HR: 0830h
AN: B41D-0922    [PDF]
TI: Impact of Calcium on Bacterial Reduction of U(VI) Under Advective Flow
AU: * Neiss, J
EM: jneiss@stanford.edu
AF: Department of Geologic and Environmental Studies, Stanford University, Stanford, CA 94305 United States
AU: Nico, P S
EM: nico@chem.csustan.edu
AF: Department of Chemistry, California State University, Stanislaus, Turlock, CA 95382
AU: Stewart, B D
EM: stewartb@stanford.edu
AF: Department of Geologic and Environmental Studies, Stanford University, Stanford, CA 94305 United States
AU: Fendorf, S
EM: fendorf@stanford.edu
AF: Department of Geologic and Environmental Studies, Stanford University, Stanford, CA 94305 United States
AB: Due to mining and nuclear-production activities, uranium is now an environmental contaminant of great concern, the hazard of which can be diminished through reduction of the oxidized species, uranyl, to reduced phases such as uraninite. Recent evidence, however, illustrates the importance of uranyl speciation on the extent of reduction. In the presence of calcium, a Ca-UO2-CO3 complex is the dominant aqueous species, greatly limiting abiotic and biotic reduction of uranium. This species is, in fact, the most stable form of U(VI) in waters equilibrated with atmospheric carbon dioxide levels and calcium concentrations $>$ 0.4 mM from pH 5 to 8. Here we explore the impact of calcium on uranium reduction rates and the concomitant biomineralization products of uranium and hydrous ferric oxide under dynamic flow conditions by a metal reducing bacterium, Shewanella putrefaciens. Using x-ray adsorption near edge structure (XANES) spectroscopy, we confirm the complete reduction of uranyl to the precipitated mineral uraninite in systems absent of calcium. While in contrast, minimal reduction transpires upon introduction of millimolar calcium concentration. Thus, calcium concentrations will have profound effects on bacterial reduction, and hence mobility, of uranium within surface and subsurface environments.
DE: 4805 Biogeochemical cycles (1615)
DE: 4825 Geochemistry
DE: 4840 Microbiology
DE: 4851 Oxidation/reduction reactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting