| In recent years,most of the blast furnace in China began to use higher iron ore containing Al2O3,due to the rising price of ironmaking raw materials.With the increase of the content of high Al2O3 iron ore,the Al2O3 content of the blast furnace slag increased significantly,which made the slag flowability and desulphurization capacity decreasing.Sulfur(S)element is mainly removed by interfacial chemical reaction.The activity of each component involved in the desulphurization reaction is an important factor affecting the desulfurization process.The activities of slag components have been one of the core problems in metallurgical thermodynamics research.The activities of the components in the metallurgical melt can be obtained or calculated in terms of chemical equilibrium and phase equilibrium,and then the effect of activities on desulphurization reaction can be discussed.Therefore,it is important to establish the activity calculation model of CaO-SiO2-MgO-Al2O3 quaternary slag system,in order to study the desulfurization ability of CaO-SiO2-MgO-Al2O3 slag system.In this paper,the activity calculation model of CaO-SiO2-Al2O3-MgO quaternary system was established according to the molecular ion coexistence theory of slag.a(CnO)in the CaO-SiO2-Al2O3-MgO quaternary system was measured using a typical experiment in order to verifiy the reliability of the model.The influences of R,w(MgO)/w(Al2O3),Al2O3 content and other factors on the activity of each component in the slag were analyzed based on the activity calculation model.Finaly the desulfurization capacity of CaO-SiO2-MgO-Al2O3 quaternary slag system was discussed too.The achievements of this study are listed as follows.(1)Combining the coexistence of molecular ion of slag with the relevant binary phase diagram,ternary phase diagram and thermodynamic data,a calculation model for predicting the activity of CaO-SiO2-Al2O3-MgO quaternary slag was established using MATLAB mathematics tool.(2)Measurement experiment of a(CaO)of the CaO-SiO2 binary system and CaO-SiO2-Al2I3-MgO quaternary were designed at 1600 ℃.The results have shown that the reaction can be reached equlibrium after 24h;Using CaO-CaF2 as the reference slag,a(CaO)in the saturated CaO-SiO2 binary system is 0.0667;a(CaO)in CaO-SiO2-Al2℃3-MgO quaternary slag system was determined by using CaO-SiO2 as the reference slag.In order to eliminate the influence of CaO-CaF2 on a(CaO)in CaO-SiO2,L,corrected index,is introduced and the corrected a(CaO)is 0.0654;a(CaO)in the CaO-SiO2-Al2O3-MgO quaternary slag system was determined based on this value and the experiment results.(3)The results show that the prediction model can calculate the activity of each component in the CaO-SiO2-Al2O3-MgO quaternary system and its reliability is validated by using the experiment data reliability.Based on the prediction model,the activity of CaSiO3 decreases and the activities of Ca2SiO4 and CaO · MgO · SiO2 increase with the increase of R,the activity of CaSiO3 decreases and the activity of Ca2SiO4 and CaO · MgO · SiO2 increase when w(MgO)/w(Al2O3)increases from 0.25 to 0.45 with fixed R of 1.05;The variety trends of the activity of CaSiO3 and the activity Ca2SiO4 at R = 1.20 are similar with those at R=1.05;The activities of CaSiO3 and Ca2SiO4 decrease and the activity of CaO · MgO · SiO2 increases with the increase of w(Al2O3)content from 12%to 18%in two slag systems with different R.(4)The desulfurization experiment results show that when the w(MgO)/w(Al2O3)=0.35,w(Al2O3)=15%,with the R increases,Ls increases;the activity of CaSiO3 decrease,the activity of CaO and Ca2SiO4 increase,w(S)smaller,desulphurization effect more evident.When w(Al2O3)=15%and R=1.20,Ls increases with the increase of w(MgO)/w(Al2O3);the activity of CaSiO3 decreases,the activity of CaO and Ca2SiO4 increases,The w[S]in the molten iron is the smallest,and the desulfurization effect is the best.With the increase of w(Al2O3),Ls increases gently and the activities of CaSiO3 and Ca2SiO4 decrease,when the w(MgO)/w(Al2O3)= 0.35 and R = 1.20. |
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