Preparació de membranes funcionalitzades de bescanvi catiònic per a estudis d’especiació d’ions metàl·lics

Abstract

The current legislation of metal pollution establishes the limit values based on the determination of total concentrations, this total concentration value don’t provide information about the distribution, mobility, biological availability and toxicity of metals. Recent studies have been demonstrated that cationic species are more bioavailability than other species forms in water. It would be necessary to advance in the knowledge of chemical speciation of metals and properties such as toxicity and bioaccumulation capacity to establish the limits of concentration based on the species. The membrane separation technique, it can be used like speciation technique in the laboratory when it applies to water samples. One of the most used techniques is a Donnan membrane technique (DMT). The concept of this technique is based on a cationic exchange process in a membrane, a potential difference generated between the two phases of the membrane causes the cationic exchange and, as a result, the metal that was initially in the feed phase is transported to the strip phase. In commercial exchange ionic membranes the metal transport is slow and for this reason it has been developed another types of membrane like pore-filled membranes. In this research, pore-filled cation-exchange membranes have been prepared by photopolymerization using different membrane supports (PP, PVDF, PES), however, these supports differ in pore size. These membrane supports have two different geometric forms: sheet membrane and hollow-fiber. To functionalize the supports, 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) was used as a monomer, a crosslinker, a UV-initiator, spacer and a solvent have been also used. Finally, a polymer PAMPS was obtained. For PES supports, the monomer Bis[2-(methacryloyloxy)ethyl] phosphate was also used to do the membrane synthesis. This last one, contains a phosphate group and forms the polymer P(bisMEP). Finally, the pore-filled membranes have been characterized by FTIR, SEM and EDX microanalysis. By IR they have been obtained information about functional groups of the membranes, however, with SEM they have been obtained information about morphology and how the polymer was in the pores of host membranes. The elemental composition of the pore-filled membranes was obtained with Microanalysis EDX. Finally, the efficiency of pore-filled membranes synthetized was evaluated on zinc transport in a membrane system. This system it could be apply in the zinc speciation in natural waters. The results weren’t the expected for two reason: one could be the no homogeneous repartition of polymer in some membranes and the other could be that the polymer didn’t improve the transport of the metal