Abstract:Anodic polarization behaviors of gold and its associated elements, e.g., silver, copper, nickel and iron, in the alkaline thiourea solution with and without Na₂SO₃ were examined. The results showed gold is hardly dissolved in the solution with Na₂SO₃because of the passivation of elemental sulfur produced by irreversible decomposition of alkaline thiourea; however, the additive Na₂SO₃ improves the stability of thiourea in alkaline media, greatly increases anodic current of gold and accelerates the selective dissolution of gold in the alkaline thiourea solution, without changing the passivation states of the associated elements of gold. Also the factors affecting the polarization of gold anode were investigated in detail, and it was found that, the Na₂SO₃ obviously decreases polarization potential of gold and the apparent activation energy of gold dissolution, and the controlling step of the dissolution of gold anode in the alkaline thiourea solution is changed from the anode dissolution reaction to the solute diffusion. The mechanism for accelerated dissolution of gold in the alkaline thiourea solution with Na₂SO₃ was considered as electrochemical reduction and catalysis, over the Na₂SO₃ concentration of 0.01~0.5 mol/L, at the potential of 0.34~0.44 V.

Key words: alkaline thiourea　sodium sulfite　polarization behavior　gold