Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobili... more Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobility of uranium in the environment and the accumulation of uranium in ore bodies, and inform our understanding of Earth's geochemical history. The molecular-scale mechanistic pathways of these transitions determine the U(IV) products formed, thus influencing uranium isotope fractionation, reoxidation, and transport in sediments. Studies that improve our understanding of these pathways have the potential to substantially advance process understanding across a number of earth sciences disciplines. Detailed mechanistic information regarding uranium redox transitions in field sediments is largely nonexistent, owing to the difficulty of directly observing molecular-scale processes in the subsurface and the compositional/physical complexity of subsurface systems. Here, we present results from an in situ study of uranium redox transitions occurring in aquifer sediments under sulfate-reducing ...
The dissolution of UO 2 in a continuously stirred tank reactor (CSTR) in the presence of Ca 2+ an... more The dissolution of UO 2 in a continuously stirred tank reactor (CSTR) in the presence of Ca 2+ and Zn 2+ was investigated under experimental conditions relevant to contaminated groundwater systems. Complementary experiments were performed to investigate the effect of adsorption and precipitation reactions on UO 2 dissolution. The experiments were performed under anoxic and oxic conditions. Zn 2+ had a much greater inhibitory effect on UO 2 dissolution than did Ca 2+ . This inhibition was most substantial under oxic conditions, where the experimental rate of UO 2 dissolution was 7 times lower in the presence of Ca 2+ and 1450 times lower in the presence of Zn 2+ than in water free of divalent cations. EXAFS and solution chemistry analyses of UO 2 solids recovered from a Ca experiment suggest that a Ca−U(VI) phase precipitated. The Zn carbonate hydrozincite [Zn 5 (CO 3 ) 2 (OH) 6 ] or a structurally similar phase precipitated on the UO 2 solids recovered from experiments performed in the presence of Zn. These precipitated Ca and Zn phases can coat the UO 2 surface, inhibiting the oxidative dissolution of UO 2 . Interactions with divalent groundwater cations have implications for the longevity of UO 2 and the mobilization of U(VI) from these solids in remediated subsurface environments, waste disposal sites, and natural uranium ores.
Reductive bioremediation is currently being explored as a possible strategy for uranium-contamina... more Reductive bioremediation is currently being explored as a possible strategy for uranium-contaminated aquifers such as the Old Rifle site (Colorado). The stability of U(IV) phases under oxidizing conditions is key to the performance of this procedure. An in situ method was developed to study oxidative dissolution of biogenic uraninite (UO 2 ), a desirable U(VI) bioreduction product, in the Old Rifle, CO, aquifer under different variable oxygen conditions. Overall uranium loss rates were 50À100 times slower than laboratory rates. After accounting for molecular diffusion through the sample holders, a reactive transport model using laboratory dissolution rates was able to predict overall uranium loss. The presence of biomass further retarded diffusion and oxidation rates. These results confirm the importance of diffusion in controlling in-aquifer U(IV) oxidation rates. Upon retrieval, uraninite was found to be free of U(VI), indicating dissolution occurred via oxidation and removal of surface atoms. Interaction of groundwater solutes such as Ca 2+ or silicate with uraninite surfaces also may retard in-aquifer U loss rates. These results indicate that the prolonged stability of U(IV) species in aquifers is strongly influenced by permeability, the presence of bacterial cells and cell exudates, and groundwater geochemistry.
