CO2 Solubility in Aqueous Electrolyte Solutions Confined in Calcite Nanopores

Geological carbon dioxide sequestration in deep saline aquifers can play a key role in the successful mitigation of greenhouse gas emissions. Several conditions have been identified that affect the solubility of CO2 in water, including temperature, pressure, pH, and salinity. At similar conditions, the solubility in bulk fluids differs from the solubility in confined porous media. We conducted equilibrium molecular dynamics (MD) simulations to investigate the solubility of CO2 in water confined in slit-shaped calcite pores. We studied the effects of brine (NaCl and MgCl2). Compared to bulk water/brine, the solubility of CO2 is lower in calcite pores and decreases as the pores narrow. Adsorption energy calculations were performed to compare our results to CO2 solubility in water-filled silica pores. These results indicate that narrower calcite pores are less attractive for the adsorption of CO2. In addition, the simulation results suggest that the difference in the positions where the ions adsorb also affects whether salts increase or decrease the solubility of CO2 in confined water. Confinement and ions also reduce the mobility of CO2 in water. These observations contribute to the design of long-term CO2 sequestration strategies as they provide boundary constraints for the amount of CO2 that can dissolve in hydrated pores, as well as the timing of CO2 transport in such systems