Mechanism Of Gas-based Direct Reduction And Melting Separation Of Highchromium Vanadium-bearing Titanomagnetite

As a kind of multiplex coexistence iron ore,high-chromium vanadium-bearing titanomagnetite has high comprehensive utilization value.The main process of using it is blast furnace process currently,while the low comprehensive utilization of valuable elements limits its development.Gas-based direct reduction followed by melting separation has certain feasibility on account of its advantages,such as independent of coke,low environmental load and comprehensive utilization of valuable elements.Reduction behavior of pellets in the shaft furnace is very important for smooth production,while the meting separation of in electric furnace affected by many factors.Hence,gas-based reduction test under isothermal condition was carried out firstly in this paper when high-chromium vanadium-bearing titanomagnetite were taken as the raw materials.The effect of reduction temperature and gas composition on the swelling index and compressive strength of pellets during reduction process was studied.Then the influence of heating rate and gas composition on the reduction extent was inspected through non-isothermal reduction test.Meanwhile,the non-isothermal kinetic model was establisted in this paper to describe the non-isothermal reduction of HCVT pellets.At last,the rational parameters were obtained through singal factor experiments.The conclusions were as follows:(1)In the initial stage of gas-based reduction of HCVT,the swelling index of pellets sharply increased while the compressive strength drops dramatically.Then the volume of pellets begains to shrink with the consequence of the swelling index decreased and compressive strength rasied.With the increasing of temperature and proportion of CO,the swelling index increased while the compressive strength decreased.(2)The phase change of HCVT during gas-based non-isothermal reduction is:Fe2O3?Fe3O4?FexO?e;Fe9TiO15+Fe2Ti3O9?Fe2.75Ti0.25O4?FeTiO3?Fe+ TiO2;(Cr0.15V0.85)2O3 + Cr1.3Feo.7O3 ?Fe2VO4+FeCr2O4?(3)With the increase of heating rate and proportion of H2,the reduction extent of gas-based non-isothermal reduction of HCVT enlarged through same time.The kinetic model fitting to describe the gas-based non-isothermal reduction of HCVT is as follows:where xH2 and xCO are the proportion of H2 and CO in the mixed gas;? is the heating rate.The approximate solution of the reduction extent can be calculated while the gas composition and the heating rate were given.(4)The rational melting separation parameters for high-chromium vanadium-bearing titanomagnetite got from gas-based direct reduction contained a C/O of 1.2,a melting temperature of 1625?,a melting time range of 40-50 min,an additive CaF2 of 2%and binary basicity of 1.1.Fe,V and Cr separated successfully with Ti under these conditions.Both the iron containing vanadium and chromium and the titanium-bearing slag were obtained.The separation mechanism of vanadium and chromium need further study.