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

The introduction of sodium sulphide as a microaddition (about 10⁵ 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 Na₂S (c), and with an increase in the time of contact between the electrode and solution (Δt) before measurements; it decreases after the polarization curve passes through its maximum at E ≅ 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 H₂SO₄, for given c and Δt values. An explanation of the discovered regularities is proposed, assuming that the dissolution process is catalyzed by sulphide ions adsorbed on the electrode.