Talanta 54 (2001) 243–253

Synthesis, characterization and structure effects onselectivity properties of silica gel covalently bonded

diethylenetriamine mono- and bis-salicyaldehyde andnaphthaldehyde Schiff,s bases towards some heavy metal

ions

Ezzat M. Soliman a,*, Mohamed E. Mahmoud b, Salwa A. Ahmed a

a Chemistry Department, Faculty of Science, El-Minia Uni6ersity, El-Minia 61519, Egyptb Chemistry Department, Faculty of Science, Alexandria Uni6ersity, Alexandria, Egypt

Received 13 June 2000; received in revised form 19 October 2000

Abstract

Four silica gel-immobilized new metal chelate Schiff,s bases were synthesized (I–IV). Silica gel chemically bondeddiethylenetriamine mono-naphthaldehyde and mono-salicyaldehyde Schiff’s bases (phases I and III) were producedvia the interaction of silica gel-modified diethylenetriamine with naphthaldehyde and salicylaldehyde, respectively.However, phases II and IV arose through the interaction of bis-naphthaldehyde and bis-salicylaldehyde Schiff,s basesof diethylenetriamine with 3-chloropropyltrimethoxysilane modified silica gel. The characterization of such newphases, their capabilities towards selective extraction or separation of Fe(III), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II)ions were studied and evaluated by both batch and column techniques as a function of pH and time of contact.Phases III and I showed high performance towards Cu(II) extraction, where their Cu(II) sorption determined to be0.957 and 0.940 mmol g−1, respectively. However, for phases IV and II, the great affinity was devoted to Fe(III)extraction followed by Cu(II) ions. The reactivity of metal ion sorption was discussed in the light of effects ofbulkiness as well as orientation of immobilized chelate on sorbent reactivity. Donor sites of phases III and I(diethylenetriamine and azomethene nitrogens along with phenolic hydroxyl group oxygen) are fully active, whereasphases IV and II are partially active with only participation of oxygen and azomethene nitrogen. The order ofincreasing thermal stability (IVBIIBIBIII) and fastness of metal uptake equilibration process coincides satisfacto-rily with decreasing bulkiness of the chelate. Results of separation under dynamic conditions of binary mixturescontaining Cu(II) with Ni(II), Zn(II), Cd(II) and Pb(II) using phase III are in accordance with its selectivity towardsCu(II) retention relative to the other coexisting ions. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Modified silica gel; Selective separation of Cu(II); Salicylaldehyde; Naphthaldehyde

www.elsevier.com/locate/talanta

* Corresponding author. Fax: +20-86-363011.E-mail address: rumenia@rusys.eg.net (E.M. Soliman).

0039-9140/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.

PII: S0 039 -9140 (00 )00648 -2

E.M. Soliman et al. / Talanta 54 (2001) 243–253244

1. Introduction

In the last two decades, great interest has beendevoted to the use of modified silica gel withorganic compounds in different analytical applica-tion areas, making use of its good mechanicalstrength, swelling stability and fast metal ex-change kinetics required for its use in differenttypes of chromatographic systems. Thus modifiedsilica gel has been the support of choice as sta-tionary phases in (HPLC) and ion chromatogra-phy techniques for separation and determinationof metal ion mixtures [1–6]. Moreover, sorbedmetal ions on modified silica gel phases were usedas stationary phases in high performance ligand-exchange liquid chromatography (HPLEC) forseparation of some organic compounds [7,8].

In fact, modification of silica gel surfaces areknown to act as a weak cation exchangers via itsweakly silanol groups, through immobilization oforganic complexing agents either chemically [9–21] or physically [21–25] greatly enhance metalexchange capacity as well as selectivity of suchproduced phases towards metal ion removal, sep-aration and/or preconcentration prior to theirdetermination by x-ray fluorescence or AAS anal-ysis. This is mainly related to the structure of theorganic compound, nature of the functional grouppresent and the incorporated (O, S, N or P) donoratoms. Consequently, a large number of silica gelsupported organic moieties have been synthesizedand applied in different research aspects. In thiscontext, we have recently developed some selec-tive modified silica gel sorbents [9–13]. Usingsilica gel chemically modified with formyl salicylicacid derivatives, selective extraction of Fe(III) wasachieved [9,10]. Modification of silica gel surfaceswith covalently bonded diethylenetriamine andtriethylenetetramine were found to be more supe-rior for preconcentration of Cu(II) and Ni(II) ionsthan silica gel bonded ethylenediamine [11].Column application of silica gel-immobilizedaminophenol and aminobenzoic acid as cationexchangers showed higher preference towardsheavy metal removal from sugar cane molassesthan alkali and alkaline earth metals [12]. How-ever, selective extraction of alkali and alkalineearth metal cations were accomplished using

