The effect of sulphide ions on anode dissolution of gold in thiocarbamide electrolytes

The introduction of sodium sulphide as a microaddition (about 10/sup 5/ mol/I) into acidic solutions of thiocarbamide causes a sharp acceleration of the anode dissolution of gold. The acceleration enhances with an increase in the concentration of Na/sub 2/S (c), and with an increase in the time of contact between the electrode and solution (/spl Delta/t) before measurements; it decreases after the polarization curve passes through its maximum at E /spl cong/ 0.5 V. Using the procedure of electrode surface renewal by cutting off a thin metal layer, we studied the regularities of gold dissolution in the solution containing 0.1 M thiocarbamide and 0.5 M H/sub 2/SO/sub 4/, for given c and /spl Delta/t values. An explanation of the discovered regularities is proposed, assuming that the dissolution process is catalyzed by sulphide ions adsorbed on the electrode.