The Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency, has produced the country’s first gold using a non-toxic chemical process in an effort to provide an alternative to cyanide and mercury to extract the yellow metal.
|Lead scientist Paul Breuer holds up a 1 ounce commemorative gold ingot from the first gold pour using CSIRO’s cyanide-free process|
The first gold is the result of early industry trials of CSIRO’s ‘going for gold’ technology and was produced in partnership with small gold miner Eco Minerals Research at a demonstration plant in the Western Australian goldfields town of Menzies.
Cyanide is used in more than 90 per cent of global gold production, but producers are facing increasingly tough regulations that prevent or restrict its use due to environmental and health concerns.
Globally, government regulations guiding the use of cyanide in gold processing are becoming increasingly rigorous. Several regional agencies in the United States, South America and Europe have banned the use of cyanide for gold extraction as a response to recent spills of toxic cyanide.
CSIRO also believes that cost-effective gold recovery alternatives are needed to address barriers to entry for small producers and new government regulations.
A typical cyanide-based processing plant is estimated to cost around AUD$30 million, whereas the new technology has a lower capital investment costing as little as AUD$2-2.5 million to build.
To reduce economic barriers to entry for small producers and help turn stranded gold deposits into production, CSIRO’s vision is to deliver the alternative process technology direct to mine sites via a mobile service.
CYANIDE AND MERCURY-FREE ALTERNATIVE
|Improved facility set-up. Image ©2018 CSIRO. All rights reserved|
|Leach solution processing plant. Image ©2018 CSIRO. All rights reserved|
The technology replaces cyanide with thiosulphate, a non-toxic alternative, and a simple process flowsheet.
Thiosulphate dissolves the fine gold – the gold that has not been recovered by gravity – out of ores at similar rates to conventional techniques. It’s safe and lowers environmental impacts.
Thiosulphate is effective at picking up gold in leach tanks to create a gold thiosulphate complex. The gold can be separated from the thiosulphate using ion exchange resins in what has traditionally been a challenging process. Whilst working on improvements to this separation process, CSIRO discovered that adding sulphite as an additive to the ion exchange resin enabled easier separation.
Over time, the method has undergone intensive laboratory testing to understand its leaching performance in association with reagent recovery and recycle, with results indicating that thiosulphate process is appropriate for the treatment of high-grade gold concentrates, and could also be valuable for use in other applications such as in-situ leaching in deep mines and for use in treating gravity gold concentrates, particularly those with high cyanide-soluble copper.
CSIRO says that the ‘Going for Gold’ process requires some additional ‘off-the-shelf’ components and a new configuration, but is not complex and can be customised to deal with different ore types.
|CSIRO’s cyanide-free gold showcases non-toxic solution|
Eco Minerals Research, in collaboration with CSIRO, are undertaking the world’s first pilot project at Menzies in Western Australia to ensure and verify scalability of the alternative technology to cyanide for gold recovery.
The AUD$2.1 million demonstration project was made possible through AUD$860,000 in funding from the Science and Industry Endowment fund (SIEF) and an Australian Government Innovation Connections grant, and will use ore from the tailings dump located in situ – approximately 70,000 tonnes with an average 1.75g/tonne and volume >1.3mt, with an estimated value of AUD$5.25m.
“This process is targeting small high-grade deposits with good gold liberation at a coarse grind size suitable for the gravity tails to be vat leached”, said CSIRO Lead scientist, Paul Breuer.
“Science enabling industry and environment to be partners not competitors, exactly as envisioned in our market vision – turning commodities into higher value, uniquely Australian products”, CSIRO Chief Executive Dr Larry Marshall said.
“It has been accelerated through CSIRO’s ON program, and could be a game-changer for small gold producers or those looking to get ahead of increasing market demand for greener commodities.
“Early industry trials like this are critical to innovation and go to the heart of CSIRO’s mission to tackle big, real-world challenges and unlock a better future for everyone.”
A tank leach process using this leach system is under development for demonstration next year. According to Dr Breuer, this would have the potential to open up the application of the technology to a greater range of ore types and scalable for large projects.
“The process is not commercially available, but we are looking for projects to further test and develop the process with the potential for adoption.”
“The first gold is a major milestone in our progress towards becoming one of the world’s first green gold producers”, Eco Minerals Research Managing Director Paul Hanna said.
“In close collaboration with CSIRO, we have gone through the design, engineering and fabrication stages and set up a processing facility in Menzies, delivering the first gold pour in just 10 months, which is a fantastic achievement.”
|Australia’s first cyanide-free gold produced with Eco Minerals Research using non-toxic extraction process|
The CSIRO research team behind the innovation has already had commercial success with another tailored cyanide-free gold solution developed with Barrick Gold specifically for their Goldstrike Mine in Nevada where it has been used for nearly four years to maintain production rates.
This tailored thiosulphate leaching process, which will not work for other ores, has enabled the Nevada mine to maintain production despite the changing nature of the orebody being mined and is expected to contribute an average of 350,000 to 450,000 oz of gold a year over the first five full years.
With the changing expectations on operators, shifting economics and increasing demands for cleaner and greener production, mining companies – large and small – may have to seriously consider the marriage of new and innovative science with their daily operations to remain economically sustainabl