The role of silver-enhanced pyrite in enhancing the electrical conductivity of sulfur product layer during chalcopyrite leaching in the Galvanox™ process

The rate of chalcopyrite leaching in ferric sulfate media during the Galvanox™ process increases significantly in the presence of silver-enhanced pyrite. The increase in the kinetics of leaching is attributed to the galvanic interaction between pyrite and chalcopyrite. Pyrite provides an additional surface area for the cathodic reaction. The oxidation reaction rate increases to compensate for the increased consumption of electrons. Pyrite is more noble than chalcopyrite; hence chalcopyrite leaches preferentially under oxidizing conditions. This leads to the acceleration of the rate of copper extraction. However, an insulating product layer of elemental sulfur forms on the surface of chalcopyrite as leaching proceeds. Formation of this non-conductive layer limits the electrical contact between pyrite and unleached chalcopyrite. In the presence of silver-enhanced pyrite, a very small proportion of the added silver to pyrite dissolves in the leaching solution and reacts with chalcopyrite particles to form silver sulfide. In this study, increases in the conductivity of the sulfur layer sufficient to allow the rapid transfer of electrons are observed, in spite of very low levels of silver in the sulfur product layer (60–100 ppm). Hence, it is shown that in the presence of silver-enhanced pyrite, the resistivity of the sulfur layer is lowered, allowing the electrical contact between pyrite and chalcopyrite to be maintained.