Lm3519611971

J.A.O. Oyekunle et al Int. Journal of Engineering Research and Application
ISSN : 2248-9622, Vol. 3, Issue 5, Sep-Oct 2013, pp.1961-1971

RESEARCH ARTICLE

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OPEN ACCESS

Adsorption Equilibrium, Kinetics and Thermodynamics of Cd
(II) and Pb (II) Removal from Synthetic Wastewater Using
Plantain Peel Charcoal
J.A.O. Oyekunle1, E.H. Umukoro1, O. Owoyomi1, A.O. Ogunfowokan1 and I.A.
Oke2
1. Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria
2. Department of Civil Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria

Abstract
The adsorption equilibrium, kinetics, and thermodynamic properties of plantain peel charcoal for the removal of
Cd2+ and Pb2+ from synthetic wastewater were investigated along with the effects of pH, temperature and
contact time on the adsorption capacity of the adsorbent. The charcoal used as the adsorbent was generated from
properly washed unripe plantain peels. Investigations of the adsorption process established the optimum
working pH (5 for Pb2+ and 7 for Cd2+) at 30 and 40oC, but with more metal ions removed at 40oC. It was
revealed that the adsorption of Cd2+ and Pb2+ on plantain peel charcoal was best described by the pseudo-second
order kinetic model with correlation coefficient (R2) ≥ 0.9975 at different temperatures. The adsorption followed
the Langmuir, Freundlich and Tempkin isotherms but could best be approximated with the Langmuir model. The
thermodynamic study showed that the adsorption of Cd2+ and Pb2+ from synthetic wastewaters using plantain
peel charcoal was a physisorption process which was spontaneous and endothermic in nature. It could be
concluded that plantain peel charcoal has the potential to serve as an efficient alternative adsorbent in clean-up
systems designed for the removal of heavy metals from industrial wastewaters.
Key words: Heavy metals, adsorption, charcoal, isotherms, wastewater, kinetic models.

I.

Introduction

Rigorous coordination of water resources all
over the world is increasingly becoming complex and
crucial because with population growth, more
pollutants are being added to the world’s inelastic
water reservoirs and a higher demand is
simultaneously being placed on water uses. One of the
main sources of water pollution is wastewater which
contains environmental and industrial pollutants [1].
These pollutants are chemicals such as volatile organic
compounds, heavy metals and dyes that are toxic to
human and aquatic lives [2]. The major sources of
heavy metals such as lead, copper, zinc and cadmium
are textile and dye, electroplating, solder, battery,
pigment and paint, agro allied, plastics and
metallurgical industries. Most organic pollutants are
susceptible to biological degradation unlike these
heavy metals which are not degradable into harmless
end-products [3]. During their transport within an
aquatic medium, for example, heavy metals may
merely undergo numerous changes in their speciation
due to dissolution, precipitation, sorption and
complexation phenomena [4]. This makes heavy
metals bioavailable to living things to varying degrees.
Some
heavy
metals
can
readily
bioaccumulate in the bodies of organisms and become
biomagnified along the food chains to reach such
levels that cause harm to human organs and systems
[5]. Chronic exposure of human beings to Cd can lead
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to renal and skeletal malfunctioning and death while
high exposure to Pb can cause damage to the kidney,
nervous, circulatory and reproductive systems. It can
also result to rheumatoid arthritis, anaemia, dizziness,
headache and insomnia.
Over the years, heavy metals treatment and
removal have been carried out by several techniques
such as electrodialysis, ion exchange resin,
ultrafilteration, cementation, solvent extraction,
chemical precipitation, reverse osmosis and
phytoremediation [6-11]. However, adsorption has
some advantages over these conventional methods
because adsorption techniques are low cost, display
metal selectivity, high efficiency, maximization of
chemical and low biological sludge, regeneration of
adsorbent and possible metal recovery [12]. Several
adsorbent materials such as plantain peel charcoal [5],
untreated powdered egg shell [13], Sago waste [14],
almond shell [15], wood saw dust [16], coconut husk
and shell [17, 18], sea weeds [19] , bagasse ash [20],
and so on, have been utilized for adsorption purposes.
The harmful effects of high levels of toxic and heavy
metal ions such as As, Cd, Pb, Hg, Cu, Mn and Zn on
the environment in general have prompted the need to
look for easy - to - afford and suitable technologies for
their removal from industrial effluents before being
discharged into water bodies.
In an earlier investigation involving four
adsorbents generated from different agricultural waste
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products [5], charcoal from plantain peel gave the best
adsorption performance. However, the mechanism by
which this was done was not investigated. Hence, its
technological applications in heavy metal removal
from wastewaters were not adequately highlighted.
Thus in the present study, the kinetics, equilibrium
and thermodynamics of Cd2+ and Pb2+ removal from
synthetic wastewater using plantain peel charcoal was
investigated in order to determine the mechanism by
which this adsorption is carried out. This
understanding could further enhance applications of
plantain peel charcoal as a suitable alternative
adsorbent to expensive ones in wastewater control and
management especially in the developing countries.

