Separation of phosphorus from dephosphorization slag modified by alkaline oxide by HCl leaching

Dephosphorization slag is one of the bulk solid wastes generated from steelmaking. If P is effectively removed from dephosphorization slag, a phosphate source which can substitute for phosphate rocks is obtained; meanwhile, the tailings can be reutilized as a feedstock in steel plant. To realize the integrated utilization of dephosphorization slag, selective leaching was applied for removing the P-bearing mineral phase from dephosphorization slag. Alkaline oxide was added as the slag modifier and HCl was selected as the acid lixiviant. The P selective leaching from dephosphorization slags modified by Na₂O or K₂O was studied at different pH values. By modification, the mass fraction of P in the 2CaO·SiO₂–3CaO·P₂O₅ phase increased, indicating that it was in favor of P₂O₅ enrichment. As the Na₂O or K₂O content increased, the P leaching ratio from slag increased at pH 4, reaching about 80%, and that of Fe was nearly zero. Na₂O and K₂O modification played a similar role in enhancing the P leaching. The effect of alkaline oxide modification became weak at pH 3, and the slag without modification also realized a good P selective leaching in the HCl solution. To facilitate the P removal, the leaching of Fe from dephosphorization slag needs to be restrained.