| Vanadium titano-magnetite(VTM)is a typical complex valuable resource in China.The typical method used to recover valuable elements from VTM concentrates is by the blast furnace smelting method.However,titanium is nearly all wasted in the form of blast furnace slag.Also,the recovery rate of V is low too by the blast furnace smelting process.In this thesis,a new pathway towards obtaining TiO2-enriched material for titanium extraction was designed.The main means is the combination of partial reduction by carbon or hydrogen and mild acid leaching by dilute H2SO4 solution.Partial reduction can destroy the stable structure of VTM,and promote the Fe leaching by mild acid to enrich TiO2 in the leaching residue.The key findings of this thesis were as follows.Even though the iron was not fully free from titanium after partial reduction,most of the iron could be transferred into the solution during leaching,leaving TiO2-enriched hydrated residue.The reduction degree and the leaching performance were co-related.The optimized conditions included reducing at 1000? for 3 h with a carbon addition of 6%mass of VTM,leaching at 80? for 3-4 h by using a 0.2 mol/L H2SO4 solution with a L/S ratio of 100:1.The TiO2-enriched residue contained hydrated water and was composed of anatase,Al2FeO4,and Fe3O4.The dehydrated residue contained 72.2 wt%TiO2,and its main phase was rutile,accompanied by Fe2TiO5 and Fe2O3.By determining the phase composition after reduction for different dosages of carbon,the reduction route of iron in the magnetite phase of VTM is original magnetite? Fe2.75Ti0.25O4?Fe2.5Ti0.5O4?FeTiO3,and FeO accompanied all transformations;however,FeO is unstable and will be reduced to Fe if the reductant is available.The main phase was Fe2.5Ti0.5O4,accompanied by some metal Fe under the optimized reduction conditions.In addition,it was calculated that the main gas by product under the optimized reduction conditions was CO.Selective leaching of Fe metal phase from the reduced VTMs by FeC13 solution could be reached.The performance of magnetite phase in FeCl3 solution shows much difference from that in mild H2SO4 solution.Under the optimal partial reduction conditions,i.e.with around 6%carbon dosage at 1000? for 3 h,the Fe/Ti mole ratio of the residue was still as high as 4.78 when leached by FeCl3 solution,corresponding to about 19%leaching rate of Fe,also indicating 19 wt%Fe metal phase in the reduced VTM;while the Fe/Ti mole ratio was around 0.2 when leached by 0.2 mol/L H2SO4 solution.It was found that the performance of V,Al,Mg,Si,Ca and Mn during FeCl3 leaching was also relatively inert,thus a new process composed by three main steps of deep carbon reduction,FeCl3 leaching and mild H2SO4 leaching,could be designed.Fe2+ enriched solution,V enriched solution and TiO2-enriched material were obtained by the new route.After reducing VTM with 15 wt%carbon dosage at 1000? for 3 h,68.7%Fe could be pre-leached by FeCl3 solution,and the Fe/Ti mole ratio decreased from 6.30 to 1.97.The residue obtained from the FeCl3 leaching step was further leached by 0.1-1.0 mol/L H2SO4 solution,other elements and the remaining 30%iron were dissolved,and a TiO2-enriched material with around 53%TiO2 was obtainedThe reductant for partial reduction of VTM can be replaced with hydrogen.It was found that the levels of temperature and reduction time can be coordinated to reach a designated value of weight loss.The leaching performance of the elements in reduced VTM was highly dependent on the reduction conditions.The leaching rate of Fe was ? 97%relied on two temperature-time ranges of[850?/0.5 h,1000?/0.5 h]and[1000?/3 h,1000?/6 h].The leaching rates of V,Mg,Al,Mn were high at[850?/0.5 h,1000?/0.5 h]and low at[1000?/3 h,1000?/6 h].Thus the process can be designed to co-leach Fe and V or solely leach Fe via tuning the reduction parameters.The leaching residues were anatase or the mixture of anatase and rutile with low crystallinity when reduced at 850-1000? for 0.5 h,then the residues were ilmenite along with some Al2FeO4 when extending the reduction time to 2 h at 1000?,and the residues were magnesium titanate with unfixed chemical compositions when the reduction time was 3-6 h at 1000?.It was demonstrated that a TiO2-enriched material with around 53%TiO2 could be obtained after partial reduction of VTM by H2 at 850-900? for 0.5 h and leaching by 0.2 mol/L H2SO4 solution.Deep reduced VTM at 1000? for 6 h by H2 could also be leached by mild H2SO4 solution to enrich TiO2,with V stayed with TiO2-enriched material.The research results in this thesis have surely confirmed the feasibility of enriching TiO2 from VTM by a new pyro-hydro combined method. |
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