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The anomalous enrichment of the rare earth elements and yttrium (REY), U, Mo, As, Se, and V in the coal-bearing intervals intercalated within the carbonate successions in South China has attracted much attention due to the highly promising recovery potential for these elements. This study investigates the mineralogical and geochemical characteristics of the late Permian coal-bearing intervals (layers A–F) intercalated in marine carbonate strata in the Xian'an Coalfield in Guangxi Province to elucidate the mode of occurrence and enrichment process of highly elevated elements. There are two mineralogical assemblages, including quartz-albite-kaolinite-carbonates assemblage in layers D–F and quartz-illite-kaolinite-carbonates assemblage in layers A–C. Compared to the upper continental crust composition (UCC), the REY, U, Mo, As, Se, and V are predominantly enriched in layers A and B, of which layer A displays the REY–V–Se–As assemblage while layer B shows the Mo–U–V assemblage. The elevated REY contents in layer B are primarily hosted by clay minerals, zircon, and monazite; Mo, U, and V show organic association; and As and Se primarily display Fe-sulfide association. Three geological factors are most likely responsible for geochemical anomaly: (1) the more intensive seawater invasion gives rise to higher sulfur, Co, Ni, As, and Se contents, as well as higher Sr/Ba ratio in layers A–C than in layers D–F; (2) both the input of alkaline pyroclastic materials and the solution/rock interaction jointly govern the anomalous enrichment of REY; and (3) the influx of syngenetic or early diagenetic hydrothermal fluids is the predominant source of U, Mo, V, Se, and As. [ABSTRACT FROM AUTHOR]

The health risks associated with exposure to respirable dust in coal mines have been attracted much attention by an increasing number of researchers. However, the accurate identification of potentially hazardous agents in respirable dusts and the evaluation of the potential health risks arising from it still remains controversial to varying degrees. A comprehensive understanding of the physicochemical properties of respirable dust is a prerequisite and an important basis for resolving this controversy. Therefore, in this study, the particle size distribution and morphology, pore structure, mineralogical and geochemical patterns, and oxidative potential (OP) of respirable coal mine dust were comprehensively investigated. Stepwise multiple linear regression was employed to identify dust components driving OP, such as anatase, tobelite, quartz, and ankerite, in respirable coal mine dust, along with Na, Ni, Se, W, and As. On this basis, we performed a single-factor risk prediction for different coal mines by considering factors that may impact miners' health, with the analyses yielding somewhat contradictory results. Therefore, a multifactor integrated prediction model is proposed using an entropy-based technique for order preference by similarity to the ideal solution to categorize coal mines in the study area into three risk categories, high-, medium-, and low-risk dust mines, which is important for the hierarchical classification and control of coal mines and for formulating appropriate dust prevention and control measures. [Display omitted] • A comprehensive investigation of the physicochemical and oxidative potential characteristics of respirable coal mine dust (RD). • Stepwise multiple linear regression was employed to identify the potentially hazardous agents of RD. • The TOPSIS was used to comprehensively evaluate health risks in various coal mines and sites within those mines. [ABSTRACT FROM AUTHOR]

Oxidative potential (OP) is considered to be an efficient indicator of particulate matter (PM) to induce oxidative stress in the lungs and is increasingly considered to be a relevant health metric. In this study, two complementary OP assays were deployed, including dithiothreitol (DTT) and ascorbic acid (AA) assays, to investigate the potential toxicity (as generators of oxidative stress) of respirable fractions (DD4, < 4 μm) of deposited dust (DD500, < 500 μm) in underground low-S and low-pyrite coal mines in Henan Province, Central China. The OPDTT of DD4 is higher than that reported for other types of atmospheric PM, whereas the OPAA of DD4 is similar and/or slightly higher. Cross-correlation and multilinear regression analyses are applied using datasets of major mineral and geochemical patterns in the DD4 samples and the respective OP values to identify the major drivers for OP in respirable coal dust. Thereafter, the patterns of DD4 are compared with those of DD500 and the parent coals to determine the sources of OP-relevant substances. OPDTT is mainly governed by some trace elements (Sb, As, Li, B, Sr, and Pb) and minor minerals (anatase, quartz, siderite), and their synergistic effect may be one of the reasons for the high DTT consumption. For OPAA, quartz, total clay (sum of illite, kaolinite, tobelite, and clinochlore) and Ni, Cr, Co, Si, and S, play an important role in regulating the OPAA of pyrite-free DD4 samples. These OP-relevant substances have three sources: coal dust, which has a similar composition in DD4, DD500, and the parent coal (such as siderite and its associated elements); gangue dust, which does not occur in the parent coal but is widely detected in DD4 and DD500 (such as quartz, kaolinite, and relevant elements); and cement dust (from gunite galleries), which is mainly calcite- and calcite-associated elements. • A study of the mineralogy, geochemistry and OP of deposited dust, respirable dust and coal in underground coal mines. • OPDTT of size-segregated respirable dust (DD4) is mainly governed by anatase, siderite, quartz, and Sb, As, Li, B, Sr, Pb. • OPAA of DD4 is regulated by anatase, tobelite, kaolinite, and total clay, as well as Ni, Cr, Co, Si, and S. • The parent coal dust, gangue dust, and cement dust are the primarily source of these hazardous materials. [ABSTRACT FROM AUTHOR]

