In order to ascertain the kaolinite crystallinity of Carboniferous Permian coal-measure kaolinite rocks, seven groups of fresh samples were collected from below the ground in the Xiaoyu mine, Datong coalfield. Microscopy, X-ray diffraction (XRD), differential thermal analysis (DTA), infrared (IR) spectroscopy and X-ray fluorescence (XRF) spectrometry methods were applied to the samples. The petrographic analysis results show that the kaolinite rocks are characterized as compact, phaneritic, clastic, sand-bearing, sandy and silty types; the kaolinite content in the Shanxi formation and upper Taiyuan formations was more than 95%, while it was 60–90% in the middle and lower Taiyuan formations. Based on the Hinckley index and the features of XRD, DTA and IR of kaolinites, crystallinity was classified as having three grades: ordered, slightly disordered and disordered. The kaolinites’ SiO₂/Al₂O₃ molar ratio was about 1.9–5.7, with a chemical index of alteration (CIA) of about 95.4–99.5. This research suggests that the kaolinite crystallinity correlates positively to its clay mineral content, purity and particle size, which are also related to the SiO₂/Al₂O₃ molar ratio and CIA. The original sedimentary environment and weathering have a direct influence on kaolinite crystallinity, and the existence of organic matter is conducive to the stable existence of kaolinite. The study results have significance for the extraction and utilization of coal-measure kaolinite and the development of kaolinite crystallography and mineralogy.

Nitrogen is one of the significant pollutants emitted from coal combustion, and the study of its distribution and occurrence is very important for the efficient and clean utilization of coal resources. Four kinds of coal with different metamorphic ranks from major coal-producing provinces of China were studied. A gravity float-and-sink experiment was applied to obtain coal samples with different densities from Shanxi Province. The microscope optical method, Kjeldahl method, and X-ray photoelectron spectroscopy (XPS) were used to assess the occurrence, form, and distribution of nitrogen in the coal. The results show that the nitrogen content was about 0.47%–1.85%, and the maximum nitrogen content was positively correlated with the rank of coal, but the difference was not obvious. In the low-rank coal, the nitrogen content was mainly related to vitrinite and inertinite, while in the middle–high-rank coal, the nitrogen content was mainly related to inertinite and minerals. Pyrrolic (N-5) and pyridinic (N-6) were the main forms of nitrogen in the low-rank coal. The contents of N-6 and N-5 decreased with increases in the coal density, but the contents of quaternary N-Q1 and quaternary N-Q2 increased. N-Q2 mainly comes from fixed ammonia nitrogen in minerals, and vitrinite and liptinite contain more N-6 and less N-Q1 than inertinite. This research provides valuable evaluation guidance for the efficient utilization of coal.

Through the stability evaluation of a slope, a landslide geological disaster can be identified, and the safety and risk control of a project can be ensured. This work proposes an improved sparrow search algorithm to optimize the slope safety factor prediction model (ISSA–BP) of a BP neural network, through an improvement in two aspects: introducing dynamic weight factors and reverse learning strategies to realize adaptive searches. The optimal value improves a defect in the traditional model, preventing it from easily falling into the local minimum. First, combined with 352 sets of actual slope data, three machine learning models were used to predict the safety factor of the slope. Then, the accuracy index was used for evaluation. Compared with other models, the MAPE, RMSE, and R² of the ISSA-BP model were 1.64%, 0.0296, and 0.99, respectively, and the error was reduced by 78% compared with the BP neural network, showing better accuracy. Finally, the three models were applied to the slope stability analysis of Tianbao Port in Wenshan Prefecture. The research shows that the predicted value of the ISSA–BP model was the closest to the actual safety factor, which verified the experimental results. The improved ISSA–BP model can effectively predict the safety factor of slopes under different conditions, and it provides a new technology for slope disaster warning and control.

The Carboniferous-Permian coal measure strata in the Qinshui Basin exhibit highly lithium (Li) enrichment, with substantial exploitation potential. To further explore the enrichment mechanism of lithium in coal measure strata, the No. 15 coal of the Taiyuan Formation from the Gaoping mine is taken as the research object, and its mineralogical and geochemistry characteristics are evaluated using optical microscopy, X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry, X-ray fluorescence, and infrared spectral. The results show that the No. 15 coal is semi-anthracite coal with low moisture, low ash, low volatility, and high sulfur. Organic macerals are primarily vitrinite, followed by inertinite, and liptinite is rare; the inorganic macerals (ash) are dominated by clay minerals (predominantly kaolinite, cookeite, illite, and NH₄-illite), calcite, pyrite, quartz, siderite, gypsum, and zircon. The average Li content in the coal is 66.59 μg/g, with higher content in the coal parting (566.00 μg/g) and floor (396.00 μg/g). Lithium in coal occurs primarily in kaolinite, illite, cookeite, and is closely related to titanium-bearing minerals. In addition, Li in organic maceral may occur in liptinite. The No. 15 coal was formed in the coastal depositional system, and the deposition palaeoenvironment is primarily a wet–shallow water covered environment in open swamp facies; the plant tissue preservation index is poor, and aquatic or herbaceous plants dominate the plant type. The reducing environment with more terrestrial detritus, an arid climate, and strong hydrodynamic effects is favorable for Li enrichment in coal. The results have important theoretical significance for exploring the enrichment and metallogenic mechanisms of Li in coal.

Coal-bearing strata in the Ningdong Coalfield (western Ordos Basin) contain elevated concentrations of critical metals; however, the processes governing their enrichment remain incompletely understood. This study integrates zircon U–Pb geochronology, LA-ICP-MS elemental mapping, sequential chemical extraction, and mineralogical and bulk geochemical analyses to constrain the provenance, host phases, and enrichment mechanisms of Li, REY, and Ga in Late Carboniferous–Early Permian coals from the Ningdong Coalfield. The No. 5 and No. 9 coals are medium-ash bituminous coals significantly enriched in Li and rare earth elements and yttrium (REY) relative to world coal averages. Zircon U–Pb ages reveal distinct provenance for the two coal seams: the No. 5 coal records a dominant, proximal volcanic source linked to the Central Asian Orogenic Belt (CAOB) at ca. 298 Ma, whereas the No. 9 coal reflects mixed contributions from both the CAOB and the Alxa Block. Tonsteins and dispersed pyroclastic materials, interpreted as altered alkaline to peralkaline volcanic ash, constitute the principal source of critical elements. Titanium-bearing vermicular kaolinite formed through in situ alteration of volcanic ash exhibits the highest Li concentrations among the host phases, whereas REY are mainly concentrated in authigenic goyazite within phosphorus-rich horizons. Coal benches adjacent to tonsteins and partings display higher concentrations of Li, REY, and Ga than the associated non-coal lithologies, indicating leaching and redistribution of these elements by acidic diagenetic fluids. The weighted mean Li2O concentrations in coal ash reach 861 μg/g and 871 μg/g for the No. 5 and No. 9 coals, respectively, exceeding the proposed recovery threshold (800 μg/g); rare earth oxides (REO) contents locally attain ~5200 μg/g, substantially surpassing the cut-off grade (1000 μg/g); and Ga in the No. 9S coal ash averages 157 μg/g, exceeding the economic cut-off (100 μg/g). These results demonstrate that coupled alkaline volcanic ash input and acidic leaching exert the primary control on critical-element enrichment in the Ningdong Coalfield, suggesting that critical-element mineralization is regionally pervasive rather than locally confined.