Effects of Low-temperature Pre-oxidation on the Titanomagnetite Ore Structure and Reduction Behaviors in a Fluidized Bed
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THE utilization of low-grade minerals such as titanomagnetite (TTM) has gained more attention in recent years, due to the increased demand for titanium dioxides and the rapid depletion of high-grade natural source ‘‘ilmenite and natural rutile’’ in the world. These have shifted attention toward the utilization of lowgrade minerals.[1,2] At present, the main route for comprehensive use of TTM is through direct smelting in the blast furnace (BF) to make iron. This process can only recover iron and vanadium, but titanium enriched in slag cannot be effectively used, because of the low concentration of titanium components in slag (22 to 25 AJALA ADEWOLE ADETORO, SHENGYI HE, and QINGSHAN ZHU are with the State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, P.R. China and also with the University of Chinese Academy of Sciences, Beijing 100049, P.R. China. Contact e-mail: [email protected] HAOYAN SUN and HONGZHONG LI are with the State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences. Manuscript submitted June 21, 2017. Article published online February 13, 2018. 846—VOLUME 49B, APRIL 2018
wt pct TiO2).[3] Moreover, due to the scattered distribution of titanium components in the various finegrained mineral phases (< 10 lm) with a complex interfacial combination, it is difficult to recover the titanium components through the traditional BF route.[4] This has prompted the exploration of new routes to utilize titanomagnetite concentrates, such as pyro-hydrometallurgical route and the acid leaching—solvent extraction route.[5,6] These processes, however, are costly, impracticable, and are characterized by high environmental pollution risk. A more promising approach is the so-called two-stage short process, ‘‘the direct reduction (DR)—electric arc furnace (EAF) melting separation processes,’’ which provides a more efficient way of utilizing both the iron and high TiO2 slag.[7] In this process, the role of the DR is to produce metallic iron of a certain metallization before EAF smelting.[8] In comparison to other direct reduction processes, the gas–solid fluidized bed reactor reduction has advantages of using ore fines; this implies large contact surface area; good solid mixing; and high heat transfer, thus improving the overall process efficiency. Extensive research has been carried out on the direct reduction of titanomagnetite ores such as Panzhihua TTM and New Zealand TTM.[9,10] It was reported that
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the reduction of titanomagnetite is slower than that of magnetite. This is because of the presence of titanium cations in the crystal structure, resulting in a higher thermodynamic stability of titanomagnetite.[10] It is well known that reduction of magnetite or ilmenite ore can be improved by pre-oxidation treatment. However, the oxidation product is hematite, and the improvement in the reducibility of magnetite by oxidation is widely attributed to the volume in
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