Adsorption characteristics of Pb(II) and Cr(III) onto C-4- methoxyphenylcalix[4]resorcinarene in batch and fixed bed column systems

Article abstract of DOI:10.1002/jccs.200700167

A study on the adsorption characteristics of Pb(II) and Cr(III) cations onto C-4-methoxyphenylcalix-[4]resorcinarene (CMPCR) in batch and fixed bed column systems has been conducted. CMPCR was produced by one step synthesis from resorcinol, 4-methoxybenza

Full text of DOI:10.1002/jccs.200700167

Journal of the Chinese Chemical Society, 2007, 54, 1167-1178
1167
Adsorption Characteristics of Pb(II) and Cr(III) onto
C-4-Methoxyphenylcalix[4]resorcinarene in Batch and Fixed Bed Column
Systems
a
Jumina, * Ratnaningsih Eko Sarjono, Brajna Paramitha, Ika Hendaryani, Dwi Siswanta,
b
a
a
a
a
a
a
c
Sri Juari Santosa, Chairil Anwar, Hardjono Sastrohamidjojo, Keisuke Ohto and Tatsuya Oshima
d
a
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Gadjah Mada University,
Sekip Utara, Yogyakarta 55281, Indonesia
b
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Indonesia Educational University,
Bandung, Indonesia
c
Department of Applied Chemistry, Faculty of Science and Engineering, Saga University,
1
-Honjo, Saga 840-8502, Japan
Department of Applied Chemistry, Faculty of Science and Engineering, Miyazaki University,
-1 Gakuenkibanadai-nishi, Miyazaki 889-2192, Japan
d
1
A study on the adsorption characteristics of Pb(II) and Cr(III) cations onto C-4-methoxyphenylcalix-
4]resorcinarene (CMPCR) in batch and fixed bed column systems has been conducted. CMPCR was pro-
[
duced by one step synthesis from resorcinol, 4-methoxybenzaldehyde, and HCl. The synthesis was carried
out at 78 °C for 24 hours and afforded the adsorbent in 85.7% as a 3:2 mixture of C4v:C2v isomer. Most pa-
rameters in batch and fixed bed column systems confirm that CMPCR is a good adsorbent for Pb(II) and
Cr(III), though Pb(II) adsorption was more favorable than that of Cr(III). The adsorption kinetic of Pb(II)
nd
and Cr(III) adsorptions in batch and fixed bed column systems followed a pseudo 2 order kinetics model.
The rate constant of Pb(II) was higher than that of Cr(III) in the batch system, but this result was contrary
to the result obtained in a fixed bed column system. Desorption studies to recover the adsorbed Pb(II) and
Cr(III) were performed sequentially with distilled water and HCl, and the results showed that the adsorp-
tion was dominated by chemisorption.
Keywords: Adsorption; Pb(II); Cr(III); C-4-Methoxyphenylcalix[4]resorcinarene; Batch system;
Fixed bed column system.
INTRODUCTION
Heavy metals are a common pollutant found in vari-
adsorption have been used to treat industrial wastes. Tradi-
tional precipitation is the most economic but is inefficient
for a dilute solution. Ion exchange and reverse osmosis are
generally effective, but have rather high maintenance and
operation costs and are subject to fouling. Adsorption is
one of the few promising alternatives for this purpose, es-
pecially using low-cost natural adsorbents such as agricul-
ous industrial effluents. The strict environmental regula-
tion on the discharge of heavy metals has led to the neces-
sity to develop various technologies for heavy metal re-
moval. Waste streams containing low-to-medium levels of
heavy metals are often encountered in metal plating facili-
ties, electroplating, mining operations, fertilizer, battery
manufacture, dye stuffs, chemical pharmaceutical, elec-
tronic device manufactures, and many others. Most heavy
metals are highly toxic and are not biodegradable; there-
fore, they must be removed from the polluted streams in or-
der to meet increasingly stringent environmental quality
standards.
1
tural wastes (maize cobs and husks, ground pine cones ),
2
3
charcoal, fly ash, zeolite, and granular activated car-
4
5,6
7
bon. New synthetic adsorbents have also been developed
in order to generate alternative materials having different
properties compared to those of natural materials.
Calix[4]resorcinarenes are a class of synthetic macro-
molecules having a tetramer of resorcine residues in a cy-
clic array and linked by a methylene bridge. The macro-
molecules are obtained by acid-catalyzed condensation of
resorcinol with a variety of aldehydes. Calix[4]resorcinarenes
Many methods including chemical precipitation, elec-
tro-deposition, ion-exchange, membrane separation, and

1
168 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Jumina et al.
represent an interesting family of structures which exhibit
the characteristic of a cavity-shaped architecture. Various
studies have illustrated their application as host molecules
for various guests, such as cations, anions, and molecules.
