Comparison of the precipitation of calcium carbonates to the dissolution of uranium in uranium mine tailings

自然资源部门是加拿大经济的一个重要领域。在已开采的许多自然资源中，铀矿开采集中在萨斯喀彻温省北部。铀矿体中除了铀氧化物外，还含有许多矿物相，需要负责任地处理。固体采矿废物可以放置在尾矿管理设施中，该设施旨在包含废物元素，并限制与外部环境的相互作用。为了了解尾矿设施在为尾矿管理设施(TMF)提供燃料的采矿作业的整个生命周期内以及在该场地退役后的表现，了解尾矿的化学成分及其随时间的变化非常重要。位于McClean Lake作业的Jeb尾矿管理设施包含许多从铀氧化物中分离出来的金属，包括铁(Fe)、砷(As)、钼(Mo)和铀(U)等元素。通过比较孔隙水样中溶解物种的浓度和尾矿中固体的分析，再加上尾矿行为的模拟，提出了如果铀氧化物固体与碳酸盐离子反应在孔隙水中生成可溶的铀酰碳酸盐络合物，那么它们可能会溶解在尾矿中。然而，碳酸盐离子也能与硫酸钙(石膏)反应生成碳酸钙，在尾矿设施的条件下(近中性pH)会析出碳酸钙。在我们最近的合作中，我们使用了X射线微探针结合显微X射线吸收近边光谱来识别TMF中的大量和微量含钙物种，包括石膏、硬石膏、方解石、文石、白云石和含钙粘土。有了这些信息，我们建议扩展这项研究，将碳酸钙的浓度随年龄的变化与固体铀矿物的浓度进行比较，并将其与TMF孔隙水中碳酸氢盐和碳酸铀酰复合体浓度的变化联系起来。这项研究是必要的，以确定碳酸钙在TMF中的沉淀是否参与了水中铀浓度的控制。

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 (TMF), 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. 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). In our most recent collaboration, we have used X-ray microprobe in combination with micro-X-ray absorption near-edge spectroscopy to identify the bulk and trace Ca-bearing species in the TMF, which include gypsum, anhydrite, calcite, aragonite, dolomite, and Ca-bearing clays. With this information in hand, we propose to expand this research to compare how the concentrations of Ca carbonates change with age to the concentrations of solid U minerals, and to relate this to variations in the aqueous bicarbonate and uranyl carbonate complex concentrations in the TMF pore water. This study is necessary to determine if the precipitation of Ca carbonates in the TMF is involved in controlling the aqueous U concentration.