Integrated Carbon Mineralization of Steelmaking Slag for Plant-Level CO₂ Sequestration, Waste Valorization, and Circular Economy

As the emissions of carbon dioxide (CO₂) from industrial facilities have been rapidly growing, the need for sustainable carbon capture and utilization technologies that can support industrial decarbonization has been increasingly growing to meet circular economy goals. The steel industry is one of the major industries that contributes to greenhouse gas emission, and produces a vast amount of steelmaking slag as industrial waste. In the current study, carbon mineralization using steelmaking slag was studied as a possible option for plant level carbon dioxide sequestration, waste valorization and sustainable material utilization. The basic oxygen furnace (BOF) and electric arc furnace (EAF) slags were thoroughly physically and chemically characterized and then the slags were carbonated under controlled operational conditions in an accelerated manner. The effect of carbonation parameters such as temperature, pressure, reaction time, particle size and liquid-solid ratio was systematically investigated using a slurry-phase carbonation reactor. It was found that the carbonation performance of BOF slag was better due to its higher calcium oxide content, higher alkalinity and better surface morphology. The optimal results included maximum CO₂ uptake of 24.8%, and carbonation efficiency of 89.4%. Based on the kinetics analysis, the carbonation reaction obeyed the surface reaction-controlled mechanism and diffusion-controlled mechanism and the shrinking core model was found to be in good agreement with the experimental results. The enhanced reactivity and improved ion diffusion behavior in BOF slag was confirmed by activation energy analysis. In addition, the engineering properties of the slag derived construction materials such as the compressive strength, carbonate stability, and durability performance were considerably enhanced with carbonation treatment. An industrial framework for combining the steel slag carbonation, flue gas application and waste heat recovery in steel-making plants on a pilot scale was also proposed. The study showed that the accelerated carbonation of steel slag has a significant potential for permanent carbon sequestration, industrial waste management, and value-added construction material production. This proposed approach offers a means of achieving carbon neutral steel production and circular economy in an environmentally sustainable and economically viable manner.