Effect of high Na2O addition on distribution of phosphorus in lowbasicity converter slag

In order to improve the dephosphorization efficiency of low-basicity converter slag and decrease the consumption of solid CaO,the effect of high Na2O addition(0-15 mass%)on the distribution of P2O5 between solid solution and matrix phase was investigated.The thermodynamic properties of slag samples were calculated by FactSage 7.0 software.Then,the dissolution behavior of phosphorus element from slag was studied.The results show that the mass fraction of 2CaO*SiO2-2CaO*Na2O*P2O5 solid solution increases when the Na2O content is increased in slag.However,the amount of formed solid solution changes little when the Na2O addition is more than 10 mass%.Moreover,the content of Na2O in solid solution would reach saturation when adding 15 mass%Na2O into the slag.With the increase in Na2O content in slag,the distribution ratio of P2O5 between solid solution and matrix phase increases.The values are evidently higher than the results reported in the literature.Meanwhile,the activity of P2O5 in matrix phase and the activity coefficient of P2O5 in solid solution are decreased with increasing the Na2O content in slag.Furthermore,the dissolution ratio of phosphorus in citric acid solution could be improved by adding Na2O into slag,but the increment of dissolution ratio would decrease when the Na2O content exceeds 10 mass%in slag.

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.