Reduction of Uranium by Bacterial Products

The Old Rifle Mill Processing site at Rifle, CO, contains uranium contaminated groundwater. The presence of uranium is one of the major problems at Department of Energy legacy sites. There is an initiative for attenuation of uranium by the Department of Energy. Uranium undergoes oxidation/reduction reactions with the substances at the site. Uranium’s oxidation state determines its solubility and mobility in the aquifer. The oxidation reduction pathways at this site have mineralogical, microbial and geochemical components. Understanding the oxidation/reduction pathways of these components will allow for better predictions of the changes and movement of uranium. Sulfide [S2- ] and Ferrous [Fe2] ions are products of microbial activity. These ions can reduce uranium [U(VI)], but bicarbonate ions [HCO3-] in the aquifers slows down the reaction. However, we believe that organic matter in the environment enhances U(VI) reduction by Fe2+and S2- in the absence of microbes. To address this, U(VI) was mixed with Fe2+ or S2- in autoclaved biomass from Rifle and artificial groundwater for seven to eleven days. Aqueous samples from the vials will be analyzed for Uranium presence using ICP-MS [Inductively Coupled Plasma- Mass Spectrometry]. The biomass from each of the samples will be analyzed using XAS [X-Ray Absorption Spectroscopy] to determine the ionization state of Uranium. Based on the data, we can conclude that there is a significant decrease of the concentration of uranium from the reaction when the biomass was not sterilized. There were no differences within in the vials that had Fe2+ or S2-. The XAS data shows a mixture of U(IV) and U(VI) in the biomasss and more U(IV) in the biomass that was not sterilized. This suggests that the bacterial products alone is not completely responsible for the reduction of uranium