Understanding Fundamental Reactions Driving CO2 Mineralization in Adsorbed Water Nanofilms

Abstract:

Carbonation of natural earth-abundant and synthetic metal silicates promises scalable solutions to permanently store CO2. With enigmatic observations of enhanced reactivities in both water- and CO2-rich fluids, understanding the kinetics proves critical in designing secure and economical geological carbon sequestration and concrete technologies. Here, we use atomistic simulations and density functional theory to probe the nature of physicochemical processes at the rock-water-CO2 interface. We show that while nanometer-thick interfacial water films persist at unsaturated conditions consistent with in situ infrared spectroscopy, hydroxylated metal silicate surfaces enhance CO2 speciation. Subsequently, through a reverse proton transport between the bicarbonate and surface hydroxides, a carbonate is produced that precipitates a surface metal carbonate complex in agreement with spectroscopic measurements. The resultant carbonate also decreases the dissolution energy barrier, whose magnitude is comparable with in operando X-ray diffraction experiments. These findings suggest that hydrated metal silicate surfaces are more basic than appreciated and long-range proton transfer mechanisms hold the key to interfacial metal carbonate nucleation and growth in low-water systems.