Adsorption Properties of Uranium (VI) Ions on Reactive Crosslinked Acrylamidoxime and Acrylic Acid Copolymer Resins

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Adsorption Properties of Uranium (VI) Ions onReactive Crosslinked Acrylamidoxime and Acrylic AcidCopolymer ResinsAyman M. Atta a , Adel A.-H. Abdel-Rahman b , Ibrahi E. El Aassy c , Fadia Y. Ahmed c &Mohammed F. Hamza ca Egyptian Petroleum Research Institute , Nasr City, Cairo, Egyptb Department of Chemistry, Faculty of Science , Menoufiya University , Shebein El- Kom,Egyptc Nuclear Materials Authority , Cairo, EgyptPublished online: 20 Dec 2010.

To cite this article: Ayman M. Atta , Adel A.-H. Abdel-Rahman , Ibrahi E. El Aassy , Fadia Y. Ahmed & Mohammed F. Hamza(2010) Adsorption Properties of Uranium (VI) Ions on Reactive Crosslinked Acrylamidoxime and Acrylic Acid Copolymer Resins,Journal of Dispersion Science and Technology, 32:1, 84-94, DOI: 10.1080/00377990903543053

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Adsorption Properties of Uranium (VI) Ions onReactive Crosslinked Acrylamidoxime and Acrylic AcidCopolymer Resins

Ayman M. Atta,1 Adel A.-H. Abdel-Rahman,2 Ibrahi E. El Aassy,3

Fadia Y. Ahmed,3 and Mohammed F. Hamza31Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt2Department of Chemistry, Faculty of Science, Menoufiya University, Shebein El- Kom, Egypt3Nuclear Materials Authority, Cairo, Egypt

Crosslinked acrylic acid (AA) acrylonitrile (AN) copolymer was prepared by suspensioncopolymerization in the presence of poly (vinyl alcohol) as suspending agent andN,N-methylenebisacrylamide (MBA) and divinylbenzene (DVB) as crosslinking agents. Themolecular ratios between AN and AA was 95: 5mol%. Different ratios 2, 5, and 10wt% ofcrosslinkers was used. The nitrile group of the copolymer was converted to acrylamidoxime inthe presence of hydroxylamine. Morphologies of the prepared resins were examined by scanningelectron microscope (SEM). Recovery of uranium ions was investigated. The adsorption of ura-nium was occurred in nitric acid, hydrochloric acid and sulfuric acid solutions. Effect of pH, timeof loading, type of acid, ratio, and type of crosslinker were investigated. Regeneration of elutedresins was determined.

Keywords Acrylamidoxime acrylic acid copolymer resins, divinylbenzene, methylenebisacry-lamid, uranium

INTRODUCTION

Over the last few years, solid phase extraction (SPE) hasbecome an eminent technique for the extraction of tracemetal ions from various geological and water systems.[1,2]

For these purposes, new types of SPE materials, such ashighly crosslinked polymers and chemically modified poly-mers, are currently being developed for more effectiveextraction.[3–7] However, some of these sorbents canco-extract many matrix species resulting to an uncleanextraction process. As a result, the necessity to developselective chelating sorbents has become an attractive areaof research. Based on this, several chelating sorbentsincluding cellulose,[8,9] silica gel,[10] activated carbon,[11]

activated alumina,[12] etc., and polymeric resins,[13,14] havebeen developed. The chelating resins containing amidoximefunctional group were studied extensively in order to applythem to the recovery of uranium from sea water, becausethe amidoxime resins adsorb urany1 ion, ðUO2þ

2 Þ selec-tively from the sea water containing various metalions.[15–20] In this respect, the aim of this work is to syn-thesis of chelating resin with highly uptake toward uranium

ions based on acrylic acid (AA) and acrylonitrile (AN)copolymers. The crosslinking was completed in the pres-ence of different concentrations and types of crosslinkerssuch as N,N-methylenebisacrylamide and divinylbenzene.

EXPERIMENTAL

Materials

Acrylonitrile, acrylic acid was obtained from Fluka,Japan. Divinylbenzene (DVB, 55%) was obtained fromSigma-Aldrich, UK. N,N-methylene bis-acrylamide(MBA) was obtained from Fluka, Switzerland. Potassiumpersulfate and sodium metabisulfite were obtained fromAdwec Co, Egypt. Source of uranium used was uranylnitrate Sigma-Aldrich. All other chemicals were Prolaboproducts and were used as received.

