Electrodeionization: An Efficient Way for Removal of Fluoride from Tap

Apr 12, 2015 - A unit is developed for the continuous production of fluoride free water using an ... The EDI process usually operates in two regimes o...
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Electrodeionization: An Efficient Way for Removal of Fluoride from Tap Water Using an Aluminum Form of Phosphomethylated Resin Swati Gahlot,† Saroj Sharma,†,‡ and Vaibhav Kulshrestha*,†,‡ †

CSIR-Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Council of Scientific & Industrial Research (CSIR), Gijubhai Badheka Marg, Bhavnagar 364 002, Gujarat, India ‡ Academy of Scientific and Innovative Research, CSIR-CSMCRI, CSIR, Gijubhai Badheka Marg, Bhavnagar 364 002, Gujarat, India S Supporting Information *

ABSTRACT: A unit is developed for the continuous production of fluoride free water using an electrodeionization (EDI) process. The experiments are carried out with a laboratory-scale unit. The EDI process usually operates in two regimes of enhanced transfer and electroregeneration. The current efficiency decreased in the second regime of the EDI system because of water dissociation. The cation-exchange membrane (CEM) and anion-exchange membrane (AEM) used for the present study are converted from a styrene−divinylbenzene-based interpolymer film by sulfonation and chloromethylation, respectively. Methyl methacrylate−ethylene glycol dimethacrylate-based amphoteric resin synthesized by radical suspension polymerization shows a 4.57 mequiv/g ion-exchange capacity with 57% water uptake. Both the membranes and resins are characterized by the means of chemical and mechanical properties. The membranes and resins show very good electrochemical properties with excellent mechanical stability. The removal of fluoride from three concentrations of tap water streams revealed the significance of the water composition on the performance of the EDI unit with respect to the selectivity of fluoride removal and energy consumption. Three potentials (9, 12, and 15 V/cell pair) are applied in different sets of experiments during EDI, out of which 12 V/cell pair was found to be more efficient with a lower power consumption of 4.6 kwh/kg and 37% current efficiency.

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INTRODUCTION The presence of various hazardous contaminants like fluoride, arsenic, nitrate, sulfate, pesticides, other heavy metals, etc., in underground water has been reported from different parts of India.1−3 In many cases, the water sources have been rendered unsafe not only for human consumption but also for other activities such as irrigation and industrial needs. Anions are commonly present in water; however, some of the anions are undesired and often responsible for serious environmental and health problems. Fluoride is one of the most abundant anions present in groundwater worldwide and responsible for problems in safe drinking water supply. Because fluorine is the most electronegative and reactive among all of the elements in the periodic table, it cannot be found in nature in its elemental state. It exists either as inorganic fluoride compounds or as organic fluoride compounds, always exhibiting an oxidation number of −1. In the environment, inorganic fluoride compounds are much more abundant than organic fluoride compounds. Therefore, now there is a need to focus greater attention on the future impact of water resource planning and development, taking into consideration all of the related issues. In India, fluoride is the major inorganic pollutant of natural origin found in groundwater. Fluoride in minute quantity is an essential component for normal mineralization of bones and formation of dental enamel.4 The safe limit of fluoride in drinking water is 1.0 mg/L.5 It has been observed that low calcium and high bicarbonate alkalinity favor high fluoride content in groundwater.6 Because of a large number of variables, the fluoride concentrations in groundwater range from well under 1.0 mg/L to more than 35.0 mg/L.7 Fluoride is found in the atmosphere, © XXXX American Chemical Society

