Enrichment of Bi-Be-Mo-Cd-Pb-Nb-Ga, REEs and Y in the Permian coals of the Huainan Coalfield, Anhui, China

Abstract

This paper presents new data concerning the geochemistry and distribution of the Bi-Be-Mo-Cd-Pb-Nb-Ga, and REY in the Panyi, Xieqiao, Xinji, Zhuji, and Zhuji Xi coals of the Huainan Coalfield. The results indicate that the Huainan bituminous coals were characterized by medium ash yields and low to medium sulfur contents. The mineral assemblage present in the Huainan coals is mainly made up of quartz, kaolinite, pyrite, and calcite. The minerals, ash yield, sulfur contents, volatile matter contents, Sr/Ba, SiO2/Al2O3, and (CaO + MgO + Fe2O3)/(SiO2 + Al2O3) ratio varied significantly in the Huainan Coalfield, which are attributed mainly to vertical variation in the depositional environment. These coals contain high contents of Ga, Nb, Mo, Be, Pb, Ba, SiO2, Fe2O3, TiO2, CaO, Na2O, Al2O3, MnO, K2O, and MgO, especially in the marine-influenced environment coals. The average contents of Ga, Nb, Mo, Be, and REY are higher than those of world-wide bituminous coals, thus a hidden treasure is a yet to-be-realized new economic potential. The Bi, Be, Mo, Nb, Ga, and REY have mixed organic-inorganic affinity, while Cd and Pb mainly have an organic affinity in the Huainan coals. Compared to the average Chinese coals, the REY are enriched in the Panyi, Xieqiao, and Xinji coals, slightly lower in the Zhuji coals and depleted in the Zhuji Xi coals. Compared to the upper continental crust, REY in the Huainan coal samples has medium-REY and light-REY enrichment. The average concentration of oxides (ash basis) of the rare earth elements and Y in the Panyi (on average 1120.3 μg/g), Xieqiao (1287.7 μg/g), Xinji (1148.7 μg/g), and Zhuji (1025.1 μg/g) coals are higher than the cut-off grade for industrial deposits of these elements and thus, the Huainan coals are considered as raw materials for the recovery of rare earth elements.