Multiscale Mechanisms of Thallium-Induced Deterioration in Zinc Electrowinning: From Interfacial Electrochemistry to Macroscopic Defect Formation and Mitigation Strategies

This study systematically investigates the impact of thallium (Tl+) on zinc electrowinning from acid sulfate electrolytes, revealing significant concentration-dependent effects. The application of additives to mitigate the detrimental effects of Tl+ was also explored. At concentrations below 0.8 mg/L, Tl+ exhibits slight decrease on current efficiency (CE) and energy consumption (EC), while higher levels (3.0–5.0 mg/L) reduce CE by 7.41–15.37% and increase EC by 9.63–30.25%. Microstructural characterization shows Tl+ induces pore formation and promotes the preferred (110) orientation. The combined results of molecular dynamics (MD), density functional theory (DFT), and electrochemical experiments reveal that thallium codeposition with zinc enhances hydrogen evolution. This enhancement stems from strong Tl+-H2O interactions, characterized by a binding energy of −13.7 eV, which induce bubble accumulation and initiate pore formation. Additionally, the potential difference between zinc (−0.76 V) and thallium (−0.34 V) facilitates localized galvanic corrosion, causing zinc redissolution. Composite additive A1 effectively mitigates these detrimental effects, increasing CE by 3.86%, reducing EC, and restoring compact (110)-oriented growth. Moreover, A1 preferentially adsorbs onto the cathode surface before H2O and Tl+, forming a protective interfacial layer that effectively suppresses the hydrogen evolution reaction (HER), thereby enhancing overall process performance.