This article was downloaded by: [University of Texas Libraries]On: 28 September 2014, At: 07:37Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Separation Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lsst20

Adsorption Behavior of Fluoride Ions on Zirconium(IV)-Loaded Orange Waste Gel from Aqueous SolutionHari Paudyal a , Bimala Pangeni a , Katsutoshi Inoue a , Miyuki Matsueda a , Ryosuke Suzuki a ,Hidetaka Kawakita a , Keisuke Ohto a , Biplob Kumar Biswas b & Shafiq Alam ca Department of Applied Chemistry , Saga University , Honjo , Saga , Japanb Department of Applied Chemistry and Chemical Engineering , Jessore Science andTechnology University , Jessore , Bangladeshc Department of Engineering and Applied Science , Memorial University , St. John's , NL ,CanadaAccepted author version posted online: 22 Aug 2011.Published online: 28 Dec 2011.

To cite this article: Hari Paudyal , Bimala Pangeni , Katsutoshi Inoue , Miyuki Matsueda , Ryosuke Suzuki , HidetakaKawakita , Keisuke Ohto , Biplob Kumar Biswas & Shafiq Alam (2012) Adsorption Behavior of Fluoride Ions onZirconium(IV)-Loaded Orange Waste Gel from Aqueous Solution, Separation Science and Technology, 47:1, 96-103, DOI:10.1080/01496395.2011.607204

To link to this article: http://dx.doi.org/10.1080/01496395.2011.607204

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Adsorption Behavior of Fluoride Ions onZirconium(IV)-Loaded Orange Waste Gel fromAqueous Solution

Hari Paudyal,1 Bimala Pangeni,1 Katsutoshi Inoue,1 Miyuki Matsueda,1

Ryosuke Suzuki,1 Hidetaka Kawakita,1 Keisuke Ohto,1 Biplob Kumar Biswas,2 andShafiq Alam3

1Department of Applied Chemistry, Saga University, Honjo, Saga, Japan2Department of Applied Chemistry and Chemical Engineering, Jessore Science and TechnologyUniversity, Jessore, Bangladesh3Department of Engineering and Applied Science, Memorial University, St. John’s, NL, Canada

Adsorption of fluoride was studied batch wise from aqueous sol-ution by using zirconium(IV)-loaded orange waste gel to achievepractical utility and evaluate the viability of the adsorption gel. Flu-oride adsorption was found to be dependent on solution pH and themaximum adsorption of fluoride was observed at pH 2–4. Themaximum sorption capacity of the gel for fluoride was evaluatedas 1.2mmol/g, which was compared to that of zirconium(IV)-loadedAmberlite 200CT, a strongly acidic cation exchange resin, whichwas only 0.5mmol/g in applied experimental condition. The influ-ence of high concentration of co-existing anions on adsorption of flu-oride was studied to evaluate selectivity and competitiveness offluoride adsorption. The presence of foreign anions such as Cl�,NO�

3 , SO2�4 , and CO2�

3 had no significant effect on fluoride adsorp-tion of the present gel. Adsorption of fluoride from actual wasteplating solution was also carried out, suggesting very effectiveadsorption at a solid/liquid ratio greater than 4 g/dm3. Repeateduse of the gel was also successfully examined over ten cycles ofadsorption-elution-regeneration without any degradation of thegel. These results suggest that the modified orange waste gel is apromising candidate for fluoride adsorption from aqueous solution.

Keywords adsorption; elution; fluoride; orange waste; saponifi-cation; zirconium(IV)-loaded adsorbents

INTRODUCTION

Fluoride is the most abundant, highly electronegative,and geogenic contaminant in groundwater worldwide.The fluoride contamination occurs in a wide range ofindustrial wastewater produced from aluminium and steel

production, refining of niobium and tantalum, electroplat-ing, silicon semiconductor manufacturing, ore beneficia-tion, thermal power production, and fertilizer production(1,2). There are several de-fluoridation processes tested oremployed globally for removal of excessive concentrationof fluoride from water. These include chemical precipi-tation (3), ion exchange (4), electrochemical treatment(5), Donnan dialysis (6,7), and adsorption (8,9). Precipi-tation technology is often used for fluoride removal byadding calcium to recover as CaF2, but this method suffersfrom the limit of fluoride removal, by the solubility pro-duct, to 5mg=dm3. The regulation of fluoride dischargelimit through wastewater in Japan has been strengthenedby lowering the permissible contaminant level from1.5mg=dm3 down to 0.8mg=dm3 in 2001 (10). Thus, thereis an extreme necessity to develop an effective technologyfor the removal and recovery of fluoride from wastewatergenerated after the calcium-precipitation before disposalinto the environmental sources. As environmental pro-tection is becoming an important global problem, bio-sorption has received significant attention as a promisingtechnique for removing dilute concentrations of toxicions.

