Electrodialysis Method Research Articles

Study of the scaling process on membranes

The state of water was studied by the method of differential scanning calorimetry in initial membranes and the membranes following their use in a water desalination process based on the baromembrane and electrodialysis methods. The analysis of data obtained makes it possible to determine the contribution of the CaSO 4 scaling process deposited on the surface of reverse osmosis and ion exchange membranes in water desalination processes. We determined that an intensive accumulation of hardly soluble CaSO 4 scale occurs on the surface of an MK-40 cation exchange membrane when the hardness water desalination process is held in an electrodialysis unit. This results in clogging of about 50% of mesopores having a radius of about 50A. In the case of using an MA-40 anion exchange membrane one could observe only insignificant blocking of micro- and macropores in the polymer frame of the membrane. Any scale on the surface of anion exchange membrane MA-40 was not found. It was established that nucleating centers of CaSO 4 formed in a solution were not located on the surface of membranes but penetrated deep into the pore space of a polymer frame in both cases of water desalination (based on electrodialysis and reverse osmosis). We calculated the amount of free and bound water in a membrane OPAM-KN under investigation following its use in processes of water desalination both with and without the addition of the PAA inhibitor. Variation of the amount of free and bound water makes it possible to assess the layout of CaSO 4 nucleating centers in the polymer matrix of the membrane or on its surface. The using of polyacrylamide as an inhibitor in a baromembrane unit results in a partial blocking of big pores in a membrane. The use of the inhibitor in the water desalination process makes a polymer layer over the membrane more compact owing to binding of nucleating centers of CaSO 4 by polyelectrolyte or by it blocking. Redistribution of pore space occurs in the membrane: a reduced radius of pores gives rise to the reduced amount of free water, while the amount of bound water increases.

Electrodialysis as a useful technique for lactic acid separation from a model solution and a fermentation broth

A two-stage electrodialysis (ED) method was used for lactic acid recovery. In the first step sodium lactate was concentrated with desalting electrodialysis using ion exchange membranes Ralex (Mega, Czech Republic). The second step was the electroconversion of sodium lactate to lactic acid by electrodialysis with bipolar membranes (EDBM) Neosepta (Tokuyama Corp., Japan). The lactic acid was recovered from model solutions and from real fermentation broth as well. The trials with model solutions were focused on determination of the suitable conditions for electrodialysis experiments and on investigation of the time course under different conditions. The fermentation broth from lactic acid fermentation had to be pretreated before electrodialysis experiments. The pretreatment consisted of ultrafiltration, decolourisation and removing of multivalent metal ions. In the first ED step the final lactate concentration of 175 g/l was obtained and afterwards the final lactic acid concentration of 151 g/l was reached in the second ED step.

Electrodialysis as a Sample Preparation Tool for Capillary Electrophoresis of Small Anions – A Proof of Principle

The use of capillary electrophoresis (CE) for biomedical applications or control of waste water effluents is often restricted, due to the complex matrix embedding trace concentrations of the analyte. Selective removal of interfering ionic species is challenging when analyte and matrix are similar in size and charge. An electrodialysis method applying a home-made module for sample desalting is described. Chloride, sulfate and nitrate ions were employed at 50 or 100 mM (referring to concentrations in real samples from clinical or environmental origin) to simulate matrix compounds. Sulfanilic acid was selected as a model analyte ion at millimolar or sub-millimolar concentrations. Process analysis was performed with ion chromatography coupled on-line. For a simple monitoring of the process in application, conductivity measurement in the sample compartment could be successfully established. Within 45 minutes, the matrix concentration was decreased by a factor of about 10, whilst the analyte was only diluted by a factor of about 3. The rate of the matrix depletion was constant over the whole process and controlled by the constant current generated from the voltage source. Speeding up the process by applying higher current densities failed, due to resulting thermal stress at the membranes. Electrodialysis results were independent of both the matrix anion and matrix cation identity, indicating a good robustness against variations of the sample matrix.

Studies on cation-exchange membranes having permselectivity between cations in electrodialysis

