Analysis of the Coalification Environment of Coal Seams No. 3 and No. 6 in the Yangye Formation of the Karatuzi Mining Area and Directions for Clean Utilisation

The Karatuzi mining area is a key coal resource base in Southern Xinjiang. This paper focuses on Coal Seams No. 3 and No. 6 of the Yangye Formation. Through coal petrology, coal quality and elemental geochemical analyses, combined with assessments of the coalification environment, coal cleanliness grades and direct liquefaction evaluation systems, this study investigates their coalification environments and potential for clean utilisation. The results indicate that both coal seams consist predominantly of the vitrinite group and are classified as medium-rank coals. The ash content of the raw coal ranged from 21.76% to 27.66%; the sulphur content of Coal Seam No. 3 is lower than that of Coal Seam No. 6, whilst the concentrations of Cl, F and As are generally low to moderate. The coalification period of the Yangye Formation was characterised by a generally humid, water-saturated peat bog environment. The raw coal from both Seam No. 3 and Seam No. 6 was classified as Grade IV unclean coal; following flotation, the ash content decreased to 7.31–7.54%, and the cleanliness grades were upgraded to Grade II and Grade III, respectively. Statistical analysis revealed significant changes in moisture content, ash content, volatile matter, sulphur content, fluorine and arsenic. Following flotation, the raw coal attains the potential for use as Grade II coal for direct liquefaction, providing a basis for the quality enhancement and clean utilisation of coal in the mining area.