Effect of manganese, magnesium, sodium and potassium sulphates on zinc electrowinning from synthetic acid sulphate electrolytes

Abstract

The effects of manganese, magnesium, sodium and potassium sulphates on the current efficiency, morphology and orientation of 24 h zinc deposits electrowon at 430 A/m 2 and 35°C from synthetic acid sulphate electrolyte have been determined. Increasing concentrations of MnSO 4 in the electrolyte decreased the current efficiency and increased the size of the zinc platelets; the preferred deposit orientation remained intermediate, but the [112] and [114] components became more prominent. The addition of MgSO 4 to the electrolyte resulted in a slight increase in current efficiency and the deposit orientation changed from intermediate to basal. At 50 g/l MgSO 4 the current efficiency decreased slightly and the deposit orientation changed from basal to [101]. Increasing concentrations of MnSO 4 in the presence of 50 g/l MgSO 4 decreased the current efficiency and changed the deposit orientation from [101] to [112] [114] [102] [103] [101]. The addition of Na 2SO 4 resulted in a small increase in current efficiency. Although the deposit orientation remained intermediate, the zinc grain size was reduced at high Na 2SO 4 concentrations. The current efficiency initially decreased with the addition of K 2SO 4 to the electrolyte, but subsequently increased and reached a maximum value at 5 g/l K 2SO 4. The current efficiency was always less at a given K 2SO 4 concentration than for an equivalent concentration of Na 2SO 4. The presence of K 2SO 4 resulted in a zinc deposit having a vertical orientation that reverted to intermediate when the electrolyte also contained MnSO 4 and MgSO 4.