Optimization Experiment of Coal-Based Reduction Smelting and Vanadium Recovery of Vanadium-Titanium Magnetite
Vanadium-titanium magnetite is an important polymetallic iron ore in China,the main valued elements are Fe,V,and Ti.Currently,the main method for processing vanadium-titanium magnetite is the blast furnace-converter furnace method,but it has the disadvantages of low vanadium recovery and the need to add common iron ore in the smelting process.Therefore,metallurgists have conducted much research on non-blast furnace methods such as reduction-magnetic separation,roasting-leaching,bioleaching,reduc-tion-magnetic separation,and melting separation.However,these methods still suffer from low vanadium recovery(≤90％)and ex-tended recovery time.In order to recover vanadium from vanadium-titanium magnetite more efficiently,vanadium-titanium magnetite from Wuling,Xinjiang,as raw material and coke as the reducing agentwere used to investigate the effects of basicity,carbon content,and melting separation temperature on vanadium recovery and slag phasein this study.The phase composition of the raw material and slag was analyzed using X-ray diffraction(XRD).The microstructure of pig iron and slag was characterized using scanning electron mi-croscopy(SEM)and energy dispersive spectroscopy(EDS).The metallization rate of the pellets was 73.56％when 5％coke was first added for pellet making,followed by roasting at 1250 ℃ for 60 min.XRD pattern of the pellets showed that magnetite and ilmenite were still present in the metalized pellets,probably due to the insufficient amount of carbon content,which would continue to be in-creased in the melting separation experiments.The melting test showed that basicity,carbon content,and melting separation tempera-ture could improve vanadium recovery,the main factor affecting vanadium recovery was the melting separation temperature,basicity,and carbon content were secondary factors.XRD pattern of the slag showed that CaSiTiO5 and W1-p(X,Y)1+pZ2O6 were produced at a basicity of 1.2,which reduced the melting point and viscosity of the slag and facilitates the melting separation of vanadium-titani-um magnetite,which resulted in the highest vanadium recovery.At a basicity of 1.3 low melting point pyroxene group minerals(Ca2MgxAl2-2xSi1+xO7 and CaMgSi2O6)were generated and the slag viscosity was further reduced,too low viscosity would cause severe iron spattering and vanadium recovery was therefore reduced.According to the slag ion theory,as the basicity increased,the complex anion structure in the slag was destroyed,promoting the migration of internal ions.Moreover,low melting point substances were gener-ated in the slag,reducing the viscosity and vanadium recovery kinetics were improved,with the vanadium content in the pig iron in-creasing from 0.51％to 0.63％and the vanadium recovery generally higher than 75％.This indicated that changing the basicity in the range of 1.0～1.3 had less effect on the vanadium recovery from the melting separation.During the increase of the melting temperature from 1450 to 1500 ℃,XRD patterns of the slag showed that the diffraction peaks were mainly for titanate compounds,and the diffrac-tion peaks of iron oxides and vanadium-containing compounds gradually disappeared,and the vanadium recovery increased rapidly from 25.58％to 98.07％.The temperature continued to increase to 1550 ℃,and the slag generated high melting point substances such as calcium titanate and spinel,and the melting temperature of the slag increased the melting temperature of the slag rises,deteriorat-ing the melting process and reducing the vanadium recovery.During the temperature change,the vanadium content of pig iron in-creased from 0.27％to 0.68％,a significant increase,which,combined with the change in the slag phase,could be considered a seri-ous influence of the melting separation temperature on the smelting process.The vanadium content of the pig iron varied between 0.5％and 0.6％during the variation of the carbon content of 10％～25％,and the vanadium recovery was generally higher than 70％.Accord-ing to XRD patterns of the slag,it could be seen that when the carbon content was 10％,the slag mainly diffraction peaks of titanate compounded,and there were more diffraction peaks of iron oxides.When the carbon content was 15％,the diffraction peaks of iron ox-ides had disappeared and the highest vanadium recovery was achieved at this time.When the carbon content was higher than 15％,low valence TiC and Fe appeared,and the intensity of diffraction peaks of titanate compounded and TiO2 decreased,indicating that exces-sive coke led to excessive reduction of TiO2,etc.in the slag,and the slag was heavily charged with iron,and the vanadium recovery decreased.SEM and EDS analyses of pig iron and slag showed that vanadium was solidly soluble in pig iron as vanadium metal,while titanium was enriched in slag as oxide,and the titanium slag could be treated to recover titanium from it.The optimum process condi-tions for the coal-based reduction melting separation of vanadium-titanium magnetite were:basicity of 1.2,melting separation tempera-ture of 1500 ℃,carbon content of 15％,and under these process conditions,the recovery of vanadium was 98.07％.
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