Numerous studies have focused on the reduction thermodynamics of ordinary iron ore;by contrast, the literature contains few thermodynamic studies on the gas-based reduction of vanadium titano-magnetite (VTM) in mixed ...Numerous studies have focused on the reduction thermodynamics of ordinary iron ore;by contrast, the literature contains few thermodynamic studies on the gas-based reduction of vanadium titano-magnetite (VTM) in mixed atmospheres of H2, CO, H2O, CO2, and N2. In this paper, thermodynamic studies on the reduction of oxidized VTM pellets were systematically conducted in an atmosphere of a C–H–O system as a reducing agent. The results indicate that VTM of an equivalent valence state is more difficult to reduce than ordinary iron ore. A reduction equilibrium diagram using the C–H–O system as a reducing agent was obtained;it clearly describes the reduction process. Experiments were performed to investigate the effects of the reduction temperature, the gas composition, and two types of iron ores on the reduction of oxidized VTM pellets. The results show that the final reduction degree increases with increasing reduction temperature, increasing molar ratio of H2/(H2 + CO), and decreasing H2O, CO2, and N2 contents. In addition, the reduction processes under various conditions are discussed. All of the results of the reduction experiments are consistent with those of theoretical thermodynamic analysis. This study is expected to provide valuable thermodynamic theory on the industrial applications of VTM.展开更多
Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range...Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from 1 473 to 1 673 K. The scanning electron microscope （SEM） was used to characterize the microstructure of product. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39 kJ/mol without adding any catalysts. Adding CaF2 or NaF of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95 and 15.79 kJ/mol, respectively. In addition, temperature was an important factor influencing on reaction rate.展开更多
The reduction of vanadium titano-magnetite pellets by H_2-CO at temperatures from 850 to 1050°C was investigated in this paper. The influences of pre-oxidation treatment, reduction temperature, and V_（H_2）/（V_...The reduction of vanadium titano-magnetite pellets by H_2-CO at temperatures from 850 to 1050°C was investigated in this paper. The influences of pre-oxidation treatment, reduction temperature, and V_（H_2）/（V_（H_2） ＋ VCO） on the metallization degree were studied. The results showed that pre-oxidation played a substantial role in the reduction of vanadium titano-magnetite pellets. During the reduction process, the metallization degree increased with increasing temperature and increasing V_（H_2） /（V_（H_2） ＋ VCO）. The phase transformation of pre-oxidized vanadium titano-magnetite pellets during the reduction process under an H_2 atmosphere and a CO atmosphere was discussed, and the reduced samples were analyzed by scanning electron microscopy（SEM） in conjunction with back scatter electron（BSE） imaging. The results show that the difference in thermodynamic reducing ability between H_2 and CO is not the only factor that leads to differences in the reduction results obtained using different atmospheres. Some of Fe_（3-x）Ti_xO_4 cannot be reduced under a CO atmosphere because of the densification of particles＇ structure and because of the enrichment of Mg in unreacted cores. By contrast, a loose structure of particles was obtained when the pellets were reduced under an H_2 atmosphere and this structure decreased the resistance to gas diffusion. Moreover, the phenomenon of Mg enrichment in unreacted cores disappeared during H_2 reduction. Both the lower resistance to gas diffusion and the lack of Mg enrichment facilitated the reduction of vanadium titano-magnetite.展开更多
The effect of microwave treatment on the grinding and dissociation characteristics of vanadium titano-magnetite(VTM) ore were investigated using scanning electron microscopy(SEM), nitrogen absorption measurements, par...The effect of microwave treatment on the grinding and dissociation characteristics of vanadium titano-magnetite(VTM) ore were investigated using scanning electron microscopy(SEM), nitrogen absorption measurements, particle size distribution measurements, X-ray diffraction(XRD) analysis, Fourier transform infrared(FT-IR) spectroscopic analysis, and magnetic separation. SEM analysis showed that microfractures appeared in the microwave-treated VTM, which is attributed to the microwaves' selective heating characteristic and the differential expansion between minerals and gangues. Nitrogen absorption showed that the microfractures were more pronounced when the microwave heating time was increased. Particle size distribution analysis showed that microwave treatment could improve the grindability of the VTM, thus increasing the weight percent of the fine-ground product. The increase in grindability was more significant with prolonged heating time. Moreover, the particle size distribution of the fine-ground product changed only slightly after the microwave treatment. XRD analysis showed that the crystallinity of the microwave-treated VTM increased with increasing microwave heating time. The magnetic separation tests revealed that the separation efficiency increased as a result of the intergranular fractures generated by microwave treatment. The Fe grade of the magnetic fraction of microwave-treated VTM was 1.72% higher than that of the raw ore. We concluded that the microwave treatment was beneficial, especially for the mineral processing characteristics.展开更多
