Processing, smelting and refining gold | World Gold Council
The Wohlwill process increases purity to about percent by electrolysis. In this process, a casting of impure gold is lowered into an electrolyte solution of hydrochloric acid and gold chloride. Under the influence of an electric current, the gold migrates to a negatively charged electrode (cathode), where it is restored to a highly pure metallic state, leaving the impurities as a separate solution or residue.