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Mineral matter, including minerals and non-mineral elements, in coal is of great significance for geological evolution, high-value coal utilization, and environment protection. The minerals and elemental geochemistry of Late Permian coals from the M8 coal seam, Shihao mine, Songzao coalfield in Chongqing, were analyzed to evaluate the sediment source, sedimentary environment, hydrothermal fluids, and utilization prospects of critical metals. The average total sulfur (4.21%) was high in coals, which mainly exists in the forms of pyritic sulfur. Kaolinite, pyrite, calcite, quartz, illite and illite/smectite (I/S) mixed layers, and anatase predominated in coals, with trace amounts of chlorite, ankerite, and siderite. Epigenetic cell- and fracture-filling pyrite, veined calcite, and ankerite were related to hydrothermal fluids and/or pore water after the diagenesis stage. Compared to the world's hard coals, As and Cd are enriched in the Shihao M8 coals, and Li, Cr, Co, Zr, Mo, Pb, and Tb are slightly enriched. These high contents of sulfophile elements may be related to seawater intrusion. The terrigenous clastics of the Shihao M8 coals originated from the felsic–intermediate rocks atop the Emeishan Large Igneous Provinces (ELIP) (Kangdian Upland), while the roof and floor samples were derived from Emeishan high-Ti basalt. Through the combination of sulfur contents and indicator parameters of Fe2O3 + CaO + MgO/SiO2 + Al2O3, Sr/Ba and Y/Ho, the depositional environment of peat swamp was found to be influenced by seawater. Although the critical elements in coal or coal ash did not reach the cut-off grade for beneficial recovery, the concentration of Li and Zr were high enough in coal ash. [ABSTRACT FROM AUTHOR]

The indicative significance of organic matter in fossil fuels, particularly polycyclic aromatic compounds (PACs), is a current research hotspot. Petrology, minerals, and organic matter in Late Permian coals from the Moxinpo (MXP) mine located in Chongqing, southwestern China, were analyzed to evaluate the coal rank, coal-forming material source and thermal maturity of organic matter, and sedimentary environment of the peat swamp. Vitrinite and inertinite were dominated by collotelinite, collodetrinite, inertodetrinite, fusinite, and semifusinite. Owing to the high maturity of the coals, liptinite was not observed under the microscope. Clay (kaolinite) and pyrite were the primary minerals in the MXP coals, followed by calcite, quartz, trace amounts of anatase, gypsum, xenotime, and bastnaesite. The minerals in the MXP coals were authigenic primarily in the epigenetic stage. The extract yield of organic matter in coals was low (0.30%), and the saturated and aromatic fractions accounted for approximately 60% of the extractable organic matter. Low ratios of saturated to aromatic compounds reflected the terrestrial higher plants input and high maturity level of the coals. The extracted yield in the host rock samples was much lower than in the coals, while the proportion of saturated hydrocarbons was relatively high. The marine-continental transitional sedimentary environment, distribution of n -alkanes, ∑ C 21 − /∑ C 22 + , and pristane (Pr)/ n -C 17 vs. phytane (Ph)/ n -C 18 indicated that the organic matter originated from the input of terrestrial higher plants and was accompanied by the contribution of marine lower phytoplankton and aquatic organisms. The coal-forming environment of the coal seam was reductive according to the Pr/Ph and sulfur-containing compounds of dibenzothiophenes and benzonaphthothiophenes. The thermodynamic stability controls the presence of polycyclic aromatic hydrocarbons in extractable organic matter. Isomeric compounds with high stability had higher concentrations, such as 2-methylnaphthalene, 2,6 + 2,7-DMN, 4- methylbiphenyl, and 2- methylphenanthrene. [Display omitted] • Macerals were primarily vitrinite and inertinite, while liptinite was absent. • Minerals were dominated by kaolinite, pyrite, calcite, and quartz in the MXP coal. • Organic matter in coals was dominated by the input of terrestrial higher plants. • Coal-forming environment was a reductive and marine-continental transitional environment. • Concentration of isomer compounds was controlled by thermodynamic stability. [ABSTRACT FROM AUTHOR]

Critical metals play an irreplaceable role in supporting the development of the global economy and emerging industries. Their short supply makes the recovery of critical metals from alternative sources, such as coal ash, a research hotspot. In this study, Chongqing Power Plant coal and its combustion products, which are rich in a variety of critical metal elements, were selected for the study. The enrichment, distribution, and occurrence mode of critical elements in the products of coal combustion was studied, and improved sequential chemical extraction procedure, and their extraction potential was proposed and discussed. The results show that the contents of the most critical elements in different coal ashes are generally high in the order of fly ash, slag, and bottom ash. The critical elements Li, Ga, Sr, Zr, Hf, Nb, Ta, and rare earth elements and yttrium (REY) are enriched in fly ash and the contents of Ga, Nb, and REY exceed their respective industrial utilization grades, which have great recovery potential. Lithium, Ga, Nb, Ta, and REY are mainly distributed in small particle sizes in non-magnetic fly ash and occur in aluminosilicate glass, followed by mullite and quartz. Three categories of extractability are proposed: easy-to-extract form, relatively easy-to-extract, and difficult-to-extract forms. Finally, future research should focus on the collaborative extraction of multiple critical elements (such as Li, Ga, Nb, and REY) from coal ash. [Display omitted] • Most critical elements in different coal ashes are high. • Critical elements Li, Ga, Sr, Zr, Hf, Nb, Ta, and REY are enriched in fly ash. • An improved sequential chemical extraction procedure was developed. • Li, Ga, Nb, Ta, and REY concentrate in small particle-sized, non-magnetic fly ash. • Three categories of extractability of critical elements are proposed. [ABSTRACT FROM AUTHOR]