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CHAPTER 6

ION-EXCHANGE

Chapter 6 Ion-Exchange

Department of Chemistry, S.P.U.

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6.1 INTRODUCTION

Ion-exchange may be defined as the reversible exchange of ions between the

substrate and surrounding medium. Ion-exchange resins are the polymers which are

capable of exchanging particular ions within the polymer with ions in a solution that

is passed through them. This ability is also seen in various natural systems such as

soils and living cells. The synthetic resins are used primarily for purifying water but

also for various other applications including separating out some elements. Ion-

exchange materials are insoluble substances containing loosely held ions which are

able to exchange with other ions in solutions which come in contact with them. These

exchanges take place without any physical alteration to the ion-exchange material.

Ion-exchange resins have the ability to absorb metal ions from large volumes

to smaller volumes in a concentrated form under appropriate conditions. Ion-exchange

technique can remove traces of ionic impurities from water/process liquors and gives

out a product of ultra pure quality in a simple, efficient and techno-economically

viable manner. The equipment required is generally compact and occupies small

space. Generally, the process is carried out at an ambient temperature and pressure

and in an intermittent manner if desired. In fact, no other technique removes traces of

ionic constituents from waste water/process liquors so rapidly, efficiently and at low

pressure as is done by the ion-exchange technique. So, today ion-exchange has

emerged out as a unit operation analogous to such classic operations as filtration,

distillation etc.

Ion-exchangers are widely used in analytical chemistry, hydrometallurgy,

antibiotic purification, separation of radio isotopes and find large scale application in

water treatment and pollution control, pharmaceutical industry, medicine, purification

of solvents and reagents and so on. [1-5]. It is also useful in many fields such as water

softening and deionization, sugar purification, extraction of uranium glycerol refining,

purification of formaldehyde and as catalysts [6-13].

The basic requirements, which are essential for any polymeric material to be useful as

an ion-exchange resins are:

(a) It must be sufficiently hydrophilic to permit diffusion of ions through the structure

at a finite and usable rate.

(b) It must contain sufficient number of accessible ion-exchangeable groups which do

not undergo degradation during use and



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(c) The swollen material must be denser than water.

The considerable interest has been developed in the synthesis of ion-exchange

resins having special properties and containing specific functional groups. These

resins are expected to work under crucial conditions of pH, temperature and at the

same time selective in adsorption of specific metal ions. The chelating ion-exchangers

are prepared by two methods. The first method is polymerization of monomers

containing an ion-exchangeable group and the second method is introduction of a

chelating functional group into the polymeric matrix.

The polymer containing 8-hydroxy quinoline and its derivatives has drawn

considerable attention due to tremendous application in ion-exchange field [14]. Kim

and co-workers [15] prepared 8-hydroxyquinoline–resorcinol (8-HQR) and 8-hyroxy

quinoline-resorcinol-salicylic acid (8-HQRS) resins by polycondensation and studied

ion-exchange capacity at different pH using Fe+3, Cu+2, Co+2, Pb+2 and Ni+2 metal ions

and found that the ion-exchange capacities of these resins were 4.1 and 5.9 meq.g-1

respectively. They also found that the maximum adsorption of these resins was

observed at pH 7.0 and the distribution coefficient of metal in these resin was

increasing with decreasing HCl concentration. Dhakite and co-workers [16] were

synthesized by the condensation of 8-hydroxyquinoline-5-sulphonic acid and biuret

with formaldehyde in the presence of hydrochloric acid as catalyst, proved to be

selective chelation ion exchange copolymer resins for certain metals. Chelation ion

exchange properties to these polymers were studied for Cu2+, Cd2+, Co2+ and Zn2+

ions. A batch equilibrium method was employed in the study of the selectivity of the

distribution of a given metal ions between the polymer sample and a solution

containing the metal ion. The study was carried out over a wide pH range and in a

media of various ions strengths. The polymer showed a higher selectivity for Cu2+

ions than for Cd2+, Co2+ and Zn2+ ions. Liu and Cheng [17] studied the interaction of

heavy metal ions and chelating ion-exchange resin containing 8-hydroxyquinoline

(8-HQ) moiety. The resin has good selectivity to absorb heavy metal ion including

Cu(II), Hg(II), Pb(II) and Mg(II) at pH 5.0. These authors suggested that the chelating

ion-exchange resin containing 8-HQ could be used to remove heavy metals from

water.

