Catalytic activity of thallium, lead, and bismuth adatoms in the gold dissolution reaction in cyanide solutions: A comparative characterization

Quartz microgravimetry is used to determine the ratio between coefficients of mass transfer (1 : 0.54 : 0.48), which characterizes relative values of rates of diffusion of hydroxy complexes of thallium, lead, and bismuth in alkaline solutions. The ratio is used when refining the condition under which on a renewable electrode in solutions containing these ions at the concentration c(i) the electrode coverage by relevant adatoms Theta(i) with increasing duration of contact of the electrode with solution reaches constant values: (c(Tl)t) = (0.54c(Pb)t) = (0.48c(Bi)t). Measured are i,t curves on a renewable gold electrode at E = const in solutions containing 0.1 M KCN, 0.1 M KOH, 0.01 M KAu(CN)(2), and 8 X 10(-6) M compounds of thallium or 1.5 X 10(-5) M, lead, or 1.6 X 10(-5) M, bismuth. Shown is that at (Theta, E) = const the currents of dissolution of gold in these solutions increase in the series Tl < Ph < Bi, which evidences an increase in this series of the catalytic activity of adatoms of these metals. Shown is that at Theta = const the catalytic action of adatoms of thallium and bismuth has an approximately additive character. The obtained data are analyzed with allowance made for the explanation offered earlier for the catalytic effect of adatoms on the anodic dissolution of gold based on the hypothesis about the shift of the potential of the free zero charge in the negative direction after substituting a metal atom for chemisorbed cyanide ions.