The vanadium titano-magnetite （VTM） iron ore fines of 110--150/xm in diameter were reduced in a trans- parent quartz fluidized bed by 70 %CO-30 % H2 （volume fraction） mixtures. MgO powders served as coating agent ...The vanadium titano-magnetite （VTM） iron ore fines of 110--150/xm in diameter were reduced in a trans- parent quartz fluidized bed by 70 %CO-30 % H2 （volume fraction） mixtures. MgO powders served as coating agent to solve sticking problem. Two coating methods were introduced in this experiment： high temperature injection method and briquetting→oxidizing roast→crushing method. According to the experimental results, the minimum effective coating amount of MgO was 0. 1 mass%. The metallization ratio （MR） of the product rose from around 58% to above 90% with the above treatments. To investigate the sticking mechanism of fine ore, the morphology evolution was in- vestigated. Instead of iron whiskers, an interlaced fibrous porous surface formed. The ulvospinel （2FeO ： TiO2 ） in VTM is more difficult to be reduced than FeO according to thermodynamic calculation. XRD results showed that MgO diffused into Fe203 lattice before forming pleonaste （MgO · Fe2O3 ） during oxidizing roast at 1273 K. The melting point of the pleonaste is 1986 K and that made contribution to prevent the sticking problem.展开更多
The microwave-assisted reduction behaviours of two low-grade iron ores having a similar Fe content of 49wt%but distinctly different mineralogical and liberation characteristics were studied.Their performances in terms...The microwave-assisted reduction behaviours of two low-grade iron ores having a similar Fe content of 49wt%but distinctly different mineralogical and liberation characteristics were studied.Their performances in terms of the iron grade and recovery as obtained from statistically designed microwave(MW)roasting followed by low-intensity magnetic separation(LIMS)experiments were compared.At respective optimum conditions,the titano-magnetite ore(O1)could yield an iron concentrate of 62.57%Fe grade and 60.01%Fe recovery,while the goethitic ore(O2)could be upgraded to a concentrate of 64.4%Fe grade and 33.3%Fe recovery.Compared with the goethitic ore,the titanomagnetite ore responded better to MW heating.The characterization studies of the feed and roasted products obtained at different power and time conditions using X-ray diffraction,optical microscopy,vibrating-sample magnetometry,and electron-probe microanalysis explain the sequential reduction in the iron oxide phases.Finally,taking advantage of the MW absorbing character of the titano-magnetite ore,a blend of the same with the goethite-rich ore at a weight ratio of 60:40(O2:O1)was subjected to MW roasting that resulted in a concentrate of 61.57%Fe grade with a Fe recovery of 64.47%.展开更多
In order to provide a reliable reference for utilizing Indonesia vanadium titano-magnetite(VTM) in blast furnace(BF) economically, metallurgical properties of iron ore sinter with addition of Indonesia VTM in mixed si...In order to provide a reliable reference for utilizing Indonesia vanadium titano-magnetite(VTM) in blast furnace(BF) economically, metallurgical properties of iron ore sinter with addition of Indonesia VTM in mixed sintering materials were investigated, including low-temperature reduction degradation index(RDI), reducibility index(RI), and softening/melting properties. Additionally, influenced mechanism of Indonesia VTM on metallurgical properties of sinter was studied. It is found that adding Indonesia VTM in sintering process quickly increases the RDI of sinters, and decreases the RI from 78.02% to 68.43%. Moreover, both beginning temperature(T_4) and final temperature(TD) of softening/melting increase gradually, and cohesive zone temperature range(T_D–T_4) enlarges from 219 oC to 315 oC. As a result, the permeability of cohesive zone gets worse, which is proven by the higher maximum pressure drop(δPmax) in softening/melting experiments. It is concluded that, after comprehensively considering all metallurgical properties mentioned above, the proper proportion of Indonesia VTM in sintering process is proposed in the new raw materials conditions.展开更多
