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.

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Coal fly ash (CFA), the main byproduct of coal combustion, has been regarded as an attractive source of rare earth elements plus yttrium (REY). Understanding how REY occurs in CFA is essential for designing an effective method for recovery of REY from CFA. To clarify the modes of occurrence of REY, we used particle size analysis, a sequential chemical extraction procedure (SCEP), and a scanning electron microscope with an energy dispersive spectrometer (SEM-EDS) to study REY in CFA from Guizhou Province, China. The relationship between the content of REY and particle size was consistent with previous results and implies that particle separation can be used to enrich the chemical extraction of REY from CFA. The results of the SCEP revealed the proportions of REY in different modes (silicate-aluminate > organic or sulfide > acid soluble > metal oxides > ion-exchangeable form) and can also be used as a guide for reagent choice in REY leaching and extraction. The results of the SEM-EDS analysis showed that REY in the CFA (La, Ce, and Nd as proxies) is significantly associated with Al and P. They also illustrated that Al has a more important role in REY occurrence than Si in aluminosilicates.

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