In recent years, different adsorbents have been reportedfor the adsorption of fluoride: for example, activated car-bon, activated alumina, bone charcoal, metal loaded syn-thetic ion exchangers, lanthanum impregnated gelatin,hydrous layer of bimetal oxide, alumina cement granule(1,11). Because the selectivity of usual anion exchangeresins to fluoride over other anionic species like sulphateand chloride which usually co-exist in water together withfluoride is low according to the well known Hoffmeister’sselectivity series (12) among anionic species, it is difficultto selectively remove small or trace amounts of fluoridefrom excess amounts of other anionic species. Lately,

Received 14 March 2011; accepted 19 July 2011.Address correspondence to Katsutoshi Inoue, Department of

Applied Chemistry, Saga University, Honjo, Saga 840-8502,Japan. Tel.: þ81 952 28 8671; Fax: þ81 952 28 8669. E-mail:inoue@elechem.chem.saga-u.ac.jp

Separation Science and Technology, 47: 96–103, 2012

Copyright # Taylor & Francis Group, LLC

ISSN: 0149-6395 print=1520-5754 online

DOI: 10.1080/01496395.2011.607204

96

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14

significant attention has been drawn to the adsorptiveremoval of fluoride from aqueous solution by developingnew adsorbents loaded with metal ions (13). The use ofwaste biomass, with simple chemical treatment, is a prom-ising technology in the lowering of fluoride concentrationto desired discharge level. The abundant natural occur-rence and presence of large amount of surface functionalgroups make various agricultural wastes a good alternativeto expensive synthetic adsorbents prepared through com-plicated synthetic routes with the uses of various toxic che-micals (14). Various biomasses such as KMnO4 modifiedrice straw carbon (15), Fe (III) loaded cotton (16), grassculture (17), protonated chitosan bead (18), Ca-pretreatedmacrophyte biomass (19), spirogyra species (20), and La(III) loaded adsorbent with various polymer matrices (21)have been investigated for fluoride removal.

In the present paper, the orange waste gel loaded withzirconium(IV) ion was investigated for the effective adsorp-tion of fluoride from aqueous solution. The utilization oforange waste as an adsorbent solves not only the problemof agricultural waste disposal but also the problem of thetreatment of the contaminant like fluoride for economicgain and environmental remediation. Further, its adsorp-tion behavior for fluoride was compared with zirconiu-m(IV) loaded commercially available strongly acidiccation exchange resin, Amberlite 200CT, which is amacro-reticular type of porous resin of polystyrene.

EXPERIMENTAL

Chemicals and Reagents

All chemicals used were of analytical grade and usedwithout further purification. The fluoride stock solution(1000mg=dm3 i.e., 52.63mmol=dm3) was prepared by dis-solving 2.21 g of sodium fluoride (Wako Chemicals, Japan)in 1000 cm3 of de-ionized water. The working solutionswere prepared by diluting the stock solution.

Preparation of Zr(IV)-loaded Saponified Orange Gel

Preparation of orange waste gel and the method ofzirconium loading have been described in detail in ourprevious paper (22). The orange juice residue was kindlysupplied by JA Saga Beverage Co., Ltd., Japan. For thepretreatment, 100 g orange waste was washed with dis-tilled water in order to remove water soluble organiccompounds that hinder the saponification process. Thuspretreated orange waste was then mixed together with8 g of calcium hydroxide and crushed into fine particleswith the help of HITACHI VA-10 juice mixer for thesaponification reaction of methylated ester part of pecticacid in orange waste. The reaction mixture was shakenfor 24 h at 303K after the addition of substantialamount of water to enhance the saponification reactionby lime water. The initial pH of the reaction mixture

was adjusted at around 12 by adding some pellets ofsodium hydroxide. After the saponification, the suspen-sion was washed with distilled water by decantationand filtration until neutral pH and finally dried in a con-vection oven at 343K for overnight. The white materialprepared in this way is calcium containing cationexchange gel, which is termed as saponified orange juiceresidue and abbreviated as SOJR hereafter. Thus pre-pared SOJR was further loaded with zirconium(IV) ionas follows. Three gram of saponified orange gel wastaken in a conical flask along with 500 cm3 of 0.1M(M¼mol=dm3) zirconium oxychloride octahydrate(ZrOCl2 � 8H2O) solution maintained at pH 2.16. Then,the mixture was agitated for 24 h at 303K for completezirconium loading. After filtration, it was washed severaltimes by distilled water followed by hot water wash inorder to remove free zirconium(IV) ion from the gel. Itwas dried in a convection oven at 343K for overnight.The product was ground by mortar and sieved to obtaina particle size of 100–150 mm. The adsorbent prepared inthis way is termed as zirconium(IV) loaded orange juiceresidue, abbreviated as SOJR-Zr hereafter, which wasstocked in a plastic bottle and used at the required time.After the dissolution of 50mg of SOJR-Zr in 10 cm3

aqua regia, the zirconium content in the solution wasanalyzed by using a Shimadzu model ICPS-8100 ICP=AES spectrometer. The total zirconium content in thedry SOJR-Zr was evaluated as 1.62mmol of zirconiu-m(IV) per gram of dry gel.

