Adsorption behaviour of non-transition metal ions on a synthetic chelating resin bearing iminoacetate functions

Separation and Purification Technology 43 (2005) 43–48

Adsorption behaviour of non-transition metal ions on a syntheticchelating resin bearing iminoacetate functions

Asem A. Atia, Ahmed M. Donia∗, Khalid Z. ELwakeelDepartment of Chemistry, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt

Received 7 April 2004; received in revised form 14 September 2004; accepted 27 September 2004

Abstract

Glycidyl methacrylate–divinylbenzene (GMA/DVB) resin bearing iminoacetate function was prepared through subsequent treatment of(GMA/DVB) resin by ethylenediamine and potassium chloroacetate, respectively. The chelating resin obtained showed a powerful adsorptioncharacter towards non-transition metal ions (Zn2+, Cd2+ and Pb2+) as well as alkaline earth metal ions (Ca2+ and Mg2+). The sodium form ofthe resin gave a slightly higher uptake capacity towards metal ions compared to the hydrogen form. The resin sample loaded with metal ionswas regenerated using HCl (0.5–2.0 M) without activity loss.©

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2004 Elsevier B.V. All rights reserved.

eywords:Chelating; Iminoacetate; Removal; Metal ions; Resins

. Introduction

Many industries such as metal plating, tanning andining operations release wastewater contaminated with

eavy metals into the environment. Various technologicalethods have been developed to control the pollution of

urface and ground water. Chelating resins with differentunctionalities have potential applications in the selectiveemoval of metal ions from industrial waste solutions [1–15].ome selected examples are iminoacetic acid [16–19], Schiffases [20,21], hydroxamic acid [22], amidoxime [23], thiol24,25], thiazole [26] and amines [27]. In our previousork, various amino chelating resins derived from glycidylethacrylate with different textural properties have been

btained [28,29]. Those resins were applied to the removalnd recovery of some heavy metal ions from aqueousolutions. The study showed that both the uptake capacitynd selectivity of the resins towards the investigated metalons depend upon amino group concentration, texturalharacteristics of the resin, type of metal ion and uptakeonditions.

The major goal of the present study is to modify theamine moiety of glycidyl methacrylate/divinylbenzene/ethylenediamine resin to iminoacetate function (EDTA-likestructure) suitable for interaction with metal ions. The uptakeas well as the elution characteristics of the resin obtained to-wards Zn2+, Cd2+, Pb2+, Mg2+ and Ca2+ will also be investi-gated.

2. Experimental

2.1. Chemicals

Glycidyl methacrylate (GMA), divinylbenzene (DVB),benzoyl peroxide (B2O2), ethylenediamine (en) and potas-sium chloroacetate were Aldrich products. All other chemi-cals were Prolabo products and were used as received. Zincchloride, cadmium nitrate, lead acetate, magnesium sulphateand calcium chloride were used as a source for Zn2+, Cd2+,Pb2+, Mg2+ and Ca2+, respectively.

∗ Corresponding author. Fax: +20 2 8356313.E-mail address:[email protected] (A.M. Donia).

2.2. Preparation of amino resin (RN)

GMA/DVB resin with molar ratio of 9.5:0.5 was preparedand loaded with ethylenediamine to give amine-bearing resin

383-5866/$ – see front matter © 2004 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2004.09.012

44 A.A. Atia et al. / Separation and Purification Technology 43 (2005) 43–48

(RN) as described in our previous work [28,29]. The con-centration of amino group in (RN) resin was calculated asreported earlier [28].

2.3. Preparation of iminoactate anchored resin

Four grams of potassium chloroacetate was dissolved indimethyl formamide/water mixture at ratio 2:1 v/v. Fourgrams of the (RN) resin, which was obtained in the previ-ous step, was added to the flask. The contents were heatedat 75–80 ◦C for 48 h in an oil bath. The product obtainedwas filtered off, washed subsequently with distilled waterand methanol, and then kept to dry. The resulting resin wasreferred as RN(COOH).

