CORROSION OF BIOGENIC URANINITE: MOLECULAR- AND INTERMEDIATE-SCALE MEASUREMENTS

Corrosion is the dominant process by which uranium will be released to ground water from uraninite formed during bioreduction. Quantitative knowledge of the rates, mechanisms, and factors governing this surface-mediated process in ground water are fundamental to developing effective remediation strategies. Uraninite corrosion exhibits differing mechanistic pathways depending upon dissolved inorganic carbonate, oxygen, and trace metal composition. A range of bicarbonate and DO concentrations are found in groundwater at contaminated U.S. Department of Energy (DOE) sites where stimulated uranium reduction has been considered. Laboratory-measured mineral dissolution rates often disagree with those occurring in the environment, necessitating direct measurement under field conditions. Factors controlling the rates of biogenic uraninite dissolution in laboratory investigations will be discussed. These will be compared to in-situ biogenic uraninite corrosion experiments at DOE’s Integrated Field Research Challenge (IFRC) site at Rifle, Colorado, designed to probe the rates and mechanisms of biogenic uraninite corrosion in ground water on time scales of weeks to years over a range of DO and carbonate concentrations. We will describe innovative permeable sampling cells used to deploy biogenic uraninite in wells at the Rifle IFRC site and present preliminary results. It is anticipated that this work will provide new and quantitative information regarding uraninite corrosion rates and mechanisms in alluvial aquifers.