-
Hindawi Publishing CorporationJournal of Applied ChemistryVolume
2013, Article ID 417180, 12
pageshttp://dx.doi.org/10.1155/2013/417180
Research ArticleInsight into Equilibrium and Kinetics of the
Binding ofCadmium Ions on Radiation-Modified Straw from Oryza
sativa
Sana Zulfiqar Ali, Makshoof Athar, Umar Farooq, and Muhammad
Salman
Institute of Chemistry, University of the Punjab, Lahore 54590,
Pakistan
Correspondence should be addressed to Umar Farooq;
[email protected]
Received 26 March 2013; Accepted 24 May 2013
Academic Editor: Luqman Chuah Abdullah
Copyright © 2013 Sana Zulfiqar Ali et al. This is an open access
article distributed under the Creative Commons AttributionLicense,
which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properlycited.
The present study reports the chemical modification of
agricultural waste (rice straw) with urea using microwave radiation
andthe efficiency evaluation of this modified rice straw for the
adsorption of a toxic heavy metal, cadmium. The elemental analysis
ofurea modified rice straw affirmed urea grafting on rice straw,
and FTIR spectra of chemically benign modified adsorbent showedthe
presence of hydroxyl, carbonyl, and amino functional groups.
Effects of process parameters (adsorbent dosage, contact
time,agitation speed, pH, and temperature) were studied in batch
mode. Parameters were optimized for the equilibrium study,
andadsorptionmechanismwas elucidated using fivemathematical models
(Langmuir, Freundlich, Temkin, Harkin-Jura,
andDubinin-Radushkevich). Binding of Cd(II) ions on modified
adsorbent followed Langmuir model, and the maximum uptake capacity
wasfound to be 20.70mg g−1. Kinetic modeling was done using six
different kinetic models. The process was considered
physisorptionaccording to the obtained activation energy value.
Thermodynamic parameters confirmed the process to be favorable and
feasible.Exothermic nature of adsorption of Cd(II) ions on urea
modified rice straw was confirmed by the negative value of ΔH∘.
1. Introduction
Rapid pace of industrialization has resulted in a number
ofproblems among which water pollution is considered to beone of
the serious problems. Industrial processes dischargehuge amounts of
untreated wastewater daily into the sur-rounding environment,
leading to detrimental effects on aqu-atic, plant, and human life.
Heavy metal such as lead, cad-mium, chromium, and copper is
regarded asmajor pollutantsin wastewater. These contaminants are of
major concernbecause they do not degrade naturally [1].
Cadmium has attracted wide attention of environmentalchemists as
one of the most toxic metals and has been cate-gorized as a human
carcinogen by USEPA (United StatesEnvironment Protection Agency),
WHO (World HealthOrganization), and NTP (National Toxicology
Program) [2].It is a nonessential and nonbiodegradable metal which
slowlyaccumulates in the human body, usually from food chain.The
permissible limits for cadmium by WHO and USEPAare 3 𝜇g L−1 and 5
𝜇g L−1, respectively. It affects lungs, liver,and pancreas and
disturbs the human DNA repair system.
Chronic cadmium poisoning causes characteristic
yellowpigmentation of teeth (the yellow ring of cadmium) [2].
It is important to treat contaminated waters on a contin-uous
basis due to need of hour. A number of technologiesare available
with varying degree of success, and among themadsorption process is
considered relatively better becauseof convenience, ease of
operation, and simplicity of design[3]. Activated carbon has been
utilized as the commercialadsorbent for the removal of pollutant
from wastewaterbecause of its excellent adsorption ability.
However, its use isrestricted due to high cost.
Recently, many nonconventional, low-cost adsorbentsincluding
natural materials, (biosorbents) and waste materi-als have been
proposed by several researchers. Cadmium hasbeen reported to be
removed and recovered from aqueoussolutions by a number of
biosorbents [4–8]. Modificationof the natural materials
(biosorbents) has gained numerouscost-effective and efficient
adsorbents for the uptake of pollu-tants from aqueous solution.
Certain physical and chemicalmethods such as heating, freezing,
drying, cross-linkingwith organic solvents, chemical reactions with
a variety of
-
2 Journal of Applied Chemistry
RS
Microwave oven
RS
UMRS
12 minutesNHCONH2
NH2CONH+
2
Scheme 1
organic and inorganic compounds, and modification undermicrowave
radiation in the absence of any solvent have beenutilized in this
regard [9–13]. The modifications produceadsorbents which have
greater exposed metal-binding sitesas compared to raw adsorbents.
The chemically modifiedadsorbent offers a larger available surface
area. The surfacechemistry is altered after modification due to the
incorpo-ration of new functional groups by changing the
alreadypresent functional groups on any adsorbent. These
modifiedfunctional groups act as complexing or chelating agents
formetals [14–16]. Modification with microwave radiation
isadvantageous because it is a simple process and does notrequire
any solvent. Also no harmful vapors are added to
theenvironment.
Rice (Oryza sativa) is one of the major crops grownthroughout
the world and is most important staple food fora large part of the
world’s human population. Rice straw,obtained as a byproduct of
rice industry, is an agriculturalwaste which is used as a
cost-effective adsorbent for a numberof pollutants including metal
ions. Rice straw is insoluble inwater, has good chemical stability,
and has high mechanicalstrength [17], making it good adsorbent
material for treatingheavy metals from wastewater.
The present study is based on the evaluation of effec-tiveness
of a modified agricultural waste (rice straw) for theremoval of
toxic Cd (II) ions from aqueous solution in a batchprocess.
Detailed equilibrium, kinetic, and thermodynamicstudies elucidate
the adsorption mechanism.
2. Materials and Methods
2.1. Collection and Urea Modification of Oryza sativa. Driedrice
straw (Oryza sativa) was collected from the PunjabUniversity area
of Lahore, Pakistan. It was washed with waterto remove the dust and
particles and was air dried. Dried ricestraw was grinded and sieved
to pass 40–60 mesh (ASTMstandard). It was again washed with water
and dried in anoven at 105–110∘C till constant mass. The dried
biomass wasmixed with urea (Merck, Germany) in 1 : 2 by mass
andirradiated in amicrowave oven (D131, Dawlance) for a periodof 12
minutes. The procedure for modification is expressedin detail
elsewhere [18] and shown in Scheme 1. This ureamodified rice straw
was designated as UMRS and stored inairtight plastic bottles for
further use.
