Kinetics of the selective chlorination of ilmenite

Abstract

Ilmenite (FeO·TiO 2) may be beneficiated by selective chlorination in which the iron is selectively chlorinated as volatile iron chlorides, leaving behind an enriched residue of rutile (TiO 2). Relatively high partial pressures of chlorine and very low partial pressures of oxygen are required for the chlorination of either iron or titanium. Under equilibrium conditions at 1200 K and 1 atm., selective chlorination of ilmenite is not thermodynamically possible in the presence of carbon. The fact that this does occur in practice, however, indicates that non-equilibrium conditions should be maintained. Batch experiments conducted between 915 and 970°C in a horizontal tube furnace showed that the kinetics of selective chlorination were limited by diffusion of iron through a product layer of TiO° which formed from the outside of a particle. This mechanism was supported by point analyses under a scanning electron microscope. The iron content of a sample was used to follow the kinetics of chlorination. It was shown that only about 4% of the titanium was lost as volatiles during chlorination. Calcium and manganese impurities to a lesser extent were removed easily during chlorination, whereas chromium, aluminium, niobium and magnesium were not removed. Vanadium and silicon could be removed only partially.