The family of calix[4]resorcinarenes has also been used for
various functions, namely as an additive in capillary elec-
The product separated from the reaction mixture in the
early minutes of reaction and gave abundant yields as light
purple precipitates. The structure of CMPCR was con-
1
firmed by proton Nuclear Magnetic Resonance ( H NMR)
and Fourier Transform Infrared (FTIR) spectrometers. It
1
was interesting to note that each signal group in the H
8
9,10
9
trophoresis, liquid membrane,
extraction, chemical
and High Performance Liquid Chromatogra-
phy (HPLC) stationary phase. However, the use of calix-
4]resorcinarenes as a heavy metal cation adsorbent is still
very limited.
C-4-Methoxyphenylcalix[4]resorcinarene (CMPCR)
NMR spectrum emerged as a couple of signals having a ra-
tio of 3:2. This fact is in accordance with the findings of
1
1,12
sensing,
1
3-16
previous workers
who found that the products of con-
[
densation between resorcinol and aromatic aldehydes were
only tetrameric resorcinarenes, and out of four diastereo-
isomeric products that could theoretically be formed, only
two diastereoisomers were obtained in reality, i.e. C4v (rccc,
crown) and C2v (rctt, chair). The ratio of C4v and C2v iso-
meric products varies with the reaction time and tempera-
ture.
is calix[4]resorcinarene which has eight benzene residues,
eight hydroxyl groups, and four methoxy groups (Fig. 1).
CMPCR was synthesized in this research through acid-cat-
alyzed condensation of resorcinol and anisaldehyde (4-
methoxybenzaldehyde). The presence of lone-pair elec-
trons in the hydroxyl and methoxy groups, and also p-elec-
trons in the aromatic residues, can be expected to exhibit
characteristic affinities to heavy metal cations, especially
Pb(II) and Cr(III). The former cation is considered to be a
softer Pearson acid than Cr(III), which was a hard Pearson
acid, while CMPCR with its hydroxyl arms and aromatic
rings can form both “hard” and a “soft” ion binding sites,
respectively. Thus, it was of interest to investigate the inter-
action of CMPCR with the two said heavy metal cations.
The interpretation of chemical shifts and the ratios of
the amount of the isomers formed were determined through
comparison between the proton NMR spectrum of the syn-
thesized CMPCR and those of the C4v and C2v isomers from
reactions products of benzaldehyde and resorcinol which
have been separated and fully characterized by previous
1
4
workers. The C2v isomer was identified by two sets of sin-
gle peaks for the ArOH (d = 8.40 and 8.46) having the
same integration, characteristic multiplet signal for the
ArH (d = 6.11-6.62), a singlet methine signal (d = 5.45),
and a singlet peak for OCH (d = 3.63). Meanwhile, the
4v isomer was identified by a single peak for the ArOH (d
H
H
H
3
H
C
H
RESULTS AND DISCUSSIONS
= 8.46), multiplet peaks for the ArH (d
H
= 6.11-6.62), a sin-
glet peak at 5.57 ppm of the bridging methine proton, and a
singlet peak at 3.69 ppm of the methoxy protons.
Interestingly, the crown isomer (C4v) of CMPCR was
Synthesis and Characterization of CMPCR
The synthesis of CMPCR went easy and was low-cost.
H CO
3
OCH3
HO
OH
OCH3
HO
OH
HO
OH
+
H / EtOH
+
o
8 C, 24 h
7
HO
OH
O
H
HO
OH
H CO
3
OCH3
CMPCR
Fig. 1. Synthesis of C-4-methoxyphenylcalix[4]resorcinarene (CMPCR).

Adsorption Characteristics of Pb(II) and Cr(III) onto CMPCR
present in higher amounts compared to the chair isomer
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1169
or 62.5% in percentage) was reached at an initial pH of
4.59.
(C2v). Hydrogen bonds occurring between adjacent hydroxyl
groups and the existence of staggered phenyl groups appar-
ently stabilize the rccc crown conformers. An extension in
reaction time led to an increase in the formation of the C2v
isomer that was not the desired product. In order to avoid a
high-cost adsorbent production, the isomeric mixture of
CMPCR was used directly in the metal adsorption experi-
ment.
