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What role does sodium cyanide play in gold extraction?
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gold processing
The Tanami gold mine, Northern Territory, Australia.
Sodium cyanide plays a central role in gold processing as the primary solvent used to dissolve metallic gold from ore, a method known as cyanidation.12
In this process, atmospheric oxygen acts as an oxidant in the presence of an aqueous sodium cyanide solution. This chemical reaction oxidizes the gold, allowing it to dissolve and form sodium cyanoaurite. The application of this solution varies based on the ore's grade:1
- Vat Leaching: Used for high-grade ores, where a slurry of ore and solvent is agitated in large tanks.1
- Heap Leaching: Used for low-grade ores, where a dilute sodium cyanide solution is sprayed over large piles of ore, percolating through them to dissolve the gold.1
Once dissolved, the gold is typically recovered using activated carbon or through precipitation methods like the Merrill-Crowe process. Because sodium cyanide is a highly toxic substance, its use requires rigorous safety standards to prevent cyanide poisoning and protect human health and the environment.123