Palladium Pressure Leaching Kinetics in Chloride Medium, from Printed Circuit Boards, in a Pressure Reactor

The recovery of palladium (Pd) from recycling printed circuit boards (PCBs) has attracted attention in recent years, because the metal is found in low concentrations in the earth's crust and the demand for it has increased due to its chemical and physical properties, therefor, in addition to being used in jewelry, it is used in catalytic converters, dentistry, medicine, watchmaking, aircraft spark plugs, and electronic products. Currently, the extraction of Pd from waste PCBs through an efficient and ecological process remains a challenge, since a process that meets these two characteristics has not been found. In the present study, palladium leaching was carried out in a PARR titanium reactor with an acid leaching agent under pressure from printed circuit boards, using [NaCl]=0.017 M, [NaClO]= 0.067 M and varying the concentration of hydrochloric acid, pressure, and temperature,. The best results were obtained using at 0.34 MPa, 70°C and [HCl] acid concentration of 4 M, This was based on the thermodynamic analysis of the Pd-Cl-H2O system, using the Eh-pH diagram. In addition, the study of the extraction kinetics was carried out to know the leaching reaction mechanism. The activation energy (Ea) was determined to be 0.03 kJ/mol. At less than 1 kJ/mol, the mechanism is expected to be diffusion through the product layer. Under these conditions, an extraction of 93% of Pd was achieved.