The influence of weathering on the reduction of llmenite with carbon

The reduction of synthetic ilmenite and three ilmenite concentrates (Westralian Sands Limited (WSL), Western Mineral Sands (WMS) and Florida) with coal at 1000 ‡C to 1100 ‡C was stud-ied using thermogravimetry and X-ray diffraction, optical microscopy, and electron probe microanalysis of the products. The rate of reduction and the size of the iron particles decrease with increasing degree of weathering of the concentrate. Stoichiometric ilmenite reduces faster than pseudorutile (Fe₂O₃-3TiO₂), which is a product of weathering. The addition of FeCl₃, which promoted the nucleation of iron, increased the rate of reduction, and significant coars-ening of the iron was obtained at 1000 ‡C. In general, the products of reaction are iron, rutile, reduced rutiles, unreduced ilmenite or a-oxide, and pseudobrookite solid solution. A small amount of manganese (1.2 to 1.6 pct MnO) present in the concentrates stabilizes a pseudobrookite phase which retains a significant amount of iron. The manganese also forms an a-oxide phase, (Fe,Mn)TiO₃, which is mainly a manganese titanate and concentrates toward the center of the reducing particles. Formerly with the Imperial College, London. Formerly with the Imperial College, London.     

Reduction behavior of llmenite with carbon at 1240 °C

A considerable body of literature“[1-17] has been published on various aspects of the solid-state reduction of ilmenite (FeTiO₃) using various reductants. All these investigations were limited up to 1200 °C. The present investigation describes the reduction behavior of two ilmenite concentrates produced by Westralian Sands Limited (WSL) and Western Mineral Sands (WMS) with Collie coal at 1240 °C. These materials were from Australia and were supplied by Tioxide International Limited, United Kingdom. The chemical analyses of these materials, given in Table I, were provided with the materials. The unmilled concentrates were sieved, and the size fraction of 10₄ to 152 μm, which accounted for ≈70 pct of the original material, was used for the experiments. The Collie coal was crushed and sieved to produce particles of the same size fraction. The purpose of this investigation is to study the effect of temperature higher than 1200 °C on the kinetics of the reduction and the formation of various phases after reduction. Formerly with the Department of Materials, Imperial College of Science, Technology and Medicine, London P. Grieveson, formerly Professor of Applied Metallurgy, Department of Materials, Imperial College of Science, Technology and Medicine, London     

Morphological Changes and Reduction Mechanism for the Weak Reduction of the Preoxidized Panzhihua Ilmenite

Morphological changes and phase transition behaviors were investigated for the weak reduction (reduction of ferric iron-to-ferrous state) of preoxidized Panzhihua ilmenite by hydrogen at 873 K to 1073 K (600 °C to 800 °C). Ilmenite was preoxidized for 4 hours at 1023 K and 1173 K (750 °C and 900 °C), respectively, before the reduction. The results revealed that there were two competing reduction routes. At high reduction temperatures, e.g., 1023 K and 1073 K (750 °C and 800 °C), ferric irons from both hematite and pseudobrookite would combine with rutile grains as formed in the preoxidation to form homogeneous ilmenite phase with pores immingled. However, at lower reduction temperatures, e.g., 873 K (600 °C), hematite and pseudobrookite are reduced mainly through direct reduction without the participation of rutile. As a result, the as-reduced ilmenites show great differences in their phase components and microstructure, especially for the Ti species. For ilmenites preoxidized at 1023 K (750 °C), most of the Ti ions present in the needlelike rutile network, but for ilmenites preoxidized at 1173 K (900 °C), Ti distributed in both irregular rutile grains and ilmenite matrix.     

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.     

Kinetics of reduction of ilmenite with graphite at 1000 to 1100 °C

Pellets prepared from mixtures of synthetic ilmenite and graphite were heated in argon at 1000 to 1100 °C and the rate of reduction was followed gravimetrically. No measurable reaction was obtained at 1000 °C but the rate was high at 1100 °C. An inflection in the reduction curve at about 2 pct weight loss at 1050 and 1100 °C was due to the difficulty in nucleating iron. The rate is increased significantly by the addition of ferric chloride which promotes the nucleation of iron. The addition of rutile decreases the rate of reduction and the addition of manganese stabilizes a pseudobrookite phase.     

