Indian Journal of Chemical Techno logy
Vol. 8, September2001, pp. 371-377
Synthesis of crosslinked methacrylic acid-co-N,N'-methylene bis acrylamide
sorbents for recovery of heavy metal ions from dilute solutions
H Hari Prasad, Ashrima Senger, Kavita Chauhan, Kirit M Popat & Pritpal Singh Anand*
Separation Technology Discipline, Central Salt & Marine Chemicals Research Institute, Bhavnagar 364 002, India
Received 19 February 200 I; revised 4 June 2001; accepted 26 June 2001
Several crosslinked porous copolymers of methacry lic acid-N,N'-methylene bis acrylamide were synthesi zed by
suspension polymerisation using benzoylperoxide as the initiator. They were characterized for physico-chemical properties
like, surface area, porosity and scientific weight capacity. The sorbents were further studied for adsorption of nickel and
copper ions from spiked metal ion solutions in static and dynamic conditions. Concentration ratios of I :60 and I :30 have
been achieved for nickel and copper ions respectively.
The disposal of sludge from the electroplating
industry effluents involves environmental and
economic problems. The first problem arises due to
limited dissolution of sludge and the latter might
result due to the presence of valuable metals in
sludge. Thus the conventional method to address this
problem is the prevention of sludge formation by
adopting a technique which results in the formation of
concentrated solutions. The composition of these
solutions will be similar to those used m
electroplating tanks and can be reused after
appropriate modification.
Weakly acidic sodium form of carboxylic acid type
cation exchangers are quite appropriate for the
removal of metals ions from dilute solutions. It is
well-established that the metal ions like Cu(II) or
Ni(ll), undergo the following reaction at pH 4 to 5.
untreated bituminous coal 1, blast furnace flyash 2 ,
supported
liquid
membranes
contmmng
trioctylamine3 , seed and seedshell of magiteraindica4 ,
congo red attached to poly(ethylene glycol
methacrylate )5,
dimethacrylate-hydroxyethy I
iminodiacetic acid and thiourea based resins 6 etc., for
the removal of metal ions from waste water. Recently,
the removal of various metal ions such as copper and
nickel by using polymethylmethacrylate microbeads
carrying ethylenediamine7, chelate polymers and ionexchange resins 8 , polymer immobilized rhizopus
oryzae9 , biopolymer chitin 10, low grade phosphate
mineral surface 11 , and saw dust 12 etc. has been
studied.
This
paper
describes
the
synthesis
and
characterization of methacryl ic acid -co-N,N'methylene bis acrylamide sorbent and their
application for the removal of nickel and copper ions
from waste water.
Ion-exchange capacity of the order of 3 equivalents
per liter of carboxylic resin can be utilized in this
processes. The exhausted resin beds can be
regenerated by dilute mineral acids resulting into
eluates which can be directly fed to electroplating
bath after minor composition make-up. This process
results into solutions containing slight excess of
sodium ions which can be minimized by incorporating
a de-ionizer.
A voluminous work has been reported by several
authors using different adsorbents such as treated and
Experimental Procedure
Materials
*For correspondence
E-mail: [email protected];
Fax : 0278-566970
Methacry lic acid, N ,N'-methylene-bis-acrylamide,
benzoyl peroxide, hydrochloric acid, n-heptane,
starch, sodium hydroxide, sodium chloride, Fast
Green FCF dye, toluene, cyclohexane, nickel
ammonium sulphate, and cupric chloride were used as
received. Benzoyl peroxide (BPO) was recrystallized
from methanol-chloroform mixture ( 1: I).
Synthesis of porous copolymer
The cross-linked copolymers were synthesized by
suspension polymerization accord ing to the reported
method 13 • In a three neck round bottom flask
372
INDIAN J. CHEM. TECHNOL., SEPTEMBER 2001
equipped with a stirrer, a thermometer and a reflux
condenser, was taken a suspension medium composed
of saturated solution of sodium chloride containing
2% (w/v) starch as suspension stabilizer. Then, a
mixture of methacrylic acid, N,N'-methylene bis
acrylamide, n-heptane and benzoyl peroxide (I % of
the monomer mixture) was added in required
proportion. The ratio of the reaction mixture
(monomer plus diluent) to suspension medium was
kept at I :4 (w/v). Copolymerization was initially
carried out at 80°C for 2 h and then at 100°C for 2 h.
