Effects of Microbial Fe(III) Reduction on the Sorption of Cs and Sr on Biotite and Chlorite

Microbially mediated reduction of Fe(III) in chlorite and biotite by Shewanella oneidensis MR-1 leads to a significant reduction in sorption of both Cs and Sr compared to the abiotic systems. As seen in previous studies, biotite is a more efficient sorbent than chlorite. Reduction of the mineral-associated Fe(III) causes increased dissolution of both minerals and reduces the sites available for Cs and Sr sorption. As this dissolution progresses it causes desorption of Cs and Sr from chlorite, but not biotite. Subsequent exposure to air increases sorption due to precipitation of secondary Fe(III) oxyhydroxide minerals derived from the Fe(II) released by bio-reduction. In contrast to successful bioremediation of redox active elements, this study suggests that microbial Fe(III) reduction could enhance the migration of Cs and Sr through phyllosilicate-dominated strata.