'Working together to promote premier, multi-disciplinary research and development in the area of minerals beneficiation'

Thandazile Moyo

PhD Project title
A Comparative Electrochemical and Leach Study of the Oxidative Dissolution of Chalcopyrite in Ammoniacal Solutions
(Duration: Oct 2012 to June 2016)

The surface chemistry of chalcopyrite in different aqueous media during leaching remains poorly understood despite the many years of research in the subject. Chalcopyrite’s slow leaching kinetics are strongly linked to the formation of a passive film on its surface. There is no consensus on the actual composition or degree of stability of this passive surface film. In ammoniacal chalcopyrite leaching processes, the deportment of iron has been reported to have significant effects on the minerals dissolution kinetics; however the exact iron chemistry remains unclear. In the chalcopyrite ammoniacal system, iron forms insoluble products, it is hypothesised that the nature and morphology of the insoluble products differs with a variance in solution conditions and that the nucleation and growth kinetics of this product are affected by the solutions hydrodynamics near the mineral surface, such that agitated systems will show better removal of iron precipitate from the surface, hence sustaining leaching.

The presence of cupric ions has been found to improve the rate of chalcopyrite leaching and the role of the cupric ion has been reported to be that of catalysing the reduction of oxygen in the oxidative dissolution of chalcopyrite. Preliminary results to this study suggest that cupric ions and oxygen have a synergistic effect on the dissolution rate of chalcopyrite. It is proposed that the reaction proceeds through the formation of an intermediate cupric ammine oxygen complex on the mineral surface, which then oxidises the chalcopyrite.

The objectives of this study are to evaluate the mechanism of chalcopyrite leaching in ammoniacal solutions, to investigate the role of cupric ions in the oxidation reaction, to determine the deportment of iron and how it contributes to surface passivation and to establish how electrochemical studies can be used to understand and predict the controlled bulk leaching of chalcopyrite in ammonical solutions.

Research Outputs

Moyo T., Petersen J., Franzidis J-P. 2013. The electrochemical oxidation of chalcopyrite in ammonia-ammonium sulphate solutions in the presence of initial cupric ions. Paper presented at the 31st Annual SAIMM Mineral Processing Conference, 6-7 August, Cape Town, South Africa.

Moyo, T., Petersen, J., Franzidis, J.-P. and Nicol, M.J. 2014. An electrochemical study of the dissolution of chalcopyrite in ammonia-ammonium solutions. Paper presented at the 32nd annual SAIMM Mineral Processing Conference, 7-8 August, Cape Town.

Moyo, T., Petersen, J., Franzidis, J.-P. and Nicol, M.J. 2014. An Electrochemical Study of the Dissolution of Chalcopyrite in Ammonia-Ammonium Sulphate Solutions. Proceedings of Hydrometallurgy 2014, Vol 1: 375-383, 25 June 2014, Victoria, B.C., Canada: Canadian Institute of Mining, Metallurgy & Petroleum, ISBN: 978-1-926872-22-3

Courses & Training

  • Research Communication & Methodology
  • Post-graduate Hydrometallurgy course