2016 Moyo Oxidative dissolution of chalcopyrite in ammoniacal solutions

Chalcopyrite is the most abundant copper sulphide and is extremely stable, which makes it resistant to traditional hydrometallurgical treatment methods, particularly atmospheric leaching. With the decline in ore grades and rising costs associated with concentration processes, there is a compelling need to revisit more economical and environmentally friendly hydrometallurgical options, particularly heap leaching. This study evaluates various hydrometallurgical systems used for chalcopyrite treatment, including ferric sulphate, chloride, and ammonia systems. Despite the established limits of ferric sulphate under atmospheric conditions, and the recent interest in chloride systems for heap leaching, the ammonia system remains largely unexplored, with previous research stemming from over 40 years ago. This thesis introduces significant findings related to the copper(I)/copper(II) redox couple's influence on oxidative leaching and identifies the often-overlooked limiting role of cathodic reactions. Furthermore, it proposes solutions to address the challenge of surface inhibiting layers that form during heap leaching, through the investigation of complexation and precipitation of cations in ammoniacal leach systems. These insights contribute to understanding and enhancing the efficiency of chalcopyrite leaching processes.