The copolymer beads thus obtained were washed with
hot water several times to remove any adhering
stabilizer and then air-dried for 16 h. They were
extracted in a soxhelet apparatus with acetone to
remove any unreacted monomers and other trapped
Table !- Preparation conditions of methacrylic acid (MAA)-coN,N'-methylene bis acylamide(N ,N'MBA) copolymer
Polymer
MAA
N,N'MBA
11-Heptane
Yield
matrix
(g)
(g)
(g)
(%)
I.
66.50
3.50
30.00
98.28
2.
76.00
4.00
20.00
98.56
3.
88.50
4.50
10.00
99.32
4.
95.00
5.00
0.00
98.64
5.
64.75
5.25
30.00
98.36
6.
74.00
6.00
20.00
99.23
7.
83.25
6.75
10.00
98.86
98.67
8.
92.50
7 .50
0.00
9.
63.00
7.00
30.00
98.21
10.
72.00
8.00
20.00
98.96
II.
8 1.00
9 .00
10.00
98.76
12.
90.00
10.00
0 .00
98.75
compounds, and air dried. A sieved fraction between 18, +52 BSS mesh size was selected for further
studies. Following this procedure, polymeric sorbents
having varying degree of cross-linking and Fm value
[Fm value is the ratio of the total quantity of the
monomer mixture to the total quantity of monomers
plus diluent (w/v)] were synthesized. The polymeric
sorbents synthesised were designated as follows:
(1)
CPR4-5-0.7-nH
(7)
CPR4-7.5-0.9-nH
(2)
CP~-5-0.8-nH
(8)
CP~-7 .5-1 .0-GEL
(3)
CP~-5-0.9-nH
(9)
CP~-10-0 . 7-nH
(4)
CP~-5-1.0-GEL
(10)
CPR4-l 0-0.8-n H
(5)
CPR4-7.5-0.7-nH
(II )
CPR4-l 0-0.9-nH
(6)
CP~-7 .5-0.8-nH
(12)
CPR4- l 0- 1.0-GEL
In this nomenclature the fi rst numerical indicates
the percentage of cross-linking monomer, the second
numerical indicates the Fm value, and nH stands for
the diluent n-heptane. The letters GEL represent
conventional gel-type matrix synthesized in the
absence of diluent. The copolymers were evaluated
for surface area by p-nitrophenol adsorption method 14 ,
porosity by Fast Green FCF dye uptake 15 , bulk
density, ion-exchange capacity, solvent uptake and
the results are tabulated in Tables 1 and 2. The data
on the uptake of metal IOns by the sorbents are
presented in Tables 3 and 4. The effect of various
parameters such as pH, dissolved salt concentration,
time variation and column operations on the sorption
of metals was studied for CPP4-10-J.O (GEL)
because, it has shown good ion exchange capacity,
Table 2- Characteri zation of polymeric adsorbents
Po lymer
matrix
IEC
(meq/g)
MR
(%)
BD
(g/mL)
FGdye
uptake(mg/g)
I.
11.54
44.29
0.4245
27.54
Solvent u12take (m U g)
Toluene
Cyclohexane
S.A
(m2/g)
0.598 1
0.4986
27.54
2.
11.1 9
57. 16
0.4510
62.76
0.31 20
0.2931
28.59
3.
10.75
63.2 1
0.4545
84.51
0.2782
0.2732
28.59
4.
11.08
51.57
0.4959
31.73
0 .2667
0. 1668
27.09
5.
11 .09
41.49
0.5129
25.7 1
0.51 05
0.4786
27.84
6.
10.83
50.49
0.5634
58.51
0. 1683
0.1567
28.59
78.80
0. 1052
0.0992
28.59
7.
10.43
53.30
0 .5829
8.
11.09
58.10
0.5882
22.54
0.0755
0.0654
27.09
9.
11 .82
49.82
0.4286
17.40
0.3 120
0.3326
28.5 1
10.
10.27
63.89
0.5042
29.94
0.1582
0.1485
54.17
11.
10. 15
54.35
0 .5042
45. 17
0. 1235
0.1123
54.17
12.
11.99
60.22
0.5480
2 1.1 1
O.Q75 1
0 .0594
41.38
IEC: !on-exchange capaci ty; MR: moisture retenti on; BD: bul k d!!nsity; FG dye: f-ast Green dye; SA: surface area
PRASAD et al.: CROSS-LINKED POROUS COPOLYMERS
373
Table 3-Effect of concentration of copper in solution on its uptake (mg/g).
Polymer
matrix
6.
0.01
22
20
66
34
28
20
7.
44
8.
66
9.
82
82
24
76
I.
2.
3.
4.
5.
10.
II.
12.
Polymer
matrix
I.
2.
