Effect of high Na₂O addition on distribution of phosphorus in low-basicity 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.