Hyperoxygenation and fine grinding enhance carbon-in-leach recovery of refractory gold: lab-to-pilot validation using the Aachen reactor

The ability to economically oxidise ores using high-shear reactors presents an opportunity to increase gold recovery from refractory sulphide ores without resorting to costly oxidative treatments. This study provides the first integrated laboratory-to-pilot validation of Aachen pre-oxidation applied to the treatment of medium-grade double-refractory gold ores within a carbon-in-leach circuit. The effects of the high-shear reactor on oxygen transfer, leaching kinetics, cyanide consumption, preg-robbing behaviour, and its synergy with fine grinding were quantitatively assessed under industrial conditions. Laboratory-scale tests demonstrated that Aachen pre-oxidation improved gold recovery by 4–6% while reducing cyanide consumption by 8–11%. Following these promising laboratory results, a pilot-scale Aachen reactor was tested on site. Dissolved oxygen increased from 6–8 mg/L to 21–32 mg/L, resulting in accelerated leaching kinetics and lower cyanide consumption. For the KD sample, characterised by high preg-robbing tendencies and gold encapsulation in sulphides, gold recovery was improved by 5% at plant granulometry and by 11% after regrinding. For the KLK sample, where gold is locked in sulphide minerals, the application of Aachen pre-oxidation, with and without grinding, showed only a 1% improvement. Furthermore, the Aachen pre-oxidation mechanism resulted in a significant 10% reduction in NaCN consumption across both samples.