Microscopic adsorption characteristics of O2 on Xishan coal gangue: Insights from structural modeling and synergistic effects of organic matter-minerals
Xuefeng Wang, Huijie Hu, Shuangli Du, Xin Kong
Abstract
To investigate the microscopic adsorption characteristics of O 2 in coal gangue, key structural parameters of Xishan coal gangue were determined through characterization techniques including ultimate analysis, X-ray diffraction (XRD), 13 C nuclear magnetic resonance ( 13 C- NMR), and X-ray photoelectron spectroscopy (XPS). An organic–mineral macromolecular structural model was constructed by integrating these results. The adsorption behavior of O 2 was systematically studied through simulations of adsorption isotherms, isosteric heat of adsorption, energy distribution, adsorption configuration and adsorption energy. Additionally, the synergistic effects between mineral and organic components on O 2 adsorption were thoroughly examined. Results showed that increasing temperature suppresses O 2 adsorption, leading to reduced adsorption capacity and isosteric heat, while increased pressure enhances adsorption with a diminishing rate of increase and concurrently lowers the isosteric heat. O 2 adsorption primarily occurs within a weak-energy micro-bulge region (−14.35 to −2.91 kJ/mol) and a high-energy peak region (−1.67 to −0.21 kJ/mol). Pressure regulates the transition of O 2 adsorption from site-selective binding to a densely packed configuration, while temperature facilitates the thermal motion of molecules to drive further diffusion of O 2 . Both factors contribute to the reduction in average adsorption energy. Radial distribution function (RDF) analysis revealed distinct peaks at 0.17 nm and 0.21 nm for H atoms in kaolinite (H K ), H atoms in quartz (H Si ), and O atoms in organic matter (O C ), indicating the presence of hydrogen bonding interactions. These interactions facilitate the preferential aggregation of O 2 molecules in organic-rich regions, thereby broadening the adsorbable energy spectrum and enhancing the efficiency of adsorption site utilization.