Ab Initio Molecular Dynamics Study of Carbonation and Hydrolysis Reactions on Cleaved Quartz (001) Surface

Geochemical trapping (i.e., mineralization) is considered to be the most efficient way for long-term CO ₂ storage in order to mitigate "global warming effect" induced by anthropogenic CO ₂ emission. The common view is that the reaction process takes hundreds of years; however, recent field pilots have demonstrated that it only took 2 years to convert injected CO ₂ to carbonates in reactive basaltic reservoirs. In this work, ab initio molecular dynamics simulations were employed to investigate chemical reactions among CO ₂ , H ₂ O, and newly cleaved quartz (001) surfaces in order to understand the mechanisms of carbonation and hydrolysis reactions, which are essential parts of CO ₂ mineralization. It is shown that CO ₂ can react with undercoordinated Si and nonbridging O atoms on the newly cleaved quartz surface, leading to formation of CO ₃ configuration that is fixed on the surface by Si-O bonds. Furthermore, these Si-O bonds can break under hydrolysis reaction, and HCO ₃ occurs simultaneously. Electron localization function and Bader charge analysis were used to describe the bonding mechanism and charge transfer during the two reaction processes. The result highlights the importance of the intermediate configuration of CO ₂ ^γ- in the carbonation reaction process. Furthermore, it confirms the formation of CO ₃ ^2- and HCO ₃ ^- . We conclude that CO ₃ ^2- and HCO ₃ ^- in the formation water do not necessarily originate from dissociation of H ₂ CO ₃ , and these anions may accelerate the CO ₂ mineralization process in the presence of required cations, such as Ca ²⁺ , Mg ²⁺ , or Fe ²⁺ .