Effects of High-Temperature Preoxidation on the Titanomagnetite Ore Structure and Reduction Behaviors in Fluidized Bed
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TITANIUM dioxide (TiO2) is the world’s third major inorganic chemical.[1] At present, ilmenite (TiO2 45 to 55 wt pct) and natural rutile (TiO2 > 94 wt pct) are the main minerals used for the production of titanium-containing compounds. Since these high-grade titanium-containing sources are decreasing in the world, the use of low-grade minerals, such as titanomagnetite (TTM, TiO2 10 to 16 wt pct), has attracted more attention, which accounts for about 91 pct of the overall titanium reserves.[2] In the TTM raw ore, besides the high-value component TiO2, there are significant amounts of iron oxides (TFe ~ 55 wt pct). Adopting the same smelting process as ilmenite (TFe ~ 35 wt pct) to produce high titanium slag using an electric arc furnace (EAF) will cause practical production problems, such as an energy consumption increase, lining erosion, and a production efficiency decrease.[3] In the past decades, much research HAOYAN SUN, QINGSHAN ZHU, FENG PAN and ZHEN WANG are with the State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, People’s Republic of China. Contact emails: [email protected] and [email protected] AJALA ADEWOLE ADETORO is with the State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, and also with the University of Chinese Academy of Sciences, Beijing, 100149, People’s Republic of China. Manuscript submitted November 27, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
has been conducted to improve the use of TTM. The direct reduction (DR)–EAF melting separation process, namely, the two-stage short process, proposed to be a more practical and effective way, and similar processes, such as COREX and FINEX, have been applied in the ironmaking industry.[4] In this process, the role of DR is to produce the reduced ore with a certain metallization degree for EAF smelting.[3] By taking advantage of the low-temperature selective reduction in the DR process, the operating load of EAF can be reduced, further extending the furnace life and improving the overall process efficiency. Due to the presence of magnetite as the main iron oxide and high content of TiO2 in the TTM raw ore, the DR rate of the complex mineral TTM is significantly lower than the common iron ore concentrate (TFe > 60 wt pct).[5] It is well known that the reducibility of magnetite can be greatly improved by preoxidation to hematite. This is explained by the volume increase of about 25 pct in the transformation of magnetite to hematite rearranged from the face-centered-cubic structure to the close-packed-hexagonal structure, which opens up the structure and facilitates the reduction.[6] The preoxidation is also a broadly adopted practice in the processing of ilmenite to enhance its reduction rate.[7,8] However, the details of the effect of preoxidation on reduction are ambiguous. Gupta suggested that pseudobrookite solid solution formed in the sintering process was reduced faster than stoichiometric ilmenite.[9] J
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