Abstract
Electrochemical methods were applied to study the anodic behavior of gold and its associated elements, e.g., silver, copper, nickel and iron, in alkaline thiourea solution in the absence and presence of Na 2SO 3. Gold is difficult to dissolve in alkaline thiourea solution because of the passivation of elemental sulfur produced by the irreversible decomposition of thiourea. However, addition of Na 2SO 3 accelerates the selective dissolution of gold in alkaline thiourea solution. The additive Na 2SO 3 improves the stability of thiourea in alkaline media, enhances the anodic polarization current of gold greatly, and does not change the passivation states of the associated elements of gold in alkaline thiourea solution. The reaction order of the anodic dissolution of gold in alkaline thiourea solution is 1.65 with respect to Na 2SO 3, over the Na 2SO 3 concentration range of 0.01 mol/l to 0.5 mol/l at the potential of 0.34 V vs. NHE. The studies on the kinetics of the dissolution of gold in alkaline thiourea solution show that the Na 2SO 3 reduces the dissolution potential of gold, and decreases the apparent reaction activation energy of gold dissolution.
Published Version
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