Enhanced separation of Pd(II) and Pt(IV) from hydrochloric acid aqueous solution using 2-((2-methoxyethyl)thio)-1H-benzimidazole

Separation of palladium (Pd) and platinum (Pt) by solvent extraction is difficult because of their extremely similar physicochemical properties. Development of new extractants with a high extraction efficiency and excellent separation selectivity is the primary focus for enhancing the separation of Pd and Pt by solvent extraction. In this study, a new extractant, 2-((2-methoxyethyl)thio)-1H-benzimidazole (MOBI), which contains N, S, and O atoms, was synthesized and used to separate Pd(II) and Pt(IV) from a hydrochloric acid aqueous solution. The experimental results revealed that Pd(II) and Pt(IV) were effectively separated under the optimal conditions: MOBI concentration of 0.005 mol·L−1, HCl concentration of 0.2 mol·L−1, organic/aqueous (O/A) phase ratio of 1.0, and contact time of 15 min. The separation coefficient between Pd(II) and Pt(IV) was 1246.40, which indicates that MOBI has a higher selectivity for Pd(II) than Pt(IV). In addition, the mechanism of coordination between Pd(II) and MOBI was demonstrated through the slope method, Fourier transform infrared spectroscopy (FTIR), hydrogen-1 nuclear magnetic resonance spectroscopy (1H NMR), and carbon-13 nuclear magnetic resonance spectroscopy (13C NMR). The results revealed that MOBI could coordinate with Pd(II) via the N atom in the benzimidazole ring of MOBI molecules to form [Pd(MOBI)2Cl2](O).