Mineralogy and Geochemistry of the M9 High-Sulfur Coal from the Renjiazhuang Mining District, China

According to coal lithotypes, the bottom, parting, roof, and 15 coal samples were collected by finely partitioning the M9 seam from the Renjiazhuang Mining District, Ningxia, China. Conventional chemical analysis, optical microscopy, scanning electron microscopy equipped with energy-dispersive X-ray spectrometry, X-ray diffractometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, and atomic absorption spectrophotometry techniques were used on these samples to research the vertical variation between geochemistry and mineralogy in the high-sulfur coal. The weighted average content of total sulfur calculated from 15 coal samples is 3.07%, which belongs to the high-sulfur coal. However, the contents of morphological sulfur of 15 piles are significantly different: the contents of pyritic and organic sulfur are observed to range from 0.02 to 1.55% and from 1.88 to 3.91%. The results show that these differences are mainly controlled by marine conditions and the contents of organic matter and kaolinite. The mineralogy of the M9 coal is dominated by kaolinite, followed by dolomite, and it also contains minor amounts of illite, feldspar, pyrite, siderite, hematite, chalcopyrite, calcite, and marcasite. Moreover, pyrite is the main sulfide in coal, and agglomerated chalcopyrite and granular galena are partially visible. The forms of pyrite include fine-grained, spherical, irregular block-shaped, and clumps. Trace elements are mainly carried by pyrite and ash so that physical coal cleaning can be applied to partially remove them, while thalassophile elements Na, Ca, and Mg are closely related to organic sulfur, indicating that the coal blending can be used to decrease their contents.