ELECTROCHEMICAL DISSOLUTION OF CALAVERITE (AUTE2) IN THIOUREA ACIDIC SOLUTIONS

Cyclic voltammetric studies of carbon paste electrodes of a synthetic gold telluride, calaverite (AuTe2), in acidic aqueous thiourea solutio ns indicate that for potentials of about 0.4 V vs SCE adsorbed thioure a decomposes to formamidine disulphide, while gold from calaverite oxi dizes and complexes with thiourea. The chemical oxidation of calaverit e with the formamidine disulphide produced occurs in parallel with the se electrodic processes. Additionally, for potentials in the vicinity of 0.5 V vs SCE tellurium from calaverite transforms to telluril ion, HTeO2+. A passive film of tellurous acid H2TeO3 forms at potentials ar ound 0.7 V vs SCE whereas at potentials above 0.9 V vs SCE the formati on 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 stage s.