Accepted Manuscript
Title: Utilization of NaOH modified Desmostachya bipinnata
(Kush Grass) Leaves & Bambusa arundinacea (Bamboo)
Leaves for Cd(II) removal from aqueous solution
Author: Ruchi Pandey Ram Lakhan Prasad Nasreen Ghazi
Ansari Ramesh Chandra Murthy
PII:
DOI:
Reference:
S2213-3437(14)00131-6
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Please cite this article as: Ruchi Pandey, Ram Lakhan Prasad, Nasreen Ghazi
Ansari, Ramesh Chandra Murthy, Utilization of NaOH modified Desmostachya
bipinnata (Kush Grass) Leaves & Bambusa arundinacea (Bamboo) Leaves for Cd(II)
removal from aqueous solution, Journal of Environmental Chemical Engineering
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Utilization of NaOH modified Desmostachya bipinnata
(Kush Grass) Leaves & Bambusa arundinacea
ip
t
(Bamboo) Leaves for Cd(II) removal from aqueous
cr
solution
Ruchi Pandeya, b, Ram Lakhan Prasadb, Nasreen Ghazi Ansaria and
a
us
Ramesh Chandra Murthy*, a
CSIR, Indian Institute of Toxicology Research, Analytical Chemistry Section,
Department of Chemistry, Faculty of Science, Banaras Hindu University,
M
b
an
Post Box-80, M.G. Marg, Lucknow-226001, India
Corresponding Author.
Abstract
te
*
d
Varanasi, 221005, India
Ac
ce
p
A fundamental investigation for the Cd(II) ions removal from aqueous solutions by NaOH
modified Desmostachya bipinnata (Kush Grass) Leaves (MDBL) and Bambusa arundinacea
(Bamboo) Leaves (MBAL) was conducted in batch experiments. The influence of different
experimental parameters such as pH, contact time, initial Cd(II) ion concentration, adsorbent
dosage, on the Cd(II) adsorption was studied. The Cd(II) uptake by MDBL and MBAL was
quantitatively evaluated using sorption isotherms. Freundlich and Langmuir isotherm models
were used to fit the equilibria data, of which Langmuir model is considered better in correlation
and the maximum adsorption capacity was found to be 15.22 mg g−1 for MDBL and 19.70 mgg1
for MBAL at room temperature. The kinetic data were found to follow closely the pseudo
second order kinetic model by both adsorbents. FTIR and SEM were recorded, before and after
adsorption, to explore number and position of the functional groups available for Cd(II) binding
on to studied adsorbents and changes in surface morphology of adsorbent. Desorption studies
show 94.18% and 92.08% recovery for adsorbed Cd(II) ions from MDBL and MBAL,
respectively using 0.1 N HNO3. Thermodynamic studies indicated that the adsorption reaction
was a spontaneous and exothermic process. It can be concluded that MDBL and MBAL are
Page 1 of 32
low-cost biosorbent alternatives for wastewater treatment, since both have a considerable high
adsorption capacity.
Highlights
Highlights
• A Novel and efficient biosorbent is developed from NaOH modification of
ip
t
•
Desmostachya bipinnata (Kush Grass) Leaves (MDBL) & Bambusa arundinacea
•
cr
(Bamboo) Leaves (MBAL) for removal of Cd(II) ions from aqueous solution.
• Apparent high adsorption capacity of 19.84 and 19.71 mg g−1 was shown by
• 94.18 percent and 92.08% desorption of adsorbed Cd(II) ions from MDBL and
an
MBAL, respectively was observed using 0.1 N HNO3.
Keywords
d
M
Graphical Abstract
Isotherm, Kinetics
te
Desmostachya bipinnata leaves, Kush grass, Bambusa arundinacea leaves, Bamboo leaves,
Ac
ce
p
•
us
MDBL and MBAL at pH = 6.5, respectively with a fast adsorption rate.
1 Introduction
An increased flux of heavy metals in the aquatic environment due to their swift use [1] in
industries, has led severe threat to human being. Beyond permitted concentration, they
can cause grave health disorders; therefore, considerable attention has been paid to
wastewater treatment prior to its discharge in the environment. Among these metallic
pollutants, Cd(II), an extremely toxic heavy metal causes a potential risk to
environmental and human health because it is incorporated into the food chain, mainly
by plant uptake [2]. The main anthropogenic pathway through which Cd(II) enters the
water bodies is via wastes from industrial processes such as electroplating, plastic
manufacturing, metallurgical processes, and Cd/Ni batteries. Over exposures may befall
even in conditions where a little amount of Cd(II) found because of its low permissible
limit (0.005 mg L−1) in drinking water [3]. So many surface chemistry practices for
Page 2 of 32
wastewater treatment such as precipitation, adsorption, membrane processes, ionic
exchange, floatation, and others [4,5] have been studied. However, because of inherent
limitation of such techniques as less competent, perceptive operating settings, and
production of sludge, they further require costly disposal [6], whereas, adsorption is by
ip
t
far the most versatile and widely used method, and activated carbon is the furthermost
commonly used adsorbent [7]. Conversely, the use of activated carbon is expensive, so
considerable interest has been shown towards the use of other efficient sorbent
cr
materials, particularly biosorbents [8]. In recent years, agricultural by-products have
been widely considered for metal sorption studies including peat, banana pith, pine bark,
us
peanut, shells, hazelnut shell, rice husk, wood, sawdust, wool, soybean and cottonseed
hulls, orange peel, leaves and compost [9-13]. In a previous study we have carried out
an
Cd(II) removal using Cucumber peel and obtained a maximum adsorption capacity of
7.142 mg g−1[14]. In the adsorption process, various metal-binding mechanisms are
thought to be involved, including ion exchange, surface adsorption, chemisorption,
M
complexation, and adsorption–complexation [15-18].
