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In order to prepare FeTi alloy using ilmenite concentrate in molten salt by electrolytic method, the electrochemical deoxidation process was studied by cyclic voltammetry and AC impedance spectroscopy. The electrolytic experiments at different time verified the electrochemical behavior. It is shown that the electrodeoxidation process for ilmenite concentrate mainly consists of two steps. Fe is reduced firstly from the ilmenite concentrate. The second step is the reduction of titanium dioxide with an intermediate product perovskite. At low voltage, the speed of electro-deoxidation process is mainly dependent on the electrochemical reaction. As the potential increases, the diffusion of ion becomes the main rate-controlling step for the electro-deoxidation of ilmenite concentrate.

Abstract In this study, hydrogen reduction of raw and preoxidized ilmenite concentrates powder, with particle size less than 74 μm, is investigated using a thermal analyzer at 1123, 1173, and 1223 K in a 30% H 2 + 70% Ar atmosphere. The reduction rate by hydrogen was found to be accelerated due to preoxidation treatment of the raw ilmenite concentrate. The reduction of both raw and preoxidized ilmenite concentrates can be divided into two stages: Fe3+→Fe2+ and Fe2+→Fe. The Fe 3 O 4 →FeO stage overlaps with the Fe 2 O 3 →Fe 3 O 4 stage during reduction process of the preoxidized ilmenite concentrate. Moreover, the preoxidation treatment can effectively decrease the reduction activation energy. The scanning electron microscopy (SEM) and the X-ray powder diffraction (XRD) techniques were used to characterize the micromorphology and phase of the products. The promotion mechanism of reduction of ilmenite by hydrogen through preoxidation treatments is also discussed. Highlights • The preoxidation treatments of ilmenite is beneficial to accelerate reduction. • The preoxidation treatments can decrease the reduction activation energy. • The promotion mechanism of hydrogen reduce preoxidized ilmenite is obtained. [ABSTRACT FROM AUTHOR]

The carbothermic reduction behavior of original ilmenite and pre-oxidized ilmenite concentrates were investigated by a non-isothermal method using a thermogravimetry facility. The reaction degree was calculated using the tail gas composition and the Starink method to analyze the activation energy of the reduction. The results demonstrated that trends of different reaction degree curves are similar under the same conditions. The average activation energy of the pre-oxidized ilmenite concentrate was less than that of the original form by approximately 25%, and the starting reduction temperature was lower by 67 K than that of the original ilmenite concentrate. However, the reduction time of the pre-oxidized ilmenite concentrate was longer than that of the original ilmenite concentrate for the same reaction degree; therefore, a slow reduction rate for the oxidization sample was observed. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS) were used to characterize the phase and micro-morphology of the two raw materials and compare the reduction products. [ABSTRACT FROM AUTHOR]

In this paper, a novel process was studied for the recovery of iron and titanium from ilmenite concentrate. The ilmenite powders first underwent an oxidation pretreatment and were reduced isothermally at 1350–1450 °C by graphite with the addition of Na 2 SO 4 . The influence of temperature, C/O molar ratio and the dosage of the added Na 2 SO 4 on the metallization ratio, phase transformation and titanium grade were studied. The results demonstrated that Na 2 SO 4 not only significantly promotes the aggregation and growth of metallic iron-grain particles but also enhances the reduction ability. Under the promotion of added Na 2 SO 4 , the highest metallization ratio reached 94%, and the theoretical calculation of the highest grade of titanium dioxide is approximately 75%. The Na 2 SO 4 additive decreases the melting point of the slag and metal, resulting in the effect of semi-melting reduction. The carbothermic reduction order of phase transitions of pre-oxidized ilmenite concentrate was also discussed. [ABSTRACT FROM AUTHOR]

The objective of this study was to establish the kinetics of oxidation of ilmenite concentrate powders, which promotes reduction via the oxidation process. In this paper, the kinetics of the oxidation of ilmenite concentrate powders from low temperature to high temperature was studied comprehensively using the thermal gravity method. The reaction mechanism and model function were studied using two different classical methods, and then the results were compared. The results showed that, when the oxidation temperature was below 973 K (700 °C), the reaction mechanism is the three-dimensional diffusion, and the model function was G α = 1 − 2 3 α − 1 − α 2 / 3 (α, reaction degree). When the temperature was above 1273 K (1000 °C), the reaction mechanism is random nucleation and subsequent growth, and the model function was G ( α ) = [− ln(1 − α )] 1/3 . No single model function can fit well the oxidation process at 1023 K (750 °C), 1073 K (800 °C), 1123 K (850 °C), and 1173 K (900 °C); thus, a multistage mechanism was proposed to explain the reaction process; this mechanism includes three-dimensional diffusion, random nucleation and subsequent growth in the order of increasing reaction degree. The apparent activation energies for the oxidation were also studied using two different methods: 199.43 and 194.01 kJ/mol at 873 K (600 °C), 923 K (650 °C), and 973 K (700 °C); 4.11 and 3.96 kJ/mol at 1273 K (1000 °C), 1373 K (1100 °C), and 1473 K (1200 °C). The relationship of oxidation degree with time and temperature is also discussed, which is helpful for the selection of the parameters of the oxidation process. [ABSTRACT FROM AUTHOR]

