Electrodeionization Process Research Articles

Removal of Nickel Ions from Dilute Heavy Metal Solutions by Electrodeionization Process

The aim of the present work was to study the effect of properties of ion exchange membrane on separation performance of electrodeionization (EDI) process for removal of nickel ions from dilute heavy metal solutions. It was shown that the properties of ion exchange membrane had a significant effect on removal of nickel ions. With feed water containing nickel ions at the concentration of 55mg•L-1, the nickel ions concentration of dilute stream was lower than 0.5mg•L-1and the nickel rejection was greater than 99% when using EDI membranes, while that was in the range of 2.48-3.55mg•L-1with conventional heterogeneous ion exchange membranes. With optimum ion exchange material and operating conditions, EDI would be a very interesting and innovative technology for the treatment of dilute heavy metal solutions.

An electrostatic shielding-based coupled electrodialysis/electrodeionization process for removal of cobalt ions from aqueous solutions

Electrode graphite powder beds were interposed between anode and cathode as intermediate electrodes inside an electrolytic setup. Due to electrostatic shielding they eliminate the applied electric field and therefore stop the electromigration of ions within their mass. It was found that the intermediate electrodes can act as ionic current sinks-ion concentrating compartments and therefore cause a new type of a membrane-less electrodialysis/electrodeionization process. The proposed electrostatic shielding based coupled electrodialysis/electrodeionization treatment of synthetic cobalt plating rinse water containing 300 mg L(-1) Co(2 + ) ions produced a low-volume Co(2 + ) concentrate which could be recycled to the electroplating bath for reuse and a diluate containing 43.8 mg L(-1) Co(2 + ) ions. The diluate was then used as feed in the subsequent electrostatic shielding electrodeionization process which produced pure water with a cobalt ion concentration less than 0.1 mg L(-1). The current efficiency was 22-29%, the enrichment factor 13.5-26.1, the current density 20-40 A m(-2) and the flow rate 1.54 × 10(-4)-4.06 × 10(-4) dm(3) s(-1). The proposed membrane free electrostatic shielding electrodialysis/electrodeionization process could be developed into a new alternative electrochemical method of cobalt or other heavy metal removal and water purification and recycling from industrial effluents laden with heavy metals.

Numerical simulation of the electrodeionization (EDI) process for producing ultrapure water

A steady-state model was established to simulate EDI process for producing ultrapure water (MixEDI), the dilute compartment of which is filled with mixed cation and anion-exchange resins. By calculating the mathematical model which includes water dissociation mechanism, ionic status of ion-exchange resin, concentration polarization status and the concentration distribution of water dissociation products are obtained. The influence of water dissociation on the current efficiency, removal rate and pH value of EDI effluent is investigated. The existence of water dissociation catalyst at anion-exchange membrane (AM) makes the water dissociation current of the AM much larger than that of CM. The result is that the amount of electro-regenerated cation-exchange resins is much larger than that of anion resins. This is the reason why the removal rate of salt cation much larger than that of salt anion in EDI for producing ultrapure water. Thus, at the target percentage removal, water dissociation at AM surface is excessive and the one at CM surface is insufficient. We assume that there is also some water dissociation catalyst at CM surface. It is found that the improved water dissociation at CM could increase the percentage removal of salt anions and the current efficiency.

Selective separation of Ni(II)/Co(II) ions from dilute aqueous solutions using continuous electrodeionization in the presence of EDTA

The selective separation of Ni 2+/Co 2+ ions from their dilute solution using continuous electrodeionization process, facilitated with complexing agent, was investigated in this study. In order to increase the selective removal of Ni 2+ ion, EDTA was used as a complexing agent and Taguchi method was implemented for systematic design of the experiments. The statistical analysis of the experimental results showed that EDTA:Ni mole ratio and feed flow rate were the most influential parameters on performance of the process with contributions of 55.3% and 28.1%, respectively. The comparative experiments proved that the effective separation of Ni 2+/Co 2+ in the absence of EDTA was impossible. Also, electrodeionization process was more effective than electrodialysis process for selective separation of Ni 2+/Co 2+ when EDTA was used in both methods. Ni 2+/Co 2+ ions molar ratio increased from its initial value of 3 to a final value of 154.6 at optimum operating condition, as predicted by Taguchi method. Finally, obtained results showed that the applied procedure can be considered as a promising method for selective separation of Ni 2+/Co 2+ ions from their dilute aqueous solution.

