What is the name of the refining process that uses electrolysis to produce high-purity gold?

The refining process that uses electrolysis to produce high-purity gold is the Wohlwill process.

Invented by Emil Wohlwill in 1874, it is an industrial electrolytic process. A relatively pure gold ingot, often called a doré bar, serves as the anode, while a sheet of pure gold or another suitable starter cathode receives the refined metal. Chloroauric acid acts as the electrolyte.

When electric current passes through the cell, gold dissolves from the anode and travels through the electrolyte before plating onto the cathode. Many impurities remain in solution or collect as anode sludge, allowing the deposited gold to reach about 99.999% purity.

The main mix-up is with the Miller process. Miller refining uses chlorine gas blown through molten gold and can produce roughly 99.5% purity; it is generally faster and simpler. The Wohlwill process is preferred when exceptionally pure gold is needed, although it requires purer feedstock and more gold tied up in the electrolyte.