High titania slag has become a good raw material in the development of titanium. Ilmenite is reduced first and then smelted in an electric arc furnace to separate iron from the high titania slag. Therefore, enhanced reduction of ilmenite concentrate can reduce smelting time and energy consumption. Wet grinding method, which is often used to reduce particle size and improve the balling ability of ilmenite, was proposed to enhance the reduction. The effect of wet grinding on the carbothermic reduction of ilmenite was investigated. The wet grinding treatment was found to result in a high reduction rate and improve metallisation. The metallisation degree of reduced ilmenite concentrate increased as the time of wet grinding increased. Under the constant reduction conditions, the degree of metallisation improved from 68.58% to 87.32% while the FeO content decreased from 10.62 to 5.28% as the wet grinding time increased from 10 to 60 min. [ABSTRACT FROM AUTHOR]

Herein, we reduce raw and pre-oxidized ilmenite concentrates by H 2 , CO, and a gas mixture (H 2 /CO = 1) at different temperatures. The results show that the reduction rate of both concentrates increases with increasing H 2 concentration. Furthermore, the reducing ability of the three types of reducing gases increases in the order of CO < H 2 < gas mixture. Moreover, we elucidate the coupling effect of H 2 –CO on the reduction process and propose a comprehensive utilization index for hydrogen-rich reduction gas. The results indicate that H 2 –CO coupling plays a positive role in both the concentrate reduction processes, improving the reduction rate and gas utilization efficiency. The maximum reducing gas comprehensive utilization indices for the hydrogen-rich reduction of the raw and pre-oxidized ilmenite concentrates are observed at 1000 and 950 °C, respectively. Additionally, changing the reducing atmosphere and pre-oxidation treatment significantly affects the distribution of metallic iron in the product particles. • The comprehensive utilization index of reducing gases in reduction was proposed. • The H 2 –CO coupling plays a positive role in both concentrates reduction processes. • The order of reducing ability of gases for both concentrates is CO < H 2 < mixtures. • The micromorphology of the reducing product is affected by the reducing atmosphere. [ABSTRACT FROM AUTHOR]

Abstract The electric arc furnace (EAF) smelting process, which produces titanium slag, is the most popular method for utilizing Panzhihua ilmenite concentrate. However, the EAF process involves high energy consumption, high pollution, and low efficiency due to the high smelting temperature, the large amount of dust produced, and the long smelting period. An economical and clean method for semi-molten reduction followed by magnetic separation to produce titanium slag from Panzhihua ilmenite concentrate was presented. In this paper, the semi-molten reduction process was studied and the effect of reduction temperature, C/O molar ratio, and the addition dosage of Na 2 SO 4 on the metallization ratio, phase transformation, and size of metallic iron grain was discussed. The results showed that Na 2 SO 4 and its subsidiary products can function as fluxing agent for decreasing the melting point of metal and slag, thus promoting the growth of metal particles, and achieving high efficiency and clean reduction of ilmenite concentrate. The action mechanism of Na 2 SO 4 addition is also discussed. Graphical abstract Unlabelled Image Highlights • Na 2 SO 4 can accelerate the carbothermic reduction rate of ilmenite concentrate. • Na 2 SO 4 can promote the growth of metallic iron particles. • Na 2 SO 4 and its subsidiary products can function as fluxing agent. • A high efficiency semi-molten state reduction of ilmenite concentrate is obtained. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of pre-oxidation treatment on the hydrogen-rich reduction of Panzhihua ilmenite concentrate powder on the reduction kinetics and mechanisms. In this study, reduction processes of raw and pre-oxidized ilmenite concentrates reduced by H 2 /CO mixtures (H 2 /CO = 0.4 and H 2 /CO = 2.5) at 950, 1000, and 1050 °C were systematically investigated using a thermal analyzer. The hydrogen-rich reduction rate was accelerated by the pre-oxidation treatment of raw ilmenite concentrate and an increase in H 2 in H 2 /CO mixtures. The hydrogen-rich reduction of raw and pre-oxidized ilmenite concentrates can be divided into two stages according to the first derivatives of the reduction process: Fe3+ to Fe2+ and Fe2+ to Fe. The results of the research on the model function demonstrated that the reaction mechanism of raw and pre-oxidized ilmenite concentrates were three-dimensional diffusion models in the first stage. In the second stage, the reaction mechanism of the raw ilmenite concentrate was a phase boundary reaction model, and for the pre-oxidized ilmenite concentrate, it was a chemical reaction model. Furthermore, the apparent activation energies of both raw and pre-oxidized ilmenite concentrates under different reducing atmospheres were determined and compared. It was demonstrated that pre-oxidation treatment could effectively reduce the apparent activation energies of the reduction reaction. It is feasible to combine the advantages of the pre-oxidation treatment and hydrogen-rich reduction with a higher hydrogen ratio for the efficient reduction of Panzhihua ilmenite concentrate. • Hydrogen-rich reduction of raw and pre-oxidized ilmenite concentrates was studied. • Pre-oxidation of ilmenite is beneficial for accelerating hydrogen-rich reduction. • Increasing the H 2 content and temperature is conducive to the reduction process. • Hydrogen-rich reduction of both ilmenite concentrates can be divided into 2 stages. • The changing activation energies of the hydrogen-rich reduction were obtained. [ABSTRACT FROM AUTHOR]

