IRJET-REMOVAL OF LEAD (II) FROM AQUEOUS SOLUTION USING NATURAL AND ACTIVATED RICE HUSK
This paper presents the experimental results on the use of rice husk in the removal of lead (II) from the aqueous solution. In this study, rice husk is used in four different forms, namely, natural un-activated form (RH), rice husk ash acquired after carbonizing rice husk without pretreatment (RHA), rice husk pretreated with phosphoric acid (PRH) and acetic acid (ARH) separately and then followed by carbonization. Through batch adsorption studies the effect of various parameters such as pH of the aqueous medium, contact time of agitation, adsorbate concentration, and adsorbent dosage were examined. The results obtained show that the adsorption of the metal ion is pH, contact time, adsorbent dosage and adsorbate concentration dependent. The maximum percentage removal of lead (II) ions is 93.36%, 94.8%, 96.72% and 99.35% with adsorbents RH, RHA, PRH and ARH, respectively. It is found that RH, RHA and PRH followed Freundlich isotherm model whereas ARH followed Langmuir isotherm model. Further, both RH and RHA follow pseudo-second order kinetics.
Content
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 02 Issue: 03 | June-2015
p-ISSN: 2395-0072
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REMOVAL OF LEAD (II) FROM AQUEOUS SOLUTION USING NATURAL
AND ACTIVATED RICE HUSK
Rajkumar V. Raikar 1, Sefra Correa 2, Praveen Ghorpade 3
1Professor,
Department of Civil Engineering, KLE Dr. MSSCET, Belgaum, Karnataka, India
Tech. Scholar, Department of Civil Engineering, KLE Dr. MSSCET, Belgaum, Karnataka, India
3Assistant Professor, Department of Civil Engineering, KLE Dr. MSSCET, Belgaum, Karnataka, India,
2M.
Abstract
This paper presents the experimental results on the use of rice husk in the removal of lead (II) from the aqueous solution. In
this study, rice husk is used in four different forms, namely, natural un-activated form (RH), rice husk ash acquired after
carbonizing rice husk without pretreatment (RHA), rice husk pretreated with phosphoric acid (PRH) and acetic acid (ARH)
separately and then followed by carbonization. Through batch adsorption studies the effect of various parameters such as pH
of the aqueous medium, contact time of agitation, adsorbate concentration, and adsorbent dosage were examined. The results
obtained show that the adsorption of the metal ion is pH, contact time, adsorbent dosage and adsorbate concentration
dependent. The maximum percentage removal of lead (II) ions is 93.36%, 94.8%, 96.72% and 99.35% with adsorbents RH,
RHA, PRH and ARH, respectively. It is found that RH, RHA and PRH followed Freundlich isotherm model whereas ARH followed
Langmuir isotherm model. Further, both RH and RHA follow pseudo-second order kinetics.
Key Words: Adsorption, Lead, Natural Adsorbents, Rice husk, Isotherms, Reaction kinetics …
--------------------------------------------------------------------***---------------------------------------------------------------------1. INTRODUCTION
Amongst the present day’s environmental issues, water
scarcity and water pollution rank equal to climate
change [1]. The industrial effluents have serious concern
as they contain heavy metals like iron (Fe), lead (Pb),
zinc (Zn), copper (Cu) etc., which are hazardous to
human health. Heavy metals being non-biodegradable
cause various diseases and disorders through
bioaccumulation. Many methods have been developed to
remove heavy metals from wastewater, such as
adsorption,
chemical
oxidation
/
reduction,
precipitation, ion exchange, electrochemical processes,
membrane filtration and reverse osmosis. These
methods tend to be expensive and often impracticable in
remote regions where heavy metal contaminants
originate from geogenic sources. On the contrary,
adsorption technique has proved to be an efficient and
cost effective among all the methods [2, 3]. Demirbas
presented a review on heavy metal adsorption onto
agro-based waste materials [4].
Lead as Pb (II) is released into the environment from
various industrial processes: industries engaged in lead
acid batteries, pulp and paper, petrochemicals,
refineries, printing, pigments, photographic materials,
explosive manufacturing, ceramics, glass, paint, oil,
metal, phosphate fertilizer, electronics, wood production
and also combustion of fossil fuel, forest fires, mining
activity, automobile emissions, sewage wastewater, sea
spray and many more [5]. Hashem [6] studied the
© 2015, IRJET.NET- All Rights Reserved
sorption of Pb (II) using okra wastes, Singh et al. [7] used
maize bran in the adsorption of lead using maize bran,
while El-Ashtoukhy et al. [8] employed pomegranate
peel as a adsorbent in the removal of lead (II) and copper
(II) from aqueous solution. Yoshita et al. [9] carried out
the study on the removal of lead by spent tea leaf residue
after instant tea extraction. Imamoglu and Tekir [10]
have studied removal of copper (II) and lead (II) ions
from aqueous solution by adsorption on activated
carbon from a new precursor hazelnut husks. The
thermodynamic study on the adsorption of Pb (II) and
Zn (II) from aqueous solution by human hair was done
by Ekop and Eddy [11]. Adie et al. [12] carried out the
comparative analysis of the adsorption of Pb (II) and Cd
(II) in wastewater using Borrassus aethiopium and Cocos
nucifera. The adsorption of lead from aqueous solution
onto untreated orange barks was studied by Azouaou et
al. [13]. Wahi et al. [14] studied the removal of mercury,
lead and copper from aqueous solution by activated
carbon of palm oil empty fruit bunch. Chairgulprasert et
al. [15] studied phytoremediation of synthetic
wastewater by adsorption of lead and zinc onto Alpinia
galangal Willd. However, the studies on the use of
activated rice husk in the removal of lead (II) are very
few. Hence, the present study emphasizes on the use
activated rice husk in the removal of lead (II) cations
from aqueous solution. The study also include fitting of
isotherms and reaction kinetics.
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2. MATERIALS AND METHODOLOGY
2.1 Materials
Lead nitrate was used for the preparation of stock Pb (II)
solution in distilled water. To control the pH value
during the experiment, hydrochloric acid and/or sodium
hydroxide solutions were used, while phosphoric acid
(H3PO4) (88%), acetic acid (CH3COOH) (99.8%) were
used for pretreatment. The equipments used for the
study are: digital pH meter, Atomic Absorption
Spectrophotometer (AAS), Scanning Electron Microscope
(SEM), rotary shaker, muffle furnace, oven, sieves and
weighing machine.
2.2 Preparation of Adsorbents
Locally available rice husk was washed with distilled
water, dried in an oven at 105oC for 24 hours to remove
the moisture content [16], ground and sieved to particle
size of < 150 µm. The powdered rice husk was used in
four forms: first one was used in its natural form and
named as “Rice husk” (RH), second form named “Rice
husk ash” (RHA) was obtained by carbonizing the
powdered rice husk in muffle furnace at 800oC for half
hour and then cooling in a dissicator, the third and
fourth forms were activated respectively with
phosphoric acid and acetic acid. The third was soaked for
36 hours in a solution of 0.1N phosphoric acid and 0.5N
acetic acid separately at an impregnation percentage of
20%, then carbonized at 650oC for 90 minutes [17]. It
was rinsed several times until the pH of the drained
water was in the range of pH 6-7 followed by oven
drying for 3 hours at 100oC to remove the moisture
content. They were named as Phosphoric acid treated
rice husk (PRH), and Acetic acid treated rice husk (ARH).
