Reoxidation of Bioreduced Uranium Under Reducing Conditions

Uranium (Nuclear Minerals) / Exploration, Mining, Marketing, & Acquisitions

Date posted: 11/20/09

Uranium mining and processing for nuclear weapons and fuel have left thousands of sites with toxic levels of this actinide in soil and ground water1. An emerging strategy for remediating such environments involves using organic carbon to promote microbially-mediated reduction and precipitation of insoluble U(IV) minerals2-4. Although previous U bioreduction studies have shown promising results, they were of short duration (up to a few months). Our longer-term (20 months) laboratory study using historically contaminated sediment has alarmingly shown that microbial reduction of U was transient even under reducing (methanogenic) conditions. Uranium was reductively immobilized during the first 100 days, but later (150 to 600 days) reoxidized and mobilized, although a microbial community capable of reducing U(VI) remained through the end of the experiment. The formation of Ca2UO2(CO3)3 complexes5 (caused by the elevated carbonate concentration from microbial respiration, etc.