Experiment and kinetic modeling for leaching of blast furnace slag using ligand

Blast furnace (BF) slag is recognized as an excellent source of precipitated calcium carbonate (PCC) and CO2 sequestrating agents because it contains a significant amount of calcium. The pH-swing method is a promising process for commercialization of the slag carbonation process among the other indirect carbonation methods due to the high selectivity of calcium extraction and production of high quality PCC. In this study, ligand-based solvents, such as acetic acid, gluconic acid, and citric acid, were examined as new leachates for the extraction step in the pH-swing process. Citric acid showed the highest efficiency, and the extraction efficiencies were estimated based on particle size distribution, concentration of solvent, solid-to-liquid ratio, stirring speed, and temperature. The calcium extraction rate increased with decreasing particle size and S/L ratio and with increasing concentration of solvent and stirring speed. However, extraction efficiency decreased significantly at high temperature because calcium-citrate complexes were precipitated. Along with the experiments, a kinetic study based on the shrinking core model was carried out at temperatures lower than 30 °C. Our results demonstrated that the extraction process was controlled by a surface chemical reaction, and the activation energy was estimated to be 50.74 kJ mol−1.