Research progress on the extraction of strategic critical metals (rare earth elements, gallium, and germanium) and the high-value utilization of major element silicon from bulk mineral-metallurgical solid waste

Strategic critical elements, including rare earth elements (REEs), gallium (Ga), and germanium (Ge), are essential raw materials in high-tech industries. The growing technological demand starkly contrasts the depletion of traditional mineral reserves and declining ore grades, exacerbating supply challenges. Mineral-metallurgical solid wastes like coal fly ash (CFA) and red mud, containing substantial amounts of these elements, present dual opportunities for resource recovery and environmental remediation. This paper reviews recent studies on the extraction and characterization techniques of REEs, Ga, and Ge from CFA and red mud, summarizing the progress of different extraction processes. Given the economic constraints of conventional approaches, this study investigates the co-recovery of REEs, Ga, Ge, and silicon from solid wastes. By developing synergistic extraction protocols for bulk metallurgical residues, this research seeks to advance high-value valorization while reconciling economic viability, strategic resource security, and environmental sustainability.