Carbothermal Reduction of a Primary Ilmenite Concentrate in Different Gas Atmospheres
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UCTION
METALLIC titanium and titania white pigment are produced from titanium tetrachloride, which is obtained by the chlorination of high-quality titania ores or synthetic rutile and slag with high titania contents. Ilmenite ore is the main titanium resource, which consists of titanium and iron oxides and impurities, such as MnO, SiO2, MgO, Al2O3, CaO, V2O5, Cr2O3, and others.[1] It is necessary to remove iron from ilmenite ores to obtain titanium-rich material for chlorination. Many methods have been proposed to refine ilmenite, including smelting, direct acid leaching, selective chlorination, and reduction.[2–5] Selective reduction of iron oxides and following leaching, such as the Becher process, is one of the most effective technologies to produce synthetic rutile. Merk and Pickles[6] studied the reduction of ilmenite by carbon monoxide at 500 °C to 1100 °C. The increase in temperature had a significant effect on the reduction rate. The reduction rate and final degree of reduction were affected by the formation of a metallic shell of iron that inhibited the transfer of CO to the reaction zone. By ball milling of the carbon–ilmenite mixture, Chen et al.[7] decreased the temperature of the carbothermal reduction of mineral ilmenite to rutile and metallic iron. A longer milling time resulted in a lower reduction MOHAMMAD A.R. DEWAN, Research Associate, GUANGQING ZHANG, Lecturer, and OLEG OSTROVSKI, Professor, are with the School of Materials Science and Engineering, University of New South Wales, UNSW, Sydney, NSW 2052, Australia. Contact e-mail: [email protected]. Manuscript submitted May 25, 2009. Article published online September 29, 2009. 182—VOLUME 41B, FEBRUARY 2010
temperature and a higher reduction rate. Park and Ostrovski[8,9] studied the reduction of titaniferrous ore using a H2-Ar gas mixture in the temperature range from 700 °C to 1100 °C and a CO-Ar-CO2 gas mixture at 1100 °C to 1200 °C. A rise in the temperature as well as in the hydrogen or carbon monoxide content in the atmospheres increased the reduction rate. The chlorination of titania requires a high temperature of 800 °C to 1100 °C. Impurities are also chlorinated in this temperature range. However, titanium carbide or oxycarbide can be chlorinated at low temperatures,[10] at which the chlorination of impurities can be avoided. Therefore, requirements of materials to be chlorinated can be released, so that titanium resources are used more effectively. The carbothermal reduction of ilmenite to titanium oxycarbide was studied.[11–17] Terry and Chinyamakobvu[12] investigated the production of titanium oxycarbide-iron composites by carbothermal reduction of ilmenite with coal in flowing argon. They reported an excellent dispersion of Ti(O,C) in an Fe matrix at temperatures above 1450 °C. Coley et al.[11] reduced Western Australia ilmenite using collie coal at 1314 °C to 1517 °C. It was suggested that titanium oxycarbide was formed from Ti3O5 at temperatures below 1413 °C and from Ti2O3 above the temperature. Welham and Williams[14] reported th
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