Fundamental Research On The Preparation Of Titanium Nitride And Direct Reduced Iron By Carbothermal Reduction Of Vanadium-bearing Titanomagnetite Concentrate

There are abundant reserves of vanadium-bearing titanomagnetite in in Panzhihua,Sichuan Province,China.To date,vanadium-bearing titanomagnetite concentrate is mainly recovered from iron and vanadium resources by blast furnace process,while titanium resources are hardly recovered.Therefore,it is urgent to develop new processes to realize the comprehensive recycling of iron,titanium and vanadium.Titanium nitride（Ti N）is a material with excellent properties,suitable for many fields such as machinery,chemical industry,aerospace,etc.,but the preparation cost of Ti N is currently high.A new idea is to use vanadium titanomagnetite to prepare Ti N materials,but this method is still lack of systematic research.In this study,vanadium-bearing titanomagnetite concentrate was used as raw material to prepare Ti N and direct reduced iron by carbothermic reduction-grinding-magnetic separation and acid leaching process,thermodynamic analysis,X-ray diffraction analysis,scanning electron microscope and energy dispersive analysis,thermogravimetric analysis and chemical analysis were used to study the formation mechanism of titanium nitride and reduced iron in the carbothermic reduction process.The effect of reduction conditions on the formation of Ti N was investigated,and it was found that the formation of Ti N was promoted by higher calcination temperature,longer calcination time and more coal addition.In addition,it is also found that the phase transformation processes of titanomagnetite,ilmenite and magnetite during the carbothermic reduction process are as follows:Fe_3-xTi_xO₄→Fe₂Ti O₄→Fe Ti O₃→M₃O₅（Fe Ti₂O₅,Mg Ti₂O₅,Ti Al₂O₅,Ti₃O₅）→（Ti,V）N,Fe Ti O₃→M₃O₅→Ti N and Fe₃O₄→Fe O→Fe.M₃O₅→Ti N is the rate-limiting step of the whole reaction.The distribution of V element is basically the same as that of Ti element,and finally most of it is enriched in（Ti,V）N and a small amount is enriched in sulfide.Impurity Mg Al₂O₄ is present in the educed product,and it is difficult to remove.The microstructure evolution was investigated throughout the reduction process.It was found that the iron particle size increased continuously with the increase of roasting time and roasting temperature.At the optimum roasting conditions,the particle size of iron particles in the roasted products mostly ranged from 30μm to 300μm,and the particle size of Ti N was about 10μm,and there was no obvious sintering between iron particles and Ti N.In addition,fine grained and chunky M₃O₅ were reduced to titanomagnetite and ilmenite,respectively,and both types of M₃O₅showed dense structures,which led to their difficulty to be reduced,especially the chunky M₃O₅.The effect and mechanism of mechanical activation on the reduction process were investigated,and it was found that mechanical activation could reduce the particle size and change the distribution of raw materials,which could ease the fusion of iron particles and sintering of slag phase in the roasted products,and then increase the contact area of reactants,accelerate the reduction reaction rate and reduce the required temperature of the reduction reaction,but failed to inhibit the formation of Mg Al₂O₄.The effects and mechanisms of additives on the reduction process were investigated,and it was found that Mg elements in the raw material are preferentially bound by boric acid and produce substances that are soluble in acid,thus inhibiting the generation of Mg Al₂O₄.The sodium component can accelerate the gasification reaction of C,accelerate the mass transfer,accelerate the carburization reaction of Fe and decrease the viscosity of the slag phase,thus accelerating the generation of Ti N.The roasted product obtained with 16%borax addition was milled and magnetically sorted to obtain reduced Fe with grades and recoveries of 94.32%and 91.46%,respectively,and Ti N with grades and recoveries of 74.09%,2,75%and 94.78%,62.57%for Ti and V,respectively.This indicates that iron,titanium and vanadium resources in the vanadium-bearing titanomagnetite have been effectively recovered.