Effect of Temperature on Carbothermic Reduction of Ilmenite

The reduction of ilmenite (FeTiO3) has been studied extensively. Temperature for the carbothermic reduction of ilmenite ranges from 900 ℃ to 1 400 ℃, and the reduction degree of Panzhihua ilmenite increases with increasing temperature. X ray diffraction analysis and SEM analysis were used to identify the phase before and after reduction, and to identify the morphology of reduced samples respectively. It is found that the reaction initiates at about 860 ℃. The reaction rate varies with temperature simultaneously. Impurities in Panzhihua ilmenite decrease the reduction degree. Magnesium and calcium oxide-rich zone is formed preventing complete reduction of Fe^2 . In general, the reaction products are iron, Ti3O5 and carbon.     

Mechanically activated carbothermic reduction of ilmenite

A systematic study of the effect of milling conditions on the low-temperature carbothermic reduction of the mineral ilmenite has been carried out. It was found that after ball milling of an ilmenite-carbon mixture at room temperature, the ilmenite was reduced to rutile and metallic iron during subsequent low-temperature annealing (760 °C for 30 minutes). A longer milling time results in a lower reduction temperature and a higher reduction rate. Higher milling intensity also leads to a lower reduction temperature. This enhanced reduction reaction induced by ball milling mainly results from the intimate mixing and large contact area between milled ilmenite and carbon particles.     

A Study of the Effect of Aluminium on the Mechanochemical Reduction of Hematite by Graphite

The effect of addition of small amounts of aluminium on mechano‐chemical reduction of hematite by graphite was studied. Various amounts of aluminium (0 to 10%) were added to a hematite‐graphite mixture, in which C/O ratio was 1:1. The hematite‐graphite‐aluminium mixtures were then subjected to ball milling followed by heating up reduction. The heating up reduction was carried out in Ar atmosphere, using TG‐DTA device. In TG‐DTA experiments, samples were heated by a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained for 30 minutes at this temperature. To clarify the reactions which took place during milling and heating up reduction, the samples were subjected to XRD examinations. It was found that the heat generated during exothermic reaction of aluminothermic reduction of hematite promoted the endothermic reaction of carbothermic reduction. In the course of heating up reduction, the carbothermic reaction occurred just after aluminothermic reaction. Increasing of aluminum content from 0 to 10% in 2 hours ball milled samples decreased the temperature of carbothermic reaction from 1020 °C to about 860 °C. The further ball milling of the samples up to 5 and 10 hours, for the samples containing 10 and 5% aluminium respectively, caused the decrease of the temperature of aluminothermic and carbothermic reactions to around the melting point of aluminium.     

钛铁矿的还原技术研究现状

在简要分析当前钛铁矿还原富集技术中存在的问题的基础上,阐述了钛铁矿的非碳热还原及常规碳热还原技术的国内外研究现状。结合微波加热的特点,重点阐述了钛铁矿的微波碳热还原的国内外研究现状。指出,微波加热应用于钛铁矿的碳热还原,能明显提高炭的还原能力,提高还原速率,缩短反应时间,大幅度降低能耗,显示出良好的经济价值和潜在的工业化前景,同时也指出了钛铁矿微波碳热还原技术中需要解决的问题。     

Reduction of Manavalakurichi ilmenite by Activated Charcoal in Presence of Catalyst

The reserves of ilmenite are abundant in India; however, it needs to be upgraded to synthetic rutile. The carbothermic reduction is one of the most effective processing methods to produce TiO₂. However, it is more energy intensive method as is carried out at high temperature. The present paper studies the carbothermic reduction of Manavalakurichi ilmenite concentrate by charcoal in the presence of sodium carbonate. The sodium carbonate as catalyst has significant effect on kinetics of reduction. It is able to save energy by reducing the reduction temperature for same degree of reduction at high temperature without catalyst.     

