REACTIVE

Reactive & Functional Polymers 65 (2005) 267–275

&FUNCTIONALPOLYMERS

www.elsevier.com/locate/react

Selective separation of mercury (II) using a syntheticresin containing amine and mercaptan as chelating groups

Asem A. Atia, Ahmed M. Donia *, Khalid Z. Elwakeel

Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt

Received 30 June 2005; accepted 5 July 2005

Available online 26 September 2005

Abstract

A chelating resin with amine–mercaptan groups has been prepared. The resin obtained showed high durabilitytowards mineral acids and alkalis. The recovery of Hg(II) was investigated by both batch and column methods. Theuptake capacity reached 3.10 mmol/g, i.e. 621.8 mg/g. The nature of interaction between the metal ion and the resinwas found to be dependent upon the acidity of the medium as well as the type of the conjugate anion. This interactionwas explained to proceed via complex formation or ion exchange mechanism. Hg(II) could be selectively separated fromCa(II), Mg(II), Pb(II), Cd(II), Cu(II) and Zn(II) at pH 2.7. The elution process of Hg(II) was tested using HCl, HNO3

and H2SO4 with different concentrations. HNO3 and H2SO4 gave a high elution ratio (>90%), whereas HCl showed alow elution ratio (�32%).� 2005 Elsevier B.V. All rights reserved.

Keywords: Mercury; Amine; Mercaptan; Chelating resins; Recovery; Ion exchange

1. Introduction

Mercury represents a serious environmentalproblem because it is widely used in many indus-tries and applications. Among of these, paperindustry, paints, cosmetics, preservatives, ther-mometers, manometers, fluorescent lamps andmercury batteries [1]. Different technological

1381-5148/$ - see front matter � 2005 Elsevier B.V. All rights reserv

doi:10.1016/j.reactfunctpolym.2005.07.001

* Corresponding author.E-mail address: ahmeddonia2003@yahoo.com (A.M.

Donia).

methods for mercury treatment were reported.The efficiency of each method depends upon thechemical nature as well as the initial concentrationof mercury and is controlled by its economical va-lue. One of the promising methods is the use ofchelating resins. Chelating resins are generally effi-cient in the removal and recovery of heavy metalions because of their physical and chemical stabil-ities. Many papers covering a vast number of dif-ferent chelating moieties immobilized on varioussynthetic and natural polymeric networks were re-ported [2–17]. Recently, we reported on the uptake

ed.

268 A.A. Atia et al. / Reactive & Functional Polymers 65 (2005) 267–275

behaviour of mercury (II) using glycidylmethacry-late (GMA)/divinylbenzene (DVB) resins pre-treated with ethylenediamine (amino-resin) andthen followed by treatment with carbon disulphide(thio-resin) [18]. Amine/mercaptan groups con-taining resin was also prepared through direct con-densation polymerization between 2-chloroethoxymethyl thiirane and diamine [16].

In the present work, a simple method for immo-bilizing GMA/DVB resin by amine/mercaptangroups has been reported. The uptake behaviourof mercury (II) on the resin obtained would be stud-ied using batch and columnmethods. Breakthroughcurves for the recovery of mercury (II) as well as theselectivity of the resin will also be investigated.

H2NCSNH2

S

GMA/DVB resin Thiirane resin

(I) (II)

O

Scheme 1.

2. Experimental

2.1. Chemicals

Glycidylmethacrylate (GMA), divinylbenzene55% (DVB), benzoyl peroxide (Bz2O2), ethylenedi-amine (ED) and thiourea were Aldrich products.All other chemicals were Prolabo products andwere used as received. Mercuric chloride and mer-curic nitrate were used as a source for Hg(II). Cad-mium nitrate, lead acetate, zinc chloride, copperacetate, calcium chloride and magnesium sulphatewere used as a source for Cd(II), Pb(II), Zn(II),Cu(II), Ca(II) and Mg(II), respectively.

