Experimental study and mechanism analysis on enhancing CO2 sequestration in steel slag by activating silicate components with potassium modification

CO2 sequestration by steel slag is one effective method for realizing the coupled functions of resource utilization of solid waste and reducing carbon emissions. However, the low carbonation capacity of steel slag, due to the inert nature of silicate components, limits its broader application. Accordingly, alkali metal potassium (K) was adopted to activate silicate components for improving the slag carbonation capacity. The carbonation performances of K-modified slags were assessed experimentally, with DFT calculations to give a deep insight into the CO2 sequestration mechanism by K-modified slag. The results reveal that K, differing in size and valence from Ca, destroys the geometric and electronic structure stability of silicates, giving their high carbonation activity. The maximum CO2 uptake reaches to 100.15 gCO2 /kgslag with 3 wt% K doping, giving a corresponding carbonation conversion of 27.1%. The DFT calculations implied a destabilized Si-O1 bond, leading to the dissociation of O1 from [SiO4] tetrahedron and promoting the CO32- group formation. Furthermore, CO2 adsorption is energetically favorable upon K doping. The findings indicate the high CO2 sequestration potential of K-modified slag and provide a theoretical basis and data reference for using K-modified slag in the resource utilization of solid waste within steel plants.