ros

deEngi

King Adbul Aziz City for Science and Technology, Saudi Arabia

water hthe feeduccessfuignican

Available online 21 November 2014

IX), that would reduceturn would essentiallye desalination, becausetly reject the sulphate

Desalination 363 (2015) 4450

Contents lists available at ScienceDirect

Desalin

j ourna l homepage: www.e laround the world [2]. However, the cost-effectiveness of these technol-ogies is still hampered by high energy consumption [3]. Thereforethe development of a technology capable of producing fresh water by

ions and operate at signicantly lower transmembrane pressurescompared with reverse osmosis membranes, can be used for waterdesalination [4].efforts are focused on suitable methods to obtain freshwater by seawater or brackish water desalination and various desalination technol-ogies, including thermalmulti-stage ash distillation and reverse osmo-sis, which have been increasingly used to enhance a fresh water supply

into divalent sulphate ions using ion-exchange (the osmotic pressure of the treated feed and inreduce the energy required for further membrannanoltration (NF) membranes, which efcienKeywords:DesalinationAnion exchange resinSulphate/chloride exchangeOsmotic pressure

exchange resin the higher chloride over sulphate selectivity. Exhausted IX resins were successfully regeneratedusing 0.2MNa2SO4 solution andmultiple regeneration/saturation cycles proved that this did not affect the resin'sperformance on chloride ion removal. It was shown that the osmotic pressure of sea water was signicantlyreduced after SO4/Cl ion exchange. Due to the drop of osmotic pressure lower energy consuming nanoltrationmembranes compared with reverse osmosis membranes might be used for salty water desalination after IXtreatment.

2014 Elsevier B.V. All rights reserved.

1. Introduction

A sharp growth in theworlds' population coupledwith urbanizationhas resulted in a rapidly increased demand for fresh water [1]. A lot of

desalting brackish and/or seawater at the lowest possible cost is ofcrucial importance.

In this work we have studied the sulphatechloride exchange insaline solutions. If monovalent chloride ions of salty water convertcontent in feed water and the higher the substitution of hydrogen atoms in amine functional group of anion Corresponding author at: Centre forWater Advanced TResearch (CWATER), College of Engineering, SwanseaUnivKingdom.

E-mail address: n.hilal@swansea.ac.uk (N. Hilal).

http://dx.doi.org/10.1016/j.desal.2014.11.0160011-9164/ 2014 Elsevier B.V. All rights reserved.been studied both on laboratory and pilot scales. It was found that sulphatechloride exchange is very fast inaqueous solutions and that the feed salt concentration and the nature of the functional group of the resin playan important role in this process. It was shown that the chloride/sulphate separation factor depends on saltReceived in revised form 16 November 2014Accepted 18 November 2014 Sulphate/chloride ion exchange in saline Sulphatechloride exchange depends on Exhausted anion exchange resins were s The osmotic pressure of sea water was s

a r t i c l e i n f o

Article history:Received 14 September 2014as been studied both on laboratory and pilot scales.salt concentration and the nature of the functional group of the resin.lly regenerated using 0.2 M Na2SO4 solution.tly reduced after SO4/Cl ion exchange.

a b s t r a c t

Removal of chloride ions from saline water with seven different ion-exchange (IX) resins in sulphate form hasH I G H L I G H T SA combined ion exchangenanoltration pI. sulphatechloride ion-exchange in saline

Nidal Hilal a,b,, Victor Kochkodan b, Hasan Al Abdulgaa Centre for Water Advanced Technologies and Environmental Research (CWATER), College ofb Qatar Environment and Energy Research Institute (QEERI), Dopha, Qatarc College of Engineering, King Faisal University, Al Ahsa, Saudi Arabiadechnologies and Environmentalersity, Swansea SA2 8PP, Unitedcess for water desalination:olutions

r c, Stephen Mandale a, Saad A. Al-Jlil d

neering, Swansea University, Swansea SA2 8PP, United Kingdom

ation

sev ie r .com/ locate /desa lMany researchers have tested IX resins for the removal of chlorideions, but in exchange of anions other than sulphate [58]. For example,the removal of chloride, nitrate and sulphate ions from aqueous solu-tions with amacroporous resin Amberlite IRN9766 in hydroxyl formwasstudied by Dron and Dodi [5]. It was shown that Langmuir adsorption

isotherms provide a good estimation of the sorption capacity on thecontrary to Freundlich and DubininRadushkevitch models.

