High-chromium Vanadium Titanium Magnetite Research Articles

High-chromium vanadium–titanium magnetite all-pellet integrated burden optimization and softening–melting behavior based on flux pellets

High-chromium vanadium–titanium magnetite all-pellet integrated burden optimization and softening–melting behavior based on flux pellets

Effects of Cr2O3 on Metallurgical Properties of High Chromium Vanadium-Titanium Magnetite Flux Pellets

Effects of Cr2O3 on Metallurgical Properties of High Chromium Vanadium-Titanium Magnetite Flux Pellets

Softening-melting Properties of High-chromium Vanadium–titanium Magnetite Pellets with Different Basicity

Softening-melting Properties of High-chromium Vanadium–titanium Magnetite Pellets with Different Basicity

Reducibility Optimization and Reaction Mechanism of High-Chromium Vanadium–Titanium Magnetite Flux Pellets

Reducibility Optimization and Reaction Mechanism of High-Chromium Vanadium–Titanium Magnetite Flux Pellets

Kinetics and mechanism of coal-based direct reduction of high-chromium vanadium–titanium magnetite

Kinetics and mechanism of coal-based direct reduction of high-chromium vanadium–titanium magnetite

Pre-reduction of carbon-containing pellets of high chromium vanadium–titanium magnetite at different temperatures

Abstract The effect of temperature on phase transformation, metallization rate, carbon residue and agglomeration of metal Fe after the pre-reduction of carbon-containing pellets in high-chromium vanadium–titanium magnetite (HCVTM) was investigated. The results indicated that titanomagnetite was finally reduced to metal Fe and (Mg, Fe)Ti2O5 without low valence titanium oxide with increasing pre-reduction temperature from 950 to 1,250℃; Vanadium magnetite produces Fe, VO and VC0.88 without V, and chromite magnetite produces Fe, Cr2O3, CrC x and a small amount of Cr. With an increase in the pre-reduction temperature, the metallization rate in the metallized pellets gradually increases, while the content of the residual carbon gradually decreases. Meanwhile, the iron particles precipitated on the surface of ore particles begin to soften into strips and finally agglomerate to form spherical iron particles, which leads to the diameter of iron particles increasing from 8.23 to 182.35 μm. When the pre-reduction temperature is 1,250℃, the maximum metallization rate in the metallized pellets is 92.49 wt% and the minimum content of residual carbon is 10.37 wt%.

Effects of extracted-vanadium residue and MgO on the basic sintering characteristics of high-chromium vanadium–titanium magnetite

Extracted-vanadium residue (EVR), formed during the smelting and extraction of High-chromium vanadium-titanium magnetite (HCVTM), should be used cyclically, and its use as a sintering material to prepare sinters for blast-furnace smelting is a viable option. The effects of EVR and MgO on the fundamental sintering characteristics of HCVTM, such as assimilative temperature, liquid phase fluidity index, adhesive phase strength, and crystal stock consolidation strength, were studied using X-ray diffraction and scanning electron microscopy, as well as phase composition analysis and microstructure analysis. The assimilative temperature (the lowest reaction temperature between sintering materials and CaO) of HCVTM by adding 0–8 wt% EVR decreased. The liquid phase fluidity index of HCVTM with six wt% EVR is best. The adhesive phase strength decreased from 1162 to 356 N. However, the crystal stock consolidation strength increased to the highest value of 2170 N by adding six wt% EVR. Based on the primary sintering characteristics effect of EVR on HCVTM, the optimum EVR amount is six wt%. After adopting the six wt% EVR added HCVTM with relatively good properties, the assimilative temperature of mixed ores increased from 1290 to 1320 °C with MgO added percent of 0–3 wt%. The liquid phase fluidity index decreased as a whole from 0.88 to 0.796–0.828, and the crystal stock consolidation strength also reduced from 2170 to 1090 N, indicating that both the liquid phase fluidity index and the crystal stock consolidation strength have changed slightly as a result of the addition of >1% MgO. However, adding 1% MgO improved the adhesive phase strength to a high value. The perovskite formation is restrained as Ti4+ diffuses into the liquid phase with the increase of MgO. Based on the effect of the fundamental sintering characteristics of EVR and MgO on HCVTM, a sintering blending ratio of 6 wt% EVR and one wt% MgO is recommended.

