College of Agriculture, Guizhou University, Guiyang 550025, China; Key Laboratory of Karst Georesources and Environment, Ministry of Education, College of Resources and Environmental Engineering, Guizhou University, Guiyang 550025, China.
102 Geological Brigade of Guizhou Bureau of Geology and Mineral, Zunyi 563003, China.
Sci Total Environ. 2023 Jun 25;879:163051. doi: 10.1016/j.scitotenv.2023.163051. Epub 2023 Mar 24.
Rare earth elements (REEs) have attracted much attention in recent decades due to their growing applications in high-tech industries. Coal and acid mine drainage (AMD) are considered promising alternative sources due to their high concentrations of REEs. Here, AMD with anomalous REEs concentrations was reported in a coal-mine area in northern Guizhou, China. The AMD had a total concentration as high as 22.3 mg/l, suggesting that regional coal seams may be enriched with REEs. Five segments from borehole samples, which contained coal, rocks from the roof and floor of the coal seam were collected from the coal mine site to investigate the abundance, enrichment, and occurrence of REE-bearing minerals. Elemental analysis showed that the REE contents in the coal, mudstone and limestone from the coal seam roof, and claystone from the floor (all dating to the late Permian) varied greatly, with averages of 388, 549, 60.1 mg/kg and 2030 mg/kg, respectively. Encouragingly, the REEs content in the claystone is over an order of magnitude higher than the average content reported in most other coal-based materials. The enrichment of REEs resources in regional coal seams is particularly associated with the contribution of REEs in the claystone that comprises the coal seam floor, rather than just the coal, as considered in previous studies. The minerals in these claystone samples were dominated by kaolinite, pyrite, quartz and anatase. Two types of REE-bearing minerals, bastnaesite and monazite, were detected in the claystone samples by SEM-EDS analysis, and they were found to be adsorbed by a large amount of clay minerals, mainly kaolinite. Additionally, the results of chemical sequential extraction also confirmed that the majority of the REEs in the claystone samples are mainly in their ion-exchangeable, metal oxide and acid-soluble forms, which are viable prospects for REE extraction. Therefore, the anomalous concentrations of REEs and most of them are in extractable phases, which demonstrates that the claystone from the floor of the late Permian coal seam should be a potential secondary source of REEs. Future studies will further consider the extraction model and the economic benefits of REEs from the floor claystone samples.
稀土元素 (REEs) 因其在高科技产业中的应用日益广泛，近年来引起了广泛关注。煤炭和酸性矿山排水 (AMD) 因其 REEs 浓度高而被认为是有前途的替代来源。本研究在中国贵州北部的一个煤矿区报道了具有异常 REEs 浓度的 AMD。AMD 的总浓度高达 22.3 mg/l，表明该地区的煤层可能富含 REEs。从煤矿区采集了五个钻孔样品，其中包含煤、煤层顶板和底板的岩石，以研究含 REE 矿物的丰度、富集和赋存状态。元素分析表明，来自煤层顶板的煤、泥岩和灰岩，以及底板的粘土岩（均为晚二叠世）的 REE 含量差异很大，平均值分别为 388、549、60.1 mg/kg 和 2030 mg/kg。令人鼓舞的是，粘土岩中的 REEs 含量比大多数其他基于煤的材料的平均含量高出一个数量级。与之前研究中认为的仅来自煤层的煤相比，区域煤层中 REE 资源的富集尤其与构成煤层底板的粘土岩中的 REEs 贡献有关。这些粘土岩样品中的矿物主要为高岭石、黄铁矿、石英和锐钛矿。通过 SEM-EDS 分析，在粘土岩样品中检测到两种类型的含 REE 矿物，氟碳铈矿和独居石，它们被大量的粘土矿物，主要是高岭石吸附。此外，化学连续提取的结果也证实，粘土岩样品中的大部分 REE 主要以可交换离子、金属氧化物和酸可溶形式存在，这是提取 REE 的可行前景。因此，粘土岩中 REE 异常高浓度且大部分为可提取相，表明晚二叠世煤层底板的粘土岩应是 REE 的潜在次生来源。未来的研究将进一步考虑从底板粘土岩样品中提取 REE 的模型和经济效益。
