Ex-Situ CO2 Mineralization: Bridging Laboratory Science and Industrial Reality. Part I: Thermodynamic Foundations, Kinetic Barriers, and Engineering Pathways to Scale

Abstract

Ex-situ CO2 mineralization offers permanent carbon storage by reacting CO2 with alkaline solids to form thermodynamically stable carbonate minerals. Unlike geological storage, which requires long-term subsurface monitoring, mineralized carbon in stable carbonate products remains fixed for >10,000 years with negligible leakage risk, although product-phase and carbon-accounting verification remain necessary. This review (Part I) examines the pathway from thermodynamic foundations through reaction kinetics and activation strategies to reactor engineering, scale-up, and the current technology landscape. Carbonation is thermodynamically favorable (ΔG° = −20 to −130 kJ/mol CO2), but practical rates depend strongly on mineralogy, particle history, reaction pathway, and transport regime. Reactive calcium-rich industrial residues can carbonate under comparatively mild conditions, whereas crystalline magnesium silicates generally require grinding, thermal or chemical activation, additives, or elevated temperature and CO2 pressure. Process-engineering approaches evaluated include direct gas–solid carbonation, aqueous slurry systems, indirect multistep routes, and intensified contactors. The technology landscape includes commercial residue-based operators such as CarbonFree, Fortera, and Neustark; demonstration ventures such as MCi Carbon, Blue Planet, and Paebbl; and emerging mine-integrated projects such as Canada Nickel’s Crawford development. The evidence indicates that feedstock-specific kinetics, activation energy demand, solids handling, product markets, and verified delivered capacity─not thermodynamic favorability alone─govern scale-up. Quantitative techno-economic and life-cycle assessments are developed in the companion paper (Part II).