The fact that the amount of metal cation adsorbed at
low pH was only a little apparently was caused by the oc-
currence of protonation of most donating groups, espe-
cially OH groups, of CMPCR. It was envisaged that the in-
teraction between CMPCR and metal cation involved an in-
teraction between an oxygen lone pair electrons and metal
+
cation vacant orbitals. As the amount of H at low pH was
The FTIR spectrum of CMPCR showed characteristic
sufficiently excessive in comparison to that of metal cation,
-
1
absorption at 3419 cm due to O-H stretching vibration. It
most of the oxygen pair electrons perhaps did coordinate
+
+
is well known that absorption bands of O-H stretching vi-
with H and not with metal cation. The size of H , which is
much smaller than that of metal cation, apparently also as-
sisted the occurrence of interaction between oxygen pair
-
brations, when free, appear at around 3600 cm , and a hy-
1
drogen bonding causes these bands to shift to the lower fre-
-
1
+
electrons of CMPCR and H . When the initial pH was suffi-
quencies. The weak frequencies at 2910-2837 cm corre-
spond to CH stretching frequencies. In addition, the IR
spectrum also displayed a significantly intense CH bending
ciently high (more than 4), there was only a limited amount
+
of H available in the system. Accordingly, the interaction
-
frequency at 1429 cm and a C-O-C stretching frequency
1
occurring in the system was dominated by the interaction
between the oxygen lone pair electrons of CMPCR and the
metal cation vacant orbital. This is the reason why the
amount of metal adsorbed at relatively high pH values was
significantly high. However, increasing initial pH to a
value higher than 5.0 is not a good idea as there has been
precipitation of some of metal cations.
-
1
at 1245 cm .
Batch System
Effect of pH
The effect of pH on the adsorptions of Pb(II) and
Cr(III) by CMPCR was studied in the pH range of 2.0 to 6.6
with the initial concentration of metal solution of about 8
mg/L, and the results are shown in Fig. 2. The amount of
Pb(II) adsorbed consistently increased by the increase of
initial pH, and it reached optimum value (3.7 mmol/g or
Cr(III) is a small metal ion which is categorized as a
hard acid. According to hard soft acids bases theory, this
metal has a great potency to form an effective complex with
CMPCR which has eight hydroxy groups and four methoxy
groups that are a Pearson hard base. The results of the ex-
periment which showed that the adsorption capacity of
Cr(III) was higher than that of Pb(II) proved that the hard-
ness of the acid and base is the key factor determining the
effectiveness of the complex formation.
8
6.25% in percentage) at an initial pH value of 4.07. Simi-
lar to Pb(II) adsorption, it was found that Cr(III) uptake in-
creased from pH 2.0 to 4.59, and then decreased from pH
4
.59 to 5.43. Optimum value of Cr(III) uptake (11.6 mmol/g
Effect of Contact Time
The result of Pb(II) and Cr(III) adsorptions at opti-
mum pH with an increase of contact time is presented in
Fig. 3. It was found that the metal uptake increased as the
contact time increased. The graph indicates that the Pb(II)
adsorption took place quickly in the early minutes of inter-
action until approximately 5 minutes giving the amount of
Pb(II) adsorbed as much as 80.46% or 3.49 mmol/g. It then
increased slowly as the interaction time was extended and it
reached its maximum adsorption value of 93.48% or 4.11
mmol/g in 180 minutes. After the interaction process took
place during the 180 minutes, the amount of Pb(II) adsorbed
Fig. 2. Effect of pH on the adsorptions of Pb(II) and
Cr(III) onto CMPCR.

1
170 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Jumina et al.
Table 1. Kinetic parameters for Pb(II) and Cr(III) adsorptions by CMPCR
Pb(II)
Kinetic Model
Cr(III)
2
2
R
R
k
k
st
1
order (Lagergren) equation
-
1.61 ´ 10 min
5
-1
-5
1.84 ´ 10 min
-1
0
0
0
.9694
0.8275
0.9993
0.8276
log(q -q) = log q - (k/2.303)t
e
e
nd
Pseudo 2 order equation
-1
-1
.9999 4.90 ´ 10 g mmol min
-1
-1
-2
-1
9.85 ´ 10 g mmol min
-1
2
t/q = ½ kqe + t/qe
nd
2
1
order equation
-
.9695 4.00 ´ 10 g mmol min
5
-1
-5
2.00 ´ 10 g mmol min
-1
-1
/(q -q) = 1/q + kt
e
e
did not change. The adsorption process at this point has
reached equilibrium between the adsorbed metal ions and
the free ions in solution.
sus t (shown in Table 1). The adsorption rate constant (k)
was calculated using slope or intercept values from the
-
1
e
equation, where q and q (both in mmol g ) are the amounts
A similar pattern to the previous result was obtained
in Cr(III) adsorption onto CMPCR. Percentage of adsorp-
tion was dependent on the shaking time; an extension of the
interaction time increased Cr(III) uptake smoothly until the
uptake reached maximum value of 62% or 8.73 mmol/g at
of metal ion adsorbed (metal uptake) at equilibrium and at
time t (min), respectively.
