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AbstractDifferent coal seams go through distinct biological, physical, and chemical processes. Polycyclic aromatic compounds (PACs) in coal may retain information about these processes, especially in low-rank bituminous coals. Three coal seams with different sulfur contents from the Ningwu Coalfield were studied to understand the relation of different sulfur contents with PAC formation in low-rank bituminous coals. Coal samples were extracted by solvent and separated using liquid chromatography. The collected aromatic hydrocarbon fractions were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). A total of 27 sulfur-containing PACs (SPACs) were identified in the high-sulfur samples, whereas only 8 SPACs were found in the low-sulfur coal and middle-sulfur coal. The total SPACs to total PACs ratios (T-SPACs/T-PACs) are 1.15%, 2.17%, and 10.65% in the low-sulfur, middle-sulfur, and high-sulfur coal, respectively. The variations of SPAC species and their content ratios indicate that SPAC formation is controlled by the sulfur contents in the low-rank bituminous coals. A total of 18 oxygen-containing PACs (OPACs) were identified in the low-sulfur coal and middle-sulfur coal, whereas only 11 OPACs were found in the high-sulfur samples. The average ratios of OPACs to the identified aromatic compounds (T-OPACs/T-PACs) are 9.81%, 9.62%, and 6.91% in the low-, middle-, and high-sulfur coals, exhibiting a negative correlation with sulfur contents and indicating that OPACs were also influenced by sulfur contents in low-rank bituminous coals. The ratios of total contents of polycyclic aromatic hydrocarbons (PAHs) to total PACs (T-PAHs/T-PACs) are 89.1%, 88.2%, and 82.0% in the low-, middle-, and high-sulfur coals, respectively, indicating a decreasing trend from low- and middle-sulfur coal to high-sulfur coal. This variation could be caused by the reaction of PAHs and sulfur to form SPACs. [ABSTRACT FROM AUTHOR]

To gain insights into the spectroscopy characteristics from coal to graphite, we investigated different metamorphic degrees of coal-based graphite which were collected from Hunan Province China. In this paper, by means of Xray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, graphite with different metamorphism degrees has been characterized to explore the evolution of macromolecular structure of organic matter during graphitization. The results show that with the increase of metamorphism degree, the 002-diffraction peak of the series of samples gradually shrinks and narrows, and the peak intensity becomes stronger, indicating that the microcrystalline structure gradually becomes regular and ordered. As the degree of graphitization increase, the uniformity of particle size in coal samples observed gradually increases, and the morphology becomes more regular, transitioning from disordered and irregular shapes to a structured large-scale flake pattern. The crystallinity improves, and the massive coal particles gradually coalesce into large plate crystals, with the inter-particle pores gradually closing. The graphite structure becomes increasingly evident. The FTIR spectra show that as the degree of graphitization increases, the peak at 1,581 cm-1 corresponding to C=C vibrations gradually intensifies. Some inert functional groups are retained throughout the graphitization process. The pores between coal particles gradually close, and the morphology of graphite particles becomes more regular and ordered. Additionally, during the graphitization process, structures similar to carbon nanotubes may develop. Throughout the structural transformation from coal macromolecules to graphite crystals, the size of the sp2 planar domains in single-layer graphene increases, and the lattice structure of carbon atoms gradually enlarges. These findings contribute to a comprehensive understanding of the properties and characteristics of coal-derived graphite, and can provide theoretical reference and basis for the metallogenic mechanism of coal-derived graphite and the efficient utilization of coal. [ABSTRACT FROM AUTHOR]

Coal seams 41 and 42 of the Heshan Coalfield belong to superhigh-organic-sulfur coals. In order to study the geochemical characteristics of the coals, 15 coal samples and 6 rock samples were collected from both coal seams and the roof/floor rocks. The samples were investigated by using conventional microscopy, inductively coupled plasma mass spectroscopy, X-ray diffraction, X-ray fluorescence, and scanning electron microscopy with an energy-dispersive X-ray spectroscopy. The results show that minerals in the coals are dominated by kaolinite and a mixed layer illite/smectite and illite; small ratios of pyrite, quartz, chlorite, smectite, calcite, and dolomite are also present. Under the microscope, these pyrites occur as framboidal, euhedral, homogeneous, anhedral, nodular, and fine dissemination shapes. In Shicun Mine, the trace elements Li, Y, Zr, Sn, Sm, and Tb are enriched; Zn and Ba are depleted. However, in the Heliluoshan Mine, Mo is significantly enriched; Li, Zr, Cs, and U are enriched; and Co and Ba are depleted. The occurrence of Li and Ga is associated mainly with organic matter and sulfate minerals. U and Mo occur in silicate minerals, carbonate minerals, illite, I/S, and pyrite. A reducing environment is beneficial for the enrichment of V, Cr, Mn, Ni, Mo, Cd, and U. The abundances of sulfur in Heshan were controlled mainly by the degree of seawater influence and hydrothermal activities. [ABSTRACT FROM AUTHOR]