Ti-Fe Separation And Mechanism Study During Microwave Carbothermal Reduction Of Vanadium-titanium Magnetit

Titanomagnetite is an important strategic mineral resource in China.At present,titanomagnetite concentrate is mainly treated through the process of blast furnace smelting,converter vanadium extraction and converter steelmaking.The advantage of this process is that it has a large scale and can effectively recover Fe and V in titanomagnetite concentrate.However,it has a long process flow,heavy dependence on coke,low resource utilization rate and titanium can not be recovered."Direct reduction-melting separation"non-blast furnace smelting resources have high utilization rate,which has always been a research hotspot in China and abroad.However,the effective separation of iron and titanium is the key bottleneck restricting the development of the direct reduction technology.This paper studies from four aspects:thermodynamic analysis,comparative experiment,dielectric test and Ti-Fe separation mechanism,to reveal the Ti-Fe separation mechanism in the microwave carbothermal reduction process of titanomagnetite:1)Thermodynamic analysis of carbothermal reduction process of titanomagnetite.A carbothermal reduction reaction system composed of solid-phase reduction and indirect gas-phase reduction was constructed.The reduction difficulty of titanomagnetite and related ferrotitanium oxides was determined from the perspective of unit oxygen atom formation enthalpy(easy to difficult:Fe O<Fe₂O₃<Fe₃O₄<Fe_3-xTi_xO₄（x=0.476）<Fe₂Ti O₅<Fe₂Ti O₄<Fe Ti O₃<Fe Ti₂O₅);It was found that the increase of Ti concentration will increase the reduction difficulty,especially the reduction difficulty of Fe_3-xTi_xO₄（x=0.476）was 10.48%higher than that of Fe₃O₄,that is,the Ti-Fe separation could strengthen the reduction process of titanomagnetite.2)Comparative experiment of microwave heating and conventional heating for carbothermal reduction of titanomagnetite.The results of single factor comparative experiment showed that the direct reduced iron product with Fe metallization rate of93.68%could be obtained under the conditions of carbon content of 20%（based on 100%of the mass of titanomagnetite）,reduction temperature of 1250℃and reduction time of60min;In the process of microwave heating carbothermal reduction,the direct reduced iron product with Fe metallization rate of 93.96%could be obtained under the conditions of carbon content of 20%（based on 100%of the mass of titanomagnetite）,reduction temperature of 1200℃and reduction time of 30min;Obvious Ti-Fe separation under the conditions of carbon content of 20%,1100℃and 30min through,while conventional heating method did not find Ti-Fe separation under the same conditions.Combined with1)it could be seen that the main reason for the shortening of reaction time and decreasing of reaction temperature during the carbothermal reduction of titanomagnetite was that microwave heating promoted the of Ti-Fe separation;3)Dielectric property test of titanomagnetite.The effect of apparent density on dielectric parameters of titanomagnetite at room temperature and the changes of dielectric parameters of itanomagnetite with different carbon content during heating up were studied;The results showed that iron oxide(Fe₃O₄:^′=19.998,^′′=3.421)has much higher dielectric properties than titanium oxide(Ti O₂:^′=2.824,^′′=0.03906),which would lead to much more diversity of response modes and higher response intensity of iron oxide to microwave than that of titanium oxide.This phenomenon was mainly related to the movement of local free electrons in the d orbit of Fe element.The active local free electron movement in iron oxide caused thermal stress between the two phases（iron oxide and titanium oxide）,which was conducive to the Ti-Fe separation.4)Enhancement of Ti-Fe separation mechanism during carbothermal reduction of titanomagnetite by microwave heating.The local conductivities of 14 crystal structures（Fe₂O₃,Fe₃O₄,Fe O,Fe,Ti O₂ with different crystal structures）of titanium oxides and iron oxide were compared and analyzed through the calculation of energy band density of states,it was finally determined that the interphase thermal stress caused by the difference of dielectric properties between titanium oxide and iron oxides and the isotropic ring current traction of adjacent Fe atoms in iron oxides caused by the difference of local conductivity in the process of chemical reactions was the driving force of Ti-Fe separation in microwave heating carbothermal reduction of titanomagnetite.