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The sandstone fissure aquifer of the Permian main mining coal seam is the direct water-filled aquifer of the coal mine in northern Anhui Province, China. Hydro-chemistry is important for solving the issue related to water disasters of coal mines, as it can be used for the determination of source of inrush water, and understanding the water-rock interaction process. In this paper, major ion concentrations of groundwater from the in the roof (RW) and floor (FW) in Haizi coal mine have been processed by statistical analysis and water-rock interaction analysis in order to study the differences of hydro-chemical characteristics and genesis. The results show that sandstone fissure water ion contents in RW and FW are obviously different; the chemistry type of FW is Ca-Mg-SO4, followed by HCO3-Cl and HCO3-Cl-SO4, and that of RW is HCO3-Cl, followed by SO4-HCO3-Cl. Compared with the fourth aquifer, Taiyuan group limestone water, goaf water, the proportion of Ca2+, Mg2+, SO42- in the FW and Cl-, HCO3- in the RW are significantly different. Factor analysis and water-rock interaction research show that the FW of 10th coal seam aquifer controlled by “removing sulfate,” silicate mineral dissolution and impact of groundwater runoff. However, the RW is mainly related with the dissolution of minerals, for example, salt minerals (e.g., mirabilite), bitter salt minerals (e.g., salt), silicate minerals, and the dissolution of gypsum.

To investigate the geochemical characteristics of thermally-altered coals formed by igneous intrusion, a series of roof and floor mudstone, thermally-altered coal, and igneous rock samples were collected from a representative borehole profile of the Pansan No. 4-2 coals of the Huainan Coalfield, Anhui Province, Eastern China. Furthermore, seven unaltered coal samples from the same coalbed were collected from seven coal mines of the Huainan Coalfield for comparison. The minerals were analyzed using X-ray diffractometry and optical microscopy. The major element oxides and trace elements were determined by X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), ICP-MS with collision/reaction cell technology, an ion-selective electrode (ISE), and a DMA-80 mercury analyzer. The results indicate that kaolinite and quartz are the dominant minerals in the thermally-altered coals, and pyrite is dominant at the contact zone between the thermally-altered coal and igneous rock. The unaltered Huainan No. 4-2 coals were slightly enriched in only Cr, Se, and W compared to the Chinese coals. However, the thermally-altered coals were slightly enriched in F and V and depleted in Co, Ni, Hg, Sb, Zn, and W compared to the Chinese coals. Although the igneous intrusion reached a thickness of 1.97 m, it had a limited effect on the trace elements of terrigenous origin, i.e., Li, F, Sr, Sn, V, Cr, Co, Ni, Cs, Sc, Ga, Rb, Zr, Nb, Ag, Cd, In, Ba, Hf, Ta, W, Th, U, and rare earth elements and Y (REY). Contact metamorphism resulted the devolatilization and redeposition of coal organic matter, which increased the Be and Ge concentrations of the thermally-altered coals adjacent to the intrusion. Copper, As, Sb, Tl, and Bi were transported by the igneous intrusion and redeposited in the thermally-altered coals. The coals were almost completely stripped of Zn, Se, Mo, Pb, and Hg by the igneous intrusion.

The geochemistry of source rock–controlled coals from the Late Triassic Daqiaodi Formation in the Dabaoding Coal Mine of the southwestern Sichuan Province was investigated. A total of 15 coal samples, 6 parting samples, and 4 roof and floor rock samples from the D15–3 and D18 coals were subjected to proximate and ultimate analyses for coal quality, by using LTA-XRD with Siroquant software for minerals, XRF for major element oxides, ICP-MS for trace elements, ICP-CCT-MS for As and Se, ISE for F, and a DMA-80 analyzer for Hg. Results indicate that the Dabaoding D15–3 and D18 coals are classified as low ash and low-volatile bituminous coal. Minerals in coals are dominated by quartz, kaolinite, illite, and dolomite. Most trace elements in the Dabaoding coals are depleted or at normal levels relative to Chinese coals or world hard coals (except for Cr with slight enrichment). The Dabaoding coals and host rocks are characterized by weakly positive Ce and Y anomalies, strongly positive Gd anomalies, and weakly negative Eu anomalies. Based on paleogeographical, mineralogical, and geochemical evidence, the sediment source rocks of the Daqiaodi coal-bearing strata are identified as the Panzhihua trachyte at the top of the Kangdian Upland, which exerted crucial impacts on the Dabaoding coals.

