Study On Thermodynamics Property Of CaO+SiO₂+Al₂O₃+MgO+FeO Slags

The activity of ferrous oxide, sulphide capacity and Phosphorus capacity of CaO+SiO₂+Al₂O₃+MgO+FeO slags were investigated using chemical thermodynamics theory and advanced experimental method.A Mo∣Mo+MoO₂∣ZrO₂(MgO)∣Fe+(FeO)+Ag∣Fe solid-electrolyte cell was used to measure the activity of FeO in CaO+SiO₂+Al₂O₃+MgO+FeO slags at 1673K. It was found that under fixed conditions of FeO, Al₂O₃ content and {(%CaO)+ %MgO}}/(%SiO₂) ratio, aFeO decreased with increasing MgO content from 5% to 10%, and increased when the content of MgO was over than 10%; aFeO rised with the increase of FeO content at a fixed (%CaO)/(%SiO₂) ratio, MgO and Al₂O₃ content. For slags of a fixed MgO, FeO and Al₂O₃ content, aFeO increased with increasing the basicity (%CaO)/(%SiO₂) from 1.03 to 1.30.The sulphide capacity of CaO+SiO₂+Al₂O₃+MgO+FeO slags was studied at 1773K using gas-slag equilibrium techniques. Utilizing Pt crucible as a reaction vessel, the slag was equilibrated with a mixture gas of CO, CO₂, SO₂ and N₂ to provide the oxygen and sulphur partial pressure. It was shown that at a fixed FeO,Al₂O₃ content and a fixed {(%CaO)+(%MgO)}/(%SiO₂) ratio, the sulphide capacity increased with increasing the content of MgO from 5% to 10% and decreased when MgO content surpass 10%. The sulphide capacity also increased with the increase of FeO content at a fixed (%CaO)/(%SiO₂) ratio, MgO and Al₂O₃ content; The rising basicity (%CaO)/(%SiO₂) from 1.04 to 1.4 at a fixed MgO, FeO and Al₂O₃ content, significantly increased the sulphide capacity。The phosphorus capacity of CaO+SiO₂+Al₂O₃+MgO+FeO slags was measured at 1673K using gas-slag-metal equilibrium techniques. An iron crucible was used as reaction vessel, and Ag-0.2%P alloy as a flux was equilibrated with slags at a constant flow of CO+CO₂ gas mixture to provide oxygen partial pressure. It was found that at a fixed {(%CaO)+(%MgO)}/(%SiO₂) ratio, MgO and FeO content, the phosphorus capacity increased with increasing MgO content from 5% to 8% and decreased with increasing over 8%. Considering the effect of MgO on Phosphorus capacity, the best interval to MgO content is from 5% to 10%. The phosphorus capacity increased with rising FeO content at a fixed (%CaO)/(%SiO₂) ratio, MgO and Al₂O₃ content. It was also shown that at a fixed content of MgO, Al₂O₃ and FeO, the phosphorus capacity increased with rising slag's basicity (%CaO)/(%SiO₂) from 1.1 to 1.5, and the relationship between basicity and the Phosphorus capacity is expressed by the formula log PO₄^3-=7.00(%CaO)/(%SiO₂)3.95.