Sustainable and green ultrasound-assisted zinc cementation for efficient removal of Cu2+ and Cd2+ from zinc sulfate electrolytes: mechanism, kinetics, and environmental benefits

Abstract

The efficient removal of copper (Cu²⁺) and cadmium (Cd²⁺) impurities from zinc sulfate electrolytes is essential for stable zinc hydrometallurgical production. However, conventional zinc powder cementation is hindered by surface passivation and slow reaction kinetics, leading to excessive zinc consumption and hazardous residue generation. In this study, a green and reagent-free ultrasound-assisted enhancement strategy is proposed to overcome these limitations. Under optimized conditions, the removal efficiencies of Cu²⁺ and Cd²⁺ increased by 7.12% and 8.68%, respectively, compared with the conventional process, achieving removal rates exceeding 95%. Meanwhile, zinc powder consumption was reduced by 15%, and the generation of purification residues was significantly suppressed, improving zinc utilization efficiency and process sustainability. Comprehensive characterization was conducted to elucidate the ultrasonic enhancement mechanisms. Ultrasonic cavitation effectively refines purification residue particles, increasing their specific surface area by 43.18%, while continuously disrupting passivation layers and exposing fresh reactive sites on zinc particles. Electrochemical analyses reveal that ultrasonic irradiation increases the exchange current density by nearly one order of magnitude and decreases charge transfer resistance by 20.13%, thereby markedly accelerating electron transfer kinetics. Furthermore, electron paramagnetic resonance results confirm the generation of highly reducing hydrogen radicals under ultrasonic irradiation, which further promotes the reduction of Cu²⁺ and Cd²⁺ ions. Overall, this work demonstrates that ultrasound can replace conventional chemical activators, offering a cleaner, more green, and highly efficient alternative for impurity removal in zinc hydrometallurgical purification processes.