Enhanced leaching of chalcopyrite at low potentials in chloride solutions 1. Concentrates

Abstract

It is well known that the leaching of chalcopyrite under ambient conditions is extremely slow even under highly oxidizing conditions. This has been attributed to so-called passivation of the mineral that occurs at potentials above about 0.65 V (SHE). However, previous reports have suggested that the mineral can be more effectively dissolved at lower potentials in sulfate solutions and mechanisisms for this reaction have been proposed. This paper will report on an extensive study of the kinetics of the dissolution of a number of chalcopyrite concentrates in chloride solutions under various conditions in specially designed reactors with the objective of developing a heap leach process for primary copper sulfide ores. It will be demonstrated that enhanced rates of dissolution can be achieved at ambient temperatures By the application of controlled potentials in the range 560-600 mV, depending on the concentration of chloride ions. However, control of the potential by the use of electrochemical or chemical oxidation of iron(II) or copper (I) ions is ineffective unless carried out in the presence of dissolved oxygen. The rates of dissolution are approximately constant for up to 80% dissolution for sized functions of the concentrates with an activation of energy of about 80 kJ/mole. Chalcopyrite from different sources appears to dissolve at approximately the same rate which is largely independent of the iron and copper ion concentrations, the acidity and chloride ion concentration but depends in some cases on the presence of additives such as fine pyrite