Multiscale characterization of microstructural reconfiguration induced by oxidation in lignite from the Lingquan...

The microstructure changes of Lingquan mine oxidized lignite at different oxidation temperatures and the influence of low-temperature oxidation on the spontaneous combustion characteristics of lignite is studied in this paper. The pore structure characteristics, surface morphology, microcrystalline structure, and functional groups of lignite in Lingquan Mine were studied using low-temperature nitrogen adsorption, SEM, XRD, and FTIR tests. The research results indicate that characteristics of mesoporous pore structure and the peak areas of functional groups of oxidized lignite are significantly different from those of original lignite. The mesoporous volume of oxidized lignite is 183.65-306.61% times that of original lignite. The mesoporous specific surface area of oxidized lignite is 140.11-180.56% times that of original lignite. The peak area of the -CH₃ functional group of oxidized lignite in the Lingquan mine is 122.68-252.74% times that of the original lignite. The peak area of the C = O functional group of oxidized lignite is 120.09-239.78% times that of the original lignite. The aromatic layer spacing d₀₀₂ of oxidized lignite increased by 0.20-1.12% compared to the original lignite. Compared with the original lignite, the average size La of the aromatic layer of oxidized lignite increased by 4.10-11.45%. The quantity of aromatic layers M_c of oxidized lignite decreased by 2.31-12.37% compared with the original lignite. The stacking height L_c of the aromatic layer of oxidized lignite decreased by 2.13-11.39% compared with the original lignite. The coalification degree P of oxidized lignite P decreased by 1.72-9.85% compared with the original lignite. This research revealed that the mesoporous volume and specific surface area of oxidized lignite in Lingquan Mine increased significantly, the surface became rougher, and the oxidation reaction space and contact area increased. The peak area of oxidized lignite -CH₃ and C = O functional groups improved significantly, enhancing the reaction activity. The spacing and average size of aromatic layers of oxidized lignite are more significant than those of original lignite. However, there are fewer aromatic layers, resulting in a looser microcrystalline structure, lower stability of molecular structure, and degree of coalification. In summary, oxidized lignite in Lingquan Mine is more prone to spontaneous combustion than original coal.