Effect Of B₂O₃ On Reductive Expansibility Of Barun Oxidized Pellets

As an important raw material for blast furnace ironmaking,the proportion of pellet ore in blast furnace charge structure increases year by year.Reduction properties of pellets,in particular,reductive expansibility,it has an important effect on ensuring the smooth running of the charge and improving the production efficiency in blast furnace ironmaking process.The aim of thesis is to improve the reduction expansibility of pellets produced from Barun iron concentrate,By studying the finished pellet strength,reduction expansion rate and reduction degree of Barun pellets with different content of B₂O₃ and the volume change of pellets in the step-by-step reduction process,the effect of B₂O₃ on the reduction expansibility of Barun pellets was revealed,the main conclusions are as follows:When the ratio of B₂O₃ is 0.5%,1%,1.5%and 2%,The yield of B₂O₃ was 79.2%,69.6%,52.1%and 66.8%,respectively,when the ratio was 1.5%,the yield of B₂O₃was 15.41%,bron and fluorine bond with the addition of B₂O₃,the volatilization was promoted and the yield of B₂O₃ was reduced.The compressive strength of roasted samples was tested,it is concluded that the compressive strength of each roasted sample increases gradually with the increase of the ratio of B₂O₃,Increased from 2687.4N/P to 3344.8N/P.With the increase of B₂O₃ ratio,the effect of B₂O₃ on the grain size of iron oxide shows that the composition of hematite in pellet increases,slag phase has increased,when the ratio of B₂O₃ is increased to 1%,a large area of hematite crystal appears,when the ratio is 2%,the content of hematite is the highest,and the effect of intercrystal is the best,the slag phase increases,and the porosity decreases.Reduction under national standard conditions,the expansion rates of the pellets with B₂O₃ ratio of 0%,0.5%,1%,1.5%and 2%are 34.32%,22.85%,11.83%,7.99%and 5.98%.With the addition of B₂O₃,the low melting point compounds formed in the pellets reduce the melting point and viscosity of slag phase,so that the strength of the pellets is enhanced,and the reduction rate is reduced.Under the same reaction time and conditions,the reaction rate decreases gradually with the increase of the ratio of B₂O₃,resulting in a decrease in the volume expansion rate of the pellets.The Fe₂O₃→Fe₃O₄ stage increases with the ratio of B₂O₃ in the sample,the volume expansion rate of Barun pellets increases first and then decreases,when the ratio of B₂O₃ is1.0%,the peak value is 28.69%;The volume expansion rate of all samples in Fe₃O₄→Fe O reduction stage is lower than that in Fe₂O₃→Fe₃O₄ reduction stage,with the increase of the ratio of B₂O₃ in the sample,the bulk expansion rate of pellets at this stage fluctuates,when the ratio of B₂O₃ was 1.5%,the volume expansion rate reached 17.74%;The volume expansion rates of the samples in the Fe O→Fe reduction stage are higher than those in the Fe₃O₄→Fe O stage except for the 1.5%ratio,with the increase of the ratio of B₂O₃ in the sample,the bulk expansion rate of pellets at this stage fluctuates,when the ratio of B₂O₃ is 1%,the volume expansion rate is 33.07%.