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

Abstract

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 CO32-/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.