The CO2 sequestration by supercritical carbonation of electric arc furnace slag

The current study puts the emphasis on developing a supercritical carbonation process of electric arc furnace slag for the CO2 sequestration. In this process, the feed is mixed with water and processed with supercritical CO2 at 40-80 degrees C and 80-120 bar for 48 h. This process offers several advantages including higher reactivity, faster kinetics, less waste generation, better economic feasibility, and less pretreatment compared with aqueous carbonation. The empirical model established by using a systematic design of experiments methodology is demonstrated to be suitable for calculating the carbonation efficiency as a function of operating parameters and performing the process optimization. With fundamental investigations into carbonation mechanisms, the slag particle size is determined to have the most significant positive impact on carbonation efficiency. The sample with a smaller particle size has a higher total carbonated volume, resulting in higher CO2 uptake. Fundamental investigations into the carbonation process indicate that the diffusion barrier to the carbonation process is a product calcium carbonate layer formed on the outer shell of the slag particle and the thickness of this layer is constant regardless of the slag particle size. Furthermore, it was revealed that the reaction mechanism of the carbonation process is mainly driven by the hydrogen ion which reacts with dicalcium silicate in EAF slag and produces dissolved calcium ions. In this study, the reaction pathway for supercritical carbonation of EAF slag is elucidated and the results of mechanistic investigations shed light on the diffusion barrier to the carbonation process and the rate-determining step. We expect the results of this study help enable the carbonation of industrial byproducts, in particular, steelmaking slag.