Electrochemical dissolution of calaverite(AuTe<inf>2</inf>) in thiourea acidic solutions

Cyclic voltammetric studies of carbon paste electrodes of a synthetic gold telluride, calaverite (AuTe2), in acidic aqueous thiourea solutions indicate that for potentials of about 0.4 V vs SCE adsorbed thiourea decomposes to formamidine disulphide, while gold from calaverite oxidizes and complexes with thiourea. The chemical oxidation of calaverite with the formamidine disulphide produced occurs in parallel with these electrodic processes. Additionally, for potentials in the vicinity of 0.5 V vs SCE tellurium from calaverite transforms to telluril ion, HTeO+2. A passive film of tellurous acid H2TeO3forms at potentials around 0.7 V vs SCE whereas at potentials above 0.9 V vs SCE the formation of gold oxides and hydroxides is apparent. Reduction of calaverite occurs at potentials less than -0.7 V vs SCE. Other cathodic peaks are associated to the reverse processes of the anodic decomposition stages.