60 research outputs found
DĂ©fluoruration des eaux par dialyse de Donnan et Ă©lectrodialyse
Les travaux rĂ©alisĂ©s dans cette Ă©tude avaient pour objectif l'application de techniques membranaires, dialyse de Donnan et Ă©lectrodialyse, au traitement d'eaux dont la teneur en fluorure est supĂ©rieure Ă la valeur maximale admissible. Ces deux techniques qui mettent en jeu des membranes Ă©changeuses d'ions, se distinguent par la nature des forces motrices de transfert. Trois eaux modĂšles relatives Ă trois pays diffĂ©rents (Maghreb, SĂ©nĂ©gal et France) ont Ă©tĂ© prĂ©parĂ©es et traitĂ©es sur pilotes prĂ©-industriels. Dans tous les cas Ă©tudiĂ©s, bien que divers anions (Cl-, HCO3-, SO42-) et cations (Na+, K+, Ca2+, Mg2+) soient prĂ©sents initialement dans les solutions Ă traiter, une concentration en fluorure conforme aux normes a pu ĂȘtre atteinte avec toutes les membranes testĂ©es.L'Ă©lectrodialyse qui abaisse la teneur de tous les ions prĂ©sents dans l'eau, anions et cations, entraĂźne une dĂ©minĂ©ralisation partielle et par consĂ©quent un adoucissement de la solution traitĂ©e. Par contre, la dialyse de Donnan, du fait de la diffusion du sel du compartiment receveur vers la solution traitĂ©e, augmente lĂ©gĂšrement la minĂ©ralisation initiale. Cette technique qui, du point de vue Ă©nergĂ©tique, est un procĂ©dĂ© plus Ă©conomique que l'Ă©lectrodialyse, semble donc plus adaptĂ©e au traitement d'eaux fluorurĂ©es Ă faible minĂ©ralisation.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 ÎŒM and a Vmax= 14.5 nmol minâ1 mg proteinâ1. 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
Mise au point d'un procédé de recyclage d'effluents par couplage électrodialyse-échange d'ions (application aux éluats issus de la régénération de résines de déminéralisation de jus sucrés)
MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF
Ătude par autodiffusion de lâhydratation de la sĂ©rum albumine humaine en fonction du pH
L'hydratation de la molĂ©cule de sĂ©rum albumine humaine (SAH), dĂ©finie comme Ă©tant la moyenne totale de la quantitĂ© dâeau transportĂ©e par unitĂ© de poids de protĂ©ine sĂšche quand les molĂ©cules de protĂ©ine migrent Ă travers la solution, a Ă©tĂ© mesurĂ©e directement par la mĂ©thode de Wang. Les coefficients d'autodiffusion de lâeau, DH2O, ont Ă©tĂ© mesurĂ©s par la mĂ©thode classique du tube capillaire en marquant les solutions par un isotope non radioactif de lâoxygĂšne : O18. Lâeau marquĂ©e Ă l'O18 est dosĂ©e par spectromĂ©trie de niasse aprĂšs Ă©change isotopique avec le gaz carbonique. Nous avons trouvĂ© pour l'hydratation, H, une valeur de 0,15 g d'eau par gramme de protĂ©ine sĂšche Ă pH = 5 et de 0,25 g d'eau par gramme de protĂ©ine sĂšche Ă pH = 2. A partir de cette mesure directe de H et de la valeur expĂ©rimentale du coefficient dâautodiffusion limite, D°SAH, de la macromolĂ©cule mesurĂ© dans les solutions prĂ©cĂ©dentes, nous avons calculĂ© le rapport des coefficients de friction de la particule. Les rĂ©sultats sont les suivants: f/f° = 1,29 Ă pH = 5 et f/f° = 1,94 Ă pH = 2. La combinaison de la mĂ©thode de Wang et dâune mĂ©thode hydrodynamique nous a donc permis de mettre en Ă©vidence Ă la fois lâaugmentation de l'hydratation et de lâassymĂ©trie de la molĂ©cule de SAH Ă pH acide, câest-Ă -dire dans un domaine oĂč la protĂ©ine subit une expansion
Physico-chemical characterization of the ionic permeability of an enteric coating polymer
International audienc
Interaction de la sérum albumine humaine et des anions trichloracétate et chlorure étudiée par autodiffusion
Nous avons utilisĂ© la variation des coefficients dâautodiffusion pour Ă©tudier lâinteraction entre les anions trichloracĂ©tatc et chlorure et la sĂ©rum albumine humaine (SAH). Pour le premier, la liaison des anions a Ă©tĂ© confirmĂ©e par dialyse dâĂ©quilibre.Le domaine de pH explorĂ© Ă©tant celui oĂč la macromolĂ©cule subit habituellement la transition [math] et lâexpansion de la tonne F, lâĂ©tude des interactions a Ă©tĂ© complĂ©tĂ©e par des mesures de coefficient d'autodiffusion de la protĂ©ine, de viscositĂ© et de titrage des solutions protĂ©iniques.Nous avons pu montrer que, contrairement Ă ce qui est obtenu lors de lâinteraction entre les anions chlorure, chloracĂ©tate et la SAH, pour une torce ionique suffisamment Ă©levĂ©e, la macromolĂ©cule reste sous la forme N compacte en solution trichloracĂ©tique.Nous avons dĂ©terminĂ© deux catĂ©gories de sites susceptibles de fixer lâion trichloracĂ©tate : n1 = 10 et n2, = 50, ainsi que les constantes de liaison correspondantes : K1 = 1 000 et [math] = 7. Les constantes thermodynamiques du systĂšme Cl- â SAH ont Ă©tĂ© dĂ©terminĂ©es
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