Morpholine-derived hydrophilic 1,10-phenanthroline-2,9-dicarboxamide for americium–lanthanide separation in phosphine oxide extraction systems

Abstract

A new hydrophilic DAPhen derivative, N²,N⁹-bis(2-morpholinoethyl)-1,10-phenanthroline-2,9-dicarboxamide (L), was synthesized and investigated as a selective aqueous-phase complexing agent for the separation of Am(III) from lanthanides in phosphine oxide-based extraction systems. Potentiometric and spectrophotometric titrations with Eu(III) demonstrated the formation of 1 : 1 and 1 : 2 complexes. X-ray crystallography revealed a unique coordination pattern with progressive substitution of nitrate anions by water molecules across the lanthanide series (La–Er), as well as protonation of morpholine nitrogen atoms under crystallization conditions. Solvent extraction experiments showed that the addition of L to aqueous nitric acid solutions reduces the distribution ratio of Am(III), thereby enhancing separation from Eu(III) and other lanthanides when combined with TOPO in kerosene or F-3. Separation factors SF(Eu/Am) of up to 26 were achieved. Although insufficient selectivity was observed for Am(III)/La(III) separation, the system demonstrates the potential for group separation of An(III) from Ln(III) with subsequent back-extraction of Am(III).