Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the ...Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the lack of sufficient research regarding the resistance of functionally graded fiber-reinforced concrete against projectile impacts has resulted in a limited understanding of the performance of this concrete type,which is necessary for the design and construction of structures requiring great resistance against external threats.Here,the performance of functionally graded fiber-reinforced concrete against projectile impacts was investigated experimentally using a(two-stage light)gas gun and a drop weight testing machine.For this objective,12 mix designs,with which 35 cylindrical specimens and 30 slab specimens were made,were prepared,and the main variables were the magnetite aggregate vol%(55%)replacing natural coarse aggregate,steel fiber vol%,and steel fiber type(3D and 5D).The fibers were added at six vol%of 0%,0.5%,0.75%,1%,1.25%,and 1.5%in 10 specimen series(three identical specimens per each series)with dimensions of 40×40×7.5 cm and functional grading(three layers),and the manufactured specimens were subjected to the drop weight impact and projectile penetration tests by the drop weight testing machine and gas gun,respectively,to assess their performance.Parameters under study included the compressive strength,destruction level,and penetration depth.The experimental results demonstrate that using the magnetite aggregate instead of the natural coarse aggregate elevated the compressive strength of the concrete by 61%.In the tests by the drop weight machine,it was observed that by increasing the total vol%of the fibers,especially by increasing the fiber content in the outer layers(impact surface),the cracking resistance and energy absorption increased by around 100%.Note that the fiber geometry had little effect on the energy absorption in the drop weight test.Investigating the optimum specimens showed that using 3D steel fibers at a total fiber content of 1 vol%,consisting of a layered grading of 1.5 vol%,0 vol%,and 1.5 vol%,improved the penetration depth by 76%and lowered the destruction level by 85%.In addition,incorporating the 5D steel fibers at a total fiber content of 1 vol%,consisting of the layered fiber contents of 1.5%,0%,and 1.5%,improved the projectile penetration depth by 50%and lowered the damage level by 61%compared with the case of using the 3D fibers.展开更多
An approach for coal-based direct reduction of vanadium−titanium magnetite(VTM)raw ore was proposed.Under the optimal reduction conditions with reduction temperature of 1140℃,reduction time of 3 h,C-to-Fe molar ratio...An approach for coal-based direct reduction of vanadium−titanium magnetite(VTM)raw ore was proposed.Under the optimal reduction conditions with reduction temperature of 1140℃,reduction time of 3 h,C-to-Fe molar ratio of 1.2꞉1,and pre-oxidation temperature of 900℃,the iron metallization degree is 97.8%.Ultimately,magnetic separation yields an iron concentrate with an Fe content of 76.78 wt.%and efficiency of 93.41%,while the magnetic separation slag has a Ti grade and recovery of 9.36 wt.%and 87.07%,respectively,with a titanium loss of 12.93%.This new strategy eliminates the beneficiation process of VTM raw ore,effectively reduces the Ti content in the iron concentrate,and improves the comprehensive utilization of valuable metals.展开更多
The isothermal oxidation kinetics of vanadium–titanium magnetite(VTM)pellets prepared with 3Co-binder(coal-based colloidal composite binder)and F-binder(pulverized Funa binder)are compared.The oxidation process was a...The isothermal oxidation kinetics of vanadium–titanium magnetite(VTM)pellets prepared with 3Co-binder(coal-based colloidal composite binder)and F-binder(pulverized Funa binder)are compared.The oxidation process was analyzed using the first-order irreversible reaction,following the shrinking unreacted nucleus model.The results demonstrate that VTM pellets prepared with 3Co-binder exhibit a faster oxidation rate than those with F-binder across the temperatures ranging from 1073 to 1473 K.In both cases,the oxidation process was controlled by an interfacial chemical reaction during the pre-oxidation stage and by internal diffusion during the mid-oxidation stage.The type of binder did not influence the primary oxidation control mechanism of the VTM pellets.However,the apparent rate constants in the pre-oxidation stage and the internal diffusion coefficients in the mid-oxidation stage were higher for pellets with 3Co-binder compared to those with F-binder.The apparent activation energies for the 3Co-binder pellets were similar to those of bentonite,indicating favorable kinetic conditions without negative impacts on the oxidation process.Nonetheless,it is important to note that pellets with F-binder required a longer oxidation time than those with 3Co-binder.展开更多
The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through ...The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through linear fitting to the kinetic equations based on the shrinking unreacted-core model. The results reveal that VTM pellets undergo oxidation in three distinct phases: pre-oxidation, mid-oxidation, and final stable phase. Notably, the mid-oxidation phase is absent in magnetite oxidation. The shrinking unreacted-core model has been proven to be suitable for modeling the process of oxidizing VTM pellets. In the pre-oxidation stage, the rate-controlling step is determined by both the oxidation temperature and the effective oxygen concentration. The influence of the effective oxygen concentration on the rate of oxidation is more pronounced at temperatures between 1073 and 1273 K, especially when the oxygen content falls below 15 vol.%. For the production of oxidized VTM pellets, it is necessary to maintain a preheating temperature above 1173 K (to accelerate the oxidation reaction) and below 1473 K (to prevent the swift formation of compact Fe2TiO5 at the shell of the pellet) in an oxygen-enriched atmosphere.展开更多
Although previous researchers have attempted to decipher ore genesis and mineralization in the Erdaokan Ag-Pb-Zn deposit,some uncertainties regarding the mineralization process and evolution of both ore-forming fluids...Although previous researchers have attempted to decipher ore genesis and mineralization in the Erdaokan Ag-Pb-Zn deposit,some uncertainties regarding the mineralization process and evolution of both ore-forming fluids and magnetite types still need to be addressed.In this study,we obtained new EPMA,LA-ICP-MS,and in situ Fe isotope data from magnetite from the Erdaokan deposit,in order to better understand the mineralization mechanism and evolution of both magnetite and the ore-forming fluids.Our results identified seven types of magnetite at Erdaokan:disseminated magnetite(Mag1),coarse-grained magnetite(Mag2a),radial magnetite(Mag2b),fragmented fine-grained magnetite(Mag2c),vermicular gel magnetite(Mag3a1 and Mag3a2),colloidal magnetite(Mag3b)and dark gray magnetite(Mag4).All of the magnetite types were hydrothermal in origin and generally low in Ti(<400 ppm)and Ni(<800 ppm),while being enriched in light Fe isotopes(δ^(56)Fe ranging from−1.54‰to−0.06‰).However,they exhibit different geochemical signatures and are thus classified into high-manganese magnetite(Mag1,MnO>5 wt%),low-silicon magnetite(Mag2a-c,SiO_(2)<1 wt%),high-silicon magnetite(Mag3a-b,SiO_(2)from 1 to 7 wt%)and high-silicon-manganese magnetite(Mag4,SiO_(2)>1 wt%,MnO>0.2 wt%),each being formed within distinct hydrothermal environments.Based on mineralogy,elemental geochemistry,Fe isotopes,temperature trends,TMg-mag and(Ti+V)vs.(Al+Mn)diagrams,we propose that the Erdaokan Ag-Pb-Zn deposit underwent multi-stage mineralization,which can be broken down into four stages and nine sub-stages.Mag1,Mag2a-c,Mag3a-b and Mag4 were formed during the first sub-stage of each of the four stages,respectively.Additionally,fluid mixing,cooling and depressurization boiling were identified as the main mechanisms for mineral precipitation.The enrichment of Ag was significantly enhanced by the superposition of multi-stage ore-forming hydrothermal fluids in the Erdaokan Ag-Pb-Zn deposit.展开更多
