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

Abstract

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.

Method of Identifying Total Sulfur Content in Coal: Geochemical and Geophysical Logging Data from the Upper Paleozoic in North China

“…The SP curve is mainly flat-shaped (Figure g,h), followed by box-shaped (Figure f). This is consistent with the local development of high-sulfur coal seams in the Shanxi Formation, which are mostly developed in the center of shallow lakes and delta plains. ,, The degree of sulfur accumulation in the coals is determined by the reducibility of the peat swamp, which is conducive to the reduction of SO 4 2– to H 2 S and of Fe 3+ to Fe 2+ and promotes the formation of pyrite. ,,, …”

“…The coal seams of Shanxi Formation were developed in the peat swamp of the delta plain, which is an open environment with relatively strong hydrodynamic conditions. ,, Sulfate is continuously migrated by water flow, and its reducibility is weakened. Additionally, Fe 3+ is difficult to reduce to Fe 2+ , which limits the formation of FeS. ,, As a result, the sulfur content in coal is relatively low. ,, …”

“…The total sulfur of the Shanxi Formation in the coal seams is lower than that in Taiyuan Formation coal seam, because the coal-forming period of Taiyuan Formation was frequently affected by the marine water. ,, Additionally, the roof of the coal seams is mostly limestone and mudstone, which can provide a rich source of sulfur and an anaerobic environment for bacteria. ,,, …”

“…10,37,38 As a result, the sulfur content in coal is relatively low. 11,37,52 There are 9 high-sulfur coal seams (S t,d ≥ 3.00%), and their logging curve shapes are collected from the Shanxi Formation (Figure 5b). The LLD curve is dominated by funnel-shaped (Figure 6f), followed by tooth-shaped (Figure 6g,i), and a small number of box-shaped (Figure 6h).…”

“…Raw coal production in China has reached 4.13 billion tons, and coal consumption accounts for 56% of the total energy consumption in 2021, which determines that coal is an irreplaceable resource for China’s economic and social development in the energy system. , A large amount of acid gases such as sulfur dioxide and carbon dioxide will be released through the direct combustion of coal, destroying the ecological environment and affecting human activities. − In a local or regional scope, on the one hand, coal containing selenium, arsenic, fluorine, and mercury will cause coal miners to suffer from such as Keshan disease, black lung disease, and liver disease. − On the other hand, coal with a remarkable enrichment of elements such as Li, Ga, and REE will have good economic value. − Apart from that, trace elements in coal are closely related to the occurrence form of sulfur in coal. − However, the sulfur content in coal exceeds 3%, which seriously restricts the mining and utilization of coal mines. , Hence, how to accurately identify coal seams with a total sulfur content of more than 3.0% or mineable coal seams with a total sulfur content of less than 3.0% plays an important role in the green mining of coal mines.…”