Uranium contamination is a major concern at Department of Energy sites and decommissioned mining and ore processing facilities around the U.S. Migration of uranium has contaminated ground water in several locations, and the threat remains for further contamination unless costly measures are taken to isolate the contaminates and stop their spread.

A major obstacle to efficient clean-up of uranium contamination is the great depth and extensive areas over which they are dispersed. Subsurface remediation techniques must therefore take advantage of naturally occurring, environmentally stable agents to stop the spread.

Manganese (Mn) oxides produced by bacteria have been shown to naturally remove large amounts of heavy metal contaminants from water. These oxides commonly form coatings on mineral grains within soils and streambeds. Now, researchers are one step closer to understanding how this process may be harnessed to clean up uranium contamination. Using two complementary synchrotron-based techniques (x-ray absorption spectroscopy and in-situ x-ray diffraction), collaborators from SSRL and Oregon Health and Science University have characterized how bacteriogenic Mn oxides sequester the highly soluble hexavalent uranium (U(VI)).

The collaborators found that in high concentrations, as U(VI) is incorporated into Mn oxides, a stable mineral is formed within which the U(VI) is trapped inside a three-dimensional matrix of "tunnels." Because the U(VI) is structurally bound within the bacteriogenic oxides, much larger amounts of contaminant can be removed from water than with techniques relying on sorption onto particle surfaces. This research could lead to improved techniques suitable for long-term stabilization of subsurface U(VI) contamination.

To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/ research/highlights_archive/mn_biooxides.html

Villalobos M., Bargar J. R., and Sposito G. (2005a) Mechanisms of Pb(II) sorption on a biogenic maganese oxide. Environmental Science and Technology 39, 569-576.

Webb S. M., Fuller C. C., Tebo B. M., and Bargar J. R. (2006) Determination of uranyl incorporation into biogenic manganese oxides using x-ray absorption spectroscopy and scattering. Environmental Science and Technology 40, 771-777.