a chelating resin containing 1-(2-thiazolylazo)-2-naphthol as the functional group; synthesis and...

Ž .Microchemical Journal 70 2001 195�203

A chelating resin containingž /1- 2-thiazolylazo -2-naphthol as the functional group;

synthesis and sorption behavior for trace metal ions

Won Leea,�, Si-Eun Leea, Chang-Heon Leeb, Young-Sang Kimc,Yong-Ill Leed

aResearch Institute for Basic Sciences and department of Chemistry, Kyunghee Uni�ersity, Seoul 130-701, South KoreabNuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Taejon 305-600, South Korea

cDepartment of Chemistry, Korea Uni�ersity, Jochiwon, Choongnam 339-700, South KoreadDepartment of Chemistry, Changwon National Uni�ersity, Changwon 641-773, South Korea

Abstract

Ž . Ž .A new polystyrene-divinylbenzene resin containing 1- 2-thiazolylazo -2-naphthol TAN functional group wasŽ . Ž . Ž .synthesized and its sorption behavior for 19 metal ions including Zr IV , Hf IV and U VI was investigated by batch

Ž . Ž .and column experiments. The chelating resin showed a high sorption affinity for Zr IV and Hf IV at pH 2. Someparameters affecting the sorption of the metal ions are detailed. The breakthrough and overall capacities were

Ž . Ž .measured under optimized conditions. The overall capacities of Zr IV and Hf IV that were higher than those of theother metal ions were 0.92 and 0.87 mmol�g, respectively. The elution order of metal ions at pH 4 was evaluated as:

Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž .Zr IV �Hf IV �Th IV �V V �Nb V �Cu II �U VI �Ta V �Mo VI �Cr III �Sn IV �W VI . Quan-Ž . Ž .titative recovery of most metal ions except Zr IV was achieved using 2 M HNO . Desorption and recovery of Zr IV3

was successfully performed with 2 M HClO and 2 M HCl. � 2001 Elsevier Science B.V. All rights reserved.4

Ž .Keywords: Chelating resin; 1- 2-thiazolylazo -2-naphthol; Sorption behavior

1. Introduction

A variety of analytical methods based on spec-trochemical analysis have been constantly re-

� �ported in previous decades 1�3 . Of the conven-tional analytical methods, inductively coupled

� Corresponding author.Ž .E-mail address: [email protected] W. Lee .

Ž .plasma atomic emission spectrometry ICP-AEShas been widely selected as the technique ofchoice to perform analysis of trace amounts ofmetal ions owing to its high sensitivity, repro-ducibility and wide dynamic concentration range.In spite of these advantages, however, separationand pre-concentration of trace levels of metalions are indispensable because spectral interfer-ence is found in the intensively complex atomicemission spectra of matrices of various samples

0026-265X�01�$ - see front matter � 2001 Elsevier Science B.V. All rights reserved.Ž .PII: S 0 0 2 6 - 2 6 5 X 0 1 0 0 1 3 2 - 1

( )W. Lee et al. � Microchemical Journal 70 2001 195�203196

such as metal alloys and ores which are of inter-est in many studies. Many separation techniques,using solvent extraction and ion exchange chro-matography, have been applied for the purpose.In particular, studies on the synthesis and sorp-tion characterization of chelating resins availablefor interesting metal ions have been extensivelycarried out in a number of laboratories becauseboth their sorption ability and sorption selectivityare superior to those of ion exchangers in trace orultra trace concentration levels.

There has been great interest in any fractiona-tion between Zr and Hf in geochemistry andcosmochemistry because any change in the Zr�Hfratio may be interpreted as a reflection of achange in the geochemical or cosmochemical en-

� �vironment 4,5 . However, Zr and Hf have ex-tremely similar chemical properties due to theiridentical atomic and ionic radii and the sorptionbehavior of Hf is very similar to Zr, which makesthem difficult to separate from each other.

This paper describes in detail the characteriza-tion of a new chelating sorbent, XAD-16-TAN,

Žwhich was synthesized by coupling 1- 2-thiazo-. Ž .lylazo -2-naphthol TAN with a diazotized

styrene-divinylbenzene, and its sorption and des-orption behavior of the chelating resin for 19

Ž . Ž . Ž .metal ions including Zr IV , Hf IV and U VI .On the basis of selective chelate forming for Zrand Hf, we paid attention to TAN which acts as atridentate ligand toward metal ions and a metal-

� �indicator in complexometric titrations 6�8 . Onthe other hand, Amberlite XAD-16 was chosen asthe matrix of the chelating sorbent because it has

Ž 2 .the largest surface area 800 m �g in a series ofAmberlite XAD co-polymers, which have the ad-vantages of having a high surface area, uniformpore distribution and rigid porous structure andwhich have been widely used as a matrix of sor-bents suitable for multi-elements pre-concentra-

� �tion from aqueous solutions 9�12 .

