chapter 6 ion exchange study 6.1....

Chapter 6 Ion Exchange Study

89

6.1. INTRODUCTION:

The term ion exchange has often been closely related to or even used synonymously

with adsorption. Ion exchange is an exchange of ions between two electrolytes or

between an electrolyte solution and a complex. In most cases the term is used to

denote the processes of purification, separation, and decontamination of aqueous and

other ion containing solutions with solid polymeric or mineralic 'ion exchangers'. Ion-

exchange may be defined as the reversible exchange of ions between the substrate and

surrounding medium. Ion-exchange resins consist of a frame work carrying positive

or negative electric surplus charge which is compensated by mobile counter ions of

the opposite charge. The counter ions can be exchanges for other ions carrying similar

charge. The exchange is stoichiometric and as a rule reversible ion-exchange is

essentially a diffusion process

The first examples of ion exchange were discovered in the early nineteenth century.

During investigations it was found that soluble materials are retained for long periods

in the soil, instead of being washed out by rain. In the latter half of the nineteenth

century it was shown that this effect was brought about by certain minerals in the soil.

These minerals, called resins are based on silicon and aluminium compounds called

zeolites. The commercial use of zeolites for water softening has been practiced

increasingly from about 1906. Synthetic cation and anion exchange resins were

developed during the 1930’s using certain types of coal treated with sulphuric acid.

The major development for the power industry came in the U.S.A. in 1944 when

resins were produced based on polystyrene which had much better characteristics than

earlier resins. These new resins are now used almost exclusively in demineralization

plants for high pressure boilers. The resin has the appearance of smooth, spherical

beads usually between 0.5 and 1 mm in diameter. However, at the molecular level,

each bead has a skeleton-like structure. The resin beads are kept in a suitable vessel

called a resin bed through which the water is passed allowing the chemical reactions

to take place. Ion-exchangers are widely used in analytical chemistry, hydro-

metallurgy, antibiotic purification and 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


Page 190

many fields such as water softening and deionization, sugar purification, extraction of

uranium glycerol refining, purification of formaldehyde and as catalysts [6-13].

Ion exchange technique can remove traces of ionic impurities from water processes

liquors and can give a product of ultra pure quality in a simple, efficient and techno

economically viable manner [14-16]. Adams and Holmes [17] first described the

granular ion-exchange resins in 1935. They discovered the ion-exchange properties of

a phenol-formaldehyde condensate resin. The term ion exchange has often been

closely related to or even used synonymously with adsorption. Exchange – adsorption

was used instead of ion exchange during the transition in understanding from base

exchange to modern cation exchange or anion exchange [18]. Here, although the term

adsorption for an ion exchange process may appear strange, phenomena associated

with ion exchange have involved mechanisms other than the ionic exchange of ions.

In the course of the increasing importance of addition polymerization materials, as

opposed to condensation polymerization products, a new class of polymeric

adsorbents has been developed, which are manufactured by suspension

polymerization leading to polymer beads and which can be effectively used because

of their porous structure as adsorbing media.

Kim et al. [19] 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 capacity 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. Yixin and others [20] studied the

interaction of heavy metal ions and chelating ion exchange resin containing 8-

hydroxyquinoline (8-HQ) moiety. The resin has good selectivity to adsorb 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. The chelating ion exchange properties of methyl

methacrylate (MMA)-8-Quinolinyl acrylate (8-QA) copolymers were studied by Patel

and co-workers [21]. Batch equilibrium method was used for five metal ions viz.,

Cu+2, Ni+2, Co+2, Zn+2 and Fe+3 to evaluate the capacity of MMA-8-QA copolymers as

cation exchanger. It was observed that due to the presence of a pendant ester-bound


Page 191

quinolinyl group, the copolymers are capable of exchanging the tested cations from

their aqueous solutions.

