Rare earth elements (REEs) are very important strategic resources, but the traditional high-quality rare earth resources are becoming increasingly scarce. Coal fly ash (CFA) in some areas in the world has a high REE content, which can be a potential supplement to the rare earth resources. CFA samples collected from the Panbei Power Plant in Guizhou Province of China, in which the REE content is 489 ppm, was used as the research object in this study. Taking three REEs (lanthanum (La), cerium (Ce), and neodymium (Nd)) with the highest content in this CFA sample as the representative and hydrochloric acid as the leaching reagent, the effects of various factors on the leaching efficiencies of REEs from CFA were investigated systematically. Further, two unreacted core shrinkage models (chemically controlled model and diffusion controlled model) were used to study the leaching kinetics of REEs from CFA. The results showed that, except for the small influence of the stirring speed, the temperature, acid concentration, liquid–solid ratio, and reaction time all have a great influence on the leaching efficiencies of REEs. Leaching efficiencies of 71.9, 66.0, and 61.9% for La, Ce, and Nd, respectively, were obtained under the conditions of a stirring speed of 200 rpm, temperature of 60 °C, HCl concentration of 3 M, liquid–solid ratio of 10 (v/m), and leaching time of 120 min. The leaching mechanism of REEs from CFA tends to be more controlled by chemical reactions. In addition, La is more easily leached from CFA than Ce and Nd. This study can provide theoretical guidance for optimizing the leaching conditions of REEs from CFA at low temperature and atmospheric pressure, thereby providing theoretical support for the early industrial development and utilization of rare earth resources in CFA.

中文翻译：

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粉煤灰中稀土元素浸出的影响因素研究

稀土元素（REEs）是非常重要的战略资源，但是传统的高质量稀土资源正变得越来越稀缺。世界某些地区的粉煤灰（CFA）的REE含量很高，这可能是对稀土资源的潜在补充。本研究以从贵州省盘北电厂采集的CFA样品中的REE含量为489 ppm为研究对象。以该CFA样品中含量最高的三种稀土元素（镧（La），铈（Ce）和钕（Nd））为代表，盐酸为浸出剂，各种因素对REEs浸出效率的影响对来自CFA的数据进行了系统的调查。进一步，使用两个未反应的岩心收缩模型（化学控制模型和扩散控制模型）研究了CFA中REE的浸出动力学。结果表明，除了搅拌速度的影响较小外，温度，酸浓度，液固比和反应时间均对稀土元素的浸出效率有很大影响。在200 rpm的搅拌速度，60°C的温度，3 M的HCl浓度，液固比为200 rpm的条件下，La，Ce和Nd的浸出效率分别为71.9％，66.0和61.9％。 10（v / m），浸出时间为120分钟。CFA中REE的浸出机理往往受到化学反应的控制。另外，La比Ce和Nd更容易从CFA中浸出。