Geochemistry characteristics and resource utilization of strategically critical trace elements from coal-related resources

Rare-metal, rare-scattered, rare-earth and noble-rare elements are strategically critical resources and important raw materials used in national economy, military, and defense,and play an irreplaceable role. With the gradual depletion of traditional mineral deposits and the increasing difficulty of mining, more and more attention has been paid to the comprehensive exploration, exploitation, and utilization of associated critical elements in coal and coal ash, which are expected to become promising alternative sources with dual values of recycling and environmental protection. Considering the geochemical characteristics and utilization of coal-related strategically critical trace elements as a whole,the paper systematically reviews the analytical methods of content and occurrence mode of these elements such as lithium, gallium, germanium, rare earth and precious metal, as well as their distribution, enrichment, modes of occurrence in Chinese coal and corresponding geochemical mechanism. Furthermore, their migration and chemical morphological transformation during coal combustion are elaborated, and the approaches of activation, leaching, followed by enrichment and purification for the extraction of typical critical elements are summarized. At last, some existing problems and future research directions in this field are put forward. This review may provide scientific reference for theoretical and technical research on the exploitation and utilization of coal and coal ash as potential resources of strategically critical elements.