The GMA/DVB resin (I) was prepared throughthe polymerization of GMA in the presence ofDVB as a cross-linking agent at a molar ratio of9.5:0.5, respectively. The procedure of preparationwas carried out as given elsewhere [19].

2.2. Preparation of methyl thiirane methacrylate

resin

Methyl thiirane methacrylate (II) intermediatewas prepared according to the early reportedmethod [20]. Three gram of the resin obtained inthe previous step and 3 g of thiourea were addedto a mixture of DMF/ethanol of ratio 3:1 (v/v),respectively. The reaction mixture was heated inoil bath at 60 �C with continuous stirring for72 h. The product was filtered off, washed with

cold methanol, acetone and then dried in air.The reaction may be represented as in Scheme 1.

2.3. Preparation of amine–mercaptan chelating

resin (R-S–N)

One gram of methyl thiirane methacrylate (II)(containing 2.53 mmol of sulphur) which obtainedin the previous step was added to 4 ml (59 mmol)ED dissolved in 12 ml DMF. ED was used in ex-cess compared to methyl thiirane methacrylate(II) to minimize the reaction of each ED withtwo thiirane residues. The reaction mixture washeated at 75–80 �C for 72 h in oil bath. A pale yel-low product (III) was formed, filtered off, washedwith cold methanol and then dried in air. The reac-tion can be represented as in Scheme 2. The IRstudies were performed using a Perkin–Elmer IR-Spectrophotometer 550 S.

2.4. Uptake measurements

2.4.1. Preparation of solutions

A stock solution (2 · 10�2 M) of each metal ionunder study was prepared in distilled water. Astock solution of EDTA (5 · 10�3 M) was pre-pared and standardized against a solution ofMgSO4 Æ 7H2O using Eriochrome Black-T (EBT)as indicator [21]. Buffers of acetic acid/acetate(pH 3.8–5.8) and ammonium hydroxide/ammo-nium chloride (pH 9–10) were used for the experi-ments that were carried out at controlled acidic orbasic conditions.

2.4.2. Uptake of metal ions using batch method

Uptake experiments of the studied metal ionsusing batch method were done by placing 0.1 gof air dry resin in a flask containing 100 ml ofthe studied metal ion at the desired initial con-

S

(II)

SH(III)

Amine-mercaptan resin

(IV)

ED

CHCH2NHCH2CH2NH2

SH

CHCH2NHCH2CH2NHCH2CH

SH

and

Scheme 2.

A.A. Atia et al. / Reactive & Functional Polymers 65 (2005) 267–275 269

centration and pH. The contents of the flaskwere equilibrated on a Vibromatic-384 shakerat 300 rpm and at about 28 �C for definite timeperiod. Five millilitre of the solution was takenafter the equilibration time then filtered off,where the residual concentration of metal ionwas determined via the titration against5 · 10�3 M EDTA using PAR as indicator forHg(II), murexide for Cu(II) and EBT for Ca(II),Mg(II), Cd(II), Zn(II) and Pb(II). The estimationof Hg(II) in a binary mixtures of Cu(II), Cd(II)and Zn(II) has been carried out according to theabove procedures using KI as a masking agentfor Hg(II) [21].

2.4.3. Effect of pH on precipitation the of Hg(II)

The effect of pH on the precipitation of Hg(II)was performed by placing 50 ml of HgCl2 solutionin a series of glass beakers. The pH of each solu-tion was adjusted using HCl and NaOH. The con-tents of each beaker was stirred gently then left tosettle, where 10 ml was centrifuged and the con-centration of soluble Hg ions was determined viatitration against EDTA using PAR as indicator.

2.4.4. Effect of pH on uptake the of Hg(II)

Uptake experiments under controlled pH werecarried out following the above procedure. The de-sired pH was controlled using the suitable buffer.For studying the uptake in strong acidic media,HCl, HNO3 or H2SO4 was used. The equilibriumtime was fixed at 3 h and 28 �C.

