1

Osu Charles I. and S.A. Odoemelam, 2012. Adsorption Isotherm Studies of Hg(II), Pb(II), and Cd(II) Ions Removal from
Aqueous Solutions Using Unmodified and Ester Modified (Esterified) Senilia senilus and Thais coronata Biomass.
Journal of Applied Technology in Environmental Sanitation, 2 (2): 77-86.
77
Research Paper
ADSORPTION ISOTHERM STUDIES OF Hg(II), Pb(II), and Cd(II) IONS
REMOVAL FROM AQUEOUS SOLUTIONS USING UNMODIFIED AND ESTER
MODIFIED (ESTERIFIED) SENILIA SENILUS AND THAIS CORONATA
BIOMASS
OSU CHARLES I.1* and S.A. ODOEMELAM2
1Department of Pure and industrial chemistry, University of Port Harcourt, PMB, 5323, Port Harcourt,
Rivers State. Nigeria.
2
*Corresponding Author: Phone: +2348037783246; Email: charsike@yahoo.com
Department of Chemistry, Michael Okpara University of Agriculture, Umudike, Nigeria.
Received: 7rd February 2012; Revised: 3rd June 2012; Accepted: 3rd June 2012
Abstract: Removal of heavy metal from aqueous solutions using developed alternative
treatment methodologies was investigated. Senilia senilus (anadara) and Thais coronata
(grastropoda) biomass were found to be a better adsorbent for the removal of Hg2+, Pb2+,
and Cd2+ .This method of heavy metals removal proved highly effective as removal
efficiency increased as the initial concentration increased. The removal was high for Hg2+
ranging from 98.00 – 99.97 %. Also, the ester modification did not enhance the
adsorption capacity. Among three adsorption isotherm tested, Freundlich adsorption
isotherm gave the best fit with r2 value ranging from 0.9887 to 1.0000 and average value
of 0.9998. The biomass and method used were efficient and cost effective, and have
successfully used for the removal of Hg2+and Cd2+ ions from aqueous solution.
Keywords: Adsorption isotherm, biomass, heavy metal ions
INTRODUCTION
Heavy metals pollution increases with the advancement in industrialization and urbanization.
The release of these heavy metals poses a significant threat to the ecosystem and public health
because of their toxicity [1, 2]. Heavy metals are not biodegradeable. When they accumulate in
the environment and in food chains, they can profoundly disrupt biological processes.
Anthropogenic activities such as agriculture, electroplating, metal finishing industries,
metallurgical industries, tannery, fertilizer industries etc increase the level of heavy metals in the
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ISSN 2088-3218
V o l u m e 2 , N u m b e r 2 : 7 7 - 8 6 , A u g u s t , 2 0 1 2
© T2012 Department of Environmental Engineering
Sepuluh Nop em ber Institute of Technolog y, Suraba ya
& Indonesian Society of Sanitary and Environmental Engineers, Jakarta
O p e n A c c e s s h t t p : / / w w w . t r i s a n i t a . o r g / j a t e s
International peer-reviewed journal

78
environment [3, 4]. Heavy metals, Hg2+ , Pb2+ and Cd2+
Due to the demerit of conventional method, biosorption has provided an alternative measure
to physicochemical methods. Recently, low cost agricultural by-products have been used to
heavy metals from aqueous solution. This include maize cob and husk [6, 7, 8]; cassava waste
[9]; sawdust and coconut fibre [8]; fluted pumkin [10] and so on. In this study, the adsorption
isotherm for the bioremediation of Hg
have health implications which include
kidney dysfunction, mental retardation, cancer, hepatic damage and hypertension [5].
2+ ,Pb2+ and Cd2+ ions on unmodified and ester modified
Thais coronate and Senilia Senilus biomass were studied. The effect of concentration of the
adsorbate on the adsorbents used was also investigated.
MATERIALS AND METHODS
Adsorption isotherm equation
Temkin, Langmuir and Freundlich adsorption isotherm were used for interpreting the
biosorption equilibrium of the metal ions. [11, 12]. The classical Langmuir equation is given as
follows:
q = (QmaxbCe)/(1 + bCe
Where, q = quantity of heavy metal ion adsorbed in milligrams per gram of the adsorbent used.
) (1)
Ce
Q
= final concentration of metal ion (mg/l) in the solution.
max
b = equilibrium constant related to the affinity of the binding sites for the metals.
= maximum amount of metal ions adsorbed per unit weight of adsorbent.
Equation (1) can be linearised as follows:
1/q = (1/qmax) + (1/qmaxb)(1/Ce
The Langmuir isotherm represents the equilibrium distribution of metal ions between the
solid and liquid phases. The essential characteristic of the Langmuir isotherm can be expressed
in terms of a dimensionless constant, separation factor or equilibrium parameter, R
) (2)
L
R
, which
indicate the shape of the isotherm and is defined as follows [13]:
L = 1/(1+ bCo
Where b is the Langmuir constant and C
) (3)
o is the initial concentration of the metal ions. The
RL
The classical Freundlich equation is given as follows:
values between zero and 1 indicate favourable adsorption [14].
q = KfCe1/n
Where, q = quantity of heavy metal adsorbed on the adsorbent (mg/g)
(4)
Ce
K
= final concentration of metal (mg/l) in the solution
f
n = an empirical constant that provides an indication of the intensity of adsorption [15]
= an empirical constant that provdes an indication of the adsorption capacity of the adsorbent.
Equation (4) can be linearised as follows:
log q = log Kf + (1/n)logCe
The adsorption constant (K
(5)
f and 1/n) were obtained by plotting log q as a function of log Ce
n values between 1 and 10 represents beneficial adsorption [16]. [17], reported that the values of
K
.
f
The classical Temkin equation is given [12] as follows:
and n determine the steepness and curvature of the isotherm. Freundlich equation is suitable
for a highly heterogeneous surface and homogeneous surface, and an adsorption isotherm
lacking a plateau, indicating a multi-layer adsorption [18].
X = a + blnCe
Where, C
(6).
e
X = amount of metal ion adsorbed per unit weight of adsorbent (mg/g)
= concentration of adsorbate in solution at equilibrium (mg/gl)

