| Vanadium titano-magnetite(VTM)owes its extremely high comprehensive utilization value due to abundantly associating valuable elements,i.e.,iron,vanadium,and titanium.The reserve of VTM resources is greater than 10 billion tons in the Panzhihua and Xichang regions of China,where the amounts of titanium,vanadium and iron account for 90.5%,62.0%and 20.0%respectively of the national total reserves.However,with the features of poor grade,fine mineral crystal size,complicated phase structure,and numerous mineral components,the complex ore brings about critical environmental problems and ineffective resource utilization in the BF-BOF process,which is the mainstream route for the comprehensive utilization of VTM currently.In recent years,a great number of new processes have been proposed and studied for the comprehensive utilization of VTM.Nevertheless,none of them have been successfully put into industrial application.In present study,a new process of metallic reduction-separation for VTM is put forward based on previous studies togther with the theory and method of modern metallurgy,physical chemistry in metallurgy,metallurgy transport principle,amongst others.The study can not only improve comprehensive utilization ratio of iron,vanadium and titaium in VTM and remit environmental problems,but also promote the technological innovations and development.Based on the analysis of the fundamental characteristics of VTM,the effects of magnetic intensity,reduction temperature,reduction time,carbon ratio and coal size on the efficiency of metallic reduct ion-magnetic separation are investigated.Simultaneously,the effects of active carbon ratio,basicity,smelting time,smelting temperature on the efficiency of electrothermal smelting separation are studied.The results show that the optimal parameters include magnetic intensity 50 mT,reduction temperature 1350?,reduction time 60 min,carbon ratio 1.2 and active carbon ratio 0.10%,basicity 1.0,smelting time 60 min and smelting temperature 1600?.Under the above conditions,the valuable metals including Fe,V and Ti have been efficiently separated from VTM.The recovery ratio of iron and vanadium in smelting iron reach 96.18%and 80.56%respectively and the recovery ratio of titanium in smelting slag and separated tailing are 18.07%and 78.04%respectively.Through thermodynamic analysis,under the conditions of reduction temperature 1350?and carbon ratio 1.0,iron and vanadium could be possibly generated during the reduction of VTM as well as their carbides and low-valence oxides.According to XRD analysis,the phase transformation of VTM carbothermic reduction is Fe3O4?FeO O Fe,FexTi3-XO4 ? Fe5TiO8? Fe3T3Oi0 ? FeTiO3 ? FeTi2O5.The dynamics mechanism of VTM carbothermic reduction is discussed by means of comprehensive thermal analysis method,which reveal that the reaction dynamics mechanism of VTM carbothermic reduction is random successive nucleation growth(n=4)and that the mechanism function is described as follows:f(a)=1/4(1-a)[-ln(1-a)]-3 When the reduction temperature is about 550?-900?,the reaction activation energy is 88.7 kJ·mol-1 and the restrictive step is the diffusion in reduction process.With 900??1350?reduction temperature,the reaction activation energy is 295.5 kJ·mol-1 and the restrictive step is the interfacial chemical reaction in reduction process.The titanium resource in the separated tailing is comprehensively utilized by means of acid leaching-hydrolysis enrichment process.Under the conditions of acid-tailing ratio 4:1,leaching temperature 60?,leaching time 80 min and liquid-solid ratio 3.2:1,the leaching ratio of titanium is 92.41%.Meanwhile,with the condition of concentration of H+ 0.75 g-L-1,hydrolysis temperature 100? and hydrolysis time 180 min,the hydrolysis ratio of titanium solution is up to 96.80%.After calcination treatment,the utilization ratio of rutile titanium dioxide is about 89.45%.In addition,the leaching dynamics analysis reveal that the leaching process is restricted by internal diffusion through solid products surface layer and that the reaction activation energy is 4.29 kJ·mol-1.Base on Gabi 6.0 and CML database,a life cycle assessment model is established to evaluate the life cycle of metallic reduction-separation for VTM process.The major sources of environmental impacts are described and pollution prevention methods are proposed.Impact assessment results indicate that the main procedures environmental contribution are mining and dressing,metallic reduction,electric furnace smelting and titanium dioxide production and the main indicator contributions are acidification potential AP(50.17%),global warming potential GWP100(22.36%)and photochemical ozone creation potential POCP(22.43%).Thus,the improvement of environmental impacts for these process should be reduced the indicator contributions of AP,GWP100,and POCP in these four procedures including mining and dressing,metallic reduction,electric furnace smelting and titanium dioxide production.The contrastive analysis on the environment impacts of the two different process,namely the new metallic reduction-separation process and the BF-BOF process,for the utilization of VTM is carried out,which reveals that the life cycle overall evaluation results of the new metallic reduction-separation process and the BF-BOF process are 1.06E-10 yr and 1.27E-10 yr respectively.So the overall environmental load of the new process is reduced by 16.54%compared with the BF-BOF process.The environmental loads of different impact categories(ADP,GWP100,EP,AP,POCP and HTP)by the metallic reduction-separation process are lower than those of the BF-BOF process,which are 38.99%,92.69%,80.57%,44.14%,61.02%and 49.31%of the latter process respectively.As a consequence,the new process of metallic reduction-separation of VTM has obvious superiority compared with the BF-BOF process with respect to the envioronmental load. |
PDF Full Text Request