Patel and co-workers [18,19] synthesized the ion-exchange resins based on

N-phenyl maleimide and studied the effect of electrolyte strength, pH and shaking



190

time on the adsorption of different metal ions. They reported that the synthesized

resins were highly selective for Cd+2 and Pb+2 ions. They also studied the separation

of Pb+2 from Ca+2, Fe+3 from Cr+3 and regenerability of these resins. Ahmad and

co-workers [20] prepared acrylic fibers, which is pretreated with hydrazine under

various concentrations to give crosslinked structure. The prepared crosslinked fiber

treated with hydroxylamine hydrochloride to develop ion-exchange fibers. The effects

of reaction conditions on physical properties, thermal characteristics, surface

morphology, ion adsorption quantity and reusability were investigated. The results

show that by increasing the reaction time, temperature and concentration of

hydroxylamine hydrochloride the ion adsorption capacity also increased. Onari [21]

synthesized ion-exchange resins having triazolylazophenol ion-exchangable group

and studied the effect of pH and shaking time on the adsorption of various metal ions

using batch equilibration method. He observed that the capacity of these polymers to

adsorb heavy metal ions reached its saturation in about 30 minutes and the polymer

can be practically employed for the removal of Ni+2 and Cu+2 ions from waste/water.

Lee and Hong [22] synthesized poly(hydroxamic acid) resins from poly(ethyl

acrylate-co-divinylbenzene) beads and their metal binding properties were determined

at specific pH. In acidic region, the chelating resin showed high adsorption capacity

for copper, iron, vanadium and uranium. Metal adsorption capacities varied according

to polymerization condition, i.e. crosslinking ratio and degree of dilution.

Gurnule and co-workers [23] synthesized terpolymer resins (4-HABF) by

condensation of 4-hydroxy acetophenone and biuret with formaldehyde in presence of

acid catalyst and using varied molar ratios of reacting monomers. Chelation ion-

exchange properties of this resin have been studied by employing batch equilibrium

method. It was employed to study selectivity of metal ion uptake over a wide pH

range and in media of various ionic strength. The overall rate of metal uptake follows

the order: Fe+3 > Cu+2 > Ni+2 > Co+2 = Zn+2 > Cd+2 > Pb+2 > Hg+2. The free radical

solution copolymerization of poly(hydroxyethyl methacrylate-co-acrylamide)

poly(HEMA-co-AAm) was studied by Maranbio and co-workers [24] in the range of

25 to 75% monomer feed ratios. They showed that poly(HEMA-co-AAm) can bind

metal ions: Cr(III), Co(II), Zn(II), Ni(II), Cu(II), Cd(II), Pb(II), Hg(II) and Fe(III) in

aqueous solution at pH 3.5 to 7.0 and the inorganic ion interaction with the

hydrophilic polymer was determined as a function of pH and filtration factor. Shah



191

and co-workers [25] reported chelating ion-exchange resin containing 8-hydroxy

quinoline and separation of metal ions by selective adsorption in the resin column.

They measured the physicochemical properties like % moisture content, void volume

fraction, total exchange capacity, rate of exchange, thermal stability and effect of

metal ion concentration on exchange capacity. The quantitative separation of

Cu(II)-Ni(II) and Zn(II)-Ni(II) was accomplished by selective adsorption in column.

