Direct mineral carbonation (MC) is used to mitigate carbon dioxide (CO₂) emissions. This method has the great advantages of reducing the amount of industrial residues and creating valuable materials by incorporating CO₂. Waste gypsum, industrial waste including flue gas desulfurization (FGD) gypsum (25.27–53.40 wt% of CaO), and phosphogypsum (30.50–39.06 wt% of CaO) can be used for direct MC (conversion rate up to 96%). Mineral carbonation converts waste gypsum into calcium carbonate (CaCO₃), which can be recycled during desulfurization. Furthermore, ammonium sulfate ((NH₄)₂SO₄), which is used as a fertilizer, can be prepared as a by-product when the carbonation reaction is performed using ammonia (NH₃) as a base. In this study, recent progress in the carbonation kinetics and preparation of CaCO₃ using FGD gypsum and phosphogypsum with NH₃ was investigated. Temperature, CO₂ partial pressure, CO₂ flow rate, and NH₃ concentration were reviewed as factors affecting carbonation kinetics and efficiency. The factors influencing the polymorphs of the prepared CaCO₃ were also reviewed and summarized. A state-of-the-art bench-scale plant study was also proposed. In addition, economic feasibility was investigated based on a bench-scale study to analyze the future applicability of this technology.

Geological CO2 sequestration in basalt formations represents a promising approach to mitigate climate change through secure carbon dioxide storage via mineral carbonation. This study investigates mineral dissolution, precipitation, and their influence on pore structure change during sequestration in basalt formations through batch experiments under controlled conditions (P: 8 MPa, T: 100 °C). The experiments were conducted in an autoclave system containing brine, where basalt sample (2 cm width and 9 cm height) was partially submerged to mimic a CO2-brine boundary during CO2 injection in basaltic formation.CT imaging technique was employed to compare changes in pore structure in basalt before and after the experiment. To evaluate impact of basalt-brine-CO2 reaction on pore structure, regions of interest (ROIs) were defined, focusing on the reacted zone and the transient zone, where mineral precipitation was most prominent. The reacted zone exhibited the formation of reddish minerals, likely iron oxide minerals, compared to unreacted zone. The transient zone, located at the CO2-brine interface, displayed the deposition of white minerals. These findings demonstrated that mineral dissolution/precipitation varied spatially, leading to heterogeneous changes in pore structure and fluid flow characteristics. The significant precipitation observed in the transient zone caused pore connectivity reduction, potentially impacting permeability and flow pathways. This study would contribute to an understanding of fluid flow behavior during long-term CO2 storage in basalt.

Ex-situ mineral carbonation, utilizing industrial by-products or natural calcium- and magnesium-bearing rocks, presents a promising avenue for CO2 removal. Both calcium and magnesium can form carbonates independently or in conjunction. While magnesium is a significant mineralization source, its presence can negatively influence carbonate precipitation and crystal stability when co-precipitated with CaCO3. This study investigates the effects of varying Mg2+/Ca2+ molar ratios on the mineral carbonation process under controlled conditions, quantitatively evaluating the resulting precipitate phases. Calcite consistently emerged as the dominant mineral phase across all tested Ca/Mg ratios. The results demonstrate that at higher Mg2+/Ca2+ ratios (≥1.0), substantial distortions occur within the calcite lattice, with magnesium ions substituting up to 6.51% of calcium ions. These distortions manifest as reduced crystal size, increased internal strain, and enhanced solubility, collectively indicating a decrease in structural stability. Furthermore, the formation of secondary phases, including aragonite and brucite, was observed at elevated Mg2+ concentrations (Mg2+/Ca2+ = 2.0), accompanied by the development of amorphous Mg-rich phases. These findings underscore the dual role of magnesium ions in carbonate mineralization: while they facilitate the formation of diverse mineral phases, they simultaneously introduce structural instabilities that may compromise the long-term durability of the mineralized products. This research provides crucial insights for optimizing mineral carbonation processes to achieve a balance between reactivity and stability, ultimately contributing to the development of more effective and reliable applications in both industrial and environmental settings.