Study On The Pre-reduction Mechanisms Of Vanadium Titano-magnetite From South Africa Via A Fluidized Bed

Vanadium titanomagnetite is not only an important source of iron,but also a major resource of vanadium and titanium,which is recognized as an important strategic resource in the world.Due to the traditional "blast furnace-converter method" has some disadvantages,such as low recovery rate of vanadium,unable to realize the recovery of titanium,and high dependence on coke.However,the "fluidized pre-reduction-electric furnace melting method"based on the non-blast furnace method has outstanding advantages,such as direct processing of fine ore,high reduction efficiency,good heat exchange and low environmental pollution.Therefore,it is of great significance for the efficient development and utilization of vanadium titanomagnetite resources to carry out related basic theoretical research on "fluidized pre-reduction-electric furnace melting method".In this paper,high-grade vanadium titanomagnetite was used as the research object,H2 is used as the reducing gas,and the fluidized pre-reduction experiment of vanadium titanomagnetite was carried out via a laboratory micro-fluidized bed reactor.Moreover,combined with X-ray diffraction(XRD),scanning electron microscope-energy dispersive spectrometer(SEM-EDS),gas composition analysis,specific surface area and pore structure analysis and so on,the key scientific issues such as phase transformation law,microstructure evolution law,thermodynamics and kinetics of fluidized pre-reduction process of vanadium titanomagnetite have been systematically studied by combining theoretical analysis with experimental research,and the following scientific results have been obtained.By using chemical analysis and taking the metallization ratio of the reduction product as the evaluation standard,the effects of factors such as gas flow rate,reduction temperature,reduction time and H2 concentration on the fluidized pre-reduction of vanadium titanomagnetite were systematically studied.The research showed that the suitable conditions of fluidization pre-reduction of vanadium titanomagnetite were gas flow rate 1000 mL/min,reduction temperature 850℃,reduction time 30 min and H2 concentration 80%.Under these conditions,the metallization rate of the reduced product is 90.22%,which could provide high-quality raw materials for the subsequent melting of electric furnace.The experimental results showed that the reduction temperature and H2 concentration were the key factors affecting the fluidized pre-reduction of vanadium titanomagnetite.Therefore,under different temperature system and different H2 concentration system,the change rule of metallization rate of reduction products was studied.The results showed that with the increase of reduction temperature,the increase of H2 concentration and the extension of reduction time,the metallization rate of the reduction products increased gradually at first and then tended to be flat.Under different reduction conditions,the degree of reaction was different.The thermodynamic calculation of the main reduction reactions in vanadium titanomagnetite was carried out by using HSC chemistry 6.0,and the theoretical reduction phase transformation processes of various iron containing compounds were obtained.Specifically,the theoretical reduction phase transition process of iron oxide was as follows:when the temperature is below 570℃,Fe2O3→Fe3O4→Fe;When the temperature is higher than 570℃.Fe2O3→Fe3O4→FeO→Fe.The theoretical reduction phase transition of ferro-titanium compounds was as follows:Fe2TiO5→Fe2TiO4→FeTiO3→FeTi2O5→TiO2→Ti3O5.The theoretical reduction phase transition of ferro-vanadium compound was as follows:FeV2O4→V2O3→VO→V.The isothermal kinetics of reduction process was studied by using gas composition online analysis and detection technology.The results showed that the optimal mechanism function model for fluidized pre-reduction process of vanadium titanium magnetite was Al model with random nucleation and one-dimensional growth,and the integral form was G(a)=-ln(1-α),the apparent activation energy was 42.65kJ/mol,and the pre-exponential factor was 0.21s-1.Therefore,the random nucleation and growth of new phase metal iron was the limiting link in the fluidized pre-reduction reaction of vanadium titanomagnetite.The study of phase transformation law showed that the pre-reduction phase transformation process of vanadium titanomagnetite was as follows:y-(Fe,Ti)2O3→Fe3-xTixO4→FeTi5O8→Fe2TiO5→Fe2TiO4→Fe+FeTiO3→Fe+TiO2.Due to the low content of vanadium magnetite(FeV2O4),it was difficult to monitor the reduction phase transition process.In addition,the study of microstructure evolution showed that with the increase of reduction temperature and reduction time,the iron oxide and ferro-titanium compounds on the surface of particles were continuously transformed into metallic iron,and the surface structure became porous and loose.At the same time,H2 molecules rapidly diffused to the inside of the particles through the pore channels on the surface of the particles,and reduced with the iron containing compounds to form a large amount of metal iron,and formed a dense metal iron ring at the outer edge.However,due to the distribution of a large number of TiO2 in the ring,the aggregation and fusion between the metal iron particles were blocked,making it difficult for the metal iron to further aggregate to the central region of the ring.The research results in this paper enriched the theoretical system of "fluidized pre-reduction-electric furnace melting" of vanadium titanomagnetite,and provided a new path for the efficient and comprehensive utilization of vanadium titanomagnetite,which had good reference significance.