Study of chloridizing volatilization roasting of cinnabar as a basis for a process to obtain mercuric and mercurous chlo
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I.
INTRODUCTION
M E R C U R I C chloride is a primary product used for obtaining various mercury compounds, as a catalyst in organic reactions, as an antiseptic, and in photography to intensify negatives. Mercurous chloride is used in pharmaceutical compounds and with mercuric chloride as a fungicide, tq Mercurous halides show promise of important applications as new materials in the fields of acoustic and optical devicesJ z~ The conventional process for obtaining mercury chlorides requires (1) obtaining metallic mercury from cinnabar by roasting t3] and (2) obtaining a mixture of mercury chlorides by reaction of Hg(0) with C12 at a temperature of 450 ~ with prolonged residence time. Thus, the production of these chlorides constitutes a process in which the mercury contained in cinnabar is reduced to Hg(0) and then is reoxidized to mercury(I) or mercury(II) using C12. The possibility of obtaining mercury chlorides directly from the ore by a chloridizing volatilization process is considered very interesting, because this eliminates the step of obtaining Hg(0) and the following oxidation to the mercury compounds, replacing both by a direct reaction of the ore with a chloridizing agent. Chloridizing volatilization roasting of metal sulfides has been proposed by numerous authors and, in many cases, has been applied on an industrial scale, t4j Several authors have studied the pyrometallurgical reaction of cinnabar with a chloridizing agent. Ionescu and Soare tSl examined the reaction between cinnabar and chlorine to obtain mercuric chloride. The reaction between anhydrous aluminum chloride and cinnabar ore was used by Chaigneau and Chastagnier t61 to prepare HgC12. A. ROCA and M. CRUELLS, Professors of Materials Science and Metallurgical Engineering, and C. NI31qEZ, Full Professor of Materials Science and Metallurgical Engineering, are with the Department of Chemical Engineering and Metallurgy, University of Barcelona, Barcelona, Spain. Manuscript submitted August 19, 1988. METALLURGICAL TRANSACTIONS B
Nfifiez et al.[7] studied the reaction between concentrated cinnabar ore and MgCI2.6H20 to obtain mercury chloride mixtures in a single step. The effects of heating rate, air flow rate, and the MgC12.6H20/cinnabar ratio were examined. A mixture of HgC12/Hg2C12 was formed in all cases, and the decomposition products of the chloridizing agent partially neutralized the sulfur gases (as SO2 and SO3). The extent of this neutralization and the HgCI2/ Hg~Clz ratio depended on the experimental conditions employed, increasing both with (a) low heating rates (long thermal cycles), (b) low air flow rates, and (c) high values of the MgCl2.6HzO/cinnabar ratio. The chloridizing reaction may be completed in 15 minutes using a thermal cycle of 150 ~ to 450 ~ The process of chloridizing cinnabar roasting is based on the reaction between the HC1 produced by the decomposition of a solid chloridizing agent (FeC13-6H20, A1C13.6H20, or MgC12.6H20), air, and cinnabar. The principal reasons for the choice of a solid chloridizing agent were (a
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