Recovery of Pd as PdO from Pd/SiO₂ catalyst by leaching using hydrochloric acid

The recovery of Pd from spent catalysts has been gaining attention due to its high economic value and limited availability in nature. To recover and reuse Pd, leaching in HCl–H₂O₂ media and recovery of Pd from the Pd/SiO₂ catalyst were investigated. The Pd/SiO₂ catalyst was leached using 3 M HCl solution with different concentrations of H₂O₂; then 0.5 M NaOH was added to precipitate the Pd ions. The leaching parameters were as follows: temperature, time, H₂O₂ concentration, and pulp density. A 100% leaching efficiency of Pd was obtained through the addition of 5 vol% H₂O₂ in 3 M HCl at pulp density of 50 g/L at 80 °C for 120 min. Complete recovery of Pd was obtained at a pH = 9 due to the hydrolysis of Pd. These results indicate that the leaching time and presence of H₂O₂ played a key role in the stable formation of aqueous Pd–Cl complexes and in improving the mass transfer efficiency. The palladium powder obtained was palladium oxide, and the purity of palladium oxide was 86.6%. Consequently, it is expected that the obtained PdO powder can be utilized in glass, ceramic, and catalyst applications.