Study on CO₂ adsorption of illite and its microstructural characterization post adsorption: High-pressure and supercritical tests

Illite, a prevalent clay mineral, is extensively found in sedimentary rocks, weathering crusts, and soils. Its adsorption capacity has attracted considerable interest for carbon dioxide (CO₂) geological sequestration research. This study aimed to investigate the fundamental CO₂ adsorption behavior of illite, as well as the effects of moisture content and temperature on this process, utilizing high-pressure adsorption and supercritical adsorption tests. Nitrogen adsorption tests were conducted to assess the variations in specific surface area, pore volume, and average pore size of illite before and after CO₂ adsorption. Additionally, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques were employed to characterize the mineral composition and elemental characteristics of raw illite, CO₂-adsorbed illite under dry conditions, and CO₂-adsorbed illite under wet conditions. The results indicated that an increase in moisture content diminishes CO₂ adsorption capacity of illite and leads to a transition of the isosteric heat of adsorption from positive to negative. Furthermore, with rising temperature and moisture content, the specific surface area, pore volume, and average pore size of illite increased following CO₂ adsorption. Additionally, CO₂ adsorption modified the mineral and elemental composition of illite. These results were essential for enhancing the fundamental understanding of CO₂ geological sequestration efficiency and hold promise as a technical foundation for engineering applications.