ELECTROCHEMICAL REGENERATION OF MERCURY-POISONED GRAPHITE AND PLATINIZED GRAPHITE IN ACID-SOLUTIONS

The behavior of mercury dispersed over graphite (G) and platinized graphite (G/Pt, with partial graphite surface coverage by platinum) was studied under conditions of cyclic anodic and cathodic polarization in H2SO4 and HCl solutions in order to regenerate the electrode surface properties. The differences in the distribution and interaction of mercury with G and G/Pt were found to give rise to differences in the mechanism of mercury oxidation and composition of the oxidation products obtained at the corresponding electrodes. Mercury adsorbed on G yields mercury(I) sulfate when subjected to oxidation in H2SO4 solution; this is not found at mercury-poisoned G/Pt electrodes. Poisoning of G/Pt electrodes with mercury gives rise to the chemical compound beta-PtHg4; this is oxidized at higher potentials than free mercury, and apparently for this reason more highly soluble mercury compounds are formed which desorb into the solution. Cyclic anodic and cathodic polarization in HCl solutions was found to be the optimum method of regeneration of mercury-poisoned G/Pt electrodes; this will practically completely restore the electrochemical properties of the electrodes.