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    ABSTRACT: Supported liquid membranes (SLMs) have demonstrated all along the years every high selectivity in facilitated transport of metal ions, however, they have some well known limitations, such as the gradual loss of the organic phase to the aqueous solutions. This paper describes two different types of novel membranes developed for the general purpose of separating and concentrating metal ions of interest in order to improve SLM physical and chemical characteristics. Both hybrid (organic—inorganic) membranes and activated composite membranes have been tested for the selective transport of Zn/Cd and Pt/Pd mixtures. For this purpose, different carriers have been used: 2-ethylhexyldithiophosphoric acid and 2-ethylhexylphosphoric acid for the separation of Zn and Cd whereas Aliquat 336 for Pt/Pd mixtures. The choice of these metal couples is related to environmental detoxification and catalyst recovery, respectively.
    Desalination 05/2009; 240(1-3):316-325. · 3.04 Impact Factor
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    ABSTRACT: This paper describes a comparative study of activated composite (ACM) and hybrid membranes (HM), both incorporating the commercial anion exchanger Aliquat 336 as a carrier, for the transport of Pt(IV) ions in chloride media. The incorporation of the carrier molecules in the polymeric network of both types of membranes is one of the approaches to overcome supported liquid membrane (SLM) instability. ACM are membranes with a bilayer structure: a porous lower polymeric support prepared by phase inversion (polysulfone) and a dense upper layer made by interfacial polymerisation (polyamide). HM are plasticized membranes consisting of a polymeric matrix of cellulose triacetate with a plasticizer and modified by the incorporation of an inorganic material (silanes) prepared by a sol–gel route. The efficiency of both types of membrane for the transport of Pt(IV) ions has been investigated, and several parameters affecting metal transport have been evaluated, such as the composition of the stripping phase and the selectivity of the membranes in the presence of Pd(II) ions. Moreover, comparative studies for both ACM and HM systems have been made by contacting the same feed solution in a triple-compartment cell. Finally, the results of these membrane systems are compared with those previously reported using polymer inclusion membranes (PIM) and SLM for the transport of Pt(IV) under similar experimental conditions.
    Journal of Membrane Science. 01/2008;
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    ABSTRACT: New hybrid membranes for metal ion transport were synthesized with the aim of improving mechanical and chemical stabilities, mean lifetime and loss of carrier. Hybrid organic–inorganic materials present several advantages with respect to organic and inorganic materials considered independently. Organic–matrix membranes usually have limitations related to chemical and thermal stabilities while organosilicone materials may present serious difficulties for film formation. The new membranes proposed here are based on a mixture of organic (cellulose triacetate, CTA) and organosilicone materials (dichlorodimethylsilane and tetraethoxysilane, DDMS and TEOS, respectively) as membrane support. Membrane preparation was optimized varying the amount of metal carrier (bis(2-ethyl hexyl phosphoric acid), D2EHPA) and plasticizer (2-nitrophenyloctyl ether, NPOE and/or tris(2-butoxyethyl)phosphate), TBEP). Total Reflection Infrared Spectroscopy, Scanning Electron Microscopy, Thermogravimetric Analysis, 29Si Nuclear Magnetic Resonance and X-Ray Diffraction were used to characterize the hybrid membranes and to correlate structural properties with permeability values for zinc metal ions.
    Journal of Membrane Science. 01/2007;
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    Desalination 11/2006; 200(1-3):100-102. · 3.04 Impact Factor
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    ABSTRACT: A membrane process for metal recovery from aqueous solutions was studied. Metal ions diffused from the feed solution to the stripping phase through an Hybrid Membrane containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) and/or di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier. Such membranes were prepared by a sol–gel route including cellulose triacetate and polysiloxanes. Transport behaviour was evaluated for both carriers under similar experimental conditions. The transport experiments reported here concerned transport at different cycles and selectivity towards different metal ions. Using D2EHPA the membrane provided a selective transport of zinc to the stripping compartment of the membrane cell, while copper and cadmium remained in the feed compartment. Whereas, using D2EHDTPA as carrier the transport rate increased and the selectivity profiles were inverted in relation with those of D2EHPA. With a mixture of both extracting agents it was observed an intermediate behaviour in selective transport, being possible to modulate it.
    Journal of Membrane Science 01/2006; 268(1):57-64. · 4.09 Impact Factor

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