IR-spectra of the synthesized resins were performed usinga Perkin-Elmer IR-spectrophotometer 550 S.

2.4. Calculation of carboxylic group in the resin

One gram of RN(COOH) was conditioned in 100 ml of0.1 M NaOH at 28 ◦C for 6 h. Afterwards the mixture was fil-tered and the concentration of the unreacted NaOH was deter-mined through the titration of 5 ml of the filtrate against 0.1 MHCl. The concentration of carboxylic group (in mmol/g) wascalculated.

2

(rwR

3

3

soaooiir

3

p1co

for definite time period. A 5 ml of the solution were takenafter the equilibrium time and then filtered off. The resid-ual concentration of metal ion was determined via titrationagainst 5 × 10−3 M EDTA using EBT as indicator [30]. Eachdata point was taken as the average of three measurementswith standard deviation of 1 ± 0.5%.

3.3. Effect of pH on the uptake of metal ion

Uptake experiments under controlled pH were carried outfollowing the above procedures for uptake experiments. ThepH was adjusted using the suitable buffer. For studying theuptake in strong acidic media, HCl was used for chloridesalts, HNO3 for nitrate salts, CH3COOH for acetate salts andH2SO4 for sulphate salts. For studying the uptake in strongbasic media NaOH was used for Zn2+, Ca2+, Mg2+ and Pb2+

while NH4OH/NH4Cl was used for Cd2+. The equilibrationwas fixed to 3 h and 28 ◦C after which the residual concen-tration of the metal ion was measured.

3.4. Precipitation limits of the studied metal ions

Fifty millilitres (5 × 10−3 M) of metal ion solution underinvestigation was placed in a glass beaker where the desiredpH was adjusted using NaOH. The precipitate formed was fil-tct

p

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3

ul5uvwo

3

ruwcj1si

.5. Sodium form of the resin RN(COONa)

Three grams of RN(COOH) was conditioned in 20 ml0.5 M) NaOH solution for 20 h at 28 ◦C on the shaker. Theesin was filtered off, washed subsequently with distilledater and methanol, and then dried in air and referred asN(COONa).

. Uptake measurements

.1. Preparation of solutions

Stock solution (1 × 10−2 M) of the metal ion undertudy was prepared in distilled water. A stock solutionf EDTA (5 × 10−3 M) was prepared and standardizedgainst a standard solution of MgSO4·7H2O using Eri-chrome Black-T (EBT) as indicator [30]. Buffer solutionsf acetic acid/acetate (pH 3.4–6.0) and ammonium hydrox-de/ammonium chloride (pH 9–10) were used for the exper-ments carried out at controlled acidic or basic conditions,espectively.

.2. Metal ion uptake experiments using batch method

Metal ion uptake experiments using batch method wereerformed by placing 0.1 g of dry resin in a flask containing00 ml of the metal ion under study at the desired initial con-entration and pH. The contents of the flask were equilibratedn a Vibromatic-384 shaker at 3000 rpm and at about 28 ◦C

ered off and 5 ml of the filtrate was taken where the residualoncentration of the metal ion was determined. The precipita-ion percent (ppt%) was calculated by the following equation:

pt% = (M1 − M2) × 100

M1(1)

here M1 and M2 are the initial and residual concentrationsf the metal ion, respectively.

.5. Uptake experiments using column method

A 0.1 g of the resin (Na-form) was placed in a mini col-mn at bed height 1.5 cm (bed volume 0.18 cm3). The so-ution of the metal ion under study at initial concentration× 10−3 M was allowed to flow gradually through the col-mn under the force of gravity at rates 1, 2, and 3 ml/min (bedolume 0.18 cm3). Five millilitres of the underflow solutionas then taken every 10 min where the residual concentrationf the metal ion under study was determined.

.6. Elution experiments

Elution experiments were performed by placing 0.1 g ofesin (Na-form) in the column then loaded with the metal ionnder study. After reaching the maximum uptake, the resinas washed carefully by flowing distilled water through the

olumn. The resin loaded by the metal ion was then sub-ected for elution using HCl (0.5, 1 and 2 M) at flow rate ofml/min. A 10 ml of the underflow solution was removed

ubsequently where the concentration of the released metalon was determined.

