Identifying calcium-containing mineral species in the JEB Tailings Management Facility at McClean Lake, Saskatchewan

• Geochemical model suggests precipitation of CaCO3 controls [HCO3−] in pore water.
• Synchrotron-based techniques used to identify Ca-bearing species in tailings.
• X-ray microprobe and μ-XANES identified Ca sulphate and carbonate minerals.
• Gypsum, anhydrite, calcite, aragonite, and dolomite were identified.

The JEB Tailings Management Facility (TMF) is central to reducing the environmental impact of the McClean Lake uranium mill facility that is operated by AREVA Resources Canada. This facility has been designed around the idea that elements of concern (e.g., U, As, Ni, Se, Mo) will be controlled through equilibrium with precipitants. Confirming the presence of calcium-containing carbonates in the JEB TMF is the first step in determining if gypsum (CaSO4·2H2O) controls the concentration of HCO3− (aq), limiting the formation of soluble uranyl bicarbonate complexes. A combination of X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), and microprobe X-ray fluorescence (XRF) mapping was used to analyze a series of tailings samples from the JEB TMF. Calcium carbonate in the form of calcite (CaCO3), aragonite (CaCO3), and dolomite (CaMg(CO3)2) were identified by analysing Ca K-edge μ-XANES spectra coupled with microprobe XRF mapping. This is the first observation of these phases in the JEB TMF. The combination of μ-XANES and XRF mapping provided a greater sensitivity to low concentration calcium species compared to the other techniques used, which were only sensitive to the major species present (e.g., gypsum).

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