The Effects of Chloride on the High-Temperature Pressure Oxidation of Chalcopyrite: Some Insights from Batch Tests—Part 1: Leach Chemistry

Abstract

The complete reaction of chalcopyrite at ≥220 °C under pressure oxidation conditions (10 or 20% w/w pulp density, PO2 700 kPa) is a clean, near complete process, yielding high copper extractions (~99%) in an acidic leach liquor composed of dissolved metal sulphates, when high-quality process water is employed. However, when the process water contains chloride ions, here 3–100 g/L, although the copper extraction rate is enhanced, complete oxidation of sulphur under batch processing conditions is delayed. Chloride addition, therefore, appears to favour an oxidation mechanism that liberates cupric ions and preferentially forms elemental sulphur over sulphate. This provides evidence for the decoupling of the copper extraction and sulphate formation reactions. Increasing the reaction temperature, here to 245 °C, increases the rate of sulphuric acid formation and decreases the iron concentration in the leach liquor. The study also examines the effects of various upfront acid and other salt additions upon copper extraction. Added sulphuric acid was shown to slow the reaction, whereas salts such a cupric chloride and sodium sulphate had small effects on the rate and extent of copper extraction.