ELECTROCHEMICAL-BEHAVIOR OF THE DISSOLUTION OF GOLD-SILVER ALLOYS IN CYANIDE SOLUTIONS

The dissolution behavior of gold and silver from Au/Ag alloys in aerat ed cyanide solutions has been investigated using rotating disc electro des. The variables studied included concentration of cyanide, oxygen p artial pressure, and rotating speed of the disc. The dissolution poten tial and the rate of dissolution were obtained in view of the anodic a nd cathodic current-potential relationships. The results were discusse d in terms of the mixed potential theory. The results showed that the dissolution : rate of gold and silver from the alloys was partially co ntrolled by chemical reaction but largely controlled by transport of e ither oxygen or cyanide, depending on their relative concentrations un der the experimental conditions employed in this study. The diffusion coefficient of free cyanide, D-CN-, was found to be (1.25 +/- 0.05) x 10(-5) cm(2)/s. The diffusion coefficient of oxygen, D-O2, was calcula ted to be (1.29 +/- 0.02) x 10(-5) cm(2)/s.