soil, and water. It enters the soil through weathering of rocks, precipitation, or waste runoff. Defluoridation of drinking water is the only practicable option to overcome the problem of excessive fluoride in drinking water in which an alternate source is not available. During the years following the discovery of fluoride as the cause of fluorosis, extensive research has been done on various methods for removal of fluoride from water and wastewater. These methods are based on the principles of adsorption, ion exchange, precipitation−coagulation, membrane separation, electrolytic defluoridation, electrodialysis, etc.8−13 Depending on the quality of water, each scheme needs a separate plan of action for reuse or disposal. In the case of water remediation, biological, chemical, and physical methods are commonly adopted. The biological treatment refers to degradation of organic compounds by the breaking and transformation of inorganic compounds by bioaided reactions. Some of the chemical treatment methods include coagulation, oxidation, electron-beam irradiation, radiocolloid treatment, and sorption to organic/inorganic substrates. The techniques in water purification can be classified into different methods. Electrodeionization (EDI) is a membrane process in which ions are removed to produce ultrapure water (8.0−18.2 MΩ conductivity). EDI has many advantages such as stable product quality and no use of acid and base for resin regeneration. It is a continuous chemical-free deionization process and is based on Received: January 28, 2015 Revised: March 30, 2015 Accepted: April 11, 2015

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DOI: 10.1021/acs.iecr.5b00369 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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distribution of the current in the bed and to allow faster establishment of steady state in the cell for EDI operation.

EED and mixed-bed ion exchange. An EDI cell consists of diluted compartments (DCs), concentrated compartments (CCs), and electrode compartments. Under the influence of an applied potential gradient, ions fed into DCs exchanged with mixed-bed resins and simultaneously transferred across the membranes (AEM and CEM) to maintain the electroneutrality in all compartments. Thus, ion-fed solutions get depleted in DCs, while in CCs, there was a concentration buildup. The use of an ion-exchange resin in DCs is a key step of the EDI process because of (i) faster ion transfer rate and (ii) reduction in the system resistance and completion of back diffusion of ions from CCs to DCs, respectively. In this process, the ratedetermining step is diffusion of ions from a bulk solution to the surface of ion-exchange resins. Also, the water splitting reaction produced H+ and OH− electrochemically for regeneration of the resin.14 Recently, EDI was successfully employed to remove/recover heavy metal ions (Ni2+, Pb2+, Zn2+, CrVI, Co2+, Cu2+, etc.) from wastewater.15−17 Moon et al. developed an EDI process for the production of high-purity water from the primary coolant obtained from a nuclear power plant. Fu et al. developed an EDI process for the softening of hard water.18 The combination of electrodialysis and ion-exchange particles for the removal of ions from solution has received a great deal of attention. One of the first to mention such a combination, in this case for the treatment of radioactive wastes, was Glueckauf.19 Much of the work, however, has been focused on the removal of monovalent ions and the production of ultrapure water,20−22 while the removal of bivalent ions has been studied to a lesser degree.23,24 Different applications of EDI for water desalination have been reported by AlMarzooqi et al. in his review.25 In this article, they focused on the demand for a low-cost and high-efficiency electrode that can be used for seawater desalination. They emphasized research to fill up the gap from laboratory scale to commercialization because EDI technology holds huge potential in desalination fields if enough research effort is dedicated to it. With the lowest energy consumption and largest energy recovery potential, continuous deionization technology offers most of the characteristics required for making the best available technology for water desalination. Arar et al. also presented a review on various EDI applications for water desalination.26 According to this article, the EDI process is very efficient in environmental protection, in the production of ultrapure water, and for the recovery of some valuable species. Weakly ionized species can also be removed by this process. The problem of different regeneration rates or flow rates in the cation- and anion-exchange resins can be eliminated in an EDI stack with completely separated cation and anion resin beds by utilizing the production of H+ and OH− ions, needed for regeneration of the ion-exchange resins, at the electrodes or in a bipolar membrane (BPM).27−29 In both cases, the amount of ions to be used for regeneration of the ion-exchange resins is set by the current applied. The performance of EDI stacks with mixed bed and separated ion-exchange beds using electrodes or BPMs for the production of H+ and OH− ions, needed for regeneration of the ion-exchange resins, is well discussed in the literature, and the improved removal of weak dissociated acids using separated beds is clearly demonstrated.30 The present paper investigates the effects of the processing parameters of the EDI process for fluoride removal from groundwater with different concentrations of fluoride. A short bed of ion-exchange resin is used to prevent a nonuniform

