Recovery of rare earth elements (REEs) from coal samples collected from the Fire Clay coal seam using diluted mineral acid solutions was investigated. The initial processing step was coal recovery using conventional froth flotation which concentrated the REEs in tailing material resulting in an upgrade to values around 700 ppm on a dry whole mass basis. Leaching experiments were performed on the flotation tailings material using a 1.2 M sulfuric acid solution adjusted to a temperature of 75 °C to study the extractability of REEs from coal material. The effect of particle size, leaching time, leaching temperature, and solid concentration on REE leaching recovery were evaluated. The kinetic data obtained from leaching over a range of temperatures suggested that the leaching process follows the shrinking core model with possibly a mixed control mechanism that may be a result of several heterogenous materials leaching simultaneously. Leaching recovery increased rapidly at the beginning of the reaction then slowed as the system reached equilibrium. The apparent activation energy determined from test data obtained over a range of temperatures using 1 M sulfuric acid was 36 kJ/mol for the first 20 min of reaction time and 27 kJ/mol for the leaching period between 20 and 120 min. The leaching of light REEs during the initial stage was determined to be driven by a chemical reaction, followed by the formation of a product layer, which required lower activation energy in the later stage of leaching. In regards to the heavy REEs, the major mechanism for leaching is desorption and the product layer formation does not affect the heavy REEs significantly.

中文翻译：

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火粘土煤层中稀土元素的浸出动力学

研究了使用稀释的无机酸溶液从火粘土煤层收集的煤样品中回收稀土元素（REE）。最初的处理步骤是使用常规泡沫浮选法回收煤炭，该方法将稀土元素浓缩在尾矿中，从而使总干重提高到700 ppm左右。使用1.2 M硫酸溶液将浮选尾矿材料进行浸出实验，将硫酸溶液调节至75°C，以研究煤中稀土元素的可萃取性。评估了粒径，浸出时间，浸出温度和固体浓度对REE浸出回收率的影响。从一定温度范围内浸出获得的动力学数据表明，浸出过程遵循收缩核模型，并可能具有混合控制机制，这可能是几种异质材料同时浸出的结果。在反应开始时，浸出回收率迅速增加，然后随着系统达到平衡而减慢。根据使用1 M硫酸在一定温度范围内获得的测试数据确定的表观活化能，在反应时间的前20分钟为36 kJ / mol，在20至120分钟的浸出期间为27 kJ / mol。确定轻质稀土元素在初始阶段的浸出是由化学反应驱动的，然后形成产物层，该产物层在浸出的后期需要较低的活化能。关于重稀土元素，