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[en] In the research the main desalination processes of sea and brackish water are analyzed and discussed. The processes can be separated into the categories of Thermal and Membrane Processes. The thermal processes can be further divided between those in which heat is supplied to the water, causing its evaporation (single-step evaporation processes, Multi flash processes and multiple effects processes of evaporation), and those, less frequently used, where the heat is instead subtracted, causing a phenomenon of crystallization. The membrane processes, on the other side, are based on the passage of salt or brackish water through synthetic semi-permeable membranes. They can be subdivided between those employing reverse osmosis processes, where the selective solvent passage through the membranes is guaranteed by high pressure differences and those based on electrodialysis.
[it]Nella ricerca vengono analizzati e discussi i principali processi di dissalazione delle acque marine e salmastre, che possono essere distinti nelle due categorie di Processi Termici e Processi a Membrana. I processi termici vengono quindi distinti tra quelli in cui viene fornito calore all'acqua, determinandone l'evaporazione (processi di evaporazione monostadio, processi multiflash e processi di evaporazione ad effetti multipli), e quelli, molto meno utilizzati, in cui il calore e invece sottratto, determinando un fenomeno di cristallizzazione. I processi a membrana, invece, prevedono il passaggio dell'acqua salata o salmastra attraverso membrane sintetiche semi-permeabili. La principale distinzione operabile tra i processi a membrana riguarda i processi ad osmosi inversa, in cui si impongono elevate differenze di pressione per consentire il passaggio attraverso le membrane del solo solvente (inibendo il passaggio degli ioni), e quelli ad elettrodialisi.
[en] In order to remove nitrate selectively from different salt-loaded water, we have studied the electrodialysis of a solution containing nitrate and acetate ions through an original ion exchange membrane. We have showed that NO3- was removed more effectively than CH3COO-. We realized electrodialysis of synthetic solutions containing first of all a single kind of anion, the ion nitrate or the ion acetate, and in the second place the mixture of both kinds of ions and at the same concentration. The ion-exchange membrane (MEA) was obtained from the company ERAS Labo , designed initially for use in alkaline fuel cells. We wanted to test its behavior for electrodialysis. The results show that this MEA behaves practically in the same way towards both kinds of ions when the solution contains only a single kind of anion, the migration rate being linked to the value of the current. But once the anions are mixed, we noticed that the migration of the ion nitrate of the central compartment into the anodic compartment was much faster than that of the ion acetate. NO3-migrating easily while the CH3COO- stops practically migrating during 10 min approximately of time of electrodialysis. This demonstrates a selectivity of this kind of membrane towards the anion nitrate. The ion mobility, the hydrated ionic radii as well as the conductivity of the ionic solution may influence the transfer through the utilized membrane.
[en] This paper presents a novel microplatform for high power generation based on reverse electrodialysis. The ideal cation-selective membrane for power generation was realized using geometrically controlled in situ self-assembled nanoparticles. Our proposed membranes can be constructed through a simple and cost-effective process that uses microdroplet control with nanoparticles in a microchannel. Another advantage of our system is that the maximum power and energy conversion efficiency can be improved by changing the geometry of the microchannel and proper selection of the nanoparticle size and material. This proposed platform can be used to supply power sources to other microdevices and contribute to a fundamental understanding of ion transport behavior and the power generation mechanism
[en] Electrodialysis (ED) did not know a mattering development in the desalination field because of problems usually related to energy consumption, the scaling and/or precipitation phenomenon of certain mineral salts (CaSO4, CaCO3, etc.). and the importance of investments which they require. So, to mitigate some of these problems and to increase the electrodialysis processes potentialities, we introduced a crystallisation inhibitor (sodium polyacrylate RPI2000) into the concentration compartment during Ed's operations. Then we studied some parameters such as the applied potential or the circulation flow of studied solutions. The inhibitor addition allowed to delay the precipitation in the ED concentration comportment, confining so the brine in a small volume and decrease the frequency of replacement of membranes, which will reduce the cost of the process. Without adding scaling inhibitors, a set of experiment was performed using synthetic water supersaturated on CaCO3 and CaSO4 at room temperature. Several flows rates are tested (80, 60, 40 and 30 L/h). We applied 20 V until the conductivity measured in the dilute compartment dropped approximately from 9000 =μS/cm to 1500 μS/cm. We used the same concentrate solution to treat many synthetic water volumes. The results showed us that more the flow is important more the phenomenon of scaling is delayed. In order to increase the performance of the electrodialysis process we applied a pulsed electric field with different duty cycle (Ton = Toff = 1, 3, 10 and 30 seconds). Then, we compare conductivity evolution in the dilute as a function of the pulse mode. The results shows a faster decrease of the concentration in the dilute under pulsed field conditions. Pulsed electric field electrodialysis seems to be very promising for future development in brackish water desalination, to some extent it can remove some well known limitations of electrodialysis. Experiments on desalination of brackish water by pulse field electrodialysis showed that chronoamperogram contains a lot information. We decided to treat the data by principal component analysis. During a long time electrodialysis it's possible to describe the evolution of the current by a linear combination of only three principal factors (C P1,C P2,C P3). If something goes wrong during electrodialysis (scaling, fouling, membrane rupture, etc.) an additional principal component is necessary to describe the time evolution of current. This give us a new tool for monitoring ED or the aging properties of membranes. We also tried to describe the phenomena that occur during an operation and predict ED behavior. To do this we implemented numerical methods to integrate explicitly the differential equations governing the transport in the case of a simple solution of NaCl. We have thus evaluated, by calculation, the concentrations at any time in the compartments of dilution and concentration. The electric field and the current are estimated. This model is being refined to better describe the experimental data accumulated, integrating the complex composition of real solutions and also the precipitation phenomena.
