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

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 B echer process. This process, carried out in a mechanically agitated reactor is a multi-phase system involving a complex interplay between mass transfe r and chemical reactions. Experimental investigations on the kinetics of th is process exhibit a constant rate period followed by a decreasing rate per iod. A process model, which takes into account gas-liquid mass transfer, so lid-liquid mass transfer, intraparticle diffusion of dissolved oxygen, surf ace reaction and homogeneous liquid phase reaction has been developed to in terpret this behaviour. The model also accounts for the influence of the pr ecipitated iron oxide (inert micro-particles) on mass transfer rates, as we ll as on the overall rate of iron removal. The results indicate that the ov erall 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 pr ocess is due to the intraparticle diffusion-controlled leaching of iron by dissolved oxygen. (C) 2000 Elsevier Science B.V. All rights reserved.