Effect of operating parameters on NaOH recovery from waste stream of Merox tower using membrane systems: Electrodialysis and electrodeionization processes

Recovery of sodium hydroxide from waste stream of Merox tower by two different processes of electrodialysis and electrodeionization was studied. During our experiments effects of applied voltage and feed flow rate on current efficiency for sodium ion, economy of the process and sodium hydroxide recovery were investigated and compared for two systems under study. The obtained results showed that the percentage recovery of sodium hydroxide was enhanced with increasing of the applied voltage. Also, comparison between results of two processes showed that electrodeionization was more successful in terms of sodium hydroxide recovery especially at low voltages. However, the difference between two processes in sodium hydroxide recovery and economy diminished at high voltages which were due to effect of partial water dissociation. Maximum sodium hydroxide recovery of 75% and 85% for electrodialysis and electrodeionization, respectively, proved that implemented processes can be considered as proper candidates for sodium hydroxide recovery from waste stream of Merox tower. However, to apply these membrane processes for this application, it is necessary to convert Na 2S salt existing in the waste stream to harmless salts by Serox process.

Recovery of nickel ions from simulated electroplating rinse water by electrodeionization process

Pure water production and recovery of Ni(2+) from dilute NiSO(4) solution via improved electrodeionization (EDI) process were investigated. It was indicated that, with the feed water containing 50 mg L(-1) Ni(2+), the dilute resistivity of the EDI could achieve 3 MOmega cm which gave a Ni(2+) rejection more than 99.8% while the Ni(2+) was concentrated as high as 1,583 mg L(-1) in the concentrate stream. The current efficiency was as high as 40% and the concentrate factor could reach 31.7. The experiment results demonstrated that, just in a single process, it was feasible to purifying and concentrating dilute nickel wastewater synchronously by the EDI technology.

ESIEX - electrical swing ion exchange: pH control for biomolecule purifications or separations

Due to their amphoteric properties, biomolecules such as amino acids, peptides and proteins are separated as a function of their charges. A classical method to separate these biomolecules is column ion exchange with pH steps. The proper pH is usually obtained in a chemical way with different buffers of variable dilutions, and this is the source of large amount of effluents. The objective of this work is to study the possibility to control the pH in an electrodeionization (EDI) process without using buffer solutions.EDI process is a hybrid technique combining electrodialysis and ion exchange (IEX). In EDI, three types of phenomena are likely to generate protons and hydroxyl ions and to play a role in pH: formation by water oxidation or reduction at electrodes, water splitting and IEX. Two parameters play a role in these processes: the choice of current density and the nature of IEX resins (anion, cation or mixed).To purify a molecule, it is for instance possible to: -keep key molecule in feed compartment and generate the other species migration: the choice of resin type and of current density must allow maintaining the pH at isoelectric point of key molecule -generate selective migration of key molecule through an ion exchange membrane: pH must allow this molecule to have the required charge-fix selectively key molecule on ion exchange resin. The experimental method realized in the present work specifically aims at identifying the coupling of processes for a dipeptide fixation on an ion exchange resin placed in one compartment of electrodialysis with bipolar membrane system.

Numerical simulation of the electrodeionization (EDI) process accounting for water dissociation

The electrodeionization process (EDI) is usually operated at overlimiting current density, and is thus characterized by water dissociation and concentration polarization. We attempt to study the useful and harmful effects of water dissociation on the EDI process. A numerical steady state model was established to simulate the process of EDI, accounting for the effects of water dissociation. The differences in concentration polarization of membranes were investigated to study the effects of water dissociation on cation and anion membranes. Protons produced by water dissociation caused the resin to transform into the H-form. The H-form resin, which has high conductivity and high transport number, depletes protons in the interstitial solution. This explains the experimentally detected phenomenon that at high current densities, the pH value of the effluency of the dilute compartment (DC) stops decreasing when current increases. We suggest that the useful role of water dissociation in EDI is due to the H-form resin bringing more salt cations of the interstitial solution into the resin phase, thus producing a high conductivity channel for the electro-migration of the salt cations. This mechanism avoids the decrease in salt ion conductivity brought about by concentration polarization. The disadvantageous effect of concentration polarization on the transportation of salt ions in interstitial solution is thus lessened. An intermediate point between the useful and harmful effects of water dissociation was determined by the dependence of current efficiency and removal rate for both cations and anions as a function of current density.

