Dissolution of Forsterite Surface in Brine at CO 2 Geo-storage Conditions: Insights from Molecular Dynamic Simulations.

Evaluating the long-term security of geological deep saline aquifers to store CO 2 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 H 2 O molecular layers, hindering CO 2 from directly contacting the surface. The dissolution rates at 350 K are increased by more than 10 12 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 MgCl 2 and CaCl 2 solutions to the surface contribute to the enhanced dissolution. In the acidic H 3 OCl solution, the electrostatic interactions between O atoms in H 3 O + and the surface facilitate the dissolution. Interestingly, the ionic clusters of CO 3 2- /HCO 3 - and Na + in Na 2 CO 3 /NaHCO 3 solution promote the dissolution process. This work provides molecular insights into forsterite dissolution in deep saline aquifers and guidance toward the optimization of CO 2 geo-storage conditions.