Anion influence in lead removal from aqueous solution by deposition onto a vitreous carbon electrode

We investigated the electrolytic removal of Pb(II) from aqueous solutions containing different electrolytes (nitrate, chloride or sulfate), by electrolysis onto reticulated vitreous carbon electrode (RVC). The efficiency of the electrolytic process of lead removal was found to be a function of electrolyte composition. The chloride containing electrolyte, provided the highest efficiency of lead removal, while removing Pb(II) from the sulfate electrolytes turned out to be a very difficult and high energy consuming process. Cyclic voltammetry and the atomic force microscopy (AFM) were used to characterize lead deposits on RVC and fractured vitreous carbon (FVC) electrodes surface. Our study showed that in the chloride solution, a significantly larger amount of lead deposit was formed than in the sulfate electrolyte. Since the same phenomenon was observed with both electrode types, the FVC electrode is established as an appropriate laboratory model for studying the RVC, which is often used in industrial applications. AFM analysis revealed that lead deposits formed from different electrolyte solutions possess different surface morphologies, indicating different mechanism of formation or different kinds of interactions between the metal adlayer and the adsorbed anions. A highly dense lead deposit, spread all over the electrode surface, in the form of a 2-D film, was found when using the chloride-containing electrolyte. This was attributed to the surface annealing effect and the increased number of nucleation sites due to chloride coadsorption at the electrode surface. Deposits formed from the sulfate electrolyte consisted of numerous, isolated and rather small lead clusters, indicating that deposition from sulfate solutions was inhibited by the formation of the passivated salt adlayer over the lead clusters.