2.2. Characterization of UMRS. The prepared materialUMRS was
characterized using FTIR, elemental analysis,and surface area. In
order to study the presence of potentialfunctional groups in UMRS,
the FTIR spectrumwas scannedin 4000–400 cm−1 using standard method
with the help of
FTIR spectrophotometer (Spectrum RX-1, Perkin Elmer).The
elemental analysis was performed using elemental ana-lyzer (EL III,
Elementar, Vario) using corn gluten as astandard. The surface area
was determined using Langmuirequilibrium model.
2.3. Batch-Stirred Biosorption Experiments. A
concentrationdifference method was used to study the effect of
variousparameters on the biosorption of Cd(II) byUMRS. Cadmium(II)
nitrate (Merck, Germany) was used to prepare theaqueous solution of
Cd(II). Distilled water was used for alltypes of solution
preparations and dilutions as per require-ment. In all experiments,
measuring/conical flasks (100mL)were used containing Cd(II)
solution (50mg/L, 50mL) ofa known concentration at a specific pH. A
known amountof UMRS (0.2–1.4 g) was added to the solution and
thenagitated on an orbital shaker (OSM-747, Vortex) at
predefinedspeed (125 rpm). After a specific period of time, the
contentswere filtered, and the filtrate was analyzed using
atomicabsorption spectrophotometer (AAnalyst 100, Perkin Elmer)to
determine the equilibrium Cd(II) ions concentrations.The difference
of initial (𝐶
0
, mg L−1) and equilibrium (𝐶𝑒
,mg L−1) metal ion concentration was considered to be sorbedby
UMRS. The removal (R%) of Cd(II) and/or the amountof Cd(II) sorbed
per unit mass of UMRS at equilibrium (𝑞
𝑒
,mg g−1) were determined using the following formula:
𝑅% =𝐶0
− 𝐶𝑒
𝐶0
× 100, (1a)
𝑞𝑒
=𝐶0
− 𝐶𝑒
𝑚× V, (1b)
where “𝑚” (g) is the mass of UMRS and “V” (L) is the volumeof
Cd(II) solution used for the experiment.
The effects of parameters like time of contact, pH, doseof UMRS,
agitation speed, temperature, and concentrationof Cd(II) ions on
the biosorption process were studied in asimilar way. Blank
experiments were performed in order tostudy the adsorption of
Cd(II) by the glassware.No detectableadsorption of Cd(II) was found
by the glassware. All thegraphs were prepared using Microsoft Excel
2003 software.Regression analyses have also been performed by
calculating𝑅2 to investigate the suitability of certain
mathematical
model. Root mean square errors (RMSE) were calculated inorder to
evaluate the error of the model predictions. Thesum of the squares
of the difference between metal removalexperimental data (𝑞exp) and
model predictions (𝑞cal) wasdivided by the number of data points
(𝑁) for each data set,and the square root of this term was taken as
follows:
RMSE = √∑(𝑞exp − 𝑞cal)
2
𝑁.
(1c)
3. Results and Discussion
3.1. Effect of pH. The pH of the solution is probably the
mostimportant parameter as it affects the charges on biomass as
-
Journal of Applied Chemistry 3
C C C
OH
OH
OH
O
O
O
+H+H
−H −H
Scheme 2
well as metal speciation in the solution. The metal speciesare
influenced by the solution pH. Cadmium ions are presentas free Cd2+
species along the whole acidic pH range. Asthe pH is increased
above pH 7.5, it starts to precipitate asCd(OH)
2
, and thus it is no more “available” for biosorption.This
narrows down the upper pH limit for the biosorption ofCd(II) by
UMRS. So, during the study of the effect of pH, therange that
should be scanned for the optimum pH is limitedto an upper value of
7.5 [16].
On the other hand, in highly acidic pH, there are a
greaternumber of H+ ions present in the solution. These H+ ionsare
readily sorbed on the sites of the biomass (UMRS) andthus protonate
it before metal ions can attack these sites.This causes UMRS to
behave as positive specie. Due to theelectrostatic repulsive force
present between two positivespecies, a limited number of Cd(II)
ions are sorbed onUMRS,and thus there should be low 𝑞
𝑒
value at low pHs. When thepH is raised from highly acidic pH,
this positive characterdecreases. UMRS, being a modified
lignocellulosic material,contains a variety of functional groups
including carbonyl,amide, hydroxyl, and thiol. The behavior of each
of thesefunctional groups changes with the change in solution
pH.For example, carboxyl groups are protonated in highly acidicpHs
(pH less than 3) acting as positively charged speciesand attracting
negative charged ions [19]. On increasingthe pH, the deprotonation
(ionization) of these functionalgroups causes them to act as
negative moieties. At thisstage, they attract and attach positive
cations like Cd(II) ionsmore readily. It may be represented as
shown in Scheme 2[16].
The protonation and deprotonation of other availablefunctional
groups can be explained on similar grounds. It canbe predicted that
at highly acidic pHs, Cd(II) binding withUMRS is reduced, and the
binding increases with increase inpH because UMRS is negatively
charged. This effect of pHof solution on biomass, thus, decides the
lower limit of pH.Based on the previous discussion, the effect of
pHwas studiedin pH range of 2–7.
The pH profile study is shown in Figure 1. It is obviousthat the
binding of Cd(II) by UMRS increased with increasein pH. This is in
conformity with the previous discussion.No significant change in
the 𝑞
𝑒
value is observed as the pHis increased above 5. This indicated
that the pH had a vitalrole in the biosorption of Cd(II) by UMRS
and themaximumbinding occurred at a pH of 5. A number of studies,
in theliterature, on the biosorptive removal of Cd(II) by
variousbiosorbents reported the optimum pH between 5-6 [18, 20–22].
Almost similar values of pH indicate that the biosorptionof Cd(II)
ions seems not to be dependent on the biosorbentmaterial. The
material only provides the lower pH limit forbiosorption of Cd(II)
ions.