II.

Materials and Methods

2.1. Preparation of adsorbent
The method adopted in an earlier study [5]
was used in this study to generate adsorbents from
locally available materials. Unripe plantain peels
collected from villages around the Obafemi Awolowo
University, Ile-Ife, Nigeria, were cut into pieces,
washed thoroughly and rinsed with tap and distilled
water respectively to remove debris and other
impurities. The plantain peel chips obtained were oven
dried at a temperature of 105oC for 72 hours. The
dried chips were carbonized by packing them into an
earthenware pot, covered and heated at high
temperature. The pot content was stirred occasionally
so as to obtain a uniform combustion product. The
covering was necessary to reduce the amount of air
contact such that complete combustion of the plantain
peel chips was prevented and well formed charcoal
was ensured. When the smoke that was coming out of
the pot had stopped, the charcoal formed was allowed
to cool and was powdered by grinding in an agate
mortar with a pestle to increase the adsorbent surface
area of contact. The powdered charcoal was
fractionated using a test sieve of 500 microns pore
size. The sieved charcoal was activated and leached
using 0.2 M sulphuric acid by soaking in the acid for
48 hours after which the charcoal was filtered, rinsed
thoroughly with doubly distilled water and dried
overnight in a Gallenkamp Oven (Model Ov-160,
England) at 130ºC.
2.2. Apparatus sterilization
All the glassware used, such as measuring
cylinders, volumetric flasks, beakers, conical flasks,
watch glass and sample bottles (polyethylene
containers) were washed thoroughly with hot liquid
detergent solution, and then rinsed with a mixture of
acetone and n-hexane. The washed polyethylene
sample bottles were further soaked in 10% HNO3 for
48 hours and subsequently rinsed with distilled water.
All the chemical reagents used were of analytical
grade.

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2.3. Adsorption procedure
All experiments were carried out using a 200
mL solution of 50 mg.L-1 of the metal ions solution
mixture in contact with 1.5 g of the charcoal in a 250
mL beaker. Each experimental solution was
appropriately adjusted to the desired pH value using
buffer solutions. Mixing was done by means of a
mechanical stirrer at an average rate of three cycles
per second for 20 minutes in a thermostated water
bath. The charcoal was filtered from the solution using
Whatman No. 42 filter paper. This process was
repeated for similar solutions at 40, 60, 80, 100, 120,
140, 160 and 180 minutes respectively.
2.3.1. Effect of pH
The effect of pH was investigated by
conducting the experiments at different pH values (3,
5, 7, and 9) at 30 and 40oC to obtain the pH of
maximum adsorption. Also, the effects of contact time
and temperature were studied at the pH of maximum
adsorption at different temperatures (10, 20, 30, 40
and 50oC) for time intervals of 20 minutes within the
range of 0 to 180 minutes within which equilibrium
had been attained.
2.3.2. Quantitative Estimation of Heavy Metals in the
Solutions
The initial and residual metal ion
concentrations in the supernatant solution were
determined using Flame Atomic Absorption
Spectrophotometer, FAAS (Buck Model 205 FAAS,
East Norwalk, USA). The amount of metal ions
adsorbed for each parameter was determined by
difference between the initial metal ion concentration
and the concentration of metal ions in the supernatant
solutions. Each determination was done in triplicate
and the mean value for each experiment was
calculated and presented. All studies were conducted
in triplicates and the mean values determined. A blank
experiment was conducted by analyzing doubly
distilled water to establish blank level.
2.3.3. Determination of Adsorption Capacities
The adsorption capacities, qe and qt, which were the
amounts of metal ions adsorbed by the adsorbent
(mg.g-1) when equilibrium was attained at time, t,
were respectively calculated by the equations:

