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的北方。铀矿体除氧化铀外还含有许多矿物相，需要以负责任的方式加以处置。固体采矿废物可以放置在尾矿管理设施中，该设施旨在容纳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提供原料的采矿作业的整个生命周期内以及在场地退役后的行为，了解尾矿的化学性质以及它们如何随时间变化非常重要。位于McClean Lake操作的JEB尾矿管理设施含有来自氧化铀分离的许多金属，包括铁（Fe），砷（As），钼（Mo）和铀（U）等元素。通过比较孔隙水样品中溶解物质的浓度和对尾矿中固体的分析，再加上对尾矿行为的建模，有人提出，如果氧化铀固体与碳酸根离子反应，在孔隙水中产生可溶的碳酸铀酰络合物，它们就可以溶解在尾矿中。然而，碳酸根离子也可与硫酸钙（石膏）反应并产生碳酸钙，碳酸钙将在尾矿设施的条件下（接近中性pH值）沉淀。在我们最近的合作中，我们已经使用X射线微探针结合微X射线吸收近边光谱，以确定散装和微量钙轴承物种的方解石，其中包括石膏，硬石膏，方解石，文石，白云石，和含钙粘土。有了这些信息在手，我们建议扩大这项研究，以比较碳酸钙的浓度如何随着年龄的变化，固体铀矿物的浓度，并将其与水碳酸氢盐和碳酸铀酰复合物的浓度在孔隙水的变化。这项研究是必要的，以确定是否沉淀的碳酸钙中的铀是参与控制水溶液中的U浓度。

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.