Reductive precipitation of uranium by Desulfovibrio desulfuricans: evaluation of cocontaminant effects and selective removal

The sulfate reducing bacterium, Desulfovibrio desulfuricans can initiate uranium precipitation from solution via direct enzymatic reduction. Additionally, separation of heavy metals from solution can occur via indirect sulfide-mediated precipitation. This study was conducted to evaluate the influence of anions (sulfate, nitrate), heavy metals (zinc, nickel and copper) and organics (acetate, malonate, oxalate and citrate) on the enzymatic reduction of U(VI) by this bacterium. Furthermore, methods were evaluated to selectively precipitate uranium or heavy metals from test solutions. Selective precipitation can significantly lower disposal costs by reducing the volume of mixed-waste sludge produced during treatment. Results indicated that sulfate/nitrate concentrations up to 5000 mg/l did not appreciably interfere with U(VI) reduction, however, anion levels greater than 10,000 mg/l significantly slowed the rate of U(VI) reduction. U(VI) was readily reduced by the bacterium when 10 mg/l of Zn or Ni was present, but Cu inhibited uranium reduction. U(VI) was reduced rapidly in the presence of a monodentate organic ligand (acetate) whereas reduction was slower in the presence of multidentate ligands. Initial results from selective precipitation experiments indicated two potential treatment approaches for isolating either uranium or the test heavy metals using D. desulfuricans. The first method involved free energy differences for U(VI) and sulfate reduction, while the second method involved complexation of reduced uranium by a chelator during metal–sulfide precipitation.