qe 

Co  Ce 

V
M
C  Ct V
qt  o
M

(1)
(2)

where Co = initial concentration of metal ion in
solution (mg.L-1);
Ce = the final concentration of metal ion in
solution at equilibrium (mg.L-1);
Ct = the final concentration of metal ion in
solution at time t (mg.L-1);
M = the mass of adsorbent (g); and
V = the volume of solution (L).
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The results were also expressed as the percentage removal
favoured the adsorption process, it showed that
(% Rp) of the metal ions from solution by the plantain peel
mobility of the metal ions increased with an increase
charcoal using the equation:
in temperature thus making the metal ions to interact
more with the surface of the adsorbent [27].
C C

%R p 

o

e

Co

 100

(3)
where Co and Ce are the initial and equilibrium
concentrations of the adsorbed solute (mg L-1)
respectively.

III.

3. Results and Discussion

3.1. Effect of pH
The effects of pH on the adsorption of Pb2+
2+
and Cd are illustrated in Fig. 1. The adsorption
capacity increased as the pH of the solution increased
[21] but decreased after pH 5 for Pb2+ and after pH 7
for Cd2+. The maximum adsorption of Pb2+ occurred at
pH 5 with a percentage removal of 90.06 % and that
of Cd2+ occurred at pH 7 with a percentage removal of
92.39 %. The value obtained for Pb2+ is comparable to
the findings when sago waste [14], tea waste [22] and
Moringa oleifera bark [23] were used as adsorbents.
The value obtained and the trend for the effect of pH
on the adsorption of Cd2+ is comparable to, but higher,
in some cases, than that observed for the adsorption of
Cd2+ using other adsorbents [24-27]. At lower pH,
there might be high competition between the cations
and hydrogen ions in solution for the active sites on
the adsorbent [25, 28] and this might lead to a
decrease in the adsorption of Cd2+. However, as the
pH increases, there is a decrease in hydrogen ions and
there would be more available sites. As a result, there
is an increase in the adsorption of Pb2+ and Cd2+ from
the solution. This probably led to an increase in the
adsorption capacity as the pH increases. At pH > 8.0,
there would be precipitation of cadmium and lead
hydroxides [14, 25] and when the hydroxyl ions are in
excess in the synthetic wastewater, there would be
hydroxyl complexes of cadmium [25]. Hence, for this
process to be an adsorption process pH values of 5 and
7 were considered the optimum pH for Pb2+ and Cd2+
and these were used for further studies.
3.2. Effects of contact time and temperature
It was observed that the removal of Pb2+ and
2+
Cd increased as the contact time increased, and
equilibrium was reached after 100 min. The adsorption
was noticed to be fast initially and then became
slower. This can be attributed to the strong attractive
forces between the metal ions and the adsorbent [27].
As illustrated in Fig. 2, the relationship between the
percentage removal of Pb2+ and Cd2+ with time is both
linear and logarithmic (curve). This can be said to be
as a result of solute - solute competition, the solute surface interaction, hydration capacity, pH and
availability of sites [28].
It was observed that increased temperature
resulted in increased adsorption of the metals from the
synthetic wastewater. Since increase in temperature
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3.3. Adsorption kinetics
The kinetic study of the process of adsorption
determines the rate at which the contaminants are
removed from synthetic wastewaters. Numerous
kinetic models have been proposed which are capable
of describing the mechanism by which the adsorption
process takes place. In order to investigate the
adsorption kinetics of the metals, the experimental
data obtained were tested with the pseudo-first order,
pseudo-second order, intraparticle and Elovich models
to know the controlling mechanism. The equation used
is the pseudo-first order kinetic equation [29] stated as
follows:

