Pressure oxidation leaching of chalcopyrite Part II: Comparison of medium temperature kinetics and products and effect of chloride ion

Pressure oxidation reaction kinetics and products are compared for the recovery of copper from a chalcopyrite concentrate under medium temperature conditions at 125-150 degrees C, as patented and promoted by various commercial operations, normally referred to as the Anglo/UBC, CESL and NSC (nitrogen species catalysed) processes. The main aim was to compare the effect of additives on the dispersion of molten sulfur and recovery of copper, and develop a better understanding of the role of chloride ion. Greater than 94% copper was extracted from the concentrate under all process conditions (except NSC) within 30 min. The extraction of the remaining copper in some instances took substantially longer due to poor dispersion of sulfur and agglomeration of the sulfide minerals. The partial oxidation of sulfide to elemental sulfur was about 70-80% at 150 degrees C and was greater in the presence of chloride ion and at higher initial acidity. Iron was leached and re-precipitated forming a number of different phases depending upon the acidity and salinity. These phases including hematite, jarosite and goethite were characterised using Quantitative X-ray Diffraction (QXRD) analysis. Hematite formation was favoured at higher temperatures ( ! 150 degrees C), low acidity and low to moderate salinity. Goethite formation was favoured at lower temperatures (< 150 degrees C) and by low acidity and low salinity. Jarosite was formed under conditions of moderate to high acidity and its formation was enhanced/stabilised in the presence of sodium ions. It was demonstrated that the basic copper salt, antlerite, could be produced under conditions of low acidity. Chloride ion addition and high acid concentrations enhanced copper extraction kinetics and recovery, and inhibited the oxidation of sulfur to sulfate. This suggests that chloride ion is adsorbed on the sulfur surface to restrict direct oxygen reaction. Chloride ion also enhances the anodic oxidation of mineral sulfides and the dispersion of molten sulfur. Crown Copyright (C) 2006 Published by Elsevier B.V. All rights reserved.