Based on the linear regression values, the kinetics of
Pb(II) and Cr(III) adsorptions onto CMPCR could be de-
nd
scribed well by all equations, but the pseudo 2 order equa-
nd
tion was the best. Thus, it appeared that pseudo 2 order
3
60 minutes (6 hours). The trend of the curve in the early
minutes was almost vertical, but then it turned into almost
horizontal in the following minutes, hence it could be said
that the adsorption went quickly until five minutes only.
was the most valid kinetics model. The Pb(II) rate constant
(k) was higher than Cr(III) rate constant for all equations,
nd
especially for the pseudo 2 order equation where the rate
constant of Pb(II) was almost five times higher than the
Cr(III) rate constant. Therefore, although the amount of
Pb(II) adsorbed was lower than that of Cr(III), Pb(II) ad-
sorption onto CMPCR went faster than Cr(III) adsorption.
Adsorption Kinetics
The experimental data of contact time effect on the
adsorptions of Pb(II) and Cr(III) were used for kinetic mod-
eling. The model equations used for fitting the data were:
st
nd
order (Lagergren), pseudo 2 order, and second order
1
Effect of Adsorbent Weight
2
equation. The correlation coefficient (R ) resulted from a
Fig. 4 shows the effect of adsorbent weight on adsorp-
tions of Pb(II) and Cr(III) onto CMPCR. The amount of
Pb(II) adsorbed consistently increased as the adsorbent
weight increased, and it reached optimum value (0.41 mmol)
e e
linear plot of log(q -q) versus t, t/q versus t and 1/(q -q) ver-
Fig. 4. Effect of adsorbent weight on the adsorptions
of Pb(II) and Cr(III) onto CMPCR.
Fig. 3. Effect of contact time on the adsorptions of
Pb(II) and Cr(III) onto CMPCR.

Adsorption Characteristics of Pb(II) and Cr(III) onto CMPCR
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1171
at an adsorbent weight of 0.1 g. The addition of adsorbent
weight enlarged the contact surface between adsorbent and
adsorbate until the exhausted condition was reached. Simi-
lar to Pb(II) adsorption, the optimum value of Cr(III)
uptake (1.06 mmol) was reached at an adsorbent weight of
Table 2. Estimated isotherm parameters for Pb(II) and Cr(III)
adsorptions
Estimated Isotherm Parameters
Models
Pb(II)
Cr(III)
2
R
2
R
k
k
0
.1 g.
Langmuir
0.9844
0.9015
152.9
485.1
0.8945
0.9837
12.3
Freundlich
40691153.4
Adsorption Isotherms
The equilibrium data in the adsorbtion of Pb(II) and
Cr(III) onto CMPCR were analyzed by using Freundlich
Table 3. Quantitative descriptions of Pb(II) and Cr(III)
adsorptions on the basis of the Langmuir isotherm
and Langmuir isotherms, i.e. log q
/q = 1/(K q .C ) + 1/q , respectively, where q
amount adsorbed at equilibrium (mmol/g), C is the solution
concentration at equilibrium (mmol/L), q (mmol/g) is the
maximum capacity of adsorption, and K is the adsorption
constant. The results of linear plots of log C versus log q
Freundlich model) and 1/q versus 1/C (Langmuir model)
e
= log K + 1/n log C
e
and
Working Range
Concentration
1
e
o
e
o
e
is the
qo
K
DG
Cation
RL
e
(mmol/g) (L/mmol)
(kJ/mol)
(mmol/L)
o
-
1
Pb(II) 1.73 ´ 10
Cr(III) 6.43 ´ 10
152.9 0.145 -29.576 0.039-0.044
012.3 0.372 -23.332 0.137-0.169
-3
e
e
(
e
e
are shown in Table 2. The K values could be calculated
from the slopes and intercepts.
and DG) on the basis of the Langmuir isotherm model are
given in Table 3.