Recent studies on selective permeation of specific cations through a cation-exchange membrane in electrodialysis, modification of the membrane and electrodialysis method, are reviewed. The studies are classified (1) to prepare the composite of the cation-exchange membrane with other polymers such as conducting polymers and cationic polyelectrolytes, (2) to change cation-exchange groups from sulfonic acid groups, which are used in conventional membranes, to other groups such as phosphonic acid groups, and (3) to electrodialyze the mixed salt solution in the presence of chelate-forming agent such as poly(ethylene glycol), crown ethers, etc. Though the formation of the layers of the conducting polymers on the surface of the cation-exchange membrane is effective on selective permeation of monovalent cations to divalent cations through the membrane, mechanism of the selective permeation is different depending on species of the conducting polymers: due to sieving of sodium ions from multivalent cations by a tight polypyrrole layer and due to stronger electrostatic repulsion force of the cationic charge in a polyaniline layer to multivalent cations than to the monovalent, which is similar to the membrane having a cationic polyelectrolyte layer on the surface. When cation-exchange groups such as phosphonic acid groups, which are strongly interacted with divalent cations, are introduced in the membrane, monovalent cations selectively permeate through the membrane. However, current efficiency in electrodialysis decreases due to strong binding of divalent cations to the groups—inactivation of cation-exchange groups. Electrodialysis in the presence of chelate-forming agents is effective on the selective permeation of specific cations that have low complex formation constants with the agents through the membrane without any decrease in the current efficiency.

A Study on Reclaimed Photoresist Developer Using an Electrodialysis Method

Photoresist developer reclamation technology and systems have been investigated and characteristics of the reclaimed developer were evaluated. High-purity tetramethylammonium hydroxide (TMAH) aqueous solution adjusted to an appropriate concentration is generally used as the photoresist developer in the lithography step for large scale integration (LSI) and liquid crystal display (LCD) manufacturing processes. TMAH was recovered by an electrodialysis (ED) method from developer waste (spent developer), and purified by ion exchange (IE) technologies. The reclaimed developer was analyzed and found to feature the same purity as fresh commercial developer and no differences in their characteristics as developer material could be determined. Our experimental reclamation system recovered more than 80% of stable TMAH from waste and, moreover, achieved large reductions in operating costs, which amounted to total cost reductions of 55–75% for LSI and 65–85% for LCD compared with the conventional systems without reclamation studied by us. In addition, environmental load was reduced.

Intercalation Method for the Synthesis of Fine Aluminium Hydroxide

A new method to synthesize fine low-alkaline aluminium hydroxide from technical-grade gibbsite has been proposed. This method is based on carrying out the cycle of intercalation–deintercalation of lithium salts within gibbsite. In order to improve the intercalation process, which requires substantial consumption of water, the electrodialysis method is proposed.

Desalting of chitin derivatives by the electrodialysis via ion‐exchange membranes

Using an electrodialysis technique, chitin derivatives in aqueous solutions containing various salts were desalted. The anodic cell (Part A: 0.1 mol/dm3 KOH, 95 ml) and the cathodic cell (Part C: 0.1 mol/dm3 HCl, 95 ml) were separated from the sample cell (Part O: 95 ml) by an anion-exchange membrane and a cation-exchange membrane, respectively. The potential between the electrodes was regulated to 10 V (free current). Because N-acetylation of chitosan and N-deacetylation of chitin were respectively performed under acidic and strongly basic conditions unless enzymatic methods were not employed, neutralization in workup produced considerable amount of salt. Therefore, chitin derivatives such as partially deacetylated chitin (DAC) and partially acetylated chitosan (PAC) were sometimes contaminated with various salts. Aqueous solutions of PAC and carboxymethylated DAC containing NaCl, AcONa or AcOH were desalted by the electrodialysis. In the case of the suspension containing AcONa and gels produced by N-acetylation reaction of chitosan with Ac2O in aqueous AcOH/MeOH, the electrodialysis of the sample suspension eliminated AcONa inefficiently. This problem was solved by the treatment of the sample suspension with a homogenizer for 1 or 2 min before the electrodialysis. Since chitin and its derivatives have received growing attention as biologically active substances, the electrodialysis method provides a convenient way for the preparation of salt-free samples of chitin derivatives. Copyright © 1999 John Wiley & Sons, Ltd.

Desalting of chitin derivatives by the electrodialysis via ion-exchange membranes

Using an electrodialysis technique, chitin derivatives in aqueous solutions containing various salts were desalted. The anodic cell (Part A: 0.1 mol/dm3 KOH, 95 ml) and the cathodic cell (Part C: 0.1 mol/dm3 HCl, 95 ml) were separated from the sample cell (Part O: 95 ml) by an anion-exchange membrane and a cation-exchange membrane, respectively. The potential between the electrodes was regulated to 10 V (free current). Because N-acetylation of chitosan and N-deacetylation of chitin were respectively performed under acidic and strongly basic conditions unless enzymatic methods were not employed, neutralization in workup produced considerable amount of salt. Therefore, chitin derivatives such as partially deacetylated chitin (DAC) and partially acetylated chitosan (PAC) were sometimes contaminated with various salts. Aqueous solutions of PAC and carboxymethylated DAC containing NaCl, AcONa or AcOH were desalted by the electrodialysis. In the case of the suspension containing AcONa and gels produced by N-acetylation reaction of chitosan with Ac2O in aqueous AcOH/MeOH, the electrodialysis of the sample suspension eliminated AcONa inefficiently. This problem was solved by the treatment of the sample suspension with a homogenizer for 1 or 2 min before the electrodialysis. Since chitin and its derivatives have received growing attention as biologically active substances, the electrodialysis method provides a convenient way for the preparation of salt-free samples of chitin derivatives. Copyright © 1999 John Wiley & Sons, Ltd.

