Pressure oxidation leaching of chalcopyrite. Part I. Comparison of high and low temperature reaction kinetics and products

Abstract The kinetics and products from the pressure oxidation of a chalcopyrite concentrate are compared under a range of reaction conditions promoted by various companies. The reaction conditions compared in this article, Part I, are referred to as the Phelps Dodge-Placer Dome and Activox® processes. The medium temperature processing of the concentrate will be reported in Part II. Experiments were conducted with the same concentrate over a temperature range of 108–220 °C with different salt and acid additions to compare the kinetics and recovery of copper, the speciation of sulfur and the deportment of iron-containing and other phases in the leach residues. The aim was to improve understanding of the mechanism and practical issues for the competing processes and to provide background knowledge often not available in the public domain. The chalcopyrite concentrate was found by Quantitative X-ray Diffraction (QXRD) analysis to contain about 80% chalcopyrite, 10% quartz, 6% pyrite and 2.5% talc and 1.5% clinochlore. It was demonstrated that greater than 94% of the copper could be extracted from the concentrate using either the Phelps Dodge-Placer Dome or Activox® process within 30 min. The extraction of the residual copper was strongly influenced by the presence of elemental sulfur. About 80–90% oxidation of sulfide to elemental sulfur occurred at 108 °C and was enhanced by the presence of the chloride ion. Above 180 °C there was complete oxidation to sulfate. However, in the presence of added chloride ion the rate of sulfate formation decreased. QXRD was employed to examine the leach residues. Iron was leached and re-precipitated forming a number of different phases depending upon the process temperature, acidity and salinity. At low temperature, in the presence of chloride, akaganeite was formed together with an uncharacterised amorphous hydrated iron oxide. Hematite formation was favoured at temperatures ≥ 150 °C, low acidity and low salinity; basic ferric sulfate formed at high temperature (220 °C), high acidity and low salinity. Goethite formation was favoured at ≤ 150 °C by low acidity and low salinity. Jarosite was formed at all temperatures under conditions of moderate to high acidity and its formation was enhanced in the presence of sodium ions. Several basic copper salts including atacamite (Cu2(OH)3Cl) and antlerite (CuSO4·2Cu(OH)2) were precipitated at 108 °C at low acidity, typically at pH > 2.8. Atacamite formed initially when the sulfate concentration was low but dissolved and the copper was re-precipitated to form antlerite as the sulfate (and copper) concentrations increased.