1 2 3 4 5 6 7 8
3.5
3
2.5
2
1.5
1
0.5
0
qe
(mg/
g)
pH
Figure 1: Effect of change in pH on biosorption of Cd(II) on
UMRS(𝐶0
= 50mg/L, time = 10min).
0
0.5
1
1.5
2
2.5
3
3.5
0 10 20 30 40 50Time (min)
qe
(mg/
g)
Figure 2: Effect of contact time on Cd(II) biosorption by
UMRS(𝐶0
= 50mg/L).
3.2. Effect of Contact Time-Biosorption kinetics. The
contacttime studies are very critical as these endow with the
min-imum time required to remove maximum amount of Cd(II)ions from
the solution and thus help in scaling up the process.The optimum
(equilibrium) time helps in studying the rate ofbiosorption
process. With the help of kinetic data, the ratedetermining step of
the transport mechanism and thus themodeling and design of the
process can be described.
The effect of contact time on the removal of Cd(II) byUMRS is
depicted in Figure 2. It was observed that by increas-ing the time
of contact, the metal removal (𝑞
𝑒
) increasedrapidly. This continued till the 𝑞
𝑒
achieved a maximum valueat a time of contact of 10 minutes.The
rapid increase in the 𝑞
𝑒
values in the initial 10 minutes can be attributed to a
greaternumber of binding sites available during initial stages.
Thisindicated the physical binding of Cd(II) ionswithUMRS [18].As
time proceeded, the number of binding sites was reduceddue to
accumulation of Cd(II) ions on the UMRS leading
-
4 Journal of Applied Chemistry
Table 1: Kinetics of the biosorption of Cd(II) onto UMRS.
Model Linear equation 𝑞𝑒 exp (mg g
−1) Model parameters
Elovich model 𝑞𝑡
=ln (𝑎 × 𝑏)
𝑏+ln 𝑡𝑏
2.924
𝑎 (mg g−1 min−1)𝑏 (gmg−1)
𝑅2
4.62 × 1029
25.640.6931
First order 1𝑞𝑡
=1
𝑞𝑒
+𝑘1
𝑞𝑒
𝑡
𝑘1
(min−1)𝑞𝑒 calc (mg g
−1)𝑅2
0.04522.9140.5245
Pseudo-first order ln (𝑞𝑒
− 𝑞𝑡
) = ln 𝑞𝑒
− 𝑘1
𝑡
𝑘1
(min−1)𝑞𝑒 calc (mg g
−1)𝑅2
0.10740.15370.4734
Second order 1𝐶𝑒
−1
𝐶0
= 𝑘2
𝑡𝑘2
(gmg−1 min−1)𝑅2
0.00260.4644
Pseudo-second order 𝑡𝑞𝑡
=1
𝑘2
𝑞2𝑒
+𝑡
𝑞𝑒
𝑘2
(gmg−1 min−1)𝑞𝑒 calc (mg g
−1)𝑅2
4.68122.9290.999
Intraparticle diffusion 𝑞𝑡
= 𝑘WM√𝑡 + 𝐶𝑘WM (mg g
−1 min−1/2)𝐶
𝑅2
0.02452.79020.6166
to the decrease in the binding of metal ions. Thus the rateof
biosorption decreases in the later stages. After a contacttime of
10 minutes, the graph becomes virtually parallel tothe time axis,
indicating the establishment of the equilibrium.Thus 10 minutes
were taken as the optimum time of contactfor the biosorption of
Cd(II) onto UMRS. This equilibrium(optimum) time is found shorter
than a number of studiesreported in the literature for the
biosorption of Cd(II) ionsonto various biosorbents [18, 20–22].
The reaction kinetics was investigated by using a numberof
different available kinetic models. The experimental dataobtained
from the contact time studies was used for thepurpose.The linear
forms of the Elovich, first-order, pseudo-first-order,
second-order, and pseudo-second-order kineticmodels [23–27] are,
respectively, given as
𝑞𝑡
=ln(𝑎 × 𝑏)𝑏
×ln 𝑡𝑏, (2a)
1
𝑞𝑡
=1
𝑞𝑒
+𝑘1
𝑞𝑒
𝑡, (2b)
ln (𝑞𝑒
− 𝑞𝑡
) = ln 𝑞𝑒
− 𝑘1
𝑡, (2c)
1
𝐶𝑒
−1
𝐶0
= 𝑘2
𝑡, (2d)
𝑡
𝑞𝑡
=1
𝑘2
𝑞2𝑒
+𝑡
𝑞𝑒
, (2e)
where 𝑎 (mg g−1min−1) gives the rate constant and 𝑏 (gmg−1)gives
rate of adsorption at zero coverage in Elovich model.𝑘1
(min−1) is the first-order rate constant, 𝑞𝑒
and 𝑞𝑡
arethe amounts of metal ions sorbed per gram of biomass(mg g−1)
at equilibrium and at time “𝑡,” respectively, and𝑘2
(mg g−1min−1) is the second-order rate constant. Theparameters
for the kinetic models were determined fromrespective plots (Figure
3) and are given in Table 1.
The experimental data were used to study the kineticsof the
process using Elovich model (Figure 3(a)). The valueof coefficient
of determination (𝑅2 = 0.6931) is quite lessthan 0.98.This low
value indicated that the kinetics of Cd(II)biosorption by UMRS
could not be discussed based onthe Elovich model. In other way,
Cd(II)-UMRS biosorptionsystem did not follow Elovich kinetic model.
The literatureshows that Elovich model is the least applied kinetic
modelto biosorption systems, and only a few examples showthe
application of this model over the whole kinetic data[28, 29].
The plots for first-order and pseudo-first-order kineticmodels
are shown in Figures 3(b) and 3(c).The comparison ofthe
experimental and calculated 𝑞
𝑒
values provides a tool fordeciding the fitting of the model over
the experimental data.As shown in Table 1, it can be observed that
the calculated 𝑞
𝑒
(2.914mg g−1) value for the first-order model is comparablewith
the experimental value (2.924mg g−1). This pointedto the possible
fitting of the model for the process. Thevalue of the first-order
rate constant 𝑘
1
is 0.0452 (min−1).However, 𝑅2 (0.5245) is quite less than 0.98.