Preparation of Zr(IV) Loaded Cation Exchange Resin

The sample of 200CT resin was kindly donated byORGANO Corporation, Tokyo, Japan. Three gram of200CT resin was mixed together with 500 cm3 of 0.1Mzirconium(IV) solution at pH 2.16 and stirred for 24 h at303K. The mixture was filtered and the resin was washedwith de-ionized water several times until it reached neutralpH; finally, the sample was dried by using a vacuum drierat 343K for overnight. The product obtained in this way istermed as 200CT-Zr hereafter. Amount of zirconium(IV)content in 200CT-Zr (0.91mmol=g) was evaluated afterthe dissolution of 200CT-Zr in aqua regia solution at solidliquid ratio of 5 g=dm3.

Characterization of Adsorbents

In order to confirm the presence of various functionalgroup, FTIR spectra of Hþ-type SOJR, zirconium(IV)loaded SOJR and zirconium(IV) loaded 200CT resin wereanalyzed by using JASCO-4 1 0 FTIR spectrometer. Thedry powder of the adsorbent was mixed with KBr (spectro-scopic grade) and grounded in a mortar. The powder mix-ture was then pressed to make the transparent pellet forspectroscopic measurement. The spectra were recordedover the range 4000–400 cm�1.

ADSORPTION BEHAVIOR OF FLUORIDE IONS 97

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14

Batch Wise Adsorption Tests

Adsorption tests of fluoride on SOJR-Zr and 200CT-Zrwere carried out in a 50 cm3 conical flask where 25mg ofthe adsorbents and 15 cm3 of 1.57mmol=dm3 fluoride sol-ution at varying pH (1–10) were added and shaken in athermostated shaker (THOMAS thermostatic shakingincubator AT24R) at a speed of 150 rpm at 303K for24 h to attain equilibrium. The pH was adjusted by addingeither 0.1M NaOH or 0.1M HCl. After 24 h of shaking,the mixture was filtered and the filtrate was diluted to therequired volume. The fluoride concentration in the testsolution was measured by using DIONEX Model ICS:1500 ion exchange chromatography. However, leakage ofthe loaded zirconium from both adsorbents was also mea-sured during this test by using a Shimadzu model ICPS-8100 ICP=AES spectrometer. The percentage adsorption(% A) and uptake capacity (q) were calculated accordingto the following equations:

%A ¼ Ci � Ce

Ci� 100 ð1Þ

q ¼ Ci � Ce

W� V ð2Þ

where, Ci and Ce (mmol=dm3) are the initial and equilib-rium fluoride concentrations, respectively, W (g) is theweight of the adsorbent, and V (dm3) is the volume of testsolution.

Isotherm studies of fluoride on both adsorbents wereconducted by varying initial fluoride concentrations (0.5–10mmol=dm3) at pH 2.4. The effect of co-existing anionson the fluoride adsorption on SOJR-Zr, on the other hand,was studied at varying pH using test solutions containingten times higher concentration of other co-existing anions(NO�

3 , Cl�, SO2�

4 and CO2�3 ) using their respective sodium

salts. The adsorption test of fluoride from actual wasteplating solution on SOJR-Zr was carried out using a sam-ple solution supplied from a plating company in Japan atdifferent adsorbent dosage ranging from 0.5–10 g=dm3.The adsorption-elution cycle test was performed to investi-gate the repeated use of SOJR-Zr in which 25mg ofSOJR-Zr along with 15 cm3 feed solution (1.57mmol=dm3) was shaken at 303K for 24 h for the adsorption of flu-oride. The elution test of the adsorbed fluoride was carriedout by shaking 15 cm3 of 0.1M NaOH together with 25mgof fluoride adsorbed SOJR-Zr under the similar conditionsas in the adsorption test. The leakage test of the loaded zir-conium from SOJR-Zr was carried out by shaking 10 cm3

of fluoride solution along with 10mg of SOJR-Zr byvarying fluoride concentrations (0.5–8mmol=dm3) at dif-ferent pH.