In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting r...In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were investigated using kinetic empirical equation by fitting and combining with X-ray diffraction,X-ray fluorescence,scanning electron microscopy,energy-dispersive spectrometry,and optical microscopy.The results show that iron reduction is controlled by the mass transfer process of(FeOx)in the slag,while vanadium reduction is controlled by both the mass transfer of(VOx)in the slag and the mass transfer of[V]in the molten iron,and the slag–metal interfacial reaction is the only pathway for vanadium reduction.The reduction of iron and vanadium is an obvious first-order reaction,with activation energy of 101.6051 and 197.416 kJ mol^(−1),respectively.Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency.The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe_(2)O_(3)→Fe_(3)O_(4)/FeV_(2)O_(4)→FeTiO_(3) and FeV_(2)O_(4)→MgV_(2)O_(5);titanium in slag is mainly in the form of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and CaTiO_(3).As the reaction time went on,the molar ratio(nTi/nMg)in Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and the Ti2O_(3) content in the slag gradually went up,while the area proportion of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)went up and then down,and the porosity of the slag and the grain size of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)got smaller.展开更多
JC Pura schist belt has gained scope recently with reports of nickel, magnetite, PGEs, and traces of gold. The layered sill in the schist belt is a linear patch of ultramafic sequences (peridotite and pyroxenite) with...JC Pura schist belt has gained scope recently with reports of nickel, magnetite, PGEs, and traces of gold. The layered sill in the schist belt is a linear patch of ultramafic sequences (peridotite and pyroxenite) with metamorphogenic magnetite mineralization. The metamorphogenic magnetite appears as interbands in layered sequences and as veins in serpentinite. The present study focuses on understanding the characteristics of metamorphogenic magnetite by petrographic and EPMA analysis. The study found that the precursor chromite grains are transformed into Cr-magnetite and magnetite in the spinel transformation system due to metamorphism and hydrothermal alteration. The Cr, Mg, Al, and Ni are depleted during transformation, and Fe is enriched. The Cr-magnetite appears homogenous in the vein due to serpentinization, indicating prograde greenschist to amphibolite facies metamorphism, and the area has suffered an episodic metamorphic process. The results of Cr-magnetite cation proportions of Cr fall within ishkulite variety data range of 0.10 - 0.50 apfu (atoms per formula unit). Cr-magnetite variety Ishkulite represents an additional miscibility gap in the Cr-Fe3+ transformation series other than ferrite chromite and chrome magnetite. The transformation process primarily involves the oxidation of chromium and the reduction of iron. The oxidation of chromite by highly oxidizing fluids with increasing pressure and temperature alters to Cr-magnetite, where chromium in the +3 state oxidizes to the +6 state, forming soluble chromate ions and diffusing with Fe3+. Then, it transforms into magnetite due to reducing conditions. Cr-magnetite vein indicates the potential for chromite deposits in the area, and hydrothermal altered magnetites could be a source for hosting valuable precious metals like gold and PGEs. Further investigations are needed to assess the mineralization potential and its extent.展开更多
High-chromium vanadium-titanium magnetite(HVTM)is a crucial polymetallic-associated resource to be developed.The allpellet operation is a blast furnace trend that aims to reduce carbon dioxide emissions in the future....High-chromium vanadium-titanium magnetite(HVTM)is a crucial polymetallic-associated resource to be developed.The allpellet operation is a blast furnace trend that aims to reduce carbon dioxide emissions in the future.By referencing the production data of vanadium-titanium magnetite blast furnaces,this study explored the softening-melting behavior of high-chromium vanadium-titanium magnetite and obtained the optimal integrated burden based on flux pellets.The results show that the burden with a composition of 70wt%flux pellets and 30wt%acid pellets exhibits the best softening-melting properties.In comparison to that of the single burden,the softening-melting characteristic temperature of this burden composition was higher.The melting interval first increased from 307 to 362℃and then decreased to 282℃.The maximum pressure drop(ΔPmax)decreased from 26.76 to 19.01 kPa.The permeability index(S)dropped from 4643.5 to 2446.8 kPa·℃.The softening-melting properties of the integrated burden were apparently improved.The acid pellets played a role in withstanding load during the softening process.The flux pellets in the integrated burden exhibited a higher slag melting point,which increased the melting temperature during the melting process.The slag homogeneity and the TiC produced by over-reduction led to the gas permeability deterioration of the single burden.The segregation of the flux and acid pellets in the HVTM proportion and basicity mainly led to the better softening-melting properties of the integrated burden.展开更多
The effect of alumina occurrence form on the metallurgical properties of both hematite and magnetite pellets was investigated at the same Al_(2)O level of 2 wt.%,including reduction index(RI),low-temperature reduction...The effect of alumina occurrence form on the metallurgical properties of both hematite and magnetite pellets was investigated at the same Al_(2)O level of 2 wt.%,including reduction index(RI),low-temperature reduction disintegration index(RDI),reduction swelling index(RSI),and high-temperature softening-dripping performance.The mineralogy of fired pellets was also studied to reveal the influence of alumina occurrence form on the phase composition and microstructure.From the results,the alumina occurrence form presents tremendous impacts on the metallurgical perfor-mance of both magnetite and hematite pellets.Addition of all alumina occurrence forms contributes to inferior reducibility of pellets,especially in the case of gibbsite for magnetite pellets with a RI of 58.4%and kaolinite for hematite pellets with a RI of 56.8%.However,addition of all alumina occurrence forms improves the RDI of magnetite pellets,while there is no significant difference among various alumina occurrence forms.In contrast,alumina occurrence forms have little influence on the RDI of hematite pellets.The presence of free alumina,gibbsite,and kaolinite tends to improve the RSI of hematite and magnetite pellets,whereas hercynite gives the opposite trend with a RSI of 25.6%.For softening-dripping performance of magnetite pellets,all alumina occurrence forms contribute to narrower softening-melting interval.Meanwhile,alumina,gibbsite,and kaolinite give narrower softening-dripping interval,at 229,217,and 88℃,respectively,whereas addition of hercynite results in the largest melting range at 276℃ due to its high melting point.Regarding hematite pellets,free alumina,gibbsite,and hercynite tend to enlarge melting range,whereas kaolinite contributes to lower dripping temperature of 1148℃ and narrow softening-dripping interval of 88℃ due to the formation of a greater amount of slag phase at high temperatures.展开更多
The sodium smelting of vanadium-titanium magnetite can achieve the comprehensive utilization of Fe,V,and Ti.However,the generation of alkaline slag during this process may cause damage to refractory materials.The wett...The sodium smelting of vanadium-titanium magnetite can achieve the comprehensive utilization of Fe,V,and Ti.However,the generation of alkaline slag during this process may cause damage to refractory materials.The wettability and corrosion behavior of alkaline slag on three types of refractory(MgO-C,SiC,and high alumina refractory)substrates were investigated at temperatures up to 1200℃.The effects of duration on the wettability of molten slag on SiC substrates were also investigated.Results showed that the high alumina refractory exhibited better wettability with the molten slag than the others,and thus,it is easier to be corroded.The results of scanning electron microscopy coupled with energy dispersive spectroscopy showed that MgO-C and high alumina refractory substrates were severely eroded.There was a visible and regular interfacial reaction layer between the slag and SiC refractory substrate,which was produced by the redox reaction between the metal oxides in the slag and the SiC refractory substrate.With the increase in holding time,the interface layer expands and silico-ferrite phases are generated at the interface.The redox reaction between Fe_(2)O_(3) and SiC substrate is the main reason for the corrosion.By comparing the differences in wettability and corrosion behavior between the alkaline slag from sodium smelting of vanadium-titanium magnetite and MgO-C,SiC and high alumina refractories,it is concluded that SiC refractory has good corrosion resistance to the slag.Iron oxides in the slag accelerate the oxidation rate of SiC refractory.展开更多