So, it can beinferred that first-order model cannot be applied to
explainthe biosorption process under study. On the other hand,the
calculated 𝑞
𝑒
(0.1537mg g−1) value for pseudo-first-ordermodel is
significantly different from the experimental 𝑞
𝑒
(2.924mg g−1) value. The value of the pseudo-first-order
rateconstant 𝑘
1
is 0.1074 (min−1). In addition, 𝑅2 value (0.4734)is quite less
than 0.98. Hence it can be concluded that Cd(II)-UMRS biosorption
system did not follow the pseudo-first-order kinetic model. This
observation is in accordance withthe studies reported in the
literature for the fitting of first-order and pseudo-first-order
kinetic models (Table 2).
The plots for second-order (𝑡 versus 1/𝐶𝑒
− 1/𝐶0
) andpseudo-second-order (𝑡 versus 𝑡/𝑞
𝑡
) kinetic models are givenin Figures 3(d) and 3(e). The value of
second-order rateconstant 𝑘
2
was quite low (0.0026 gmg−1min−1).The𝑅2 valuefor the
second-order kineticmodel (0.4644) indicted that this
-
Journal of Applied Chemistry 5
0
0.5
1
1.5
2
2.5
3
3.5
0 1 2 3 4
qt
ln t
y = 0.039x + 2.790
R2 = 0.693
(a)
0.34
0.344
0.348
0.352
0.356
0.36
0 0.5 1 1.5
1/q
t
1/t
y = 0.015x + 0.343
R2 = 0.524
(b)
−7
−6
−5
−4
−3
−2
−1
0
0 20 40 60t
y = −0.107x − 1.872
R2 = 0.473
ln(q
e−qt)
(c)
t
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 20 40 60
y = 0.002x + 0.207
R2 = 0.464
1/Ce
(d)
t
0
2
4
6
8
10
12
14
16
0 20 40 60
t/qt
y = 0.341x + 0.024
R2 = 0.999
(e)
0
1
2
3
4
0 2 4 6 8
qt
y = 0.024x + 2.790
R2 = 0.616
t1/2
(f)
Figure 3: Kinetic models for the binding of Cd(II) onto UMRS (a)
Elovich, (b) first-order, (c) pseudo-first-order, (d) second-order,
(e)pseudo-second-order, and (f) intraparticle diffusion models.
-
6 Journal of Applied Chemistry
Table 2: Comparison of capacity of UMRS with some other reported
biosorbents.
Biomass Biosorption capacity (𝑞𝑚
, mg g−1) Equilibrium modela Kinetic modelb ReferenceSulfonated
Juniperus monosperma wood 1.68 — PSO [42]Juniperus monosperma 2.80
— PSO [42]Zea mays 3.61 — [43]Coconut copra meal 4.92 L, RP —
[44]Nauclea diderrichii 6.30 L PSO [45]Triticum aestivum (straw)
11.56 L — [21]Triticum aestivum (straw) 14.56 L PSO [40]Water
Hyacinth 14.67 — PSO [46]Papaya wood 17.22 L PSO [47]Spent grain
17.30 L — [6]Urea modified Oryza sativa 20.70 L PSO Present
workRhizopus cohnii 40.50 L — [48]aL: Langmuir model; RP:
Redlich-Peterson model.bPSO: pseudo-second-order model.
model cannot be applied to investigate the kinetics of
Cd(II)-UMRS biosorption system.
When the experimental data was used to draw the graphfor
pseudo-second-order kinetic model, straight plot for thewhole set
of data was observed.The comparison of calculated𝑞𝑒
(2.929mg g−1) and experimental 𝑞𝑒
(2.924mg g−1) valuesshowed that the difference between the two
was too small tobe significant.This indicated the possible fitting
of the kineticmodel for the process.The coefficient of
determination (𝑅2 =0.9999) pointed to that the pseudo-second-order
kineticmodel could be used for the investigation of kinetics of
theCd(II) biosorption by UMRS.
It was found that Elovich, first-order, pseudo-first-order,and
second-order models failed to explain the kinetics ofCd(II)
biosorption by UMRS. In some cases, the experi-mental and
calculated 𝑞
𝑒
values were in close proximity; yetthe coefficient of
determination was opposing the fitting ofthe model (first-order
model). Pseudo-second-order kineticmodel was the best model,
showing fitting over the wholeset of experimental kinetic data.
Hence, it can be concludedthat pseudo-second-order model was
suitable to explain thekinetics of the system under study, that is,
Cd(II)-UMRSbiosorption system. A number of authors have studied
thebiosorption of divalent metal ions onto various biosorbentsand
reported that such studies mostly followed pseudo-second-order
kinetics (Table 2).
In order to have an insight into the rate determiningstep, Weber
and Morris model, that is, intraparticle diffusion(IPD)model, was
employed [30].The linear form is shown asfollows: (2f);
𝑞𝑡
= 𝑘WM√𝑡, (2f)
where 𝑘WM is the intraparticle diffusion rate constant(mg
g−1min−1/2). A straight line passing through the originin 𝑞𝑡
versus 𝑡1/2 plot will indicate that the sorption processis
governed by intraparticle diffusion; that is,
intraparticlediffusion is the rate determining step; otherwise
boundarylayer diffusion is the rate controlling step.
As shown in Figure 3(f), the varying extent of the bindingof
Cd(II) during initial and final stages of the experimentled to a
plot virtually parallel to time axis. As the curve didnot start
from the origin (the intercept is not zero), so it canbe inferred
that intraparticle diffusion did not play a role inthe rate
determining step. So, boundary layer diffusion wasthe rate
determining step, and the biosorption of Cd(II) byUMRS was governed
by boundary layer diffusion. The valueof 𝑘WM is shown in Table 1.
However, further studies arerequired to establish this
observation.