RESULTS AND DISCUSSION

Characterization of the Adsorbents

Orange waste is rich in pectin compounds that can bechemically modified to SOJR by lime water which func-tions as anion exchanger once it is loaded with multivalentmetal ions like zirconium(IV) ion. Since SOJR is also akind of Ca2þ-type pectic acid gel, Hþ-type SOJR gel wasprepared by washing SOJR with 0.1M HCl in order toinvestigate the effect of loaded metal ions in the FTIR spec-tra. Figure 1 shows the FTIR spectra of Hþ-type SOJR,SOJR-Zr, and 200CT-Zr. The FTIR spectrum of Hþ-typeSOJR shows the intense peak at 3436 cm�1 which is due to-OH stretching vibration of polymeric compounds. Thepeak at 2888.28 cm�1 is due to -CH stretching vibration.The peak at 1714.21 cm�1 is due to the stretching vibrationof carboxyl group. In SOJR-Zr, the peak at 1714.21 cm�1

in H-SOJR is shifted to 1651.25 cm�1. The coordinationof carboxyl group with zirconium(IV) ion weakens theC=O bond strength and stretching vibration shift to lowerfrequency. In 200CT-Zr, the peak at around 1140 to1270 cm�1 is due to the S=O stretching vibration. Thetwo peaks at 1082.21 and 1051.13 cm�1 is indicative ofthe presence of sulphonate salt i.e., sulphonate salt of zirco-nium(IV) ion.

Effect of Contact Time

The test to examine the effect of contact time on fluorideadsorption on SOJR-Zr and 200CT-Zr were carried out inthe range of 5min to 24 h with an initial fluoride concen-tration of 0.84mmol=dm3 at 303K to find the minimumcontact time to reach adsorption equilibrium as shown inFig. 2. It is evident from this figure that the adsorptionrate was so fast that 0.25 and 0.19mmol=dm3 of fluoridewas found to be adsorbed on SOJR-Zr and 200CT-Zr,

FIG. 1. Fourier transform infrared spectra of (a) SOJR-H, (b)

200CT-Zr, and (C) SOJR-Zr.

98 H. PAUDYAL ET AL.

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14

respectively, in the first 2 h, after which the adsorption ratestarted to decrease and the adsorption gradually attainedequilibrium within 8 h for both the adsorbents. Conse-quently, in the subsequent work, 24 h was taken as the con-tact time for fluoride adsorption to ensure absoluteequilibrium.

Effect of pH on the Adsorption of Fluoride

The pH of the aqueous solution is an important para-meter that controls the adsorption at the solution-adsorbentinterface. Therefore, the effects of equilibrium solution pHon fluoride adsorption by SOJR-Zr and 200CT-Zr wereinvestigated at different pH values ranging from 1 to 10by keeping other parameters (contact time, initial fluorideconcentration, adsorbent dosages, and temperature) con-stant as shown in Fig. 3. It is apparent from this figure that% adsorption of fluoride increased with increasing pH in thepH range of 1–3 for both adsorbents and then decreasedwith further increase in pH. The low adsorption at lowpH (pH< 2) may be due to the formation of weakly ioniz-able hydrofluoric acid (pKa of HF¼ 3.2), which is difficultto be adsorbed. The maximum fluoride adsorption wasfound to occur at pH 2–4 for both adsorbents tested.Consequently, pH 2.4 was termed as the optimum pH andthe isotherm experiments, which will be described in theSection titled ‘‘Adsorption Isotherms of Fluoride’’, werecarried out at this pH. As will be described in the subsequentsection in detail, the adsorption of fluoride on both adsor-bents takes place via ligand exchange reaction betweenhydroxyl ions present in the coordination sphere of loadedzirconium(IV) and fluoride ions in the aqueous solution.Consequently, the decrease in % adsorption in the higherpH range can be attributed to the competitive adsorptionof hydroxyl ions for the adsorption sites.

In the previous literatures (1,13,16) regarding fluorideadsorption using metal-loaded adsorbents, less attention

had been drawn to the leakage of the loaded metal ions.Since the leakage of the loaded metal ions from the adsor-bents is supposed to deteriorate the uptake capacity, theleakage of the loaded zirconium was measured at varyingpH in this study in order to investigate the stability as wellas reusability of the adsorbents. As shown in Fig. 3, it wasobvious that the extent of leaking of zirconium(IV) from200CT-Zr resin was 45% (at pH 1.5) while that fromSOJR-Zr was very insignificant throughout the tested pHrange.

