Mineralogical changes occurring during the ferric lon leaching of bornite
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INTRODUCTION
FERRIC sulfate and ferric chloride leaching processes are being evaluated as alternatives to conventional copper smelting technologies. 1 Although the hydrometallurgical route suffers from a higher energy requirement, it has the great advantage of producing elemental sulfur rather than SO2 gas, the collection and treatment of which has long plagued the copper smelting industry. Bornite is a minor copper ore mineral in many commercial copper concentrates. Hence, the behavior of bornite in ferric sulfate and ferric chloride media is of some industrial importance, and several studies on the reaction of bornite with ferric ion media have been done. Dutrizac et al. 2 summarized the early leaching studies of bornite and discussed the leaching kinetics in ferric sulfate solutions. The reaction is characterized by a very rapid initial stage, a rapid second stage, and an extremely slow third stage. Ugarte and Burkin 3 elaborated on the reactions in ferric sulfate media and confirmed the presence of three reaction stages, the first two of which are rapid. Most recently, Pesic 4 and Pesic and Olson 5 have reported on the dissolution of bornite in ferric chloride media; they noted two stages of reaction together with a "transition period" between the two stages. Again, a rapid initial reaction followed by much slower dissolution kinetics was observed. Although there is no unanimity concerning the leaching reactions involved, the leaching of bornite by ferric ion seems to proceed through steps which, in their simplest form, consist of: 1. The rapid removal of copper from the bornite while leaving its structure relatively undisturbed; this product con-
J.E. DUTRIZAC, Head, Metallurgical Chemistry Sectxon, and T.T. CHEN and J. L. JAMBOR, Research Scientists, Process Mineralogy Section, are with the Mineral Sciences Laboratories, CANMET, Energy, Mines and Resources, Canada. Manuscnpt submitted January 8, 1985. METALLURGICALTRANSACTIONS B
forms to nonstoichiometric bomite which has cell dimensions slightly smaller than those of bornite. 2. The conversion of the copper-deficient bornite to a copper-iron sulfide having an ideal formula of Cu3FeS4 but whose composition range is extremely large. The formation of chalcopyrite2 or other phases 3 has also been reported to accompany the Cu3FeS4 phase. In their detailed study of bomite leaching, Pesic and Olson 4'5 identified chalcopyrite lamellae, covellite, and digenite in many of their leach residues. 3. The decomposition of the Cu3FeS4 phase to sulfur and soluble copper and iron; this reaction occurs to a significant extent only at elevated temperatures. Some authors have attempted to equate the Cu3FeS4 phase with the mineral idaite. Although the natural occurrence of a compound of an approximate composition Cu3FeS4 has been reported on several occasions, the lack of correlative X-ray data has cloaked the species status in ambiguity. Idaite, first described from the Ida mine, Southwest Africa by Frenzel, ~ was suggested to be Cu3FeS6, based on the similarity of the X
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