a b s t r a c t BDTH 2 , 1,3-benzenediamidoethanethiol (common name) and closely related derivati... more a b s t r a c t BDTH 2 , 1,3-benzenediamidoethanethiol (common name) and closely related derivatives were specifically designed to become insoluble after the formation of linear, covalent bonds to aqueous mercury(II). BDTH 2 (IUPAC nomenclature, N,N 0 -bis(2-mercaptoethyl)isophthalamide) emerged as the preeminent reagent for the complete precipitation of mercury from water after several years of studies with a wide range of compounds having one, two, three, and four thiol groups. BDTH 2 does not become inactive through oxidation to disulfide and can be applied to mercury-containing water as acidic, basic, and ethanolic solutions. The BDT-Hg precipitate is extremely stable and leaches low-ppm levels of mercury only under extremely acidic and basic conditions. BDTH 2 is also effective in the aqueous precipitation of other soft, divalent metals, such as copper, cadmium, lead, and the main group elements, arsenic and selenium. The insolubility of the BDT-M compounds can be attributed to the presence of strong, non-polar, covalent M-S bonding within a water-insoluble organic framework. BDTH 2 has no known biological toxicity and is being sold as a nutritional supplement under the trade name OSR-1. This review describes the chemistry, precipitation, and leaching studies of BDTH 2 with mercury.
... Lexington, Kentucky Director: Dr. David A. Atwood, Professor of Chemistry Lexington, Kentucky... more ... Lexington, Kentucky Director: Dr. David A. Atwood, Professor of Chemistry Lexington, Kentucky 2010 ... Dr. Lovell, thanks for coming in so late in the game to see me to the finish line. ... contemporaries in the group, especially Eduardo Santillán-Jiménez and Christopher iii Page 10. ...
The use of benzene-1,3-diamidoethanethiol as a covalent surface coating for the prevention of met... more The use of benzene-1,3-diamidoethanethiol as a covalent surface coating for the prevention of metal leaching was demonstrated with several sulfide minerals including cinnabar (HgS), pyrite (FeS 2 ), chalcopyrite (CuFeS 2 ), covellite (CuS), galena (PbS), realgar (As 4 S 4 ) and sphalerite (ZnS). The minerals were coated with sufficient H 2 BDT to bind the surface metals in a 1:1 ratio. Leaching at pH 1, 3 and 7 was then conducted on both treated and untreated minerals. ICP and CVAFS (for mercury) analyses revealed that the coated minerals showed a dramatic reduction in metal leaching as compared to uncoated control samples. X-ray photoelectron spectroscopy indicated the formation of covalent bonds between the sulphur of the ligand and the metals from the minerals. days . All concentrations (25, 50, 75 and 100 mg/L) of SLS reduced sulfate production for the first 12 days. The 25-and 50-mg/L concentrations reduced sulfate formation over a 26-day period. However, after 12 days, the 75 mg SLS/L stimulated sulfur formation. Use of 100 mg SLS/L completely inhibited sulfate formation for the first 12 days with significant reductions for the remaining 14 days. The use of optimum, controlled doses of SLS is very important in this method.
Benzene-1,3-diamidoethanethiol (BDETH 2 ) is an exceptional precipitant for removing soft heavy m... more Benzene-1,3-diamidoethanethiol (BDETH 2 ) is an exceptional precipitant for removing soft heavy metals from water. The present work will detail the bonding arrangement of BDETH 2 to the metals Cd, Hg, and Pb, along with the full characterization data of the BDET−M compounds. It was found that the Hg compound has a linear S−M−S geometry. The characterization data consisted of Mp, EA, IR, Raman, MS, XANES, EXAFS, and solid-state multinuclear NMR. Krepps, M. K.; Atwood, D. A. Water Res. 2000, 34, 3005. (2) Matlock, M. M.; Howerton, B. S.; van Aelstyn, M. A.; Henke, K. R.; Atwood, D. A. Water Res. 2003, 37, 579. (3) Matlock, M. M.; Howerton, B. S.; van Aelstyn, M. A.; Nordstrom, F. L.; Atwood, D. A. EnViron. Sci. Technol. 2002, 36, 1636. (4) Matlock, M. M.; Howerton, B. S.; Atwood, D. A. Ind. Eng. Chem. Res. 2002, 41, 1579. (5) Matlock, M. M.; Howerton, B. S.; Robertson, J. D.; Atwood, D. A.
Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobili... more Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobility of uranium in the environment and the accumulation of uranium in ore bodies, and inform our understanding of Earth's geochemical history. The molecular-scale mechanistic pathways of these transitions determine the U(IV) products formed, thus influencing uranium isotope fractionation, reoxidation, and transport in sediments. Studies that improve our understanding of these pathways have the potential to substantially advance process understanding across a number of earth sciences disciplines. Detailed mechanistic information regarding uranium redox transitions in field sediments is largely nonexistent, owing to the difficulty of directly observing molecular-scale processes in the subsurface and the compositional/physical complexity of subsurface systems. Here, we present results from an in situ study of uranium redox transitions occurring in aquifer sediments under sulfate-reducing ...
The dissolution of UO 2 in a continuously stirred tank reactor (CSTR) in the presence of Ca 2+ an... more The dissolution of UO 2 in a continuously stirred tank reactor (CSTR) in the presence of Ca 2+ and Zn 2+ was investigated under experimental conditions relevant to contaminated groundwater systems. Complementary experiments were performed to investigate the effect of adsorption and precipitation reactions on UO 2 dissolution. The experiments were performed under anoxic and oxic conditions. Zn 2+ had a much greater inhibitory effect on UO 2 dissolution than did Ca 2+ . This inhibition was most substantial under oxic conditions, where the experimental rate of UO 2 dissolution was 7 times lower in the presence of Ca 2+ and 1450 times lower in the presence of Zn 2+ than in water free of divalent cations. EXAFS and solution chemistry analyses of UO 2 solids recovered from a Ca experiment suggest that a Ca−U(VI) phase precipitated. The Zn carbonate hydrozincite [Zn 5 (CO 3 ) 2 (OH) 6 ] or a structurally similar phase precipitated on the UO 2 solids recovered from experiments performed in the presence of Zn. These precipitated Ca and Zn phases can coat the UO 2 surface, inhibiting the oxidative dissolution of UO 2 . Interactions with divalent groundwater cations have implications for the longevity of UO 2 and the mobilization of U(VI) from these solids in remediated subsurface environments, waste disposal sites, and natural uranium ores.
Reductive bioremediation is currently being explored as a possible strategy for uranium-contamina... more Reductive bioremediation is currently being explored as a possible strategy for uranium-contaminated aquifers such as the Old Rifle site (Colorado). The stability of U(IV) phases under oxidizing conditions is key to the performance of this procedure. An in situ method was developed to study oxidative dissolution of biogenic uraninite (UO 2 ), a desirable U(VI) bioreduction product, in the Old Rifle, CO, aquifer under different variable oxygen conditions. Overall uranium loss rates were 50À100 times slower than laboratory rates. After accounting for molecular diffusion through the sample holders, a reactive transport model using laboratory dissolution rates was able to predict overall uranium loss. The presence of biomass further retarded diffusion and oxidation rates. These results confirm the importance of diffusion in controlling in-aquifer U(IV) oxidation rates. Upon retrieval, uraninite was found to be free of U(VI), indicating dissolution occurred via oxidation and removal of surface atoms. Interaction of groundwater solutes such as Ca 2+ or silicate with uraninite surfaces also may retard in-aquifer U loss rates. These results indicate that the prolonged stability of U(IV) species in aquifers is strongly influenced by permeability, the presence of bacterial cells and cell exudates, and groundwater geochemistry.
