Partic. vol. 14 pp. 83-90 (June 2014)
doi: 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

qszhu@home.ipe.ac.cn

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