Influence of phase and microstructure on the rate of hydrochloric acid leaching in pretreated Panzhihua ilmenite--颗粒学报PARTICUOLOGY

Zhu, Q., Zhang, J., & Li, H. (2014). Influence of phase and microstructure on the rate of hydrochloric acid leaching in pretreated Panzhihua ilmenite. Particuology, 14, 83–90. https://doi.org/10.1016/j.partic.2013.08.002

Influence of phase and microstructure on the rate of hydrochloric acid leaching in pretreated Panzhihua ilmenite

Qingshan Zhu ^a *, Jianbo Zhang ^{a b}, Hongzhong Li ^a

a State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
b University of Chinese Academy of Sciences, Beijing 100049, China

10.1016/j.partic.2013.08.002

Volume 14, June 2014, Pages 83-90

Received 25 June 2013, Accepted 31 August 2013, Available online 22 October 2013.

E-mail: qszhu@home.ipe.ac.cn

Highlights

• Phase and structure changes during high-temperature oxidation and reduction were investigated.

• Influence of oxidation on leaching process is primarily attributed to the phase change.

• Reduction of as-oxidized ilmenite speeds up iron leaching due to microcracks and holes formation.

• The iron leaching rate is in the order of hematite > ilmenite ≫ pseudobrookite in hydrochloric acid.

Abstract

The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate of Panzhihua ilmenite. The as-pretreated ilmenite was leached with 20% HCl at 105 °C. The leaching process was controlled by the phases and microstructures that evolved during the pretreatment processes. The leaching kinetics of pure hematite, ilmenite and pseudobrookite were characterized to clarify the phase effect on the iron-leaching rate; the rate of iron leaching occurs in the following order in the HCl solution: hematite (ferric iron) > ilmenite (ferrous iron) ≫ pseudobrookite (ferric iron). Therefore, the often-cited notion that ferrous iron dissolves faster in HCl solutions than ferric iron when explaining the pretreatment effects is inaccurate. Moreover, the oxidation pretreatment (at 600–1000 °C for 4 h) cannot destroy the dense structure of the Panzhihua ilmenite. Therefore, the influence exerted by the oxidation on the leaching process is primarily determined by the phase change; oxidation at 600 and 700 °C slightly increased the rate of iron leaching because the ilmenite was transformed into hematite, while the oxidation at 900–1000 °C significantly reduced the rate of iron leaching because a pseudobrookite phase formed. The reduction effect was subsequently investigated; the as-oxidized ilmenite was reduced under H2 at 750 °C for 30 min. The reduction significantly accelerated the rate of subsequent iron leaching such that nearly all of the iron had dissolved after leaching for 2 h in 20% HCl at 105 °C. This enhanced iron-leaching rate is mainly attributed to the cracks and holes that formed during the reduction process.

Graphical abstract

Keywords

Ilmenite; Oxidation; Reduction; Hydrochloric acid leaching

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