The physical characteristics of all adsorbents were
measured using standard procedures. The data are
presented in Table 1.
Table 1: Characteristics of adsorbents
Adsorbent
pH
RH
RHA
PRH
ARH
5.26
5.59
2.30
4.12
Bulk density
(gm/cc)
0.5604
0.5011
0.6105
0.5890
Particle density
(gm/cc)
1.0428
1.0345
1.0495
1.0466
2.3 Adsorption experiments
Batch adsorption experiments were carried out at room
temperature by shaking a series of beakers containing
the desired dose of adsorbent in a known concentration
of lead solution. Samples of lead solution were
withdrawn at different time intervals, filtered and the
filtrate was analyzed for the trace of heavy metal
content. Experiments were carried out at optimum pH
values. The initial pH of the solution was adjusted to the
© 2015, IRJET.NET- All Rights Reserved
desired value either by hydrochloric acid or sodium
hydroxide solution. The percent removal of lead from
solution was calculated using Eqs. (1).
Percent removal
(Co Ci )
100
Co
(1)
where Co is initial concentration of lead metal, Ci is final
concentration of lead metal. Isotherm studies were
conducted by varying the initial concentration of lead
solution from 10 to 50 mg/L. A known amount of
different adsorbents was then added into solutions
followed by agitation at 120 rpm.
3. RESULTS AND DISCUSSIONS
3.1 Determination of Optimum pH
To study the effect of pH on adsorption of lead (II) ions,
the batch equilibrium studies at pH values in the range of
3-7 were carried out. The results are furnished in Table 2
and the variation is presented in Fig 1. From Table 2 it
can be observed that the percentage removal of lead is
maximum in the pH range of 4-5 with RH and RHA.
However, with PRH, the pH range is 5-6 and ARH it is in
the range of 6-7. Therefore, the optimum pH range is
chosen as 4-5 for RH and RHA, which is same as stated
by Vieira et al. [3]. However, for PRH and ARH, the pH
range of 5-6 was chosen. According to Issabayeva et al.
[18] the speciation profiles of single lead species at a
total concentration of 10 mg/L is in Pb2+. The main
species in the pH range 3-5 were Pb2+, PbNO3+ and
aqueous Pb(NO3)2; their concentrations did not change
until pH = 6. The formation of solid (precipitation)
Pb(OH)2 started at pH = 6.3 and that of other soluble
hydroxides namely PbOH+, aq Pb(OH)2, and PbOH3occurred after pH = 7. Therefore, a pH range of 3-7 was
used during the analysis. The optimum value of pH
depends on the adsorbents characteristics. Table 3 gives
the optimum value of pH reported by various
investigators with different adsorbents used in the
removal of lead.
Table 2: Effect of pH on percentage removal of lead
using different adsorbents
pH
3
4
5
6
7
Percentage removal of lead with adsorbent
RH
RHA
PRH
ARH
78.12
91.24
86.14
82
79.34
92.19
93.76
91.56
79.28
92.16
94.99
93.77
77.42
88.74
94.83
94.99
75
88.53
94.32
96.43
Table 3: Optimum pH value for different adsorbents
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Adsorbent
Okra waste
Maize bran
Pomegranate
peel
Hazelnut husks
Orange barks
Activated
carbon of palm
oil empty fruit
bunch
Alpina galangal
willd
RH and RHA
PRH and ARH
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pH
range
4-6
3.2-8
Optimum
pH
5
6.5
4.5-9.4
5.6-7.6
1-4.6
6.7-7
-
4.5
Wahi et al. [14]
2-7
6
Chairgulprasert et
al. [15]
3-7
3-7
4-5
5-6
Present study
Authors
Hashem [6]
Singh et al. [7]
El-Ashtoukhey et al.
[8]
Imamoglu et al. [10]
Azouaou et al. [13]
Fig. 1 Effect of pH on the percentage removal of lead
with different adsorbents
3.2 Effect of varying lead concentration
(b)
Fig. 2 Variation of adsorption efficiency with initial
lead concentration using (a) RH and RHA and (b) PRH
and ARH
The removal of lead is dependent on the initial lead
concentration. Figs. 2 (a) and (b) show the effect of
initial lead concentration on the percent removal of lead
ions, respectively. From Fig. 2 (a) it is observed that, for
RH the percentage removal increased drastically from
85.16% to 93.36% with an increase in initial lead
concentration from 10 mg/L to 30 mg/L and thereafter it
decreased sharply, while for RHA the percentage
removal increase from 93.3% with an initial lead
concentration of 10 mg/L to 94.8% at 20 mg/L.
However, from Fig. 2 (b) it can be inferred that, the
percentage removal of lead with adsorbent PRH
decreases from 85.84% to 81.2% when initial lead
concentration increased from 10 mg/L to 30 mg/L and
thereafter the efficiency gradually increased. For ARH
the percentage removal decreases steeply from 94.89%
with initial concentration of lead at 10 mg/L to 80.7 %
with initial concentration of lead at 50 mg/L. Similar
results were also observed by Wong et al. [19] for
tartaric acid treated rice husk. This is because, at low
metal ion/adsorbent ratios, metal ion adsorption
involves higher energy sites giving higher adsorption
efficiency. On the other hand, as the metal ion/adsorbent
ratio increases, the higher energy sites are saturated and
adsorption begins on lower energy sites, resulting in
decreases in the adsorption efficiency. The comparative
study on the maximum percentage removal of lead at
optimum adsorbate concentration investigated by
various researchers is furnished in Table 4.
Table 4: Maximum percentage removal of lead at
optimum adsorbate concentration
(a)
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Range of
Initial lead
initial lead
%
concentratio
Adsorbent concentratio removal
n of
Authors
n (mg/L)
of lead adsorbate
(mg/L)
Okra waste
25-100
99
100
Hashen [6]
Maize bran
100-150
96.8
100
Singh et al.
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Pomegranat
e peel
Hazelnut
husks
Alpina
galangal
willd
Tartaric acid
treated rice
husk
RH
RHA
PRH
ARH
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[7]
ElAshtoukhey
et al. [8]
Imamoglu et
al. [10]
10-50
95-100
10
5-200
97.2
5-30
95.2
50
Chairgulpras
ert et al. [15]
400-800
90-100
400
Wong et al.
[19]
10-50
10-50
10-50
10-50
93.36
94.8
85.84
94.89
30
20
10
10
Present study
(b)
3.3 Effect of contact time
The variation between adsorption efficiency in terms of
percentage removal of lead and contact time is shown in
Fig. 3. From Fig. 3 (a) it is observed that for RH, the lead
removal percentage is least of 74.64% at 60 minutes of
contact time and highest of 76.69% at contact period of
120 minutes, while for RHA the percentage removal
increased from 87.09% at 60 minutes contact time to
91.67% at 150 minutes of contact time. Similar value of
equilibrium time was also observed by Jameel and
Hussain [20] for RHA. From Fig. 3 (b) it is observed that
the percentage removal of lead with PRH increased with
an increase in contact time. At 60 minutes of reaction
time, 88.79% of lead removal is observed, as the
adsorption reaction was allowed for 180 minutes more
lead removal efficiency of 92.2% is observed. For
adsorbent ARH, it increased from 92.22% at 60 minutes
contact time to 95.8% at 180 minutes contact time.
