Dissolution of Forsterite Surface in Brine at CO₂ Geo-storage Conditions: Insights from Molecular Dynamic Simulations

Evaluating the long-term security of geological deep saline aquifers to store CO₂ requires a comprehensive understanding of mineral dissolution properties. Molecular dynamics simulations are performed to study the dissolution of forsterite in deep saline aquifers. The forsterite surface is found to be covered by three H₂O molecular layers, hindering CO₂ from directly contacting the surface. The dissolution rates at 350 K are increased by more than 10¹² with the presence of Mg defects or salt ions in solutions. The more disordered surface in pure water caused by Mg defects accounts for the acceleration of dissolution, while absorbed Cl^- ions on the surface in NaCl and KCl solutions accelerate the dissolution through electrostatic interactions. Comparatively, the frequent attacks from alkaline earth cations in MgCl₂ and CaCl₂ solutions to the surface contribute to the enhanced dissolution. In the acidic H₃OCl solution, the electrostatic interactions between O atoms in H₃O⁺ and the surface facilitate the dissolution. Interestingly, the ionic clusters of CO₃^2-/HCO₃^- and Na⁺ in Na₂CO₃/NaHCO₃ solution promote the dissolution process. This work provides molecular insights into forsterite dissolution in deep saline aquifers and guidance toward the optimization of CO₂ geo-storage conditions.