The oxidised slurry then moves to the carbon leach circuit to dissolve the gold out of the rock. This is done via gravity fed tanks and chemicals like sodium cyanide. The sodium cyanide leaches the gold from the rocks turning it into a liquid. This process can take days! By the time the rock particles reach the last tank (this bit takes multiple days!) almost all of the gold is recovered.
At the same time, activated carbon (coconut husks) are pumped upstream through the tank system to catch the leached liquid gold. Once full of gold the carbon travels to a gold desorption column designed to wash the gold out of the carbon.
When this process is complete, all that is left is eluate containing hot water, gold solution, cyanide, and caustic soda. The eluate is transported to the gold room and electroplated onto cathodes wrapped in steel wool.
The steel wool is then melted in a furnace and causes the gold to sink to the bottom and remaining waste (slag) to rise to the top. As the bar is poured, the slag pours out, followed by the gold, causing the slag to overflow out of the mould, leaving behind the gold.
And finally, we have our gold bar!
A sample is taken to send to the state’s Mint to determine the quality before the gold bar is then removed and cleaned. It is weighed and numbered before being shipped to the Mint.
So, there you have it! The long and incredible process people in the gold industry use to get this precious mineral from ground to Mint.