Enhanced separation of trivalent lanthanoids by solvent extraction with 18-crown-6 and EDTA complexonate.

The selectivities during solvent extraction of lanthanoids with macrocycles can be modified with complexonates in the aqueous phase. In the case of solvent extraction of lanthanoids with 18-crown-6 and trichloroacetic acid (TCA), addition of EDTA to the aqueous phase enhances the selectivities of lanthanoids by 3-7 times compared to those without the complexonate. This is due to the fact that the stability of lanthanoid-EDTA complexes increases in the opposite direction to the crown-TCA complexes across the lanthanoid series. The selectivities observed in this system are among the largest reported for the light lanthanoids. The effect of the complexonate on lanthanoid extraction can be explained by a simple model presented in this paper.