Coal deposits as promising alternative sources for gallium

Gallium (Ga), which is a rare valuable metal, has been found to be anomalously enriched in coal to the extent that it may be considered as an economic resource. Recovery of Ga from coal or coal combustion byproducts offers a promising alternative way to obtain this metal, and such techniques could probably lead to economic gains and positive impacts on the environment. Thus, geochemical research and technical investigations of Ga-bearing coal would be helpful in assessing the potential for economic extraction of the Ga. The present review of Ga in coal focuses on analytical methods that can be used to determine Ga concentrations, patterns of Ga enrichment in coal and formation of economic Ga-enriched coal deposits, modes of occurrence of Ga and its origins, the behavior of Ga during coal combustion and gasification, and currently available recovery techniques for Ga. Moreover, insufficiencies in previous research are identified and future research needs regarding Ga in coal are evaluated and discussed.