Electrochemical Study of a Simulated Spent Pickling Solution

Abstract

[EN] The electrochemical behaviour of the main components of the rinsing pickling solutions of the hot dip galvanizing industry, Zn(2+) and Fe(2+) in HCl, was studied by cyclic voltammetry. The effect of different variables (such as the scan rate, the inversion potential, the addition of zinc, stirring of the solution and the presence of iron) on the current-potential curves was studied. The electrochemical reduction of zinc proceeded by a typical nucleation process. Decreasing the HCl concentration enhanced the zinc UPD process because of the less influence of the hydrogen evolution reaction (HER), and a prepeak corresponding to the zinc UPD process was observed previously to the zinc OPD step. The effect of the scan rate on the OPD peak was studied and showed that the Zn(2+) reduction was an irreversible process which was not only controlled by diffusion but also charge transfer kinetics. The diffusion coefficient of zinc was calculated (1.66. 10(-9) m(2) s(-1)). In view of iron deposition, it was confirmed that the pH is an essentially important factor and at low pH values was virtually impossible to deposit iron. The electrochemical study of mixtures containing both zinc and iron showed that the presence of zinc produced an inhibition of the iron deposition process which was confirmed by the observation of the deposits. The SEM images revealed only the presence of zinc grains. However, if the ratio Fe(II)/Zn(II) was higher, the voltammograms main features were more similar to those obtained for pure iron solutions.