Research that began almost 20 years ago in Perth has enabled the world’s largest gold producer to commercialise a process that uses a non-toxic chemical in gold recovery. Tony Heselev reports

Gold recovery without using toxic cyanide © Damien Smith Photography

Process productivity article from resourceful: Issue 6, March 2014 

When Barrick Gold’s thiosulphate leaching process goes into full-scale production at the company’s Nevada Goldstrike mine later this year, it will prove that in some applications, gold can be recovered without using the potentially toxic cyanide.

This has been a key challenge for the gold industry since the 1970s. Tackling it successfully will represent a significant achievement and the culmination of many years of research and development in the US, Canada and Australia.

Senior Manager at Barrick Gold, Dr Yeonuk Choi, says CSIRO’s work has helped make the gold recovery process more efficient.

‘CSIRO has been spending a few years on this specific area so it was a good match,’ he says.

‘This is the very first commercial operation where this type of technology is being used in the world so we are very thrilled.’

Replacing cyanide with the non-toxic thiosulphate will reduce the risks and environmental impacts of gold processing and may open up opportunities in areas where gold cyanidation is banned (including in several European countries and American states).

Importantly, it will enable the Nevada mine to maintain production despite the changing nature of the orebody being mined (which has become increasingly carbonaceous) and is expected to contribute an average of 350,000 to 450,000 ounces of gold a year over the first five full years.

‘We are always looking for the best solution and this process is the best economic option,’ Dr Choi says.

CSIRO research has been instrumental in developing the process and enabling it to be commercialised.

‘The main reason we approached CSIRO is that they have a very good reputation at our Australian office in Perth, and they have very good publications so we knew the expertise from the start,’ Dr Choi says.

Thiosulphate had been found to be effective at leaching gold but recovering the gold using ion exchange resins had proved difficult. CSIRO researchers discovered that adding sulphite to the resin elution process made gold recovery from the resin much easier.

Paul Breuer, Precious Metals Research Leader at CSIRO, says that researchers at the then Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions were working on alternatives to cyanide in the late 1990s and early 2000s.

Researchers who had previously worked on electroless plating of gold came up with the crucial idea of adding sulphite in the resin elution process.

CSIRO initially received funding and support from Barrick Gold to develop the resin elution process, with the focus in the past three years being on applying that knowledge to a demonstration plant at Goldstrike.

Dr Breuer says the industry and regulators are watching Barrick Gold’s progress carefully.

‘Everybody is waiting to be first to be second, but it’s a new technology and thiosulphate is not economic for all orebodies,’ he says.

‘It’s in niche applications, particularly where cyanide is banned or not viable, that it will make inroads.’

Dr Breuer sees opportunities for the development of thiosulphate processes in treating low- grade deposits and deep mines, where in-situ leaching would be safer for workers and the environment, and in treating gravity gold concentrates, particularly those with high cyanide soluble copper.

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