Anaerobic oxidation of U(IV) may proceed by different pathways: abiotic, direct (enzymatic) biotic oxidation, or coupled biotic-abiotic molecular mechanisms (e.g., U(IV) oxidation mediated by biogenic Fe(III) oxides or oxyhydroxides). To elucidate the key biotic and abiotic mechanisms underlying U(IV) oxidation, flow-through column experiments were carried out with and without addition of Thiobacillus denitrificans. This bacterium contains membrane-associated c-type cytochormes that are thought to be the primary biochemical pathway for anaerobic, nitrate-dependent U(IV) and Fe(II) oxidation. Precipitated solids collected before and after reaction were characterized by synchrotron X-ray absorption spectroscopy at the U L-III edge. Information from XAS together with the solution results allow examination of oxidation mechanisms and coupled redox process, and quantification of the rates of U release. Reactive transport modeling including equilibrium (aqueous complexation, sorption) and kinetic reactions are used to link molecular-scale mechanisms to macroscopic-scale observations.

Mechanisms and kinetics of anaerobic abiotic and nitrate-dependent bacterial U(IV) oxidation

243rd National Meeting (2012)

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