Carbonation of natural earth-abundant and synthetic metal silicates promises scalable solutions to permanently store CO2. With enigmatic observations undermining the rate-limiting role of dissolution in carbonation, understanding the kinetics proves critical in designing secure and economical geological carbon sequestration and ex situ sequestration technologies. Here, we use reactive and classical atomistic simulations and density functional theory to probe the nature of physicochemical processes at the rock-water-CO2 interface. Using Grand Canonical Monte Carlo simulations of H2O-CO2 fluid mixtures at technologically-relevant thermodynamic conditions, we show that nanometer-thick interfacial water films persist at unsaturated conditions consistent with in situ infrared spectroscopy. We subsequently use Density Functional Theory at B3LYP and D3 dispersion correction level and the nudged elastic band technique to show that hydroxylated metal silicate surfaces catalyze CO2 speciation to bicarbonate. Subsequently, through a long-range proton hole transport between the bicarbonate and surface hydroxides, a carbonate is produced and directly precipitates on the surface to form a metal carbonate core. The corresponding activation energies calculated by our ReaxFF potential are comparable with in operando X-ray diffraction measurements. These findings suggest hydrated metal silicate surfaces are more basic than appreciated and long-range interfacial proton hole mechanisms govern the early-stage carbonate nucleation in low-water systems.

Interfacial reaction pathways for docking CO2 in metal silicate rocks

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.