2. Experimental

2.1. Materials

Amberlite XAD-16 resin was a product of

Aldrich. The 100�200 mesh resin was successivelyŽ .washed with H O�methanol 70:30, v�v , 2 M2

Ž .NaOH�methanol 50:50, v�v , H O�methanol2Ž . Ž .50:50, v�v , 2 M HCl�methanol 50:50, v�v ,

Ž .THF�methanol 50:50, v�v , acetone andŽmethanol, and finally with H O�methanol 50:50,2

.v�v . The resin was dried in a vacuum oven at60�C. TAN was obtained from Sigma. Metal stocksolutions were prepared by diluting ICP standard

Ž .solutions 1000 �g�ml, AccuStandard . All thechemicals were of analytical reagent grade.

2.2. Apparatus

The concentrations of metal ions were de-termined by an inductively coupled plasma atomic

Žemission spectrometer IRIS�AP, Thermo-Jarrel.Ash . Functional groups of intermediates and a

final chelating resin obtained in the synthesisprocess were identified with a FT-IR spectrome-

Ž .ter IFS 28, Bruker . Elemental analysis was car-Žried out using elemental analyzer Eager 200,

.CEst .

2.3. Synthesis of XAD-16-TAN chelating resin

XAD-16-TAN chelating resin was prepared as� �described previously 13 . To a mixture of HNO3

Ž .and H SO 40:60, v�v on an ice bath, 5 g of2 4Amberlite XAD-16 resin was added slowly over aperiod of 30 min with stirring. The mixture washeated to 59�60� and kept at this temperature for1 h. The contents were poured into a glass columnfilled with ice water, filtered off and washed withdistilled water to pH 4�5. The nitrated resinŽ .XAD-16-NO was then reduced by refluxing for224 h in a mixture of concentrated HCl and ethanolŽ .45:50, v�v containing 50 g of stannous chloride.After cooling to ambient temperature, the reduc-tion product was filtered off, washed with a mix-

Žture of concentrated HCl and ethanol 45:50,.v�v , 2 M NaOH and distilled water, successively.

Ž .Finally, the aminated resin XAD-16-NH was2soaked in 1 M HCl for 1 day and diazotized bythe slow addition of 1 M NaNO at 0�3�C. After2diazotization was completed, the diazotized resinwas rapidly filtered off, washed with an ice-cold1% NaCl to pH 4 and subsequently coupled with

( )W. Lee et al. � Microchemical Journal 70 2001 195�203 197

Fig. 1. Chelate formation of the metal ion with TAN on theXAD-16-TAN chelating resin.

5 g of TAN in a mixture of 10% NaOH andmethanol. After stirring for 30 min, the resultingproduct was filtered off, washed with distilledwater and 1 M HCl until free from alkali, fol-lowed by drying at 60�C over P O in vacuum.2 5Hereafter, the chelating resin was designatedXAD-16-TAN, corresponding to the number ofthe Amberlite XAD-16 resin. The chelate forma-tion of the metal ion with TAN, functional groups

� �of the chelating resin, is depicted in Fig. 1 14 .

2.4. Chemical stability of the resin

Solutions of 1�5 M HCl and NaOH were addedto the polyethylene bottle containing 30 mg ofXAD-16-TAN. It was shaken continuously for 7days, filtered off and washed with distilled wateruntil it became neutral. After drying, the sorption

Ž .capacity for Cu II was measured by batch equi-librium experiments.

2.5. Sorption studies

The sorption behaviors of XAD-16-TAN forŽ . Ž . Ž . Ž . Ž . Ž .Zr IV , Hf IV , U VI , Cr III , Mo VI , W VI ,Ž . Ž . Ž . Ž . Ž . Ž .V V , Ta V , Nb V , Fe III , Sn IV , Co II ,Ž . Ž . Ž . Ž . Ž . Ž .Cu II , In III , Mn II , Ni II , Pb II , Th IV ,Ž .Zn II were studied by batch and column meth-

ods.