A.A. Atia et al. / Separation and Purification Technology 43 (2005) 43–48 45

Scheme 1.

4. Results and discussions

The IR spectrum of the resin RN(COOH) displays a num-ber of bands near 3300–2500 and 1742 cm−1. These bands areassigned to � O H and � C O of the carboxylic group, respec-tively [31]. The observed bands at 2930–2950 and 1073 cm−1

are characteristic for aliphatic � C H and � C N, respec-tively. On the other hand, � NH2 in the spectrum of resin-amine (RN) at 3372 and 3290 cm−1 disappeared on treatmentwith the potassium chloroacetate. This indicates that the car-boxylation process proceeded. The suggested structure of theresin obtained was given in Scheme 1.

The amino and carboxyl groups content in both (RN) andRN(COOH) are 4.1 and 5.9 mmol/g, respectively. This con-firms the formation of both amino and carboxyl groups con-taining resins. On the other hand, the carboxyl group contentrepresents three-halves (3/2) of the amino group content. Thisindicates the complete carboxylation of the two amino groupsas shown in Scheme 1.

4.1. Uptake of metal ions using batch method

Table 1 represents a comparison between the adsorp-tion capacity of the Na- and H-forms of the resin. Theobserved differences may be attributed to the higher ionicn −ttCr((wZime

TSp

M

CPZCM

Fig. 1. Uptake of the studied metal ions by resin RN(COONa) as func-tion of conditioning time at natural pH and 28 ◦C from initial concentration5 × 10−3 M.

them. This indicates that the resin could be promising in thefield of water treatment (e.g. hardness and heavy metal re-moval). On the other hand, the EDTA-like structure of theresin may enhance its affinity towards a broad spectrum ofdifferent metal ions (transition/non-transition) in aqueous so-lutions. Fig. 1 shows the change of the uptake as a functionof time for the studied metal ions at equilibrium pH (Cd2+

6.6, Pb2+ 6.0, Zn2+ 6.5, Ca2+ 6.4, Mg2+ 7.0). The 50% ofthe total uptake was reached within 20 min whereas 90% up-take was achieved within 40 min. Equilibrium uptake wasachieved within 100 min for all the studied metal ions.

4.2. Effect of pH on the uptake of metal ion

The effect of the pH of the medium on the uptake was stud-ied and the results are shown in Fig. 2. The highest uptakevalues were recorded at the natural pH of the metal ion so-lution (Cd2+ 6.4, Pb2+ 5.8, Zn2+ 6.3, Ca2+ 6.15, Mg2+ 6.84).This may be attributed to the presence of free lone pair ofelectrons on nitrogen atom as well as the presence of car-boxylate anion ( COO−) suitable for coordination with the

Fa

ature of the Na-form giving RN(COO ) sites relativeo that of H-form which are controlled by the pH ofhe medium. The uptake in both forms follows the orderd2+ > Pb2+ > Zn2+ > Ca2+ > Mg2+. It is also seen that the

esin showed high affinity towards the studied metal ionsCd2+, Zn2+ and Pb2+) relative to the parent amine resinRN), which was previously studied by us [28,29]. In thatork the resin (RN) showed lower uptake towards Cd2+,n2+ and Pb2+ while no appreciable uptake was recorded

n the case of Ca2+ and Mg2+. The higher uptake of thoseetal ions by RN(COONa) and RN(COOH) resins can be

xplained by the higher affinity of carboxyl group towards

able 1aturation capacity of resins RN(COONa) and RN(COOH) at equilibriumH (Cd2+ 6.6, Pb2+ 6.0, Zn2+ 6.5, Ca2+ 6.4, Mg2+ 7.0)

etal ion Capacity of the resin (mmol/g)

RN(COONa) RN(COOH)

d2+ 1.30 1.10b2+ 1.00 0.95n2+ 1.10 0.80a2+ 1.00 0.90g2+ 0.90 0.80

t 28 ◦C.

