Zn leaching recovery and mechanisms from end-of-life tire rubber

Experiments were conducted to investigate the leaching behavior of Zn from end-of-life tire rubber. XRD and XPS analyses showed that the Zn-containing phase in the material was mainly ZnO. SEM-EDS analysis confirmed the presence of both exposed and encapsulated ZnO particles. Acid leaching tests indicated that the carbon black comprised in the material can be oxidized and dissolved by HNO₃, resulting in the dissolution of completely encapsulated ZnO particles with thinner covering layers. Then, leaching tests using HNO₃ as the lixiviant were performed by varying acid concentration and leaching temperature. The results showed over 98% of Zn can be recovered using 2.0 mol/L HNO₃ at 90 ℃ after 400 min of reaction. Leaching kinetic results were best fit with the Avrami model, indicating the leaching process was controlled by diffusion. The activation energy determined by Arrhenius formula was 12.92 kJ/mol, which further supports the proposed diffusion controlled leaching process.