Study On High Temperature Reduction Properties Of Mineral Phases In Fe₂O₃-CaO-Al₂O₃-SiO₂ System

In recent years,the price of iron ore continues to rise,high-grade ore is increasingly depleted,and iron and steel mills inevitably have to use more and more raw materials with high gangue content.The deterioration of raw materials poses new challenges to the sintering process.In the sintering process,silico-ferrite of calcium and aluminium?SFCA?is the most important binder phase in high-basicity sinter,and its quantity and structure play an important role in the strength and reducibility of the sinter.This study systematically studied the reduction of the calcium ferrite phases from the binary calcium ferrite to the ternary,quaternary and quinary elements.The main research conclusions include:In the solid-state reaction of Fe₂O₃-CaO system,CaO·2Fe₂O₃?CF₂?,CaO·Fe₂O₃?CF?and 2CaO·Fe₂O₃?C₂F?are generated according to the different molar ratios of Fe₂O₃ and CaO.In the solid-state reaction of Fe₂O₃-CaO-Al₂O₃ system,CFA is mainly formed when the content of Al₂O₃ is low.As the content of Al₂O₃ continues to increase,it will combine with CaO to form CaO·2Al₂O₃,and Fe₂O₃ appears in free form.In the solid-state reaction of Fe₂O₃-CaO-SiO₂ system,SFC is mainly formed when the SiO₂content is low,and it will combine with CaO to form 2CaO·SiO₂ as the SiO₂ content continues to increase,and Fe₂O₃ appears as a free form.In the solid-state reaction of Fe₂O₃-CaO-MgO system,MgO and Fe₂O₃ form magnesium-magnesium spinel.The remaining CaO and CaO·Fe₂O₃ form 2CaO·Fe₂O₃.The results of Fe₂O₃-CaO system phase reduction behavior show that CF₂ first reaches the reduction end,followed by CF,C₂F reaches the end point of the reduction,and the rate of CF₂ reduction Above CF,C₂F has the slowest rate of reduction.The apparent activation energies of the reduction of CF,CF₂,and C₂F were 46.89,34.37,and 51.74 kJ·mol^-1,respectively.All three reactions were controlled by the two-dimensional unreacted nuclear model?A₂?.In the reduction pathway,CF₂decomposes first to produce iron oxide and CF,CF reduces C₂F,and C₂F reduces to iron;CF reduces CF₂,CF₂ reduces to iron,and CF₂ reduces to iron.For the phase reduction of Fe₂O₃-CaO-Al₂O₃ system,the reaction is mainly divided into two stages,ie,the degree of reduction is 0-0.2 and 0.2-1.The addition of Al₂O₃ reduces the degree of reduction,but the content of Al₂O₃ has little effect on the degree of reduction.Moreover,the addition of Al₂O₃ slows down the reduction of CF,but with the continued addition of Al₂O₃,both H and CFA increase at the same time,and the effects of the two cancel each other,which has little effect on the reduction rate.The apparent activation energies of CF2A,CF4A and CF8A were 91.05,64.83 and 59.47kJ·mol^-1,respectively.The reduction of CF2A is controlled by the A₂ mode,and the reduction of CF4A is accompanied by the interaction of A2 and the 2D interface reaction model?R₂?.CF8A is mainly controlled by the three-dimensional unreacted nuclear model?A₃?in the early stage of the reaction,and gradually proceeds with the reduction.Switch to A₂ mode.In the phase reduction of Fe₂O₃-CaO-SiO₂ system,when SiO2 is 2%-4%,it has an inhibitory effect on the reduction of calcium ferrite,so that the reduction and reduction rate,as the SiO₂ content continues to increase,the inhibitory effect gradually increases.The reaction is mainly divided into three stages,ie,the degree of reduction is 0-0.1,0.1-0.2,and 0.2-1.However,when the SiO₂ content reaches 8%,the effect of SiO₂changes from inhibition to promotion of calcium ferrite due to the formation of more Fe₂O₃.Reduction,the reaction is mainly divided into two stages,namely the degree of reduction 0-0.2 and 0.2-1.The apparent activation energies of CF2S,CF4S and CF8S were 24.48,44.84 and 8.71 kJ·mol^-1,respectively.The mode function of CF2S and CF4S in the early stage of the reaction is A₂,which is then controlled by the two modes A₂ and R₂;CF8S is only controlled by the A₂ mode.In terms of phase reduction of Fe₂O₃-CaO-MgO system,the addition of MgO has an inhibitory effect on the reduction of CF,resulting in a reduction in the degree of reduction of CF.The reaction is mainly divided into two stages,namely the degree of reduction of 0-0.2 and 0.2-1.And,with the increase of MgO content,the reaction rate is faster,but the speed in the later period is reduced.Overall,the reduction rate of CF is reduced.The apparent activation energies of CF2M,CF4M and CF8M were 37.31,17.27 and 29.15 kJ·mol^-1,respectively.The reduction of CF2M and CF4M is mainly controlled by A₂ mode,and CF8M is controlled by A₂ and R₂ together.In the reduction of the quaternary calcium ferrite system,the reaction is mainly divided into two stages,ie,the degree of reduction is 0-0.2 and 0.2-1.When the aluminum-silicon ratio is 1,CF has the lowest degree of reduction.With the increase of aluminum-silicon ratio,the reaction rate in the first stage did not change much,but the reaction rate in the second stage increased significantly.In the reduction of the five-element ferric-calcium system,the reaction is mainly divided into two stages,ie,the degree of reduction is 0-0.2 and 0.2-1.The addition of MgO inhibited the reduction of CF,resulting in a reduction in the reduction rate and a reduction in the reduction rate.