Kinetics of anodic dissolution of gold in alkali-cyanide solutions: Effectof lead ions

Effective order of the gold dissolution reaction by cyanide ions, p, transf er coefficient alpha, and exchange current io are measured at constant cove rages of the gold surface by lead adatoms, theta. Constancy of theta is ens ured by maintaining the time period Deltat, during which the electrode is i n contact with solution after the renewal of its surface and before taking measurements, constant. Solutions under study contain (0.5-2) x 10(-5) M le ad acetate, 0.05-0.2 M KCN, 0.1 M KOH, and 0.01 M KAu(CN)(2). With increasi ng Deltat, quantities p, alpha and i(0) increase from, respectively, 0.17, 0.1, and 10(-5) A dm(-2) (in 0.05 M KCN) to p congruent to 1.2, alpha congr uent to 0.45,and i(0) congruent to 10(-4)A dm(-2) The increase in p suggest s that the limiting stage alters in the presence of lead adatoms: in additi on to adsorbed cyanide ions, as is the case with pure alkali-cyanide soluti ons, it involves cyanide ions located outside the adsorption layer. A feasi ble mechanism for the acceleration of gold dissolution by lead adatoms is o ffered.