Structural changes and kinetics in the gaseous reduction of hematite

The mechanism of the gaseous reduction of hematite grains to magnetite was studied. Grav-imetric measurements were carried out for the reduction of Carol Lake hematite pellets and grains in CO-CO₂ atmospheres over the temperature range 500 to 1100°C. The pore size distribution in the reduced magnetite was measured by mercury porosimetry. Partially reduced grains were examined by optical microscopy. At temperatures below 800°C, the reduction of a hematite grain to magnetite occurred at a well-defined shrinking-core inter-face. The average pore size in magnetite formed at 600°C was found to be 0.03 μm. An es-timate of the rate of CO diffusion through pores of this size indicated that the reaction rate at 600°C was controlled by a step near the hematite-magnetite interface. At temperatures above 800°C, the reaction mechanism became altered due to the preferential growth of magnetite along a single direction in each hematite grain. The reduction rate decreased with an increase in temperature, and no microporosity was present in magnetite formed at 1000°C and above. It was postulated that the reaction rate was controlled by the rate of formation of fresh nuclei and by their rate of subsequent growth. Formerly Professor of Applied Metallurgy, Imperial College     

Rate processes and structural changes in gaseous reduction of hematite particles to magnetite

Carol Lake hematite particles were reduced to magnetite at 600 and 1000 °C using CO + CO₂ mixtures. The rate of reduction was measured in gravimetric tests and structural changes followed by optical microscopy, BET surface area, and mercury porosimetry. At 600 °C, the reduction of each grain approximately followed the shrinking core model, and fine pores were created in the magnetite produced. The volume of pores was constant at a porosity level of 8.8 pct, but the average pore size depended on the rate of oxygen removal, and finer pores were obtained under conditions of fast reduction. The reaction followed a different path at 1000 °C and proceeded by sideway thickening of a finite number of magnetite lamellae formed parallel to each other in each grain. Reduced particles showed reentrant surface depressions and cracks, but no porosity. Reaction mechanisms were postulated to relate these structural features to the progress of the reaction. Examination of the reaction steps indicated that the separation of oxygen from solid surfaces was likely to be the rate determining step at both temperatures. This was reflected in rate measurements by a strong dependence on CO pressure while the influence of oxygen activity (as represented by CO₂/CO ratio) was of secondary importance at 1000 °C and negligible at 600 °C. A detailed analysis of reaction rates could not be made, however, because the particles were of a wide range of sizes and their structure changed during reduction. formerly Research Student at Imperial College, London, formerly Professor of Metallurgy, Imperial College, London,     

The effects of nucleation and growth on the reduction of Fe2O3 to Fe3O4

The kinetics of reduction of hematite powder to magnetite in CO-CO₂ gas mixtures at temperatures between 500 and 663 °C have been measured. The reactions are described in terms of a simple nucleation and growth model. The chemical reaction rate constants for the reduction of hematite to magnetite are obtained and the nucleation frequencies of magnetite on hematite are calculated for a range of temperatures and oxygen partial pressures. A possible technique for the improvement of the “reducibility” of dense hematite ores is suggested. Formerly at Metallurgy Department, Strathclyde University, Glasgow, Scotland.     

Feasibility study of the new rutile extraction process from natural ilmenite ore based on the oxidation reaction

Phase relations in the Fe₂O₃-FeTiO₃-TiO₂ system were investigated by equilibrating synthetic samples in evacuated sealed quartz tubes at a temperature of 1373 K. The equilibrium partial pressure of oxygen was measured by the electromotive force (EMF) method in the temperature range of 1273 to 1373 K. The phase diagram and oxygen partial pressure diagram in the titanium-iron-oxygen ternary system were then constructed at 1373 K. Rutile extraction from natural ilmenite ore was discussed from the thermodynamic viewpoint. It is found that rutile can be produced from common natural ilmenite ores not only by the reduction as the conventional titanium-rich slag process but also by an oxidation. Then, the oxidation experiment was conducted in air using Australian ilmenite ore to obtain rutile as one of the coexistent phases. Magnetic separation and leaching experiments for synthesized pseudobrookite and reagent rutile were conducted to confirm the possibility of separation of rutile from pseudobrookite. A new rutile extraction process was then proposed.     

