Natural Resources, 2010, 1, 104-109
doi:10.4236/nr.2010.12011 Published Online December 2010 (http://www.SciRP.org/journal/nr)
Adsorption of Pb(II) onto Modified Rice Bran
Hengpeng Ye*, Zhijuan Yu
School of Chemistry and Material Science, South Central University for Nationalties, Wuhan, China.
Received November 3rd, 2010; revised November 25th, 2010; accepted November 26th, 2010.
ABSTRACT
In this study, the modified rice bran was tested to remove Pb(II) from water. Batch experiments were carried out to
evaluate the adsorption characteristics of the modified rice bran for Pb(II) removal from aqueous solutions. The ad-
sorption isotherms, thermodynamic parameters, kinetics, pH effect, and desorbability were examined. The results show
that the maximum adsorption capacity of the modified rice bran was approximately 70.8 mg Pb(II)/g absorbent at tem-
perature of 25℃ and at the initial Pb(II) concentration of 400 mg/L and pH 7.0. And the adsorption isotherm data
could be well fitted by both Langmuir equation and Freundlich equation. Thermodynamic studies confirmed that the
process was spontaneous and endothermic. The adsorbed amounts of Pb(II) tend to increase with the increase of pH.
The adsorption kinetic data can be satisfactorily described by either of the power functions and simple Elovich equa-
tions. The desorbability of Pb(II) is about 15-20%, and it is relatively difficult for the adsorbed Pb(II) to be desorbed.
The relatively low cost and high capabilities of the rice bran make it potentially attractive adsorbent for the removal of
Pb(II) from wastewater.
Keywords: Rice Bran, Pb(II) Removal, Adsorption Capacity, Adsorption Isotherm
1. Introduction
Duo to the toxicological importance in the ecosystem,
agriculture and human health, pollution by heavy metals
has received wide spread attention in the recent years.
Lead, an element which has been used by man for years,
can be regarded as a longstanding environmental con-
taminant. All lead compounds are cumulative poisons.
Several industries like mining, printing, painting, dyeing,
battery manufacture and other industries discharge ef-
fluent containing lead, to surface water. Lead has toxic
effects on neurobehavioral development and on the brain
cell function [1]. The accumulation of lead in river beds
[2] has been detected and gives cause for concern. This
underlines the need for developing methods for effective
removal of lead from water at least below the regulatory
level.
However, there are several methods for the treatment
of wastewaters containing Pb(II), including ion exchange,
adsorption, precipitation and membrane separation [3].
During last decades, the process of adsorption using ac-
tivated carbon [4-5] has been found to be an efficient
technology for the removal of Pb(II) from wastewater.
Though the removal of Pb(II) through adsorption is quite
effective, its use is restricted sometimes due to the higher
cost of activated carbon and difficulties associated with
regeneration. Attempts have therefore been made to util-
ize natural as well as waste materials as alternative ad-
sorbents. However, preparation of carbons from low-cost
materials [6-7], use of clay minerals [8-9], waste materi-
als [10-12], and wheat bran [13-14] are some of the al-
ternatives of costly activated carbons. Although many of
these adsorbents can effectively remove Pb(II), most of
them present some disadvantages such as poor adsorption
capacity, low efficiency/cost ratio and ineffectiveness for
low metal concentrations.
China produces millions of tons of rice annually. Rice
bran is a by-product of the rice milling industry and the
amount of rice bran available is far in excess of any local
uses, thus frequently causing disposal problems. Therefore,
rice bran is very inexpensive, with a cost of 1/50-1/40 of
that of active carbon, and thus its use would significantly
lower the cost of wastewater treatment. In addition, the
use of rice bran would represent effective utilization of
waste matter. The modified rice bran has been success-
fully used to remove Cd(II) from water [15].
