A thorough assessment of mineral carbonation of steel slag and refractory waste

Escalating industrial CO2 emissions necessitate innovative carbon capture and utilization strategies. This study explores the potential of mineral-carbonation of steelmaking slags, particularly White Slag (WS) and various Refractory Wastes (RWs), to mitigate CO2 emissions and valorize industrial wastes. Experiments were performed with waste materials from the production lines at CELSA (Barcelona, Spain). We delved into direct aqueous carbonation, evaluating the performance and characteristics of these wastes under different experimental conditions. Our findings reveal that all slags can effectively sequester CO2. This process is effective not only for pure CO2 but also for diluted flue gases under mild conditions (≤ 100 ºC, ≤ 6 bar). Specifically, WS exhibited peak CO2 sequestration capacities (SC) of 359.79 gCO2/kgslag (pure CO2) and 276.65 gCO2/kgslag (diluted flue gas). In contrast, the RWs presented different kinetic, reaching a maximum SC of 311 gCO2/kgslag after prolonged times. Given the large inhomogeneity of RWs, individual analysis of distinct RW fractions revealed significant variations in carbonation performance. Tundish RW exhibited the highest CO2 sequestration capacity, emphasizing the importance of waste source and mineral composition in the carbonation. Chemical and morphological evaluations confirmed the transformation of CaO to CaCO3, with MgO remaining largely inert. Additionally, the process indicated potential environmental benefits by reducing the mobility of toxic metals, particularly Pb, suggesting an ancillary avenue for waste treatment. This study underscores the utility of CO2 mineralization as a dual-benefit approach within the circular economy framework, offering insights into its application for sustainable waste management and CO2 emission reduction in the steel industry.