Potential for economic solar desalination in the Middle East

Fresh water forms only about 1% of the total water available on earth. Technologies for the desalination of seawater have considerably matured in the last decade. However, the energy required for the desalination is usually expensive in arid areas where fresh water is required. Renewable energy provides a clean, free, and low-maintenance source of energy for desalination, limited only by their initial cost, and the variability of the available energy. In this paper the potential use of solar energy for the desalination of seawater in the Middle East is evaluated. Multi-Stage Flash (MSF) desalination requires large amounts of energy, while Reverse Osmosis (RO) desalination is more energy efficient. Solar distillation is a very simple and direct method that may be used, requiring only large flat areas of land, having no running energy costs and being very suitable for remote areas. Photovoltaics is another promising renewable energy source for seawater desalination in the Middle East. It is best suited for the RO and Electrodialysis (ED) methods. The desalination plant doesn't need to run continuously, and therefore no storage batteries are required. Diesel and / or natural gas may be used as a backup energy.

Fast growth and evaluation of potassium dihydrogen phosphate single crystals by electrodialysis with pH control

A novel technique of pH control is proposed in the electrodialysis method of a three-chamber structure. This technique allows using small-sized equipment for the growth of large potassium dihydrogen phosphate (KDP) single crystals. High-quality KDP crystals can be grown at a growth rate of 3 mm/day. Larger growth rates cause spontaneous nucleation, which can be suppressed using a solution doped with 0.3 ppm Cr 3+ and 1.5 ppm Al 3+. As a result of doping, good optical quality single crystals could be grown at a growth rate of 6.6 mm/day, and the unwanted spontaneous nucleation was suppressed.

Electrodialysis for clean-up of strongly alkaline samples in ion chromatography

An electrodialysis method is described for the off-line neutralization of strongly alkaline samples containing trace levels of common inorganic anions. This method uses an electrodialysis cell comprising three compartments separated from each other by cation-exchange membranes. These compartments comprise an anode compartment housing, a platinum wire anode and 10 ml of a suitable hydrogen ion donating medium, a sample compartment which contains 1 ml of the alkaline sample, and a cathode compartment housing a platinum wire cathode and a dilute solution of sodium hydroxide. During electrodialysis at either constant applied current or constant applied power, hydrogen ions from the anode compartment displace sodium ions from the sample, thereby effecting neutralization. Experimental parameters, such as the magnitude of the applied current or power, the type of cation-exchange membrane used and the design of the cell have been studied and optimum results were obtained using a Neosepta CM-2 membrane, of area 616 mm 2 supported between two perspex discs, with an applied current of 150 mA or applied power of 3 W. Under these conditions, a 1 ml sample of 1 M sodium hydroxide could be neutralized in 11 min. The most effective hydrogen ion donating medium consisted of a 2:1 (w/v) slurry of BioRad AG 50W-X8 (200–400 mesh, H + form) cation-exchange resin in 1 m M octanesulfonic acid. Recoveries of solute anions (3–10 μg/ml) from the dialysed solution were close to quantitative, except for fluoride and nitrite, which gave recoveries of less than 60%. It is suggested that low recoveries for these ions are due to formation of neutral, protonated species within the membrane with subsequent loss by diffusion.

The treatment of cupric chloride solution after the etching process by ion exchange membrane electrodialysis

The cupric chloride solution whih is discharged as wastewater after the etching process was treated by ion exchange membrane electrodialysis. This method not only reuses the water by desalination, which may or may not be connected with ion exchange, it also concentrates the cupric chloride and metal copper can be recovered by electrolysis or some other suitable method, making it a closed system. The results of practical operation show that the electrodialysis method is comparble with precipitation from the point of view of cost and efficiency. We demonstrated that the plant could be operated successfully without damage to the home-made ion exchange membrane and without electrodeposition of the metal copper on the cathode. Furthermore, the energy consumption was less than 3 kWh/t water. The cupric ion concentration of 2,000 mg/l in the wastewater was reduced to less than 1 mg/l at discharge.

Fast growth of KDP single crystals by electrodialysis method

An electrodialysis method has been adopted to the solution growth of 5 cm×5 cm single crystals of KDP. The c-axis growth rate of 3 mm/day was obtained by using Cr3+ ion as dopant. The assessment of the grown crystal has been done by means of an etching method to make a comparison with the crystals grown by the temperature falling method.

