Miller Process

The basic process of refining gold by the use of chlorine, which was first developed at the Sydney Mint in Australia by Dr. F.B.Miller. It is based upon the fact that chlorine readily combines with silver and any base metals to form chlorides, while gold is unaffected. Doré is placed in clay pots in a furnace; once it is molten, chlorine is pumped into each pot and is absorbed by the base metals, forming volatile chlorides. After two to three hours, the pot is removed from the furnace and the molten chlorides skimmed off, leaving gold of 996-997 fineness that can be poured into moulds. Once perfected, the Miller process largely replaced the Wohlwill process for refining most of the world’s gold production.