CO₂ sequestration by carbonation of steelmaking slags in an autoclave reactor

Carbon dioxide (CO₂) sequestration experiments using the accelerated carbonation of three types of steelmaking slags, i.e., ultra-fine (UF) slag, fly-ash (FA) slag, and blended hydraulic slag cement (BHC), were performed in an autoclave reactor. The effects of reaction time, liquid-to-solid ratio (L/S), temperature, CO₂ pressure, and initial pH on CO₂ sequestration were evaluated. Two different CO₂ pressures were chosen: the normal condition (700psig) and the supercritical condition (1300psig). The carbonation conversion was determined quantitatively by using thermo-gravimetric analysis (TGA). The major factors that affected the conversion were reaction time (5min to 12h) and temperature (40-160°C). The BHC was found to have the highest carbonation conversion of approximately 68%, corresponding to a capacity of 0.283kgCO₂/kgBHC, in 12h at 700psig and 160°C. In addition, the carbonation products were confirmed to be mainly in CaCO_3, which was determined by using scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) to analyze samples before and after carbonation. Furthermore, reaction kinetics were expressed with a surface coverage model, and the carbon footprint of the developed technology in this investigation was calculated by a life cycle assessment (LCA).