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

Effects of Monovalent and Divalent Cations on Ca2+ Fluxes Across Chromaffin Secretory Membrane Vesicles

Abstract: Bovine chromaffin secretory vesicle ghosts loaded with Na+ were found to take up Ca2+ when incubated in K+ media or in sucrose media containing micromolar concentrations of free Ca2+. Li+- or choline+loaded ghosts did not take up Ca2+. The Ca2+ accumulated by Na+-loaded ghosts could be released by the Ca2+ ionophore A23187, but not by EGTA. Ca2+ uptake was inhibited by external Sr2+, Na +, Li +, or choline +. All the 45Ca2+ accumulated by Na+-dependent Ca2+ uptake could be released by external Na +, indicating that both Ca2+ influx and efflux occur in a Na+-dependent manner. Na + -dependent Ca2+ uptake and release were only slightly inhibited by Mg2+. In the presence of the Na+ ionophore Monensin the Ca2+ uptake by Na +-loaded ghosts was reduced. Ca2+ sequestered by the Na+-dependent mechanism could also be released by external Ca2+ or Sr2+ but not by Mg2+, indicating the presence of a Ca2+/Ca2+ exchange activity in secretory membrane vesicles. This Ca2+/Ca2+ exchange system is inhibited by Mg2+, but not by Sr2+. The Na + -dependent Ca2+ uptake system in the presence of Mg2+ is a saturable process with an apparent Km of 0.28 μM and a Vmax= 14.5 nmol min−1 mg protein−1. Ruthenium red inhibited neither the Na+/Ca2+ nor the Ca2+/Ca2+ exchange, even at high concentrations

Photosynthesis dependent acidification of perialgal vacuoles in theParamedum bursaria/Chlorella symbiosis. Visualization by monensin

After treatment with the carboxylic ionophore monensin theChlorella containing perialgal vacuoles of the greenParamecium bursaria swell. TheParamecium cells remain motile at this concentration for at least one day. The swelling is only observed in illuminated cells and can be inhibited by DCMU. We assume that during photosynthesis the perialgal vacuoles are acidified and that monensin exchanges H+ ions against monovalent cations (here K+). In consequence the osmotic value of the vacuoles increases. The proton gradient is believed to drive the transport of maltose from the symbiont into the host. Another but light independent effect of the monensin treatment is the swelling of peripheral alveoles of the ciliates, likewise indicating that the alveolar membrane contains an active proton pump

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

Nanofiltration modeling: a comparative study of the salt filtration performance of a charged ceramic membrane and an organic nanofilter using the computer simulation program nanoflux

International audienc

Modeling of multi-electrolyte transport in charged ceramic and organic nanofilters using the computer simulation program NanoFlux

International audienc

Simultaneous recovery of heavy metals (Pb, Cd, Zn) from diluted solutions by electroextraction technique

Cadmium is mainly used in galvanoplasty and stabilisation of plastic materials. It accumulates continuously in soils. The analysis of soil samples gave concrete evidence of increase of concentration of this element during the past centunary [1]. Furthermore Cd and Pb attack selectively the kidneys and the liver with enzymatic troubles. The work has enabaled to put into evidence the contribution of the presence of resin to the conventional electrodialysis process. The optimal conditions for the elimination of Cd++, Zn++ and Pb++ ions were determined. These included influence of resin, imposed current density, flow rate of the feeding solution (diluat), different supporting electrolytes used during the electroextraction (HNO3, HCl and H2SO4) and concentration of the solution to be treated [2-3-4]. Furthermore the competition between the electroextraction of the metallic cations Cd++, Zn++and Pb++ was investigated for different mixtures