The low-temperature oxidation of coal is a core process that induces spontaneous combustion disasters in coal mines. Through comprehensive analysis of nitrogen adsorption isotherms, fractal dimensions, gas-release characteristics during programmed-temperature oxidation, and Raman spectroscopy, the synergistic effects of pore structure, temperature, and molecular activity in low-temperature coal oxidation are systematically clarified. The pore fractal architecture regulates the staged oxidation process and heat-release behavior of coals with different metamorphic degrees by controlling oxygen adsorption-diffusion pathways and coupled heat and mass transfer processes. Medium-rank coals are more prone to exothermic oxidation during the accelerated oxidation stage, whereas high-rank coals are easily oxidized in the rapid-oxidation stage after undergoing structural damage. Before and after oxidation, the surface fractal dimension D 1 , in the low-pressure region, decreases from 2.42 to 2.63 to 2.16-2.41, while the structural fractal dimension D 2 , in the high-pressure region, increases from 2.45 to 2.66 to 2.59-2.75. The comprehensive Raman parameter (AD /ATotal) indicates that higher-rank coal samples initially possess more stable aromatic structures. An increase in the AD /ATotal ratio above 90 degrees C indicates oxidative cleavage of aromatic skeleton and generation of active oxygen-containing functional groups. Furthermore, changes in the volume ratio of CO and CO2 (R value), Graham index, and AD /ATotal ratio collectively suggest 60-70 degrees C as the critical temperature range for slow oxidation and 90-130 degrees C as rapid oxidation stage. This study reports a theoretical multi-scale "pore-temperature-structure-activity" framework, and the spontaneous combustion of coal by low-temperature oxidation is jointly due to fractal pore structure, temperature, and molecular evolution.

In the field of coal mine safety, radon detection technology is mainly used to identify the sources of coal spontaneous combustion (CSC) fires. Here, a method for calculating the rate of transmission of radon gas in the rock layer overlying the CSC region is proposed. The radon transmission rate in rock as a function of temperature was investigated through laboratory-scale experiments. In addition, numerical simulations were carried out in COMSOL to calculate the changes in the radon concentration and radon transmission rate in the overlying rock layer after 30, 60, and 85 days of CSC. Finally, field experiments were conducted by drilling samples at different locations in the mine site and analyzing the levels of radon daughter nuclei present. The results show that radon release peaks at 250 °C, reaching 3.1-3.9 times the value at 30 °C. Simulated peak radon transmission rates after 60 and 85 days of CSC are 52.7% and 40.8% higher, respectively, than after 30 days. Field-measured average transmission rates in fire zones are 42.8%-50.5% higher than in the non-fire zone. A previously unreported nonlinear profile of radon transmission rate with distance is revealed: the rate increases sharply to a peak from the fire source, then gradually declines and stabilizes. The enhancement effect of CSC weakens with increasing distance. Porosity variations at layer interfaces induce only minor fluctuations in transmission rate. The results of this study can help to improve the current understanding of the mechanism of long-distance radon transmission in rock formations and guide the accurate application of radon detection technology in the field.

To explore efficient valorization of coal-based solid wastes, a multivalent-ion-coordinated composite colloid (PFM) was synthesized using activated fly ash (AFA) solution and coal mine sludge (CMS) as primary components, with sodium polyacrylate (PAAS) as matrix material. Orthogonal experiments evaluating the gelation time, viscosity, permeability, and thermal stability of the colloid identified the optimal formulation as 3% PAAS, 30% AFA solution, and 15% CMS. SEM analysis revealed a dense colloid microstructure, in which high-valence metal cations (Fe³⁺, Al³⁺) released from FA and CMS undergo complexation crosslinking with the functional groups (-COONa, -COOH, and -CONH₂) of PAAS and hydrolyzed polyacrylamide (HPAM). Concurrent intermolecular hydrogen bonding among these groups generates a three-dimensional co-crosslinked polymer network with uniformly embedded solid particles, providing excellent water retention and structural stability. The inhibition tests demonstrate that the colloid effectively suppresses CO generation during coal oxidation, achieving maximum inhibition values of 50% for lignite and 46% for coking coal. Thermodynamic analysis showed that the treated coal samples exhibited reduced mass loss rates and exothermic peak intensities, alongside increased characteristic temperatures and activation energies, suggesting a lower coal spontaneous combustion (CSC) tendency. In-situ FTIR analysis confirmed that the addition of the colloid inhibits aliphatic hydrocarbons in raw coal and reduces the formation of oxygen-containing functional groups. Furthermore, the flame-retardant mechanism of the colloid was systematically elucidated. Therefore, the PFM composite colloid is an environmentally friendly and efficient fire prevention material. Its application not only reduces costs and environmental impacts but also enables the synergistic utilization of multiple coal-based solid wastes.

