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Effect of Temperature and Fluxing Agents on Reaction Mechanism in Ilmenite Ore Smelting Process

Effect of Temperature and Fluxing Agents on Reaction Mechanism in Ilmenite Ore Smelting Process
Alternative Author(s)
Issue Date
2019. 8
As titanium has good physical and chemical properties, e.g. excellent strength, corrosion resistance, fatigue resistance, fracture toughness, and high-temperature characteristics, its demand steadily increases. The major raw material for titanium extraction is rutile (~95% TiO2), which quickly is being depleted. Therefore, ilmenite (FeTiO3, 30-65% TiO2) as a substitutional resource is in the spotlight. There are previous studies about the removing Fe from the ilmenite. However, most of them are about hydrometallurgical processes using acids. The pyrometallurgical process, i.e. smelting process not only could obtain slag with high Ti purity by high temperature heat treatment but also has advantage of using pig iron produced as a by-product as EAF scrap. Therefore, it is important to investigate of ilmenite smelting process. In the first part, the carbothermic smelting reduction process of ilmenite ore at high temperature was investigated by thermodynamic calculations in conjunction with smelting experiments. Based on thermodynamic calculations, conducting the smelting process at a higher temperature was recommended to achieve a larger amount of FeO reduction, i.e., higher Ti-enrichment, as less precipitate and thus large amounts of a liquid slag were predicted. However, even though the reduction of FeO in ilmenite ore at the initial stage seemed to be faster as the temperature increased, no significant difference in the TiO2 or FeO concentration was observed after the reaction was complete, regardless of the temperature. This was caused by the precipitation of pseudobrookite due to the local depletion of FeO during reaction at higher temperatures, by which further reduction reaction was prohibited. The apparent rate constant increased with increasing temperature and the activation energy of the reduction process was estimated to be 144 kJ/mol, from which it was concluded that the reduction reaction of FeO in ilmenite slag by carbonaceous reductant was generally controlled through the mass transfer in the slag phase. Additionally, the formation of TiC also occurred in the iron bath. At 1923 K (1650 C), approx. 20 pct more TiC was generated as compared to TiC formation at 1823 K (1550 C), which also prevented further reduction of Fe at higher temperatures. In the second part, we focused on the energy saving process by considering two factors to improve the efficiency of ilmenite reduction reaction. One is increasing the reduction driving force during smelting. Activity of FeO is the major factor to control reduction in driving force. The other factor is delay in formation of the pseudobrookite phase, a high-melting point precipitation phase. In this system, MgO in ilmenite could be used to form pseudobrookite. To control these factors, in this study, flux agent (i.e., Na2O and SiO2) addition was considered. The thermochemical simulation program, FactSageTM7.0 was used to calculate the viscosity of slag and the activity of components as fluxing agents were added. High-temperature experiments using an induction furnace were also conducted to confirm the computational results. To determine the composition of final slag, X-ray fluorescence analysis was executed. As a result of Fe and Ti behaviours in slag, SiO2 addition showed no significant difference from the slag without flux. However, Fe reduction in ilmenite, i.e. TiO2-enrichment, was more accelerated when Na2O was added. X-ray diffraction, scanning electron microscopic and transmission electron microscopic analyses results also showed that even 1-3wt% Na2O addition significantly influenced TiO2-enrichment compared to no flux addition.
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