Extraction of lanthanoids(III) with several β-diketones and the formation of aqueous chelates

The extraction constants represented by K-ex = [LnA(3)](o)[H+](3)[Ln(3+)](-3)[HA](o)(-3) were determined across the lanthanoid series , in the extraction of lanthanoids(III) with acetylacetone (Haa), benzoylacetone (Hbza), benzoyltrifluoroacetone (Hbfa), and hexafluoroacetylacetone (Hhfa) from 0.1 mol dm(-3) NaClO4 into CHCl3 at 25 degreesC. The extraction constants increased along with increasing the lanthanoid atomic number. However, the degree of the variation of the extraction between adjacent lanthanoids decreased in the sequence of Haa similar or equal to Hbza > Hbfa > Hhfa, i.e., the extraction constants with beta-diketones, possessing a smaller number of F atoms, showed the larger variation for the lanthanoid. In addition, when the stability constants of the aqueous chelates of lanthanoids(III) with Hhfa and Haa were determined by potentiometric titration and the solvent-extraction technique, the constants of the aa chelates increased along with the atomic number, while those of the hfa chelates did not change over the series. Accordingly, it was concluded that the increase of K-ex with Haa for the lanthanoid series depends on the change in the stability constants as well as the distribution constants of the extracted species, while the similar values of K-ex with Hhfa across the series was contributed by similar stability constants.