Acid Leaching for Phosphorus Separation from the Co-processing of Dephosphorization Slag and Basic Oxygen Furnace Slag: Kinetics Investigation

To realize efficient P removal and resource utilization of steelmaking slag, a synthetic slag with appropriate basicity was produced by co-processing the practical dephosphorization slag and basic oxygen furnace slag. The selective leaching behavior and dissolution kinetics of P were investigated. The results indicated that the P dissolution efficiency and reaction rate were significantly influenced by the variety in stirring rate and pH. However, the decreasing solid/liquid ratio and particle size can significantly enhance the reaction rate, while exerting a slight impact on the P dissolution efficiency. The leaching temperature had less influence on both P dissolution efficiency and reaction rate. Under the optimal leaching conditions, the leaching reaction of the P-condensed phase primarily occurred within the initial 3 min, and, finally, the P dissolution efficiency reached 87.5%, with an extremely low dissolved amount of Fe. After leaching, the Fe-rich residue consisted of massive Fe2O3, MgO, and MnO, with only 0.32% P2O5. This residue can be used as a raw material or flux in steel plants. Furthermore, it was found that the selective leaching of P was controlled by diffusion through the product layer, with the apparent activation energy of 5.80 kJ/mol. The empirical equation has been established.