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EXPERIMENTAL SECTION Materials. Methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDMA), styrene (St), divinylbenzene (DVB), chlorosulfonic acid (CSA), etc., of analytical reagant grade were obtained from SD Fine Chemicals, India. All chemicals were used without further purification. Doubledistilled water was used in all of the experiments. Synthesis of Cross-Linked Polymer Beads and Their Functionalization. Cross-linked porous p(MMA-coEGDMA) was synthesized by a radical suspension polymerization technique. The model composition of p(MMA-coEGDMA) designated as APP3-20-0.8-HPT and reported by Popat et al. has been selected for the synthesis.31 Starch used as the stabilizer in this paper has been replaced by poly(vinyl alcohol) (PVA) for our work. The stabilizer plays an important role in the suspension polymerization systems to control the droplet coalescence by covering the monomer droplet surfaces with both physical and/or anchoring adsorption and thus getting the polymer beads of desired size for further modification. The exotherm generated during the synthesis is successfully controlled by PVA, and finally polymer beads of controlled particle size are obtained. It has been found that PVA is a better stabilizer than starch to improve the whole system during the synthesis. Cross-linked porous MMA-co-EGDMA was synthesized by a radical suspension polymerization technique. The organic mixture comprised MMA, EGDMA, and MMA + EGDMA (80% w/w)−n-heptane (20% w/w) as the monomer, crosslinkng agent, and porogen, respectively. Initially, an aqueous solution containng PVA (1.5 wt %) and NaCl (0.15 wt %) as a suspension medium was heated to 90 ± 2.0 °C under constant agitation and thereafter was cooled to 80 ± 2.0 °C. The organic phase containing MMA (64% w/w) and EGDMA (16% w/w) mixed with BPO (1% w/w of a monomer mixture) as an initiator in n-heptane was poured in an aqueous solution under stirring conditions at 80 ± 2.0 °C. The polymerization was carried out in a three-necked round-bottom flask equipped with a stirrer, a thermometer, and a reflux condenser. Initially, polymerization was carried out at 80 ± 2.0 °C for 2 h; thereafter, the temperature was increased to 100 ± 2.0 °C for another 2 h. After completion of the reaction, the temperature was cooled to room temperature. The resulting polymer beads were filtered out from the reaction kettle and washed with hot water several times to remove the unreacted monomers and adhering PVA. The dried and extracted polymeric beads were further studied using a product of −18 + 52 BSS mesh size. Functionalization of synthesized polymeric beads was carried out by amination, followed by a phosphomethylation reaction. For the amination reaction, swollen beads (swollen in methanol prior to the reaction) were added to triethylenetetramine in a three-necked round-bottom flask. The reaction was carried out at 195 ± 2.0 °C for 8 h. After reaching to room temperature, the beads were washed with methanol and cold water and kept overnight in deionized water to wash out unreacted amine. For the phosphomethylation reaction, the aminated resin was added to a formaldehyde solution (36%), 180 g of phosphorus acid in 500 mL of deionized water, and concentrated HCl in a roundbottom flask. The reaction mixture was refluxed at 98 ± 2.0 °C for 8 h under constant stirring, then cooled at room B

DOI: 10.1021/acs.iecr.5b00369 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research temperature and filtered, and washed thoroughly with water to remove any unreacted reagents. The amphoteric resin is conditioned by treatment using 1.0 M HCl and 1.0 M NaOH solutions alternatively with intermediate treatment using distilled water. The resin was finally converted to the Na+ form. Thereafter, the Na+ form of resin was converted into the Al3+ form by treating it with an excess of 1.0 M aqueous aluminum sulfate solution. The excess loading of Al3+ was washed out with distilled water. This Al3+loaded resin was used in EDI for the fluoride uptake study. The chemical reaction of the Al3+ form of a phosphomethylated resin and their interaction with fluoride are shown in Scheme 1.