2.4.5. Uptake experiments using column method

About 0.1 g of the resin was placed in a glass col-umn (10-cm length and 0.4-cm diameter). Solutionof Hg(II) with initial concentration of 2 · 10�2 Mwas allowed to flow gradually through the columnunder the force of gravity at different rates (1, 2, 3and 4 ml/min). Ten millilitre of the underflow solu-tion was subsequently removed, where the residualconcentration for Hg(II) was determined.

2.4.6. ElutionElution experiments were performed by placing

0.1 g of the resin in the column then loaded withHg(II) at flow rate of 1 ml/min. After reachingthe maximum uptake (3.10 mmol/g), the resinwas washed carefully by flowing distilled waterthrough the column. The resin loaded by Hg(II)was then subjected for elution using different min-eral acids (HCl, HNO3 and H2SO4) with differentconcentrations. The concentration of the releasedHg(II) at 10 ml intervals of the down-flow was de-tected via titration against EDTA (5 · 10�4 M).The elution process continued till the down-flowbecomes free of Hg(II).

3. Results and discussion

The yield of thiirane resin (II) and amine/mer-captan resin (R-S–N) (III) was 70% and 80%,respectively. The elemental analysis of thiirane resin(II) showed that it contains 8.10% of sulphur(equivalent to 2.53 mmol/g). The elemental analysis

270 A.A. Atia et al. / Reactive & Functional Polymers 65 (2005) 267–275

data showed also that the resin R-S–N contains4.53% and 7.40% for nitrogen and sulphur, respec-tively. These percentages correspond to 3.23 and2.30 mmol/g of N and S, respectively. Theoreti-cally, the molar ratio of N/S = 2 and 1 for struc-ture III and IV, respectively. An average of N/S = 1.5 which almost matches the molar ratio ob-tained from elemental analysis (N/S = 1.4). Thisindicates the presence of the two suggested struc-tures. The resin obtained was found to be stableagainst mineral acids and alkalis.

The results of IR showed that the epoxy bandat 1265 cm�1 in the spectrum of GMA/DVB resin(I) disappeared in that of R-S–N (III). Moreover,the spectrum of R-S–N is characterized by mN–Hat 3442/3250 cm�1 and mC–N at 1439 and1327 cm�1. The observed peak at 2529 cm�1 isalso characteristic for mS–H [10,16].

3.1. Uptake of Hg(II) by the resin using batch

method

Fig. 1 shows the change in the uptake of Hg(II)from its aqueous solutions at pH 5 (natural) as afunction of time by the resin. It is seen that 50%of the total uptake reached within 20 min, whereascomplete uptake equilibrium was achieved within90 min.

0 100 200 300 400 500

Time (min)

0

1

2

3

4

Upt

ake,

mm

ol/g

Fig. 1. Uptake of Hg(II) by resin R-S–N as a function of time.

3.2. Effect of pH on the uptake of Hg(II)

The effect of the acidity of the medium on theuptake of Hg(II) was studied and the data are pre-sented in Fig. 2. The highest uptake value was re-corded at the pH 5 (natural). This may beattributed to the presence of free lone pair of elec-trons on nitrogen and sulphur atoms (or deproto-nation of –SH group) suitable for coordinationwith the metal ion to give the corresponding re-sin–metal complex. The higher affinity of Hg(II)towards the –SH sites may be attributed to the softbase nature of (S) atom which capable for interac-tion with Hg(II). The decrease of the uptake in theacidic media may be attributed to the protonationof the lone pair of nitrogen along with the lowerdissociation of the SH group that hinder the com-plex formation. These findings are in agreementwith that early reported by others [11,22]. The up-take of Hg(II) beyond the natural pH (pH > 5) isdoubtful to be attributed only to the interactionof the free Hg(II) cations with the active sites onthe resin but also to the formation of metalhydroxide species such as soluble Hg(OH)+ and/or insoluble precipitate of Hg(OH)2. This conclusionwas taken from the precipitation curve of Hg(II) asa function of pH (Fig. 3). The precipitation percent

0 2 4 6 8 10 12

pH

0

1

2

3

4

5

6

7

Upt

ake,

mm

ol/g

Fig. 2. Effect of pH on the uptake of Hg(II) by resin R-S–N.