3.
4.
5.
6.
7.
8.
9.
0.01
26
22
36
48
34
46
46
56
82
0.02
48
45
88
~
56
48
62
94
132
120
68
112
0.03
58
62
134
%
98
66
76
130
136
128
106
140
Concentration of Cu(Il) ion solution (M)
0.04
0.05
0.06
0.07
76
120
134
134
89
125
138
145
152
176
ISO
174
I~
1%
172
I~
134
148
170
ISO
164
170
98
120
84
108
11 8
122
174
202
138
138
154
182
192
200
186
140
150
148
128
188
230
248
230
0.08
146
145
172
168
146
118
154
190
144
226
Table 4-Effect of concentration of nickel in solution on its uptake (mg/g).
Concentration of Ni(II) ion solution (M)
O.Q2
0.03
0.04
0.05
0.06
0.07
0.08
26
55
76
80
89
120
137
48
75
74
70
11 0
135
142
78
76
86
82
120
146
152
100
76
79
88
126
156
168
43
120
124
65
90
146
167
58
74
92
119
132
148
186
110
143
76
124
68
156
198
74
147
153
134
176
62
106
68
148
164
179
128
0.09
144
142
170
172
176
178
106
206
164
210
160
224
0.1
142
140
170
ISO
178
168
106
230
176
232
0.09
137
147
156
168
0.1
150
152
188
187
183
190
210
194
184
171
215
173
224
184
10.
II.
12.
54
68
66
84
82
102
98
127
105
150
high metal uptake and physical stability compared to
others.
Spectral characterization
Fr-IR spectra were obtained on a Bio-Rad FfS40Ff-IR spectrophotometer as KBr pellet.
Uptake of nickel and copper
Static equil ibrium studies were carried out by
equilibrating separately 50 mL of metal io.n solutions
{Ni(Il)/Cu(Il)} of predecided concentration (0.0 I M)
with about 0.2 g of sorbent with occasional stirring at
room temperature for 16 h. The concentration of
metal ions was evaluated by E DT A method 16 . The
same procedure was followed for determining the
effect of different parameters such as pH of
equilibrating solution, concentration of metal ions in
solution and kinetics of metal ion uptake. In the case
145
160
168
192
170
220
of studies involving the effect of di ssolved salts in
solution on the sorption of metal tons the
concentration of metal ion was 0.1 M.
The uptake of nickel and copper ions was also
studied under dynamic conditions by percolating I 00
ppm of spiked metal ion solutions through the resin
bed at different service flow rates, till e ffluent showed
leakage of metal ions of I mg/L. The adsorbed metal
ions on the sorbent bed were el uted by passing I N
hydrochloric acid fo r nickel and a mixture of 2 N
sulphuric acid +2% sodium chloride for copper ions.
Results and Discussion
Polymer synthesis
Crosslinked copolymers of methacrylic acid and
N,N'-methylene bis acylamide were prepared by
suspension polymerization using benzoylperoxide as
INDIAN J. CHEM. TECHNOL., SEPTEMBER 2001
374
160
BPO
l
80{
120
1HJ
lHJ
-CHz-r-CHl -<jH -t-CHz
COOH
GO
I
~H
(1~2
~OOH
~0
-CHz- f --{Hz -CH -CH2
CHJ
..
"'
COOH
so
"'"'
;!
a.
:::>
fOOH
-Cj-
40
CHJ
Fig. !-Structure of crosslinked copolymer.
(A)
pH
Fig. 3-Effect of p H on the uptake of metal ions. , Cu(IJ): 0-0
Ni(Il): tl-tl
3000
·,-~
---------
Fig. 2-lnfrared spectra of (A) copolymer, (B) copolymer+ Cu+2
complex. (C) copolymer + Ni+2 complex, Cu(ll): 0-0 Ni(ll):
tl- tl
the initiator under different conditions. The chemical
structure of the copolymer is shown in Fig. !
Characterisation
From the data in Table 1, it is very clear that very
hi gh yields of cross-linked copolymers could be
obtained under the experimental conditions. It is very
clear from the data in Tables 1 and 2 that toluene and
cyclohexane uptake decreases with increase in Fm
value at the same cross-linking density and this value
is minimum for gel polymers. For example, the
cyclohexane uptake has been decreased from 0.4786
to 0.0654 when Fm value was increased from 0.7 to
1.0 at the cross-linking density of 7.5. The polymers
prepared at lower Fm value have low bulk density.