dq
 k1 qe  qt 
dt
where qt and

(4)

q e (mg.g-1) are the amounts of metal ion

adsorbed at time t (min) and at equilibrium
respectively, and k1(min-1) is the rate constant of the
pseudo-first order kinetics. After integration by the
application of boundary conditions, t = 0 to t = t, and q
= 0 to q =

q e , the above equation becomes:

ln qe  qt   ln qe  k1t

A linear plot of

ln qe  qt 

(5)
against t should give a

slope of k1 and an intercept corresponding to

ln qe .

Linear plot of ln(qe - qt) against t were obtained, and
the calculated qe , k2, and R2 were determined and
presented in Table 1.
The pseudo-second order equation used [30]
can be written as:

dq
2
 k 2 qe  qt 
dt

(6)

where k2 (g mg-1min-1) is the rate constant of pseudosecond order equation. On integrating the equation by
applying boundary conditions, t = 0 to t = t and q = 0
to q = qt and on linearizing, it becomes:

t
1
t


2
qt k 2 qe
qe

qe

(7)

and k2 can be calculated from the slope and

intercept of a linear plot of t/qt against t. Straight-line
plots of t/qt against t at different temperatures for the
adsorption of Pb2+ and Cd2+ are shown in Fig. 3.
The adsorption data were processed using the
intraparticle diffusion which is given as:
1
2

qt  k p t  I

(8)

where kp and I are the intraparticle diffusion rate
constant (mg.g-1min-1/2) and intercept (mg.g-1)
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respectively. The value of I explains the thickness of
the boundary layer, and the larger the value of I, the
thicker the boundary layer. A plot of the amount
adsorbed against the square root of time would be
linear if intraparticle diffusion takes place in the
adsorption process and it is the rate controlling step if
the line passes through the origin [31].
The Elovich model is an equation that is
based on adsorption capacity of adsorbents [13, 32]
and it is generally written as:

dqt
  exp qt 
dt

(9)

where α is the initial adsorption rate (mg.g-1min-1) and
β is the desorption constant (g.mg-1). The equation was
simplified [33] by assuming αβt >> t and by applying
boundary conditions, t = 0 to t = t and q = 0 to q = q t,
to become

1
1
qt  ln    ln t 



(10)

Thus, if the adsorption by the adsorbent fits the
Elovich model, a plot of qt against ln (t) would give a
straight line with a slope and an intercept that
correspond to (1/β) and 1 /  ln  , respectively.
The linearity of the plots for pseudo-second
order (Fig. 3) and the values of the coefficient of
correlation, which were greater than 0.960, showed
that Pb2+ and Cd2+ removal kinetics fitted very well
into the pseudo-second order kinetics (Table 1). It can
be seen from Table 1 that the values of the
experimental qe were in agreement with the calculated
qe values obtained from the pseudo-second order
linear plots while the R2 values showed that the
pseudo-first order, intraparticle diffusion and Elovich
models were not significantly involved in the
adsorption of the metals.



