A New Approach for the Leaching of Palladium from Spent Pd/C Catalyst in HCl-H2O2 System

Recovery of the spent precious metal catalysts by suitable methods is very important for chemical industries. This work introduces a new method to provide the optimal conditions of the leaching of palladium from spent Pd/C catalyst in HCl-H2O2 system. Response surface methodology (RSM) and the Box-Behnken method with four independent variables including HCl concentration (wt %), H2O2 concentration (wt %), leaching temperature (degrees C) and leaching time (min) are used for building a new correlation. The transmission electron microscopy (TEM) images, wide-angle X-ray diffraction (XRD) patterns and adsorption/desorption isotherms of N-2 are used to study the changes of catalyst surface during the leaching process. According to the outputs of the new model, the predicted value for the maximum palladium recovery is equal to 80.6%, which is comparable with the experimental value (82.5%) in the same condition. The feasibility of complete palladium recovery from spent Pd/C catalyst by leaching method is also evaluated. The results show that leaching in extremely oxidizing conditions cannot lead to the complete palladium recovery from Pd/C catalyst because a considerable portion of the palladium remains on the carbon support surface. Moreover, the leaching process significantly can affect the surface properties of the activated carbon supports.