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

We investigated the electrolytic removal of Pb(II) from aqueous solutions c ontaining different electrolytes (nitrate, chloride or sulfate), by electro lysis onto reticulated vitreous carbon electrode (RVC). The efficiency of t he electrolytic process of lead removal was found to be a function of elect rolyte composition. The chloride containing electrolyte, provided the highe st efficiency of lead removal, while removing Pb(II) from the sulfate elect rolytes turned out to be a very difficult and high energy consuming process . Cyclic voltammetry and the atomic force microscopy (AFM) were used to cha racterize lead deposits on RVC and fractured vitreous carbon (FVC) electrod es 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 e lectrode 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 dif ferent surface morphologies, indicating different mechanism of formation of 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 e lectrolyte. This was attributed to the surface annealing effect and the inc reased number of nucleation sites due to chloride coadsorption at the elect rode surface. Deposits formed from the sulfate electrolyte consisted of num erous, isolated and rather small lead clusters, indicating that deposition from sulfate solutions was inhibited by the formation of the passivated sal t adlayer over the lead clusters. (C) 1999 Elsevier Science Ltd. All rights reserved.