Heterogeneous reduction of U6+ by structural Fe2+ from theory and experiment

Skomurski, Frances N.; Ilton, Eugene S.; Engelhard, Mark H.; Arey, Bruce W.; Rosso, Kevin M.

doi:10.1016/j.gca.2011.08.006

Cited by 66 publications

(91 citation statements)

References 77 publications

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“…However, there is also evidence that direct reduction to U(IV) occurs and is accompanied by the release of Fe(II) into solution (31). The discrepancy in reduction mechanisms observed among studies is likely due to the fact that control on the extent of U(VI) reduction is wrought by the combination of two competing factors: the Fe 2+ /Fe 3+ ratio at the surface of iron minerals and the U coordination environment (32).…”

Section: Discussionmentioning

confidence: 99%

“…However, the data suggest that, in contrast to the biotic system, the fractionation generated by reduction processes persists in the product due to limited isotopic exchange between U(IV) and U(VI). Uranium in all three valences states [U(VI), U(V), and U(IV)] was reported to be sequestered at the surface or within the bulk of the Fe-bearing mineral (32,33), precluding such exchange. This sequestration is also true for aqueous Fe(II)-mediated A B Fig.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

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

137

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: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

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

137

153

View full text Add to dashboard Cite

show abstract

“…15 More generally, the availability of Fe(II) at the mineral-water interface, either as the result of adsorption or in surface sites, can impact the extent of U(VI) reduction, ranging from complete to partial reduction. 13,[16][17][18][19][20][21] Studies to date have provided U(VI) reduction rates for a wide range of solution conditions and mineral characteristics. However, a molecular-scale view of the process is lacking.…”

Section: +mentioning

confidence: 99%

U(VI) Sorption and Reduction Kinetics on the Magnetite (111) Surface

Singer

Chatman

Ilton

et al. 2012

Environ. Sci. Technol.

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continuous batch-flow conditions. We observed, in real-time and in situ, adsorption and reduction of U(VI) and subsequent growth of UO 2 nanoprecipitates using atomic force microscopy (AFM) and newly developed batch-flow U L III -edge grazing-incidence x-ray absorption spectroscopy near-edge structure (GI-XANES) spectroscopy. U(VI) reduction occurred with and without CO 3 present, and coincided with nucleation and growth of UO 2 particles. When Ca and CO 3 were both present no U(VI) reduction occurred and the U surface loading was lower. In situ batch-flow AFM data indicated that UO 2 particles achieved a maximum height of 4-5 nm after about 8 hours of exposure, however, aggregates continued to grow laterally after 8 hours reaching up to about 300 nm in diameter. The combination of techniques indicated that U uptake is divided into three-stages; (1) initial adsorption of U(VI),(2) reduction of U(VI) to UO 2 nanoprecipitates at surface-specific sites after 2-3 hours of exposure, and (3) completion of U(VI) reduction after ~6-8 hours. U(VI) reduction also corresponded to detectable increases in Fe released to solution and surface topography changes.Redox reactions are proposed that explicitly couple the reduction of U(VI) to enhanced release of Fe(II) from magnetite. Although counter intuitive, the proposed reaction stoichiometry was shown to be largely consistent with the experimental results. In addition to providing molecularscale details about U sorption on magnetite, this work also presents novel advances for collecting surface sensitive molecular-scale information in real-time under batch-flow conditions. 3

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“…Consequently, the Fe-based sequestration of U in the Fe-rich veins could also be related to the formation of magnetite, 10Å mica, and chlorite that are known for the surface catalyzed U-reduction (Moyes et al, 2000;Dodge et al, 2002;Ilton et al, 2004;Scott et al 2005;Skomurski et al, 2011). Chlorite has been observed to reduce U(VI) in the CO 3 -rich systems (Singer et al, 2009), analogous to the observed formation of calcite-rich veins.…”

Section: Fe-rich Veins -Natural Analogue For Gel Formation During Thementioning

confidence: 81%

“…( Moyes et al, 2000;Dodge et al, 2002;Ilton et al, 2004;Scott et al, 2005;Féron et al, 2008;Ferriss et al, 2009;Singer et al, 2009;Skomurski et al, 2011;Burger et al, 2013).…”

Section: Fe-rich Veins -Natural Analogue For Gel Formation During Theunclassified