In situ removal of uranium from ground water

A bioremediation concept has been developed to remove low concentrations of uranium from ground water. We selected the Tuba City UMTRA mill tailings site in Arizona and studied the ground water/host rock system and the biochemical reactions to precipitate and immobilize uranium in situ in the form of uraninite (UO 2 ). Besides uranium, the ground water is contaminated with nitrate and sulfate. The sandstone contains small amounts of reducible elements such as Mn(IV) and Fe(III). Indigenous bacteria were identified capable of catalyzing bio-chemical reactions in the sequence dissolved O 2 , NO 3 − , Mn(IV), U(VI), Fe(III), SO 4 2− . The reactions have been studied in the laboratory in column experiments. Final uranium concentrations of < 15 µg/L (significantly less than the U.S.-EPA ground water protection standard of 44 µg/L) were reached after a few weeks at 16°C. Data are presented necessary to understand and to design the biochemical processes and their effectiveness in a given hydrogeological environment.