Uranium Biosequestration and Biosequestered Uranium Re-oxidation Multicomponent Transport Modeling

Abstract:

This study aims to characterize and quantify biosequestration of uranium and biosequestered uranium re-oxidation through use of a multicomponent transport model. Column experiment were conducted with aquifer sediments and groundwater from an alluvial aquifer at the Monument Valley UMTRA site, which is a former ore processing facility. Eventually ore processing activities caused uranium and co-contaminants such as nitrate and sulfate to leach and form a groundwater contaminant plume. Ethanol was chosen as an electron donor to stimulate indigenous bacteria to sequester uranium. Significant decreases in uranium, nitrate, and sulfate were observed during the experiment. Furthermore, iron and manganese concentrations dramatically increased during the ethanol injection. Rebound in concentrations were observed for uranium, sulfate, and nitrate after electron donor injection ceased. Moreover, sequestered uranium and sulfate were re-oxidized during the injection of electron-donor free groundwater. The multicomponent transport model is used to characterize and delineate interdependency of the biosequestration and re-oxidation reactions under variable chemical conditions. The reaction network includes uranium sorption to the aquifer sediments, mineral precipitation and dissolution of iron and manganese, and secondary redox reactions for the re-oxidation of the reduced components. The simulations results are compared with the experimental results, and forward simulations were conducted for different scenarios.