Ratna and co-workers [26] synthesized spherical beads from the copolymers

of styrene and methyl acrylate which were sulfonated using concentrated sulfuric

acid. They studied ion-exchange capacity of the sulfonated copolymer which

increases with time. The developed ion-exchange resin also demonstrated better

performance in demineralization of water as compared with the conventional

polystyrene based beads. Rivas and co-workers [27] synthesized water insoluble

functional copolymers and studied their metal ion uptake properties for silver(I),

copper(II), cadmium(II), zinc(II), lead(II), mercury(II), chromium(III) and

aluminium (III). Ozturk and Kose [28] studied the boron removal from aqueous

solutions using Dowex 2 x 8 anion exchange resin. The sorption behaviour of resin

was investigated as a function of pH, contact time and temperature, initial boron

concentration of solution, resin dosage and effect of other resins. The maximum

sorption value for boron was observed at pH 9.0. Kaliyappan and co-workers [29]

synthesized 8-(acryloyloxy) quinoline (8-AOQ) and polymerized it in methyl ethyl

ketone at 70oC using BPO initiator. They prepared polychelates by addition of

aqueous solution of Th(II) / Cd(II) / Zn(II) / Ni(II) and Mg(II) ions into the polymer in

aqueous NaOH. The IR spectra of these polychelates suggest that metals are

coordinated through oxygen of the ester carbonyl and the nitrogen atom. Roozemond

and co-workers [30] have carried out more systematic work in this direction for the

separation of metal ions from their mixtures. They reported that Cu+2 and Cd+2 metal

ions were successively eluted from the chelated resin quantitatively and the

regenerated resin could be reused many times.

Rivas and Villegas [31] synthesized crosslinked poly[3-(methacryloylamino)-

propyl]-dimethyl (3-sulfopropyl)ammonium hydroxide-co-2-acrylamidoglycolic acid

[PCMAAPDSA-co-AGCO] by radical polymerization and tested the synthesized

polymer as an absorbent under competitive and noncompetitive conditions for Cu(II),

Cd(II), Hg(II), Zn(II), Pb(II) and Cr(III) by batch and column equilibrium procedures.



192

They reported that resin metal ion equilibrium was achieved before 1 hr. The resin

showed a maximum retention capacity value of 1.084 meq.g-1 for Hg(II) at pH 2.0.

The recovery of the resin was investigated at 20ºC under different concentrations of

HNO3 and HClO4. Shah and co-workers [32] synthesized chelating ion-exchange

resin from salicylic acid-formaldehyde-resorcinol (SFR) using DMF as solvent at

80ºC. The effect of pH, metal ion concentration and rate of exchange of metal ions

were also studied by employing batch equilibrium method. Masram and co-workers

[33] synthesized terpolymer resin from salicylic acid-hexamethylenediamine-

formaldehyde (SHMF) by the condensation of salicylic acid and

hexamethylenediamine with formaldehyde in the presence of hydrochloric acid

catalyst. Chelation ion-exchange properties of synthesized terpolymer have been

studied for Fe+3, Cu+2, Ni+2, Co+2, Zn+2, Cd+2 and Pb+2 ions employing batch

equilibrium method. It was employed to study the selectivity of metal ion uptake

involving the measurements of distribution of a given metal ion between the polymer

sample and a solution containing the metal ion. The study was carried out over wide

pH range and in the media of various ionic strengths. The terpolymer showed a higher

selectivity for Fe+3, Cu+2 and Ni+2 ions than for Co+2, Zn+2, Cd+2 and Pb+2 ions.

Rivas and co-workers [34] studied the effect of poly(acrylic acid) (PAA) in the

metal binding ability of Cu+2, Cd+2, Co+2, Pb+2, Zn+2, Ni+2 and Cr+3 to poly(sodium-2-

(N-acrylamido)-2-methyl-propanesulfonate) (PAMPS). At pH 3.0 and in presence of

PAA, the fraction of metal ions bound to the polymer decreases, as the sulfonate

molar fraction with respect to carboxylate groups decreases. A copolymer composed

by sodium-2-(N-acrylamido)-2-methyl-propanesulfonate and acrylic acid showed the

same binding ability than a mixture of PAMPS and PAA under the same relative

sulfonate/carboxylate composition. Lin and co-workers [35] studied the removal of

Cu+2 and Ni+2 from aqueous solutions using chelating exchange resin Amberlite IRC

748 by batch and fixed-bed ion-exchange processes. Rivas and co-workers [36]

synthesized water insoluble polymers containing multiligand groups. The uptake

metal ion properties were studied by batch equilibrium procedure for copper (II) and

uranyl ions.