To investigate the feasibility of co-sintering of fluxed iron ore with magnetite concentrates, the mineralogical properties of a novel fluxed iron ore were studied using particle size analysis, microscopic morphology ...To investigate the feasibility of co-sintering of fluxed iron ore with magnetite concentrates, the mineralogical properties of a novel fluxed iron ore were studied using particle size analysis, microscopic morphology characterization, and X-ray diffraction Rietveld analysis. Following that, the experiments for granulation performance and basic sintering characteristics were designed under seven different fluxed iron ore ratios, and the integrated ranking of different fluxed iron ore ratios was determined using gray relation analysis. Finally, the results of the industrial trails were combined with the feasibility analysis. Test and experimental results show that the fraction of the fluxed iron ore particles larger than 0.5 mm can account for more than 48%, and the particles have two morphologies: spherical-rough and flaky-smooth. Ca elements are found in the form of calcite (CaCO3) and dolomite (CaMg(CO3)2). The average particle size of granules and powder removal rate can be improved from 2.50 to 3.16 mm and 39.60% to 24.20%, respectively, with the increase in the fluxed iron ore ratio. Furthermore, the fluxed iron ore can improve assimilability and liquid fluidity of magnetite concentrates. In terms of overall granulation performance and sintering characteristics, the fluxed iron ore ratios are graded from best to worst as follows: 12%, 15%, 9%, 18%, 21%, 6% and 3%. The industrial trails show that when the fluxed iron ore ratio is increased, the beneficial effect of the superior sintering characteristics of the fluxed iron ore itself is ideally balanced with the negative effect of the lower amount of additional CaO at 12% ratio, and thus, it is feasible to bring the fluxed iron ore into production at a level of roughly 12%.展开更多
Magnetite from hydrothermal deposits may show compositional zoning with various mineral inclusions in response to the evolution of hydrothermal fluids.Magnetite from the Fenghuangshan Cu-Fe-Au skarn deposit(eastern Ch...Magnetite from hydrothermal deposits may show compositional zoning with various mineral inclusions in response to the evolution of hydrothermal fluids.Magnetite from the Fenghuangshan Cu-Fe-Au skarn deposit(eastern China)is a common mineral formed in the earlier stage of skarnization.Magnetite grains have dark gray and light gray zones and contain diverse mineral inclusions.Dark gray zones have higher Si,Ca,Al,and Mg contents than light gray zones.The magnetite matrix from dark gray zones shows superstructure along the[0-11]zone axis in fast Fourier transform patterns,different from magnetite in light gray zones with normal structure.Three types of mineral inclusions are identified within magnetite:nano-,micron-and submicron-nanometer inclusions.Nanoinclusions hosted in dark gray zones are actinolite,diopside,and trace element-rich magnetite,and these are likely formed by growth entrapment during magnetite crystallization at the skarn stage.The chainwidth order-disorder intergrowths of diopside nanoinclusion likely indicate fluctuating fluid compositions in a lattice scale.Submicron to nanometer inclusions at the boundary between dark gray and light gray zones are quartz,titanite,and Ti-rich magnetite,which were formed via a dissolution and reprecipitation process at the quartz-sulfide stage.Micron-inclusions randomly distributed in both dark and light gray zones include calcite,ankerite,quartz,and chlorite,and these were formed via penetration of fluids at the carbonate stage.Zoned magnetite was formed by fluid replacement,overgrowth,and fluid infilling.Our study highlights the importance of mineral inclusion assemblages,and textural and chemical zonation of magnetite in constraining fluid evolution.展开更多
To comprehensively utilize the low-iron high-vanadium-titanium magnetite,a new method of vortex smelting reduction of vanadium-titanium magnetite was proposed,and the enrichment and reconstitution regularity of Ti-bea...To comprehensively utilize the low-iron high-vanadium-titanium magnetite,a new method of vortex smelting reduction of vanadium-titanium magnetite was proposed,and the enrichment and reconstitution regularity of Ti-bearing phases in the slag was investigated through X-ray fluorescence spectrometry,X-ray photoelectron spectroscopy,X-ray diffraction analysis,and optical microscopy.The phase diagram revealed that the preferential crystallization of MgTi_(2)O_(5) can be achieved by adjusting the CaO,MgO,and TiO_(2) contents of slag.The predominant Ti-bearing phases in the slag obtained from the reduction process are MgxTi_(3_x)O_(5)(0≤x≤1)and CaTiO_(3).FeTiO_(3) is present at carbon-iron ratio(CR)=1.3,while MgTi_(2)O4 and TiC are formed at CR=1.3.The enrichment of TiO_(2) in the slag increases first and then decreases as the CR increases,and at CR=1.1,the enrichment of TiO_(2) in the slag reaches 51.3 wt.%.Additionally,the concentrations of MgxTi_(3_x)O_(5)(0≤x≤1)and CaTiO_(3) in the slag,along with the grain width of MgxTi_(3_x)O_(5)(0≤x≤1),decrease with the increase in CR.展开更多
Basicity has an important effect on the sinter quality, especially for low-titanium vanadium-titanium sinter. The effect of basieity on sintering behavior of low-titanium vanadium-titanium mixture, and the transferenc...Basicity has an important effect on the sinter quality, especially for low-titanium vanadium-titanium sinter. The effect of basieity on sintering behavior of low-titanium vanadium-titanium mixture, and the transference and distribution of element in sintering process were researched by sinter pot test, mineralogical analysis, scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） analysis. The results show that CaO preferentially reacts with TiO2, generating pervoskite, so that the total liquid phase content of the sinter is low. There is an increase in the perovskite concentration of the sinter with the basicity ranging from 1.9：1 to 2.7：1. With increasing the basicity, the calcium ferrite content increases slightly and then rises rapidly, while the silicate content decreases and the metallurgical property of the sinter is improved. As for the distribution of these elements in the sinter, Ti occurs mainly in perovskite, V occurs mainly in silicate, and Fe occurs mainly in magnetite and hematite. The most abundant occurrence of Ca and Si occurs in silicate and perovskite. With increasing the basicity, the contents of A1 and Mg increase in calcium ferrite, while they decrease in other minerals.展开更多
The solid-state reduction kinetics of pre-oxidized vanadium-titanium magnetite concentrate was studied. The phase and microstructure of the reduction product were characterized by XRD, SEM and EDS methods, based on wh...The solid-state reduction kinetics of pre-oxidized vanadium-titanium magnetite concentrate was studied. The phase and microstructure of the reduction product were characterized by XRD, SEM and EDS methods, based on which the mechanism of the solid-state reduction was investigated. The results showed that using coal as reductant at 950-1100 °C, the solid-state reduction of the pre-oxidized vanadium-titanium magnetite concentrate was controlled by interface chemical reaction and the apparent activation energy was 67.719 k J/mol. The mineral phase transformation during the reduction process can be described as follows： pre-oxidized vanadium-titanium magnetite concentrate → ulvospinel → ilmenite → Fe Ti2O5 →（FenTi1-n）Ti2O5. M3O5-type（M can be Fe, Ti, Mg, Mn, etc） solid solutions would be formed during the reduction process of the pre-oxidized vanadium-titanium magnetite concentrate at 1050 °C for 60 min. The poor reducibility of iron in M3O5 solid solutions is the main reason to limit the reduction property of pre-oxidized vanadium-titanium magnetite concentrate.展开更多
Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina productio...Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production.The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation.The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution.The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration,suggesting that Fe（OH）3- and Fe（OH）4- form by dissolving Fe and Fe2O3,respectively,in alkaline aqueous solution and further react to form Fe3O4.Moreover,aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution,and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.展开更多
Stable colloidal suspension of magnetite/starch nanocomposite was prepared by a facile and aqueous-based chemical precipitation method, Magnetite/carbon nanocomposite thin films were subsequently formed upon carboniza...Stable colloidal suspension of magnetite/starch nanocomposite was prepared by a facile and aqueous-based chemical precipitation method, Magnetite/carbon nanocomposite thin films were subsequently formed upon carbonization of the starch component by heat treatment under controlled conditions. The initial content of native sago starch as the carbon source was found to affect the microstructure and electrochemical properties of the resulted magnetite/carbon nanocomposite thin films, A specific capacitance of 124 F/g was achieved for the magnetite/carbon nanocomposite thin films as compared to that of 82 F/g for pure magnetite thin films in Na2SO4 aqueous electrolyte.展开更多
By means of isothermal oxidation and chemical analysis, great importance was attached to the parameters that made effects on the oxidation degree of vanadium, titanium-bearing magnetite pellet in high-temperature proc...By means of isothermal oxidation and chemical analysis, great importance was attached to the parameters that made effects on the oxidation degree of vanadium, titanium-bearing magnetite pellet in high-temperature processing （1 073- 1 323 K）. Based on the experimental data, oxidation kinetics of pellet was analyzed according to shrinking unreacted-core model subsequently. Experiment results display that the oxidation degree of pellet increases with increasing of oxidation time, oxidation temperature and oxygen content, as well as shrinking of pellet diameter. Under the condition of oxidation time 20 min, oxidation temperature 1223 K, oxygen content 15%, and pellet diameter 12 mm, oxidation degree of pellet reaches 92.92%. The analysis of oxidation kinetics indicates that oxidation process of pellet is controlled by chemical reaction with activation energy 68.64 kJ/mol at a relatively lower temperature （1073-1 173 K）. Oxidation process of pellet is mixed-controlled by chemistry reaction and diffusion with activation energy 39.66 kJ/mol in the temperature range of 1 173-1 273 K. When oxidation temperature is higher than 1 273 K, the limited link of oxidation reaction is the diffusion control with the activation energy 20.85 kJ/mol. These results can serve as a reference to the production of vanadium, titanium-hearing magnetite pellet.展开更多
The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chro- mium-bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO c...The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chro- mium-bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening-melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%-3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening-melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO con- tents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium-titanium magnetite in a blast furnace.展开更多
Western Australian magnetite concentrates normally have ultrafine granularity and much higher specific surface areas than Chinese magnetite concentrates owing to the significant pre-grinding and beneficiation for sale...Western Australian magnetite concentrates normally have ultrafine granularity and much higher specific surface areas than Chinese magnetite concentrates owing to the significant pre-grinding and beneficiation for saleable iron grade. Such characteristics will inevitably affect the subsequent pelletization process. However, very few investi- gations have been done before. Thus, the oxidation and induration characteristics of pellet made from a Western Aus- tralian ultrafine magnetite concentrate were revealed by conducting routine preheating-roasting tests in an electric tube furnace and investigating the microstructure of fired pellets under an optical microscope in comparison with that of pellets made from typical Chinese magnetite concentrate. The liquidus regions of CaO-SiO2-Fe2O3 and CaO-SiO2- Al2O3 ternary systems in air at various temperatures were calculated by FactSage software to explain the importance of liquid phase in the consolidation of fired pellets. The results show that pellet made from ultrafine magnetite con- centrate possesses better oxidability and preheating performance than that made from Chinese magnetite concentrate. However, it has inferior roasting performance, usually requiring conditions of roasting at 1280℃ for at least 30 rain to acquire sufficiently high compressive strength, which are attributed to higher temperature sensitivity caused by its smaller particle size and less formation of liquid phase because of low impurities like CaO and Al2O3 in raw materials. Correspondingly, its roasting performanee can be significantly improved by blending with Chinese magnetite concen- trates or increasing the pellet basicity （WCaO/WSiO2）. By comprehensive evaluation, blending with Chinese iron ore concentrates is an appropriate way to utilize Western Australia ultrafine magnetite concentrates.展开更多
文摘Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the lack of sufficient research regarding the resistance of functionally graded fiber-reinforced concrete against projectile impacts has resulted in a limited understanding of the performance of this concrete type,which is necessary for the design and construction of structures requiring great resistance against external threats.Here,the performance of functionally graded fiber-reinforced concrete against projectile impacts was investigated experimentally using a(two-stage light)gas gun and a drop weight testing machine.For this objective,12 mix designs,with which 35 cylindrical specimens and 30 slab specimens were made,were prepared,and the main variables were the magnetite aggregate vol%(55%)replacing natural coarse aggregate,steel fiber vol%,and steel fiber type(3D and 5D).The fibers were added at six vol%of 0%,0.5%,0.75%,1%,1.25%,and 1.5%in 10 specimen series(three identical specimens per each series)with dimensions of 40×40×7.5 cm and functional grading(three layers),and the manufactured specimens were subjected to the drop weight impact and projectile penetration tests by the drop weight testing machine and gas gun,respectively,to assess their performance.Parameters under study included the compressive strength,destruction level,and penetration depth.The experimental results demonstrate that using the magnetite aggregate instead of the natural coarse aggregate elevated the compressive strength of the concrete by 61%.In the tests by the drop weight machine,it was observed that by increasing the total vol%of the fibers,especially by increasing the fiber content in the outer layers(impact surface),the cracking resistance and energy absorption increased by around 100%.Note that the fiber geometry had little effect on the energy absorption in the drop weight test.Investigating the optimum specimens showed that using 3D steel fibers at a total fiber content of 1 vol%,consisting of a layered grading of 1.5 vol%,0 vol%,and 1.5 vol%,improved the penetration depth by 76%and lowered the destruction level by 85%.In addition,incorporating the 5D steel fibers at a total fiber content of 1 vol%,consisting of the layered fiber contents of 1.5%,0%,and 1.5%,improved the projectile penetration depth by 50%and lowered the damage level by 61%compared with the case of using the 3D fibers.
