Study on adsorption-diffusion-seepage behavior of oxygen in coal gangue under the coupling of temperature and pressure

Abstract

This research delves into the fundamental aspects of oxygen adsorption, diffusion, and seepage within gangue slits, aiming to avert the spontaneous combustion of coal gangue hills. Employing methodologies such as molecular dynamics (MD), Grand Canonical Monte Carlo simulations (GCMC), and the finite element simulation, the intricate behavior of O2 molecules within the coal gangue's slit structure is modeled under varying temperature and pressure conditions. The outcomes evince that augmented pressure facilitates oxygen adsorption while diminishing the diffusion coefficient. Conversely, elevated temperature curtails adsorption but augments the diffusion coefficient. At a pressure of 10 MPa, the system energy of oxygen-coal gangue undergoes the most substantial change (92.18 kcal/mol), and the energy peak exhibits the broadest displacement (0.7 kcal/mol), thus signifying the preeminence of pressure conditions in governing O2 adsorption and diffusion. At temperatures below 423.15 K, O2 molecules and coal gangue primarily undergo physical adsorption, with an amplified exposure of kaolinite (0 0–1) surfaces in coal gangue correlating to intensified adsorption. Within the pressure range of 0.2–10 MPa, the percolation process of oxygen in gangue slits unfolds across four discernible stages, with the structural characteristics of the slit channel, gas diffusion capacity, and oxygen consumption rate of coal gangue exerting a profound influence on the process. Based on these research findings, the reduction of pressure proves to be more efficacious in regulating the spontaneous combustion of coal gangue as compared to temperature control.