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Reduction leaching of chalcopyrite Hackl, Ralph Peter


This study has been concerned with developing novel reduction leach methods for chalcopyrite (CuFeS₂) copper concentrates. It has been found that chalcopyrite can be essentially completely converted to chalcocite (Cu₂S) by leaching in strong copper sulphate solutions at elevated temperatures, using either pressurized hydrogen gas or metallic copper powder as reductants. The essential leach reactions appear to obey the following overall stoichiometry: CuFeS₂ + 3Cu²⁺ + 2H₂ → 2Cu₂S + Fe²⁺ + 4H⁺; CuFeS₂ + Cu²⁺ + 2Cu° → 2Cu₂S + Fe²⁺. Reaction rates are increased by increasing leach temperature, decreasing concentrate and copper powder particle size, and the presence of a cuprous-stabilizing agent. The sulphide minerals bornite (Cu₅FeS₄) and pyrite (FeS₂), comnonly found in copper concentrates, are also quantitatively converted by reduction leaching under these conditions. Microscopic evidence indicates that chalcocite forms as layers which crack and spall away from the reacting sulphides, allowing complete extraction of iron to take place. The mechanism for reaction probably involves transport of cuprous ions both in aqueous solution and in the solid state (Cu₂S), and solid state diffusion of iron outward. Cuprous ions are formed as an intermediate species during the leach, either by reaction of cupric ions with hydrogen or with copper metal. This species then probably reacts with the chalcopyrite mineral as follows: CuFeS₂ + 4Cu⁺ → 2Cu₂S + Fe²⁺ + Cu²⁺. Potential methods of incorporating reduction leaching into a hydrometallurgical process for treating copper concentrates are discussed.

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