Study on the Influence of Acid Erosion on the Macro-, Mesoscopic-, and Microscopic Evolution Characteristics of Anthracite

In light of the poor permeability of coal reservoirs in China and the associated challenges in gas extraction, this study investigates the macro-, meso-, and micropore evolution of anthracite under acid erosion using low-temperature nitrogen adsorption, scanning electron microscopy, and high-temperature, high-pressure adsorption experiments. The main findings are as follows: after acid treatment, the specific surface area of anthracite decreases compared with the raw coal, indicating that the untreated coal provides more adsorption sites, while the acid dissolution reduces the coal surface’s adsorption capacity. Analysis using the BJH pore size distribution model shows that the pore volume of anthracite declines after acidification, with the reduction being particularly pronounced for adsorption pores. Calculations based on the FHH fractal model reveal that the original coal has a more complex pore structure than the acid-treated sample, with a surface fractal dimension of 2.6883 for the raw coal compared to 2.5506 for the acid-treated coal, indicating a simplification of the pore structure after acid treatment. After acidification treatment, the adsorption constant (a) of the coal sample decreased from 23.32 cm 3 /g to 21.18 cm 3 /g, corresponding to a reduction rate of 9.17%, whereas the desorption efficiency increased from 78.23% to 81.65%.