Reactivity and Dissolution Characteristics of Naturally Altered Basalt in CO₂-Rich Brine: Implications for CO₂...

Hydrothermally altered basaltic rocks are widely distributed and more accessible than fresh basaltic rocks, making them attractive feedstocks for permanent CO₂ storage through mineralization. This study investigates the reactivity and dissolution behaviors of altered basalt during the reaction with CO₂-rich fluids and compares it with unaltered basalt through batch hydrothermal experiments using a brine that simulates reservoir conditions with 5 MPa CO₂ gas at 100 °C. When using basalt powders to evaluate reactivity, results show that although the leaching rates of elements (Mg, Al, Si, K, and Fe) from altered basalt were generally an order of magnitude lower than those from unaltered basalt in a CO₂-saturated acidic environment, similar elemental leaching behavior was observed for the two basalt samples, with Ca and Mg having the highest leaching rates. However, in a more realistic environment simulated by block experiments, different leaching behaviors were observed. When the CO₂-rich fluid reacts with altered basalt, rapid and preferential dissolution of smectite occurs, providing a significant amount of Mg to the solution, while Ca dissolution lags. This implies that when altered basalt is utilized for CO₂ mineralization, the carbonation step may differ from that of fresh basalt, with predominant Mg carbonation followed by Ca carbonation. This rapid dissolution of Mg suggests that altered basalt is a promising feedstock for CO₂ mineralization. This study provides theoretical support for developing technologies to utilize altered basalt for carbon storage.