In the present study, Cd(II) sorption using Desmostachya bipinnata (Kush Grass)
d
Leaves (DBL) and Bambusa arundinacea (Bamboo) Leaves (BAL), members of true
te
grass family: Poaceae, had been studied and as both adsorbents correspond to same
family, their major constituents must be same. These materials are the major organic
Ac
ce
p
components of the solid waste, comprising about 14.6% of total municipal solid waste
(MSW) and about 50% of the organic fraction of the MSW [19]. However, in the entire
world, India has the huge rate of biomass production, including organic wastes, such as
grass, leaves and flowers. Therefore, it is essential to search for a better use of these
abundant agricultural wastes such as, remediation of heavy metal from contaminated
aqueous solutions. Both materials found abundantly throughout the year, and these
kinds of materials exhibit strong potential due to their high content of lignin and cellulose
[20] that abide numerous polar functional groups, including phenolic and carboxylic acid
groups, which may be involved in metal binding [21,22]. Due to the low cost, DBL and
BAL are an attractive and inexpensive option for the adsorption of Cd(II) ion from
aqueous solution. Further NaOH was used in the modification process because it can
enhance surface characteristics of DBL and BAL with increased adsorption capacity
[23]. The adsorption capacity of modified DBL and BAL (MDBL & MBAL, respectively)
was investigated by batch experiments. The influences of parameters such as pH,
Page 3 of 32
adsorbent dosage, contact time, initial ion concentration were investigated and the
experimental data obtained were evaluated and fitted using adsorption equilibrium and
kinetic models.
ip
t
2 Materials and methods
2.1 Adsorbent & chemicals
cr
DBL and BAL were obtained from the Indian Institute of Toxicology Research, Gheru
Campus (Lucknow, India). Both were dried under the sunlight for 2 days then, ground,
us
washed several times with double distilled water (DDW) and afterwards screened to
obtain 80 µm sized particles. These samples were modified using 0.5 M NaOH solution
with 1:20 for 30 min (solid–liquid ratio) [24]. The MDBL and MBAL were again dried at
MDBL & MBAL are presented in Table 1.
an
100 °C for 24 h and stored in an airtight container. The physical characteristics of the
M
Table 1 Physical characteristic of MDBL & MBAL.
Parameter
MBAL
≤ 80
0.144
0.196
0.127
0.166
Porosity (%)
0.113
0.15
Moisture content (%)
10.93
8.30
Ash content (%)
2.57
1.42
Phzpc
5.50
5
Particle density
Ac
ce
p
Bulk density (g ml−1)
d
≤ 80
te
Particle size (µm)
MDBL
The stock solution of Cd(II) (1000 mg L−1) was prepared in DDW using Cd
(NO3)2.4H2O salt (Merck); all working solutions were prepared by diluting the stock
solution with DDW.
2.2 Biosorption experiments
Batch experiments were executed for adsorption studies. A Pre-weighted sample of the
adsorbents (MDBL & MBAL) with a measured volume of Cd(II) solution were taken in
100 mL Erlenmeyer flask and stirred in an incubator shaker (250 rpm) at a steady
Page 4 of 32
temperature (25 ± 2 °C), for 240 min to ensure equilibrium. After shaking the flasks for
regular intervals, samples were withdrawn, filtered and the filtrates were analyzed by
Atomic absorption Spectrophotometer (PerkinElmer AAnalyst 300, USA) for the
concentration of Cd(II). A first series of sorption experiments was carried out with an
ip
t
initial concentration of 20 mg L−1. In these experiments the most favorable pH of
biosorption was determined. Subsequently, the influence of adsorbent dosage, contact
time, initial ion concentration was also evaluated. Percentage metal removal was
us
cr
calculated using the following formula:
(1)
where C0 is initial and Ct is the final concentration of Cd(II). The morphological
characteristics of adsorbents were evaluated by using a scanning electron microscope
an
(SEM) and disposition of the functional group present on the adsorbent surface were
spectrophotometer.
2.3 Adsorption isotherms studies
M
studied before and after biosorption using Fourier Transform Infrared (FTIR)
d
Isotherm studies were recorded by varying the initial concentration of Cd(II) solutions
te
from 10–150 mg L−1 with MDBL and MBAL separately. A known amount of adsorbents
was then added into solutions in different flasks followed by agitating them at 250 rpm till
Ac
ce
p
equilibrium. The metal ion concentrations, retained in the adsorbent phase qe (mgg−1)
which is defined as adsorption capacity, was calculated by using the following mass
balance equation for the process at equilibrium condition:
(2)
where V is the volume of solution (L) and W is the mass of adsorbate (g).
2.4 Desorption study
Desorption experiments were performed to consider the practical usefulness of the
biosorbents. After the biosorption studies, 0.2 g of metal loaded sorbent were agitated in
100 mL of 0.1 M HCl and 0.1 M HNO3 same as described by Witek-Krowiak [25]. After
60 min of contact time the metal concentration in the solution was determined. To check
the applicability as the best eluent the sorption desorption steps were repeated five
times.
Page 5 of 32
3 Results and discussion
3.1 Characteristic of MDBL & MBAL before and after adsorption
Presence of functional groups on MDBL & MBAL powder were analyzed using FTIR, as
ip
t
shown in Fig. 1(A) and (B). Occurrences of diverse type of functional groups are
confirmed by the peaks, and their detailed illustration is shown in Table 2. Mainly, metal
ions were bonded by functional groups such as carboxylic groups (pectin, hemicellulose
cr
and lignin), phenolic groups (lignin and extractives) and a little amount may also
adsorbed by hydroxyl (cellulose, lignin, extractives, and pectin) and carbonyl groups
us
(lignin) [26]. After sorption, several functional groups which were initially present
disappear, while some other had their position altered and thus confirming the active
an
participation of bonded OH groups, secondary amine group, carboxyl groups, C−O
stretching of ether groups and −C−C− group [3,27] as shown in Fig. 1(A) and (B) and
Table 2. Hence, the good sorption properties of both MDBL and MBAL towards Cd(II)
M
ions can be ascribed to the presence of these functional groups on their surfaces.
Fig. 2(A) and (B) shows SEM images for MDBL and MBAL before and after the
adsorption process, respectively. From Fig. 2(A & B), it is clearly visible that before
d
adsorption, both the adsorbents have rough heterogeneous porous surface and a large
te
number of steps and kinks on the adsorbent surface, with wrecked edges [28]. The
change in the morphology of the adsorbent after adsorption indicates that there is a
Ac
ce
p
good possibility for Cd(II) ions to be trapped and adsorbed onto the surface.
Fig. 1FTIR spectra of MDBL (A) and MBAL (B)
before and after Cd(II) adsorption.
Table 2 Functional groups and mode of vibration from the FTIR spectrum of
MDBL and MBAL before and after adsorption.
