Mechanism of direct CO2 sequestration by alkali metal K-activated steel slag

CO2 sequestration through steel slag is one of the effective approaches to simultaneously realize the resource utilization of industrial solid waste, reduce carbon emissions, and enhance the stability of steel slag as a construction base, with considerable application prospects. Nevertheless, the components responsible for CO2 sequestration in steel slag predominantly exist as silicates, whose chemical inertness leads to suboptimal CO2 sequestration efficiency in the slag. Based on the strategy of activating the silicate components in steel slag with the alkali metal potassium (K) to improve the CO2 sequestration performance of steel slag, both experiments and theoretical calculations were performed to give a deep insight into the effect and mechanism of K modification on enhancing the CO2 sequestration capability of steel slag. In experiments, CO2 sequestration capacity of steel slag modified with 3 wt.% K reached 100.15 g/kg at 1000 K. Theoretical analysis has revealed that although K exhibits low reactivity, it enhances the electronic transition and amplifies charge localization at specific sites within Ca2SiO4, consequently improving its CO2 sequestration capacity. However, an excessive doping of K led to the partial inactivation of some active sites within Ca2SiO4. Furthermore, CO2 chemisorption on Ca2SiO4 surface predominantly occurs through the chelate configuration of CO32-, suggesting the formation of a CaCO3 precursor. Thus, both the experimental results and theoretical calculations reveal the role of K on enhancing CO2 sequestration capability of steel slag. In summary, K modification offers promising prospects for improving CO2 sequestration properties of steel slag and provides support for the industrial implementation of carbon sequestration by steel slag.