The strongly basic ion exchanger Amberlite IRA-420 resin in OH formhas been used for chloride ion removal from chloride-polyethyleniminesolution at different temperatures to evaluate the possibility to apply theIX technology to convert the polyethylenimine occulant in chlorideform into an adhesive product for printing applications [6]. The equilib-rium isotherms of chloride ions in aqueous solution on Amberlite IRA-420 have been obtained and the kinetic studies indicated that the chlo-ride ions are slowly removed when the polyethylenimine is in solution

has been studied by Boari et al. [10,11]. It was shown that the selectivity

It should bementioned that Purolite A500TLSO4, Purolite A400TLSO4and Ambersep 900SO4 resins are available in SO42 form, while PuroliteA850 resinwas shipped in Cl form and it was transferred to SO42 formby treatment with 2 M H2SO4.

Purolite A109, Purolite A149S and Purolite A111 resinswere provid-ed in free base form and according to a procedure suggested by themanufacture the resins were treated with 5 wt.%. Na2SO4 and washedwith distilledwater to convert the resin from free base to sulphate form.

Purolite A500TLSO4, Purolite A850, Purolite A109, Purolite A149S,Purolite A111 and Ambersep 900SO4 are macroporous resins, while

45N. Hilal et al. / Desalination 363 (2015) 4450for the bivalent ion depends strongly on the basicity of the resin and theafnity of every resin for the sulphate ion increases with the dilution ofthe aqueous phase andwith the equilibrium temperature. The obtainedresults showed that in heterovalent exchange processes an importantrole is played by the phenomena connected with the electrostaticinteractions.

Direct sulphatechloride ion exchange for removal of chloride ionsfromwater has been studied by few investigators. Sarkar and SenGupta[12] illustrated that sulphate/chloride selectivity depends on degree ofthe substitution of hydrogen atom in the amine functional group ofthe anion exchange resin. For most of their experiments Purolite A850anion-exchange resin of a gel type with quaternary ammonium func-tional group was used.

The aim of this work is to use various commercial anion exchangeresins and test their performance in exchange with chloride ions atdifferent water salinities. The IX studies were carried out in batch andcontinuous modes to investigate the sulphatechloride exchange equi-librium, effect of resin dosage and operating conditions on the IX pro-cess and on the shape of breakthrough curves of the resins. For therst time we have used two mutually interlinked routes to study sul-phatechloride exchange in aqueous solutions, which included boththe experimental studies on a laboratory scale and further scaling upand optimization of a pilot scale IX system.

2. Materials and methods

2.1. IX resins

Seven IX resins, Purolite A500TLSO4, Purolite A400TLSO4, PuroliteA850, Purolite A109, Purolite A149S, Purolite A111 and Ambersep900SO4 which contain quaternary, tertiary, secondary and primaryaminogroups in the polymer matrix have been used in this work. Thecharacteristics of the resins are presented in Table 1.

Table 1Physical and chemical characteristics of IX resins used in the study.

IX resin Polymer matrix

Purolite A500TLSO4 Polyacrylic crosslinked with divinylbenzeneAmbersep 900SO4 Polystyrene crosslinked with divinylbenzenePurolite A400TLSO4 Polystyrene crosslinked with divinylbenzenePurolite A109 Polystrene crosslinked with divinylbenzenePurolite A149S Polystrene crosslinked with divinylbenzenePurolite A111 Polystrene crosslinked with divinylbenzenePurolite A850 Polyacrylic crosslinked with divinylbenzenedue to the ionic pair formation.The layered double hydroxides such ZnAlNO3 containing nitrate as

the interlayer anion has been studied as an anion exchangermaterial toremove chloride ions from aqueous solution [9]. The effect of dosage ofIXmaterial, solution pHand temperature on the removal efciency havebeen investigated. It was found that the inuence of solution pHwasnotvery signicant in the range 5.08.0, and the rate of anion-exchange in-creases upon raising the temperature of aqueous solution.

Chloridesulphate exchange for sulphate removal from the seawater fed to an evaporation plant by means of anion exchange resinsPurolite A400TLSO4 is in a gel form.

2.2. Batch studies with IX resins

The batch studies with IX resins were performed using NaClsolutions of various concentrations, considering that sodium chloride(i.e. Na+ and Cl ions) is the primary constituent of brackish water orsea water. NaCl stock solution (32.0 g/L) was prepared by weighingand dissolving an appropriate amount of NaCl salt in Millipore-Qwater. The testing solutions were prepared by an appropriate dilutingof the stock NaCl solution. The pH values of the solutions were about7, as was measured with a JenWay 3540 pH metre.