Cr(VI) removal by continuous electrodeionization: Study of its basic technologies

The capabilities of continuous electrodeionization process (CEDI) and its basic technologies (electrodialysis (ED) and ion exchange (IX)) were analyzed in order to remove hexavalent chromium from synthetic solutions at pH 5. A cell with two chambers (dilute and concentrate) was used. Two cation exchange membranes (CM-1) and one anion exchange membrane (AFN) (40 cm2 effective area) were employed in the experimental setup. IX technology was single evaluated using an IRA-67 anionic resin to know its independent performance from the other technologies, whereas ED was studied in the cell; Ilim determination was done by I vs. U plots and factors of 0.7 Ilim and 0.85 Ilim were applied to ED process. Finally, EDI process was studied at the same conditions that ED in order to know the resin bed role. During IX the removal reached was 50%; ED 98% after 6.25 h operation with an energy consumption of 1.21 kW h/m3; EDI (anionic bed) accomplishing 97.55% chromium removal (energy consumption of 0.91 kW h/m3). Finally EDI with mixed bed removed 99.8% in 1.3 h and of 0.167 kW h/m3 of energy consumption.

Simulation and Optimal Design of Electrodeionization Process: Separation of Multicomponent Electrolyte Solution

Electrodeionization (EDI) technology combines the operation principle of both ion exchange and electrodialysis in one single unit and overcomes the disadvantages of either unit. This technology has been widely used in the production of ultrapure water due to its better performance and economical operation at low feed concentrations. As a result, there have been several studies that deal with application of this technology for the removal of ions from water. However, except for a few studies, most of the reported works deal with the experimental study of EDI. This study deals with the development of a mathematical model for deionization of electrolyte solutions containing more than one ion and ions that are multivalent in nature. The model validity is verified by comparing the results with a few experimental observations. This is followed by a sensitivity study of the EDI unit to explore the effect of various operating and system parameters on the ion removing ability of the EDI unit. Consequently, a syste...

Removal of low concentrations of hardness ions from aqueous solutions using electrodeionization process

A specially designed electrodeionization (EDI) stack was used for deep softening from simulated aqueous solutions containing low concentrations of hardness ions. Characteristics of the current–voltage ( I– V) and resistance–voltage ( R– V) curves of EDI and electrodialysis (ED) were compared at first, and then removal of Ca 2+ ions was carried out in a continuous experiment under a constant applied voltage. In order to further investigate the abilities of EDI to remove hardness without chemical regeneration, performances of different processes were compared under various experimental conditions of applied voltage, concentrate flow rate, and feed solution composition. It was shown that with feed Ca 2+ concentration of 5 mg dm −3, the dilute resistivity of 3.45 MΩ cm was obtained when under optimized operation conditions. It was also found that applied voltage and concentrate flow rate had remarkable impacts on the migration of Ca 2+ ions. A dimensionless coefficient K t was put forward to distinguish the “enhanced transfer” and “electoregeneration” mechanisms. It was found that scaling formation due to water dissociation on the membranes surface could be avoided under reasonable operation conditions. In addition, no significant influence on final hardness rejection was revealed with multi-species of feed solutions (Ca/Mg). The experimental results have demonstrated the feasibility of deep water softening by improved EDI technology.

A new process for desalination and electrodeionization of water by means of electrostatic shielding zones – ionic current sinks.

