Extraction studies of lanthanide(III) ions with N,N ' -dimethyl-N,N '-diphenylpyridine-2,6-dicarboxyamide (DMDPhPDA) from nitric acid solutions

The new diamide compound, N,N'-dimethyl-N,N'-diphenylpyridine-2,6-dicarboxyamide (DMDPhPDA), was synthesized and the distribution ratios of lanthanides from 1 to 5 M nitric acid solutions into DMDPhPDA CHCl3 solution were determined. The extraction mechanism of lanthanide with DMDPhPDA was discussed based on the slope analysis of acid and ligand concentration dependencies and the variation of distribution ratio along the lanthanides series. The number of DMDPhPDA molecules in extracted complexes increase from 3 for lighter lanthanides to 4 for heavier lanthanides. From the previous EXAFS study of a complex similar in structure, Ln(III) would form an inner-sphere complex with the two DMDPhPDA molecules and an outer-sphere complex with the third and/or fourth DMDPhPDA molecules in addition to an inner-sphere complex. Nitric acid concentration has more influence on the distribution ratio and the difference of distribution ratio among lanthanides than the ligand concentration.