PNNL

Abstract

Carbon mineralization in humidified CO2 offers a promising route to mitigate anthropogenic emissions in a world stressed by water security. Despite its technological importance, our understanding of carbonation in water-poor environments lags, as traditional dissolution-precipitation pathways struggle to explain the adsorbed water nanofilm-mediated reactivity. Here, we utilize in operando X-ray diffraction (XRD) and advanced molecular simulations to investigate nanoconfined reactions driving forsterite carbonation, the magnesium-rich olivine. By examining statistically rare Mg2+ ion dissolution and transport using thermodynamically consistent atomistic models of the forsterite-water-CO2 interface, and comparing these with in operando XRD activation energies, we identify both processes to be rate-limiting at saturation. Our simulations reveal a mechanistic view of interfacial carbonation, where dissolution and precipitation are mediated by anomalous quasi two-dimensional diffusion that involves intermittent diffusive hopping in the outer-sphere desorbed state, separated by crawling events that are spatially short but temporally long. This understanding transcends carbon mineralization, with implications for geosystems contaminant transport, multifunctional materials, water desalination, and molecular recognition.