For batch IX studies, weighted amounts of air-dried sulphate-formsof the resins were added in NaCl solutions with concentrations of30550 meq/L. Then the samples were agitated with a shaker (Innova44, New Brunswick Scientic) at a constant speed of 150 rpm for0.124.0 h at room temperature. With time, 0.51.0 mL aliquots wereperiodically collected and analyzed to determine contents of Cl andSO42 ions in the probes using an ion chromatograph (Dionex IC900)with AS14A (4 mm) anion-exchange column.

The removal efciency of Cl ions with IX resins was calculated as:

Removal efficiency c0c =c0 100%;

where c0 and c are chloride concentrations (mg/L) in the solution beforeand after IX treatment.

2.3. Column studies with IX resins

Column IX tests were performed to elucidate a shape of break-through curves of IX resins and to evaluate the effect of operatingconditions for optimization of SO42/Cl exchange process. A glass chro-matographic type column with an internal diameter of 2.0 cm and thecolumn aspect ratio (height: width) of 20:1 was used for theseexperiments. The feed solution was delivered to the column using aperistaltic pump (Watson-Marlow 101 U/R) at a ow rate of 0.120.45 mL/s. From the outlet of the column, the efuent fractions of20 mL each were collected and analyzed with IC.

2.4. Pilot scale IX system

To progress the experimentalwork to pilot scale trials a pilot scale IXsystem has been designed and built. The process and instrumentationdiagram (P&ID) of the designed IX system is presented in Fig. 1. The sys-tem is constructed from polyvinylchloride pipe work and two 100 L

Functional group Shipped form Resin particle size

Quaternary ammonium SO42 425850 mTrimethyl ammonium SO42 3001200 mQuaternary ammonium SO42 425850 mPrimary amine Free base 4251000 mSecondary amine Free base 4251200 mTertiary amine Free base 3001200 mQuaternary ammonium Cl 3001200 m

a pi

46 N. Hilal et al. / Desalination 363 (2015) 4450poly-glass IX columns. Three large capacity tanks (1000 L) are used tostore and supply the feed, regeneration and rinse solutions requiredfor IX operation. A speed controllable pump P3 and xed speed

Fig. 1. P&ID ofpumps P4 and P5 have been used for delivering the solutions to the IXcolumns. All of the equipment is supported on a stainless steel framemounted on castors. Performance monitoring is facilitated by inclusionof a owmetre and a pressure gauge linked back to a central display onthe control panel.

The designed pilot IX rig for water desalination have been used tostudy the effect of ow rate through the IX column, the resins loadingand feed salinity on the efciency of sulphate/chloride exchangeprocess.

Osmotic pressure of saline water before and after IX treatmenthas been measured with Gonotec Osmomat 030 osmometer (GonotecGmbH, Germany).

3. Results and discussion

3.1. Batch studies on sulphatechloride exchange with IX resins

A set of experimentswere conducted to determine the time requiredfor IX resin in sulphate form to reach SO42/Cl equilibrium in salinewater in accordance with the following reaction:

(RN+)2SO42+ 2NaCl 2(RN+)Cl+ SO42+ 2Na+,

where (RN+)2SO42 is a polymer matrix of IX resin in sulphate form.It was found that the chloridesulphate exchange proceeds very fast

in aqueous solutions of high salinity. For example, as seen in Fig. 2, only510 min is needed to reach SO42/Cl equilibrium in 10 g/L NaClsolution. The chloride removal efciency after equilibrium is in therange of 5459% for all three resins. Purolite A500TLSO4 managed toremove 59% of chloride ions in the solution, while Purolite A400TLSO4and Ambersep900SO4 removed 56% and 54% respectively.The very fast kinetics of sulphatechloride IX process suggests thatin aqueous solutions of high salinity IX resistances from diffusion ofthe counterions both through a liquid lm surrounding the IX resin in

lot IX system.solution (Nernst lmwith no convection) and inside IX resins are insig-nicant. This assumption is conrmed by the data presented in Fig. 3. Ascan be seen from this gure, the prolonging of IX treatment from 1 h to42 h did not practically lead to increase the removal of chloride ionsfrom water.

