| Titanium,vanadium and chromium are recognized as major strategic resources in various countries all over the world.They are widely used in fields of iron and steel industry,metallurgical industry,chemical industry,aerospace,and other fields,which are very important to national economic development and national security.The vast majority of China's chromium resources are stored in the high chromium vanadium-bearing titanomagnetite in the hongge mining area in Sichuan Province.Under the environment of the shortage of domestic chromium resources,the comprehensive utilization of the high-chromium vanadium-bearing titanomagnetite needs to be solved urgently.At present,the utilization methods of high chromium vanadium-bearing titanomagnetite are the same as ordinary vanadium-bearing titanomagnetite,including blast furnace method and direct reduction-electric furnace melting method,but all of them have long process flow,low resource utilization rate,high energy consumption,environmental load and other issues.In order to solve the above problems,a new technology of comprehensive utilization of high chromium vanadium-bearing titanomagnetite is proposed in this paper.The process mainly includes one-step high temperature process and one-step water leaching process.After that,iron and chromium,vanadium,titanium are enriched in pig iron,vanadium-bearing leaching solution and titanium-bearing leaching residue,respectively.A series of reactions occurred during the high temperature process for high chromium vanadium-bearing titanomagnetite,including the reduction of iron oxide to metal iron,sodium oxidation of vanadium oxide into water-soluble sodium vanadate,the reduction,carbonation and dissolved in molten iron of chromium,the separation of molten slag and iron phase.Therefore,the new process is called "reduction-sodium oxidation-smelting separation coupled technology." The technological process has the advantages of short process,low energy consumption,high comprehensive utilization of resources and small environmental pollution,and provides an innovative idea for efficient comprehensive utilization of high chromium vanadium-bearing titanomagnetite.The dissertation's innovative achievements are as follows:(1)The feasibility of thermodynamic analysis of reduction and sodium oxidation coupling process was studied,and it is found that the reduction of iron oxide to metal iron and the sodium oxidation of vanadium oxide to water-soluble sodium vanadate can theoretically be achieved simultaneously in the coupling process;(2)In the mixture of the vanadium-bearing titanomagnetite concentrate,the reduction agent and the sodium salt,when the molar ratio of carbon to iron is in the range of 2.0 to 3.2,the added amount of sodium carbonate is in the range of 40 wt%to 100 wt%,and when the roasting temperature is in the range of 1150-1200?,the reduction of iron oxide,the sodium oxidation of vanadium oxide and the separation of molten slag and iron can be achieved simultaneously during the calcination,that is,after the direct reduction-sodium oxidation-smelting separation process,the iron and chromium are enriched in the massive iron phase for the subsequent special steel preparation.The vanadium and titanium are enriched in the roasted slag for the subsequent extraction and utilization of vanadium and titanium.(3)A systematic study on the influencing factors of slag-iron melting process found that many factors have an impact on the slag-iron melting process,including the type of reduction agent,type of sodium salt,calcination temperature,calcination time,the amount of sodium carbonate,the thickness of the material layer;comprehensively considering the effect of slag-iron smelting separation and the distribution of vanadium and chromium in the iron and slag phase,the best roasting conditions are obtained and showed as follows,reduction agent anthracite,additive sodium carbonate,roasting temperature 1200 ?,roasting time 2 h,molar ratio of carbon to iron 2.6,70%addition of sodium carbonate,layer thickness 42.5 mm.Under optimal roasting conditions,the recovery rate of iron was 98.15%,the iron grade in the iron phase was 95.44%,96.19%of the chromium was in the iron phase and 84.9%of the vanadium was in the slag phase.(4)The grade of vanadium in the iron phase will change with the roasting conditions.The grade of chromium in the iron phase will not change with the roasting conditions,and will always be kept at about 0.925%.The migration of vanadium in the slag and iron phase is related to the recovery rate of iron and the separation effect of slag and iron.The migration of chromium in the slag and iron phase is only related to the recovery rate of iron,that is,the separation effect of slag and iron.(5)The leaching process of vanadium in roasted slag was optimized.The optimal leaching conditions of vanadium were particle size-0.035 mm,leaching temperature 90 ?,liquid-solid ratio 4:1,stirring speed 400 r/min and leaching time 30 min.The leaching rate of vanadium was 85.62%,the activation energy of vanadium leaching process was 19.27 kJ/mol.The leaching process was controlled by internal diffusion.(6)The results of leaching residue and leachate analysis showed that the content of Fe,Ti,V and Cr in leaching residue were 7.27%,13.22%,0.078%and 0.006%respectively.Leaching residue mainly consists of sodium aluminosilicate and a small amount of calcium titanate which can be used as raw material for the production of titanium dioxide.The leachate contains 3.68 g/L V2O5,50.39 g/L NaOH,0.3 g/L SiO2 and 1.5 g/L Al(OH)3.(7)The reduction process of iron oxide in the reduction-sodium oxidation coupling process was studied.It is found that the roasted product mainly contains three phases,including metallic iron phase,titanium-rich phase and silicate phase.With the prolongation of roasting time,iron,titanium and silicon elements gradually migrate and aggregate to form an iron phase,a titanium-rich phase and a silicate phase,and the boundaries between them gradually become clear;at the same roasting time,the increasing roasting temperature,the increasing molar ratio of carbon to iron,the increasing addition amount of sodium carbonate are favorable for the aggregation of iron,titanium,and silicon in the respective enrichment phase and the separation of the phases from each other.With the prolongation of roasting time,vanadium and chromium gradually migrate into the silicate phase and the iron phase,respectively.And the increasing roasting temperature,the increasing molar ratio of carbon to iron,and the increasing addition of sodium carbonate all contribute to the enrichment of vanadium and chromium into the silicate and iron phases.(8)The reaction mechanism of iron-vanadium-chromium-titanium oxides during reduction-sodium oxidation was studied.It was found that when the molar ratio of Na2CO3 to C is greater than 0.5:3.33 in Cr2O3-C-Na2CO3 ternary system,the Cr2O3 is sodiumized and oxidized to Na2CrO4,when the molar ratio of Na2CO3 to C is less than 0.5:3.33,the Cr2O3 is preferentially sodiumized to NaCrO2,and the rest of the Cr2O3 is reduced to chromium carbide by C,and the type of chromium carbide gradually changes from Cr7C3 to Cr3C2 with the increase of C.V2O3 can be oxidized into water-soluble vanadate in V2O3-C-Na2C03 ternary system,and the types of vanadate gradually follow the order of NaVO3-Na4V2O7-Na3VO4 with the increase of Na2CO3.But in the process of transformation there will be the emergence of water-insoluble vanadium bronze.In addition,the addition of C will consume a part of Na2CO3,and this interaction takes precedence over that of V2O3 so that the same amount of V2O3 needs more Na2CO3.In the Fe2O3-C-Na2CO3 ternary system,when the molar ratio of Na2CO3 to C is greater than 0.52:1.68,the presence of excess Na2CO3 will affect the reduction of Fe2O3,Fe2O3 will react with Na2CO3.And with the increase of Na2CO3 content,the reaction product will transform following the order of Na2.4Fe10.99016.03 ? NaFeO2 ? Na4Fe2O5.In TiO2-C-Na2CO3 ternary system,with the increase of Na2CO3,the transformation order of titanate is Na2TiO3?Na16Ti10O28?Na4TiO4 and when Na2CO3 are in excess,only Na4TiO4 exists in the reaction product. |
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