Beneficiation of ilmenite

Abstract

Reduction of WMS ilmenite was carried out in the temperature range 1314^oC to 1517^oC using Collie coal as a reductant, and in the range 600^oC to 800^oC using hydrogen. In both temperature ranges, the rate of reaction increased with temperature. The mechanism of reduction, in both temperature ranges, was determined by considering rate data and X-ray diffraction results. In the higher temperature range the reduction products were titanium-oxycarbide and iron and the mechanism of oxycarbide formation was dependent on temperature, oxygen partial pressure and carbon activity. In the lower temperature range reduced rutile and iron were formed, and the mechanism was assessed to be similar to that reported in the literature for other ilmenite ores. Microstructural examination showed that at 1413^oc and 1314^oC the titanium oxycarbide was dispersed evenly in the iron, and E.P.M.A. showed that all manganese was confined to the iron phase. At 1517^oC agglomeration of the oxycarbide phase occurred and manganese was found to be trapped at the pores. Decarburisation of the iron phase, was found to cause separation of the oxycarbide from the iron. Sessile drop experiments were carried out to examine the wetting characteristics of titanium carbide and iron with various carbon contents. The results of wetting experiments are explained in terms of associative adsorption of carbon and titanium. In the lower temperature range, kinetic measurements using a thermogravimetric technique, showed that the reaction is controlled by a mixture of gaseous diffusion and chemical reaction. In the later stages of reduction at 700^oC and 800^oC diffusion through a solid iron layer controls. The effects of preoxidation and heat treatment in an inert atmosphere were investigated. The former was found to accelerate and the latter to slow down the reaction. These effects are explained in terms of surface area available for reaction. A limited number of experiments were carried out on WSL, Norwegian and Natal ilmenite, and compared with the results for low temperature reduction of WMS ore. Prereduced ilmenite was carburised in CO/H₂ at 700^oC and the effect of this treatment on phase separation after subsequent heat treatment at 1300^oC investigated. Agglomeration of iron was found to be inhibited by sintering of the oxide grains.