2.6. Effect of pH on the sorption of metal ions

A 50-mg sample of the resin was shaken with50 ml of the mixed solution containing 10 �g�ml

of each metal ion at pH 1�6. The pH of thesolution was adjusted to the desired value withhydrochloric acid or ammonia solution. After 24h, the residual concentrations of the metal ionswere measured by ICP-AES.

2.7. Kinetics of the sorption of metal ions on XAD-16-TAN

A 15-mg sample of the resin was shaken withŽ .30 ml of 0.01 M acetate buffer solution pH 3

Ž .containing 10 �g�ml of the Zr IV . Aliquots ofthe solutions were withdrawn at various intervals

Ž .and the residual concentration of the Zr IV wasmeasured.

2.8. Effect of masking agent on the sorption of metalions

A 15-mg sample of the resin was shaken withŽ .50 ml of 0.01 M acetate buffer solution pH 4

containing 10 �g�ml of each metal ion and 0.5�10Ž .mM of ethylenediaminetetraacetic acid EDTA ,

Ž .cyclohexanediaminetetraacetic acid CDTA , andŽ .nitrilotriacetic acid NTA as a masking agent,

respectively. After 24 h, the residual concentra-tions of the metal ions were measured.

2.9. Breakthrough experiment

For the column experiment, 5 �g�ml of themixed metal solution buffered to pH 4 was passed

Ž .through polyacryl column 0.4�5 cm , packedwith 100 mg of the resin suspended in distilledwater and pre-conditioned with the 0.01 M ac-

Ž .etate buffer solution pH 4 . The solution waseluted at a flow rate of 0.2 ml�min. The effluentfractions were collected in 5-ml portions and ana-lyzed for the presence of the metal.

2.10. Desorption studies

The mixed metal solution containing 5 �g�mlof each metal ion was prepared with 0.01 M

Ž .acetate buffer solution pH 4 . A 5-ml aliquot waspassed through the column of XAD-16-TAN at aflow rate of 0.2 ml�min. After washing with 5 ml

Ž .of 0.01 M acetate buffer pH 4 and 5 ml of


Table 1Analytical data of the intermediates, synthesized resin and TAN monomer

�1Ž .Intermediates & IR spectrum of functional group cm mmol of functional group�g resinchelating resin a b cŽ .�N�O �N�H �C�N thia. �NO �NH �TAN2 2

Ž .XAD-16-NO 1526 s 5.962Ž .1350 s

Ž .XAD-16-NH 1626 s 3.852Ž .XAD-16-TAN 1640 m 1.25Ž .TAN monomer 1640 vs

thia.: thiazole group, m: medium, s: strong, vs: very strong. a,c: elemental analysis, b: non-aqueous titration method.

distilled water successively, the metal ions sorbedon the chelating resin were desorbed with 20 mlof 0.1�2 M HCl, HNO and HClO at a flow rate3 4of 0.1 ml�min. The effluent fractions were col-lected in 3-ml portions and analyzed for the pres-ence of the metal.

3. Results and discussion

3.1. Characteristics of XAD-16-TAN chelating resin

For the identification of functional groups, in-frared spectra of the intermediates, the TANmonomer and XAD-16-TAN chelating resin wereanalyzed by the KBr pellet method and the posi-tions of absorption bonds corresponding to thefunctional groups are listed in Table 1. XAD-16-NO exhibits two strong bands at 1526 and 13502cm�1 which are characteristic of nitro groups.However, these bands decrease in the infraredspectrum of XAD-16-NH and a strong band due2to amine groups was observed at 1626 cm�1. Thismeans that NO groups bonded to the XAD-162resin were reduced to NH . In the spectrum of2XAD-16-TAN, the absorption bands at 1490 and1400 cm�1 due to the C�C and C�N stretchingvibration of the thiazole group in TAN moleculesis observed. From these results, it can be con-firmed that the TAN molecules bonded to theXAD-16 resin. The data from elementary analy-ses of the synthesized resin are also listed inTable 1. The amount of TAN in the resin was1.25 mmol g�1.

Chemical stability was evaluated by measuringŽ .the change in sorption capacity for Cu II after

successive contact of XAD-16-TAN with acidicand alkaline solutions in various concentrationranges. As the results show, the chelating resinwas stable in acidic and alkaline solutions below 5M and can be reused more than five times.

