Oxidative Remobilization of Biogenic Uranium(IV) Precipitates: Effects of Iron(II) and pH

Authors

Lirong Zhong, Pacific Northwest National LaboratoryFollow
Chongxuan Liu, Pacific Northwest National LaboratoryFollow
John M. Zachara, Pacific Northwest National LaboratoryFollow
David Kennedy, Pacific Northwest National LaboratoryFollow
James E. Szecsody, Pacific Northwest National LaboratoryFollow
Brian Wood, Pacific Northwest National Laboratory

Date of this Version

2005

Citation

J. ENVIRON. QUAL., VOL. 34, SEPTEMBER–OCTOBER 2005; doi:10.2134/jeq2005.0057

Abstract

The oxidative remobilization of uranium from biogenic U(IV) precipitates was investigated in bioreduced sediment suspensions in contact with atmospheric O2 with an emphasis on the influence of Fe(II) and pH on the rate and extent of U release from the solid to the aqueous phase. The sediment was collected from the U.S. Department of Energy Field Research Center (FRC) site at Oak Ridge, Tennessee. Biogenic U(IV) precipitates and bioreduced sediment were generated through anaerobic incubation with a dissimilatory metal reducing bacterium Shewanella putrefaciens strain CN32. The oxidative remobilization of freshly prepared and 1-yr aged biogenic U(IV) was conducted in 0.1 mol/L NaNO₃ electrolyte with variable pH and Fe(II) concentrations. Biogenic U(IV)O_2(s) was released into the aqueous phase with the highest rate and extent at pH 4 and 9, while the U remobilization was the lowest at circumneutral pH. Increasing Fe(II) significantly decreased remobilization to the aqueous phase. From 70 to 100% of the U in the sediments used in all the tests was extractable at the experiment termination (41 d) with a bicarbonate solution (0.2 mol/L), indicating that biogenic U(IV) was oxidized regardless of Fe(II) concentration and pH. Sorption experiments and modeling calculations indicated that the inhibitive effect of Fe(II) on U(IV) oxidative remobilization was consistent with the Fe(III) oxide precipitation and U(VI) sorption to this secondary phase.