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 Na_(2)O or K_(2)O was studied at different pH values.By modification,the mass fraction of P in the_(2)CaO∙SiO_(2)–3CaO∙P_(2)O_(5)phase increased,indicating that it was in favor of P_(2)O_(5)enrichment.As the Na_(2)O or K_(2)O content increased,the P leaching ratio from slag increased at pH 4,reaching about 80%,and that of Fe was nearly zero.Na_(2)O and K_(2)O 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.

Distribution of P2O5 between solid solution and liquid phase in dephosphorization slag of CaO-SiO2-FeO-P2O5-Na2O system

A multi-phase slag containing Na2O is potential to efficiently dephosphorize high-P hot metal.After dephosphorization,the generated slag with high P2O5 content is regarded as a P resource.Because P2O5 was mainly concentrated in the 2CaO SiO2-3CaO P2O5 solid solution,the recovery of P from dephosphorization slag primarily depends on the separation of the solid solution from other phases.The distribution ratios of P2O5 between solid solution and liquid phase in the CaOSiO2-FeO-P2O5-Nslag system were investigated.The results indicated that the addition of Na2O facilitated the enrichment of P2O5 in the solid solution because it increased not only the distribution ratio of P2O5 but also the mass fraction of the solid solution.The distribution ratio of P2O5 was independent of the P2O5 content in slag.A higher P2O5 content in slag resulted in higher P2O5 and Na2O contents in the solid solution.The distribution ratio of P2O5 increased with the total Fe content in the liquid phase,regardless of the valence of Fe.An increase in the FeO content in slag brought a higher P2O5 content in the solid solution.As slag basicity increased,the distribution ratio of P2O5 increased,but the P2O5 content in the solid solution decreased.