This study systematically investigates the combustion characteristics, active functional group evolution, and kinetic behavior of bituminous coal (BC) when co-combusted individually with five different types of biomass (soybean straw, peanut shell, walnut shell (WNS), wheat straw, and corn straw), at mass ratios of 1:9, 3:7, 5:5, 7:3, and 9:1. The investigation was conducted by TG-DSC, in-situ FTIR spectroscopy, and the Coats-Redfern integral kinetic method. The results demonstrate that biomass incorporation reduces the ignition and burnout temperatures of the blended fuels, enhances their combustion reaction rate, and elevates the overall combustion characteristic index, eventually enhancing the combustion reactivity of BC. The kinetic analysis of the WNS - BC blends reveals that the activation energy during the volatile release stage progressively decreases from 58.5508 kJ & sdot;mol(-1) (pure BC) to 20.7019 kJ & sdot;mol(-1) (WNS9BC1 blend) due to the synergistic effect of WNS incorporation in enhancing BC combustion and facilitating combustion reactions. FTIR spectroscopy analysis indicates that increase in the WNS proportion gradually enhances the peak areas of the -CH3 and -CH2 groups. At the WNS:BC mass ratio of 5:5, the conversion of C=O groups is more extensive, which inhibits the formation of -C-O- functional groups through oxidation while facilitating the conversion of more C=O functional groups into -COOH groups. These -COOH groups are more prone to decarboxylation during subsequent thermal treatment, which is accompanied by the release of volatile matter. Furthermore, the co-combustion of the five selected biomass materials with coal exhibits significant synergistic effects. A comprehensive multi-scale evaluation suggests that the optimal recommended mass ratio of WNS with BC is 30-50 wt.%.

It is imperative to have an in-depth understanding of coal spontaneous combustion based on multi-scale characterization of the activation energy not only for preventing fires in the coal industry but also for reducing emissions of hazardous gases. In this study, three coal samples with different degrees of metamorphism were selected. Activation energies for CO and CO2 generation during spontaneous combustion were determined using isothermal oxidation. The activation energy related to mass changes during spontaneous combustion was calculated using thermogravimetric analysis. The kinetic characteristics of heat release throughout the spontaneous combustion process were analyzed via differential scanning calorimetry (DSC). In-situ Fourier transform infrared spectroscopy was used to characterize the activation energies of methyl and methylene groups during coal spontaneous combustion. Kinetic parameters obtained through various methods revealed activation energy increasing progressively. The oxidation of methyl and methylene groups occurs during the initial O-2 chemisorption and complex formation stage, marking the onset of chain reactions, with low activation energy (similar to 20 kJ mol(-1)). As the reaction proceeds, mass change is driven by the combined effects of active functional group oxidation and intermediate decomposition, with activation energy of similar to 30-81 kJ mol(-1). The activation energies obtained from DSC reflect the cumulative effects of multistep reactions in spontaneous combustion, ranging from similar to 28 to 90 kJ mol(-1). With increasing temperature, peroxy complexes are decomposed with the emission of CO and CO2. This stage exhibits the highest activation energy (similar to 33-151 kJ mol(-1)). Based on the activation energy evolution through different pathways, a "dual-pathway synergistic oxidation" theory was proposed, describing both the self-oxidation behavior of similar functional groups and the self-oxidation behavior of identical reaction sequences.

