Dissolution Behaviors of Naturally Altered Basalts in a Brine at 100 °C for In-Situ CO₂ Mineralization

The use of basaltic formations and existing wells in oil and gas fields for carbon dioxide (CO₂) mineralization holds both technical and economic advantages. However, these basaltic rocks have often undergone natural alteration, and their reactivity in CO₂ mineralization remains uncertain. To address this knowledge gap, the present study investigated the dissolution behaviors of both altered and unaltered basaltic rocks in a brine that simulating the real reservoir condition with 5 MPa CO₂ gas at 100 ℃ through laboratory batch experiments. The experimental results indicate that the reactivity of altered basalt is comparable to that of unaltered basalt, with the former exhibiting faster leaching of Mg compared to the latter within a 15-day period. This can be attributed to the rapid dissolution of smectite, a type of clay mineral present in altered basaltic rocks. Meanwhile, there was no significant decrease observed in the leaching of Ca. It is important to note that the dissolution of basalt in a CO₂-rich environment led to the formation of amorphous calcium carbonate (ACC), accompanied by the precipitation of amorphous SiO₂, indicating the initial stages of CO₂ geological mineralization. Taken together, these results suggest that altered basaltic rocks can also be utilized for CO₂ mineralization at moderate temperatures.