Highly efficient extraction of palladium(II) in nitric acid solution by a phenanthroline-derived diamide ligand

The solvent extraction of Pd 2+ in nitric acid solution by a phenanthroline-derived diamide ligand of N,N′ -diethyl- N,N′ -ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen) and the complexation between them were described. By using meta -nitrobenzotrifluoride (F-3) as a diluent, Et-Tol-DAPhen ligand extracted Pd 2+ with strong extractability and excellent selectivity in comparison with traditional amine extractants Aliquat 336 nitrate and tri- n -octylamine. Job's method and mole ratio method suggested the formation of a 1:1 complex of Pd 2+ with Et-Tol-DAPhen. The extraction was a spontaneous and exothermic process of decreased entropy. Furthermore, the analyses of Fourier transform infrared spectra (FT-IR), UV-vis titration, and single-crystal X-ray diffraction revealed that the composition of the extracted species was [Et-Tol-DAPhen·Pd(NO 3 ) 2 ]. Based on the results of solvent extraction and complexation study, a neutral complexation extraction model was proposed. Meanwhile, the stability constant for the complexation of Pd 2+ with Et-Tol-DAPhen was also presented.