Aqueous hybrid liquid membrane - A novel system for separation of solutes using water-soluble polymers as carriers

A novel aqueous hybrid liquid membrane (AHLM) system comprising three separate aqueous liquid phases was developed for the separation of solutes, such as metal ions and acids. Water-soluble polyelectrolytes were used as carriers in aqueous membrane solutions, separated from the feed and strip streams by charged membranes. Separation of metal cations was tested in the AHLM system consisting of aqueous polyanion solutions (polyvinylsulfonic acid, PVSA, or its sodium salt), as the liquid membrane phase, and cation-exchange membranes as barriers between the phases. While treating an aqueous solution containing a mixture of copper and cadmium salts, high selectivity to copper (>20) was found, combined with relatively high transport rate (3.5 x 10(-6) mol/m(2) s). The separation of anions was tested in AHLM systems containing aqueous solutions of branched polyethylenimine (BPEI) as the membrane phase. Anion-exchange membranes were used as barriers between the phases. While treating aqueous solutions containing copper and cadmium in their anionic complex form, high selectivity to cadmium (>25) was found. The transport rate of Cu was about three orders of magnitude lower than that in the case of PVSA liquid membrane. In the separation of carboxylate anions, BPEI carrier shows relatively low selectivity: S-La/Ac = 1.7 and S-Cit/La = 2.8. The transport rate of lactate is 2.6 x 10(-5) mol/m(2) s. Transport mechanisms are discussed for all these AHLM systems. AHLM solve most of the problems associated with other types of liquid membranes. Since the membrane is stable and no organic solvent is used, there is no contamination of the feed and strip (product) phases. Higher selectivities and transport rates are attainable. (C) 1999 Elsevier Science B.V. All rights reserved.