Kapadia et al[22, 23] have synthesized the phenol-acetaldehyde type cation

exchange resins using various phenol derivatives such as salicylic acid, pyrocatechol,

8-hydroxyquinoline, 3-hydroxy-2-naphthoic acid, gallic acid, -resorcylic acid and

anthranilic acid, and measured the total exchange capacity, moisture content and

selectivity of the resins towards Ca+2, Mg+2, Co+2, Ni+2, Zn+2 and Cu+2 at pH 2.8. They

also determined the metal distribution coefficient as a function of pH. Patel and

others[24,25]synthesized the ion exchange resins based on N-phenyl maleimide and

studied the effect of electrolyte strength, pH and shaking 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. Chowdhury and co-workers [26] synthesized

the graft copolymer of poly( acrylic acid ) and poly(vinyl alcohol) in the presence of

methylene bisacrylamide crosslinker and investigated of its efficiency in removing

lead ion from aqueous solution.

Dhakite and co-workers [27] 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 Cu+2, Cd+2, Co+2 and Zn+2 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 Cu+2 ions than for Cd+2, Co+2 and Zn+2

ions. The novel ion-exchange resin beads showed an in-built acid-base indicator

property; the yellow color in the acid medium changes to an intense pink color at the

equivalence point. Also, the ion-exchange capacity of the sulfonated copolymer

increases with time, reaches a maximum and decreases thereafter. The developed ion-

exchange resin also demonstrated better performance in demineralization of water as

compared with the conventional polystyrene-based beads. Sanjiokumar Rahangdale

[28] synthesized a terpolymer resin by condensation of 2,4-dihydroxyacetophenon

(2,4-HA) and biuret (B) with formaldehyde (F) in the presence of an acid catalyst. He


Page 192

studied chelating ion-exchange properties of this polymer for Fe3+, Cu2+, Ni2+,Co2+,

Zn2+, Cd2+ and Pb2+ ions. A batch equilibrium method was employed in the study of

the selectivity of metal ion uptake. The study was carried out over a wide pH range

and in media of various ionic strengths. The polymer showed highest selectivity for

Fe3+, Cu2+ ions than for Ni2+, Co2+, Zn2+, Cd2+ and Pb2+ ions. Study of distribution

ratio as a formation of pH indicates that the amount of metal ion taken by resin is

increases with the increasing pH of the medium.

The present chapter deals with application of novel acrylic copolymers of VMA

with QMA in removal of metal ions. A batch equilibrium technique was used to

determine the optimum conditions for removal of metal ions from the aqueous

solution. This work comprises the following aspects of the cation exchange study.

To determine optimum pH of the metal ion uptake by the copolymers.

To determine the distribution coefficient of metal ions between (solid) and

aqueous phase (liquid).

To study the effect of ionic strength on metal ion uptake by using different

electrolytes at different concentrations.

To determine the time required to reach the state of equilibrium under the given

experimental conditions i.e., rate of metal up take.

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:

A batch equilibrium technique [29,30] was used to determine the optimum

metal uptake conditions such as pH, electrolyte and its concentration, time (rate of

metal uptake) and ion exchange capacity of the poly(VMA-co-QMA) with different

feed composition. Copolymers were equilibrated with each of the different metal ion

solutions. The copolymer was filtered off, washed and then the concentration of the


Page 193

metal ion remaining in the solution was determined by back titration with 0.01 M

EDTA [31-37].

i. Effect of pH on metal ion uptake:

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

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.

ii. Estimation of distribution ratio (KD) of metal ions at different 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.


Page 194

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 [38]. The results are presented in Tables 6.6 to 6.10.

)(

)(

gmpolymerofWeight

mlsolutionofVolume

soluioninionmetalofAmount

polymeronuptakeionmetalofAmountK D

iii. Influence of an electrolyte on metal-ion 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 unabsorbed 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.


Page 195

iv. Evaluation of the rate of metal uptake:

In order to estimate the time required to reach the state of equilibrium under given

experimental conditions a series of experiments were carried out in which the metal

ion taken up by the polymer was estimated from time to time in the presence of 1.0 M

NaNO3 solution. It was assumed that, under given conditions, the state of equilibrium

was established within 24 hrs. The rate of metal ion uptake is expressed as the

percentage of the amount of metal ions taken up after a certain time related to that in

the state of equilibrium [39]. The experimental procedure is given below:

The polymer (50 mg) was shaken with 1M NaNO3 solution (40 ml) at pH 5.5 for 24

hrs. Metal ion solution (0.1M, 2 ml) was added and the pH of the solution was

adjusted by using either 0.1 M NaOH or 0.1 M HNO3. With each cation, nine samples

were prepared and shaken for 1, 2, 3, 4, 5, 6, 7 and 24 hrs. respectively at 30°C. The

pH was checked periodically and adjusted to 5.5 by using 0.1 M NaOH. The polymer

was filtered off, washed and then the concentration of metal ion remaining in the

solution was determined by back titration with 0.01 M EDTA. 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.


Page 196

Table 6.1: Effect of pH on Cu+2 metal ion binding capacity of poly(QMA) and poly(VMA-co-QMA)

Weight of polymer : 50 mg

Metal ion : 0.1 M Cu(NO3 )2 (2 ml)

Electrolyte : 1.0 M NaNO3 (40 ml)

Sample Metal ion uptake (meq.g-1 )

Code pH of the medium

No. 3. 0 3. 5 4. 0 5. 0 5. 5 6. 0

32 0.10 0.20 0.35 0.55 0.88 0.92

33 0.28 0.43 0.35 0.51 0.98 1.40

34 0.33 0.52 0.54 0.68 1.15 1.68

35 0.48 0.81 0.98 1.82 2.02 2.46

36 0.93 1.40 1.80 2.10 2.28 2.82

37 0.98 1.65 1.95 2.42 2.56 2.88


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Table 6.2: Effect of pH on Ni+2 metal ion binding capacity of poly(QMA) and poly(VMA-co-QMA)


Metal ion : 0.1 M Ni(NO3 )2 (2 ml)




No. 3. 0 3. 5 4. 0 5. 0 5. 5 6. 0

32 0.31 0.25 0.32 0.26 0.59 0.68

33 0.49 0.40 0.52 0.61 1.04 1.08

34 0.55 0.74 0.88 0.90 1.02 1.14

35 0.66 0.98 1.12 1.75 1.96 2.08

36 0.89 1.18 1.57 1.89 1.97 2.24

37 0.97 1.68 1.83 2.09 2.42 2.59


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Table 6.3: Effect of pH on Co+2 metal ion binding capacity of poly(QMA) and poly(VMA-co-QMA)


Metal ion : 0.1 M Co(NO3 )2 (2 ml)




No. 3. 0 3. 5 4. 0 5. 0 5. 5 6. 0

32 -- 0.14 0.18 0.22 0.27 0.83

33 0.08 0.22 0.43 0.52 0.98 1.25

34 0.18 0.38 0.65 0.95 1.34 1.48

35 0.43 0.60 0.96 1.33 1.68 1.98

36 0.68 0.52 1.12 1.62 1.98 2.30

37 0.77 0.89 1.65 1.93 2.42 2.75


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Table 6.4: Effect of pH on Zn+2 metal ion binding capacity of poly(QMA) and poly(VMA-co-QMA)


Metal ion : 0.1 M Zn(NO3 )2 (2 ml)




No. 3. 0 3. 5 4. 0 5. 0 5. 5 6. 0

32 0.10 0.08 0.08 0.20 0.29 0.60

33 0.23 0.26 0.47 0.59 1.23 0.32

34 0.32 0.44 0.58 0.83 1.18 0.43

35 0.48 0.52 0.78 0.98 0.77 1.78

36 0.55 0.70 0.70 1.64 1.98 2.00

37 0.58 0.75 1.06 1.48 1.83 2.10


Page 200

Table 6.5: Effect of pH on Fe+3 metal ion binding capacity of poly(QMA) and poly(VMA-co-QMA)


Metal ion : 0.1 M Fe(NO3 )3 (2 ml)




No. 1. 5 2. 0 2. 5 3. 0 3. 5

32 0.17 0.20 0.27 0.34 0.39

33 0.26 0.44 0.58 0.49 0.65

34 0.48 0.57 0.83 0.69 0.90

35 0.55 0.65 0.94 1.12 1.60

36 0.68 0.78 1.02 1.89 2.07

37 0.98 1.21 1.75 2.01 2.29


Page 201

Table 6.6: Distribution ratio of Cu+2 ion adsorbed by the polymer and remained in the solution at equilibrium


