THE USE OF ADDITIVES IN THE LEACHING OF PRIMARY COPPER SULFIDES IN ACIDIC FERRIC SULFATE MEDIA UNDER RECYCLE SOLUTION CONDITIONS OBSERVED IN HEAP LEACHING

摘要

The present account summarises some of the main findings of a research program carried out at Murdoch University that has investigated the effects of common leaching process control parameters, major species present in the leach system, and additives on the rate and extent of copper extraction from low-grade ores in which chalcopyrite (CuFeS2) was a dominant copper source mineral, under heap leach recycle solution conditions. The primary aim of this paper is to demonstrate the benefits of certain additives on the leaching of chalcopyrite under these conditions.Determining an effective, low cost extraction process for copper from chalcopyrite is important, as chalcopyrite is the most abundant copper mineral in the earth's crust and most of the reserves are of low grade and not suitable for conventional flotation/pyrometallurgical processing. The current research focus for the treatment of these low-grade chalcopyrite ores is hydrometallurgical processing, with the most viable option from a cost perspective being heap leaching with the aid of bacteria in a sulfate media. However, it is well known that chalcopyrite is refractory under those conditions, with slow leaching kinetics and poor overall extraction due to passivation of the chalcopyrite surface. Extensive research has demonstrated that the addition of certain additives can significantly improve the copper extraction. Yet there has been little research into how these additives affect the extraction of copper under recycle leach solution conditions, or the mechanism of copper extraction. Investigating this process under recycle leach conditions is important because in heap leaching, many of the low-grade deposits require long treatment periods to liberate the copper from a coarsely ground feed so the leach solution is recycled multiple times and it has very high activity with respect to many species. The studies at Murdoch University consisted of batch leach tests, detailed structural and mineralogical characterisation of samples and thermochemical modelling. The results demonstrate that silver has a strong catalysing effect on the extraction of copper from chalcopyrite ore under leach recycle conditions, and at a high enough dosage can effectively overcome surface passivation, enabling almost complete extraction of copper. The addition of activated carbon, chloride ions or wetting agent was also shown to promote the extraction of copper. Varying the concentration of additives and other process conditions has enabled the critical concentration of each additive for effective treatment to be determined. The data from the study informed the development of a theory for the reaction mechanism through which silver promotes copper extraction, enabling the identification of (secondary) synergistic additives that should significantly reduce the required silver dosage and make this treatment cost effective in practice.