We constructed electrostatic shielding zones made of electrode graphite powder and used them as a new type of ionic and electronic current sinks. Because of the local elimination of the applied electric field, voltage and current within the current sinks, ions are led inside them and accumulate there. The sinks become ion concentrating compartments whereas the adjacent compartments become ion depleting compartments. The proposed electrodeionization process uses no permselective ion exchange membranes. We implemented it in electrodialysis desalination of a synthetic brackish 0.03 M NaCl solution and obtained potable water with a NaCl concentration <500 mg L -1 . Furthermore, we performed electrodialysis of 0.002 M NiSO4 and electrodeionization of 0.001 M NiSO4 solutions with simultaneous electrochemical regeneration of the used ion exchange resin beds. By the continuous mode of electrodeionization of the 0.001 M NiSO4 solution we obtained pure water with a Ni 2+ ion concentration of less than 0.5 mg L -1 at a flow rate of 2.3 x10 -4 L s -1 diluate stream

ELECTRO-DEIONIZATION OF Cr (VI)-CONTAINING SOLUTION. PART I: CHROMIUM TRANSPORT THROUGH GRANULATED INORGANIC ION-EXCHANGER

Kinetics of Cr (VI) → OH− exchange on both hydrogel and xerogel of hydrated zirconium dioxide was investigated. Self-diffusion coefficient of Cr (VI) species has been determined by analysis of kinetic curves. Transport of Cr (VI) anions through the inorganic ion exchangers under the influence of applied voltage was also researched. In the case of hydrogel, the ions are transported mainly through the solid phase. Diffusion coefficient of chromate anions through this material was estimated as 9.00 × 10−12 m2 s−1. This is in agreement with self-diffusion coefficient of Cr (VI) obtained from kinetic measurements (1.60 × 10−12–9.92 × 10−12 m2 s−1). Owing to the rather high mobility of Cr (VI) through hydrogel of hydrated zirconium dioxide, this material was recommended for electro-deionization processes. On the other hand, the use of polymer anion-exchange membrane must be excluded to prevent poisoning of the inorganic ion exchanger with Cr (III) cations to be formed during chemical interaction of Cr (VI) with organic materials.

Performance evaluation of electrodeionization process based on ionic equilibrium with plate and frame modules

The paper describes results of experiments carried out in plate and frame electrodeionization (EDI) modules, aiming to elucidate ion mass transfer phenomena between ion-exchange resin and membrane for more effective desalination. The selective separation rate of different ions in process was investigated with conventional theories such as double electric layer and the Donnan theory to check its consistence. Further, as comparing with ordinary electrodialysis (ED) process, no obvious limiting current point was observed in EDI performance, which was usually used as a criterion for process optimization. Behavior of ion migration in the fluids with different configurations under different operating parameters was also examined and the ionic equilibrium analysis of EDI process was found to be beneficial to determine whether it was in the steady state or in the regeneration stage of operation.

Removal of metal ions from electroplating effluent by EDI process and recycle of purified water

In this paper, an improved configuration of the membrane stack was adopted in the electrodeionization (EDI) cell to prevent precipitation of bivalent metal hydroxide during the running. The operational parameters that influenced the electro-regeneration of cation exchange resins loaded with nickel ions were optimized, and the result showed that addition of a small amount of Na 2SO 4 into the electrode solution, moderate increase of applied voltage and initial metal ion concentration could get better regeneration effect. A steady and continuous process of electroplating wastewater treatment could be achieved with current efficiency of 33–38%, removal efficiency of at least 99.8% and enrichment factor of 22–36. Concentration of metal ions in purified water was 0.03–0.09 mg/L for nickel, 0.07–0.10 mg/L for copper, 0.06–0.15 mg/L for zinc, 0.07–0.10 mg/L for cadmium and 0.08–0.17 mg/L for chromium, respectively. This demonstrated the applicability of recovering heavy metals and purified water from electroplating effluent for industrial reuse.

Experimental Tests and Modelling of an Electrodeionization Cell for the Treatment of Dilute Copper Solutions

AbstractThe paper presents the results of experimental and theoretical investigations of an electrodeionization process for the removal of metal cations from dilute solutions. The ability of this technique to treat 100 ppm copper solutions using cationic membranes and ion‐exchange resins between the membranes was studied. Fair abatement yields were obtained in the 100 mm high resin bed in long‐term runs, and solutions of an appreciable copper ion concentration could be produced in the cathode chamber. The process capacity was limited by significant deposition of copper at the cathode, non‐even distribution of current density, and side‐diffusion to the anode chamber. Additional tests were then carried out using a 15 mm resin bed. The more even current distributions allowed the effect of the resin stiffness and the current density on the removal yield to be thoroughly observed. Steady‐state operation of the resin bed was modelled using generalized expressions of the various transport rates. Results of the model clearly showed the significance of solid‐liquid interactions on the transport processes.

