Experimentally Determined Uranium Isotope Fractionation During Reduction of Hexavalent U by Bacteria and Zero Valent Iron

Rademacher, Laura K.; Lundstrom, Craig C.; Johnson, Thomas M.; Sanford, Robert A.; Zhao, J; Zhang, Zhaofeng

doi:10.1021/es0604360

Cited by 60 publications

(64 citation statements)

References 44 publications

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“…The lack of isotope fractionation for sulfide-or organic-mediated reduction may be attributed to direct two-electron transfer from organic matter or S 2− to U(VI), resulting in the sequestration of U(IV) and a strongly unidirectional reaction with insignificant isotope fractionation. The same lack of fractionation was observed in two other studies using reducing agents that operate via twoelectron transfer: zerovalent iron by which Fe(0) transfers two electrons to U(VI) to form Fe(II) and U(IV) (34) and zerovalent zinc by which Zn 2+ and U(IV) are produced (9).…”

Section: Discussionsupporting

confidence: 71%

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: Discussionsupporting

confidence: 71%

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

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“…At the same time, the sulfate and sulfide concentrations in M-24 also dropped, but the decrease in sulfate was not as pronounced as in M-21. The small fractionation between the δ 34 S values of sulfate and sulfide (to <2‰) in these wells during this time period is a clear indication of sulfate limitation (17,21). This is also the time period during which the U(VI) concentrations rebounded to near background levels (Figure 2h).…”

Section: Resultsmentioning

confidence: 72%

“…Recent studies have also demonstrated enrichment of 238 U relative to 235 U in residual U(VI) during microbial uranium reduction (21). However, the use of sulfur isotopes as indicators of bioremediation progress has been limited to laboratory experiments and nonamended field-scale studies (22).…”

Section: Introductionmentioning

confidence: 99%

Sulfur Isotopes as Indicators of Amended Bacterial Sulfate Reduction Processes Influencing Field Scale Uranium Bioremediation

Druhan

Conrad

Williams

et al. 2008

Environ. Sci. Technol.

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Aqueous uranium (U(VI)) concentrations in a contaminated aquifer in Rifle Colorado have been successfully lowered through electron donor amended bioreduction. Samples collected during the acetate amendment experiment were analyzed for aqueous concentrations of Fe(II), sulfate, sulfide, acetate, U(VI), and δ34S of sulfate and sulfide to explore the utility of sulfur isotopes as indicators of in situ acetate amended sulfate and uranium bioreduction processes. Enrichment of up to 7‰ in δ34S of sulfate in down-gradient monitoring wells indicates a transition to elevated bacterial sulfate reduction. A depletion in Fe(II), sulfate, and sulfide concentrations at the height of sulfate reduction, along with an increase in the δ34S of sulfide to levels approaching the δ34S values of sulfate, indicates sulfate limited conditions concurrent with a rebound in U(VI) concentrations. Upon cessation of acetate amendment, sulfate and sulfide concentrations increased, while δ34S values of sulfide returned to less than −20‰ and sulfate δ34S decreased to near-background values, indicating lower levels of sulfate reduction accompanied by a corresponding drop in U(VI). Results indicate a transition between electron donor and sulfate-limited conditions at the height of sulfate reduction and suggest stability of biogenic FeS precipitates following the end of acetate amendment.

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“…Rademacher et al [35] investigated the process of uranium(VI) removal by Fe 0 by means of isotope fractionation and reported that "Fe 0 reduced U VI , but the reaction failed to induce an analytically significant isotopic fractionation". This obviously questionable conclusion was consistent with the MTW concept and the results of Gu et al [36] Jia et al [12] investigated the adsorption of triazoles by iron hydroxides/oxides (Fe 2 O 3 , ferrihydrites) and elemental iron.…”

Section: Experimental Observationsmentioning

confidence: 99%

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

Noubactep¹

2008

TOENVIRSJ

110

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Abstract:The mechanism of aqueous contaminant removal by elemental iron (Fe 0 ) materials (e.g., in Fe 0 -H 2 O systems) has been largely discussed in the "iron technology" literature. Two major removal mechanisms are usually discussed: (i) contaminant adsorption onto Fe 0 oxidation products, and (ii) contaminant reduction by Fe 0 , Fe II or H/H 2 . However, a closer inspection of the chemistry of the Fe 0 -H 2 O system reveals that co-precipitation could be the primary removal mechanism. The plausibility of contaminant co-precipitation with iron corrosion products as independent contaminant removal mechanism is discussed here. It shows that the current concept does not take into account that the corrosion product generation is a dynamic process in the course of which contaminants are entrapped in the matrix of iron hydroxides. It is recalled that contaminant co-precipitation with iron hydroxides/oxides is an unspecific removal mechanism. Contaminant co-precipitation as primary removal mechanism is compatible with subsequent reduction and explains why redoxinsensitive species are quantitatively removed. Adsorption and co-precipitation precede reduction and abiotic reduction, when it takes place, occurs independently by a direct (electrons from Fe 0 ) or an indirect (electrons from Fe II /H 2 ) mechanism.

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Experimentally Determined Uranium Isotope Fractionation During Reduction of Hexavalent U by Bacteria and Zero Valent Iron

Cited by 60 publications

References 44 publications

Uranium isotopes fingerprint biotic reduction

Uranium isotopes fingerprint biotic reduction

Sulfur Isotopes as Indicators of Amended Bacterial Sulfate Reduction Processes Influencing Field Scale Uranium Bioremediation

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

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