The dependencies of dosage of Ambersep900SO4, Purolite A500TLSO4and Purolite A500TLSO4 resins on concentration of Cl and SO42 ions infeed water at IX treatment of NaCl solutions over a concentration rangeof 1.032.0 g/L are presented in Fig. 4. As expected, a content of chlorideions in the feed solutions decreaseswith an increase of the resin dosage.This is attributed to higher IX capacitywith an increase of the resin load-ing. Addition ofmore resin beadswill increase the total number of avail-able exchange sites and subsequently, the capacity to take in more

0

1000

2000

3000

4000

5000

6000

7000

0 100 200 300 400 500Time, min

Cl- C

once

ntra

on,

mg/

L Purolite A500TLSO4

Purolite A400TLSO4

Ambersep 900SO4

Fig. 2. Concentration of chloride ions over time during IX treatment of 10.0 g/L NaCl solu-tion with Purolite A500TLSO4, Purolite A400TLSO4 and Ambersep 900SO4 resins.

chloride ionswill increase. It is seen that, all resins performed quite sim-ilarlywith 1015% variation between them in chloride removal efcien-cy. Nevertheless, Purolite A500TLSO4 resin managed to outperform theother resins in the chloride removal tests.

It might be also seen in Fig. 4 that chloride removal fromwater withresins increases with a decrease of feed salinity and, for example, forPurolite A500SO4 resin the removal reaches 80, 68, 54 and 32% forNaCl concentrations of 1.0; 5.0; 10.0; and 32.0 g/L respectively.

3.2. Effect of amine functional group in IX resins on SO42/Cl exchange in

saline conditions

The relative preference of chloride over sulphate ion in IX processwith the anion-exchange resinmay be evaluated using a separation fac-

where YCl and YSO4 denote equivalent fractions of chloride and sulphateions in resin, while XSO4 and XCl are equivalent fractions of sulphate andchloride ions in the aqueous phase, respectively.

To investigate a possibility to manipulate the chloride/sulphate sep-aration factor by controlling the degree of substitution of the hydrogenatom in the amine functional groups we have used Purolite A109,Purolite A149S, Purolite A111 and Purolite AT500SO4 resins, which con-tain primary, secondary, tertiary and quaternary groups in the polymermatrix, respectively. All these resins are ofmacroporous anion exchangetype with polysterene matrix cross-linked with divinylbenzene.

Based on the data on IX equilibrium, the IX isotherms for sulphatechloride exchange have been calculated. The values of separation factorcan be determined from a constant-temperature equilibrium plot ofresin-phase concentration of chloride ion versus its aqueous-phase con-centration as shown in Fig. 5.

As seen in this gure the relative chloride afnity over sulphate fordifferent amine functional groups can be present as Quaternary(Purolite AT500SO4) N Tertiary (Purolite A111) N Secondary (PuroliteA149) N Primary (Purolite A109). It may be concluded that the higherthe substitution of the hydrogen atom in amine functional group byan alkyl group is the higher chloride over sulphate selectivity for theanion exchange resin. The obtained data are in good agreement withprevious studies on anion exchange resins demonstrated that the chem-ical nature of amine functionality in IX resins correlated to divalentmonovalent anion selectivity [12,14,15].

It was found that the efciency of sulphatechloride exchangeessentially depends on the concentration of feed solutions. As seen inFig. 6, a strong base anion exchange Purolite AT500 SO4 resin depictsfavourable isotherms (convex to X-axis) at NaCl concentrationshigher than 0.1 eq./L. At this condition chloride ion, with equivalent

0

5

10

15

20

25

30

0,2 0,5 1 3 5 8

Resin dosage, g/100 ml

Rem

oval

, %

42h

1h

Fig. 3. Removal of chloride ions from 32.0 g/L NaCl solution after IX treatment withAmbersep 900SO4 resin at various resin dosages. Contact time is 1 h and 42 h.