30MVA直流电弧炉冶炼钛渣配碳比研究

工业生产中,为生产出合格的钛渣必须加入适量的碳作为还原剂,将高价氧化物还原为低价氧化物。云南某公司30 MVA大型密闭直流电弧炉(DC炉)生产运行过程中,通过控制无烟煤用量与钛精矿用量之比——配碳比(ratio of anthracite to ilmenite,简称AIR),使生产在输入能量一定、钛精矿成分稳定的条件下力求获得良好的产品品质。生产通过中空石墨电极将钛精矿和无烟煤加入DC炉内,熔炼温度控制为1973～2023 K;熔炼输入功率为15 MVA;入炉钛精矿粒度为0.1～0.33 mm;入炉无烟煤粒径为5～25 mm的比例大于85%。理论上熔炼还原1 t钛精矿,将会产出526 kg渣和368 kg金属铁,O/I比率约为89.4%,理论配碳比约为7.895%。通过生产物料衡算得出,一定熔炼周期内的AIR平均值为12.228%,O/I比率平均值为81.317%。在配碳量不足的情况下,钛精矿中的FeO易于离解出氧并与碳结合,使FeO还原反应优先于TiO2等氧化物,碳最大可能的消耗在FeO的还原上;配碳量越高,则碳将用于还原难还原的氧化物(如MgO,CaO,MnO等)上,使FeO的还原受到抑制。配碳比还会影响DC电炉熔渣流动性和挂渣层。试生产熔炼周期内,通过调整AIR,实现了钛渣中TiO2品质的提高,其含量可从82%提高到89%以上。     

Influence of Temperature on Reaction Mechanism of Ilmenite Ore Smelting for Titanium Production

Metallurgical and Materials Transactions B - The carbothermic smelting reduction process of ilmenite ore at high temperature was investigated by thermodynamic calculations in conjunction with...     

Gas Ionizationon During Carbothermic Reduction in Microwave Field and Its Effect

 Ionization of gas on carbothermic reduction of metal oxides containing coal by microwave heating is studied in the paper. The result of using the conventional heating method to conduct the carbothermic reduction of metal oxides containing coal is obviously weaker than that of the microwave heating in the term of the reduction time, temperature, atom mole ratio of carbon and oxygen. After studied on the cause, it is believed that gas is ionized in carbothermic reduction of solid-solid phrase between metal oxides and coals, which accelerates progress of carbon gasification and significantly improves kinetic conditions of carbothermic reduction.     

Effects of Temperature on Vacuum Carbothermic Reduction of Panzhihua Ilmenite Concentrate

Metallurgist - The vacuum carbothermic reduction of ilmenite concentrate was analyzed using SEM, EDS, and XRD, in combination with analysis of the Fe metallization rate. Results show that...     

硼铁精矿的碳热还原动力学

为了揭示硼铁精矿的碳热还原机理,以高纯石墨为还原剂,进行硼铁精矿含碳球团等温还原实验,并采用积分法进行动力学分析.还原温度分别设定为1000、1050、1100、1150、1200、1250和1300℃,配碳量即C/O摩尔比=1.0.当还原度为0.1<α<0.8时,温度对活化能和速率控制环节有重要影响:还原温度≤1100℃时,平均活化能为202.6 k J·mol^-1,还原反应的速率控制环节为碳的气化反应;还原温度>1100℃时,平均活化能为116.7 k J·mol^-1,为碳气化反应和Fe O还原反应共同控制.当还原度α≥0.8时(还原温度>1100℃),可能的速率控制环节为碳原子在金属铁中的扩散.碳气化反应是含碳球团还原过程中主要速率控制环节,原因在于硼铁精矿中硼元素对碳气化反应具有较强烈的化学抑制作用.     

As2O3真空碳热还原制备粗金属砷的热力学研究

采用HSC Chemistry 5.0热力学分析软件研究了As2O3真空碳热还原制备粗金属砷过程的吉布斯自由能与温度的关系,重点研究了挥发过程、碳热还原过程及砷蒸汽冷凝过程。结果表明,常压下As2O3在773K时以As4O6(g)双原子气态形式挥发,而在100Pa下挥发只需473K即可,与实际情况一致;As2O3(g)气体参与碳热还原过程的可能性较小,As2O3(s)粉末、As4O6(g)气体在100Pa真空压力下参与碳热还原反应温度分别是473～810K、873K,该温度均低于常压碳热还原过程所需温度(893～1 203℃);砷蒸汽的冷凝过程是As4(g)蒸汽先凝结成液态砷后,再冷凝成固态粗金属砷。     

Influence of pellet composition and structure on carbothermic reduction of silica

