Due to its environmental and resource impacts, the geochemistry of uranium in coal is of both academic and practical significance. In order to give a comprehensive summary about the geochemistry of uranium in coals, the abundance, distribution, and modes of occurrence of uranium in Chinese coals were reviewed in this paper. Although some coals from southwestern and northwestern China are significantly enriched in uranium, the common Chinese coals are of a comparable uranium concentration to the world coals. The roof and floor rocks, and parting of coalbeds, or coal benches that are close to the surrounding rock are favorable hosts for uranium in one coalbed. The uranium concentrations in coals of different ages decrease in this order, e.g., Paleogene and Neogene > Late Permian > Late Triassic > Late Carboniferous and Early Permian > Late Jurassic and Early Cretaceous > Early and Middle Jurassic. Uranium in Chinese coals is mainly associated with organic matter, and is correspondingly enriched in subbituminous coal and lignite.

In China, the world's largest producer of coal, the mean value of uranium in coal is 3 mg/kg, which is near the published value for uranium in coal in the United States and the world coal average. There are a few examples of Chinese coal that have exceptionally high concentrations of uranium and may be considered as a uranium source. In Hubei province in southern China a special type of stone-coal from the lower Silurian has a uranium concentration of 180 to 280 mg/kg in the coal ash. A few samples from Jurassic coal in Xinjiang of northwest China have more than 200 mg/kg uranium. The uranium in coal is mainly associated with organic matter in low rank coal. In high rank coal the uranium probably occurs in the minerals. In nature, the uranium-rich deposit is rare, and usually small in scale. Uranium abundance and occurrence in different places and strata, especially in coal stone in the South China and in marine shale, have potential hazards on the environment.

Fluorine, a hazard that is associated with coal, has resulted in serious environmental issues during the production and utilization of coal. In this paper, we provide a detailed review of fluorine in Chinese coal, including the distribution, concentration, modes of occurrence, genetic factors, and environmental effects. The average concentration of fluorine in Chinese coal is 130.0 mg/kg, which is slightly higher than coal worldwide (88.0 mg/kg). The enrichment of fluorine in Chinese coal varies across different coal deposit regions, and it is especially high in Inner Mongolia (Junger coalfield, Daqingshan coalfield) and southwest China (coal mining regions in Yunnan, Guizhou province). The fluorine distribution is uneven, with a relatively high content in southwest coal (including Yunnan, Guizhou, Chongqing, and Sichuan provinces), very high content in the coal of North China (Inner Mongolia) and South China (Guangxi), and is occasionally found in the northwest (Qinghai). Fluorine occurs in various forms in coal, such as independent minerals (fluorine exists as fluorapatite or fluorite in coal from Muli of Qinghai, Taoshuping of Yunnan, Guiding of Guizhou, and Daqingshan of Inner Mongolia), adsorption on minerals (fluorine in coal from Nantong, Songzao of Chongqing, Guxu of Sichuan, and Shengli, Daqingshan, and Junger from Inner Mongolia), substitution in minerals (Wuda coal, Inner Mongolia), and a water-soluble form (Haerwusu coal, Inner Mongolia). The enrichment of fluorine is mainly attributed to the weathering of source rock and hydrothermal fluids; in addition to that, volcanic ash, marine water influence, and groundwater affect the fluorine enrichment in some cases. Some environmental and human health problems are related to fluorine in coal, such as damage to the surrounding environment and husbandry (poisoning of livestock) during the coal combustion process, and many people have suffered from fluorosis due to the burning of coal (endemic fluorosis in southwest China).

