Study On Fluidity And Structure Of High Al₂O₃ Primary Slag In Blast Furnace Cohesive Zone

With the continuous consumption of high-quality iron ore,the development and utilization of low-grade iron ore has become a necessary path for the sustainable development of the iron and steel industry.Among the proven available ore resources,high-alumina iron ore accounts for a large part,and high-alumina iron ore will become the main raw material for steel smelting.The massive use of high alumina iron ore will inevitably lead to the increase of Al₂O₃ content in the slag,and the slag system will change from the existing conventional silicate system to aluminosilicate or even aluminate system.The preliminary systematic research of the subject group has proved that the metallurgical properties of aluminate type final slag can fully meet the needs of blast furnace smelting,but the influence of Al₂O₃ on the initial slag behavior in the soft melt zone of blast furnace is not yet clear,so the study Therefore,the study of the effect of alumina content on the rheological behavior of blast furnace initial slag is of great theoretical and engineering application value for the development of a mature high alumina iron ore for blast furnace scale utilization.In this paper,the effects of different Al₂O₃ content and Al₂O₃/Si O₂ mass ratio on the fluidity,melting temperature and carbon thermal reduction reaction properties of slag were studied with Ca O-Si O₂-6.5 mass%Mg O-30 mass%Fe O-Al₂O₃ five element high alumina primary slag.The results show that the viscosity tends to increase and then decrease with the increase of Al₂O₃ content,the free running temperature of slag tends to increase and then decrease,and the viscous activation energy of slag tends to increase and then decrease,with the turning point around 18.5 mass%of Al₂O₃ content.The melting temperature of the slag undergoes a rising-declining-rising phase,indicating that it is possible to raise the alumina content to have a composition range where the melting temperature meets the requirements of high alumina ore smelting.The carbothermal reduction of the blast furnace primary slag becomes gradually more difficult with increasing alumina content,and the reduction effect starts to improve again after the turning point.With the increase of Al₂O₃/Si O₂ mass ratio,the viscosity value increases and then decreases;the free running temperature of slag increases rapidly and then decreases slightly;the viscous activation energy of slag shows a rapid increase and then decreases,and the turning point is near the Al-Si ratio of 0.93.The liquid-phase line temperature of slag continues to rise with the increase of Al-Si ratio.The carbon thermal reduction of the blast furnace primary slag gradually becomes difficult with the increase of Al-Si ratio.Finally,the structure of the slag was studied using Raman spectroscopy,and the variation of the percentage content of each polymeric structural unit of Al-O,Fe-O,and Si-O with different Al₂O₃ contents and Al₂O₃/Si O₂ mass ratios was obtained.With the increase of Al₂O₃ content,the percentage content of Al(Q²)polymerization units gradually increased overall;the percentage content of[Fe O₄]tetrahedral and Si(Q²+Q³)polymerization units showed a trend of increasing and then decreasing;the percentage content of Al(Q⁰+Q¹)polymerization units gradually decreased overall;the percentage content of Si(Q⁰+Q¹)and[Fe O₆]octahedral polymerization units percentage content first decreases and then increases;the ratio of percentage content of Al(Q²/(Q⁰+Q¹))polymerization units shows an overall increase;the ratio of percentage content of Fe([Fe O₄]/[Fe O₆])polymerization units first increases and then decreases;the ratio of percentage content of Si((Q²+Q³)/(Q⁰+Q¹))polymerization units first increases and then decreases,and the turning point is around 18.5 percent.When Al₂O₃ gradually replaces Si O₂,the percentage content of Al(Q²)polymerization unit,[Fe O₄]tetrahedral,and Si(Q²+Q³)polymerization unit first increases and then decreases,and the turning position is near the Al-Si ratio is 0.93;Al(Q⁰+Q¹),Si(Q⁰+Q¹),and[Fe O₆]octahedral polymerization unit shows a decrease and then increased The percentage ratios of Fe([Fe O₄]/[Fe O₆])polymerization unit,Si((Q²+Q³)/(Q⁰+Q¹))polymerization unit,and Al(Q²/(Q⁰+Q¹))polymerization unit all show an increase and then a decrease,and the turning point is near the Al-Si ratio of 0.93.