Effect of Cr2O3 addition on oxidation induration and reduction swelling behavior of chromium-bearing vanadium titanomagnetite pellets with simulated coke oven gas

The oxidation induration and reduction swelling behavior of chromium-bearing vanadium titanomagnetite pellets(CVTP)with Cr2O3 addition were studied,and the reduction swelling index(RSI)and compressive strength(CS)of the reduced CVTP with simulated coke oven gas(COG)injection were investigated.The results showed that the CS of the CVTP decreases and the porosity of the CVTP increases with increasing amount of Cr2O3 added.The Cr2O3 mainly exists in the form of(Cr,Fe)2O3 solid solution in the CVTP and as Fe-Cr in the reduced CVTP.The CS of the reduced CVTP increases and the RSI of the reduced CVTP decreases with increasing amount of Cr2O3 added.The limited aggregation and diffusion of metallic iron contribute to the formation of dense lamellar crystals,which leads to the slight decrease for reduction swelling behavior of reduced CVTP.This work provides a theoretical and technical basis for the utilization of CVTP and other Cr-bearing ores such as chromite with COG recycling technology.

Effect of reductant type on the embedding direct reduction of beach titanomagnetite concentrate

Iron and titanium were recovered from beach titanomagnetite(TTM) concentrate by embedding direct reduction and magnetic separation. The reduction products and the effects of the reductant type and reduction temperature on the reduction behavior were investigated. The results showed that the reduction of TTM concentrate was strongly related to the gasification reactivity of the reductant. Bitumite presented a better product index than wheat-straw biochar and coke, mainly because the gasification reactivity of bitumite was better than that of the other reductants. In addition, high temperatures were not beneficial to embedding direct reduction because of the emergence of a molten phase and iron-joined crystals, which in turn reduced the diffusion rate of the reducing gas and impeded the reduction reaction in the central area of the roasted briquette. The use of bitumite as the reductant at a C/Fe molar ratio of 1.4 and a reduction temperature of 1200°C for 120 min resulted in direct-reduction iron powder assaying 90.28 wt% TFe and 0.91 wt% TiO_2 with an iron recovery of 91.83% and titanium concentrate assaying 46.01 wt% TiO_2 with a TiO_2 recovery of 91.19%. Titanium existed mainly in the form of anosovite and ilmenite in the titanium concentrate.

Effects and mechanisms of fluorite on the co-reduction of blast furnace dust and seaside titanomagnetite

The co-reduction roasting and grinding-magnetic separation of seaside titanomagnetite and blast furnace dust was investigated with and without fluorite addition at a reduction roasting temperature of 1250°C for 60 min, a grinding fineness of-43 μm accounting for 69.02 wt% of the total, and a low-intensity magnetic field strength of 151 kA/m. The mineral composition, microstructure, and state of the roasted products were analyzed, and the concentrations of CO and CO_2 were analyzed in the co-reduction roasting. Better results were achieved with a small fluorite dosage(≤4 wt%) in the process of co-reduction. In addition, F^- was found to reduce the melting point and viscosity of the slag phase because of the high content of aluminate and silicate minerals in the blast furnace dust. The low moisture content of the blast furnace dust and calcic minerals inhibited the hydrolysis of CaF_2 and the loss of F^-. Compared with the blast furnace dust from Chengdeng, the blast furnace dusts from Jiugang and Jinxin inhibited the diffusion of F-when used as reducing agents, leading to weaker effects of fluorite.

Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate

Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate(VTC) were investigated. It was found that calcium compounds had great effects on the metallization rate of the reduction product, the order of the metallization rate of reduction product being CaCO3 > no additive > CaSO4 > CaCl2, which indicated that the addition of CaCO3 was more conducive to promoting the reduction of iron than other calcium compounds. Gas analysis showed that there were mainly two processes in the carbothermic reduction of VTC, a solid–solid and a solid–gas reaction. The concentrations of CO and CO2 were highest when CaCO3 was added, while that in a roasting system decreased the most when CaCl2 was added. X-ray diffraction(XRD) analysis showed that calcium compounds could change the reduction process of ilmenite in VTC. The phase compositions of the reduction products were changed from metallic iron(Fe) and anosovite(FeTi2O5) to metallic iron(Fe) and perovekite(CaTiO3) when calcium compounds were added. Additionally, CaSO4 and CaCl2 could significantly promote the growth of metallic iron particles, though the existence of Fe-bearing Mg2TiO4 in reduction products was not conducive to the reduction of iron. The formation of FeS would further hinder the reduction of iron after adding CaSO4.

Effects of smelting parameters on the slag/metal separation behaviors of Hongge vanadium-bearing titanomagnetite metallized pellets obtained from the gas-based direct reduction process

Smelting separations of Hongge vanadium-bearing titanomagnetite metallized pellets（HVTMP）prepared by gas-based direct reduction were investigated,and the effects of smelting parameters on the slag/metal separation behaviors were analyzed.Relevant mechanisms were elucidated using X-ray diffraction analysis,FACTSAGE 7.0 calculations,and scanning electron microscopy observations.The results show that,when the smelting temperature,time,and C/O ratio are increased,the recoveries of V and Cr of HVTMP in pig iron are improved,the recovery of Fe initially increases and subsequently decreases,and the recovery of Ti O_2 in slag decreases.When the smelting Ca O/Si O_2 ratio is increased,the recoveries of Fe,V,and Cr in pig iron increase and the recovery of Ti O_2 in slag initially increases and subsequently decreases.The appropriate smelting separation parameters for HVTMP are as follows：smelting temperature of 1873 K;smelting time of 30–50 min;C/O ratio of 1.25;and Ca O/Si O_2 ratio of 0.50.With these optimized parameters（smelting time：30 min）,the recoveries of Fe,V,Cr,and Ti O_2 are 99.5%,91.24%,92.41%,and 94.86%,respectively.

Carbothermic reduction of vanadium titanomagnetite with the assistance of sodium carbonate

The carbothermic reduction of vanadium titanomagnetite concentrate(VTC)with the assistance of Na_(2)CO_(3)was conducted in an argon atmosphere between 1073 and 1473 K.X-ray diffraction and scanning electron microscopy were used to investigate the phase transformations during the reaction.By investigating the reaction between VTC and Na_(2)CO_(3),it was concluded that molten Na_(2)CO_(3)broke the structure of titanomagnetite by combining with the acidic oxides(Fe_(2)O_(3),TiO_(2),Al_(2)O_(3),and SiO_(2))to form a Na-rich melt and release FeO and MgO.Therefore,Na_(2)CO_(3)accelerated the reduction rate.In addition,adding Na_(2)CO_(3)also benefited the agglomeration of iron particles and the slag–metal separation by decreasing the viscosity of the slag.Thus,Na_(2)CO_(3)assisted carbothermic reduction is a promising method for treating VTC at low temperatures.

Effects of the continuous cooling process conditions on the crystallization and liberation characteristics of anosovite in Ti-bearing titanomagnetite smelting slag

This study involved the investigation of the effects of the continuous cooling process conditions on the crystallization and liberation characteristics of anosovite in Ti-bearing titanomagnetite smelting slag. The samples were heated until melting and then the temperature was held at 1650℃ for nearly 0.5 h;subsequently, the samples were cooled at different cooling rates to different temperatures and water-quenched after being held for different times at these temperatures. Last, the obtained crystallized samples were used to analyze the crystallization and liberation characteristics. It was found that, during the continuous cooling process, anosovite particles were found to initially precipitate in the slag at a relatively high crystallization temperature, showing the characteristics of euhedral crystal. The precipitation and growth of anosovite grain is strong and the morphology of anosovite was basically not affected by the continuous cooling conditions. From the morphology perspective, the formed anosovite is an excellent Ti-rich phase to be selective separated. The formation of spinel and diopside is negative for the liberation and selective separation of the anosovite phase. The crystallization diagrams of TiO2-MgO-CaO-SiO2-Al2O3-FeO slag undergoing different continuous cooling processes were constructed to help to determine the optimal continuous cooling–quenching condition for selective separation of anosovite. Moreover, the addition of B2O3 can enlarge the range of the optimal continuous cooling–quenching conditions for selective separation of anosovite.

Formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate by adding CaCO3

The formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate(VTC)by adding CaCO3 was investigated.Thermodynamic analysis was employed to show the feasibility of calcium titanate formation by the reaction of ilmenite and Ca CO3 in a reductive atmosphere,where ilmenite is more easily reduced by CO or carbon in the presence of CaCO3.The effects of CaCO3 dosage and reduction temperature on the phase transformation and metallization degree were also investigated in an actual roasting test.Appropriate increase of CaCO3 dosages and reduction temperatures were found to be conducive to the formation of calcium titanate,and the optimum conditions were a CaCO3 dosage of 18 wt%and a reduction temperature of 1400°C.Additionally,scanning electron microscopy–energy dispersive spectrometry(SEM–EDS)analysis shows that calcium titanate produced via the carbothermic reduction of VTC by CaCO3 addition was of higher purity with particle size approximately 50μm.Hence,the separation of calcium titanate and metallic iron will be the focus in the future study.

Non-isothermal reduction kinetics of titanomagnetite by hydrogen

Reduction of titanomagnetite （TTM） powders by H2-Ar gas mixtures was investigated under a non-isothermal condition by using a thermogravimetric analysis system. It was found that non-isothermal reduction of TTM proceeded via a dual-reaction mechanism. The first reaction was reduction of TTM to wustite and ilmenite, whereas the second one was reduction of wiistite and ilmenite to iron and titanium dioxide. By using a new model for the dual reactions, which was in an analytical form and incorporated different variables, such as time, temperature, particle size, and hydrogen partial pressure, rate-controlling steps for the dual reactions were obtained with the apparent activation energies calculated to be 90-98 and 115-132 kJ/mol for the first and second reactions, respectively.

A method for recovery of iron,titanium,and vanadium from vanadium-bearing titanomagnetite

An innovative method for recovering valuable elements from vanadium-bearing titanomagnetite is proposed. This method involves two procedures： low-temperature roasting of vanadium-bearing titanomagnetite and water leaching of roasting slag. During the roasting process, the reduction of iron oxides to metallic iron, the sodium oxidation of vanadium oxides to water-soluble sodium vanadate, and the smelting separation of metallic iron and slag were accomplished simultaneously. Optimal roasting conditions for iron/slag separation were achieved with a mixture thickness of 42.5 mm, a roasting temperature of 1200°C, a residence time of 2 h, a molar ratio of C/O of 1.7, and a sodium carbonate addition of 70 wt%, as well as with the use of anthracite as a reductant. Under the optimal conditions, 93.67% iron from the raw ore was recovered in the form of iron nugget with 95.44% iron grade. After a water leaching process, 85.61% of the vanadium from the roasting slag was leached, confirming the sodium oxidation of most of the vanadium oxides to water-soluble sodium vanadate during the roasting process. The total recoveries of iron, vanadium, and titanium were 93.67%, 72.68%, and 99.72%, respectively.

