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How does roasting make refractory gold ores easier to process?

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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.

Roasting makes refractory gold ores easier to process by destroying interfering sulfide minerals, such as pyrite, pyrrhotite, or arsenopyrite, that prevent the gold from being accessed by cyanide leach solutions.1

In refractory ores, these sulfides can consume cyanide reagents, adsorb dissolved gold (a process known as preg-robbing), or physically encapsulate the gold particles, rendering them inaccessible to standard extraction methods. By roasting the ore at temperatures between 450° and 750° C (840° to 1,380° F), these sulfides are destroyed through oxidation, which frees the gold and allows it to be successfully recovered via cyanidation.1

Alternatively, this oxidation can be achieved using autoclaves, which treat the ore in a high-pressure, high-temperature environment to create a porous structure that provides the necessary access for leaching solutions.12