Solvent extraction of europium(III) from nitrate medium with 4-acyl-isoxazol-5-ones and 4-acyl-5-hydroxy-pyrazoles. Effect of salts and diluents

The solvent extraction of europium(III) from nitrate medium (0.1 M or 1 M) with acidic chelating extractants HL in chloroform, at 25 degrees C, has been studied. The extractants are either 3-phenyl-4-acylisoxazol-5-ones (acyl = benzoyl, "HPBI", and p-tert-butylbenzoyl, "HPtbBI"), or substituted 4-acyl-5-hydroxypyrazoles 1-(p-nitro-phenyl)-3-phenyl-4-lauroyl-5-hydroxypyrazole, 'UNPPLP", and 1-phenyl-3-methyl-4-(p-tert-butylbenzoyl)-5-hydroxy-pyrazole, "HPMtbBP", of various acidities. In all cases europium is extracted by cation exchange as EuL3,org. Because of their higher acidity, extractions performed with 4-acylisoxazol-5-ones occur at lower pH range than with 4-acylpyrazol-5-ones. The order of extraction efficiency is: HPMtbBP (pK(a)=4.1)< IINPPLP (pK(a)=3.2)<HPtbBI (pK(a)= 1.3)<HPBI (pK(a) = 1.2). The nature of the cation of the inorganic salt used to fix the ionic strength has no effect on the extraction. Due to the competitive complexation of Eu3+ by NO3- in the aqueous phase, the extraction from nitrate medium is less efficient than from perchlorate medium: the order of extraction is NaNO3 approximate to KNO3 approximate to LiNO3<NaClO4. Extraction was also studied in other diluents and increased in the order: chloroform < 1,2-dichloroethane <= benzene approximate to toluene approximate to hexane. The same order was observed for europium extraction with several other beta-diketones. On the basis of values found in literature, trends of extraction of europium with beta-diketones in several diluents are proposed. (C) 2006 Elsevier B.V. All rights reserved.