Electrorefining of zinc from hot-dip galvanizing slag in a choline chloride/ethylene glycol based deep eutectic solvent

This study investigates the electrorefining of zinc derived from hot-dip galvanizing (HDG) slag, employing a deep eutectic solvent (DES) composed of choline chloride and ethylene glycol, commonly referred to as Ethaline DES. A thorough electrochemical analysis was carried out to examine the oxidative dissolution behaviors of metallic zinc and associated impurity metals, along with the reduction behavior of Zn(II) ions. These findings demonstrate that, in the Ethaline-ZnCl 2 DES system, zinc undergoes oxidation preferentially compared to impurities, enabling selective extraction of zinc from HDG slag. Furthermore, the reduction potential of Zn(II) is observed to be more positive than that of the impurity metal ions, favoring its preferential deposition at the cathode. Increasing the temperature and incorporating an appropriate quantity of water significantly reduce the viscosity and improve conductivity of the Ethaline DES system, thereby enhancing charge transfer and diffusion of Zn(II) ions while lowering the energy barrier for Zn(II) reduction. Under optimized electrorefining conditions, the resulting cathodic zinc achieves a purity of 99.967 %, with a current efficiency of 95.14 % and an energy consumption of 787 ± 26 kWh/t. This work proposes a sustainable and energy-efficient method for the electrorefining of zinc from HDG slag, presenting a viable pathway for the valorization of this metallurgical byproduct.