Fourier transform infrared spectroscopy (FTIR) was used to study the molecular structure of four medium- and low-temperature heat-treated medium-rank coals. The FTIR spectral parameters, which consist of CH₂/CH₃, aromaticity (f_a), aromatic carbon rate (f_C), aromatic hydrogen rate (f_H), oxygen-containing (C–O) rate (IR), organic matter maturity (M), and the degree of aromatic condensation (Dc), indicate different characteristics, including changes in the aromatic hydrocarbon structure, fatty hydrocarbon structure, hydroxyl structure, and oxygen-containing functional groups of medium-rank coal. The results show that with the increase in heat treatment temperature, the sulfur content in coal gradually decreases, but the C/H ratio gradually increases. Meanwhile, the content of kaolinite and pyrite in coal gradually decreases, whereas the content of dolomite and hematite gradually increases. With the increase in heat treatment temperature, the relative content of ether oxygen hydroxyl groups in the hydroxyl structure significantly decreases, but the relative content of self-associated hydroxyl groups increases. The relative content of alkyl ether (C–O) in oxygen-containing functional groups gradually increases, whereas the relative content of aromatic nucleus C=C vibration presents a trend of first increasing and then decreasing. In addition, –CH₂– is the majority in the structure of fatty hydrocarbons, and the absorption peak intensity of asymmetric –CH₃ stretching vibration increases with the increase in heat-treated temperature. The structure of aromatic hydrocarbons mainly consists of four substituted benzene rings (except for R-303.15 K), in which the relative content of the trisubstituted benzene ring decreases with the increase in heat treatment temperature. With the increase in the heat-treated temperature of medium-rank coal, Dc, f_H, f_C, and f_a show a trend of first increasing and then decreasing, M and IR reveal a trend of first decreasing and then increasing, and CH₂/CH₃ present a gradually decreasing trend. In conclusion, during the increase in the heat treatment temperature of medium-rank coal, the length of the fatty side chains in the fatty hydrocarbon structure becomes shorter, the number of branch chains continuously increases, and the maturity and condensation degree of organic matter first increases and then decreases. On this basis, further research on the effect of coal gasification suggests combining various technologies such as ¹³C NMR, XRD, and TG-MS to obtain semi-quantitative structural information of molecules in coal from different perspectives.

The treatment of sludge has received a lot of attention due to its intractable status and potential resource value. In order to explore methods of sludge resource utilization and to reduce the harm of heavy metals in municipal sewage, this study analyzed the preparation method of a modified sludge adsorbent (MSA). Another common waste (fly ash) was added to raw domestic sludge (RDS) in a certain proportion and developed to have the ability to adsorb heavy metals through multiple steps such as drying, mixing, activation and carbonization. The adsorption performance of the modified sludge adsorbent (MSA) was verified by simulating wastewater containing Cu²⁺ and Cd²⁺, and the surface and structural properties were studied from a microscopic perspective with the aid of SEM and XRD. This study showed that the MSA was characterized by increased microporosity, an enlarged surface area and enhanced activity of functional groups, and the best performance for heavy metal adsorption was found when the RDS was mixed with fly ash at a ratio of 4:3 and a pH of 8. The highest removal rates for the heavy metals Cu²⁺ and Cd²⁺ were 99.6% and 99.7%, respectively. The adsorption kinetics and adsorption isotherms indicated that the adsorption behavior of the MSA was controlled by both physical and chemical adsorption, and the best fit of the Langmuir adsorption isotherm model revealed the predominance of monolayer adsorption. The present study is a meaningful exploration of the resource utilization of sludge and fly ash and can provide a cheaper and more effective material for addressing heavy metal pollution in domestic sewage.

The research of sulfur content and logging parameters in coal seams is of great significance for accurate mining and efficient utilization of coal. Taking 81 coal samples collected from the Upper Paleozoic in North China as an example, coulometric titration and chemical reagent methods were used to determine the contents of total sulfur and morphological sulfur in coal seams, and correlation analysis and multivariate linear fitting methods were used to analyze the relationship between total sulfur in coal and the shape and peak value of logging curve. The results show that the content of total sulfur in the Upper Paleozoic coal seams ranges from 0.19% to 12.36%. The morphological sulfur in coal is mostly pyrite sulfur, followed by organic sulfur and sulfate sulfur. The logging curves of the deep lateral resistivity log (LLD), natural gamma ray (GR), short-distance gamma gamma (CGS), and spontaneous potential (SP) in coal seams from Shanxi Formation are funnel-shaped, tooth-shaped, box-shaped, and flat-shaped, respectively. The shapes of LLD corresponding to a few coal seams with a sulfur content of less than 3.0% are finger-shaped and bell-shaped, and GR is finger-shaped. The GR, CGS, acoustic (AC), and density (DEN) curves corresponding to Taiyuan Formation coal seams with a total sulfur content more than 3.0% (S_t,d ≥ 3.0%) are mainly box-shaped, and the LLD curve corresponding to high-sulfur coal seams is mostly tooth-shaped. The LLD, GR, CGS, and AC curves are second only to funnel-shaped, and the DEN curve is tooth-shaped. The LLD, GR, AC, CGS, and DEN curves of coal seams with a total sulfur content less than 3.0% are mainly box-shaped. GR, AC, and DEN curves are next to tooth-shaped, LLD is bell-shaped, and CGS curve is finger-shaped. The total sulfur content in coal has a negative correlation with LLD and CGS values and a positive correlation with GR, AC, DEN,and SP values. The prediction model of total sulfur in coal is established by using a multivariate linear fitting method through geophysical logging parameter values, which can provide a method for comprehensively quantifying the change of total sulfur content in coal seams.

