Chemical and morphological transformation of ilmenite during modification roasting with chlorine in fluidized bed

Abstract

The modification roasting of ilmenite with gaseous chlorine in fluidized bed at 650 °C–750 °C was conducted, prior to hydrochloric leaching for preparation of synthetic rutile. The modification effects were characterized by redox titration, X-ray diffraction, scanning electron microscopy and X-ray fluorescence spectroscopy analysis. During the modified roasting, one third of reacted ferrous iron in ilmenite was chlorinated to form gaseous FeCl3 while the remaining part was oxidized to ferric state. The oxidation rate was found quite fast which was controlled by chemical reaction mechanism. At 650 °C, Fe2Ti3O9 crystallographic shear phase was the major solid product of roasting, as temperature rose, rutile and hematite phases became the main products. Morphologically, the Fe2Ti3O9 product caused no effect on the morphology of oxidized ilmenite, as gaseous FeCl3 generated and volatilized, submicron cracks were extended in the particles. When roasting at 750 °C, rutile phase emerged and nucleated quickly throughout the particles, and the formed rutile grains became the skeleton while volatilization removal of FeCl3, the roasted ilmenite kept their stability and formed target phase with porous structure. Besides, the silicate gangue of mineral was modified from smooth glass morphology to porous structure with more than 50% of calcium in silicate rapidly chloridized. After hydrochloric leaching, the acquired synthetic rutile from modified ilmenite reached a grade of 85.26 wt.% TiO2, and the harmful MgO and CaO contents were reduced to 0.55 wt.% and 0.19 wt.% respectively. The new process of chlorine modification-hydrochloric leaching shows a great applied prospect for synthetic rutile from low-grade ilmenite.

Topics & Concepts