Enhanced Olivine Reactivity in Wet Supercritical CO₂ for Engineered Mineral Carbon Sequestration

The success of CO₂ mineralization as a potential solution for reducing carbon emissions hinges on understanding chemical interactions between basaltic minerals and CO₂-charged fluids. This study provides a detailed analysis of olivine dissolution in CO₂-water mixtures at 90 and 150 °C, 2-9 MPa, and for 8 and 24 h, in both water- and CO₂-dominant conditions. By using olivine crystal sections instead of powders, surface agitation is prevented, closing the gap between laboratory studies and natural settings. Surface chemistry, texture, and cross-sectional properties were examined pre- and postreaction using a multiscale approach combining spectroscopic and imaging techniques. Results show that wet supercritical CO₂ environments lead to significant olivine dissolution, forming Mg-depleted, Si-enriched etched surfaces, and under certain conditions, the formation of passivating silica precipitates. In contrast, reactions in aqueous fluids caused minimal changes in surface chemistry and texture with no silica precipitation. These observations indicate that reaction extent in the CO₂-rich phase is greater relative to water-rich mixtures at equivalent temperature, pressure, and reaction duration. The presence of silica precipitates incorporating leached metals indicates limited transport of reactant away from reaction sites in a CO₂-rich medium. This study semi-quantitatively evaluates reaction extents in both CO₂-rich and aqueous systems across a wide range of parameters, demonstrating faster mineralization in CO₂-rich environments and highlighting their potential for enhancing the CO₂ storage efficiency.