3.3. Effect of Concentration-EquilibriumModeling. Therole
ofadsorption in the biosorption of Cd(II) ions by UMRS can
beexplained by the use of equilibriummodeling.The adsorptionmodels
indicate how Cd(II) ions distribute between theliquid and solid
phases at equilibrium. A number of differentmodels have been
employed for the purpose in the presentstudy. These models, namely,
Langmuir equation (3a) [31],Freundlich equation (3b) [32], Temkin
equation (3c) [33],Harkin-Jura equation (3d) [34], and
Dubinin-Radushkevichequation (3e) [35], are given as,
respectively,
𝑞𝑒
=𝑞𝑚
𝐾𝐿
𝐶𝑒
1 + 𝐾𝐿
𝐶𝑒
, (3a)
𝑞𝑒
= 𝐾𝐹
𝐶1/𝑛
𝑒
, (3b)
𝑞𝑒
=𝑅𝑇
𝑏ln (𝐴𝑇
𝐶𝑒
) , (3c)
𝑞𝑒
= (𝐴
𝐵 − log𝐶𝑒
)
1/2
, (3d)
𝑞𝑒
= 𝑞𝑚
exp (−𝛽𝜀2) , (3e)
where 𝐾𝐿
, 𝐾𝐹
, 1/𝑛, 𝐴𝑇
, 𝑏, 𝐴, 𝐵, 𝛽, and 𝜀 are the constants ofthese models.
Experimental data for the biosorption of Cd(II) ions byUMRS is
plotted as 𝐶
𝑒
versus 𝑞𝑒
graph (Figure 4). The fitting
-
Journal of Applied Chemistry 7
Table 3: Equilibrium models studied at 303K.
Model Equation Parameters
Langmuir 𝑞𝑒
=𝑞𝑚
𝐾𝐿
𝐶𝑒
1 + 𝐾𝐿
𝐶𝑒
𝑞𝑚
(mg g−1)𝐾𝐿
(Lmg−1)𝑅𝐿
𝑅2
RMSE
20.700.0409
0.7576–0.23810.98550.65
Freundlich 𝑞𝑒
= 𝐾𝐹
𝐶1/𝑛
𝑒
𝐾𝐹
(mg g−1)𝑛
𝑅2
RMSE
1.20181.65750.91281.22
Temkin 𝑞𝑒
=𝑅𝑇
𝑏ln (𝐴
𝑇
𝐶𝑒
)
𝐾𝑇
(Lmg−1)𝐵 (RT/b, kJmol−1)
𝑅2
RMSE
1.90222.16120.9740.30
Harkin-Jura 𝑞𝑒
= (𝐴
𝐵 − log𝐶𝑒
)
1/2
𝐴
𝐵
𝑅2
RMSE
2.46061.17220.60021.14
D-R 𝑞𝑒
= 𝑞𝑚
exp (−𝛽𝜀2)
𝑞𝑚
(mg g−1)𝛽
𝐸 (kJmol−1)𝑅2
RMSE
5.85321 × 10
−6
0.7070.8140.97
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30
ExperimentalLangmuirFreundlich
Harkin-JuraD-RTemkin
Ce
qe
Figure 4: Equilibrium modeling of Cd(II) biosorption on
UMRS.
of the equilibrium models is also represented on the sameplot.
The values of different equilibrium parameters and 𝑅2values have
been determined with the help of these plots andare shown in Table
3.
The Langmuir model is one of the most frequentlyused equilibrium
models and is employed to determine themaximum capacity of the
biosorbent to bind the metal ions.It assumes that the
uptake/binding of Cd(II) ions occurs onthe homogenous surface by
monolayer adsorption withoutany interaction between adsorbed ions.
The nonlinear form
of Langmuir model is used to explain the behavior of
theCd(II)-UMRS biosorption process. It can be observed thatthe
Langmuir equilibrium curve significantly overlaps theexperimental
data (Figure 4). The 𝑅2 value that is 0.9878(greater than 0.98)
points to the inference that the Langmuirmodel can explain the
equilibrium of the biosorption processunder study. The biosorption
capacity of UMRS (𝑞
𝑚
) wasfound to be 20.7mg g−1, and the adsorption constant𝐾
𝐿
wasfound to be 0.0409 Lmg−1.
The 𝑞𝑚
value thus calculated was used to determine thespecific surface
area (𝑆
𝐿
, m2 g−1) of the material (UMRS) byusing the following
mathematical relationship:
𝑆𝐿
=𝑁𝐴
𝐴𝑞𝑚
𝑀, (3f)
where 𝑁𝐴
is Avogadro number (6.02 × 1023), 𝐴 refers tocross sectional
area of metal ion (Å2), and 𝑀 is the atomicmass of the metal ion.
The specific surface area is calculatedon the basis of the 𝑞
𝑚
value, and it shows the surface areaper gram of the material
occupied by the metal ions. Theatomic mass of cadmium is 112, and
the cross sectional area is3.73 Å2 (the radius of Cd(II) ions for
close packed monolayeris 1.09 Å [18]). The specific surface area
of UMRS for Cd(II)biosorption was found to be 4.15m2 g−1.
The feasibility of Langmuir model is usually expressedby a
dimensionless constant separation factor or equilibriumparameter
𝑅
𝐿
, defined as
𝑅𝐿
=1
1 + 𝐾𝐿
𝐶0
, (3g)
where “𝐾𝐿
” is the Langmuir constant. The value of 𝑅𝐿
indicates the type of isotherm as unfavorable (𝑅𝐿
> 1), linear
-
8 Journal of Applied Chemistry
(𝑅𝐿
= 1), irreversible (𝑅𝐿
= 0), or favorable (0 < 𝑅𝐿
< 1)[36].The 𝑅
𝐿
values were calculated to lie in 0.7576–0.2381. Asthese values
lie between 0 and 1, it can be deduced that theadsorption of Cd(II)
ions onto UMRS is favorable under thestudied conditions.
The Freundlich model assumes the nonzero interactionsbetween the
adsorbate particles and is based on multilayeradsorption on
heterogeneous surface. The nonlinear plot forthe model is shown in
Figure 4. The comparison of the curvefor the Freundlich model with
the experimental data showsthat this model can explain the
biosorption of Cd(II) ions forthe initial set of data only. The
coefficient of determination(𝑅2 = 0.9867) for initial range also
supports the observation.The 1/𝑛 value is less than 1, and it shows
that the sorption ofmetal ions is favorable on UMRS. As the
Freundlich modelstates that the adsorption is exclusively physical
one [18, 37],so it can be inferred that Cd(II) ions are sorbed
physically onthe heterogeneous surface (ofUMRS) forming a layers
havingnonzero interactions between them.
