Dual-stage mineral carbonation approach to improve Ca and Fe reactivity in carbon sequestration of steel slag under optimized conditions

Abstract: This study investigates the carbonation and re-carbonation behavior of Ca and Fe in steel slag under varying conditions of aqueous mineral carbonation to enhance the CO2 sequestration capacity. A series of mineral carbonation experiments was performed using steel slag as the feedstock material under varying CO2 pressure and temperature. The results demonstrate distinct behavior of reactive Ca and Fe, indicating the importance of process optimization in feedstock material containing multi-element that are potential for mineral carbonation. The initial carbonation cycle achieved Ca carbonation efficiencies of 68–72%, while Fe carbonation efficiency remained limited at 10–12%. A subsequent re-carbonation cycle, performed after pH adjustment, indicated significant improvement in overall mineral conversion. Fe carbonation efficiency was increased by an additional 38% and Ca by 21%, resulting in nearly complete Ca utilization, i.e., 100% conversion and up to 48% Fe conversion. Enhanced CO2 pressure and temperature, and re-carbonation cycle have led to improved carbonation efficiencies for both Ca and Fe. Under optimized conditions, the process yielded high CO2 sequestration capacities, with the formation of CaCO3 in the range of 694–743 g/kg slag and FeCO3 between 101 and 482 g/kg slag. The findings demonstrates the important role of enhanced CO2 pressure and temperature, and multiple carbonation cycles in improving mineral conversion efficiency. Thus, the combined carbonation and re-carbonation routes offer an opportunity for effective sequestration and permanent storage of CO2 in steel slag, which is aligned with sustainable use of industrial residue for carbon mitigation.

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