Uranium’s Mobility In The Environment

The primary approach to cleaning up uranium-contaminated sites from mining and processing ore for nuclear fuel has been to reduce U⁶⁺ to U⁴⁺. The latter species was thought to be stable and immobile in the environment as crystalline UO₂. New research shows, however, that U⁴⁺ may not be as immobile as believed. In recent years, scientists have found that microbe-induced reducing conditions yield U⁴⁺ bound in amorphous aggregates rather than in UO₂. By studying contaminated wetlands in France, a group led by Rizlan Bernier-Latmani of the Swiss Federal Institute of Technology, Lausanne, has found that U⁴⁺ bound in aggregates can be scavenged by colloids rich in organic matter and iron. Groundwater may then carry the colloids out of the soil and into nearby waterways (Nat. Commun. 2013, DOI: 10.1038/ncomms3942). The results of the study “have broad relevance to a variety of environments where uranium redox cycling occurs through natural processes as well as those deliberately induced as part of remedial efforts,” says Kenneth H. Williams, chief scientist of a Department of Energy field station at a uranium-contaminated aquifer in Rifle, Colo.