The melting zone in a cupola has temperatures greater than 1773 K and a reducing atmosphere. This condition is suitable for the carbothermic reduction of silica. The key to the applicability of carbothermic reduction of silica for ferroalloy production is rapid in situ production of SiC and its subsequent dissolution in the hot metal. The main objective of this investigation was to study the kinetics of the carbothermic reduction process and determine the optimum parameters for rapid and complete in situ conversion of silica to SiC. At temperatures above 1773 K, the key reactions in the carbothermic reduction process are (1) SiO₂ (s)+CO (g)=SiO (g)+CO₂ (g), (2) SiO (g)+2C (s)=SiC (s)+CO (g), (3) C (s)+CO₂ (g)=2CO (g). To meet the objective of this study, conditions must be such that the surface reactions occurring at the carbon and silica surfaces are rate limiting and the entire silica is converted to SiC. Pellet composition and structure in terms of carbon to silica ratio, their particle sizes, and compaction pressure that ensure surface reaction is rate controlling were determined. The gas-solid reaction kinetics was mathematically modeled in terms of the process parameters. The reaction kinetics improved by reducing both carbon and silica particle sizes. However, below a certain critical particle size, there was no significant improvement in the reaction kinetics. For complete conversion of SiO₂ (s) to SiC (s), excess carbon and critical porosity are necessary to ensure that the entire SiO (g) generated by Reaction [1] is consumed via Reaction [2] within the pellet.     

The electrowinning of lithium from chloride-carbonate melts

It is shown that lithium can be electrowon from a lithium chloride-carbonate electrolyte with current efficiencies as high as 90 pct from cells where the catholyte and anolyte are separated by a porous diaphragm and lithium carbonate is fed to the anolyte. The reduction of carbonate ions at the cathode was kept to a minimum by the porous diaphragm. The primary product of the reaction of carbonate ions with the carbon anode was carbon dioxide. Various cell designs were investigated, and a packed-bed anode consisting of a graphite tube containing a bed of graphite particles showed the greatest promise in providing a dimensionally stable current collector with preferential consumption of the bed material. Formerly University Lecturer, Department of Materials Science and Metallurgy, University of Cambridge     

On the Behaviour of Hematite and Graphite Blend during Ball Milling and Heating Up Reduction of Milled Mixture

The effect of ball milling under argon and air atmospheres on the reaction behaviour of the mixture of sintered hematite and graphite was investigated. Thermo‐gravimetry / differential thermal analysis (TG‐DTA) was adopted to determine the effect of milling time on the reduction process during heating up under Ar atmosphere. The samples were heated at a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained at this temperature for 30 minutes. TGL (thermo‐gravimetry loss) curves showed a decrease of onset temperature of reduction with increase of milling time. XRD patterns of milled samples at room temperature revealed that the peaks of graphite disappeared after 48 hours milling. This represents the transformation of crystalline structure of graphite to the amorphous structure. By increasing the milling time to 72 hours, magnetite peaks appeared in the XRD pattern as a result of reduction of hematite with graphite during milling. However, the amount of magnetite formed during milling process increased as milling proceeded. The powders milled under Ar atmosphere became more active than the powders milled under air and consequently the carbothermic reduction of hematite in powders milled under Ar atmosphere was observed at lower temperatures compared with air‐milled powders. It was observed that the reduction time of hematite in powder mixture was decreased with increase of sintering time of hematite prior to milling.     

Vacuum Carbothermic Reduction of Panzhihua Ilmenite Concentrate: A Thermodynamic Study

Electric arc furnace is mainly used in the production of high titania slag; however, since impurities cannot be eliminated, this causes difficulty in the production of titania pigment with chlorination process. Consequently, removing impurities is the crucial way to deal with low-grade ilmenite, especially for the Panzhihua ilmenite concentrate in China. This article studied the theoretical calculation of vacuum carbothermic reduction of Panzhihua ilmenite concentrate. Thus, when the temperature was higher than 1600°C and the carbon amount was greater than 12%, all of the Fe almost entered into the gas phase. When the temperature was higher than 1300°C and the carbon amount was greater than 14%, magnesium also entered the gas phase. When the temperature was higher than 1100°C, most of the element manganese was volatilized in the gas phase. The TiO₂ grade increased with the increase in carbon amount (14%). When the temperature was higher than 1600°C and the carbon amount was less than 14%, the TiO₂ grade in the slag phase could reach the maximum value, which can be used for the chlorination process to prepare titanium dioxide.     

