HR: 1340h
AN: B33C-1433    [Abstracts]
TI: Structural Chemistry of Cation-Reacted Bacteriogenic UO2
AU: * Schofield, E
EM: eleanors@slac.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, United States
AU: Bargar, J
EM: bargar@slac.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, United States
AU: Bernier-Latmani, R
EM: rizlan.bernier-latmani@epfl.ch
AU: Sharp, J
EM: jonathan.sharp@epfl.ch
AF: Ecole Polytechnique Federale de Lausanne, CH 1 644 Station 6, Lausanne, Ch-1015, Switzerland
AU: Veeramani, H
EM: harish.veeramani@epfl.ch
AF: Ecole Polytechnique Federale de Lausanne, CH 1 644 Station 6, Lausanne, Ch-1015, Switzerland
AU: Clark, D
EM: dlclark@lanl.gov
AF: Los Alamos National Laboratory, MS-G756 ADSMS, Los Alamos, NM 87545, United States
AU: Conradson, S
EM: conradson@lanl.gov
AF: Los Alamos National Laboratory, MS-G756 ADSMS, Los Alamos, NM 87545, United States
AU: Mehta, A
EM: mehta@slac.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, United States
AB: The chemical stability of bacteriogenic uraninite, "UO2", is one of the seminal issues governing its success as an in-situ immobilization strategy in contaminated subsurface locations. Little detail is known about the structure and reactivity of this material, but based on comparison to its closest abiotic analog, UO2+x (0 < x < 0.25), we expect that it is complex and disordered, likely to exhibit non-stoichiometry, and capable of structurally incorporating common ground water cations and U(VI). Such fundamental changes in mineralogy are expected to substantially impact its stability in ground water. In this study, the product of microbial U(VI) reduction under varying conditions of pH, carbonate and divalent cation concentration was investigated. To facilitate x-ray scattering and oxidation kinetics measurements, cleaning methods were investigated to separate the biooxide and organic components. The local and long-range atomic and nano-scale structures of the wet oxides have been measured using EXAFS, WAXS, XPS and TEM. The lattice parameter of the nanoparticulate phase is seen to be consistent with bulk UO2. The first oxygen shell is distorted, indicating a nonstoichiometric composition. A significant change in the lattice parameter and local structure is produced when bacteriogenic UO2 is reacted with divalent cations and NaOH. These findings suggest that bacteriogenic UO2 and its reactivity can be modified by groundwater composition.
DE: 0416 Biogeophysics
DE: 0418 Bioremediation
DE: 0419 Biomineralization
SC: Biogeosciences [B]
MN: 2007 Fall Meeting