Metal ion : 0.1 M Cu(NO3 )2 (2 ml)


Sample Distribution ratio (KD )


No. 3. 0 3. 5 4. 0 5. 0 5. 5 6. 0

32 11 14 20 28 44 47

33 41 53 71 103 120 187

34 59 107 117 157 252 305

35 87 123 138 205 267 375

36 110 145 232 295 338 405

37 115 210 254 308 398 442


Page 202

Table 6.7: Distribution ratio of Ni+2 ion adsorbed by the polymer and remained in the solution at equilibrium


Metal ion : 0.1 M Ni(NO3 )2 (2 ml)




No. 3. 0 3. 5 4. 0 5. 0 5. 5 6. 0

32 11 15 19 25 44 47

33 32 40 63 78 81 92

34 54 109 87 137 126 131

35 85 120 137 282 356 360

36 99 155 256 373 486 565

37 105 172 305 389 660 723


Page 203

Table 6.8: Distribution ratio of Co+2 ion adsorbed by the polymer and remained in the solution at equilibrium


Metal ion : 0.1 M Co(NO3 )2 (2 ml)




No. 3. 0 3. 5 4. 0 5. 0 5. 5 6. 0

32 9 12 15 20 24 29

33 21 29 36 63 98 102

34 45 58 104 136 213 267

35 61 78 123 198 276 291

36 79 84 156 234 333 364

37 90 104 189 281 365 399


Page 204

Table 6.9: Distribution ratio of Zn+2 ion adsorbed by the polymer and remained in the solution at equilibrium


Metal ion : 0.1 M Zn(NO3 )2 (2 ml)




No. 3. 0 3. 5 4. 0 5. 0 5. 5 6.0

32 02 5 7 15 20 24

33 06 27 39 58 76 102

34 22 40 66 81 125 144

35 35 53 99 115 187 189

36 59 66 123 131 210 240

37 64 82 135 169 269 280


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Table 6.10: Distribution ratio of Fe+3 ion adsorbed by the polymer and remained in the solution at equilibrium


Metal ion : 0.1 M Fe(NO3 )3 (2 ml)




No. 1. 5 2. 0 2. 5 3. 0 3. 5

32 7 15 18 32 38

33 28 30 45 78 70

34 34 68 78 107 134

35 55 85 96 146 166

36 63 98 115 165 178

37 71 105 134 192 194


Page 206

Table 6.11: Effect of electrolyte concentration on metal ion adsorption capacity of

poly(QMA) and poly(VMA-co-QMA)


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

Code No.Electrolyte

concentration(Mol.lit-1 )Cu+2 Ni+2 Co+2 Zn+2 Fe+3

32

0.05

0.10

0.50

1.00

0.05

0.12

0.23

0.26

0.21

0.34

0.48

0.61

0.35

0.43

0.52

0.67

1.18

1.46

0.98

0.42

0.80

0.65

0.38

0.25

33

0.05

0.10

0.50

1.00

0.28

0.51

0.75

1.12

0.83

1.05

1.22

1.42

0.63

0.79

0.88

0.95

1.98

1.80

1.46

0.94

1.65

1.34

1.20

0.83

34

0.05

0.10

0.50

1.00

1.02

1.68

1.86

2.05

1.32

1.77

1.98

2.08

0.77

0.93

1.15

1.33

2.21

1.89

1.65

1.14

2.70

2.25

1.74

1.26

35

0.05

0.10

0.50

1.00

1.45

1.83

2.02

2.18

1.58

2.05

2.18

2.31

0.97

1.08

1.32

1.44

2.78

2.55

2.21

1.32

2.89

2.51

1.98

1.39

36

0.05

0.10

0.50

1.00

1.85

2.41

2.45

2.54

1.89

2.15

2.32

2.78

1.21

1.47

1.71

1.87

3.09

2.80

2.48

1.59

3.35

2.78

2.33

1.81

37

0.05

0.10

0.50

1.00

2.05

2.25

2.50

2.62

2.08

2.41

2.76

3.23

1.33

1.55

1.82

2.08

3.23

2.85

2.58

1.83

3.75

3.14

2.59

2.12


Page 207




Electrolyte: Na2SO4 solution (40 ml)


