Direct acid pressure leaching of chalcocite concentrate

Summary

A hydrometallurgical process for the recovery of pure copper from an intimate mixture of chalcocite and pyrite is discussed. The dissolution of the copper can be accomplished by pressure leaching in an ammoniacal ammonium sulfate solution which results in the production of byproduct ammonium sulfate. In some locations this byproduct is undesirable, and an alternative process has been developed in which the chalcocite concentrate is leached directly in dilute sulfuric acid under an overpressure of air. This procedure converts the sulfide sulfur in the chalcocite to elemental sulfur and gives copper extractions of up to 98%. Any pyrite in the chalcocite concentrate is only slightly attacked during the leach and can thus be conveniently separated from the copper bearing solution together with the elemental sulfur. Sulfuric acid and ferric sulfate which are produced by the oxidation of a small portion of the pyrite, are removed from the leach solution by the addition of limestone. The copper is then recovered from the neutralized solution either by electrolysis or by reduction with hydrogen under pressure. The sulfuric acid which is regenerated in the copper winning operation is recirculated to the leaching step.

The principal advantage of the process is that the bulk of the sulfide sulfur in the concentrate remains as unattacked pyrite or is converted to the elemental form, avoiding the need for a sulfuric acid plant to be integrated with the copper refining operation or discharge of sulfur dioxide to the atmosphere.