Effects of Na₂O and BaO Additions on Phosphorus Distribution between CaO-MgO-FetO-SiO₂-Slags and Liquid Iron

Abstract

Experiments have been made to study the effect of Na₂O(7-13wt%) and BaO(4wt%) additions on the phosphorus distribution between liquid iron and CaO-MgO-Fe_tO-SiO₂-P₂O₅(≤1wt%) slags at 1550°C. The effect of Na₂O and BaO on the logarithm of the equilibrium quotient, k_p=(%P₂O₅)/([%P]²(%Fe_tO)⁵), was found to be 1.2 and 0.9 times as large as that of CaO on weight percent basis, respectively. The values for log k_p can be expressed as log k_p=0.145[(%CaO)+0.3(%MgO)-0.5(%P₂O₅) +1.2(%Na₂O)+0.9(%BaO)]+22 810/T-20.506
The effect of Na₂O or BaO on the activity coefficients of P₂O₅ was also studied by the Turkdogan and Pearson's treatment. The following expression for the log γP₂O₅ is obtained for the Na₂O- or BaO-containing slaps. log γP₂O₅=-1.02(23N_CaO+17N_MgO+8N_FetO-26N_P2O5 +33N_Na2O+42N_BaO)-22990/T+9.490
It was found from the plot of activity coefficients of Fe_tO vs. mole fraction of SiO₂ that activity coefficients of Fe_tO decrease with the addition of Na₂O, while it does not change with the addition of BaO. The dephosphorization equilibrium was discussed on the basis of the theoretical optical basicity proposed by Duffy and Ingram. The following equation was obtained as a function of optical basicity. log N_PO^3-4/([P][O]^5/2)=22.22∧_th+30890/T-28.752 where, N_PO^3-4: the anionic fraction of PO^3-₄ ion [ ]: weight percent in metal phase.