CEM was carried out using the standard method of sulfonation using a CSA solution in dichloroethane (30:70 v/v). For AEM, quaternary ammonium as a functional group was added to the films. The membranes were conditioned by treatment with 1 M HC1 and 1 M NaOH successively and then thoroughly washed with distilled water before their equilibration in a 1 M electrolyte solution. Chemical, Structural, and Mechanical Characterization. The samples were characterized by means of their chemical and structural properties, and details of the characterization are included in the Supporting Information (SI). Physiochemical Characterization. The water uptake behavior of membranes and resins was determined by recording the weight gain after equilibration in water for 24 h. The ionexchange capacity (IEC) of the membranes was estimated by acid−base titration. The conductivity of the membranes was measured by a two-probe method. The counterion-transport number of the membranes was calculated by the membrane potential. Details of the experiments are given in the SI. Fluoride Uptake Behavior of Resin under Static Conditions. For the study of fluoride ions under static conditions, the synthesized resin was converted to the Na+ form by using a sufficiently excess quantity of an aqueous sodium hydroxide solution. After the resin was washed with deionized water, converted Al3+ forms by using aluminum sulfate. To study the kinetics of fluoride sorption, 50 mL aliquots were withdrawn at time intervals to determine the residual concentration of fluoride ions. The concentration of fluoride ion in the equilibrating solution was evaluated by a fluoride-selective electrode using an ion analyzer. EDI Process for Fluoride Removal. An in-house-prepared EDI system was used for fluoride removal. Interpolymer cationexchange (CEM) and anion-exchange (AEM) membranes were used for experiments. The schematic diagram of the EDI cell is presented in Scheme 2. The parallel-cum-series flow arrangement was used to monitor each flow stream in the respective compartments. Initially, tap water with a known concentration of fluoride solution and volume was fed into the DC, while distilled water was fed into the CC. Peristaltic pumps were used to feed the solutions (1000 cm3) in a recirculation mode into the respective compartments with a constant flow rate (0.01 m3/h) to maintain the turbulence. A direct-current power supply was used to apply constant potential across the

Scheme 1. Reaction Scheme for Resin and Their Fluoride Uptake

Synthesis of Ion-Exchange Membranes. The heterogeneous-type interpolymer ion-exchange membranes used in these investigations were prepared.32 Interpolymer was prepared by radical polymerization of St−DVB in the presence of xylene as the solvent at 100 °C by a reactive melt-processing method. Once polyethylene (PE) was observed to be melted in the reactor, forming homogeneous dough, additional toluene (∼4 L) was added slowly. St was added into the molten mixture of PE in the presence of DVB and benzoyl peroxide (BPO), and polymerization was allowed to continue for 4 h at the same temperature. For production of the interpolymer film, a blowfilm extruder was used. Extrusion was carried out at 190−200 °C. The final thickness of the interpolymer film was 150−200 μm. Functionalization of the PE−PSt interpolymer films to

