Transition Metal Complexes with 8-Hydroxyquinoline and Kelex 100 in Micellar Systems. Stoichiometry of the Complexes and Kinetics of Dissociation in Acid Media

Abstract

Complexation of metal ions by micelle-solubilized extractants can be used for the development of new extraction processes. Metal extraction in micellar systems is in many respects analogous to solvent extraction if one considers the use of ultrafiltration as a means to separate the micellar pseudophase from the continuous aqueous phase. The present paper is intended to further characterize the nature of the complexes obtained in micellar systems (especially their stoichiometry and their stability as a function of pH) and to compare the results with those previously obtained in classical biphasic systems. The extractant molecules considered in this work were 8-hydroxyquinoline (HQ) and its alkylated analogue (C₁₁-HQ) derived from Kelex 100. Their complexes with Ni²⁺, Co²⁺, and Cu²⁺ have been investigated in micellar solutions made of cetyltrimethylammonium bromide (CTAB), 1-butanol, and water. The stoichiometry of the complexes was determined using Job's continuous variation method, and their kinetics of dissociation was investigated with the stopped-flow technique. Practical selective recovery of the different metal ions from their complexes in micelles was shown to be possible using ultrafiltration.