Lithium recovery from typical coal-based solid wastes: Critical technologies, challenges, and prospects

The extraction of lithium mainly depends on salt-lake brine and lithium ore. With the rapid growth of the new energy automobile industry, there has been a surge in demand for lithium resources. Coal-based solid wastes, particularly coal gangue (CG) and coal fly ash (CFA) are rich in lithium with significant reserves, thus presenting a new potential source of lithium resources. This paper describes the types of CG and CFA and their main methods of utilization, describes the content of critical elements in CG and CFA, and analyses their respective lithium occurrence modes. Currently, the technology for recovering lithium from CG and CFA mainly focuses on pre-treatment, lithium leaching, and selective extraction of lithium from the leaching solution. Pre-treatment technology can be divided into pre-enrichment and pre-activation. Physical separation methods such as magnetic separation, screening, and flotation can selectively enrich lithium in the mineral phase containing it. Activation technology (mechanical activation or chemical roasting activation) is used to release lithium by destroying the stable structure of its mineral phase. Lithium leaching technology includes extracting valuable elements from CG and CFA with reagents such as acid and base; Subsequently, extraction technology is employed to selectively extract lithium from a composite leaching solution. Moreover, this study deduces the economic feasibility of lithium extraction from coal-based solid wastes through specific case analyses. The primary objective of this study is to enhance awareness regarding the development of novel sources for lithium resources, while also serving as a reference for the high-value utilization of CG and CFA.