Scheme 2. Schematic Representation for Fluoride Removal by the EDI Process

C

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beads, (B and Bl) aluminum-loaded forms of the resin, and (C and Cl) fluoride-loaded forms of the resin. It is clear from the images that the resin is microporous and spherical in nature, which can absorb more fluoride. Electrochemical Properties of Ion-Exchange Membranes and Resins. The physicochemical and electrochemical properties of the CEM and AEM used for EDI are included in Table 1. The thickness of these membranes was 150 μm. The water content and IEC for the CEM and AEM were estimated as reported earlier.11,12 The CEM exhibited about 25% water content and the AEM about 15%. In general, the introduction of fixed charges on the membrane matrix leads to their IEC values. In general, membranes with the same degree of crosslinking and composition absorb the same amount of water, where the density of ionizable groups is the same throughout the membrane matrix.33,34 An increase in the hydrophilic species such as the ionic group concentration with the IEC indicates the density of ionizable hydrophilic groups in the membrane matrix, which are responsible for the ionic conductivity in the ion-exchange membrane. The IEC values for both membranes showed reasonably good IEC values, as shown in Table 1. The membrane resistance was measured in equilibration with 0.1 M NaF solutions, and relevant data are also presented in Table 1. When electrolyte solutions of unequal concentration are separated by a membrane, an electrical potential difference develops across the membrane because of the tendency of oppositely charged ions to move with different mobilities. The magnitude of the membrane potential depends on the electrical characteristics of the membrane in addition to the nature and concentration of the equilibrating electrolyte solutions.34 Counterion-transport number values were estimated from membrane potential measurement and found to be nearly unit for both cases.35 The functionalized resins were conditioned by treatment with 1 N HCl and 1N NaOH alternately between washings with deionized water. Finally aminated weak base resins were converted to chloride forms, and phosphonic acid resin was taken in H+ form, washed with methanol until it becomes acid free, and evaluated for capacity and water content. A total of 0.5 g of wet resin was taken in a well-stoppered conical flask, followed by the addition of 50 mL of a 0.1 N NaOH solution, and equilibrated for 16 h with occasional shaking. Then the 10 mL of NaOH aliquot was taken in one conical flask and titrated against standard 0.1 N HCl to determine the total exchange capacity. The IEC of the resin was computed using the abovementioned formula and found to be 4.57 and 8.25 mequiv/g for aminated and (aminomethyl)phosphonic acid type resins (Table 1). The kinetics of fluoride sorption in static conditions are shown in Table S1 in the SI; the fluoride uptake behavior of resin absorbed from the aqueous solution of 10 ppm was found to be 50% of its initial value within 5 min of time. Mechanical Properties of Ion-Exchange Membranes. Strain−stress curves for the AEM and CEM are presented in Figure 3, and the corresponding values of the elastic modulus, maximum stress, and elongation at break are also presented in the same figure. The elastic modulus for AEM was calculated as 1.5 MPa and that for CEM as 1.35 MPa, while 137% elongation showed in the AEM and 194% for the CEM; the values are better than those of commercially available ion-exchange membranes. The results show that the membranes are very stable and flexible because PE is the base material.32−36 Current−Voltage (i−v) Curves in EDI. In Figure 4, the curves show three typical characteristic regions, viz., ohmic,

electrodes, and the resulting current variation was recorded as a function of time. The changes in the conductivity and pH of DC and CC outputs were regularly monitored by placing the conductivity and pH electrodes in the respective containers during all of the experiments. The fluoride concentration in the permeate was measured periodically after 15 min. The i−v curves of the CEM and AEM in the EDI process were also recorded in equilibration with a 0.10 M NaF solution. The energy consumption and current efficiency (CE) are important parameters for any electrochemical process to assess the suitability of a membrane for the same. The energy consumption (W, kWh/kg, of NaF removed) can be obtained by the equation24 W (kWh/kg) =

∫0

t

VI dt m

(1)

where V is the applied voltage, I is the current, t is the time allowed for the electrochemical process, and m is the weight of salt removed. The current efficiency (CE), defined as the fraction of Coulombs utilized for salt removal, may be obtained by CE (%) =

mnF × 100 MQ

(2)

where F is the Faraday constant, M is the molecular weight of salt, n is the stoichiometric number, and Q is the charge.

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RESULTS AND DISCUSSION Chemical and Structural Characterization of IonExchange Membranes and Resins. The FTIR spectra of resins and ion-exchange membranes are shown in Figures 1 and

Figure 1. FTIR spectrum for an ion-exchange resin.

S1 in the SI, respectively. The peak at 3636 cm−1 corresponds to the O−H vibration of the alcohol group. Peaks at 1655 and 1462 cm−1 are CC and −C−H vibrations of alkene and alkane, respectively. The 1167 cm−1 frequency is due to the C− N stretching. The frequency at 1066 cm−1 shows the C−O stretching. Both the CEM and AEM display almost similar FTIR spectra because of the presence of PE, St, and DVB. The broad peak near 3350 cm−1 shows the N−H stretching. The peak at 2915 cm−1 corresponds to the C−H stretching of alkane. The frequency at 2362 cm−1 is due to the presence of the CN group. The vibrational frequency at 1651 cm−1 is due to the CO band of the amide group. The strong peak at 1032 cm−1 shows the C−O stretching. Figure 2 shows the scanning electron microscopy (SEM) images for (A and Al) microporous D

DOI: 10.1021/acs.iecr.5b00369 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 2. SEM images for (A and Al) microporous beads, (B and Bl) aluminum-loaded forms of the resin, and (C and Cl) fluoride-loaded forms of the resin.

