The mechanism of chalcopyrite leaching in the presence of silver-enhanced pyrite in the Galvanox™ process

A dramatic improvement in the leaching kinetics of chalcopyrite in ferric sulfate media was observed upon the addition of silver-enhanced pyrite. In this process, pyrite samples are pretreated with a miniscule amount of silver and used as a catalyst in atmospheric leaching of chalcopyrite. The aim of this study was to understand the mechanism of this process and to reveal the role of silver and pyrite in accelerating the rate of chalcopyrite leaching. It is shown that this process, known as Galvanox™, is the galvanically assisted leaching of chalcopyrite, where pyrite provides an alternative surface for ferric reduction. As the leaching reaction proceeds, in the absence of silver-enhanced pyrite, a non-conductive sulfur layer forms on the surface of chalcopyrite. This layer prevents electrical contact between pyrite and chalcopyrite particles in the slurry. However, it is observed that, in the presence of silver-enhanced pyrite, a small proportion of the added silver to the pyrite dissolves and reacts with the elemental sulfur around chalcopyrite particles to form silver sulfide. In spite of the very low silver level in this layer, its conductivity increases significantly and allows the transfer of electrons from chalcopyrite to pyrite. In this study, it is shown that pyrite and silver have critical roles in enhancing the kinetics of chalcopyrite leaching. Pyrite provides an alternative surface area for ferric reduction. Silver increases the catalytic properties of pyrite and therefore, the rate of ferric reduction on the surface of silver-enhanced pyrite is faster than this rate on the surface of natural pyrite. Another role of silver is to decrease the resistivity of the sulfur product layer and to facilitate the electrical contact between pyrite and chalcopyrite.