UO2 stability determines the success of bioremediation of uranium involving reduction of U(VI) to U(IV). When reducing conditions are no longer maintained, Biological Mn redox cycling may significantly affect the oxidation of UO2 and remobilization of uranium. As an intermediate in Mn biogeochemical cycling, soluble Mn(III) has recently been found as an important environmental oxidant at the oxic-anoxic interface in the subsurface environment. This study quantified the kinetics of oxidative UO2 dissolution by soluble Mn(III) stabilized by pyrophosphate. Soluble Mn(III) induced rapid UO2 dissolution at a rate higher than by a comparable concentration of dissolved O2. Mn(III) could directly oxidize UO2 without involving MnO2, and the expected 2:1 reaction stoichiometry was observed. The reactivity of Mn(III) in oxidizing UO2 was higher at lower pyrophosphate:Mn(III) ratios and lower pH. Rapid Mn(III) disproportionation occurred at pH 9.0, and UO2 oxidation was driven by both MnO2 and soluble Mn(III). Self-consistent kinetic models were derived with excellent fits of the experimental results. The quantification of the reaction kinetics of oxidative UO2 dissolution by soluble Mn(III) may help interpreting the enhanced UO2 oxidation mediated by biological Mn redox cycling.

Kinetics of oxidative UO<sub>2</sub> dissolution by soluble Mn(III)

246th National Meeting (2013)

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Kinetics of oxidative UO2 dissolution by soluble Mn(III)

Kinetics of oxidative UO₂ dissolution by soluble Mn(III)