Britannica Sources used in this answer

How does the Wohlwill process use electrolysis to refine gold?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A diagram showing the periodic table entry for gold, with the symbol Au, atomic number 79, atomic weight 196.96657, electron configuration, and labels for its properties as a solid transition metal with a face-centered cubic crystal structure. — gold The precious metal gold is a chemical element with the symbol Au. Its square on the periodic table details some of its properties, including its atomic weight, atomic number, and crystal structure.

The Wohlwill process is an electrolytic method used to refine gold to a high purity of approximately 99.99 percent.1

In this procedure, a casting of impure gold serves as the anode (the positively charged electrode) and is submerged in an electrolyte solution consisting of hydrochloric acid and gold chloride. When an electric current is applied, the following occurs:12

Anode Dissolution: The impure gold anode dissolves into the electrolyte solution.1
Impurity Separation: Impurities either dissolve into the solution or settle at the bottom of the tank as an insoluble slime.1
Gold Deposition: Driven by the electric field, the gold ions migrate to the cathode (the negatively charged electrode), where they are deposited in a highly pure metallic state.1

While this method is highly effective for achieving superior purity, it is often considered costly because it requires maintaining a significant inventory of gold within the electrolyte solution.1