A.A. Atia et al. / Reactive & Functional Polymers 65 (2005) 267–275 271

increases dramatically just after the natural pHand complete proceeded around pH 7.

The effect of the conjugate anion on the uptakeof Hg(II) by R-S–N resin was investigated usingdifferent mineral acids as well as using differentmercury salts. The data obtained are listed inTable 1. Starting with HgCl2, an appreciable up-take values were reported in case of HCl whilevery low uptake was noticed for HNO3 orH2SO4. The observed higher uptake in case ofHCl may be explained by the formation of anioncomplex such as HgCl�3 [23]. This anion could beable to exchange through the Cl�, which is elec-trostatically attached to the resin, according tothe following reaction [14]:

HgCl3-

+NH+Cl- NH+HgCl3-

Cl-+

0 2 4 6 8 10 12

pH

0

20

40

60

80

100

Pre

cipi

tatio

n, %

Fig. 3. Precipitation of Hg(II) as a function of pH at initialconcentration 2 · 10�2 M.

Table 1Effect of conjugate anion on the uptake of Hg(II) by resin R-S–N

pH Uptake (mmol/g)

HgCl2

HCl HNO3 H2SO4

1.0 0.80 0.10 0.102.0 1.60 0.20 0.102.5 1.76 0.83 0.503.0 2.02 1.60 1.10

Such an ion exchange mechanism requires the for-mation of the complex (HgCl�3 ). The minor uptakein the case of HNO3 or H2SO4 may be attributedto: (i) The complex Hg–nitrate or Hg–sulphate an-ions (similar to HgCl�3 ) may not be available; (ii)The higher stability of (R-NH+)NO�

3 or the (R-NH+)2 SO

2�4 which retards the ion exchange mech-

anism [13].Starting with Hg(NO3)2, an appreciable uptake

values were reported in case of HCl or HNO3,while very low uptake was recorded in case ofH2SO4 at pH range 1–2. As explained earlier,the uptake in the case of HCl was attributed tothe formation of the complex anions HgCl�3 . Inaddition, the lower uptake in case of H2SO4 isattributed to the strong binding of SO2�

4 groupto the amino sites of the resin rendering the ionexchange mechanism [13]. The appreciable uptakein case of HNO3 may be explained by the lowerbinding of NO�

3 to Hg(II) [23]. This promotesthe interaction of Hg(II) with the active sites ofthe resin.

The recorded uptake at pH 2.5–3.0 may beattributed to the beginning of complex formationdue to the partial deprotonation of the active sites(–SH) on the resin.

3.3. Selectivity of the resin for mercury sorption

The relatively higher uptake of Hg(II) at lowerpH values may be useful in the selective separationof Hg(II) from other metal ions. The uptakebehaviour of Hg(II), Cd(II), Zn(II), Cu(II), Pb(II),Ca(II) and Mg(II) was studied at pH 2.7 and sameother adsorption conditions. The results are re-ported in Table 2 which show maximum uptakevalues of 2.0, 0.2, 0.1, 0.2, 0.0, 0.0 and 0.0 mmol/g,

Hg(NO3)2

HCl HNO3 H2SO4

0.70 0.70 0.100.90 1.40 0.201.30 1.60 0.801.80 1.90 1.00

Table 2Maximum uptake capacity of resin R-S–N towards differentmetal ions at pH 2.7 and initial concentration of 5 ·10 �3 M ofeach metal ion

Metal ion Uptake (mmol/g)

Hg(II) 2.0Cd(II) 0.2Zn(II) 0.1Cu(II) 0.2Pb(II) 0.0Ca(II) 0.0Mg(II) 0.0

272 A.A. Atia et al. / Reactive & Functional Polymers 65 (2005) 267–275

for Hg(II), Cd(II), Zn(II), Cu(II), Pb(II), Ca(II)and Mg(II), respectively. Selective separation ofHg(II) from its binary mixtures with other metalions was also examined where similar results forthat of individual metal ions were obtained. Thisimplies that the studied resin could be used suc-

0 4 8 12 16 20 24 28

Equilibrium concentration, mM

1

2

3

4

5

Upt

ake,

mm

ol/g

Fig. 4. Adsorption isotherms of Hg(II) using resin R-S–N.

