The leaching of chalcopyrite with ferric chloride
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INTRODUCTION
THE dissolution of chalcopyrite in
acidic ferric chloride solution has been studied by many researchers. 1-13Some of those researchers postulated that dissolution occurs electrochemically. Papers reported by Jones and Peters 7 and Palmer et al. 11 are good examples. On the other hand, the anodic behavior of chalcopyrite in chloride media was investigated by Ammou-Chokroum et al. 13'14 They studied the dissolution of chalcopyrite in acidic solutions and postulated that the initial stage of dissolution involves the formation of hydrogen sulfide, ferrous ions, and covellite. Furthermore, they postulated that the ohmic potential drop across the precipitated chalcocite plays an important role in establishing the electrochemical behavior of chalcopyrite. Jones 15 studied the electrochemistry of chalcopyrite dissolution and found that for relatively low applied potentials, activation polarization is observed. For higher potentials, the transport of cuprous ions through the mineral lattice was thought to be rate controlling. Jones data indicate that under those conditions involved in ferric chloride leaching where the potential applied to the anodic site is relatively low, activation polarization assumes importance. Parker e t al. 16.17studied potentiostatic oxidation of chalcopyrite and found the current-time dependence which indicated that the rate of chalcopyrite dissolution was being retarded by diffusion of products through a slowly thickening layer. They concluded that the passivation layer consisted of a copper-bearing species and suggested a copper polysulfide. McMillan e t al. 18 studied anodic dissolution of chalcopyrite in both acidic sulfate and acidic chloride media and
TETSUJI HIRATO, Graduate Student, YASUHIRO AWAKURA, Instructor, and HIROSHI MAJIMA, Professor, are with the Department of Metallurgy, Kyoto University, Kyoto, Japan 606. MAKOTO KINOSHITA, formerly Graduate Student, Kyoto University, is now Research Engineer, Mitsubishi Metal Corporation, Osaka Refinery, Kita-ku, Osaka, Japan 530. Manuscript submitted May 6, 1985. METALLURGICALTRANSACTIONSB
suggested the formation of a surface layer which slows the rate of electron transfer. Biegler and Home 19 studied the electrochemistry of surface oxidation of chalcopyrite in acid solution and found the formation of a passivating film stable at 298 K. Relating to the electrochemistry of chalcopyrite, the anodic behavior of chalcopyrite in sulfate-bearing solutions was examined by Warren, 2~Warren e t a l . , 21 and in ammoniacal solutions by Warren and Wadsworth. 22 Recently Wadsworth pointed out the importance of the use of electrochemical measurements, either anodic or cathodic, in understanding dissolution kinetics. 23 The following points made by him seem to be very important: the experimental methods used are sufficiently sensitive to see transient phase changes that may or may not be of major importance during the gross or massive leaching of sulfide concentrates. The characterization of initial kinetics which is possible by electrochem
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