Sample

Code No.Electrolyte


32

0.05

0.10

0.50

1.00

0.67

0.55

0.35

0.32

0.40

0.28

0.18

0.08

0.35

0.21

0.10

--

0.25

0.20

0.14

0.05

0.21

0.06

0.05

2.18

33

0.05

0.10

0.50

1.00

1.14

0.98

0.73

0.70

0.95

0.67

0.45

0.41

0.88

0.71

0.53

0.37

0.96

0.84

0.57

0.42

0.95

0.58

0.45

0.29

34

0.05

0.10

0.50

1.00

2.45

2.15

1.57

1.44

1.36

1.27

0.92

0.85

1.12

0.86

0.68

0.35

1.28

1.08

0.89

0.65

1.04

0.81

0.65

0.52

35

0.05

0.10

0.50

1.00

3.39

3.21

2.86

2.21

2.11

1.88

1.05

0.93

1.62

1.18

1.08

0.64

1.14

1.01

0.85

0.58

1.95

1.21

0.73

0.68

36

0.05

0.10

0.50

1.00

3.76

3.31

2.83

2.45

2.40

2.15

1.63

1.32

2.05

1.67

1.34

0.93

1.44

1.15

0.96

0.69

2.21

1.47

1.06

0.78

37

0.05

0.10

0.50

1.00

3.96

3.33

2.88

2.35

2.78

2.49

1.77

1.43

2.36

1.87

1.45

1.21

1.58

1.32

1.01

0.69

1.73

1.33

0.86

2.28


8




Electrolyte: NaCl solution (40 ml)


Sample

Code No.Electrolyte


32

0.05

0.10

0.50

1.00

0.10

0.15

0.18

0.21

0.08

0.22

0.25

0.27

--

0.02

0.06

0.11

0.12

0.07

0.03

--

0.14

0.11

0.03

--

33

0.05

0.10

0.50

1.00

0.35

0.48

0.53

0.78

0.62

0.89

0.95

1.04

0.20

0.34

0.44

0.49

0.64

0.55

0.41

0.23

0.90

0.65

0.47

0.28

34

0.05

0.10

0.50

1.00

0.85

1.13

1.64

1.79

0.83

1.10

1.45

1.87

0.38

0.65

0.98

1.12

1.17

0.95

0.74

0.43

1.74

0.77

0.61

0.44

35

0.05

0.10

0.50

1.00

1.20

2.31

2.39

2.68

1.02

1.81

2.23

2.87

0.40

0.75

1.15

1.35

1.53

1.31

0.98

0.45

1.90

1.15

0.83

0.77

36

0.05

0.10

0.50

1.00

1.53

2.34

2.97

3.21

1.28

2.36

2.72

3.19

0.53

0.97

1.37

1.85

1.78

1.65

1.17

0.87

2.38

1.43

1.05

0.62

37

0.05

0.10

0.50

1.00

1.87

2.38

2.89

3.12

1.64

2.23

2.81

3.35

0.82

1.05

1.34

1.71

2.21

1.49

1.03

0.88

2.60

1.79

1.36

0.98


Page 209

Table 6.14: Rate of Cu+2 metal ion uptake by poly(QMA) and poly(VMA-co-QMA) as a function of time

Weight of sample : 50 mg

Metal ion : 0.1 M Cu(NO3)2 (2 ml)


pH of the medium : 5.5

Sample % attainment of equilibriuma

Code Time (hrs)

No. 1.0 2.0 3.0 4.0 5.0 6.0 7.0

32 14.9 20.4 33.4 48.1 70.9 86.8 91.6

33 21.8 25.2 36.1 42.4 82.4 85.7 95.7

34 27.6 32.5 40.2 58.2 76.5 79.5 93.4

35 18.7 23.7 28.9 55.4 85.6 90.2 --

36 31.1 34.8 41.4 50.5 77.7 82.9 96.5

37 30.8 35.9 49.8 64.5 79.8 88.3 94.9

a With respect to 100% equilibrium after 24 hrs.


