Kinetic studies of extraction for a mixture of some europium phosphonate complexes and 2-benzoyl or 2-anilinopyridine in n-hexane

The kinetics and mechanism of solvent extraction of Eu3+ from an aqueous phase of 0.1 M ionic strength (Na+, HClO4) at pH 3.2 and 25 degrees C by a mixture of ethylhydrogen benzyl phosphonate (HEBzP), ethylhydrogen benzoyl phosphonate (HEBoP), and 2-benzoylpyridine (BP), or 2-anilinopyridine was studied using a stirred Lewis cell. The extraction was investigated over a wide range of extractant concentrations and pH. The kinetic data were treated according to the mass transfer with chemical reaction (MTWCR) model, in which the extraction rate was shown to be controlled by a mechanism involving. diffusion of the extractant into the aqueous phase boundary layer followed by addition of the first ligand to the europium ion. The rate constants K-HL = 2.49 +/- 0.02 X 10(3) M-2 min(-1), K-L = 10.35 +/- 0.05 x 10(2) M-2 min(-1), and K-LS = 1.105 +/- 0.12 x 10(3) M-2 min(-1) (HL, HEBzP; S, AP). (C) 1998 Academic Press.