Fundamental Study On Innovative Process Of Gas-based Shaft Furnace Direct Reduction-Melting Separtion For High Chromium Vanadium-bearing Titanomagnetite

Vanadium,titanium,and chromium recognized as the strategic resources around worldwide are the important material guarantees for the national economic development and national security due to its wide uses in the various fields such as metallurgical,chemical,aerospace,and military.High chromium vanadium-bearing tiatanomagnetite that vital carrier of vanadium,titanium,and chromium has a rich reserve in China and owns high comprehensive utilization value.However,high chromium vanadium-bearing tiatanomagnetite with the characteristics of poor,fine,dispersive,and distributed is a typically polymetallic and complex iron ore,meanwhile,this ore resource is of various mineral species,complicated mineral structures,small particles,and close coexistence.Therefore,it is really difficult to process and utilize.At present,the high chromium vanadium-bearing titanomagnetite is smelt by the blast furnace-converter process,but the utilization rates of valuable components are quite low,concomitantly,the environment load is also serious.Based on the above discussions,how to achieve the efficient and clean utilization of high chromium vanadium-bearing titanomagnetite as well as improving the recovery rates of valuable components is an important way to solve the strategic demands of vanadium,titanium,and chromium resource,and it has significant influences on the steel industry and even national economy.On the basis of the summary and review of the previous studies,the novel process of gas-based shaft furnace direct reduction-melting separation for high chromium vanadium-bearing titanomagnetite is proposed in the work.An imported high chromium vanadium-bearing titanomagnetite is applied as the raw material.Aiming at the key steps in the new process,the various researches from different aspects have been conducted,such as the pellet oxidation roasting behaviors and consolidation mechanism,the coupled function mechanism of valuable components during pellet oxidation roasting,the phase transformation and reduction behaviors during gas-based shaft furnace direct reduction,the kinetics of gas-based reduction,the controlling mechanism of key parameters and the optimization and behaviors of melting separation.The study of pellet oxidation roasting behavior and consolidation mechanism indicates that both increasing the roasting temperature and prolonging the roasting time are conductive to enhance the compressive strength of the oxidized pellet.During the oxidation process,the phase transformation of the valuable components are listed as follows:Fe3O4 ? Fe2O3;Fe2.75Ti0.25O4 ? Fe9TiO15 + FeTiO3 ?Fe9TiO15 ? Fe2Ti3O9;Fe2VO4 ? V2O3 ? V2O3 + V1.7Cr0.3O3;FeCr2O4 ? Cr2O3 ?Fe1.2Cro.8O3 + V1.7Cro.3O3.The detailed oxidation consolidation process for high chromium vanadium-bearing titanomagnetite pellet can be divided into the three steps:oxidation(below 900 ?),recrystallization-consolidation development(900?1100 ?),and recrystallization-consolidation interconnection(1100?1300?).Through the study on the coupled function mechanism of valuable components during the pellet oxidization roasting,it is shown that the pellet compressive strength decreases as increased the content of TiO2,V2O5,and Cr2O3.The pellet reduction swelling index is improved by TiO2 but worsened by V2O5 and Cr2O3.The decrease of compressive strength is aggravated seriously by the coupled effect of TiO2&V2O5.And the compressive strength of TiO2&V2O5&Cr2O3 pellets is worse than one-component TiO2,V2O5,and Cr2O3 pellet.The research on the phase transformation and reduction behaviors during gas-based shaft furnace direct reduction indicates that the HYL-ZR gas-based shaft furnace direct reduction process is recommended to dispose this difficult reduction composite iron ore like high chromium vanadium-titanomagnetite.The pellet reduction ratio is improved by increasing the reduction temperature and the content of H2.Under the conditions containing a temperature of 1100?,an atmosphere of H2/CO=5/2,and a reduction time of 35 min,the reduction ratio of high chromium vanadium-bearing titanomagnetite pellet can reach 95%.The phase transformation during reduction is hypothesized to proceed as follows:Fe2O3 ?Fe3O4 ? FeO ? Fe;Fe9TiO15 + Fe2Ti3O9 ? Fe2.75Ti0.25O4 ? FeTiO3 ? TiO2;V1.7Cr0.3O3+V2O3 ? V2O3 ? Fe2VO4;Fe1.2Cro.8O3 ? Cr2O3 ? FeCr2O4.In the initial stage of gas-based reduction,the pellet reduction swelling index sharply increases,then appears a turning point and the swelling index increasing tendency becoms slow,afterwards the pellet shows shrinking.While at the initial reduction,the pellet compressive strength decreases dramactically,and the strength is lost nearly 80%.The increasing content of H2 in the reduction atmosphere is conductive to improve the reduction swelling and enhance the pellet strength.According to the research on the kinetics of gas-based reduction,rising the reduction temperature and increasing the content of H2 in reduction atmosphere are good for advancing the reduction kinetic.Based on the unreacted core model with several reaction interfaces,the non-isothermal gas-based shaft furnace direct reduction for high chromium vanadium-bearing titanomagnetite pellet is establised,through which,the kinetic models for any reduction conditions can be calculated while the gas composition and the heating rate are given.The correlation coefficients are all greater than 0.99,which indicates that the reduction ratio of high chromium vanadium-bearing titanomagnetite pellet during the non-isothermal gas-based reduction can be described rationally by this obtained model.Base on the study of the controlling and mechanism of key parameters for melting separation,the iron containg vanadium and chromium along with the slag bearing titanium is obtained.The too less carbon is not enough for the deep reductions and carburation,but the excessive carbon will result in the overreduction of titanium oxides and the bad viscosity of slag,which is bad for the melting separation.The appropriate additive CaF2 is contributed to the smooth separation.The effect of temperature on the melting separation kinetic is more considerable than thermodynamic.The melting separation is improved dramatically as increased temperature and time properly.With the increasing of basicity in a certain range,the melting separation kinetic is advanced,which is attributed to the enlarged liquid phase,decreased viscosity and slag melting point,and increased surface tension.But when the basicity is too high,the amount of slag is larger and the melting slag point is increased instead,which are bad for improving the recovery rates of the valuable components.By the optimization of multi-index synthetic weighted scoring method,the rational melting separation parameters are obtained and include a C/O ratio of 1.20,a CaF2 additive of 2%,a melting temperature of 1650?,a melting time of 45 min,and a basicity of 1.10.Under these conditions,the recoveries of Fe,V,Cr,and TiO2 reach 99.87%,98.26%,95.32%,and 95.04%respectively;the mass fraction of Fe,V,Cr,and TiO2 are 94.16%,0.94%,0.76%,and 38.21%respectively.The basicity most strongly affects the melting separation,followed by the melting temperature and melting time.High chromium vanadium-bearing titanomagnetite metallized pellet melting separation process contains four key behaviors:Fe-C melt formation and Fe(1)generation,slag melting initiation and slag(1)generation,start of iron-slag separation,and continuous aggregation and growth of iron or slag and then accomplishment of iron-slag separation.As for the iron aggregation and growth,it should go through the iron crystal nucleus formation,reaction interface formation and enlargement,and following reaction interface decrease.The new process put forward in this work is conductive to achieve the theory improvement and technique innovation of comprehensive utilizing high chromium vanadium-bearing titanomagnetite.And it also provides the important theoretical foundation for the design,exploitation,and industrial application of large-scale comprehensive utilization process for Panzhihua high chromium vanadium-bearing titanomagnetite.Thereby,it will promote the development of the comprehensive utilization technologies for high chromium vanadium-bearing titanomagnetite.