Mechanism and leaching kinetics of silver recovery from zinc leaching residues by ultrasonic synergism with sodium chlorate

Zinc leaching residue is a typical solid waste produced in the hydrometallurgical zinc smelting process, which contains rich silver resources. The traditionally used leaching process for silver recovery suffers from time-consuming and low leaching percentage. In this paper, a new method for the extraction of silver from zinc leaching residues by utilizing ultrasound synergized with sodium chlorate is presented. With the introduction of ultrasound, the silver leaching percentage reached 85.02 %, which was 36.83 % higher compared to the leaching percentage under conventional conditions. Leaching kinetics experiments showed that the apparent activation energy of ultrasonic synergistic leaching process was reduced by 10.11 kJ/mol. In addition, in order to study the mechanism of ultrasonic synergistic leaching of silver, post-experimental leaching residue was analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Ultrasound can strip zinc ferrate envelopes and promote the reaction of silver with sodium chlorate solution. With the aim of further clarification of the mechanism of ultrasound synergistic sodium chlorate leaching of silver, the leach solution was also examined by electron paramagnetic resonance (EPR). Compared with traditional leaching processes, this study has the advantages of lower energy consumption, shorter leaching time, and higher leaching percentage. Therefore, the synergistic effect of ultrasound and sodium chlorate is an environmentally friendly and efficient technology for recovering silver from zinc leaching residues.