macrocyclic crownether-modified silica gel [26,27].In addition, bonded silica gel phases and polyaza-mixed (S or O) donor atoms exhibit a remarkableselectivity towards retention of transition metalions [28,29]. Considering the growing interest inmodification of silica gel, we report here methodsof synthesizing four new multidentate diethylene-triamine mono and bis salicyaldehyde and naph-thaldehyde Schiff,s bases covalently bonded tosilica gel were used as inorganic solid support.The characterization of such new phases and theiraffinity towards selective extraction and separa-tion of Fe(III), Ni(II), Cu(II), Zn(II), Cd(II) andPb(II) ions were explored based on the structureand reactivity relationship.

2. Experimental

2.1. Materials

The silica gel used was of TLC grade (70–230mesh size and 60 A, pore diameter), purchasedfrom Woelm pharm, Eschwege, Germany. 3-Chloropropyl-trimethoxysilane, diethylenetri-amine as well as naphthaldehyde andsalicylaldehyde were purchased from AldrichChemical Company, USA. Organic solvents usedwere of spectroscopic grade.

At first, Silica gel was activated with concen-trated hydrochloric acid for 4 h under refluxconditions, then filtered off, washed thoroughlywith doubly distilled water till acid-free andfinally dried at 150°C for 6 h.

2.2. Synthesis of multidentate diethylenetriaminebis-naphthaldehyde (DETA-BN) anddiethylenetriamine bis-salicyaldehyde (DETA-BS)Schiff’ s bases

The two bis-Schiff,s bases were produced imme-diately on mixing diethylenetriamine with naph-thaldehyde or salicyaldehyde in benzene orethanol in 1:2 molar ratio, respectively. The reac-tion mixture in ethanol was refluxed for 2 h toensure the completion of the reaction. (DETA-BN) was separated by filtration, its purity waschecked by TLC and elemental analysis. (DETA-BS) was purified and checked as reported [30].

E.M. Soliman et al. / Talanta 54 (2001) 243–253 245

2.3. Synthesis of silica gel modified multidentatediethylenetriamine mono- and bis-naphthaldehydeSchiff ,s bases (SGM-DETA-MN, phase I) and(SGM-DETA-BN, phase II), as well as, mono-and bis-salicylaldehyde Schiff ,s bases(SGM-DETA-MS, phase III) and(SGM-DETA-BS, phase IV)

The synthesis of such newly synthesizedmodified silica gel phases (I–IV) was accom-plished according to the following steps: at firstchloro-modified silica gel (CMSG) was produceddirectly via the interaction of activated silica geland 3-chloro-propyltrimethoxysilane as previ-ously described [11]. Then, (CMSG) was reactedin two pathways: In the first, it was reacted withdiethylenetriamine (DETA) to yield silica gelmodified diethylenetriamine (SGM-DETA) [11],which undergoes Schiff,s base formation reactionwith 2-hydroxy-1-naphthaldehyde and salicyalde-hyde to produce (SGM-DETA-MN, phase I)and (SGM-DETA-MS, phase III), respectively.In the second path, (CMSG) was directly re-acted with the pre-synthesized multidentate, bis-naphthaldehyde (DETA-BN) anddiethylenetriamine bis-salicyaldehyde (DETA-BS)Schiff,s bases [31]. Thus, 4 g of (CMSG) wereadded to 4.8 mmol of (DETA-BN) or (DETA-BS) Schiff,s base in 200 ml benzene in the pres-ence of 1 ml triethylamine and refluxed for 12 h,then left to cool. The new phases (SGM-DETA-BN, phase II) and (SGM-DETA-BS, phase IV)thus produced were separated by filtration,washed with benzene and diethylether and finallydried under vacuum at 60°C for 2 h. The syn-thetic routes of the new phases (I–IV) are illus-trated in Scheme 1.