Synthesis of Polyacrylonitrile Acrylic Acid (DVB, MBA)

Copolymerization and crosslinking of acrylonitrile andacrylic acid, with 95:5mol ratios of monomers, in the pres-ence of divinylbenzene or methylenebisacrylamid as cross-linking agent were carried out in three-necked flask at 40�Cunder nitrogen atmosphere. The water, used as solvent) tomonomer ratios kept as 10 vol%. Potassium persulfate andsodium metabisulfite (0.0576 and 0.0557mol% with respect

Received 15 September 2009; accepted 9 November 2009.Address correspondence to Ayman M. Atta, Egyptian

Petroleum Research Institute, Hay Elzohour, Nasr City 11727,Cairo, Egypt. E-mail: [email protected]

Journal of Dispersion Science and Technology, 32:84–94, 2011

Copyright # Taylor & Francis Group, LLC

ISSN: 0193-2691 print=1532-2351 online

DOI: 10.1080/00377990903543053

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to monomers feed) was used as redox initiator. Poly (vinylalcohol) 730ml to 100 gm monomers of was added as sus-pending agent. The monomers were added slowly to thereaction mixture in 25–30 minutes and polymerizationwas continued for 90 minutes (including the time requiredfor the addition of the monomer mixture) with good agi-tation. The polymer was isolated by filtration washed withwater and methanol and dried under vacuum at 50�C.

Synthesis of Am/AA (DVB, MBA) Resin

Preparation of Hydroxylamine

Hydroxylamine hydrochloride (40.1 g) was dissolvedin 290ml, of methanolic solution (methanol: water 5 : 1),respectively. The hydroxyl amine neutralized by sodiumhydroxide solution till pH 10 and the precipitated NaClremoved by filtration.

Preparation of Polyacrylamidoxime Acrylic Acid(Am/AA) Resin

The resins (30 g) having different mol of ratios (95: 5: 2%;95: 5: 5%; and 95: 5: 10% of acylonitrile, acrylic acid cross-linker, respectively) were reacted with the prepared NH2OHsolution at 70�C for 2 hours. The prepared acrylamidoxime=acrylic acid (DVB, MBA) resin was separated by filtrationand washed several time by methanolic solution then treatedwith 0.1MHCl solution for at least 5 minutes. Finally, resinwas filtered and washed several times by methanolic solutionand dried at 50�C to constant weight.

The crosslinked Am=AA polymers with MBA and DVB2, 5, and 10W% were designated as F1, F2, F3, F4, F5, andF6, respectively.

Characterization

FTIR spectra of hydrogels loaded with uranyl ions wererecorded using JASCO 460 plus FTIR spectrometer.

Scanning electron microscopy (SEM) was used to studythe morphological properties of the crosslinked copolymerbefore and after adsorption of uranium. Specimens werecoated with gold in SEM coating equipment and magnifiedto 1500� for 10.00 mm and scanning electron micrographswere taken with a JEOL JSM–5400 scanning microscope.

Uptake of Uranyl Ions Using Batch Adsorption Method

A simple and sensitive spectrophotometric method basedon colored complexes with Arsenazo III in aqueous mediumwas used for determination of uranium.[21] The concen-tration of UO2þ

2 ions in the solution was determined witha Thermo3000 UV-visible spectrophotometer by measuringabsorbance at kmax of 650nm for uranium. All glassware foradsorption experiments was washed with 1.0M HNO3 andrinsed thoroughly with deionized water. A 0.1 g of dry resingel was placed in a flask containing 100ml of uranyl solutionat a temperature of 25�C. The contents of the flask were

shacked at 1000 rpm for various time intervals. After theequilibration time, 5ml of the solution were taken. Theinitial pH of the working solutions was 4.0, when the adsorp-tion equilibrium was reached, it was filtrated to separatehydrogel and the solution. The concentration of the free ura-nium (VI) ions in the filtrate was determined. The dataobtained in batch studies were used to calculate the equilib-rium metal uptake capacity. It was calculated for each sam-ple of uranium(VI) by using the following expression:q¼ (C0�Ce) �V=W; q is the amount of UOþ2

2 adsorbedonto unit mass of the copolymer (g=g); C0 and Ce are theconcentrations of the uranium in the initial solution and inthe aqueous phase after treatment for certain period of time,respectively (mg=l); V is the volume of the aqueous phase (l);and m is the mass of the copolymer used (g).

Effect of pH on the Uptake of Uranyl Ions

Uptake experiments under controlled pH were carriedout by placing 0.1 g of dry gel in a series of flasks contain-ing uranyl ions solution 100 (mg=l) for a pH range of 2 to 8at 25�C, respectively. The desired pH was adjusted usingHCl and NH4OH. After the equilibration the supernatantof each flask was obtained and the residual metal ion con-centration was determined as shown above.

