)Fe(0.19)SiO(4)) powder to determine the effects of pressure (10-100 bar CO(2)), temperature (25-100 °C), and salinity (0-50,000 mg/L NaCl) on its dissolution rate at conditions relevant to GCS. Dissolution rates and products were determined by analysis of the aqueous phase, equilibrium and reaction path modeling, and solid phase characterization by scanning electron microscopy and X-ray diffraction. After an initially rapid dissolution period, the dissolution rate declined significantly, an effect that is attributed to the formation of a silica-rich layer at the forsterite surface. The initial dissolution rate increased with increasing temperature and increasing CO(2) pressure; the effect of CO(2) was through its influence on the pH. The dissolution rate was enhanced by NaCl, which may have been due to its inhibition of the formation of a silica-rich surface layer. The experimental results provide information about magnesium silicate dissolution at conditions that will be encountered during GCS that can be used to predict the fate of CO(2) and the evolution of subsurface geochemistry following CO(2) injection.

  5. Electrochemical in-situ dissolution study of structurally ordered, disordered and gold doped PtCu3 nanoparticles on carbon composites

    NASA Astrophysics Data System (ADS)

    Jovanovič, Primož; Šelih, Vid Simon; Šala, Martin; Hočevar, Samo B.; Pavlišič, Andraž; Gatalo, Matija; Bele, Marjan; Ruiz-Zepeda, Francisco; Čekada, Miha; Hodnik, Nejc; Gaberšček, Miran

    2016-09-01

    Commercial deployment of low-temperature-fuel cells is still hugely restricted by platinum alloy catalysts corrosion. Extensive research of the last years is focused on increasing stability of the catalyst composite, however a comprehensive understanding is still lacking. In pursuing this fundamentally and practically very important objective we present a comparative corrosion study of a PtCu3 nano-alloy system by investigating the effects of structural ordering and gold doping. For that purpose a recently developed electrochemical flow cell (EFC) coupled to inductively coupled plasma mass spectrometer (ICP-MS) is employed. This approach provides potential- and time-resolved insight into dissolution process at extremely low concentrations (ppb level). Our results show a structure-dependent copper corrosion, where ordering and gold-doping significantly improve copper retention in the native alloy. Two assumptions can be drawn from the measured Pt dissolution profiles: (i) a better Pt re-deposition efficiency in catalysts with higher porosity and (ii) the beneficial effect of Au surface doping that lowers the amount of dissolved Pt amount and shifts the Pt cathodic dissolution to lower potentials. A 2.6 nm Pt/C standard catalyst with the same carbon loading shows a much lower stability which is due to the well-known particle size effect.

  6. Subduction Metamorphism of Ophicarbonates beyond the Stability of Antigorite: insights into Carbonate Dissolution vs. Decarbonation from the Almirez ultramafic massif (S. Spain)

    NASA Astrophysics Data System (ADS)

    Menzel, Manuel; Garrido, Carlos J.; López Sánchez Vizcaíno, Vicente; Marchesi, Claudio; Hidas, Károly

    2017-04-01

    Subduction zone processes play a key role in determining the time and length-scales of long-term element cycles like the deep carbon cycle. Recent improvements in thermodynamic modelling of fluid properties at high pressure and new experiments have underlined the importance of carbonate dissolution by subduction fluids from dehydration reactions for the transfer of carbon out of the subducting slab. However, natural case studies are scarce, in particular regarding the impact of fluids generated by serpentinite dehydration, which are considered as a major dissolution agent for carbon due to the high temperature of antigorite breakdown (about 650°C) and the potentially large volumes of hydrated peridotites occurring in the upper part of the subducting oceanic mantle lithosphere. Here we report the occurrence of meta-ophicarbonate lenses within prograde Chl-harzburgites in the Almirez ultramafic massif (Betic Cordillera, S. Spain). The presence of these lenses indicates that carbonate minerals were preserved beyond the stability conditions of antigorite and were not dissolved by deserpentinization fluids. The largest meta-ophicarbonate lens in the Almirez Chl-harzburgites measures 8 x 160 m and is composed of a high-grade assemblage of olivine, Ti-clinohumite, diopside, chlorite, dolomite, calcite and Cr-bearing magnetite with a granofelsic to banded appearance. In this assemblage we identified, for the first time in the Betic Cordillera, aragonite inclusions in olivine and diopside using coupled EBSD and chemical mapping. Calcite-dolomite thermometry and thermodynamic equilibrium modelling constrain the peak metamorphic conditions to 1.7 - 1.9 GPa and 680 °C at very low XCO2. These conditions compare well with P-T-estimates for the surrounding Chl-harzburgites. There is strong evidence that the protolith of the carbonate rocks within Chl-harzburgites was an ophicarbonate zone: bulk rock contents of Ni and Cr are similarly high in the carbonate rocks as in Atg

  7. Influence of dissolution rate and pH of oral medications on drug-induced esophageal injury.

    PubMed

    Bailey, R T; Bonavina, L; Nwakama, P E; DeMeester, T R; Cheng, S C

    1990-06-01

    The in vitro dissolution time and pH were measured for 16 drug products in capsule or tablet form representative of oral medications known to cause esophageal injury. The test drugs included Vibramycin, Minocin, quinidine sulfate, Cleocin HCl, Indocin, Tolectin 200, ferrous sulfate, vitamin C, aspirin, Procardia, phenobarbital, Dilantin, Butazolidin, Noctec, K-Dur, and Quinaglute. Artificial saliva (10 mL) was placed in a small beaker along with a pH probe connected to a digital display pH meter and a strip-chart recorder. The salivary pH was measured at baseline and continuously during the dissolution of each test medication and the time taken for complete dissolution was recorded. This experiment was repeated six times for each drug. Baseline and final dissolution pH were compared statistically for differences using the Wilcoxon matched-pairs signed-ranks test. Significance was established at the 0.05 level. Only three medications tested (vitamin C, aspirin, and Dilantin) produced a dissolution pH outside the range of physiological esophageal pH values. Although the majority of the test drugs significantly altered the baseline pH, the final dissolution pH did not fall outside the physiologic range. Nine of the 16 test drugs dissolved completely within 10 minutes, whereas the remaining 7 drugs took 30 minutes or longer (up to 24 hours) to dissolve. We conclude that the dissolution pH of potentially caustic medications does not appear to be a primary mechanism of drug-induced esophageal injury, whereas a rapid dissolution rate may play an important role in the pathogenesis of the lesion.

  8. 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.

  9. 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

  10. The influence of polymorphism on the manufacturability and in vitro dissolution of sulindac-containing hard gelatin capsules.

    PubMed

    Guadalupe Sánchez-González, Elizabeth; Yépez-Mulia, Lilian; Jesús Hernández-Abad, Vicente; Jung Cook, Helgi

    2015-05-01

    Drug polymorphism could affect drug product dissolution, manufacturability, stability and bioavailability/bioequivalence. The impact of polymorphism on the manufacturability and in vitro dissolution profiles of sulindac capsules has not been studied yet. To evaluate the impact of polymorphism on the manufacturability and in vitro dissolution of sulindac hard gelatin capsules. Sulindac crystal forms I and II (SLDI and SLDII, respectively) were prepared and characterized. Powder formulations containing one of the polymorphs, lactose and magnesium stearate (at three different levels) were prepared and their flow properties determined. Hard gelatin capsules were filled with the formulations and tested for fill-weight variations. Drug dissolution for SLDI- and SLDII-containing hard gelatin capsules was determined. Differences in flow properties for each polymorph were observed, as well as for their formulations, which in turn affected capsule weight homogeneity. Statistically significant differences in the rate and extent of drug release were observed between SLDI- and SLDII-containing capsules. Formulations containing SLDI showed a better manufacturability and a better dissolution profile than those with SLDII. Sulindac crystalline form I was the best candidate for hard gelatin capsule formulation because of its technological and in vitro dissolution properties.

  11. Influence of Wind Pressure on the Carbonation of Concrete.

    PubMed

    Zou, Dujian; Liu, Tiejun; Du, Chengcheng; Teng, Jun

    2015-07-24

    Carbonation is one of the major deteriorations that accelerate steel corrosion in reinforced concrete structures. Many mathematical/numerical models of the carbonation process, primarily diffusion-reaction models, have been established to predict the carbonation depth. However, the mass transfer of carbon dioxide in porous concrete includes molecular diffusion and convection mass transfer. In particular, the convection mass transfer induced by pressure difference is called penetration mass transfer. This paper presents the influence of penetration mass transfer on the carbonation. A penetration-reaction carbonation model was constructed and validated by accelerated test results under high pressure. Then the characteristics of wind pressure on the carbonation were investigated through finite element analysis considering steady and fluctuating wind flows. The results indicate that the wind pressure on the surface of concrete buildings results in deeper carbonation depth than that just considering the diffusion of carbon dioxide. In addition, the influence of wind pressure on carbonation tends to increase significantly with carbonation depth.

  12. Influence of polymer molecular weight on in vitro dissolution behavior and in vivo performance of celecoxib:PVP amorphous solid dispersions.

    PubMed

    Knopp, Matthias Manne; Nguyen, Julia Hoang; Becker, Christian; Francke, Nadine Monika; Jørgensen, Erling B; Holm, Per; Holm, René; Mu, Huiling; Rades, Thomas; Langguth, Peter

    2016-04-01

    In this study, the influence of the molecular weight of polyvinylpyrrolidone (PVP) on the non-sink in vitro dissolution and in vivo performance of celecoxib (CCX):PVP amorphous solid dispersions were investigated. The dissolution rate of CCX from the amorphous solid dispersions increased with decreasing PVP molecular weight and crystallization inhibition was increased with increasing molecular weight of PVP, but reached a maximum for PVP K30. This suggested that the crystallization inhibition was not proportional with molecular weight of the polymer, but rather there was an optimal molecular weight where the crystallization inhibition was strongest. Consistent with the findings from the non-sink in vitro dissolution tests, the amorphous solid dispersions with the highest molecular weight PVPs (K30 and K60) resulted in significantly higher in vivo bioavailability (AUC0-24h) compared with pure amorphous and crystalline CCX. A linear relationship between the in vitro and in vivo parameter AUC0-24h indicated that the simple non-sink in vitro dissolution method used in this study could be used to predict the in vivo performance of amorphous solid dispersion with good precision, which enabled a ranking between the different formulations. In conclusion, the findings of this study demonstrated that the in vitro and in vivo performance of CCX:PVP amorphous solid dispersions were significantly controlled by the molecular weight of the polymer. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. Characterization of reactive flow-induced evolution of carbonate rocks using digital core analysis- part 1: Assessment of pore-scale mineral dissolution and deposition

    NASA Astrophysics Data System (ADS)

    Qajar, Jafar; Arns, Christoph H.

    2016-09-01

    The application of X-ray micro-computed tomography (μ-CT) for quantitatively characterizing reactive-flow induced pore structure evolution including local particle detachment, displacement and deposition in carbonate rocks is investigated. In the studies conducted in this field of research, the experimental procedure has involved alternating steps of imaging and ex-situ core sample alteration. Practically, it is impossible to return the sample, with micron precision, to the same position and orientation. Furthermore, successive images of a sample in pre- and post-alteration states are usually taken at different conditions such as different scales, resolutions and signal-to-noise ratios. These conditions accompanying with subresolution features in the images make voxel-by-voxel comparisons of successive images problematic. In this paper, we first address the respective challenges in voxel-wise interpretation of successive images of carbonate rocks subject to reactive flow. Reactive coreflood in two carbonate cores with different rock types are considered. For the first rock, we used the experimental and imaging results published by Qajar et al. (2013) which showed a quasi-uniform dissolution regime. A similar reactive core flood was conducted in the second rock which resulted in wormhole-like dissolution regime. We particularly examine the major image processing operations such as transformation of images to the same grey-scale, noise filtering and segmentation thresholding and propose quantitative methods to evaluate the effectiveness of these operations in voxel-wise analysis of successive images of a sample. In the second part, we generalize the methodology based on the three-phase segmentation of normalized images, microporosity assignment and 2D histogram of image intensities to estimate grey-scale changes of individual image voxels for a general case where the greyscale images are segmented into arbitrary number of phases. The results show that local (voxel

  14. Characterization of reactive flow-induced evolution of carbonate rocks using digital core analysis- part 1: Assessment of pore-scale mineral dissolution and deposition.

    PubMed

    Qajar, Jafar; Arns, Christoph H

    2016-09-01

    The application of X-ray micro-computed tomography (μ-CT) for quantitatively characterizing reactive-flow induced pore structure evolution including local particle detachment, displacement and deposition in carbonate rocks is investigated. In the studies conducted in this field of research, the experimental procedure has involved alternating steps of imaging and ex-situ core sample alteration. Practically, it is impossible to return the sample, with micron precision, to the same position and orientation. Furthermore, successive images of a sample in pre- and post-alteration states are usually taken at different conditions such as different scales, resolutions and signal-to-noise ratios. These conditions accompanying with subresolution features in the images make voxel-by-voxel comparisons of successive images problematic. In this paper, we first address the respective challenges in voxel-wise interpretation of successive images of carbonate rocks subject to reactive flow. Reactive coreflood in two carbonate cores with different rock types are considered. For the first rock, we used the experimental and imaging results published by Qajar et al. (2013) which showed a quasi-uniform dissolution regime. A similar reactive core flood was conducted in the second rock which resulted in wormhole-like dissolution regime. We particularly examine the major image processing operations such as transformation of images to the same grey-scale, noise filtering and segmentation thresholding and propose quantitative methods to evaluate the effectiveness of these operations in voxel-wise analysis of successive images of a sample. In the second part, we generalize the methodology based on the three-phase segmentation of normalized images, microporosity assignment and 2D histogram of image intensities to estimate grey-scale changes of individual image voxels for a general case where the greyscale images are segmented into arbitrary number of phases. The results show that local (voxel

  15. A Novel Method for Molybdenum-99/Technetium-99m Recovery via Anodic Carbonate Dissolution of Irradiated Low-Enriched Uranium Metal Foil

    SciTech Connect

    Brown, Michael A.

    2015-01-21

    A new method is presented here for digesting irradiated low-enriched uranium foil targets in alkaline carbonate media to recover 99Mo. This method consists of the electrolytic dissolution of uranium foil in a sodium bicarbonate solution, followed by the precipitation of carbonate, base-insoluble fission products, activation products, and actinides with calcium oxide; most of the molybdenum, technetium, and iodine remain in solution. An electrochemical dissolver and mixing vessel were designed, fabricated, and tested for the processing of a full-sized irradiated foil under ambient pressure and elevated temperature. Over 92% of the fission-induced Mo-99 was recovered in a product solution that was compatible with an anion-exchange column for retaining molybdenum and iodine.

  16. 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.

  17. Glacial-Holocene paleoceanography of the western equatorial Pacific: Carbonate dissolution and sea surface temperatures in the south China and Sulu Seas

    SciTech Connect

    Miao, Qingmin; Thunell, R.C. . Dept. of Geological Sciences)

    1992-01-01

    Six sediments cores from the South China Sea (SCS) and four from the Sulu Sea (SS) have been used in a detailed study of sea surface temperature changes in these two basins during the last 25,000 year. Sea surface temperature (SST) estimates were derived using a planktonic foraminiferal transfer function (FP-12E). The water depths for the cores range 500 m to more than 4,000 m. The time series (SST) records indicate that winter and summer temperatures during the Holocene were approximately 27 C and 29.5 C, respectively, for both the (SC) and (SS). During the last glacial maximum, summer sea surface temperatures were approximately 28.5 C in the (SCS) and 29 C in the (SS), and thus very similar to the Holocene. In contrast, glacial winter (SST) are estimated at 21 C for the (SCS) and 24 C for the (SS). This decrease in glacial winter (SST) results in a much larger seasonality during the last glacial compared to the Holocene. Variation in intensity of the monsoon system and surface water exchange rates between basins are the major factors controlling glacial-interglacial SST fluctuations in the (SC) and (SS). The primary factor influencing the accuracy of the SST estimates is the quality of preservation of planktonic foraminiferal assemblages. Results show that increasing levels of dissolution result in systematically cooler SST estimates. This is due to the fact that warm water foraminifera tend to be more solution susceptible and as dissolution progresses the assemblage becomes enriched in the more resistant, cool water taxa. Since dissolution is more intense during interglacials than glacials in the Pacific, dissolution tends to reduce the amplitude of the true glacial-interglacial temperature difference.

  18. Influence of Mechanical Stirring on the Crucible Dissolution Rate and Impurities Distribution in Directional Solidification of Multicrystalline Silicon

    NASA Astrophysics Data System (ADS)

    Popescu, Alexandra; Vizman, Daniel

    2015-12-01

    In this study, time dependent three-dimensional numerical simulations were carried out using the STHAMAS3D software in order to understand the effects of forced convection induced by mechanical stirring of the melt, on the crucible dissolution rate and on the impurities distribution in multicrystalline silicon (mc-Si) melt for different values of the diffusion coefficient. Numerical simulations were performed on a pilot scale furnace with crucible dimensions of 38x38x40cm3. The computational domain used for the local 3D-simulations consists of melt and crystal. The dissolution rate was estimated from the total mass of impurities that was found in the silicon melt after a certain period of time. The obtained results show that enhanced convection produced by a mechanical stirrer leads to a significant increase of the dissolution rate and also to a uniform distribution of impurities in the melt.

  19. Influence of process water quality on hydrothermal carbonization of cellulose.

    PubMed

    Lu, Xiaowei; Flora, Joseph R V; Berge, Nicole D

    2014-02-01

    Hydrothermal carbonization (HTC) is a thermal conversion process that has been shown to be environmentally and energetically advantageous for the conversion of wet feedstocks. Supplemental moisture, usually in the form of pure water, is added during carbonization to achieve feedstock submersion. To improve process sustainability, it is important to consider alternative supplemental moisture sources. Liquid waste streams may be ideal alternative liquid source candidates. Experiments were conducted to systematically evaluate how changes in pH, ionic strength, and organic carbon content of the initial process water influences cellulose carbonization. Results from the experiments conducted evaluating the influence of process water quality on carbonization indicate that changes in initial water quality do influence time-dependent carbonization product composition and yields. These results also suggest that using municipal and industrial wastewaters, with the exception of streams with high CaCl2 concentrations, may impart little influence on final carbonization products/yields.

  20. Dissolution of trace metals from lava ash: influence on the composition of rainwater in the Mount Etna volcanic area.

    PubMed

    Cimino, G; Toscano, G

    1998-01-01

    Dissolution of trace metals from lava ash of the Mount Etna volcano in aqueous suspensions is studied as a function of solution pH and aerosol mass loading. The rate of dissolution and the final concentration increase with decreasing pH. Leaching experiments are found to be consistent with the observations of these metals in rainwater of the volcanic area. Elements such as Fe and Mn are important in the aqueous oxidation of SO(2) which increases the acidity of the rainwater. Leaching of Na, Ca, K, Fe and Mg may have a buffering effect in reacting with cloud and aerosol droplets.

  1. Determining the impacts of fermentative bacteria on wollastonite dissolution kinetics.

    PubMed

    Salek, S S; Kleerebezem, R; Jonkers, H M; Voncken, J H L; van Loosdrecht, M C M

    2013-03-01

    Silicate minerals can be a source of calcium and alkalinity, enabling CO2 sequestration in the form of carbonates. For this to occur, the mineral needs to be first dissolved in an acidifying process such as the biological process of anaerobic fermentation. In the present study, the main factors which govern the dissolution process of an alkaline silicate mineral (wollastonite, CaSiO3) in an anaerobic fermentation process were determined. Wollastonite dissolution kinetics was measured in a series of chemical batch experiments in order to be able to estimate the required amount of alkaline silicate that can neutralize the acidifying fermentation process. An anaerobic fermentation of glucose with wollastonite as the neutralizing agent was consequently performed in a fed-batch reactor. Results of this experiment were compared with an abiotic (control) fed-batch reactor in which the fermentation products (i.e. organic acids and alcohols) were externally supplied to the system at comparable rates and proportions, in order to provide chemical conditions similar to those during the biotic (fermentation) experiment. This procedure enabled us to determine whether dissolution of wollastonite was solely enhanced by production of organic acids or whether there were other impacts that fermentative bacteria could have on the mineral dissolution rate. The established pH profiles, which were the direct indicator of the dissolution rate, were comparable in both experiments suggesting that the mineral dissolution rate was mostly influenced by the quantity of the organic acids produced.

  2. Solubility and dissolution kinetics of gypsum as a function of CO2 partial pressure: Implications for geological carbon sequestration William Wolfe, Philip Bennett The University of Texas at Austin, Jackson School of Geosciences

    NASA Astrophysics Data System (ADS)

    Wolfe, W. W.; Bennett, P.

    2011-12-01

    The storage of carbon dioxide in deep saline (non-potable) aquifers has received increasing attention as a possible near term solution to the emission of carbon dioxide into the atmosphere. As a result of CO2 introduction, a wide array of geochemical reactions will occur involving both the aqueous phase and the solid mineral phase. Potential CO2 storage formations are typically saline Na:Cl or NaCa:ClSO4 type water. To gain insight into the dynamics of this system under the conditions of carbon sequestration we examined the solubility and dissolution/precipitation rates of gypsum in aqueous solutions as a function of CO2 partial pressure. Experimental variables ranged from 30-60 degrees C, 0.1-5 molar NaCl, and 1-130 atmospheres of CO2. Most standard geochemical models predict that gypsum solubility will increase with increasing dissolved CO2 due to the increased acidity driving the protonation of sulfate to form bisulfate: H+ + SO4= <=> HSO4- Thus decreasing sulfate concentration and driving further dissolution of gypsum. However, our findings show that increasing dissolved CO2 results in the precipitation of gypsum, with gypsum solubility decreasing by up to 30-50% at all temperatures examined. Solutions initially at equilibrium with gypsum will nucleate and precipitate gypsum as pCO2 increases. This behavior was predicted by Li and Duan, (2011) based on model results but no experimental evidence was found by the authors. Potential factors for this behavior include a decrease in the activity of water due to hydration of dissolved CO2, or possibly the destabilization of the CaSO4 neutral complex increasing the activity of free Ca++ and SO4= in solution, driving the precipitation of gypsum. We are exploring both of these possible scenarios. The saline aquifers of the Texas gulf coast are a potential target for carbon dioxide sequestration, and many of these aquifers have high Ca and SO4 concentrations due to reaction with gypsum. Precipitation of gypsum under high

  3. Microstructural record of cataclastic and dissolution-precipitation processes from shallow crustal carbonate strike-slip faults, Northern Calcareous Alps (Austria)

    NASA Astrophysics Data System (ADS)

    Bauer, Helene; Grasemann, Bernhard; Decker, Kurt

    2015-04-01

    The concept of coseismic slip and aseismic creep deformation along faults is supported by the variability of natural fault rocks and their microstructures. Faults in carbonate rocks are characterized by very narrow principal slip zones (cm to mm wide) containing (ultra)cataclastic fault rocks that accommodate most of the fault displacement. Fluidization of ultracataclastic sub layers and thermal decomposition of calcite due to frictional heating have been proposed as possible indicators for seismic slip. Dissolution-precipitation (DP) processes are possible mechanism of aseismic sliding, resulting in spaced cleavage solution planes and associated veins, indicating diffusive mass transfer and precipitation in pervasive vein networks. We investigated exhumed, sinistral strike-slip faults in carbonates of the Northern Calcareous Alps. The study presents microstructural investigations of natural carbonate fault rocks that formed by cataclastic and dissolution-precipitation related deformation processes. Faults belong to the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system that was formed during eastward lateral extrusion of the Eastern Alps in Oligocene to Lower Miocene. The investigated faults accommodated sinistral slip between several tens and few hundreds of meters. Microstructural analysis of fault rocks was done with scanning electron microscopy and optical microscopy. Deformation experiments of natural fault rocks are planned to be conducted at the Sapienza University of Roma and should be available at the meeting. The investigated fault rocks give record of alternating cataclastic deformation and DP creep. DP fault rocks reveal various stages of evolution including early stylolites, pervasive pressure solution seams and cleavage, localized shear zones with syn-kinematic calcite fibre growth and mixed DP/cataclastic microstructures, involving pseudo sc- and scc'-fabrics. Pressure solution seams host fine grained kaolinit, chlorite

  4. Influence of Carbon on the Electrical Properties of Crustal Rocks

    SciTech Connect

    Mathez, E. A.

    2002-11-19

    The report summarizes work to determine the nature and distribution of carbon on microcracks in crystalline rocks by time-of-flight secondary ion mass spectroscopy. It also summarizes the results of a workshop devoted to investigating how carbon in rocks influences electrical conductivity and whether carbon on fracture surfaces can account for the electrical conductivity structure of the crust.

  5. Influence of spray drying and dispersing agent on surface and dissolution properties of griseofulvin micro and nanocrystals.