  

3.4. Adsorption isotherms
In this study, the Langmuir, Freundlich and
Tempkin equations were used to estimate the
adsorption data. Langmuir adsorption isotherm
assumes a monolayer adsorption with a uniform
energy on an adsorbent surface [34]. It is given as:

QK C
qe  0 L e
1  K L Ce
where

qe

(11)

is the amount of heavy metal adsorbed on

the adsorbent (mg.g-1),
-1

Ce

is the final concentration

of metal (mg.L ) in the solution, Q0 is the maximum
possible amount of metallic ion adsorbed per unit
weight of adsorbent (mg.g-1) and KL is an equilibrium
constant related to the affinity of the binding sites for
the metals (L.mg-1). The equation can be rearranged
linearly as follows:

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Ce
C
1

 e
qe K LQ0 Q0
(12)
The Langmuir isotherm was used to test the
experimental data for the removal of both metals using
plantain peel charcoal by plotting Ce/qe against Ce
(Fig. 4 and Fig. 5), and the values of Q0, kL and R2
were determined and are presented in Table 2.
The Freundlich model assumes that there is a
heterogeneous surface with a distribution of heat of
adsorption that is not uniform over the surface of the
adsorbent. The Freundlich adsorption isotherm is
mathematically expressed as:

qe  k F Ce

1/ n

(13)
where

qe

is the amount of metal adsorbed on the

adsorbent (mg g-1),

Ce

is the final concentration of

metal (mg.L-1) in the solution, k F is an empirical
constant that provides an insight into the adsorption
capacity of the adsorbent (L.g-1), and 1/n is an
empirical constant that provides an indication of the
intensity of adsorption.
Equation [13] can be linearized as follows:

1
log qe  log k F  log Ce
n
(14)
Linear plots showing the Freundlich isotherm for the
adsorption of Pb2+ and Cd2+ were obtained by plotting
log qe versus log Ce. The values of kF, 1/n and R2 were
obtained and are given in Table 2.
Tempkin isotherm assumes that the fall in the
heat of sorption is linear rather than logarithmic. It
contains a factor that describes the interactions
between the adsorbent and the adsorbates. The
Tempkin isotherm is given as follows:

qe 

RT
ln kT Ce
b

(15)

This can be linearized as

qe  B1 ln kT  B1 ln Ce
where B1 

(16)

RT
b

kT is the equilibrium binding constant (L.mg-1) which
corresponds to the maximum binding energy. R is the
gas constant (8.314J.mol-1K-1), T is the absolute
temperature (K) and B1 is related to heat of adsorption
(mg.g-1). The plot of qe versus ln Ce gave straight-line
plots. The values of kT, B1 and R2 were calculated and
are presented in Table 2. The values of R2 (greater than
0.960) showed that the adsorption of Pb2+ and Cd2+ on
the surface of plantain peel charcoal can be described
with the Langmuir, Freundlich and Tempkin isotherms
with the best fit obtained from Langmuir isotherm.
This implies that the adsorption process occurs at well
1964 | P a g e

defined sites that are homogenous and there was, most
likely, a monolayer adsorption onto the surface of the
plantain peel charcoal.
3.5. Thermodynamics of adsorption
The practical applicability of an adsorption
process is indicated by thermodynamic parameters
such as changes in Gibbs free energy (ΔG), enthalpy
(ΔH) and entropy (ΔS). The values of these
parameters would determine whether the adsorption
process is spontaneous or not, endothermic or
exothermic and also determine the degree of
disorderliness. The parameters can be determined
from the following equations [21,35]:
G  H  TS
(17)

CA
(18)
CS
S H
(Van’t Hoff Equation)
ln K C 

R RT

KC 

(19)
where Kc is the equilibrium constant, CA is the amount
of solute adsorbed and CS is the equilibrium
concentration of the solute in the solution.
The thermodynamic parameters were
determined by plotting ln Kc versus 1/T. The values of
ΔS and ΔH were calculated from the intercept and
slope and are presented in Table 3. At all temperatures
under which the adsorption was studied, ΔH was
found to be positive and this means that the adsorption
process was endothermic. This is supported by the
increase in the amount adsorbed as the temperature
increased. The positive values of ΔS suggest that there
was an increased randomness on the solid - solution
interface during the adsorption of the metals on the
surface of the plantain peel charcoal. The negative
values of ΔG meant that the adsorption process was
spontaneous and the decreased values of ΔG as the
temperature increased implied that the process was
more spontaneous at higher temperatures [21]. Free
energy changes for physisorption reaction are usually
between -20 to 0 kJ.mol-1 while the values for
chemisorption reaction are between -80 to -400
kJ.mol-1 [36]. Thus, the values of ΔG obtained in the
present study confirmed the adsorption process to be
of the physisorption type.

