This proposal studies a vesicular membrane based biomimetic system for removing hazardous metals cation from aqueous streams. In preliminary work, the PI has used equilibrium detergent dialysis to fabricate unilamellar vesicles made of soybean phosphatidylcholine harboring a lipophilic metal carrier, the ionophone A23187, in the vesicle membrane, and a chelating agent (NTA, nitrilotiacetate) in the vesicle interior. When the vesicle dispersion is mixed with an aqueous solution containing the metal cations, the cations become bound to the metal carrier in the membrane. The complex is soluble in the membrane, and it diffuses across the lamella to the inside surface of the membrane vesicle where the metal ion is released. The released ion complexes with the chelator, thereby keeping the concentration of the ion- lipophile complex at the inside surface of the vesicle membrane extremely small. With this value small, the driving force for diffusion of additional complexes of the ion and the lipophile remains large, and the vesicle continues to strongly uptake the metal ions. Results of batch experiments in which the vesicles were mixed solutions containing only Cu(II), Cd(II), or Pb(II) cations demonstrate that the vesicles are effective scavengers of these metal ions with rapid uptake and high loading. The primary problem with this technique is the high cost of the lipophilic carrier and the phosphidylcholine. The proposed research will explore less costly lipophilic carriers such as cleft type metal binding agents and crown ether-based agents, and less costly components for the vesicles such as alkyl benzene sulfonate surfactants. Competitive metal ion uptake will also be studied, and a bench scale continuous metal recovery system will be tested which uses hollow fiber membrane cartridges to contact the vesicle dispersion and the waste stream in a countercurrent mode.