As a transitional scale between molecular and particle scales, the mesoscale can explore the adsorption mechanism of coal and oxygen at the molecular level while preserving the structural properties of particles. To investigate the mechanism of the pore structure of coal samples on the physical adsorption of oxygen, a macromolecular model of C302H175O13N3S2 was independently constructed by analyzing the characteristics of lean coal samples. Based on the macromolecular model, six mesoscale models with different pore densities (0.80, 0.95, 1.10, 1.25, 1.40, and 1.55) were constructed by adjusting the density distribution of molecular clusters. Using Materials Studio simulation software for grand canonical Monte Carlo calculations, the adsorption characteristics of oxygen in pore structures under mesoscale models were explored. Molecular dynamics simulations were conducted on the most stable coal-oxygen configuration during the above process to investigate the adsorption characteristics of pore oxygen. The results indicate that the pore structure in coal samples is the primary adsorption area for oxygen molecules, and the adsorption of oxygen molecules within the same pore is equivalent, with the same adsorption state in each pore. Changes in pore size directly affect the adsorption and aggregation of oxygen in the pore structure. There are significant differences in the density distribution of oxygen in mesoscale models with different pore structures. As the density increases, the oxygen density distribution decreases significantly. The distribution of pore structure directly determines the diffusion ability of pore oxygen. As the porosity of coal samples decreases, the diffusion coefficient of oxygen molecules continues to decrease, indicating that the binding ability of the pore structure to pore oxygen continues to increase. The adsorption mechanism of oxygen by the pore structure is also influenced by key functional groups in coal molecules. Research has shown that oxygen-containing functional groups are significantly more prominent, particularly O=C-OH and O=S=O, which demonstrate strong adsorption capacity, and -OH and O=C-H are relatively enhanced. However, the pore structure has a certain influence on the adsorption of different functional groups. As the porosity decreases, the binding ability of C6 and C-O-C weakens, whereas the binding ability of O=C-OH, O=S=O, O=C-H, and OH increases.

The effectiveness of gas discharge depends on the geological conditions and drilling parameters. Investigating gas seepage behavior near boreholes under fluid-solid coupling conditions can provide theoretical support for scientifically determining the effective discharge radius (EDR) and ensuring mining safety. In this study, taking Xinyuan Coal Mine as the engineering background, a fluid-solid coupled model describing gas migration was developed. The effects of the discharge duration, borehole diameter, permeability, and borehole layout on the spatiotemporal evolution of gas around boreholes and EDR were investigated. The results indicate that gas pressure around the borehole continuously decreases with time, and the affected zone expands elliptically. The EDR exhibits a power-law relationship with time. Increasing the borehole diameter enlarges the EDR, with the effect being particularly significant in the initial stage of gas discharge. After 5 h of gas discharge, the EDR in high-permeability coal seams is approximately twice that in low-permeability coal seams. Compared to the triple-flower patterns, the square pattern produces a larger EDR at the same time. The EDR calculated based on the measured values of the drill cuttings volume S value and drill cuttings desorption gas volume K 1 value shows a high degree of consistency with the simulation results. After 5 h of gas discharge using the square pattern, the gas volume fraction at the upper corner of the working face dropped to the safe level of 6%, enabling mining to resume.

In the coal storage areas of coastal ports and waterlogged areas at the bottom of mines, continuous exposure of the coal body to hot-humid airflow affects its low-temperature oxidation behavior. To determine the effect of hothumid airflow on the mechanism of coupled coal-oxygen-water reaction, coal samples under different air relative humidity (ARH) conditions were analyzed by scanning electron microscopy, Fourier-transform infrared spectrometry, and thermogravimetry. The results show that under ARH, the number of pores in the coal body increase, and condensed moisture clogs the pore structure. Calculations using the Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Friedman kinetic models indicate that ARH 30 and 90 promote coal spontaneous combustion (CSC) before the transition temperature point, while inhibiting CSC after the transition temperature. The mean activation energies correlate well with oxygen-containing functional groups and aliphatic substances, and the good agreement of the correlation coefficient values between -C=O, -CH2, and activation energies indicate an increasing phase change with the progress of CSC. Furthermore, the presence of humidity promotes -COOH and -OH generation, and this effect is more pronounced at an ARH 30. The results of this study provide a new theoretical basis for heat and humidity control in mine environments and coal storage in coastal ports.

