Fundamental Research On Agglomeration Of Magnesium-Titanium Bearing Pellet With Low Silica

The energy consumption of steel industry accounts for about 15%of the total energy consumption in China.However 70%of energy consumption is from ironmaking process.So beneficiated burdens are necessary for ironmaking to reduce energy consumption.Iron ore pellet has many advantages compared to sinter,such as low energy consumption,high iron grade,goodreducibility,anduniform particle size etc.With the deterioration of iron ore resources quality and demand of blast furnace hearth protection,the functional role of iron ore pellet is developing in recent years.Magnesium bearing pellet was developed to improve fluidity of high alumina slag,andpellet with high TiO₂ content was produced for blast furnace hearth protection.However,there is no relevant study about magnesium-titanium bearing pellet,especially with low silica.Fundamental research on production technology of magnesium-titanium bearing pellet with low silica was studied using low silicon iron ore concentrate,magnesiumadditives and titanium iron ores in this paper based on straight grate induration machine in Shougang Jingtang Steel Corporation.It has important scientific significance and practical value.Firstly,the pelletizing,green ball quality,metallurgical property of pellet agglomerated by single iron ore concentrate with low silica were studied and also the effect of SiO₂ content on pellet reductionswelling was studied.When the SiO₂ content of pellet is 1.8%,the reduction swelling index is reached 76%,which belong to serious swelling and unable to be used in blast furnace.There occurred large amount of iron whiskers in low silica pellet because of few liquid phase formed in fired pellet.The reduction swelling index of pellet can be decreased with increasing of SiO₂ content,which can be decreased to lower than 20%while SiO₂ content was increased to above 3.4%.However,increasing of SiO₂ content is adverse to reduce slag and fuel rate of blast furnace.So controlling of reduction swelling index is the key question for reducing of pellet SiO₂ content.Secondly,effect of MgO content and various magnesium additives on low silica pellet metallurgical properties were studied.The effect of firing temperature on low silica pellet metallurgical property,reduction kinetics of low silica magnesium bearing pellet were research in this paper.There exist unreacted MgO in pellet while firing temperature is low.The magnesium ferrite phase can be increased while pellet fired under high temperature.The reduction swelling index is decreased to 16.5%while the MgO content is increased to 3.4%.The reducibility and smelting performance of pellet can be improved significantly when adding MgO.Calcined olivine,serpentine and magnesium powder were benifical to control low silica pellet reduction swelling index,among which magnesium powder is more conductive to produce low silica pellet.The reduction process of pellet with appropriate MgO content and firing temperature is controlled by solid diffusion,therefore the formation of iron whisker was restricted and reduction swelling index can be improved.Then,the effect of TiO₂ content and synergistic effect and mechanism of MgO and TiO₂ on low silica pellet compressive strength and metallurgical properties were studied.The reduction swelling index of low silica pellet can be improved while addingTiO₂,however,it will deteriorate the reducibility of pellet.The metallurgical properties can be improved while MgO is added.The SiO₂ content of pellet can be decreased without deterioration of swelling while MgO and TiO₂ added together in pellet,which form magnesium ferrite and titanium magnetite.The SiO₂ content of pellet can be decreased to 2.8%while MgO and TiO₂ content reached 1.7%and 1.2%respectively.It is indicated that,titanium iron ore with high magnetite and ilmenate has little effect on pellet compressive strength and benifical to control pellet reduction swelling.The firing temperature is needed to increase 10? while titanium iron ore added into pellet.Lastly,production technology of low silica magnesium-titanium bearing pellet on straight grate induration machine was studied.The application effect of low silica magnesium-titanium bearing pellet in super large blast furnace was analysed together.The firing temperature of low silica magnesium-titanium bearing pellet is higher than magnesium bearing pellet.The compressive strength and metallurgical properties of pellet can be improved by appropriate roasting system.The SiO₂ content of pellet is decreased from 3.5%to 2.82%,MgO content is increased to 1.7%,TiO₂ content is increased to 1.2%and reduction swelling index is controlled lower than 20%.The low silica magnesium-titanium bearing pellet was used in super large blast furnace with 5500m3 in Shougang Jingtang Steel Corporation and high technical and economical index were obtained.The slag and fuel rate of blast furnacewere decreased 12.6kg/tHMand 5.3kg/tHM respectively.