79
a & b = are constants related to adsorption capacity and intensity of adsorption. The adsorption
constants a and b were obtained by plotting lnCe against X.
Collection and preparation of samples
The marine animal shells was collected from Okirika village of Rivers state of Nigeria and
was washed thoroughly, clean of adhering dirt, rinsed thoroughly with de-ionized water and dried
in the oven at 105 oC for two days. The process helped to remove moisture present in the
material, which was different from the chemisorbed water normally, released during carbonization
reactions of elevated temperature. Higher temperature of 150 o
H
C was used to ensure complete
dehydration. The purpose of dehydration was to effect de-sorption of physically absorbed water
which may catalyze the decomposition of the char carbon thereby producing a very low carbon.
2O + C ------------ H2
After oven drying, the sample was macerated into powdered form. The powdered form of the
sample obtained was first sieved through a 1000 µm mesh and then through 500 µm meshes.
+ CO
Chemical activation of the adsorbent
The sieved sample was soaked in 0.3 M HNO3 for 24 hours at room temperature. The
adsorbents was then filtered through what man no. 41 filter paper and rinsed thoroughly with de-
ionized water to maintain a pH of 7.4. The rinsed adsorbent was kept in an oven at 100oC for 12
hours for the moisture and finally stored in a tight plastic container. The treatment of the
absorbent with 0.3 M HN03 aids to oxidize the adhering organic material, removal of any debris or
soluble bio-molecules that might interact with the metal ions during the sorption. This process is
called chemical activation.
Chemical modification of the absorbent
The oven dried chemical activated sample was weighed and divided into two parts. 200g of
first part was left untreated was labeled the unmodified sea animal shell A and B (USASA and
USASB) where A is shell of Senilia Senilus (Anadara) and B is Thais Coronata (Grastropoda)
biomass. 400g of second part was treated with 5 dm3 of 3 M Oxalic acid solution for 24 hours at
28o C in a well ventilated place according to the method of [19]. The biosorbent was then
esterified [15, 20] by suspending the adsorbent in 2.6 L of ethanol and 240 Ml of concentrated
hydrochloric acid. The mixture was shaken for 5 hours at 150 rpm, filtered and the residue was
washed thoroughly with distilled water to maintain pH of 6.9 and finally oven dried at 100o C,
stored and was labeled modified sea animal shell A and B (MSASA and MSASB). Surface
functional group can be introduced via chemical modification [19, 15 , 20]. All reagents used were
analytical grades, purchased and used without further purification.
Effect of metal ion concentration
The metal ions solution with standard concentrations of 2 mgL-1, 4 mgL-1, 8 mgL-1 and 10
mgL-1 were made from analytical grade standards Cd2+ ( from CdCl2 ), Pb2+ from (Pb(NO3)2 ),
and Hg(II) from ( HgCl2 ). 2g sample of the adsorbents both modified and unmodified of particle
size 500 µm were put into 100 Ml solutions of each of the various metal ion solutions of different
initial concentrations prepared above in a conical flask. The samples were left to stand for 10
minutes in a rotary shaker at a constant speed of 150 rpm, at a temperature of 29o C. At the end
of the time, the mixtures were filtered and the various metal ions content of the filtrates were
determined by AAS.