ReaxFF molecular dynamics simulations were employed to investigate the behavior of ammonia and ethanol mixed fuel in different conditions, focusing on their combustion reaction mechanisms, intermediates, free radicals, and final product formation at different equivalence ratios. The results reveal that ammonia is primarily consumed by OH free radicals, leading to the formation of the NH2 free radical. NH2 radical undergoes further transformations, forming H2NO, H3NO, HNO, HO2, NO, NO2, HONO, and NH free radicals. The CH3, an intermediate of ethanol, influences the abundance of other free radicals such as H and OH, which also leads to a significant increase in CH2O. In oxygen-rich conditions, OH, HO2, and H2O2 demonstrate higher concentrations compared to oxygen-poor conditions. The NOx species include NO, NO2, and NO3 in rich- and stoichiometricoxygen conditions, whereas in oxygen-poor conditions, only NO is formed. The number of H2O decreases as the proportion of ethanol decreases due to the lack of O atoms, and the amount of H2 continues to increase in the oxygen-poor system. The limited availability of oxygen alters the reaction mechanism, reducing the occurrence of primary form reactions of H2O with the assistance of O, OH, and HO2. Instead, an increasing number of branching chain reactions become prominent at high temperature, leading to the formation of a significant amount of H2.

Application of industrial solid waste, fly ash (FA), in fire-resistant materials is an effective approach to utilize its resources. In this study, fly ash was activated using an alkali-salt composite activation method, wherein the solution of activated fly ash (AFA) served as the base liquid. Cationic polyacrylamide (CPAM) was added, and a foam system was obtained by blending AOS powder (an alkyl sulfonate with excellent acid and alkali resistance) and AEG (alcohol ether glycoside). The mixture was stirred thoroughly to obtain organic gel foam of activated fly ash (APF). In the AFA base liquid, high-valent metal ions underwent graft copolymerization with CPAM polymers to form a three-dimensional network structure. Low-valent metal ions, gel-like substances, calcium vanadates, and unreacted fly ash residues were encapsulated within this framework and they filled the colloidal pores and increased the gel strength. The physical properties, such as permeability, water retention, and stickability of the gel foam were evaluated. Additionally, its chemical properties were determined through inhibition experiments, thermogravimetric analysis, and infrared spectroscopy. Experimental results indicated that the organic gel foam of activated fly ash effectively inhibited coal spontaneous combustion. Finally, the synergistic fire-preventing mechanism of the gel foam was explored on the basis of its active components, gelation mechanism, and flame-retardant properties.

To explore the multi-field coupling disaster-causing laws near fault tectonic, the multi-physical field evolution characteristics of conventional coal seams and the fault-containing coal seams were compared and analysed, and the energy change laws during the mining process of fault-containing coal seams were investigated. The findings reveal that compared to conventional coal seams, stress concentration and gas accumulation inside fault-containing coal seams were more significant. Elastic energy and gas expansion energy dominate the evolution of the outburst process. Elastic strain can lead to an increase in gas expansion energy within the coal seam. The proportion of free gas expansion energy in the total energy is relatively small, and its contribution to gas outburst is also relatively small. The key to gas outburst lies in the instantaneous release of a large amount of adsorbed gas expansion energy. The research findings are important for understanding the multi-field coupling disaster mechanism near fault tectonic.

The use of colloidal materials is one of the most effective methods for controlling coal spontaneous combustion (CSC). A novel dual-aggregate composite colloid (DFPE) is developed, composed of diatomite and fly ash (FA) as aggregates, sodium polyacrylate (PAAS) as the binder, and anhydrous calcium sulfoaluminate (CSA) as the thickener. The optimal composition, determined through gelation time, viscosity, and permeability tests, consists of 70 % aggregates, 15 % PAAS, and 15 % anhydrous CSA. During the gelation process, the metal cations and residual inert components released by the aggregates play a crucial role in enhancing the structural stability and fire resistance of the DFPE composite colloid. Furthermore, the flame-retardant properties of the colloid were evaluated through suppression tests, thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) spectroscopy. The results indicate that the dual-aggregate composite colloid effectively suppresses CO release at high temperatures. Specifically, at 200 degrees C, the inhibition rates of CO were 54.17 % and 32.26 %, respectively. The treated coal samples exhibited reductions in the exothermic peak, shifts in the temperature point, and increased activation energy values, indicating a reduced likelihood of CSC. FTIR spectroscopy showed that the colloid effectively inhibits the oxidation of aliphatic hydrocarbon and hydroxyl functional groups, thereby reducing the rate of the coal-oxygen reaction. Furthermore, the fire prevention and extinguishing mechanism of the DFPE composite colloid was discussed. Therefore, this colloid is a structurally stable, high-performance material, making it an ideal choice for fire prevention and extinguishing applications.