Table 1. Thickness (l), Water Content (φw), IEC, Membrane Resistance (Rm), and Counterion-Transport Number (tmi ) Values for the CEM, AEM, and Ion-Exchange Resin Used for EDI property

CEM

AEM

l (μm) φw (%) IEC (mequiv/g) Rm (Ω cm) tmi

150 25.0 1.80 2.73 0.94

150 15.0 1.69 5.32 0.92

IER 57.15 4.57

Figure 4. Applied potential versus current density for the EDI process.

Figure 3. Stress versus strain spectra for ion-exchange membranes.

nonohmic, and plateau length. The potential is varied from 1 to 20 V/cell pair. It is also observed from figure that the current density increases linearly with the applied potential from 1 to 10 V/cell pair and thus shows ohmic behavior. From 10 to 16 V/cell pair, the graph shows almost a plateau region. Above 16 V/cell pair, the current density again increases rapidly. So, we choose a plateau region for our EDI experiment. Effect of the Applied Potential on Fluoride Removal during the EDI Process. The effect of the applied potential on fluoride removal during the EDI process is shown in Figure 5. Three potentials (9, 12, and 15 V/cell pair) are applied in different sets of experiments during EDI. The 10 ppm of fluoride is circulated with 500 ppm of tap water during experiments. At 9 V/cell pair, fluoride removal is quite low compared to that of 12 and 15 V/cell pair. Fluoride removal

Figure 5. Time versus fluoride removal with 10 ppm of fluoride in 500 ppm of tap water at different applied potentials.

increases with time, and about 55% of fluoride was removed in 60 min at 9 V/cell pair while 73 and 76% of fluoride was removed at 12 and 15 V/cell pair, respectively. The higher removal of fluoride at higher potential is due to higher water dissociation and fast resin regeneration. Figure 6 presents a fluoride content versus time graph and shows that initially fluoride removal is faster and then gets slower. In the first 30 min, 60% of fluoride was removed, while only 16% was E

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Figure 6. Time versus fluoride removal from 500 ppm of tap water with 10 ppm of fluoride at 15 V applied potential. Fluoride in the CC is also shown in the inset.

Figure 8. Fluoride and total dissolved solid (TDS) removal at 12 V applied potential with 10 ppm fluoride concentration in different TDS tap water.

removed in the next 30 min. That may be due to the presence of a small amount of fluoride in the second 30 min. The concentration of fluoride increases in the CC with time. Effect of the Fluoride Concentration Interfering Ions during the EDI Process. Figure 7 presents time versus

Table 2. Energy Consumption (P) and Current Efficiency (CE) of Fluoride Removal (10 ppm in 500 ppm Tap Water) with Different Applied Potentials fluoride with 500 ppm tap water

fluoride only

P (kWh/kg)

CE (%)

P (kWh/kg)

CE (%)

4.7 4.6 6.2

38 37 22.4

136.3 125.99 179.8

1.79 1.93 1.08

15 V 12 V 9V

operating conditions of the EDI cell as well as the nature and electrochemical properties of the membranes. The CE and P for 9 V/cell pair applied potential are found to be 22.4% and 6.30 kWh/kg, respectively, and 37.0% and 4.6 kWh/kg for 12 V/cell pair applied potential. CE and P for 12 V/cell pair applied potential are also calculated to be similar to those for 12 V/cell pair with lower power consumption. All over 12 V/cell pair applied potential is most suitable for fluoride removal during EDI. Regeneration of the resin is the most important parameter for EDI operation, which prevents the resin from being exhausted. Table 3 shows EDX analysis of unused and