The present chapter deals with the ion-exchange study of the synthesized

polymers. This study is carried out with the following aims:



193

1. To determine the effect of pH of the aqueous medium on the metal adsorption

capacity of the polymers.

2. To determine the distribution of metal ions between polymeric and aqueous

phase.

3. To determine the rate of metal adsorption by polymers as a function of time.

4. To determine the effect of various electrolyte and their ionic strength on the

metal adsorption capacity of the polymers and

5. To evaluate the selectivity of different metal ions towards adsorption by the

polymers.

6.2 EXPERIMENTAL

A. Materials

Analytical grade ethylene diamine tetra acetic acid disodium salt (EDTA),

copper nitrate, cobalt nitrate, zinc nitrate, nickel nitrate and ferrous nitrate were used.

Double distilled water was used through out the study.

B. General Procedure:

The ion-exchange properties of poly(8-QMA) and copolymers of

poly(CMA-co-8-QMA) were investigated by batch equilibration method [37,38]. The

polymer samples were ground to fine powder and dried in a vacuum at 60oC for 24

hrs. The dried polymers were used for the ion-exchange study. Five metal ions Cu+2,

Ni+2, Zn+2, Co+2 and Fe+3 in the form of aqueous metal nitrate solution were used. The

ion-exchange study was carried out using three experimental variables: (i) pH of the

aqueous medium (ii) Electrolyte and its ionic strength and (iii) shaking time. Among

these three variables, two were kept constant and only one was varied at a time to

evaluate its effect on metal uptake capacity of the polymers. The details of

experimental procedure are as given below.

(a) Effect of pH of the aqueous medium on metal binding capacity:

The effect of pH on the metal binding capacity of the polymers was estimated

at room temperature in the presence of 1.0 M NaNO3 solution as an electrolyte.

The polymer sample (50 mg) was suspended in the electrolyte solution (1.0 M

NaNO3, 40 ml) and pH of the suspension was adjusted to required value by addition

of either 0.1 M HNO3 or 0.1 M NaOH solution. The conical flask with this content

was stoppered and placed on the mechanical stirrer for 24 hrs shaking, to allow the



194

swelling of the polymer at room temperature. The metal ion solution (0.1 M metal

nitrate, 2 ml) was added to this and the pH of the content was adjusted to the required

value. The content was mechanically stirred for 24 hrs and then filtered and washed

with the distilled water. The filtrate was collected in a conical flask and the

unadsorbed metal was estimated by back titration with standard EDTA solution using

appropriate indicator. A separate blank experiment (without adding polymer sample)

was also carried out in the same manner. From the difference between a sample and

blank reading, the amount of metal adsorbed by the polymer was calculated and

expressed in terms of milliequivalent per gram of the polymer (meq.g-1).

The above experiment was performed using 0.1 M metal nitrate solutions of

Cu+2, Ni+2, Co+2, Zn+2 and Fe+3 in the presence of 1.0 M NaNO3 as an electrolyte at

the pH values of 3.0, 3.5, 4.0, 5.0, 5.5 and 6.0. For Fe+3 the experiments were carried

out at pH of 1.5, 2.0, 2.5, 3.0 and 3.5. The results of these experiments are presented

in Tables 6.1 to 6.5.

(b) Distribution ratios of metal ions as a function of pH:

The distribution of each metal ion (Cu+2, Ni+2, Co+2, Zn+2 and Fe+3) between

polymer and aqueous phase was estimated at different pH, using 1.0 M NaNO3

solution. 50 mg polymer was stirred in 1.0 M NaNO3 solution (40 ml) at required pH

value for 24 hrs. To the swelled polymer 0.1 M metal ion solution (2 ml) was added

and the pH was adjusted to the required value by addition of either 0.1 M HNO3 or

0.1 M NaOH. The content was mechanically stirred for 24 hrs. The experiments were

carried out from 3.0 to higher permissible pH for Cu+2, Ni+2, Co+2 and Zn+2. In case of

Fe+3 the study was carried out from pH 1.5 to 3.5.

