Obiettivo - To establish membrane processes for the treatment of water and liquid industrial waste. The approached problems are specific for the Magreb : natural water for drinking and industrial liquid waste from metal industries and from tanneries, the latter being rich on chrome;- While for the natural waters the objective is to eliminate pollutants in order to reach drinking water quality standards, the objective for industrial waste treatment includes the need to recycle the contaminating substances, in particular if they are rather valuable. This implies the need to include an inorganic pre-treatment;- For drinking water the coupling of different membrane technologies is envisaged (microfiltration (MF) for eliminating batteries and sediments, ultrafiltration (UF) or nanofiltration (NF) for the cleaning from macromolecules and organic molecules, electrodialysis for the separation of dissolved salts). For the tangential filtration new membranes will be developed and it is intended to produce newer, cheaper membranes from marocain clays.- Membrane synthesis, modification and selection - The membranes for the pressure-driven processes are inorganic membranes developed from new filters made from Moroccan clays and from cordierite as support materials. Monochannel and multichannel configurations have been elaborated by extruding a ceramic paste ; the pore diameters vary from 2.5 to 6.5 µm and the porous volume is about equal to 40 %. The materials used for preparing the membranes are : Moroccan clay, zirconia, titania, hafnia and potassium titanyl phosphate (KTiOPO4) with pore diameters varying from 1.8 nm to 0.2 µm.- Microfiltration membranes have been prepared the powder suspension method ; ultra and nanofiltration membranes by the sol-gel method. - For the treatment of waste acids, the electrodialyser must be equipped with anion exchange membranes (AEM) having a low proton leakage. These AEM will be associated with cation exchange membranes (CEM) highly permeable to protons but not permeable to bivalent cations. - In this research, we have studied effluents of galvanisation plants and of tanneries. The first effluent contains Zn2+ ions in the presence of Cl- ions. As these two ions form complexes, therefore the AEM must not be permeable to the anionic complexed species (ZnCl3-, ZnCl42-) which, in the concentration range are present in the media. - The new CEM are obtained by adsorbing, at the surface of the membrane, layers of a positively charged polyelectrolyte : the poly-ethylene-imine (PEI). The CEM selected for the treatment of tannery effluents, must be highly resistant to poisoning by Cr3+ ions because this multicharged ion gives strong interactions with the fixed ion exchanging sites of the membrane material.- Characterisation of the membrane materials and membrane properties - With inorganic membranes, interactions between salt solutions and membrane materials play an important role for the selectivity of the membranes and must be studied. The total charge of the membrane material can be determined with the help of electrophoretic measurements. The powdered material was put in salt solutions at different pH. The mobility of the particles was measured under an electric field. The pH at which the mobility is equal to zero is called Iso Electric Point. For higher pH the material is negatively charged, for lower pH the material is positively charged. This point explains the difference in the selectivity for various membranes. For instance, in the pH range 2.5 to 10, KTiOPO4 membrane is negatively charged. That means that cations will be attracted and anions will be repulsed by the membrane. The respective charge of cations and anions will determine higher or lower rejection rate.- As a result of ED membrane characterisation, the following table collects the data obtained with a commercial CEM membrane after surface modification by adsorbing PEI from a solution of this polyelectrolyte. The selectivity to proton with respect to bivalent cations is quantified by measuring the Ni2+ transport number through the membrane between two solutions containing a mixture of acid (1N ) with a nickel salt (1N). We can see that the transport number of the bivalent cation is reduced from 0.28 to 0.11 by the adsorption of PEI. The increase of the electrical resistance remains acceptable. - For the treatment of effluents containing zinc and chloride ions, a complete study of the behaviour of some membranes has been performed in these media; the main characteristics have been measured : water content, electric resistance, ions amount inside the membrane, self-diffusion and electrotransport fluxes.- Results of process experiments- The inorganic membranes have been introduced into modules for treating several kinds of waters. Waste water was analysed in differents points of rivers near the city of FES. Rejections of industries like dairy, oil mill or tannery, which are responsible for a large part of the pollution, were also analysed. - Numerous filtrations of water and industrial rejections were performed using the filters prepared during this work. In a first time, a laboratory pilot was used ( the surface of the membrane was about 30 cm2), then, in a second time filtration tests were conducted with a bigger pilot that can use about 1 m2 membrane surface. Using the 3 types of microfiltration membranes we can observe : - a complete rejection of suspended substances by measuring the turbidity ; - a decrease by a factor of 10 of the chemical and biochemical oxygen demands.