46 A.A. Atia et al. / Separation and Purification Technology 43 (2005) 43–48

Fig. 3. Precipitation curves of the metal ions as function of solution pH atinitial concentration 5 × 10−3 M.

metal ion to give the corresponding resin–metal complex. Thedecrease of uptake in acidic media may be attributed to theprotonation of the lone pair of electrons on nitrogen and/orthe lower dissociation extent of the carboxyl group, whichhinder the interaction of metal ion. The uptake of the metalions beyond the natural pH is doubtful to be attributed only tothe interaction of the free metal ions with the active sites onthe resin. It may also be attributed to the formation of solubleor insoluble metal hydroxide species. This explanation wasconfirmed from the precipitation curves of metal ions as afunction of pH, Fig. 3. The observed lowering in the uptakeat pH 10 for Zn2+, Cd2+ and Pb2+ may be attributed to theformation of soluble metal hydroxide or ammonia/metal ioncomplexes, which have lower affinity towards the resin. Theobserved higher uptake values for Ca2+ and Mg2+ at higherpH values can be attributed to the interaction of the free metalions with the highly dissociated carboxyl groups on the resin.

Adsorption isotherms are used to describe the relationshipbetween the amount of adsorption and equilibrium concen-tration of metal ions at constant temperature. Fig. 4 showsthe adsorption isotherms of the studied metal ions at naturalpH and 28 ◦C. Inspection of Fig. 4 reveals that the uptake in-

F2

creases with the increase of equilibrium concentration untilreaching the saturation value after which, the concentrationno longer affects the uptake capacity. The affinity of the ad-sorbent towards the metal ions may be verified by plottingthe adsorption data according to Langmuir adsorption model[32]:

Ce

qe= Ce

qs+ 1

Kqs(2)

whereCe is the equilibrium concentration of the metal ion, qeis the adsorbing capacity in equilibrium state, qs is the satu-rated adsorbing capacity andK is the binding constant. In factthe adsorption isotherms of both Ca2+ and Mg2+ adsorbed onthe resin (sodium form) were found to fit Langmuir model(Fig. 5a) whereas the adsorption of Zn2+, Cd2+ and Pb2+ doesnot perfectly fit (Fig. 5b). This behaviour can be explainedon the basis of the nature of ( COONa) group as well as thesolubility product of M(OH)2 (where M = metal ion). The ad-sorption process proceeds via the replacement of Na+ by themetal ion. The released Na+ to the medium increases its basic-ity leading to the formation of insoluble M(OH)2 according to

Fig. 5. Fitting the adsorption data according to Langmuir isotherm: (a) Ca2+

and Mg2+ on RN(COONa); (b) Cd2+, Pb2+ and Zn2+ on RN(COONa); (c)Cd2+, Pb2+ and Zn2+ on RN(COOH).

ig. 4. Adsorption isotherms of the metal ions on resin RN(COONa) at8 ◦C.

A.A. Atia et al. / Separation and Purification Technology 43 (2005) 43–48 47

Table 2Parameters of Langmuir adsorption isotherm for the adsorption of Ca2+andMg2+ on the resin RN(COONa)

Metal ion qs (mmol/g) K (L/mmol) R2

Ca2+ 1.20 0.88 0.995927Mg2+ 1.11 0.92 0.996351

the solubility product values. The solubility products valuesare 4.12 × 10−17, 5.27 × 10−15, 1.42 × 10−20, 5.61 × 10−12

and 4.68 × 10−6 for Zn(OH)2, Cd(OH)2, Pb(OH)2, Mg(OH)2and Ca(OH)2, respectively [33]. So, the observed deviationfrom Langmuir in the case of Zn2+, Cd2+ and Pb2+ may beattributed to the lower solubility products of their hydroxiderelative to that of Mg(OH)2 and Ca(OH)2. The higher solu-bility products of Mg- and Ca-hydroxides retard the precip-itation of these metal ions. This explanation was confirmedby the results obtained from the uptake studies of Zn2+, Cd2+

and Pb2+ on the H-form of the resin. The uptake data werefound to fit Langmuir isotherm as shown in Fig. 5c. The bind-ing constant (K) values of Mg2+ and Ca2+ with the Na-formand Zn2+, Cd2+ and Pb2+ with the H-form of the resin aregiven in Tables 2 and 3, respectively.