Mechanism of Fluoride Adsorption

It is inferred that, in the loading of zirconium(IV) onSOJR, carboxyl groups contained in SOJR forms stable5-membered chelate with zirconium(IV) ion while, in thecase of 200CT, dissociated sulfonic groups electrostaticallyinteract with zirconium(IV) ion. Here, among four positivecharges of zirconium(IV) ion, although one or two areinferred to be neutralized by carboxylic or sulfonic groups,others are not neutralized by these functional groups due tostrong steric hindrance of polymer matrices but are neutra-lized by anionic species like hydroxyl ions existing in theaqueous solution. Since the zirconium(IV) ion tends to beextensively polymerized and hydrolyzed even at very lowconcentration and it converts into tetranuclear [Zr4(OH)8(H2O)16]

8þ and octanuclear [Zr8(OH)20(H2O)24]12þ ions

(23), a lot of hydroxyl ions as well as water molecules are,therefore, available in coordination sphere of zirconiu-m(IV), which facilitates ligand exchange with fluorideanions. The mechanism of fluoride adsorption is proposedtogether with elution as shown in Scheme 1. The adsorptionof fluoride by 200CT-Zr also takes place by the similarmechanism as in the case of SOJR-Zr. The equilibriumpH of the solution was found to be increased after the

FIG. 3. Effect of pH on the adsorption of fluoride using (.) SOJR-Zr

and (~) 200CT-Zr resin and subsequent leakage of loaded Zr(IV) from

(�) SOJR-Zr and (D) 200CT-Zr resin. Conditions: Dry weight of the

adsorbent¼ 25mg, volume of test solution¼ 15 cm3, concentration of flu-

oride ion¼ 1.57mmol=dm3, contact time¼ 24 h, temperature¼ 303K.

FIG. 2. Effect of contact time on fluoride adsorption using SOJR-Zr and

200CT-Zr. Conditions: Dry weight of the adsorbent¼ 25mg, volume of

test solution¼ 15 cm3, fluoride concentration¼ 0.84mmol=dm3, pH¼ 2.4,

temperature¼ 303K.

ADSORPTION BEHAVIOR OF FLUORIDE IONS 99

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14

adsorption of fluoride for both adsorbents, indicating thathydroxyl ions are released during adsorption, which furthersupports the mechanism mentioned above.

Adsorption Isotherms of Fluoride

The adsorption isotherms of fluoride on SOJR-Zr and200CT-Zr are depicted in Fig. 4(a), which shows

classic L-type isotherms with steep initial portions at lowconcentration and plateau at high concentration of fluor-ide, suggesting that monolayer adsorption takes place onboth adsorbents. Consequently, the data was analyzed onthe basis of the Langmuir adsorption isotherm (Fig. 4(b))to evaluate the maximum sorption capacity and bindingconstant for both adsorbents as listed in Table 1.

As shown in this table, the adsorbent prepared inexpen-sively from orange waste exhibited much higher adsorptioncapacity for fluoride than a commercially available syn-thetic resin (200CT-Zr). High fluoride uptake capacityand almost no Zr-leakage even at low pH make SOJR-Zra promising candidate for fluoride adsorption. Althoughit is difficult to compare the SOJR-Zr gel directly withother adsorbents because of different experimental con-ditions, it is found that the adsorption capacity for fluorideby the present adsorption gel is reasonably higher thanother adsorbents as shown in Table 2.

Effect of Competing Anions

The fluoride contaminated water contains not only flu-oride but also other anions like CO2�

3 , SO2�4 , NO�

3 , andCl� that can compete with the fluoride during sorption.Hence, the adsorption behavior of fluoride on SOJR-Zrwas investigated in the presence of these competing anionsin large excess. Figure 5 shows the adsorption of fluoride(1.57mmol=dm3) on SOJR-Zr in the presence of 10 timeshigher concentration of co-existing anions as a functionof equilibrium pH. This figure clearly indicates that theadsorption of fluoride on SOJR-Zr is not influenced bythe excess concentration of other anions, that is, fluoridecan be selectively removed by SOJR-Zr, which is a distinctadvantage over other adsorbents reported earlier(16,19,24,25).

SCH. 1. Mechanism of fluoride adsorption and its desorption using alkaline solution.

FIG. 4. (a) Adsorption isotherms of fluoride on SOJR-Zr and 200CT-Zr

and (b) corresponding Langmuir plots. Conditions: Dry weight of adsor-

bent¼ 25mg, volume of fluoride solution¼ 15 cm3, initial pH of the

solution¼ 2.4, contact time¼ 24 h, temperature¼ 303K.