Effect of Initial Concentration of Uranyl Ions on the Uptake

The effect of initial concentration of the metal ion on theuptake by the resins obtained was carried out by placing0.1 g of dry resin in a series of flasks containing uranyl ionsat different concentrations and pH 4. The contents of theflasks were equilibrated on the shaker at 25�C. After theequilibration, the supernatant of each flask was obtainedand the residual metal ion concentration was determinedas shown above.

Polymer Regeneration

Elution of UOþ22 ions by three types of eluents was stud-

ied. 4M HCl and 2M HNO3 solutions were used as acidiceluents whereas 1M Na2CO3 was used as basic eluent. TheAm=AA gels loaded with UOþ2

2 were placed in this elutionmedium and stirred (at a stirring rate of 100 rpm) for 24hours at room temperature. The final concentration of

UOþ22 in the aqueous phase was determined spectrophoto-

metrically. The elution ratio was calculated from theamount of UOþ2

2 adsorbed on the hydrogels and the finalconcentration of UOþ2

2 in the elution medium, by usingthe following expression:

Efficiency of regeneration ð%Þ

¼

total adsorption capacityin the second run

total adsorption capacityin the first run

� 100 . . . ½1�

URANIUM IONS UPTAKE ON AN RESINS 85

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RESULTS AND DISSCUSION

It was previously reported[22,23] that the conversion ofthe copolymerization of AN was increased with theaddition of the vinyl acid comonomer. This is probablybecause the polymer radical with an acid unit at the chainend is considerably more active than is the polyacrylonitrile(PAN) growing radical, which means that the addition ofeither of the monomers will be more rapid than in the caseof a radical terminating in an AN unit.[22] On the otherhand, the distribution of monomeric units is random andin no case is the homopolymer formation expected. Reac-tivity ratios of AN and these vinyl acids copolymerssynthesized by different methods have also been reported.Bajaj et al.[23] reported the reactivity ratios of r1 (AN)and r2 (AA) for copolymers prepared by aqueous suspen-sion polymerization using a redox initiator at 40�C. Itwas determined that the reactivity of monomers in a systemdepends on the method of polymerization and the mediumand temperature of the polymers. However, irrespective ofthe method of polymerization, the acidic comonomers arefound to be more reactive than is AN. In this respect, r1and r2 were found to be 0.34 and 3.25 in aqueous suspen-sion polymerization of AN and AA, respectively. Thesevalues, rl and r2, were found to be 0.495 and 2.502 in sol-ution DMF. This means that the produced AN=AA copo-lymer forms random copolymer having high AA content.From the previous discussion, we selected acrylonitrileand acrylic acid, with 95:5mol ratios of monomers, to pro-duce crosslinked copolymers in the presence of divinylben-zene or methylenebisacrylamid as crosslinking agent.Potassium persulfate and sodium metabisulfite was usedas redox initiator. Poly (vinyl alcohol) was added as sus-pending agent. The mechanism of copolymerization canbe illustrated as previously reported.[24,25] When AN=AAcopolymer was synthesized with the solvent water suspen-sion technique, oligomeric radicals may have formed inthe initial stages of polymerization, precipitated out aftera certain critical molecular weight was attained, and thenacted as primary particles. Propagation then occurred inthe water phase depending on the contents of monomersin feed. In the present system, because of the insolubilityoligomeric radicals, propagation followed the suspensionpolymerization technique more. A two-locus polymeriza-tion mechanism was assumed (i.e., water phase and oligo-meric radicals phase). Propagation then mostly occurredin the oligomeric radicals phase. AN units were more easilyabsorbed by polymer radicals than by AA units. The solu-bility of AA was greater than that of AN in water. Theimpacting opportunities between AA units and polymerradicals rose, and this led to a random array of AA unitsin the copolymer chain. Accordingly, AN=AA mol ratio(95:5) was selected to produce copolymer rich with ANcontents. On the other hand, DVB and MBA were used

to study the effect of crosslinker chemical structure oncrosslinking reaction of AN=AA copolymers.