3.2. Sorption of metal ions on XAD-16-TAN resin

The sorption of metal ions on chelating resin isdependent on the pH of a sample solution due tothe competitive reaction between chelate forminggroups and hydrogen ions in the solutions. Theeffect of the pH on the sorption of 19 metal ionsin the pH range 1�6 was examined by a batchexperiment and the results are presented in Figs.

Ž .2 and 3. The optimum pH is 2�5 for Zr IV , 2�4Ž . Ž . Ž . Ž .for Hf IV , 4 for Nb V and V V , 5 for U VIŽ . Ž .and Cu II , 3 for Th IV . The selectivity order of

Ž .metal ions is evaluated as follows: Zr IV �HfŽ . Ž . Ž . Ž . Ž . Ž .IV �Th IV �V V �Cu II �Nb V �U VI

Ž . Ž . Ž . Ž . Ž .Mo VI � Ta V � Cr III � W VI � In III �Ž . Ž . Ž . Ž . Ž .Fe III �Sn IV �Pb II �Ni II �Co II �Mn

Ž . Ž .II �Zn II . This order is in good agreement� �with that of the Irving�Williams series 15 and

also the stability constants of the chelates formed� �between TAN and the metal ions 16 . In particu-

lar, this chelating resin was highly selective forŽ . Ž .Zr IV and Hf IV at pH 2 when the sorption

percentage of other metal ions were very low.From this apparent selectivity of the resin, it is

Ž . Ž .clear that the separation of Zr IV and Hf IVfrom mixtures of metal ions is possible by usingXAD-16-TAN resin.

3.3. Mechanism and kinetics of the sorption

The kinetics of the sorption was studied using


Fig. 2. Effect of pH on the sorption of metal ions withXAD-16-TAN chelating resin. Resin weight: 50 mg; conc. ofmetal ions: each 10 �g�ml�50 ml; shaking time: 24 h.

Ž .Zr IV which showed the best sorption affinity forthe resin. As shown in Fig. 4, the sorption wasfast and the time taken to reach equilibrium wasapproximately 2 h. This demonstrates that XAD-16-TAN is suitable for the ion chromatographicseparation of the metal ions studied.

� �According to previous results 17�20 , the ex-change reaction of the sorption procedure of

Fig. 3. Effect of pH on the sorption of metal ions withXAD-16-TAN chelating resin. Resin weight: 50 mg; conc. ofmetal ions: each 10 �g�ml�50 ml; shaking time: 24 h.

Fig. 4. Sorption equilibrium of XAD-16-TAN chelating resinaccording to shaking time. Resin weight: 30 mg; conc. of metal

Ž .ion: Zr IV 10 �g�ml�30 ml; matrix: pH 3, 0.01 MHAc�NH Ac buffer solution.4

metal ions was regarded as taking place throughtwo mechanisms of film diffusion and particlediffusion. If the rate-determining step is particlediffusion, diffusion through the ion-exchange par-ticle, the following equations derived by Boyd et

� �al. 21 .

�6 1 2Ž . Ž .F�1� exp �n Bt 1Ý2 2� nn�1

Žwhere F is the amount of exchange at time. Ž .t � the amount of exchange at infinite time and

Ž .B is the sorption rate. Eq. 2 , between F andtime t was developed by Boyd et al.

Ž . Ž .� ln 1�F �k t 2d

Ž .where k is sorption rate constant. From Eqs. 1dŽ . Ž .and 2 , Eq. 3 is obtained.

Ž . Ž .� ln 1�F �cBt�k t 3d

where c is a constant. Therefore, if a linear plotof Bt vs. t is obtained, the rate-determining stepcan be expected as particle diffusion.

In the experiment, F is obtained from theŽ .sorption percentage change of Zr IV according

to the shaking time and Bt is obtained from the


Fig. 5. Sorption rate of XAD-16-TAN chelating resin accord-ing to shaking time. Resin weight: 30 mg; conc. of metal ion:

Ž .Zr IV 10 �g�ml�30 ml; matrix: pH 3, 0.01 M HAc�NH Ac4buffer solution.

F value. Values of Bt for each F value are given� �by Reichenberg 22 . As shown in Fig. 5, the plot

of Bt vs. t is linear; therefore, it can be seen thatthe rate determining step is diffusion through theparticle.

