EXPERIMENTAL STUDY ON CO₂ MINERALIZATION AND STORAGE EFFICIENCY IN POROUS BASALT

Basalt carbon storage holds promise for fundamentally addressing engineering challenges such as CO₂'s tendency to leak and the difficulty of long-term storage. The CO₂ mineralization reaction mechanism within pore structures is the core of basalt carbon storage. To tackle the problem of accurately describing CO₂ mineralization reactions within pore structures, this study took basalts from the northern Qiong area of the Leizhou Peninsula as the research subject. Under unified reaction conditions (30 ℃, 6 MPa CO₂-saturated solution, 30 days), experiments on CO₂ mineralization reaction and storage efficiency were conducted using basalt samples of different scales. The study analyzed the dissolution intensity and rates of different divalent cations, the distribution and impact of secondary minerals within pores of different scales, as well as CO₂ mineralization efficiency and storage capacity. The main findings are as follows: (1) The pore structure of basalt reservoirs significantly retards and inhibits the CO₂ mineralization reaction. Although the overall cation dissolution concentration followed the order Ca²⁺>Fe²⁺>Mg²⁺, this trend emerged latest at the pore scale, with the concentrations of the three ions being only 0.29, 0.39, and 0.47 times those in 38~43 μm powder samples, respectively. By day 30 of the reaction, the ion release rates at the pore scale were only 0.2 times(Ca²⁺), 0.5 times(Fe²⁺), and 0.17 times(Mg²⁺) those of the powder samples. (2)Mineralization products varied with basalt sample morphology. Powder samples produced CaCO₃ after reaction, with a TGA-derived carbonate equivalent of approximately 10.19 wt%, in good agreement with the XRD-determined value of 9.13 wt%. In contrast, the porous core samples exhibited markedly weaker carbonate thermal decomposition signals; combined TGA and SEM-EDS analysis indicated that the mineralization products were dominated by clay minerals and aluminosilicate secondary phases, with carbonate mineralization remaining limited. (3) Significant differences in CO₂ sequestration efficiency were observed between sample types. The apparent CO₂ consumption efficiency of the porous core samples was only 0.842%, substantially lower than the 5.08% and 4.91% recorded for the 38~43 μm and 63~75 μm powder samples, respectively. The corresponding apparent CO₂ consumption was 27.09 kg^- · t^-1, representing merely 13% ~14% of that achieved by the powder samples. TGA further confirmed that the solid-phase carbonate-bound CO₂ in powder samples reached approximately 44.80 kg^- · t^-1, whereas that in porous core samples was only about 4.25 kg^- · t^-1. These results demonstrate that, under low-pH conditions, carbonate mineralization in intact porous basalt is considerably constrained, likely owing to the limited reactive surface area accessible within the pore network. This research reveals that pore structure is a key factor constraining the rate, efficiency, and capacity of CO₂ mineralization reactions. In the prediction and assessment of storage projects, the influence of pore structure should be dynamically considered, and storage processes should be optimized in real time to enhance the CO₂ mineralization reaction rate and storage capacity.