This study aims to investigate the depositional environment, sediment sources, and elemental occurrence of Upper Paleozoic coal in the Renjiazhuang Mining District, Western Ordos Basin. Furthermore, SEM-EDX, optical microscope (OM), ICP-AES, ICP-MS, and AAS were used. Compared with hard coal of the world, M3 coals were enriched in Ga, Li, Zr, Be, Ta, Hf, Nb, Pb, and Th, M5 coals were enriched in Li (CC = 10.21), Ta (CC = 6.96), Nb (CC = 6.95), Be, Sc, Ga, Hf, Th, Pb, Zr, In, and REY, while M9 coals were enriched in Li (CC = 14.79), Ta (CC = 5.41), Ga, W, Hf, Nb, Zr, Pb, and Th. In addition, minerals were mainly composed of kaolinite, dolomite, pyrite, feldspar, calcite, and quartz, locally visible minor amounts of monazite, zircon, clausthalite, chalcopyrite, iron dolomite, albite, fluorite, siderite, galena, barite, boehmite, and rutile. In addition, maceral compositions of M3 coals and M9 coals were dominated by vitrinite (up to 78.50%), while M5 coals were the main inertite (up to 76.26%), and minor amounts of liptinite. REY distribution patterns of all samples exhibited light REY enrichment and negative Eu anomalies. The geochemistry of samples (TiO₂ and Al₂O₃, Nb/Y and Zr × 0.0001/TiO₂ ratios, and REY enrichment types) indicates that the sediment sources of samples originated from felsic igneous rocks. Indicator parameters (TPI, GI, VI, GWI, V/I, Sr/Ba, Th/U, and Ce_N/Ce_N*) suggest that these coals were formed in different paleopeat swamp environments: M3 coal was formed in a lower delta plain and terrestrial (lacustrine) facies with weak oxidation and reduction, and M5 coal was formed in a terrestrial and dry forest swamp environment with weak oxidation–oxidation, while M9 coal was formed in a seawater environment of humid forest swamps and the transition from the lower delta plain to continental sedimentation with weak oxidation and reduction. Statistical methods were used to study the elemental occurrence. Moreover, Li, Ta, Hf, Nb, Zr, Pb, and Th elements were associated with aluminosilicates, and Ga occurred as silicate.

With the large-scale closure of coal mines leading to groundwater pollution, in order to systematically identify the sources of major chemical ions in surface water and groundwater. This study comprehensively applied methods such as Piper’s trilinear diagram, linear fitting, and correlation analysis to quantitatively analyze the hydrochemical characteristics of closed coal mining areas in southwest Shandong and to clarify the sources of geochemical components in surface water and groundwater, and the PMF model was used to analyze the sources of chemical components in mine water and karst water. The results show that the concentrations of TDS ( Total Dissolved Solids), SO₄²⁻, Fe, and Mn in the mine water of the closed coal mine area are higher than in the karst water. Both water bodies are above groundwater quality standards. Ca²⁺, SO₄²⁻, and HCO₃⁻ dominate the ionic components in surface water and different types of groundwater. The hydrochemical types of surface, pore, and mine waters are mainly SO₄-HCO₃-Ca, whereas SO₄-HCO₃-Ca and HCO₃-SO₄-Ca dominate karst waters. SO₄²⁻ is the leading ion in the TDS of water bodies. The mineralization process of surface water is mainly controlled by the weathering of silicate minerals, while that of the groundwater is mainly controlled by the dissolution of carbonate minerals. The impact of mining activities on surface water and groundwater is significant, while the impact of agricultural activities on surface water and groundwater is relatively small. The degree of impact of coal mining activities on SO₄²⁻ concentrations in surface water, pore water, and karst water, in descending order, is karst water, surface water, and pore water. The PMF (Positive Matrix Factorization) model analysis results indicate that dissolution of carbonate minerals with sulphate and oxidation dissolution of sulfide minerals are the main sources of chemical constituents in mine waters. Carbonate dissolution, oxidation dissolution of sulfide minerals, domestic sewage, and dissolution of carbonate minerals with sulphate are ranked as the main sources of chemical constituents in karst water from highest to lowest. These findings provide a scientific basis for the assessment and control of groundwater pollution in the areas of closed coal mines.