Functional group
Stretching vibration of bonded −OH
Cd (II)
Cd (II)
loaded
loaded
MDBL
MDBL
MBAL
MDBL
(cm )
(cm )
(cm )
(cm−1)
3418.35
3415.14
3402.93
3431.08
−1
−1
−1
Page 6 of 32
group on surface
Asymmetrical stretching vibration of
2922.73
2920.52
2922.59
2923.30
1631.46
1639.24
1634.58
1644.39
−
1516.20
−
Strong stretching vibration of C−O from
carboxylic acid in presence of
Generation of this peak after adsorption
cr
intermolecular H bonding
bending vibration of N−H and stretching
vibration of C−N
Bending vibration oh OH and stretching
vibration of C−O−C in lignin structure
Bending vibration of OH and stretching
−
1376.61
1514.93
1059.02
1103.39
1246.16
1252.85
−
−
1049.61
1073.96
−
−
664.60
563.42
602.96
466.37
469.10
M
C−O stretching of carboxylic acid
1377.07
an
1380.35
us
is outcome of an overlapped band of
C−C stretching of aromatic ring
ip
t
−CH3
d
vibration of C−O−C in lignin structure
te
Fingerprint region: adsorption cannot be
clearly assigned to any particular
Ac
ce
p
vibration because they correspond to
605.21
complex interacting vibration systems
Fig. 2Scanning electron micrograph showing morphology of MDBL (A) and MBAL
(B) before and after Cd(II) adsorption.
3.2 Effect of pH
The pH plays a very significant role in the sorption of heavy metals by affecting the
surface charge of adsorbent, the degree of ionization, and speciation of adsorbate.
Thus, the effects of initial pH of the solution on the Cd(II) removal efficiency were studied
at different pH ranging from 3.5 to 8.5. A sharp increase in the Cd(II) removal was
observed from 64.4% to 77.6% and 60.88%–75.2% at pH 6.5 (Fig. 3) for MDBL and
MBAL, respectively and after that with a slight decrease, the value became constant
Page 7 of 32
because of saturation of active sites on the adsorbents surface. So the pH 6.5 was
selected as the best pH to study the overall adsorption process. Precipitation of Cd(II)
ions was observed at pH 8 [29]. At low pH, the little removal efficiency is due to
occurrence of higher concentration of protons in the solution which compete with the
ip
t
Cd(II) ions for the adsorption sites of the adsorbents. As the pH increases, the H+
concentration decreases, leading to enhanced Cd(II) uptake. The effect of pH can be
explained in terms of pHzpc of the adsorbent. The pH at, which the charge of the whole
cr
surface is zero is referred as the zero point of charge (pHzpc) and above which the
surface become negatively charged. The obtained pHzpc of MDBL and MBAL is 5 and 5.5
us
respectively by using the batch equilibration technique [30]. Positively charged Cd(II)
species are soft acids and as a rule the interaction of Cd2+ and Cd (OH)+ with the
an
negatively charged adsorbent surface containing carboxyl and hydroxyl groups are
responsible for the sorption of Cd(II) ions and also supported by FTIR studies. At low pH,
particularly below pHzpc the Cd2+ and Cd (OH)
+
species present in the solution may
M
exchange with H+ from peripheral. Apparently, at very low pH (≤ 3), the presence of
higher concentrations of H+ ions in the mixture, owes electrostatic repulsion between
both positively charged adsorbent surface and metal ion. A decreasing trend in
d
adsorption was also observed at very high pH also, and this may be due to the formation
te
of soluble hydroxy complexes [31]. Dissociation of the –COOH groups (pKa = 3. 8-5.0) is
the plausible reason for becoming the surface of MDBL and MBAL negatively charged at
Ac
ce
p
optimum pH 6.5 and thus, favorable to the adsorption of Cd(II) at this pH [32]. Cd(II) may
most likely be bound on the MDBL and MBAL surface via an ion exchange mechanism
as following equation:
(3)
Fig. 3Effect of pH on Cd(II) adsorption by MDBL and MBAL at 25 °C
(condition: 20 mg L−1 of Cd(II) solution, 250 rpm, 1 g L−1 adsorbent dosage,
60 min).
(where -R represents the matrix of the adsorbents).
3.3 Effect of biosorbent dosage
Page 8 of 32
One of another important parameter that strongly affects the sorption capacity is the
biosorbent dosage. As shown in Fig. 4 with the increasing adsorbent dosage from 2 to
12 g L−1, it can easily be inferred that the percent removal of metal ions boosts from
63.95% to 85.50% and 65.50%–82.05% for MDBL and MBAL, respectively, whereas the
ip
t
amount adsorbed per unit mass decreases. It is apparent that the percent removal of
heavy metals increases rapidly with an increase in the dosage of the adsorbents due to
the greater availability of the exchangeable sites or surface area [3], whereas the
cr
decrease in Cd(II) uptake with increasing adsorbent dosage is mainly due to
unsaturation of adsorption sites through the adsorption reaction and the similar results
an
us
were obtained in a study performed by Chen et al. [33].
Fig. 4Effect of adsorbent dosage for Cd(II) adsorption by MDBL and MBAL at
M
25 °C (condition: 20 mg L−1 of Cd(II) solution, 250 rpm, 60 min).
3.4 Effect of initial ion concentration
d
The Cd(II) ion uptake is particularly reliant on the initial Cd(II) concentration. At the lower
range, Cd(II) is adsorbed by specific active sites, while at higher sides; decreased
te
adsorption is due to the saturation of adsorption sites and also because of lack of
sufficient surface area to accumulate further available ions. This is due to the
Ac
ce
p
competition for the available active sites on the surface. The influence of the initial Cd(II)
concentration on its removal with MDBL and MBAL shown in Fig. 5, where a decrease in
removal percent from 74.2–66.60% and 77.90-62.61% (for Co = 10 − 150 mg L−1) could
be observed respectively.
Fig. 5Effect of initial Cd(II) ion concentration for adsorption process by MDBL and
MBAL at 25 °C (condition: 1 g L−1 adsorbent dosage, 250 rpm, 60 min).
3.5 Effect of contact time
The effect of contact time on adsorption was studied up to 240 min. It appeared from
Fig. 6 that the metal uptake is very rapid up to 90 and 180 min of equilibrium for MBAL
and MDBL respectively, after that Cd(II) uptake does not significantly change with time.
Page 9 of 32
Therefore, 240 min of contact time is chosen to achieve the equilibrium [34]. For 20 mg
L−1 of Cd(II) concentration with an increase in contact time from 10–180 min for MDBL
and 10–150 min for MBAL, the percentage Cd(II) sorption increased from 36.80–89.55%
and 29.15–90.05%, respectively and after which a plateau is obtained, which showed
ip
t
saturation of the active points (Fig. 6). The subsequent increase in contact time had no
cr
effect on Cd(II) adsorption.
