Enhanced Carbonation of Free CaO in Basic Oxygen Furnace Slag Under High Temperature and Moderate Pressure and Its Kinetics

Basic oxygen furnace (BOF) slag is an industrial waste produced from steel-making. It can be utilized as building material, but its high content of free CaO (f-CaO) causes volume expansion of materials and limits its utilization. However, carbonation of BOF slag can decrease the f-CaO content, improve stability, and reduce carbon emissions. This study investigated the influence of temperature, pressure, liquid to solid, reaction time, and stirring pattern on f-CaO consumption and CO₂ sequestration, which reached a maximum f-CaO consumption and CO₂ sequestration of 99.58% and 5.12% (51.2 g CO₂/Kg BOF slag), respectively, under optimum conditions. According to the results of the XRD patterns of carbonated slag, no peaks of CaO were detected, the peaks of Ca₂Fe₂O₅ and Ca₂SiO₄ were slightly reduced, and new peaks of CaCO₃ were detected. The reaction process has been described by a shrinking core model revealing that the diffusion of reactants through the product layer was the rate-limiting step for carbonation. The kinetic equation for CO₂ sequestration was derived as: InK =  − 2132.83·T⁻¹–9.1543. This approach presents a green, cost-effective, and rapid method for enhancing steel slag utilization while capturing and storing CO₂. The method proposed in this paper holds significant potential for wider adoption.