Environmental Geochemistry Of Mercury In Coal

Mercury (Hg) is a toxic, persistent, and globally distributed pollutant due to its characteristic properties such as low melting and boiling points, conversion between chemical forms and participation in biological cycles. During combustion Hg in coal is almost totally emitted to the atmosphere and result in environmental contamination and human health problem. Combining with the knowledge of coal geochemistry, coal geology, coal chemistry and environmental geochemistry, the environmental geochemistry of Hg in coals was investigated using instrument analysis, chemical experiments, and microprobe analysis, and the results indicate as follows.(1) By combining our results with the literature values, we have a database of Hg content in 1,712 samples of Chinese coals, and using this database, the variation of Hg in Chinese coals was investigated according to coal basins, geological ages and coal ranks. The results show most Chinese coals have Hg content in the range of 0.1 to 0.3 mg/kg, with an average of 0.19 mg/kg, and the Hg content in coals varies in different coal basins, geological ages and coal ranks.(2) The author groping investigated abundance and mode of occurrence of Hg in low sulfur coals, and the original results indicates that the organic-bound and sulfide-bound Hg are the main forms in most low-sulfur coals;(3) Hg in the Huaibei Coalfield, Anhui Province was systematically studied, especially on distribution, modes of occurrence, and enrichment of Hg in coals influence by magmatic intrusion. The results indicates that magmatic intrusion not only results in enrichment of Hg in coals but also influences modes of occurrence of Hg in coals, silicate-bound Hg is the main form in coals intruded by magmatic;(4) Hg in coals of different coal ranks, high-Cl, high-sulfur, weathered and unweathered were selected to determine their forms, and the results indicates that modes of occurrence of Hg are different in these special coals.(5) The Huaibei Coalfield in Anhui Province and the Yanzhou Coalfield in Shandong Province were selected as studied areas. Hg enrichment in these coals were investigated according to factors such as coal-forming plants, character of source rock, sedimentary environment, hydrotherm such as magmatism and others, and the results indicates that Hg enriched in coals are formed in multiphase and multigenesis.(6) Character of Hg distribution and migration during coal mining, accumulation and utilization has been investigated in this study, and the results shows:â‘ Physical coal cleaning techniques such as coal washing is not effective in Hg reduction;â‘¡Leaching experiment indicates migration of Hg varies with conditions of pH values, times and temperatures;â‘¢Dump accumulation has resulted in water contamination in coal mining area. Mercury emission to atmosphere during coal combustion increased from 1980 to 2007, and has resulted in serious environmental contamination in China, particularly in the northeastern and southwestern China, where a high Hg content in the atmosphere occurs.