NMR INVESTIGATION OF THE SOLUBILIZATION OF A HYDROPHOBIC EXTRACTANT IN A CTAB/BUTANOL MICELLAR SYSTEM

This work concerns the use of micellar systems or microemulsions as the extracting phase for metal ions in place of an organic solvent. It focuses on the solubilization in cetyltrimethylammonium bromide (CTAB)-butanol-water ternary systems, of an extractant of industrial origin : 7-(4-ethyl-l-methyloctyl)8-hydroxyquinoline (C 11 -HQ), obtained from Kelex 100. The presence of cosurfactant allows high incorporation of the extractant, which can be viewed as a microemulsification of oil in water. 1 H NMR chemical shift, linewidth and relaxation time measurements have been used to determine the location of C 11 -HQ in the micelle pseudophase as a function of different parameters : concentration of C 11 -HQ, pH and the presence of metal ions. A novel feature is the evidence for a transition between a state where the extractant is essentially located in the amphiphilic palisade, to a state where it is located in the centre of the micelles. This transition occurs when the surfactant to extractant ratio becomes lower than 8. The data also suggest that the location of the Zn 2+ complex of C 11 -HQ depends on its stoichiometry.