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

自然资源部门是加拿大经济的一个重要领域。在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。铀矿体除氧化铀外，还含有许多矿物相，需要以负责任的方式处理。固体采矿废物可以放置在尾矿管理设施中，该设施旨在容纳废物元素并限制与外部环境的相互作用。要了解尾矿设施在尾矿管理设施的采矿作业的整个生命周期内以及在场地退役后的表现，了解尾矿的化学成分及其随时间的变化是很重要的。位于麦克林湖作业的JEB尾矿管理设施含有从氧化铀分离出来的许多金属，包括铁（Fe）、砷（As）、钼（Mo）和铀(U)等元素。在这项持续的研究合作中，我们将研究尾矿设施的样品，以更好地了解尾矿中发现的含钙物种。通过比较孔隙水样品中溶解物质的浓度和对尾矿中固体物质的分析，再加上对尾矿行为的建模，我们提出，如果氧化铀固体与碳酸盐离子反应，在孔隙水中产生可溶的碳酸铀酰配合物，那么氧化铀固体就可以溶解在尾矿中。但碳酸钙离子也可与硫酸钙（石膏）反应生成碳酸钙，在尾矿设施条件下（pH接近中性）碳酸钙会析出。确定尾矿中是否存在碳酸钙（方解石）是了解如何控制（和减少）孔隙水中可溶性铀酰物种存在的重要一步。预计在尾矿中会有无定形和结晶的含钙化合物，如果有方解石，也会有微量的方解石。在这项工作中，将使用x射线吸收光谱、x射线显微探针和x射线衍射来确定尾矿中存在的含钙物质，并确定方解石是否形成。

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.