Kinetics of chalcopyrite leaching by sodium nitrate in sulphuric acid

Hydrometallurgical processes offer a great potential for treating chalcopyrite ores and concentrates, and it results in increased metal recoveries and reduced air pollution hazards. In recent years interest for application of various reagents in a hydrometallurgical processing of sulphide concentrates has increased. The objective of this work was to examine the leaching of the chalcopyrite concentrate, from “Rudnik” flotation plant, by sodium nitrate in sulphuric acid media. The probabilities of various chemical reactions occurring was based upon literature data, thermodynamic analysis, and the products formed during the leaching process. The influence of various parameters was studied to optimize the conditions and to determine the kinetics of the reaction. An increase in temperature, sulphuric acid and sodium nitrate concentration, and decrease in stirring speed and particle size, enhanced the leaching rate of copper. The experimental data were best fitted by a mixed control kinetic model. An activation energy of 83 kJ/mol was found. Elemental sulphur was formed as the main leaching product and tended to inhibit the leaching rate. The leaching mechanism was confirmed by characterizing the concentrate and the leach residue using XRD and SEM/EDX analysis.