47N. Hilal et al. / Desalination 363 (2015) 4450tor SO4Cl , which represented as [13]:

ClSO4 YClXCl

XSO4YSO4

0

20

40

60

80

100

0 2 4 6Resin dosage, g

Rem

oval

ee

cien

cy,

%

A500TLSO4

A400TLSO4

Ampersep 900a)

0

20

40

60

80

0 2 4 6Resin dosage, g

Rem

oval

ee

cien

cy, %

A500TLSO4

A400TLSO4

Ampersep 900

c)

Fig. 4. Removal of Cl ions in (a) 1.0 g/L; (b) 5.0 g/L; (c) 10.0 g/L; (d) 32.0 g/L NaCl solutions atfractions on the resin and in the solution plotted on Y and X axes, is pre-ferred to sulphate ion during the IX process. At NaCl concentration inthe solution of 0.02 eq./L the resin depicts unfavourable isotherm(convex to Y-axis) that means that sulphate ions are preferred to chlo-ride ions. This phenomenon of reducing preference for higher-valent

0

20

40

60

80

0 1 2 3 4 5 6Resin dosage, g

Rem

oval

ee

cien

cy, %

A500TLSO4

A400TLSO4

Ampersep 900

b)

0

10

20

30

40

0 2 4 6Resin dosage, g

Rem

oval

ee

cien

cy, %

A500TLSO4

A400TLSO4

Ampersep 900

d)different dosages of Purolite A500TLSO4, Purolite A400TLSO4 and Ambersep 900SO4 resins.

of IX resin proceeds faster (a breakthrough point shifts to smaller BV

0,01

0,1

1

10

0 0,1 0,2 0,3 0,4 0,5

NaCl concentraon, eq/L

Sepa

rao

n fa

ctor

AT500

A111

A149

A109

Fig. 5.SO4Cl separation factor for Purolite resinswith different amino groups at various feedNaCl concentrations.

0

800

1600

2400

3200

0 5 10 15 20 25 30Bed volume

C, m

eq/l Chloride (3)

Sulphate (3)

Chloride (2)

Sulphate (2)

Chloride (1)

Sulphate (1)

Fig. 7. Breakthrough curves of chloride and sulphate ions during ltration of 5 g/L NaClsolution through a column with (1) Purolite A400TLSO4, (2) Ambersep 900SO4 and(3) Purolite A500TLSO4 resins.

48 N. Hilal et al. / Desalination 363 (2015) 4450ions with increasing ionic strength of the solution has been calledelectroselectivity and it might be explained in terms of the Donnanpotential [16]. As the aqueous phase dilution increases the Donnanpotential attracts the mobile charges with a force that is proportionalto their charge density. At low feed concentrations therefore, the diva-lent SO42, ion will be preferred to the Cl ion. The absolute value ofDonnan potential decreases as the aqueous concentration increasesandwill eventually become zero at certain values of the concentrations.These values are typical for each particular resin and once they areexceeded, there will be an inversion of selectivity when the separationfactor SO4Cl = 1.

As seen in Fig. 6, for the strong base anion exchange resin PuroliteAT500SO4 the reversal of chloridesulphate selectivity occurs at NaClconcentration of approximately 0.1 eq./L. At higher NaCl concentrationthe separation factor SO4Cl N 1 and this means that chloride ion will bepreferred to the sulphate ion for the resin. The higher the solution con-centration, the higher the SO4Cl separation factor (Fig. 5).

3.3. Small scale IX column studies on SO42/Cl exchange

Fig. 7 illustrates the breakthrough curves of Cl and SO4 2.ionswithvarious IX resins during IX treatment of 5 g/L NaCl solution. It is seenthat all the resins were able to remove almost all chloride ions in therst 67 bed volumes (BV) of the feed solution but the breakthroughpoints for the Purolite resins started approximately one BV later thanfor Ambersep 900SO4 resin.

Fig. 8 compares breakthrough curves of chloride and sulphate ions atdifferent NaCl feed concentrations using Purolite A500TLSO4 resin. Asseen in this gure the breakthrough points and the sharpness of thebreakthrough curves are strongly affected by the level of NaCl concen-tration in the feed. At high concentration of NaCl solutions, saturation0

0,2

0,4

0,6

0,8

1

0 0,2 0,4 0,6 0,8X, Cl

Y,Cl

0.1 eq/L

0.02 eq/L

0.2 eq/L

Fig. 6. Chloride IX isotherms for Purolite AT500SO4 resin during treatment of NaCl solu-tions of different concentrations.values), but breakthrough curves for chloride ions are sharper.

3.4. Pilot scale IX column studies on SO42/Cl exchange

An effect of ow rate through the IX column in a range of 1.05.0L/min on chloride removal from feed NaCl solution is shown in Fig. 9.As seen in this gure, the slower ow velocities through the column thesharper the breakthrough curve for Cl ions and the shorter the length ofmass transfer zone. Higher ow rates through the column tend to at-ten the breakthrough curve and lengthen the mass transfer zone.These nding may be explained by the fact that slow ow rate throughthe column facilitates the reaching of ion exchange sites in the resinbeds with targeted chloride ions.