After 24 hrs, the mixture was filtered, the filtrate and washing were collected.

Amount of the metal ion which remained in the aqueous phase was estimated by back

titration with standard EDTA solution using appropriate indicator. Similarly blank

experiment was carried out without adding polymer sample. The amount of metal

adsorbed by the polymer was calculated from the difference between sample and

blank reading. The original metal ion concentration is known and the metal ion

adsorbed by the polymer was estimated. The distribution ratio ‘KD’ is calculated from

the following equation.



195

Amount of metal adsorbed on resin Volume of solution KD = X Amount of metal in solution Weight of resin

The results are presented in Tables 6.6 to 6.10.

(c) Effect of electrolyte and its ionic strength on metal uptake:

The effect of electrolyte and its ionic strength on metal uptake by polymers

was estimated at pH 5.5 for Cu+2, Ni+2, Co+2, Zn+2 and at pH 3.0 for Fe+3 using three

different electrolytes with four different concentrations of each.

The polymer sample (50 mg) was suspended in the electrolyte solution (40 ml)

of known concentration. The pH of the suspension was adjusted to the required value

by addition of either 0.1 M HNO3 or 0.1 M NaOH and the contents were

mechanically stirred for 24 hrs. To this, metal nitrate solution (0.1 M, 2 ml) was

added and the pH of the content was adjusted to the required value. The content was

mechanically stirred for 24 hrs and then filtered and washed with the distilled water.

The filtrate was collected in a conical flask and the unadsorbed metal was estimated

by back titration with standard EDTA solution using appropriate indicator. A separate

blank experiment (without adding polymer sample) was also carried out in the same

manner. From the difference between a sample and blank reading, the amount of

metal adsorbed by the polymer was calculated and expressed in terms of

milliequivalent per gram of the polymer (meq.g-1).

The above experiment was performed using 0.1 M metal nitrate solutions of

Cu+2, Ni+2, Co+2, Zn+2at pH 5.5 and of Fe+3 at pH 3.0 in the presence of three different

electrolytes (NaNO3, Na2SO4 and NaCl) each with four different concentrations (0.05,

0.1, 0.5 and 1.0 M). The results of these experiments are presented in Tables 6.11 to

6.13.

(d) Estimation of the rate of metal uptake as a function of time:

In order to estimate the time required to attain the state of equilibrium under

the prescribed experimental conditions, a series of experiments were conducted in

which the amount of metal ion adsorbed by the polymer was estimated at specific

time intervals.



196

The polymer sample (50 mg) was mechanically stirred with 1.0 M NaNO3

solution (40 ml) at required pH value for 24 hrs to allow the swelling of the polymer.

Metal ion solution (0.1 M metal nitrate, 2 ml) was added to this and pH of the content

was adjusted to the required value by addition of either 0.1 M HNO3 or 0.1 M NaOH.

The contents were mechanically stirred for different time intervals (1.0, 2.0, 3.0, 4.0,

5.0, 6.0, 7.0 and 24 hrs). After the specific time interval, the particular suspension was

filtered and washed with the distilled water. The filtrate was collected and the

unadsorbed metal was estimated by titration with standard EDTA solution using

appropriate indicator. From the difference between the original amount of metal

added at the beginning of the experiment and the amount of unadsorbed metal, the

amount of metal adsorbed by the polymer after a specific time interval was calculated.

It was assumed that, under the prescribed experimental conditions, the system attains

the state of 100% equilibrium after 24 hrs.

