A preconditioning process for extended passivation of alloyed lead anodes in zinc electrowinning

Abstract

On the basis of an old Cominco, Trail. B.C., idea of preconditioning silver (0.8 wt%) alloyed lead electrodes for a proper passivation, optimal, chemically balanced and more economical process has been developed for use in Zn electrowinning. A relatively short time anodic polarization of Fb(As) electrodes in sulphuric acid containing fluoride ions, (as a stimulating agent for protective and compact layer formation of beta-PbO2), is found to give a compact, homogeneous, long lasting passivation layer of beta-PbO2. The presence of a small amount of F--ions in the passive layer of beta-PbO2 enables the passive oxide deposit to behave as long lasting, Monitoring of Pb-ions emission testifies that the preconditioned electrode will have more than ten years of life zinc electrowinning. An additional contribution is the exchanged chemical balance of manganese species in solution: the detrimental MnO2 production is dramatically reduced. The most important achievement of the process represents, winning of pure zinc.