Temkin model provides information about the heat ofadsorption
and the adsorbent-adsorbate interaction on thesurfaces. Harkin-Jura
model indicates the multilayer adsorp-tion. The parameters for the
both equilibrium models areshown in Table 3, and the fitting with
the experimental datais represented in Figure 4. It can be observed
that both themodels do not fit with the experimental data, although
dataseemed to follow Temkin model at the later ends (𝐶
𝑒
>
14mgL−1). Although certain information about the nature
ofsorption are achieved yet due to disagreement of the
experi-mental data with the models, these information/models arenot
suitable to explain the process, and further studies arerequired to
establish the facts. However, 𝐵
𝑇
value (less than8) indicated low heat of adsorption and very
weak interactionsuggesting the process to be physisorption [38,
39].
The physical or chemical nature of biosorption of Cd(II)onto
UMRS can be assessed by determining the energy ofsorption (𝐸) using
the following equation:
𝐸 =1
√2𝛽, (3h)
where 𝛽 is a coefficient related to the mean free energy
ofadsorption (mol2 J−2).The value of𝛽 can be determined usingthe
Dubinin-Radushkevich (D-R) model. The adsorptionprocess will be a
physical adsorption for𝐸 < 8 kJmol−1, and itwill be
chemisorption for 8 < 𝐸 < 16 kJmol−1 [40].The valueof energy
(𝐸) was found to be less than 0.71 kJmol−1, andthus the sorption of
Cd(II) by UMRS was physical in nature.This is in accordance with
the inference obtained from theTemkin model. Figure 4 shows that
D-R model is not beingfollowed by the Cd(II)-UMRS biosorption
system. 𝑅2 valueis quite less than 0.98. Hence, the values of
Polanyi potential(𝜀),𝛽 and the energy of sorption (𝐸) were
determinedwithoutsignificant accuracy. As the systems did not
follow thismodel,the inference about the nature of adsorption
process seemednot to be reliable.
3.4. Effect of Temperature: Feasibility of the Process. The
effectof change in temperature on the Cd(II)-UMRS sorption
Table 4: Values of thermodynamic parameters for
Cd(II)-UMRSsystem.
Temperature(K)
ΔG∘(kJmol−1)
ΔH∘(kJmol−1)
ΔS∘(J K−1 mol−1)
293.16 −1126.58 117.81 409.08303.16 −7979.85313.16 −9308.26
systemwas studied to resolve the thermodynamic parametersand to
investigate the nature/feasibility of the process. It wasobserved
that the sorption capacity increased with increasein temperature.
The 𝑞
𝑒
values increased during the studiedtemperature range (293–313 K)
from 1.9175 to 3.0400mg g−1of UMRS (figure not shown).This
indicated that the sorptionof Cd(II) by UMRS was an endothermic
process and thatUMRS could be effectively used for the biosorptive
removalof Cd(II) ions from aqueous solutions at relatively
highertemperatures.
The experimental data were used to determine the ther-modynamic
parameters like changes in standard free energy(Δ𝐺∘), enthalpy
(Δ𝐻∘), and entropy (Δ𝑆∘) using the followingequations:
Δ𝐺∘
= −𝑅𝑇 ln𝐾𝐷
, (4a)
Δ𝐺∘
= Δ𝐻∘
− 𝑇Δ𝑆∘
, (4b)
where 𝑇 is the absolute temperature (K) and 𝐾𝐷
[(𝐶0
−
𝐶𝑒
)/𝐶𝑒
] is the distribution coefficient.The thermodynamic parameters
given in Table 4 were
determined from the plot of Δ𝐺∘ versus 𝑇 (Figure 5(a)).The
negative values of Δ𝐺∘ at the studied temperaturerange indicated
that the sorption of Cd(II) by UMRS wasthermodynamically feasible
and spontaneous. The decreasein the value of Δ𝐺∘ with temperature
further showed theincrease in feasibility of sorption at elevated
temperatures.In other words, the sorption was endothermic in
nature.The positive value of Δ𝐻∘ also supported this statement.
Thepositive value ofΔ𝑆∘ showed the increased randomness at
thesolid-solution interface during the sorption ofmetal ions, andit
also reflected the affinity of UMRS for metal ions [41].
3.4.1. Activation Energy. Activation energy (𝐸𝑎
) is an impor-tant parameter related to the strength and type of
forcespresent between Cd(II) ions and UMRS. It was determinedusing
the following linear Arrhenius equation [26]:
ln 𝑘2
= ln𝐴1
−𝐸𝑎
𝑅𝑇, (4c)
where 𝑘2
is known as the pseudo-second-order rate constant,𝐴1
is the Arrhenius constant,𝐸𝑎
refers to energy of activation(kJ mol−1), 𝑅 is the ideal gas
constant (8.3134 Jmol−1 K−1),and 𝑇 is the temperature of the medium
(K). A graph wasplotted between ln𝑘
2
and 1/𝑇. The values of energy of activa-tion (𝐸
𝑎
) and Arrhenius contact (𝐴) were determined from
-
Journal of Applied Chemistry 9
0
−2000
−4000
−6000
−8000
−10000
−12000290 295 300 305 310 315
T (K)
y = −409.08x + 117814
R2 = 0.8681
ΔG0
(a)
0
0.5
1
1.5
2
2.5
3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40 3.45(1/T) ×10−3
lnk2
y = −4.1419x + 14.99
R2 = 0.9668
(b)
Figure 5: (a) Thermodynamic modeling and (b) activation energy
for the Cd(II) onto UMRS under optimum conditions.
the slope and intercept of the linear plot (Figure 5(b)).The
𝐸𝑎
value is found to be 34.42 kJmol−1 indicating relatively
weakforces to be involved in the biosorption process indicating
theprocess to be physisorption.
