Characterization of radionuclides in uranium mine tailings with synchrotron-based hard X-ray microprobe techniques

Abstract of the technical paper presented at:
II International Conference on Radioecological Concentration Processes, Seville, Spain
November 6–9, 2016

Prepared by:
Steve Mihok, Karina Lange and Julie Brown
Canadian Nuclear Safety Commission

Antonio Lanzirotti
University of Chicago

Abstract:

The ultimate disposal of uranium mine tailings containing long-lived radionuclides requires information on their solid form and potential for environmental transfer over time. Synchrotron X-ray micro-spectroscopy techniques (SXRMS) are useful for addressing this issue as these methods are able to simultaneously characterize the micro-scale distribution of multiple elements, as well as their incorporation into and association with mineral phases.

A study was therefore initiated at the U.S. Department of Energy’s Advanced Photon Source to test the ability of SXRMS to characterize the distribution and forms of uranium in tailings, with some exploratory work also done on thorium and radium. Tailings at different depths were obtained from the JEB pit at the McClean Lake mine in Canada. Mapping of uranium distribution by µXRF (X-ray fluorescence) showed that uranium was spatially dispersed and not just localized in high uranium particulates. Initial characterization of mineralogy in localized particles with high uranium by µXRD (X-ray diffraction) did not identify the presence of distinct, crystalline uranium minerals. The µXRD analyses showed that tailings contained abundant illite, hematite and gypsum. Uranium L3 XANES results (µX-ray absorption near edge spectroscopy) indicated that uranium was dominantly in the hexavalent state.

Our preliminary work has shown that synchrotron applications can provide unique insights into the geochemistry and mineralogy of uranium in tailings. These findings can provide solid lines of evidence to inform long-term management strategies and to support regulatory licensing decisions on the decommissioning and remediation of operating and legacy uranium mines in Canada.

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