Experimental and modelling studies on the aeration leaching process for metallic iron removal in the manufacture of synthetic rutile

Abstract

The aeration leaching process for the removal of metallic iron from reduced ilmenite is a crucial step in the manufacture of synthetic rutile by the Becher process. This process, carried out in a mechanically agitated reactor is a multi-phase system involving a complex interplay between mass transfer and chemical reactions. Experimental investigations on the kinetics of this process exhibit a constant rate period followed by a decreasing rate period. A process model, which takes into account gas–liquid mass transfer, solid–liquid mass transfer, intraparticle diffusion of dissolved oxygen, surface reaction and homogeneous liquid phase reaction has been developed to interpret this behaviour. The model also accounts for the influence of the precipitated iron oxide (inert micro-particles) on mass transfer rates, as well as on the overall rate of iron removal. The results indicate that the overall iron removal process kinetics can be considered as constituted by an external mass transfer-controlled period followed by an internal diffusion-controlled regime. The sluggish kinetics observed towards the end of the process is due to the intraparticle diffusion-controlled leaching of iron by dissolved oxygen.