Mass transfer from an oxygen jet to liquid silver

A subsonic jet of pure oxygen discharging from a converging nozzle with a throat diameter of 2.5 mm was directed vertically on the surface of molten silver maintained at 1000°C. The effects of variation in lance height (5 to 25 cm), jet momentum (3000 to 56000 dyne), jet temperature (600° to 1000°C) and interfacial area (45 sq cm to 182 sq cm) were studied. In all cases the oxygen concentration in the silver was measured by lime stabilized zirconia probes. The mean liquid phase mass transfer coefficients calculated for transfer across the total surface area of the bath of 182 sq cm, ranged from 0.001 to 0.015 cmJs. The higher values were obtained with high jet momentums or with low values of the lance height. A decrease in the surface area of the bath to 45 sq cm only slightly reduced the rate of transfer and resulted in a threefold increase in the mass transfer coefficient based on the reduced area. The mass transfer coefficients were independent of the jet temperature providing the jet momentum was maintained constant and there were no thermal gradients in the liquid silver. A. CHATTERJEE, formerly Member of the John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology, London, England. D. H. WAKELIN, formerly Member of the John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology.     

Kinetics of manganous oxide sulfidization in carbonyl sulfide (COS) contaminated atmospheres

To contribute to the mitigation of man-made emission of sulfurous compounds, the susceptibility of manganous oxide for carbonyl sulfide under reducing atmospheres (C-O-S system) has been investigated over the temperature range 700 to 1010 °C (973 to 1283 K). The kinetic investigation employed thermogravimetry and anin situ solid electrolyte oxygen probe to follow the topochemical reaction of spherical MnO pellets under various experimental conditions. The apparent activation energy of sulfidization of manganous oxide, under measured oxygen potentials in the C-O-S system, was determined to be 12.06 (±1.5) kcal/mol (52.33 (±6.28) kJ/mol). Overall sulfidization appeared to proceed by mixed control involving convective mass transfer of COS across the boundary layer and diffusion through the product layer. Formerly with the Department of Theoretical Metallurgy, Royal Institute of Technology, Stockholm     

Kinetics of manganous oxide sulfidization in carbonyl sulfide (COS) contaminated atmospheres

To contribute to the mitigation of man-made emission of sulfurous compounds, the susceptibility of manganous oxide for carbonyl sulfide under reducing atmospheres (C-O-S system) has been investigated over the temperature range 700 to 1010 °C (973 to 1283 K). The kinetic investigation employed thermogravimetry and anin situ solid electrolyte oxygen probe to follow the topochemical reaction of spherical MnO pellets under various experimental conditions. The apparent activation energy of sulfidization of manganous oxide, under measured oxygen potentials in the C-O-S system, was determined to be 12.06 (±1.5) kcal/mol (52.33 (±6.28) kJ/mol). Overall sulfidization appeared to proceed by mixed control involving convective mass transfer of COS across the boundary layer and diffusion through the product layer. Formerly with the Department of Theoretical Metallurgy, Royal Institute of Technology, Stockholm     

A New Approach to Processing Rutile from Ilmenite Ore Utilizing the Instability of Pseudobrookite

Rutile (TiO₂) is a vital industrial material used in pigments and in many other valuable chemicals. A new production process to synthesize rutile from natural ilmenite ore and therefore overcome the environmental problems associated with conventional rutile extraction processes was developed. Because the simple phase separation of ilmenite (FeTiO₃) into Fe₂O₃ and TiO₂ occurs due to air oxidation, extracting TiO₂ by removing Fe₂O₃ may be possible if pseudobrookite (Fe₂TiO₅), known as a stable compound in the Fe₂O₃-TiO₂ system at higher temperatures, is of unstable phase in the lower-temperature range. In order to clarify the potential of this new approach, the phase stability of pseudobrookite in the lower-temperature range is discussed. The free energy of formation of pseudobrookite from the respective pure oxides was measured at temperatures ranging from 1073 K to 1473 K by the chemical equilibrium technique using Al₂O₃ as the reference oxide. The observed free energy is given as a function of temperature: ?G⁰ = 7715 ? 7.7T (J/mol). The results indicate that pseudobrookite has an unstable phase below 929 K. This has important industrial implications as a new approach to producing synthetic rutile from ilmenite ore by oxidation at low temperatures and acid leaching.     

