Mineralogical characterization of arsenic, iron, and nickel in uranium mine tailings using XAS and EMPA

In northern Saskatchewan, Canada, high-grade uranium ores and the resulting tailings can contain high levels of arsenic (As), iron (Fe), and nickel (Ni). An environmental concern in the uranium mining industry is the long-term stabilization of these elements of concern (EOCs) within tailings management facilities thereby mitigating their transfer to the surrounding groundwater. Characterization of these As-, Fe- and Ni-bearing minerals and complexes must be carried out to evaluate their solubility and long-term stability within the tailings mass. Synchrotron-based bulk x-ray absorption spectroscopy (XAS) has been used to study the speciation of these EOCs in mine tailing samples obtained from the Deilmann Tailings Management Facility (DTMF) at Key Lake, Saskatchewan. Electron microprobe analysis (EMPA) and synchrotron-based micro-focussing x-ray fluorescence mapping and absorption spectroscopy (μXRF; μXAS ) have also been employed to study spatial distribution and speciation at the micron scale. Comparisons of K-edge absorption spectra of tailings samples and reference compounds indicate the dominant oxidation states of As, Fe, and Ni in the mine tailings samples are +5, +3, and +2, respectively, largely reflecting their deposition in an oxidized environment and complexation within stable oxic phases. Backscattered electron (BSE) images of the tailings from the electron microprobe indicate the presence of gypsum/lime nodules surrounded by metallic rims mainly consisting of As, Fe, and Ni. μXRF elemental mapping confirms these EPMA results. μXAS collected within the metal-bearing rims indicates As and Fe is present mainly in the +5 and +3 oxidation state, respectively. (author)