Multiphase Monte Carlo and Molecular Dynamics Simulations of Water and CO2 Intercalation in Montmorillonite and Beidellite

Multiphase Gibbs ensemble Monte Carlo simulations were carried out to compute the free energy of swelling for Na montmorillonite and Na-beidellite interacting with CO2 and H2O at pressure and temperature conditions relevant for geological storage aquifers. The calculated swelling free energy curves show stable monolayer and bilayer configurations of the interlayer species for Na-montmorillonite, while only the monolayer structure is found to be stable for Na-beidellite. The calculations show that CO2 is intercalated into hydrated clay phases at concentrations greatly exceeding its solubility in bulk water. This suggests that expandable clay minerals are good candidates for storing carbon dioxide in interlayer regions. For Na-beidellite the CO2 molecule distribution is mainly controlled by the position of the isomorphic substitutions, while for Na-montmorillonite the hydrated sodium ions play an important role in establishing the CO2 distribution.