and Tempkin isotherms, but it was the Langmuir
isotherm that most fittingly described the data. The
thermodynamic studies showed that the adsorption
process was endothermic in nature and this was
confirmed by the increase in the adsorption capacity
with rise in temperature. Also, the adsorption process
in each case was a spontaneous physisorption reaction.
The results obtained showed that plantain peel
charcoal has the potential to effectively reduce the
levels of heavy metal ions such as Pb2+ and Cd2+ from
synthetic wastewaters and industrial effluents. Hence,
it could replace the very expensive adsorbents in water
and environmental engineering designs for industrial
effluent treatments especially in the third world
countries.

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IV.

CONCLUSION

This study investigated the kinetics,
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T. Chirenje, L.Q. Ma, L. Lu, Retention of Cd,
Cu, Pb and Zn by Wood Ash, Lime and Fume
Dust, Water, Air, and Soil Pollution 171,
2005, 301-314.
Hanggara, S., Nguyen, D.B., Pham, X.T.:
Removal of Cd (II) from synthetic
wastewater by Bruguiera Sexangula Poir
Tannin-based absorbent. Journal of Applied
Sciences in Environmental Sanitation 3(2),
E1-E10 (2008).
M. Malakootian, J. Nouri, and H. Hossaini,
Removal of heavy metals from paint
industry's wastewater using Leca as an
available adsorbent, Int. J. Environ. Sci.
Tech. 6 (2), 2009, 183-190.
O. Hamdaoui, and M. Chiha, Removal of
Methylene Blue from synthetic wastewaters
by wheat bran, Acta Chim. Slov. 54, 2007,
407-418.
I.A.Oke, S. Lukman, O.A. Obijole, N.B.
Omodara, E.A. Adekunbi, and M.A. Asani,
Removal of Pb2+ from synthetic wastewaters
using a common household waste (used
batteries): Kinetics models, Proceedings of
Faculty of Technology, Obafemi Awolowo
University, Ile-Ife 3, 2011, 153-163.
S.Z. Lagergren, Theorie der sogenannten
adsorption geloster stoffe, K. Sven.
Vetenskapsakad. Handl. 24, 1898, 1–39.
Y.S. Ho, and G. Mackay, Pseudo-second
order model for sorption processes, Process.
Biochem. 34(5), 1999, 451-465.
S. Senthikumaar, P. Kalaamani, K. Porkodi,
P.R. Varadarajan, and C.V. Subburaam,
Adsorption of dissolved reactive red dye
from aqueous phase onto activated carbon
prepared from agricultural waste, Bioresour.
Technol. 97(14), 2006, 1618–1625.
S.H. Chien, and W.R. Clayton, Application of
Elovich equation to the kinetics of phosphate
release and sorption on soils, Soil Sci. Soc.
Am. J. 44, 1980, 265-268.
S. Rajeshwari, R. Venckatesh, and G.
Sangeetha, Preparation and characterization
of activated carbons from Parthenium
biomass by physical and chemical activation
techniques, E-Journal of Chemistry 7(4),
2010, 1314-1319.
I. Langmuir, The constitution and
fundamental properties of solids and liquids.
Part. I: Solids, Journal of the American
Chemical Society 38(11), 1916, 2221-2295.
A. Ozcan, E.M. Oncu, and A.S. Ozcan,
Kinetics, isotherm and thermodynamic
studies of adsorption of Acid Blue 193 from
synthetic wastewaters onto natural sepiolite,
Colloid. Surf. A. Physicochem. Eng. Aspects
277, 2006, 90-97.

