Extraction and Back-Extraction of Metal Ions in Micellar Systems Using Ultrafiltration: Thermodynamic and Kinetic Aspects

Abstract The present paper is intended to demonstrate the strong analogy existing between solvent extraction and "micellar extraction," where the hydrophobic core of micelles plays the part of the organic phase. The separation of the micellar pseudophase is achieved by ultrafiltration. The parameters influencing the extraction of different metal ions (Ni 2+ , Co 2+ , and Cu 2+ ) by 8-hydroxyquinoline (HQ) or its alkylated analogue (C 11 -HQ, derived from Kelex 100), solubilized in cationic (CTAB/butanol) or nonionic micelles (C 12 EO 6 ), are examined with particular attention to the kinetic aspects involved. Significant enrichments in one of the metal ions present in the solution have been obtained on the basis of their complexation kinetics. The latter are shown, from stopped-flow measurements, to be affected by the addition of small amounts of hydrocarbons. The back-extraction of the metal ions, following dissociation of the complexes in the acid range of pH, is also investigated. The data obtained demonstrate the possibility of performing metal ion extraction in systems that are essentially aqueous, which may prove to be advantageous for the development of new processes of extraction preserving the environment.