Processes during the electrorefining and electrowinning of lead

The anodic and cathodic processes in the fluorosilicate electrolytes during galvanostatic deposition under (DC) and polarity reversal current (PRC) regimes were investigated. It was established that, during the process of lead electrorefining from concentrated electrolyte without applying PRC, at c.d. i = 300 A/m(2) (3 A/dm(2)), after 60-80 h of the 95 h operation cycle, a limiting anodic polarization barrier value (Delta phi(A)cr = 200 mV) is attained. In this case bismuth and antimony start to dissolve actively from the anodes and are deposited onto the cathode, while under PRC conditions Delta phi(A)cr is not reached even after 95 h. The cathodic deposits are rounded crystal grains and display pronounced epitaxial growth. Spectral analysis shows that Sb is the main impurity of cathodic lead instead of Bi. During the electrowinning of the lead, without using H3PO4 as an inhibitor of beta-PbO2 parasitic deposition onto the inert graphite anodes, it was established that a critical value of the anodic potential phi(A)cr = 1430-1500 mV/SCE) exists, under which beta-PbO2 is not deposited. If H3PO4 is present, beta-PbO2 is not deposited onto the graphite anodes at any values of the anodic potential.