Development of a regrind-flotation pre-treatment methodology for the carbon-in-leach circuit of a copper-gold processing plant

Abstract

This study examined the performance of the Carbon-in-Leach (CIL) circuit in copper-gold plants. The objective was to identify factors normally limiting the gold recovery in the CIL circuit processing the copper flotation tailings of copper-gold plants, and then propose a means to improve it. The chosen case study was a copper-gold plant treating a porphyry-style copper-gold deposit containing free gold, gold associated with copper sulphides and gold associated with iron sulphides. Diagnostic leaching assessments and mineral liberation analysis revealed that the occlusion of gold by iron sulphide minerals and the fine grained size of gold were contributing factors to the low gold recovery in the CIL circuit. Fine grinding of the CIL feed significantly increased gold recovery from the leaching process. However, fine grinding also increased the amount of copper which was cyanide soluble, resulting in significantly higher cyanide consumption. A processing methodology was therefore proposed to regrind the CIL feed followed by selective copper flotation as an appropriate pre-treatment method for the CIL circuit. Laboratory and pilot plant scale studies developed the flotation conditions required to maximise copper and gold recovery whilst maintaining selectivity against iron-sulphide minerals. The flotation concentrate produced from the CIL feed was of sufficient copper grade to be returned to the preceding copper flotation circuit. The flotation tailings when treated by cyanidation exhibited the same gold recoveries as the fine grinding-leach process methodology but with increased copper recovery and reduced cyanide consumption. This regrind-flotation pre-treatment methodology for the CIL circuit in copper-gold plants has been implemented and is in full scale production at the case study plant, Telfer. Plant-scale measurements during commissioning revealed that the increase of overall gold recovery from the CIL feed achieved during laboratory development has been replicated in the full-scale plant.