基金funded by the National Natural Science Foundation of China(Nos.U20A20145,51774205)the Open Project from Engineering Research Center of the Ministry of Education,Sichuan University,China.
文摘An approach for coal-based direct reduction of vanadium−titanium magnetite(VTM)raw ore was proposed.Under the optimal reduction conditions with reduction temperature of 1140℃,reduction time of 3 h,C-to-Fe molar ratio of 1.2꞉1,and pre-oxidation temperature of 900℃,the iron metallization degree is 97.8%.Ultimately,magnetic separation yields an iron concentrate with an Fe content of 76.78 wt.%and efficiency of 93.41%,while the magnetic separation slag has a Ti grade and recovery of 9.36 wt.%and 87.07%,respectively,with a titanium loss of 12.93%.This new strategy eliminates the beneficiation process of VTM raw ore,effectively reduces the Ti content in the iron concentrate,and improves the comprehensive utilization of valuable metals.
基金supported by National Natural Science Foundation of China(No.52204302)Young Elite Scientist Sponsorship Program by CAST(No.YESS20220533)Hunan Provincial Natural Science Foundation of China(No.2022JJ40625).
文摘The isothermal oxidation kinetics of vanadium–titanium magnetite(VTM)pellets prepared with 3Co-binder(coal-based colloidal composite binder)and F-binder(pulverized Funa binder)are compared.The oxidation process was analyzed using the first-order irreversible reaction,following the shrinking unreacted nucleus model.The results demonstrate that VTM pellets prepared with 3Co-binder exhibit a faster oxidation rate than those with F-binder across the temperatures ranging from 1073 to 1473 K.In both cases,the oxidation process was controlled by an interfacial chemical reaction during the pre-oxidation stage and by internal diffusion during the mid-oxidation stage.The type of binder did not influence the primary oxidation control mechanism of the VTM pellets.However,the apparent rate constants in the pre-oxidation stage and the internal diffusion coefficients in the mid-oxidation stage were higher for pellets with 3Co-binder compared to those with F-binder.The apparent activation energies for the 3Co-binder pellets were similar to those of bentonite,indicating favorable kinetic conditions without negative impacts on the oxidation process.Nonetheless,it is important to note that pellets with F-binder required a longer oxidation time than those with 3Co-binder.
基金supported by the National Natural Science Foundation of China(No.52204302)Young Elite Scientist Sponsorship Program by CAST(No.YESS20220533)+1 种基金Hunan Provincial Natural Science Foundation of China(No.2022JJ50274)China Baowu Low Carbon Metallurgy Innovation Foundation(No.BWLCF202103).
文摘The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through linear fitting to the kinetic equations based on the shrinking unreacted-core model. The results reveal that VTM pellets undergo oxidation in three distinct phases: pre-oxidation, mid-oxidation, and final stable phase. Notably, the mid-oxidation phase is absent in magnetite oxidation. The shrinking unreacted-core model has been proven to be suitable for modeling the process of oxidizing VTM pellets. In the pre-oxidation stage, the rate-controlling step is determined by both the oxidation temperature and the effective oxygen concentration. The influence of the effective oxygen concentration on the rate of oxidation is more pronounced at temperatures between 1073 and 1273 K, especially when the oxygen content falls below 15 vol.%. For the production of oxidized VTM pellets, it is necessary to maintain a preheating temperature above 1173 K (to accelerate the oxidation reaction) and below 1473 K (to prevent the swift formation of compact Fe2TiO5 at the shell of the pellet) in an oxygen-enriched atmosphere.
基金financially supported by the Heilongjiang Provincial Key R&D Program Project(No.GA21A204)Heilongjiang Provincial Natural Science Foundation of China(No.LH2022D031)the Research Project of Heilongjiang Province Bureau of Geology and Mineral Resources(No.HKY202302).
文摘Although previous researchers have attempted to decipher ore genesis and mineralization in the Erdaokan Ag-Pb-Zn deposit,some uncertainties regarding the mineralization process and evolution of both ore-forming fluids and magnetite types still need to be addressed.In this study,we obtained new EPMA,LA-ICP-MS,and in situ Fe isotope data from magnetite from the Erdaokan deposit,in order to better understand the mineralization mechanism and evolution of both magnetite and the ore-forming fluids.Our results identified seven types of magnetite at Erdaokan:disseminated magnetite(Mag1),coarse-grained magnetite(Mag2a),radial magnetite(Mag2b),fragmented fine-grained magnetite(Mag2c),vermicular gel magnetite(Mag3a1 and Mag3a2),colloidal magnetite(Mag3b)and dark gray magnetite(Mag4).All of the magnetite types were hydrothermal in origin and generally low in Ti(<400 ppm)and Ni(<800 ppm),while being enriched in light Fe isotopes(δ^(56)Fe ranging from−1.54‰to−0.06‰).However,they exhibit different geochemical signatures and are thus classified into high-manganese magnetite(Mag1,MnO>5 wt%),low-silicon magnetite(Mag2a-c,SiO_(2)<1 wt%),high-silicon magnetite(Mag3a-b,SiO_(2)from 1 to 7 wt%)and high-silicon-manganese magnetite(Mag4,SiO_(2)>1 wt%,MnO>0.2 wt%),each being formed within distinct hydrothermal environments.Based on mineralogy,elemental geochemistry,Fe isotopes,temperature trends,TMg-mag and(Ti+V)vs.(Al+Mn)diagrams,we propose that the Erdaokan Ag-Pb-Zn deposit underwent multi-stage mineralization,which can be broken down into four stages and nine sub-stages.Mag1,Mag2a-c,Mag3a-b and Mag4 were formed during the first sub-stage of each of the four stages,respectively.Additionally,fluid mixing,cooling and depressurization boiling were identified as the main mechanisms for mineral precipitation.The enrichment of Ag was significantly enhanced by the superposition of multi-stage ore-forming hydrothermal fluids in the Erdaokan Ag-Pb-Zn deposit.