In view of the difficulty of accurately characterizing the dynamic process of coal-oxygen physisorption using existing models, this study constructed three-dimensional (3D) porous adsorption models of coal based on a noise algorithm, and the kinetics of coal oxygen physisorption was investigated based on this model. The degree of metamorphism and pore characteristics of the coal samples were determined via industrial analysis and pore structure characterization, and high-pressure isothermal adsorption experiments were carried out to determine the isothermal adsorption lines of coal oxygen at different temperatures. The experimental data were fitted to construct a mathematical model under the joint influence of temperature and pressure, and a 3D porous adsorption model for coal was constructed based on the experimental results to explore the adsorption kinetic process. Revealing that the amount of oxygen adsorbed was negatively correlated with temperature, and coal samples with less deterioration possessed larger specific surface areas and pore volumes, resulting in a stronger oxygen adsorption ability. The coal-oxygen isothermal adsorption data fitted well with the Langmuir adsorption model, and the fitted oxygen adsorption values were similar to the experimental data. Numerical simulations using the constructed models indicated that the adsorption process of oxygen on the coal particle surface could be divided into three stages: (1) the seepage stage, in which oxygen is adsorbed by the outer surface of the coal body and its surface pores; (2) the surface diffusion stage, in which oxygen diffuses to the inner region of the coal particles through their pores; and (3) the deep adsorption stage, in which oxygen is adsorbed in the deep pores of the coal particles, enabling complete adsorption. Coal-oxygen adsorption reached equilibrium in a short time, the amount of oxygen adsorbed rapidly increased during the initial stage of adsorption, approaching the maximum value at 0.4 ms, and then the adsorption rate gradually decreased into the slow adsorption stage, finally reaching equilibrium at 1.0 ms. The model results indicated that oxygen adsorption was negatively correlated with temperature and positively correlated with adsorption equilibrium pressure, which aligned with the experimental rule.

Four surfactants with strong individual performances were selected from 13 typical surfactants, based on foaming and stability tests. The four surfactants were combined in pairs to determine the optimal complex ligand. Finally, three stabilizers and three wetting agents were selected based on their optimal compatibility with the complex ligand to prepare the OCAA dust suppressant. The optimal volume ratio of dusting agent components (fatty alcohol polyoxyethylene ether sodium sulfate (AES), modified alkyl glycoside (APG0811), coconut acid methyl monoethanolamide (CMMEA), and sodium salt of dioctyl sulfosuccinate (OT-45)) was 5:5:3:1. A combination of experimental and simulation methods was used to investigate the wetting mechanism of OCAA dust suppressant on lignite, bituminous coal, and anthracite. The contact angles of dust suppressant solution with lignite, bituminous coal, and anthracite decreased by 75.75 %, 78.57 %, and 85.80 %, respectively, as compared to water. FTIR results of OCAA dust suppressant solution showed higher peak intensity of the hydrophilic -OH functional group, compared to that of water. Particle size analysis indicated that the median diameters (D50) of immersed lignite, bituminous coal, and anthracite increased by 44.68 %, 55.73 %, and 68.00 %, respectively. This increase was attributed to a higher concentration of hydrophilic functional groups, which promoted particle agglomeration and resulted in larger particle sizes. Finally, molecular dynamics modeling was used to analyze the wetting adsorption mechanism of OCAA dust suppressant at the coal dust interface. Upon addition of the OCAA dust suppressant, the diffusion coefficients of lignite, bituminous coal, and anthracite were reduced by 12.60 %, 8.78 %, and 2.80 %, respectively, relative to pure water. The reduction in diffusion coefficients was indicative of decreased water mobility, suggesting greater adsorption of water molecules onto the coal particles. This transitioned the coal surface from hydrophobic to hydrophilic, which was consistent with the infrared spectroscopy results.