The objective of this work was to study the feasibility
of using modified rice bran as adsorbents for the removal
of Pb(II) from wastewater. Rice bran was chosen due to
its granular structure, insolubility in water, chemical sta-
bility and local availability. In this work, batch experi-
ments were carried out to evaluate the adsorption char-

Adsorption of Pb(II) onto Modified Rice Bran
105
acteristics of the modified rice bran for Pb(II) removal
from aqueous solutions. The adsorption isotherms, ther-
modynamic parameters, kinetics, pH effect, and desorb-
ability were examined.
2. Materials and Methods
2.1. Materials
The used rice bran was purchased at a local market. It
was dried in an oven at 105 for a period of℃ 24 h, and
then ground and sieved to obtain uniform material (< 75
μm). The chemical compositions and physical properties
of rice bran are given in Table 1. The BET surface area
was measured by the N2 adsorption-desorption technique
using a NOVA-1000 (Ver.3.70) analyzer. The bulk den-
sity of the adsorbent was determined with a densitometer.
Mercury porositometry determined porosity of the ad-
sorbent. Chemical analysis of the rice bran showed the
presence of various oxides of Ca, Si, Mn, Mg, and Fe.
About 20 g of dried rice husks were treated with 200
mL 3 M sodium hydroxide at 60 for℃ 2 h in a paraffin
bath. The sodium hydroxide used was an equivalent
amount required to remove all silica present in the husks.
The husks were then filtered and washed with distilled
water until the filtrate was neutral. The treated husks
were dried at 105 in an oven and℃ left overnight. The
dried husk was carbonized with 50 mL 30% sodium hy-
droxide under nitrogen atmosphere at temperatures rang-
ing from 400 to 650, for ℃45 min. Then the carbonized
husks were washed with distilled water until the filtrate
was about pH 6–7. The samples were then dried at 105 ℃
in an oven overnight and ball-milled into powder that
passed through 75 μm mesh.
2.2. Experimental Procedure
In the present investigation the batch mode of operation
was selected in order to measure the progress of adsorp-
tion. It was carried out by shaking 100 mg of modified
rice bran with 100 mL aqueous solution of adsorbate
(Pb(NO3)2) of different concentrations (30, 60, 90, 120,
150, 200, 300, 400 mg/L) at different temperature (15℃,
25℃, 35℃) and different pHs (3.1, 4.5, 6.2, 7.0, 7.6, 8.1)
in different glass bottles in a shaking thermostat at a con-
stant speed of 120 rpm. The pH of the adsorbate solution
Table 1. Chemical compositions and physical properties of
rice bran.
Chemical composition Physical properties
Moisture 8.25% Surface area (m2/g) 438.05
Volatile matter 42.80% Bulk density (g/cm3) 0.3086
Fixed carbon 30.56% Porosity (fraction) 0.38
Ash (oxides of Ca,
Mn, Si, Fe, Mg, etc.) 18.39%
was adjusted by manually adding 0.1 M HNO3 or 0.1 M
NaOH solutions using a pH meter. The progress of ad-
sorption was noted at different time intervals till the at-
tainment of saturation. At the completion of predeter-
mined time intervals, the adsorbate and adsorbent were
separated by centrifugation at 12000 rpm for 25 minutes
in a Sorvall RC-5C centrifuge. And the supernatant liq-
uid was analyzed for Pb(II). Desorption experiments
were conducted by shaking 100 mg of adsorbent con-
taining adsorbed Pb(II) with 100 mL of distilled-deion-
ized water at 25℃ and pH 7.0.
Blank samples were run under similar conditions of
concentration, pH, and temperature without adsorbent in
all cases to correct for any adsorption on the internal
surface of the bottles. The duplicate experiments demon-
strated the high repeatability of this adsorption method
and the experimental error could be controlled within
5-10%.
2.3. Analysis of Pb(II)
Pb(II) was estimated through atomic absorption spectro-
photometer using a Varian Spectra AA 10 Plus atomic
absorption spectrophotometer, at wavelength of 217 nm.