TABLE 1Langmuir parameters for the adsorption of fluoride by

SOJR-Zr and 200CT-Zr

Adsorbents qmax (mmol=g) b (dm3=mmol) R2

SOJR-Zr 1.2 120.5 0.98200CT-Zr 0.5 7.3 0.99

100 H. PAUDYAL ET AL.

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14

Adsorption of Fluoride from Actual Plating Solution

Figure 6 shows the effect of adsorbent dosage on %adsorption of fluoride from actual waste plating solutioncontaining 38.5mg=dm3 that is, 2.02mmol=dm3 fluorideat pH 3 by using SOJR-Zr. It is evident from this figurethat fluoride adsorption increases with increasing solid=liquid ratio up to 3 g=dm3 and at solid=liquid ratio greaterthan 4, a complete adsorption of fluoride was achieved.

With the increase in adsorbent dosage, the number ofactive sites per unit volume of suspended solutionincreases, which leads to the increase in the adsorption offluoride. In spite of the presence of other anions (Cl�:29.2, SO2�

4 : 24.2 and PO3�4 : 12.9mg dm�3) and metal ions

(Ca: 550, Si: 100, Ni: 73, Al: 55, Fe: 51, Zn: 13, Ti: 4.2,and Cu: 2.4mg dm�3) in the actual plating solution, fluor-ide was found to be preferentially removed by SOJR-Zrunder the stated experimental conditions. This resultensures to meet the Japanese environmental standard forfluoride (0.8mg=dm3 or 0.042mmol=dm3). Moreover, zir-conium leakage from the gel was found to be very insignifi-cant in this case. Thus, SOJR-Zr can be expected as anexcellent adsorption gel to treat the fluoride-containingwaste effluent solution for safety disposal.

Leakage of Loaded Zirconium(IV) from the Gel

No leakage of loaded zirconium(IV) from the gel duringadsorption and elution should be ensured for the reuse andregeneration of adsorption gel. Figure 7 shows the percent-age leakage of the loaded zirconium(IV) from SOJR-Zr asa function of fluoride concentration at various pH. Theresult shows that the leakage increases with increasing flu-oride concentration above 1.57mmol=dm3 at low pH whileit is negligible (less than 1%) or insignificant even at highfluoride concentration in basic pH range, suggesting thatthe use of dilute alkali solution for the elution of fluoridefrom saturated gel has no problem for regeneration pur-pose while the adsorption should be carried out for diluteconcentration of fluoride (lower than 1.57mmol=dm3) atlow pH. Zirconium(IV) ions in SOJR-Zr is so effectivelyimmobilized on polymer matrices with carboxylic groupand oxygen atom of pyranose ring of orange pectic acidthus a negligible leakage is observed even at low pH(2–3) in the absence of fluoride ions. But, in the presenceof fluoride ions, the Zr-O bond is weakened by the strong

TABLE 2Comparison of the maximum adsorption capacity for

fluoride on different adsorbents

Adsorbents pHTemp.(K)

qmax

[mmol=g] Ref.

SOJR-Zr gel 2.4 303 1.2 Presentwork

200CT-Zr resin 2.4 303 0.5 Presentwork

Hydrous MnO2-coatedalumina

4–6 298 0.37 (9)

La3þ impregnatedcrosslinked gelatin

5–7 298 1.12 (13)

KMnO4 modified ricestraw carbon

2 303 0.81 (15)

Fe(III) loaded cottoncellulose

4 298 0.97 (16)

Protonated chitosan bead 7 303 0.38 (18)Ca-pretreated macrophytebiomass

6 – 0.11 (19)

Spirogyra species IO1 7 303 0.06 (20)Hydrous Fe-Sn bimetaloxide

5.5 303 0.55 (27)

FIG. 5. Competitive adsorption of fluoride ion on SOJR-Zr against

various anions. Conditions: Dry weight of adsorbent¼ 25mg, volume of

test solution¼ 15 cm3, contact time¼ 24 h, temperature¼ 303K.

FIG. 6. Fluoride removal from actual waste plating solution by using

SOJR-Zr. Conditions: pH¼ 3, contact time¼ 24 h, temperature¼ 303K.

ADSORPTION BEHAVIOR OF FLUORIDE IONS 101

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14

interaction between fluoride ions in aqueous solution andloaded zirconium(IV) ions due to high stability constantsof fluoride complexes of zirconium(IV) (26), though it pro-vides the driving force for the adsorption reaction betweenloaded zirconium(IV) ion and fluoride ion. This effect isinsignificant, however, at neutral or high pH, due to thestronger interaction between the zirconium(IV) ion andhydroxyl ions.