Interdiffusion kinetics and solid-state reaction mechanism between Cr2O3 and calcium ferrite based on diffusion couple method

The presence of Cr2O3 was found to reduce the quality of sinter from high-chromium vanadium-titanium magnetite obtained by a blast furnace-basic oxygen furnace process. The kinetics and reaction mechanism of the solid-state reaction between Cr2O3 and calcium ferrite (CF) were studied by a diffusion couple method. The phase of the product and the change in the concentration of Ca and Cr across the diffusion layers were analyzed by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). Based on the concentration profile of Cr element, the interdiffusion coefficient in different stages of the Cr2O3-calcium ferrite system which were affected by temperature and atmosphere were calculated by the Wagner method. The results indicated that the interdiffusion coefficient increases from 1373 K to 1473 K. The interdiffusion coefficient in the diffusion product (CaCr2O4) layer was the largest. At 1373–1473 K, the interdiffusion coefficient of the system was in the order of 10-12~10-10 cm2/s in air. The diffusion activation energy ED in air ranged from 25.78 kJ/mol to 123.26 kJ/mol.The thickness of the product layer and the interdiffusion coefficient in N2 were smaller than those in air. A hypothesis in which oxygen participates in the mass transfer is proposed.

Isothermal reduction behavior and kinetics of Russian high-chromium vanadium-titanium magnetite pellets under gas atmospheres of CO–CO2–N2 and CO–N2 at 873 K–1173 K

ABSTRACT In this paper, detailed investigations on the reduction characteristics and kinetics mechanism of Russian high-chromium vanadium–titanium magnetite pellets under gas atmospheres of CO–CO2–N2 and CO–N2 at 873 K–1173 K were made, and comparisons of the atmospheres were researched. It was found that the reduction temperature and gas atmosphere have great effects on pellet reduction at this temperature range, and the reverse reduction appeared uniquely for some time after 2 h reduction in the CO2-bearing gas atmosphere. The reduction was further researched with crushing strength tests, X-ray diffraction (XRD) patterns, and SEM microscopic examination, and results showed that the cause of the change in crushing strength, the phase transformation patterns, and microstructures were consistent across both atmospheres. For the CO–CO2–N2 gas atmosphere, the controlling step was predominantly the interfacial chemical reaction with the reaction activation value of 38.01 kJ/mol at the initial stage. This gradually became mixed control of the interfacial chemical reaction and gas internal diffusion through the solid product layer, with the reduction proceeding with 23.55 kJ/mol before 120 min. However, the controlling step became irregular after 120 min. For the CO–N2 gas atmosphere, the rate controlling step was predominantly the interfacial chemical reaction with 31.41–38.27 kJ/mol at the initial stage, after which the rate controlling mechanism was the mixed control with 17.97–19.33 kJ/mol until 180 min mark.

Effect of Basicity on Sintering Behavior and Metallurgical Properties of High-Chromium Vanadium-Titanium Magnetite

Basicity has an important effect on the behavior of high-chromium vanadium-titanium magnetite (HCVTM) sinter. The effect of basicity on sintering, reduction, and softening-melting properties was investigated in an experiment-scale sinter pot. The results showed that with the basicity increasing from 1.7 to 2.5, the vertical sinter speed, the productivity, the particle size, the reduction disintegration index (RDI), and the reducibility index (RI) increased. The yield increased first and then decreased, while the tumble index (TI) had the opposite trend. The perovskite content increased first and then stabilized, and the silico-ferrite of calcium and aluminum (SFCA) increased from the basicity of 2.3. The HCVTM sinter had a better tendency of the softening behavior with the basicity increase. In addition, the melt droplet comprehensive index S increased, which indicated that the increase in basicity negatively affected the droplet performance. As the basicity increased, the comprehensive index value increased. Considering the adverse effect of basicity on softening-melting properties, the best recommended value is 2.3.

