The cyanidation of gold. II. The cathodic reduction of oxygen

An extensive study has been undertaken of the reduction of oxygen on various gold electrodes under conditions appropriate to the cyanide leaching of gold. Voltammetric studies with various gold electrodes and ring-disk electrode measurements with pure gold have demonstrated that the 2-step reduction involving peroxide as an intermediate is complex with variable extents of production of peroxide and reduction to water depending on the electrode material and solution purity. There is thus no simple stoichiometry for the reduction of oxygen although the use of a 2-electron reduction is probably the best approximation under plant conditions. This is contrary to the often accepted 4-electron process.

The nature of the gold surface is important with lower reactivity of gold‑silver alloy and plant electrodes relative to pure gold. The sensitivity of oxygen to the presence of underpotentially deposited lead has been demonstrated in solutions contaminated with lead ions. Lead ions have a significant catalytic effect on the kinetics of oxygen reduction that can be attributed to the known effect of underpotentially deposited lead on the reduction of oxygen on gold electrodes in acidic and highly alkaline solutions. Thus, both the anodic dissolution of gold and the cathodic reduction of oxygen are catalysed in the presence of low concentrations of lead ions.