Concentration, distribution, and modes of occurrence of selenium in Huaibei coalfield, Anhui province, China

Selenium, a toxic element, is highly enriched in the coals of the Huaibei coal deposit, China. For this study, Se content along with rock-forming and trace element abundances was determined in 123 coal and 19 rock samples collected from the main coal seams in seven coal mines in the Huaibei coalfield. This was done to investigate the Se geochemistry in the Huaibei coals. Compared with average Chinese coal and other coals around the world, the Huaibei coals are enriched in Se by a factor of five. Differences in the boron content in the sequence of Huaibei coal seams show that the depositional environment of the formations hosting the coal seams evolved from a delta front to a prodelta setting and then to a delta plain environment. Selenium is distributed unevenly both horizontally and vertically in the Huaibei coal deposit. Pearson correlation coefficients between Se with several elements (Ca, Fe, and S) indicate that iron-bearing clay minerals and carbonates are the dominant carriers of Se in coals of the Lower Shihezi Formation. Selenium in coals from No. 3 and No. 10 coal seams are mainly associated with sulfide minerals. The well-developed faults in Huaibei coalfield may have contributed to the enrichment of Se in Huaibei coals.