Let us consider, ‘X’ mg of metal ion is adsorbed after 1.0 hr and ‘Y’ mg of

metal ion is adsorbed after 24 hrs, then the % of metal ion adsorbed after 1.0 hr will

be (X x 100) / Y. Using this expression, the amount of metal adsorbed by the polymer

after specific time intervals was calculated and expressed in terms of % metal ion

adsorbed. This experiment was performed using 0.1 M metal nitrate solutions of Cu+2,

Ni+2, Co+2, Zn+2 at pH 5.5 and Fe+3 at pH 3.0. The results are presented in Tables 6.14

to 6.18.



197



198



199



200



201



202



203



204



205



206



207

Table 6.11: Effect of electrolyte concentration on metal ion adsorption capacity of poly(8-QMA) and poly(CMA-co-8-QMA)

Weight of polymer : 50 mg Electrolyte : NaNO3 solution (40 ml) pH of the medium : 5.5 (for Cu+2, Ni+2, Zn+2 and Co+2) and 3.0(for Fe+3)

Sample Electrolyte Metal ion uptake(meq.g-1)

Code concentration No. (Mol.lit-1 ) Cu+2 Ni+2 Co+2 Zn+2 Fe+3

2

0.05

0.10

0.50

1.00

-

0.08

0.16

0.35

-

0.05

0.18

0.37

-

0.04

0.14

0.08

0.66

0.30

0.14

0.08

0.20

0.14

0.10

0.08

3

0.05

0.10

0.50

1.00

0.08

0.12

0.38

0.64

0.10

0.18

0.48

0.52

-

0.05

0.28

0.52

0.64

0.60

0.31

0.18

0.72

0.68

0.24

0.20

4

0.05

0.10

0.50

1.00

0.50

0.54

0.76

0.92

0.52

0.58

0.84

0.88

0.32

0.38

0.56

0.90

1.02

0.96

0.62

0.32

1.08

1.00

0.70

0.32

5

0.05

0.10

0.50

1.00

0.62

0.66

0.82

1.18

0.68

0.72

0.92

1.02

0.44

0.48

0.60

1.20

1.28

1.24

0.90

0.41

1.40

1.36

0.92

0.38

6

0.05

0.10

0.50

1.00

0.78

0.82

1.08

1.48

0.86

0.92

1.32

1.38

0.72

0.76

0.98

1.58

1.40

1.32

0.98

0.48

1.52

1.46

1.02

0.56

7

0.05

0.10

0.50

1.00

1.76

1.92

2.68

3.04

1.82

2.04

2.80

3.12

0.82

0.98

1.46

2.92

3.20

2.92

1.06

0.80

3.36

2.94

1.96

1.02



208


Weight of polymer : 50 mg Electrolyte : Na2SO4 solution (40 ml) pH of the medium : 5.5 (for Cu+2,Ni+2, Zn+2 and Co+2) and 3.0 (forFe+3)

Sample Electrolyte Metal ion uptake (meq.g-1)


2

0.05

0.10

0.50

1.00

0.10

0.08

0.04

-

0.08

0.08

0.06

-

0.06

0.06

0.04

-

0.06

0.06

0.04

-

0.08

0.08

0.04

-

3

0.05

0.10

0.50

1.00

0.22

0.20

0.08

0.04

0.20

0.16

0.06

0.06

0.16

0.10

0.08

0.04

0.16

0.12

0.06

0.04

0.10

0.08

0.04

0.04

4

0.05

0.10

0.50

1.00

0.72

0.66

0.48

0.40

0.66

0.60

0.32

0.30

0.36

0.30

0.20

0.16

0.22

0.18

0.10

0.06

0.20

0.18

0.08

0.06

5

0.05

0.10

0.50

1.00

1.06

0.98

0.74

0.70

1.02

0.96

0.68

0.62

0.90

0.86

0.52

0.48

0.68

0.64

0.50

0.46

0.60

0.54

0.38

0.32

6

0.05

0.10

0.50

1.00

1.54

1.48

1.14

1.10

1.42

1.34

1.08

1.02

1.40

1.38

1.06

1.00

1.22

1.20

0.96

0.90

1.10

1.04

0.90

0.86

7

0.05

0.10

0.50

1.00

3.22

2.98

2.42

2.08

2.94

2.52

2.04

1.78

2.72

1.88

0.90

0.86

2.02

1.78

0.82

0.66

1.96

1.70

0.62

0.56



209


Weight of polymer : 50 mg Electrolyte : NaCl solution (40 ml) pH of the medium : 5.5 (for Cu+2, Ni+2, Zn+2 and Co+2)and 3.0 (for Fe+3)

