Merrill–Crowe process

The solution is separated from the ore by methods such as filtration and counter current decantation (CCD), and then the gold is cemented by adding zinc dust, which precipitates the gold: zinc has a higher affinity for the cyanide ion than gold. Silver and copper may also precipitate. The precipitate is further refined, e.g., by smelting, to remove the zinc and by treating with nitric acid to dissolve the silver.