에너지환경지구화학 연구실Energy Environmental Geochemistry Lab

Of the various CO₂ trapping mechanisms, mineral carbonation is considered one of the most secure approaches for long-term geological carbon storage. Basaltic formations are attractive due to their abundance of Ca- and Mg-bearing minerals; however, mineral carbonation is often limited by insufficient release of reactive Ca ions. Here, circulating fluidized bed combustion (CFBC) fly ash was evaluated as an additional Ca source to enhance mineral carbonation in basaltic systems. Batch experiments using 0.64 M Na₂CO₃ showed no detectable carbonate formation in the basalt system consistent with XRD results and a low total carbon content of 0.18 %. In contrast, the addition of CFBC fly ash resulted in calcite formation and increased total carbon content up to 11.22 %. A reference system composed of CaCl₂·2H₂O and Na₂CO₃ showed a higher carbon content of 15.56 %, thus confirming the formation of carbonate precipitates under Ca-rich conditions.

Geochemical modeling based on batch conditions showed that the calcite saturation index (SI) increased from 0.53 to 3.41 with CFBC fly ash addition under alkaline conditions. Under CO₂-rich conditions, increasing CO₂ pressure (up to 5 MPa) decreased pH from 9.84 to 5.46 and reduced calcite SI from 3.46 to 0.67 due to carbonate speciation shifts. These results demonstrate that mineral carbonation in basaltic systems is primarily controlled by Ca availability in Na₂CO₃-based alkaline systems, whereas under CO₂ (g)-rich conditions, pH and carbonate speciation govern mineral stability and precipitation behavior.