However, equilibrium will be achieved beyond 180
minutes. Table 5 presents the optimum agitation time
corresponding to maximum percentage removal of lead
as reported by earlier investigator. In general, the
optimum contact time is around 150 minutes.
Fig. 3 Variation of adsorption efficiency with varying
contact time using (a) RH and RHA (b) PRH and ARH
3.4 Effect of adsorbent dosage
Fig. 4 illustrates the variation of adsorption efficiency
with varying adsorbent dosage using different
adsorbents, which shows that the adsorption efficiency
increases with an increase in adsorbent dosage. As
presented in Fig. 4 (a), RH the adsorption efficiency
increases from 79.91% to 84.72% with adsorbent
dosage from 1 gm to 2 gm, while for RHA it increased
from 89.62% to 90.39% for adsorbent dosage from 1 gm
to 2 gm. Fig. 4 (b) represents the effect of PRH and ARH
adsorbent dosage on percentage removal of lead. It can
be observed from Fig. 4 (b) that the percentage removal
of lead with adsorbent PRH gradually increases from 1
gm to 3 gm and at 4 gm there is a sudden increase in
percentage removal of lead by 96.72%. However, with
ARH, there is increase in percentage removal of lead
between 1 gm to 2 gm and beyond 2 gm the percentage
removal of lead is minimal. For ARH, the results are
97.65% at 1 gm, 99.11% with 2 gm and highest at
99.35% with 4 gm. This is due to greater availability of
surface area or active sites. The comparative study on
the optimum dosage of adsorbents corresponding to
maximum percentage removal is given in Table 6. The
optimum dosage depends on type of adsorbent due to
their varying surface area.
Table 5: Maximum percentage removal at optimum
agitation time
Adsorbent
Pomegranat
e peel
(a)
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Hazelnut
husks
Alpina
galangal willd
Tartaric acid
treated rice
Range of
%
Optimum
agitation removal agitation
time (min) of lead time (min)
0-180
90-100
120
2-50
90-100
50-60
30-180
95.2
150
0-230
90-100
120
Author
ElAshtoukhey et
al. [8]
Imamoglu et
al. [10]
Chairgulpras
ert et al. [15]
Wong et al.
[19]
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Adsorbent
Range of
%
adsorbent
removal
dosage
of lead
(gm)
Pomegranate
2.5-12.5
peel
Spent tea leaf
0.5-2
Hazelnut
0.05-0.5
husks
Activated
Borrassus
0.5-2.5
aethiopium
seed shells
Activated
carbon of
palm oil
0.2-1
empty fruit
bunch
Alpina
0.5-2
galangal willd
RH
0.5-2
RHA
0.5-2
PRH
1-4
ARH
1-4
husk
Straws of
15-150
rice
Raw
silkworm
0-50 hours
chrysalides
Acid washed
silkworm
0-25 hours
chrysalides
Orange peel
activated
20-120
carbon
RH
60-180
RHA
60-180
PRH
60-180
ARH
60-180
Optimum
dosage of
adsorbent
(gm)
95
12.5
55.2
2
97.2
0.3
99.75
2.5
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Author
El-Ashtoukhey
et al. [8]
Yoshita et al. [9]
Imamoglu et al.
[10]
Adie et al. [12]
(b)
100
0.2
Wahi et al. [14]
95.2
0.5
Chairgulprasert
et al. [15]
90.39
84.72
96.72
99.35
2
2
4
4
Present study
92.5
90-105
4.68
25-50
Siddiqui et al.
[21]
Paulino et al.
[22]
4.27
25
100
60-120
76.69
91.67
92.2
95.8
120
150
180
180
(a)
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Bernard et al.
[23]
Present study
Fig. 4 Variation of adsorption efficiency with varying
adsorbent dosage using (a) RH and RHA (b) PRH and
ARH
Table 6: Maximum percentage removal at optimum
dosage of adsorbent
3.5 Adsorption isotherms
The equilibrium data for adsorption are usually
presented in the form of adsorption isotherms, which
gives the equilibrium relationship between the
concentration of the adsorbate held on the surface of a
adsorbent and the concentration (or partial pressure) of
the adsorbate in the fluid phase at a given temperature.
The concentration of the adsorbate on the surface of the
solid is expressed as the amount of the substance
adsorbed per unit mass of the adsorbent. In case of
solutions it is expressed as mass adsorbate per unit
volume of solution or in mass units such as ppm (mg/L)
[24]. Commonly used adsorption isotherms are
Freundlich and Langmuir isotherms. In the present
study, experimental data was fitted into the Freundlich
and Langmuir isotherm models.
Freundlich and
Langmuir isotherm plots of lead adsorption using RH,
RHA, PRH and ARH are as shown in Figs. 5 – 8,
respectively. The coefficients of regression R2 with
adsorbent RH are found to be respectively 0.875 and
0.832 for Freundlich and Langmuir isotherms. For RHA,
R2 values are 0.943 and 0.876 for Freundlich and
Langmuir isotherms. Similarly, with PRH, R2 values are
0.982 and 0.753 for Freundlich and Langmuir isotherms
and with ARH, R2 values are found to be 0.954 and 0.976
for Freundlich and Langmuir isotherms, respectively.
The regression coefficient for Freundlich isotherm is
greater than Langmuir isotherm and thus Freundlich
isotherm fits better with RH, RHA, and PRH than
Langmuir isotherm. In the case of ARH, Langmuir
isotherm is found to be the best fit isotherm. The
comparative results on the fitted isotherms using
Freundlich and Langmuir isotherm are presented in
Table 7.
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(b)
(a)
Fig. 6 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by RHA
(b)
Fig. 5 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by RH
(a)
(b)
(a)
Fig. 7 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by PRH
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to the pseudo-second order model than the pseudo-first
order model. Fig. 9 and Fig. 10 show the kinetic plots for
RH and RHA, respectively. In case of PRH and ARH,
equilibrium was found achieve beyond 180 minutes and
equilibrium point is unknown, hence, reaction kinetic
study has been applied only to RH and RHA.
(a)
(a)
(b)
Fig. 8 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by ARH
Adsorbent
RH
RHA
PRH
ARH
Table 7: Fitted isotherm parameters
(b)
Freundlich isotherm
N
k
R2
1.564 1.527 0.875
0.963 1.636 0.943
1.173 0.423 0.982
2.207 0.977
0.954
Fig. 9 (a) Pseudo-first order kinetic plot and (b) Pseudosecond order kinetic plot of RH
Langmuir isotherm
Qm
b
R2
1.412 8.636
0.832
1.492 -18.11 0.876
7.812 0.053
0.753
3.067 0.486 0.976
(a)
3.6 Reaction kinetics
Reaction kinetics also called chemical kinetics is used to
know the rates of chemical processes and laws for the
same. It includes the investigations on the influence of
different chemical processes on speed of chemical
reaction and yield information. It also helps in the
development of mathematical models of a chemical
reaction. Some of the laws used are zero-order, firstorder, second-order etc. To analyze the adsorption
kinetics of lead metal ions, the pseudo-first and pseudosecond order models were applied to data in the present
study. The determinant coefficient (square of correlation
coefficient) for the pseudo-second-order model was
0.998 for RH and 0.999 for RHA respectively, being
significantly higher than that for the pseudo-first-order
model presented in Table 8. It suggests that the lead
adsorption process of the RH and RHA is fitted very well
© 2015, IRJET.NET- All Rights Reserved
(a)
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through the carbonization of rice husk (RHA) the
moisture content decreases, changes in the physical and
chemical properties of rice husk improves adsorption
efficiency of RHA.