Study of ionic catalytic systems by the electrodialysis method

AbstractA special method of electrodialysis has been developed for investigation of the kinetics and mechanism of polymerization reactions involving ions. The ionic composition of homogeneous systems such as Cp2TiRClAlRCl2, RTiCl3 + AlRCl2, Ti(OR)4 + AlR3, and (RLi)n has been studied. The composition of catalytically active ions has been determined. Using the regularities of “open” systems, the methods of determining the carbocation reactivity under electrodialysis conditions havebeen worked out. The impulse electrodialysis method has been suggested for studying ionic polymerization kinetics and evaluating the rate constants ofion reactions with the monomer and gegenion.

Removal of sodium dodecyl sulfate from proteins

A convenient and relatively simple electrodialysis method for the removal of sodium dodecyl sulfate (SDS) from proteins is described. Six samples can be processed simultaneously. The kinetics of removal of SDS from proteins by equilibrium dialysis and electrodialysis have been studied.

Ionic residual conduction in the isotropic phase of a nematic liquid crystal

Electrical measurements were performed by the electrodialysis method at 124°C, on the isotropic phase of a liquid crystal (E.P.P.H. : p(ethoxy phenylazo) phenyl heptanoate, nematic range 60–119°C). A discussion of the results, based on the relaxation of ionic dissociation equilibrium displaced by electrolysis, shows that the electrical behaviour of the purest liquid is not specific but arises from well-defined natural slow dissociation of impurities in minute concentrations. The dissociation and recombination kinetic constants of an overall equivalent electrolyte, and the mobilities of resulting ions, are determined.

The electrodialysis of anabaena flos-aquae A-37

A method for the electrolytic depletion of ions from Anabaena flos-aquae A-37 was described. The electrolytic depletion of Na +, K +, Ca 2+, and Mg 2+ was determined to be 96.4%, 64.4%, 50.0%, and 5.4%, respectively. The alga survived the electrolytic treatment to the extent of from 40 to 50%. From these data is was suggested that the electrodialysis method described is a workable research tool for the removal of ions from the organism.

Further developments in the high temperature electrodialysis

The high temperature electrodialysis method being developed in the Negev Institute for Arid Zone Research utilizes the Joule heat evolved in the process to increase the temperature of operation thus reducing the energy consumption of the process. Initial calculations indicated that by suitable increase of temperature the energy consumption may be reduced as much as 60–70%. The economics of the process seem sufficiently favourable to justify its application to sea water desalination. During the first period of the research it was shown that commercially available membranes preserve their electrochemical properties at elevated temperatures, and their functional groups withstand high temperature conditions. Deterioration of membranes, if it occurs, is due to disintegration of the matrix of the membranes. More extensive investigation of the changes in membrane resistance with temperature has shown that it decreases much more markedly below the range 70–80°C than above it. It was also found that electro-osmotic water transfer through membranes increases, especially in the higher temperature region (70–100°C). This behavior of membranes was reflected in the results obtained from laboratory scale high temperature electrodialysis experiments. The saving of energy consumption by increasing the temperature of operation from 30°C to 70°C was 60–70%, with different types of membranes. Further increase in temperature contributed less substantially to the decrease in energy consumption. During these experiments it became evident that electrodialysis apparatus built from conventional materials of construction using general purpose ion-exchange membranes may be successfully operated for prolonged periods, up to at least 70°C.

Separation of cesium and strontium by electrodialysis

Electrodialysis methods employing Permutit anion exchange membranes (3148) and cation exchange membranes (3142) have been investigated for the separation of strontium from cesium. The methods were based on the formation of strontium chelate complexes with EDTA and DTPA. Separations of radio-strontium and radio-cesium in equilibrium with their daughter decay products were made with two-cell and three-cell electrodialysers. The best results were obtained with EDTA at an initial pH of 11·0 employing anion exchange membranes. The data suggest that this method is feasible for the separation and purification of radioactive cesium and strontium.

The electrodialysis of the aqueous solution of surface active agent

A new electrodialysis method for the study of micelle formation on aqueous solution of surface active substance is proposed. This method has advantages among other procedures using semipermeable membrane, in that (1) the time required for the measurement is far less than that of any other methods, thus the membrane can be practically rendered to be semipermeable for micelles, and (2) it is not essentially required to add an inorganic salt to inhibit the micelle permeation, so we are able to know, without extrapolation, the behavior of surface active substance free from the salt influence. We observed a sharp break point on the dialysis curve, and found that the point corresponded with the accepted CMC value of 7.4 × 10−3 mol/l for sodium dodecyl sulfate.