Biodesulfurization of vanadium-bearing titanomagnetite concentrates and pH control of bioleaching solution

Vanadium-bearing titanomagnetite concentrates were desulfurized with Acidithiobacillus ferrooxidans （A. ferrooxidans）. The sulfur content of the concentrates was reduced from 0.69wt% to 0.14wt% after bioleaching for 15 d with a 10% pulp density at 30℃. Maintaining a stable pH value during biodesulfurization was critical because of high acid consumption, resulting from a combination of nonoxidative and oxidative dissolution of pyrrhotite in acid solution. It is discovered that the citric acid-disodium hydrogen phosphate buffer of pH 2.0 can control the solution pH value smoothly in the optimal range of 2.0-3.0 for A. ferrooxidans growth. Using the buffer in the volume fraction range of 5.0%-15.0% stimulates A. ferooxidans growth and improves the biodesulfurization efficiency. Compared with the buffer-free control case, the maximum increase of biodesulfurization rate is 29.7% using a 10.0vol% buffer. Bioleaching provides an alternative process for desulfurization of vanadium-bearing titanomagnetite ores.

Phase transformation behavior of titanium during carbothermic reduction of titanomagnetite ironsand

The reduction of titanomagnetite（TTM） ironsand, which contains 11.41wt% TiO_2 and 55.63wt% total Fe, by graphite was performed using a thermogravimetric analysis system under an argon gas atmosphere at 1423–1623 K. The behavior and effects of titanium in TTM ironsand during the reduction process were investigated by means of thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. During the reduction procedure, the titanium concentrated in the slag phase, where the phase transformation followed this sequence： Fe O ＋ FeTiO_3 → Fe_2 TiO_4 → FeTiO_3 → FeTi_2O_5 → TiO_2. The calculated results for the reduction kinetics showed that the carbothermic reduction was controlled by the diffusion of ions through the product layer. Furthermore, the apparent activation energy was 170.35 k J·mol^（-1）.

Isothermal reduction of titanomagnetite concentrates containing coal

The isothermal reduction of the Panzhihua titanomagnetite concentrates （PTC） briquette containing coal under argon atmosphere was investigated by thermogravimetry in an electric resistance furnace within the temperature range of 1250-1350°C. The samples reduced in argon at 1350°C for different time were examined by X-ray diffraction （XRD） analysis. Model-fitting and model-free methods were used to evaluate the apparent activation energy of the reduction reaction. It is found that the reduction rate is very fast at the early stage, and then, at a later stage, the reduction rate becomes slow and decreases gradually to the end of the reduction. It is also observed that the reduction of PTC by coal depends greatly on the temperature. At high temperatures, the reduction degree reaches high values faster and the final value achieved is higher than at low temperatures. The final phase composition of the reduced PTC-coal briquette consists in iron and fer-rous-pseudobrookite （FeTi2O5）, while Fe2.75Ti0.25O4, Fe2.5Ti0.5O4, Fe2.25Ti0.75O4, ilmenite （FeTiO3） and wustite （FeO） are intermediate products. The reaction rate is controlled by the phase boundary reaction for reduction degree less than 0.2 with an apparent activation energy of about 68 kJ·mol-1 and by three-dimensional diffusion for reduction degree greater than 0.75 with an apparent activation energy of about 134 kJ·mol-1. For the reduction degree in the range of 0.2-0.75, the reaction rate is under mixed control, and the activation energy increases with the increase of the reduction degree.

Effect of Cr_2O_3 addition on the oxidation induration mechanism of Hongge vanadium titanomagnetite pellets

As part of a research project to develop a novel clean smelting process for the comprehensive utilization of Hongge vanadium titanomagnetite（HVTM）, in this study, the effect of Cr2O3 addition on the oxidation induration mechanism of HVTM pellets（HVTMPs） was investigated in detail. The results showed that the compressive strength of the HVTMPs was greatly weakened by the Cr2O3 addition, mainly because of a substantial increase in the porosity of the HVTMPs. The Cr2O3 addition marginally affected the phase composition but greatly affected the microstructural changes of the HVTMPs. Increased amounts of Cr2O3 resulted in a decrease in the uniform distribution of the hematite grains and in an increase in the Fe–Cr solid solutions（Fe1.2Cr0.8O3 and Fe0.7Cr1.3O3） embedded in the hematite grains. Moreover, the compact hematite was destroyed by forming a dispersed structure and the hematite recrystallization was hindered during the oxidation induration, which adversely affected the compressive strength. On the basis of these results, a schematic was formulated to describe the oxidation induration mechanism with different amounts of added Cr2O3. This study provides theoretical and technical foundations for the effective production of HVTMPs and a reference for chromium-bearing minerals.

