The process of "high temperature carbonization and low temperature chlorination", considered as one of the most promising technologies, can extract over 60% titanium from blast furnace slag containing TiO 2 at a concentration of 20%-25%. The primary equipment for high temperature carbonization is an electric furnace lined with MgO-C bricks. In this study, post-mortem analysis was conducted to investigate the corrosion and failure mechanisms of MgO-C refractory bricks taken from different areas of a circular electric furnace after 1200 cycles of service. Through XRD, SEM-EDS, and thermodynamic calculation analysis, the reaction and corrosion mechanism between MgO-C bricks and the slag were analyzed. The results demonstrated that the gradual corrosion of the brick was primarily attributed to the alternating effects of carbon oxidation and MgO dissolution. Moreover, an increase in temperature led to a higher corrosion rate of the refractories. At temperatures exceeding 1560 degrees C, the pre -formed barrier layer composed of MgAl 2 O 4 and MgTi 2 O 4 melted into the slag. And as TiO 2 content decreased and TiC content increased, there was a gradual decline in the erosive impact of the slag. Furthermore, the failure mechanisms of refractory bricks in different areas varied due to the distinctive structure of the electric furnace. The bricks at the slag line area were mainly destroyed by slag corrosion, oxidation and thermal shock spalling, which had the shortest service life.

采用热分析动力学方法,研究了Na2CO3作用下硅镁质型红土镍矿非等温碳热还原的动力学规律,确定了主要的动力学参数,查明了还原过程的物相变化.结果表明:添加Na2CO3可降低碳热还原开始温度约250℃,并加速碳的气化反应;碳热还原过程可分为三个阶段,即初始阶段(α=0～0.15)、中期阶段(α=0.15～0.60)和衰变阶段(α=0.60～1.0).初始阶段的活化能随着还原反应的进行由223 kJ/mol快速下降到76 kJ/mol,受二维扩散控制;中期阶段活化能先增加后降低,该阶段受化学反应控制;衰变阶段主要发生FeO及Fe2SiO4的还原反应,活化能由184 kJ/mol缓慢减小到132 kJ/mol,随后又增加到173 kJ/mol,该阶段受化学反应控制.与无添加剂相比,添加Na2CO3后极大地促进了红土镍矿的碳热还原,降低了整个过程的活化能.

The effect of the Al2O3 content and basicity (the molar ratio of MgO to SiO2) on the viscosity of a SiO2–MgO–FeO–Al2O3–CaO slag was studied to fully understand the smelting process of the ferronickel alloy. Experimental results show that the slag is a mixture of liquid and solid phases at the experimental temperature. The viscosity decreased as the basicity increased and increased as the Al2O3 content increased. To determine the effect of the Al2O3 content and basicity on the structure of the molten slag, Raman spectroscopy was performed on the slag sample, which was quenched from the high temperature with water. The Raman spectra showed that the fractions of the polymerization structural units decreased significantly as the basicity of the slag increased, resulting in a decrease in the apparent viscosity. However, Al2O3 acts as a network former in the slag system, thereby making the slag structure further polymerized and increasing the viscosity.

Evolving knowledge of the structure and physical properties of metallurgical slags is summarized in current review. Slag structure, compositional effects, role of cations in structural modifications, parameters used to represent the structure, structural analysis techniques and effects of structure on properties of blast furnace slag (BFS) studied in details. The basicity, polymerization (Q) or depolymerization (NBO/T), optical basicity, Q(n) values, concentrations of bridging O's (O degrees), non-bridging O's (O-) and free O's (O2-) in slag are useful to represent the structure of slag. Methods and techniques utilized to study the slags are also discussed. The BFS is characterized by using X-ray Diffraction and Spectroscopy, Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Photoelectron Spectroscopy (XPS) and Nuclear Magnetic Resonance (NMR) Spectroscopy. The physical properties such as surface tension, viscosity, density, thermal expansion and diffusion, electrical conductivity and resistivity of slags are reviewed thoroughly which are heavily dependent on structure of slag. Viscosity is affected by polymerization or depolymerization of slag structure and cation size; electrical resistivity depends on Q, size of cations and number of available cations; thermal expansion depends on Q and cation field strength (i.e. z/r(2)); thermal conductivity is linked with rigidity of slag network which is also dependent on Q and metal-oxygen (M-O) bond strength. Degree of polymerization or depolymerization of slag structure also effect the surface and interfacial tension, it decreases as metal-oxygen (M-O) bond strengths (i.e. z/r(2), cation field strength) decrease.

