The anodic dissolution of mercury in sulphide ion solutions

The anodic dissolution of mercury in sulphide ion solutions has been studied by the faradaic impedance method, using in situ, generation of the dissolving species. The mercury passes into solution as the soluble complex ion HgS₂²⁻. The rate-determining step in the dissolution reaction has been identified as a heterogeneous single-electron transfer process which is first order in [S²⁻] and a reaction mechanism-is-proposed on this basis. Double-layer capacity measurements have been made in the presence of the dissolution reaction and these indicate the absence of any strong specific anion adsorption at the electrode. The shape of the electrocapillary curve for sulphide solutions is discussed in the light of these observations.