Electrochemical behavior and the mechanism of nickel ion removal during zinc sulfate electrolysis via ultrasonic purification

The purification of zinc sulfate electrolyte is an essential process in zinc hydrometallurgy. The agglomeration of zinc powder and difficulty in removing nickel ions are considered the main challenges in the purification of zinc sulfate electrolyte. Herein, we developed an ultrasonic method to substitute nickel ions with zinc with a high removal efficiency (95.27 %) under optimized conditions. The removal percentage under the ultrasonic condition was 25.26 % higher than that under the conventional condition. Physical characterization indicates that the ultrasonic field reduces zinc powder agglomeration, breaks up inclusions and the passivation layer, and enhances the mass transfer during the nickel removal reaction. Electrochemical studies reveal that ultrasonic vibrations and cleaning reduce the overpotential of nickel removal through zinc powder replacement. In-situ modification of the zinc anode enhances zinc powder activity and increases the potential difference in zinc‑nickel primary batteries, thereby boosting the reaction's thermodynamic driving force. Finally, the COMSOL numerical simulation theoretically verified that the heat and mass transfer processes of the solution were accelerated under the ultrasonic condition. The findings of this study can guide the purification process in zinc hydrometallurgy and provide novel insight into ultrasonically boosted chemical reactions.