Effect of Ethylene Glycol on the Dissolution of Palladium with HCl Solution Containing Oxidizing Agents and Selective Precipitation of Pd(IV) Compound

Abstract

There is growing interest in the recovery of pure palladium (Pd) compound from cemented Pd from spent electroplating solutions due to increasing demand for Pd, and there is considerable motivation to develop an efficient recovery process. In conventional methods of leaching Pd metal, HCl solutions containing oxidizing agents are employed. In this work, ethylene glycol (EG) replaced water as a diluent in the HCl solution containing oxidizing agents such as H2O2, NaClO and NaClO3. Leaching of the Pd metal and the subsequent precipitation of the Pd(IV) compound was investigated. Among the three kinds of oxidizing agent, NaClO3 showed the best Pd metal leaching efficiency from a metallic mixture of Pd and Zn from HCl in EG solution. The role of EG in enhancing the leaching and precipitation is discussed in light of its interaction with other components in the solutions. To precipitate the Pd(IV) compound with NH4Cl, it is important that the dissolved Pd ion exists as Pd(IV). Therefore, NaClO3 was again added to the leaching solution to verify the oxidation of Pd(II) to Pd(IV). Extra pure ammonium hexachloropalladate ((NH4)2PdCl6) was recovered by precipitation from the leaching solution of the cemented Pd under the optimum conditions. Compared to conventional HCl systems, the present process shows some advantages, by reducing both chemical dosage and energy consumption. The results confirm a process can be developed for the recovery of the Pd(IV) compound from spent electroplating solutions containing a small amount of Pd(II).