Amidoximation reaction of crosslinked AN=AA copoly-meric hydrogels was confirmed by FTIR analysis. In thisrespect, FTIR spectra of AN=AA and Am=AA crosslinkedwith 5% of either DVB or MBA were selected and arerepresented in Figures 1a–d. The spectra of crosslinkedAN=AA with either DVB or MBA show the same bandsat 1735.8 cm�1 for C=O streatching band of carboxylicacid, 2244.4 cm�1 for CN streatching band, 3567.5 cm�1

for OH streatching band of carboxylic group. New bandat 1673 cm�1 was observed in Figure 1b for C=O stretchingamid of MBA. New bands at 1654.7 cm�1 C=N stretchingof amidoxime and 3369.6 cm�1 NH, OH stretching of ami-doxime of Am=AA copolymers Figures 1c and 1d. In caseof polyacrylamidoxime acrylic acid resins, Am=AA, C=Ostreatching of carboxylic acid did not appeare. This canbe attributed to the hydroged bond occured in resin as inScheme 1. It was previously reported[26] that the increasein AN content of gel causes a decrease in both percentageswelling and efficiency of amidoximation conversion. In thepresent study, it was observed that the band 2244.4 cm�1

for CN streatching band was completely disappeared uponamidoximation of CN with hydroxyl amine. This band wascompletely disappeared for copolymers crosslinked with10wt% of either DVB or MBA. While the crosslinkedAm=AN copolymer with 2–5wt% of either DVB or MBAwas not completely disappeared. This means that the con-version of CN of AN=AA to amidoxime group was affec-ted by the type and crosslinker concentrations. It wasobserved that the amidoxime group content was increasedfor Am=AA crosslinked with DVB. This can be attributedto higher reactivity of DVB with AA or AN polymers andcopolymers than MBA crosslinker. This indicated that thesuspension crosslinking and copolymerization of AN=AAis more effective with DVB than MBA crosslinker. Thiscan be attributed to the difference in the solubility betweenDVB and MBA crosslinkers in water solvent. DVB unitswere more easily absorbed by polymer radicals than byMBA units. The solubility of MBA was greater than thatof DVB in water. The impacting opportunities betweenMBA units and polymer radicals rose, and this led to a ran-dom array of MBA units in the copolymer chain whichincreased with increasing of MBA content. On the otherhand, the formation of uniform crosslinked AN=AA=DVB increases the probability to conversion of CN toamidoxime than random AN=AA=MBA resins.

The structural morphology of Am=AA, different DVBand MBA contents, was studied by scanning electronmicroscopy and shown in Figures 2c and 2d. The SEMmicrographs of the Am=AA hydrogel revealed a porousinternal structure. This porosity confirms the three-dimensional structure of the hydrogel. SEM micrographs

86 A. M. ATTA ET AL.

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clearly illustrate the dependence of hydrogel morphologyon the type and concentration of DVB and MBAcrosslinkers.

Am=AA=MBA 2% exhibit a large number of shortfinger-like cavities beneath the upper layer, the size of poresis observed to decrease from bottom to the top of the gel.In contrast, Am=AA=DVB 2% exhibits a large amount ofhoneycomb-like cavities beneath the upper layer, and thereare many small pores in the big pore. It is assumed thatAm=AA=DVB 2% can be applied for metal adsorption

because of its porous structure. On the other hand,Figure 2d represents the effect of DVB concentration oninner structure of gel. The pore size decreases with theincrease of DVB concentration. The proper reduction ofpore size is beneficial to the ability of absorb and retainthe UO2þ

2 ions solution. It was also observed that Am=AA=DVB displays a more open and porous channel struc-ture than Am=AA=MBA, thus displays a faster swellingresponse rate. Consequently it is expected that themorphologies of the crosslinked Am=AA copolymers has

FIG. 1. FTIR spectra of (a) AN=AA=DVB, (b) AN=AA=MBA, (c) Am=AA=DVB, and (d) Am=AA=MBA resins.


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an influence on the swelling ability of corresponding super-absorbent. The SEM micrographs, not represented forbrevity, of the hydrogels after absorbing UOþ2

2 ions,showed a different morphology in which the pores arenot observed.

Adsorption of UOþ22 Ions by Crosslinked Am=AA

Copolymeric Resins

The crosslinked copolymers amidoximated under opti-mal conditions (Am=AN) were left in the uranyl ion solu-tions, until they reach their maximum adsorptionequilibrium. Postdetermination of uranyl ion concentra-tions was carried out as mentioned in the experimental sec-tion. Accordingly, due to the incompletion of conversion ofall nitrile groups to amidoxime groups, the active siteswhich is able to interact with UO2þ

2 ions becomes relativelylow causing a subsequent reduction in the adsorption capa-cities. FTIR was ocurred on loaded Am=AA copolymerswith UO2þ

2 ion also to resin after elution with strong acidmedia as 4N HCl to elucidate that strong acid not affecton chemical structure of resins used. The FTIR spectraof loaded and eluted Am=AA copolymers were selectedand are represented in Figures 3a and 3d. Bands at1651.1 cm�1 streatching C=N produced of amidoxime,3386.9 cm�1 streatching NH group of amidoxime and thatof carboxylic acid were observed for loaded Am=AAresins. For Am=AA resins after elution (Figures 3c and3d), bands at 1652 cm�1 streatching C=N of amidoxime,3336.9 cm�1 streatching NH group of amidoxime and thatof carboxylic acid. Due to the interactions with UO2þ