This study investigates the impact of water on oxygen adsorption in coal using quantum simulations, focusing on three typical oxygen-containing functional groups in lignite. Key factors, including equilibrium configurations, electrostatic potential, and reduced density gradients of water and oxygen molecules adsorbed on the coal surface, were analyzed. Thermal analysis and quantum chemical calculations were also performed to determine enthalpy changes and activation energies in oxidation reactions. The results indicate that water influences oxygen adsorption on coal surfaces through both physical and chemical mechanisms. Physically, water molecules form hydrogen bonds with the oxygen-containing groups in coal, altering the electronic density distribution and enhancing oxygen adsorption. Chemically, water reduces activation energy, modifies reaction barriers, and facilitates spontaneous combustion at lower temperatures, while also increasing enthalpy changes of oxidation reactions. Overall, water plays a dual role in regulating coal oxidation: it enhances adsorption through hydrogen bonding while also altering reaction pathways and lowering energy barriers, thereby promoting coal oxidation.

Oxidized coal in mines often undergoes secondary oxidation upon re-exposure to air, which can lead to spontaneous combustion. This study simulates the secondary oxidation process of oxidized coal through TG-DSC and in-situ FTIR experiments. The self-ignition characteristic parameters of the water evaporation and gas adsorption stage (Stage I), the oxygen absorption and weight gain stage (Stage II), and the functional groups' evolution were measured. The results indicate that the coal sample pre-oxidized at 160 degrees C (Coal-160) exhibited the lowest activation energy and the most heat during secondary oxidation, with activation energies of 63.17 kJ/mol and 92.49 kJ/mol for Stages Iand II, respectively. The heat released was 12.38 J/g and 269.53 J/g for Stages Iand II, respectively, indicating the highest risk of spontaneous combustion. The pre-oxidation process accelerates the consumption of -OH in the coal and promotes the formation of -CH2, -CH3, and oxygen-containing functional groups. In Stage I, the formation and transformation of -CH2 and -CH3 are the main functional groups driving heat release in the oxidized coal. In Stage II, -COOH and C=O play a significant role in heat release. During the secondary oxidation process, the content of aliphatic hydrocarbons, C=O, and -COOH structures in Coal-160 always maintained the highest level. The initial content of key groups and their changes in different stages are the inherent reasons that affect the heat release of different oxidized coal samples.

It is important to gain an in-depth understanding of the structure of fire prevention and extinguishing materials during self-heating of coal. In this paper, an Al3+-CMC/PAM-MMT fire prevention and extinguishing gel with double-network was prepared using sodium carboxymethyl cellulose (CMC) and polyacrylamide (PAM) as raw materials, and aluminum citrate (AlCit) and sodium montmorillonite (Na-MMT) as auxiliary materials, by introducing the fully physically crosslinking effect. The optimal amounts of CMC, PAM, AlCit and MMT were determined to be 2%, 3%, 8%, and 3%, respectively, based on gelation time, stability, and resistance of the gel. The micromorphological image of the double-network gel exhibited a laminar structure of parallel-aligned fibrous networks, where the pores and channels exhibited more complex shapes and became smaller in size, highlighting the superiority of the double-network architecture. The rheological tests showed that the double-network gel had superior structural stability and viscosity under varying shear rates, making it more effective in covering the fire source, enhancing extinguishing efficiency. Additionally, its higher storage and loss moduli indicated stronger elasticity and mechanical properties compared to the single-network gel, emphasizing its advantages in energy storage and recovery. The characterization of active functional groups showed that there was an effective suppression of reactions involving hydroxyl, hydrocarbon, and carbonyl functional groups, during the spontaneous combustion process of coal, following treatment with the gel. Additionally, a proposed mechanism for the gel formation was presented. In the sealing performance test, the pressure-bearing capacity of the double-network gel was approximately twice that of the single-network gel. It indicated that the multi-level structure formed by the gel led to higher density of physical cross-linking points, which provided better sealing performance. Thermogravimetric analysis showed significant decrease in total calorific value and increase in activation energy of coal, after treatment with the gel, rendering it more difficult for spontaneous coal combustion. In the small-scale fire extinguishing performance test, the double network of Al3+-CMC/PAM-MMT gel demonstrated effective suppression of spontaneous combustion of coal and reduced the susceptibility to re-ignition. The fire prevention mechanism of the gel was further explored experimentally.

