Chapter 6 Ion Exchange Study 6.1....
Transcript of Chapter 6 Ion Exchange Study 6.1....
Chapter 6 Ion Exchange Study
Page 189
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
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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
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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
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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
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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.
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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.
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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.
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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)
Weight of polymer : 50 mg
Metal ion : 0.1 M Ni(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 0.31 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)
Weight of polymer : 50 mg
Metal ion : 0.1 M Co(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 -- 0.14 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)
Weight of polymer : 50 mg
Metal ion : 0.1 M Zn(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 0.08 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
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Table 6.5: Effect of pH on Fe+3 metal ion binding capacity of poly(QMA) and poly(VMA-co-QMA)
Weight of polymer : 50 mg
Metal ion : 0.1 M Fe(NO3 )3 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 ml)
Sample Metal ion uptake (meq.g-1 )
Code pH of the medium
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
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Table 6.6: Distribution ratio of Cu+2 ion adsorbed by the polymer and remained in the solution at equilibrium
Weight of polymer : 50 mg
Metal ion : 0.1 M Cu(NO3 )2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 ml)
Sample Distribution ratio (KD )
Code pH of the medium
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
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Table 6.7: Distribution ratio of Ni+2 ion adsorbed by the polymer and remained in the solution at equilibrium
Weight of polymer : 50 mg
Metal ion : 0.1 M Ni(NO3 )2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 ml)
Sample Distribution ratio (KD )
Code pH of the medium
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
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Table 6.8: Distribution ratio of Co+2 ion adsorbed by the polymer and remained in the solution at equilibrium
Weight of polymer : 50 mg
Metal ion : 0.1 M Co(NO3 )2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 ml)
Sample Distribution ratio (KD )
Code pH of the medium
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
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Table 6.9: Distribution ratio of Zn+2 ion adsorbed by the polymer and remained in the solution at equilibrium
Weight of polymer : 50 mg
Metal ion : 0.1 M Zn(NO3 )2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 ml)
Sample Distribution ratio (KD )
Code pH of the medium
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
Weight of polymer : 50 mg
Metal ion : 0.1 M Fe(NO3 )3 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 ml)
Sample Distribution ratio (KD )
Code pH of the medium
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
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Table 6.11: Effect of electrolyte concentration on metal ion adsorption capacity of
poly(QMA) and poly(VMA-co-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
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
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Table 6.12: Effect of electrolyte concentration on metal ion adsorption capacity of
poly(QMA) and poly(VMA-co-QMA)
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(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
0.67
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
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Table 6.13: Effect of electrolyte concentration on metal ion adsorption capacity of
poly(QMA) and poly(VMA-co-QMA)
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
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
0.10
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
Chapter 6 Ion Exchange Study
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)
Electrolyte : 1.0 M NaNO3 (40 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.
Chapter 6 Ion Exchange Study
Page 210
Table 6.15: Rate of Ni+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 Ni(NO3)2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 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 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
a With respect to 100% equilibrium after 24 hrs.
Chapter 6 Ion Exchange Study
Page 211
Table 6.16: Rate of Co+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 Co(NO3)2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 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 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
a With respect to 100% equilibrium after 24 hrs.
Chapter 6 Ion Exchange Study
Page 212
Table 6.17: Rate of Zn+2 metal ion uptake by poly(QMA) and poly(VMAM-co-QMA) as a function of time
Weight of sample : 50 mg
Metal ion : 0.1 M Zn(NO3)2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 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 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 --
a With respect to 100% equilibrium after 24 hrs.
Chapter 6 Ion Exchange Study
Page 213
Table 6.18: Rate of Fe+3 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 Fe(NO3)2 (2 ml)
Electrolyte : 1.0 M NaNO3 (40 ml)
pH of the medium : 3.0
Sample % attainment of equilibriuma
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 -- --
a With respect to 100% equilibrium after 24 hrs.
Chapter 6 Ion Exchange Study
Page 214
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].
Chapter 6 Ion Exchange Study
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:
Chapter 6 Ion Exchange Study
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.
Chapter 6 Ion Exchange Study
Page 217
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