80
RESULTS AND DISCUSSION
Fig. 1: Effect of concentration for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous
solution using USASA and USASB
Fig. 2: Effect of concentration for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous
solution using MSASA and MSASB
Fig. 3: Langmuir plot for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous solution
using USASA and USASB
96.000
96.500
97.000
97.500
98.000
98.500
99.000
99.500
100.000
0 2 4 6 8 10 12
%adsorbed
Concentration (mgL-1)
USASA Hg(II)
USASA Pd(II)
USASA Cd(II)
96.000
96.500
97.000
97.500
98.000
98.500
99.000
99.500
0 2 4 6 8 10 12
%adsorbed
Concentration (mgL-1)
MSASA Hg(II)
MSASA Pb(II)
MSASA Cd(II)
0.00000
0.00020
0.00040
0.00060
0.00080
0.00100
0 0.1 0.2 0.3 0.4
Ce/qe(mgl)
Ce (mgL-1)
USASA Hg(II)
USASA Pb(II)
USASA Cd(II)

81
Fig. 4: Langmuir plot for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous solution
using MSASA and MSASB
Fig. 5: Freundlich isotherm plot for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous
Fig. 6: Freundlich isotherm plot for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous
0.00000
0.00010
0.00020
0.00030
0.00040
0.00050
0.00060
0.00070
0.00080
0.00090
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Ce/qe(mgl)
Ce (mgL-1)
MSASA Hg(II)
MSASA Pb(II)
MSASA Cd(II)
MSASB Hg(II)
0.000
1.000
2.000
3.000
4.000
5.000
6.000
7.000
-6.000 -5.000 -4.000 -3.000 -2.000 -1.000 0.000
lnqeln ce
USASA Hg(II)
USASA Pb(II)
USASA Cd(II)
USASB Hg(II)
0.000
1.000
2.000
3.000
4.000
5.000
6.000
7.000
-5.000 -4.000 -3.000 -2.000 -1.000 0.000
lnqe
ln ce
MSASA Hg(II)
MSASA Pb(II)

82
Fig. 7: Temkin isotherm plot for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous
Fig. 8: Temkin isotherm plot for the adsorption of Hg2+, Pb2+ and Cd2+ ions from aqueous
Table 1: Values of Freundlich constants for the adsorption of Hg2+,Pb2+,and Cd2+
Metal ions
ions from
aqueous solution using USASA and MSASA
USASA MSASA
K 1 / n r² K 1 / n r²
Hg(II) 763.87 0.4332 0.9999 863.76 0.5657 0.9961
Pb(II) 746.05 0.469 0.9823 965.46 0.6553 0.9939
Cd(II) 937.86 0.4933 0.9734 924.91 0.5587 0.9709
0.000
100.000
200.000
300.000
400.000
500.000
600.000
-6.000 -5.000 -4.000 -3.000 -2.000 -1.000 0.000
qe(mg/g)
ln ce
USASA Hg(II)
USASA Pb(II)
USASA Cd(II)
USASB Hg(II)
0.000
100.000
200.000
300.000
400.000
500.000
600.000
-5.000 -4.000 -3.000 -2.000 -1.000 0.000qe(mg/g)
ln Ce
MSASA Hg(II)
MSASA Pb(II)
MSASA Cd(II)
MSASB Hg(II)

83
Table 2: Values of Freundlich constants for the adsorption of Hg2+,Pb2+, and Cd2+ ions from
aqueous solution using USASB and MSASB
USASB MSASB
Metal ions K 1 / n r² K 1 / n r²
Hg(II) 759.45 0.4618 0.9989 882.46 0.5437 0.9831
Pb(II) 765.32 0.4361 0.9723 786.11 0.5003 0.9542
Cd(II) 1004.25 0.5472 0.9569 951.84 0.588 0.9743
Table 3: Values of Langmuir constants for the adsorption of Hg2+,Pb2+, and Cd2+ ions from
aqueous solution using USASA and MSASA
USASA MSASA
Metal ions KL(dm3 qmaxg) r² S KF QmaxL r² S
Hg(II)
F
0.056 555.556 0.9685 0.816993 0.1333 646.967 0.9638 0.556234
Pb(II) 0.118 588.235 0.9071 0.679348 0.2308 769.23 0.971 0.519967
Cd(II) 0.059 568.232 0.9897 0.809061 0.1333 666.667 0.938 0.652231
Table 4: Values of Langmuir constants for the adsorption of Hg2+,Pb2+,and Cd2+ ions
From aqueous solution using USASB and MSASB
USASB MSASB
Metal ions KL(dm3 qmaxg) r² S KF qmaxL r² S
Hg(II)
F
0.118 588.235 0.9527 0.679348 0.133 666.667 0.9638 0.652742
Pb(II) 0.118 588.235 0.9002 0.679348 0.133 666.667 0.8102 0.652742
Cd(II) 0.125 625 0.9913 0.666667 0.143 714.286 0.9358 0.636132

