The use of sequential extraction to determine the distribution and modes of occurrence of mercury in Permian Huaibei coal, Anhui Province, China

Sequential extraction tests using a Flow Injection Mercury System (FIMS) were done on 34 samples collected from the number 3, 4, 5, 7, and 10 coal seams in the Huaibei Coalfield; average total mercury (Hg) concentrations for the seams were 0.13, 0.18, 0.54, 0.34, and 0.19 mg/kg respectively. The average value for all of the coal samples was 0.26 mg/kg, which is higher than most Chinese and U.S. coals. Six modes of Hg occurrence were recognized, including: water-leachable, ion-exchangeable, organic-bound, carbonate-bound, silicate-bound, and sulfide-bound Hg. With rare exception, little Hg was found in water-soluble, ion-exchangeable or carbonate-bound forms. Sulfide-bound Hg and organic-bound Hg dominated seams 3, 4, and 10, whereas silicate-bound Hg dominated seams 5 and 7. The relatively high Hg values observed in seams 5 and 7, especially in parting samples, are attributed to Hg enrichment by magmatic intrusions.