Chalcopyrite leaching by CuCl 2 in strong NaCI solutions
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FOR the last ten years, the search for pollution free hydrometallurgical processes as an alternative to the pyrometallurgical route in copper concentrate processing has been accelerating. Among the proposed hydrometallurgical alternatives, cupric chloride leaching looks promising since it leads to substantial sulfide leaching rates at relatively low potentials, where sulfate formation can be avoided. A double leach by CuC12 at 90 ~ can dissolve more than 98 pct of the copper and iron in the chalcopyrite within six hours.' No pressure vessels are requested, since the oxidation of Cu(1) into Cu(I/) by air is a fast reaction and hence leach liquor regneration can be achieved at atmospheric pressure. This concept was suggested at the end of the 19th century z,3 but no development followed, mainly because of corrosion problems. Whereas ferric chloride leaching of chalcopyrite is already fairly well known, data are still needed on cupric chloride leaching. The scope of the work presented in this paper is to experimentally measure chalcopyrite leaching rates by CuCI 2 in strong NaCI solutions. A parallel study of solution potential leads to a better understanding of the chloride ion effect on chalcopyrite dissolution. EXPERIMENTAL The reaction under study is written as CuFeS z + 3 C u ( / / ) ~ 4 Cu(I) + F e ( / / ) + 2S ~
[1]
The solubility of copper in the cuprous oxidation state is very low in aqueous solutions in the absence of any complexing agent; therefore strong brines which supply C1- for cuprous complexing are needed for Reaction [1 ] to become effective. The copper concentrate used in this study is a Chilean concentrate containing mainly chalcopyrite. Pyrite and several copper sulfides (chalcocite, covellite) M. BONAN, formerly with Ecole des Mines, is now with Israel Mining Industries. J. M. DEMARTHE is Director of the Centre de Recherche de Trappes, Minemet Recherche, Trappes, France. H. RENON is Professor, Ecole des Mines, and Director of the Centre R6acteurs et Processus, Ecole des Mines, Equipe de Recherche Associ~e au CNRS no 768, Paris, France. F. BARATIN is Maitre de Recherches, Centre R6acteurs et Processus. Manuscript submitted December 15, 1978. METALLURGICAL TRANSACTIONS B
were also present in minor amounts. Ninety percent of the iron and eighty percent of the copper in the concentrate were present in the chalcopyrite phase. The concentrate was screened, and, unless specified, only the most abundant size fraction, which was the + 56~t - 71/~ fraction representing about 25 pct of the starting material, was used in the experiments. Chemical assay of that fraction is Cu 34 pct, Fe 25 pct, S 31.5 pct. The leaching experiments were performed under conditions designed to maintain the potential and the pH of the solutions relatively constant. A small amount of copper concentrate (about 5 g) and large amount of cupric and cuprous chlorides (from 0.1 to 0.5 mol/dm3) were introduced initially into a one liter leaching tank, together with 0.1 mol/dm3 HC1, and generally 4 mol/dm3 NaC1. The presence of air in
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