Microscopic Mechanism of Coal Wetting-Dissolution under Surfactant-Assisted Acidification Conditions

Coal wetting-acidification is a promising method to enhance the coal dust control and gas permeability. To elucidate the internal transformation process of coal wetting-dissolution, this study employs contact angle measurements, low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray diffraction to investigate the wetting characteristics and pore structure changes of coal before and after treatment with acid and surfactant composite reagents. The interaction mechanisms between mineral dissolution and wetting-dissolution characteristics are explored. Results indicate that surfactant-assisted acidification reduces the coal contact angle by approximately 60%, significantly enhancing coal wettability. Post-treatment with the composite reagent alters the pore structure of coal through chemical reactions, increasing the total pore volume and average pore diameter by factors of 2.0 and 1.5, respectively. Fractal theory analysis shows reductions in the fractal dimensions D₁ and D₂ by 24.1% and 10.3%, respectively, compared to raw coal, indicating decreased surface roughness and improved pore connectivity. The addition of [BMIM]BF₄ ionic liquid inhibits surfactant activity, leading to an increased contact angle and decreased coal wettability, which in turn reduce the average pore size. A positive correlation is observed between coal wettability and dissolution; as wettability increases, acid solution facilitates the dissolution of more mineral impurities, thereby increasing the total pore volume and average pore size. The findings on wetting-dissolution transformation and ionic liquid inhibition align with experimental results on contact angle and average pore size, elucidating the microscopic mechanism of coal wetting-dissolution.