SH

CHCH2NHCH2CH2NH2 and

HgHg

Scheme 3

cessfully in the selective separation of Hg(II) fromthe other investigated metal ions.

3.4. Effect of initial concentration on the uptake of

Hg(II)

Adsorption isotherms are used to describe therelationship between the amount of adsorptionand the equilibrium concentration of the metal ionsat a certain temperature. Fig. 4 shows the adsorp-tion isotherms of Hg(II) by the resin at natural pHand 28 �C. Inspection of Fig. 4 reveals that the up-take increases with the increase of equilibrium con-centration until reaching a saturation value (3.10mmol/g) after which, the concentration no longeraffects the uptake capacity. This value of Hg(II) up-take is considered quiet reasonable compared tothiol containing resins studied by others where anuptake value of 0.5–1.0 mmol/g was reported [24].The ligand occupation (%) of the resin towards Hgcould be verified using the relation [25].

ligand occupation ð%Þ

¼ uptake of Hg in mmol=g

concentration of active sites in mmol=g� 100

The uptake of Hg obtained experimentally inboth cases of structure III or IV is 3.10 mmol/gcorresponding to a molar ratio of Hg/active sites(N + S) = 56%. Theoretically and based on theproposed chelating structures shown in Scheme 3,the Hg/active sites (N + S) = 66% and 50% forstructure III and IV, respectively. Thus, an aver-age of Hg/active sites (N + S) = 58% is obtainedwhich is comparable with the percent obtainedexperimentally (56%). This is further evidencefor the presence of both structures III and IVwith the latter more pronounced. The bindingconstant of the metal ions with an adsorbentmay be verified by plotting the adsorption dataaccording to the Langmuir isotherm [26].

SH

CHCH2NHCH2CH2NHCH2CH

SHHg Hg

.

Table 3Parameters of Langmuir adsorption isotherm for Hg(II) onresins

Resin Metal ion qs (mmol/g) K (L/mmol)

R-S–N Hg(II) 3.10 2.00R-Na Hg(II) 1.75 0.87R-Sa Hg(II) 2.00 1.00

a Taken from [18] for comparison.

0 40 80 120 160 200

ml added

0

1

2

3

4

5

Upt

ake,

mm

ol/g

Flow rate

1 ml/min

2 ml/min

3 ml/min

4 ml/min

Fig. 5. Effect of flow rate on the uptake of Hg(II) by resinR-S–N.

A.A. Atia et al. / Reactive & Functional Polymers 65 (2005) 267–275 273

Ce

qe¼ Ce

qsþ 1

Kqs.

where Ce is the equilibrium concentration of themetal ion, mmol/L, qe is the adsorbing capacityin equilibrium state, mmol/g, qs is the saturatedmercury uptake capacity on the resin, mmol/gand K is the equilibrium constant (binding con-stant), L/mmol. Plotting of Ce/qe vs. Ce gives astraight line, indicating that the adsorption corre-sponds to Langmuir isotherm. The straight linehas intercept and slope values equal to 1/Kqs and1/qs, respectively. The values of K and qs for theadsorption data of Hg(II) by the resin were ob-tained and reported in Table 3. As indicated inTable 3, the investigated resin displays higher uptakecapacity (qs = 3.10 mmol/g) as well as higher bind-ing constant (K = 2.0) towards Hg(II) relative tothat reported earlier in our previous work for re-sin-amine, R-N (qs = 1.75, K = 0.87) and for re-sin-thio, R-S (qs = 2.0, K = 1.0) [18]. Thisbehaviour can be explained on the basis of thehigher chelating power of R-S–N chelating resinthrough amine–mercaptan sites to give highly sta-ble Hg-complex with two fused five membered che-late rings. Whilst in the case of Hg-complexs withR-N and R-S resins only one chelate ring may beformed.