Fig. 6Effect of contact time on Cd(II) adsorption by MDBL and MBAL, at 25 °C,
us
(condition: 20 mg L−1 of Cd(II) solution, 250 rpm, 1 g L−1 adsorbent dosage).
an
3.6 Adsorption isotherms
The equilibrium isotherm study is very essential for designing adsorption systems and
also facilitate the comprehensive of the interaction involved between adsorbate and
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adsorbent. The adsorption data were analyzed Freundlich (1906) and Langmuir (1918)
isotherm models. The linearized forms of the Freundlich isotherm can be expressed as
(4)
(5)
Ac
ce
p
te
d
in Eq. 4[35] and of Langmuir isotherm as in Eq. 5[35] below:
where Ce (mg L−1) is the equilibrium Cd(II) concentration in solution, qe and qmax
(mgg−1) are the equilibrium and maximum adsorption capacities (mgg−1), 1/n is the
heterogeneity factor, kF (Lg−1) and kL(Lg−1) are Freundlich and Langmuir constant
respectively. The values of Freundlich and Langmuir parameters were obtained based
on the linear correlation between the values of (i) log qe vs. log Ce and (ii) (Ce/qe) vs. Ce,
respectively.
Fig. 7(a) and (b) shows the adsorption isotherms of Cd(II) using MDBL and MBAL,
respectively. Freundlich isotherm is the most basic relationship describing non-ideal and
reversible adsorption, valid for heterogeneous surface having non uniform energy
distribution and is not restricted to monolayer formation [36]. In the present study
(Table 3) at increasing temperature, higher kF values and n > 1 indicated, favorable
process [37] and are classified as L type isotherm reflecting a high affinity between
Page 10 of 32
adsorbent and adsorbate thus shows beneficial adsorption for MDBL and MBAL, and is
indicative of chemisorption [38].
ip
t
Fig. 7Langmuir isotherm for MDBL
and MBAL at 25 °C.
cr
Table 3 Adsorption isotherm parameters at different temperatures.
Freundlich
Freundlich
us
n
L )
R
2
(mg g )
−1
kL
R2
(min−1)
298
1.251 ± 0.057
1.505 ± 0.002
0.977
15.222 ± 0.162
0.077 ± 0.006
0.997
308
1.460 ± 0.067
1.522 ± 0.045
0.979
19.843 ± 0.570
0.090 ± 0.006
0.992
318
1.552 ± 0.028
1.501 ± 0.006
0.955
15.540 ± 0.085
0.104 ± 0.003
0.995
298
1.424 ± 0.025
1.472 ± 0.016
0.977
19.705 ± 0.097
0.064 ± 0.001
0.987
308
1.961 ± 0.020
0.949
18.483 ± 0.151
0.107 ± 0.001
0.986
318
2.024 ± 0.061
0.933
17.331 ± 0.425
0.135 ± 0.008
0.993
d
MBAL
qmax
1/n
1.596 ± 0.011
te
MDBL
(mg1−1/n g−1
M
(K)
kF
an
Temp
Langmuir
1.602 ± 0.018
Ac
ce
p
The Langmuir model is based on the hypothesis that all binding sites are, likewise,
active on the energetically homogeneous surface, and monolayer surface formation
takes place without any interaction between the adsorbed molecules [12]. As it can be
seen from Table 3, the coefficients of determination (R2 > 0.980) at varying temperatures
proved that the linear fit of the Langmuir model agrees well for both the adsorbents.
Initially, on increasing temperature from 298 to 308K adsorption capacity increases
for MDBL and decreasing values were noticed from 308–318 K. On the other side
continuous decrease in adsorption capacity is observed for MBAL up to 318 K, and it
may be due to either the damage of adsorbent’s active binding sites [39] or increasing
propensity of desorption of Cd(II) ions from the interface to the solution [40]. This is
because at the higher temperature the thickness of the boundary layer decreases and
thus tendency of the metal ion to escape from the biomass surface to the solution phase
increases [41]. This trend in the result indicates the exothermic nature of Cd(II)
Page 11 of 32
adsorption. The admirable qmax data as shown in the Table 3, it is obvious that MDBL
and MBAL exhibited a favorable combination of a high number of accessible adsorption
sites, and evidenced excellent promising adsorbents for Cd(II) ions from aqueous
solution.
ip
t
Freundlich and Langmuir equations have their own limitations in describing the
equilibrium data adequately. Both are based on utterly unlike principles, and the fact that
the experimental fallouts fit one or another equation, imitates a purely mathematical apt
cr
[13]. So here it may be concluded from Table 3, that the Cd(II) adsorption isotherm
exhibit Langmuir behavior with comparative high coefficients of determination
us
(R2 > 0.980) than Freundlich isotherm.
an
3.7 Thermodynamic study
Langmuir isotherm constant kL for varying temperatures, i.e. 298, 308 and 318 K has
been used to evaluate the thermodynamic parameters, the change in Gibbs free energy
M
(ΔGo), enthalpy (ΔHo) and entropy (ΔSo) for the adsorption process [38], and the
te
d
following equations are used for the calculations for these parameter:
(6)
(7)
Ac
ce
p
where R is the universal gas constant (1.987 cal mol−1) and T is the temperature (K).
The entropy (ΔSo) and enthalpy (ΔHo) change were obtained from the slope and
intercept of the plot of log kL against 1 T−1 (Fig. 8), respectively. All the thermodynamic
parameters of the adsorption process are shown in Table 4. As expected, the negative
ΔG° value indicates feasibility and spontaneity of the adsorption process. The change of
the standard free energy decreases with increasing temperature regardless the nature of
adsorbent, indicate that a better adsorption is actually obtained at the higher
temperature [42]. Moreover, the standard free energy change for multilayer adsorption
was more than −20 kJ mol−1 and less than zero. It should be noted that the magnitude of
ΔG◦ values is in the range of multilayer adsorption [43]. Each metal ion has to displace
more than one ion of the solvent. The net result corresponds to the endothermic process
[44]. Moreover, the positive ΔS° value corresponds to the increased randomness at the
solid/liquid interface during the adsorption process, which suggests that Cd(II) ions
Page 12 of 32
replace some water molecules from the solution previously adsorbed on the surface of
adsorbent. Positive value of ΔH◦ shows the endothermic nature of reaction [45]. The
values of adsorption (ΔH°) obtained in this study (< 20 kJ mol−1) are consistent with
ip
t
hydrogen bond and dipole bond forces for both adsorbents [46].
Fig. 8Plot of ln KL versus 1/T for Cd(II)
cr
sorption onto MDBL and MBAL.
Table 4 Thermodynamic parameters at different temperatures for Cd(II)
us
adsorption using MDBL and MBAL.