(a)
(a)
(b)
(b)
(c)
(c)
(d)
(d)
(e)
(e)
(b)
Fig. 10 (a) Pseudo-first order kinetic plot and (b)
pseudo-second order kinetic plot for RHA
R2
0.998
0.999
K2
0.049
0.337
Qe (cal)
0.815
0.929
Qe (exp)
0.766
0.916
R2
0.774
0.958
K1
0.025
0.0276
Qe
(cal)
0.378
0.238
Qe (exp)
Pseudo-second-order
0.766
Pseudo-first-order
0.916
RHA
RH
Adsorbent
Table 8: Reaction Kinetics
3.7 Surface morphology
According to Tarley and Arruda (2004), the material
(adsorbent) morphology may facilitate the adsorption of
metals in different parts of this material. Therefore,
based on morphology, as well as the fact that the highest
concentration of silica is present in the outer film of RH,
this material presents a morphological profile with the
potential to retain metal ions [6]. Fig. 11 shows a SEM
micrograph of a sample of RH and RHA obtained,
showing that RH is intact and has a smooth surface.
Through calcination the organics are decomposed and
the ash obtained may constitute of amorphous silica with
high porosity having potential application as ligand in
metals adsorbent, whereas RHA obtained, showing a
very porous tracery surface morphology, with a high
surface area. Similar results have been observed by
Madrid et al. [25]. RHA is silica rich which serves as a
good adsorbent. According to Vieira et al. [3], RH and
RHA are predominantly mesoporous materials and the
calcinations of RH caused an increase in the surface area,
the presence of –OH, Si–O–Si and Si–H groups on the
RHA surface were important for metal adsorption [6].
Hence, in this study, the maximum percentage removal
of lead is higher with RHA than that with RH. Further,
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Fig. 11 Scanning electron micrographs (SEM) for RH
(left picture) and RHA (right picture) at magnifications
of (a) (50x), (b) (100x), (c) (500x), (d) (1000x) and (e)
(5000x)
4. CONCLUSIONS
The experimental results on removal of lead (II) with unactivated and activated rice husk are presented in the
paper. Through chemical activation of the adsorbent, the
percentage removal efficiency of an adsorbent can be
increased. Hence, activated rice husk shows greater
efficiency than un-activated rice husk. Highest
percentage lead removal with adsorbent RH found is
93.36 % at pH 4-5, initial concentration of lead 30 mg/L,
Page 1684
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contact time of 60 minutes and adsorbent dosage of 1
gm. When RHA is used, the maximum percentage
removal is found as 94.8 % at pH 4-5, initial
concentration of lead 20 mg/L, contact time of 60
minutes, adsorbent dosage of 1 gm. However, with PRH,
the highest percentage removal of lead is 96.72 % at pH
5-6, initial concentration of lead 10mg/L, contact time of
60 minutes and adsorbent dosage of 4 gm. Similarly, for
ARH, the maximum lead removal is found to be 99.35%
at pH 5-6, initial concentration of lead solution 10 mg/L,
contact time of 60 minutes and adsorbent dosage of 4
gm. Rice husk, Rice husk ash and phosphoric acid treated
rice husk followed Freundlich isotherm model whereas
acetic acid treated rice husk followed Langmuir isotherm
model. Rice husk and rice husk ash follow pseudosecond order kinetics. From this study, it is inferred that
rice husk, an abundantly available agricultural waste can
be used as a low cost adsorbent. The higher adsorption
capacity is favored by higher number of active binding
sites, improved ion exchange properties and
enhancement of functional groups after chemical
treatment.
[8]
[9]
[10]
[11]
[12]
REFERENCES
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[2]
[3]
[4]
[5]
[6]
[7]
Foo, K. Y., and Hameed, B. H. “Utilization of Rice
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of the Colloidal Agricultural Waste”, Adv. Colloid
Interfac., vol. 152, pp. 39-47, 2009.
Liaoa, D., Zhengb, W., Li, X., Yangb, Q., Yueb, X.,
Guob, L., and Zengb, G., “Removal of Lead (II) from
Aqueous Solutions using Carbonate Hydroxyapatite
extracted from Egg Shell Waste”, Journal of
Hazardous Material, vol. 177, pp. 126–130, 2010.
Vieira, M. G. A., de Almeida Neto, A. F., Carlos da
Silva, M. G., Nóbrega, C. C., and Melo Filho, A. A.,
“Characterization and Use of In Natura and Calcined
Rice Husks for Biosorption of Heavy Metals Ions
from Aqueous Effluents”, Brazilian Journal of
Chemical Engineering, Vol. 29 (3), pp. 619 – 633,
2012.
Demirbas, A., “Heavy Metal Adsorption onto AgroBased Waste Materials: A review”, Journal of
Hazardous Materials, vol. 157, pp. 220-229, 2008.
Kumar, P. S., Vincent, C., Kirthika, K., and Kumar, K.
S., “Kinetics and Equilibrium Studies of Lead (II)
Ion Removal from Aqueous Solutions by Use of
Nano-Silversol-Coated Activated Carbon”, Brazilian
Journal of Chemical Engineering., vol. 27 (2), pp.
339-346, 2010.
Hashem, M. A., “Adsorption of Lead Ions from
Aqueous Solution by Okra Wastes”, International
Journal of Physical Science, vol. 2 (7), pp. 178-184,
2007.
Singh, K. K., Talat, M., and Hasan, S. H., “Removal of
Lead from Aqueous Solutions by Agricultural Waste
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[13]
[14]
[15]
[16]
[17]
[18]
Maize Bran”, Bioresource Technology, vol. 97, pp.
2124-2130, 2006.
El-Ashtoukhy, E.-S. Z., Amin, N. K., and Abdelwahab,
O., “Removal of Lead (II) and Copper(II) from
Aqueous Solution using Pomegranate Peel as a
New Adsorbent”, Desalination, vol. 223, pp. 162173, 2008,.
Yoshita, A. Lu, J. L. Ye, J. H. and Liang, Y. R.,
“Sorption of Lead from Aqueous Solutions by Spent
Tea Leaf”, African Journal of Biotechnology, vol. 8,
pp. 2212-2217, 2010.
Imamoglu, M., and Tekir, O., “Removal of Copper
(II) and Lead (II) Ions from Aqueous Solutions by
Adsorption on Activated Carbon from A New
Precursor Hazelnut Husks”, Desalination, vol. 228,
pp. 108-113, 2008.
Ekop, A. S., and Eddy, N. O., “Thermodynamic Study
on the Adsorption of Pb (II) and Zn (II) from
Aqueous Solution by Human Hair”, E-Journal of
Chemistry, vol 7 (4), pp 1296-1303, 2010.