Microbial decomposition of carbon and biogenic methane in coal is one of the most important issues in CBM exploration. Using metagenomic technologies, the microbial C–N–S functional genes in different hydraulic zones of high-rank coal reservoirs were systematically studied, demonstrating the high sensitivity of this ecosystem to hydrodynamic conditions. The results show that the hydrodynamic strength of coal reservoir #3 in the Shizhuangnan block gradually weakened from east to west, forming a transitional feature from a runoff area to a stagnant area. Compared with runoff areas, stagnant areas have higher reservoir pressure, gas content, and ion concentrations. The relative abundance of genes associated with C, N, and S cycling increased from the runoff area to the stagnant area, including cellulose-degrading genes (e.g., cellulose 1,4-beta-cellobiosidase), methane metabolism genes (e.g., mcr, fwd, mtd, mer, and mtr), N-cycling genes (e.g., nifDKH, amoB, narGHI, napAB, nirK, norC, and nosZ), and S-cycling genes (e.g., dsrAB, sir, cysN, sat, aprAB, and PAPSS). This indicates that the stagnant zone had a more active microbial C–N–S cycle. The machine learning model shows that these significantly different genes could be used as effective indices to distinguish runoff and stagnant areas. Carbon and hydrogen isotopes indicate that methane in the study area was thermally generated. Methanogens compete with anaerobic heterotrophic bacteria to metabolize limited substrates, resulting in a low abundance of methanogens. In addition, the existence of methane-oxidizing bacteria suggests that biogenic methane was consumed by methanotrophic bacteria, which is the main reason why biogenic methane in the study area was not effectively preserved. In addition, weakened hydrodynamic conditions increased genes involved in nutrient cycling, including organic matter decomposition, methanogenesis, denitrification, and sulfate reduction, which contributed to the increase in CO₂ and consumption of sulfate and nitrate from runoff areas to stagnant areas.

To understand the geochemical characteristics of late Paleozoic coal in the Changzhi and Jincheng mining areas in the southeastern Qinshui Basin, major and rare earth element analyses were conducted through inductively coupled plasma-mass spectrometry (ICP-MS), X-ray fluorescence spectrometry (XRF), and proximate analysis. The results show that the study coals are bituminous A rank and anthracite C rank (R _o,ran: 1.6-3.24%) with low-ash, low-moisture, low-volatile, and low- to medium-sulfur characteristics. The main forms of sulfur in the study coals are organic sulfur, followed by pyritic sulfur, only some coals with high sulfur contents in the Taiyuan Formation (SGJ, WTP, FHS) are mainly pyritic sulfur, and the contents of sulfate sulfur are extremely low. The major elements of the late Paleozoic coal in the southeastern Qinshui Basin are mainly SiO₂ (4.77%) and Al₂O₃ (3.64%), followed by Fe₂O₃ (1.22%), CaO (1.53%), FeO (0.48%), MgO (0.25%), Na₂O (0.21%), P₂O₅ (0.18%), TiO₂ (0.15%), and minor K₂O (0.04%) (on a whole-coal basis). Through correlation analysis and cluster analysis, the occurrence states of major elements in the Shanxi and Taiyuan Formations are different. The average rare earth elements and yttrium (REY) value in the study area is 88.68 μg/g (on a whole-coal basis). The mean light REY (LREY)-to-heavy REY (HREY) ratio is 26.33. The mean values of δEu, δCe, Y, and Gd are 0.60, 0.99, 1.07, and 1.02, respectively. The Shanxi Formation is dominated by the L-type REY enrichment, while the Taiyuan Formation is dominated by the M-H-type REY enrichment. The fractionation degree of REY in the Taiyuan Formation is lower than that in the Shanxi Formation. Rare earth elements in Shanxi coal mainly occur in clay minerals, and some rare earth elements are adsorbed and enriched by vitrinite. Rare earth elements in Taiyuan coal mainly occur in clay minerals and pyrite, and some rare earth elements occur in inertinite. A warm, humid, low-salinity, oxidizing, and acidic environment was favorable for REY enrichment. The coal-forming environment was weakly oxidizing and reducing, and the paleosalinity of the water was relatively high during late Paleozoic coal deposition in the southeastern Qinshui Basin. The paleotemperature of the Shanxi Formation is higher than that of the Taiyuan Formation. The provenance is mainly from an upper crustal felsic source region, the source rocks are mainly post-Archean sedimentary and calcareous mudstones mixed with some granite and alkaline basalt from the Yinshan Upland, and the tectonic setting of the source area mainly includes island arcs and active continental margins.