基金supported by the National Natural Science Foundation of China(U1908225)the Fundamental Research Funds for Central Universities(N2225012 and N232405-06).
文摘In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were investigated using kinetic empirical equation by fitting and combining with X-ray diffraction,X-ray fluorescence,scanning electron microscopy,energy-dispersive spectrometry,and optical microscopy.The results show that iron reduction is controlled by the mass transfer process of(FeOx)in the slag,while vanadium reduction is controlled by both the mass transfer of(VOx)in the slag and the mass transfer of[V]in the molten iron,and the slag–metal interfacial reaction is the only pathway for vanadium reduction.The reduction of iron and vanadium is an obvious first-order reaction,with activation energy of 101.6051 and 197.416 kJ mol^(−1),respectively.Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency.The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe_(2)O_(3)→Fe_(3)O_(4)/FeV_(2)O_(4)→FeTiO_(3) and FeV_(2)O_(4)→MgV_(2)O_(5);titanium in slag is mainly in the form of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and CaTiO_(3).As the reaction time went on,the molar ratio(nTi/nMg)in Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and the Ti2O_(3) content in the slag gradually went up,while the area proportion of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)went up and then down,and the porosity of the slag and the grain size of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)got smaller.
文摘JC Pura schist belt has gained scope recently with reports of nickel, magnetite, PGEs, and traces of gold. The layered sill in the schist belt is a linear patch of ultramafic sequences (peridotite and pyroxenite) with metamorphogenic magnetite mineralization. The metamorphogenic magnetite appears as interbands in layered sequences and as veins in serpentinite. The present study focuses on understanding the characteristics of metamorphogenic magnetite by petrographic and EPMA analysis. The study found that the precursor chromite grains are transformed into Cr-magnetite and magnetite in the spinel transformation system due to metamorphism and hydrothermal alteration. The Cr, Mg, Al, and Ni are depleted during transformation, and Fe is enriched. The Cr-magnetite appears homogenous in the vein due to serpentinization, indicating prograde greenschist to amphibolite facies metamorphism, and the area has suffered an episodic metamorphic process. The results of Cr-magnetite cation proportions of Cr fall within ishkulite variety data range of 0.10 - 0.50 apfu (atoms per formula unit). Cr-magnetite variety Ishkulite represents an additional miscibility gap in the Cr-Fe3+ transformation series other than ferrite chromite and chrome magnetite. The transformation process primarily involves the oxidation of chromium and the reduction of iron. The oxidation of chromite by highly oxidizing fluids with increasing pressure and temperature alters to Cr-magnetite, where chromium in the +3 state oxidizes to the +6 state, forming soluble chromate ions and diffusing with Fe3+. Then, it transforms into magnetite due to reducing conditions. Cr-magnetite vein indicates the potential for chromite deposits in the area, and hydrothermal altered magnetites could be a source for hosting valuable precious metals like gold and PGEs. Further investigations are needed to assess the mineralization potential and its extent.
基金supported by the National Natural Science Foundation of China (Nos.52174277 and 52204309)the China Postdoctoral Science Foundation (No.2022M720683).
文摘High-chromium vanadium-titanium magnetite(HVTM)is a crucial polymetallic-associated resource to be developed.The allpellet operation is a blast furnace trend that aims to reduce carbon dioxide emissions in the future.By referencing the production data of vanadium-titanium magnetite blast furnaces,this study explored the softening-melting behavior of high-chromium vanadium-titanium magnetite and obtained the optimal integrated burden based on flux pellets.The results show that the burden with a composition of 70wt%flux pellets and 30wt%acid pellets exhibits the best softening-melting properties.In comparison to that of the single burden,the softening-melting characteristic temperature of this burden composition was higher.The melting interval first increased from 307 to 362℃and then decreased to 282℃.The maximum pressure drop(ΔPmax)decreased from 26.76 to 19.01 kPa.The permeability index(S)dropped from 4643.5 to 2446.8 kPa·℃.The softening-melting properties of the integrated burden were apparently improved.The acid pellets played a role in withstanding load during the softening process.The flux pellets in the integrated burden exhibited a higher slag melting point,which increased the melting temperature during the melting process.The slag homogeneity and the TiC produced by over-reduction led to the gas permeability deterioration of the single burden.The segregation of the flux and acid pellets in the HVTM proportion and basicity mainly led to the better softening-melting properties of the integrated burden.
基金supported by the National Natural Science Foundation of China(No.52004339)the Key Research and Development Project of Hunan Province,China(No.2022SK2075)+1 种基金China Baowu Low Carbon Metallurgy Innovation Foudation(BWLCF_(2)02216)the Open Sharing Fund for the Large-Scale Instruments and Equipment of Central South University(CSUZC202207).
文摘The effect of alumina occurrence form on the metallurgical properties of both hematite and magnetite pellets was investigated at the same Al_(2)O level of 2 wt.%,including reduction index(RI),low-temperature reduction disintegration index(RDI),reduction swelling index(RSI),and high-temperature softening-dripping performance.The mineralogy of fired pellets was also studied to reveal the influence of alumina occurrence form on the phase composition and microstructure.From the results,the alumina occurrence form presents tremendous impacts on the metallurgical perfor-mance of both magnetite and hematite pellets.Addition of all alumina occurrence forms contributes to inferior reducibility of pellets,especially in the case of gibbsite for magnetite pellets with a RI of 58.4%and kaolinite for hematite pellets with a RI of 56.8%.However,addition of all alumina occurrence forms improves the RDI of magnetite pellets,while there is no significant difference among various alumina occurrence forms.In contrast,alumina occurrence forms have little influence on the RDI of hematite pellets.The presence of free alumina,gibbsite,and kaolinite tends to improve the RSI of hematite and magnetite pellets,whereas hercynite gives the opposite trend with a RSI of 25.6%.For softening-dripping performance of magnetite pellets,all alumina occurrence forms contribute to narrower softening-melting interval.Meanwhile,alumina,gibbsite,and kaolinite give narrower softening-dripping interval,at 229,217,and 88℃,respectively,whereas addition of hercynite results in the largest melting range at 276℃ due to its high melting point.Regarding hematite pellets,free alumina,gibbsite,and hercynite tend to enlarge melting range,whereas kaolinite contributes to lower dripping temperature of 1148℃ and narrow softening-dripping interval of 88℃ due to the formation of a greater amount of slag phase at high temperatures.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDC04010100)National Key Research and Development Program of China(Grant No.2018YFC1900500)+1 种基金the Special Project for Transformation of Major Technological Achievements in Hebei Province(Grant No.19044012Z)the Science and Technology Program of Hengshui(Grant No.2020016004B).
