Selective extraction of americium(III) over macroscopic concentration of lanthanides(III) by synergistic system of TPEN and D2EHPA in 1-octanol

The synergistic extraction with N,N,N',N'-tetrakis(2-methylpyridyl)-ethylenediamine (TPEN) and di(2-ethylhexyl)phosphoric acid (D2EHPA) in 1-octanol demonstrates good selectivity for Am(III) over Ln(III) in solutions containing macroscopic concentrations of the latter. The maximum apparent separation factor, which is defined as the ratio of the distribution ratio of Am(III) to that of Eu(III), is ca. 80 at the molar ratio of D2EHPA to TPEN, 2.0. This ratio corresponds to the result of the spectrophotometric titration, which indicates that TPEN and D2EHPA associate in 1-octanol and two D2EHPA molecules coordinate to Eu(III)-TPEN complex, [Eu(TPEN)](3+). In the present study, association of D2EHPA and TPEN is one of the most important factors for the synergistic extraction and the complexation of TPEN and D2EHPA with Eu(III).