Chemical species of Ge/W/Ga in lignite and their enrichment in thermal treatment

The Lincang lignite contains abundant metal elements such as Ge, W, and Ga, which can be regarded as an important raw material for metal extraction. In this study, chemical species of Ge, W, and Ga in lignite and their changes during calcination were investigated. The results revealed that Ge and W can form complexes with humic acid, primarily existing in the organic matter of lignite, which can be pre-enriched through density separation of lignite. In comparison, Ga is dispersed in lignite, existing in the forms of humic substance, other organically bound, and residue. Thermal treatment can change the distribution of Ge, W, and Ga in lignite and promote their enrichment to some extent. The maximum enrichment factor for Ge, W, and Ga are 1.97, 1.48, and 2.75, respectively. As the temperature increases, their chemical species are changed. Ge is converted into an active form that readily reacts with acids. W and Ga are mainly converted into the residue form and humic substance form, respectively, and these two forms are not active. Hence, the leaching rate of Ge can be increased by 29.64%, while the leaching rates of W and Ga did not show significant enhancement.