The Donglin Coal Mine, an important mine in the Nantong coalfield in southwestern Chongqing, is immediately adjacent to the Songzao coalfield. To investigate the mineralogy and geochemistry of Donglin coals, profile channel samples from the mineable Nos. 4 and 6 coals were collected. The minerals, major element oxides, and trace elements were analyzed by LTA-XRD in combination with Siroquant software, XRF, ICP-MS, ICP-CCT-MS (As and Se), ISE (F), and DMA-80 Hg analyzer (Hg). The results indicate that the Donglin low volatile bituminous coals were characterized by low ash yields and high total sulfur contents. The minerals varied between the Nos. 4 and 6 coals, differentiated by montmorillonite, calcite, ankerite, and pyrite. Despite the low boron concentration, Donglin coals were influenced by brackish water during coal accumulation. Selenium (10.9 mg/kg), F (431 mg/kg), Hg (0.350 mg/kg), Nb (20.7 mg/kg), and Ta (3.68 mg/kg) in the No. 4 coals, and F (425 mg/kg), Be (7.11 mg/kg), Ga (14.5 mg/kg), Ge (22.5 mg/kg), Zr (218 mg/kg), Nb (35.5 mg/kg), and Ta (4.42 mg/kg) in the No. 6 coals are slightly enriched. Four vertical distributions of elements were demonstrated, i.e., roof, floor, roof and floor, and middle enrichments. The slightly enriched trace elements and UCC-normalized REY distribution patterns of the Donglin coals jointly eliminated the impact of various volcanic ashes and terrigenous input from the Kangdian Oldland during the Late Permian. However, the roof rock samples shared the geochemical feature of mafic tonstein (enriched Sc, V, Cr, Co, and Ni), while the floor rock of the No. 6 coals resembles alkali tonsteins (enriched Ga, Zr, Nb, Ta, Hf, and REY). Lithium, Ga, Zr, Ag, Cd, In, Sn, Cs, Hf, Bi, Th, and U occurred in kaolinite and/or montmorillonite in the No. 4 coals, while Li, Nb, Ag, Cd, In, Cs, Ba, and Th occurred in kaolinite in the No. 6 coals. Vanadium, Sr, and Mo in the No. 4 coals, and Sr and Sc in the No. 6 coals were associated with calcite and/or ankerite. Arsenic, Se, Hg, Sb and Tl, and Hg and Mo were associated with pyrite in the Nos. 4 and 6 coals, respectively. Lithium, Be, Ge, and Sb in the No. 4 coals and Be and Ge in the No. 6 coals might be of organic affinity.

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.

Uranium, which is of chemotoxic and radiotoxic, is connately present in coals. In view of its dual roles in resource recovery and environmental impact, the geochemistry of uranium in Chinese coals and its atmospheric emission by coal-fired plants in China are discussed in this article. The average uranium concentration of the majority of Chinese coals is 2.43 mg/kg, which is comparable to that of world coals. However, in coals from certain local regions of China, i.e. Yunnan, Guizhou, Guangxi, Xinjiang, Inner Mongolia, and Chongqing Provinces, the uranium is significantly enriched; and even abnormally enriched to form coal-hosted uranium deposits, e.g. coals from the Yili and Tarim Basins of Xinjiang Province, Bangmai Basin of Yunnan Province, and Mabugang Basin of Guangdong Province. Uranium in Chinese coals is associated with organic matter, silicates, pores, pelitic components, phosphate minerals, and uranium minerals. The enrichment of uranium in Chinese coals is attributed to the weathering of source rocks, volcanic ashes, magmatic intrusion, marine water influence, groundwater, hydrothermal fluids, organic matter, palaeoclimate, and the geologic conditions of coal-accumulating basins. Uranium is prior to partition into fly ash. About 62.9 tons of uranium were released into atmosphere from Chinese coal-fired power plants in 2014. Some environmental and human health problems were historically related to uranium in coal worldwide.