The large quantity of sediment produced in the hearth during vanadium titano-magnetite smelting in a blast furnace（BF） affects the stability of the blast furnace operation. Testing and analysis of the sediment in th...The large quantity of sediment produced in the hearth during vanadium titano-magnetite smelting in a blast furnace（BF） affects the stability of the blast furnace operation. Testing and analysis of the sediment in the hearth of Chengde Iron and Steel Company？s BF No.7 revealed that it was mainly concentrated in the location below the tuyere and above the iron notch. Notably, some of the bonding material（sediment） consisted of greater than 50% pig iron, and the pig iron distributed in the slag was granular. It is proposed that a large quantity of Ti C and Ti（C,N） are deposited on the surface of the pig iron. These high melting point materials mix with iron drops, preventing the slag from flowing freely, thus leading to the formation of bonding materials. In addition, the viscosity and melting temperature of the slag in the tuyere areas fluctuate greatly, and thus the properties of the slag are unstable. Moreover, the slag contains large quantities of carbon, which results in the reduction of Ti O2. The resultant precipitation of Ti is followed by the formation of Ti C in the slag, which also leads to an increase in the viscosity of the slag and difficulty in achieving separation of the slag-iron. In fact, all of these factors interact with each other, and as a result, sediment is formed when the operating conditions in the hearth fluctuate.展开更多
High-manganese containing vanadium waste-water(HMVW)is commonly produced during the vanadium extraction process from vanadium titano-magnetite.HMVW cannot be reused and discharged directly,and is harmful to the enviro...High-manganese containing vanadium waste-water(HMVW)is commonly produced during the vanadium extraction process from vanadium titano-magnetite.HMVW cannot be reused and discharged directly,and is harmful to the environment and affect product quality due to heavy metals in the wastewater.The wastewater is usually treated by lime neutralization,but valuable metals(especially V and Mn)cannot be recovered.In this study,an efficient and environmentally friendly method was developed to recover valuable metals by using a solvent extraction-precipitation process.In the solvent extraction process,98.15%of vanadium was recovered,and the V2Os product,with a purity of 98.60%,was obtained under optimal conditions.For the precipitation process,91.05%of manganese was recovered as MnCO3 which meets the III grade standard of HG/T 2836-2011.Thermodynamic simulation analysis indicated that MnCO3 was selectively precipitated at pH 6.5 while Mg and Ca could hardly be precipitated.The results of X-ray diffraction and scanning electron microscopy demonstrated that the obtained V2Os and MnCO3 displayed a good degree of crystallinity.The treated wastewater can be returned for leaching,and resources(V and Mn)in the wastewater were utilized efficiently in an environmentally friendly way.Therefore,this study provides a novel method for the coextraction of V and Mn from HMVW.展开更多
基金financially supported by the Ministry of Land and Resources Public Welfare Industry Research Project, China (No. 201511062-02)
文摘Numerous studies have focused on the reduction thermodynamics of ordinary iron ore;by contrast, the literature contains few thermodynamic studies on the gas-based reduction of vanadium titano-magnetite (VTM) in mixed atmospheres of H2, CO, H2O, CO2, and N2. In this paper, thermodynamic studies on the reduction of oxidized VTM pellets were systematically conducted in an atmosphere of a C–H–O system as a reducing agent. The results indicate that VTM of an equivalent valence state is more difficult to reduce than ordinary iron ore. A reduction equilibrium diagram using the C–H–O system as a reducing agent was obtained;it clearly describes the reduction process. Experiments were performed to investigate the effects of the reduction temperature, the gas composition, and two types of iron ores on the reduction of oxidized VTM pellets. The results show that the final reduction degree increases with increasing reduction temperature, increasing molar ratio of H2/(H2 + CO), and decreasing H2O, CO2, and N2 contents. In addition, the reduction processes under various conditions are discussed. All of the results of the reduction experiments are consistent with those of theoretical thermodynamic analysis. This study is expected to provide valuable thermodynamic theory on the industrial applications of VTM.
基金Item Sponsored by National Key Technology Research and Development Program of China(2008BAB32B05)
文摘Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from 1 473 to 1 673 K. The scanning electron microscope （SEM） was used to characterize the microstructure of product. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39 kJ/mol without adding any catalysts. Adding CaF2 or NaF of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95 and 15.79 kJ/mol, respectively. In addition, temperature was an important factor influencing on reaction rate.