[en] In this article, ion-selective nanochannels are numerically studied to investigate the power generation capability of a concentration gradient in conjunction with reverse electrodialysis. The generation of power from the nanochannel when it is placed between two reservoirs containing sodium chloride solutions with different concentrations is investigated. The current-potential characteristics of the nanochannel were calculated by solving the Poisson equation and the Nernst-Planck equation. The effects of engineering parameters on the power generation density are investigated
[en] The removal of As(V) and the simultaneous generation of powder of copper from an electrolyte made of As(V) - Cu(II) - H2SO4 was studied by using electro dialysis at several current densities, temperatures and aeration of the electrolyte. The removal of arsenic was proportional to the current density, temperature and aeration used. The removal of arsenic reached a value of 0.14 mmol/h at 500 A/m2, 25 degree centigrade and without aeration, this value increased to 0.31 mmol/h by increasing the aeration to 6.6 l/h. The Cu(II) was recovered in a 98 % as a fine arsenic free powder of metallic copper with oxides of copper. The arsenic was removed from the electrolyte by adsorption onto the anodic slimes generated from the lead anode oxidation. (Author) 24 refs.
[en] Surface modification of polyvinylchloride based heterogeneous cation exchange membrane was performed by graft polymerization of PAA and PAA-co-PANI/MWCNTs nanoparticles. The ion exchange membranes were prepared by solution casting technique. Spectra analysis confirmed graft polymerization clearly. SEM images illustrated that graft polymerization covers the membranes by simple gel network entanglement. The membrane water content was decreased by graft polymerization of PAA-co-PANI/MWCNTs nanoparticles on membrane surface. Membrane transport number and selectivity declined initially by PAA graft polymerization and then began to increase by utilizing of composite nanoparticles in modifier solution. The sodium and barium flux was improved sharply by PAA and PAAco- 0.01%wt PANI/MWCNTs graft polymerization on membrane surface and then decreased again by more increase of PANI/MWCNTs nanoparticles content ratio in modifier solution. The electrodialysis experiment results in laboratory scale showed higher dialytic rate in heavy metals removal for grafted-PAA and grafted-PAA-co-PANI/MWCNTs modified membrane compared to pristine one. Membrane areal electrical resistance was also decreased by introducing graft polymerization of PAA and PAA-co-PANI/MWCNTs NPs on membrane surface.
[en] The processes based on the separation by membranes seem to become very powerful tools for the purification and the retraining of the fluids. Competed by the inverse osmosis in the domain of the desalination of waters, the electrodialysis (ED) occupies a large place in the agro-alimentary industries to treat the co-products on the one hand and to contribute to the retraining of containing sewages of the heavy metals and toxic, on the other hand. Although it is appreciable for cost and reliability in several domains, the ED suffers to scaling problem caused by the concentration of some ions. Since the technique is used currently for the desalination of water in some industries, we have opted to study mechanisms of membrane scaling by calcium carbonate, one of salts the more frequently met in the stations of desalination in Tunisia. The survey uses a method of accelerated scaling of a pilot unit of electrodialysis. By means of this method, we studied the effect of the initial pH and the composition of water on the kinetics of the scaling formation. The treated waters are synthetic solutions. The results showed that the CO2 quantity initially dissolved in the solutions is an important factor in the scaling process. According to the composition of water, domains of CO2 pressure were defined in whom a small variation can generate the rupture of the metastability state in the compartment of concentration and provoke CaCO3 nucleation in the compartment of concentration and/or on the membranes and conducts. The presence in solution of magnesium in only a Ca/Mg ratio of 0,5 delayed considerably the CaCO3 nucleation. This ratio is considered like a low bottom limit of magnesium action, ion to natural inhibitory effect present in the natural waters.