Uranium is one of the most common and problematic contaminants at legacy Department of Energy sites. Groundwater contamination is particularly problematic because it occurs at depth, is present in large volumes, and cannot be easily accessed for clean-up. One method of remediation being investigated is the bioreduction of soluble U(VI) to insoluble U(IV) complexes through the in-situ stimulation of metal-reducing bacteria. Understanding the structure of these uranium complexes can help us determine their fate and stability in groundwater and map out the biological process of uranium reduction by metal-reducing bacteria. In this study, we used the synchrotron-based techniques, X-ray absorption spectroscopy (XAS) and X-ray microscopy (XRM), to determine the geometric structure of the uranium species found in the contaminated sediments at Old Rifle, Colorado. From our XRM images, uranium is shown to be highly associated with iron and sulfur, two species found in naturally reduced zones (NRZ) at the Old Rifle site. XAS data show that reduced U(IV) is bounded to oxygen, forming stable uraninite (UO2) complexes. More analysis is needed for a complete picture of the structure of these uranium complexes.


Environmental Chemistry | Environmental Monitoring | Physical Chemistry


John Bargar

Lab site

SLAC National Accelerator Laboratory (SLAC)

Funding Acknowledgement

This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation.



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