Metal ion transport through microemulsion liquid membranes

Abstract

Reversed micelles of AOT and C 12EO 4 are used as mobile carriers to transport metal ions between two liquid-liquid interfaces. For this purpose w/o microemulsions are replacing classical liquid membranes separating two aqueous compartments, one “source” compartment containing the solute to be transported and one “receiving” compartment in which ion transfer can be monitored. Two types of detection have been used: UV-visible absorption (picrate transport) and atomic absorption (Ni 2+ transport). Different parameters influencing the transport rate are examined: nature and composition of the microemulsion, nature of the salt (anion effect), pH of the receiving phase. The transport mechanism is shown to be different for the C 12EO 4 and the AOT systems and models are proposed for the interfacial transfer step. Coupled transport experiments are also reported in which two different carriers are operating in the liquid membrane: reversed micelles and extractant molecules (crown-ethers or Kelex 100). Synergy effects for metal ion transport have been found in some cases but not in others. These results are discussed in terms of diffusion of the carriers in the stagnant layers. They provide useful guides for further investigations concerning the development of liquid membrane separation processes based on microemulsion systems.