Identification of calcium carbonate in uranium mine tailings by X-ray spectroscopy and X-ray diffraction

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The natural resource sector is an important area of Canada's economy. Of the many natural resources that are mined, uranium mining is centred in northern Saskatchewan. The uranium ore bodies contain many mineral phases beside uranium oxide that need to be disposed of in a responsible fashion. Solid mining waste can be placed in a tailings management facility, which is designed to contain the waste elements and limit interaction with the external environment. To understand how a tailings facility will behave throughout the lifetime of the mining operations that feed the tailings management facility, and after the site has been decommissioned, it is important to understand the chemistry of the tailings and how they change with time. The JEB tailings management facility located at the McClean Lake operation contains many metals from the separation of uranium oxide, including iron (Fe), arsenic (As), molybdenum (Mo), and uranium (U), among other elements. In this continued research collaboration, we will study samples from the tailings facility to develop a better understanding of the calcium (Ca)-bearing species found in the tailings. By comparing the concentration of dissolved species in pore water samples and analysis of the solids in the tailings, coupled with modelling of the behaviour of the tailings, it has been proposed that uranium oxide solids could become soluble in the tailings if they react with carbonate ions to produce soluble uranyl-carbonate complexes in the pore water. However, carbonate ions could also react with calcium sulphate (gypsum) and produce calcium carbonate, which would precipitate under the conditions of the tailings facility (near neutral pH). Determining if calcium carbonate (calcite) is present in the tailings is an important step to understanding how to control (and decrease) the presence of soluble uranyl species in the pore water. It is anticipated that both amorphous and crystalline calcium-containing compounds will be present in the tailings, and that calcite, if present, will be found in trace quantities. In this work, X-ray absorption spectroscopy, X-ray microprobe, and X-ray diffraction will be performed to identify the Ca-bearing species present in the tailings and determine if calcite forms.