Abstract <p>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&#xa0;g/kg slag and FeCO₃ between 101 and 482&#xa0;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.</p> Graphical Abstract <p></p>