Rare earth elements (REE) are necessary for advanced technological and energy applications. To support the emerging need, it is necessary to identify new domestic sources of REE and technologies to separate and recover saleable REE product in a safe and economical manner. Underclay rock associated with Central Appalachian coal seams and prevalent in coal utilization waste products is an alternative source of REE to hard rock ores that are mainly composed of highly refractory REE-bearing minerals. This study utilizes a suite of analytical techniques and benchtop leaching tests to characterize the properties and leachability of the coal seam underclays sampled. Laboratory bench-top and flow-through reactor leaching experiments were conducted on underclay rock powders to produce a pregnant leach solution (PLS) that has relatively low concentrations of gangue elements Al, Si, Fe, and Th and is amenable to further processing steps to recover and produce purified REE product. The leaching method described here uses a chelating agent, the citrate anion, to solubilize elements that are adsorbed, or weakly bonded to the surface of clay minerals or other mineral solid phases in the rock. The citrate PLS produced from leaching specific underclay powders contains relatively higher concentrations of REE and lower concentrations of gangue elements compared to PLS produced from sequential digestion using ammonium sulfate and mineral acids. Citrate solution leaching of underclay produces a PLS with lower concentrations of gangue elements and higher concentrations of REE than achieved with hydrochloric acid or sulfuric acid. The results provide a preliminary assessment of the types of REE-bearing minerals and potential leachability of coal seam underclays from the Central Appalachian basin.

中文翻译：

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从阿巴拉契亚中部煤层地下粘土中浸提稀土元素

稀土元素（REE）是先进技术和能源应用所必需的。为了满足新出现的需求，有必要确定国内新的稀土资源和技术，以安全，经济的方式分离和回收可销售的稀土产品。与阿巴拉契亚中部煤层有关并在煤炭利用废物中普遍存在的地下岩石是硬岩矿石的一种替代稀土元素，而硬岩矿石主要由高度难熔的含稀土矿物组成。这项研究利用一套分析技术和台式浸出试验来表征所采样煤层底土的性质和可浸出性。在底泥岩粉上进行了实验室台式和流通式反应器浸出实验，以产生母液浸出溶液（PLS），该溶液的煤relatively石元素Al，Si，Fe和Th的浓度相对较低，并且适合进一步加工步骤回收并生产纯化的REE产品。这里描述的浸出方法使用螯合剂柠檬酸根阴离子来溶解被吸附或弱结合到岩石中粘土矿物或其他矿物固相表面的元素。与使用硫酸铵和无机酸顺序消化制得的PLS相比，从浸出特定底层粘土粉制得的柠檬酸盐PLS含有相对较高的REE和较低浓度的脉石元素。与用盐酸或硫酸相比，底泥的柠檬酸盐溶液浸出产生的LS石含量较低，其脉石元素浓度较高，REE浓度较高。研究结果初步评估了中阿巴拉契亚盆地含稀土元素矿物的类型和煤层地层的潜在浸出性。