文摘The sodium smelting of vanadium-titanium magnetite can achieve the comprehensive utilization of Fe,V,and Ti.However,the generation of alkaline slag during this process may cause damage to refractory materials.The wettability and corrosion behavior of alkaline slag on three types of refractory(MgO-C,SiC,and high alumina refractory)substrates were investigated at temperatures up to 1200℃.The effects of duration on the wettability of molten slag on SiC substrates were also investigated.Results showed that the high alumina refractory exhibited better wettability with the molten slag than the others,and thus,it is easier to be corroded.The results of scanning electron microscopy coupled with energy dispersive spectroscopy showed that MgO-C and high alumina refractory substrates were severely eroded.There was a visible and regular interfacial reaction layer between the slag and SiC refractory substrate,which was produced by the redox reaction between the metal oxides in the slag and the SiC refractory substrate.With the increase in holding time,the interface layer expands and silico-ferrite phases are generated at the interface.The redox reaction between Fe_(2)O_(3) and SiC substrate is the main reason for the corrosion.By comparing the differences in wettability and corrosion behavior between the alkaline slag from sodium smelting of vanadium-titanium magnetite and MgO-C,SiC and high alumina refractories,it is concluded that SiC refractory has good corrosion resistance to the slag.Iron oxides in the slag accelerate the oxidation rate of SiC refractory.
基金supported by the National Natural Science Foundation of China(52174291)the Beijing New-star Plan of Science and Technology(Z211100002121115)+2 种基金the Central Universities Foundation of China(06500170)the Guangdong Basic and Applied Basic Research Fund Joint Regional Funds-Youth Foundation Projects(2020A1515111008)the China Postdoctoral Science Foundation(2021M690369).
文摘To investigate the feasibility of co-sintering of fluxed iron ore with magnetite concentrates, the mineralogical properties of a novel fluxed iron ore were studied using particle size analysis, microscopic morphology characterization, and X-ray diffraction Rietveld analysis. Following that, the experiments for granulation performance and basic sintering characteristics were designed under seven different fluxed iron ore ratios, and the integrated ranking of different fluxed iron ore ratios was determined using gray relation analysis. Finally, the results of the industrial trails were combined with the feasibility analysis. Test and experimental results show that the fraction of the fluxed iron ore particles larger than 0.5 mm can account for more than 48%, and the particles have two morphologies: spherical-rough and flaky-smooth. Ca elements are found in the form of calcite (CaCO3) and dolomite (CaMg(CO3)2). The average particle size of granules and powder removal rate can be improved from 2.50 to 3.16 mm and 39.60% to 24.20%, respectively, with the increase in the fluxed iron ore ratio. Furthermore, the fluxed iron ore can improve assimilability and liquid fluidity of magnetite concentrates. In terms of overall granulation performance and sintering characteristics, the fluxed iron ore ratios are graded from best to worst as follows: 12%, 15%, 9%, 18%, 21%, 6% and 3%. The industrial trails show that when the fluxed iron ore ratio is increased, the beneficial effect of the superior sintering characteristics of the fluxed iron ore itself is ideally balanced with the negative effect of the lower amount of additional CaO at 12% ratio, and thus, it is feasible to bring the fluxed iron ore into production at a level of roughly 12%.
基金financially supported by the CAS Hundred Talents Program to Xiao-Wen Huangthe National Natural Science Foundation of China(No.42173070)the Special Fund of the State Key Laboratory of Ore Deposit Geochemistry(No.202101)。
文摘Magnetite from hydrothermal deposits may show compositional zoning with various mineral inclusions in response to the evolution of hydrothermal fluids.Magnetite from the Fenghuangshan Cu-Fe-Au skarn deposit(eastern China)is a common mineral formed in the earlier stage of skarnization.Magnetite grains have dark gray and light gray zones and contain diverse mineral inclusions.Dark gray zones have higher Si,Ca,Al,and Mg contents than light gray zones.The magnetite matrix from dark gray zones shows superstructure along the[0-11]zone axis in fast Fourier transform patterns,different from magnetite in light gray zones with normal structure.Three types of mineral inclusions are identified within magnetite:nano-,micron-and submicron-nanometer inclusions.Nanoinclusions hosted in dark gray zones are actinolite,diopside,and trace element-rich magnetite,and these are likely formed by growth entrapment during magnetite crystallization at the skarn stage.The chainwidth order-disorder intergrowths of diopside nanoinclusion likely indicate fluctuating fluid compositions in a lattice scale.Submicron to nanometer inclusions at the boundary between dark gray and light gray zones are quartz,titanite,and Ti-rich magnetite,which were formed via a dissolution and reprecipitation process at the quartz-sulfide stage.Micron-inclusions randomly distributed in both dark and light gray zones include calcite,ankerite,quartz,and chlorite,and these were formed via penetration of fluids at the carbonate stage.Zoned magnetite was formed by fluid replacement,overgrowth,and fluid infilling.Our study highlights the importance of mineral inclusion assemblages,and textural and chemical zonation of magnetite in constraining fluid evolution.
基金financially supported by the National Natural Science Foundation of China (U1908225)the Fundamental Research Funds for Central Universities (N2225012 and N232405-06).
文摘To comprehensively utilize the low-iron high-vanadium-titanium magnetite,a new method of vortex smelting reduction of vanadium-titanium magnetite was proposed,and the enrichment and reconstitution regularity of Ti-bearing phases in the slag was investigated through X-ray fluorescence spectrometry,X-ray photoelectron spectroscopy,X-ray diffraction analysis,and optical microscopy.The phase diagram revealed that the preferential crystallization of MgTi_(2)O_(5) can be achieved by adjusting the CaO,MgO,and TiO_(2) contents of slag.The predominant Ti-bearing phases in the slag obtained from the reduction process are MgxTi_(3_x)O_(5)(0≤x≤1)and CaTiO_(3).FeTiO_(3) is present at carbon-iron ratio(CR)=1.3,while MgTi_(2)O4 and TiC are formed at CR=1.3.The enrichment of TiO_(2) in the slag increases first and then decreases as the CR increases,and at CR=1.1,the enrichment of TiO_(2) in the slag reaches 51.3 wt.%.Additionally,the concentrations of MgxTi_(3_x)O_(5)(0≤x≤1)and CaTiO_(3) in the slag,along with the grain width of MgxTi_(3_x)O_(5)(0≤x≤1),decrease with the increase in CR.
