parting

parting, in metallurgy, the separation of gold and silver by chemical or electrochemical means. Gold and silver are often extracted together from the same ores or recovered as by-products from the extraction of other metals. A solid mixture of the two, known as bullion, or doré, can be parted by boiling in nitric acid. The silver is dissolved as silver nitrate, leaving a residue of gold that is filtered off and washed; silver is precipitated out of solution by the addition of ferrous sulfate. This is the traditional method used in assaying the content of gold and silver samples.

Most gold and silver are parted electrolytically after being recovered in the slimes left over from copper refining or as a metallic by-product of lead or zinc smelting. The bullion is cast into anodes, which are placed into an electrolytic cell and subjected to an electric current. Silver dissolves in the electrolyte and then deposits onto the cathodes. Gold and trace amounts of silver are recovered in the slimes and are parted either electrolytically or by boiling in sulfuric acid and potassium nitrate to dissolve the silver.