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Rare metal elements in the primary coal seam of Changzhi coalfield in Southeast Shanxi, China

Geochemistry characteristics of rare metal elements of No.15 Permian coal seam in Changzhi coalfield, such as concentration, distribution, occurrence, and mining value were investigated by low-temperature ashing prior to powder X-ray diffraction, X-ray fluorescence, inductively coupled plasma mass spectrometry, and field emission scanning electron microscopy equipped with energy-dispersive X-ray analysis. The results showed that the ∑REE concentrations ranged from 19.12 to 268.21 μg/g, with an average value of 91.74 μg/g; the average concentrations of Ga, Ge, and Th were 11.03, 1.96, and 15.09 μg/g, respectively. The concentration of rare earth elements (REEs), Th, Ga, and Ge, are all below the minimum industrial grade. However, the concentrations of rare earth oxides and Ge in high-temperature ash of some coal benches are higher than the minimum recoverable value and are thus potentially recoverable. The vertical distribution of REEs is uneven, with a maximum value adjacent to a minimum value. The source of the different layers of REEs was stable and influenced by seawater. Moreover, the ∑REE, Ga, and Th are enriched with the inorganic minerals and correlated with kaolinite. Ga and Th are also correlated with illite. Significant fractionation of REE is observed during the process of combustion.