2.4. Metal capacity as a function of pH andshaking time

The metal capacities of such chemicallymodified silica gel phases toward Fe(III), Ni(II),Cu(II), Zn(II), Cd(II)and Pb(II) were determinedin triplicate under static conditions by the batchequilibrium method, in which 30 mg of thephase was added to 1 ml of 0.1 M metal ionand 9 ml of buffer solution at different pH val-

ues, and the total volume was completed to 30ml by doubly distilled water in a 50-ml flask.This mixture was mechanically shaken for 30min at room temperature to attain equilibrium.The mixture was then filtered off, washed withdoubly distilled water and the unextracted metalion in the filtrate was determined by complexo-metric EDTA titration using the proper bufferand indicator. Metal chloride solutions were pre-pared in 0.1 M hydrochloric acid to avoid hy-drolysis. Acetate buffer as well as 1 M sodiumacetate solutions were used to cover the pHrange of 1.35–6.60.

The effect of shaking time on metal exchangecapacity was determined under the same batchconditions at different equilibrium periods (2, 5,10, 20 and 30 min.) at the selected optimum pHof maximum uptake.

2.5. Temperature effect on the stability of thephases

To investigate temperature effect, five weightsof 50 mg each of the phase were kept for 1 h at50 to 250°C, respectively in an electric oven,then left to cool. To show the extent of liganddecomposition or hydrolysis (i.e., stability of thephase), 30 mg of thermally treated phase alongwith untreated one taken as standard, were usedto evaluate the metal sorption capacity of, forexample, Cu(II) ions, under the same conditionspreviously described for batch experiment and atpH of maximum uptake, and then comparingmetal capacity values obtained with that of thestandard.

2.6. Separation of binary mixtures containingCu(II) ions under dynamic conditions

Binary mixtures of Cu(II) with Ni(II), Zn(II),Cd(II) and Pb(II) ions, (2 ppm each, in 50 mlbuffered solution at pH 3.5, 4.0, and 6.0), werepassed over 30 mg of phase III similar to anenrichment filter [32], based an borosilicate glasswool in 50 ml burette columns with a flow rateof 1 ml min−1. Concentrations of non-retainedmetal ions in the effluents were determined byAAS.

E.M. Soliman et al. / Talanta 54 (2001) 243–253246

2.7. Apparatus

IR spectra of the phases before and after metalion sorption were obtained from KBr pellets byusing Shimadzu 470 infrared spectrophotometer.A Fisher Scientific Accumet pH meter Model 810calibrated against two standard buffer solutionsat pH 4.0 and 9.2 was used for all pH-measure-ments. Atomic absorption measurements wereperformed with a Perkin Elmer 2380 Spectrome-try to quantify metal ions present in mixture.

3. Results and discussion

3.1. Infrared spectral studies and surface co6erage

The four new silica gel phases (I–IV) were apale yellow color. An obvious color change oc-curred after metal ion sorption by the phases dueto complex formation. For example, the color ofphase III, SGM-DETA-MS changed from paleyellow to dark brown, orange, blue, dark yellow,pale yellow and yellowish-brown after sorption of

Scheme 1. Synthetic routes to phases I–IV.

E.M. Soliman et al. / Talanta 54 (2001) 243–253 247

Fe(III), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II)ions, respectively at optimum pH values wheremaximum metal uptake occurred. The binding ofthe multidentate Schiff,s base complexing agentsto silica gel surface was confirmed by IR spectralanalysis of the new phases (I–IV), where newbands not present in parent silica arose because ofincorporation of aromatic rings of salicylic andnaphthalene. Thus, aromatic g(C=C), located inthe range 1588–1541 cm−1 along with strongbands appeared at 1634, 1629, 1636 and 1627cm−1 in the IR spectra of phases I–IV, and wererespectively characterized to azomethene stretch-ing vibration g(C=N) indicating Schiff,s base for-mation [9]. Moreover, g(O–H) due to aromatichydroxyl groups and g(N–H) of aliphatic di-ethylenetriamine located as overlapped bands inthe range 3840–2975 cm−1. After metal ion sorp-tion, bands caused by g(C=N) as well as g(O–H)and g(N–H) significantly changed either positionsor features as a result of complex formation,which clearly indicates that both nitrogen andoxygen donor atoms are the binding sites formetal ions. On the other hand, the surface cover-age of these multidentate Schiff,s base complexingagents chemically bound to silica surface wasfound to be 0.94, 0.68,0.96 and 0.64 mmol g−1

for phases I–IV, respectively based on probemethod [33].