The data on Table 2 shows high values of correlation
2
coefficients (R ) indicating linear relationships, which con-
Referring to the separation factor value (R
viously seen from Table 3 that CMPCR is a good adsorbent
for Pb(II) and Cr(III) cations. In either case, the R value
falls between 0 and 1, which is indicative of favourable ad-
sorption. The R value also shows that the adsorption of
L
), it is ob-
2
firm the applicability of both adsorption isotherms. The R
L
values of Pb(II) adsorption were 0.9844 and 0.9015 for
Langmuir and Freundlich models, respectively, indicating
that the adsorption data fitted the Langmuir model the best.
L
Pb(II) was more favourable than that of Cr(III). Similarly,
the negative DG values confirm the spontaneous nature and
feasibility of the adsorption processes, both for Pb(II) and
Cr(III) adsorptions.
2
On the contrary, the R values of Cr(III) adsorption were
0
.8945 and 0.9837 for Langmuir and Freundlich models,
respectively, indicating that the adsorption data fitted the
Freundlich model the best. The adsorption constant (K) of
Pb(II) was higher than that of Cr(III) in the Langmuir iso-
therm. On the other hand, the adsorption constant (K) of
Pb(II) was lower than that of Cr(III) in the Freundlich iso-
therm.
Fixed Bed Column System
The percentage of metal adsorbed in a fixed bed col-
umn system is shown in Fig. 5. Pb(II) was adsorbed com-
pletely (about 100%) at some early fractions until about 14
The essential characteristic of the Langmuir isotherm
may be expressed in terms of the dimensionless separation
1
7-19
parameter, R
L
,
which is indicative of the isotherm shape
that predicts whether an adsorption system is ‘favourable’
or ‘unfavourable’. R
L
is defined as: R
L
o
= 1/(1 + KC
o
),
where K is the adsorption constant, and C
is the initial con-
centration of adsorbate (g/L). The adsorption is favourable
when 0 < R < 1, and the lower the value of R indicated a
more favourable adsorption.
L
L
Variation of Gibbs free energy (DG) for the retention
of adsorbate on adsorbent was determined from the adsorp-
tion constant with the aid of equation DG = -RT ln K. Some
Fig. 5. Percentage of Pb(II) and Cr(III) adsorbed by
CMPCR.
o L
quantitative descriptions of adsorption system (q , K, R ,

1
172 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Jumina et al.
fractions (70 mL). This fact showed that CMPCR can be a
good adsorbent for Pb(II). In the next fractions, percent of
Pb(II) adsorbed decreased until the column was exhausted,
i.e. when the effluent concentration equals to influent con-
The breakthrough curve of Pb(II) adsorption is pre-
sented in Fig. 6. It can be seen that a 5% breakthrough point
(BT), 50% BT, and a 100% BT occurred after passing of the
feeding solution of about 70, 110 and 250 mL or about 58
bed volume (BV), 92 BV, and 208 BV, respectively. Shorter
breakthrough points took place in the Cr(III) case wherein
5% BT, 50% BT, and 100% BT occurred after the feeding
solution reached up to 5, 12, and 110 mL or about 4, 10 and
17.3 BV, respectively.
th
centration. This exhausted column took place in the 50
fraction (250 mL), but the throughput volume applied to
the column was 300 mL. In an other case, the amount of
Cr(III) adsorbed at the first fraction (5 mL) was 100%, but
in the next fractions, percent of Cr(III) adsorbed lessened
nd
until the column was exhausted which occurred in the 22
The column test also showed that the total uptake of
fraction or 110 mL; meanwhile, the throughput volume ap-
plied to the column was 135 mL.
Pb(II) (q
e
) was 4.166 mg Pb(II) per g of CMPCR, or 20.11
mmol/g (Fig. 7). This value of adsorption column capacity
Fig. 6. Breakthrough curve of Pb(II) adsorption by CMPCR (Co = initial metal ion concentration, C = metal ion concentra-
tion in the effluent).
Fig. 7. The total uptake of Pb(II) adsorption.

Adsorption Characteristics of Pb(II) and Cr(III) onto CMPCR
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1173
was significantly higher compared to the value of adsorp-
tion capacity in a batch system that has a maximum capac-
ity of about 0.85 mg/g or 4.1 mmol/g. The initial break-
Pb(II) was 160 minutes (66 BV) and t
minutes (8 BV). Similar to the exhaustion point (t
has significantly longer t than Cr(III), i.e. t of Pb(II) was
500 minutes (208 BV) and t of Cr(III) was 220 minutes (al-
b
of Cr(III) was 10
e
), Pb(II)
e
e
through occurred at column loading of about 2.6 mg/g (q
This means that the amount of Pb(II) adsorbed has reached
3% of the total uptake, although the Pb(II) solution ap-
b
).
e
most 92 BV). A big breakthrough point was desired, but a
big exhaustion point was not expected. A big breakthrough
point means the amount of metal adsorbed is fairly high,
but a big exhaustion point means high operational cost.