An effect of resin loading in the column in a range of 10.050.0 L onchloride removal from NaCl solution is shown in Fig. 10. As seen in thisgure, an increase in resin dosage sharply elongates the operation timeuntil the breakthrough point of Cl ions takes place in treated water.

3.5. Osmotic pressure of salty water after IX treatment

It is known that osmotic pressure of the solution depends on thenumber of osmotic active particles in the solutions according to theVant-Hoff equation [17]:

nCRT ;

where is osmotic pressure in kPa; n is number of osmotic active parti-cles per mole; C is molar concentration in mol/L; R is universal gas con-stant (8.31441 Nm/molK) and T is temperature in K.

10

0,2

0,4

0,6

0,8

0 5 10 15 20

Bed volume

Rela

ve

conc

entr

aon Chloride, 5 g/L

Sulphate, 5 g/L

Chloride, 10 g/L

Sulphate, 10 g/L

Chloride, 15 g/L

Sulphate, 15 g/L

Chloride, 32 g/L

Sulphate, 32 g/L

Fig. 8. Breakthrough curves of the chloride and sulphate ions during ltration of NaClsolution through the column with Purolite A500TLSO4 resin at various feed concentra-tions, g/L: 5, 10, 15 and 32. Relative ion concentration corresponds to outlet over inlet IXconcentration.

solutions will be produced as NF reject stream, when salty water afterIX treatment will be further desalted with NFmembranes. Na2SO4 solu-tion when passing through an exhausted IX resin in chloride formwould transform it back to the sulphate form according to followingreaction:

2(RN+)Cl+Na2SO4 f (RN+)2SO42+ 2NaCl

where (RN+)Cl is a polymer matrix of IX resin in chloride form.

0

500

1000

1500

2000

2500

3000

0 50 100 150 200 250Time of IX operaon. min

C, m

g/L

1.5 L/min2.5 L/min5 L/min

Fig. 9.Chloride concentrations in the eluent versus time of operation of the IX columnwithPurolite AT500SO4 resin at various ow rates through the column, L/min: 1.5; 2.5 and5.0 Vresin is 10 L. Concentration of NaCl is 2.3 g/L.

0

4000

8000

12000

16000

0 1 2 3 4Bed volume

C, m

-eg/

l

Cl

SO4

a)

2000

2500

Bed volume

, kPa Sea water

b)

Fig. 11. Concentration of chloride and sulphate ions (a) and osmotic pressure of the solu-tions (b) during IX treatment of Swansea Bay sea water with Purolite A500TLSO4 resin.

49N. Hilal et al. / Desalination 363 (2015) 4450If salty water with a high content of chloride ions is passed throughan anion exchange resin in sulphate form then, due to exchange of twochloride ionswith one sulphate ion, the feed after IX treatmentwill havelower osmotic pressure and as a result a lower operating pressuremightbe used to run the further membrane desalination process.

Fig. 11 illustrates the breakthrough curves of Cl and SO4 2.ions andosmotic pressure of the solutions during IX treatment of Swansea Baysea water with Purolite AT500SO4 resin. The total salt content in seawater was 32.0 g/L, the concentrations of sulphate and chloride ionswere 2.43 and 17.46 g/L, respectively. As can be seen in Fig. 11a, almostall chloride ionswere removed from the feed seawater due to exchangewith sulphate ions until a break through point of the IX columnhas beenreached. As a result of efcient SO42/Cl exchange the osmotic pressureof sea water dropped essentially after IX treatment (Fig. 11b). Thisreduction of osmotic pressure gives a possibility to reduce the requiredenergy for further NF desalination of the salinewater after IX treatment,since NF membranes, which efciently reject the sulphate ions andoperate at signicantly lower transmembrane pressure comparedwith RO membranes, can be used for water desalination.