Controlling the generation of perovskite (CaO center dot TiO2, CT) during sintering with vanadium-titanium magnetite (VTM) is the key to improve the strength and yield of VTM sinters. This study determined whether adding pre-formed calcium ferrite (CaO center dot Fe2O3, CF) effectively prevents the formation of CT during sintering with VTM. The formation behavior of CT in the CF-T system was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Phase composition analysis by XRD indicates that CT is formed significant quantities in the CF-T system when the temperature is higher than the melting temperature of CF. DSC analysis shows that the CF-T samples undergo two reaction stages in continuous heating. Namely, CF first melts and forms its liquid phase, then TiO2 substitutes Fe2O3 in liquid CF to produce CT. SEM images confirm that CT could be generated at regions with a high concentration of CF. Non-isothermal DSC measurements on the formation kinetics of CT indicate that its activation energy reaches 252.00 kJ/mol and that the model function is f(alpha)=(1-alpha)(2), revealing a second-order reaction based on Malek analysis. The kinetics equation of CT formation can be expressed by ln(d alpha/dt) = 2 ln(1-alpha) - 216805+70382 alpha/RT+ 16.71 + 10.33 alpha. Quantitative calculation on enthalpy change by DSC curves shows that raising heating rates enhance the consolidation ability of CF-T samples as the melting of CF increases and the formation of CT decreases. (C) 2019 Elsevier B.V. All rights reserved.

A novel method of smelting a mixture of two types of laterite ore (saprolitic and limonitic) to prepare ferronickel has been investigated. Thermodynamic analysis revealed that the melting temperature of the slag phase dropped below 1400°C with increasing FeO content, which can be regulated by adjusting the ratio of limonite and the carbon content. The experimental results also proved that the melting degree of the reduced pellets increased with increasing limonitic laterite ratio and that the reduction as well as magnetic separation was enhanced when the reduction was carried out in the presence of limonitic laterite ore. A ferronickel product with 8.08 wt.% Ni, 80.09 wt.% Fe, and 3.75 wt.% C was prepared by heating the mixture to 1380°C in the presence of 6 wt.% carbon content and 5 wt.% limonitic laterite ore, followed by magnetic separation. The Ni and Fe recoveries were 89.26% and 81.64 wt.%, respectively.

In this study, the kinetics of reduction of Panzhihua ilmenite concentrate by graphite under an argon atmosphere using the non-isothermal method was investigated by thermogravimetric analysis and mass spectrometry at heating rates of 10, 15, and 20 K center dot min(-1). Both the reactants and products were analysed by X ray powder diffraction (XRD) and scanning electron microscopy (SEM) to identify their phases and morphologies, respectively. The Malek method was used to analyse the reaction mechanism and model function. The results show that the reduction of ilmenite concentrate proceeded in three stages: mixed control, chemical reaction, and three-dimensional diffusion in that order. The Starink method was used to calculate the activation energy. The average apparent activation energies for the carbothermic reduction of raw ilmenite concentrate were 478, 617, and 468 kJ mol(-1) for the first, second, and third stage, respectively. The oxygen potential of tail gas during the reduction process was also obtained.

Sodium sulfate has proven to be an effective additive for enhancing the reduction and metal aggregation during the carbothermic reduction of Ni laterite ore. In this study, the effect of Na2SO4 on the non-isothermal reduction kinetics of Ni laterite ore with solid C was investigated. The kinetic parameters and mechanism function were determined. The reduction mechanism was also analyzed by combining X-ray diffraction analysis with evolved-gas analysis. The results indicated that the reduction process was divided into three stages on the basis of the conversion degree. The average activation energy was 323.0 kJ/mol for the initial stage of alpha = 0-0.40, 161.2 kJ/mol for the middle stage of alpha = 0.40-0.80, and 161.3 kJ/mol for the decaying stage of alpha = 0.80-1.00. Three-dimensional diffusion equation was determined as the mechanism function in the initial and middle stage. The chemical reaction function exhibited the best fit in the decaying stage. (C) 2019 Elsevier B.V. All rights reserved.

