Research into alternative lixiviants to cyanide for gold recovery has received much attention in recent years. This has been largely driven by the health, safety and environmental risks associated with the use of cyanide, as well as the low leaching efficiency of gold and/or the high cyanide consumption that is associated with the cyanidation of certain ores (eg carbonaceous ores and high-copper-containing gold ores). Among the potential alternative lixiviants, thiosulfate appears to be the most promising, with the first commercial operation having commenced in 2014 at Barricks Goldstrike operation in Nevada, USA. CSIRO Mineral Resources, in partnership with Barrick, made a significant contribution to this commercial application of thiosulfate. CSIRO Mineral Resources has also separately developed a thiosulfate-based gold extraction reagent. This reagent has been undergoing intensive testing in the laboratory and in the field in preparation for commercialisation (through an agreement with Clean Mining Limited). The testing includes not only its leaching performance on a variety of ore types (including concentrates and tails), but also its health, safety and environmental benefits. This paper presents the leaching results for various gold ores using the CSIRO reagent, subsequent gold recovery from the pregnant leach solution and cyclic testing of an integrated process flowsheet incorporating leaching, pregnant-leach-solution treatment and the recycling of various solution streams. Thiosulfate consumption, polythionate generation and their deportment in the process are also discussed. The reagent is being developed to initially target markets where cyanide cannot be used and to unlock stranded small, high-grade deposits. For the latter market, simple process flowsheet options, such as vat, heap or in-situ leaching, have also been tested. A demonstration plant that processes fifty tonnes of ore per vat was commissioned in March 2018 and operated successfully for more than six months to validate the reagent performance and proof of concept. The CSIRO reagent was evaluated to have no acute or chronic eco-toxicity and is not classified as Dangerous Goods for transportation.
CITATION:Dai, X, Breuer, P, Hewitt, D, Pranolo, Y, Meakin, R, Rajasingam, R and Robertson, W, 2019. Laboratory and field evaluations of a new non-toxic gold leach reagent, in Proceedings World Gold 2019, pp 339353 (The Australasian Institute of Mining and Metallurgy: Melbourne).