Kinetics of Uranium(VI) Reduction by Hydrogen Sulfide in Anoxic Aqueous Systems

Hua, Bin; Xu, Huifang; Terry, Jeff; Deng, Baolin

doi:10.1021/es051804n

Cited by 133 publications

(146 citation statements)

References 30 publications

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“…Aqueous sulfide U(VI) reduction experiments were conducted in duplicate using serum bottles with butyl rubber septa and anoxic solutions as previously described (38). All bottles and solutions were thoroughly purged with ultra high purity He before initiation of the experiments to remove O 2 .…”

Section: Methodsmentioning

confidence: 99%

Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

136

153

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Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

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Section: Methodsmentioning

confidence: 99%

Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

136

153

View full text Add to dashboard Cite

show abstract

“…[22,23] Uranium can also be reduced by precipitated or biogenically produced Fe-sulfide and by aqueous sulfide under anoxic conditions. [15,[24][25][26][27] Enzymatic reduction of U VI has been observed by iron and sulfate reducing bacteria. [28,29] Although both As III and As V can be adsorbed to iron minerals, As can be released, not only by desorption, but by microbial reduction of iron mineral phases, resulting in mineral dissolution.…”

Section: Introductionmentioning

confidence: 99%

Effect of biogeochemical redox processes on the fate and transport of As and U at an abandoned uranium mine site: an X-ray absorption spectroscopy study

Troyer

Stone

2014

Environ. Chem.

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Environmental context. Uranium and arsenic, two elements of human health concern, are commonly found at sites of uranium mining, but little is known about processes influencing their environmental behaviour. Here we focus on understanding the chemical and physical processes controlling uranium and arsenic transport at an abandoned uranium mine. We find that the use of sedimentation ponds limits the mobility of uranium; however, pond conditions at our site resulted in arsenic mobilisation. Our findings will help optimise restoration strategies for mine tailings.Abstract. Although As can occur in U ore at concentrations up to 10 wt-%, the fate and transport of both U and As at U mine tailings have not been previously investigated at a watershed scale. The major objective of this study was to determine primary chemical and physical processes contributing to transport of both U and As to a down gradient watershed at an abandoned U mine site in South Dakota. Uranium is primarily transported by erosion at the site, based on decreasing concentrations in sediment with distance from the tailings. Sequential extractions and U X-ray absorption near-edge fine structure (XANES) fitting indicate that U is immobilised in a near-source sedimentation pond both by prevention of sediment transport and by reduction of U VI to U IV . In contrast to U, subsequent release of As to the watershed takes place from the pond partially due to reductive dissolution of Fe oxy(hydr)oxides. However, As is immobilised by adsorption to clays and Fe oxy(hydr)oxides in oxic zones and by formation of As-sulfide mineral phases in anoxic zones down gradient, indicated by sequential extractions and As XANES fitting. This study indicates that As should be considered during restoration of uranium mine sites in order to prevent transport.

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“…The solubility of tetravalent uranium species is lower by several orders of magnitude and usually controlled by uraninite (UO 2 ). In anoxic aqueous systems, reduction of U(VI) to UO 2 can occur either chemically, e.g., by hydrogen sulfide (Hua et al 2006), by surface catalyzed reactions involving coadsorption of Fe(II) and U(VI) on iron(III) oxides (Behrends and Van Cappellen 2005;Fredrickson et al 2000;Jeon et al 2005), or microbially, i.e., catalyzed by enzymes.…”

Section: Introductionmentioning

confidence: 99%

“…While the above investigations were carried out at neutral pH and fixed carbonate concentrations, two additional studies demonstrated the inhibition of U(VI) bioreduction by dissolved inorganic carbon (DIC). Investigating the kinetics of abiotic U(VI) reduction by hydrogen sulfide in anoxic aqueous systems, Hua et al (2006) reported that the reduction was almost completely inhibited at the following conditions: [DIC] ≥ 15 mM at pH 6.89, [DIC] ≥ 4 mM at pH 8.01, and [DIC] ≥ 2 mM at pH 9.06. These combinations of DIC concentrations and pH suggest an anti-correlation between the concentration of U(VI)-carbonate complexes and reduction rate.…”

Section: Introductionmentioning

confidence: 99%