Research On The Effects Of High Silicon Low Iron Hematite Concentrate On Roasting Behavior And Mechanism Of Oxidized Pellets

Iron ore pellet is one of the high quality ironmaking burdens.China's current iron ore pellet production is usually use magnetite concentrate as the main raw material.However,the high-quality magnetite resources in China will be exhausted,it is increasingly important to broaden the range of raw materials for pellet production and improve the quality of pellets.Compared with magnetite,domestic low-iron high-silicon hematite is usually rich in resources and low in price.However,these resources have not been applied on a large scale due to the higher consolidation temperature,the narrow roasting range and the higher requirements of roasted equipment.In this paper,a low-iron high-silica hematite concentrate?Iron ore A?and some magnetite concentrates were used as the main raw materials to study the effect of low-iron high-silica hematite concentrate ratio on pellet preparation process and pellet quality.The chemical compositions,microstructure and reduction performances of pellets were studied to reveal the effects of low-iron high-silicon hematite concentrate on pellet roasting behavior and consolidation mechanism.The industrial cage test is used to verify the adverse effects of adding Iron ore A on pellet quality.The measures of the calcination temperature or the extension of the calcination time are mentioned,and the negative influence of the addition of the Iron ore A is reduced,so that the low-iron high-silicon hematite concentrate can be applied to the grate-rotary kiln pellet production.In this paper,the effect of adding Iron ore A on the preparation characteristics of green pellets was studied.The results show that the properties of pelletizing raw materials can be improved by the pre-treatment of damp milling,and then the quality of the pellets can be obviously improved.Under the same damp milling conditions,the Iron ore A ratio in the mixed concentrate is increased from 0 to 50%.The compressive strength of 14.4 N?P^-11 increased by 17.5 N?P^-11 and then decreased by 14.3N?P^-1.The drop strength of the green ball decreased from 8.7 times?0.5m^-1to 3.2times?0.5m^-1.The effects of Iron ore A on the roasting behavior,consolidation characteristics and reduction properties of pellets were investigated.The results show that under the same preheating roasting conditions,when the Iron ore A ratio is increased from 0 to50%,the preheating pellet strength is reduced from 588 N?P^-1to 196 N?P^-1,and the roasted strength of pellet is reduced from 4925 N?P^-11 to 1868 N?P^-1.The study found that the new Fe₂O₃ has high activity and strong migration ability.The particles are connected by platelets into crystals.The primary Fe₂O₃ particles have low activity and weak migration ability.They are interconnected by microcrystalline connections,and the structure is loose and the pores are more.The strength is not as good as the new Fe₂O₃ crystal.As the A ratio increased from 0 to 50%,the reduction expansion rate of pellets decreased from 11.76%to 8.05%.the degree of reduction increased from 59.35%to70.11%.This is because the increase of the ratio of the Iron ore A will increase the content of gangue minerals such as SiO₂ in the pellet,resulting in an increase in the liquid phase content of the high melting point of the olivine,which can resist the stress of the pellet reduction and reduce the reduction expansion rate.The porosity of the pellet increases,and the degree of reduction of the pellet is increased.The industrial cage test found that compared with the Based Scheme?magnetite?,the strength of the low-iron high-silicon hematite concentrate 1-3%of the cage pellets was reduced by 91 N?P^-1,respectively 176 N?P^-11 and 282 N?P^-1,the reduction ratio of industrial pellets decreased from 11.16%to 10.34%,and the degree of reduction decreased from 60.77%to 59.78%,this is because the liquid phase is increased with the increased of SiO₂.The original Fe₂O₃ content is very low,and surrounded by the newly formed Fe₂O₃,the porosity of the pellet is not lowered.Laboratory results demonstrating the strength of the Iron ore A against pellet strength were verified,the pellet strength could be increased to satisfied production needs by appropriately increasing the roasting temperature and prolonging the roasting time.