Molecular mechanisms of CO₂ mineralization on wetting nanoscale surfaces using molecular simulations and metadynamics.

Abstract

Carbonatable minerals on earth have significant potential to act as gigatonne-scale CO₂ sinks. Many carbon removal managements rely on CO₂ mineralization on wetting mineral surfaces. Realizing their carbon removal potential requires a fundamental understanding of the atomic-scale mechanisms of mineral carbonation. This study employs reactive/non-reactive molecular simulations and well-tempered metadynamics to elucidate the complete interfacial CO₂ mineralization pathways within a portlandite mesopore adsorbed with a nanometric water film. Here we reveal quantitatively, for the first time, a global CO₂ mineralization spectrum describing the local molecular environment and the thermodynamics of the five critical steps: water adsorption, calcium dissolution, CO₂ adsorption, CO₂ speciation, and CaCO₃ ion pairing. We identify kinks as the primary reactive sites for surface dissolution and demonstrate how the water film's acid-base environment modulates these processes, creating an energetically favorable reaction loop for sustained CO₂ mineralization. We uncover that quasi-neutral to slightly basic conditions optimize mineralization efficiency by balancing the opposing effects of pH on calcium dissolution and CO₂ speciation.