3.5. Dose of UMRS. Dose of biomass is very important
indetermining the minimum amount required to treat a solu-tion of
given metal concentration. By increasing the amountof biomass, the
number of available sites is also increased.Theeffect of dose of
UMRS on percentage adsorption of Cd(II)ions was studied at an
initial concentration of 50mg L−1 byvarying the amount from 0.2 to
1.4 g per 50mL of Cd(II)solution. At optimum conditions, it was
observed that byincreasing the dose, the 𝑞
𝑒
values also increased initially(figure not shown). After
increasing the dose to 0.8 g per50mL, the 𝑞
𝑒
values decreased. The increase in 𝑞𝑒
can beattributed to the increase in the number of sites at
UMRS.After maximum Cd(II) ions are attached at 0.8 g per 50mL,the
increase in dose caused 𝑞
𝑒
values to decrease. As 𝑞𝑒
valuesare calculated by dividing 𝐶
0
− 𝐶𝑒
by mass of UMRS, so 𝑞𝑒
values decreased, although the removal (𝑅%) increased.
Inaddition, the decrease may be attributed to overlapping
oraggregating of sites at UMRS resulting in decrease in totalUMRS
surface area available to Cd(II) ions. It can be inferredthat 0.8 g
of UMRS was sufficient to detoxify a solutioncontaining 50mg Cd(II)
per liter of solution.
3.6. Effect of Agitation Speed. Agitation speed is considered
asone of the important process parameter which significantlyaffects
the biosorption of Cd(II) onto UMRS. When UMRSis made to come into
contact with Cd(II) bearing solution,the metal ions present close
to it are readily attached. Thisgenerates a concentration gradient
in the metal-biomasssystem. By agitating the metal-biomass system,
the effect ofsuch a concentration gradient is minimized, and the
metalions present in the solution are distributed evenly in
thesolution. Moreover, agitation distributes the biomass in
thesolution more evenly as compared to the situation whenthere is
no agitation. On the other hand, agitation also causesdesorption of
the loosely bound metal ions from the surfaceof biomass. So an
optimum speed of agitation is very much
Table 5: Characterization of UMRS.
Elemental analysisC (%)H (%)N (%)S (%)
49.986.867.080.82
FTIR analysis (cm−1) 3819.1; 3287.4; 2349.4; 1697.9; 1429.1;
1048.8;768.5; 674.9
essential for the efficient removal of metal ions from
thesolution.
The effect of agitation speed was monitored on thebiosorption of
Cd(II) by UMRS by varying the speed from50 to 250 rpm at optimum
conditions (figure not shown). Asthe agitation speed was increased,
𝑞
𝑒
value initially increasedand reached a maximum at 125 rpm. After
that, the increasein speed caused the biosorption of Cd(II) to
decrease. Ifagitation speed is low UMRS accumulates in the
solutioninstead of distributing in the solution. Various active
sites areburied forming layers of UMRS on one another and thus
donot participate in the biosorption process. So sorption
occursonly at the top surface layer resulting in lesser 𝑞
𝑒
values.On the other hand, at higher agitation speeds,
desorptionof bound Cd(II) ions increases, and the
sorption-desorptionequilibrium is shifted towards the desorption
and the 𝑞
𝑒
values decreases. On the basis of the previous discussion,
anagitation speed of 125 rpm was selected as an optimum speedfor
the Cd(II) biosorption by UMRS.
3.7. Characterization of UMRS. Elemental analysis and
FTIRanalysis were carried out using powdered, dried urea modi-fied
rice straw.The characterization revealed the informationregarding
adsorption sites in terms of functional groups.Simple rice straw
consists of cellulose (32.24%), hemicellulose(21.34%), lignin
(21.44%), and mineral ash (15.05%) [37].The elemental analysis of
urea modified rice straw showedrelatively higher percentage of
carbon, hydrogen, oxygen, andnitrogen (Table 5). The percentage of
nitrogen, that is, 7.08%is of special concern. The high content of
nitrogen in UMRSpointed to the fact that after modification urea
was attachedto already present functional groups present in the
rice straw.
-
10 Journal of Applied Chemistry
3819.12
3736.433612.40
3287.46
2113.69
2349.46
1697.78
1651.29
1429.15
1048.81
768.53674.90
T (%
)
4000 2000 1000 600.0(cm−1)
157.1156155154153152151150149148147146145144143142141140139138
136.7
Figure 6: FTIR of UMRS.
O
CUMRS
Cd(II)
UMRS CO-N
Cd(II)
Figure 7: Proposed attachment/binding sites of Cd(II) ions onto
theUMRS biosorbent (𝐶
0
= 50mg/L).
The FTIR is an important technique to identify
potentialfunctional groups thatmay participate in the binding
ofmetalions. The characteristic FTIR bands for UMRS (Figure 6)
aregiven in Table 5. A number of peaks/bands can be recognized.The
broadband in 3000–2800 cm−1 region is mainly due toO–H stretching
vibrations. The N–H and C–H bands alsoarise in this region, and
these are buried under the broadO–H band, although some very weak
peaks may be seen.The presence of C≡C and C≡N can be observed by
the peakaround 2300 and 2100 cm−1. The sharp peak at 1697.78
cm−1may be attributed to the carbonyl groups of aldehydes
andketones present in the large molecules in the cell wall of
thebiosorbent material. The presence of a band near 1650
cm−1pointed to the presence of amide group. The C–H bendingand
C–O–C stretching may be observed around 1430 and1050 cm−1,
respectively. Thus it can be inferred that UMRSis polyfunctional in
nature. Cd(II) has been found to attachwith the oxygen and nitrogen
containing functional groupspresent in the biomass. As UMRS is rich
in these functionalgroups, it can be used for the binding of Cd(II)
ions in asignificant amount. The binding may be proposed as shownin
Figure 7.
