NSLS-II Seminar

The DOE is steward to a large legacy of subsurface uranium contamination from research and weapons production activities. But despite extensive laboratory studies of the chemical and physical behavior of U, efforts to recover -- or even to contain -- this U have not been very successful. This is largely due to the complexities of often-competing chemical, physical and biological processes, combined with heterogeneities from the meter to the submicron scale as well as seasonal and climatological variations.
Understanding this complexity requires, first, identification of a system with sufficient complexity but well-understood boundaries, and second, application of a broad suite of analytical tools. I will describe a natural U-containing sediment/water system that offers insights into long-term U behavior and hope for future remediation and recovery efforts. Examination of this system employs a range of synchrotron imaging and spectroscopic techniques, to explore molecular-scale processes involving U, Fe, Mn, S, P, Th and organic components: microbeam x-ray fluorescence mapping and tomography of elemental distribution and associations, microbeam and bulk x-ray absorption spectroscopy to identify speciation and oxidation state, lower-energy XAS, novel use of M-edge and dual-energy XAS, and IR microspectroscopy. These are combined with isotopic studies (U, Th, S, and C systems), which can be used to track chemical and physical processes back in time.