A study of chromite carbochlorination kinetics
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I. INTRODUCTION
ALTHOUGH chromium is found in a variety of miner¨ als[1] (crocoıte PbCrO4, vauquelinite Pb2Cu[CrO4][PO4], uvarovite Ca3Cr2[SiO4]3, merumite 4 (Cr, Al)2O3 3 H2O, etc.), the main ore of chromium is the chromite mineral, which is a spinel with the simple formula FeCr2O4. Chromite belongs to the spinel group, and its space group is Fd3m.[2] However, naturally occurring chromite ore is characterized by the substitution of Fe21 by Mg21 and that of Cr31 by Al31 and Fe31, with the following general formula: (Mg, Fe21)(Cr, Al, Fe)31 2 O4. Figure 1 shows the chromite structure, where the iron and magnesium occupy the tetrahedral sites while the chromium, aluminum, and iron fill the octahedral ones.[3] The gangue is essentially composed of orthopyroxene, olivine, and plagioclase, as well as hydrous alteration products such as serpentine, chlorite, and talc. About 75 pct of chromite is used for ferrochromium production. Moreover, chromite is used for chemical, refractory, and foundry applications. Natural characteristics such as the chromium-to-iron ratio, the chromite grain size, and the SiO2, Al2O3, MgO, and P contents can be as important as the Cr2O3 content in determining the suitability of a chromite product for various end uses, as well as its market price. Table I[4] represents some chromite specifications for different uses. Thus, the metallurgical chromite is characterized by its high chromium content and a Cr/Fe ratio higher than 2. Conventional mineral processing cannot modify the composition of chromite. This composition can be modified only by using chemical or thermal methods. Chlorination appeared to be a potential approach for beneficiation of poorchromite concentrates and/or ores.[5–8] This article deals with the carbochlorination of chromite concentrate to increase its N. KANARI, Researcher, and I. GABALLAH, Senior Researcher, are with the Laboratoire Environnement et Mineralurgie, associated with the Centre National de la Recherche Scientifique, Mineral Processing and Environmental Engineering Team, INPL-ENSG, LEM, 54501 Vandoeuvre Cedex, France. E. ALLAIN, Scientist, is with the Center of Pyrometallurgy, Department of Metallurgical Engineering, University of Missouri Rolla, Rolla, MO 65409-1460. Manuscript submitted December 29, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
Cr/Fe ratio through selective chlorination of iron compounds. The effect of several parameters on the reaction of the chromite mineral with Cl2 1 CO was studied by using thermogravimetric measurements. The literature is rich with respect to the thermodynamic and kinetic aspects of chlorination of simple oxides contained in chromite (FeO, Fe2O3, Cr2O3, MgO, Al2O3, and SiO2), using different chlorinating agents. Results of this bibliographic study are summarized in References 5 through 8. However, few articles were devoted to the chlorination of chromite ores and concentrates. Athawale and Altekar[9] investigated the selective chlorination of iron oxides contained in a chromite concentrate, by using HCl in a fluidized
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