This study systematically investigates the mineralogical and geochemical variations in parent coal, coal gangue (roof, parting, and floor), deposited coal mine dust (DD), and respirable fractions of DD (RD) in an underground coal mine using the blasting mining method in China to evaluate the major sources of DD. The emission of dust in this study is affected by coal gangue sources during the mining process, which causes different geochemical patterns in the DD samples. Moreover, weathering of the cement gunite walls plays an important role in the enrichment of specific elements in the DD from air uptake and air out galleries. Furthermore, the spatial variation in RD characteristics, including mineralogy, geochemistry, and oxidative potential (OP), is discussed, with emphasis on the major health-relevant species and elements. Organic species from coal dust seem to be the essential components contributing to OP rather than metals, although some metals (e.g., Cr, Co, Ge, Se, Zn, Ba, Rb, Cs, Sn, and Pb) influence OP to some degree. [Display omitted] • Deposited coal mine dust, parent coal, and gangue in an underground coal mine using blasting mining method were studied. • Gangue and cement dust mixed into coal dust result in the enrichment of abundant elements. • The primary species driving the oxidative potential are site-dependent. • Organic species, quartz, calcite, and Cr, Co, Ge, Zn, Ba, Rb are highly correlated with toxicity. [ABSTRACT FROM AUTHOR]

This paper represents the first integrated research on the mineralogical, geochemical and stable isotope characteristics of the Upper Triassic high‑sulfur coals from the Khanh Hoa open-pit mine, Thai Nguyen Coalfield, NE Vietnam. Formed in a marine-influenced carbonate succession, the Khanh Hoa coal is characterized by medium ash yield, low volatile matter yield, and high sulfur content. Minerals in the Khanh Hoa coal are predominantly composed of authigenic calcite in the upper portion; and pyrite, quartz, with minor amounts of tobelite ([(NH 4), K] (Si, Al) 4 Al 2 O 10 (OH) 2), gypsum in the middle and lower portions. The high‑sulfur Khanh Hoa coal is enriched in an As-Mo-Sb-U-Cs-P assemblage, which presents both an organic and inorganic mode of occurrence, and is largely ascribed to hydrothermal fluids. The δ 13C values of the Khanh Hoa coal range from −24.77‰ to −22.80‰ (avg. −23.33‰), reflecting a change in sedimentation pattern (from transgressive to high stand system upwards). The δ 15N values of the Khanh Hoa coal range from 2.41‰ to 3.73‰ (avg. 3.30‰), possibly resulted from influenced by seawater influence and a redox environment. The mineralogical, geochemical and isotopic characteristics reflected that the high‑sulfur Khanh Hoa coal was formed/preserved in marine-influenced anoxic environment, with low detrital input, and strong activities of multi-stage hydrothermal solutions. [ABSTRACT FROM AUTHOR]

Underground coal mining produces large amounts of mine water annually in the Shendong mining area of China. Due to the severe scarcity of water resources, mine water is extensively used for productive, domestic, and ecological demands. However, mine water exhibits high fluoride levels. For water-use security, reduction of fluoride exposure and environmental protection, knowledge of sources and geochemical controls of fluoride enrichment in mine water is required. The results showed that F− concentrations of mine waters vary from 0.05 to 11.65 mg/L, with a mean value of 1.96 mg/L, and 51% of the mine waters contain F− concentrations exceeding the Chinese drinking water standard (1 mg/L). The overall mine water quality is influenced by cation exchange, mineral dissolution, pyrite oxidation, silicate weathering and so on. The high-fluoride mine waters are all associated with Na–type, with a remarkable cation composition feature of higher Na+ and lower Ca2+ and Mg2+ concentrations. Overall, the high-fluoride mine waters are well-matched with the water environment with higher pH, TDS, and EC levels. PCA reveals that the geochemical controls on the enrichment of F− in mine waters include dissolution of fluoride-bearing minerals and F−-OH− ion exchange; the former process is mainly caused by the decrease in Ca2+ concentrations resulting from Na + -Ca2+ cation exchange and mineral precipitation, and the latter process benefits from a highly alkaline water environment, facilitating the substitution of OH− in the mine water for F− within or absorbed on the minerals. Evaporation also controls F− enrichment in local areas. [Display omitted] • 51% of mine water samples exceed the Chinese drinking water limit for fluoride (1 mg/L). • The overall mine water quality is influenced by cation exchange, dissolution of minerals and so on. • NaHCO 3 type mine water possesses the highest average fluoride concentration. • Fluoride concentrations are overall proportional to higher pH, TDS, and EC levels. • Fluoride enrichment is related to ion exchange, mineral precipitation, and evaporation. [ABSTRACT FROM AUTHOR]