In this study, the effect of the addition of Na 2 CO 3 on the isothermal kinetics of carbothermic reduction of low-grade ilmenite concentrate is studied; this is a novel technique for obtaining high-quality upgraded titanium slag for chlorination through semi-molten states. The results indicate that the addition of Na 2 CO 3 can reduce the initial temperature of the reaction and promote reduction, which is beneficial for improving the reaction kinetics by enhancing the carbon gasification reaction. The iron metal produced during the reaction tends to migrate and increase with the formation of the molten phase. The reduction of ilmenite concentrate gradually changes from being controlled by the interfacial chemical reaction to being controlled by diffusion with the increase in Na 2 CO 3. At 0%, 3%, and 6% Na 2 CO 3 , the apparent activation energies were 105.01, 112.07, and 123.48 kJ/mol, respectively. [Display omitted] • The mechanism and kinetics of the ilmenite concentrate with Na 2 CO 3 were studied. • The addition of Na 2 CO 3 reduces the reaction initial temperature, promotes reduction. • Improve the reaction kinetics by enhancing the carbon gasification reaction. • Different mechanisms transformation with different addition of Na 2 CO 3 is proposed. [ABSTRACT FROM AUTHOR]

• Isothermal kinetics of reduction and nitridation of ilmenite concentrate by ammonia gas is studied. • Both model–free and model–fitting methods are used to compare the isothermal kinetics. • The mechanism function and apparent activation energy of the reduction and nitridation stages are obtained. • The mechanism on reduction and nitridation is discussed. Low-temperature chlorination is considered a suitable process for ilmenite containing high contents of MgO and CaO. However, reduction carbonization or nitridation is essential to convert titanium oxide to carbide or nitride, which can be enriched by magnetic separation. In this paper, the isothermal reduction–nitridation kinetics of Panzhihua ilmenite concentrate in an ammonia atmosphere was investigated. Both model–free and model–fitting methods were used to compare the isothermal kinetics. The reaction process can be divided into two successive stages: the reduction reaction and the nitridation reaction. The average apparent activation energy for the reduction reaction was 139.63 kJ/mol, obtained by the model–free method. The reduction process can also be subdivided into two stages by the model–fitting method. The chemical reaction (G(α) = 1–(1– α)1/3 = kt) and three–dimensional diffusion (G (α) = [1–(1– α)1/3]2 = kt) were identified as the mechanism function for the reduction process. The activation energies of these two stages were 121.73 kJ/mol and 141.40 kJ/mol, respectively. The function G(α) = 1–(1– α)1/3 = kt , which also corresponds to the chemical reaction mechanism (R 3), exhibited the best fit for the nitridation stage. The corresponding activation energy was 32.10 kJ/mol. Metallic iron and Ti 3 O 5 were formed in the reduction stage, while Ti 3 O 5 was then transformed to Ti(N,O) in the nitridation stage. [ABSTRACT FROM AUTHOR]

The deep reduction of ilmenite concentrates through carbothermic way with the addition of Na 2 CO 3 to produce high-quality titanium slag and iron powder is a novel energy-efficient process to utilise the low-grade ilmenite concentrate effectively. The growth behaviour of iron grain in this process is of great significance for the subsequent separation between iron and slag. Thus, the growth behaviour and kinetics of iron grain in this process under different Na 2 CO 3 concentrations were investigated. The results show that the increase of reduction temperature, time, and Na 2 CO 3 addition promoted the growth of iron grains. Particularly, the influence of additives was more significant when the reduction temperature was over 1300 °C. The growth of iron grain gradually changed from being controlled by surface diffusion to being controlled by grain boundary diffusion with increasing Na 2 CO 3 addition. Growth models of iron grain under different Na 2 CO 3 concentrations were also established in this study. [Display omitted] • The growth and kinetics of iron of the ilmenite concentrate with Na 2 CO 3 was studied. • The increase of reduction temperature, time, and Na 2 CO 3 addition promoted the growth of iron. • Faster diffusion and the formation of larger iron grains with addition of Na 2 CO 3. • Different growth models of iron grain with different Na 2 CO 3 concentrations were established. [ABSTRACT FROM AUTHOR]