Highly Selective and Green Recovery of Lithium from Coal Gangue Using Recyclable Ammonium Fluoride Leaching System

With the discovery of super-enriched lithium (Li) in coal, coal-based Li deposit is a promising resource to meet Li demand. However, traditional Li extraction methods are mainly through acid leaching, which complicates the subsequent purification process. Herein, a method of selective lithium leaching employing recyclable ammonium fluoride (NH₄F) was proposed. The influences of roasting temperature and leaching conditions were explored in detail. Under the optimal conditions, the Li leaching rate reaches 81.42%, while Fe, Al, Mg, Ca and Na are < 3%. Besides, NH₄F could be generated and sent back into the leaching process. The roasting and leaching mechanisms assumed that kaolinite is transformed into metakaolinite after roasting. The Al-containing lattice structure is destroyed, and the Li residing in it is also released and becomes soluble Li, while other metal elements stay. This study provides a highly selective and green Li extraction process from coal-based Li deposits.