Eureka! A solid gold solution to make Archimedes proudPosted: June 16, 2015
By Roger Nicoll
‘Eureka!’ cried the Ancient Greek scholar Archimedes as he (allegedly) ran naked through the streets of Syracuse. He’d just discovered a method to prove the purity of gold by measuring its density, and was decidedly proud of his finding.
Thankfully, these days we favour blog posts to running naked through the streets when we make important new discoveries… but it doesn’t mean we can’t still give a good shout:
‘Eureka! We’ve found a way to produce cyanide-free gold!’
We’ve been working with an American company, Barrick, at their Goldstrike plant in Nevada, to produce the first ever gold bar that doesn’t involve the use of cyanide extraction. Cyanide is, of course, highly toxic and a potential environmental hazard. The new process we’re so excited about uses a chemical called thioshulphate, which will greatly reduce the environmental risks and costs associated with gold production.
Thiosulphate has long been seen as a potential alternative to cyanide for liberating gold from ores, but it has proved difficult to master – until now. Thanks to the new process, which incorporates patented technology we’ve developed with Barrick, the company will be able to process and profit from four million tonnes of stockpiled ore that was uneconomic to process by traditional methods.
As part of the thiosulphate process at Goldstrike, gold-bearing ore is heated in large pressure chambers, or autoclaves. It’s then pumped as a thick slurry of ore, air, water and limestone into the new ‘resin-in-leach’ circuit that takes place inside large stainless steel tanks.
Within the tanks, the slurry interacts with thiosulphate and a fine, bead-like substance called resin that collects the gold. At full capacity, 13,400 tons of ore can be processed daily, with leaching taking place simultaneously in two sets of seven tanks.
Our very own minerals expert Danielle Hewitt had a hands-on role in developing and proving the CSIRO technology incorporated at the Goldstrike plant. But for security reasons, it was strictly hands-off the resulting gold bar.
“This was a golden moment more than 20 years in the making, including three years working with Barrick to refine the commercial process,” said Danielle.
She said the new process will contribute an average of 350 to 450 thousand extra ounces of gold each year to the operation, allowing the large plant to keep operating.
The new technology could also have some benefits closer to home, with the potential to safely recover gold in Australia where cyanide would otherwise pose a significant environmental risk and environmental protection cost.
As with Archimedes, another gold standard solution.