Enhanced leaching of chalcopyrite at low potentials in chloride solutions 3. Ores

It is well known that the leaching of chalcopyrite under ambient conditions is extremely slow even under highly oxidizing conditions. This has been attributed to so-called passivation of the mineral that occurs at potentials above about 0.65 V (SHE). A study has been made of the rate of leaching of copper in dilute chloride solutions from a low-grade ore which contained chalcopyrite as the only copper sulfide mineral. Leaching has been carried out in batch stirred reactors using milled ore and in 1 m columns using crushed ore in solutions of chloride at various potentials. It has been observed that enhanced rates of dissolution of copper from chalcopyrite in chloride media can be achieved at ambient temperatures by the application of controlled potentials in a "potential window" between 560 and 600 mV (SHE). These results generally confirm the results presented in Part 1 of this series of papers which detailed the results obtained on the dissolution of a concentrate from the same ore. A reduced sensitivity of the rate of leaching in columns to the potential has been observed which is interpreted in terms of a potential distribution at the surface of chalcopyrite grains. This potential distribution can vary both locally due to mineralogical effects and vertically due to potential variations down the column as observed in the differences of the potential in the column inlet and outlets. A linear rate of approximately 0.1% copper dissolution from a low grade chalcopyrite ore under typical heap leach conditions has been measured in a solution of 50 g/L chloride at a pH of 1 and a potetitia1 of about 600 mV for the feed solution