Optimization Research On Reductive Dephosphorization Of High Phosphorus Si-Mn Alloy

There are rich manganese ore resources in China,but most of them are lean ores.High grade manganese ore resources almost completely rely on import,which leads to the high production costs.The manganese ore contains high impurities such as phosphorous and sulfur elements in Chengkou,Xiushan etc.,Chongqing.The phosphorous content in Si-Mn alloy produced by these low grade ores exceeds seriously.The low alloy product value restricts the efficient development of the local manganese enterprise.Si-Mn alloy is a kind of alloy has large production and used widely.The quality of Si-Mn alloy determines the grade of steel at a certain extent as the alloy is usually used as deoxidizer and alloy addition during steelmaking.The phosphorous in the alloy would pollute the steel liquid which causes the steel"cold crisp"to reduce the quality of steel.So,to control the phosphorous content of Si-Mn alloy and make it meet the requirements of national standard is the important subject in ferroalloy field.In this paper,the problem of dephosphorization in high-phosphorous Si-Mn alloy from Chengkou County was studied.The thermodynamic model of alloy melt and slag were established based on the coexistence theory.The experiment of reductive dephosphorization was carried by induction and MoSi₂ furnace.The effect of slag composition and process conditions on reductive dephosphorization was investigated by using ICP and XRD.The industrial experiment of reductive dephosphorization of Si-Mn alloy was carried by induction furnace.Some conclusions as follows:（1）Based on the thermodynamic model of the slag,it was found that the dephosphorization ability of the slag increased with the increase of CaO content in the CaO-SiO₂-Al₂O₃ slag system.And the dephosphorization ability of the slag was increased with the decrease of CaO content and the increase of MgO content in the CaO-SiO₂-Al₂O₃-MgO slag system.（2）For high fluoride CaO-CaF₂ slag system,dephosphorization effect was best when the CaO percentage was 25%in the initial slag,and the dephosphorization rate was75%.For lowfluorideCaO-SiO₂-Al₂O₃-MgO-CaF₂ slagsystem,dephosphorization effect was best when the ratio of the slag was 42:6:35:2:15,and the dephosphorization rate reached 85%.As for CaO-SiO₂-Al₂O₃ system,the addition of Na₂O was not in favor of dephosphorizing.Dephosphorization efficiency was better when the slag composition was in the low-melting-point area with low SiO₂ content of1400℃.And the dephosphorization rate was highest,reaching 71%when the slag composition was 58%CaO-4%SiO₂-36%Al₂O₃-2%Na₂O.（3）The system atmosphere has a certain effect on dephosphorization.The results showed that the dephosphorization effect in argon atmosphere was better than that in the air atmosphere when the silicon calcium alloy and aluminum dephosphorization agent were used respectively for dephosphorization.The optimum dephosphorization temperature of different dephosphorizer was different.When the silicon calcium alloy was used,the optimum temperature of dephosphorization was 1420℃and when Al-based dephosphorizer was used,the optimum temperature of dephosphorization was 1400℃.The oxidation loss of dephosphorizer would be reduced to improve the dephosphorization effect when the addition of dephosphorizer was mixed loading combined with flushing.（4）The Dephosphorization rate reached 70%,when the Al-based dephosphorizer and CaO-SiO₂-Al₂O₃-MgO-CaF₂ slag system were used for industrial experiments.