Selective and Regenerable Metal Sorbing Vesicles for Metal Ion Recovery

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CTS-9525019 Monbouquette UCLA The central goal of this research is to demonstrate the feasibility of novel metal-sorbing vesicle media for the selective recovery of toxic heavy metal ions, such as Cu2+, Cd2+ and Pb2+, from dilute aqueous solution in a continuous process. Metal-sorbing vesicles, which are submicron-diameter, surfactant bilayer membrane capsules, have been engineering to scavenge and to concentrate metal ions by virtue of a lipophilic metal carrier in the vesicle wall and a water-soluble, meal-chelating agent dissolved in the aqueous vesiclle interior. The carrier facilitates transport of the charged metal ion across the otherwise impermeable lipiid bilayer while the encapsulated chelating agent provides the driving force for metal ion uptake. Batch results show that suspensions of engineered metal-sorbing vesicles, which present 103-104m2 of surface area per liter of suspension, can selectively reduce Pb2+ or Cu2+ concentrations from 1-5 ppm to low ppb levels in minutes or less while concentrating the metal by 3 orders of magnitude. These results were used to design a bench-scale continuous metal-ion extractin process where the vesicles and the feed stream were contacted using a hollow-fiber ultrafiltration cartridge. Lead ions were selectivly separated in this continous systems, which was described well by a simple mathematical model. However, this continuous system did not include a vesicle regeneration stage for metal ion release such that the vesicles could be reused repeatedly. During the proposed three-year project, this separations technology will be brought forward in three areas critical to the establishment of technical feasibility: design for selectivity, continous processing with vesicle regeneration, and vesicle stability enhancement. The overall selectively of the metal-sorbing vesicle depends in a non-additive way on the relative affinity of both carrier and chelator for the ions present in solution. A proposed qualitative model of this fundamentally new mechanisms in separations shows that the overall systems can be orders of magnitude more selective than the carrier or chelator alone if their selectivity profiles are properly matched. The selectivity of vesicles harboring carefully chosen carrier and chelator pairs will be determined to confirm the qualititative model of metal-sorbing vesicle selectivity. As for vesicle reusability, preliminary data indicates that metal-laden vesicles can be regenerated in minutes at slightly elevated temperature and a moderate pH of 2.0. A metal-sorbing vesicle regeneration process will be further investigated, optimized and integrated into a bench-scale continuous metal-ion recovery system. A descriptive mathematical model of the system, useful for process design, will be constructed and tested by comparison to experimental results. Finally, polymerized vesicles of various chemistry will be tested for improved stability at the elevated levels of detergent, alcohols, and Ca2+ ions, for example, that could be encountered in an actual process stream. Coupled to this study will be an assessment of the permeability and regenerability properties of the polymerized vesicles, as these properties have a direct impact on the efficacy of the proposed continuous metal recovery systems. Currently there is no data available in the literature on carrier mediated transport across polymerized vesicle bilayers.