2 ions,there are some shifts on some characteristic bands. Theband for C=N at 1600 cm�1 shifts approximately 60 cm�1.This difference can be better seen in the difference spectrumgiven in Figure 3a. The increases in the band intensities aredue to O=U=O bands, which appear at the same regionswith the functional groups.[27] There are also band shiftsat 3400 cm�1 for the interaction of NH2 with UO2þ

2

ions. The shift at 1500 cm�1 belongs to C=N stretching

vibrations for amidoxime also proves the interaction of

UO2þ2 ions with COOH group. The most important band

which is linear O=U=O stretching vibration appears at937 cm�1.[27] Figure 3a also shows that the bands due toCOOH, amide carbonyl and hydroxyl groups decrease intransmittance after the chelation of uranyl ions. This isattributed to the decrease in the dipole moment of COOH,amide and hydroxyl groups as a result of electron donationon the metal ion from the nitrogen and oxygen atoms. Inthe present system, there are many type of suggested inter-action between (amidoxime=carboxylic group) and uranyions that indicated in Scheme 2. The interaction can bebetween amidoxime carboxylic in different types as inSchemes 2a and 2b or between amidoxime it selfScheme 2c or carboxylic acid it self Scheme 2d.

Effect of Crosslinker Type and Concentration on UO2þ2

Ions Uptake

Polymeric materials having polyfunctional groups notonly possess good hydrophilic properties, but also havegood ion exchange properties which make them suitablefor metal recovery from aqueous solutions. The wateruptake and, therefore, the metal-ion uptake increase in pro-portion to the kind and amount of hydrophilic groupsbecause the diffusion of aqueous solutions in more hydro-philic polymers will be faster than in less hydrophilic poly-mers, which is the rate-determining step for adsorption.[28]

Tables 1–3 show the variation of UO2þ2 ions uptake with

crosslinker percentage and type in the hydrogels at pH 6.It is clear that the UO2þ

2 ions uptake decrease with theincrement of crosslinker percentage of the copolymer, thisindicates that the crosslinker contents in the hydrogel struc-ture are primarily responsible for the specific binding of the

UO2þ2 ions due to the coordination between UO2þ

2 ions andthe active functional groups of the networks. It was foundthat crosslinker rich compositions did not possess highmetal uptake that it possess low degree of swelling at

UO2þ2 ions feed solutions, which prevent the diffusion of

the metal ions inside the hydrogel. As the crosslinker con-tent decreases, the swelling ability of the hydrogel increases.The metal ion uptakes for the various samples are in theorder of their hydrophilic character. Higher water uptakeof the sorbent shows higher metal ion uptake. This behaviorwas reported for crosslinked polyacrylamide-hydroxamicacid sorbents[29] and for polyacrylamide-2-Hydroxypropylmethacrylate (HPMA) copolymers.[30]

Rivas et al. reported that the uranyl ions retention ofcrosslinked poly (1-vinyl imidazole-co-2-acrylamido-2-methyl-1-propanesulfonic acid) is greater than that of(1-vinyl imidazole-co acrylic acid) at the same pH.[30] Itwas expected that the hydrophilicity of the MBA crosslin-ker can increase the UO2þ

2 ions uptakes due to hydrophili-city of MBA. It was also observed that the incorporation of

SCH. 1. Hydroged bond occured in Am=AA resins.


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DVB crosslinker instead of MBA in the network structureincreases the UO2þ

2 ions uptakes. This can be attributed tothe formation of homogeneous networks when DVB usedas crosslinker in suspension copolymerization of AA andAN copolymer as illustrate in the previous section.

Effect of contact time on the adsorption of UO2þ2 ions

at pH 6 for Am=AA crosslinked with MBA and DVB

hydrogels is illustrated in Figure 4. The percentage of

UO2þ2 ions uptake was observed to increase with time

and this trend was observed for all the hydrogels. The plotsshowed that kinetics of adsorption of UO2þ

2 ions consistedof two phases: an initial rapid phase where adsorption wasfast and contributed significantly to equilibrium uptake,and a slower second phase whose contribution to the total

FIG. 2. FTIR spectra of loaded (a) Am=AA=DVB, (b) Am=AA=MBA with uranyl ions, and eluted (c) Am=AA=DVB, and (d) Am=AA=MBA resins

in 4M HCl medium.