Reduction Behavior of Panzhihua Titanomagnetite Concentrates with Coal

The reduction behavior of the Panzhihua titanomagnetite concentrates (PTC) briquette with coal was investigated by temperature-programmed heating under argon atmosphere in a vertical tube electric furnace. The mass loss behavior of the PTC-coal mixture was checked by thermogravimetric analysis method in argon with a heating rate of 5 K (5 °C)/ min. It was found that there are five stages during the carbothermic reduction process of the PTC. The devolatilization of coal occurred in the first stage, and reductions of iron oxides mainly occurred in the second and third stages. The reduction rate of iron oxide in the third stage was much higher than that in the second stage because of the significant rate of carbon gasification reaction. The iron in the ilmenite was reduced in the fourth stage. In the final stage, the rutile was partially reduced to lower valence oxides. The phase transformation of the briquette reduced at different temperatures was investigated by X-ray diffraction (XRD). The main phases of sample reduced at 1173 K (900 °C) are metallic iron, ilmenite (FeTiO₃), and titanomagnetite (Fe_3–x Ti _x O₄). The traces of rutile (TiO₂) were observed at 1273 K (1000 °C). The iron carbide (Fe₃C) and ferrous-pseudobrookite (FeTi₂O₅) appeared at 1473 K (1200 °C). The titanium carbide was found in the sample reduced at 1623 K (1350 °C). The shrinkages of reduced briquettes, which increased with increase in the temperature, were found to depend greatly on the temperature. With increasing the reduction temperature to 1573 K (1300 °C), the iron nuggets were observed outside of the samples reduced. The nugget formation can indicate a new process of ironmaking with titanomagnetite similar to ITmk3 (Ironmaking Technology Mark 3).     

Studies on the reduction of hematite by carbon

Single pellet experiments have been carried out in a nitrogen atmosphere to study the reduction of hematite by graphite in the temperature range 925 to 1060°C. The effect of variables such as c/Fe₂O₃ molar ratio, pellet size, and so forth, has been investigated. Gas analysis data show a continuous decrease in CO₂/CO ratio during reduction, the values being far away from Fe/FeO equilibrium for wustite reduction by CO. The activation energies associated with different degrees of reduction appear to be widely different suggesting a possible changeover in reaction mechanism during the progress of reduction. X-ray diffraction studies confirm the stepwise nature of hematite reduction. Formerly Research Scholar in the Department of Metallurgy, Indian Institute of Science, Bangalore-560012, India,     

Correlation of structure and superconducting properties in Nb(Cb)-Ti quaternary alloys

The aging behavior of a Nb-Ti alloy containing 60 wt pct Ti and small additions of oxygen and erbium or scandium was characterized and related to superconducting properties. The ternary and quaternary alloys were cold reduced and aged for various times at temperatures between 250° and 1000°C. ω and α phase transformations and oxide precipitation processes were followed by lattice parameter, diffraction intensity, resistivity, and metallographic studies, and correlated with superconducting critical magnetic field and critical current density measurements. The optimum 1 hr aging temperatures for producing ω and α phase precipitation were found to be 400° and 500°C, respectively. Aging at 1000°C produced only oxide precipitation. It was found that oxygen, erbium, and scandium stabilize the α phase but have little effect on ω precipitation. The ω phase proved the most effective fluxoid pinning precipitate. The fine scale dispersoid provided an extremely high number density of pinning sites. Formerly Research Assistant, Department of Metallurgy and Materials Science, M.I.T., Cambridge, Mass. Formerly Research Assistant, Department of Metallurgy and Materials Science, M.I.T. Formerly Research Associate, Department of Metallurgy and Materials Science, M.I.T.     

Order hardening in equiatomic CuPt

Samples of equiatomic CuPt were quenched from above the ordering temperature into icy brine, annealed at 300°, 500°, and 700°C, and examined by microhardness, optical microscope, electron microscope, and X-ray diffraction techniques. In samples annealed for short times at 300° and 500°C a fine-domained mottled structure consisting of all four orientation variants of the ordered cell is seen. Continued annealing produces a coarsedomained grain boundary component which X-ray diffraction shows to have a higher degree of order than the mottled structure. At lower temperatures the grain boundary component grows and replaces the mottled structure to complete the ordering transition. At high temperatures the mottled structures coarsen into order twins lying on (110) and (100) type planes. The transformation to order and the resulting hardness changes are seen to depend largely on the internal strains resulting from the cubic to rhombohedral distortion. Formerly Graduate Student, Metallurgy Program, Department of Chemical Engineering, Georgia Institute of Technology, Atlanta, Ga.     

Electrotransport of carbon,nitrogen, and oxygen in hafnium metal

The electrotransport velocities of carbon, nitrogen, and oxygen in alpha and beta hafnium were determined for the temperature range of 1650 to 2130°C. Diffusion coefficients and effective valences were also obtained for each solute. These data were used to predict the degree of purification achievable in a hafnium rod after electrotransport at 2000°C for different times. A comparison was made between the predicted and experimentally observed results. Formerly Graduate Assistant, Department of Metallurgy, Iowa State University     

Acid dissolution of willemite (Zn,Mn)2 SiO4) and hemimorphite (Zn4Si2O7(OH)2 H2O)

The influence of temperature, pH, acid type, and surface area on the kinetics of the acid dissolution of natural and synthetic willemites and natural hemimorphites has been investigated. Specific rate constants, based upon areas determined by krypton adsorption measurements, were estimated from the experimental data obtained. For both willemite and hemimorphite, the rates of dissolution in different acids are shown to be related to the relative strengths of zinc-acid anion complexes. The reactivity of willemite toward acids increases with increasing replacement of zinc by manganese. Mixed chemical/diffusion control is responsible for the observed rates of willemite dissolution under the conditions studied (HNO₃, HCl, HClO₄, H₃PO₄, H₂SO₄, pH 0.31 to 3.00,T 21 to 94 °C). Estimates of the relative contributions of chemical and diffusional resistances to the overall rate have been made for the dissolution of manganese-free willemite in sulfuric acid solutions. The experimentally measured rates have been demonstrated to be in reasonable agreement with predicted overall dissolution rates. Proposals are made regarding the nature of the diffusion and chemical steps involved in the dissolution process. Hemimorphite was found to be considerably more reactive than willemite and its dissolution is primarily diffusion controlled under the conditions studied (T 20 to 76 °C, pH 2 to 3.5). Formerly a Postgraduate Research Student, Department of Metallurgy and Materials Science, Royal School of Mines, Imperial College, London     

Diffusivity of hydrogen in liquid nickel and copper

The diffusivity of hydrogen in liquid nickel was determined from 1468° to 1550°C by a capillary gas-reservoir technique. The diffusion cell was semiinfinite in length and consisted of Specpure nickel in an alumina capillary. An argon and hydrogen gas flow maintained a constant hydrogen potential at the metal/gas interface. A controlled furnace hot zone of length 23 cm was obtained using eight separate windings of Pt-40 pct Rh wire. The temperature profile in this zone was adjusted so that the top of the cell was hotter than the bottom, to eliminate convection. The experiments were terminated by a rapid nonaqueous quench. The diffusion columns were then sectioned and analyzed by vacuum extraction. Diffusivities were calculated using a solution to Fick’s Second Law. At 1468°C,D = 3.17 x 10⁻³ sq cm per sec with σ = ±0.76 × 10⁻³; at 1550°C,D = 3.48 × 10⁻³ sq cm per sec with σ = ±0.54 × 10⁻³. The diffusivity of hydrogen in liquid copper was determined using a shallow melt and analyzing for the total diffusate content; at 1101°C,D = 0.99 x 10⁻³ sq cm per sec with a = ±0.25 × 10⁻³; at 1201°C,D = 1.26 × 10⁻³ sq cm per sec with σ = ±0.16 × 10⁻³. Formerly with the Nuffield Research Group in Extraction Metallurgy at Imperial College, London, England This paper is based upon a thesis submitted by J. H. WRIGHT in partial fulfillment of the requirements of the degree of Doctor of Philosophy at the University of London.