Recovery of zinc from hot-dip galvanizing slag through an ozone-assisted leaching and precipitation process with a reusable leaching system

Hot-dip galvanizing slag, a zinc-rich industrial byproduct, presents both resource potential and environmental challenges in conventional hydrometallurgical recovery due to excessive acid consumption and limited selectivity. This study presents a novel ozone (O 3 )-assisted leaching and precipitation strategy for selective zinc recovery from hot-dip galvanizing slag. By leveraging the synergistic effects of O 3 oxidation and a choline chloride-ethylene glycol (ChCl-2EG) deep eutectic solvent (DES), the proposed method achieves efficient metal leaching (Zn: 99.6 %, Fe: 99.3 %, Al: 99.5 %) through controlled acidification. Subsequent water addition induces structural transformation of zinc complexes from [ZnCl 4 ]²⁻ to [ZnCl 4 (H 2 O) 2 ]²⁻, enabling phase separation. Precise pH control at 2.8 using oxalic acid results in selective zinc precipitation with 91.1 % efficiency while maintaining iron and aluminum in the solution. The residual solution undergoes distillation for water removal and recycling, demonstrating stable performance over five consecutive cycles. This closed-loop process eliminates excessive acid usage, reduces liquid waste by 85 %, and achieves 94 % reagent recovery efficiency, establishing an environmentally benign pathway for zinc resource reclamation.