Figure 7. Time versus fluoride removal at 12 V applied potential with different fluoride concentrations in 500 ppm tap water.

fluoride removal with different fluoride contents at 12 V/cell pair applied potential. In the first 15 min, 30.7%, 27.8%, and 24% of fluoride was removed with feed 10, 15, and 20 ppm of fluoride, respectively. After 60 min, the total fluoride removal is about 73.2% of feed 10 ppm, which is 24% higher than that of feed 20 ppm of fluoride. The change in the removal efficiency may be due to the interfering ions during removal of fluoride. Figure 8 presents time versus interfering ions and fluoride removal during EDI. It can be seen from the figure that, at higher concentration of feed tap water (1500 ppm), fluoride removal is 65.4%, which is 12.4% lower compared to lower feed tap water (500 ppm). At the same time, 38% of salt was also removed from 1500 ppm feed tap water. Salt removal for all three feed concentrations (500, 1000, and 1500 ppm) is about 37.5−40% which is almost the same in all of the experiments. Current Efficiency, Power Consumption, and Resin Regeneration during the EDI Process. Table 2 shows the power consumption and current efficiency data to evaluate the performance of the EDI system with different applied potentials. It is observed that P decreased while CE increased with an increase in the applied potential from 9 to 15 V/cell pair. Efficiency parameters (P and CE) depend on the

Table 3. EDX Analysis of Unused and 500 h Used Resin wt % element

unused

500 h used

O Al P

65.09 21.89 13.02

55.95 27.08 16.97

500 h used resin. It is clear from elemental analysis that the resin is regenerated during the EDI process and found have properties similar to those of the unused resin.

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CONCLUSION The purpose of these experiments is to determine the behavior of a combined electrodialysis/ion-exchange system for fluoride removal. The prepared membranes and resins show excellent electrochemical properties with mechanical stability. From the i−v curve, it is optimized that the system should be operated between 9 and 16 V/cell pair. It is also observed that the applied potential of 12 V/cell pair is most appropriate for F

DOI: 10.1021/acs.iecr.5b00369 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research fluoride removal with interfering ions. Initially, the fluoride removal efficiency of the system is faster and then reduced because of an increase in the resistance of the system. It is also expected that the resin filled between the AEM and CEM reducing the resistance of the EDI system. This type of system can be used for the removal of fluoride from tap water in the presence of other salts. It is also clear from the results that EDI brings versatile solutions to the separation of ions because of its capacity for removing a wide range of contaminant concentrations compared to the other separation processes. The process also offers the benefit of continuous removal of species to a very high degree with cost effectiveness and environmental protection.

