The effect of U(VI) bioreduction kinetics on subsequent reoxidation of biogenic U(IV)

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• 作者：John M. Senko ; Shelly D. Kelly ; Alice C. Dohnalkova ; Jeffrey T. McDonough ; Kenneth M. Kemner ; William D. Burgos
• 关键词：intertidal ; saltmarsh ; mangrove ; foraminifera ; taphonomy ; infauna ; fossil assemblage
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2007
• 出版时间：1 October 2007
• 年：2007
• 卷：71
• 期：19
• 页码：4644-4654
• 全文大小：678 K

文摘

Microbially mediated in situ reduction of soluble U(VI) to insoluble U(IV) (as UO₂) has been proposed as a means of preventing the migration of that radionuclide with groundwater, but preventing the oxidative resolubilization of U has proven difficult. We hypothesized that relatively slow rates of U(VI) bioreduction would yield larger UO₂ precipitates that would be more resistant to oxidation than those produced by rapid U(VI) bioreduction. We manipulated U(VI) bioreduction rates by varying the density of Shewanella putrefaciens CN32 added to U(VI) containing solutions with lactate as an electron donor. Characterization of biogenic UO₂ particles by extended X-ray absorption fine-structure spectroscopy and transmission electron microscopy revealed that UO₂ nanoparticles formed by relatively slow rates of U(VI) reduction were larger and more highly aggregated than those formed by relatively rapid U(VI) reduction. UO₂ particles formed at various rates were incubated under a variety of abiotically and biologically oxidizing conditions. In all cases, UO₂ that was formed by relatively slow U(VI) reduction was oxidized at a slower rate and to a lesser extent than UO₂ formed by relatively rapid U(VI) bioreduction, suggesting that the stability of UO₂ in situ may be enhanced by stimulation of relatively slow rates of U(VI) reduction.