Adie, D. B., Okuofu, C. A., and Osakwe, C.,
“Comparative Analysis of the Adsorption of Heavy
Metals in Wastewater using Borrassus Aethiopium
and Cocos Nucifera”, International Journal of
Applied Science and Technology, vol. 2 (7), pp. 314322, 2012.
Azouaou, N., Sadaoui, Z., and Mokaddem, H.,
“Adsorption of Lead from Aqueous Solution onto
Untreated Orange Barks: Equilibrium, Kinetics and
Thermodynamics”, EDP Sciences, 2014.
Wahi, R., Ngaini, Z., and Jok, V. U., “Removal of
Mercury, Lead and Copper from Aqueous Solution
by Activated Carbon of Palm Oil Empty Fruit
Bunch”, World Applied Sciences Journal, vol. 5, pp.
84-91, 2009.
Chairgulprasert, V., Japakeya, A., and Samaae, H.,
“Phytoremediation of Synthetic Wastewater by
Adsorption of Lead and zinc onto Alpinia galanga
Willd”, Songklanakarin Journal of Science and
Technology, vol. 35 (2), pp. 227-233, 2013.
El-Said, A. G., Badawy, N. A., and Garamon, S. E.,
“Adsorption of Cadmium (II) and Mercury(II) onto
Natural Adsorbent Rice Husk Ash (RHA) from
Aqueous Solutions: Study in Single and Binary
System”, Journal of American Science, vol. 6 (12), pp.
400-409, 2010.
Thajeel, A. S., Raheem, A. Z., and Al-Faize, M. M.,
“Production of activated carbon from local raw
materials using physical and chemical preparation
method”, Journal of Chemical and Pharmaceutical
Research, vol. 5(4), pp. 251-259, 2013.
Issabayeva, G., Aroua, M. K., and Nik Meriam Nik
Sulaiman, “Removal of Lead from Aqueous
Solutions on Palm Shell Activated Carbon”,
Bioresource Technology, vol. 97, pp 2350–2355,
2006.
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e-ISSN: 2395-0056
Volume: 02 Issue: 03 | June-2015
p-ISSN: 2395-0072
[19]
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Wong, K. K., Lee, C. K., Low, K. S., and Haron, M. J.,
“Removal of Cu and Pb by Tartaric acid Modified
Rice Husk from Aqueous Solutions”, Chemosphere,
vol. 50, pp. 23-28, 2003.
[20] Jameel, A. A., and Hussain, A. Z., “Removal of Heavy
Metals from wastewater using Activated Rice Husk
Carbon as Adsorbent”, Indian Journal of
Environmental Protection, vol. 29 (3), pp. 263-265,
2009.
[21] Siddiqui, B., Anwar, J., and Zaman, W., “Adsorption
studies for the amputation of Lead from Squander
Waters by using Straws of Oryza Sativa (Rice)”,
Journal of Scientific Research, vol. 39 (1), pp. 9-14,
2009.
[22] Paulino, A. T., Minasse, F. A. S., Guilherme, M. R.,
Reis, A. V., Muniz, E .C., and Nozaki, J., “Novel
Adsorbents based on Silkworm Chrysalides for
Removal of Heavy Metals from Wastewaters”,
Journal of Colloid Interface Science, vol. 301, pp.
479-487, 2006.
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[23]
Bernard, E., and Jimoh, A., “Adsorption of Pb, Fe,
Cu and Zn from Industrial Electroplating
Wastewater by Orange Peel Activated Carbon”,
International Journal of Engineering and Applied
Sciences, Vol. 4 (2), pp. 95-103, 2013.
[24]
Gavhane, K. A., Mass Transfer-II, Chemical
Engineering, Nirali Prakashan, 5th Edition, 2006.
[25]
Madrid, R., Nogueira, C. A., and Margarido, F.,
“Production and Characterisation of Amorphous
Silica from Rice Husk Waste”, Fourth International
Conference on Engineering for Waste and Biomass
Valorisation, Porto, Portugal, 2012.
Page 1686
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REMOVAL OF LEAD (II) FROM AQUEOUS SOLUTION USING NATURAL
AND ACTIVATED RICE HUSK
Rajkumar V. Raikar 1, Sefra Correa 2, Praveen Ghorpade 3
1Professor,
Department of Civil Engineering, KLE Dr. MSSCET, Belgaum, Karnataka, India
Tech. Scholar, Department of Civil Engineering, KLE Dr. MSSCET, Belgaum, Karnataka, India
3Assistant Professor, Department of Civil Engineering, KLE Dr. MSSCET, Belgaum, Karnataka, India,
2M.
Abstract
This paper presents the experimental results on the use of rice husk in the removal of lead (II) from the aqueous solution. In
this study, rice husk is used in four different forms, namely, natural un-activated form (RH), rice husk ash acquired after
carbonizing rice husk without pretreatment (RHA), rice husk pretreated with phosphoric acid (PRH) and acetic acid (ARH)
separately and then followed by carbonization. Through batch adsorption studies the effect of various parameters such as pH
of the aqueous medium, contact time of agitation, adsorbate concentration, and adsorbent dosage were examined. The results
obtained show that the adsorption of the metal ion is pH, contact time, adsorbent dosage and adsorbate concentration
dependent. The maximum percentage removal of lead (II) ions is 93.36%, 94.8%, 96.72% and 99.35% with adsorbents RH,
RHA, PRH and ARH, respectively. It is found that RH, RHA and PRH followed Freundlich isotherm model whereas ARH followed
Langmuir isotherm model. Further, both RH and RHA follow pseudo-second order kinetics.
Key Words: Adsorption, Lead, Natural Adsorbents, Rice husk, Isotherms, Reaction kinetics …
--------------------------------------------------------------------***---------------------------------------------------------------------1. INTRODUCTION
Amongst the present day’s environmental issues, water
scarcity and water pollution rank equal to climate
change [1]. The industrial effluents have serious concern
as they contain heavy metals like iron (Fe), lead (Pb),
zinc (Zn), copper (Cu) etc., which are hazardous to
human health. Heavy metals being non-biodegradable
cause various diseases and disorders through
bioaccumulation. Many methods have been developed to
remove heavy metals from wastewater, such as
adsorption,
chemical
oxidation
/
reduction,
precipitation, ion exchange, electrochemical processes,
membrane filtration and reverse osmosis. These
methods tend to be expensive and often impracticable in
remote regions where heavy metal contaminants
originate from geogenic sources. On the contrary,
adsorption technique has proved to be an efficient and
cost effective among all the methods [2, 3]. Demirbas
presented a review on heavy metal adsorption onto
agro-based waste materials [4].
