Effect of Lead Ions on the Kinetics of Gold Deposition from Cyanide Electrolytes

Abstract

The depolarization of the gold electrodeposition in the presence of lead ions depends on their concentration and the duration of electrode contact with solution preceding a potential scan in an extremum fashion. At constant coverages of the gold surface by lead adatoms θ, the process rate depends on the overvoltage in accord with the Tafel equation. Effective values of the exchange current i ₀ and transfer coefficient α increase with θ from i ₀ ≅ 3 × 10^–5 A cm^–2 and α = 0.23 in pure solutions to 3 × 10^–4 A cm^–2 and 0.53 at θ ≅ 0.4. The reaction order by cyanide ions is independent of θ and equals nearly –0.9. Effects of lead adatoms on the kinetics of cathodic and anodic processes are compared and the obtained data may be brought to conformance given that their mechanisms in pure solutions differ and converge in the presence of lead adatoms.