Indirect CO₂ mineral sequestration by steelmaking slag with NH4Cl as leaching solution

The steelmaking slag (SL) is used for indirect CO₂ mineral sequestration. The optimized carbonation conditions include: initial pressure 10bar, 60°C, 400rpm/min, 60min duration. The high purity (96±2wt%) calcium carbonate is obtained under the optimized carbonation condition. The crystallite magnesium carbonate together with other impurities such as aluminum oxide, ferrous oxide, silica oxide, also exists in the precipitate with composition percentage below 2wt%. The characterization of the obtained precipitates at different temperatures by SEM shows the gradual morphological changes from scalenohedral to rhombohedral crystal with increase of carbonation temperature (within 20-80°C). The kinetic shows a fast reaction rate with 11.8kJ/mol apparent activation energy, indicating a diffusion determined core-shrinking reaction during carbonation. The CO₂ capture capacity was compared to different sequestration routes using different industrial wastes. The maximum capacity from our experimental result could reach 211kg CO₂/ton SL with the contribution of CaCO₃/MgCO₃ together with Mg(HCO₃)₂ in capturing CO₂.