In this study, the effect of sodium sulfate on preparation of ferronickel from nickel laterite by carbothermal reduction was investigated. The thermodynamic analysis showed that the addition of sodium sulfate can effectively enlarge the region of liquid slag in the phase diagram. The experimental results of carbothermal reduction revealed that sodium sulfate was capable of enhancing the reduction of nickel laterite, as well as promoting the aggregation and growth of nickel-iron particles considerably. Both the size of ferronickel particles and the grade of Ni in the magnetic material increased with increase in the dosage of sodium sulfate. The Ni grade and its recovery ratio were only 2.4 mass% and 58.1% when the raw material was reduced in the absence of sodium sulfate. However, with addition of 8.0 mass% sodium sulfate, the grade of Ni in magnetic material and the recovery of Ni reached up to 9.7 mass% and 89.1%, respectively. The contents of S, P, C and Si in the magnetic materials was also discussed. In addition, the reaction mechanisms of reduction in the presence of sodium sulfate was revealed by investigating the phase transformation, growing character of ferronickel as well as TG and evolved gas analysis. The effective utilization coefficient of nickel (EN) which is a new characterization method of normalization was proposed to compare different studies on preparation of ferronickel from various nickel laterite.

In this paper, the non-isothermal reduction kinetics of nickel laterite with graphite was investigated under argon atmosphere. The reduction of nickel laterite was carried out at different heating rates (10, 15 and 20 K/min) and the evolved gas was detected by mass spectrometer in real time. The activation energies were determined by Kissinger-Akahira-Sunose (KAS) method and the reaction kinetics were determined by model-fitting (Coats-Redfern) method. The results showed that the reduction process can be divided into three stages according to the conversion degree (alpha): alpha = 0-0.45, alpha = 0.45-0.75, and alpha = 0.75-1.0, respectively. In the first stage, the average activation energy was 351.03 kJ/mol and the kinetic model fitted the two-dimensional diffusion function. In the second stage, the model of three-dimensional diffusion function was determined as the kinetic function and the average activation energy was 322.89 kJ/mol. In the third stage, the average activation energy was 341.45 kJ/mol and the kinetic model was in accordance with the chemical reaction function. The phase transformation as well as reaction mechanism during reduction were also analyzed which explained the reduction kinetics of nickel laterite. (C) 2018 Elsevier B.V. All rights reserved.

The sticking phenomenon between molten slag and refractory is one of the crucial problems when preparing ferronickel from laterite ore using rotary hearth furnace or rotary kiln processes. This study aims to ameliorate sticking problems by using silicon dioxide (SiO2) to adjust the melting degree of the briquette during reduction roasting. Thermodynamic analysis indicates that the melting temperature of the slag gradually increases with an increase in the SiO2 proportion (SiO2/(SiO2 + Al2O3 + MgO) mass ratio). Experimental validations also prove that the briquette retains its original shape when the SiO2 proportion is greater than 75wt%, and sticking problems are avoided during reduction. A ferronickel product with 8.33wt% Ni and 84.71wt% Fe was prepared via reductive roasting at 1500°C for 90 min with a SiO2 proportion of 75wt% and a C/O molar ratio of 1.0 followed by dry magnetic separation; the corresponding recoveries of Ni and Fe reached 75.70% and 77.97%, respectively. The microstructure and phase transformation of reduced briquette reveals that the aggregation and growth of ferronickel particles were not significantly affected after adding SiO2 to the reduction process.

In this study, microwave heating was used to dry the nickel laterite which contains plenty of free water, crystal water and hydroxy water. The results showed that compared with the conventional drying process, the microwave drying greatly improved the drying efficiency of nickel laterite. The whole microwave drying process can be divided into three stages according to the drying rates, namely, the rising stage, stable stage and declining stage. The effects of microwave power output and particle size were also studied in the range of 0.8–2.0 KW microwave power and 3–6 cm of particle size. The results showed that the drying time significantly decreased with the increase of microwave power and decrease of particle size. The phases transition of the sample during the microwave drying process were also discussed.

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 Na2SO4 on the metallization ratio, phase transformation, and size of metallic iron grain was discussed. The results showed that Na2SO4 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 Na2SO4 addition is also discussed.

Injection of natural gas into the tuyere raceway of a blast furnace (BF) can effectively decrease the use of coke, as well as reduce CO2 emission. Therefore, the reduction behaviour of sinters, which account for 60% of the raw materials charged into the BF process under H2, is important for natural gas utilisation. This study used thermogravimetric analysis under H2 atmosphere to investigate the reduction kinetics of dicalcium ferrite (2CaO·Fe2O3, C2F) and calcium ferrite (CaO·Fe2O3, CF), which are the dominant components in fluxed sinters. Results indicated that CF reduction has a larger maximum reduction degree and a higher reaction constant than C2F. The apparent activation energy of CF is also larger than that of C2F, thereby illustrating that C2F reduction proceeds more easily than CF. X–ray diffraction measurements indicated that C2F is reduced to CaO and Fe in a single step, whereas CF is reduced with four steps in the following order: CaO·FeO·Fe2O3, CaO·3FeO·Fe2O3, C2F and Fe. Sharp and ln–ln methods revealed that C2F reduction is described by 2D Avrami–Erofeev (A–E) equation and that of CF is expressed by 2D A–E equation but tends slightly to 3D A–E equation in the late stage. A–E equations were verified to be consistent with the experimental reduction degree data of C2F and CF. A kinetics model that links reduction routes to model functions was proposed to describe the powder reduction of C2F and CF. Comparisons of the reduction behaviours of C2F or CF by H2 and CO implied that the reduction rate rises and activation energy declines during the reduction of samples by H2.

