Microfractal characteristics of acidified coal under different temperature and adsorption pressure conditions

With the increasing mining depth and ground temperature, to study the changes in the microstructure of acidified coal under high-temperature conditions, isothermal adsorption experiments, low-temperature nitrogen adsorption experiments, and scanning electron microscopy experiments were used to study the pore–fracture structure evolution mechanism of acidified coal under different adsorption pressures and temperatures and to investigate the fractal characteristics of acidified coal by using the Frenkel–Halsey–Hill model and fractal theory and establish a pore fractal calculation model. The study revealed that the number of open pores and inkwell pores in coal after acidification treatment increased, and the pore–fracture connectivity increased. The percentage of micropores in the acidified coal increased, the total pore volume and specific surface area increased, the fractal dimension D1 on the surface of the coal samples increased, the roughness increased, and the adsorption capacity increased. Under high-pressure conditions, the adsorption state gas (CH4) content increased, the inhibition of oxidation increased, and the reduction in the temperature of thermal damage to the coal sample increased. The research results explored the microscopic characteristics of acidified coal under different adsorption pressures and temperatures and provided a theoretical basis for reducing the risk of spontaneous combustion in the goaf and improving the permeability of coal seams.