Study on Pore Structure Evolution and Mechanical Properties Response of Anthracite under Acidification

Abstract This study focuses on low-permeability anthracite rich in silicate minerals from a mining area in Guizhou. Acidification conditions were optimized via X-ray diffraction and static dissolution experiments. Meanwhile, nuclear magnetic resonance, atomic force microscopy, and uniaxial compression tests were employed to systematically investigate the evolution of pore structure and the response mechanism of mechanical properties of anthracite under acidification and to reveal the variation law of its mechanical properties from an energy perspective. The results show that the optimal acidification condition for the experimental coal samples is treatment with 6% hydrofluoric acid solution for 24 h. After acidification, the microporosity of the coal samples decreases by 5.71%, while mesoporosity and macroporosity increase by 692% and 64.71%, respectively, thereby improving pore connectivity. The average peak stress, peak strain, and elastic modulus of the acidified coal samples decrease by 26.85%, 23.38%, and 3.56%, respectively, indicating significant deterioration of mechanical properties. In addition, the total energy at complete failure of the acidified coal drops to 52.27% of that of the original coal samples, and the coal exhibits reduced brittleness and enhanced ductility. The modification of coal pores and fractures by acid solution is the main cause of mechanical property degradation: acidification not only promotes the development of coal pores and fractures to form a complex network structure but also generates numerous structural weak planes in the coal matrix. These defects damage the structural integrity of coal, ultimately leading to the decline in its mechanical performance. The research results provide a theoretical basis for parameter optimization in fracture creation and permeability enhancement of coal seams by acid fracturing.