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 67K 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.

Non-isothermal multiple scanning rate analysis method was used to analyse the solid-state reduction of nickel laterite by carbon. According to the TG curves, the activation energies were calculated and the most probable mechanism functions were determined by the Malek method. The results show that the process can be divided into three stages according to the reaction degree (alpha): 0-40%, 40-70%, 70-100%, respectively. In the stage of 0 <= alpha <= 0.40, the most probable mechanism function fits the chemical reaction order function. In the stage of 0.40 <= alpha <= 0.70 and 0.70 <= alpha <= 1.0, the process may not be exactly described by one mechanism function.

Shrinking core model is widely applied to describe the reduction of iron ore pellets, but limited to the illustration on powder sample. The reduction of powder materials is commonly observed in blast furnace production but has been rarely investigated. In this study, thermal kinetics analysis was conducted to describe the powder reduction of dicalcium ferrite (2CaO center dot Fe2O3, C2F), calcium ferrite (CaO center dot Fe2O3, CF), and hematite (Fe2O3, H), with particle sizes below 70 mu m. Isothermal reduction experiments were performed through thermogravimetry analysis under CO atmosphere. The reduction degrees and reaction rate constants increased in the order of C2F, CF, and H at 1123,1173, and 1223 K The reduction rate analysis illustrated that the reduction of C2F, CF, and H appeared as one-, two-, and three-stage reactions, respectively. Moreover, the reduction of C2F and CF proceeded as the 2D reaction mechanism described by Avrami-Erofeev (A-E) equation. The reduction of H was initially controlled by 2D, followed by the 3D A-E kinetics equation. Phase with superior reducibility could be reduced by CO in more dimensions of sample layers. The reduction degrees and rate change expressed by A-E equations were verified to be in accordance with the experimental data. A new kinetics model was proposed to elucidate the reduction of C2F, CF, and H in ultrafine powder compared with that in pellets. The reduction process in the powdered samples comprised independent reduction stages caused by uniform CO diffusion in powdered particles. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

In this study, microwave heating was used to dry nickel laterite, which contains significant quantities of free water, crystal water, and hydroxy water. The results show that the main phase of crystal water is Ca3Al6Si10O32(H2O)(13), and the main phases of hydroxy water are FeO(OH) and Mg-5(Al, Cr)AlSi3O10(OH)(8). The microwave drying process of nickel laterite can be divided into two stages: the removal of free water and the coupled removal of free water, crystal water, and hydroxy water. The effect of particle size and microwave power output were studied, and these indicate that the drying time and specific energy consumption decrease with increasing particle diameter and microwave power. The effective diffusivity and activation energy were calculated, and these are larger in the second stage than that in the first stage. The activation energies are 27.66 and 32.80W/g for the first and second stages, respectively. The phase transition of the product, schematic drying mechanism, and feasibility analysis of the microwave drying process are also discussed.

Since the SiO2 content in nickel laterite is high, it is suggested to add a certain amount of lime into the slag for achieving good fluidity and desulfurization capacity in industrial smelting process. However, it leads to additional cost of lime and the increase in slag volume, then the decrease of effective furnace volume. In order to avoid this problem, the partial reduction of Fe2O3 is suggested, then a considerable amount of SiO2, less MgO and FeO, and very little CaO slag is formed, which has been less studied in the literature. In this study, the effects of binary basicity (MgO/SiO2: mole ratio) and FeO content on the slag viscosity were investigated. The experimental results indicate that the slag viscosity decreases with basicity increasing, and a sharp change of viscosity which was called "turning point" appeared in the vicinity of 1500°C. The slag viscosity certainly drops from 4.5 P to 3.0 P by raising the FeO content from 15% to 25% at 1490°C. In addition, the critical temperature of the slag drops with increasing binary basicity or FeO content.