Long-term CO₂ mineralization and geochemical alteration in basalts from Saudi Arabia: Implications for carbon storage

Carbon dioxide (CO₂) mineralization in mafic igneous rocks is a promising pathway for permanent and secure geological carbon storage, offering a scalable solution for long-term climate mitigation. In this study, we present a systematic, long-duration investigation of CO₂–rock interactions using two compositionally distinct basalt types from Saudi Arabia: scoriaceous basalt (SB) and dense basalt (DB). These were subjected to supercritical CO₂ in brine at 50 °C and 10 MPa for three months, simulating subsurface carbon storage conditions. Our approach integrates advanced analytical techniques including X-ray diffraction (XRD), micro-computed tomography (μCT), scanning electron microscopy (SEM), X-ray fluorescence (XRF), total inorganic carbon (TIC) analysis, and inductively coupled plasma optical emission spectroscopy (ICP-OES) to track both geochemical transformations and microstructural evolution. The results reveal distinct reactivity and alteration mechanisms. SB, with an initial porosity of 5.7%, exhibited a 161% increase (to 14.9%), indicating substantial dissolution and secondary porosity development that enhanced fluid accessibility and promoted carbonate formation. DB, initially less porous (0.53%), showed an increase to 1.03% (approximately two-fold), with mineralization largely confined to microfractures and discrete voids. μCT and SEM confirm pore-structure modification and localized carbonate precipitation in both lithologies, with SB showing more pervasive transformation consistent with its vesicular texture and greater mineral accessibility. Geochemical analyses revealed greater calcium release and higher TIC accumulation in SB, indicating stronger reactivity. These findings underscore the suitability of Saudi basalts for long-term in situ CO₂ storage and provide a comparative dataset for optimizing basalt-hosted carbon storage systems under extreme experimental conditions.