Purification of a diluted solution containing nickel using electrodeionization

It was found that the effective diffusion coefficient of Ni 2+ in a macroporous strongly acidic cation-exchange resin, which was determined with the electromigration method, depends on acidity and flow rate of the solution. The values of diffusion coefficient were found to be 1.18×10 −13–1.9×10 −12 m 2 s −1. Acidification of the solution prevents formation of insoluble nickel compounds on the surface of particles and membranes. At the same time an increase in flow rate (pressure drop) through the ion exchanger results in a rise of ion transport, probably due to an improvement of packing. The ion exchanger previously loaded with Ni 2+ was tested by the electrodeionization process of nickel removal from a diluted solution. Optimal conditions for realizing the discontinuous process were determined. It was found that Ni 2+ ions are transported both through the ion exchanger and solution. The solution purification degree reached 40%.

Influence of voltage and flow rate on electrodeionization (EDI) process efficiency

Electrodeionization (EDI) is being applied more and more to produce ultrapure water, especially in the semi-conductor industry. The continuous electrical regeneration of the ion-exchange (IEX) mixed bed is the main advantage of this recent technology. EDI couples two well known effects: electrodialysis and IEX. In spite of its rapid development, there are no established theories, design equations nor clear mechanisms of regeneration and transport. The present research work deals with EDI process efficiency. We have investigated the influence of the applied voltage V and the flow rate Q on cell efficiency by measuring current intensity I, and inlet C in and outlet C out concentrations of the treated solution. The efficiency R is defined by: R (%) = 100 (∆ C/ C in) Q/ Q where C = C in− C out and Q∆ C = J is the mass transfer flux. The main finding was that an original, empirical, and simple equation between the efficiency R and the flow rate Q is established: R = K′∆ VQ − n where n ≈ 0.5 or Log R = Log ( K′∆ V)− n Log ( Q), a linear logarithmic equation between R and Q. The mass transfer flux J = Q∆ C is then directly proportional to Q and inversely to Q : J = K ⁢ Q n ≈ K ⁢ Q 0.5 . This is an important result because it presents strong analogies with the habitual equations of electrochemical hydrodynamics (rotating, porous and packed-bed electrodes). The other interesting results are: (1) the current vs. voltage characteristic curve is constituted of three main linear parts, with an optimal zone (4.5–12 V); and (2) the water dissociation threshold voltage was clearly shown (12 V) and coincides with the beginning of a decrease in efficiency.

The production of high purity water by continuous electrodeionization with bipolar membranes: Influence of the anion-exchange membrane permselectivity

Continuous electrodeionization is used widely today for the production of high purity water. The conventional electrodeionization process using mixed-bed ion-exchange resins has several shortcomings, such as incomplete removal of weak acids and diluate conductivity above that of completely deionized water. In this study, the performance of a modified continuous electrodeionization stack using separated beds of cation- and anion-exchange resins and a bipolar membrane as source of regenerating protons and hydroxide ions is considered. Two modifications of this design, one with and one without a so-called protection compartment are compared with each other. The role of the co-ion transport through an anion-exchange membrane of incomplete permselectivity on the process performance is discussed theoretically and shown experimentally as function of the current density, the hydrostatic pressure and the flow velocity in the concentrate compartment, as well as the nature of the protection compartment rinse water. Using the protection compartment, the co-ion transport into the diluate could be eliminated and a specific conductivity of the product water of less than 0.056 μS/cm was achieved.

Phosphoric acid purification by a membrane process: Electrodeionization on ion-exchange textiles

The electroextraction of mineral impurities from phosphoric acid was achieved by electrodeionization process (EDI) combining ion-exchange membranes (IEM) and textiles (IET). The treated solution was an industrial phosphoric acid solution at high concentration (54% P 2O 5) and five times diluted (11% P 2O 5) containing mainly the following heavy metals: magnesium, iron, chromium, zinc, cadmium. Immersion of textiles in phosphoric acid solutions at various concentrations showed their good chemical resistance in this medium. Exchange kinetics with IET was very fast. The use of two kinds of textiles (cation and anion exchange) indicated that the metal pollutants may be found in both cationic and anionic form. From EDI measurements, purification ratios close to 30% for all elements (excepted for Fe) were obtained after 5 h of treatment.