Kinetic mechanism of CO₂-coal/rock dissolution and mineralization under temperature and pressure constraints in mined-out area: Implications for pore network reconstruction and carbon storage safety

CO₂ geological sequestration constitutes a critical negative emission technology reserve for addressing carbon emissions in coal industries. Decommissioned subsurface voids, with their substantial storage capacity and controllable engineering conditions, emerge as ideal geological reservoirs for carbon storage that combine scalability and safety advantages. This investigation employed a self-developed hydrogeochemical reaction simulation apparatus to systematically conduct CO₂-water-coal/rock interaction experiments under controlled thermobaric conditions (25 °C, 45 °C; 0.5–2.5 MPa). The study quantitatively analyzed elemental release-migration patterns and aqueous phase ion concentration evolution pre- and post-reaction, investigated mineralogical phase transitions and pore architecture modifications in mined-out area environments, and elucidated the coupled mechanisms of mineral dissolution-carbonization, elemental migration, and secondary mineral precipitation. Key findings reveal: (1) Hyperbaric conditions significantly enhance CO₂ dissolution and acidification-driven mineral dissolution, while elevated temperature initially inhibits CO₂ solubility but subsequently promotes carbonate precipitation through Ca²⁺/Mg²⁺ liberation, demonstrating thermobaric co-regulation of dissolution-precipitation equilibria; (2) Low-activation-energy carbonate minerals (calcite: 12.4 kJ/mol, dolomite: 36.16 kJ/mol) dominate short-term dissolution processes, whereas silicate phases (e.g., kaolinite) govern long-term reservoir stability through dissolution-reprecipitation transformations; (3) CO₂-fluid-rock interactions induce distinct pore structure evolution-coal matrices exhibit macropore volume expansion (+5.98 % maximum) due to initial microporous dominance (39.42 %), while rock strata demonstrate staged porosity differentiation from carbonate dissolution-secondary precipitation; (4) Mined-out area storage optimization requires dual consideration of reservoir-caprock characteristics: reservoir design should balance short-term dissolution-enhanced porosity with long-term mineralization stabilization, while caprock selection favors silicate-rich formations achieving pore sealing through hydration-induced swelling. This research establishes fundamental theoretical and experimental frameworks for safe and efficient CO₂ sequestration in abandoned mine voids by revealing the dissolution-mineralization dynamics governing reservoir integrity.