84
Table 5: Values of Temkin constants for the adsorption of Hg2+,Pb2+,and Cd2+ ions
From aqueous solution using USASA and MSASA.
USASA MSASA
Metal ions a b r a2 B r
Hg(II)
2
551.69 102.42 0.9481 566.76 123.39 0.9561
Pb(II) 539.9 108.21 0.8875 608.99 155.86 0.9632
Cd(II) 610.92 120.54 0.9823 597.04 132.01 0.9213
Table 6: Values of Temkin constants for the adsorption of Hg2+,Pb2+,and Cd2+ ions
from aqueous solution using USASB and MSASB.
USASB MSASB
Metal ions a b r a2 B r
Hg(II)
2
548.46 108.46 0.9364 581.98 134.34 0.9592
Pb(II) 545.95 100.53 0.8698 550.3 114.59 0.8467
Cd(II) 631.03 135.05 0.9884 604.01 139.02 0.9271
The effect of concentration of the adsorbates was illustrated in figure 1 and 2. The results
were found to be highly concentration dependent. The percentage removal efficiency shows a
decreasing trend with increasing concentration of the adsorbate. At concentration of 10 ppm, the
removal efficiency rarely falls below 80% for the Hg(II), Pb(II), and Cd(II) ions.
Decrease in sorption percentage at higher concentrations might be due to the relatively
smaller numbers of active sites available at higher adsorbate concentrations. But with increasing
of the initial concentration of the adsorbate, the total amount of metal ions removal in mg/g is
increased. The decrease in percentage removal can also be explained by the fact that as the
concentration of the adsorbate increases so does the metal loading on the adsorbent. For
example, a concentration of 10 ppm will have higher surface loading as compared to
concentration of 2 ppm or 4 ppm. Because it causes an equal increase in number of metal ions
coming in contact with the adsorbent increases during same time while on the other hand the
number of adsorbing sites available for adsorption are constant for all concentration. So, when
the concentration is higher, more number of ions will be competing for same adsorption sites and
will go through without being adsorbed.
The adsorption data obtained with the adsorbent correlates well with the Frundlich,
Langmuir, and Temkin adsorption models and were illustrated in figure 3 to 8. The Langmuir
equation was chosen for the estimation of maximum adsorption capacity corresponding to
complete monolayer coverage on the biomass surface [21]. The Langmuir model assumes the
surface of the sorbent to be homogenous and the sorption energies to be equivalent for each
sorption site. The essential characteristics of the Langmuir model can be expressed in terms of a

85
dimensionless constant, separation factor or equilibrium parameter, RL. From the results in table
3 to 4, the RL values were found to be greater than zero and less than one i.e 0 < RL < 1.
According to [14], RL
Freundlich model was chosen to estimate the adsorption intensity of the sorbent towards the
sorbate. [21]. K
value between 0 and 1 indicates favorable adsorption. This means that a
favorable adsorption was observed in this study.
F, and n determine the curvature and steepness of the isotherm [8]. The values of
n also indicate the affinity of the sorbent towards the biomass. The values of n, KF and r2
The values for the constant and r
were
shown on table 1 and 2. The 1 / n values ranged from 0.4332 – 0.4933 USASA; 0.5587 – 0.6553,
MSASA; 0.4361 – 0.5472, USASB; and 0.5003 – 0.5880. The values of 1/n for the unmodified
samples were less than the modified samples. These suggest that the unmodified adsorbents
had a greater sorption capacity than the modified adsorbents. Also, the value of n is greater than
unity for the metal ions indicating that adsorption of the metal ions were favorable.
2 for Temkin isotherm is presented in table 5 – 6. The r2
values ranged from 0.8875 – 0.9823, USASA; 0.9213 – 0.9632, MSASA; 0.8698 – 0.9884,
USASB; and 0.8467 – 0.9592, MSASB. Examination of these plots suggests that the Freundlich,
Temkin and Langmuir isotherm fit the experiment but Freundlich isotherm is a better model than
Langmuir and Temkin isotherm with respect to their r2 values which is greater than 0.9000 and
less than 1.
CONCLUSION
Senilia Senilus and Thais Coronata biomass are agricultural waste, which are found to be
useful for the removal of heavy metal from aqueous solution. The adsorption capacity increased
with increasing concentration of the adsorbate. Freundlich adsorption isotherm proved best fit,
followed by the Langmuir isotherm and then Temkin isotherm. The modification of the adsorbent
using esterification have been shown not to enhance the adsorption capacity, probably, this is
attributed due to ester groups attached to the adsorbents.
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