Kinetics of chlorination and carbochlorination of molybdenum trioxide
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INTRODUCTION AND LITERATURE REVIEW
MOLYBDENUM is principally used as an alloying agent in steels, cast irons, and superalloys to enhance hardness, strength, toughness, and wear corrosion resistance. The Mo compounds are also used in chemical applications such as catalysts (i.e., petroleum hydrorefining catalysts), lubricants, and pigments, l~l Because of environmental regulations, cheap, efficient, and flexible techniques have to be investigated for the recovery of metals from industrial wastes such as spent catalysts. Chlorination could be one of these techniques, m This article summarizes a study of chlorination kinetics of M003 with Clz-air, C12-N2, and C12-CO-N2 gas mixtures. It was realized in the framework of a research program focused on the recovery of Co, Ni, Mo, and V from spent hydrorefining catalysts by selective chlorination.t3.4.Sl The literature review reveals that the chlorination of MoO3 has been investigated using various chlorinating agents. The chlorination products are generally oxychlorides, especially M002C12, while chlorides can be obtained only at very low oxygen partial pressures. The essential features of articles published on this subject are subsequently summarized. Bernard et al. [6] studied the effect of carbon nature (graphite or active carbon or black carbon) on the chlorination of M002 and M o O 3 using C12. The reaction product was molybdenum oxychlorides. According to these authors, in the presence of graphite, only MOO2C12 is obtained during the chlorination of MoO2 and M o O 3 at temperatures lower than 600 ~ A mixture of M o O 2 C I 2 and MoOCI4 is formed in the presence of active carbon from MoO2 starting at 250 ~ and from M o O 3 starting at 300 ~ Furthermore, the authors found that, in the I. GABALLAH, Senior Researcher, Laboratoire Environnement et Minrralurgie, associated with the Centre National de la Recherche Scientifique, Mineral Processing and Environmental Engineering team, and M. DJONA and E. ALLAIN, Researchers, Mineral Processing and Environmental Engineering team, are with the Institut National Polytechnique de Lorraine, 54501 Vandoeuvre, France. Manuscript submitted August 10, 1994. METALLURGICAL AND MATERIALSTRANSACTIONS B
presence of carbon, M002C12 reacts with C12 to give MoOC14. They stated that the initial temperature of formation of oxychlorides decreases as a function of the nature of carbon in the following order: Graphite > black carbon > active carbon In another publication, the same authors proposed a thermodynamic analysis of the formation of M002C12, MoOC14, and MoC% by chlorination of oxides, taking into account the catalytic effect of graphite and active carbon.I v] Guethert et al. 181 also performed a thermodynamic analysis of the Mo-O-C1 system. They then experimented on the chlorination of MoO3 with a Clz + Oz + N2 (0.034 + 0.001 + 0.965 atm) in a tube subjected to a temperature gradient from 15 ~ to 500 ~ After analysis of the reaction products, the authors concluded that only MoO2Clz is formed, in agreement with thermodynamic predictio
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