The study of thermodynamics and kinetics of leaching rare earth elements (REEs) is a fundamental aspect in understanding the mechanism behind the leaching process. Leaching of REEs from coal ash with aqueous solution of organocarboxylic acid is a heterogeneous fluid-particle system. In the present study, the leaching mechanisms of these three potential organocarboxylic acids, tartaric acid, lactic acid, and citric acid were examined over a range of temperature (30–90°C) at various leaching durations. The kinetic data thus obtained were found to follow deviation from the conventional shrinking core model (SCM). A mixed mechanism model was deduced to be the optimum fit to the data with high precision (R² > 0.95) and desired graphical linearity with closer interception to the origin. Aluminosilicate matrix remained unaltered after acid treatment which is the unchanged core concluded as from the kinetic mechanism. Morphological analysis using Scanning Electron Microscope (SEM) and particle size determinations were suggestive of significant reduction in grain size post leaching with organocarboxylic acids, tartaric acid being the most effective of all.

中文翻译：

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使用低分子量有机羧酸从煤灰中浸出稀土元素：络合概述和动力学评估

稀土元素浸出的热力学和动力学研究是理解浸出过程背后机制的一个基本方面。用有机羧酸水溶液从煤灰中浸出稀土元素是一种非均相流体-颗粒系统。在本研究中，在不同的浸出持续时间和温度范围（30-90°C）下检查了这三种潜在的有机羧酸、酒石酸、乳酸和柠檬酸的浸出机制。由此获得的动力学数据被发现与传统的收缩核心模型（SCM）存在偏差。推导出混合机构模型最适合高精度数据（R ² > 0.95) 和所需的图形线性度，截距更接近原点。酸处理后，硅铝酸盐基质保持不变，这是从动力学机制得出的未改变的核心。使用扫描电子显微镜 (SEM) 进行的形态分析和粒度测定表明，有机羧酸浸出后晶粒尺寸显着减小，其中酒石酸是最有效的。