Research On Coal-based Direct Reduction And Melting Separation Of A High-chromium Vanadium-titanium Magnetite

Panxi region of China is endowed with large reserves of vanadium-titanium magnetite,and the reserves of high-chromium vanadium-titanium magnetite is about 3.6 billion tons.It is a kind of complex iron ore which contains various valuable metal elements such as iron,vanadium,titanium,chromium,etc.So it has a high comprehensive utilization value.Because the mineral composition of the high-chromium vanadium-titanium magnetite is complex,it is more difficult to make blocks,smelt in blast furnace,utilize of iron,vanadium,titanium and chromium comprehensively.Therefore,reasonable and efficient use of high-chromium vanadium-titanium magnetite,to improve the comprehensive utilization of iron,vanadium,titanium,chromium,is a major issue to be solved,currently.In this paper,the coal-based direct reduction and melting separation of a high-chromium vanadium-titanium magnetite collected from Panzhihua was studied using thermodynamics analysis,kinetic analysis,X-ray diffraction analysis and scanning electron microscopy.On this basis,the thermodynamics,kinetics of direct reduction process and the influence of parameters on the metallization rate,shrinkage ratio,mineral phase and microstructure of the reduction products were systemically studied.After melting separation,the recovery of iron,vanadium,titanium and chromium was measured.This can provide a experimental theoretical basis for the development and utilization of the high-chromium vanadium-titanium magnetite.The thermodynamics of coal-based direct reduction of high-chromium vanadium-titanium magnetite showed that the gasification of carbon played an very important role in the reduction process.The temperature at which magnetite was initially reduced by fixed carbon was 645?.The reduction order of the minerals in the high-chromium vanadium-titanium magnetitethe by fixed carbon was magnetite,ulvospinel,ilmenite,vanadium-iron spinel,chromite.And the order of metal reduction was iron,chromium,vanadium,titanium.The metallization rate and shrinkage ratio of the high-chromium vanadium-titanium magnetite under the protection of nitrogen were influenced by the ratio of carbon to oxygen,reduction temperature and reduction time,The metallization rate of reduced product reached 97.68%,the long axis,short axis and high shrinkage ratio of the reduced pellets reached to 20.00%,19.77%and 23.18%,respectively,when high-chromium vanadium-titanium magnetite with carbon to oxygen ratio of 1.0 was reduced for 30 min at 1350?.At the same condition,the main mineral phases of reduction product were metallic iron,Fe_0.5Mg_0.5Ti₂O₅,TiO₂,MgTi₂O₅,(Fe-Cr),TiN.The distribution of iron in the reduced product was approximately same as the distribution of chromium,titanium and iron were separated,vanadium distributed in the distribution of iron and titanium,silicon and aluminum were distributed consistently to form the silicate phase.The kinetics of coal-based direct reduction of high-chromium vanadium-titanium magnetite showed that the isothermal reduction kinetics of carbon-bearing pellets of C/O being 1.0 was divided into three stages with the increase of reduction degree.The total reaction rate was controlled by the rate of nucleation and growth at the initial stage and the optimal kinetic function was G(?)=[-ln(1-?)]^2/3.The total reaction rate was controlled by the rate both of Boudouard reaction,phase boundary reaction and the three-dimensional diffusion at the middle stage.The total reaction rate was controlled by the rate the three-dimensional diffusion at the final stage and the optimal kinetic function was G(?)=[1-(1-?)^1/3]².The results of melting separation experiments showed that the melting effect of metallized pellets after carbon-bearing pellets with carbon to oxygen ratio of 1.0 being reduced 30 min at 1350? under the nitrogen atmosphere was not very good.There was still a large amount of metallic iron in the slag phase after melting separation,most of vanadium entered the slag phase,only a small fraction of vanadium entered the iron phase,most of TiO₂ entered the slag phase,chromium distributed both in the iron phase and slag phase.The recovery of iron,TiO₂,vanadium and chromium were 46.80%,62.71%,28.76%and 49.89%,respectively.The results presented in this paper can provide insights on the process of coal-based direct reduction of high-chromium vanadium-titanium magnetite and advances on theoretical system of coal-based direct reduction of polymetallic ore,it can be used as a reference for the high-efficient comprehensive utilization of high-chromium vanadium-titanium magnetite.