Tick-borne recurrent fever. Description of 5 cases

The effect of sodium and potassium ions on intracellular acid production and acid excretion by glycolyzing cells of Streptococcus mutans was examined. S. mutans NCTC 10449 grown under glucose-limited and strictly anaerobic conditions in a continuous culture system was loaded with bis(carboxyethyl)-carboxyfluorescein, a pH-sensitive fluorescent dye, washed and suspended in 0.00-0.30 M NaCl/KCl solution. The dye allowed for the continuous monitoring of intracellular pH while proton excretion was measured simultaneously with a pH-stat. Sodium ions inhibited and potassium ions, at low pH, accelerated the amount of measurable acid excreted extracellularly. In the presence of both NaCl and KCl, proton excretion following the addition of glucose was slightly higher or similar to that observed in the presence of 0.15 M KCl alone. Sodium and potassium ions did not affect the proton-ATPase enzyme or the intracellular level of ATP, suggesting that these ions did not directly effect proton pumping activity itself. The inhibition of proton excretion by sodium ions was considered to have probably occurred as a result of an indirect inhibition of proton-ATPase activity by the low intracellular pH induced by sodium ions.     

Conference Report - 4th European Continuous Casting Conference

Abstract

In this research carbothermic reduction of mechanically activated hematite–graphite–copper mixture was investigated. The effects of Copper and milling time on reduction behaviour of mixtures were studied by differential thermal analysis and thermogravimetry experiments. SEM and XRD techniques were also used to evaluate microstructure and phase constituent of the samples. By mechanical activation of the hematite–graphite–copper mixture the reduction temperature could be decreased >200°C. The presence of copper in mixture has an additional effect on the initiation of the Boudouard reaction at lower temperatures. Thus the gaseous reduction of Hematite with CO was started at a temperature as low as 790°C when Cu was used in the activated mixture.     

碳热还原法回收不锈钢尾渣中铁和铬的试验

 在理论分析的基础上,对国内某钢厂不锈钢尾渣进行高温碳热还原试验研究,研究了碳当量、碱度、反应温度和保温时间对铁、铬还原率的影响。结果表明,增加碳当量、降低碱度和提高反应温度均能提高铁、铬的还原率,铁的还原率最高可以达到93.29%,铬的还原率最高为76.49%。其中碳当量较低时,铁、铬的还原率均较低,随着碳当量的增加,在铁的还原率趋于稳定后,铬的还原率会大幅上升;碱度为1.4～1.2时,铁和铬的还原趋于平缓;当保温时间超过60 min后,延长时间并不能显著地提高铁、铬的还原率。     

Carbothermal Reduction of a Primary Ilmenite Concentrate in Different Gas Atmospheres

The carbothermal reduction of a primary ilmenite concentrate was studied in hydrogen, argon, and helium. Ilmenite and graphite were uniformly mixed and pressed into pellets. Reduction was studied in isothermal and temperature-programmed reduction experiments in a tube reactor with continuously flowing gas. CO, CO₂, and CH₄ contents in the off-gas were measured online using infrared sensors. The phase composition of reduced samples was characterized by X-ray diffraction (XRD). Oxygen and carbon contents in reduced samples were determined by LECO analyzers (LECO Corporation, St. Joseph, MI). The main phases in the ilmenite concentrate were ilmenite and pseudorutile. The reaction started with the reduction of pseudorutile to ilmenite and titania, followed by the reduction of ilmenite to metallic iron and titania. Titania was reduced to Ti₃O₅ and even more to Ti₂O₃, which was converted to titanium oxycarbide. Reduction was faster in hydrogen than in helium and argon, which was attributed to involvement of hydrogen in the reduction reactions. The formation of titanium oxycarbide in hydrogen started at 1000 °C and was completed in 300 minutes at 1200 °C, and 30 minutes at 1500 °C. The formation of titanium oxycarbide in argon and helium started at 1200 °C and was not completed after 300 minutes at 1300 °C.     

真空碳热还原制备Mg-Sr合金的反应热力学

介绍了真空碳热还原制备Mg-Sr合金新思路,研究了其还原反应的反应式、吉布斯自由能及临界还原温度。结果表明,真空碳热还原MgO,SrO的混合物可以得到Mg-Sr合金;其他因素不变的情况下,还原反应吉布斯自由能随反应温度的提高而减小,随系统气压的降低而减小,随反应生成的Sr,Mg混合蒸气中Sr摩尔分数的减小而减小;反应温度的提高、系统气压的降低和Sr摩尔分数的减小均有利于还原反应的进行;当系统气压为10 Pa,Sr摩尔分数为0.1时,临界反应温度为1353 K;相同系统气压下,碳热还原制备Mg-Sr合金的临界反应温度低于真空碳热炼锶、炼镁的临界温度,反应更易于进行;常规真空硅热还原制备金属镁(皮江法)的反应温度1473 K,气压13.3 Pa下,无论反应生成的Sr,Mg混合蒸气中Mg,Sr相对比例如何,真空碳热还原制备Mg-Sr合金的反应均具备热力学可行性。