1966 | P a g e

M.J. Jaycock, and G.D. Parfitt, Chemistry of
Interfaces (Ellis Horwood Ltd., Chichester,
U.K., 1981).
o

30 C
o
40 C

3

4

5

6
pH

7

8

-1

6.4
6.2
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6

Amount adsorbed (mg.g )

-1

Amount adsorbed (mg.g )

[36]

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9

6.2
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6

o

30 C
o
40 C

3

4

5

6 7
pH

Pb2+

8

9

Cd2+

Percentage removal (%)

percentage removal (%)

Figure 1: Effect of pH on the Adsorption of Pb 2+ and Cd2+ on Plantain Peel Charcoal

100
80
60
o

10 C
o
20 C
o
30 C
o
40 C

40
20
0

o

50 C

100
80
o

10 C
o
20 C
o
30 C
o
40 C
o
50 C

60
40
20
0

-20 0 20 40 60 80 100120140160180200

-20 0 20 40 60 80 100120140160180200

time (min)

time (min)

Pb2+

Cd2+

Figure 2: Effect of Time and Temperature on the Adsorption of Pb 2+ and Cd2+ on Plantain Peel Charcoal

20
10

50

100
Time (min)

Pb2+

150

-1

-1

t / qt (min.g.mg )

30

t / qt (min.g.mg )

o

10 C
o
20 C
o
30 C
o
40 C
o
50 C

40

28
26
24
22
20
18
16
14
12
10
8
6
4
2

o

10 C
o
20 C
o
30 C
o
40 C
o
50 C

50

100

150

Time (min)

Cd2+

Figure 3: Pseudo-second Order Adsorption Kinetics of Pb2+ and Cd2+ Removal by Plantain Peel Charcoal

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1967 | P a g e


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o

10 C
o

20 C

6
Ce / qe(g.L-1)

C e / qe (g.L

-1

)

3.2

5

4

3.0
2.8
2.6

18

20

22

13

-1
Ce (mg.L )

14
-1
Ce (mg.L )

15

o

40 C

o

30 C

1.5
C e / qe (g.L-1)

Ce / qe (g.L-1)

3.0
2.8
2.6
2.4

1.0

0.5

2.2
12

13

4

14

Ce (mg.L-1)

6
-1
Ce (mg.L )

8

Ce / qe (g.L-1)

50oC

0.6

0.4

0.2
2

3
Ce (mg.L-1)

4

Figure 4: Langmuir Isotherms for Pb2+ Removal by Plantain Peel Charcoal

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1968 | P a g e


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o

20 C

o

10 C
2.5

Ce / qe (g.L-1)

-1
Ce / qe (g.L )

2.0
2.0

1.5

1.5

1.0

1.0
6

8

10
Ce (mg.L-1)

4

12

6

8
Ce (mg.L-1)

10

12

o

o

40 C

1.5
Ce / qe (g.L-1)

Ce / qe (g.L-1)

30 C

1.0

4

6
8
Ce (mg.L-1)

2

1

5

10
Ce (mg.L-1)

o

50 C

Ce / qe (g.L-1)

1.5

1.0

0.5

2

4
6
Ce (mg.L-1)

8

Figure 5: Langmuir Isotherms for Cd2+ Removal by Plantain Peel Charcoal

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1969 | P a g e


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Table 1: Kinetic Constants for Pb2+ Adsorption on Plantain Peel Charcoal at Different Temperatures (T (oC); (qe) exp (mg.g-1); (qe) cal (mg.g-1);
k1 (min-1); k2 (g.mg-1.min-1); kp (mg.g-1.min-1/2); α (mg.g-1.min-1); and β (g.mg-1))
Pb2+

(qₑ) exp.

