Research On Effect Of Gangue Composition SiO₂ And CaO On Swelling Index Of Hematite Reduction At Different Stages

The energy saving and emission reduction of blast furnace production can be realized by increasing the ratio of pellet to furnace.However,the expansion behavior of high basicity pellets,especially autosoluble pellets(R=0.33-1.0)in the reduction process of blast furnace limits the development of pellets in the burden structure.At the same time,SiO₂,CaO are closely related to the reduction expansion of pellets.Therefore,it is of great significance to study the influence of SiO₂,CaO and alkalinity on the reduction expansion of pellets at different reduction stages,so as to solve the problem of reduction expansion of pellets and increase the proportion of pellets with high basicity.In this paper,pure Fe₂O₃,SiO₂ and CaO were used as raw materials,the contents of SiO₂ and CaO were changed,and the method of adding CaO was used to obtain briquettes with different composition and basicity.Firstly,thermodynamic analysis was carried out on the roasting process of pellets at 1250?to determine the ore phase composition of the pellets after roasting.Then,By controlling the composition of reducing atmosphere,stage reduction experiments were carried out on pellets to analyze the influence of different SiO₂,CaO contents and alkalinity on the reduction degreereduction expansion rate and micro-morphology of pellets at each stage,respectly.Consequently,the effects of SiO₂,CaO and alkalinity on the reduction expansion of hematite pellets at different stages were revealed.The conclusions are as follows.(1)SiO₂-containing pellets CaO-containing pellets and fluxed pellets all make the hematite continuous crystal state worse after roasting.SiO₂components in SiO₂-agglomerates are uniformly distributed in hematite.Increasing the dispersion of hematite hinders hematite from continuous crystallization;CaO and Fe₂O₃ combines to produce slag phase and generate holes during CaO-agglomerates roasting,which prevents hematite from forming crystal connection.CaO,SiO₂ and Fe₂O₃ combine with each other to produce slag phase,andradite and forsterite respectively in the roasting process of basicity-agglomerates,which hinders hematite continuous crystallization.(2)A small amount of volume expansion occurs in the SiO₂-containing pellets in the Fe₂O₃?Fe₃O₄ stage,and a large amount of volume shrinkage occurs in the FeO?Fe stage;the CaO-containing pellets have a small volume expansion in the Fe₂O₃?Fe₃O₄ stage,and a large amount of volume expansion occurs in the FeO?Fe stage;When the basicity of auto-dissolving pellets R<1.0,a small amount of volume expansion occurs in the Fe₂O₃?Fe₃O₄ stage,and a large amount of volume expansion occurs in the stage of FeO?Fe;when the basicity of auto-soluble pellets R>1.0,a large amount of volume occurs in the stage Fe₂O₃?Fe₃O₄ Expansion,a small amount of volume expansion occurs in the FeO?Fe stage.(3)Concatenation of SiO₂-containing pellets in FeO?Fe stage is the main reason for volume shrinkage;CaO-containing pellets and iron whiskers produced by auto-dissolving pellets in FeO?Fe stage are the main reasons for reduction expansion;CaO Promote the growth of iron whiskers.When the basicity of auto-dissolving pellets is R<1.0,the growth of iron whiskers is promoted.When the basicity is R>1.0,the growth of iron whiskers is inhibited.