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In order to effectively mitigate the oxidation reactions of coal (RC) and gangue (RG) at low temperatures, a comprehensive study was conducted on the mineral composition, structural characteristics, and oxidation behaviors of RC and RG from the same coal seam. Additionally, the thermodynamic attributes of their oxidation processes were evaluated. The results indicate that the mineral composition of RC and RG is similar, primarily comprising kaolinite. However, there are substantial differences in structural characteristics, with RG exhibiting a more stable structure, smaller aromatic layer spacing, and higher degree of graphitization. Additionally, the molecular arrangement is densely packed and orderly, displaying characteristics akin to those of " highly metamorphic coal-like ". RC has a high content of aromatic hydrocarbons and aliphatic hydrocarbons, with long side chains, rendering it more susceptible to oxidation and possessing stronger combustion activity. Upon entry into the oxidation process, RG exhibits a lower initial exothermic temperature due to its strong thermal conductivity and large thermal diffusion coefficient. However, it simultaneously has fewer active functional groups and a higher ash content, limiting its sustained exothermic capacity and prolonging the processes of slow endothermic and rapid exothermic reactions. Conversely, RC, with its high carbon content and abundant active substances, releases heat during oxidation that is 1.7–3.5 times greater than that of RG. Importantly, when RC and RG oxidize together, they exhibit a synergistic effect, promoting the reaction. In the slow endothermic stage, the average activation energy required for CG is 2.64 kJ·mol−1 lower than that for RC. In the rapid exothermic and slow exothermic stages, the actual heat release of CG exceeds the theoretical heat release by 15.95–64.71 J·g−1 and 13.88–56.77 J·g−1, respectively. [ABSTRACT FROM AUTHOR]

• The gangue micropores are converted into mesopores and macropores. • The content of various functional groups increased and reached the maximum at S60. • Dry cracking temperature increases, other characteristic temperatures decrease. • The combustion properties all following the chemical reaction mechanism(n = 3). A large amount of coal gangue (CG) produced in coal mining accumulates to form CG hills, and the combustion properties change under the effect of leaching, increasing the risk of spontaneous combustion. The study was mainly carried out by nitrogen adsorption, infrared spectroscopy and thermogravimetry on the physicochemical properties of the CG under different immersion times (30, 60, 90 days). And the activation energy of the immersion CG at different oxidation or combustion states was calculated. The results show that the pyrite contained in gangue is oxidized after immersion, and the heat released by oxidation and the acid solution formed have an obvious effect on the pore expansion of gangue. The mesoporous and macroporous increase by 2.61% and 0.95% respectively, which strengthens the physical and chemical adsorption of oxygen for CG. The immersion process also destroys the structure of the gangue, transforming stable functional groups into active ones, especially the most significant increase in hydroxyl and oxygen-containing functional groups. The characteristic temperature changed under the action of water immersion, the cracking temperature increased, and other characteristic temperatures decreased, among which the ignition temperature decreased by about 20℃. In addition, the water immersion process inhibits the low-temperature oxidation stage of CG and promotes the high-temperature combustion stage, and the risk of spontaneous combustion is the strongest after 60 days of immersion in water. The results can provide guidance for the prevention of spontaneous combustion in drenched CG hills. [ABSTRACT FROM AUTHOR]

• R 3 -CH structure especially the H atom is the most active site in coal self-heating with oxygen. • The free energy barrier of oxygen attacking R 3 -CH site is 8.28 kJ/mol. • The aromatic hydrocarbon radicals and hydroxyl radicals are significant for coal self-heating. • The carbon radical combining with an O plays a vital role in initial coal spontaneous combustion. R 3 -CH structure is a typical active group during coal self-heating. In this paper, Ph-CH(CH 3)–CH 2 -Ph was selected to analyze reaction activity as well as mechanism between R 3 -CH structure and oxygen in coal self-heating by Multiwfn and Gaussian calculation. The results demonstrate that R 3 -CH structure especially the H atom is the most active site in coal self-heating with oxygen. The oxygen attacks R 3 -CH site in the Ph-CH(CH 3)–CH 2 -Ph, which results in the breaking of C–H bond and formation of O–H bond. The free energy barrier of this oxidation reaction is 8.28 kJ/mol and the heat release of the process is 86.89 kJ/mol, which indicates that it can easily occur at room temperature. From the perspective of products, the aromatic hydrocarbon radicals and hydroxyl radicals related to the initial spontaneous combustion of coal are generated, which is of great significance for the further development of coal self-heating. Subsequently, the carbon radical is combined with a single oxygen atom to generate oxygen-containing free radical which plays vital roles in initial coal spontaneous combustion. [ABSTRACT FROM AUTHOR]