Efficient removal of Cd 2+ impurity from zinc sulfate electrolytes by zinc powder replacement under ultrasound assisted Cu 2+ additive

Cadmium ion impurity in zinc sulfate electrolyte causes serious harm to zinc electrodeposition, so the removal of cadmium ion is very important. We propose a method for enhancing the removal of Cd 2+ by zinc powder displacement using ultrasound assisted cationic Cu 2+ additive. When the concentration ratio of Cu 2+ to Cd 2+ is 1:4 and the ultrasonic amplitude is 40 %, the removal efficiency of Cd 2+ reaches 99.8 % and increases about 32.3 % in just 30 min, while the consumption of zinc powder is merely 1.49 times that of impurity ions, markedly surpassing the performance under conventional conditions (67.5 %). Additionally, the addition of Cu 2+ yields a Cd 2+ replacement efficiency of 76.2 %, suggesting that Cu 2+ has the potential to enhance the reduction of Cd 2+. Furthermore, the kinetic activation energy of zinc powder replacement for removal of Cd 2+ is only 19.42 kJ/mol under the condition of ultrasound assisted cationic Cu 2+ additive, which is lower than that of other purification technologies. The reaction is under electrochemical control when the Cd 2+ concentration surpasses 1400 mg/L, shifting to diffusion control when the Cd 2+ concentration falls below 1200 mg/L. The removal mechanism of cadmium ion mainly includes opening zinc powder inclusions and inhibiting the formation of alkaline zinc salts under the condition of ultrasound assisted cationic Cu 2+ additive. The satisfactory results obtained in this study provide valuable insights for the application of ultrasonic technology in chemical industry.