Enhanced thallium removal from zinc sulfate solutions using Lead(II) addition

Abstract

Zinc sulfate (ZnSO4) solutions with high thallium (Tl) concentrations induce cathode corrosion during Zn electrodeposition. Existing Tl extraction methods consume excessive Zn and often result in incomplete removal. This research introduces an optimized technique that incorporates lead(II) (Pb(II)) to form a Pb–Tl compound during Zn cementation. An initial thermodynamic analysis of Tl–Pb–Zn–H2O system reveals challenges in fully substituting Tl using just Zn powder due to minimal potential differences. However, with Pb(II) integration, this potential difference can be boosted to 312 mV. Experimental findings demonstrate that using solely Zn powder, even at 50 times the theoretical quantity, achieved a Tl extraction efficiency of only 50.32%. By adjusting the ratio of Pb(II) to Tl(I) to 1:1, this efficiency soared to 98.93%, while the required Zn powder amount was reduced by 20 times. Using Back Scanning Electron Microscopy (BSEM), deposits of Tl and Pb on Zn powder were confirmed, with elemental distributions perfectly aligned. Tests on ZnSO4 solutions with a Zn2+ ion concentration of 60 g/L still resulted in a 94.07% Tl extraction rate. When applied to actual ZnSO4 electrolytes from a Zn smelting process, the extraction rate remained high at 92.02%. Overall, this research underlines the superior Tl extraction capability of Pb(II) enhanced method over conventional procedures.