Processing, smelting and refining gold World Gold Council
TheMiller process uses gaseous chlorine to extract impurities when gold is at melting point; impurities separate into a layer on the surface of the molten purified gold. The Miller process is rapid and simple, but it produces gold of only about 99.5percent purity. The Wohlwill process increases purity to about 99.99 percent by electrolysis.