ΔGo
Temp (K)
(kJ mol−1)
298
–
ΔHo (kJ mol−1)
ΔSo (J mol−1
K−1)
M
MDBL
an
Thermodynamic parameters
0.389 ± 0.143
–
d
308
5.50 ± 0.916
1.58 ± 0.089
9.283 ± 6.564
2.673 ± 1.890
Ac
ce
p
318
te
1.506 ± 0.174
MBAL
298
308
318
–
1.112 ± 0.053
–
0.661 ± 0.064
–
1.731 ± 0.031
–
2.051 ± 0.085
3.8 Kinetic study
Adsorption kinetic studies are important as they provide valuable information about the
mechanism of the adsorption process [47] such as mass transfer and chemical reaction.
In the present study, applicability of the pseudo-first-order [Eq. 8] [48] and pseudo-
Page 13 of 32
second-order kinetics [Eq. 9] [37] based on solid capacity and solid phase sorption has
been evaluated, respectively.
(8)
ip
t
(9)
cr
qe and qt are adsorption capacities (mgg−1) at equilibrium and at time t respectively.
k1ad is the first order rate constant (Lmin.−1) and k2ad is the rate equilibrium constant (g mg−1
(10)
an
us
min−1) for pseudo second order kinetics.
where h is the initial sorption rate (mg g−1 min−1) [49].
In the present study, at different initial ion Cd(II) concentration all the kinetic data
M
were considered up to 240 min for pseudo-second-order rate model, but for pseudo-firstorder rate model, only initial kinetic data up to 150 and 120 min for MDBL and MBAL
respectively have been used, because using a whole range of contact time, the
d
calculated values of qe (mgg−1) from pseudo-first-order rate model is physically
te
unacceptable. The pseudo-first-order rate model does not fit well to the whole range of
contact time in several other cases also and is generally applicable to the initial phase of
Ac
ce
p
the adsorption processes [49,50].
The equilibrium adsorption capacity and the second-order rate constant were
calculated from the slope and the intercept of the plot t/qt against t (Fig. 9a & b). A
competitively high adsorption capacity (qe) was obtained for MBAL than MDBL. The data
illustrated good compliance with the pseudo-second order rate law based on sorption
capacity because the coefficients of determination, R2 from Table 5 were higher than
0.990 for both MDBL and MBAL. It can also be perceived by values of Table 5 that, for
both the adsorbents, with an increase in initial metal concentration, the adsorption
capacity increases while the rate constant of adsorption (k2ad) decreases. A similar
observation was also reported by some earlier researchers [49]. The observed decrease
in the rate constants with an increase in initial metal ion concentration may be because,
at higher concentration, the average distance between the adsorbed ion is contracted to
a point where each affect the charge distribution of its adjacent ions. The second-order
Page 14 of 32
rate constant decreases with an increase in initial Cd(II) concentration, while the initial
sorption rate, h, generally increases with an increasing initial Cd(II) concentration at all
temperatures. This interaction can alter the ability of the ions to adsorb onto adsorbent,
hence higher concentration of metal ions may limit the ability of the biomass to adsorb
ip
t
metal ions and consequently sorption process may require several cycles in order to
cr
meet regulatory standards [31].
Fig. 9Kinetic parameters for the
us
adsorption of Cd(II) on MDBL and
MBAL at various initial Cd(II) ion
an
concentrations.
Table 5 Parameters of pseudo-first-order and pseudo-second-order kinetics for Cd(II) adsorption us
PseudoPseudo-first order
Co
(mg g−1)
d
L−1)
MBAL
PseudoPseudo-second order
k1ad
(min−1)
te
qe, cal
R2
qe, cal
k2ad
(mg g−1)
(g mg1 min−1)
h
20
1.097 ± 0.054
0.008 ± 0.001
0.924
1.882 ± 0.020
0.058 ± 0.004
0.194 ± 0.0
30
2.105 ± 0.023
0.012 ± 0.001
0.985
2.828 ± 0.006
0.030 ± 0.001
0.236 ± 0.0
50
3.546 ± 0.014
0.008 ± 0.001
0.978
4.785 ± 0.001
0.010 ± 0.000
0.233 ± 0.0
20
1.528 ± 0.014
0.007 ± 0.001
0.920
2.384 ± 0.007
0.028 ± 0.0002
0.157 ± 0.0
30
2.880 ± 0.018
0.013 ± 0.001
0.930
3.586 ± 0.025
0.016 ± 0.0004
0.213 ± 0.0
50
5.389 ± 0.092
0.014 ± 0.001
0.963
5.950 ± 0.007
0.011 ± 0.0004
0.396 ± 0.0
Ac
ce
p
MDBL
(mg
M
and MBAL at various initial Cd(II) ion concentration.
3.9 Sorption mechanism
The kinetic data were analyzed by intraparticle diffusion model [Eq. 11] to elucidate the
key steps involved during the adsorption process.
(11)
Page 15 of 32
ki is the intra-particle diffusion rate constant (mg g−1 min0.5).
In this direction, the kinetic data obtained by plotting qt vs. t0.5 plays a significant role
to understand the mechanism of adsorption: as migration of metal species from the
solution to adsorbent, diffusion, intraparticle diffusion through boundary layer and
ip
t
adsorption to the internal sorbent surface. Table 6 shows that with an increase in the
initial Cd(II) concentration, the intra-particle diffusion rate constant (ki) also increases
cr
because ki is directly related to qe and intra-particle diffusivity (I).
Table 6 Intra-particle diffusion parameters for Cd(II) adsorption using MDBL and MBAL at various i
Co
(mg
I
(mg g−1
L−1)
(mg g−1)
min−1/2)
20
–
0.308 ± 0.016
0.239 ± 0.061
R2
I
ki2
I
(mg g−1)
(mg g−1 min−1/2)
R2
(
0.996
1.049 ± 0.070
0.057 ± 0.007
0.927
2
0.050 ± 0.111
0.316 ± 0.026
0.9967
2.092 ± 0.154
0.046 ± 0.013
0.9841
2
50
0.244 ± 0.551
0.301 ± 0.238
0.962
2.830 ± 0.010
0.009 ± 0.0002
0.999
4
20
0.660 ± 0.127
0.566 ± 0.075
0.985
1.125 ± 0.010
0.160 ± 0.101
0.965
2
0.172 ± 0.029
0.989
1.432 ± 1.155
0.040 ± 0.008
0.735
3
0.485 ± 0.043
0.985
2.718 ± 1.143
0.247 ± 0.110
0.913
5
te
d
30
Ac
ce
p
MBAL
an
ki1
M
MDBL
us
Intra particle diffusion
30
–
1.286 ± 0.658
50
0.742 ± 0.198
The plots of qt vs. t0.5 at different initial Cd(II) ion concentrations (Fig. 10a & b) show
multi-linearity characterizations for both the adsorbents, indicates the occurrence of a
three step adsorption process [51]. For all three stages, the intra particle diffusion
constant (ki1, ki2, ki3) for MDBL and MBAL are shown in Table 6, that shows first sharp
section is the external surface adsorption or an instantaneous adsorption stage, then
intraparticle diffusion decelerated down and stabilized [52]. The initial kinetic data do not
pass through the origin for both the absorbents, so on the basis of these data it is
obvious that, intra-particle diffusion is not the sole rate controlling step [53]. So here the
overall mechanism involves adsorption and intra-particle diffusion.
