H).drometallurgy, 23 (1989) 77-90 77 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands The Leaching of Iron Oxides in Boehmitic Bauxite by Hydrochloric Acid GEORGE PATERMARAKIS and YANNIS PASPALIARIS Department o[ Mining and Metallurgical Engineering, Laboratory of Metallurgy, National Technical University of Athens, Athens (Greece) (Received May 24, 1988; revised and accepted December 11, 1988) ABSTRACT Patermarakis, G. and Paspaliaris, Y., 1989. The leaching of iron oxides in boehmitic bauxite by hydrochloric acid. HydrometaUurgy, 23: 77-90. The leaching of iron oxides from boehmitic bauxite with hydrochloric acid has been investigated by means of optical microscopy, electron microscopy and electron microprobe analysis methods. Similar rectangular parallelepiped-shaped bauxite specimens were used for the leaching experi- ments. The experiments were carried out in a magnetically-stirredspherical reactor, thermostat- ically controlled at different temperatures and concentrations of hydrochloric acid. The kinetics of iron removal were followed by measuring the width of the reacted shell which was formed around the bauxite specimens during leaching. The experimental results suggested that the shrinking unreacted core model applies. The kinetic equation y= k C t 2/3 was found to fit the experimental results satisfactorily. An activation energy of 19.6 kJ mol-1 was found, supporting the idea that the slow stage of the overall reaction is the diffusion of hydrochloric acid through the pores formed mainly by dissolution of hematite phases. In all leaching conditions employed the complete re- moval of iron did not occur. The residual iron in the reacted layer did not appear to be significantly affected by variation of the leaching conditions for which the proposed model applies. INTRODUCTION The removal of iron oxides from bauxites has recently been investigated [ 1- 3 ] for the following reasons: (a) Low iron bauxites (less than 2 wt.% Fe2Q) find application in the pro- duction of refractories [ 2 ]. (b) Prior removal of iron from bauxite before the Bayer process reduces the environmental contamination due to red-mud rejection and makes recov- ery of valuable elements such as vanadium, gallium etc., possible [2]. (c) The iron-free bauxite may be used either for producing alumina by the Bayer process or cell-grade aluminium chloride directly from the ore [ 3 ]. Various methods of iron removal have been reported [ 1-3 ] namely: reaction 0304-386X/89/$03.50 © 1989 Elsevier Science Publishers B.V.