Separation of palladium(II) from mixtures of non-ferrous metal ions by solvent extraction

The possibility of Pd(II) ions separation from mixtures of Co(II), Ni(II), Cu(II) and Pd(II) ions by solvent extraction was studied, using 1-hexyl-2methylimidazole in chloroform as the extractant. The initial concentration of each ion was 10 mM. The tests were carried out at a temperature of 25°C, at a constant strength of the aqueous solution of I = 0.5, as maintained by the KCl solution. It was demonstrated that differences in the stability and structure of their coordination sphere as well as solubility of complexes with the extractant could be used for separating the Co(II), Ni(II), Cu(II) and Pd(II) ions by solvent extraction. Pd(II), which forms flat-square complexes in the solutions, passes easily into the organic phase and is easier separated from the mixture of Co(II), Ni(II), Cu(II) ions, which form octahedral or tetrahedral complexes. Extraction percentages were calculated. For the respective metals, their values increase for increasing concentrations of the extractant in the aqueous phase. The extraction percentage decreases in the following order: Pd(II) > Cu(II) > Co(II) > Ni(II). In the case of the quaternary mixture, the highest extraction percentage for Pd(II) (70%) was obtained at a pH=7.33. Separation coefficients were also calculated. The highest separation coefficients were obtained for the system: Pd(II)/Ni(II), Pd(II)/Co(II); at a pH of 5.4 for an aqueous solution, their values are 13.3 and 7.7, respectively.