Effects of Organic Additives and Antimony Addition to the Zn Electrowinning Solutions on the Current Efficiency and Crystal Structure of Zinc Deposition

The effects of organic additives and Sb(III) addition to the Zn electrowinning solutions on the current efficiency and crystal structure of zinc deposition were investigated. When only 1 mg/L of sodium lauryl sulfate (SLS), polyethylene glycol (PEG), or gelatin was added, the current efficiency for Zn deposition increased slightly regardless of the type of organic additives. The current efficiency was highest when the gelatin was added, indicating that the gelatin suppresses the hydrogen evolution more effectively than Zn deposition. When only Sb(III) was added into the solution, the current efficiency of Zn increased slightly at 5 μg/L, but decreased at above 10 μg/L. When both organic additives and 5 μg/L of Sb(III) were added, the current efficiency of Zn was similar to that when the organic additive alone was added, showing no synergistic effect of organic additive and Sb. The large holes resulting from the foam mark of hydrogen evolution clearly decreased when PEG and gelatin were added. This is probably attributed to hydrogen gas being more easily desorbed from the cathode by addition of gelatin and PEG. The presence of 10 μg/L Sb(III) in addition to gelatin and PEG further reduced the number of the holes on Zn deposits. The crystal orientation of Zn deposited from solutions containing both organic additives and Sb(III) showed a similar tendency to that deposited from solutions containing organic additive alone. However, the preferred orientation of a specific plane decreased when PEG and Sb(III) were added simultaneously. The crystal grain size of Zn decreased with the addition of Sb(III), despite the decrease in overpotential. Upon simultaneous addition of SLS or PEG with Sb(III), the grain size of Zn was clearly smaller than that deposited from the solutions added only with organic additive, indicating a synergistic effect of the addition of organic additives and Sb(III).