The total metal uptake of both Pb(II) and Cr(III) ex-
periments showed different values, i.e. Pb(II) was 4.166
mg/g, whereas Cr(III) was only 0.89 mg/g. However, if the
metal uptake values were expressed in mol/g, then these
values were almost the same, i.e. Pb(II) was 20.11 mmol/g,
and Cr(III) was 17.21 mmol/g. Therefore, it can be said that
CMPCR adsorbed Pb(II) better than Cr(III), although the
adsorption consumed more operational costs.
6
plied was only 26% of total volume, or 74% of the operat-
ing cost would be consumed for taking 37% of the rest of
Pb(II). Likewise, at C/Co = 0.5, the amount of Pb(II) ad-
sorbed reached almost 77%, i.e. 3.2 mg/g, and consumed as
much as 36% of the operating cost.
The curve in Fig. 8 shows that the total uptake of
e
Cr(III) (q ) was 0.895 mg/g or 17.21 mmol/g. Similar to
Pb(II), the value of Cr(III) adsorption column capacity was
significantly higher compared to the value of adsorption
capacity in a batch system that has a maximum capacity of
about 0.61 mg/g or 11.6 mmol/g. The initial breakthrough
The breakthrough curve was used to calculate the
occurred at column loading of about 0.22 mg/g (q
b
) or
4.7% of total uptake, and Cr(III) solution applied was
.7% of total volume. At C/Co = 0.5, the amount of Cr(III)
length of unused bed (HUNB), the length of used bed (H
U
),
6,20
and the overall mass-transfer coefficient (K a). Table 4
2
3
c
adsorbed reached almost 45.8%, i.e. 0.41 mg/g, and con-
sumed as much as 8.8% of the operating cost. This means
that 91.2% operating cost would be consumed for taking
5
4.2% of the rest of Cr(III). The results clearly showed that
running a column as long as 8.8% of the throughput volume
or about 12 mL) was more efficient than running the col-
umn until exhaustion.
Fig. 9 presents breakthrough curves and uptakes of
(
Pb(II) and Cr(III). The figure shows that Pb(II) and Cr(III)
adsorptions have almost the same shape, but the former has
quite a spread shape. Pb(II) curve has a breakthrough point
Fig. 9. Comparison of breakthrough curve and metal
uptake between Pb(II) and Cr(III).
b b
(t ) which was significantly bigger than Cr(III), i.e. t of
Fig. 8. The total uptake of Cr(III) adsorption.

1
174 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Jumina et al.
Table 4. The breakhthrough data and mass transfer parameters of Pb(II) and Cr(III)
adsorptions
Parameter
Pb(II)
Cr(III)
tb (breakthrough point)
te (exhausted point)
160 min
500 min
10 min
220 min
HUNB (the length of unused bed)
1.63 cm (68%)
0.77 cm (32%)
2.28 cm (95%)
0.12 cm (5%)
H (the length of used bed)
U
K a (the mass-transfers
c
-1
-1
1
.22 min
0.88 min
coefficient)
shows that HUNB on Cr(III) adsorption was longer than on
Pb(II). In the design of an adsorption column, it is impor-
tant to minimize the length of the unused bed (HUNB). This
length represents the length of mass-transfer zone, which is
the part of the column where adsorbent is not completely
used, but adsorption is still occurring. On the contrary, the
Table 5. The Thomas model parameters of Pb(II) and Cr(III)
adsorptions
Parameter
The coefficient of correlation (R )
Pb(II)
Cr(III)
2
0.954
0.485
0.650
0.459
-
1
-1
The rate constant (k, mg min )
The maximum capacity according to the
Thomas model (Xm; mg/g)
3.935
1.177
0.895
U
length of used bed (H ) represents the part of the column
The maximum capacity according to
4
.166
in which adsorbent is completely saturated by adsorbate.
Therefore, at this point, Pb(II) adsorption was better than
Cr(III), because it has minimum HUNB. A similar matter
experiment result (q ; mg/g)
e
Cr(III) adsorptions present a shape characterized by strong
capacity adsorption during the first few minutes of contact,
followed by slow increase until a state of equilibrium was
reached. As an approximation, the removal of cations can
be said to take place in two distinct steps: a relatively fast
phase followed by a slower one.
was observed at the overall mass-transfer coefficient (K
c
a).
