Fractionation of europium isotopes in extraction systems: Eu(III), HDEHP/Eu(III), H⁺ (Cl⁻, NO ⁻₃ , SO ²⁻₄ ). Ligand isotope effect

Abstract

The^151/153Eu isotope effects were investigated for the lignad exchange reaction between Eu(III) ions in the extraction system: [Eu(III),di(2-ethylhexyl) phosphoric acid]_org↔[Eu(III), H⁺A⁻(A⁻=Cl⁻,NO ⁻₃ ,SO ²⁻₄ )]_aq. It was observed that the heavy isotope¹⁵³Eu was preferentially fractionated into the organic phase. The following values of the unit separation gains, ε=ln(q), were found: 7.3·10⁻⁵ for Cl⁻, 13.0·10⁻⁵ for NO ⁻₃ , and 9.4·10⁻⁵ for SO ²⁻₄ . The direction of the effect was opposite, and its absolute value was about one order of magnitude lower, in respect to the effect observed in the redox exchange, Eu(II)↔Eu(III), in a similar extraction system.