a b s t r a c t BDTH 2 , 1,3-benzenediamidoethanethiol (common name) and closely related derivati... more a b s t r a c t BDTH 2 , 1,3-benzenediamidoethanethiol (common name) and closely related derivatives were specifically designed to become insoluble after the formation of linear, covalent bonds to aqueous mercury(II). BDTH 2 (IUPAC nomenclature, N,N 0 -bis(2-mercaptoethyl)isophthalamide) emerged as the preeminent reagent for the complete precipitation of mercury from water after several years of studies with a wide range of compounds having one, two, three, and four thiol groups. BDTH 2 does not become inactive through oxidation to disulfide and can be applied to mercury-containing water as acidic, basic, and ethanolic solutions. The BDT-Hg precipitate is extremely stable and leaches low-ppm levels of mercury only under extremely acidic and basic conditions. BDTH 2 is also effective in the aqueous precipitation of other soft, divalent metals, such as copper, cadmium, lead, and the main group elements, arsenic and selenium. The insolubility of the BDT-M compounds can be attributed to the presence of strong, non-polar, covalent M-S bonding within a water-insoluble organic framework. BDTH 2 has no known biological toxicity and is being sold as a nutritional supplement under the trade name OSR-1. This review describes the chemistry, precipitation, and leaching studies of BDTH 2 with mercury.
... Lexington, Kentucky Director: Dr. David A. Atwood, Professor of Chemistry Lexington, Kentucky... more ... Lexington, Kentucky Director: Dr. David A. Atwood, Professor of Chemistry Lexington, Kentucky 2010 ... Dr. Lovell, thanks for coming in so late in the game to see me to the finish line. ... contemporaries in the group, especially Eduardo Santillán-Jiménez and Christopher iii Page 10. ...
The use of benzene-1,3-diamidoethanethiol as a covalent surface coating for the prevention of met... more The use of benzene-1,3-diamidoethanethiol as a covalent surface coating for the prevention of metal leaching was demonstrated with several sulfide minerals including cinnabar (HgS), pyrite (FeS 2 ), chalcopyrite (CuFeS 2 ), covellite (CuS), galena (PbS), realgar (As 4 S 4 ) and sphalerite (ZnS). The minerals were coated with sufficient H 2 BDT to bind the surface metals in a 1:1 ratio. Leaching at pH 1, 3 and 7 was then conducted on both treated and untreated minerals. ICP and CVAFS (for mercury) analyses revealed that the coated minerals showed a dramatic reduction in metal leaching as compared to uncoated control samples. X-ray photoelectron spectroscopy indicated the formation of covalent bonds between the sulphur of the ligand and the metals from the minerals. days . All concentrations (25, 50, 75 and 100 mg/L) of SLS reduced sulfate production for the first 12 days. The 25-and 50-mg/L concentrations reduced sulfate formation over a 26-day period. However, after 12 days, the 75 mg SLS/L stimulated sulfur formation. Use of 100 mg SLS/L completely inhibited sulfate formation for the first 12 days with significant reductions for the remaining 14 days. The use of optimum, controlled doses of SLS is very important in this method.
Benzene-1,3-diamidoethanethiol (BDETH 2 ) is an exceptional precipitant for removing soft heavy m... more Benzene-1,3-diamidoethanethiol (BDETH 2 ) is an exceptional precipitant for removing soft heavy metals from water. The present work will detail the bonding arrangement of BDETH 2 to the metals Cd, Hg, and Pb, along with the full characterization data of the BDET−M compounds. It was found that the Hg compound has a linear S−M−S geometry. The characterization data consisted of Mp, EA, IR, Raman, MS, XANES, EXAFS, and solid-state multinuclear NMR. Krepps, M. K.; Atwood, D. A. Water Res. 2000, 34, 3005. (2) Matlock, M. M.; Howerton, B. S.; van Aelstyn, M. A.; Henke, K. R.; Atwood, D. A. Water Res. 2003, 37, 579. (3) Matlock, M. M.; Howerton, B. S.; van Aelstyn, M. A.; Nordstrom, F. L.; Atwood, D. A. EnViron. Sci. Technol. 2002, 36, 1636. (4) Matlock, M. M.; Howerton, B. S.; Atwood, D. A. Ind. Eng. Chem. Res. 2002, 41, 1579. (5) Matlock, M. M.; Howerton, B. S.; Robertson, J. D.; Atwood, D. A.
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