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(10) Reardon, E. J.; Wang, Y. A Limestone Reactor for Fluoride Removal from Wastewaters. Environ. Sci. Technol. 2000, 34 (15), 3247−3253. (11) Amer, Z.; Bariou, B.; Mameri, N.; Taky, M.; Nicolas, S.; Elmidaoui, A. Fluoride removal from brackish water by electrodialysis. Desalination 2001, 133 (3), 215−223. (12) Mameri, N.; Lounici, H.; Belhocine, D.; Grib, H.; Piron, D. L.; Yahiat, Y. Defluoridation of Sahara water by small plant electrocoagulation using bipolar aluminium electrodes. Sep. Purif. Technol. 2001, 24 (1−2), 113−119. (13) Hichour, M.; Persin, F.; Sandeaux, J.; Gavach, C. Fluoride removal from waters by Donnan dialysis. Sep. Purif. Technol. 1999, 18 (1), 1−11. (14) Kass, A.; Gavrieli, I.; Yechieli, Y.; Vengosh, A.; Starinsky, A. The impact of freshwater and wastewater irrigation on the chemistry of shallow groundwater: a case study from the Israeli Coastal Aquifer. J. Hydrol. 2005, 300 (1−4), 314−331. (15) Xing, Y.; Chen, X.; Yao, P.; Wang, D. Continuous electrodeionization for removal and recovery of Cr(VI) from waste water. Sep. Purif. Technol. 2009, 67, 123−126. (16) Bergmann, M. E. H.; Iourtchouk, T.; Rittel, A.; Zuleeg, H. Feasibility studies of discontinuous electro-regeneration processes in environmentally-friendly plating for chromate separation from a binary system. Electrochim. Acta 2009, 54 (9), 2417−2424. (17) Dermentzis, K. Removal of nickel from electroplating rinse waters using electrostatic shielding electrodialysis/electrodeionization. J. Hazard. Mater. 2010, 173 (1−3), 647−652. (18) Fu, L.; Wang, J.; Su, Y. Removal of low concentrations of hardness ions from aqueous solutions using electrodeionization process. Sep. Purif. Technol. 2009, 68 (3), 390−396. (19) Glueckauf, E. Electro-deionization through a packed bed. Br. Chem. Eng. 1959, 4, 646−651. (20) Walters, W. R.; Weiser, D. M.; Marek, L. Y. Concentration of Radioactive Aqueous Wastes. Electromigration Through Ion-Exchange Membranes. Ind. Eng. Chem. 1955, 47 (1), 61−67. (21) Neumeister, H.; Fü rst, L.; Flucht, R.; Nguyen, V. D. Electrodeionization, High-Purity Water by Electrochemical Treatment. Ultrapure Water 1996, 13, 60−64. (22) Ganzi, G. C.; DiMascio, F.; Giuffrida, A. J.; Wilkins, F.; Springthorpe, P. Electrodeionization Apparatus and Method. U.S. Patent 5,868,915, 1999. (23) Grebenyuk, V. D.; Chebotareva, R. D.; Linkov, N. A.; Linkov, V. M. Electromembrane extraction of Zn from Na-containing solutions using hybrid electrodialysis-ion exchange method. Desalination 1998, 115 (3), 255−263. (24) Linkov, N. A.; Smit, J. J.; Linkov, V. M.; Grebenyuk, V. D. Electroadsorption of Ni2+ ions in an electrodialysis chamber containing granulated ion-exchange resin. J. Appl. Electrochem. 1998, 28 (11), 1189−1193. (25) AlMarzooqi, F. A.; Ghaferi, A. A. A.; Saadat, I.; Hilal, N. Application of Capacitive Deionisation in water desalination: A review. Desalination 2014, 342, 3−15. (26) Arar, Ö .; Yüksel, Ü .; Kabay, N.; Yüksel, M. Various applications of electrodeionization (EDI) method for water treatmentA short review. Desalination 2014, 342, 16−22. (27) Selegny, E.; Korngold, E. Method of separation of ions from a solution. U.S. Patent 3,686,089, 1972. (28) Nagasubramanian, K. Desalting Aqueous Streams via Filled Electrodialysis. U.S. Patent 6,017,433, 2000. (29) Parsi, E. J. Apparatus for the removal of dissolved solids from liquids using bipolar membranes. U.S. Patent 4,871,431, 1989. (30) Thate, S.; Specogna, N.; Eigenberger, G. A Comparison of Different EDI Concepts used for the Production of High-Purity Water. Ultrapure Water 1999, 16, 42−56. (31) Popat, K. M.; Anand, P. S.; Dasare, B. D. Selective removal of fluoride ions from waterby the aluminum form of the aminomethylphosphonic acid-type ion exchanger. React. Polym. 1994, 23, 23−32.

ASSOCIATED CONTENT

S Supporting Information *

Details of the chemical, structural, and physiochemical characterization and membrane stability (sections S1−S3), FTIR spectra for ion-exchange membranes (Figure S1), and a fluoride uptake study using resin beads (Table S1). This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] or [email protected]. Fax: +91-0278-2566970. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS V.K. is grateful to Department of Science and Technology, New Delhi, India, for providing financial support under the WTI scheme. Authors are also grateful to the Analytical Discipline and Centralized Instrument facility, CSMCRI, Bhavnagar, India, for instrumental support.

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REFERENCES

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DOI: 10.1021/acs.iecr.5b00369 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.iecr.5b00369 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX