Magnetizing roasting of leucoxene concentrate

The phase transformations occurring during magnetizing roasting of leucoxene concentrate in the temperature range 600–1300°C are studied. It is demonstrated, that in the temperature range 600–800°C, only iron oxides are reduced to a metallic state; at temperatures above 800°C, combined reduction of iron and titanium oxides takes place. At 1050°C, reduced specimens are represented by the Ti₅O₉ and Ti₆O₁₃ Magnéli phases. The formation of iron metatitanate (FeTiO₃), under reduction conditions and the existence of ferrous iron ions in the Magnéli phases slightly degrade the magnetic properties of the products of magnetizing roasting. In high temperature region (1200–1300°C), a similar effect is exerted by the formation of iron dititanate or anosovite in the system. The possibilities of eliminating the undesired factors decreasing the magnetic properties of the products of magnetizing roasting are determined.     

High-temperature phase relations and thermodynamics in the iron-titanium-oxygen system

Phase equilibria and thermodynamics in the FeO-TiO₂-Ti₂O₃ ternary system were studied at 1500 °C and 1600 °C. In particular, the liquid slag-phase region and its saturation boundary with respect to metallic iron, titania, and lower titanium oxides was investigated. The liquid slag-phase region extends substantially toward an anosovite (Ti₃O₅) composition, and considerable concentrations of divalent iron coexist with trivalent titanium in the liquid-slag phase. This seems to be a consequence of the complete solid solution between ferrous pseudobrookite (FeTi₂O₅) and anosovite (Ti₃O₅), which exists at subsolidus temperatures. The liquid-slag field is significantly enlarged toward the anosovite composition upon increasing the temperature from 1500 °C to 1600 °C. Activities of the components “FeO” and TiO₂ in the liquid-slag region were determined by Gibbs-Duhem integration of the measured oxygen partial pressures at 1500 °C. The FeO shows moderate negative deviation, while titania shows a slight negative deviation in FeO-rich slags and a positive deviation in high-titania slags. The experimentally measured activity values were modeled using regular and biregular solution models, and good agreement was obtained with the biregular solution model.     

Oxidation State of Titanium in CaO‐SiO2‐TiOx Slags at 1873K

Oxidation state of titanium was determined in CaO‐SiO₂‐TiO_x slags in the composition range 25‐53 percent CaO, 27‐46 percent SiO₂, 10‐55 percent TiO_x at 1873K using gas equilibration method. In the experiments, slags with different titanium oxide contents were equilibrated with a known carbon monoxide and carbon dioxide ratio. The results were used to determine the Ti³⁺ and Ti⁴⁺ contents as well as the activity coefficient ratio of corresponding oxides in the slag. The dependence of the activity coefficient ratio as a function of oxygen partial pressure was determined.     

Effect of titania on the characteristics of blast furnace slags

The objective of this study was to understand the effect of 1 – 2 % titania on the high-temperature properties of blast furnace slags containing high alumina and magnesium oxide. The viscosity and liquidus temperature of semi-synthetic blast furnace slags were measured using a viscometer and a hot stage microscope, respectively, and the data were used to develop a statistical model for predicting the liquidus temperature and viscosity of blast furnace slags. Samples of the titanium bearing accretions were collected during tearing-out of the hearths of Tata Steel's blown-out D and E blast furnaces. They were subjected to various physico-chemical analyses (e.g. chemical, XRD, optical microscopy, SEM and image analysis) in order to understand the mechanism of hearth protection. In the range of composition studied, the liquidus temperature is found to lie between 1365 to 1430°C and the viscosity, between 0.30 to 0.60 Pa · s. Increase in titania fluidizes the slag and also makes it easy-melting. The titanium bearing compounds in the slag show traces of TiC, TiN, Ti₂N, TiO, Ti₂O₃, Ti₃O₅ and Ti₅O₉. A mechanism of formation of these precipitates is proposed in this paper.     

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.     

Solubility of oxygen in Fe–Co melts containing titanium

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO₂) =–7.194; logK(TiO₂) =–6.125; logK(Ti₃O₅) =–16.793; logK(Ti₂O₃) =–10.224) to cobalt (logK(CoO · TiO₂) =–8.580; logK(TiO₅) =–7.625; logK(Ti₃O₅) =–20.073; logK(Ti₂O₃) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO₂, TiO₂, Ti₃O₅, and Ti₂O₃ are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO₂ ? TiO₂ decreases from 1.0 × 10^–4% Ti in iron to 1.9 × 10^–6% Ti in cobalt. The titanium content at the equilibrium point TiO₂?Ti₃O₅ increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti₃O₅ ? Ti₂O₃ decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.     

Understanding the Magnesiothermic Reduction Mechanism of TiO<Subscript>2</Subscript> to Produce Ti

Titanium dioxide (TiO₂) powders in the mineral form of rutile were reduced to metallic and an intermediate phase via a magnesiothermic reaction in molten Mg at temperatures between 973 K and 1173 K (700 °C and 900 °C) under high-purity Ar atmosphere. The reaction behavior and pathway indicated intermediate phase formation during the magnesiothermic reduction of TiO₂ using XRD (X-ray diffraction), SEM (scanning electron microscope), and TEM (transmission electron microscope). Mg/TiO₂ = 2 resulted in various intermediate phases of oxygen containing titanium, including Ti₆O, Ti₃O, and Ti₂O, with metallic Ti present. MgTi₂O₄ ternary intermediate phases could also be observed, but they were dependent on the excess Mg present in the sample. Nevertheless, even with excessive amounts of Mg at Mg/TiO₂ = 10, complete reduction to metallic Ti could not be obtained and some Ti₆O intermediate phases were present. Although thermodynamics do not predict the formation of the MgTi₂O₄ spinel phase, detailed phase identification through XRD, SEM, and TEM showed significant amounts of this intermediate ternary phase even at excess Mg additions. Considering the stepwise reduction of TiO₂ by Mg and the pronounced amounts of MgTi₂O₄ phase observed, the rate-limiting reaction is likely the reduction of MgTi₂O₄ to the Ti_tO phase. Thus, an additional reduction step beyond thermodynamic predictions was developed.     

Enrichment of Fe‐Containing Phases and Recovery of Iron and Its Oxides by Magnetic Separation from BOF Slags

Steel slag normally contains a large amount of iron and its oxides. Therefore, it is a potential renewable resource in case of inadequate iron ore supply. To recover the metals from steel slag, two types of BOF slags were remelted at 1873 K. The liquid slags were cooled using four types of cooling conditions, namely, water granulation, splashing, air cooling, and furnace cooling, to investigate the influence of cooling rate on mineral components, especially the enrichment behavior of Fe‐containing minerals. Subsequently, wet magnetic separation was conducted to examine the relations between iron recovery ratio and cooling conditions. The results show that the slags under the four cooling conditions mainly contained dicalcium silicate, RO phase, Fe_tO, 2CaO(Fe,Al)₂O₃, and calcium ferrite. However, tricalcium silicate, 12CaO·7Al₂O₃, M‐A spinel, and free CaO and MgO were occasionally observed. The amount of glass matrix decreased, the Fe‐containing minerals increased, and the minerals more fully crystallized when the cooling rate of the liquid slag was decreased. From granulation to furnace cooling of the slags, the iron content in the recovered concentrate and the iron recovery ratio both increased. This result is in agreement with the findings on phase transformation through SEM analysis.     

Thermodynamics of TiO x in blast furnace-type slags

Equilibrium studies between CaO-SiO₂-10 pct MgO-Al₂O₃-TiO_1.5-TiO₂ slags, carbon-saturated iron, and a carbon monoxide atmosphere were performed at 1773 K to determine the activities of TiO_1.5 and TiO₂ in the slag. These thermodynamic parameters are required to predict the formation of titanium carbonitride in the blast furnace. In order to calculate the activity of titanium oxide, the activity coefficient of titanium in carbon-saturated iron-carbon-titanium alloys was determined by measuring the solubility of titanium in carbon-saturated iron in equilibrium with titanium carbide. The solubility and the activity coefficient of titanium obtained were 1.3 pct and 0.023 relative to 1 wt pct titanium in liquid iron or 0.0013 relative to pure solid titanium at 1773 K, respectively. Over the concentration range studied, the effect of the TiO _x content on its activity coefficient is small. In the slag system studied containing 35 to 50 pct CaO, 25 to 45 pct SiO₂, 7 to 22 pct Al₂O₃, and 10 pct MgO, the activity coefficients of TiO_1.5 and TiO₂ relative to pure solid standard states range from 2.3 to 8.8 and from 0.1 to 0.3, respectively. Using thermodynamic data obtained, the prediction of the formation of titanium carbonitride was made. Assuming hypothetical ‘TiO₂,’ i.e., total titanium in the slag expressed as TiO₂, and using the values of the activity coefficients of TiO_1.5 and TiO₂ determined, the equilibrium distribution of titanium between blast furnace-type slags and carbon-saturated iron was computed. The value of [pct Ti]/(pct ‘TiO₂’) ranges from 0.1 to 0.2.     

Transient Behavior of Inclusion Chemistry,Shape, and Structure in Fe-Al-Ti-O Melts: Effect of Titanium Source and Laboratory Deoxidation Simulation

During ladle processing of interstitial-free (IF) steel melts, it is possible for transient titanium-containing oxides to be formed if the local titanium/aluminum (Ti/Al) ratio is locally and temporarily increased after aluminum killing. The phase stability diagrams suggest that if the Ti/Al ratio is increased, then Al₂TiO₅ and/or a liquid Al-Ti-O region can become stable, and eventually at even higher Ti/Al ratios, Ti₃O₅ becomes stable. In this study, the Ti/Al ratio was successively altered to investigate (1) how the inclusions evolved after titanium addition to aluminum-killed iron melts and (2) whether the inclusions present after sufficient time were those predicted by thermodynamics. When the Ti/Al ratio was maintained at 1/4, such that Al₂O₃ is the only thermodynamically stable oxide, the results show that transient titanium-containing oxides exist temporarily after titanium addition, but with time, the predominant inclusion was Al₂O₃, which would generate little shape change and produce transient stage inclusions with less titanium contents. When the Ti/Al ratio was increased to 1/1 (Al₂O₃ still being the only thermodynamically stable oxide), the results show a more distinct increase in the titanium content of the transient inclusions. The transient reaction was, in this case, accompanied by an irreversible shape change from spherical to irregular inclusions. When the Ti/Al ratio in the melt was increased to 15/1 within the Al₂TiO₅ stable phase region, the inclusion population evolved from spherical-dominant ones to irregular ones. It was found that the final inclusion chemistry has more titanium but less aluminum content compared with the expected from the Al₂TiO₅ chemistry. Besides, the transmission electron microscopy (TEM) results showed the existence of Ti₂O. When the Ti/Al ratio in the melt was increased such that Ti₃O₅ is the thermodynamically stable inclusion (Ti/Al ratio of 75/1 or ∞), the inclusions evolved after titanium addition toward TiO_x inclusions, which is accompanied by a shape change from spherical to irregular. The TEM results revealed and confirmed the existence of metastable Ti₂O besides the thermodynamically stable Ti₃O₅, and it was consistent with the results based on oxidation studies of thin layers of titanium with Al₂O₃ substrate. It was discovered that Ti₂O has the tendency of transforming into the thermodynamically stable phase Ti₃O₅ under certain conditions.     

Physicochemical aspects of titanium slag production and solidification

The titanium-rich slags produced by ilmenite smelting are unusual in several respects, including their low viscosity, high electrical conductivity, propensity to solidify predominantly as one phase (pseudobrookite), and reactivity (with oxidizers) in the liquid and solidified form. The low viscosity is related to the unexpectedly “basic” behavior of Ti⁴⁺; the high conductivity is likely through an electron transfer mechanism involving the Ti⁴⁺-Ti³⁻ pair; the oxidation behavior is caused by the presence of a significant amount of Ti³⁺. Possible reasons for the nearly single-phase structure of the solidified slag are considered, and it is concluded that the most likely cause is the presence of a eutectic groove close to the M₃O₅ (pseudobrookite) composition. This conclusion was tested by examining the compositions and microstructure of slag samples from a pilot smelter. The results show that the slags do contain a small amount of rutile, in line with predictions. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

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).     

The Influence of SiO2 on the Extraction of Ti Element from Ti‐bearing Blast Furnace Slag

The present paper investigated the crystallization behavior of Ti‐concentrating phases in titanium‐bearing blast furnace slags influenced by the silica content. The objective was to recycle the titanium from titanium‐bearing blast furnace slags by enriching Ti element in anosovite. The effect of SiO₂ on the formation of anosovite in the titanium‐bearing blast furnace slags was studied under C/CO equilibrated atmospheres using a combination of X‐ray Diffraction (XRD) and Energy Dispersive X‐ray Spectroscopy (EDX). It was found that, under the C/CO equilibrated atmospheres, the formed primary phases transformed from perovskite to anosovite by adding SiO₂ up to 35 wt% in the slags. The related mechanism was investigated according to the theory of molten slags structure and the principle of thermodynamics.     

Étude de la valorisation de la magnétite titanifère de la région de Magpie,Québec: Partie II — Composition et structure de la fonte et de la scorie obtenues par fusion réductrice d'un concentré magnétique

Abstract

A magnetic concentrate from Magpie titaniferous iron ore has been smelted in a pilot scale arc furnace. A pig iron containing most of the chromium and vanadium of the ore has been obtained, while the titanium remained in the slag. The main phases occurring in this slag are a pseudobrookite-type solid solution, a spinel and several silicates. The composition of pseudobrookite depends on the reducing conditions and can reach 90% TiO₂. The spinel composition is on the MgAl₂O₄ side of the MgAl₂O₄-Mg₂TiO₄ solid solution.

Résumé

Des essais de fusion réductrice au four électrique en présence de carbone, ont été réalisés sur un concentré magnétique du minerai de Magpie. Ce traitement permet d'obtenir une fonte contenant la plus grande partie du chrome et du vanadium, et une scorie titanifere. Cette dernière est constituée d'une pseudobrookite, d'un spinelle et de silicates. La pseudobrookite est une solution solide de composition variable suivant le degré de réduction et titrant plus de 90% en TiO₂. Le spinelle est de composition voisine de MgAl₂O₄.     

Reaction of the hydrogen-absorbing intermetallic compound TiFe with oxygen. III. Phase composition of the scale formed on TiFe

We have studied the phase composition of the overlayer of scale which forms on TiFe at 700°C and 900°C (τ=5 h) by x-ray and metallographic analysis. The upper layers of the scale were shown to consist of TiO₂ and Fe₂O₃ after heat treatment at 700°C, but the lower layers contain mainly TiO₂, FeO, and Fe. The underlayer on the boundary with the scale contains Ti₄Fe₂O (η-phase). The inert marker is covered with rutile at 900°C, and FeTiO₃ + TiO₂ is below the marker. But the next (relatively thick) internal layer consists of FeTiO₃, TiO₂, and Fe. Large pores associated with intensive growth of the FeO phase are detected in the scale formed at 700°C. As a result, the scale cracks. At 900°C, the scale is denser because the pores and cracks are covered by rutile. We have shown that FeO (p-type semiconductor) is nonstoichiometric in the upper layers of the scale, and TiO₂ (n-type semiconductor) is nonstoichiometric close to the boundary with the alloy. The results obtained correlate with the results for the oxidation kinetics previously studied for FeTi, and support a change in the oxidation mechanism when the temperature increases from 700°C to 900°C. Such a change occurs because of the influence of diffusion of the metal ion on oxygen diffusion through the boundary between the scale and the alloy: diffusion of iron through the vacancies in the FeO lattice at 700°C, and interstitial diffusion of titanium ions in the TiO₂ lattice at 900°C.     

Titanium-vanadium slags produced upon the direct reduction of iron from titanomagnetite concentrates

The phase compositions of complex titanium-vanadium slags that form upon the processing (using the direct reduction of iron) of titanium-magnetite concentrates of ten CIS deposits are studied by X-ray diffraction and optical and scanning electron microscopies. Depending on the phase composition, these slags can be divided into the following three groups: spinellide, anosovite-spinellide, and anosovite slags. The general laws of element distribution between slag phases are determined. In the titanium-vanadium slags, vanadium is shown not to form individual phases and to enter into the compositions of solid solutions, namely, ansovite and spinellides. In ansovite, vanadium is present in the trivalent state in the form of V₂TiO₅. In the absence of the ansovite phase, vanadium concentrates in spinellide solid solutions, which are partly represented by MTiO₄ solutions. The solubility of vanadium in the spinellide MgAl₂O₄ is controlled by the MgO: Al₂O₃ molar ratio in a slag, and part of the aluminum is substituted by vanadium with the formation of an Mg(Al,V)₂O₄ solid solution only if aluminum is deficient.     

Phase transitions during reducing roasting of a leucoxene concentrate with carbon

The phase transitions during the reducing roasting of a leucoxene concentrate with carbon are studied to obtain an anosovite product. Thermodynamic modeling of the reducing roasting is performed, and the influence of the temperature and the amount of a reducing agent on the reduction of rutile to Ti₃O₅-based anosovite is studied. Almost complete reduction of rutile to anosovite occurs in a temperature range of 1350–1400°C in the presence of 2.5–5.0% carbon. The Magnéli phases of various compositions are predominantly formed at lower temperatures and smaller amounts of the reducing agent. At temperatures higher than 1400°C and a reducing agent amount >2.5%, rutile reduction results in the formation of anosovite along with an undesirable titanium carbide phase.     

Effect of Mg on the evolution of non-metallic inclusions in Mn–Si–Ti deoxidised steel during solidification: experiments and thermodynamic calculations

Abstract

The effects of Mg on the evolution of non-metallic inclusions in Mn–Si–Ti deoxidised steels during solidification were investigated in a study based on experiments and thermodynamic calculations. The inclusions were composed of the MgO–MnO–Ti₂O₃–TiO₂ oxide, MnS, and TiN. With the increase of Mg concentration in steels, the phases of oxide inclusions were changed, in the order of pseudobrookite (Ti₃O₅–MnTi₂O₅), ilmenite (MgTiO₃–MnTiO₃–Ti₂O₃), spinel (Mg₂TiO₄–MgTi₂O₄–Mn₂TiO₄–MnTi₂O₄) and MgO. Thermodynamic calculations for inclusion evolutions were in good agreement with the experimental results.     

Effect of TiO2‐content on Reduction of Iron Ore Agglomerates

The effect of titanium oxide on iron ore agglomerates is studied by the use of test sinter, test pellets and synthetic briquettes under laboratory conditions. Titanium favours secondary hematite rather than magnetite, which is the main phase in the sinter of Rautaruukki's Raahe plant. Additionally, the effects of sinter RDI and pellet LTD on the blast furnace process are evaluated using the test results of basket trials in LKAB's Experimental Blast Furnace. The effect of titanium in synthetic hematite is studied as hematite is reduced to magnetite in the RDI test. This occurrence causes deterioration in burden permeability. Synthetic titanium‐bearing iron oxides under controlled conditions are investigated at the University of Oulu. The effect of TiO₂, in solid solution in magnetite, on the magnetite to hematite oxidation is studied separately in order to simulate the final stage of the sintering process. In other experiments, hematite samples doped with various contents of TiO₂ are studied using thermogravimetry under a controlled gas atmosphere (CO/CO₂/H₂/N₂). The TiO₂ content of hematite has a clear effect on reduction degradation. Also increasing content of TiO₂ in solid solution in magnetite radically accelerates the oxidation rate. In the pilot tests, TiO₂ content has a similar negative effect on the reduction strength of both sinter and pellets