Geochemistry of Carboniferous-Permian Coal from the Wujiawan Mine, Datong Coalfield, Northern China: Modes of Occurrence, Origin of Valuable Trace Elements, and Potential Industrial Utilization

This paper provides new geochemical data focusing on valuable elements in the coal, parting, and floor samples in the No. 5 coal seam of the Taiyuan Formation from the Wujiawan mine, Datong coalfield, northern China. The minerals mainly consist of kaolinite, calcite, and pyrite, as well as trace amounts of quartz and illite. The No. 5 coal is enriched in Li, Ga, high field strength elements (HFSEs), and rare earth elements and yttrium (REY) when compared with world hard coals. Of particular interest is the high average concentration of Li (67.66 mu g/g), which is around seven times higher than the value for world hard coals. Lithium, Ga, and HFSEs have strong inorganic affinities, whereas REY have organic affinities. The main carrier of Li, Ga, and HFSEs is aluminosilicate minerals, while REY appear to occur with organophosphorus. These HFSEs are enriched, both in the parting and in the adjacent coal samples. This suggests that these elements are likely to leach out during the diagenetic process. The distribution patterns of REY, along with the ratio of Al2O3/TiO2 and the figure of Zr/TiO2 vs. Nb/Y are suggestive of their derivation from felsic parent material. In the northern and eastern part of the Datong coalfield, there are several regions where the Li content is higher than the mineable grade, in particular in the northern Datong coalfield where there is a mine with an Li content of 294.6 mu g/g. This is significantly higher than the mineable grade. Therefore, there is a potential for financially viable recovery of Li in these coals of the Datong coalfield.