Lead as Pb (II) is released into the environment from
various industrial processes: industries engaged in lead
acid batteries, pulp and paper, petrochemicals,
refineries, printing, pigments, photographic materials,
explosive manufacturing, ceramics, glass, paint, oil,
metal, phosphate fertilizer, electronics, wood production
and also combustion of fossil fuel, forest fires, mining
activity, automobile emissions, sewage wastewater, sea
spray and many more [5]. Hashem [6] studied the
© 2015, IRJET.NET- All Rights Reserved
sorption of Pb (II) using okra wastes, Singh et al. [7] used
maize bran in the adsorption of lead using maize bran,
while El-Ashtoukhy et al. [8] employed pomegranate
peel as a adsorbent in the removal of lead (II) and copper
(II) from aqueous solution. Yoshita et al. [9] carried out
the study on the removal of lead by spent tea leaf residue
after instant tea extraction. Imamoglu and Tekir [10]
have studied removal of copper (II) and lead (II) ions
from aqueous solution by adsorption on activated
carbon from a new precursor hazelnut husks. The
thermodynamic study on the adsorption of Pb (II) and
Zn (II) from aqueous solution by human hair was done
by Ekop and Eddy [11]. Adie et al. [12] carried out the
comparative analysis of the adsorption of Pb (II) and Cd
(II) in wastewater using Borrassus aethiopium and Cocos
nucifera. The adsorption of lead from aqueous solution
onto untreated orange barks was studied by Azouaou et
al. [13]. Wahi et al. [14] studied the removal of mercury,
lead and copper from aqueous solution by activated
carbon of palm oil empty fruit bunch. Chairgulprasert et
al. [15] studied phytoremediation of synthetic
wastewater by adsorption of lead and zinc onto Alpinia
galangal Willd. However, the studies on the use of
activated rice husk in the removal of lead (II) are very
few. Hence, the present study emphasizes on the use
activated rice husk in the removal of lead (II) cations
from aqueous solution. The study also include fitting of
isotherms and reaction kinetics.
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2. MATERIALS AND METHODOLOGY
2.1 Materials
Lead nitrate was used for the preparation of stock Pb (II)
solution in distilled water. To control the pH value
during the experiment, hydrochloric acid and/or sodium
hydroxide solutions were used, while phosphoric acid
(H3PO4) (88%), acetic acid (CH3COOH) (99.8%) were
used for pretreatment. The equipments used for the
study are: digital pH meter, Atomic Absorption
Spectrophotometer (AAS), Scanning Electron Microscope
(SEM), rotary shaker, muffle furnace, oven, sieves and
weighing machine.
2.2 Preparation of Adsorbents
Locally available rice husk was washed with distilled
water, dried in an oven at 105oC for 24 hours to remove
the moisture content [16], ground and sieved to particle
size of < 150 µm. The powdered rice husk was used in
four forms: first one was used in its natural form and
named as “Rice husk” (RH), second form named “Rice
husk ash” (RHA) was obtained by carbonizing the
powdered rice husk in muffle furnace at 800oC for half
hour and then cooling in a dissicator, the third and
fourth forms were activated respectively with
phosphoric acid and acetic acid. The third was soaked for
36 hours in a solution of 0.1N phosphoric acid and 0.5N
acetic acid separately at an impregnation percentage of
20%, then carbonized at 650oC for 90 minutes [17]. It
was rinsed several times until the pH of the drained
water was in the range of pH 6-7 followed by oven
drying for 3 hours at 100oC to remove the moisture
content. They were named as Phosphoric acid treated
rice husk (PRH), and Acetic acid treated rice husk (ARH).
The physical characteristics of all adsorbents were
measured using standard procedures. The data are
presented in Table 1.
Table 1: Characteristics of adsorbents
Adsorbent
pH
RH
RHA
PRH
ARH
5.26
5.59
2.30
4.12
Bulk density
(gm/cc)
0.5604
0.5011
0.6105
0.5890
Particle density
(gm/cc)
1.0428
1.0345
1.0495
1.0466
2.3 Adsorption experiments
Batch adsorption experiments were carried out at room
temperature by shaking a series of beakers containing
the desired dose of adsorbent in a known concentration
of lead solution. Samples of lead solution were
withdrawn at different time intervals, filtered and the
filtrate was analyzed for the trace of heavy metal
content. Experiments were carried out at optimum pH
values. The initial pH of the solution was adjusted to the
© 2015, IRJET.NET- All Rights Reserved
desired value either by hydrochloric acid or sodium
hydroxide solution. The percent removal of lead from
solution was calculated using Eqs. (1).
Percent removal
(Co Ci )
100
Co
(1)
where Co is initial concentration of lead metal, Ci is final
concentration of lead metal. Isotherm studies were
conducted by varying the initial concentration of lead
solution from 10 to 50 mg/L. A known amount of
different adsorbents was then added into solutions
followed by agitation at 120 rpm.
3. RESULTS AND DISCUSSIONS
3.1 Determination of Optimum pH
To study the effect of pH on adsorption of lead (II) ions,
the batch equilibrium studies at pH values in the range of
3-7 were carried out. The results are furnished in Table 2
and the variation is presented in Fig 1. From Table 2 it
can be observed that the percentage removal of lead is
maximum in the pH range of 4-5 with RH and RHA.
However, with PRH, the pH range is 5-6 and ARH it is in
the range of 6-7. Therefore, the optimum pH range is
chosen as 4-5 for RH and RHA, which is same as stated
by Vieira et al. [3]. However, for PRH and ARH, the pH
range of 5-6 was chosen. According to Issabayeva et al.
[18] the speciation profiles of single lead species at a
total concentration of 10 mg/L is in Pb2+. The main
species in the pH range 3-5 were Pb2+, PbNO3+ and
aqueous Pb(NO3)2; their concentrations did not change
until pH = 6. The formation of solid (precipitation)
Pb(OH)2 started at pH = 6.3 and that of other soluble
hydroxides namely PbOH+, aq Pb(OH)2, and PbOH3occurred after pH = 7. Therefore, a pH range of 3-7 was
used during the analysis. The optimum value of pH
depends on the adsorbents characteristics. Table 3 gives
the optimum value of pH reported by various
investigators with different adsorbents used in the
removal of lead.
Table 2: Effect of pH on percentage removal of lead
using different adsorbents
pH
3
4
5
6
7
Percentage removal of lead with adsorbent
RH
RHA
PRH
ARH
78.12
91.24
86.14
82
79.34
92.19
93.76
91.56
79.28
92.16
94.99
93.77
77.42
88.74
94.83
94.99
75
88.53
94.32
96.43
Table 3: Optimum pH value for different adsorbents
Page 1678
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Volume: 02 Issue: 03 | June-2015
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Adsorbent
Okra waste
Maize bran
Pomegranate
peel
Hazelnut husks
Orange barks
Activated
carbon of palm
oil empty fruit
bunch
Alpina galangal
willd
RH and RHA
PRH and ARH
www.irjet.net
pH
range
4-6
3.2-8
Optimum
pH
5
6.5
4.5-9.4
5.6-7.6
1-4.6
6.7-7
-
4.5
Wahi et al. [14]
2-7
6
Chairgulprasert et
al. [15]
3-7
3-7
4-5
5-6
Present study
Authors
Hashem [6]
Singh et al. [7]
El-Ashtoukhey et al.
[8]
Imamoglu et al. [10]
Azouaou et al. [13]
Fig. 1 Effect of pH on the percentage removal of lead
with different adsorbents
3.2 Effect of varying lead concentration
(b)
Fig. 2 Variation of adsorption efficiency with initial
lead concentration using (a) RH and RHA and (b) PRH
and ARH
The removal of lead is dependent on the initial lead
concentration. Figs. 2 (a) and (b) show the effect of
initial lead concentration on the percent removal of lead
ions, respectively. From Fig. 2 (a) it is observed that, for
RH the percentage removal increased drastically from
85.16% to 93.36% with an increase in initial lead
concentration from 10 mg/L to 30 mg/L and thereafter it
decreased sharply, while for RHA the percentage
removal increase from 93.3% with an initial lead
concentration of 10 mg/L to 94.8% at 20 mg/L.
