Separation of palladium and platinum metals by selective and simultaneous leaching and extraction with aqueous/non-aqueous solutions

Abstract

The recovery of Pd and Pt from secondary resources has attracted much attention due to their unique chemical properties and economic values. The difference in the reduction potential of Pd(II) and Pt(IV) was utilized in the separation of the two metals by employing aqueous and non-aqueous solutions together. The two metals were selectively separated by employing simultaneous leaching and extraction occurred in one operation. A mixture of concentrated HCl, TBP (tributyl phosphate) in kerosene and H2O2 was able to selectively dissolve Pd over Pt metal and thus it was possible to separate the two metals by leaching and extraction. Replacement of H2O2 and kerosene with NaClO3 as an oxidizing agent and MIBK (methyl isobutyl ketone) as a polar diluent in the solvent mixture resulted in complete dissolution/extraction of Pt. The optimum conditions such as reaction time, temperature, stirring speed, the weight ratio of solid to HCl, TBP and oxidizing agents were obtained for the selective and complete leaching and extraction of Pd and Pt. The simultaneous leaching and extraction systems is more efficient than aqueous system of HCl and H2O2 in terms of selectivity and leaching ability for Pd. The Pd(II) and Pt(IV) ions in the loaded TBP phases were completely stripped by a mixture of HCl and thiourea and the purity of these metal ions in the respective stripping solutions was higher than 99.9%. A simple process can be developed to separate Pd and Pt metals by selective dissolution.