Pseudo-first Order
(qₑ)
calc.
k₁

R²

Pseudo-second Order
(qₑ)
calc.
k₂
R²

Intraparticle Diffusion

Elovich Model

I

kp

R²

α

β

R²

4.3870

1.6120

0.0110

0.5732

4.4283

0.0453

0.9975

3.3064

0.0841

0.6924

318.0316497

2.7180

0.7789

4.9810

1.0045

0.0188

0.6807

4.9831

0.1005

0.9996

4.5056

0.0347

0.7453

2.7166E+11

6.7485

0.7894

5.1430

0.3580

0.0151

0.0117

5.0335

95.1079

0.9995

4.7860

0.0231

0.2508

1.14433E+16

8.6987

0.4210

6.2290

1.1427

0.0221

0.3677

6.2625

0.0817

0.9995

5.4052

0.0680

0.6083

1117053.774

3.2215

0.7607

6.4740

0.8464

0.0357

0.3003

6.5479

0.0784

0.9999

5.9056

0.0473

0.8258

84664117007

4.9015

0.8976

Cd2+
6.0050

1.9567

0.0483

0.6432

6.2570

0.0259

0.9987

4.5061

0.1278

0.7622

211.2068

1.8080

0.8356

6.1190

2.6072

0.0276

0.8834

6.3569

0.0216

0.9986

4.5976

0.1217

0.9015

515.1650

1.9668

0.9088

6.1400

1.6810

0.0258

0.9144

6.3040

0.0316

0.9994

5.0347

0.0885

0.9298

35815.2586

2.7023

0.9401

6.1600

3.8145

0.0518

0.6992

6.4616

0.0209

0.9990

4.4268

0.1464

0.8449

78.3989

1.5846

0.9159

6.5380

5.5849

0.0546

0.8055

6.7986

0.0238

0.9990

5.0757

0.1217

0.8729

1190.9028

1.9491

0.8995

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Table 2. Isothermal Constants for Pb2+ and Cd2+ Adsorption on Plantain Peel Charcoal at Different Temperatures
(Q0 (mg.g-1); KL (L.mg-1); KF (L.g-1); KT (L.mg-1); and B1 (mg.g-1))
Pb2+
Langmuir

Freundlich

Tempkin

T

Kₑ

Q₀

R²

KF

1/n

R²

KT

B1

R²

10

-0.1248

2.3619

0.9976

29.4965

-0.6694

0.9958

0.0112

-2.6621

0.9984

20

-0.2590

3.4695

0.9996

13.2306

-0.3846

0.9987

0.0053

-1.8503

0.9993

30

-0.2952

3.6369

0.9991

12.1143

-0.3508

0.9966

0.0044

-1.7288

0.9981

40

-1.6537

5.1637

0.9989

7.2482

-0.1235

0.9785

0.0001

-0.7262

0.9830

50

-7.5986

5.9280

0.9998

6.6190

-0.0545

0.9835

0.0000

-0.3429

0.9854

Cd2+
10

-0.7956

4.5286

0.9987

8.2120

-0.1938

0.9879

0.0007

-1.0680

0.9916

20

-1.0165

4.7831

0.9980

7.7625

-0.1632

0.9790

0.0003

-0.9247

0.9847

30

-1.3310

5.0462

0.9987

7.4574

-0.1385

0.9821

0.0001

-0.8052

0.9865

40

-1.0052

4.6685

0.9970

7.7300

-0.1663

0.9695

0.0003

-0.9326

0.9780

50

-5.7019

5.5853

0.9986

6.5423

-0.0646

0.9467

0.0000

-0.3957

0.9546

Table 3: Thermodynamic Parameters for Pb2+ and Cd2+ Adsorption on Plantain Peel Charcoal (T/K; ΔS/kJ mol1.K-1; ΔH/kJ.mol-1 ; and ΔG/kJ.mol-1)
ΔG(kJ.mol-1)
ΔS (J.mol-1.K-1)

ΔH (kJ.mol-1)

283K

293K

303K

313K

323K

2+

0.1965

54.8191

-0.7875

-2.7524

-4.7173

-6.6822

-8.6471

Cd2+

0.1092

26.2154

-4.6764

-5.7680

-6.8596

-7.9512

-9.0428

Metals
Pb

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