4.3. Studies on the uptake of metal ions using columnmethod

Fig. 6a–c give the uptake of the metal ions (Cd2+, Mg2+

and Ca2+) by the Na-form of the resin as a function of timeat flow rates 1, 2 and 3 ml/min (bed volume 0.18 cm3). It wasfound that as the flow rate decreases longer time is requiredto achieve the saturation capacity. On the other hand as theflow rate increases, the uptake capacity increases at the sameflsrbhtt2utah0ocl

TPP

M

CPZ

Fig. 6. Effect of flow rate on the uptake of the metal ions by resinRN(COONa) from initial concentration 5 × 10−3 M: (a) Cd2+, (b) Ca2+,and (c) Mg2+.

4.4. Elution experiments

Elution of the studied metal ions from resin was testedusing HCl with different concentrations (0.5, 1 and 2 M) usingcolumn method. The desorption ratio was calculated from theamount of metal ions adsorbed on the resin and the amountof the metal ions desorbed from the resin and according tothe following equation [34]:

amount of metal ion desorbed to the elution medium

amount of metal ion sorbed on the resin× 100

(3)

The elution data are given in Fig. 7a–c. Generally, theelution efficiency using 130–140 ml of 0.5 M HCl was higherthan 90% for the studied metal ions. The 40–50 ml of (2 M)HCl was found to be the most effective eluting agent (elutionefficiency 93–100%). The regenerated resin sample was usedfor recovery of metal ions without activity loss more than 10cycles.

owing time. This is attributed to the large volume of theolution passing at the higher flow rate achieving early satu-ation of active sites. In conclusion, lower flow rate furnishesetter contact between the resin and the metal ions whereasigher flow rate gives the advantage of saturation at shortime. So, the engineer should manage the process accordingo the priority. It is also seen that the rates of flowing aboveml/min is less effective to give considerable changes in theptake values. It is also worth mentioning that the adsorp-ion capacity of the resin using column method (1.44, 1.24nd 1.15 mmol/g for Cd2+, Ca2+ and Mg2+, respectively) isigher than the corresponding batch method (1.2, 1.00 and.95 mmol/g for Cd2+, Ca2+ and Mg2+, respectively). Thebserved higher uptake capacity in some cases of columnompared to that of batch method can be attributed to theower desorption rate in the former case.

able 3arameters of Langmuir adsorption isotherms for the adsorption of Cd2+,b2+ and Zn2+ on the resin RN(COOH)

etal ion qs (mmol/g) K (L/mmol) R2

d2+ 1.25 1.38 0.988109b2+ 1.20 0.76 0.994401n2+ 1.04 0.63 0.988109

48 A.A. Atia et al. / Separation and Purification Technology 43 (2005) 43–48

Fig. 7. Elution of metal ions from resin RN(COONa) by HCl with differentconcentrations using column: (a) Cd2+, (b) Ca2+, and (c) Mg2+.

5. Conclusions

In conclusion, the prepared resin with iminoacetate func-tions showed high affinity towards Zn2+, Cd2+, Pb2+, Mg2+

and Ca2+. The Na-form of the resin gave uptake capacityslightly higher than the H-form. The uptake obtained by thecolumn method was relatively higher than that obtained bythe batch one. The resin obtained may be promising in thefield of the removal of heavy metals and hardness from drink-ing water and industrial wastes. HCl with different concentra-tions (0.5–2 M) was found to be the effective as eluting agent.The regenerated resin may be used repeatedly for recoveryof metal ions without significant activity loss.

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