The relationship between the open-circuit potential of a galena electrode and the dissolved lead concentration

Abstract

Electrochemical experiments and thermodynamic mass balance calculations have been conducted to determine the relationship between the open-circuit potential of a galena electrode and the dissolved lead concentration at pH = 0, 1.1 and 4.6. The experiments have been performed in such a way that the potential covers the range from reducing values where Pb 0 is present on the electrode surface to oxidizing ones where the anodic dissolution of PbS takes place. The results indicate that the response of this system is characterized by a region at low potentials where the electrode behaves essentially as a Pb 0 electrode and another at higher potentials where the electrode has reverted to its original PbS character. The transition between these two regions is sharp and occurs when all (pH=0 and 1.1) or most (pH=4.6) of the Pb 0 has dissolved from the surface. The pH has also been found to have a significant effect on the reversibility of the system. At pH=0, the potential obeys Nernstian behavior along both portions of the electrode response. Raising the pH to 1.1 causes the observed potentials along the lower Pb 0-like segment to deviate anodically from the reversible values. When a pH of 4.6 is reached, the upper segment shows an anodic shift as well.