Défluoruration des eaux par dialyse de Donnan et électrodialyse

Les travaux réalisés dans cette étude avaient pour objectif l'application de techniques membranaires, dialyse de Donnan et électrodialyse, au traitement d'eaux dont la teneur en fluorure est supérieure à la valeur maximale admissible. Ces deux techniques qui mettent en jeu des membranes échangeuses d'ions, se distinguent par la nature des forces motrices de transfert. Trois eaux modèles relatives à trois pays différents (Maghreb, Sénégal et France) ont été préparées et traitées sur pilotes pré-industriels. Dans tous les cas étudiés, bien que divers anions (Cl-, HCO3-, SO42-) et cations (Na+, K+, Ca2+, Mg2+) soient présents initialement dans les solutions à traiter, une concentration en fluorure conforme aux normes a pu être atteinte avec toutes les membranes testées.L'électrodialyse qui abaisse la teneur de tous les ions présents dans l'eau, anions et cations, entraîne une déminéralisation partielle et par conséquent un adoucissement de la solution traitée. Par contre, la dialyse de Donnan, du fait de la diffusion du sel du compartiment receveur vers la solution traitée, augmente légèrement la minéralisation initiale. Cette technique qui, du point de vue énergétique, est un procédé plus économique que l'électrodialyse, semble donc plus adaptée au traitement d'eaux fluorurées à faible minéralisation.The purpose of this work was to apply Donnan dialysis (DD) and electrodialysis (ED) for removing fluoride ion from waters where the concentration exceeds acceptable values. The techniques both use ion-exchange membranes but involve different driving forces: the difference in the electrochemical potential on both sides of the membrane for DD and the difference in the electric potential in ED.Both techniques were applied to treat model waters, the compositions of which were very close to those of natural waters contaminated by fluorides. Three standard waters related to three different countries (Maghreb, Senegal and France) were prepared and treated with pre-industrial pilots. The active membrane area was 1760 cm2 for Donnan dialysis, 552 and 2000 cm2 for electrodialysis. Two anion exchange membranes, DSV from Asahi Glass and AFX from Tokuyama Soda, were tested in Donnan dialysis. Three electrodialysis stacks equipped with different anion and cation exchange membranes, AMV-AM1/CMV from Asahi Glass, AMX/CMX and ACS/CMS from Tokuyama Soda, were used. Conductivity, pH and the concentrations of each ionic species were monitored during membrane treatment. The initial fluoride concentration were 9.5, 6.08 and 2.66 mg L-1 in each standard water, respectively.In all cases, despite the presence of different anions (Cl-, HCO3-, SO42-) and cations (Na+, K+, Ca2+, Mg2+) generally present in ground waters, a fluoride concentration in agreement to the norms (< 1.5 mg L-1) could be achieved regardless of the composition of the treated waters or the nature of the tested membranes. Electrodialysis decreased the anion and cation concentrations and induced a partial demineralization (about 70%) and consequently a softening of the treated water. On the contrary in Donnan dialysis, due to the electrolyte diffusion from the receiving compartment to the treated solution, the mineralization of the treated water increased slightly (about 10%). In this latter process, the anion concentration declined while no changes were observed in the cation concentration, except for sodium because of the electrolyte leakage. The DSV membrane was the most effective anion exchange membrane to use in DD. In ED, the AMV-AM1/CMV stack was selected on the basis of the demineralization and softening ratio, and the energy consumption.Donnan dialysis, which from an energy consumption point of view is more economical than ED, thus seems more adapted to the treatment of low mineralization waters

Influence of the nature of cation on water splitting at the interface of a cation exchange membrane during electrodialysis

The phenomenon of water splitting occuring at the interface of a Selemion CMV cation exchange membrane in contact with solutions containing successively monovalent, divalent and trivalent cations was investigated. Under identical hydrodynamic conditions, this investigation is based on recording j-V curves, measurement of transport numbers and pH variations. Water splitting is not a direct consequence of concentration polarization phenomenon. The cation nature and especially its acidic character is an important parameter which explains the difference in the behavior of the Selemion CMV membrane in contact with solutions of different cations

Sulfonated polyimides as proton conductor exchange membranes. Physicochemical properties and separation H+/Mz+ by electrodialysis comparison with a perfluorosulfonic membrane

International audienceThe properties of new sulphonated polyimide membranes (SP) - ion exchange isotherms, electrical conductivity, selectivity and proton-cation electrotransport - are compared with that of perfluorinated Nafion® membrane. Both membranes when in contact with H+/Mz+ aqueous solutions (MzM+=Na+, Cu2+, Cr3+) present an affinity to cations which increases with their valencies; however the affinity of one of the SP membranes for protons is approximately 10% higher than that of Nafion The proton transport number is also 10% higher for this SP membrane than for Nafion Using SP membranes for electrodialysis of H+/Cu2+ solutions produces solutions about 10% more concentrated in H+ and about 40% less concentrated in Cu2+ ions than with Nafion® membranes in the same conditions. The difference in conductivity may be explained by differences in ionic clustering because of differences in the polymer structure of the two membranes, block copolymer for SP and statistic copolymer for Nafion The difference in properties for the two SP membranes is explained in terms of the chemical structure of the non-sulfonated diamine groups used in the polymer synthesis. These SP membranes seem to be interesting materials for electromembrane processes in acid medi

Denitrification of drinking water by the association of an electrodialysis process and a membrane bioreactor: feasibility and application

International audienc

Electrolyte permeability and potential study of human basement membrane

The diffusion of electrolytes through a human basement membrane (anterior lens capsule) was studied in order to understand the interaction mechanism between the membrane and ions. The membrane potential was also measured by use of the Gibbs-Donnan system. The T.M.S. (Teorell, Meyer, Sievers) theory was applied for analysis of experimental data. The results show that the human basement membrane behaves as a barrier against to electrolyte diffusion due to the presence of ionogenic groups in this type of biomembrane. The comparison with the results obtained from similar studies of the bovine basement membrane was also carried out

Physico-chemical characterization of the ionic permeability of an enteric coating polymer

International audienc

Improvements of the selectivity of ionic transport through electrodialysis membranes in relation with the performances of separation electromembrane processes

Separation electromembrane processes such as electrodialysis or electro-electrodialysis are being applied to bioindustries and to the treatment of industry waste waters. For these purposes, the selectivity of ion transport has to be improved in order to obtain performances of the process which are compatible with the technico-economical conditions. In this paper, we examine four particular cases where the analysis of the ion transport selectivity has been developed in relation with better performances of the electromembrane processes : (i) Reduction of the proton leakage through anion exchange membranes in contact with acidic solutions. (ii) Specific transport of protons through cation exchange membranes in contact with solutions containing both an acid and a bivalent metallic ion. (iii) Reduction of cation leakage through bipolar membranes. (iiii) Loss of permselectivity of cation exchange membranes due to the poisoning of the membrane by organic ion