Extraction of some lanthanides by 12-crown-4 and 15-crown-5 from perchlorate media as ion pairs

The extraction of the trivalent lanthanides Eu, Tm and Yb(Ln) by crown ethers (CE) 12-crown-4 (12C4) and 15-crown-5 (15C5) in chloroform from perchlorate aqueous media of constant ionic strength is investigated. The effect of [H⁺], [CE] and [ClO₄^–] on the respective distribution ratio (D) is elucidated. Slope analysis of these results indicated that the extracted species are of the type Ln(OH)₂⁺·ClO₄^–(CE)₂. The extraction constants obtained are in the sequence 15C5>12C4 for the CE's and EuTm99.5% by three (or four) successive extraction and strippings.