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metal adsorption was relatively small. The rapid uptakeof UO2þ

2 may indicate that most of the active sites of thehydrogels are exposed for interaction with the metalions.[31] The first phase is interpreted to be the instan-taneous adsorption stage or external surface adsorption.The second phase is interpreted to be the gradual adsorp-tion stage where intraparticle diffusion controls the adsorp-tion rate until finally the metal uptake reaches equilibrium.After 360 minutes (6 hours), the change of adsorptioncapacities for UO2þ

2 ions did not show notable effects. Asa consequence, a 360-minute period was chosen as the reac-tion time required to reach pseudo-equilibrium in thepresent ‘‘equilibrium’’ adsorption experiments. Reportedexperimental data on sorption kinetics of uranium on poly-meric adsorbents have shown a wide range of values.

Effect of pH on UO2þ2 Ions Uptake

It is well known that the initial pH value of the solutionis a critical parameter that can affect the hydrogel perform-ance by influencing its swelling and ion uptake capability.The pH has two kinds of influence on metal sorption:an effect on the solubility and speciation of metal ions insolution, and on the overall charge of the sorbent. Forselective adsorption, besides the use of a specific ligandmodified sorbent, selectivity could be achieved by adjustingthe pH of the medium to different values.[32] The pHdependence of adsorption values of UO2þ

2 was representedin Figure 5; it is obvious that the adsorption of UO2þ

2 onto

the Am= AA hydrogels is pH dependent. The results showthat uranium adsorption by the hydrogels is low at pH 3.0,but increased with increasing pH and then reached themaximum at pH 8.0. Uptake of UO2þ

2 by hydrogels at neu-tral or slightly acidic conditions may be explained to pro-ceed via complex formation between the metal ions andthe active sites on the resins.[33,34] As the pH decreases,

SCH. 2. Postulated interaction of Am=AA resins of (a) amidoxime=

carboxylic groups (b) amidoxime=carboxylic groups, (c) amidoxime

groups, and (d) carboxylic groups with uranyl ions.

FIG. 3. SEM morphologies of crosslinked Am=AA resins with (a)

MBA 2wt%, (b) DVB 2wt%, (c) MBA 10wt%, and (d) DVB 10wt% of

crosslinkers.


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the active sites become protonated and their ability forinteraction with UO2þ

2 decreases because at lower pH,hydrogen ions may be competing with the metal ions.Many authors reported various species of uranium at dif-ferent pH values,[35,36] among these species, UO2þ

2 ,UO2(OH)þ, UO2(OH)2(aq), UO2ðOHÞ�3 , ðUO2Þ2ðOHÞþ2

2 ,

ðUO2Þ3ðOHÞþ5 , ðUO2Þ3ðOHÞ�7 , ðUO2Þ4ðOHÞþ7 were

detected. At pH� 5, UOþ22 and UO2(OH)þ predominate

and are responsible for uranium uptake by hydrogels.[37]

Different researchers indicated complex formation between

UO2þ2 and=or UO2(OH)þ with different functional

groups.[38,39] The carboxylic, amidoxime, and amide groupsare active sites in the Am=AA hydrogels which may partici-pate in chelation. Decreasing the acidity of the mediumcauses the active sites to become protonated leading tothe depression in the uptake capacity due to the electro-static repulsion with the positively charged uranyl species.It is well known in adsorption mechanisms, that a decreasein solubility favors an improvement in adsorption perform-ance. The further increase of pH was followed by adecrease in the uptake of uranyl ions, because there is adecrease in dissolved uranyl ion concentration at higher

TABLE 2Adsorption of UO2þ

2 on Am=AA in hydrochloric acid media as function of time at pH¼ 6 and 25�C

Uranium concentration mg=g resin from hydrochloric acid solutions

Code Symp. Ratios 1 h 2 h 3 h 4 h 5 h 6 h 20 h

F1 P.Am.AA.MBA 95:5:2% 34 110 190 210 250 307 355F2 P.Am.AA.DVB 95:5:2% 45 109 197 250 289 320 380F3 P.Am.AA.MBA 95:5:5% 39 90 151 190 255 261 320F4 P.Am.AA.DVB 95:5:5% 35 92 155 181 220 271 315F5 P.Am.AA.MBA 95:5:10% 31 55 91 177 190 201 210F6 P.Am.AA.DVB 95:5:10% 21 61 103 131 166 181 192


2 on Am=AA in nitric acid media as function of time at pH¼ 6 and 25�C

Uranium concentration mg=g resin from nitric acid solution




2 on Am=AA in sulfuric acid media as function of time at pH¼ 6 and 25�C

Uranium concentration mg=g resin from sulfuric acid solution




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FIG. 5. Uranyl ions uptake (mg=g) of PAmAA(MBA=DVB) resins in hydrochloric acid solutions at (a) pH¼ 2, (b) pH¼ 4, and (c) pH¼ 8 solutions.