However, from Fig. 2 (b) it can be inferred that, the
percentage removal of lead with adsorbent PRH
decreases from 85.84% to 81.2% when initial lead
concentration increased from 10 mg/L to 30 mg/L and
thereafter the efficiency gradually increased. For ARH
the percentage removal decreases steeply from 94.89%
with initial concentration of lead at 10 mg/L to 80.7 %
with initial concentration of lead at 50 mg/L. Similar
results were also observed by Wong et al. [19] for
tartaric acid treated rice husk. This is because, at low
metal ion/adsorbent ratios, metal ion adsorption
involves higher energy sites giving higher adsorption
efficiency. On the other hand, as the metal ion/adsorbent
ratio increases, the higher energy sites are saturated and
adsorption begins on lower energy sites, resulting in
decreases in the adsorption efficiency. The comparative
study on the maximum percentage removal of lead at
optimum adsorbate concentration investigated by
various researchers is furnished in Table 4.
Table 4: Maximum percentage removal of lead at
optimum adsorbate concentration
(a)
© 2015, IRJET.NET- All Rights Reserved
Range of
Initial lead
initial lead
%
concentratio
Adsorbent concentratio removal
n of
Authors
n (mg/L)
of lead adsorbate
(mg/L)
Okra waste
25-100
99
100
Hashen [6]
Maize bran
100-150
96.8
100
Singh et al.
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Volume: 02 Issue: 03 | June-2015
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Pomegranat
e peel
Hazelnut
husks
Alpina
galangal
willd
Tartaric acid
treated rice
husk
RH
RHA
PRH
ARH
www.irjet.net
[7]
ElAshtoukhey
et al. [8]
Imamoglu et
al. [10]
10-50
95-100
10
5-200
97.2
5-30
95.2
50
Chairgulpras
ert et al. [15]
400-800
90-100
400
Wong et al.
[19]
10-50
10-50
10-50
10-50
93.36
94.8
85.84
94.89
30
20
10
10
Present study
(b)
3.3 Effect of contact time
The variation between adsorption efficiency in terms of
percentage removal of lead and contact time is shown in
Fig. 3. From Fig. 3 (a) it is observed that for RH, the lead
removal percentage is least of 74.64% at 60 minutes of
contact time and highest of 76.69% at contact period of
120 minutes, while for RHA the percentage removal
increased from 87.09% at 60 minutes contact time to
91.67% at 150 minutes of contact time. Similar value of
equilibrium time was also observed by Jameel and
Hussain [20] for RHA. From Fig. 3 (b) it is observed that
the percentage removal of lead with PRH increased with
an increase in contact time. At 60 minutes of reaction
time, 88.79% of lead removal is observed, as the
adsorption reaction was allowed for 180 minutes more
lead removal efficiency of 92.2% is observed. For
adsorbent ARH, it increased from 92.22% at 60 minutes
contact time to 95.8% at 180 minutes contact time.
However, equilibrium will be achieved beyond 180
minutes. Table 5 presents the optimum agitation time
corresponding to maximum percentage removal of lead
as reported by earlier investigator. In general, the
optimum contact time is around 150 minutes.
Fig. 3 Variation of adsorption efficiency with varying
contact time using (a) RH and RHA (b) PRH and ARH
3.4 Effect of adsorbent dosage
Fig. 4 illustrates the variation of adsorption efficiency
with varying adsorbent dosage using different
adsorbents, which shows that the adsorption efficiency
increases with an increase in adsorbent dosage. As
presented in Fig. 4 (a), RH the adsorption efficiency
increases from 79.91% to 84.72% with adsorbent
dosage from 1 gm to 2 gm, while for RHA it increased
from 89.62% to 90.39% for adsorbent dosage from 1 gm
to 2 gm. Fig. 4 (b) represents the effect of PRH and ARH
adsorbent dosage on percentage removal of lead. It can
be observed from Fig. 4 (b) that the percentage removal
of lead with adsorbent PRH gradually increases from 1
gm to 3 gm and at 4 gm there is a sudden increase in
percentage removal of lead by 96.72%. However, with
ARH, there is increase in percentage removal of lead
between 1 gm to 2 gm and beyond 2 gm the percentage
removal of lead is minimal. For ARH, the results are
97.65% at 1 gm, 99.11% with 2 gm and highest at
99.35% with 4 gm. This is due to greater availability of
surface area or active sites. The comparative study on
the optimum dosage of adsorbents corresponding to
maximum percentage removal is given in Table 6. The
optimum dosage depends on type of adsorbent due to
their varying surface area.
Table 5: Maximum percentage removal at optimum
agitation time
Adsorbent
Pomegranat
e peel
(a)
© 2015, IRJET.NET- All Rights Reserved
Hazelnut
husks
Alpina
galangal willd
Tartaric acid
treated rice
Range of
%
Optimum
agitation removal agitation
time (min) of lead time (min)
0-180
90-100
120
2-50
90-100
50-60
30-180
95.2
150
0-230
90-100
120
Author
ElAshtoukhey et
al. [8]
Imamoglu et
al. [10]
Chairgulpras
ert et al. [15]
Wong et al.
[19]
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p-ISSN: 2395-0072
Adsorbent
Range of
%
adsorbent
removal
dosage
of lead
(gm)
Pomegranate
2.5-12.5
peel
Spent tea leaf
0.5-2
Hazelnut
0.05-0.5
husks
Activated
Borrassus
0.5-2.5
aethiopium
seed shells
Activated
carbon of
palm oil
0.2-1
empty fruit
bunch
Alpina
0.5-2
galangal willd
RH
0.5-2
RHA
0.5-2
PRH
1-4
ARH
1-4
husk
Straws of
15-150
rice
Raw
silkworm
0-50 hours
chrysalides
Acid washed
silkworm
0-25 hours
chrysalides
Orange peel
activated
20-120
carbon
RH
60-180
RHA
60-180
PRH
60-180
ARH
60-180
Optimum
dosage of
adsorbent
(gm)
95
12.5
55.2
2
97.2
0.3
99.75
2.5
www.irjet.net
Author
El-Ashtoukhey
et al. [8]
Yoshita et al. [9]
Imamoglu et al.
[10]
Adie et al. [12]
(b)
100
0.2
Wahi et al. [14]
95.2
0.5
Chairgulprasert
et al. [15]
90.39
84.72
96.72
99.35
2
2
4
4
Present study
92.5
90-105
4.68
25-50
Siddiqui et al.
[21]
Paulino et al.
[22]
4.27
25
100
60-120
76.69
91.67
92.2
95.8
120
150
180
180
(a)
© 2015, IRJET.NET- All Rights Reserved
Bernard et al.
[23]
Present study
Fig. 4 Variation of adsorption efficiency with varying
adsorbent dosage using (a) RH and RHA (b) PRH and
ARH
Table 6: Maximum percentage removal at optimum
dosage of adsorbent
3.5 Adsorption isotherms
The equilibrium data for adsorption are usually
presented in the form of adsorption isotherms, which
gives the equilibrium relationship between the
concentration of the adsorbate held on the surface of a
adsorbent and the concentration (or partial pressure) of
the adsorbate in the fluid phase at a given temperature.
