Influence of pulverization on the micropore structure of coal and its fractal characteristics

This study conducted extensive repetitive experiments by continuously adjusting the adsorption equilibrium judgement criteria to obtain reliable low-pressure CO₂ adsorption (LPGA-CO₂) isotherms at 273 K for coal samples of different particle sizes. And the Horvath-Kawazoe (HK) model and density functional theory (DFT) were then employed to analyze the true evolution laws of micropore size distribution and its fractal characteristics in coal samples during the pulverization. It was found that constrained by the gas adsorption kinetics in large-particle coal samples, coal particles exceeding 0.3 mm are not recommended for porosity testing using LPGA-CO₂ (273 K). As coal particle size decreased from 0.3 mm to 0.075 mm, the most probable pore size in the micropore size distribution decreased, while micropore volume and surface area initially increased linearly. Below 0.075 mm, these parameters exhibited irregular, overall declining trends. These findings suggest that when the coal sample is crushed to a particle size below 0.075 mm, the internal closed pores are continuously opened, thereby promoting an increase in micropore volume. Concurrently, with increasing pulverization intensity, the micropore fractal dimension exhibited a linear rise from 2.029 to 2.337, demonstrating significantly enhanced surface roughness and spatial heterogeneity in micropores as coal particle size decreased.