Method for Lowering Free-Cyanide Concentration in Gold-Plating Baths
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
In gold-plating baths based on K Au(CN)2-, reduction of gold I at the cathode results in the release of free cyanide. High free cyanide levels are undesirable for several reasons. At the anode, cyanide encourages the oxidation of gold I cyanide to the gold III cyanide complex, Au(III) (CN)4(-), and the oxidation of cobalt II to cobalt III cyanide complexes which do not have the desired hardening effect on the gold deposit. The build-up of gold III cyanide in the bath causes an undesirable decrease in the plating current efficiency because each gold III ion requires three electrons to be reduced to gold metal as opposed to only one electron per gold I.