Leaching of vanadium,sodium,and silicon from molten V?Ti-bearing slag obtained from low-grade vanadium-bearing titanomagnetite

The water leaching process of vanadium, sodium, and silicon from molten vanadium-titanium-bearing（V-Ti-bearing） slag obtained from low-grade vanadium-bearing titanomagnetite was investigated systematically. The results show that calcium titanate, sodium aluminosilicate, sodium oxide, silicon dioxide and sodium vanadate are the major components of the molten V-Ti-bearing slag. The experimental results indicate that the liquid-solid（L/S） mass ratio significantly affects the leaching process because of the respective solubilities and diffusion rates of the components. A total of 83.8% of vanadium, 72.8% of sodium, and 16.1% of silicon can be leached out via a triple counter-current leaching process under the optimal conditions of a particle size below 0.074 mm, a temperature of 90°C, a leaching time of 20 min, an L/S mass ratio of 4：1, and a stirring speed of 300 r/min. The kinetics of vanadium leaching is well described by an internal diffusion-controlled model and the apparent activation energy is 11.1 kJ/mol. The leaching mechanism of vanadium was also analyzed.

Factor analysis on the purity of magnesium titanate directly prepared from seashore titanomagnetite concentrate through direct reduction

Magnesium titanate was prepared directly through external coal reduction of seashore titanomagnetite concentrate and magnesium oxide(MgO).The effects of roasting temperature and the type and dosage of reductants on the purity of generated magnesium titanate particles were systematically investigated.Scanning electron microscopy and energy-dispersive spectroscopy analyses were performed to characterize the magnesium titanate particles and observe their purity under different conditions.Results showed that the roasting temperature remarkably influenced the purity of magnesium titanate.At 1200,1300,and 1400℃,some magnesium ferrite and magnesium aluminate spinel were dissolved in magnesium titanate.However,as the roasting temperature increased to 1500℃,relatively pure magnesium titanate particles were generated because no magnesium ferrite was dissolved in them.The type and dosage of the reductants also remarkably affected the purity of magnesium titanate.The amount of fine metallic iron disseminated in the magnesium titanate particles obviously decreased when lignite was used as a reductant at a dosage of 70wt%.Thus,high-purity magnesium titanate particles formed.At a roasting temperature of 1500℃and with 70wt%lignite,the magnesium titanate product with a yield of 30.63%and an iron content of 3.01wt%was obtained through magnetic separation.

Oxidation behavior of low-grade vanadiferous titanomagnetite concentrate with high titanium

In order to clarify the oxidation mechanisms and make better use of the low-grade vanadiferous titanomagnetite concentrate with high titanium(LVTC),the oxidation behavior of LVTC was investigated.The results showed that oxidation degree was achieved within 90 min when temperature was not lower than 700°C,and the main phases of the oxidized LVTC consisted of Fe9TiO15,Fe2O3,CaSiTiO5 and a small amount of Fe2.75Ti0.25O4.Increasing temperature is favorable to the formation of Fe2TiO5.The surface of LVTC gradually becomes rough,with fine particles of needle-like and granular shape appearing on the surface,which finally turn from laminar to creamy,spread out,and are interspersed with many tiny holes.The phase oxidation paths in LVTC were as follows:(1)Fe2.75Ti0.25O4→Fe9TiO15+Fe2O3;(2)Fe2.75Ti0.25O4→Fe2O3+FeTiO3→Fe2TiO5;(3)FeTiO3→Fe2O3+Fe2Ti3O9→Fe2TiO5.LVTC is predominantly mesoporous whether oxidized or not,with the pores mainly distributed in the range of 2–40 nm,and the specific surface area of LVTC decreases significantly with increasing temperature.