FIG. 4. Uranyl ions uptake (mg=g) of PAmAA(MBA=DVB) resins from nitric acid solutions at pH¼ 6.


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pH due to the formation of solid schoepite (4UO2 � 9H2O)reducing uranium adsorption. In mildly acidic and neutralpHs 6.0–8.0, Am=AA hydrogels are effective for removalof UO2þ

2 from aqueous solutions. It was also observed thatthe uranyl ions uptake for Am=AA crosslinked with DVBin most cases is higher than that crosslinked with MBAcrosslinker. This can be attributed to the porosity andhomogeneity of Am=AA=DVB networks.

Regeneration of Hydrogels

To repeatedly reuse the hydrogels for the recovery ofuranium, uranium adsorbed on the resin must be easilyeluted with a certain kind of eluents. Regeneration calcu-lated after 6 cycles for all crosslinked Am=AA polymers.The data of regeneration of Am=AA in 4M HCl wereselected and represented in Table 4. It was determined thatthe regeneration efficiency was increased in case of highlycrossed resin than that of lower crosslinked resin. The elu-tion was investigated by batch method using 2M HNO3,4M HCl, and 1M Na2CO3, respectively. UOþ2

2 ionsadsorbed on the hydrogels show a higher elution in acidicmedia than in basic media. UOþ2

2 ions adsorbed on thehydrogels were eluted close to 80% by nitric acid, 90% byhydrochloric acid and 70% by sodium carbonate.

CONCLUSIONS

The previous results can be concluded and summarizedas following:

. Molecular ratio between acrylonitrile and acrylicacid (95:5) is selected to produce crosslinkedcopolymers using suspension copolymerizationtechnique in the presence of divinylbenzene ormethylenebisacrylamid as crosslinking agent, pot-assium persulfate, and sodium metabisulfite) asredox initiator, poly (vinyl alcohol) as suspendingagent and water as solvent.

. Amidoximation reaction of crosslinked AN=AAcopolymeric hydrogels was confirmed by FTIR

analysis. The conversion of CN of AN=AA toamidoxime group was affected by the type andcrosslinker concentrations. It was observed thatthe amidoxime group content was increased forAm=AA crosslinked with DVB.

. The suspension crosslinking and copolymeriza-tion of AN=AA is more effective with DVB thanMBA crosslinker.

. The SEM micrographs of the Am=AA hydrogelrevealed a porous internal structure.

. The incorporation of DVB crosslinker instead ofMBA in the network structure increases the

UO2þ2 ions uptakes. This can be attributed to

the formation of homogeneous networks whenDVB used as crosslinker in suspension copoly-merization of AA and AN copolymer.

. The adsorption of UO2þ2 onto the Am=AA hydro-

gels is pH dependent. As pH increase the uptakeof uranyl ions increase due to increasing ofchelating properties of amidoxime and carboxylicacid.

REFERENCES

[1] Kantipuly, C., Katragadda, S., Chow, A., and Gesser, H.D.(1990) Talanta, 37: 491–517.

[2] Nalwa, H. (2001) Advanced Functional Molecules and Poly-mers; Singapore: Gordon and Breach Science, vol. 4, p. 323.

[3] Fritz, J.S. (1999) Introduction and Principles. Analytical SolidPhase Extraction; New York: Wiley-=VCH, p. 1–14.

[4] Torre, M. and Marina, M.L. (1994) CRC Crit. Rev. Anal.Chem., 24: 327–361.

[5] Pathak, R. and Rao, G.N. (1996) Anal. Chim. Acta, 335:283–290.

[6] Schumuckler, G. (1965) Talanta, 12: 281–290.[7] Juang,R.S. (1999)Proc. Natl. Sci. Counc. ROCA, 23: 353–364.[8] Perenyi, K.Z., Lasztity, A., Horvath, Z., and Levai, A. (1998)

Talanta, 47: 67–679.[9] Kabay, N., Demiricioglu, M., Yayli, S., Yuksel, M., Saglam,

M., and Levison, P.R. (1999) Sep. Sci. Technol., 34: 41–51.[10] Yamini, Y., Chaloosi, M., and Ebrahimzadeh, H. (2002)

Talanta, 56: 797–803.