3.6. Regeneration of exhausted IX resins

A need for frequent regeneration using external regenerationsolutions is a weak side of IX when the process is used to treat waterwith a high salt concentration [13]. The IX operational costs may besharply reduced if internal reagent solution is used for regeneration.In this study we have evaluated a possibility to use Na2SO4 solutions

for regeneration of the exhausted IX resins. Such concentrated Na2SO4

0

500

1000

1500

2000

2500

0 50 100 150 200 250

Time of IX operaon, min

C, m

g/L

10 L

20 L

50 L

Fig. 10. Chloride concentrations in the eluent versus time of operation of the IX columnwith Purolite AT500SO4 resin at various resin loading, L: 10, 20 and 50. CNaCl is 2.3 g/L;ow rate through the column is 1.5 L/min.1000

1500

0 1 2 3

Osm

otic

pre

ssur

e IX-treated sea water0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30Bed volume

Rele

vent

conc

entr

aon

Chloride (10 g/L)

Sulphate (10 g/L)

Chloride (28 g/L)

Sulphate (28 g/L)

Chloride (50 g/L)

Sulphate (50 g/L)

Fig. 12. Regeneration of Purolite A500TLSO4 resin with 10.0, 28.0 and 50.0 g/L Na2SO4solutions. Relative ions concentration corresponds to outlet over inlet IX concentration.

The experimental results clearly indicate that the feedwater concen-tration and thenature of the functional groupof the resin play an impor-tant role in the SO42/CI exchange process. It was found that the higherthe substitution of hydrogen atoms in amine functional group of anionexchange resin is the higher chloride over sulphate selectivity andthat the chloride/sulphate separation factor depends on salt content in

[6] M. Carmona, A. Perez, A. de Lucas, L. Rodriques, J.F. Rodriguez, Removal of chlorideions from an industrial polyethylenimine occulant shifting it into an adhesive pro-

[9] L. Lv, P. Sun, Z. Gu, H. Du, X. Pang, X. Tao, R. Xu, L. Xu, Removal of chloride ion from

3000

4000

5000

eq/l Chloride (1 run)

Sulphate (1 run)

50 N. Hilal et al. / Desalination 363 (2015) 4450If successful, using this internal regent would sharply reduce thecost of water desalination because no external regeneration solution isrequired for regeneration of an exhausted IX column after SO42/Cl

exchange.Na2SO4 solutions of concentration of 10.0, 28.0 and 50.0 g/L were

tested for the regeneration of Purolite A500TLSO4 resin. As seen inFig. 12, it took around 25 BV of the 10 g/L Na2SO4 solution to regeneratePurolite A500TLSO4 resin. On the other hand, only 16 BV of the 28 g/LNa2SO4 solution were needed to regenerate the same resin, while50 g/L Na2SO4 solution performed only slightly better and 15 BV wereneeded for regeneration. Hence, Na2SO4 regeneration solution withconcentration of 28 g/L was used for further studies. It may be assumedthat solutions of similar concentrationwould be produced as a retentateduring NF treatment of brackish water with sodium chloride content of2.5 g/L.

To evaluate whether the resins performance changes after theregeneration the IX resins were exhausted and regenerated multipletimes. The multiple breakthrough curves of chloride and sulphate ionswith regenerated Purolite A500TLSO4 resin during treatment of 10 g/LNaCl solution are presented in Fig. 13. After each exhaustion run theresin was regeneratedwith 0.2MNa2SO4 solution. As seen in this gurethe regenerated resin performs very consistently on each run afterregeneration. This nding of reversibility of the sulphatechlorideexchange process is very important because no external regenerationsolution is required for regeneration of exhausted IX column afterSO42/Cl exchange.

4. Conclusions

0

1000

2000

0 2 4 6 8 10 12 14Bed volume

C, Chloride (2 run)

Sulphate (2 run)

Chloride (3 run)

Sulphate (3 run)

Fig. 13. Breakthrough curves of chloride and sulphate ions with regenerated PuroliteA400TLSO4 resin during treatment of 10 g/L NaCl solution (three exhaustion runs).0.2 M Na2SO4 solution has been used for IX resin regeneration after each saturation run.Seven different IX resins, namely Ambersep 900SO4, Purolite A850,Purolite A500TLSO4, Purolite A400TLSO4, Purolite A109, Purolite A149Sand Purolite A111, which contain primary, secondary, tertiary and qua-ternary amino groups in the polymer matrix, were used in the work tostudy sulphatechloride exchange process in saline solutions. It wasfound that sulphatechloride exchange is very fast at saline conditionsand less than 10min is needed to reach the sulphatechloride equilibri-um. Very fast kinetics of sulphatechloride exchange suggests that insalty solutions IX resistances from the liquid phase lm- and intra-particle diffusion are insignicant. It was shown that optimization ofsulphatechloride exchange process may be done by adjusting theow rate through the column.aqueous solution by ZnAlNO3 layered double hydroxides as anion-exchanger, J.Hazard. Mater. 161 (2009) 14441449.

