The influence of microwave pre-treatment of the leach behaviour of disseminated sulphide ore

Heap leaching has become a widely used method of extracting metals from low grade ores. The simplicity of heap leach process design and low capital and operating costs are the main drivers. However, heap leaching in general has the drawbacks of low recoveries and long extraction times. In this regard, rock permeability is a key requirement for this technology to be viable. The aim of this study is to investigate whether heap leaching efficiency can be improved by introducing micro fractures and cracks into the ore by the application of high power microwave energy, which has already been shown to enhance comminution. This paper presents the effect of microwave pre-treatment on copper extraction during leaching. The study shows that for a low grade ore containing finely disseminated sulphide mineral phases, the pre-treatment of ore particles in a high intensity microwave field increases the copper extraction over that for un-treated ore particles. It is suggested that microwave pre-treatment increases the internal surface area of the ore particles by creating fractures along grain boundaries, so exposing locked Cu-bearing mineral phases to the leach solution. It is proposed that leaching of exposed mineral phases will enhance the extraction of copper as compared to leaching of untreated ore particles. Further, the addition of wetting agents increases the copper extraction, as compared to samples of microwave pre-treated ore particles leached without wetting agents. The influence of microwave pre-treatment on the recovery vs. residence time of heap leaching of a low grade ore, with finely disseminated sulphide mineral phases, is discussed. (C) 2011 Elsevier B.V. All rights reserved.