基金Projects(2012AA062302,2012AA062304) supported by the National High Technology Research and Development Program of China(863 Program)Projects(51090384,51174051) supported by the National Natural Science Foundation of ChinaProject(2012DFR60210) supported by the International Cooperation of Ministry of China
文摘Basicity has an important effect on the sinter quality, especially for low-titanium vanadium-titanium sinter. The effect of basieity on sintering behavior of low-titanium vanadium-titanium mixture, and the transference and distribution of element in sintering process were researched by sinter pot test, mineralogical analysis, scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） analysis. The results show that CaO preferentially reacts with TiO2, generating pervoskite, so that the total liquid phase content of the sinter is low. There is an increase in the perovskite concentration of the sinter with the basicity ranging from 1.9：1 to 2.7：1. With increasing the basicity, the calcium ferrite content increases slightly and then rises rapidly, while the silicate content decreases and the metallurgical property of the sinter is improved. As for the distribution of these elements in the sinter, Ti occurs mainly in perovskite, V occurs mainly in silicate, and Fe occurs mainly in magnetite and hematite. The most abundant occurrence of Ca and Si occurs in silicate and perovskite. With increasing the basicity, the contents of A1 and Mg increase in calcium ferrite, while they decrease in other minerals.
基金Project(NCET-10-0834)supported by the Program for New Century Excellent Talents in University,China
文摘The solid-state reduction kinetics of pre-oxidized vanadium-titanium magnetite concentrate was studied. The phase and microstructure of the reduction product were characterized by XRD, SEM and EDS methods, based on which the mechanism of the solid-state reduction was investigated. The results showed that using coal as reductant at 950-1100 °C, the solid-state reduction of the pre-oxidized vanadium-titanium magnetite concentrate was controlled by interface chemical reaction and the apparent activation energy was 67.719 k J/mol. The mineral phase transformation during the reduction process can be described as follows： pre-oxidized vanadium-titanium magnetite concentrate → ulvospinel → ilmenite → Fe Ti2O5 →（FenTi1-n）Ti2O5. M3O5-type（M can be Fe, Ti, Mg, Mn, etc） solid solutions would be formed during the reduction process of the pre-oxidized vanadium-titanium magnetite concentrate at 1050 °C for 60 min. The poor reducibility of iron in M3O5 solid solutions is the main reason to limit the reduction property of pre-oxidized vanadium-titanium magnetite concentrate.
基金Project(51374239)supported by the National Natural Science Foundation of China
文摘Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production.The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation.The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution.The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration,suggesting that Fe（OH）3- and Fe（OH）4- form by dissolving Fe and Fe2O3,respectively,in alkaline aqueous solution and further react to form Fe3O4.Moreover,aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution,and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.
基金supported by Universiti Malaysia Sarawak (UNIMAS) through the award of a special fundamental research grant 01(K03)/557/2005(56)
文摘Stable colloidal suspension of magnetite/starch nanocomposite was prepared by a facile and aqueous-based chemical precipitation method, Magnetite/carbon nanocomposite thin films were subsequently formed upon carbonization of the starch component by heat treatment under controlled conditions. The initial content of native sago starch as the carbon source was found to affect the microstructure and electrochemical properties of the resulted magnetite/carbon nanocomposite thin films, A specific capacitance of 124 F/g was achieved for the magnetite/carbon nanocomposite thin films as compared to that of 82 F/g for pure magnetite thin films in Na2SO4 aqueous electrolyte.
基金Item Sponsored by National Science Fund for Distinguished Young Scholars of China(50725416)National Natural Science Foundation of China(50804059)+1 种基金National Key Programof Science and Technology of China(2008BAB32B06)Graduate Degree Thesis Innovation Foundation of Hunan Province and Central South University of China(1960-71131100053)
文摘By means of isothermal oxidation and chemical analysis, great importance was attached to the parameters that made effects on the oxidation degree of vanadium, titanium-bearing magnetite pellet in high-temperature processing （1 073- 1 323 K）. Based on the experimental data, oxidation kinetics of pellet was analyzed according to shrinking unreacted-core model subsequently. Experiment results display that the oxidation degree of pellet increases with increasing of oxidation time, oxidation temperature and oxygen content, as well as shrinking of pellet diameter. Under the condition of oxidation time 20 min, oxidation temperature 1223 K, oxygen content 15%, and pellet diameter 12 mm, oxidation degree of pellet reaches 92.92%. The analysis of oxidation kinetics indicates that oxidation process of pellet is controlled by chemical reaction with activation energy 68.64 kJ/mol at a relatively lower temperature （1073-1 173 K）. Oxidation process of pellet is mixed-controlled by chemistry reaction and diffusion with activation energy 39.66 kJ/mol in the temperature range of 1 173-1 273 K. When oxidation temperature is higher than 1 273 K, the limited link of oxidation reaction is the diffusion control with the activation energy 20.85 kJ/mol. These results can serve as a reference to the production of vanadium, titanium-hearing magnetite pellet.
基金the National Natural Science Foundation of China (51574067)the National High Technology Research and Development Program of China (2012AA062302 and 2012AA062304)the Fundamental Research Funds for the Central Universities of China (N110202001)
文摘The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chro- mium-bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening-melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%-3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening-melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO con- tents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium-titanium magnetite in a blast furnace.
基金supported by Hunan Provincial Co-innovation Center for Clean and Efficient Utilization of Strategic Metal Mineral Resources
文摘Western Australian magnetite concentrates normally have ultrafine granularity and much higher specific surface areas than Chinese magnetite concentrates owing to the significant pre-grinding and beneficiation for saleable iron grade. Such characteristics will inevitably affect the subsequent pelletization process. However, very few investi- gations have been done before. Thus, the oxidation and induration characteristics of pellet made from a Western Aus- tralian ultrafine magnetite concentrate were revealed by conducting routine preheating-roasting tests in an electric tube furnace and investigating the microstructure of fired pellets under an optical microscope in comparison with that of pellets made from typical Chinese magnetite concentrate. The liquidus regions of CaO-SiO2-Fe2O3 and CaO-SiO2- Al2O3 ternary systems in air at various temperatures were calculated by FactSage software to explain the importance of liquid phase in the consolidation of fired pellets. The results show that pellet made from ultrafine magnetite con- centrate possesses better oxidability and preheating performance than that made from Chinese magnetite concentrate. However, it has inferior roasting performance, usually requiring conditions of roasting at 1280℃ for at least 30 rain to acquire sufficiently high compressive strength, which are attributed to higher temperature sensitivity caused by its smaller particle size and less formation of liquid phase because of low impurities like CaO and Al2O3 in raw materials. Correspondingly, its roasting performanee can be significantly improved by blending with Chinese magnetite concen- trates or increasing the pellet basicity （WCaO/WSiO2）. By comprehensive evaluation, blending with Chinese iron ore concentrates is an appropriate way to utilize Western Australia ultrafine magnetite concentrates.
