Kinetic study on leaching of Zn and Cu from spent low-temperature shift catalyst (CuO/ZnO/Al₂O₃): application of taguchi design

The recovery of valuable metals from the spent catalysts has become a part of exhaustive research not only due to reducing the inventory cost of catalysts but also for minimizing the spent catalyst generation to prevent environmental pollution. In the present investigation, the kinetic study of the hydrometallurgical based leaching of Zn and Cu from the spent low-temperature shift catalyst (CuO/ZnO/Al₂O₃) have been performed. Additionally, the process parameters affecting the leaching process have been optimized by Taguchi’s orthogonal array design. The results of the kinetic analysis indicated that the leaching process was mainly controlled by the diffusion through the porous product layer. The activation energy for the leaching of Zn and Cu were estimated as 18.63 kJ/mol and 18.14 kJ/mol respectively. Quantitative leaching of Zn (96.71%) and Cu (94.82%) was observed under the optimum levels such as HCl concentration − 3 M, leaching time − 3 h, stirring speed—600 rpm, S/L − 0.01, particle size − 90 µm and temperature – 80  C.