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How does pressure oxidation in an autoclave prepare refractory ores for gold extraction?

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A worker in safety gear walks beside a conveyor belt carrying ore at the Tanami gold mine in the arid, expansive landscape of the Tanami Desert. — gold processing The Tanami gold mine, Northern Territory, Australia.

Refractory ores contain sulfide minerals—such as pyrite, pyrrhotite, or arsenopyrite—that prevent cyanide leach solutions from accessing and dissolving the gold particles. Pressure oxidation in an autoclave is a critical pretreatment process used to overcome this barrier.12

In this process, a finely ground ore slurry is heated to approximately 175 °C (350 °F) and subjected to high pressure within a multi-compartment reactor. By introducing gaseous oxygen into the slurry, the sulfide minerals are oxidized, which destroys the interfering sulfide matrix. This chemical transformation converts the ore into a porous structure, effectively exposing the gold particles. Once the oxidation is complete, the gold is liberated and becomes accessible for standard cyanidation, allowing for efficient solubilization and extraction.21