Observation of diffusion behavior between Cr2O3 and calcium ferrite based on diffusion couple method at 1373 K

The existence of Cr2O3 has an effect on the quality of high-chromium vanadium-titanium magnetite sinter. In order to investigate the influence of Cr2O3 on the quality of sinter in the solid-phase reaction stage of sintering process, the solid-phase reactions of Cr2O3-calcium ferrite (CF) system at 1373 K in air at different times were studied by diffusion couple method. The change of diffusion interface and the migration of Ca, Cr and Fe were observed by emission scanning electron microscopy. The results show that in the process of diffusion, the diffusion thickness of Ca2+ in CF layer was 10.22 μm, and that of Ca2+ in Cr2O3-CF diffusion couple was 57.65 μm at 1373 K for 8 h. The relationship between the thickness of the product layer and time at 1373 K for 0 h–20 h was obtained. The diffusion of Ca2+ to the Cr2O3 layer is the driving force of the solid phase reaction, and the diffusion of Ca2+ in the ferrite layer is the limiting link of the solid phase reaction, the order of magnitude of diffusion coefficient of Cr2O3-CF diffusion couple was 10−11 cm2 s−1. Ca2+ in calcium ferrite is likely to combine with Cr3+ to form CaCr2O4. The production of calcium ferrite will be reduced when Cr2O3 is present in sintering material. Meanwhile, the solid phase product CaCr2O4 in the diffusion process has the properties of high melting point and difficult reduction. The shortage of liquid phase due to high melting point and the difficulty in reduction may affect the quality of sinter.

Investigations of MgO on Sintering Performance and Metallurgical Property of High-Chromium Vanadium-Titanium Magnetite

High-chromium vanadium-titanium magnetite (HCVTM) in the Hongge region has been used as an essential mineral resource in ironmaking. The effects of MgO on sintering performance and metallurgical properties were investigated by sintering pot tests, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). HCVTM sinters with varying MgO contents (2.7–3.5%), which was achieved by adding dolomite, were tested for yield, strength, reduction degradation index (RDI), reduction index (RI), and softening-melting properties. The productivity and the comprehensive index were evaluated. The results show that yield and productivity increased, while the vertical sintering speed and the tumbler index (TI) initially increased then decreased with the increase of MgO content. The mineral structure of HCVTM sinter changed from a non-uniform state to a uniform state with increased MgO content. Most of the Mg2+ entered the magnetite lattice, while a small amount entered the perovskite and the calcium silicate. The increase of MgO content improved RDI and softening-melting properties while reducing RI. The best recommended amount of MgO was 3.3% from the comprehensive index.

Effect of coke breeze content on sintering mechanism and metallurgical properties of high-chromium vanadium-titanium magnetite

ABSTRACT The coke ratio has an important effect on the behaviour of high-chromium vanadium–titanium magnetite (HCVTM) sintering. The effect of coke breeze content on sintering properties and mechanism of HCVTM was investigated in an experimental-scale sintering pot. And the softening-melting test was carried out to study the metallurgical properties of sinter. The results showed that with increasing coke breeze content from 4.0% to 6.0%, the mineral phase grains of HCVTM sinter refined. Further, the mineral content of FeO, silicate, perovskite, and magnetite increased while calcium ferrite and haematite decreased. The vertical sintering speed (VSS), tumble index (TI), productivity, and reduction disintegration index (RDI) increased while yield and reducibility index (RI) of HCVTM sinter decreased, and the softening-melting behaviour of HCVTM sinter improved with the increasing of coke breeze content.

Effects of basicity and temperature on mineralogy and reduction behaviors of high-chromium vanadium-titanium magnetite sinters

The effects of basicity and temperature on the reduction process of Hongge high-chromium vanadium-titanium magnetite (HCVTM) sinter were investigated in this work. The main characterization methods of X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and metallographic microscope were employed in this study. In this work, the reduction of HCVTM sinter with different temperature and basicity were experimented. The Fe, FeO, and TiO in reductive samples increase with increasing basicity and temperatures. The increase of basicity and temperature is favorable to the reduction of HCVTM sinter. The Fe phase has out-migration tendency to the surface of sinter while the perovskite and silicate phases have in-migration tendency to the inside of sinter. The reduction degradation index (RDI) decreases while the reduction index (RI) increases with increasing basicity. The RI increases from 67.14% to 82.09% with increasing temperature from 1073 K to 1373 K.

