Study On Thermodynamics And Kinetics Of Ilmenite Concentrates By H₂-CO Reduction

There exists the abundant mineral resource of titanium in China, more than90%of which deposited in province Sichuan of the country, is the richest in titaniumresource in the world. With the rapid development of mechanization andmodernization of metallurgical industry, the output, which is mainly made byconsuming of energy and resources, is biggest in the world so that it must producemuch metallurgical waste gas containing energy of hydrogen and carbon monoxide.Therefore, titanium resources and waste gas energy owned dominant positionobviously in our country. Therefore, efficient separation of multivalent metal intitamium resource is carried out by using reduction of H2and CO, which is in accordwith development of freen metallurgical requriments with saving energy andreducing pollutant smission. It is of great significance to study the above in theoryand practice.Aiming at comprehensive utilization of titanium resources and metallurgicalwaste gas, reduction characteristics and kinetics were studied in the atmosphere ofhydrogen, carbon monoxide or their mixture gas by using chemical analysis,scanning electron microscopy, optical microscopy and X-ray diffraction and so on.We successed preliminarily in separating of titanium and iron from reductionproducts of preoxidation ilmenite concentrate. Several significative tries were donein the experimental process.In order to investigate metallization rate of reduction products reduced bydifferent gas of100ml·min-1, the method of measuring the metal iron concentrationwas optimized by FeCl3dissolution-K₂Cr₂O₇titrmetric method. The optimal processparameters were as follows: the sample quality of0.1g, the composition andconcentration of FeCl₃of100ml and10g·L^-1, the electromagnetic stirring time of60min, K₂Cr₂O₇concentration of0.01N. The method, standard error of which was0.24%, was consistant with national standard of early Russian and satisfied with chemical analysis.Considering the factors of metallization rate and reaction time and so on, theoptimal reduction process parameters were obtained. As follows: hydrogenconcentration of more than50%in mixture gas, reduction temperature of1150oC,reduction time of90min. The weight loss and metallization rate can reach12%and87%respectively. The final reduction product phases contained mainly Fe and M₃O₅solid solution. Influence of reaction temperature on composition of Fe and Ti phasein the reduction process. Fe₂O₃was only reduced below600oC and FeTiO₃wasgradually reduced to Fe, TiO₂and TinO₂n-1. The intensities for M₃O₅solid solutionappeared at1000oC increased gradually with adding of reduction temperature. Thephase of carbon and ferric carbide could occur in the reduction products if reductiongas contained carbon monoxide below1000oC, or the intensities of diffractions wereweak and could disappear above1000oC.FeTiO₃phases, weight increment of which reached maximum, were oxidized toFe₂Ti₃O₉and Fe₂O₃at900oC in the oxidation process, and then weight changedecreased gradually until oxidation products were mainly composed of Fe2TiO5andTiO2at1200oC. Microstructure evolution indicated that a lot of internal porositiesappeared in the oxidation process could provide reaction path and space forreduction gas diffusion from outside into intior and productive gas separation fromreduction products, which could raise reaction velocity. Sulphur concentrationproducts decreased with increasing of reaction temperature in the processing ofoxidation and desulphurization ratio could reach99%at1200oC.Preoxidation treatment not only raised the reduction speed and metallizationrate of products but also decreased reaction temperature in the reduction process.Metallization rate of reduction products could reach93%and was more6%than thatfrom ilmenite concentrate by H₂-CO. The optimal reduction process parameters wereas follows: hydrogen concentration of more than50%, reaction temperature of1100oC, reduction time of80min. The final reduction product, same as that of ilmenite concentrate, consisted of iron and M3O5solid solution with less Feconcentration. The preoxidation ilmenite concentrates were reduced more quickly bycarbon monoxide than by hydrogen and the speed increased with increasing ofcarbon monoxide concentration.The reduction kinetics of ilmenite concentrates and preoxidation products wereinvestigated by diffusion and chemical reaction model. The results shew thatreduction process satisfied unreacted ores model and reaction mechanism wasdifferent owing to oxidation of ilmenite concentrates. The reaction of Fe³⁺ Fe²⁺inthe reduction of ilmenite concentrates and preoxidation products was controlled bydiffusion and chemical reaction model respectively below950oC, or by bothdiffusion and chemical reaction. The reaction mechanism of Fe³⁺ Fe²⁺was same asthe above from950oC to1200oC, but the apparent activation energy of them wasfrom59to74kJ·mol-1and48to68kJ·mol-1, and decreased with the increasing ofhydrogen concentration in mixture. In general, the energy was more in the reductionof ilmenite concentrates than preoxidation products in the constant atmosphere.The analysis of phase, macrograph and microstructure indicated that Fe2TiO5was reduced gradually to FeTiO₃, TiO₂and TinO2n-1, which was proved by oxygenpartial press with ln（PO2/Pθ） from-14to-16, then TiO₂, TinO2n-1and MgO, MnOand so on formed M₃O₅solid solution. The solid solutions, which consisted mainlyof Mn and Al and so on, appeared on outer rims or the cracks; this could inhibitdiffusing of reduction gas from outerside into intior and separating of product gasfrom the reduced samples. The solid solutions of Mg, Ti and less Fe phasesoccurred in all of particle so that the structure was dense. The formation of bothsolid solutions could decrease the activity and reduction degree of the reactant,which was main season of decreasing the metallization rate and reaction speed.Besides, the binding phases, which were informed from Ca, Si, O and less Febetween the volids of different particles, made the reduction products form thetense structure. Forecasting model of metallization rate of preoxidation ilmenite concentrate is deduced in hydrogen of above50%at1100℃. The model is shown as following:The forecasting model is fit with the experimental datas of the paper. It can forecast quantitatively the metallization rate of preoxidation ilmenite concentrate under the condition of different hydrogen and carbon monoxide concentration and reaction time at1100℃.