The band pass was 1 nm. The adsorbed Pb(II) was cal-
culated from the difference of the Pb(II) in solution and
the known initial concentration. Each analysis point was
an average of three independent parallel sample solutions.
Triplicate tests showed that the standard deviation of the
results was ±3%.
3. Results and Discussion
3.1. Pb(II) Adsorption Isotherm
Experiments were performed at different initial Pb(II)
concentrations (30, 60, 90, 120, 150, 200, 300, 400 mg/L)
at temperature of 15, 25, 35℃, respectively, and pH of
7.0. The results of the Pb(II) adsorption isotherm ex-
periments are shown in Figure 1. It can be found that the
Pb(II) adsorption capacity of the modified rice bran in-
creased with the Pb(II) equilibrium concentration in-
creasing from 0 to 100 mg/L. This capacity was ap-
proximately 59.5, 68.0, 75.8 mg Pb(II)/g absorbents re-
spectively at temperature of 15, 25, 35℃ and at the Pb(II)
equilibrium concentration of 100 mg/L and pH 7.0. With
a further increase of the Pb(II) equilibrium concentration,
the increase of the adsorption capacity was less signify-
cant.
Two typical isotherms, as described below in Equa-
tions (1)-(2), were used for fitting the experimental data:
Freundlich equation:
1n
ee
qKC (1)
Langmuir equation:

Adsorption of Pb(II) onto Modified Rice Bran
106

1
emee
qqbC bC (2)
where qe is the amount adsorbed at equilibrium (mg/g),
and Ce is the equilibrium concentration (mg/L). The other
parameters are different isotherm constants, which can be
determined by regression of the experimental data. In this
study, the isotherm data from Figure 1 were fitted to the
above two models by non-linear regression using the
method of least squares. The estimated model parameters
with the correlation coefficient (R2) and the standard er-
ror of estimate (SE) are shown in Table 2. The fitting
curves from the two isotherms are also illustrated in Fig-
ure 1. It is shown that the experimental data of Pb(II)
adsorption on modified rice bran could be well fitted by
the two isotherms. Clearly, Langmuir equation provided
better fitting in terms of R2 and SE values.
The Pb(II) adsorption on different materials has been
widely studied during recent years, such as, on granu-
lated blast-furnace slag [10], bentonite [8], bagasse fly
ash [12], zeolite [9], sepiolite [9], etc. At respective
optimal pH value and approximately the same Pb(II)
equilibrium concentration, their reported Pb(II) adsorp-
tion capacities (mg/g) are given in Table 3. For com-
parison, the Pb(II) adsorption capacity of the modified
Figure 1. Pb(II) adsorption isotherm.
Table 2. Estimated isotherm parameters for Pb(II) adsorp-
tion.
Freundlich equation
(1n
ee
qKC)
Langmuir equation
( 
1
eme e
qqbC bC)
Temperature K 1/n R2 SEqm
(mg/g)
b
(L/mg) R2SE
15℃ 29.9 0.162 0.925 1.33 60.1 1.22 0.9750.625
25℃ 32.6 0.248 0.910 1.62 73.9 0.708 0.9360.772
35℃ 34.2 0.303 0.898 1.92 78.9 0.552 0.9220.836
Table 3. Pb(II) adsorption capacities of different low cost
and easily available materials (at 20-25℃).
Material Capacity (mg/g) Source
granulated blast-furnace slag 34.0 [10]
bentonite 21.5 [8]
bagasse fly ash 4.1 [12]
zeolite 30.5 [9]
sepiolite 38.2 [9]
wheat bran 68.79 [13-14]
rice bran 73.9 This study
rice bran obtained in this study is also listed in Table 3.
In comparison with granulated blast-furnace slag [10],
bentonite [8], bagasse fly ash [12], zeolite [9], sepiolite
[9], and wheat bran [13-14], the relatively low cost and
high capabilities of rice bran make it potentially attract-
tive adsorbent for the removal of Pb(II) from wastewater.
