Efficient Leaching of Rare Earth Elements from Coal Gangue: A Mild Acid Process with Reduced Impurity Extraction

This study comprehensively investigated the extraction of rare earth elements (REEs) from coal gangue using various analytical techniques. The results showed a significant enhancement in REE extraction efficiency, particularly for light rare earth elements, after roasting at 600 °C, while also elucidating the mechanism of roasting activation. The study also considered the leaching characteristics of both REEs and major elements (Al and Fe), exploring how to reduce the leaching rates of major elements by optimizing leaching parameters, such as acid concentration, liquid–solid ratio, and temperature. A process was proposed for extracting REEs under mild conditions (50 °C, 0.5-M HCl, 20-g/L solid–liquid ratio), achieving an extraction recovery of approximately 80% for REEs, with aluminum and iron leaching rates kept as low as 5.16% and 6.03%, respectively. The study clarified the mechanisms influencing these behaviors. By integrating experimental data with theoretical models, the leaching kinetics of REEs were thoroughly analyzed, revealing the controlling steps and key influencing factors during the leaching process. Overall, this study highlighted the potential value of REEs in coal gangue and provided key insights into their efficient extraction and utilization, helping to alleviate the shortage of REE resources and promote the comprehensive use of coal gangue. However, further research is needed to minimize the environmental impact of the extraction process and to explore more environmentally friendly extraction technologies and methods.