Page 16 of 32
Fig. 10Intra
particle diffusion model for Cd(II) adsorption by MDBL and MBAL at
10
various initial Cd(II) ion concentrations.
ip
t
3.10 Desorption
Apart from adsorption, desorption also plays an important role to define the versatility of
cr
an adsorbent as it allows reuse of adsorbent and recovering of valuable heavy metals.
Dssorption studies were carried using 0.1 N HNO3 and 0.1 N HCl. Results showed that
us
MDBL achieved 94.18% and 93.65% desorption of adsorbed Cd(II) ions using HNO3 and
HCl, whereas for MBAL, attained desorption is 92.08% using HNO3 and 91.60% using
HCl, respectively. It indicates that HNO3 acts as a better eluting agent for Cd(II) ions
an
from the used biosorbent than HCl. After the desorption of Cd(II) ions, both sorbents
were washed thoroughly with DDW. Five cycles of successive sorption-desorption were
M
carried out to test the reusability of MDBL and MBAL using 0.1 N HNO3 and the outcome
indicated that the adsorption capacity decreases in the range of 93.75-80% and 91.13-
d
73.80% of HNO3 regenerated MDBL and MBAL, respectively.
te
3.11 Comparison of MDBL & MBAL with other adsorbents
The adsorption capacity of Cd(II) onto MDBL & MBAL was noticeable as compared with
Ac
ce
p
other NaOH treated adsorbents reported in literature as sawdust (73.62 mg g−1) [54],
Juniper fiber (29.54 mg g−1) [55], Rice husk (20.24 mg g−1) [56], Coconut bagasse (17.51
mg g−1) [57] and spent grains (17.3 mg g−1) [58]. It can be observed that a pH near about
6.0 was found to be an optimum in nearly all cases with the same modification method.
The adsorption capacity differences of metal uptake are due to the properties of each
adsorbent such as structure, functional groups and surface area. Thus the capacities
found in this work with MDBL (19.84 mg g−1) and MBAL (19.71 mg g−1) are significant
related to other.
4 Conclusion
In this detailed study, the NaOH modified DBL and BAL have been found to be very
effective biosorbents for Cd(II) ions removal from aqueous solution. The data of the
present study is comparable, as the both materials represent same family. All the
operational parameters such as the pH, adsorbent dosage, contact time and initial metal
Page 17 of 32
ion concentrations evidently affected the removal efficiency. The Langmuir adsorption
isotherm fits well to the equilibrium adsorption data and suggest that the monolayer and
homogeneous adsorption process take place. The adsorption process follows a pseudosecond-order kinetics rate model. The overall mechanism involves adsorption and intra-
ip
t
particle diffusion. Regeneration of used MDBL and MBAL can be performed efficiently
using 0.1 N HNO3 as an eluting agent. The adsorption process was spontaneous and
exothermic under natural conditions. These results demonstrate the remarkable potential
cr
of MDBL and MBAL as the low-cost substitutes with a considerable high adsorption
us
capacity of 15.22 mg g−1 and 19.70 mg g−1, respectively at room temperature.
Acknowledgments
an
The authors would like to acknowledge and extend their heartfelt gratitude to the
Director, CSIR-Indian Institute of Toxicology Research, Lucknow, and to, the HOD,
M
Department of Chemistry, Faculty of Science, BHU, Varanasi for taking interest in the
study. The authors thank the Council of Science and Technology, Uttar Pradesh, India
te
References
d
(Project Code, GAP-271) for providing their financial support for this research work.
1. Volesky B., Holan Z.R. Biosorption of heavy metals Biotechnology Progress 1995;11:235-
Ac
ce
p
250.7619394 DOI:10.1021/bp00033a001
2. Ayuso E.A.. Cadmium in soil-plant systems: An overview International Journal of Environment
and Pollution 2008;33:275-291. DOI:10.1504/IJEP.2008.019399
3. Rao M.M., Ramesh A., Rao G.P., Seshaiah K. Removal of copper and cadmium from the
aqueous solutions by activated carbon derived from Ceiba pentandra hulls Journal of
Hazardous Materials 2006;129:123-129.16191464 DOI:10.1016/j.jhazmat.2005.08.018
4. Kocaoba S., Akcin G. Removal of chromium (III) and cadmium (II) from aqueous solutions
Desalination 2005;180:151-156. DOI:10.1016/j.desal.2004.12.034
5. Govindasamy, V., Rengasamy, T., Mahendra Das, D.K., Removal of Cd2+ ions from aqueous
solution using live and dead Bacillus subtilis (2011)
Page 18 of 32
6. Ahluwalia S.S., Goyal D. Microbial and plant derived biomass for removal of heavy metals from
wastewater Bioresource Technology 2007;98:2243-2257.16427277
DOI:10.1016/j.biortech.2005.12.006
7. Starvin A.M., Rao T.P. Removal and recovery of mercury(II) from hazardous wastes using 1-
ip
t
(2-thiazolylazo)-2-naphthol functionalized activated carbon as solid phase extractant Journal
of Hazardous Materials 2004;113:75-79.15363516 DOI:10.1016/j.jhazmat.2004.04.021
8. Ng J.C., Cheung W.H., McKay G. Equilibrium studies for the sorption of lead from effluents
cr
using chitosan Chemosphere 2003;52:1021-1030.12781235 DOI:10.1016/S0045-
us
6535(03)00223-6
9. Nagy B., Măicăneanu A., Indolean C., Burcă S., Silaghi-Dumitrescu L., Majdik C. Cadmium (II)
ions removal from aqueous solutions using Romanian untreated fir tree sawdust a green
an
biosorbent Acta Chimica Slovenica 2013;60:263-273.23878929
10. Saeed A., Iqbal M., Höll W.H. Kinetics, equilibrium and mechanism of CD2+ removal from
aqueous solution by mungbean husk Journal of Hazardous Materials 2009;168:1467-
M
1475.19386413 DOI:10.1016/j.jhazmat.2009.03.062
11. Shaheen S.M., Eissa F.I., Ghanem K.M., Gamal El-Din H.M., Al Anany F.S.Al. Heavy metals
d
removal from aqueous solutions and wastewaters by using various byproducts Journal of
Environmental Management 2013;128:514-521.23831673
te
DOI:10.1016/j.jenvman.2013.05.061
Ac
ce
p
12. Feng N.-c., Guo X.-y., Liang S. Kinetic and thermodynamic studies on biosorption of Cu(II) by
chemically modified orange peel Transactions of Nonferrous Metals Society of China
2009;19:1365-1370. DOI:10.1016/S1003-6326(08)60451-3
13. Vassileva P., Detcheva A., Uzunov I., Uzunova S. Removal of metal ions from aqueous
solutions using pyrolyzed rice husks: Adsorption kinetics and equilibria Chemical
Engineering Communications 2013;200:1578-1599. DOI:10.1080/00986445.2012.755519
14. Pandey R., Ansari N.G., Murthy R.C., Prasad R.L. Cd(II) adsorption from aqueous solution
onto Cucumis sativus Peel: Equilibrium, thermodynamic and Kinetic Study Journal of
Ecophysiology & Occupational Health 2013;13:75-84.
