Ab lnitio 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 CO2 storage in order to mitigate global warming effect induced by anthropogenic CO2 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 CO2 to carbonates in reactive basaltic reservoirs. In this work, ab initio molecular dynamics simulations were employed to investigate chemical reactions among CO2, H2O, and newly cleaved quartz (001) surfaces in order to understand the mechanisms of carbonation and hydrolysis reactions, which are essential parts of CO, mineralization. It is shown that CO2 can react with undercoordinated Si and nonbridging O atoms on the newly cleaved quartz surface, leading to formation of CO3 configuration that is fixed on the surface by Si-O bonds. Furthermore, these Si-O bonds can break under hydrolysis reaction, and HCO3 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 CO2 gamma- in the carbonation reaction process. Furthermore, it confirms the formation of CO32- and HCO3-. We conclude that CO32- and HCO3- in the formation water do not necessarily originate from dissociation of H2CO3, and these anions may accelerate the CO2 mineralization process in the presence of required cations, such as Ca2+, Mg2+, or Fe2+.