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Environment

Uranium’s Mobility In The Environment

Remediation strategies for mining and processing sites that assume uranium(IV) compounds are immobile may not work as expected

by Jyllian Kemsley
December 23, 2013 | A version of this story appeared in Volume 91, Issue 51

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Credit: Nat. Commun.
Colloidal threads rich in organic matter and iron, shown in this TEM image, can carry uranium out of soil and into water supplies.
TEM micrograph of colloids from uranium-contaminated soil.
Credit: Nat. Commun.
Colloidal threads rich in organic matter and iron, shown in this TEM image, can carry uranium out of soil and into water supplies.

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.

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