DRDGOLD announced that the new, R12 million copper elution circuit at its Far West Gold Recoveries (FWGR) surface retreatment operation south-west of Johannesburg is expected to deliver an additional 1.2kg to 1.8kg of gold per month which would otherwise be lost to refining charges.
FWGR is currently retreating material reclaimed from the Driefontein No.5 dam. The material reclaimed contains high levels of copper which competes with gold and co-adsorbs on to activated carbon. Copper and gold are removed from the carbon and subsequently recovered together in the electro winning process.
A consequence has been that gold purity in the bullion has been low due to high levels of copper. Copper in bullion incurs penalty charges of between 1 and 5% at refinery level; FWGR has been allocated on average 98% of its gold production in the past, with 2% lost to refining charges.
To remedy this situation, FWGR conducted test work to determine how to reduce the copper levels in its bullion. This test work indicated that up to 74% copper could be desorbed from carbon without significantly desorbing gold.
Further, it showed that, if FWGR were to achieve bullion purities above 60%, the refinery’s gold allocation would shift upward from 98% to 99.5%.
This led to the construction and commissioning of the copper elution circuit to improve FWGR’s payable gold content. Construction began in January 2021, commissioning in May and steady state operation was achieved in June.
The initial plant results show that, on average, 69% of the copper is stripped from the loaded carbon. The first smelt contained mostly copper-eluted carbon and yielded a gold purity of 48.76% compared to the previous five smelts, which averaged 33.64%.
The second smelt went to 50% purity and was able to get 99% payable content, and the third smelt has achieved 53.6%, again achieving 99% payable content. The goal is to move to 60%, at which point FWGR will receive 99.5% payable content.