The acidic ferric sulfate leaching of primary copper sulfides under recycle solution conditions observed in heap leaching. Part 1. Effect of standard conditions

Understanding the dissolution of copper from chalcopyrite is important as chalcopyrite is the most abundant copper mineral in the earth's crust. The main method for extraction of copper from chalcopyrite is by flotation concentration before being smelted and electro-refined. However, this process is not suitable for the treatment of the vast reserves of low grade chalcopyrite ores, where hydrometallurgical extraction through heap leaching is a better option. While pressure or high temperature leaching with the addition of sodium chloride or HCl have been proposed to extract copper from chalcopyrite concentrates, this process is too expensive to treat low grade copper ores. Currently the research focus to develop a treatment process involves the use of bacteria to oxidise the sulfide minerals and produce sulfuric acid. Given the slow extraction rates of this process it requires decades to extract all the copper from the mineral which would mean the leach solution would therefore be recycled during the process once the copper had been removed. While previous studies have reported the effect of leach temperature, pH (acid concentration) and E-h on copper extraction, these have only considered initial leaching conditions. Studies using recycle leach solution conditions have not been undertaken, and this is the focus of the study reported here. The recycle solution conditions were based on a simulated long term solution composition. This article is part of a series of papers that has investigated the effect on copper and iron extraction from chalcopyrite which has evaluated conditions, major species and additives under recycle leach concentrations. This article examines the effect of the conditions, specifically temperature, pH, E-h and solids density. It was determined that the temperature had the most significant effect on the copper and iron extraction while the pH, E-h or solids density had no appreciable effect on the extraction of either copper or iron under the recycle leach conditions tested. While the effect of temperature on chalcopyrite dissolution is known, the activation energy, the rate of dissolution and the degree of copper extraction is lower under these high solute or recycle concentrations. Similar observations were found when studying pyrite but this study attributed the lowering of these parameters under recycle conditions to the sulfate concentration causing a diffusion layer around the mineral particles which alters or slows the response of pH, E-h or temperature on the dissolution reaction.