Sample Electrolyte Metal ion uptake (meq.g-1 )


2

0.05

0.10

0.50

1.00

-

-

0.06

0.08

-

-

0.04

0.08

-

-

-

0.04

0.04

-

-

-

0.06

0.06

0.04

-

3

0.05

0.10

0.50

1.00

0.04

0.06

0.14

0.18

0.08

0.12

0.20

0.24

-

-

0.08

0.10

-

-

0.08

0.06

-

0.04

0.06

0.10

4

0.05

0.10

0.50

1.00

0.50

0.54

0.60

0.64

0.48

0.52

0.68

0.72

0.04

0.06

0.12

0.14

0.20

0.16

0.06

0.04

0.22

0.26

0.34

0.38

5

0.05

0.10

0.50

1.00

0.54

0.58

0.78

0.82

0.62

0.64

0.86

0.96

0.28

0.32

0.48

0.54

0.72

0.68

0.40

0.36

0.76

0.72

0.50

0.46

6

0.05

0.10

0.50

1.00

0.66

0.72

0.86

0.92

0.78

0.82

0.98

1.08

0.42

0.46

0.56

0.60

0.82

0.76

0.54

0.50

0.90

0.86

0.62

0.58

7

0.05

0.10

0.50

1.00

1.08

1.42

1.64

2.60

2.08

2.40

2.88

3.02

0.62

1.14

1.92

2.06

2.04

1.38

0.96

0.92

2.12

1.58

1.34

0.98



210



211



212



213



214



215

6.3 RESULTS AND DISCUSSION

From the ion-exchange study with various metal ions under different

experimental conditions the behaviour of the synthesized polymers as chelating

ion-exchangers with respect to experimental variables is discussed as follows.

(a) Effect of pH on the metal binding capacity:

The metal binding capacity depends on the pH of the aqueous medium to a

great extent. The study of the influence of pH of the aqueous medium on the metal

uptake capacity of the polymers was carried out in the presence of a constant amount

of 1.0 M NaNO3 solution at various pH values between 3.0 to 6.0 for Cu+2, Ni+2, Zn+2

and Co+2 metal ions. The study was restricted up to pH 6.0 because at higher pH, due

to hydrolysis of metal salt metal hydroxides are formed which interfere with the ion-

exchange process of the respective metal ions. The ion-exchange study with Fe+3 in

the above mentioned pH range is quite difficult as it forms hydroxide even at pH 4.0.

Hence, its study was carried out separately at various pH values between 1.5 to 3.5

and these results are not compared with results of other metal ions. Tables 6.1 to 6.5

incorporate the results of the effect of pH on the metal binding capacity of the

polymers. It is observed from these results that the relative amount of the metal ion

adsorbed by the polymers increases with increasing pH of the medium. It is also

observed that particular metal ion is adsorbed selectively compared to others at certain

pH. The data clearly indicates that for all the polymers Ni+2 gets adsorbed selectively

to the highest extent and Zn+2 ion is adsorbed to the least extent over the entire pH

range studied. This suggests the possible use of these polymers for separation of Ni+2,

Cu+2 and Co+2 from Ni+2 – Zn+2, Cu+2 – Zn+2, and Co+2 – Zn+2 mixtures respectively.

The trend of metal adsorption by the polymers follows the order: Ni+2 > Cu+2 > Co+2 >

Zn+2. This clearly shows that almost all the polymers have highest affinity for Ni+2

and least for Zn+2. The lowest affinity of Zn+2 may be attributed to the very low

stability constants of complexes of Zn+2 with the ligands [39].