3.2. Thermodynamic Parameters
Thermodynamic parameters such as free energy (ΔG0),
enthalpy (ΔH0), and entropy (ΔS0) change of adsorption
can be evaluated from Equations (3):
,
dee
K
qC

(3)
where Kd is the sorption distribution coefficient. The Kd
values are used to determine the ΔG0, ΔH0, and ΔS0,
0ln ,
d
GRTK (4)
where ΔG0 (cal mol-1) is the free energy of adsorption, T
(Kelvin) is the absolute temperature, and R is the uni-
versal gas constant.
The Kd may be expressed in terms of the ΔH0 (kcal
mol-1) and ΔS0 (cal mol-1 K-1) as a function of tempera-
ture:

00
ln ,
d
K
HRTSR (5)
The values of ΔH0 and ΔS0 can be calculated from the
slope and intercept of a plot of ln Kd vs. 1/T.
Thermodynamic parameters such as free energy of
adsorption (ΔG0), the heat of adsorption (ΔH0), and stand
entropy changes (ΔS0) during the adsorption process at
the initial Pb(II) concentration of 30 mg/L were calcu-
lated using Equations (3), (4), and (5). The temperature
range used was from 15 to 35℃. The Gibbs free energy
indicates the degree of spontaneity of the sorption proc-
ess and the higher negative value reflects more energetic-
cally favorable sorption. (ΔH0) and (ΔS0) were obtained
from the slope and intercept of a plot of ln Kd against 1/T
(Figure 2). The values of the parameters thus calculated
are recorded in Table 4. Negative values of ΔG0 indicate
the spontaneous nature of the adsorption process. The
value of ΔG0 becomes more negative with increasing

Adsorption of Pb(II) onto Modified Rice Bran
107
temperature. This shows that an increase in temperature
favors the adsorption process. The positive values of ΔH0
indicate that the adsorption process was endothermic in
nature and the negative values of ΔS0 suggest the prob-
ability of favorable adsorption.
3.3. Effect of pH
Experiments were performed at different pH (3.1, 4.5,
6.2, 7.0, 7.6, 8.1) and the initial Pb(II) concentration of
150 mg/L at 25℃. The results of the effect of pH on ad-
sorption of Pb(II) are presented in Figure 3. It was found
that the total amount of adsorption of Pb(II) onto modi-
fied rice bran increases with an increase of pH from 3.1
to 8.1. Similar trends were also observed for Pb(II) ad-
sorption on granulated blast-furnace slag [10], and on red
mud [11]. The pH of the aqueous solution is an important
variable that influences the adsorption of Pb(II) at the
solid-liquid interfaces. However, the modified rice bran
possesses a negative surface charge in solution. As pH
changes, surface charge also changes, and the sorption of
charged species is affected (attract ion between the posi-
tively charged metal ion and the negatively charged rice
bran surface). Furthermore, a lower pH value causes the
rice bran surface to carry more positive charges and thus
would more significantly repulse the positively charged
species (Pb(II)) in solution.
Figure 2. A plot of ln K
d against 1/T for Pb(II) adsorption
by rice bran.
Table 4. Thermodynamic parameters for adsorption of
Pb(II) on rice bran.
–ΔG0 (cal mol-1) ΔH0 –ΔS0
15℃ 25℃ 35℃ (kcal mol-1) (cal mol-1 K-1)
577.0 1039 1585 13.92 50.29
3.4. Pb(II) Adsorption Kinetic
Experiments were performed at the initial Pb(II) concen-
tration of 150 mg/L and at temperature of 15, 25, 35℃,
respectively. The results of Pb(II) adsorption kinetic ex-
periments are shown in Figure 4. It can be seen that the
majority of Pb(II) adsorption on the modified rice bran
were completed in 5-15 minutes. For example, after 15
minutes of adsorption, the Pb(II) adsorbed on the rice
bran at 15, 25, 35℃ was, respectively, 89.1%, 91.3%,
92.4% of that at 180 minutes.
