The degradation of aluminium cathodes by fluoride ion during zinc electrowinning

The influence of fluoride ions on aluminium cathode surface degradation during zinc electrowinning has been studied. Electrolyte with a composition similar to that employed in plant operations has been used. A direct correlation is shown between the electrolyte fluoride content and the number of deposition cycles possible before zinc removal becomes difficult. The role of initial nucleation and starting electrode morphology is discussed in terms of the degree of adherence observed. Electrochemical tests have also been made on the electrodes at various stages of the process in an attempt to gain a better fundamental understanding of the mechanisms responsible for the adherence. The results indicate that the severity, of the adherence is generally determined by the amount of residual zinc remaining on the surface after stripping and the fluoride content of the solution during plating. The contribution of physical surface condition alone seems to be less significant than the chemical conditions imposed during deposition.