Occurrence modes and comprehensive utilization of critical metal resources associated with coal: A review

Abstract

Coal serves not only as a crucial energy resource but also as a significant reservoir of critical metal elements, including Lithium (Li), Gallium (Ga), Germanium (Ge), and rare earth elements (REE). This paper provides a systematic review of the enrichment characteristics, occurrence modes, and comprehensive utilization potential of these critical metals in coal. Globally, the distribution of these metal resources exhibits significant regional heterogeneity. While the concentration in most coals falls below industrial cut-off grades, anomalous enrichment in specific coal basins results in Li, Ga, Ge, and REE concentrations far exceeding global averages, highlighting their considerable potential as unconventional metal deposits. The occurrence modes of these metals are diverse: Li is primarily hosted in mineral phases; Ga exists in inorganic, organic, and complex forms; Ge shows a strong association with organic matter; and REE are mainly present in adsorbed/isomorphic forms within clay minerals, while also displaying organic affinity. Direct extraction of metals from raw coal is often cost-prohibitive; effective recovery is therefore more feasible when integrated with coal processing. Metals are further enriched in solid wastes such as coal gangue, fly ash, and bottom ash, from which recovery is more economically and technically viable. Current comprehensive utilization primarily employs integrated mineral processing-hydrometallurgy approaches. Future research should focus on elucidating the precise occurrence forms of metals in coal and solid wastes, optimizing pre-treatment methods, and selecting effective activators and leachants. Advancing the synergistic extraction and green recovery of multiple associated resources from coal and its by-products is essential for achieving high-value, comprehensive utilization of coal-based resources.

Keywords

Coal-associated resources / Lithium / Gallium / Germanium / Rare earth elements / Extraction and separation

CRediT authorship contribution statement

Qin Zhang: Writing – review & editing, Writing – original draft, Supervision, Resources, Project administration, Funding acquisition, Conceptualization. Wei Cheng: Writing – review & editing, Writing – original draft. Tiebin Zhang: Investigation, Formal analysis, Data curation. Hongbo Liu: Supervision. Jiwei Yuan: Supervision. Aoao Chen: Investigation, Formal analysis, Data curation. Tingshun Wang: Data curation. Qian Liu: Data curation. Jianghe Wang: Data curation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This study was supported by the Key Support Project of Regional Innovation and Development Joint Fund of the National Natural Science Foundation of China (No. U24A2095).

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