How does the Merrill-Crowe process use zinc powder to recover gold?

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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.

The Merrill-Crowe process is a method used to recover gold from a pregnant (gold-bearing) solution after it has been separated from ore solids.

To initiate the process, the gold-bearing solution is first deoxygenated to remove dissolved oxygen, which prevents the re-dissolution of the metal. Once deoxygenated, the solution is passed through a filter press. During this stage, zinc metal powder is added to the solution. Through a chemical reduction reaction, the zinc displaces the gold from the solution, causing the gold to precipitate as a solid that is then collected on the filter.1

This technique is a critical step in gold processing, particularly when dealing with solutions where gold has been dissolved via cyanidation.1