Synergistic ozone-ultrasound method for high efficiency cobalt recovery from zinc purification residue

The sustainable recovery of cobalt from secondary resources is critical for mitigating supply risks and advancing circular economy practices. This work presents an innovative integrated hydrometallurgical process for cobalt recovery from zinc purification residue (ZPR). Through orthogonal array optimization, sulfuric acid leaching achieved high extraction efficiencies under mild conditions: 98.9% for Zn, 99.9% for Cd, and 85% for Co. A subsequent secondary leaching step ensured complete transfer of valuable metals into solution while simultaneously generating high-purity PbSO 4 as a by-product. For cobalt recovery, oxidative precipitation was significantly enhanced by combining ozone oxidation with ultrasound, which improved the efficiency to 58.4% by intensifying mass transfer and radical generation. Further integration of ZnO for precise pH control dramatically increased the cobalt precipitation efficiency to over 98%. Kinetic studies revealed a mixed-control mechanism with an apparent activation energy (E a ) of 22.9 kJ/mol. The final product was characterized as nanostructured CoOOH. This study establishes an efficient and controllable strategy for cobalt recovery from secondary zinc resources, contributing to a circular economy for critical metals. • Integrated hydrometallurgical process enables cobalt recovery from zinc residue. • After secondary leaching, Zn, Cd, and Co are fully recovered, leaving only PbSO 4 . • Ultrasound-assisted ozone oxidation increased cobalt precipitation to over 98%. • This process produces nanostructured CoOOH, supporting circular metal recovery.