Thermodynamic study of direct reduction of high-chromium vanadium–titanium magnetite (HCVTM) based on phase equilibrium calculation model

High-chromium vanadium–titanium magnetite (HCVTM) is a good valuable resource with high iron content in the form of complex iron ore which contains various valuable metal elements such as iron, vanadium, titanium, chromium. Direct reduction of HCVTM is studied based on thermodynamic analysis. Combined TG experimental verification and equilibrium calculation model was used to analyze the reaction sequence and equilibrium amount in this paper. The contents in HCVTM reduction system are simplified as 18 kinds of chemical compositions. Reductions of Fe3O4 and FeO·TiO2 are the main reduction reactions and are mainly reduced by C. The reduction reaction sequence of FeO·TiO2 is FeO·TiO2, TiO2, TiC, and Ti; the reduction reaction sequence of Fe3O4 is Fe3O4, FeO, and Fe. The minimum reduction temperature of HCVTM is 860 °C. The reduction of Cr is difficult to implement, and the minimum reduction temperature of V is above 700 °C. The gas phase in this system is mainly CO when the temperature is above 1000 °C. CO partial pressure curve of gasification reaction is in the shape of ‘S’ with increase of temperature. When the temperature is 1350 °C, C/O is 1.0 and reduction time is 30 min, HCVTM can be reduced thoroughly and the reduction degree can reach to 0.98. When C/O is lower than 1.0, FeTi2O5 is the reduction intermediate products from FeO·TiO2. When C/O is 1.0, diffraction peaks of Fe3O4 and FeO·TiO2 disappear, and they are reduced to Fe and TiO2.

Influence of basicity and temperature on bonding phase strength, microstructure, and mineralogy of high-chromium vanadium–titanium magnetite

To develop a smelting process for the comprehensive utilization of high-chromium vanadium−titanium magnetite (HCVTM), the micro-sinter test was applied to investigate the influence of basicity and temperature on the HCVTM sinters. The bonding phase strength (BS) was tested via an electronic universal testing machine. The phase transformations of the HCVTM sinters were detected via X-ray diffraction (XRD), whereas the structure and mineralogy of the HCVTM sinters under different temperatures and basicities were detected via scanning electron microscopy in combination with energy-dispersive spectroscopy (SEM–EDS). Our results demonstrate that the BS of the HCVTM sinters exhibits a slightly increasing tendency with an increase in temperature when the basicity is 2.4 and within the range of 2.8–4.0. Many cracks, small size crystals, and dependent phase structures are generated by increasing the sinter basicity. The BS is lower than 4000 N when the basicity is 2.2 and 2.8. When the temperature is in the range of 1280–1300°C, the BS exceeds 4000 N with the basicity of 2.0, 2.4, and 3.4–4.0. The pore size of the HCVTM sinters increases with the increase of the temperature. The perovskite decreases, whereas the silicate phase increases with basicity higher than 3.2. This study provides theoretical and technical foundations for the effective production of HCVTM sinters.

Study of the High Temperature Metallurgical Properties of On-Site Samples with Vanadium–Titanium Magnetite

In China, two typical vanadium–titanium magnetite ores were used as raw materials in iron making. In order to obtain the differences in the high temperature metallurgical properties of these ores, the phase and microstructure of on-site sinter, pellet, slag and laboratorial non-dripped slag were analyzed by XRD and SEM–EDS. The results show that the phases of two typical sinter and pellet have no significant changes, but the microstructures are different. The softening start temperature and softening zone of high chromium vanadium–titanium magnetite (HCVTM) burden are higher than ordinary vanadium–titanium magnetite (VTM) burden. The melting start temperature of HCVTM burden is higher and melting–dripping zone is smaller than VTM burden, which is beneficial to the blast furnace smelting. In addition, the calculation results using Factsage 7.0 are in accord with the experimental results. The primary crystal field of slag of HCVTM is the melilite, and the liquidus temperature is 1409.81 °C; the primary crystal field of slag of VTM is CaTiO3, and the liquidus temperature is 1418.51 °C.