3.2. Metal uptake properties of the newlysynthesized phases I–IV as a function of pH andshaking time

The pH of the medium is one of the mostimportant factors controlling the limit of ex-tractability of metal ions by the collecting phases.Results of metal capacity values in mmol g−1 foruptake of Fe(III), Ni(II), Cu(II), Zn(II), Cd(II)and Pb(II) at different hydrogen ion concentra-tion using the newly synthesized silica gel phasesI–IV, act as solid phase extractors and are com-piled in Table 1. Based on these values, the fol-lowing could be deduced: all the phases showedlow efficiency towards extraction of metal ionsfrom aqueous solutions at low pH values due toprotonation of chelation sites in the ligands thatinhibit their binding to metal ions [34]. The order

of metal ion sorption by phase III, SGM-DETA-MS and phase I, SGM-DETA-MN is generallythe same, where metal capacity values at optimumpH decrease in the following order:

Cu(II)\ Fe(III)\ Zn(II)\ Cd(II)\Pb(II)\ Ni(II) for phase IIICu(II)\ Fe(III)\ Zn(II) \Cd(II) \Ni(II)$Pb(II) for phase Iindicating that the highest affinity is towards

Cu(II) extraction, and the lowest exhibited byNi(II) or Pb(II) ions. Thus 0.957 and 0.165 mmolg−1 are the metal capacity values for extraction ofCu(II) and Ni(II), respectively, using phase III.However, for phase IV, SGM-DETA-BS andphase II, SGM-DETA-BN, the highest affinitywas devoted to Fe(III) followed by Cu(II) sorp-tion where the following order occurs.

Fe(III)\ Cu(II)\ Pb(II)\ Zn(II)= Ni(II)\Cd(II) for phase IVFe(III)\ Cu(II)\ Zn(II)\ Cd(II)\Pb(II)\ Ni(II) for phase IIMoreover, both phases III and I with mono

salicylic and naphthalene rings showed generallygreater metal capacity values than the bis-valuesof phases IV and II. This may be discussed interms of the structure of the complexing agentand steric hindrance relationship. Thus, for phaseIII and I, the donor sites diethylenetriamine andazomethene nitrogens as well as phenolic hy-droxyl group oxygen are easily available to partic-ipate by binding to a metal ion withoutrestrictions. However, the participation of di-ethylenetriamine nitrogens in phases IV and II issterically hindered by two benzene or naphthalenerings. This assumption was strengthened by focus-ing attention to values of Cu(II) uptake by thefour phases, which were evaluated to be (0.957,0.940 mmol g−1) and (0.429, 0.412 mmol g−1) forphases III, I andIV, II, respectively. The highercapacity values of phases III, I than that of phasesIV, II clearly indicates that the coordination sitesin phases III and I are fully active, but in phasesIV and II only the azomethene nitrogen andphenolic oxygen are active. Effect of orientationof the immobilized chelates on their reactivitymay be illustrated as shown in Scheme 2. This isalso in accordance with the Person principle [35]for soft and hard acids and bases, where phases

E.M. Soliman et al. / Talanta 54 (2001) 243–253248

Table 1Metal uptake capacities (mmol g−1) of phases I–IV at different pH values*

Phase I Phase II Phase III Phase IVMetal ion pH

0.294 0.310Fe(III) 0.2941.35 0.3101.50 0.375 0.392 0.359 0.379

0.3922.00 0.441 0.310 0.3920.408 0.4572.50 0.392 0.392

3.30 0.412 0.457 0.478 0.4784.00 0.676** 0.676** 0.709** 0.643**

0.016 0.099Ni(II) 0.0001.45 0.0990.016 0.066 0.000 0.0002.000.016 0.0662.30 0.000 0.049

4.15 0.148 0.082 0.016 0.0000.148 0.156** 0.066 0.263**5.100.255** 0.132 0.165**6.20 0.115

Cu(II) 1.60 0.181 0.264 0.132 0.1982.25 0.379 0.412 0.346 0.313

0.577 0.3132.90 0.445 0.3464.30 0.940** 0.346 0.874 0.429**5.25 0.841 0.412** 0.858 0.396

