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. 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 commercialized the thiosulphate leaching process and it will be in full-scale production at its Nevada Goldstrike mine later this year.