Adsorption of Pb(II) has higher K a than Cr(III) adsorp-
c
tion, thus, CMPCR was more appropriate to remove Pb(II)
than Cr(III).
2
0
Table 5 presents the parameters of the Thomas model,
which were calculated by linear regression. The linearised
Thomas equation did not describe the breakthrough data
2
very well since the values of R were not very good, espe-
Kinetics of heavy metal adsorption can be modeled
by the first order Lagergren equation, the pseudo second or-
der rate equation, and the second order rate equation. The
cially for Cr(III) adsorption. The Thomas rate constant (k)
of Pb(II) adsorption was slightly bigger than that of Cr(III).
It was interesting to compare the maximum capacity of bed
according to the Thomas model and the experimental re-
sult, since those values were fit enough. Based on the data
at this point, the Thomas model can be considered as the
appropriate model for the adsorption.
results of linear plots of log (q
e t t
-q ) versus t, t/q versus t, and
1
/(q -q ) versus t are shown in Table 6. The rate constant (k)
e
t
values can be calculated from the slopes or intercepts ac-
cording to its equation. According to the data in the Table,
the pseudo second-order reaction rate model adequately
Kinetic Aspect
The results of the kinetics studies on the adsorption of
Pb(II) and Cr(III) are shown in Fig. 10. The time needed to
reach equilibrium for Pb(II) adsorption was about 250 min-
utes (4.16 hours), which was longer than that required in
the batch system (180 minutes). On the other hand, the time
needed to reach equilibrium for Cr(III) adsorption was
about 110 minutes (1.83 hours), which was shorter than
that required in the batch system (360 minutes).
According to the graph, the kinetics of Pb(II) and
Fig. 10. Kinetics of Pb(II) and Cr(III) adsorptions.

Adsorption Characteristics of Pb(II) and Cr(III) onto CMPCR
Table 6. Kinetics parameters for Pb(II) and Cr(III) adsorptions
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1175
Pb(II)
Cr(III)
Reaction Rate
2
2
Model
R
k
R
k
st
-3
1.95 ´ 10 min
-1
-3
3.90 ´ 10 min
-1
1
order
0.9026
0.9569
0.3452
0.9229
0.9695
0.4479
nd
Pseudo 2 order
nd
-4
6.97 ´ 10 g mmol min
-1
-1
-1
-2
1.28 ´ 10 g mmol min
-1
-1
-1
-1
-1
2.62 ´ 10 g mmol min
-1
-1
7.76 ´ 10 g mmol min
2
order
described the kinetics of both Pb(II) and Cr(III) adsorp-
tions with the highest correlation coefficient. Therefore, it
was possible that both adsorbent and adsorbate gave contri-
bution to the reaction rate. Nevertheless, the rate adsorp-
tion constants of a fixed bed column system appeared in
contrary performance compared to the batch system. In the
fixed bed column system, the rate constant of Pb(II) was
lower than that of Cr(III), thus it could be considered that
Pb(II) adsorption ran slower than Cr(III).
tion (more than 98%). Most Pb(II) and Cr(III) adsorbed
onto CMPCR were estimated via ionic and hydrogen bond-
ing mechanism.
EXPERIMENTAL SECTION
Reagents
Metal solutions were prepared by diluting 1000 mg/L
Pb(NO
acid to desired concentrations. An adjustment of pH was
carried out by adding slowly NaOH and/or HNO solu-
3 2 3 3
) and Cr(NO ) standard solution in aqueous nitric
Desorption
A desorption test was done sequentially to leach heavy
metal cations which have been adsorbed onto CMPCR.
This experiment was conducted to recover the column and
to estimate the types of adsorption mechanisms, hence dif-
ferent solutions was eluted to the column. The principle of
this model is the usage of different desorption agents which
have a desorption ability that increased sequentially, i.e. (1)
desorption by water to confirm the adsorption mechanism
physically (entrapment), (2) desorption by acid solution
3
tion(s) into the metal solutions followed by stirring until
the desired pH was reached. Chemicals needed for synthe-
sizing CMPCR were resorcinol, 4-methoxybenzaldehyde,
HCl, and ethanol. All materials required were reagent
grade from E Merck.
Instruments
In this experiment, equipment involving a set of re-
1 13
flux utilities, Buchner funnels, H and C NMR spectrom-
(
HCl), which was used to leach metal cations adsorbed by
chemical adsorption via ion exchange or hydrogen bond
mechanism.
The result of Pb(II) desorption is performed in Fig.