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Table 6.15: Rate of Ni+2 metal ion uptake by poly(QMA) and poly(VMA-co-QMA) as a function of time


Metal ion : 0.1 M Ni(NO3)2 (2 ml)




Code Time (hrs)

No. 1.0 2.0 3.0 4.0 5.0 6.0 7.0

32 19.7 28.5 37.6 46.9 72.8 86.5 95.5

33 25.4 27.8 29.2 30.8 58.9 78.9 92.8

34 17.8 30.7 36.8 44.5 60.8 81.8 90.3

35 26.5 29.8 31.5 42.7 64.2 83.2 96.4

36 25.6 28.0 35.7 49.9 70.4 89.9 95.8

37 29.7 32.5 36.9 45.3 77.9 86.5 94.7



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Table 6.16: Rate of Co+2 metal ion uptake by poly(QMA) and poly(VMA-co-QMA) as a function of time


Metal ion : 0.1 M Co(NO3)2 (2 ml)




Code Time (hrs)

No. 1.0 2.0 3.0 4.0 5.0 6.0 7.0

32 21.8 29.3 35.4 51.8 67.5 86.5 90.1

33 20.5 27.1 32.1 44.2 61.2 81.5 92.6

34 15.4 21.8 24.7 47.4 58.5 77.3 94.5

35 19.5 23.2 30.3 55.3 63.3 72.8 96.2

36 12.9 18.5 25.3 49.8 70.4 76.3 90.8

37 23.4 28.8 44.5 60.2 75.6 89.7 93.8



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Table 6.17: Rate of Zn+2 metal ion uptake by poly(QMA) and poly(VMAM-co-QMA) as a function of time


Metal ion : 0.1 M Zn(NO3)2 (2 ml)




Code Time (hrs)

No. 1.0 2.0 3.0 4.0 5.0 6.0 7.0

32 40.5 34.5 58.2 68.9 89.8 98.3 --

33 36.4 40.2 60.3 75.2 90.1 97.5 --

34 33.6 44.8 51.6 71.9 88.7 95.4 99.8

35 38.7 41.5 62.2 80.1 92.3 99.8 --

36 41.2 46.2 58.5 72.9 91.8 96.4 --

37 42.3 49.4 66.9 82.2 95.9 98.0 --



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Table 6.18: Rate of Fe+3 metal ion uptake by poly(QMA) and poly(VMA-co-QMA) as a function of time


Metal ion : 0.1 M Fe(NO3)2 (2 ml)




Code Time (hrs)

No. 1.0 2.0 3.0 4.0 5.0 6.0 7.0

32 47.5 61.0 73.5 88.7 94.4 -- --

33 48.9 60.3 75.8 88.5 95.9 -- --

34 51.2 56.3 68.5 77.7 89.6 99.2 --

35 50.3 52.8 69.4 80.6 97.8 98.3 --

36 44.6 58.4 71.8 89.6 98.2 -- --

37 53.5 60.5 77.5 92.4 99.8 -- --



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6.3. RESULTS AND DISCUSSION

From the ion exchange study with various metal ions under different

experimental conditions, the behavior of the synthesized polymers as chelating ion

exchangers with respect to experimental variables is discussed.

i. 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 Cu+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 Cu+2,

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

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

Zn+2. This clearly shows that almost all the polymers have highest affinity for Cu+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 [40].


Page 215

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

distribution coefficient for divalent metal ions decreases in the following order:

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

The data clearly shows that almost all polymers have higher affinity for Cu+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.

iii. 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 [41].

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. Therefore, the ion-exchange study

with respect to pH and shaking time was carried out in the presence of 1.0 M NaNO3

solution.

iv. Rate of metal uptake as a function of time:


Page 216

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

conditions, the state of equilibrium is established within 24 hrs. Kunin and co-workers

[42] 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 % 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 5 to 6 hrs.,

whereas Cu+2, Co+2 and Ni+2 ions required 6 to 7 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, Co+2, Ni+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, Co+2 and Ni+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.


Page 217

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chapter 6 ion exchange study 6.1....

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