Study on Influence Factors of Leaching of Rare Earth Elements from Coal Fly Ash

摘要

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 degrees 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.