11. According to the graph, water leached Pb(II) poorly,
only about 4.61%, whereas 1 M HCl solution leached Pb(II)
completely, up to 99.24%. Based on the data, Pb(II) adsorp-
tion by CMPCR was dominated by chemisorption (more
than 95%); on the contrary, physisorption ruled the adsorp-
tion mechanism in a small portion (less than 5%).
Fig. 12 depicts the result of Cr(III) desorption. Ac-
cording to the graph, the elution tendency as percentage
recovery of Cr(III) followed the sequence: distilled H
2
O
(
1.7%) < 0.1 M HCl (98.12%). Water acted very poor as a
Cr(III) desorption agent, whereas 0.1 M HCl solution was
an excellent Cr(III) desorption agent. Similar to Pb(II) ad-
sorption, Cr(III) adsorption was dominated by chemisorp-
Fig. 11. Sequential desorption of Pb(II) by water and
HCl 1 M.

1
176 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Jumina et al.
Fig. 12. Sequential desorption of Cr(III) by water and 0.1 M HCl.
eter (Jeol JNM-AL300 FT NMR System, 300 MHz), and
FTIR spectrophotometer (Shimadzu FTIR 8201PC) were
used for CMPCR synthesizing and characterization. Pump,
glass column, stirrer, Atomic Absorption Spectrophotome-
ter (AAS; Perkin Elmer Analyst-100), and pH meter (Hanna),
were used for adsorption experiment and determination of
Pb(II) and Cr(III) concentrations.
corrected by a blank solution. The blank solution was simi-
lar to the adsorption sample except for the existence of the
adsorbent. The amount of metal cation adsorbed was calcu-
lated from the difference between the metal cation concen-
tration before and after the adsorption experiment. The
metal uptake, q (mg metal ion/g CMPCR) was determined
as follows:
Synthesis of CMPCR
q = (C
o
-C) ´ V/m
(1)
Into a solution of resorcinol (2.2 g, 0.02 mol) and
4
9
-methoxybenzaldehyde (2.72 g, 0.02 mol) in 20 mL of
5% ethanol was added 4 mL of hydrochloric acid. The so-
o
where C and C are the initial and the final metal ion con-
centrations (mg/L), respectively; V is the volume of solu-
tion (mL); and m is the CMPCR weight (g) in dry form. For
each metal cation, the experiment was done in 3 conditions,
i.e. variation of pH, shaking time, and adsorbent weight.
The fixed bed column adsorption experiment was
done in a descendant flow. The equipment used is depicted
in Fig. 13. The metal solutions were prepared by diluting
1000 mg/L metal cation standard solution in aqueous nitric
acid to the desired concentration. Adjustment of pH of the
metal solutions was carried out by adding slowly NaOH
lution was stirred and refluxed at 78 °C for 24 hours. The
product that separated was filtered. The solid was washed
using ethanol-water repeatedly and then dried to give the
desired compound as a light purple solid in 85.7% (3.91 g):
1
mp > 390 °C (dec), H NMR (300 MHz, 298 K, DMSO,
TMS) d
CH), 6.11-6.62 (24H, m, ArH), 8.44 (4H, s, ArOH), 8.46
4H, s, ArOH); C4v isomer: 3.69 (18H, s, OCH ), 5.57 (6H,
H 3
: C2v isomer: 3.63 (12H, s, OCH ), 5.45 (4H, s,
(
3
s, CH), 6.11-6.62 (36H, m, ArH), 8.46 (12H, s, ArOH).
3
and/or HNO solutions followed by stirring until the de-
Adsorption Procedures
sired pH was reached. This metal solution was passed
through the column in a down flow at a fixed flow rate. The
solution which passed through the column was fractionated
A batch experiment was conducted by adding 0.1 g of
CMPCR (its particle size was < 100 mesh) into 10 mL of
metal cation sample solution having a concentration of 8
mg/L. The mixture was shaken at room temperature for a
certain period of time. The adsorbent was filtered out and
dried in a desiccator. Concentration of metal ion was then
measured by AAS. The data obtained was compared and
3
into 5 cm portions, and the effluent concentration was de-
termined by AAS. Fractions of the effluent were collected
until the ratio of effluent concentration (C) to initial con-
centration (Co) equals to one.
The ratio of C/Co called as breakthrough was plotted

Adsorption Characteristics of Pb(II) and Cr(III) onto CMPCR
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1177
Fig. 13. Apparatus for fixed bed column adsorption experiment.
against the volume of the solution passed in the column or
against the time to obtain a breakthrough curve. The break-
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