PNNL

Abstract

An attractive remediation strategy for the removal of highly soluble U(VI) from groundwater is microbial reduction of soluble U(VI) to U(IV) as insoluble uraninite. The feasibility of this remediation strategy depends on the rate and extent of microbial reduction of U(VI) in the presence of ions commonly found in groundwater that can form complexes with uranyl. Recently, Ca in solutions with U(VI) has been shown to inhibit microbial reduction of U(VI). Indirect evidence supports the formation of a Ca-UO2-CO3 complex that may be responsible for the limited microbial reduction of U(VI) in the presence of Ca, but direct evidence for the formation of a Ca-UO2-CO3 complex is needed for verification. X-ray absorption fine-structure measurements of solutions containing 50*M U(VI) and 30mM bicarbonate, with and without 5mM Ca, were made to determine whether a Ca-UO2-CO3 complex was present. These results are discussed.