3.4. Effect of masking agent on the sorption of metalions

The applicability of masking agents such asCDTA, EDTA, and NTA to further selective sep-aration of metal ions from mixed metal solutionswas investigated. The results are illustrated inFigs. 6�8. As shown in Fig. 6, the sorption per-

Ž .centage of most metal ions containing Cr III ,Ž . Ž . Ž .Sn IV , W VI and Ta V was less than 30%

when adding more than 5 mM of CDTA. How-Ž . Ž .ever, the sorption percentages of Th IV , Nb V

Ž . Ž . Ž .and V V were 40% and Zr IV , Hf IV weremore than 70% when 10 mM CDTA was added.Also, CDTA had little effect on the sorption ofŽ .U VI . From this result, it was confirmed that the

Ž . Ž .masking effect of CDTA on Zr IV , Hf IV ,Ž . Ž . Ž . Ž .U VI , Th IV , Nb V and V V was lower thanŽ . Ž . Ž . Ž .Cr III , Sn IV , W VI and Ta V . The effect of

EDTA was shown in Fig. 7. In the case wheremore than 5 mM of EDTA was added, most

Fig. 6. Effect of CDTA concentration on sorption of metalions with XAD-16-TAN chelating resin. Resin weight: 50 mg;conc. of metal ions: each 10 �g�ml�50 ml; matrix: pH 4, 0.01M HAc�NH Ac buffer solution; shaking time: 24 h.4

Ž . Ž . Ž .metal ions containing Cu II , Nb V , V V andŽ .Th IV showed low sorption percentages of 6, 5,

10 and 25%, respectively. On the other hand, theŽ . Ž .sorption amounts of Zr IV and Hf IV were less

Ž . Ž . Ž . Ž .than Cu II , Nb V , V V and Th IV in EDTAsolutions, and then their sorption percentageswere more than 80% at 5 mM EDTA. Theseresults seem to indicate that EDTA can be effec-

Fig. 7. Effect of EDTA concentration on sorption of metalions with XAD-16-TAN chelating resin. Resin weight: 50 mg;conc. of metal ions: each 10 �g�ml�50 ml; matrix: pH 4, 0.01M HAc�NH Ac buffer solution; shaking time: 24 h.4


Fig. 8. Effect of NTA concentration on sorption of metal ionswith XAD-16-TAN chelating resin. Resin weight: 50 mg; conc.of metal ions: each 10 �g�ml�50 ml; matrix: pH 4, 0.01 MHAc�NH Ac buffer solution; shaking time: 24 h.4

tively used as a masking agent for the selectiveŽ . Ž .separation of Zr IV and Hf IV from the other

Ž . Ž .metal ions. As shown in Fig. 8, Zr IV and Hf IVhad very low sorption percentages of 17% and10%, respectively in 10 mM NTA solution. Also,

Ž .NTA had little effect on the sorption of U VI .The effect of masking on most metal ions except

Ž . Ž . Ž .Zr IV , Hf IV and U VI was shown as NTA�EDTA�CDTA.

3.5. Column breakthrough studies

The metal sorption capacity of XAD-16-TANwas measured to estimate how large a quantity ofthe chelating resin would be needed for the quan-titative recovery of an interesting metal ion froman aqueous solution. In order to obtain an opti-mum chromatographic condition, the effect offlow rate on the sorption of metal ions was inves-

Ž .tigated with Cu II . Overall capacity was calcu-Ž .lated by measuring the amount of Cu II sorbed

on XAD-16-TAN at the point where C�C , i.e.0Ž .Cu II concentration ratio of the effluent to in-

fluent is 0.5 on the breakthrough curves, and thebreakthrough capacity, C�C was 0.001. As shown0in Fig. 9, the breakthrough and overall capacityincreased with decreasing flow rate. This isprobably because the retention time of metal ionson the chelating resin increased with decreasing aflow rate. However, the capacities at the flow rateof 0.1�0.2 ml�min showed little difference.