基金financially supported by the Fundamental Research Funds for the Central Universities(2014zzts273)
文摘The reduction of vanadium titano-magnetite pellets by H_2-CO at temperatures from 850 to 1050°C was investigated in this paper. The influences of pre-oxidation treatment, reduction temperature, and V_（H_2）/（V_（H_2） ＋ VCO） on the metallization degree were studied. The results showed that pre-oxidation played a substantial role in the reduction of vanadium titano-magnetite pellets. During the reduction process, the metallization degree increased with increasing temperature and increasing V_（H_2） /（V_（H_2） ＋ VCO）. The phase transformation of pre-oxidized vanadium titano-magnetite pellets during the reduction process under an H_2 atmosphere and a CO atmosphere was discussed, and the reduced samples were analyzed by scanning electron microscopy（SEM） in conjunction with back scatter electron（BSE） imaging. The results show that the difference in thermodynamic reducing ability between H_2 and CO is not the only factor that leads to differences in the reduction results obtained using different atmospheres. Some of Fe_（3-x）Ti_xO_4 cannot be reduced under a CO atmosphere because of the densification of particles＇ structure and because of the enrichment of Mg in unreacted cores. By contrast, a loose structure of particles was obtained when the pellets were reduced under an H_2 atmosphere and this structure decreased the resistance to gas diffusion. Moreover, the phenomenon of Mg enrichment in unreacted cores disappeared during H_2 reduction. Both the lower resistance to gas diffusion and the lack of Mg enrichment facilitated the reduction of vanadium titano-magnetite.
基金financially supported by the National Natural Science Foundation of China (Nos. 51574082 and 51874077)the Fundamental Research Funds for the Central University of China (Nos. N150202001 and N172507012)
文摘The effect of microwave treatment on the grinding and dissociation characteristics of vanadium titano-magnetite(VTM) ore were investigated using scanning electron microscopy(SEM), nitrogen absorption measurements, particle size distribution measurements, X-ray diffraction(XRD) analysis, Fourier transform infrared(FT-IR) spectroscopic analysis, and magnetic separation. SEM analysis showed that microfractures appeared in the microwave-treated VTM, which is attributed to the microwaves' selective heating characteristic and the differential expansion between minerals and gangues. Nitrogen absorption showed that the microfractures were more pronounced when the microwave heating time was increased. Particle size distribution analysis showed that microwave treatment could improve the grindability of the VTM, thus increasing the weight percent of the fine-ground product. The increase in grindability was more significant with prolonged heating time. Moreover, the particle size distribution of the fine-ground product changed only slightly after the microwave treatment. XRD analysis showed that the crystallinity of the microwave-treated VTM increased with increasing microwave heating time. The magnetic separation tests revealed that the separation efficiency increased as a result of the intergranular fractures generated by microwave treatment. The Fe grade of the magnetic fraction of microwave-treated VTM was 1.72% higher than that of the raw ore. We concluded that the microwave treatment was beneficial, especially for the mineral processing characteristics.
基金Sponsored by National Natural Science Foundation of China(51234001)National Basic Research Program of China(2012CB720401)
文摘The vanadium titano-magnetite （VTM） iron ore fines of 110--150/xm in diameter were reduced in a trans- parent quartz fluidized bed by 70 %CO-30 % H2 （volume fraction） mixtures. MgO powders served as coating agent to solve sticking problem. Two coating methods were introduced in this experiment： high temperature injection method and briquetting→oxidizing roast→crushing method. According to the experimental results, the minimum effective coating amount of MgO was 0. 1 mass%. The metallization ratio （MR） of the product rose from around 58% to above 90% with the above treatments. To investigate the sticking mechanism of fine ore, the morphology evolution was in- vestigated. Instead of iron whiskers, an interlaced fibrous porous surface formed. The ulvospinel （2FeO ： TiO2 ） in VTM is more difficult to be reduced than FeO according to thermodynamic calculation. XRD results showed that MgO diffused into Fe203 lattice before forming pleonaste （MgO · Fe2O3 ） during oxidizing roast at 1273 K. The melting point of the pleonaste is 1986 K and that made contribution to prevent the sticking problem.
基金The authors are thankful to the Director,CSIR-IMMT,Bhubaneswar for his permission to publish this paper and the Ministry of Steel,Government of India,for their financial support(F.No.11(12)/GBS/2014-TW).
文摘The microwave-assisted reduction behaviours of two low-grade iron ores having a similar Fe content of 49wt%but distinctly different mineralogical and liberation characteristics were studied.Their performances in terms of the iron grade and recovery as obtained from statistically designed microwave(MW)roasting followed by low-intensity magnetic separation(LIMS)experiments were compared.At respective optimum conditions,the titano-magnetite ore(O1)could yield an iron concentrate of 62.57%Fe grade and 60.01%Fe recovery,while the goethitic ore(O2)could be upgraded to a concentrate of 64.4%Fe grade and 33.3%Fe recovery.Compared with the goethitic ore,the titanomagnetite ore responded better to MW heating.The characterization studies of the feed and roasted products obtained at different power and time conditions using X-ray diffraction,optical microscopy,vibrating-sample magnetometry,and electron-probe microanalysis explain the sequential reduction in the iron oxide phases.Finally,taking advantage of the MW absorbing character of the titano-magnetite ore,a blend of the same with the goethite-rich ore at a weight ratio of 60:40(O2:O1)was subjected to MW roasting that resulted in a concentrate of 61.57%Fe grade with a Fe recovery of 64.47%.
