Electrochemical noise studies of the corrosion behaviour of lead anodes during zinc electrowinning maintenance

Following anodic polarisation of lead anodes with different silver contents (0.5–0.7%) during Zn electrowinning, the discharge and corrosion of lead anode during the decay period at open circuit potential in sulphuric acid bath have been studied by electrochemical noise analysis (ENA) method. Potential and current decay behaviour over 16 h shows 4 and 2 main characteristic regions, respectively. The wavelet transform has been employed to analyse the ENA data. The results of wavelets have demonstrated that energy distribution plot “EDP” was a powerful tool to provide useful information about the dominant process for different discharge and corrosion stages and mechanisms. The discharge is predominant than corrosion for all anodes for the regions I, II and III, and ENA feature of events changes from large timescale to low timescale, diffusion control or exfoliation to metastable pitting and pit growth, respectively. Region IV, only observed for 0.6% and 0.7%Ag, corresponds to general and metastable pitting corrosion under diffusion control. It has been found that anode containing lower silver content have more corrosion products even after 16 h of decay (discharge and attack dominated by pitting corrosion type with the highest corrosion due to the longest period of pitting during the 16 h).