Direct aqueous carbonation of dephosphorization slag under mild conditions for CO2 sequestration and utilization: Exploration of new dephosphorization slag utilization

Dephosphorization slag is not effectively utilized owing to its characteristics of having high phosphorus (P) content and being rich in free CaO. In this study, direct aqueous carbonation of dephosphorization slag under mild conditions (i.e., atmospheric pressure, unconcentrated CO2, and room temperature) was investigated to explore the potential for CO2 sequestration and utilization, as well as to improve its properties for further utilization. The maximum CO2 uptake capacity of 0.06 g-CO2/g-slag was achieved at a solid–liquid ratio of 25 g/L with 14% introduced-CO2 concentration. Depending on the pH value, P was fixed by crystallization with calcium (Ca), which was verified by the crystalline phases of the carbonated slag and elemental concentrations of the solution. The particle collision mechanism was confirmed by characterization of the particle-size distribution and crystalline phases of the carbonated slag, demonstrating detachment of CaCO 3 from the slag surface, which was more significant at high solid–liquid ratios. The rate-limiting step is controlled by CO2 dissolution and CaCO 3 precipitation. The carbonated slag was determined to be stable, and it can be used for further applications.