Three-liquid-phase extraction and separation of V(V) and Cr(VI) from acidic leach solutions of high-chromium vanadium–titanium magnetite

Abstract A new method by liquid–liquid–liquid three phase system, consisting of acidified primary amine N1923 (abbreviated as A-N1923), poly(ethylene glycol) (PEG) and (NH4)2SO4 aqueous solution, was suggested for the separation and simultaneous extraction of V(V) and Cr(VI) from the acidic leach solutions of high-chromium vanadium–titanium magnetite. Experimental results indicated that V(V) and Cr(VI) could be selectively enriched into the A-N1923 organic top phase and PEG-rich middle phase, respectively, while Al(III) and other co-existing impurity ions, such as Si(IV), Fe(III), Ti(IV), Mg(II) and Ca(II) in acidic leach solutions, could be enriched in the (NH4)2SO4 bottom aqueous phase. During the process for extraction and separation of V(V) and Cr(VI), almost all of impurity ions could be removed. The separation factors between V(V) and Cr(VI) could reach 630 and 908, respectively in the organic top phase and PEG middle phase, and yields of recovered V(V) and Cr(VI) in the top phase and middle phase respectively were all above 90%. Various effects including aqueous pH, A-N1923 concentration, PEG added amount and (NH4)2SO4 concentration on three-phase partitioning of V(V) and Cr(VI) were discussed. It was found that the partition of Cr(VI) into the PEG-rich middle phase was driven by hydrophobic interaction, while extraction of V(V) by A-N1923 resulted of anion exchange between NO3− and H2V10O284 −. Stripping of V(V) and Cr(VI) from the top organic phase and the middle PEG-rich phase were achieved by mixing respectively with NaNO3 aqueous solutions and NaOH-(NH4)2SO4 solutions. The present work highlights a new approach for the extraction and purification of V and Cr from the complex multi-metal co-existing acidic leach solutions of high-chromium vanadium–titanium magnetite.

Effect of diboron trioxide on the crushing strength and smelting mechanism of high-chromium vanadium–titanium magnetite pellets

The effect of diboron trioxide (B2O3) on the crushing strength and smelting mechanism of high-chromium vanadium–titanium magnetite pellets was investigated in this work. The main characterization methods were X-ray fluorescence, inductively coupled plasma–atomic emission spectroscopy, mercury injection porosimetry, X-ray diffraction, metallographic microscopy, and scanning electron microscopy–energy-dispersive X-ray spectroscopy. The results showed that the crushing strength increased greatly with increasing B2O3 content and that the increase in crushing strength was strongly correlated with a decrease in porosity, the formation of liquid phases, and the growth and recrystallization consolidation of hematite crystalline grains. The smelting properties were measured under simulated blast furnace conditions; the results showed that the smelting properties within a certain B2O3 content range were improved and optimized except in the softening stage. The valuable element B was easily transformed to the slag, and this phenomenon became increasingly evident with increasing B2O3 content. The formation of Ti(C,N) was mostly avoided, and the slag and melted iron were separated well during smelting with the addition of B2O3. The size increase of the melted iron was consistent with the gradual optimization of the dripping characteristics with increasing B2O3 content.

Influence of Coke Ratio on the Sintering Behavior of High-Chromium Vanadium-Titanium Magnetite

High-chromium vanadium and titanium magnetite (HCVTM) sinter has poor properties. The coke ratio has an important effect on the behavior of HCVTM sintering as it affects the mineral phases in the high-chromium vanadium and titanium sinter (HCVTS) via changing the sintering temperature and atmosphere. In this work, the sintering behavior of HCVTM mixed with varying coke ratios was investigated through sintering pot tests, X-ray diffraction (XRD), gas chromatographic analysis, and mineral phase analysis. The results show that, with the increase of the coke ratio from 4.0% to 6.0%, leading to the increase of the combustion ratio of the flue gas, the vertical sintering rate and sinter productivity decrease. Meanwhile, with the change of the coke ratio, the content of magnetite, silicate, and perovskite increase, while the hematite and calcium ferrite decrease. In addition, the tumble strength and reduction ability of HCVTS decrease, and its degradation strength increase. It was found that the appropriate coke ratio for the sintering process was 5.0 wt %.