A spectroelectrochemical study of surface species formed in the gold/thiosulfate system

Surface-enhanced Raman scattering (SERS) spectroscopy has been applied to identify species formed during gold leaching in thiosulfate media. Surface coverages of copper and sulfur for various thiosulfate dissolution systems were determined electrochemically and by X-ray photoelectron spectroscopy. A gold sulfide monolayer was shown to be formed slowly in the potential region where leaching occurs. At higher potentials, more sulfur is adsorbed but, rather than creating a multilayer, sulfur-sulfur linkages are formed with the sulfur atoms no longer being covalently bonded to gold. SERS spectra show the presence of polythionates on the gold surface in addition to gold sulfide and S-0. At longer exposure times, thiosulfate is oxidized to elemental sulfur and sulfate, both products being identified by normal Raman spectroscopy from the leach solution. In typical thiosulfate/ammonia/copper (II) leach solutions, copper is present on the surface of gold in addition to sulfur. In these situations, ammonia is coadsorbed. (c) 2006 The Electrochemical Society.