Study On Basic Properties And Dephosphorization Behavior Of Steelmaking Slag Based On Red Mud Based Flux

With the rapid development of society,the quality requirements of steel in various industries are getting higher and higher.The efficient removal of phosphorus is one of the key factors to ensure the quality of steel.The CaO-FetO-SiO2 slag was formed in the traditional steelmaking process.High melting point and poor fluidity of CaO-FetO-SiO2 slag are key factors of limiting high-efficiency smelting.The specific performance is that the dephosphorization efficiency is low in the early stage,and the dephosphorization load is large in the late stage of smelting,resulting in peroxidation tapping and low purity of molten steel.Therefore,it is necessary to add flux to the CaO-FetO-SiO2 slag to promote lime dissolution,to improve dephosphorization kinetics and reaction efficiency.Due to environmental pollution problems,the use of the flux CaF2 has been significantly restricted in steelmaking.Although increasing the FeO content can also reduce the melting point of slag,this method causes iron loss and seriously affects the purity of molten steel.Therefore,it is necessary to find suitable steelmaking flux and develop a new steelmaking slag system to make it no longer dependent on FeO and CaF2 slagging,and achieve high-efficiency dephosphorization in the early stage of steelmaking.Many studies have shown that Al2O3 and Na2O can lower the melting point of CaO-FetO-SiO2 slag system and improve the fluidity of initial slag.Red mud is rich in Al2O3 and Na2O.The application of red mud in steelmaking can improve the disadvantages of traditional CaO-FetO-SiO2 slag,such as high melting point and slagging hard,and develop a new type of CaO-FetO-SiO2-Al2O3-Na2O steelmaking slag system to achieve high-efficiency dephosphorization in the early stage of converter steelmaking.And the high-efficiency dephosphorization in the early stage is very conducive to high-carbon tapping,which can effectively avoid peroxidation tapping and improve the cleanliness of steel.This paper uses research methods of theoretical analysis,laboratory experiment,intermediate expansion test and industrial test to systematically study the basic physicochemical properties of CaO-FetO-SiO2-Al2O3-Na2O slag and the application of red mud based flux in steelmaking.The main research contents and results are as follows:(1)The basic physical properties such as melting properties and viscosity characteristics of CaO-FetO-SiO2-Al2O3-Na2O slag were studied.The results showed that Al2O3 and Na2O can significantly enlarge the liquid phase area of CaO-FeO-SiO2 slag and reduce the melting point of slag.In the CaO-Fe2O3-SiO2-MgO-Al2O3-Na2O-P2O5 slag system,the slag viscosity decreased with the increase of Na2O,and increased with the increase of Al2O3 content.However,the viscosity remained low after the addition of Al2O3 even at a low temperature of 1350℃.The influence of Al2O3 on the viscosity of steelmaking slag system was limited.(2)In order to investigate the dephosphorization ability of CaO-FetO-SiO2-Al2O3-Na2O-(TiO2)slag system,the distribution ratios of phosphorus between CaO-FetO-SiO2-Al2O3-Na2O-(TiO2)slag and carbon-saturated iron,the phosphate capacities of the slag system and the phosphorus enrichment behavior were studied.The distribution ratios of phosphorus between slag and carbon-saturated iron decreased with the increase of Al2O3 content and temperature,and increased with the increase of Na2O content and basicity,and increased first and then decreased with an increase in the FeO content.The phosphate capacities of slag decreased with the increase of FeO,Al2O3 content and temperature,and increased with the increase of Na2O content and basicity.Phosphorus is mainly present in the P-rich phase of InC2S-C3P solid solution in CaO-SiO2-Fe2O3-MgO-Al2O3-Na2O-TiO2 slag.Al2O3,TiO2 and Na2O can promote the enrichment of phosphorus and increase the P2O5 content in the P-rich phase.The order of influence on phosphorus enrichment is TiO2>Al2O3>Na2O.(3)In order to initially explore the application effect of CaO-FetO-SiO2-Al2O3-Na2O based slag formed by red mud using in steelmaking,the application of red mud in dephosphorization of hut metal was studied through laboratory basic experiments.The results suggested that Bayer high-iron red mud has good fluxing effect.Compared with the traditional CaO-FetO-SiO2 dephosphorization slag system,the red mud based flux has better slag-iron separation effect with the metal phase.The slag-iron interface is clear,and the slag was easy separated from the iron phase in the red mud based flux.When the mass ratio of Bayer high-iron red mud and CaO was controlled within the range of 1-2,the final[P]of molten iron can be reduced to below 0.018%,and the dephosphorization rate was greater than 80%.(4)The simulation experiments of converter oxygen blowing steelmaking were conducted in a 10 kg induction furnace.The results suggested that Bayer red mud-based flux has good slag fluidity,and good dephosphorization effect can be achieved in the situation of high[C]of 2.0%to 3.0%.The hot metal[P]can be removed to below 0.018%,and the dephosphorization rate is higher than 88%.This is of great importance for the production of clean steel.In the simulating experiment of converter steelmaking for medium-high phosphorus hot metal,when the red mud:CaO ratio was 1:1.2 and slag ratio was 8%,high dephosphorization rate(～95%)and low final[P](=0.02%)was achieved in the situation of high[C]=1.36%.In the experiment of red mud carbonaceous pellets used in converter steelmaking,when adding proper amount of carbon to the red mud pellet(C/O molar ratio controlled at 1～1.2),it can effectively reduce the effect of red mud itself on the temperature drop of hot metal,and not affect its dephosphorization effect,which are very conducive to adapt to the current large scrap steel ratio smelting process.(5)The expansion test was carried out in a 200 kg induction furnace to further study the application of red mud based flux in steelmaking.The results showed that Bayer red mud based flux has good dephosphorization and fluxing effect.High dephosphorization rates(～90%)and low final[P](<0.02%)were obtained under semi-steel conditions([C]=2.5～3.0%).When[C]was reduced to a very low level(≈0.01%),the final[P]in steel can still be controlled within 0.02%,and no rephosphorization occurred.The FeO content in the final slag can be controlled within 8.5%,which can greatly reduce the iron loss.(6)Based on the previous laboratory research and intermediate expansion test,the technical feasibility and actual fluxing,slagging and dephosphorization effect of applying red mud based flux in industrial production scale were further studied.The results of industrial test showed that red mud based flux can quickly help melt the slag in the early stage of steelmaking,solve the "back to dry" phenomenon in the middle and late stage of steelmaking,and avoid using fluorite-based flux.It had better dephosphorization effect,and its average end point phosphorus was reduced by 0.012%and the dephosphorization rate was increased by 12%.Deep dephosphorization and high carbon tapping can be achieved under semi-steel conditions.The FeO content in final slag can be reduced to 12～15%,which is beneficial to improve the quality of steel.