- The rejection rate for (i) sulphate and chloride ions is equal to 30%, (ii) for monovalent cations is equal to 50%. Divalent cations are not rejected by the membrane. This can be due to the complexity of the medium to be filtered.- An interesting point is the rejection of heavy metals and particularly chromium in case of tannery. The rejection rate is equal to about 73 and 92% when the alone clay support and titania microfiltration membrane coated on this support were used respectively.- All these results show the interest of membrane processes for the treatment of waste water and industrial rejections.- On the other hand, some electrodialysis experiments have been performed with solutions of HCl +ZnCl2, using AFN as an anion exchange membrane and several cation exchange membranes : it could be shown that better electrodialysis performances are obtained with surface modified membranes. For instance, when the treated solution contains the acid and the zinc salt at the same concentration (1N), the final concentrations in the concentrate are 2.5 M HCl and 0.15 M Zn2+.- In the case of industrial effluents containing chromium, the problem in not easy to solve because of the complexity of the solutions to be treated. So, we first studied, by electrodialysis, synthetic solutions containing chromium sulphate in presence of chloride ions. - Experiments have been made with industrial effluents from tanneries. The obtained results' evidence that the elimination of chromium using this technique is possible. However, some problems must be taken into consideration :- water dissociation that can occur and is strongly catalysed by chromium ions.- the competition between Na+ and Cr3+ that is very in favour of monovalent cations during the transfer through the cation exchange membranes; so, it will be necessary to do preliminary electrodialysis in order to desaline completely the chromium solutions to be treated. - Finally, some experiments were performed by a technique that couples together electrodialysis and ion exchange, using textiles (sulfonic or carboxylic) instead of resins (EDI). When such a textile conditioned in the acid form is equilibrated with a chromium nitrate solution, the ionic exchange occurs, especially with sulfonic textiles that can be then regenerated by immersion into a solution 1 M HCl. So, the experiments can be performed with a five compartments classical electrodialyser in which the central compartment is filled with the textile that fixes chromium ions. The first results that have been obtained are very encouraging, especially for dilute solutions because, in these cases, electrodialysis is not convenient and must be used only for concentrated solutions.- Conclusion- The researches performed in this program have induced significant improvements in the treatment of waste waters by membrane technology. New membranes have been elaborated and characterised : inorganic membranes for pressure diven filtrations and surface modified membranes for electrodialysis. Pilot experiments performed with these membranes have confirmed their interest for large scale applications of the processes.- Production of new ceramic membranes for nanofiltration, ultrafiltration and microfiltration from marocain clays;- Physicochemical characterisation of membranes of ion permeability and of ceramic membranes;- Study of the interactions between the solid phases as a basis for selecting the appropriate membrane for a given purpose. This interaction is particularly unknown for marocain clays;- Preindustrials, including electrodialysis, electro-electrodialysis or tangential filtration;- Trials of reconcentration through acid electrodialysis of acid waste streams containing metallic salts;- Assessment of the economics of such a technology. Programma(i) IC-AVICENNE - Avicenne Initiative (Science and technology cooperation with the Maghreb and the countries of the Mediterranean Basin), 1991- Argomento(i) Data not available Invito a presentare proposte Data not available Meccanismo di finanziamento CSC - Cost-sharing contracts Coordinatore ECOLE NATIONALE SUPÉRIEURE DE CHIMIE DE MONTPELLIER Contributo UE Nessun dato Indirizzo Rue de l'Ecole Normale 8 34296 MONTPELLIER Francia Mostra sulla mappa Costo totale Nessun dato Partecipanti (4) Classifica in ordine alfabetico Classifica per Contributo UE Espandi tutto Riduci tutto Centre de Développement des Matériaux Algeria Contributo UE Nessun dato Indirizzo Draria W. de Tipaza Mostra sulla mappa Costo totale Nessun dato U.S.T.H.B. Algeria Contributo UE Nessun dato Indirizzo El Alia-Bab Ezzorian Alger Mostra sulla mappa Costo totale Nessun dato Université de Fès Marocco Contributo UE Nessun dato Indirizzo Atlas Fès Fès Mostra sulla mappa Costo totale Nessun dato Université de Montpellier II (Université des Sciences et Techniques du Languedoc) Francia Contributo UE Nessun dato Indirizzo 1919 route de Mende 34033 Montpellier Mostra sulla mappa Costo totale Nessun dato