TABLE 4Data of regeneration efficiency of Am=AA resins using 4M HCl after 6 cycles

Resin information Efficiency in each cycle (%)

Code Symbol. Ratio 2nd 3rd 4th 5th 6th

F1 P.Am.AA.MBA 95:5:2% 97 96 94.5 93 90F2 P.Am.AA.DVB 95:5:2% 97 96 95.5 94 93.5F3 P.Am.AA.MBA 95:5:5% 98 96.5 96 95 94F4 P.Am.AA.DVB 95:5:5% 98 97 96 95.5 94.5F5 P.Am.AA.MBA 95:5:10% 98 97 96.5 95.8 95F6 P.Am.AA.DVB 95:5:10% 98.3 97.5 97 96 95


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[11] Park, G.I., Park, H.S., and Woo, S.I. (1999) Sep. Sci. Tech-nol., 34: 833–854.

[12] Schmitt, G.L. and Pietrzyk, D. (1985) J. Anal. Chem., 57:2247–2253.

[13] Myasocdova, G.V. and Sarrin, S.B. (1987) CRC Crit. Rev.Anal. Chem., 17: 1–63.

[14] Hennion, M.C. (1999) J. Chromatogr. A, 856: 3–54.[15] Kobuke, Y., Tanaka, H., and Ogoshi, H. (1990) Polymer J.,

22: 179–182.[16] Vernon, F. andEccles,H. (1976)Anal. Chim. Acta, 82: 369–375.[17] Omichi, H., Katakai, A., and Okamoto (1985) J. Sep. Sci.

Technol., 20: 163–178.[18] Kabay, N. and Egawa, H. (1994) Sep. Sci. Technol., 29:

135–150.

[19] Egawa, H., Nakayama, M., Nonaka, T., and Su Sgihara, E.(1987) J. Appl. Polym. Sci., 33: 1993–2005.

[20] Nakayama, M., Uemura, K., Nonaka, T., and Egawa, H.(1988) J. Appl. Polym. Sci., 36: 1617–1625.

[21] Kuroda, R., Kurosaki, M., Hayashibe, Y., and Ishimaru, S.(1990) Talanta, 37: 619–624.

[22] Bajaj, P., Sen, K., and Bahrami, S.H. (1996) J. Appl. Polym.Sci., 59: 1539–1550.

[23] Bajaj, P., Paliwal, D.K., and Gupta, A.K. (1993) J. Appl.Polym. Sci., 49: 823–833.

[24] Bajaj, P., Sreekumar, T.V., and Sen, K. (2001) J. Appl.Polym. Sci., 79: 1640–1652.

[25] Wu, C.-X., He, J.-M., and Shi, F.-Z. (1991) Acta Polym.Sinica, 1: 121–124.

[26] Pekel, N., Ahiner, N.S., and Guven, O. (2000) Rad. Phys.Chem., 59: 485–491.

[27] Rivas, B.L., Maturana, H.A., Ocampo, X., and Perie, I.M.(1996) J. Appl. Polym. Sci., 58: 2201–2205.

[28] Oren, S., Caykara, T., Kantoglu, O., and Guven, O. (2000)J. Appl. Polym. Sci., 78: 2219–2226.

[29] Pal, S., Ramachandhran, V., Prabhakar, S., Tewari, P.K.,and Sudersanan, M. (2006) J. Macromolecular Sciencew, A:Pure and Applied Chemistry, 43: 735–747.

[30] Chauhan, G., Chauhan, S., Chauhan, K., and Sen, U. (2006)J. Appl. Polym. Sci, 99: 3040–3049.

[31] Atia, A. (2005) Hydrometallurgy, 80: 13–22.[32] Han, U., Zou, W., Wang, Y., and Zhu, L. (2007) J. Environ.

Radioact., 93: 127–143.[33] Cardenas, G., Orlando, P., and Edelio, T. (2001) Int. J. Biol.

Macromol., 28: 167–174.[34] Becker, T., Schlaak, M., and Strasdeit, H. (2000) React.

Funct. Polym., 44: 289–298.[35] Froideval, A., Del Nero, M., Barillon, R., Hommet, J., and

Mignot, G. (2003) J. Colloid Interface Sci., 266: 221–235.[36] Hennig, C., Reich, T., Dahn, R., and Scheidegger, A.M.

(2002) Radiochimica Acta, 90: 653–657.[37] Denizli, A., Say, R., Bora, G., and Suleyman, P. (2004)

React. Funct. Polym., 85: 123–130.[38] Pekel, N., Sahiner, N., Akkas, P., and Guven, O. (2000)

Polym. Bull., 44: 593–600.[39] Zhang, A., Asakura, T., and Uchiyama, G. (2003) React.

Funct. Polym., 57: 67–76.


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Documents

Adsorption Properties of Uranium (VI) Ions on Reactive Crosslinked Acrylamidoxime and Acrylic Acid Copolymer Resins