The Effect of Tin Concentration on the Electrode Processes of Tin Electro-Refining in HCl Solutions

Tin refining in solutions containing just the necessary concentration of HCl for stability (1 mol/dm 3 ), has been investigated in different types of electrolysis cells.A rotating cathode with a centrally placed vertical axis was used to demonstrate the importance of the cathode crystal structure.A computer controlled special potentiostat and current supply was developed for the purpose of potentiostatic and galvanostatic experiments.The virtually even surface of the rotating cathode could offer a uniform conditions over also the anode surface.Cathodic and anodic current densities vs. overpotential were plotted and analysed, as well as cathode potential vs. time at different current densities, applying different tin concentrations.At low tin concentrations, the diffusion limiting current sets in early at the, followed by a shift of the dominant cathodic process for hydrogen evolution, whereas at higher tin concentrations tin deposition was undisturbed.Anodic processes were found virtually unaffected by any of the applied conditions.The optimum energy requirement was found at 30-90 g/dm 3 Sn in the 1M HCl solution at ~ 300 A/m 2 anodic current density.1.