The Pb(II) adsorption kinetic data (Figure 4) were fit-
ted with several kinetic models (first order, second,
power function, and simple Elovich [16]) by none-liner
regression. The first- and second-order kinetic models
were ruled out because their correlation coefficients (R2)
for the present experimental data were too small (< 0.6).
Power function and simple Elovich kinetic equations and
Figure 3. Effect of pH on adsorption of Pb(II).
Figure 4. Pb(II) adsorption kinetics.

Adsorption of Pb(II) onto Modified Rice Bran
108
estimated parameters with R2 and SE are shown in Table
5. Based on R2 and SE, the kinetics of Pb(II) adsorption
on the rice bran can be satisfactorily described by either
of the power functions and simple Elovich equations.
Therefore, the fitting curves resulting from both equa-
tions are plotted in Figure 4 as well. The high applicabil-
ity of the simple Elovich equation for the present kinetic
data is generally in agreement with other researchers’
results that the Elovich equation was able to describe
properly the kinetics of Pb(II) adsorption on lignite [17]
and diatomite [18].
3.5. Pb(II) Desorption Studies
The tests of Pb(II) desorption were conducted with four
initial Pb(II) concentrations (60, 120, 200, 400 mg/L) as
shown in Table 6. The Pb(II) desorbability can be de-
fined as the ratio of the desorbed Pb(II) over the total
adsorbed Pb(II) by the adsorbent. Therefore, the desorb-
ability of Pb(II) can be used to indicate the degree of
Pb(II) desorption from the adsorptive materials. The data
in Table 6 show that the desorbability of Pb(II) is about
15-20%. And the amount of the desorbed Pb(II) is
slightly increased with the increase of the adsorbed
Pb(II). These results indicate that the Pb(II) adsorption
on the modified rice bran is not completely reversible
and the bonding between the rice bran and adsorbed
Pb(II) is likely strong. And it is relatively difficult for the
adsorbed Pb(II) to be desorbed from the modified rice
bran.
Table 5. Estimated kinetic model parameters for Pb(II)
adsorption.
Freundlich equation
(b qat)
Langmuir equation
(lnqabt )
Temperature a b R2 SE a b R2SE
15℃ 16.3 0.455 0.966 0.386 10.8 17.5 0.9850.352
25℃ 18.9 0.493 0.928 0.779 13.6 20.2 0.9630.422
35℃ 29.3 0.354 0.958 0.512 24.6 18.6 0.9780.403
Table 6. Desorbability of the adsorbed Pb(II) on rice bran.
Initial Concentration
(mg/L)
Adsorbed Pb(II)
(mg/g)
Desorbed Pb(II)
(mg/g)
Desorbability
(%)
60 36.8 5.6 15.3
120 64.0 11.6 18.1
200 68.4 12.8 18.8
400 70.8 13.6 19.2
4. Conclusions
The modified rice bran has been found to be a very ef-
fective adsorbent for the efficient removal of Pb(II) from
water. The maximum adsorption capacity of the modified
rice bran was approximately 70.8 mg Pb(II)/g absorbent
at temperature of 25℃ and at the initial Pb(II) concentra-
tion of 400 mg/L and pH 7.0. And the adsorption iso-
therm data could be well fitted by both Langmuir equa-
tion and Freundlich equation. Thermodynamic studies
confirmed that the process was spontaneous and endo-
thermic. The adsorbed amounts of Pb(II) tend to increase
with the increase of pH. The adsorption kinetic data can
be satisfactorily described by either of the power func-
tions and simple Elovich equations. The desorbability of
Pb(II) is about 15-20%, and it is relatively difficult for
the adsorbed Pb(II) to be desorbed. The relatively low
cost and high capabilities of the rice bran make it poten-
tially attractive adsorbent for the removal of Pb(II) from
wastewater.
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