基金Projects(51604069,51604049,U1508213) supported by the National Natural Science Foundation of ChinaProject(N162504004) supported by the Fundamental Research Funds for the Central Universities,ChinaProjects(2017YFB0603800,2017YFB0603801) supported by the National Key R&D Program of China
文摘In order to provide a reliable reference for utilizing Indonesia vanadium titano-magnetite(VTM) in blast furnace(BF) economically, metallurgical properties of iron ore sinter with addition of Indonesia VTM in mixed sintering materials were investigated, including low-temperature reduction degradation index(RDI), reducibility index(RI), and softening/melting properties. Additionally, influenced mechanism of Indonesia VTM on metallurgical properties of sinter was studied. It is found that adding Indonesia VTM in sintering process quickly increases the RDI of sinters, and decreases the RI from 78.02% to 68.43%. Moreover, both beginning temperature(T_4) and final temperature(TD) of softening/melting increase gradually, and cohesive zone temperature range(T_D–T_4) enlarges from 219 oC to 315 oC. As a result, the permeability of cohesive zone gets worse, which is proven by the higher maximum pressure drop(δPmax) in softening/melting experiments. It is concluded that, after comprehensively considering all metallurgical properties mentioned above, the proper proportion of Indonesia VTM in sintering process is proposed in the new raw materials conditions.
基金Item Sponsored by National Natural Science Foundation of China(U1360205)
文摘The large quantity of sediment produced in the hearth during vanadium titano-magnetite smelting in a blast furnace（BF） affects the stability of the blast furnace operation. Testing and analysis of the sediment in the hearth of Chengde Iron and Steel Company？s BF No.7 revealed that it was mainly concentrated in the location below the tuyere and above the iron notch. Notably, some of the bonding material（sediment） consisted of greater than 50% pig iron, and the pig iron distributed in the slag was granular. It is proposed that a large quantity of Ti C and Ti（C,N） are deposited on the surface of the pig iron. These high melting point materials mix with iron drops, preventing the slag from flowing freely, thus leading to the formation of bonding materials. In addition, the viscosity and melting temperature of the slag in the tuyere areas fluctuate greatly, and thus the properties of the slag are unstable. Moreover, the slag contains large quantities of carbon, which results in the reduction of Ti O2. The resultant precipitation of Ti is followed by the formation of Ti C in the slag, which also leads to an increase in the viscosity of the slag and difficulty in achieving separation of the slag-iron. In fact, all of these factors interact with each other, and as a result, sediment is formed when the operating conditions in the hearth fluctuate.
基金This study was financially supported by Project of National Natural Science Foundation of China(Grant Nos.51774215,51474162,and 51774216)Project of Hubei Province Science Foundation of China(No.2018CFA068).
文摘High-manganese containing vanadium waste-water(HMVW)is commonly produced during the vanadium extraction process from vanadium titano-magnetite.HMVW cannot be reused and discharged directly,and is harmful to the environment and affect product quality due to heavy metals in the wastewater.The wastewater is usually treated by lime neutralization,but valuable metals(especially V and Mn)cannot be recovered.In this study,an efficient and environmentally friendly method was developed to recover valuable metals by using a solvent extraction-precipitation process.In the solvent extraction process,98.15%of vanadium was recovered,and the V2Os product,with a purity of 98.60%,was obtained under optimal conditions.For the precipitation process,91.05%of manganese was recovered as MnCO3 which meets the III grade standard of HG/T 2836-2011.Thermodynamic simulation analysis indicated that MnCO3 was selectively precipitated at pH 6.5 while Mg and Ca could hardly be precipitated.The results of X-ray diffraction and scanning electron microscopy demonstrated that the obtained V2Os and MnCO3 displayed a good degree of crystallinity.The treated wastewater can be returned for leaching,and resources(V and Mn)in the wastewater were utilized efficiently in an environmentally friendly way.Therefore,this study provides a novel method for the coextraction of V and Mn from HMVW.
