Specific responses of minerals during the dissolution of basalt for geological storage of CO2

Abstract

Dissolution experiments involving basalt grains (grain size: 0.841–1.190 mm) were conducted under CO₂-saturated conditions to investigate mineralogical changes and fluid chemistry dynamics relevant to geological CO₂ storage. The experiments were initially performed at 35 °C (up to 137 days) and subsequently at 50 °C (up to 210 days). Mineralogical analyses were conducted using scanning electron microscopy with backscattered electron imaging (SEM-BSE), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). The initial dissolution stage was characterized by rapid olivine dissolution, causing substantial early release of magnesium (Mg) and iron (Fe). Labradorite dissolution became increasingly significant after the temperature increase to 50 °C, enhancing mobilization of calcium (Ca), magnesium (Mg), and aluminum (Al). SEM-BSE analyses revealed distinctive dissolution textures on olivine grains, characterized by pronounced Mg depletion and Fe enrichment. Fluid chemistry results reflected these mineralogical changes, indicating rapid initial Mg release, sustained mobilization of silicon (Si) and Fe from ongoing olivine dissolution, and elevated Ca and Al concentrations after temperature elevation due to increased dissolution of plagioclase (labradorite) and, to a lesser extent, augite. Secondary silica precipitation occurred during later reaction stages, inferred from decreasing dissolved Si concentrations. These findings emphasize temperature- and mineral-specific dissolution behaviors, providing critical insights for optimizing basalt-hosted CO₂ sequestration.