(b) Distribution ratios of metal ions as a function of pH:

The effect of pH on the amount of metal ion distributed between two phases

(in polymer and remained in solution) can be explained by the results shown in Tables

6.6 to 6.10. It is observed from the results that the value of the distribution coefficient

of each metal ions increases rapidly with an increase in the pH of the solution. It is



216

also observed from the results that for all the polymers, the value of distribution

coefficient for divalent metal ions decreases in the following order:

Ni+2>Cu+2>Co+2>Zn+2

The data clearly shows that almost all polymers have higher affinity for Ni+2 and

lower affinity for Zn+2 and the amount of metal ions taken up by the polymers

increases with increasing pH of the medium at equilibrium.

(c) Effect of electrolyte and its concentration on the metal binding capacity:

The results of the effect of the nature and concentration of an electrolyte on

the amount of various metal ions adsorbed by the polymers from their solutions at

room temperature are shown in the Tables 6.11 to 6.13. Examination of these results

shows that the amount of metal ion adsorbed by a given amount of polymer is

affected considerably by the nature and concentration of the electrolyte present in the

solution. It is also observed from the results that the amount of Cu+2, Ni+2 and Co+2

ions adsorbed by the polymers increases with increasing concentration of NO3- and

Cl- ions, whereas that of Zn+2 ion, the adsorption decreases with increasing NO3- and

Cl- ions concentration. But in case of SO4-2 ion, the adsorption of Cu+2, Ni+2, Zn+2,

Co+2 and Fe+3 ions decreases with increasing concentration of SO4-2 ion. The

adsorption of Fe3+ ion decreases with the increasing concentration of NO3- and Cl-

ions. This may be explained in terms of the stability constants of the complexes of

Cu+2, Ni+2, Zn+2, Co+2 and Fe+3 cations with the NO3-, Cl- and SO4

-2 anions [40].

It may be inferred from the results that on an average, the metal ion adsorption

by the polymers is much better in the presence of 1.0 M NaNO3 solution. Moreover, it

is reported that nitrate and chloride ions have a tendency to form strong complexes

with many metal ions compare to the sulfate ions [37]. Therefore, the ion-exchange

study with respect to pH and shaking time was carried out in the presence of 1.0 M

NaNO3 solution.

(d) Rate of metal uptake as a function of time:

It was assumed in the present study, that under the prescribed experimental

conditions, the state of equilibrium is established within 24 hrs. Kunin and Barry [41]

also reported that equilibrium for adsorption of metal ion by ion-exchange resins are

attained in minutes or in hours. The results of the rate of metal uptake by the polymers

as a function of time are shown in the Tables 6.14 to 6.18. It is expressed in terms of



217

% of the metal ions adsorbed by the polymers after regular time intervals with respect

to 100% adsorption after 24 hrs i.e. in the state of equilibrium. The rate of metal ion

adsorption by the polymers was determined for various metal ions to establish the

shortest time for which equilibrium could be attained so that while operating such

conditions could be maintained. The term “rate” refers to the speed of change in the

concentration of the metal ion in the aqueous solution, which is in contact with the

polymer. The examination of the data shows that amongst the five metal ions studied,

Zn+2 and Fe+3 ions required the shortest time of about 4.0 to 6.0 hrs, whereas Cu+2,

Ni+2 and Co+2 ions required 6.0 to 7.0 hrs to reach the state of equilibrium. It is also

observed from the results that the rate of metal adsorption by the polymers follows the

order of (Fe+3, Zn+2) > (Cu+2, Ni+2, Co+2). Due to this difference in the uptake rate of

metals, it may be possible to separate Zn+2 and Fe+3 ions from their mixtures with

Cu+2, Ni+2 and Co+2 ions using these polymers. Moreover, since the time required for

almost complete saturation of the adsorption capacity of the polymers is considerably

short, these polymers may be utilized for the extraction of heavy metal ions from the

aqueous solutions.



218

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