Sulfur variability and element geochemistry of the No. 11 coal seam from the Antaibao mining district, China

The roof, bottom and 24 coal ply samples were collected by finely partitioning No. 11 coal seam from Antaibao mining district, Shanxi, China in terms of lithotypes. Proximate and sulfur analyses, ICP-AES, ICP-MS, AFS, XRD, SEM–EDX techniques were used on these samples, in order to investigate the vertical variability and origin of sulfur and also the geochemistry of major and trace elements in the seam. The weighted mean content of total sulfur of the 24 coal plies is 2.4 wt%, belonging to the medium-sulfur coal, but there are great differences in the contents of total sulfur and forms of sulfur between the 24 plies: total sulfur content >3.0 wt% for 5 plies, organic sulfur content >1.0 wt% for 13 plies and pyritic sulfur content >2.0 wt% for 4 plies. It is found that the differences were mainly caused by the degree of marine influences and the contents of clay minerals as well as the organic matter. The ply 21 has an abnormal high content of inorganic sulfur (pyritic sulfur 9.45 wt% and sulfate sulfur 5.97 wt%). This was caused by the presence of bauxite minerals-bearing kaolinite in the underlying ply 22 blocking the further infiltration of sulfate from the overlying plies during the deposition. The seam is dominated in kaolinite and, to a lesser extent, in pyrite, and there also exist minor amounts of szomolnokite, diaspore, boehmite, calcite, siderite, dolomite, magnesite, feldspar, gypsum. Szomolnokite and gypsum possibly resulted from the oxidation of pyrite. The seam is greatly characterized by finely-grained pyrite concentrating in cutinite. Hazardous trace elements Hg, Pb and As are mainly concentrated in pyrite, so that they can be partially removed by physical coal cleaning with an aim of removal of sulfur, while thalassophile elements Br, Ca, Cl, Mg and Sr, are clearly associated with the organic sulfur, reflecting that their contents can be decreased by coal blending means due to a partial organic affinity.