15. Alyüz B., Veli S. Kinetics and equilibrium studies for the removal of nickel and zinc from
aqueous solutions by ion exchange resins Journal of Hazardous Materials 2009;167:482488.19201087 DOI:10.1016/j.jhazmat.2009.01.006
Page 19 of 32
16. Kumar A., Rao N.N., Kaul S.N. Alkali-treated straw and insoluble straw xanthate as low cost
adsorbents for heavy metal removal - Preparation, characterization and application
Bioresource Technology 2000;71:133-142. DOI:10.1016/S0960-8524(99)00064-4
17. Gu X., Evans L.J. Surface complexation modelling of Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II)
ip
t
adsorption onto kaolinite Geochimica et Cosmochimica Acta 2008;72:267-276.
DOI:10.1016/j.gca.2007.09.032
18. Schneider I.A.H., Rubio J., Smith R.W. Biosorption of metals onto plant biomass: Exchange
us
2001;62:111-120. DOI:10.1016/S0301-7516(00)00047-8
cr
adsorption or surface precipitation? International Journal of Mineral Processing
19. Hameed B.H.. Grass waste: A novel sorbent for the removal of basic dye from aqueous
solution Journal of Hazardous Materials 2009;166:233-238.19111987
an
DOI:10.1016/j.jhazmat.2008.11.019
20. Mann D.G.J., Labbé N., Sykes R.W., Gracom K., Kline L., Swamidoss I.M., Burris J.N., Davis
M., Stewart C.N. Rapid assessment of lignin content and structure in switchgrass (Panicum
M
virgatum L.) grown under different environmental conditions BioEnergy Research
2009;2:246-256. DOI:10.1007/s12155-009-9054-x
d
21. Matheickal J.T., Yu Q., Woodburn G.M. Biosorption of cadmium(II) from aqueous solutions by
pre-treated biomass of marine alga DurvillAea potatorum Water Research 1999;33:335-342.
te
DOI:10.1016/S0043-1354(98)00237-1
Ac
ce
p
22. Ting Y.P., Prince I.G., Lawson F. Uptake of cadmium and zinc by the alga chlorella vulgaris:
II. Multi-ion situation Biotechnology and Bioengineering 1991;37:445-455.18597390
DOI:10.1002/bit.260370506
23. Ghali L., Msahli S., Zidi M., Sakli F. Effect of pre-treatment of luffa fibres on the structural
properties Materials Letters 2009;63:61-63. DOI:10.1016/j.matlet.2008.09.008
24. Carvalho M.L., Sousa Jr R. Jr., Rodríguez-Zúñiga U.F., Suarez C.A.G., Rodrigues D.S.,
Giordano R.C., Giordano R.L.C. Kinetic study of the enzymatic hydrolysis of sugarcane
bagasse Brazilian Journal of Chemical Engineering 2013;30:437-447. DOI:10.1590/S010466322013000300002
25. Witek-Krowiak A.. Application of beech sawdust for removal of heavy metals from water:
Biosorption and desorption studies European Journal of Wood and Wood Products
2013;71:227-236. DOI:10.1007/s00107-013-0673-8
Page 20 of 32
26. Prasanna Kumar Y.P.., King P., Prasad V.S.R.K. Adsorption of zinc from aqueous solution
using marine green algae-Ulva fasciata sp Chemical Engineering Journal 2007;129:161166. DOI:10.1016/j.cej.2006.10.023
27. Sheng P.X., Ting Y.-P., Chen J.P., Hong L. Sorption of lead, copper, cadmium, zinc, and
ip
t
nickel by marine algal biomass: Characterization of biosorptive capacity and investigation of
mechanisms Journal of Colloid and Interface Science 2004;275:131-141.15158390
DOI:10.1016/j.jcis.2004.01.036
cr
28. Bhattacharyya K.G., Sharma A. Adsorption of Pb(II) from aqueous solution by Azadirachta
indica (Neem) leaf powder Journal of Hazardous Materials 2004;113:97-109.15363519
us
DOI:10.1016/j.jhazmat.2004.05.034
29. Leyvaramos R., Bernaljacome L.A., Acostarodriguez I. Adsorption of cadmium(II) from
an
aqueous solution on natural and oxidized corncob Separation and Purification Technology
2005;45:41-49. DOI:10.1016/j.seppur.2005.02.005
30. Stankovic J.B., Milonjic S.K., Zec S.P. The influence of chemical and thermal treatment on the
M
point of zero charge of hydrous zirconium oxide Journal of the Serbian Chemical Society