Kinetic study on microwave-enhanced direct reduction of titanomagnetite concentrate with coal

Titanomagnetite concentrate is one of the important titanium resources.The apparent activation energy(Ea)of the direct reduction of titanomagnetite concentrate was composed of two parts(average activation energy:E_(a)=E_(a-L)+E_(a-Step1),where E_(a-L) is the lattice energy of titanomagnetite concentrate,and is the activation energy of step 1 for the reduction of titanomagnetite concentrate in the route of.Fe^(3+)→^(Step1)Fe^(2+)→^(Step2)Fe_(2)O^(2)→^(Step3)Fe^(0)).Ea(583.43 kJ/mol),(426.4 kJ/mol),and(157.0 kJ/mol)were calculated by the model-free methods based on thermogravimetry and Dmol3 module.Combined with the analysis of activation energy fluctuation and the shifting trend of related mechanism functions,the reduction kinetic system with three main characteristics,namely nucleation,diffusion and concentration fluctuation,was established.In addition,the scanning electron microscopy comparison analysis of the samples from microwave reduction and conventional reduction shows that microwave heating could realize the microstructure Ti-Fe separation and reduce the lattice energy of the titanomagnetite concentrate,thus enhancing the reduction process by 7.68%from the perspective of activation energy.

Reduction behavior and mechanism of Hongge vanadium titanomagnetite pellets by gas mixture of H2 and CO

Hongge vanadium titanomagnetite（HVTM）pellets were reduced by H2-CO gas mixture for simulating the reduction processes of Midrex and HYL-III shaft furnaces.The influences of reduction temperature,ratio ofφ（H2）toφ（CO）,and pellet size on the reduction of HVTM pellets were evaluated in detail and the reduction reaction kinetics was investigated.The results show that both the reduction degree and reduction rate can be improved with increasing the reduction temperature and the H2 content as well as decreasing the pellet size.The rational reduction parameters are reduction temperature of 1050℃,ratio ofφ（H2）toφ（CO）of 2.5,and pellet diameter in the range of 8-11 mm.Under these conditions（pellet diameter of 11mm）,final reduction degree of 95.51% is achieved.The X-ray diffraction（XRD）pattern shows that the main phases of final reduced pellets under these conditions（pellet diameter of 11 mm）are reduced iron and rutile.The peak intensity of reduced iron increases obviously with the increase in the reduction temperature.Besides,relatively high reduction temperature promotes the migration and coarsening of metallic iron particles and improves the distribution of vanadium and chromium in the reduced iron,which is conducive to subsequent melting separation.At the early stage,the reduction process is controlled by interfacial chemical reaction and the apparent activation energy is 60.78kJ/mol.The reduction process is controlled by both interfacial chemical reaction and internal diffusion at the final stage,and the apparent activation energy is 30.54kJ/mol.

Analysis of Vanadium-Bearing Titanomagnetite Sintering Process by Dissection of Sintering Bed

Many problems appear in the sintering process of vanadium-bearing titanomagnetite, such as high energy consumption and low productivity; simer quality is also very poor for its low tumble strength and high reduction deg- radation. Sinter productivity and quality are dominated by bed permeability and mineralogy structure, which are highly influenced by the thermal state of sintering bed, so the sintering process of titanomagnetite is researched by bed dissection in this work. Temperature evolution curves of sinter materials were measured, and the results show that melting duration, peak temperature duration and sintering temperature of different layers differ greatly from each other; flame front speed and vertical sintering speed of bed lower region are much smaller than those of bed up- per region. Simultaneously, sinter samples were collected from different layers, and their mineralogy characteristics are analyzed; sinters from bed lower region have poor mineralogy structure, and the amounts of perovskite and dieM- cium silicate increase intensively, which are bad for sinter strength and reduction degradation property. Measures are proposed to improve the quality and productivity of titanomagnetite sinter.