Characteristics of trace elements in coal and comparison of coal-forming environment in Shizuishan Area

In order to clearly understand the characteristics of trace elements and coal-forming environment characteristics of Jurassic coal and Carboniferous-Permian coal in Shizuishan Area, and to explain the differences in the characteristics of trace elements in coal, this paper was carried out. The Jurassic coal in Rujigou area and the Carboniferous-Permian coal in Shitanjing Area were taken as samples. The samples were analyzed by industrial analysis, maceral observation, low-temperature ashing, and instrumental neutron activation analysis. The concentration coefficient and mathematical statistics were used to analyze the enrichment characteristics and symbiotic relationship of trace elements, and the geochemical parameters were used to comprehensively study the difference of coal-forming environment characteristics, and the influence of coal-forming environment on the coal characteristics was pointed out. The results show that Jurassic coal and Carboniferous-Permian coal have great differences in trace element characteristics. There is no element enrichment in Jurassic coal, most elements are deficient, and Se, Zr, Hf, W, Th are lightly enriched in Carboniferous-Permian coal. According to the symbiotic relationship, trace elements can be divided into two groups which are highly correlated with water and alkali metal elements in coal and those highly correlated with terrigenous debris. Jurassic coal and Carboniferous-Permian coal are in oxidation-transition environment, but the coal-forming environment of Jurassic coal is more high temperature and dry, and the paleo-salinity, alkalinity, and swamp closure are stronger. The transition of the coal-forming environment to high temperature and dryness enhances the sealing of the swamp. As a result, the elements such as Se, Zr, Hf, W, and Th, which are slightly enriched in the Carboniferous-Permian coals, become normal- deficient in the Jurassic coals, and the contents of other terrigenous clasts-related elements decrease. Oxidation intensifies the migration of U element in coal in two ages. Alkali environment may have a certain influence on the enrichment process of Se, and also promote the deposition of Ba, Co, As, Ni, Cr in Jurassic coal. At the same time, the coal-forming environment also has a certain influence on coal quality and mineral characteristics.