The concentration of the adsorbate on the surface of the
solid is expressed as the amount of the substance
adsorbed per unit mass of the adsorbent. In case of
solutions it is expressed as mass adsorbate per unit
volume of solution or in mass units such as ppm (mg/L)
[24]. Commonly used adsorption isotherms are
Freundlich and Langmuir isotherms. In the present
study, experimental data was fitted into the Freundlich
and Langmuir isotherm models.
Freundlich and
Langmuir isotherm plots of lead adsorption using RH,
RHA, PRH and ARH are as shown in Figs. 5 – 8,
respectively. The coefficients of regression R2 with
adsorbent RH are found to be respectively 0.875 and
0.832 for Freundlich and Langmuir isotherms. For RHA,
R2 values are 0.943 and 0.876 for Freundlich and
Langmuir isotherms. Similarly, with PRH, R2 values are
0.982 and 0.753 for Freundlich and Langmuir isotherms
and with ARH, R2 values are found to be 0.954 and 0.976
for Freundlich and Langmuir isotherms, respectively.
The regression coefficient for Freundlich isotherm is
greater than Langmuir isotherm and thus Freundlich
isotherm fits better with RH, RHA, and PRH than
Langmuir isotherm. In the case of ARH, Langmuir
isotherm is found to be the best fit isotherm. The
comparative results on the fitted isotherms using
Freundlich and Langmuir isotherm are presented in
Table 7.
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(b)
(a)
Fig. 6 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by RHA
(b)
Fig. 5 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by RH
(a)
(b)
(a)
Fig. 7 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by PRH
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to the pseudo-second order model than the pseudo-first
order model. Fig. 9 and Fig. 10 show the kinetic plots for
RH and RHA, respectively. In case of PRH and ARH,
equilibrium was found achieve beyond 180 minutes and
equilibrium point is unknown, hence, reaction kinetic
study has been applied only to RH and RHA.
(a)
(a)
(b)
Fig. 8 (a) Freundlich and (b) Langmuir isotherm plot of
lead adsorption by ARH
Adsorbent
RH
RHA
PRH
ARH
Table 7: Fitted isotherm parameters
(b)
Freundlich isotherm
N
k
R2
1.564 1.527 0.875
0.963 1.636 0.943
1.173 0.423 0.982
2.207 0.977
0.954
Fig. 9 (a) Pseudo-first order kinetic plot and (b) Pseudosecond order kinetic plot of RH
Langmuir isotherm
Qm
b
R2
1.412 8.636
0.832
1.492 -18.11 0.876
7.812 0.053
0.753
3.067 0.486 0.976
(a)
3.6 Reaction kinetics
Reaction kinetics also called chemical kinetics is used to
know the rates of chemical processes and laws for the
same. It includes the investigations on the influence of
different chemical processes on speed of chemical
reaction and yield information. It also helps in the
development of mathematical models of a chemical
reaction. Some of the laws used are zero-order, firstorder, second-order etc. To analyze the adsorption
kinetics of lead metal ions, the pseudo-first and pseudosecond order models were applied to data in the present
study. The determinant coefficient (square of correlation
coefficient) for the pseudo-second-order model was
0.998 for RH and 0.999 for RHA respectively, being
significantly higher than that for the pseudo-first-order
model presented in Table 8. It suggests that the lead
adsorption process of the RH and RHA is fitted very well
© 2015, IRJET.NET- All Rights Reserved
(a)
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through the carbonization of rice husk (RHA) the
moisture content decreases, changes in the physical and
chemical properties of rice husk improves adsorption
efficiency of RHA.
(a)
(a)
(b)
(b)
(c)
(c)
(d)
(d)
(e)
(e)
(b)
Fig. 10 (a) Pseudo-first order kinetic plot and (b)
pseudo-second order kinetic plot for RHA
R2
0.998
0.999
K2
0.049
0.337
Qe (cal)
0.815
0.929
Qe (exp)
0.766
0.916
R2
0.774
0.958
K1
0.025
0.0276
Qe
(cal)
0.378
0.238
Qe (exp)
Pseudo-second-order
0.766
Pseudo-first-order
0.916
RHA
RH
Adsorbent
Table 8: Reaction Kinetics
3.7 Surface morphology
According to Tarley and Arruda (2004), the material
(adsorbent) morphology may facilitate the adsorption of
metals in different parts of this material. Therefore,
based on morphology, as well as the fact that the highest
concentration of silica is present in the outer film of RH,
this material presents a morphological profile with the
potential to retain metal ions [6]. Fig. 11 shows a SEM
micrograph of a sample of RH and RHA obtained,
showing that RH is intact and has a smooth surface.
Through calcination the organics are decomposed and
the ash obtained may constitute of amorphous silica with
high porosity having potential application as ligand in
metals adsorbent, whereas RHA obtained, showing a
very porous tracery surface morphology, with a high
surface area. Similar results have been observed by
Madrid et al. [25]. RHA is silica rich which serves as a
good adsorbent. According to Vieira et al. [3], RH and
RHA are predominantly mesoporous materials and the
calcinations of RH caused an increase in the surface area,
the presence of –OH, Si–O–Si and Si–H groups on the
RHA surface were important for metal adsorption [6].
Hence, in this study, the maximum percentage removal
of lead is higher with RHA than that with RH. Further,
© 2015, IRJET.NET- All Rights Reserved
Fig. 11 Scanning electron micrographs (SEM) for RH
(left picture) and RHA (right picture) at magnifications
of (a) (50x), (b) (100x), (c) (500x), (d) (1000x) and (e)
(5000x)
4. CONCLUSIONS
The experimental results on removal of lead (II) with unactivated and activated rice husk are presented in the
paper. Through chemical activation of the adsorbent, the
percentage removal efficiency of an adsorbent can be
increased. Hence, activated rice husk shows greater
efficiency than un-activated rice husk. Highest
percentage lead removal with adsorbent RH found is
93.36 % at pH 4-5, initial concentration of lead 30 mg/L,
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contact time of 60 minutes and adsorbent dosage of 1
gm. When RHA is used, the maximum percentage
removal is found as 94.8 % at pH 4-5, initial
concentration of lead 20 mg/L, contact time of 60
minutes, adsorbent dosage of 1 gm. However, with PRH,
the highest percentage removal of lead is 96.72 % at pH
5-6, initial concentration of lead 10mg/L, contact time of
60 minutes and adsorbent dosage of 4 gm. Similarly, for
ARH, the maximum lead removal is found to be 99.35%
at pH 5-6, initial concentration of lead solution 10 mg/L,
contact time of 60 minutes and adsorbent dosage of 4
gm. Rice husk, Rice husk ash and phosphoric acid treated
rice husk followed Freundlich isotherm model whereas
acetic acid treated rice husk followed Langmuir isotherm
model. Rice husk and rice husk ash follow pseudosecond order kinetics. From this study, it is inferred that
rice husk, an abundantly available agricultural waste can
be used as a low cost adsorbent. The higher adsorption
capacity is favored by higher number of active binding
sites, improved ion exchange properties and
enhancement of functional groups after chemical
treatment.
[8]
[9]
[10]
[11]
[12]
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