0.841 0.330 0.957**6.55 0.313

Zn(II) 0.1811.50 0.198 0.181 0.2310.231 0.2472.25 0.198 0.231

2.90 0.165 0.198 0.247 0.2470.181 0.263** 0.214 0.263**4.350.148 0.1655.20 0.231 0.214

6.60 0.437** 0.231 0.552** 0.181

Cd(II) 1.35 0.066 0.082 0.066 0.0990.033 0.1482.10 0.049 0.148

2.70 0.099 0.181 0.066 0.0824.40 0.082 0.181 0.115 0.132

0.148 0.2145.20 0.165 0.1480.329**6.60 0.390** 0.371** 0.165**

0.082 0.082Pb(II) 0.0991.70 0.1653.10 0.247** 0.247** 0.181 0.280**3.45 0.198 0.198 0.180 0.165

0.198 0.2144.25 0.239** 0.1980.148 0.148 0.148 0.0665.100.181 0.148 0.1816.05 0.181

* on N=3 Standard deviation values are in the range of 0.000–0.009 based on n=3.** Maximum metal capacity values at 30-min shaking time.

III and I act as nitrogen-rich solid phase extrac-tors. In addition, there is an improvement ofCu(II) uptake by phases III or I in comparisonwith uptake using silica gel modified diethylenetri-amine alone, which is reported to be 0.574 mmolg−1 [11]. On the other hand, values of Cu(II)uptake by phases IV or II are nearly double thevalue reported for silica gel modified with the

structurally analogs 2-aminophenol with O and Ndonors to be 0.24 mmol g−1 [12], showing thatthe ligands immobilized phases IV and II act as abinuclear chelating agent. Similarly, Zn(II) uptakeby the newly synthesized phases I–IV exhibit thesame behavior as for Cu(II) extraction wheremetal capacities were 0.552, 0.437 mmol g−1 forphases III, I and 0.263, 0.263 mmol g−1 for

E.M. Soliman et al. / Talanta 54 (2001) 243–253250

Fig. 1. (a) % extraction of Cu(II) as a function of shaking time using pahes III and IV; (b) % extraction of Fe(III) as a functionof shaking time using pahes III and IV.

IV and III were evaluated to be 31.2, 50.0%; 49.9,91.3%; 62.7, 71.7%; 40.1, 53.4%; and 47.0, 75.7%,respectively. On the other hand, extraction ofCu(II) by phase III at all time intervals indicateda fast equilibration process relative to phase IV asshow in Fig. 1a. However, the extraction ofFe(III) by phase IV is faster than that of phaseIII, Fig. 1b, indicating the high affinity of Fe(III)ions to act as a hard acid to bind with thepositionally active (non-sterically hindered) oxy-gen incorporated bis-salicylaldehyde Schiff,s baseligand, as shown in Scheme 2.

3.3. Recycling of the modified silica gel phasesI–IV

To investigate the possibility of these new silicagel phases I–IV for further extraction of metalions after first use, it was planned to selectethylenediaminetetracetic acid (EDTA) as astrong complexing agent to back extract the metalion from the formed metal chelate, by a batchrecycling process. Thus, 150 mg each of phase I,phase III after sorption of Cu(II) ions and phaseII and phase IV after sorption of Fe(III) ions atoptimum pH values were mixed with excess (0.01M-EDTA) solution and shaken for 30 min,filtered, washed with double distilled water andthen dried. It was firstly observed that the original

color of the phases were restored and the resultsof metal capacity values determined after twosorption–desorption processes were close to theiroriginal values. Consequently, efficiency of metaluptake percentages were determined to be 10090.5 and 9491.2 for phases I, III and II, IV,respectively.

3.4. Thermal stability of the phases I–IV

Both phases III and I showed thermal stabilitycompared with that of phases IV and II judgingfrom values of metal capacity determined bybatch method for uptake of Cu(II) ions afterthermal treatment of the phases I–IV for 1 h atelevated temperatures (50–250°C). It is clear fromFig. 2 that phases III and I exhibit pronouncedthermal stability where no loss in their efficiencyfor Cu(II) uptake was observed till 100°C (com-pared with their standard values at room temper-ature without thermal treatment) and a lowpercentage of decreasing efficiency for Cu(II) up-take by phase III, which was evaluated to be 5.5,20.0 and 37.5% at 150, 200, and 250°C, respec-tively. Based on the data obtained, the order ofincreasing thermal stability exhibited by phasesI–IV may be given as follows: IVBIIBIBIII.This order coincides satisfactorily with decreasingbulkiness of the chelating Schiff,s bases covalently

E.M. Soliman et al. / Talanta 54 (2001) 243–253 251

bonded to silica gel surface, leading to thermalinstability, followed by decomposition and de-creasing efficiency of metal ion sorption. On theother hand, thermal stability of phase III illustratesits potential use as stationary phase in columnsused in gas chromatography.