It is imperative to have an in-depth understanding of the pathway and mechanism of coal-oxygen-water coupling reaction during low-temperature oxidation of coal, not only for preventing fires in the coal industry but also for reducing emissions of hazardous gases. In this study, in-situ Infrared spectroscopy characterization and quantum chemical calculations were combined to investigate in detail the chemical interactions between coal, moisture, and oxygen. In-situ infrared oxidation experiments ascertained the types and amounts of hydroxyl, aliphatic hydrocarbon, and carbonyl functional groups in lignite coal samples with varied moisture content during LTO. Subsequently, three typical molecular structures of functional groups mainly involved in the coal-oxygen reaction were chosen as the research representatives, and their reactivity was analyzed using density functional theory (DFT). Thus, the main reaction pathways of these functional groups during the LTO of coal were studied using quantum chemical methods. The results indicated that the moisture in coal significantly affected the coal-oxygen reaction by altering the chemisorption processes in the coal-oxygen combination and the active sites in coal molecules. Quantitative calculation of thermodynamic parameters such as the enthalpy and activation energy showed that moisture had a promoting effect on some reaction steps while hindering others. Moreover, the mechanism of coal-oxygen-water coupling reaction was also explored based on the reaction sequence of intermediate complexes.

Determining the transmission rate of radon gas in overburden strata is crucial for conducting a comprehensive study of radon gas's longitudinal and long-distance migration mechanisms. This study investigates the mineral components of rocks in the underground strata of the mining area using the X-ray diffraction method. Additionally, it examines the pore structure parameters of the rocks at different depths using the low-temperature nitrogen adsorption method. This research introduces an approach to inversion calculate the radon gas transmission rate through the activity ratio of radon's characteristic daughters based on the decay law and activity balance of 210Po and 210Pb daughters. In addition, it determines the transmission rates of radon gas in overlying strata at various depths through this method. The relationship between the rock's mineral composition and pore structure is investigated, and the effects of pore structure and mineral composition on the radon gas transmission rate are analyzed. The findings indicated that the pore structure exerts a dual impact on radon gas transport: macropores serve as channels for upward radon gas transport, while micropores offer most of the adsorption area. In contrast, the radon gas transmission rate is indirectly influenced by the mineral composition content associated with the medium's adsorption capacity and pore structure. In the studied lithologies, an increase in quartz content promotes radon gas transmission, while an increase in clay mineral content impedes it. Finally, the mechanisms of radon gas transport, daughter adsorption, and the impacts of rock pore structure and mineral composition on the radon transmission rate are discussed.

Surface isotope radon detection technology, as an effective method of detecting hidden fire sources, has been widely applied in numerous coal mines experiencing coal spontaneous combustion. Current research on radon sources in goaf primarily focuses on the release characteristics of radon during the process of coal spontaneous combustion. However, the actual goaf, composed of residual coal and fallen rocks, represents a geological space where the release of radon from high-temperature rocks during coal spontaneous combustion should not be overlooked. This study conducted experiments on the release of radon from coal and rock at various temperatures and void ratios. On the basis of these experiments, two models were established for goaf associated with coal spontaneous combustion: Model I considered the release of radon solely from coal, and Model II considered the release of radon from both coal and rock. This study found that between 30 and 400 degrees C, the amount of radon released from coal initially increased with increasing temperature before decreasing, while the overall trend for radon released from rock was one of increase. As the void ratio increased, the overall release of radon from coal and rock decreased. Compared with Model I, Model II more accurately reflected the characteristics of radon release in goaf associated with coal spontaneous combustion, with higher concentrations of radon accumulating at the top of the goaf and a more evident radon source. In the early stage of coal spontaneous combustion (at 50-120celcius), the concentration of radon source showed a positive linear correlation with the temperature of the fire source, providing theoretical support for early prediction and forecasting of coal spontaneous combustion.