Fig. 9. Effect of flow rate on sorption of metal ion with XAD-16-TAN chelating resin. Resin weight: 50 mg; conc. of metal ion:Ž .Cu II 10 �g�ml; matrix: pH 4, 0.01M HAc�NH Ac buffer solution; one fraction: 5 ml.4


Fig. 10. Breakthrough curves of metal ions with XAD-16-TAN chelating resin. Resin weight: 100 mg; conc. of metal ions: each 5�g�ml; matrix: pH 4, 0.01M HAc�NH Ac buffer solution; flow rate: 0.2 ml�min; one fraction: 5 ml.4

Therefore, the optimum flow rate was 0.2 ml�minin that it has shorter elution time. At a flow rateof 0.2 ml�min, breakthrough curves of the 12

Ž . Ž . Ž . Ž . Ž .metal ions Zr IV , Th IV , U VI , Cu II , Hf IV ,Ž . Ž . Ž . Ž . Ž . Ž .W VI , Mo VI , Ta V , Sn IV , Cr III , V V ,

Table 2Breakthrough capacity and overall capacity of metal ions withXAD-16-TAN chelating resin

Metal ion Breakthrough Overallcapacity capacitymmol�g resin mmol�g resin

Ž .Zr IV 0.74 0.92Ž .Hf IV 0.69 0.87Ž .Th IV 0.56 0.76Ž .V V 0.53 0.70Ž .Nb V 0.43 0.58Ž .Cu II 0.34 0.49Ž .U VI 0.29 0.41Ž .Ta V 0.25 0.36Ž .Mo VI 0.21 0.31Ž .Cr III 0.15 0.23Ž .Sn IV 0.13 0.21Ž .W VI 0.11 0.19

Resin weight: 100 mg; conc. of metal ions: each 5 �g�ml;matrix: pH 4, 0.01 M HAc�NH Ac buffer solution; flow rate:40.2 ml�min; one fraction: 5 ml.

Ž .Nb V are illustrated in Fig. 10. The inflections ofthe breakthrough curves were sufficiently sym-metrical for volume corresponding to half of ini-tial concentration and well separated, indicatingthat it should be possible to separate these metalions from their mixtures on a column of XAD-16-

� �TAN 23 . The resulting breakthrough and overallcapacities are listed in Table 2. The elution orderof metal ions obtained from this result at pH 4

Ž . Ž . Ž .was evaluated as Zr IV � Hf IV � Th IVŽ . Ž . Ž . Ž . Ž .�V V �Nb V �Cu II �U VI �Ta V �Mo

Ž . Ž . Ž . Ž .VI �Cr III �Sn IV �W VI . The overall ca-Ž . Ž .pacities of Zr IV and Hf IV which were higher

than the other metal ions were 0.92 and 0.87mmol�g, respectively. These results can be ex-

Ž . Ž .pected as Zr IV and Hf IV were selectively sor-bed on the chelating resin.

3.6. Desorption of metal ions

For the quantitative recovery of trace metalions and reuse of resin, the characteristics ofdesorption were investigated with desorptionagents such as HClO , HCl and HNO at a flow4 3rate of 0.1 ml�min. The results listed in Table 3

Ž . Ž . Ž .show that Zr IV , Hf IV , Th IV were at least


Table 3Desorption characteristics of metal ions on various desorptionagents with XAD-16-TAN chelating resin

Ž .Metal ion Recovery %

2 M HClO 2 M HCl 2 M HNO4 3

Ž .Zr IV 100 95 19Ž .Hf IV 90 100 100Ž .Th IV 94 100 100Ž .V V 20 82 48Ž .Nb V 26 90 62Ž .Cu II 38 46 100Ž .U VI 80 78 100Ž .Ta V 42 93 90Ž .Mo VI 89 27 79Ž .Cr III 45 20 100Ž .Sn IV 57 5 100Ž .W VI 92 30 84

Resin weight: 100 mg; conc. of metal ions: each 5 �g�ml;sorption flow rate: 0.2 ml�min; desorption flow rate: 0.1ml�min; desorption agent volume: each 15 ml.

90% recovered by elution with 2 M HClO and 24M HCl. When HCl was used, the high desorption

Ž . Ž .affinity was observed because Zr IV and Hf IVformed stable complexes of ZrCl2� and HfCl2�

6 6with chloride ions. Significantly, most metal ions

Ž .studied in the present study except Zr IV , werecompletely recovered using 2 M HNO . The re-3

Ž .covery percentage of Zr IV was, however, 19%.Ž .This is presumably because Zr IV has low stabil-

Žity constant of complex with nitrate ion log K f 1.�0.8 . Considering the different desorption be-

Ž .havior of Zr IV shown in these results, it isŽ .expected that Zr IV can be separated from other

Ž .metal ions containing Hf IV .

Acknowledgements

ŽThis work was supported by grant No. 1999-1-.124-001-3 from the interdisciplinary research

program of the KOSEF.

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a chelating resin containing 1-(2-thiazolylazo)-2-naphthol as the functional group; synthesis and...

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