Regeneration of Fluoride-Adsorbed SOJR-Zr and itsRepeated Usages

The repeated use of adsorbent is important and essentialfor its application to the real system. As seen from Fig. 4,

fluoride is effectively adsorbed onto the SOJR-Zr in the pHrange 2–4 while it is poorly adsorbed at pH higher than 8.From this result, adsorbed fluoride can be expected to beeasily eluted by using dilute alkaline solutions like 0.1MNaOH in order to regenerate the gel for further use. Wecarried out cycle tests (adsorption-elution-adsorption) tofind the reusability of the gel where 0.1M NaOH solutionwas used as eluent as shown in Fig. 8. It is evident from thisfigure that fluoride removal efficiency of this adsorbent isnot changed drastically even after ten repeated cycles, indi-cating that the zirconium(IV) is effectively immobilized onSOJR, suggesting that good adsorption as well as good elu-tion can be achieved without any degradation of theadsorbent.

CONCLUSION

The results of this study have demonstrated that orangewaste, an agro-industrial waste, can be used as a feedmaterial for high-capacity adsorbent for fluoride removalfrom aqueous solutions. Time required to reach equilib-rium was evaluated as 8 h for an initial fluoride concen-tration of 0.84mmol=dm3. The optimal adsorption wasobserved at pH 2.4 while the adsorption closely followedthe Langmuir adsorption isotherm, which indicated thatthe monolayer adsorption was involved in the process offluoride adsorption. A comparative study of adsorptioncapacities showed that the sorption capacity (1.2mmol=g)of SOJR-Zr was higher than that (0.5mmol=g) of the com-mercial resin (200CT-Zr). The presence of CO2�

3 , SO2�4 ,

NO�3 and Cl- had only insignificant effect on fluoride

adsorption, which indicated the high selectivity of theSOJR-Zr for fluoride. Adsorption of fluoride on SOJR-Zrwas inferred to take place according to the ligand exchangemechanism (substitution of hydroxyl ligands by fluorideions). Complete adsorption of fluoride from the actualplating solution was found to be achieved regardless ofthe presence of other oxoanions as well as cations. Thestudy on elution demonstrated that SOJR-Zr can be easilyregenerated by dilute NaOH solution (0.1M). Thus,SOJR-Zr could be employed as an excellent and efficientadsorbent for fluoride ion adsorption from aqueoussolution.

ACKNOWLEDGEMENTS

The present work was financially supported by NewEnergy and Industrial Development Technology Organiza-tion (NEDO) for the project on Water-saving RecyclingSystems.

REFERENCES

1. Lio, X.P.; Shi, B. (2005) Adsorption of fluoride on

zirconium(IV)-impregnated collagen fiber. Environ. Sci. Technol., 39:

4628–4632.

FIG. 8. Adsorption elution cycle of fluoride by SOJR-Zr. Conditions:

Dry weight of adsorbent¼ 25mg, fluoride concentration¼ 1.57mmol=

dm3, volume of fluoride solution¼ 15 cm3, volume of eluent (0.1M

NaOH)¼ 15 cm3, contact time¼ 24 h, temperature¼ 303K.

FIG. 7. Leakage of loaded zirconium(IV) ion from SOJR-Zr at varying

concentration of fluoride at different pH. Conditions: Dry weight of

adsorbent¼ 10mg, volume of fluoride solution¼ 10 cm3, contact

time¼ 24 h, temperature¼ 303K.

102 H. PAUDYAL ET AL.

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14

2. Turner, B.D.; Binning, P.; Stipp, S.L.S. (2005) Fluoride removal by

calcite: Evidence for fluorite precipitation and surface adsorption.

Environ. Sci. Technol., 39: 9561–9568.

3. Huang, C.J.; Liu, J.C. (1999) Precipitate floatation of fluoride

containing waste water from semiconductor manufacturer. Water

Res., 33: 3405–3412.

4. Meenakshi, S.; Viswanathan, N. (2007) Identification of selective

ion-exchange resin for fluoride sorption. J. Colloid Interface Sci.,

308: 438–450.

5. Drouiche, N.; Graffour, N.; Lounici, H.; Mameri, N.; Maallemi, A.;

Mahmoudi, H. (2008) Electrochemical treatment of chemical polish-

ing wastewater: Removal of fluoride-sludge characteristics-operating

cost. Desalination, 223: 134–142.

6. Hichour, M.; Persin, F.; Sandeaux, J.; Gavach, C. (2000) Fluoride

removal from waters by Donnan dialysis. Sep. Purif. Technol., 18:

1–11.

7. Kir, E.; Alkan, E. (2006) Fluoride removal by Donnan dialysis with

plasma-modified and unmodified anion-exchange membranes. Desali-

nation, 197: 217–224.

8. Tor, A. (2006) Removal of fluoride from an aqueous solution by using

montmorillonite. Desalination, 201: 267–276.

9. Teng, S.X.; Wang, S.G.; Gong, W.X.; Liu, X.W.; Gao, B.Y. (2009)

Removal of fluoride by hydrous manganese oxide-coated alumina:

Performance and mechanism. J. Hazard. Mater., 168: 1004–1011.