[10] G. Boari, L. Liberti, C. Merli, R. Passino, Exchange equilibria on anion resins, Desalina-tion 15 (1974) 145166.

[11] A. Aveni, G. Boari, L. Liberti, M. Santori, Sulphaste removal and dealkalization onweak resins of the feed water for evaporation desalting plants, Desalination 16(1975) 145149.

[12] S. Sarkar, A.K. SenGupta, A new hybrid ion exchange-nanoltration (HIX-NF) sepa-ration process for energy-efcient desalination: process concept and laboratoryevaluation, J. Membr. Sci. 324 (1) (2008) 7684.

[13] A.A. Zagorodnii, Ion ExchangeMaterials: Properties and Applications, Elsevier, 2007.[14] L. Liberti, D. Petruzzelli, F.G. Helfferich, R. Passino, Chloride/sulfate ion exchange

kinetics at high solution concentration, React. Polym. 5 (1987) 3747.[15] G. Boari, L. Liberti, C. Merli, R. Passino, Study of the SO42/Cl exchange on a weak

anion resin, Ion Exch. Membr. 2 (1974) 5966.[16] F. Helfferich, Ion Exchange, Dover Publications, NY, 1995.[17] A.V. Adamson, A textbook of Physical Chemistry, Academic Pres, 1973.moter using the anion exchange resin Amberlite IRA-420, React. Funct. Polym. 68(2008) 12181224.

[7] P. Del Hoyo, F. Moure, M. Rendueles, M. Diaz, Demineralization of animal bloodplasma by ion exchange and ultraltration, Meat Sci. 76 (3) (2007) 402410.

[8] S. Evans, R. Gomes, Desalination of Rhine River water by ion exchange part 1. Pilotplant studies of lime slurry regeneration, Desalination 19 (1) (1976) 433438.feed water. It was found that Purolite A500TLSO4 resin is themost ben-ecial among the used IX resins for SO42/CI exchange process in salinesolutions.

Saturated IX resins were successfully regenerated using 0.2 MNa2SO4 solution andmultiple regeneration and saturation cycles provedhave no affected on the IX performance.

It was shown that the osmotic pressure of sea water dropped essen-tially after IX treatment and due to such drop NF membranes would beused for furtherwater desalination instead of ROmembranes, which arecurrently used for removal of chloride ions from brackishwater and seawater. Because NFmembranes operate at signicantly lower transmem-brane pressure compared with RO membranes, the required energy formembrane desalination might be essentially reduced.

Acknowledgement

The authors would like to thank King Adbul Aziz City for Science andTechnology for funding this work.

References

[1] The United Nations World, Water Development Report 3: Water in a ChangingWorld, UNESCO Publishing, Paris, 2009.

[2] M.A. Shannon, P.W. Bohn, M. Elimelech, J.G. Georgiadis, B.J. Marinas, A.M. Mayes,Science and technology for water purication in the coming decades, Nature 452(2008) 301310.

[3] M. Elimelech, W.A. Phillip, The future of seawater desalination: energy, technology,and the environment, Science 333 (2011) 712717.

[4] H.A. Abdulgader, V. Kochkodan, N. Hilal, Hybrid ion exchangepressure drivenmem-brane processes in water treatment: a review, Sep. Purif. Technol. 116 (2013)253264.

[5] J. Dron, A. Dodi, Comparison of adsorption equilibrium models for the study of CL,NO3 and SO42 removal from aqueous solutions by an anion exchange resin, J. Haz-ard. Mater. 190 (13) (2011) 300307.m

A combined ion exchangenanofiltration process for water desalination: I. sulphatechloride ion-exchange in saline solutions1. Introduction2. Materials and methods2.1. IX resins2.2. Batch studies with IX resins2.3. Column studies with IX resins2.4. Pilot scale IX system

3. Results and discussion3.1. Batch studies on sulphatechloride exchange with IX resins3.2. Effect of amine functional group in IX resins on SO42/Cl exchange in saline conditions3.3. Small scale IX column studies on SO42/Cl exchange3.4. Pilot scale IX column studies on SO42/Cl exchange3.5. Osmotic pressure of salty water after IX treatment3.6. Regeneration of exhausted IX resins

4. ConclusionsAcknowledgementReferences