    PubMed

    Shah, Dhaval A; Patel, Manan; Murdande, Sharad B; Dave, Rutesh H

    2016-11-01

    The purpose for the current research is to compare and evaluate physiochemical properties of spray-dried (SD) microcrystals (MCs), nanocrystals (NCs), and nanocrystals with a dispersion agent (NCm) from a poorly soluble compound. The characterization was carried out by performing size and surface analysis, interfacial tension (at particle moisture interface), and in-vitro drug dissolution rate experiments. Nanosuspensions were prepared by media milling and were spray-dried. The SD powders that were obtained were characterized morphologically using scanning electron microscopy (SEM), polarized light microscopy (PLM), and Flowchem. Solid-state characterization was performed using X-ray powder diffraction (XRPD), Fourier transfer infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC) for the identification of the crystalline nature of all the SD powders. The powders were characterized for their redispersion tendency in the water and in pH 1.2. Significant differences in redispersion were noted for both the NCs in both dissolution media. The interfacial tension for particle moisture interface was determined by applying the BET (Braunauer-Emmett-Teller) equation to the vapor sorption data. No significant reduction in the interfacial tension was observed between MCs and NCs; however, a significant reduction in the interfacial tension was observed for NCm at both 25 °C and 35 °C temperatures. The difference in interfacial tension and redispersion behavior can be attributed to a difference in the wetting tendency for all the SD powders. The dissolution studies were carried out under sink and under non-sink conditions. The non-sink dissolution approach was found suitable for quantification of the dissolution rate enhancement, and also for providing the rank order to the SD formulations.

  6. Pore-scale simulation of calcium carbonate precipitation and dissolution under highly supersaturated conditions in a microfludic pore network

    NASA Astrophysics Data System (ADS)

    Yoon, H.; Dewers, T. A.; Valocchi, A. J.; Werth, C. J.

    2011-12-01

    Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks or confined aquifers and cause mineral precipitation. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at pore-scale. Pore-scale models of coupled fluid flow, reactive transport, and CaCO3 precipitation and dissolution are applied to account for transient experimental results of CaCO3 precipitation and dissolution under highly supersaturated conditions in a microfluidic pore network (i.e., micromodel). Pore-scale experiments in the micromodel are used as a basis for understanding coupled physics of systems perturbed by geological CO2 injection. In the micromodel, precipitation is induced by transverse mixing along the centerline in pore bodies. Overall, the pore-scale model qualitatively captured the governing physics of reactions such as precipitate morphology, precipitation rate, and maximum precipitation area in first few pore spaces. In particular, we found that proper estimation of the effective diffusion coefficient and the reactive surface area is necessary to adequately simulate precipitation and dissolution rates. As the model domain increases, the effect of flow patterns affected by precipitation on the overall reaction rate also increases. The model is also applied to account for the effect of different reaction rate laws on mineral precipitation and dissolution at pore-scale. Reaction rate laws tested include the linear rate law, nonlinear power law, and newly-developed rate law based on in-situ measurements at nano scale in the literature. Progress on novel methods for upscaling pore-scale models for reactive transport are discussed, and are being applied to mineral precipitation patterns observed in natural analogues. H.Y. and T. D. were supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of

  7. [Study on influence between activated carbon property and immobilized biological activated carbon purification effect].

    PubMed

    Wang, Guang-zhi; Li, Wei-guang; He, Wen-jie; Han, Hong-da; Ding, Chi; Ma, Xiao-na; Qu, Yan-ming

    2006-10-01

    By means of immobilizing five kinds of activated carbon, we studied the influence between the chief activated carbon property items and immobilized bioactivated carbon (IBAC) purification effect with the correlation analysis. The result shows that the activated carbon property items which the correlation coefficient is up 0.7 include molasses, abrasion number, hardness, tannin, uniform coefficient, mean particle diameter and effective particle diameter; the activated carbon property items which the correlation coefficient is up 0.5 include pH, iodine, butane and tetrachloride. In succession, the partial correlation analysis shows that activated carbon property items mostly influencing on IBAC purification effect include molasses, hardness, abrasion number, uniform coefficient, mean particle diameter and effective particle diameter. The causation of these property items bringing influence on IBAC purification is that the activated carbon holes distribution (representative activated carbon property item is molasses) provides inhabitable location and adjust food for the dominance bacteria; the mechanical resist-crash property of activated carbon (representative activated carbon property items: abrasion number and hardness) have influence on the stability of biofilm; and the particle diameter size and distribution of activated carbon (representative activated carbon property items: uniform coefficient, mean particle diameter and effective particle diameter) can directly affect the force of water in IBAC filter bed, which brings influence on the dominance bacteria immobilizing on activated carbon.

  8. Mineral Influence on Microbial Survival During Carbon Sequestration

    NASA Astrophysics Data System (ADS)

    Santillan, E. U.; Shanahan, T. M.; Wolfe, W. W.; Bennett, P.

    2012-12-01

    CO2 sequestered in a deep saline aquifer will perturb subsurface biogeochemistry by acidifying the groundwater and accelerating mineral diagenesis. Subsurface microbial communities heavily influence geochemistry through their metabolic processes, such as with dissimilatory iron reducing bacteria (DIRB). However, CO2 also acts as a sterilant and will perturb these communities. We investigated the role of mineralogy and its effect on the survival of microbes at high PCO2 conditions using the model DIRB Shewanella oneidensis MR-1. Batch cultures of Shewanella were grown to stationary phase and exposed to high PCO2 using modified Parr reactors. Cell viability was then determined by plating cultures after exposure. Results indicate that at low PCO2 (2 bar), growth and iron reduction are decreased and cell death occurs within 1 hour when exposed to CO2 pressures of 10 bar or greater. Further, fatty acid analysis indicates microbial lipid degradation with C18 fatty acids being the slowest lipids to degrade. When cultures were grown in the presence of rocks or minerals representative of the deep subsurface such as carbonates and silicates and exposed to 25 bar CO2, survival lasted beyond 2 hours. The most effective protecting substratum was quartz sandstone, with cultures surviving beyond 8 hours of CO2 exposure. Scanning electron microscope images reveal biofilm formation on the mineral surfaces with copious amounts of extracellular polymeric substances (EPS) present. EPS from these biofilms acts as a reactive barrier to the CO2, slowing the penetration of CO2 into cells and resulting in increased survival. When biofilm cultures were grown with Al and As to simulate the release of toxic metals from minerals such as feldspars and clays, survival time decreased, indicating mineralogy may also enhance microbial death. Biofilms were then grown on iron-coated quartz sand to determine conversely what influence biofilms may have on mineral dissolution during CO2 perturbation

  9. Enhancement of the dissolution rate and bioavailability of fenofibrate by a melt-adsorption method using supercritical carbon dioxide

    PubMed Central

    Cha, Kwang-Ho; Cho, Kyung-Jin; Kim, Min-Soo; Kim, Jeong-Soo; Park, Hee Jun; Park, Junsung; Cho, Wonkyung; Park, Jeong-Sook; Hwang, Sung-Joo

    2012-01-01

    Background: The aim of this study was to enhance the bioavailability of fenofibrate, a poorly water-soluble drug, using a melt-adsorption method with supercritical CO2. Methods: Fenofibrate was loaded onto Neusilin® UFL2 at different weight ratios of fenofibrate to Neusilin UFL2 by melt-adsorption using supercritical CO2. For comparison, fenofibrate-loaded Neusilin UFL2 was prepared by solvent evaporation and hot melt-adsorption methods. The fenofibrate formulations prepared were characterized by differential scanning calorimetry, powder x-ray diffractometry, specific surface area, pore size distribution, scanning electron microscopy, and energy-dispersive x-ray spectrometry. In vitro dissolution and in vivo bioavailability were also investigated. Results: Fenofibrate was distributed into the pores of Neusilin UFL2 and showed reduced crystal formation following adsorption. Supercritical CO2 facilitated the introduction of fenofibrate into the pores of Neusilin UFL2. Compared with raw fenofibrate, fenofibrate from the prepared powders showed a significantly increased dissolution rate and better bioavailability. In particular, the area under the drug concentration-time curve and maximal serum concentration of the powders prepared using supercritical CO2 were 4.62-fold and 4.52-fold greater than the corresponding values for raw fenofibrate. Conclusion: The results of this study highlight the usefulness of the melt-adsorption method using supercritical CO2 for improving the bioavailability of fenofibrate. PMID:23118538

  10. Impacts of seawater saturation state (ΩA = 0.4-4.6) and temperature (10, 25 °C) on the dissolution kinetics of whole-shell biogenic carbonates

    NASA Astrophysics Data System (ADS)

    Ries, Justin B.; Ghazaleh, Maite N.; Connolly, Brian; Westfield, Isaac; Castillo, Karl D.

    2016-11-01

    Anthropogenic increase of atmospheric pCO2 since the Industrial Revolution has caused seawater pH to decrease and seawater temperatures to increase-trends that are expected to continue into the foreseeable future. Myriad experimental studies have investigated the impacts of ocean acidification and warming on marine calcifiers' ability to build protective shells and skeletons. No studies, however, have investigated the combined impacts of ocean acidification and warming on the whole-shell dissolution kinetics of biogenic carbonates. Here, we present the results of experiments designed to investigate the effects of seawater saturation state (ΩA = 0.4-4.6) and temperature (10, 25 °C) on gross rates of whole-shell dissolution for ten species of benthic marine calcifiers: the oyster Crassostrea virginica, the ivory barnacle Balanus eburneus, the blue mussel Mytilus edulis, the conch Strombus alatus, the tropical coral Siderastrea siderea, the temperate coral Oculina arbuscula, the hard clam Mercenaria mercenaria, the soft clam Mya arenaria, the branching bryozoan Schizoporella errata, and the coralline red alga Neogoniolithon sp. These experiments confirm that dissolution rates of whole-shell biogenic carbonates decrease with calcium carbonate (CaCO3) saturation state, increase with temperature, and vary predictably with respect to the relative solubility of the calcifiers' polymorph mineralogy [high-Mg calcite (mol% Mg > 4) ≥ aragonite > low-Mg calcite (mol% Mg < 4)], consistent with prior studies on sedimentary and inorganic carbonates. Furthermore, the severity of the temperature effects on gross dissolution rates also varied with respect to carbonate polymorph solubility, with warming (10-25 °C) exerting the greatest effect on biogenic high-Mg calcite, an intermediate effect on biogenic aragonite, and the least effect on biogenic low-Mg calcite. These results indicate that both ocean acidification and warming will lead to increased dissolution of biogenic

  11. Interactions between sparfloxacin and antacids - dissolution and adsorption studies.

    PubMed

    Hussain, Fida; Arayne, M Saeed; Sultana, Najma

    2006-01-01

    Sparfloxacin is a broad-spectrum oral fluoroquinolone antimicrobial agent with a long elimination half-life, extensively used against both Gram-positive as well as Gram-negative microorganism. Concurrent administration of antacids and sparfloxacin decreases the gastrointestinal absorption of sparfloxacin and therapeutic failure may result. The present study was designed to evaluate the influence of some antacids on the availability of sparfloxacin. The release of sparfloxacin from tablets in the presence of antacids like sodium bicarbonate, calcium hydroxide, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, magnesium trisilicate and magaldrate has been studied on BP 2003 dissolution test apparatus. These studies were carried out in simulated gastric and intestinal juices for three hours at 37 degrees C. The results confirmed that the dissolution rate of tablets was markedly retarded in the presence all of antacids studied, whereas magaldrate and calcium carbonate exhibited relatively higher adsorption capacities in simulated gastric juice and magnesium trisilicate and calcium hydroxide in simulated intestinal juice.

  12. Carbon nanotube proximity influences rice DNA

    NASA Astrophysics Data System (ADS)

    Katti, Dinesh R.; Sharma, Anurag; Pradhan, Shashindra Man; Katti, Kalpana S.

    2015-07-01

    The uptake of carbon nanotubes (CNT) influences the output of plants, potentially through interactions between the DNA and CNTs. However, little is known about the changes in the plant DNA due to CNT proximity. We report changes in rice plant DNA in the proximity of single walled CNT (SWCNT) using molecular dynamics simulations. The DNA experiences breaking and forming of hydrogen bonds due to unzipping of Watson-Crick (WC) nucleobase pairs and wrapping onto SWCNT. The number of hydrogen bonds between water and DNA nucleobases decreases due to the presence of SWCNT. A higher number of guanine-cytosine (Gua-Cyt) WC hydrogen bonds break as compared to adenine-thymine (Ade-Thy), which suggests that Gua and Cyt bases play a dominant role in DNA-SWCNT interactions. We also find that changes to non-WC nucleobase pairs and van der Waals attractive interactions between WC nucleobase pairs and SWCNT cause significant changes in the conformation of the DNA.

  13. Influence of low concentration V and Co oxide doping on the dissolution behaviors of simplified nuclear waste glasses

    SciTech Connect

    Lu, Xiaonan; Neeway, James J.; Ryan, Joseph V.; Du, Jincheng

    2016-11-01

    Transition metal oxides are commonly present in nuclear waste and they can alter the structure, property and especially dissolution behaviors of the glasses used for waste immobilization. In this paper, we investigated vanadium and cobalt oxide induced structural and properties changes, especially dissolution behaviors, of International Simple Glass (ISG), a model nuclear waste glass system. Static chemical durability tests were performed at 90 °C with a pH value of 7 and a surface-area-to-solution-volume of 200 m-1 for 112 days on three glasses: ISG, ISG doped with 0.5 mol% Co2O3, and ISG doped with 2.0 mol% V2O5. ICP-MS was used to analyze the dissolved ion concentrations. It was found that doping with vanadium and cobalt oxide, even at the low doping concentration, significantly reduced the extent of the ISG glass dissolution. Differential Scanning Calorimetry (DSC) analysis showed that vanadium oxide doping reduced the glass transition temperature (Tg) while cobalt oxide did not significantly change the Tg of ISG. X-ray diffraction (XRD), Raman spectrometry and scanning electron microscopy (SEM) were used to analyze the glass samples before and after corrosion to understand the phase and microstructure changes.

  14. Lithological and hydrological influences on ground-water composition in a heterogeneous carbonate-clay aquifer system

    USGS Publications Warehouse

    Kauffman, S.J.; Herman, J.S.; Jones, B.F.

    1998-01-01

    The influence of clay units on ground-water composition was investigated in a heterogeneous carbonate aquifer system of Miocene age in southwest Florida, known as the Intermediate aquifer system. Regionally, the ground water is recharged inland, flows laterally and to greater depths in the aquifer systems, and is discharged vertically upward at the saltwater interface along the coast. A depth profile of water composition was obtained by sampling ground water from discrete intervals within the permeable carbonate units during coring and by squeezing pore water from a core of the less-permeable clay layers. A normative salt analysis of solute compositions in the water indicated a marine origin for both types of water and an evolutionary pathway for the clay water that involves clay diagenesis. The chemical composition of the ground water in the carbonate bedrock is significantly different from that of the pore water in the clay layers. Dissolution of clays and opaline silica results in high silica concentrations relative to water in other parts of the Intermediate aquifer system. Water enriched in chloride relative to the overlying and underlying ground water recharges the aquifer inland where the confining clay layer is absent, and it dissolves carbonate and silicate minerals and reacts with clays along its flow path, eventually reaching this coastal site and resulting in the high chloride and silica concentrations observed in the middle part of the Intermediate aquifer system. Reaction-path modeling suggests that the recharging surficial water mixes with sulfate-rich water upwelling from the Upper Floridan aquifer, and carbonate mineral dissolution and precipitation, weathering and exchange reactions, clay mineral diagenesis, clay and silica dissolution, organic carbon oxidation, and iron and sulfate reduction result in the observed water compositions.A study was conducted to clarify the influence of clay units on ground-water composition in a heterogeneous

  15. The impact of sulfuric and nitric acid on carbonate dissolution and the associated deficit of CO2 uptake in the Upper-Middle Reaches of Wujiang River

    NASA Astrophysics Data System (ADS)

    Qibo, H.

    2016-12-01

    The goal of this study was to highlight the impact of sulfuric and nitric acid on carbonate dissolution and the associated deficit of CO2 uptake by carbonate weathering in the Upper-Middle Reaches of Wujiang River, a karstic landform-dominated area where anthropogenic activities are extensively spread. To understand the chemical weathering processes and associated deficit of CO2 consumption, the hydrochemistry and carbon isotope of DIC from 41 and 26 karst groundwater samples were collected in rainy and post-rainy season, respectively. The results showed that Ca2+ and Mg2+ were the dominant cations, accounting for 55.87% to 98.52%, and HCO3- was the dominant anions, accounting for 63.63% to 92.87%. In most samples, the concentrations of Ca2+ and Mg2+ exceeding the equivalent concentration of HCO3- with a changeable molar ratio between ( Ca2++Mg2+) and HCO3- of 1.09 to 2.12. Being significantly higher of the δ13CDIC values (-11.38‰ on average) than the value (-11.5‰) which determined by carbonic acid and a high positive significant correlation with[SO42-+NO3-]/HCO3-, suggested that additional SO42- and NO3- were required to compensate the excess of cations. Therefore, beside carbonic acid, the nitric and sulfuric acid as additional proton-promoted weathering agents may also play an important role in carbonate weathering. The contribution of atmospheric/soil CO2 (CO2ATM-SOIL) to the total aquatic HCO3- decreased by 15.67% and 14.16% on average due to nitric and sulfuric acids in rainy and post-rainy season, respectively. Therefore, in study area, the equal deficit of soil CO2 uptake by carbonate weathering reach 29.80% when nitric and sulfuric acids were considered. Based on this consideration, the absorption of CO2 by carbonate weathering might be overestimated by previous research in karst areas.

  16. Impact of nitrogenous fertilizers on carbonate dissolution in small agricultural catchments: Implications for weathering CO 2 uptake at regional and global scales

    NASA Astrophysics Data System (ADS)

    Perrin, Anne-Sophie; Probst, Anne; Probst, Jean-Luc

    2008-07-01

    The goal of this study was to highlight the occurrence of an additional proton-promoted weathering pathway of carbonate rocks in agricultural areas where N-fertilizers are extensively spread, and to estimate its consequences on riverine alkalinity and uptake of CO 2 by weathering. We surveyed 25 small streams in the calcareous molassic Gascogne area located in the Garonne river basin (south-western France) that drain cultivated or forested catchments for their major element compositions during different hydrologic periods. Among these catchments, the Hay and the Montoussé, two experimental catchments, were monitored on a weekly basis. Studies in the literature from other small carbonate catchments in Europe were dissected in the same way. In areas of intensive agriculture, the molar ratio (Ca + Mg)/HCO 3 in surface waters is significantly higher (0.7 on average) than in areas of low anthropogenic pressure (0.5). This corresponds to a decrease in riverine alkalinity, which can reach 80% during storm events. This relative loss of alkalinity correlates well with the NO3- content in surface waters. In cultivated areas, the contribution of atmospheric/soil CO 2 to the total riverine alkalinity (CO 2 ATM-SOIL/HCO 3) is less than 50% (expected value for carbonate basins), and it decreases when the nitrate concentration increases. This loss of alkalinity can be attributed to the substitution of carbonic acid (natural weathering pathway) by protons produced by nitrification of N-fertilizers (anthropogenic weathering pathway) occurring in soils during carbonate dissolution. As a consequence of these processes, the alkalinity over the last 30 years shows a decreasing trend in the Save river (one of the main Garonne river tributaries, draining an agricultural catchment), while the nitrate and calcium plus magnesium contents are increasing. We estimated that the contribution of atmospheric/soil CO 2 to riverine alkalinity decreased by about 7-17% on average for all the studied

  17. Arsenic release from flooded paddy soils is influenced by speciation, Eh, pH, and iron dissolution.

    PubMed

    Yamaguchi, N; Nakamura, T; Dong, D; Takahashi, Y; Amachi, S; Makino, T

    2011-05-01

    Arsenic (As) is highly mobilized when paddy soil is flooded, causing increased uptake of As by rice. We investigated factors controlling soil-to-solution partitioning of As under anaerobic conditions. Changes in As and iron (Fe) speciation due to flooded incubation of two paddy soils (soils A and B) were investigated by HPLC/ICP-MS and XANES. The flooded incubation resulted in a decrease in Eh, a rise in pH, and an increase in the As(III) fraction in the soil solid phase up to 80% of the total As in the soils. The solution-to-soil ratio of As(III) and As(V) (R(L/S)) increased with pH due to the flooded incubation. The R(L/S) for As(III) was higher than that for As(V), indicating that As(III) was more readily released from soil to solution than was As(V). Despite the small differences in As concentrations between the two soils, the amount of As dissolved by anaerobic incubation was lower in soil A. With the development of anaerobic conditions, Fe(II) remained in the soil solid phase as the secondary mineral siderite, and a smaller amount of Fe was dissolved from soil A than from soil B. The dissolution of Fe minerals rather than redox reaction of As(V) to As(III) explained the different dissolution amounts of As in the two paddy soils. Anaerobic incubation for 30 d after the incomplete suppression of microbial activity caused a drop in Eh. However, this decline in Eh did not induce the transformation of As(V) to As(III) in either the soil solid or solution phases, and the dissolution of As was limited. Microbial activity was necessary for the reductive reaction of As(V) to As(III) even when Eh reached the condition necessary for the dominance of As(III). Ratios of released As to Fe from the soils were decreased with incubation time during both anaerobic incubation and abiotic dissolution by sodium ascorbate, suggesting that a larger amount of As was associated with an easily soluble fraction of Fe (hydr) oxide in amorphous phase and/or smaller particles. Copyright

  18. Influence of Wind Pressure on the Carbonation of Concrete

    PubMed Central

    Zou, Dujian; Liu, Tiejun; Du, Chengcheng; Teng, Jun

    2015-01-01

    Carbonation is one of the major deteriorations that accelerate steel corrosion in reinforced concrete structures. Many mathematical/numerical models of the carbonation process, primarily diffusion-reaction models, have been established to predict the carbonation depth. However, the mass transfer of carbon dioxide in porous concrete includes molecular diffusion and convection mass transfer. In particular, the convection mass transfer induced by pressure difference is called penetration mass transfer. This paper presents the influence of penetration mass transfer on the carbonation. A penetration-reaction carbonation model was constructed and validated by accelerated test results under high pressure. Then the characteristics of wind pressure on the carbonation were investigated through finite element analysis considering steady and fluctuating wind flows. The results indicate that the wind pressure on the surface of concrete buildings results in deeper carbonation depth than that just considering the diffusion of carbon dioxide. In addition, the influence of wind pressure on carbonation tends to increase significantly with carbonation depth. PMID:28793462

  19. Porosity evolution during experimental diagenesis of carbonates: influence of salinity

    NASA Astrophysics Data System (ADS)

    Neveux, Lucille; Grgic, Dragan; Carpentier, Cedric; Pironon, Jacques

    2015-04-01

    The existence of high quality (high porosity - high permeability) reservoirs in carbonated rocks at great depth highlights a paradox. Indeed, classical modeling of rock evolution during burial forecasts a strong decrease of porosity with depth, thus predicting a lack of economically interesting reservoirs under 4000 m. So how these reservoirs come to exist? The understanding of the way porosity is altered at great depth may indicate potential reservoir rocks. By which processes is porosity modified? To answer these questions, an experimental approach has been conducted, using a specifically designed apparatus that enable, in laboratory, the simulation of deeply buried reservoirs in situ conditions (high pressures and temperature as well as the circulation of fluids). The nature of carbonated rocks (bioclastic and oolitic) has been investigated as well as the nature of the percolating fluid (with and without NaCl). To characterize the evolution of the porosity and of the porous network, analysis via nanotomography, mercury intrusion porosimetry and specific surface area were used. The results obtained in this study show that the main diagenetic process of porosity loss is the pressure solution creep (PSC), reducing by at least three the initial porosity. PSC results in both dissolution and precipitation, processes that lead to a great modification of the rock porous network. This modification is more pronounced in the oolitic limestone than in the bioclastic one. The presence of NaCl in the fluid leads to a greater dissolution of carbonate matter but also to a precipitation of salt minerals partially blocking the porous network. The dataset obtained from these experiments shows the importance of the nature of the deposit rock but also of the nature of the percolating fluid. It can be concluded that pore fluid chemistry and, by consequence, its origin is of great importance in the study of porosity modification with depth.

  20. Preparation of a novel starch-derived three-dimensional ordered macroporous carbon for improving the dissolution rate and oral bioavailability of water-insoluble drugs.

    PubMed

    Liu, Ying; Wu, Chao; Hao, Yanna; Xu, Jie; Zhao, Ying; Qiu, Yang; Jiang, Jie; Yu, Tong; Ji, Peng

    2016-01-25

    In our study, soluble starch was applied as a novel carbon source for preparing three-dimensional ordered macroporous carbon (3DOMC) using monodisperse silica nanospheres as the hard template. The 3DOMC was used as an insoluble drug carrier when it was found that it could markedly improve the water solubility of felodipine (FDP). The structural features of 3DOMC were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The 3DOMC structure was found to have a higher drug loading than microporous and mesoporous structures, and the interconnected nanostructure effectively inhibited the formation of drug crystals. FDP, belonging to the Biopharmaceutics Classification System II (BCSII), was chosen as the model drug and was loaded into the 3DOMC structure by solvent evaporation. The state of FDP in the 3DOMC structure was characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The results obtained showed that FDP was present in the pores in an amorphous or microcrystalline state. In vivo and in vitro experiments indicated that 3DOMC could significantly improve the drug dissolution rate, but the FDP-3DOMC self-made common tablets had the disadvantage of a burst effect. For this reason, osmotic pump technology was used to control the drug release rate. We developed a potentially useful insoluble drug carrier for pharmaceutical applications.

  1. Development of a Novel Milling System Using Supercritical Carbon Dioxide for Improvement of Dissolution Characteristics of Water-Poorly Soluble Drugs.

    PubMed

    Fern, Jennifer Chia Wee; Nakamura, Hideya; Watano, Satoru

    2016-01-01

    The aim of this study is to develop a novel milling system using supercritical carbon dioxide (SC-CO2) for the improvement of dissolution characteristics of water-poorly soluble drugs. SC-CO2 possesses high potential in the application of nanotechnology, due to the attractive properties of SC-CO2 fluid such as cheap, inert and non-polluting. In addition, SC-CO2 has density comparable to a liquid, viscosity similar to a gas, and high diffusion capacity. Most of all, carbon dioxide exists as gas in room temperature and pressure, which enables the removal of fluid instantaneously. In this study, a novel method of milling using SC-CO2 was proposed to produce fine-drug particles. SC-CO2 milling was conducted and its performance was compared with the ones by various milling methods such as jet milling, dry milling and wet milling. A comparison on the effect of each milling medium on its milling performance, drug size distribution, and particle morphology was conducted. Operating variables of the SC-CO2 milling system were also investigated to clarify the factors affecting the milling properties and to improve drug release characteristics of water-poorly soluble drugs.

  2. Uniform nano-sized valsartan for dissolution and bioavailability enhancement: influence of particle size and crystalline state.

    PubMed

    Ma, Qiuping; Sun, Hongrui; Che, Erxi; Zheng, Xin; Jiang, Tongying; Sun, Changshan; Wang, Siling

    2013-01-30

    The central purpose of this study was to evaluate the impact of drug particle size and crystalline state on valsartan (VAL) formulations in order to improve its dissolution and bioavailability. VAL microsuspension (mean size 22 μm) and nanosuspension (30-80nm) were prepared by high speed dispersing and anti-solvent precipitation method and converted into powders through spray drying. Differential scanning calorimetry studies indicated amorphization of VAL in the spray-dried valsartan nanosuspension (SD-VAL-Nano) but recrystallization occurred after 6 months storage at room temperature. The spray-dried valsartan microsuspension (SD-VAL-Micro) conserved the crystalline form. The VAL dissolution rate and extent were markedly enhanced with both SD-VAL-Micro and SD-VAL-Nano as compared to crude VAL crystals over the pH range of 1.2-6.8. Pharmacokinetic studies in rats demonstrated a 2.5-fold increase in oral bioavailability in the case of SD-VAL-Nano compared with the commercial product while the SD-VAL-Micro provided a much less desirable pharmacokinetic profile. In conclusion, reducing particle size to the nano-scale appears to be a worthwhile and promising approach to obtain VAL products with optimum bioavailability. In addition, the impact of crystalline state on the bioavailability of nano-sized VAL might be not as big as that of particle size. Copyright © 2012 Elsevier B.V. All rights reserved.

  3. Oxidative dissolution of copper and zinc metal in carbon dioxide with tert-butyl peracetate and a beta-diketone chelating agent.

    PubMed

    Visintin, Pamela M; Bessel, Carol A; White, Peter S; Schauer, Cynthia K; DeSimone, Joseph M

    2005-01-24

    A series of beta-diketone ligands, R(1)COCH(2)COR(2) [tmhdH (R(1) = R(2) = C(CH(3))(3)); tfacH (R(1) = CF(3); R(2) = CH(3)); hfacH (R(1) = R(2) = CF(3))], in combination with tert-butyl peracetate (t-BuPA), have been investigated as etchant solutions for dissolution of copper metal into carbon dioxide solvent. Copper removal in CO(2) increases in the order tfacH < tmhdH < hfacH. A study of the reactions of the hfacH/t-BuPA etchant solution with metallic copper and zinc was conducted in three solvents: scCO(2) (supercrical CO(2)); hexanes; CD(2)Cl(2). The etchant solution/metallic zinc reaction produced a diamagnetic Zn(II) complex, which allowed NMR identification of the t-BuPA decomposition products as tert-butyl alcohol and acetic acid. Gravimetric analysis of the amount of zinc consumed, together with NMR studies, confirmed the 1:1:2 Zn:t-BuPA:hfacH reaction stoichiometry, showing t-BuPA to be an overall two-electron oxidant for Zn(0). The metal-containing products of the copper and zinc reactions were characterized by elemental analysis, IR spectroscopy, and, as appropriate, NMR spectroscopy and single-crystal X-ray diffraction [trans-M(hfac)(2)(H(2)O)(CH(3)CO(2)H) (1, M = Cu; 2, M = Zn)]. On the basis of the experimental results, a working model of the oxidative dissolution reaction is proposed, which delineates the key chemical variables in the etching reaction. These t-BuPA/hfacH etchant solutions may find application in a CO(2)-based chemical mechanical planarization (CMP) process.

  4. Influence of carbon nanomaterials on the properties of paint coatings

    NASA Astrophysics Data System (ADS)

    Zhdanok, S. A.; Krauklis, A. V.; Borisevich, K. O.; Prokopchuk, N. P.; Nikolaichik, A. V.; Stanovoi, P. G.

    2011-11-01

    The conditions for obtaining carbon nanomaterials with the use of a low-temperature plasma are described. The product obtained was analyzed using the electron microscopy and a laser diffraction particle-size analyzer. The influence of the carbon nanomaterials on the physicochemical properties of paint coatings, their adhesion, impact and bending strengths, hardness, and protection characteristics was investigated.

  5. DISSOLUTION OF PLUTONIUM CONTAINING CARRIER PRECIPITATE BY CARBONATE METATHESIS AND SEPARATION OF SULFIDE IMPURITIES THEREFROM BY SULFIDE PRECIPITATION

    DOEpatents

    Duffield, R.B.

    1959-07-14

    A process is described for recovering plutonium from foreign products wherein a carrier precipitate of lanthanum fluoride containing plutonium is obtained and includes the steps of dissolving the carrier precipitate in an alkali metal carbonate solution, adding a soluble sulfide, separating the sulfide precipitate, adding an alkali metal hydroxide, separating the resulting precipitate, washing, and dissolving in a strong acid.

  6. 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.

  7. Explanation for the enhanced dissolution of silica column packing in high pH phosphate and carbonate buffers.

    PubMed

    Tindall, G W; Perry, R L

    2003-02-28

    It has been reported that at high pH, the rate of bonded phase packing degradation in methanol/water mobile phases is greater for carbonate and phosphate buffers than for amine buffers. This conclusion was based on buffer pH determined in the aqueous buffer before dilution with methanol. Changes in buffer species pKa, and therefore buffer pH, upon methanol dilution are consistent with the observed degradation results. Measurements of pH in the methanol/water solutions confirm that the carbonate and phosphate buffers were considerably more basic than the amine buffer, even though all the buffers were pH 10 before dilution with methanol. These results demonstrate that it can be misleading to extrapolate aqueous pH data to partially aqueous solutions. Measurements of pH in the mixed solvent provide more reliable predictions of column and sample stability.

  8. The influence of saliva on the dissolution of calcium fluoride after application of different fluoride gels in vitro.

    PubMed

    Hellwig, Elmar; Polydorou, Olga; Lussi, Adrian; Kielbassa, Andrej M; Altenburger, Markus J

    2010-10-01

    To determine the formation and dissolution of calcium fluoride on the enamel surface after application of two fluoride gel-saliva mixtures. From each of 80 bovine incisors, two enamel specimens were prepared and subjected to two different treatment procedures. In group 1, 80 specimens were treated with a mixture of an amine fluoride gel (1.25% F-; pH 5.2; 5 minutes) and human saliva. In group 2, 80 enamel blocks were subjected to a mixture of sodium fluoride gel (1.25% F; pH 5.5; 5 minutes) and human saliva. Subsequent to fluoride treatment, 40 specimens from each group were stored in human saliva and sterile water, respectively. Ten specimens were removed after each of 1 hour, 24 hours, 2 days, and 5 days and analyzed according to potassium hydroxide-soluble fluoride. Application of amine fluoride gel resulted in a higher amount of potassium hydroxide-soluble fluoride than did sodium fluoride gel 1 hour after application. Saliva exerted an inhibitory effect according to the dissolution rate of calcium fluoride. However, after 5 days, more than 90% of the precipitated calcium fluoride was dissolved in the amine fluoride group, and almost all potassium hydroxide-soluble fluoride was lost in the sodium fluoride group. Calcium fluoride apparently dissolves rapidly, even at almost neutral pH. Considering the limitations of an in vitro study, it is concluded that highly concentrated fluoride gels should be applied at an adequate frequency to reestablish a calcium fluoride-like layer.

  9. Copper corrosion in irradiated environments: The influence of H{sub 2}O{sub 2}on the electrochemistry of copper dissolution in HCl electrolyte

    SciTech Connect

    Smyrl, W.H.; Bell, B.T.; Atanasoski, R.T.; Glass, R.S.

    1986-12-01

    The anodic dissolution of copper was examined in deaerated, 0.1 M HCl aqueous solution in the presence of H{sub 2}O{sub 2}. Concentrations of H{sub 2}O{sub 2} up to 0.2 M were studied at a rotating copper disk-platinum ring electrode. The open circuit potential (OCP) of copper was found to depend on both peroxide concentration and rotation rate. The OCP shifts towards more positive values with increasing H{sub 2}O{sub 2} concentration (C) and decreasing rotation rate. The current-voltage curves for anodic dissolution of copper were also influenced by the presence of peroxide. The curves recorded with the potential scanned in the positive direction showed the expected 60 mV slope, but the reverse scans showed significant departures. At a given potential scan rate, hysteresis was observed which was larger for higher H{sub 2}O{sub 2} concentrations, lower rotation rates, and more positive anodic potential limits. Monitoring the cuprous ions at the outer Pt ring revealed that there was a complex set of events taking place at the copper surface, including film formation and the appearance of cupric ions. 13 refs., 7 figs.

  10. 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.

  11. An AFM study of calcite dissolution in concentrated electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Ruiz Agudo, E.; Putnis, C. V.; Putnis, A.; Rodriguez-Navarro, C.

    2009-04-01

    Calcite-solution interactions are of a paramount importance in a range of processes such as the removal of heavy metals, carbon dioxide sequestration, landscape modeling, weathering of building stone and biomineralization. Water in contact with minerals often carries significant amounts of solutes; additionally, their concentration may vary due to evaporation and condensation. It is well known that calcite dissolution is affected dramatically by the presence of such solutes. Here we present investigations on the dissolution of calcite in the presence of different electrolytes. Both bulk (batch reactors) experiments and nanoscale (in situ AFM) techniques are used to study the dissolution of calcite in a range of solutions containing alkaly cations balanced by halide anions. Previous works have indicated that the ionic strength has little influence in calcite dissolution rates measured from bulk experiments (Pokrovsky et al. 2005; Glendhill and Morse, 2004). Contrary to these results, our quantitative analyses of AFM observations show an enhancement of the calcite dissolution rate with increasing electrolyte concentration. Such an effect is concentration-dependent and it is most evident in concentrated solutions. AFM experiments have been carried out in a fluid cell using calcite cleavage surfaces in contact with solutions of simple salts of the alkaly metals and halides at different undersaturations with respect to calcite to try to specify the effect of the ionic strength on etch pit spreading rate and calcite dissolution rate. These results show that the presence of soluble salts may critically affect the weathering of carbonate rocks in nature as well as the decay of carbonate stone in built cultural heritage. References: Pokrosky, O.S.; Golubev, S.V.; Schott, J. Dissolution kinetics of calcite, dolomite and magnesite at 25°C and 0 to 50 atm pCO2. Chemical Geology, 2005, 217 (3-4) 239-255. Glendhill, D.K.; Morse, J.W. Dissolution kinetics of calcite in Na

  12. Cyclic magnetite dissolution in Pleistocene sediments of the abyssal northwest Pacific Ocean: Evidence for glacial oxygen depletion and carbon trapping

    NASA Astrophysics Data System (ADS)

    Korff, Lucia; Dobeneck, Tilo; Frederichs, Thomas; Kasten, Sabine; Kuhn, Gerhard; Gersonde, Rainer; Diekmann, Bernhard

    2016-05-01

    The carbonate-free abyss of the North Pacific defies most paleoceanographic proxy methods and hence remains a "blank spot" in ocean and climate history. Paleomagnetic and rock magnetic, geochemical, and sedimentological methods were combined to date and analyze seven middle to late Pleistocene northwest Pacific sediment cores from water depths of 5100 to 5700 m. Besides largely coherent tephra layers, the most striking features of these records are nearly magnetite-free zones corresponding to glacial marine isotope stages (MISs) 22, 12, 10, 8, 6, and 2. Magnetite depletion is correlated with organic carbon and quartz content and anticorrelated with biogenic barite and opal content. Within interglacial sections and mid-Pleistocene transition glacial stages MIS 20, 18, 16, and 14, magnetite fractions of detrital, volcanic, and bacterial origin are all well preserved. Such alternating successions of magnetic iron mineral preservation and depletion are known from sapropel-marl cycles, which accumulated under periodically changing bottom water oxygen and redox conditions. In the open central northwest Pacific Ocean, the only conceivable mechanism to cause such abrupt change is a modified glacial bottom water circulation. During all major glaciations since MIS 12, oxygen-depleted Antarctic Bottom Water (AABW)-sourced bottom water seems to have crept into the abyssal northwest Pacific below ~5000 m depth, thereby changing redox conditions in the sediment, trapping and preserving dissolved and particulate organic matter and, in consequence, reducing and dissolving both, biogenic and detrital magnetite. At deglaciation, a downward progressing oxidation front apparently remineralized and released these sedimentary carbon reservoirs without replenishing the magnetite losses.

  13. [Modeling the Influencing Factors of Karstification and Karst Carbon Cycle in Laboratory].

    PubMed

    Zhao, Rui-yi; Lü, Xian-fu; Duan, Yi-fan

    2015-08-01

    To analyze the influencing factors of karstification and karst carbon cycle, a simulation experiment was carried out and 6 soil columns were designed. The results showed that the content of H2O4, hydrodynamic condition and thickness of the soil had important influence on karstification and karst carbon cycle. For the soil columns which were covered by the same thickness of soil, the concentrations of Ca2+ + Mg2+ and SO4(2-) followed the order of B20-2 > B20-1 > B20-3, B50-2 > B50-1 > B50-3. This meant that input of H2SO4 enhanced the karstification and increasing infiltration water had significant dilution effect on the chemical properties. For the soil columns with different thickness of soil but with the same slag pile and hydrodynamic conditions, the concentrations of Ca2+ + Mg2+ and SO4(2-) followed the order of B50-1 > B20-1, B50-2 > B20-2, B50-3 > B20-3. It was demonstrated that more carbonate rock was dissolved under the thick soil columns. In addition, the net consumption of CO2 mainly depended on the content of H2SO4 in this experiment due to slight contribution of H2CO3 to carbonate rock dissolution. More content of H2SO4 brought about less net consumption of C02, but B50-2 was an exception. Organic matter and other nutrients might be input into deep soil with the slag pile, and they promoted the production of soil C)2. Therefore, more CO2 was consumed due to the increased contribution of H2CO to karstification.

  14. Influence of carbonization methods on the aromaticity of pyrogenic dissolved organic carbon

    USDA-ARS?s Scientific Manuscript database

    Dissolved organic carbon (DOC) components of soil amendments such as biochar will influence the fundamental soil chemistry including the metal speciation, nutrient availability, and microbial activity. Quantitative correlation is necessary between (i) pyrogenic DOC components of varying aromaticity...

  15. Diamond dissolution and the production of methane and other carbon-bearing species in hydrothermal diamond-anvil cells

    USGS Publications Warehouse

    Chou, I.-Ming; Anderson, Alan J.

    2009-01-01

    Raman analysis of the vapor phase formed after heating pure water to near critical (355-374 ??C) temperatures in a hydrothermal diamond-anvil cell (HDAC) reveals the synthesis of abiogenic methane. This unexpected result demonstrates the chemical reactivity of diamond at relatively low temperatures. The rate of methane production from the reaction between water and diamond increases with increasing temperature and is enhanced by the presence of a metal gasket (Re, Ir, or Inconel) which is compressed between the diamond anvils to seal the aqueous sample. The minimum detection limit for methane using Raman spectroscopy was determined to be ca. 0.047 MPa, indicating that more than 1.4 nanograms (or 8.6 ?? 10-11 mol) of methane were produced in the HDAC at 355 ??C and 30 MPa over a period of ten minutes. At temperatures of 650 ??C and greater, hydrogen and carbon dioxide were detected in addition to methane. The production of abiogenic methane, observed in all HDAC experiments where a gasket was used, necessitates a reexamination of the assumed chemical systems and intensive parameters reported in previous hydrothermal investigations employing diamonds. The results also demonstrate the need to minimize or eliminate the production of methane and other carbonic species in experiments by containing the sample within a HDAC without using a metal gasket.

  16. Kinetic Controls on the Desorption/Dissolution of Sorbed U(VI) and their Influence on Reactive Transport

    SciTech Connect

    Zachara, John M.; Chongxuan Liu; Qafoku, Nikolla P.; McKinley, James P.; Catalano, Jeffrey G.; Brown, Gordon E., Jr.; Davis, James A.

    2006-04-05

    A number of published studies have sought to understand geochemical kinetic process of uranium (U) that are relevant to nuclear waste sites and repositories by studying the weathering of U ore bodies and downgradient transport of weathering products. Such studies have provided important insights on processes operative over many thousand to millions of years. This project also seeks knowledge on the geochemical kinetics of U, but for shorter in-ground time periods (e.g., 20-50 years) relevant to DOE legacy waste sites. Several representative field sites were selected for intense study at Hanford as part of EMSP research to provide: (1) fundamental insights on intermediate duration geochemical events of U controlling fate and transport, and (2) key scientific information needed for remedial action assessment and informed decision making. The site discussed in this poster is the 300 A uranium plume. This plume is located at the south end of Hanford and discharges directly to the Columbia River. The plume resulted from the discharge of fuels fabrication wastes (nitric acid solutions containing U and Cu) and cladding dissolution wastes (basic sodium aluminate) to the North and South Process Ponds between 1943 and 1975 near the Columbia River. A Kd-based remedial action assessment fifteen years ago predicted that the plume would dissipate to concentrations below the DWS within 10 y. As a result of this assessment, an interim, MNA remedial decision was agreed to by DOE and state/federal regulators. It has been 15 y since the above assessment, and groundwater concentrations have not decreased (attenuated) as projected. Stakeholders are now demanding remedial intervention, and DOE seeks science-based conceptual and numeric models for more accurate future projections. The objectives are: (1) Identify the chemical speciation (e.g., adsorption complexes precipitates), mineral residence, and physical location of contaminant U in a depth sequence of sediments from the disposal

  17. Influence of different microphysical schemes on the prediction of dissolution of nonreactive gases by cloud droplets and raindrops

    SciTech Connect

    Huret, N.; Chaumerliac, N.; Isaka, H.; Nickerson, E.C. |

    1994-09-01

    Three microphysical formulations are closely compared to evaluate their impact upon gas scavenging and wet deposition processes. They range from a classical bulk approach to a fully spectral representation, including an intermediate semispectral parameterization. Detailed comparisons among the microphysical rates provided by these three parameterizations are performed with special emphasis on evaporation rate calculations. This comparative study is carried out in the context of a mountain wave simulation. Major differences are essentially found in the contrasted spreading of the microphysical fields on the downwind side of the mountain. A detailed chemical module including the dissolution of the species and their transfer between phases (air, cloud, and rain) is coupled with the three microphysical parameterizations in the framework of the dynamical mesoscale model. An assessment of the accuracy of each scheme is then proposed by comparing their ability to represent the drop size dependency of chemical wet processes. The impact of evaporation (partial versus total) upon the partition of species between gas and aqueous phases is also studied in detail.

  18. How Bedrock Nitrogen Influences Carbon Storage

    NASA Astrophysics Data System (ADS)

    Rios, C.; Mitchell, S. A.

    2016-12-01

    The purpose of this research is to examine how trees, specifically Douglas fir (Pseudotsuga menziesii) responds at sites with high amounts of nitrogen (N) from rocks. In forests where Douglas firs are found, their growth is usually limited by the amount of N available to them. By providing the trees with more N from the rocks, the trees can consume more carbon (C) from the atmosphere. This explores carbon sequestration, capturing C from the atmosphere in the biomass of the trees and reducing the amount of CO2 in the atmosphere. My hypothesis is that trees with access to more N from the rocks, which acts like a fertilizer, will be larger and capture more C from the atmosphere storing it as biomass. We will be collecting measurements from 12 sites in northern California. The sites range from 60 to 1000 parts per million (ppm) of N in the rocks. We will use the diameter at breast height (DBH) measurements to calculate the leaf area index (LAI), which tells us how much C the trees are holding per acre. Contributing to the research will also be the counting tree rings which indicate the age of trees, so we may also see if trees are able to see if trees with more N are growing more annually. The larger amount of N taken from the bedrock resulted in more CO2 taken from the atmosphere as biomass. This resulted in more photosynthetic vegetation per unit area which means the trees are more productive. Carbon stored at these sites helps to slow the effects of increasing atmospheric CO2.

  19. Carbon dioxide storage in marine sediments - dissolution, transport and hydrate formation kinetics from high-pressure experiments

    NASA Astrophysics Data System (ADS)

    Bigalke, N. K.; Savy, J. P.; Pansegrau, M.; Aloisi, G.; Kossel, E.; Haeckel, M.

    2009-12-01

    By satisfying thermodynamic framework conditions for CO2 hydrate formation, pressures and temperatures of the deep marine environment are unique assets for sequestering CO2 in clathrates below the seabed. However, feasibility and safety of this storage option require an accurate knowledge of the rate constants governing the speed of physicochemical reactions following the injection of the liquefied gas into the sediments. High-pressure experiments designed to simulate the deep marine environment open the possibility to obtain the required parameters for a wide range of oceanic conditions. In an effort to constrain mass transfer coefficients and transport rates of CO2 in(to) the pore water of marine sediments first experiments were targeted at quantifying the rate of CO2 uptake by de-ionized water and seawater across a two-phase interface. The nature of the interface was controlled by selecting p and T to conditions within and outside the hydrate stability field (HSF) while considering both liquid and gaseous CO2. Concentration increase and hydrate growth were monitored by Raman spectroscopy. The experiments revealed anomalously fast transport rates of dissolved CO2 at conditions both inside and outside the HSF. While future experiments will further elucidate kinetics of CO2 transport and hydrate formation, these first results could have major significance to safety-related issues in the discussion of carbon storage in the marine environment.

  20. Influence of public transport in black carbon

    NASA Astrophysics Data System (ADS)

    Vasquez, Y.; Oyola, P.; Gramsch, E. V.; Moreno, F.; Rubio, M.

    2013-05-01

    As a consequence of poor air quality in Santiago de Chile, several measures were taken by the local authorities to improve the environmental conditions and protect the public health. In year 2005 the Chilean government implemented a project called "Transantiago" aimed to introduce major modifications in the public transportation system. The primary objectives of this project were to: provide an economically, socially and environmentally sustainable service and improve the quality of service without increasing fares. In this work we evaluate the impact of the Transantiago system on the black carbon pollution along four roads directly affected by the modification to the transport system. The black carbon has been used to evaluate changes in air quality due to changes in traffic. The assessment was done using measurements of black carbon before Transantiago (June-July 2005) and after its implementation (June-July 2007). Four sites were selected to monitor black carbon at street levels, one site (Alameda) that represents trunk-bus streets, i.e., buses crossing the city through main avenues. Buses using these streets had an important technological update with respect to 2005. Two streets (Usach and Departamental) show a mixed condition, i.e., they combine feeder and trunk buses. These streets combine new EURO III buses with old buses with more than 3 years of service. The last street (Eliodoro Yañez) represent private cars road without public transportation and did not experience change. Hence, the results from the years 2005 and 2007 can be directly compared using an appropriate methodology. To ensure that it was not the meteorological conditions that drive the trends, the comparison between year 2005 and 2007 was done using Wilcoxon test and a regression model. A first assessment at the four sites suggested a non decrease in black carbon concentration from 2005 to 2007, except for Alameda. A first statistical approach confirmed small increases in BC in Usach and E

  1. The influence of reducing conditions on the dissolution of a Mn-rich slag from pyrometallurgical recycling of alkaline batteries.

    PubMed

    Pareuil, Priscilla; Hamdoun, Hakim; Bordas, François; Joussein, Emmanuel; Bollinger, Jean-Claude

    2011-01-01

    The redox potential (Eh) is a key parameter for controlling the release of elements from solid materials. Nevertheless, this parameter is seldom taken into account during risk assessment studies within any regulatory framework. We studied the incidence of redox changes to the solid materials using two batch procedures: i) a gradient of redox conditions obtained using sodium ascorbate solutions at various concentrations; ii) N(2) bubbling in water. These experiments were performed on two Mn-rich slag samples coming from a pyrometallurgical plant that recycles alkaline batteries. Both samples differed slightly in their chemical composition and solid characterization (i.e. presence of Mn oxide) and presented different behaviours. The present study focused on the release of the main slag elements (i.e. Mn and Si) chosen as indicators of the dissolution of primary silicate phases. Solid phase analyses (SEM-EDS and XRD) were coupled with the monitoring of elements in leachates in order to understand their behaviour and the mechanisms involved. The results indicated that the solid composition plays an important role in the release mechanisms. The presence of Mn oxide enhanced the mobilization of Mn in the greatest reducing conditions (-320 ± 5 mV/SHE), to the extent that 42% of the total Mn was leached. This demonstrated the significance in studying the solid phases (using SEM-EDS and XRD) before and after any leaching experiment. From a laboratory practice point of view, it was easier to use sodium ascorbate and allowed, in our case, greater reducing conditions to be reached. Copyright © 2010 Elsevier Ltd. All rights reserved.

  2. Dissolution Mediated Boron and Carbon Storage during Exhumation of HP Metapelites: Examples from New Hampshire Tourmaline-Graphite Intergrowths

    NASA Astrophysics Data System (ADS)

    Galvez, M.; Rumble, D.; Cody, G. D.; Sverjensky, D. A.

    2013-12-01

    measurements done on other metasomatic or biogenic graphite displaying high structural ordering. Other textural habit of graphite are radiating crystals of graphite preferentially growing along crystalline planes of wall rock minerals (e.g. plagioclases) and at the interface between grain edge. We test whether a C and B(OH)3° (×As, Cu) rich acidic vapor unmixing from a salt-rich aqueous fluid exsolved from crystallizing igneous bodies can account for some geochemical and textural greisen-type metasomatic features of these outcrops. Other mechanical and geochemical processes participating in the process will be discussed. This work is direct evidence that respeciation and/or fluid-rock interaction at varying P,T,fH2,pH conditions of fluids during exhumation, as well as interaction between magmatic bodies and metasedimentary units play a key role in the cycling of light elements during exhumation. Rumble, D., III, and Hoering, T.C., 1986, Carbon isotope geochemistry of graphite vein deposits from New Hampshire, U.S.A: Geochimica et Cosmochimica Acta, v. 50, p. 1239-1247. Galvez ME, Beyssac O, Martinez I, Benzerara K, Chaduteau C, Malvoisin B, Malavieille J (2013) Graphite formation by carbonate reduction during subduction. Nature Geoscience 6 (6):473-477

  3. Mineral Dissolution and Precipitation due to Carbon Dioxide-Water-Rock Interactions: The Significance of Accessory Minerals in Carbonate Reservoirs (Invited)

    NASA Astrophysics Data System (ADS)

    Kaszuba, J. P.; Marcon, V.; Chopping, C.

    2013-12-01

    Accessory minerals in carbonate reservoirs, and in the caprocks that seal these reservoirs, can provide insight into multiphase fluid (CO2 + H2O)-rock interactions and the behavior of CO2 that resides in these water-rock systems. Our program integrates field data, hydrothermal experiments, and geochemical modeling to evaluate CO2-water-rock reactions and processes in a variety of carbonate reservoirs in the Rocky Mountain region of the US. These studies provide insights into a wide range of geologic environments, including natural CO2 reservoirs, geologic carbon sequestration, engineered geothermal systems, enhanced oil and gas recovery, and unconventional hydrocarbon resources. One suite of experiments evaluates the Madison Limestone on the Moxa Arch, Southwest Wyoming, a sulfur-rich natural CO2 reservoir. Mineral textures and geochemical features developed in the experiments suggest that carbonate minerals which constitute the natural reservoir will initially dissolve in response to emplacement of CO2. Euhedral, bladed anhydrite concomitantly precipitates in response to injected CO2. Analogous anhydrite is observed in drill core, suggesting that secondary anhydrite in the natural reservoir may be related to emplacement of CO2 into the Madison Limestone. Carbonate minerals ultimately re-precipitate, and anhydrite dissolves, as the rock buffers the acidity and reasserts geochemical control. Another suite of experiments emulates injection of CO2 for enhanced oil recovery in the Desert Creek Limestone (Paradox Formation), Paradox Basin, Southeast Utah. Euhedral iron oxyhydroxides (hematite) precipitate at pH 4.5 to 5 and low Eh (approximately -0.1 V) as a consequence of water-rock reaction. Injection of CO2 decreases pH to approximately 3.5 and increases Eh by approximately 0.1 V, yielding secondary mineralization of euhedral pyrite instead of iron oxyhydroxides. Carbonate minerals also dissolve and ultimately re-precipitate, as determined by experiments in the

  4. The Effects of Microbial Surface Attachment on the Dissolution Kinetics of Plagioclase Feldspar

    NASA Astrophysics Data System (ADS)

    Conrad, P. G.; Luttge, A.

    2003-12-01

    The rate of mineral dissolution can be influenced by the attachment of microbes to a mineral surface. We have previously reported the effect of Shewanella oneidensis (MR-1) biofilm formation on the dissolution kinetics of calcite, dolomite and rhodochrosite, where the organisms completely control dissolution kinetics by recognizing high-energy surface sites overlying screw dislocations and attaching to those sites, inhibiting the opening of etch pits and significantly retarding dissolution. Note that calcite and dolomite are not known to possess nutritional significance for MR-1; and while this facultative anaerobe can reduce both Mn and Fe, our experiments were all conducted with aerobic organisms. In recent experiments, we have observed that this inhibitory effect requires the cells to be alive; dead cells do not prevent the opening of etch pits and subsequent dissolution of the carbonate crystals under conditions in which they would otherwise dissolve. Now we report on the effects of the MR-1 biofilm formation on the more slowly dissolving end-member plagioclase feldspar, anorthite (CaAl2Si2O8). The influence of organisms on feldspar weathering rates, in particular the Ca-rich plagioclases, has been the subject of considerable interest because of their crustal abundance and role in the maintenance of atmospheric CO2. (Schwartzman and Volk, 1989, Schwartzman, 1995 and others). Our methodology of direct observation of microbial attachment, biofilm propagation and effects on mineral dissolution provides a quantitative measure of biological contribution to weathering of single crystal minerals for subsequent use in biogeochemical modeling.

  5. Dissolution kinetics of calcium carbonate minerals in H 2OCO 2 solutions in turbulent flow: The role of the diffusion boundary layer and the slow reaction H 2O + CO 2 → H + + HCO 3-

    NASA Astrophysics Data System (ADS)

    Liu, Zaihua; Dreybrod, Wolfgang

    1997-07-01

    Dissolution and precipitation of calcium carbonate minerals in aqueous solutions with turbulent flow are controlled by a diffusion boundary layer (DBL) adjacent to the surface of the mineral, across which mass transfer is effected by molecular diffusion. A rotating disk technique was used to investigate the effect of the DBL on the dissolution rates of CaCO 3. This technique allows an exact adjustment of the thickness of the DBL by controlling the rotation speed of a circular sample of CaCO 3. Measurements of the dissolution rates in H 2OCO 2Ca 2+-solutions in equilibrium with various partial pressures of CO 2 from 1·10 -3 up to 1 atm showed a dependence of the rates R on the rotation frequency ω, given by R ∝ ωn. The exponent n varies from 0.25 at low Pco 2 to about 0.01 at a Pco 2 of 1 atm. This reveals that the rates are not controlled by mass transport only, which would require n = 0.5. The experimental data can be explained employing a theoretical model, which also takes into account the slow reaction CO 2 + H 2O → H + + HCO 3- and the chemical reactions at the surface (Dreybrodt and Buhmann, 1991). Interpretation of the experimental data in view of this model reveals that conversion of CO 2 plays an important role in the control of the rates. At high PCO 2 and large DBL thickness (ε > 0.001 cm), conversion of CO 2 occurs mainly in the DBL and, therefore, becomes rate limiting. This is corroborated by the observation that upon addition of the enzyme carbonic anhydrase, which catalyzes CO 2-conversion, the dissolution rates are enhanced by 1 order of magnitude. From our experimental observations we conclude that the theoretical model above enables one to predict dissolution rates with satisfactory precision. Since the precipitation rates from supersaturated solutions are determined by the same mechanisms as dissolution, we infer that this model is also valid to predict precipitation rates. The predicted rates for both dissolution and precipitation

  6. Dissolution of man-made vitreous fibers in rat alveolar macrophage culture and Gamble's saline solution: influence of different media and chemical composition of the fibers.

    PubMed Central

    Luoto, K; Holopainen, M; Karppinen, K; Perander, M; Savolainen, K

    1994-01-01

    The effect of different chemical compositions of man-made vitreous fibers (MMVF) on their dissolution by alveolar macrophages (AM) in culture and in Gamble's solution was studied. The fibers were exposed to cultured rat AMs, culture medium alone; or Gamble's saline solution for 2, 4, or 8 days. The dissolution of the fibers was studied by measuring the amount of silicon (Si), iron (Fe), and aluminum (Al) in each medium. The AMs in culture dissolved Fe and Al from the fibers but the dissolution of Si was more marked in the cell culture medium without cells and in the Gamble's solution. The dissolution of Si, Fe, and Al was different for different fibers, and increased as a function of time. The Fe and Al content of the fibers correlated negatively with the dissolution of Si by AMs from the MMVF, i.e., when the content of Fe and Al of the fibers increased the dissolution of Si decreased. These results suggest that the chemical composition of MMVFs has a marked effect on their dissolution. AMs seem to affect the dissolution of Fe and Al from the fibers. This suggests that in vitro models with cells in the media rather than only culture media or saline solutions would be preferable in dissolution studies of MMVFs. PMID:7882911

  7. Warming influenced by the ratio of black carbon to sulphate and the black-carbon source

    NASA Astrophysics Data System (ADS)

    Ramana, M. V.; Ramanathan, V.; Feng, Y.; Yoon, S.-C.; Kim, S.-W.; Carmichael, G. R.; Schauer, J. J.

    2010-08-01

    Black carbon is generated by fossil-fuel combustion and biomass burning. Black-carbon aerosols absorb solar radiation, and are probably a major source of global warming. However, the extent of black-carbon-induced warming is dependent on the concentration of sulphate and organic aerosols-which reflect solar radiation and cool the surface-and the origin of the black carbon. Here we examined the impact of black-carbon-to-sulphate ratios on net warming in China, using surface and aircraft measurements of aerosol plumes from Beijing, Shanghai and the Yellow Sea. The Beijing plumes had the highest ratio of black carbon to sulphate, and exerted a strong positive influence on the net warming. Compiling all the data, we show that solar-absorption efficiency was positively correlated with the ratio of black carbon to sulphate. Furthermore, we show that fossil-fuel-dominated black-carbon plumes were approximately 100% more efficient warming agents than biomass-burning-dominated plumes. We suggest that climate-change-mitigation policies should aim at reducing fossil-fuel black-carbon emissions, together with the atmospheric ratio of black carbon to sulphate.

  8. Dissolution Dominating Calcification Process in Polar Pteropods Close to the Point of Aragonite Undersaturation

    PubMed Central

    Bednaršek, Nina; Tarling, Geraint A.; Bakker, Dorothee C. E.; Fielding, Sophie; Feely, Richard A.

    2014-01-01

    Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Ωar). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Ωar∼0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Ωar levels slightly above 1 and lower at Ωar levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Ωar derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Ωar levels close to 1, with net shell growth ceasing at an Ωar of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean. PMID:25285916

  9. Dissolution dominating calcification process in polar pteropods close to the point of aragonite undersaturation.

    PubMed

    Bednaršek, Nina; Tarling, Geraint A; Bakker, Dorothee C E; Fielding, Sophie; Feely, Richard A

    2014-01-01

    Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Ω(ar)). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Ω(ar) ∼ 0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Ω(ar) levels slightly above 1 and lower at Ω(ar) levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Ω(ar) derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Ω(ar) levels close to 1, with net shell growth ceasing at an Ω(ar) of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean.

  10. Cementite dissolution in heavily cold drawn pearlitic steel wires

    SciTech Connect

    Languillaume, J.; Kapelski, G.; Baudelet, B.

    1997-03-01

    The influence of cold wire drawing on the structure of a pearlitic steel containing 0.7 wt% of carbon and subjected to a strain of approximately 3.5 has been studied. The as-deformed microstructure is very fine, with an interlamellar spacing close to 20 nm, and contains high internal elastic strains. The main result concerns the cementite phase which undergoes a dissolution, at least partial, during wire drawing. The proposed interpretation of the cementite dissolution is based on the destabilization of this phase due to the increase of its free energy arising from thinning of cementite lamellae and creation of slip steps during wire drawing. Post-deformation annealings lead to restoration of the phase equilibrium by precipitation of the cementite, and also to recovery of the defects, mainly interfaces, stored in the microstructure during deformation.

  11. Influence of chemical structure on carbon isotope composition of lignite

    NASA Astrophysics Data System (ADS)

    Erdenetsogt, Bat-Orshikh; Lee, Insung; Ko, Yoon-Joo; Mungunchimeg, Batsaikhan

    2017-04-01

    During the last two decades, a number of studies on carbon isotopes in terrestrial organic matter (OM) have been carried out and used to determine changes in paleoatmospheric δ13C value as well as assisting in paleoclimate analysis. Coal is abundant terrestrial OM. However, application of its δ13C value is very limited, because the understanding of changes in isotopic composition during coalification is relatively insufficient. The purpose of this study was to examine the influence of the chemical structure on the carbon isotope composition of lignite. Generally, lignite has more complex chemical structures than other higher rank coal because of the existence of various types of oxygen-containing functional groups that are eliminated at higher rank level. A total of sixteen Lower Cretaceous lignite samples from Baganuur mine (Mongolia) were studied by ultimate, stable carbon isotope and solid-state 13C CP/MAS NMR analyses. The carbon contents of the samples increase with increase in depth, whereas oxygen content decreases continuously. This is undoubtedly due to normal coalification process and also consistent with solid state NMR results. The δ13C values of the samples range from -23.54‰ to -21.34‰ and are enriched in 13C towards the lowermost samples. Based on the deconvolution of the NMR spectra, the ratios between carbons bonded to oxygen (60-90 ppm and 135-220 ppm) over carbons bonded to carbon and hydrogen (0-50 ppm and 90-135 ppm) were calculated for the samples. These correlate well with δ13C values (R2 0.88). The results indicate that the δ13C values of lignite are controlled by two mechanisms: (i) depletion in 13C as a result of loss of isotopically heavy oxygen-bounded carbons and (ii) enrichment in 13C caused by a loss of isotopically light methane from aliphatic and aromatic carbons. At the rank of lignite, coal is enriched in 13C because the amount of isotopically heavy CO2 and CO, released from coal as a result of changes in the chemical

  12. Factors influencing organic carbon preservation in marine sediments

    NASA Technical Reports Server (NTRS)

    Canfield, D. E.

    1994-01-01

    The organic matter that escapes decomposition is buried and preserved in marine sediments, with much debate as to whether the amount depends on bottom-water O2 concentration. One group argues that decomposition is more efficient with O2, and hence, organic carbon will be preferentially oxidized in its presence, and preserved in its absence. Another group argues that the kinetics of organic matter decomposition are similar in the presence and absence of O2, and there should be no influence of O2 on preservation. A compilation of carbon preservation shows that both groups are right, depending on the circumstances of deposition. At high rates of deposition, such as near continental margins, little difference in preservation is found with varying bottom-water O2. It is important that most carbon in these sediments decomposes by anaerobic pathways regardless of bottom-water O2. Hence, little influence of bottom-water O2 on preservation would, in fact, be expected. As sedimentation rate drops, sediments deposited under oxygenated bottom water become progressively more aerobic, while euxinic sediments remain anaerobic. Under these circumstances, the relative efficiencies of aerobic and anaerobic decomposition could affect preservation. Indeed, enhanced preservation is observed in low-O2 and euxinic environments. To explore in detail the factors contributing to this enhanced carbon preservation, aspects of the biochemistries of the aerobic and anaerobic process are reviewed. Other potential influences on preservation are also explored. Finally, a new model for organic carbon decomposition, the "pseudo-G" model, is developed. This model couples the degradation of refractory organic matter to the overall metabolic activity of the sediment, and has consequences for carbon preservation due to the mixing together of labile and refractory organic matter by bioturbation.

  13. 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.

  14. Tidal influences on carbon assimilation by a salt marsh

    NASA Astrophysics Data System (ADS)

    Kathilankal, James C.; Mozdzer, Thomas J.; Fuentes, Jose D.; D'Odorico, Paolo; McGlathery, Karen J.; Zieman, Jay C.

    2008-10-01

    Salt marshes are among the most productive ecosystems on Earth, and play an important role in the global carbon cycle. Net carbon dioxide (CO2) ecosystem exchanges in coastal salt marshes remain poorly investigated. In Spartina alterniflora dominated North American Atlantic coast marshes, the lack of a clear understanding of how Spartina alterniflora responds to flooding limits our current ability to understand and predict salt marsh response to sea-level rise. Here we investigate the processes influencing ecosystem-level carbon exchanges between a S. alterniflora dominated salt marsh on the eastern shore of Virginia and the atmosphere. We examined the impacts of tidal inundation on the marsh-atmosphere carbon exchanges through a combination of eddy covariance measurements and in situ photosynthetic measurements. Maximum daytime carbon fluxes were observed during the middle of the growing season (July and August) and amounted to -10 μmol CO2 m-2 s-1, and the marsh assimilated 130 gC m-2 during the 2007 growing season. Our study is the first to quantify the effects of tidal inundation on marsh plants, which caused anywhere from 3% to 91% reductions in atmospheric carbon fluxes, with a mean reduction of 46 ± 26%, when compared to non-flooded conditions.

  15. Carbon fixation efficiency of plants influenced by sulfur dioxide.

    PubMed

    Chung, Chung-Yi; Chung, Pei-Ling; Liao, Shao-Wei

    2011-02-01

    In the land ecosystem, the forest can absorb the carbon dioxide (CO2) in the atmosphere and turn the CO2 into organic carbon to store it in the plant body. About 2×10(11) tons of CO2 changes through photosynthesis into organic matter by plant annually. In this research, ten kinds of woody plants were selected for assessing the carbon fixation ability influenced by sulfur dioxide (SO2). The tested trees were put into a fumigation chamber for 210 days in a 40-ppb SO2 environment. The results of this study showed that there was no clear symptom of tested trees under a 40-ppb SO2 environment. The tested trees could tolerate this polluted environment, but it will impact their CO2 absorption ability. The carbon fixation ability will reduce as the polluted period lengthens. The carbon fixation potential of tested trees ranged from 2.1 to 15.5 g·CO2/m2·d with an average of 7.7 g·CO2/m2·d. The changes in CO2 absorption volume for Messerschmidia argentea were more stable during the fumigation period with a variation of 102%. Among the tested trees, Diospyros morrisiana had the best carbon fixation potential of 9.19 g·CO2/m2·d and M. argentea had the least with 2.54 g·CO2/m2·d.

  16. Influence of Cd, Co, and Zn on inorganic carbon acquisition and carbon metabolism in Emiliania huxleyi.

    NASA Astrophysics Data System (ADS)

    Sutton, J. N.; Boye, M.; De La Broise, D.; Probert, I.

    2014-12-01

    Trace elements are essential micronutrients for primary producers; hence they influence the global carbon cycle and contribute to the regulation of Earth's climate. Over the past 25 years, the influence of Fe concentration on phytoplankton production has been well studied and this research has been instrumental in our understanding of the influence that biology has on the sequestration of atmospheric CO2. However, other trace elements that are directly involved in carbon metabolism by primary producers, such as Zn, Cd, and Co, have received less attention. We examined the physiological response of two strains of Emiliania huxleyi to a range of realistic trace element concentrations (Zn, Cd, Co) in the marine environment under batch, semi-continuous, and continuous culture conditions. In addition, the continuous culture system was maintained at a pH of 8.15 ±0.02 by a sensor and regulator-controlled CO2­ injection system. The results from this study will highlight the influence that trace element composition of seawater has on the growth rate, elemental quota, inorganic carbon uptake, and carbon metabolism of Emiliania huxleyi. Potential limitations for the interpretation of paleo-productivity records will be discussed.

  17. Light noble gas dissolution into ring structure-bearing materials and lattice influences on noble gas recycling

    NASA Astrophysics Data System (ADS)

    Jackson, Colin R. M.; Parman, Stephen W.; Kelley, Simon P.; Cooper, Reid F.

    2015-06-01

    Light noble gas (He-Ne-Ar) solubility has been experimentally determined in a range of materials with six-member, tetrahedral ring structures: beryl, cordierite, tourmaline, antigorite, muscovite, F-phlogopite, actinolite, and pargasite. Helium solubility in these materials is relatively high, 4 × 10-10 to 3 × 10-7 mol g-1 bar-1, which is ∼100 to 100,000× greater than He solubility in olivine, pyroxene, or spinel. Helium solubility broadly correlates with the topology of ring structures within different minerals. Distinctive He-Ne-Ar solubility patterns are associated with the different ring structure topologies. Combined, these observations suggest ring structures have a strong influence on noble gas solubility in materials and could facilitate the recycling of noble gases, along with other volatiles (i.e., water, chlorine, and fluorine), into the mantle. Measurements of Ne and Ar solubility in antigorite, however, are highly variable and correlated with each other, suggesting multiple factors contribute the solubility of noble gases in serpentine-rich materials.

  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. Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes.

    PubMed

    Stoica-Guzun, Anicuta; Stroescu, Marta; Jinga, Sorin; Jipa, Iuliana; Dobre, Tanase; Dobre, Loredana

    2012-07-01

    The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl(2)) and sodium carbonate (Na(2)CO(3)) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals. Copyright © 2011 Elsevier B.V. All rights reserved.

  20. Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA

    NASA Astrophysics Data System (ADS)

    Liu, Chongxuan; Zachara, John M.; Qafoku, Odeta; McKinley, James P.; Heald, Steve M.; Wang, Zheming

    2004-11-01

    The dissolution of uranium was investigated from contaminated sediments obtained at the US. Department of Energy (U.S. DOE) Hanford site. The uranium existed in the sediments as uranyl silicate microprecipitates in fractures, cleavages, and cavities within sediment grains. Uranium dissolution was studied in Na, Na-Ca, and NH 4 electrolytes with pH ranging from 7.0 to 9.5 under ambient CO 2 pressure. The rate and extent of uranium dissolution was influenced by uranyl mineral solubility, carbonate concentration, and mass transfer rate from intraparticle regions. Dissolved uranium concentration reached constant values within a month in electrolytes below pH 8.2, whereas concentrations continued to rise for over 200 d at pH 9.0 and above. The steady-state concentrations were consistent with the solubility of Na-boltwoodite and/or uranophane, which exhibit similar solubility under the experimental conditions. The uranium dissolution rate increased with increasing carbonate concentration, and was initially fast. It decreased with time as solubility equilibrium was attained, or dissolution kinetics or mass transfer rate from intraparticle regions became rate-limiting. Microscopic observations indicated that uranium precipitates were distributed in intragrain microfractures with variable sizes and connectivity to particle surfaces. Laser-induced fluorescence spectroscopic change of the uranyl microprecipitates was negligible during the long-term equilibration, indicating that uranyl speciation was not changed by dissolution. A kinetic model that incorporated mineral dissolution kinetics and grain-scale, fracture-matrix diffusion was developed to describe uranium release rate from the sediment. Model calculations indicated that 50-95% of the precipitated uranium was associated with fractures that were in close contact with the aqueous phase. The remainder of the uranium was deeply imbedded in particle interiors and exhibited effective diffusivities that were over three

  1. The Influence of Drug Physical State on the Dissolution Enhancement of Solid Dispersions Prepared Via Hot-Melt Extrusion: A Case Study Using Olanzapine

    PubMed Central

    Pina, Maria Fátima; Zhao, Min; Pinto, João F; Sousa, João J; Craig, Duncan Q M

    2014-01-01

    In this study, we examine the relationship between the physical structure and dissolution behavior of olanzapine (OLZ) prepared via hot-melt extrusion in three polymers [polyvinylpyrrolidone (PVP) K30, polyvinylpyrrolidone-co-vinyl acetate (PVPVA) 6:4, and Soluplus® (SLP)]. In particular, we examine whether full amorphicity is necessary to achieve a favorable dissolution profile. Drug–polymer miscibility was estimated using melting point depression and Hansen solubility parameters. Solid dispersions were characterized using differential scanning calorimetry, X-ray powder diffraction, and scanning electron microscopy. All the polymers were found to be miscible with OLZ in a decreasing order of PVP>PVPVA>SLP. At a lower extrusion temperature (160°C), PVP generated fully amorphous dispersions with OLZ, whereas the formulations with PVPVA and SLP contained 14%–16% crystalline OLZ. Increasing the extrusion temperature to 180°C allowed the preparation of fully amorphous systems with PVPVA and SLP. Despite these differences, the dissolution rates of these preparations were comparable, with PVP showing a lower release rate despite being fully amorphous. These findings suggested that, at least in the particular case of OLZ, the absence of crystalline material may not be critical to the dissolution performance. We suggest alternative key factors determining dissolution, particularly the dissolution behavior of the polymers themselves. PMID:24765654

  2. The influence of drug physical state on the dissolution enhancement of solid dispersions prepared via hot-melt extrusion: a case study using olanzapine.

    PubMed

    Pina, Maria Fátima; Zhao, Min; Pinto, João F; Sousa, João J; Craig, Duncan Q M

    2014-04-01

    In this study, we examine the relationship between the physical structure and dissolution behavior of olanzapine (OLZ) prepared via hot-melt extrusion in three polymers [polyvinylpyrrolidone (PVP) K30, polyvinylpyrrolidone-co-vinyl acetate (PVPVA) 6:4, and Soluplus® (SLP)]. In particular, we examine whether full amorphicity is necessary to achieve a favorable dissolution profile. Drug–polymer miscibility was estimated using melting point depression and Hansen solubility parameters. Solid dispersions were characterized using differential scanning calorimetry, X-ray powder diffraction, and scanning electron microscopy. All the polymers were found to be miscible with OLZ in a decreasing order of PVP>PVPVA>SLP. At a lower extrusion temperature (160°C), PVP generated fully amorphous dispersions with OLZ, whereas the formulations with PVPVA and SLP contained 14%-16% crystalline OLZ. Increasing the extrusion temperature to 180°C allowed the preparation of fully amorphous systems with PVPVA and SLP. Despite these differences, the dissolution rates of these preparations were comparable, with PVP showing a lower release rate despite being fully amorphous. These findings suggested that, at least in the particular case of OLZ, the absence of crystalline material may not be critical to the dissolution performance. We suggest alternative key factors determining dissolution, particularly the dissolution behavior of the polymers themselves.

  3. 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

  4. Dissolution of steel slags in aqueous media.

    PubMed

    Yadav, Shashikant; Mehra, Anurag

    2017-07-01

    Steel slag is a major industrial waste in steel industries, and its dissolution behavior in water needs to be characterized in the larger context of its potential use as an agent for sequestering CO2. For this purpose, a small closed system batch reactor was used to conduct the dissolution of steel slags in an aqueous medium under various dissolution conditions. In this study, two different types of steel slags were procured from steel plants in India, having diverse structural features, mineralogical compositions, and particle sizes. The experiment was performed at different temperatures for 240 h of dissolution at atmospheric pressure. The dissolution rates of major and minor slag elements were quantified through liquid-phase elemental analysis using an inductively coupled plasma atomic emission spectroscopy at different time intervals. Advanced analytical techniques such as field emission gun-scanning electron microscope, energy-dispersive X-ray, BET, and XRD were also used to analyze mineralogical and structural changes in the slag particles. High dissolution of slags was observed irrespective of the particle size distribution, which suggests high carbonation potential. Concentrations of toxic heavy metals in the leachate were far below maximum acceptable limits. Thus, the present study investigates the dissolution behavior of different mineral ions of steel slag in aqueous media in light of its potential application in CO2 sequestration.

  5. Influence of particle size distribution, organic carbon, pH and chlorides on washing of mercury contaminated soil.

    PubMed

    Xu, Jingying; Kleja, Dan B; Biester, Harald; Lagerkvist, Anders; Kumpiene, Jurate

    2014-08-01

    Feasibility of soil washing to remediate Hg contaminated soil was studied. Dry sieving was performed to evaluate Hg distribution in soil particle size fractions. The influence of dissolved organic matter and chlorides on Hg dissolution was assessed by batch leaching tests. Mercury mobilization in the pH range of 3-11 was studied by pH-static titration. Results showed infeasibility of physical separation via dry sieving, as the least contaminated fraction exceeded the Swedish generic guideline value for Hg in soils. Soluble Hg did not correlate with dissolved organic carbon in the water leachate. The highest Hg dissolution was achieved at pH 5 and 11, reaching up to 0.3% of the total Hg. The pH adjustment was therefore not sufficient for the Hg removal to acceptable levels. Chlorides did not facilitate Hg mobilization under acidic pH either. Mercury was firmly bound in the studied soil thus soil washing might be insufficient method to treat the studied soil. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

  6. Initial microfluidic dissolution regime of CO2 bubbles in viscous oils

    NASA Astrophysics Data System (ADS)

    Sauzade, Martin; Cubaud, Thomas

    2013-11-01

    We examine the initial dynamical behavior of dissolving microbubbles composed of carbon dioxide gas in highly viscous silicone oils over a range of flow rates and pressure conditions. Microfluidic periodic trains of CO2 bubbles are used to probe the interrelation between bubble dissolution and high-viscosity multiphase flows in microgeometries. We investigate bubble morphology from low to large capillary numbers and calculate the effective mass diffusion flux across the interface by tracking and monitoring individual bubbles during shrinkage. The initial flux is characterized using a dissolution coefficient that reveals the influence of the oil molecular weight on the dissolution process. 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.

  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. 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.

  9. Temperature influences carbon accumulation in moist tropical forests.

    PubMed

    Raich, James W; Russell, Ann E; Kitayama, Kanehiro; Parton, William J; Vitousek, Peter M

    2006-01-01

    Evergreen broad-leaved tropical forests can have high rates of productivity and large accumulations of carbon in plant biomass and soils. They can therefore play an important role in the global carbon cycle, influencing atmospheric CO2 concentrations if climate warms. We applied meta-analyses to published data to evaluate the apparent effects of temperature on carbon fluxes and storages in mature, moist tropical evergreen forest ecosystems. Among forests, litter production, tree growth, and belowground carbon allocation all increased significantly with site mean annual temperature (MAT); total net primary productivity (NPP) increased by an estimated 0.2-0.7 Mg C x ha(-1) x yr(-1) x degrees C(-1). Temperature had no discernible effect on the turnover rate of aboveground forest biomass, which averaged 0.014 yr(-1) among sites. Consistent with these findings, forest biomass increased with site MAT at a rate of 5-13 Mg C x ha(-1) x degrees C(-1). Despite greater productivity in warmer forests, soil organic matter accumulations decreased with site MAT, with a slope of -8 Mg C x ha(-1) x degrees C(-1), indicating that decomposition rates of soil organic matter increased with MAT faster than did rates of NPP. Turnover rates of surface litter also increased with temperature among forests. We found no detectable effect of temperature on total carbon storage among moist-tropical evergreen forests, but rather a shift in ecosystem structure, from low-biomass forests with relatively large accumulations of detritus in cooler sites, to large-biomass forests with relatively smaller detrital stocks in warmer locations. These results imply that, in a warmer climate, conservation of forest biomass will be critical to the maintenance of carbon stocks in moist tropical forests.

  10. Influence of carbon steel grade on the initial attachment of bacteria and microbiologically influenced corrosion.

    PubMed

    Javed, M A; Neil, W C; Stoddart, P R; Wade, S A

    2016-01-01

    The influence of the composition and microstructure of different carbon steel grades on the initial attachment (≤ 60 min) of Escherichia coli and subsequent longer term (28 days) corrosion was investigated. The initial bacterial attachment increased with time on all grades of carbon steel. However, the rate and magnitude of bacterial attachment varied on the different steel grades and was significantly less on the steels with a higher pearlite phase content. The observed variations in the number of bacterial cells attached across different steel grades were significantly reduced by applying a fixed potential to the steel samples. Longer term immersion studies showed similar levels of biofilm formation on the surface of the different grades of carbon steel. The measured corrosion rates were significantly higher in biotic conditions compared to abiotic conditions and were found to be positively correlated with the pearlite phase content of the different grades of carbon steel coupons.

  11. Influence of drinking patterns of carbonated beverages on dental erosion.

    PubMed

    Bassiouny, Mohamed A; Yang, Jie

    2005-01-01

    As a hard tissue dental disease, dental erosion has a multifactorial etiology. The majority of dental erosion that originates from extrinsic sources is the result of dietary intake, particularly acidic beverages. Several preventive means have been proposed to minimize the damage to the dentition, including a reduction in the consumption of causative beverages and the adoption of a specific method of drinking, utilizing a straw instead of a cup. This article presents two cases involving the clinical and radiographic features of erosion lesions associated with chronic and excessive intake of acidic carbonated beverages. These examples embody how drinking patterns influence the formation of erosion lesions in various anatomic locations within the dentition. The clinical and radiographic evidence presented in this report cautions against the use of nonspecific terms, such as "cup versus straw," and instead suggests implementing a more precise description of the suggested method. In view of the extensive damage inflicted by the chronic, excessive intake of carbonated beverages, preventive measures are considered to be the only effective course of management. This article offers illustrative examples of erosion lesions associated with long-term excessive intake of carbonated beverages. The influence of the drinking method--that is, a straw positioned into the labial vestibule versus a cup--on the anatomic location of the erosion lesions will be demonstrated through clinical and radiographic evidence.

  12. Modeling dissolution in aluminum alloys

    NASA Astrophysics Data System (ADS)

    Durbin, Tracie Lee

    2005-07-01

    alloys when compared with published experimental results. The influence of inter-particle spacing is examined and shown to have a significant effect on dissolution kinetics. Finally, the impact of multiple particles of various sizes interacting in an aluminum matrix is investigated. It is shown that smaller particles dissolve faster, as expected, but influence the dissolution of larger particles through soft-impingement, even after the smaller particles have disappeared.

  13. Influence of diagenesis on the stable isotopic composition of biogenic carbonates from the Gulf of Tehuantepec oxygen minimum zone

    NASA Astrophysics Data System (ADS)

    Blanchet, C. L.; Kasten, S.; Vidal, L.; Poulton, S. W.; Ganeshram, R.; Thouveny, N.

    2012-04-01

    In order to evaluate the influence of diagenetic and post-sampling processes on the stable oxygen and carbon isotope compositions of biogenic carbonates, we conducted a multiproxy study of organic-rich sediments from the eastern Pacific oxygen minimum zone. Core MD02-2520, which was retrieved from the Gulf of Tehuantepec (Mexico), has seasonal laminations and covers the last 40 kyr. Together with the presence of gypsum crystals and inorganic calcite aggregates, the occurrence of large excursions in the stable oxygen and carbon isotope records of both planktonic and benthic foraminifera (as large as +3‰ in δ18O and -5‰ in δ13C) point to significant secondary transformations. Storage-related gypsum precipitation was ruled out since it implies sulfide reoxidation by oxygen that triggers biogenic calcite dissolution, which proved to be of minor importance here. Instead, precipitation of authigenic calcite during early diagenesis appears to be the most likely process responsible for the observed isotopic excursions. The δ13C composition for inorganic calcite aggregates (-5 to -7‰) suggests a major contribution from anaerobic oxidation of organic matter. The δ34S composition for gypsum crystals (-10 to +15‰) suggests a major contribution from anaerobic reoxidation of authigenic sulfides, potentially involving reactions with metal oxides and sulfur disproportionation. A minor part of the gypsum might possibly have formed as a result of local pore water salinity increases induced by gas hydrate formation.

  14. 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.

  15. Mechanistic Approach to Understanding the Influence of USP Apparatus I and II on Dissolution Kinetics of Tablets with Different Operating Release Mechanisms.

    PubMed

    Lu, Zheng; Fassihi, Reza

    2017-02-01

    This article provides an analysis of dissolution kinetics associated with formulations subjected to different dissolution methods with the purpose of revealing credible direction on selection of apparatus type and hydrodynamics on in vitro drug release profiles using three different formulations. The dissolution kinetics of immediate release (IR) and controlled release (CR) ibuprofen tablets under different hydrodynamic conditions were determined, and potential existence of any correlation between USP apparatus I and II were analyzed using adequate kinetic models. Two types of CR tablets based on PEO (polyethylene oxide-N80) and HPMC (hydroxypropyl methylcellulose- K100M) polymers were prepared. Marketed ibuprofen 200-mg IR tablets were also used. Dissolution studies were carried out using USP 34 apparatuses I and II methods at stirring speed of 100 and 50 rpm in 900 mL phosphate buffer, pH 7.2 at 37°C. The drug release profiles for each formulation was determined and statistically analyzed using model-dependent, model-independent (f 2 ), and ANOVA methods. No significant dissolution differences existed between IR tablets, whereas CR tablets were significantly impacted by apparatus types and hydrodynamics. PEO matrices displayed higher sensitivity to hydrodynamics relative to HPMC matrices, and differences in dissolution profiles were confirmed by ANOVA and boxplot analysis. It is concluded that in the case of CR systems, selection of apparatus type and adherence to the monograph specifications and hydrodynamic conditions is critical, while for IR tablets, both apparatus types and agitation rates had no significant impact on drug release rate, suggesting the possibility of apparatus interchangeability if desired.

  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. 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.

  18. Influence of soil moisture-carbon cycle interactions on the terrestrial carbon cycle over Europe

    NASA Astrophysics Data System (ADS)

    Mystakidis, Stefanos; Davin, Edouard L.; Gruber, Nicolas; Seneviratne, Sonia I.

    2016-04-01

    Water availability is a crucial limiting factor for terrestrial ecosystems, but relatively few studies have quantitatively assessed the influence of soil moisture variability on the terrestrial carbon cycle. Here, we investigate the role of soil moisture variability and state in the contemporary terrestrial carbon cycle over Europe. For this we use a Regional Earth System Model (RESM) based on the COSMO-CLM Regional Climate Model, coupled to the Community Land Model version 4.0 (CLM4.0) and its carbon-nitrogen module. The simulation setup consists of a control simulation over the period 1979-2010 in which soil moisture is interactive and three sensitivity simulations in which soil moisture is prescribed to a mean, a very dry or a very wet seasonal cycle without inter-annual variability. The cumulative net biome productivity varies markedly between the different experiments ranging from a strong sink of up to 6PgC in the wet experiment to a source of up to 1.2PgC in the dry experiment. Changes in the land carbon uptake are driven by a combination of two factors: the direct impact of soil moisture on plant's carbon uptake (essentially in southern Europe) and an indirect effect through changes in temperature affecting ecosystem respiration (mainly in central and northern Europe). We find that removing temporal variations in soil moisture dampens interannual variations in terrestrial carbon fluxes (Gross Primary Productivity, respiration, Net Biome Productivity) by more than 50% over most of Europe. Moreover, the analysis reveals that on annual scale about two-thirds of central Europe and about 70% of southern Europe display statistically significant effect of drying and/or wetting on the terrestrial carbon budget and its components. Our findings confirm the crucial role of soil moisture in determining the magnitude and the inter-annual variability in land CO2 uptake which is a key contributor to the year-to-year variations in atmospheric CO2 concentration.

  19. Influence of (calcium-)uranyl-carbonate complexation on U(VI) sorption on Ca- and Na-bentonites.

    PubMed

    Meleshyn, A; Azeroual, M; Reeck, T; Houben, G; Riebe, B; Bunnenberg, C

    2009-07-01

    The influence of uranyl-carbonate and calcium-uranyl-carbonate complexations on the kinetics of U(VI) (approximately 3.4 x 10(-3) mol L(-1)) sorption from NaNO3 and Ca(NO3)2 solutions on Na- and Ca-bentonites at circumneutral ambient conditions was investigated. Complexation of U(VI) in Ca2UO2(CO3)3(aq) aqueous species, dominating the U(VI) speciation in Ca(NO3)2 solution, reduces its adsorption on bentonite by a factor of 2-3 in comparison with that in (UO2)2CO3(OH)3- species, dominating in NaNO3 solution, within the studied period of time (21 days). As a result of the dissolution of accessory calcite, Ca2UO2(CO3)3(aq) can be formed in the initially Ca-free solution in contact with either Na- or Ca-bentonite. U(VI) adsorption on Na-bentonite is a factor of approximately 2 higher than that on Ca-bentonite for solutions with the Ca2UO2(CO3)3(aq) complex dominating aqueous U(VI) speciation. This favors use of Na-bentonite over that of Ca-bentonite in final disposal of radioactive waste. Furthermore, the observed strong correlation between U(VI) adsorption and Mg release as a result of montmorillonite dissolution indicates in agreement with previous findings that under the applied conditions U(VI) is adsorbed on the edge surface of montmorillonite, which is a major mineral phase of the studied clays.

  20. 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.

  1. Advances in principal factors influencing carbon dioxide adsorption on zeolites

    PubMed Central

    Bonenfant, Danielle; Kharoune, Mourad; Niquette, Patrick; Mimeault, Murielle; Hausler, Robert

    2008-01-01

    We report the advances in the principal structural and experimental factors that might influence the carbon dioxide (CO2) adsorption on natural and synthetic zeolites. The CO2 adsorption is principally govern by the inclusion of exchangeable cations (countercations) within the cavities of zeolites, which induce basicity and an electric field, two key parameters for CO2 adsorption. More specifically, these two parameters vary with diverse factors including the nature, distribution and number of exchangeable cations. The structure of framework also determines CO2 adsorption on zeolites by influencing the basicity and electric field in their cavities. In fact, the basicity and electric field usually vary inversely with the Si/Al ratio. Furthermore, the CO2 adsorption might be limited by the size of pores within zeolites and by the carbonates formation during the CO2 chemisorption. The polarity of molecules adsorbed on zeolites represents a very important factor that influences their interaction with the electric field. The adsorbates that have the most great quadrupole moment such as the CO2, might interact strongly with the electric field of zeolites and this favors their adsorption. The pressure, temperature and presence of water seem to be the most important experimental conditions that influence the adsorption of CO2. The CO2 adsorption increases with the gas phase pressure and decreases with the rise of temperature. The presence of water significantly decreases adsorption capacity of cationic zeolites by decreasing strength and heterogeneity of the electric field and by favoring the formation of bicarbonates. The optimization of the zeolites structural characteristics and the experimental conditions might enhance substantially their CO2 adsorption capacity and thereby might give rise to the excellent adsorbents that may be used to capturing the industrial emissions of CO2. PMID:27877925

  2. Anticorrosive Influence of Acetobacter aceti Biofilms on Carbon Steel

    NASA Astrophysics Data System (ADS)

    France, Danielle Cook

    2016-09-01

    Microbiologically influenced corrosion (MIC) of carbon steel infrastructure is an emerging environmental and cost issue for the ethanol fuel industry, yet its examination lacks rigorous quantification of microbiological parameters that could reveal effective intervention strategies. To quantitatively characterize the effect of cell concentration on MIC of carbon steel, numbers of bacteria exposed to test coupons were systematically controlled to span four orders of magnitude throughout a seven-day test. The bacterium studied, Acetobacter aceti, has been found in ethanol fuel environments and can convert ethanol to the corrosive species acetic acid. A. aceti biofilms formed during the test were qualitatively evaluated with fluorescence microscopy, and steel surfaces were characterized by scanning electron microscopy. During exposure, biofilms developed more quickly, and test reactor pH decreased at a faster rate, when cell exposure was higher. Resulting corrosion rates, however, were inversely proportional to cell exposure, indicating that A. aceti biofilms are able to protect carbon steel surfaces from corrosion. This is a novel demonstration of corrosion inhibition by an acid-producing bacterium that occurs naturally in corrosive environments. Mitigation techniques for MIC that harness the power of microbial communities have the potential to be scalable, inexpensive, and green solutions to industrial problems.

  3. Moving and Union Dissolution

    PubMed Central

    BOYLE, PAUL J.; KULU, HILL; COOKE, THOMAS; GAYLE, VERNON; MULDER, CLARAH.

    2008-01-01

    This paper examines the effect of migration and residential mobility on union dissolution among married and cohabiting couples. Moving is a stressful life event, and a large, multidisciplinary literature has shown that family migration often benefits one partner (usually the man) more than the other. Even so, no study to date has examined the possible impact of within-nation geographical mobility on union dissolution. We base our longitudinal analysis on retrospective event-history data from Austria. Our results show that couples who move frequently have a significantly higher risk of union dissolution, and we suggest a variety of mechanisms that may explain this. PMID:18390300

  4. 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)

  5. Elevated CO2 affects shell dissolution rate but not calcification rate in a marine snail

    PubMed Central

    Nienhuis, Sarah; Palmer, A. Richard; Harley, Christopher D. G.

    2010-01-01

    As CO2 levels increase in the atmosphere, so too do they in the sea. Although direct effects of moderately elevated CO2 in sea water may be of little consequence, indirect effects may be profound. For example, lowered pH and calcium carbonate saturation states may influence both deposition and dissolution rates of mineralized skeletons in many marine organisms. The relative impact of elevated CO2 on deposition and dissolution rates are not known for many large-bodied organisms. We therefore tested the effects of increased CO2 levels—those forecast to occur in roughly 100 and 200 years—on both shell deposition rate and shell dissolution rate in a rocky intertidal snail, Nucella lamellosa. Shell weight gain per day in live snails decreased linearly with increasing CO2 levels. However, this trend was paralleled by shell weight loss per day in empty shells, suggesting that these declines in shell weight gain observed in live snails were due to increased dissolution of existing shell material, rather than reduced production of new shell material. Ocean acidification may therefore have a greater effect on shell dissolution than on shell deposition, at least in temperate marine molluscs. PMID:20392726

  6. Elevated CO2 affects shell dissolution rate but not calcification rate in a marine snail.

    PubMed

    Nienhuis, Sarah; Palmer, A Richard; Harley, Christopher D G

    2010-08-22

    As CO(2) levels increase in the atmosphere, so too do they in the sea. Although direct effects of moderately elevated CO(2) in sea water may be of little consequence, indirect effects may be profound. For example, lowered pH and calcium carbonate saturation states may influence both deposition and dissolution rates of mineralized skeletons in many marine organisms. The relative impact of elevated CO(2) on deposition and dissolution rates are not known for many large-bodied organisms. We therefore tested the effects of increased CO(2) levels--those forecast to occur in roughly 100 and 200 years--on both shell deposition rate and shell dissolution rate in a rocky intertidal snail, Nucella lamellosa. Shell weight gain per day in live snails decreased linearly with increasing CO(2) levels. However, this trend was paralleled by shell weight loss per day in empty shells, suggesting that these declines in shell weight gain observed in live snails were due to increased dissolution of existing shell material, rather than reduced production of new shell material. Ocean acidification may therefore have a greater effect on shell dissolution than on shell deposition, at least in temperate marine molluscs.

  7. The Volcanic History of Mars and Influences on Carbon Outgassing

    NASA Astrophysics Data System (ADS)

    Bleacher, J. E.; Whelley, P.

    2015-12-01

    Exploration of Mars has revealed some of the most impressive volcanic landforms found throughout the solar system. Volatiles outgassed from volcanoes were likely to have strongly influenced atmospheric chemistry and affected the martian climate. On Earth the role of carbon involved in volcanic outgassing is strongly influenced by tectonic setting, with the greatest weight percent contributions coming from partial mantle melts associated with hot spot volcanism. Most martian volcanic centers appear to represent this style of volcanism. Thus, one important factor in understanding the martian carbon cycle through time is understanding this volatile's link to the planet's volcanic history. The identified volcanic constructs on Mars are not unlike those of the Earth suggesting similar magmatic and eruptive processes. However, the dimensions of many martian volcanic features are significantly larger. The distribution of volcanoes and volcanic deposits on Mars are not spatially or temporally uniform. Large volcanoes (> 100 km diameter) are spatially concentrated in volcanic provinces that likely represent focused upwellings or zones of crustal weakness that enabled magma ascension. Smaller (10s km diameters) volcanoes such as cones, low shields and fissures are often grouped into fields and their lava flows coalesce to produce low slope plains. In some cases plains lava fields are quite extensive with little to no evidence for the volcanic constructs. Although martian volcanism appears to have been dominated by effusive eruptions with likely contributions from passive degassing from the interior, explosive volcanic centers and deposits are known to exist. After the development of a martian crust the planet's volcanic style appears to have evolved from early explosive activity to effusive activity centered at major volcanoes to effusive distributed activity in fields. However, questions remain as to whether or not these styles significantly overlapped in time and if so

  8. Influence of sulfur compounds on the terrestrial carbon cycle

    NASA Astrophysics Data System (ADS)

    Eliseev, A. V.

    2015-11-01

    Using the climate model developed at the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM), numerical experiments have been conducted in line with the Coupled Model Intercomparison Project Phase 5 (CMIP5), but scaling the anthropogenic emissions of sulfur compounds into the troposphere by ±25%. Two types of impacts of sulfur compounds on climate and the global carbon cycle are considered: climate impact (CI, associated with the influence of tropospheric sulfates on climate and, as a consequence, on the carbon cycle characteristics) and ecological impact (EI, associated with the influence of SO2 on the rate of photosynthesis of terrestrial plants). The climate impact was found to be generally more important than the ecological one. However, in a number of regions, the EI is comparable to CI, including in the southeast parts of North America and, especially, of Asia. The contribution of EI to the change in global characteristics of terrestrial ecosystems in the 20th century is likewise considerable. The CI is generally more sensitive to the uncertainty in anthropogenic emissions of sulfur compounds into the troposphere than the EI.

  9. The effects of different coatings on zinc oxide nanoparticles and their influence on dissolution and bioaccumulation by the green alga, C. reinhardtii.

    PubMed

    Merdzan, Vladimir; Domingos, Rute F; Monteiro, Carlos E; Hadioui, Madjid; Wilkinson, Kevin J

    2014-08-01

    Determining the environmental risk of nanoparticles (NPs) requires an in-depth understanding of the NP core, the particle surface coatings and the interactions of the two with environmental matrices. Non-coated ZnO NPs (nZnO) are known to release ionic Zn, contributing directly to the toxicity of these particles. On the other hand, relatively less data are available for particles that have coatings designed to increase particle stability. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Zn salt or nZnO with different stabilizers: (i) bare nZnO, (ii) polyacrylic acid-stabilized, nZnO-PAA, or a (iii) sodium hexametaphosphate-stabilized, nZnO-HMP. Multiple techniques were used to quantify particle agglomeration and dissolution. The dissolution of the NPs depended on the stabilizer, with the largest dissolution obtained for the bare nZnO (near total dissolution), followed by the nZnO-PAA. When exposed to the bare and PAA-stabilized nZnOs, bioaccumulation was largely accounted for by free Zn. On the other hand, the bioaccumulation of nZnO-HMP was greater than could be attributed to the release of free Zn from the particles. The increased Zn bioaccumulation was hypothesized to have resulted from the biological stimulation of C. reinhardtii due to phosphate from the particle coating. Copyright © 2014 Elsevier B.V. All rights reserved.

  10. Influence of carbon nanotubes on the bioavailability of fluoranthene.

    PubMed

    Linard, Erica N; van den Hurk, Peter; Karanfil, Tanju; Apul, Onur G; Klaine, Stephen J

    2015-03-01

    Concurrent with the increase in the use of carbon nanotubes (CNTs) in society is the rise of their introduction into the environment. Carbon nanotubes cause adverse effects themselves, and they have the potential to adsorb contaminants such as polycyclic aromatic hydrocarbons (PAHs). Although CNTs have a high adsorption capacity for PAHs and these contaminants can co-occur in the environment, few studies have characterized the bioavailability of CNT-adsorbed PAHs to fish. The goal of the present study was to characterize the bioavailability of fluoranthene adsorbed to suspended multiwalled-carbon nanotubes (MWNTs) in freshwater containing natural organic matter (NOM). Adsorption isotherms indicated that NOM influenced the adsorption of fluoranthene to MWNTs, although in the absence of MWNTs it did not influence the bioavailability of fluoranthene to Pimephales promelas. Pimephales promelas were exposed for 16 h in synthetic moderately hard water containing fluoranthene in the presence of different concentrations of NOM, and fluoranthene adsorbed to MWNTs in the presence of NOM. Bioavailable fluoranthene was quantified in each exposure through bile analysis using fluorescence spectrophotometry. By comparing the concentration of fluoranthene metabolites in the bile with the concentration of fluoranthene added to MWNT and NOM solutions, the relative bioavailability of fluoranthene adsorbed to MWNTs was quantified. Results indicate that approximately 60% to 90% of the fluoranthene was adsorbed to the MWNTs and that adsorbed fluoranthene was not bioavailable to P. promelas. The results also suggest that fluoranthene is not desorbed from ingested MWNT, and the bioavailable fraction is only the freely dissolved fluoranthene in the aqueous phase.

  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. Nighttime dissolution in a temperate coastal ocean ecosystem increases under acidification.

    PubMed

    Kwiatkowski, Lester; Gaylord, Brian; Hill, Tessa; Hosfelt, Jessica; Kroeker, Kristy J; Nebuchina, Yana; Ninokawa, Aaron; Russell, Ann D; Rivest, Emily B; Sesboüé, Marine; Caldeira, Ken

    2016-03-18

    Anthropogenic emissions of carbon dioxide (CO2) are causing ocean acidification, lowering seawater aragonite (CaCO3) saturation state (Ω arag), with potentially substantial impacts on marine ecosystems over the 21(st) Century. Calcifying organisms have exhibited reduced calcification under lower saturation state conditions in aquaria. However, the in situ sensitivity of calcifying ecosystems to future ocean acidification remains unknown. Here we assess the community level sensitivity of calcification to local CO2-induced acidification caused by natural respiration in an unperturbed, biodiverse, temperate intertidal ecosystem. We find that on hourly timescales nighttime community calcification is strongly influenced by Ω arag, with greater net calcium carbonate dissolution under more acidic conditions. Daytime calcification however, is not detectably affected by Ω arag. If the short-term sensitivity of community calcification to Ω arag is representative of the long-term sensitivity to ocean acidification, nighttime dissolution in these intertidal ecosystems could more than double by 2050, with significant ecological and economic consequences.

  13. Quantifying the Potential Influence of Carbonate Saturation State on Benthic Foraminiferal Mg/Ca

    NASA Astrophysics Data System (ADS)

    Martin, P. A.; Lea, D. W.; McCorkle, D. C.

    2002-05-01

    Benthic foraminiferal Mg/Ca paleothermometry is based on an empirical relationship between the Mg/Ca of benthic foraminifera recovered from core tops and in situ bottom water temperatures (Rosenthal, 1997; Martin et al, in press; Lear et al, in review). While there is a tight correlation between shell Mg/Ca and temperature over a broad range of temperatures (-1 to 20 degrees C), Mg/Ca variation over the small range of deep water temperatures reveals departures from the calibration curve at low temperatures. Lower Mg/Ca values are generally associated with the deepest sites from the Atlantic and Pacific, contributing to an apparently steeper Mg/Ca-T response for abyssal benthics. The steeper response of abyssal benthics may reflect an influence of decreasing carbonate saturation with depth. Dissolution or other saturation related effects have already been documented for Mg in planktonic foraminifera and for other metals (Cd, Ba, and Zn) in benthic foraminifera shells (see Marchitto and ref. therein). Although it is difficult to definitively separate the effects of various environmental parameters (including temperature, depth, and relative saturation states), which often change in unison, we can use to the core top Mg/Ca data to estimate the potential influence of saturation state. An alternative calibration of the benthic Mg/Ca - T relationship can be derived based on core top benthic foraminifera only from sites bathed in waters above carbonate saturation, which yields a slightly smaller change in Mg/Ca per degree C (~9.5% vs. 11%) but better explains benthic Mg/Ca from the coldest sites (-1oC). Using this alternative Mg/Ca -T relation and a subset of the data from the Ceara Rise and Ontong Java Plateau, we can estimate a maximum Mg/Ca offset attributable to saturation state. The uncertainty this implies for downcore reconstructions varies widely (exceeding 1.5oC), depending on the hydrographic setting and which proxy is used to estimate saturation state.

  14. 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.

  15. Influence of pH modifiers on the dissolution and stability of hydrochlorothiazide in the bi- and three-layer tablets.

    PubMed

    Blatnik, Sandra Urek; Dreu, Rok; Srčič, Stanko

    2015-12-01

    During the past few years, the studies of bi- and multi-layered tablets increased due to the consumption of several different drugs per day by a patient and requests for appropriate patient compliance. The demographic shift toward older population increases the use of combination therapy as polypharmacy. Hydrochlorothiazide (HCTZ), as a model drug, is most commonly used in the treatment of hypertension, congestive heart failure and as a diuretic. The aim of the present study is to investigate the effect of the local environment on dissolution and stability behaviour of HCTZ in fixed multilayered tablet combinations, which are commonly used in polypharmacy. For this purposes, three different systems were introduced: (i) two conventional tablets (HCTZ and pH modifying placebo), (ii) 2-layer tablets (HCTZ, pH modifying placebo) and (iii) 3-layer tablets (HCTZ, barrier and pH modifying placebo). Disintegration of tablets, dissolution of HCTZ from tablets and HCTZ related substances were monitored for all systems. Results showed that there was a significant difference between dissolution profiles of the conventional two-tablet system (HCTZ tablet and pH modifying tablet) and the 2-layer and 3-layer tablets, which include the pH modifying layer. In the case of the conventional two-tablets system, 85 % of HCTZ was dissolved in less than 15 minutes. The dissolution profiles of HCTZ from 2-layered and 3-layered tablets showed a decrease in the dissolution rate. In addition, during the stability studies, it has been confirmed that the typical degradation product of HCTZ is formed, impurity B (4-amino-6-chloro-1,3-benzenedisulfonamide), which implies formation of formaldehyde as hydrolytic impurity not reported in the Ph. Eur. (16). Both impurities are particularly raised in 2-layered tablets with alkaline and neutral placebo layers. Stability of HCTZ was improved in the case of the 3-layer tablet, where the intermediate separation layer of glycerol monostearate was present

  16. Influence of chemistry and climate on large induced large scale stresses in anisotropically fractured carbonates.

    NASA Astrophysics Data System (ADS)

    Toussaint, R.; Cornet, F.

    2012-04-01

    We will explore a simple model coupling for carbonate rocks the fracture density and orientation, the water chemistry and transport, the dissolution reactions and the expected irreversible rock deformation. Adding elasticity and boundary conditions, plus an estimation of the water source composition in the formation, we will estimate orders of magnitudes of the stress changes that can be expected from these processes in sedimentary basins over long times. We will in particular examine whether such intrinsic deformation mechanism can give a hint to explain the observed anisotropic stresses, in orientation and magnitude, in zones above the C.O.X. argillite formation in the Paris Basin, where the horizontal stress anisotropy has been shown to be important, whereas stress decoupling from the deep crustal roots should be effective, and no strong anisotropy would be expected in the absence of active deformation mechanism. In the Paris basin, the analysis of log cores shows that fractures and joints, up to meter-long ones, are common anisotropic features present in the carbonate rocks. Dissolution of calcite along these oriented features removes material with an a priori oriented flux reflecting this structural anisotropy, resulting in a non-isotropic deformation associated to this dissolution. We will present a simple model where dissolution and transport of dissolved calcite is associated with the deformation of the carbonate rock. Estimating the reaction constants, the chemical composition variation of the meteoric water, the rock permeability and the fracture density from observations around the Bure underground laboratory, we will estimate the order of magnitude of the deformations expected from these types of mechanisms. Such estimates have already been performed for dissolution along stylolites, e.g. by Clark, 1966; Renard et al., 2004; Schmittbuhl et al., 2004; Koehn et al., 2007. We will adapt these to reflect the anisotropic feature of the fractures present in

  17. Aggregate distribution and associated organic carbon influenced by cover crops

    NASA Astrophysics Data System (ADS)

    Barquero, Irene; García-González, Irene; Benito, Marta; Gabriel, Jose Luis; Quemada, Miguel; Hontoria, Chiquinquirá

    2013-04-01

    Replacing fallow with cover crops during the non-cropping period seems to be a good alternative to diminish soil degradation by enhancing soil aggregation and increasing organic carbon. The aim of this study was to analyze the effect of replacing fallow by different winter cover crops (CC) on the aggregate distribution and C associated of an Haplic Calcisol. The study area was located in Central Spain, under semi-arid Mediterranean climate. A 4-year field trial was conducted using Barley (Hordeum vulgare L.) and Vetch (Vicia sativa L.) as CC during the intercropping period of maize (Zea mays L.) under irrigation. All treatments were equally irrigated and fertilized. Maize was directly sown over CC residues previously killed in early spring. Composite samples were collected at 0-5 and 5-20 cm depths in each treatment on autumn of 2010. Soil samples were separated by wet sieving into four aggregate-size classes: large macroaggregates ( >2000 µm); small macroaggregates (250-2000 µm); microaggregates (53-250 µm); and < 53 µm (silt + clay size). Organic carbon associated to each aggregate-size class was measured by Walkley-Black Method. Our preliminary results showed that the aggregate-size distribution was dominated by microaggregates (48-53%) and the <53 µm fraction (40-44%) resulting in a low mean weight diameter (MWD). Both cover crops increased aggregate size resulting in a higher MWD (0.28 mm) in comparison with fallow (0.20 mm) in the 0-5 cm layer. Barley showed a higher MWD than fallow also in 5-20 cm layer. Organic carbon concentrations in aggregate-size classes at top layer followed the order: large macroaggregates > small macroaggregates > microaggregates > silt + clay size. Treatments did not influence C concentration in aggregate-size classes. In conclusion, cover crops improved soil structure increasing the proportion of macroaggregates and MWD being Barley more effective than Vetch at subsurface layer.

  18. Elevated CO2 influences microbial carbon and nitrogen cycling

    PubMed Central

    2013-01-01

    Background Elevated atmospheric CO2 (eCO2) has been shown to have significant effects on terrestrial ecosystems. However, little is known about its influence on the structure, composition, and functional potential of soil microbial communities, especially carbon (C) and nitrogen (N) cycling. A high-throughput functional gene array (GeoChip 3.0) was used to examine the composition, structure, and metabolic potential of soil microbial communities from a grassland field experiment after ten-year field exposure to ambient and elevated CO2 concentrations. Results Distinct microbial communities were established under eCO2. The abundance of three key C fixation genes encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), carbon monoxide dehydrogenase (CODH) and propionyl-CoA/acetyl-CoA carboxylase (PCC/ACC), significantly increased under eCO2, and so did some C degrading genes involved in starch, cellulose, and hemicellulose. Also, nifH and nirS involved in N cycling were significantly stimulated. In addition, based on variation partitioning analysis (VPA), the soil microbial community structure was largely shaped by direct and indirect eCO2-driven factors. Conclusions These findings suggest that the soil microbial community structure and their ecosystem functioning for C and N cycling were altered dramatically at eCO2. This study provides new insights into our understanding of the feedback response of soil microbial communities to elevated CO2 and global change. PMID:23718284

  19. The dissolution of an anthracite coal with perchloric acid

    SciTech Connect

    Hood, G.E.; Hyatt, A.G.; McGowan, C.W.

    1996-10-01

    Lignite coal, bituminous coal and several oil shales have previously been dissolved using perchloric acid of varying boiling point and subsequent oxidizing ability. These organic deposits generally dissolved between 150 and 160{degrees}C. This indicated that the aliphatic ether oxygen bond was being broken during the dissolution process. This dissolution process was performed on an anthracite coal because of the coal`s low oxygen content. The anthracite coal dissolved between 180 and 190{degrees}C making it similar to high-vol bituminous coal from New Zealand. Earlier work has indicated that carbon-carbon double bonds are being attacked during the dissolution process at the higher temperatures.

  20. Calcite Dissolution: An in situ Study in the Panama Basin.

    PubMed

    Thunell, R C; Keir, R S; Honjo, S

    1981-05-08

    The results of an in situ study of calcite dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.

  1. Calcite dissolution: an in situ study in the Panama Basin

    SciTech Connect

    Thunell, R.C.; Keir, R.S.; Honjo, S.

    1981-05-08

    The results of an in situ study of calcite dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.

  2. Instant and supersaturated dissolution of naproxen and sesamin (poorly water-soluble drugs and supplements) nanoparticles prepared by continuous expansion of liquid carbon dioxide solution through long dielectric nozzle

    NASA Astrophysics Data System (ADS)

    Arita, Toshihiko; Manabe, Noriyoshi; Nakahara, Koichi

    2012-11-01

    Nanoparticles (NPs) of naproxen (a nonsteroidal anti-inflammatory drug, BCS Class 2) and sesamin (a poorly water-soluble lignan) were investigated. By applying a newly developed rapid expansion system of liquid carbon dioxide solutions equipped with a dielectric nozzle, well-separated and fine both naproxen NPs (averaged particle size (APS) = 46.9 nm) and sesamin NPs (APS = 60.2 nm) were obtained without heating, surfactants, and co-solvents. Obtained naproxen and sesamin NPs had large surface/weight ratio, therefore, they showed instant dissolution to water until about ten percent higher than the saturated concentrations. In addition, the technique developed in the study has big advantage on producing especially drug NPs because the NPs produced by the method never includes neither poisonous additives (especially co-solvents and detergents) nor thermally denatured compounds.

  3. Influence of nesting shell size on brightness longevity and resistance to ultrasound-induced dissolution during enhanced B-mode contrast imaging.

    PubMed

    Wallace, N; Dicker, S; Lewin, P; Wrenn, S P

    2014-12-01

    values for the duration of the 40min trial. The results are consistent with two distinct stages of gas transport: in the first stage, passive diffusion occurs under ambient conditions across the microbubble monolayer within the first few minutes after formulation until the aqueous interior of the microcapsule is saturated with gas; in the second stage ultrasound drives additional gas dissolution even further due to pressure modulation. It is important to understand the chemistry and transport mechanisms of this contrast agent under the influence of ultrasound to attain better perspicacity for enhanced applications in imaging. Results from this study will facilitate future preclinical studies and clinical applications of nested microbubbles for therapeutic and diagnostic imaging.

  4. Effect of Microbial and Other Naturally Occurring Polymers on Mineral Dissolution

    SciTech Connect

    Welch, S. A.; Vandevivere, P.

    1994-11-21

    Several naturally occurring polymers were tested for their effect on mineral dissolution. Polymers composed primarily of neutral sugars had no effect on dissolution, even at concentrations 1000 times greater than average dissolved organic carbon concentrations found in groundwater. In contrast, alginate, a polysaccharide composed of two uronic acids, inhibited dissolution by 80% at the highest concentration used. A high-molecular-weight polyaspartate also inhibited dissolution, though a lower-molecular-weight polyaspartate had no affect.

  5. Social and cultural influences on management for carbon sequestration on US family forestlands: a literature synthesis

    Treesearch

    A. Paige Fischer; Susan. Charnley

    2010-01-01

    Nonindustrial private—or "family"—forests hold great potential for sequestering carbon and have received much attention in discussions about forestry-based climate change mitigation. However, little is known about social and cultural influences on owners' willingness to manage for carbon and respond to policies designed to encourage carbon-oriented...

  6. Molecular dynamics simulation of NaCl dissolution.

    PubMed

    Lanaro, Gabriele; Patey, G N

    2015-03-19

    Molecular dynamics simulations are used to investigate the dissolution of NaCl nanocrystals (containing ∼2400 ions) in water. We focus on systems under sink conditions at 300 K, but the influences of concentration and temperature are also investigated. Cubical, spherical, tablet-shaped, and rod-shaped nanocrystals are considered, and it is shown that the initial shape can influence the dissolution process. Dissolution is observed to occur in three stages: an initial period where the most exposed ions are removed from the crystal surface, and the crystal takes on a solution-annealed shape which persists throughout the second stage of dissolution; a second long intermediate stage where dissolution roughly follows a fixed rate law; and a final stage where the small residual crystal (≲200 ions) dissolves at an ever increasing rate until it disappears. The second stage of dissolution which applies for most of the dissolution process is well described by classical rate equations which simply assume that the dissolution rate is proportional to an active surface area from which ions are most easily detached from the crystal. The active area depends on the initial crystal shape. We show that for our model NaCl nanocrystals the rate-determining step for dissolution under sink conditions is ion detachment from the crystal, and that diffusion layers do not exist for these systems.

  7. 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.

  8. 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.

  9. 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.…

  10. 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.

  11. 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.…

  12. Formation of CO2, H2 and condensed carbon from siderite dissolution in the 200-300 °C range and at 50 MPa

    NASA Astrophysics Data System (ADS)

    Milesi, Vincent; Guyot, François; Brunet, Fabrice; Richard, Laurent; Recham, Nadir; Benedetti, Marc; Dairou, Julien; Prinzhofer, Alain

    2015-04-01

    Laboratory experiments were conducted to investigate the chemical processes governing the carbon speciation associated to hydrothermal decomposition of siderite. Experiments were carried out in sealed gold capsules using synthetic siderite and deionised water. The samples were reacted at 200 and 300 °C, under a pressure of 50 MPa. Siderite dissolved to reach the 3FeCO3 + H2O = Fe3O4 + 3CO2 + H2 equilibrium and magnetite, Fe3O4, was produced accordingly. The gas phase was dominated by CO2, H2 and CH4, the latter being in strong thermodynamic disequilibrium with CO2. Contrary to the other gas products, H2 concentration was found to decrease with run duration. TEM observations showed the occurrence of condensed carbon phases at the surfaces of magnetite and residual siderite grains. Thermodynamic calculations predict the formation of condensed carbon in the experiments according to the reaction: CO2 + 2H2 ⇒ C + 2H2O, which accounted for the observed H2 concentration decrease up to the point where H2 and CO2 activities were buffered by the graphite-siderite-magnetite assemblage. The well-organized structure of the carbon coating around magnetite emphasizes the high catalytic potential of magnetite surface for carbon reduction and polymerization. The formation of such C-rich phases may represent a potential source of CH4 by hydrogenation. On the other hand, the catalysis of Fischer-Tropsch type reactions may be poisoned by the presence of carbon coating on mineral surfaces. In any case, this study also demonstrates that abiotic H2 generation by water reduction, widely studied in recent years in ultrabasic contexts, can also occur in sedimentary contexts where siderite is present. We show that, in the latter case, natural H2 concentration will be buffered by a condensed carbon phase associated with magnetite.

  13. Downstream drug product processing of itraconazole nanosuspension: Factors influencing tablet material properties and dissolution of compacted nanosuspension-layered sugar beads.

    PubMed

    Tan, En Hui; Parmentier, Johannes; Low, Ariana; Möschwitzer, Jan Peter

    2017-08-30

    There has been limited research done on the downstream processing of nanosuspensions into solid oral dosage forms. This paper demonstrates the bead layering process with a layering level at 150% and 240%, as well as the selection and justification of the outer phase excipients for tabletability and disintegrating properties. In a previous study, an itraconazole nanosuspension stabilised by SDS and HPMC E5 was layered onto sugar beads with coating polymer HPMC VLV. In the current study, compression studies with these layered beads utilising the small bead size at 150% or 240% layering levels with outer phase cushioning excipients MCC, copovidone or isomalt were performed. Other excipients such as co-compressed crospovidone-PEG 4000; DCP functioning as a disintegrant; and HPC as a binder was also added. Target output variables were achieved with a balance between an adequate tensile strength and fast dissolution rate with a release of 99.0% (±1.0% SD) within 10min, which is in accordance with the FDA guidance for dissolution testing. The results show that the compaction of nanosuspension-layered beads is a suitable process for processing an itraconazole nanosuspension into a solid dosage form such as a compacted tablet without compromising on drug release. Copyright © 2017 Elsevier B.V. All rights reserved.

  14. Coupled Mineral Dissolution and Precipitation Reactions in Shale-Hydraulic Fracturing Fluid Systems

    NASA Astrophysics Data System (ADS)

    Joe-Wong, C. M.; Harrison, A. L.; Thomas, D.; Dustin, M. K.; Jew, A. D.; Brown, G. E.; Maher, K.; Bargar, J.

    2015-12-01

    Hydraulic fracturing of low-permeability, hydrocarbon-rich shales has recently become an important energy source in the United States. However, hydrocarbon recovery rates are low and drop rapidly after a few months. Hydraulic fracture fluids, which contain dissolved oxygen and numerous organic additives, induce dissolution and precipitation reactions that change the porosity and permeability of the shale. To investigate these reactions, we studied the interactions of four shales (Eagle Ford, Barnett, Marcellus, and Green River) with a simulated hydraulic fracture fluid in batch reactors at 80 °C. The shales were chosen for both economic viability and chemical variety, allowing us to explore the reactivities of different components. The Eagle Ford shale is carbonate rich, and the Green River shale contains significant siderite and kerogen. The Barnett shale also has a high organic content, while the Marcellus shale has the highest fractions of clay and pyrite. Our experiments show that hydrochloric acid in the fluid promotes carbonate mineral dissolution, rapidly raising the pH from acidic to circumneutral levels for the Eagle Ford and Green River shales. Dissolution textures in the Green River shale and large cavities in the Barnett shale indicate significant mineralogical and physical changes in the reacted rock. Morphological changes are not readily apparent in the Eagle Ford and Marcellus shales. For all shales, ongoing changes to the solution Al: Si ratio suggest incongruent aluminosilicate dissolution. Siderite or pyrite dissolution occurs within days and is followed by the formation of secondary Fe precipitates in suspension and coating the walls of the reactor. However, little evidence of any coatings on shale surfaces was found. The net effect of these reactions on porosity and permeability and their influence on the long-term efficacy of oil and gas recovery after hydraulic fracturing are critical to the energy landscape of the United States.

  15. Redox-driven conductance switching via filament formation and dissolution in carbon/molecule/TiO2/Ag molecular electronic junctions.

    PubMed

    Ssenyange, Solomon; Yan, Haijun; McCreery, Richard L

    2006-12-05

    Carbon/molecule/TiO2/Au molecular electronic junctions show robust conductance switching, in which a metastable high conductance state may be induced by a voltage pulse which results in redox reactions in the molecular and TiO2 layers. When Ag is substituted for Au as the "top contact", dramatically different current/voltage curves and switching behavior result. When the carbon substrate is biased negative, an apparent breakdown occurs, leading to a high conductance state which is stable for at least several hours. Upon scanning to positive bias, the conductance returns to a low state, and the cycle may be repeated hundreds of times. Similar effects are observed when Cu is substituted for Au and for three different molecular layers as well as "control" junctions of the type carbon/TiO2/Ag/Au. The polarity of the "switching" is reversed when the Ag layer is between the carbon and molecular layers, and the conductance change is suppressed at low temperature. Pulse experiments show very erratic transitions between high and low conductivity states, particularly near the switching threshold. The results are consistent with a switching mechanism based on Ag or Cu oxidation, transport of their ions through the TiO2, and reduction at the carbon to form a metal filament.

  16. Influence of carbonization conditions on the pyrolytic carbon deposition in acacia and eucalyptus wood chars

    SciTech Connect

    Kumar, M.; Gupta, R.C.

    1997-04-01

    The amount of deposited pyrolytic carbon (resulting from the cracking of volatile matter) was found to depend on wood species and carbonization conditions, such as temperature and heating rate. Maximum pyrolytic carbon deposition in both the acacia and eucalyptus wood chars has been observed at a carbonization temperature of 800 C. Rapid carbonization (higher heating rate) of wood significantly reduces the amount of deposited pyrolytic carbon in resulting chars. Results also indicate that the amount of deposited pyrolytic carbon in acacia wood char is less than that in eucalyptus wood char.

  17. 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

  18. Protein carbon content evolves in response to carbon availability and may influence the fate of duplicated genes

    PubMed Central

    Bragg, Jason G; Wagner, Andreas

    2007-01-01

    Natural selection can influence even the lowest level of biological organization, the atomic composition of biological macromolecules. In analysing genome-scale gene expression data, we find that ancestral yeast strains preferentially express proteins with low carbon content during carbon limitation, relative to strains selected in the laboratory under carbon limitation. The likely reason is that the artificially selected strains acquire adaptations that refine their response to the limitation or partly circumvent the limiting condition. This finding extends previous work which shows that natural selection can act on the atomic costs of proteins. We also show that genes with high carbon and nitrogen content are less likely to have duplicates, indicating that atomic composition also plays a role in evolution by gene duplication. Taken together, our results contribute to the emerging view that protein atomic composition influences genome and transcriptome evolution. PMID:17264057

  19. Catalysis and chemical mechanisms of calcite dissolution in seawater.

    PubMed

    Subhas, Adam V; Adkins, Jess F; Rollins, Nick E; Naviaux, John; Erez, Jonathan; Berelson, William M

    2017-07-18

    Near-equilibrium calcite dissolution in seawater contributes significantly to the regulation of atmospheric [Formula: see text] on 1,000-y timescales. Despite many studies on far-from-equilibrium dissolution, little is known about the detailed mechanisms responsible for calcite dissolution in seawater. In this paper, we dissolve (13)C-labeled calcites in natural seawater. We show that the time-evolving enrichment of [Formula: see text] in solution is a direct measure of both dissolution and precipitation reactions across a large range of saturation states. Secondary Ion Mass Spectrometer profiles into the (13)C-labeled solids confirm the presence of precipitated material even in undersaturated conditions. The close balance of precipitation and dissolution near equilibrium can alter the chemical composition of calcite deeper than one monolayer into the crystal. This balance of dissolution-precipitation shifts significantly toward a dissolution-dominated mechanism below about [Formula: see text] Finally, we show that the enzyme carbonic anhydrase (CA) increases the dissolution rate across all saturation states, and the effect is most pronounced close to equilibrium. This finding suggests that the rate of hydration of [Formula: see text] is a rate-limiting step for calcite dissolution in seawater. We then interpret our dissolution data in a framework that incorporates both solution chemistry and geometric constraints on the calcite solid. Near equilibrium, this framework demonstrates a lowered free energy barrier at the solid-solution interface in the presence of CA. This framework also indicates a significant change in dissolution mechanism at [Formula: see text], which we interpret as the onset of homogeneous etch pit nucleation.

  20. Assessing the influence of reacting pyrite and carbonate minerals on the geochemistry of drainage in the Coeur d'Alene mining district

    USGS Publications Warehouse

    Balistrieri, L.S.; Box, S.E.; Bookstrom, A.A.; Ikramuddin, M.

    1999-01-01

    The relative abundance of minerals that react to generate or consume acid in mineralized areas is critical in determining the quality of water draining from such areas. This work examines the fundamental reactions that influence the pH and composition of drainage from mine adits and tailings piles. We construct triangle diagrams that predict stoichiometric relationships between concentrations of dissolved SO4 dissolved Ca and Mg, and either alkalinity or acidity by considering reactions involving the oxidation of pyrite, dissolution of carbonate minerals, and precipitation of iron oxide and iron hydroxysulfate minerals. Drainage data from the Coeur d'Alene mining district are used to test our stoichiometric approach. Comparisons between theoretical predictions and drainage data indicate that the range of pH values in the mining district is due to reacting pyrite to carbonate mineral ratios that range from near 0/1 to 1/1. Calcite and ankerite are the dominant carbonate minerals that buffer the acid produced during pyrite oxidation and ferrihydrite or schwertmannite precipitation.The relative abundance of minerals that react to generate or consume acid in mineralized areas is critical in determining the quality of water draining from such areas. This work examines the fundamental reactions that influence the pH and composition of drainage from mine adits and tailings piles. We construct triangle diagrams that predict stoichiometric relationships between concentrations of dissolved SO4, dissolved Ca and Mg, and either alkalinity or acidity by considering reactions involving the oxidation of pyrite, dissolution of carbonate minerals, and precipitation of iron oxide and iron hydroxysulfate minerals. Drainage data from the Coeur d'Alene mining district are used to test our stoichiometric approach. Comparisons between theoretical predictions and drainage data indicate that the range of pH values in the mining district is due to reacting pyrite to carbonate mineral ratios

  1. Manganese Influences Carbonate Precipitation in a Laminated Microbial Mat

    NASA Astrophysics Data System (ADS)

    Krusor, M.; Grim, S. L.; Wilmeth, D.; Johnson, H.; Berelson, W.; Stevenson, B. S.; Stamps, B. W.; Corsetti, F. A.; Spear, J. R.

    2015-12-01

    Investigating mineralization within modern microbial mats informs our interpretation of ancient microbialites and the mineralization process. Microbial mats in Little Hot Creek (LHC), California contain 4 distinct layers with different microbiota. Each layer of the mat is supersaturated with regard to calcium carbonate (CaCO3), which increases with depth. Total organic carbon decreases with depth through the mat. We used 13C-labeled bicarbonate incubations of each mat layer to calculate growth rates of organic carbon and CaCO3 within the mat. Incubations were also amended with Mn or Mg to test their effect on rates of CaCO3 and organic carbon formation. The Mn-amended top layer increased CaCO3 precipitation and organic carbon growth. Mn increased organic carbon production in the lowest layer to a lesser extent, but not growth of CaCO3. Mn addition had no effect on growth rates in the two intervening layers. Mg amendment stimulated only organic carbon formation in the top layer, with little to no effect on the lower layers or overall CaCO3 formation. We attribute the elevated CaCO3 precipitation noted after Mn addition to increased oxygenic photosynthetic activity. Oxygenic photosynthesis requires Mn as an enzyme cofactor and promotes carbonate precipitation. We propose that the phototrophic community was responsible for most of the CaCO3 precipitation in the upper layer. Phototrophs gradually moved upwards for optimal access to sunlight, and as the mat grew, "tenant" microorganisms inhabited the lower carbonate layers while the "builders" remained on top. The relatively constant percentages of inorganic carbon below the top layer combined with observed minimal CaCO3 precipitation under laboratory conditions suggest that additional research into potential metabolisms that impact carbonate formation would be informative. These results improve our understanding of the linkages between microbial metabolisms, carbonate precipitation in microbial mats, and the potential

  2. Century-scale patterns and trends of global pyrogenic carbon emissions and fire influences on terrestrial carbon balance

    NASA Astrophysics Data System (ADS)

    Yang, Jia; Tian, Hanqin; Tao, Bo; Ren, Wei; Lu, Chaoqun; Pan, Shufen; Wang, Yuhang; Liu, Yongqiang

    2015-09-01

    Fires have consumed a large amount of terrestrial organic carbon and significantly influenced terrestrial ecosystems and the physical climate system over the past century. Although biomass burning has been widely investigated at a global level in recent decades via satellite observations, less work has been conducted to examine the century-scale changes in global fire regimes and fire influences on the terrestrial carbon balance. In this study, we investigated global pyrogenic carbon emissions and fire influences on the terrestrial carbon fluxes from 1901 to 2010 by using a process-based land ecosystem model. Our results show a significant declining trend in global pyrogenic carbon emissions between the early 20th century and the mid-1980s but a significant upward trend between the mid-1980s and the 2000s as a result of more frequent fires in ecosystems with high carbon storage, such as peatlands and tropical forests. Over the past 110 years, average pyrogenic carbon emissions were estimated to be 2.43 Pg C yr-1 (1 Pg = 1015 g), and global average combustion rate (defined as carbon emissions per unit area burned) was 537.85 g C m-2 burned area. Due to the impacts of fires, the net primary productivity and carbon sink of global terrestrial ecosystems were reduced by 4.14 Pg C yr-1 and 0.57 Pg C yr-1, respectively. Our study suggests that special attention should be paid to fire activities in the peatlands and tropical forests in the future. Practical management strategies, such as minimizing forest logging and reducing the rate of cropland expansion in the humid regions, are in need to reduce fire risk and mitigate fire-induced greenhouse gases emissions.

  3. 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.

  4. The influence of bubbles on the perception carbonation bite.

    PubMed

    Wise, Paul M; Wolf, Madeline; Thom, Stephen R; Bryant, Bruce

    2013-01-01

    Although many people naively assume that the bite of carbonation is due to tactile stimulation of the oral cavity by bubbles, it has become increasingly clear that carbonation bite comes mainly from formation of carbonic acid in the oral mucosa. In Experiment 1, we asked whether bubbles were in fact required to perceive carbonation bite. Subjects rated oral pungency from several concentrations of carbonated water both at normal atmospheric pressure (at which bubbles could form) and at 2.0 atmospheres pressure (at which bubbles did not form). Ratings of carbonation bite under the two pressure conditions were essentially identical, indicating that bubbles are not required for pungency. In Experiment 2, we created controlled streams of air bubbles around the tongue in mildly pungent CO2 solutions to determine how tactile stimulation from bubbles affects carbonation bite. Since innocuous sensations like light touch and cooling often suppress pain, we predicted that bubbles might reduce rated bite. Contrary to prediction, air bubbles flowing around the tongue significantly enhanced rated bite, without inducing perceived bite in blank (un-carbonated) solutions. Accordingly, though bubbles are clearly not required for carbonation bite, they may well modulate perceived bite. More generally, the results show that innocuous tactile stimulation can enhance chemogenic pain. Possible physiological mechanisms are discussed.

  5. The Influence of Bubbles on the Perception Carbonation Bite

    PubMed Central

    Wise, Paul M.; Wolf, Madeline; Thom, Stephen R.; Bryant, Bruce

    2013-01-01

    Although many people naively assume that the bite of carbonation is due to tactile stimulation of the oral cavity by bubbles, it has become increasingly clear that carbonation bite comes mainly from formation of carbonic acid in the oral mucosa. In Experiment 1, we asked whether bubbles were in fact required to perceive carbonation bite. Subjects rated oral pungency from several concentrations of carbonated water both at normal atmospheric pressure (at which bubbles could form) and at 2.0 atmospheres pressure (at which bubbles did not form). Ratings of carbonation bite under the two pressure conditions were essentially identical, indicating that bubbles are not required for pungency. In Experiment 2, we created controlled streams of air bubbles around the tongue in mildly pungent CO2 solutions to determine how tactile stimulation from bubbles affects carbonation bite. Since innocuous sensations like light touch and cooling often suppress pain, we predicted that bubbles might reduce rated bite. Contrary to prediction, air bubbles flowing around the tongue significantly enhanced rated bite, without inducing perceived bite in blank (un-carbonated) solutions. Accordingly, though bubbles are clearly not required for carbonation bite, they may well modulate perceived bite. More generally, the results show that innocuous tactile stimulation can enhance chemogenic pain. Possible physiological mechanisms are discussed. PMID:23990956

  6. Optimization of carbon dioxide supply in raceway reactors: Influence of carbon dioxide molar fraction and gas flow rate.

    PubMed

    Duarte-Santos, T; Mendoza-Martín, J L; Acién Fernández, F G; Molina, E; Vieira-Costa, J A; Heaven, S

    2016-07-01

    Influence of CO2 composition and gas flow rate to control pH in a pilot-scale raceway producing Scenedesmus sp. was studied. Light and temperature determined the biomass productivity whereas neither the CO2 molar fraction nor the gas flow rate used influenced it; because pH was always controlled and carbon limitation did not take place. The CO2 molar fraction and the gas flow rate influenced carbon loss in the system. At low CO2 molar fraction (2-6%) or gas flow rate (75-100l·min(-1)) the carbon efficiency in the sump was higher than 95%, 85% of the injected carbon being transformed into biomass. Conversely, at high CO2 molar fraction (14%) or gas flow rate (150l·min(-1)) the carbon efficiency in the sump was lower than 67%, 32% of the carbon being fixed as biomass. Analysis here reported allows the pH control to be optimized and production costs to be reduced by optimizing CO2 efficiency. Copyright © 2016 Elsevier Ltd. All rights reserved.

  7. Influence of Plasma Jet Temperature Profiles in Arc Discharge Methods of Carbon Nanotubes Synthesis

    PubMed Central

    Raniszewski, Grzegorz; Wiak, Slawomir; Pietrzak, Lukasz; Szymanski, Lukasz; Kolacinski, Zbigniew

    2017-01-01

    One of the most common methods of carbon nanotubes (CNTs) synthesis is application of an electric-arc plasma. However, the final product in the form of cathode deposit is composed of carbon nanotubes and a variety of carbon impurities. An assay of carbon nanotubes produced in arc discharge systems available on the market shows that commercial cathode deposits contain about 10% CNTs. Given that the quality of the final product depends on carbon–plasma jet parameters, it is possible to increase the yield of the synthesis by plasma jet control. Most of the carbon nanotubes are multiwall carbon nanotubes (MWCNTs). It was observed that the addition of catalysts significantly changes the plasma composition, effective ionization potential, the arc channel conductance, and in effect temperature of the arc and carbon elements flux. This paper focuses on the influence of metal components on plasma-jet forming containing carbon nanotubes cathode deposit. The plasma jet temperature control system is presented. PMID:28336884

  8. Stability analysis of dissolution-driven convection in porous media

    NASA Astrophysics Data System (ADS)

    Emami-Meybodi, Hamid

    2017-01-01

    We study the stability of dissolution-driven convection in the presence of a capillary transition zone and hydrodynamic dispersion in a saturated anisotropic porous medium, where the solute concentration is assumed to decay via a first-order chemical reaction. While the reaction enhances stability by consuming the solute, porous media anisotropy, hydrodynamic dispersion, and capillary transition zone destabilize the diffusive boundary layer that is unstably formed in a gravitational field. We perform linear stability analysis, based on the quasi-steady-state approximation, to assess critical times, critical wavenumbers, and neutral stability curves as a function of anisotropy ratio, dispersivity ratio, dispersion strength, material parameter, Bond number, Damköhler number, and Rayleigh number. The results show that the diffusive boundary layer becomes unstable in anisotropic porous media where both the capillary transition zone and dispersion are considered, even if the geochemical reaction is significantly large. Using direct numerical simulations, based on the finite difference method, we study the nonlinear dynamics of the system by examining dissolution flux, interaction of convective fingers, and flow topology. The results of nonlinear simulations confirm the predictions from the linear stability analysis and reveal that the fingering pattern is significantly influenced by combined effects of reaction, anisotropy, dispersion, and capillarity. Finally, we draw conclusions on implications of our results on carbon dioxide sequestration in deep saline aquifers.

  9. The influence of surface effect on vibration behaviors of carbon nanotubes under initial stress

    NASA Astrophysics Data System (ADS)

    Chen, X.; Fang, C. Q.; Wang, X.

    2017-01-01

    An analytical method is presented to solve the influence of surface effect on non-coaxial resonance of multi-walled carbon nanotubes embedded in matrix utilizing laminated structures model. Due to coupled van der Waals forces between adjacent tubes and surface effect exerted carbon nanotubes, the resonance frequencies and amplitude ratios of multi-walled carbon nanotubes under initial stresses show that the resonant characteristics of the multi-walled carbon nanotubes become complex and the numbers of vibrational modes do not keep increase under identical conditions after considering surface effects. The result obtained can be used as a beneficial reference for investigating the electronic and physical behaviors of carbon nanotubes.

  10. Influence of different geographical factors on carbon sink functions in the Pearl River Delta.

    PubMed

    Xu, Qian; Dong, Yuxiang; Yang, Ren

    2017-03-08

    This study analyzed carbon fixation across different land use types in the Pearl River Delta to identify the influence of different geographical factors on carbon fixation ability. The methodology was based on interpreting land use data from TM imagery, MODIS13Q1 data, and climate data, using the improved CASA and GeogDetector models. The results show that: (1) From 2000 to 2013, the total carbon sink increased slightly, from 15.58 × 10(6) t to 17.52 × 10(6) t, being spatially low at the center and increasing outwards; (2) Proxy variables (topography and landform characteristics), influencing urbanization, significantly affect the carbon sink function of the Pearl River Delta region. The proportion of urban and other construction land showed increasing effect on the regional carbon sink each year. However, the spatial structure of land in the study area changed from complex to simple, with enhanced stability; consequently, the influence of landscape characteristics (landscape dominance and landscape perimeter area fractal dimension) on the regional carbon sink gradually decreased; (3) The influence of the same factors differed with different land use types. Slope and altitude were found to have the greatest influence on the carbon sink of cultivated land, while landscape perimeter area fractal dimension more significantly affected the forest carbon sink.

  11. Interface dissolution control of the [sup 14]C profile in marine sediment

    SciTech Connect

    Keir, R.S. ); Michel, R.L. )

    1993-08-01

    The process of carbonate dissolution at the sediment-water interface has two possible end-member boundary conditions. Either the carbonate particles dissolve mostly before they are incorporated into the sediment by bioturbation (interface dissolution), or the vertical mixing is rapid relative to their extermination rate (homogeneous dissolution). In this study, a detailed radiocarbon profile was determined in deep equatorial Pacific sediment that receives a high rate of carbonate supply. In addition, a box model of sediment mixing was used to simulate radiocarbon, carbonate content, and excess thorium profiles that result from either boundary process following a dissolution increase. Results from homogeneous dissolution imply a strong, very recent erosional event, while interface dissolution suggests that moderately increased dissolution began about 10,000 years ago. In order to achieve the observed mixed layer radiocarbon age, increased homogeneous dissolution would concentrate a greater amount of clay and [sup 230]Th than is observed, while for interface dissolution the predicted concentrations are too small. These results together with small discontinuities beneath the mixed layer in [sup 230]Th profiles suggest a two-stage increase in interface dissolution in the deep Pacific, the first occurring near the beginning of the Holocene and the second more recently, roughly 5,000 years ago. 30 refs., 8 figs., 3 tabs.

  12. Interface dissolution control of the 14C profile in marine sediment

    USGS Publications Warehouse

    Keir, R.S.; Michel, R.L.

    1993-01-01

    The process of carbonate dissolution at the sediment-water interface has two possible endmember boundary conditions. Either the carbonate particles dissolve mostly before they are incorporated into the sediment by bioturbation (interface dissolution), or the vertical mixing is rapid relative to their extermination rate (homogeneous dissolution). In this study, a detailed radiocarbon profile was determined in deep equatorial Pacific sediment that receives a high rate of carbonate supply. In addition, a box model of sediment mixing was used to simulate radiocarbon, carbonate content and excess thorium profiles that result from either boundary process following a dissolution increase. Results from homogeneous dissolution imply a strong, very recent erosional event, while interface dissolution suggests that moderately increased dissolution began about 10,000 years ago. In order to achieve the observed mixed layer radiocarbon age, increased homogeneous dissolution would concentrate a greater amount of clay and 230Th than is observed, while for interface dissolution the predicted concentrations are too small. These results together with small discontinuities beneath the mixed layer in 230Th profiles suggest a two-stage increase in interface dissolution in the deep Pacific, the first occurring near the beginning of the Holocene and the second more recently, roughly 5000 years ago. ?? 1993.

  13. Land-Use Influences Carbon Fluxes in Northern Kazakhstan

    USDA-ARS?s Scientific Manuscript database

    An understanding of carbon cycling is important to maintain sustainable rangeland ecosystems. Rangelands in the western U.S. are similar to those in Central Asia. We used a combination of meteorological and computer modeling techniques to quantitatively assess carbon loss and gain for four major l...

  14. Fuel moisture influences on fire-altered carbon in masticated fuels: An experimental study

    NASA Astrophysics Data System (ADS)

    Brewer, Nolan W.; Smith, Alistair M. S.; Hatten, Jeffery A.; Higuera, Philip E.; Hudak, Andrew T.; Ottmar, Roger D.; Tinkham, Wade T.

    2013-03-01

    Biomass burning is a significant contributor to atmospheric carbon emissions but may also provide an avenue in which fire-affected ecosystems can accumulate carbon over time, through the generation of highly resistant fire-altered carbon. Identifying how fuel moisture, and subsequent changes in the fire behavior, relates to the production of fire-altered carbon is important in determining how persistent charred residues are following a fire within specific fuel types. Additionally, understanding how mastication (mechanical forest thinning) and fire convert biomass to black carbon is essential for understanding how this management technique, employed in many fire-prone forest types, may influence stand-level black carbon in soils. In this experimental study, 15 masticated fuel beds, conditioned to three fuel moisture ranges, were burned, and production rates of pyrogenic carbon and soot-based black carbon were evaluated. Pyrogenic carbon was determined through elemental analysis of the post-fire residues, and soot-based black carbon was quantified with thermochemical methods. Pyrogenic carbon production rates ranged from 7.23% to 8.67% relative to pre-fire organic carbon content. Black carbon production rates averaged 0.02% in the 4-8% fuel moisture group and 0.05% in the 13-18% moisture group. A comparison of the ratio of black carbon to pyrogenic carbon indicates that burning with fuels ranging from 13% to 15% moisture content resulted in a higher proportion of black carbon produced, suggesting that the precursors to black carbon were indiscriminately consumed at lower fuel moistures. This research highlights the importance of fuel moisture and its role in dictating both the quantity and quality of the carbon produced in masticated fuel beds.

  15. [Research on carbon reduction potential of electric vehicles for low-carbon transportation and its influencing factors].

    PubMed

    Shi, Xiao-Qing; Li, Xiao-Nuo; Yang, Jian-Xin

    2013-01-01

    Transportation is the key industry of urban energy consumption and carbon emissions. The transformation of conventional gasoline vehicles to new energy vehicles is an important initiative to realize the goal of developing low-carbon city through energy saving and emissions reduction, while electric vehicles (EV) will play an important role in this transition due to their advantage in energy saving and lower carbon emissions. After reviewing the existing researches on energy saving and emissions reduction of electric vehicles, this paper analyzed the factors affecting carbon emissions reduction. Combining with electric vehicles promotion program in Beijing, the paper analyzed carbon emissions and reduction potential of electric vehicles in six scenarios using the optimized energy consumption related carbon emissions model from the perspective of fuel life cycle. The scenarios included power energy structure, fuel type (energy consumption per 100 km), car type (CO2 emission factor of fuel), urban traffic conditions (speed), coal-power technologies and battery type (weight, energy efficiency). The results showed that the optimized model was able to estimate carbon emissions caused by fuel consumption more reasonably; electric vehicles had an obvious restrictive carbon reduction potential with the fluctuation of 57%-81.2% in the analysis of six influencing factors, while power energy structure and coal-power technologies play decisive roles in life-cycle carbon emissions of electric vehicles with the reduction potential of 78.1% and 81.2%, respectively. Finally, some optimized measures were proposed to reduce transport energy consumption and carbon emissions during electric vehicles promotion including improving energy structure and coal technology, popularizing energy saving technologies and electric vehicles, accelerating the battery R&D and so on. The research provides scientific basis and methods for the policy development for the transition of new energy vehicles

  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

    Primary mineral dissolution products, such as silica (Si), calcium (Ca) and magnesium (Mg), play an important role in numerous biologic and geochemical cycles including microbial metabolism, plant growth and secondary mineral precipitation. The flux of these and other dissolution products into the environment is largely controlled by the rate of primary silicate mineral dissolution. Bacteria, a ubiquitous component in water-rock systems, are known to facilitate mineral dissolution and may play a substantial role in determining the overall flux of dissolution products into the environment. Bacterial cell walls are complex and highly reactive organic surfaces that can affect mineral dissolution rates directly through microbe-mineral adsorption or indirectly by complexing dissolution products. The effect of bacterial surface adsorption on chemical weathering rates may even outweigh the influence of active processes in environments where a high proportion of cells are metabolically dormant or cell metabolism is slow. Complications associated with eliminating or accounting for ongoing metabolic processes in long-term dissolution studies have made it challenging to isolate the influence of cell wall interactions on mineral dissolution rates. We utilized Bacillus subtilis endospores, a robust and metabolically dormant cell type, to isolate and quantify the effects of bacterial surface reactivity on forsterite (Mg2SiO4) dissolution rates. We measured the influence of both direct and indirect microbe-mineral interactions on forsterite dissolution. Indirect pathways were isolated using dialysis tubing to prevent mineral-microbe contact while allowing free exchange of dissolved mineral products and endospore-ion adsorption. Homogenous experimental assays allowed both direct microbe-mineral and indirect microbe-ion interactions to affect forsterite dissolution rates. Dissolution rates were calculated based on silica concentrations and zero-order dissolution kinetics

  17. Carbon Dioxide Corrosion and Acetate: A Hypothesis on the Influence of Microorganisms

    DTIC Science & Technology

    2008-11-01

    reducing bacteria residing in pipeline facilities can influence corrosion through the production of carbon dioxide and acetate under the prevailing...anaerobic conditions. The exacerbation of carbon dioxide corrosion of carbon steel in the presence of acetic acid is a well-known phenomenon in the...and that the microbial diversity inherent in petroleum reservoirs largely reflects that in pipelines. 20090306219 15. SUBJECT TERMS acetate

  18. Influence of glucose solubility and dissolution rate on the kinetics of lipase catalyzed synthesis of glucose laurate in 2-methyl 2-butanol.

    PubMed

    Flores, Maria Victoria; Naraghi, Kaynoush; Engasser, Jean-Marc; Halling, Peter J

    2002-06-30

    The lipase catalyzed acylation of glucose by dodecanoic acid in 2-methyl 2-butanol was studied. The initial reaction rate was strongly dependent on the dissolved glucose concentration in the medium. Several methods were shown to increase dissolved glucose concentrations and initial reaction rates, namely, the use of solid beta-glucose, amorphous solid glucose, and supersaturated glucose solution. Supersaturated glucose solutions in 2-methyl 2-butanol showed a high stability even in the presence of solid crystalline glucose. During the reaction, the dissolved glucose concentration falls as the reaction proceeds, before recovering later as more of the excess solid dissolves. However, the ester synthesis rate continues to fall even after glucose concentration reaches its minimum, so glucose dissolution rate limitation is not responsible for the synthesis rate decline. Experiments with added molecular sieves show that the main reason is the accumulation of product water. In the presence of molecular sieves, 70% of glucose was converted to ester, independent of the initial soluble glucose in the medium. Copyright 2002 Wiley Periodicals, Inc.

  19. Influence of Cu2S precipitates dissolution on ferrite grain growth during heat treatment in the non-oriented electrical steel sheet

    NASA Astrophysics Data System (ADS)

    Wu, Yuan; Li, Fangjie; Wang, Ting; Zhao, Dan; Huang, Hefei; Li, Huigai; Zheng, Shaobo

    2017-05-01

    The factor to deduce grain growth of non-oriented electrical steel sheet during heat treatment was researched in this paper. Scanning electron microscope equipped with electron backscatter diffraction (EBSD), X-ray diffraction and transmission electron microscope were used to characterize the microstructure, dislocation density and precipitate, respectively. The EBSD results indicated that the grain size increased from 18.7 μm to 56 μm after heat treatment. Meanwhile, the characterization of grain size distribution, dislocation density and precipitates revealed that the dissolution of Cu2S precipitates, which act as inhibitor, may lead to the grain growth. In addition, the pinning force of grain boundary and the driving force of grain growth were calculated. Based on experiments results and theoretical calculations, the Cu2S precipitates with diameter of less than 39 nm and volume fraction of 1.74 × 10-4 would be sufficient to inhibit the ferrite grain growth. Heat treatment provides an efficient way to prompt the grain growth.

  20. Ocean acidification: Towards a better understanding of calcite dissolution

    NASA Astrophysics Data System (ADS)

    Wilhelmus, Monica M.; Adkins, Jess; Menemenlis, Dimitris

    2016-11-01

    The drastic increase of anthropogenic CO2 emissions over the past two centuries has altered the chemical structure of the ocean, acidifying upper ocean waters. The net impact of this pH decrease on marine ecosystems is still unclear, given the unprecedented rate at which CO2 is being released into the atmosphere. As part of the carbon cycle, calcium carbonate dissolution in sediments neutralizes CO2: phytoplankton at the surface produce carbonate minerals, which sink and reach the seafloor after the organisms die. On time scales of thousands of years, the calcium carbonate in these shells ultimately reacts with CO2 in seawater. Research in this field has been extensive; nevertheless, the dissolution rate law, the impact of boundary layer transport, and the feedback with the global ocean carbon cycle remain controversial. Here, we (i) develop a comprehensive numerical framework via 1D modeling of carbonate dissolution in sediments, (ii) approximate its impact on water column properties by implementing a polynomial approximation to the system's response into a global ocean biogeochemistry general circulation model (OBGCM), and (iii) examine the OBGCM sensitivity response to different formulations of sediment boundary layer properties. We find that, even though the burial equilibration time scales of calcium carbonate are in the order of thousands of years, the formulation of a bottom sediment model along with an improved description of the dissolution rate law can have consequences on multi-year to decadal time scales.

  1. 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.

  2. Soil organic carbon accumulation and influencing factors at the saltmarsh of Yangtze Estuary

    NASA Astrophysics Data System (ADS)

    Li, X.; Jiang, J.; Xue, L.

    2016-02-01

    Soil organic carbon sequestration in the coastal saltmarsh is considered to be an important part of "blue carbon" because of its high carbon accumulation rate and low greenhouse gas emission. However, the factors influencing the carbon accumulation ability is not yet fully revealed yet due to lack of knowledge about underground biomass and root zone soil processes. Based on the field investigation at the young salt marsh of the East Chongming Headland, Yangtze Estuary, we tried to link the spatial and vertical distribution of soil organic carbon with key influencing factors such as above ground and underground biomass, surface elevation, salinity, and sediment particle size, through ArcGIS Kriging interpolation, SPSS correlation and path analyses. We found that: 1) The spatial distribution of soil organic carbon was relatively high in the northern part and high tidal zone of East Chongming Headland, with soil salinity, biomass and elevation as main influencing factors; 2) The vertical distribution of soil organic carbon was closely related to soil salinity, biomass, and 0-31 μm soil particles; 3) The carbon sequestration rate showed a decrease trend with time of vegetation establishment. To promote carbon sequestration in coastal wetlands for mitigating climate change, protection of "old marsh" and creating "new marsh" are both needed in the future management.

  3. [Influence of biological activated carbon dosage on landfill leachate treatment].

    PubMed

    Cui, Yan-Rui; Guo, Yan; Wu, Qing

    2014-08-01

    Effects of biological activated carbon (BAC) dosage on COD removal in landfill leachate treatment were compared. The COD removal efficiency of reactors with 0, 100 and 300 g activated carbon dosage per litre activated sludge was 12.9%, 19.6% and 27.7%, respectively. The results indicated that BAC improved the refractory organic matter removal efficiency and there was a positive correlation between COD removal efficiency and BAC dosage. The output of carbon dioxide after 8h of aeration in reactors was 109, 193 and 306 mg corresponding to the activated carbon dosages mentioned above, which indicated the amount of biodegradation and BAC dosage also had a positive correlation. The combination of adsorption and bioregeneration of BAC resulted in the positive correlation betweem organic matter removal efficiency and BAC dosage, and bioregeneration was the root cause for the microbial decomposition of refractory organics.

  4. Influence of dopants, particularly carbon, on β-rhombohedral boron

    NASA Astrophysics Data System (ADS)

    Werheit, H.; Flachbart, K.; Pristáš, G.; Lotnyk, D.; Filipov, V.; Kuhlmann, U.; Shitsevalova, N.; Lundström, T.

    2017-09-01

    Due to the high affinity of carbon to boron, the preparation of carbon-free boron is problematic. Even high-purity (6 N) β-rhombohedral boron contains 30-60 ppm of C. Hence, carbon affects the boron physical properties published so far more or less significantly. We studied well-defined carbon-doped boron samples based on pure starting material carefully annealed with up to about 1% C, thus assuring homogeneity. We present and discuss their electrical conductivity, optical absorption, luminescence and phonon spectra. Earlier attempts of other authors to determine the conductivity of C-doped boron are revised. Our results allow estimating the effects of oxygen and iron doping on the electrical conductivity using results taken from literature. Discontinuities at low T impair the electronic properties.

  5. Influence of carbon nanotubes coatings onto carbon fiber by oxidative treatments combined with electrophoretic deposition on interfacial properties of carbon fiber composite

    NASA Astrophysics Data System (ADS)

    Deng, Chao; Jiang, Jianjun; Liu, Fa; Fang, Liangchao; Wang, Junbiao; Li, Dejia; Wu, Jianjun

    2015-12-01

    To improve the interfacial performance of carbon fiber (CF) and epoxy resin, carbon nanotubes (CNTs) coatings were utilized to achieve this purpose through coating onto CF by the treatment with hydrogen peroxide and concentrated nitric acid combined with electrophoretic deposition (EPD) process. The influence of electrophoretically deposited CNTs coatings on the surface properties of CFs were investigated by Fourier transform infrared spectrometer, atomic force microscopy, scanning electron microscopy and dynamic contact angle analysis. The results indicated that the deposition of carbon nanotubes introduced some polar groups to carbon fiber surfaces, enhanced surface roughness and changed surface morphologies of carbon fibers. Surface wettability of carbon fibers may be significantly improved by increasing surface free energy of the fibers due to the deposition of CNTs. The thickness and density of the coatings increases with the introduction of pretreatment of the CF during the EPD process. Short beam shear test was performed to examine the effect of carbon fiber functionalization on mechanical properties of the carbon fiber/epoxy resin composites. The interfacial adhesion of CNTs/CF reinforced epoxy composites showed obvious enhancement of interlaminar shear strength by 60.2% and scanning electron microscope photographs showed that the failure mode of composites was changed after the carbon fibers were coated with CNTs.

  6. 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.

  7. 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.

  8. Lithological influence of aggregate in the alkali-carbonate reaction

    SciTech Connect

    Lopez-Buendia, A.M. . E-mail: angel.lopez@aidico.es; Climent, V. . E-mail: vcliment@grupogla.com; Verdu, P.

    2006-08-15

    The reactivity of carbonate rock with the alkali content of cement, commonly called alkali-carbonate reaction (ACR), has been investigated. Alkali-silica reaction (ASR) can also contribute in the alkali-aggregate reaction (AAR) in carbonate rock, mainly due to micro- and crypto-crystalline quartz or clay content in carbonate aggregate. Both ACR and ASR can occur in the same system, as has been also evidenced on this paper. Carbonate aggregate samples were selected using lithological reactivity criteria, taking into account the presence of dedolomitization, partial dolomitization, micro- and crypto-crystalline quartz. Selected rocks include calcitic dolostone with chert (CDX), calcitic dolostone with dedolomitization (CDD), limestone with chert (LX), marly calcitic dolostone with partial dolomitization (CD), high-porosity ferric dolostone with clays (FD). To evaluate the reactivity, aggregates were studied using expansion tests following RILEM AAR-2, AAR-5, a modification using LiOH AAR-5Li was also tested. A complementary study was done using petrographic monitoring with polarised light microscopy on aggregates immersed in NaOH and LiOH solutions after different ages. SEM-EDAX has been used to identify the presence of brucite as a product of dedolomitization. An ACR reaction showed shrinkage of the mortar bars in alkaline solutions explained by induced dedolomitization, while an ASR process typically displayed expansion. Neither shrinkage nor expansion was observed when mortar bars were immersed in solutions of lithium hydroxide. Carbonate aggregate classification with AAR pathology risk has been elaborated based on mechanical behaviours by expansion and shrinkage. It is proposed to be used as a petrographic method for AAR diagnosis to complement the RILEM AAR1 specifically for carbonate aggregate. Aggregate materials can be classified as I (non-reactive), II (potentially reactive), and III (probably reactive), considering induced dedolomitization ACR

  9. Analysis of the Parameters Influencing the Quench-Aging Behavior of Ultra-Low-Carbon Steels

    NASA Astrophysics Data System (ADS)

    Massardier, V.; Merlin, J.

    2009-05-01

    The influence of the annealing temperature and of the grain size on the quench-aging behavior of ultra-low-carbon (ULC) steels was investigated by thermoelectric power measurements (TEPs) and mechanical testing. The TEP technique showed that the quench aging of ULC steels occurs in two distinct stages: (1) the segregation of carbon atoms to the grain boundaries and (2) the precipitation of iron carbides. It was suggested that the degree of grain boundary coverage by the carbon atoms resulting from the annealing or aging conditions influences the development of the yield point of ULC steels.

  10. Phase II of a Six sigma Initiative to Study DWPF SME Analytical Turnaround Times: SRNL's Evaluation of Carbonate-Based Dissolution Methods

    SciTech Connect

    Edwards, Thomas

    2005-09-01

    The Analytical Development Section (ADS) and the Statistical Consulting Section (SCS) of the Savannah River National Laboratory (SRNL) are participating in a Six Sigma initiative to improve the Defense Waste Processing Facility (DWPF) Laboratory. The Six Sigma initiative has focused on reducing the analytical turnaround time of samples from the Slurry Mix Evaporator (SME) by developing streamlined sampling and analytical methods [1]. The objective of Phase I was to evaluate the sub-sampling of a larger sample bottle and the performance of a cesium carbonate (Cs{sub 2}CO{sub 3}) digestion method. Successful implementation of the Cs{sub 2}CO{sub 3} fusion method in the DWPF would have important time savings and convenience benefits because this single digestion would replace the dual digestion scheme now used. A single digestion scheme would result in more efficient operations in both the DWPF shielded cells and the inductively coupled plasma--atomic emission spectroscopy (ICP-AES) laboratory. By taking a small aliquot of SME slurry from a large sample bottle and dissolving the vitrified SME sample with carbonate fusion methods, an analytical turnaround time reduction from 27 hours to 9 hours could be realized in the DWPF. This analytical scheme has the potential for not only dramatically reducing turnaround times, but also streamlining operations to minimize wear and tear on critical shielded cell components that are prone to fail, including the Hydragard{trademark} sampling valves and manipulators. Favorable results from the Phase I tests [2] led to the recommendation for a Phase II effort as outlined in the DWPF Technical Task Request (TTR) [3]. There were three major tasks outlined in the TTR, and SRNL issued a Task Technical and QA Plan [4] with a corresponding set of three major task activities: (1) Compare weight percent (wt%) total solids measurements of large volume samples versus peanut vial samples. (2) Evaluate Cs{sub 2}CO{sub 3} and K{sub 2}CO{sub 3

  11. 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.

  12. Potential Influence of Perchlorate on Organic Carbon in Martian Regolith

    NASA Astrophysics Data System (ADS)

    Oze, C.; Vithanage, M. S.; Kumarathilaka, P. R.; Indraratne, S.; Horton, T. W.

    2014-12-01

    Perchlorate is a strong oxidizer present at elevated concentrations in surface martian regolith. Chemical and isotopic modification of potential organic carbon with perchlorate in martian regolith during H2O(l) interactions is unknown. Here we assess the relationship between martian levels of perchlorate and organic carbon present in life harbouring geologic material from Earth. These materials represent chemical (i.e., processed serpentine soils from Sri Lanka) and temperature (i.e., hydrothermal jarosite/goethite deposit from White Island, New Zealand) extremes to where life exists on Earth. Preliminary evidence demonstrates that organic carbon decreases and δ13C values are modified for ultramafic sediment in both perchlorate kinetic and incubation experiments. In hydrothermal jarosite/goethite with microbial communities present, total and organic carbon is maintained and little modification in δ13C values is apparent. These preliminary results suggest that surface hydrothermal deposits with mineralogically 'protected' organic carbon are preferable sites to assess the potential of life on Mars.

  13. Influence of paleoenvironment on the carbon isotope compositions of pedogenic carbonate formed in Paleozoic vertic paleosols

    SciTech Connect

    Mora, C.I.; Driese, S.G.; Seager, P.G. . Dept. of Geological Sciences)

    1992-01-01

    Pedogenic carbonate occurs in numerous vertic-featured paleosols developed in Paleozoic red bed successions of the southern and central Appalachians. The authors note systematic differences in the delta C-13 values of soil carbonate developed during pedogenesis in coastal-marine and distal alluvial plain environments as compared to pedogenesis in proximal alluvial plain environments. These differences have been measured in pedogenic carbonate occurring in late Silurian (Bloomsburg Fm.) vertic-featured paleosols. Evidence for pre-existing marine skeletal material in these paleosols has been observed only in the lowermost portions of the Bloomsburg Fm.; other paleosols were apparently devoid of any precursor carbonate phase. Therefore, the heavier isotopic signatures of pedogenic carbonate within coastal-marine and distal alluvial plain environments may be due to contributions from marine spray, marine or brackish groundwaters, or to less-extensive biological activity. Although carbonate nodules are commonly developed in all environments, rhizoliths appear to be more abundant in paleosols developed in proximal alluvial plain environments. Despite the large differences in carbon isotope compositions attributed to paleoenvironment, these vertic-featured paleosols share common patterns of carbonate cementation and isotopic trends (nodules enriched in C-13 relative to rhizoliths). Thus, despite the different pedogenic paleoenvironments, there were similar physico-chemical controls on soil carbonate precipitation. Better understanding of the paleoclimatic information retained in paleosols will require thorough petrographic, sedimentologic and geochemical studies.

  14. Influence of organic carbon and metal oxide phases on sorption of 2,4,6-trichlorobenzoic acid under oxic and anoxic conditions.

    PubMed

    Ololade, Isaac Ayodele; Oladoja, Nurudeen Abiola; Alomaja, Folasade; Ololade, Oluwaranti Olubunmi; Olaseni, Esan O; Oloye, Femi Francis; Adelagun, Ruth O A

    2015-01-01

    Chlorobenzoic acids represent crucial recalcitrant metabolites in the environment; thus, the influence of soil components on the sorption of 2,4,6-trichlorobenzoic acid (TCB) under oxic and anoxic conditions was studied. The surficial physiognomies of untreated and isolated soil samples were studied using FTIR, XRD, specific surface area, and PZC determination. The roles of redox potential, dissolved organic carbon (DOC), and pH, particularly under anoxic condition, were appraised. Batch equilibrium adsorption studies on soils of variable Fe/Mn oxides and organic carbon showed that adsorption was low across all components (log Koc = 0.82-3.10 Lg(-1)). The sorption of 2,4,6-TCB was well described by the pseudo second-order kinetic model. The fluctuation of both redox potential and pH during anoxic experiment had a negative impact on the sorption, partitioning, and the oxidation of organic matter. Linear relationships were observed for Kd with both soil total organic carbon (TOC) and surface area (SA). The results showed the existence of DOC-mediated sorption of 2,4,6-TCB which seems to be enhanced at lower pH. The reductive dissolution, particularly of iron compounds, possibly impeded sorption of 2,4,6-TCB under anoxic condition. It could be inferred that habitats dominated by fluctuating oxygen concentrations are best suited for the development of environmental conditions capable of mineralizing 2,4,6-TCB and similar xenobiotics.

  15. Assessing the influence of reacting pyrite and carbonate minerals on the geochemistry of drainage in the Coeur d'Alene mining district

    SciTech Connect

    Balistrieri, L.S.; Box, S.E.; Bookstrom, A.A.; Ikramuddin, M.

    1999-10-01

    The relative abundance of minerals that react to generate or consume acid in mineralized areas is critical in determining the quality of water draining from such areas. This work examines the fundamental reactions that influence the pH and composition of drainage from mine adits and tailings piles. The authors construct triangle diagrams that predict stoichiometric relationships between concentrations of dissolved SO{sub 4}{sup {minus}}, dissolved Ca and Mg, and either alkalinity or acidity by considering reactions involving the oxidation of pyrite, dissolution of carbonate minerals, and precipitation of iron oxide and iron hydroxysulfate minerals. Drainage data from the Coeur d'Alene mining district are used to test their stoichiometric approach. Comparisons between theoretical predictions and drainage data indicate that the range of pH values in the mining district is due to reacting pyrite to carbonate mineral ratios that range from near 0/1 to 1/1. Calcite and ankerite are the dominant carbonate minerals that buffer the acid produced during pyrite oxidation and ferrihydrite or schwertmannite precipitation.

  16. Influence of EPS isolated from thermophilic sulphate-reducing bacteria on carbon steel corrosion.

    PubMed

    Dong, Ze Hua; Liu, Tao; Liu, Hong Fang

    2011-05-01

    Extracellular polymeric substances (EPS) were isolated by centrifugation of thermophilic sulphate-reducing bacteria (SRB) grown in API-RP38 culture medium. The protein and polysaccharide fractions were quantified and the highest concentrations were extracted from a 14-day old culture. The effect of EPS on carbon steel corrosion was investigated by electrochemical techniques. At 30°C, a small amount of EPS in 3% NaCl solution inhibited corrosion, whilst excessive amounts of EPS facilitated corrosion. In addition, the inhibition efficiency of EPS decreased with temperature due to thermal desorption of the EPS. The results suggest that adsorbed EPS layers could be beneficial to anti-corrosion by hindering the reduction of oxygen. However, the accumulation of an EPS film could stimulate the anodic dissolution of the underlying steel by chelation of Fe2+ ions.

  17. Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

    DOE PAGES

    Reinoso-Maset, Estela; Steefel, Carl I.; Um, Wooyong; ...

    2017-06-01

    Uranyl oxyhydroxide minerals are important weathering products in uranium-contaminated surface and subsurface environments that regulate dissolved uranium concentrations. However, dissolution rates for this class of minerals and associated dissolution mechanisms have not been previously reported for circumneutral pH conditions, particularly for the case of flow through porous media. In this paper, the dissolution rates of K- and Na-compreignacite (K2(UO2)6O4(OH)6·8H2O and Na2(UO2)6O4(OH)6·8H2O respectively) were measured using flow-through columns reacted with two simulated background porewater (BPW) solutions of low and high dissolved total carbonate content (ca. 0.2 and 2.8 mmol L-1). Column materials were characterized before and after reaction with electron microscopy,more » bulk chemistry, and EXAFS to identify structural and chemical changes during dissolution and to obtain insight into molecular-scale processes. The reactive transport code CrunchFlow was used to calculate overall dissolution rates while accounting for fluid transport and changes in mineral volume and reactive surface area and results were compared to steady-state dissolution rate calculations. In low carbonate BPW systems, interlayer K and Na were initially leached from both minerals, and in Na-compreignacite, K and minor divalent cations from the input solution were incorporated into the mineral structure. Results of characterization analyses suggested that after reaction both K- and Na-compreignacite resembled a disordered K-compreignacite with altered surfaces. A 10-fold increase in dissolved carbonate concentration and corresponding increase in pH (from 6.65 to 8.40) resulted in a net removal of 58-87%