Our cost-effective technology uses a non-toxic chemical to replace cyanide in gold recovery, and is increasing productivity for the world’s largest gold producer.
Removing a potentially toxic issue
The sustainability of the gold industry is being challenged by reducing grades, more complex ores and increasingly stringent environmental conditions. We are helping the industry reduce the risks and environmental impact of current processing operations and developing alternative processes that use less-toxic alternatives to cyanide.
In nature, gold occurs mostly as native metal and is alloyed with various amounts of silver. Gold is present in ores at concentration as low as one part per million. Before it can be used the gold must first be separated from the ore.
Usually mined ore is ground to expose the gold particles and then leached using cyanide. This creates a soluble gold–cyanide complex, which is further processed to recover the gold. However, cyanide is highly toxic.
A non-toxic alternative
We have developed a safe gold recovery process that avoids the use of cyanide.
The novel gold recovery process replaces cyanide with thiosulphate – a non‑toxic chemical – helping to reduce the risks and environmental impact of gold processing operations.
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. Working to improve this separation process, we discovered that adding sulphite as an additive to the ion exchange resin enabled easier separation.
The thiosulphate process is appropriate for the treatment of high-grade gold concentrates, and could also be valuable for use in other applications. For example, in-situ leaching in deep mines and for use in treating gravity gold concentrates, particularly those with high cyanide-soluble copper.
Improving productivity at Goldstrike mine
The world’s largest gold producer, Barrick Gold, has commercialised the thiosulphate leaching process and it will be in full-scale production at its Nevada Goldstrike mine later this year.
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 the use of cyanide 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 complex) and is expected to contribute an average of 350,000 to 450,000 ounces of gold a year over the first five full years.
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