3.5. Separation of Cu(II) ions present in binarymixtures under dynamic conditions using phaseIII

Silica gel-modified diethylenetriamine mono-sal-icylaldehyde Schiff,s base (phase III), was chosen tostudy the possibility of its potential use for pur-poses of selective separation of Cu(II) present inbinary mixtures with other metal ions. In fact,selective extraction or separation of a given metalion in presence of other metal ions is controlled bythree main factors. The first is the nature of thedonating sites in the ligand that are capable ofselective binding to the central metal ion. Thesecond is the nature of the metal ion to be selec-tively extracted: either it acts as a hard or soft acid.The hydrogen ion concentration of metal ionsolution is the third key factor in the study ofselective extraction or separation. However, tem-perature and time of equilibration are other impor-tant factors that must be considered duringseparation process by keeping them constant orvariable. On the other hand, the distribution coeffi-

cient (Kd) can be taken as a representative value forthe selectivity measurements if all the tested metalions, and not only the individual ions, compete witheach other in binding to the selective functionalgroups of the metal chelate forming sorbent. So,separation under flowing conditions was performedby passing binary mixtures of Cu(II) ions withNi(II), Zn(II), Cd(II) and Pb(II) ions in a 50-mlburette column supported in glass wool over 30 mgof phase III as a thin layer [32], with a flow rateof 1ml min−1. Based on the amount of metal ionremaining in the effluent solution and that retainedby the phase, Kd values could be calculated. Con-sequently, the separation factor a, used as a mea-sure of chromatographic separation possible, isgiven by the relation a=Kd1/Kd2 where, Kd1 and Kd2

are the distribution coefficients of the two metalions present together. The greater the a value, theeasier the separation.

The separation parameter a for separation ofCu(II)-containing binary mixtures using phase IIIat pH values of 3.5, 4.0 and 6.0 are shown in Table2. The potential use of this phase for selectiveseparation of Cu(II) ions is possible as shown fromthe values of separation factor a at pH 4.0 or 3.5.

a=KdCu (II)/Kd

M (II)

determined to be 150.0, 8.7, 4.1 and 3.0 forM(II)=Ni(II), Cd(II), Pb(II) and Zn(II), respec-

Fig. 2. (a) Effect of thermal treatment on efficiency of Cu(II) uptake using phases III and IV; (b) Effect of thermal treatment onefficiency of Cu(II) uptake using phases I and II.

E.M. Soliman et al. / Talanta 54 (2001) 243–253252

Tab

le2

Sele

ctiv

ity

para

met

era

for

sepa

rati

onof

Cu(

II)

bina

rym

ixtu

res

usin

gph

ase

III

unde

rdy

nam

icco

ndit

ions

3.5

4.0

6.0

pH

Cu–

Ni

Cu–

Ni

Cu–

Cd

Cu–

Pb

Cu–

Zn

Cu–

Ni

Cu-

Cd

Cu-

Pb

Cu-

Zn

Cu–

Cd

Cu–

Pb

Bin

ary

mix

ture

Cu–

Zn

9.8

4.5

4.2

7.75

6.10

3.85

2.6

138

a15

0.0

8.7

3.0

4.1

E.M. Soliman et al. / Talanta 54 (2001) 243–253 253

tively, at pH 3.5. These values are better thanseparation at pH 6.0, where a values were foundto be 7.75, 6.10, 3.85 and 2.60 for M(II)=Ni(II),Cd(II), Pb(II) and Zn(II) respectively. However,in all cases, the separation of Cu–Ni binary mix-ture is the easiest (S\2). Generally, the results ofseparation are in accordance with the highestefficiency of phase III towards Cu(II) uptake rela-tive to the other coexisting metal ions.

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