10. Wajima, T.; Umeta, Y.; Narita, S.; Sugawara, K. (2009) Adsorption

behavior of fluoride ion using a titanium hydroxide derived adsorbent.

Desalination, 249: 323–330.

11. Ayoub, S.; Gupta, A.K. (2009) Performance evaluation of alumina

cement granules in removing fluoride from natural and synthetic

waters. Chem. Eng. J., 150: 485–491.

12. Mike�ss, O. (1998) High-performance liquid chromatography of biopo-

lymers and bio-oligomers, Part A: principles, materials and techni-

ques. Journal of Chromatographic Library, 41A: 70–71.

13. Zhou, Y.; Yu, C.; Shan, Y. (2004) Adsorption of fluoride from aque-

ous solution on La3þ-impregnated cross-linked gelatin. Sep. Purif.

Technol., 36: 89–94.

14. Hasar, H. (2003) Adsorption of Nickel(II) from aqueous solution

onto activated carbon prepared from almond husk. J. Hazard. Mater.,

97: 49–57.

15. Daifullah, A.A.M.; Yakout, S.M.; Elreefy, S.A. (2010) Adsorption of

fluoride in aqueous solution using KMnO4 modified activated carbon

derived from steam pyrolysis of rice straw. J. Hazard. Mater., 147:

633–643.

16. Zhao, Y.; Li, X.; Liu, L.; Chen, F. (2008) Fluoride removal by

Fe(III)-loaded ligand exchange cotton cellulose adsorbent from drink-

ing water. Carbohydra. Polym., 72: 144–150.

17. Franzaring, J.; Klumpp, A.; Fangmeier, A. (2007) Active bio-

monitoring of airborne fluoride near an HF producing factory using

standardized grass culture. Atmos. Environ., 41: 4828–4840.

18. Viswanathan, N.; Sundaram, C.S.; Meenakshi, S. (2009) Removal of

fluoride from aqueous solution using protonated chitosan beads.

J. Hazard. Mater., 161: 423–430.

19. Miretzky, P.; Murroz, C.; Chavez, A.C. (2008) Fluoride removal from

aqueous solution by Ca-pretreated macrophyte biomass. Environ.

Chem., 5: 68–72.

20. Mohan, V.S.; Ramanaiah, S.V.; Rajkumar, B.; Sharma, P.N. (2007)

Bio-sorption of fluoride from aqueous solution onto algal spirogyra

IO1 and evaluation of adsorption kinetics. Biores. Technol., 98:

1006–1011.

21. Fang, L.; Ghimire, K.N.; Kuriyama, M.; Inoue, K.; Makino, K.

(2003) Removal of fluoride using some lanthanum loaded adsorbent

with different functional groups and polymer matrices. Chem. Tech-

nol. Biotechnol., 78: 1038–1047.

22. Biswas, B.K.; Inoue, J.; Inoue, K.; Ghimire, K.N.; Harada, H.; Ohto,

K.; Kawakita, H. (2008) Adsorptive removal of As(V) and As(III)

from water by a Zr(IV)-loaded orange waste gel. J. Hazard. Mater.,

154: 1066–1074.

23. Cotton, F.A.; Wilkinson, G.; Murillo, C.A.; Bochmann, M. (1999)

Advanced inorganic chemistry, 6th Ed.; John Wiley and Sons, Inc.,

Singapore.

24. Viswanathan, N.; Sundaram, C.S.; Meenakshi, S. (2009) Sorption

behavior of fluoride on cross-linked chitosan beads. Colloids and

Surfaces B: Biointerface, 72: 88–93.

25. Samatya, S.; Yusksel, U.; Yuksel, M.; Kabay, N. (2007) Removal of

fluoride from water by metal ions (Alþ3, Laþ3, and ZrOþ2) loaded

natural zeolite. Sep. Sci. Technol., 42: 2033–2047.

26. Hogfeldt, E. (1982) Stability constants of metal-ion complexes Part A:

Inorganic Ligand. IUPAC Chemical Data Series, No 21, Pergamon

Press Ltd., Oxford OX3 0BW, England.

27. Biswas, K.; Gupta, K.; Ghosh, U.C. (2009) Adsorption of fluoride by

hydrous Fe(III)-Sn(IV) bimetal oxide from the aqueous solutions.

Chem. Eng. J., 149: 196–206.

ADSORPTION BEHAVIOR OF FLUORIDE IONS 103

Dow

nloa

ded

by [

Uni

vers

ity o

f T

exas

Lib

rari

es]

at 0

7:37

28

Sept

embe

r 20

14