2013;78:987-995. DOI:10.2298/JSC121010149S
d
31. Raji C., Manju G.N., Anirudhan T.S. Removal of heavy metal ions from water using sawdust260.
te
based activated carbon Indian Journal of Engineering and Materials Sciences 1997;4:254-
Ac
ce
p
32. Huang X., Gao N.Y., Zhang Q.L. Thermodynamics and kinetics of cadmium adsorption onto
oxidized granular activated carbon Journal of Environmental Sciences (China)
2007;19:1287-1292.18232220 DOI:10.1016/S1001-0742(07)60210-1
33. Chen G., Zeng G., Tang L., Du C., Jiang X., Huang G., Liu H., Shen G. Cadmium removal
from simulated wastewater to biomass byproduct of Lentinus edodes Bioresource
Technology 2008;99:7034-7040.18313919 DOI:10.1016/j.biortech.2008.01.020
34. Feng N.-c., Guo X.-y. Characterization of adsorptive capacity and mechanisms on adsorption
of copper, lead and zinc by modified orange peel Transactions of Nonferrous Metals Society
of China 2012;22:1224-1231. DOI:10.1016/S1003-6326(11)61309-5
35. Tofighy M.A., Mohammadi T. Adsorption of divalent heavy metal ions from water using carbon
nanotube sheets Journal of Hazardous Materials 2011;185:140-147.20926186
DOI:10.1016/j.jhazmat.2010.09.008
Page 21 of 32
36. Foo K.Y., Hameed B.H. Insights into the modeling of adsorption isotherm systems Chemical
Engineering Journal 2010;156:2-10. DOI:10.1016/j.cej.2009.09.013
37. Ho Y.S., McKay G. The kinetics of sorption of divalent metal ions onto sphagnum moss peat
Water Research 2000;34:735-742. DOI:10.1016/S0043-1354(99)00232-8
ip
t
38. Boparai H.K., Joseph M., O’Carroll D.M. Kinetics and thermodynamics of cadmium ion
removal by adsorption onto nano zerovalent iron particles Journal of Hazardous Materials
cr
2011;186:458-465.21130566 DOI:10.1016/j.jhazmat.2010.11.029
39. Ozer A., Ozer D. Comparative study of the biosorption of Pb(II), Ni(II) and Cr(VI) ions onto S.
us
cerevisiae: Determination of biosorption heats Journal of Hazardous Materials
2003;100:219-229.12835024 DOI:10.1016/S0304-3894(03)00109-2
40. Saltali K., Sari A., Aydin M. Removal of ammonium ion from aqueous solution by natural
an
Turkish (Yildizeli) zeolite for environmental quality Journal of Hazardous Materials
2007;141:258-263.16930832 DOI:10.1016/j.jhazmat.2006.06.124
M
41. Horsfall M. Jr., Spiff A.I. Sorption of lead, cadmium, and zinc on sulfur-containing chemically
modified wastes of fluted pumpkin (Telfairia occidentalis Hook f.) Chemistry & Biodiversity
2005;2:373-385. DOI:10.1002/cbdv.200590017
d
42. Zaki A.B., El-Sheikh M.Y., Evans J., El-Safty S.A. Kinetics and mechanism of the sorption of
te
some aromatic amines onto Amberlite IRA-904 anion-exchange resin Journal of Colloid and
Interface Science 2000;221:58-63.10623452 DOI:10.1006/jcis.1999.6553
Ac
ce
p
43. Bekçi Z., Seki Y., Yurdakoç M.K. Equilibrium studies for trimethoprim adsorption on
montmorillonite KSF Journal of Hazardous Materials 2006;133:233-242.16310307
DOI:10.1016/j.jhazmat.2005.10.029
44. Singh B.K., Rawat N.S. Comparative sorption equilibrium studies of toxic phenols on fly ash
and impregnated fly ash Journal of Chemical Technology AND Biotechnology 1994;61:307317. DOI:10.1002/jctb.280610405
45. Malkoc E., Nuhoglu Y. Determination of kinetic and equilibrium parameters of the batch
adsorption of Cr(VI) onto waste acorn of Quercus ithaburensis Chemical Engineering and
Processing: Process Intensification 2007;46:1020-1029. DOI:10.1016/j.cep.2007.05.007
46. Cardoso N.F., Lima E.C., Royer B., Bach M.V., Dotto G.L., Pinto L.A.A., Calvete T.
Comparison of Spirulina platensis microalgae and commercial activated carbon as
adsorbents for the removal of reactive Red 120 dye from aqueous effluents Journal of
Page 22 of 32
Hazardous Materials 2012;241–242:146-153.23040660
DOI:10.1016/j.jhazmat.2012.09.026
47. El-Khaiary M.I., Malash G.F., Ho Y.-S. On the use of linearized pseudo-second-order kinetic
equations for modeling adsorption systems Desalination 2010;257:93-101.
ip
t
DOI:10.1016/j.desal.2010.02.041
48. Yuh-Shan H.. Citation review of Lagergren kinetic rate equation on adsorption reactions
cr
Scientometrics 2004;59:171-177. DOI:10.1023/B:SCIE.0000013305.99473.cf
49. Ho Y.S., McKay G. The sorption of lead(II) ions on peat Water Research 1999;33:578-584.
us
DOI:10.1016/S0043-1354(98)00207-3
50. Chatterjee S., Woo S.H. The removal of nitrate from aqueous solutions by chitosan hydrogel
beads Journal of Hazardous Materials 2009;164:1012-1018.18977085
an
DOI:10.1016/j.jhazmat.2008.09.001
51. Wu F.C., Tseng R.L., Juang R.S. Comparisons of porous and adsorption properties of
M
carbons activated by steam and KOH Journal of Colloid and Interface Science 2005;283:4956.15694423 DOI:10.1016/j.jcis.2004.08.037
52. Cheung W.H., Szeto Y.S., McKay G. Intraparticle diffusion processes during acid dye
d
adsorption onto chitosan Bioresource Technology 2007;98:2897-2904.17110098
te
DOI:10.1016/j.biortech.2006.09.045
53. Gerçel Ö., Gerçel H.F. Adsorption of lead(II) ions from aqueous solutions by activated carbon
Ac
ce
p
prepared from biomass plant material of Euphorbia rigida Chemical Engineering Journal
2007;132:289-297. DOI:10.1016/j.cej.2007.01.010
54. Memon S.Q., Memon N., Shah S.W., Khuhawar M.Y., Bhanger M.I. Sawdust--a green and
economical sorbent for the removal of cadmium (II) ions Journal of Hazardous Materials
2007;139:116-121.16844287 DOI:10.1016/j.jhazmat.2006.06.013
55. Min S.H., Han J.S., Shin E.W., Park J.K. Improvement of cadmium ion removal by base
treatment of juniper fiber Water Research 2004;38:1289-1295.14975662
DOI:10.1016/j.watres.2003.11.016
56. Kumar U., Bandyopadhyay M. Sorption of cadmium from aqueous solution using pretreated
rice husk Bioresource Technology 2006;97:104-109.15936939
DOI:10.1016/j.biortech.2005.02.027
57. Sousa F.W., Oliveira A.G., Ribeiro J.P., De Keukeleire D., Sousa A.F., Nascimento R.F.
Single and multielementary isotherms of toxic metals in aqueous solution using treated
Page 23 of 32
coconut shell powder Desalination and Water Treatment 2011;36:289-296.
DOI:10.5004/dwt.2011.2597
58. Low K.S., Lee C.K., Liew S.C. Sorption of cadmium and lead from aqueous solutions by spent
Ac
ce
p
te
d
M
an
us
cr
ip
t
grain Process Biochemistry 2000;36:59-64. DOI:10.1016/S0032-9592(00)00177-1
Page 24 of 32