This was observed during earlier studies with porous
polymers 17 . Fast Green FCF dye uptake increases with
the increase in Fm value at a particular cross-linking
density and decreases with the increase in crosslinking density at a constant Fm value. It is wellknown that sorption of dyes by porous polymers is a
surface phenomenon and increased dye sorption is
evidently due to increase in surface area CFm 0.7-0.9)
which is more pronounced at higher cross-linking
density. Surface area measurements by p -nitrophenol
adsorption reveal that there is a considerable increase
in surface area in the case of 10% cross-linked
polymers than those for 5 and 7.5 % sorbents. At
higher cross-linking density the surface area is
contributed by inter-molecular distances as well.
Spectral characterisation
Fig. 2A shows the IR spectrum of copolymer. The
broad band around 3486 is attributed to COOH and
amide NH groups. A strong peak at 17 19 em·' is due
to amide carbonyl stretchings of carboxylic acid and
PRASAD et al.: CROSS-LINKED POROUS COPOLYMERS
amide group. The bands at 1479 and 1391 em·' can he
attributed to the stretching of C-0 and 0-H of the
carboxylic group.
Fig. 2 B & C represent the IR spectra of the
sorbents obtained after equilibrating with metal ions .
In the spectra of metal complexed sorbents the band
due to OH group of carboxylic acid is observed
around 3448 em·'. The band due to carbonyl group of
carboxylic and amide functionalities have been
shifted towards lower frequency range by about
15 cm·'due to metal complexation.
., 2.1
0
Ol
0
1.8
1.21-----,.......,---===,..--------.-:::--~
3.7
2-8
3.2
tog Ce
Fig. 4-Freundlich isotherm plot for the absorption of metal ion.
Cu(II): 0 - 0 Ni(II): !:l- !:l
2.0
r:::t
'QJ
375
1.8
r:::t
01
.9
1.6
1.4'"----~---~r----1:1----r-----,,.---<-
so
20
120
2 0
Time (min)
Fig. 5-Lagergran plot for specific rate constant of metal ion
uptake. Cu(II): 0 - 0 Ni(ll): !:l- !:l
Effect of metal ion concentration on uptake
The data on the removal of Ni(Il) and Cu(II) from
different concentrations ( 0.01 M to 0.1 M) of metal
ions in solution by sorbent is presented in Tables 3
and 4. The examination of data reveals that the
amount of adsorbed metal ion increases with the
increase in concentration of metal ion in solution. At
lower concentration of metal ions, the number of
metal ions available in solution is less as compared to
the available sites on the sorbent. However, at higher
concentration the available sites of sorption remain
the same whereas more metal ions are available for
sorption and subsequently the sorption becomes
almost constant hereafter.
Effect of pH on uptake of metal ions
The removal of Cu(II) and Ni(II) from aqueous
solutions by sorption is highly dependent on pH of the
solution which affects the surface charge on the
- - - - - ·- - - - - - - - - - - - -
--~>----------~
-
-;; 90
0\
E
0
w
Ill
~ 60
Vl
0
<{
...J
~
w
2: 30
6
22
28
Fig. 6- Plot o f amount of metal adsorbed versus t 112 for the determination of metal ion diffusion
INDIAN J. CHEM. TECHNOL., SEPTEMBER 2001
376
Sorption dynamics
(8)
250
The data on the uptake of metal ions by the sorbent
has been plotted according to Freundli ch isotherm
equation,
20
LogQe= log Kt + lin log Ce
~
a>
150
E
llJ
::.:::
;'! 250 .
Q
:::>
(A)
150
400
600
where Ce is the equilibrium concentration (mg/L), Qe
is the amount adsorbed at equilibrium (mg/g), K1 and
lin are Freundlich constants rel ated to sorption
capacity and intensity of adsorption. A linear
relationship was observed between log Qe and log Ce
from
the plotted parameters indicating the
applicability of Freundlich equation (Fig. 4).
Freundlich constants K1 and 1/n were calculated as
1.862 and 0.6 for Ni (II) and 2.188 and 0.625 for
Cu(II) ions. Values of l<n<10 show the positive
sorption of metal ions on the sorbene 0 .
The specific rate constant, 'kr' for the sorption of
Ni(II) and Cu(ll) on the sorbent was determined by
. 21
L agergran equatiOn
.
CONCE NTRATION OF SALT (pp m)
Fig
7-Effect of dissolved salt concentration on Cu(II)
uptake.(A) : Cu(II), (B) : Ni(Il), NaHC0 3: 0 - 0 MgCI2 : 1'1.- 1'1.
CaCI2 : *- * NaCI: 0 - 0 , Na 2S04 : 0-0
sorbent 18 . The experiments with solution pH as a
vari able were conducted to determine the optimum
pH where maximum metal adsorption occurs and the
results are shown in Fig. 3. Adsorption of metal ion
was increased with increase in pH up to a certain
value and thereafter decreased. The maximum
adsorption took place around pH 7.94 for Nt2 and
4.68 for Cu+2 ions. The presence of C=O also plays a
role in the sorption of metal io ns due to the po lar
attracti ons between the metal ions and keto group 19 •
F
> C=O + M +2
___.
R ) C=O + M (OHt
R C=O ···M+2
___. R C=O · ·M(OHt
An increase in p H increases the negatively charged
nature of the sorbent surface. This leads to an increase
in the electrostatic attraction between positive
substrate and negative sorbent and results in increase
in the adsorption of metal ions. The decrease in
removal of metal ions at lower p H is apparently due
to the higher concentratio n of H+ ions present in the
reaction mixture which compete with the metal ions
for the sorption sites on the sorbent surface. Decrease
in sorption at higher pH is due to the formati on of
insoluble hydroxy compl exes of metal ions.
log(qe-q ) = log qe -(k1 X t)/2.303
where qe and q (mglg) are the amo unts of metal ion
adsorbed at equilibrium and at time t, respectively .
The straight line plot (Fig. 5) of Jog(qe -q) versus t at
30 °C indicates the validity of the Lagergran equation
for the present system and explains that the process
follows first order kinetics. The values of kr were
calculated from the slope of the plot and found to be
9.212x l0- 3 /m in and 1.365x10- 3/min for Cu(II ) and
Ni (11) respectively.
Intra-particle diffusion
Besides sorption of metal ions at the outer surface
of the sorbent beads the possibility of intra-particle
diffusion from the outer surface to the pores of the
resin was observed by plotting the amount of metal
sorbed versus t 112 (Fig .6). The curved portion
represents the film diffusion and subsequent linear
portion represents intra-particle diffusion 22 .
Effect of salt concentration
Figure 7 (A) and (B) show that at lower
concentration of dissolved salts the resin shows more
uptake. But, this is reduced considerably at higher
concentration o f salts thereby indicating that chemisorption and io n-exchange are taking place
simultaneously. In the case of Cu+2 the uptake is
lower when Ca+2 and HC0 3- ions are present
PRASAD et al.: CROSS-LINKED POROUS COPOLYMERS
compared to those of NaCI, MgCI 2 , and Na 2S04. This
may be happening due to the precipitation of cu+2
ions at alkaline pH in Ca+2 and HC0 3. solutions. In the
case of Ni(ll), the presence of dissolved salts at lower
concentrations (200 to 400 ppm) do not affect the
uptake of Ni(II).
operations by regenerating with 1 N HCI and 1 N
NaOH. The concentration ratios of nearly 1:60 and
I :30 were achieved for Ni(II) and Cu(II) ions,
respectively.
References
I
Column operations
The performance of sorbent in continuous column
operations was studied by conducting column runs
using about 25 mL bed volume of sorbate and an
influent having I 00 ppm metal ion concentration. The
boundary between the used and unused portions of the
bed appears quite sharp as it moves down the column
with progressive exhaustion of the bed. The capacity
of sorbent for I ppm leakage at different influent flow
rates such as 5 B.V/h., 10 B.V/h. and 15 B.V/h. were
determined. As the flow rate increases the removal of
metal ions decreases because of the lesser contact
time with the sorbent.
377
2
3
4
5
6
7
8
9
Desorption
10
The exhausted beds were stripped off by passing
1 N HCI and a mixture of 2 N H 2S04+2% NaCI for
Ni(II) and Cu(II) respectively. In the case of Ni(II) the
metal ions were eluted with 75 mL eluting agent at
the flow rate of I B.V /h. About I 00 mL of eluting
agent was required to elute the Cu(ll) ions at the rate
of 0.5 B.V/h.
II
Conclusions
Ni(II) and Cu(II) at lower concentrations can be
removed from aqueous effluents by usi ng methacrylic
acid - N,N'-methylene bis acrylamide sorbent. The
adsorption is mainly due to COOH and amide
(C=ONH) groups. At lower service flow rates the
sorbent can treat more bed volumes of metal ion
solutions than at higher flow rates. The loaded Ni(II)
and Cu(II) metal ions can be stripped off by mineral
acids such as I N HCI and 2N H 2S04+ 2% NaCI ,
respectively , and the bed can be reused for further
16
12
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14
15
17
18
19
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