Morphological Changes of Panzhihua Ilmenite During Oxidation Treatment
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WITH the depletion of rutile minerals worldwide, ilmenite becomes the main source to obtain high-grade synthetic rutile. In the existing upgrading routes, such as the Becher process,[1] the Benilite process,[2] etc., the process of oxidation-reduction-hydrochloric leaching has shown significant advantages as its wide applicability for nearly all kinds of ilmenite ores.[3] Because the oxidation process as a pretreatment has significant influence on the following reduction and leaching processes, e.g., many studies have proved that preoxidation can significantly enhance the reduction rate of ilmenite[4–6] and prevent the pulverization of product during the leaching process,[7,8] a full understanding of it is extremely important for the industry. During the oxidation process, phase transitions and morphological changes take place. Many previous researchers have studied the phase transitions of ilmenite oxidation.[9–16] It is generally accepted that the oxidation products are usually Fe2TiO5 (pseudobrookite), TiO2 JIANBO ZHANG and CHAO LEI, Ph.D. Candidates, are with the State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, P.R. China, and with the University of Chinese Academy of Sciences, Beijing 100049, P.R. China. QINGSHAN ZHU, ZHAOHUI XIE, and HONGZHONG LI, Professors, are with the State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences. Contact e-mail: [email protected] Manuscript submitted January 6, 2013. Article published online May 11, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
(rutile), and Fe2O3 (hematite) at temperatures equal to or above 1173 K (900 C).[9,10,13,14,16] But there are some conflicting reports over the oxidation products in the low and moderate temperatures, i.e., temperatures below 1073 K (800 C). Some researchers[9–12] found that the Fe2Ti3O9 phase was one of the main oxidation products in the low and moderate temperature ranges, whereas TiO2 was not. However, different products were reported for the same temperature ranges of oxidation.[13–15] Fortunately, a breakthrough was made by Fu et al.[16] recently, who illustrated the formation of Fe2Ti3O9 and TiO2 occurred as competing reactions [1] and [2] by investigating the oxidation of ilmenites with different sizes under different oxygen pressures. 4FeTiO3 þ O2 ! 2Fe2 O3 þ 4TiO2
½1
12FeTiO3 þ 3O2 ! 4Fe2 Ti3 O9 þ 2Fe2 O3
½2
It was observed that more Fe2Ti3O9 was produced from ilmenites with a smaller particle size at higher oxygen pressure, whereas TiO2 is the main product with a large particle size at a low oxygen pressure. Therefore, the conflicting results of the oxidation products are possibly a reflection of the competing reactions between Fe2Ti3O9 and TiO2, as the use of ilmenite powders with different particle sizes or different structure. Detailed studies about the morphological changes that give more visual information on the reaction path and mechanism of ilmenite oxidation are relatively few
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