3.5. Uptake of Hg(II) using column method

Fig. 5 shows the uptake of Hg(II) by the resinas a function of flow rate. The data indicate thatthe maximum uptake is related to the flow rate.Generally, and for all flow rates, as the volume

Elution ratioð%Þ ¼ Amount of metal ion desorbe

Amount of metal ion s

pass increases, the uptake value increases. It isalso seen that the volume of metal ions requiredfor complete saturation (3.10 mmol/g) is 90, 110,130 and 160 ml for the flow rates 1, 2, 3 and4 ml/min, respectively. This means that as flowrate increase large volume of metal ion neededfor complete saturation. This can be attributedto the lower time of contact between resin activesites and metal ions. On the other hand, the low-er flow rates give higher uptake values at thesame volume of metal ion passes. This can alsorelate to the contact time.

3.6. Column elution

Elution of Hg(II) from the resin packed in thecolumn was tested using HCl, HNO3 and H2SO4

acids with different concentrations and at flow rateof 1 ml/min. The elution ratio was calculated fromthe amount of metal ions adsorbed on the resinsand the desorbed amount in the elution mediumaccording to the following equation [18]:

d to the elution medium

orbed on the resin� 100

274 A.A. Atia et al. / Reactive & Functional Polymers 65 (2005) 267–275

The elution results are shown in Figs. 6(a)–(c).In general, the elution efficiency of HNO3 andH2SO4 is better than that of HCl. For example,

0 40 80 120 1600

20

40

60

80

100

Elu

tion

ratio

, %

HCl

0.1 M

0.5 M

1.0 M

2.0 M

6.0 M

0 40 80 120 1600

20

40

60

80

100

Elu

tion

ratio

,%

HNO3

0.1 M

0.5 M

1.0 M

2.0 M

6.0 M

0 40 80 120 160

ml added

0

20

40

60

80

100

Elu

tion

ratio

, %

H2SO4

0.1 M

0.5 M

1.0 M

2.0 M

6.0 M

a

b

c

Fig. 6. Column elution of Hg(II) from resin R-S–N by differentacids: (a) HCl; (b) HNO3; (c) H2SO4.

the elution percentage using 40 ml (6 M) of HCl,HNO3 and H2SO4 are 32%, 90%, and 94%, respec-tively. The lower elution efficiency of HCl may beexplained on the basis of the uptake of Hg(II)through ion exchange mechanism at higher con-centration of HCl due to the formation ofHgCl�3 . In our previous work [18], it was reportedthat elution of Hg(II) from R-N and R-S resinsreached 97% and 94%, respectively using 0.5 NHNO3. This again indicates the higher binding ofHg(II) with the resin R-S–N relative to that of res-ins R-N and R-S which has been reflected in the(K) value in both cases. It is also seen that as theconcentration and the volume added of the eluentincrease the percentage of the elution increases.

4. Conclusions

Mercaptan-amine chelating resin has been pre-pared by subsequent treatment of glycidylmethac-rylate/divinyl benzene resin with thiourea andethylenediamine. The uptake of Hg(II) by the resinobtained was investigated using batch and columnmethods. Hg(II) showed higher affinity towardsthe resin to give maximum capacity of3.10 mmol/g. The effect of the conjugate anionon the uptake from acidic media was investigated.The resin obtained showed higher selectivity to-wards Hg(II) over other metal ions. Breakthroughcurves on the elution of the adsorbed Hg(II)loaded on the resin surface were carried out usingHCl, HNO3 and H2SO4. It was recommended touse HNO3 or H2SO4 acids (not HCl) for the elu-tion process.

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