4. Conclusion
The present study was based on the efficiency evaluation ofa low
cost urea modified agricultural waste material for theadsorption of
Cd(II) ions from water. Characterization ofthe modified adsorbent
using FTIR and elemental analysisaffirmed the urea modification by
showing peaks of amidegroup and a high nitrogen content,
respectively. Process
parameters were optimized for equilibrium study. Accordingto the
results maximum adsorption was observed when 0.8 gper 50mL of
modified adsorbent remained in contact with50mg L−1 Cd(II) ions
solution for 10min at pH 6 keepingagitation speed 125 rpm at
temperature 303K. Five differ-ent adsorption isotherms (Langmuir,
Freundlich, Temkin,Harkin-Jura, and Dubinin-Radushkevich) were used
for theadsorption modeling and equilibrium study. It was
observedthat Langmuir model better fitted to the equilibrium
data,the maximum uptake capacity was found to be 20.70mg g−1,and
𝑅
𝐿
factor showed the favorability of the adsorptionprocess. Temkin
isotherm indicated physisorption to be theoperating process for the
uptake of Cd(II) ions by urea mod-ified adsorbent due to weak
interactions and lower heat ofadsorption. 𝐸 value obtained from D-R
model corroboratedthis statement. Kinetics of the process was
investigated bysix different kinetic models. The kinetic study
indicated thatadsorption mechanism obeyed pseudo-second-order
kineticmodel. Intraparticle diffusion model proposed boundarylayer
diffusion as rate determining step for the process.Thermodynamic
parameters such as Δ𝐺∘, Δ𝐻∘, and Δ𝑆∘showed the exothermic nature of
the process along with itsfeasibility and spontaneity. Increase in
entropy Δ𝑆∘ indicatedthe favorability of adsorption of Cd(II) ions
by urea modifiedrice straw affirming its effectiveness and
application forwaste water treatment. Thus urea modified rice straw
canbe considered a cost effective and benign adsorbent for
theremoval of heavymetal ions such asCd(II) ions from
aqueoussolutions.
References
[1] K. E. Giller, E.Witter, and S. P.Mcgrath, “Toxicity of
heavymet-als to microorganisms and microbial processes in
agriculturalsoils: a review,” Soil Biology and Biochemistry, vol.
30, no. 10-11,pp. 1389–1414, 1998.
[2] M. P. Waalkes, “Cadmium carcinogenesis,” Mutation
Research,vol. 533, no. 1-2, pp. 107–120, 2003.
[3] S. D. Faust and O. M. Aly, Adsorption Process for Water
Treat-ment, Butterworths Publishers, Stoneham, Mass, USA, 1987.
[4] S. S. Ahluwalia and D. Goyal, “Microbial and plant
derivedbiomass for removal of heavy metals from wastewater,”
Biore-source Technology, vol. 98, no. 12, pp. 2243–2257, 2007.
[5] S. Doyurum and A. Çelik, “Pb(II) and Cd(II) removal
fromaqueous solutions by olive cake,” Journal of Hazardous
Materi-als, vol. 138, no. 1, pp. 22–28, 2006.
[6] K. S. Low, C. K. Lee, and S. C. Liew, “Sorption of
cadmiumand lead from aqueous solutions by spent grain,”
ProcessBiochemistry, vol. 36, no. 1-2, pp. 59–64, 2000.
[7] Y. C. Sharma, “Economic treatment of cadmium(II)-rich
haz-ardous waste by indigenous material,” Journal of Colloid
AndInterface Science, vol. 173, no. 1, pp. 66–70, 1995.
[8] K. K. Singh, A. K. Singh, and S. H.Hasan, “Low cost
bio-sorbent“wheat bran” for the removal of cadmium from
wastewater:kinetic and equilibrium studies,”Bioresource Technology,
vol. 97,no. 8, pp. 994–1001, 2006.
[9] S. Deng and Y. P. Ting, “Polyethylenimine-modified
fungalbiomass as a high-capacity biosorbent for Cr(VI) anions:
sorp-tion capacity and uptake mechanisms,” Environmental Scienceand
Technology, vol. 39, no. 21, pp. 8490–8496, 2005.
-
Journal of Applied Chemistry 11
[10] A. J. Francis, C. J. Dodge, J. B. Gillow, and H. W.
Papenguth,“Biotransformation of uranium compounds in high
ionicstrength brine by a halophilic bacterium under
denitrifyingconditions,” Environmental Science and Technology, vol.
34, no.11, pp. 2311–2317, 2000.
[11] S. Lin and G. D. Rayson, “Impact of surface modification
onbinding affinity distributions of Datura innoxia biomass tometal
ions,” Environmental Science and Technology, vol. 32, no.10, pp.
1488–1493, 1998.
[12] J. Wang, “Biosorption of copper(II) by chemically
modifiedbiomass of Saccharomyces cerevisiae,” Process Biochemistry,
vol.37, no. 8, pp. 847–850, 2002.
[13] J. Wang and C. Chen, “Biosorption of heavy metals by
Saccha-romyces cerevisiae: a review,”BiotechnologyAdvances, vol.
24, no.5, pp. 427–451, 2006.
[14] E. L. Errasquı́n and C. Vázquez, “Tolerance and uptake
ofheavy metals by Trichoderma atroviride isolated from
sludge,”Chemosphere, vol. 50, no. 1, pp. 137–143, 2003.
[15] U. S. Orlando, A. U. Baes, W. Nishijima, andM. Okada,
“Prepa-ration of chelating agents from sugarcane bagasse
bymicrowaveradiation as an alternative ecologically benign
procedure,”Green Chemistry, vol. 4, no. 6, pp. 555–557, 2002.
[16] U. Farooq, J. A. Kozinski, M. A. Khan, and M. Athar,
“Biosorp-tion of heavy metal ions using wheat based
biosorbents—areview of the recent literature,” Bioresource
Technology, vol. 101,no. 14, pp. 5043–5053, 2010.
[17] F. A. Chandio, J. Changying, A. A. Tagar, I. A. Mari, T.
Guan-gzhao, and D. M. Cuong, “Comparison of mechanical proper-ties
of wheat and rice straw influenced by loading rates,”AfricanJournal
of Biotechnology, vol. 12, pp. 1068–1077, 2013.
[18] U. Farooq Umar, M. A. Khan, M. Athar, and J. A.
Kozinski,“Effect of modification of environmentally friendly
biosorbentwheat (Triticum aestivum) on the biosorptive removal of
cad-mium(II) ions from aqueous solution,” Chemical
EngineeringJournal, vol. 171, no. 2, pp. 400–410, 2011.
[19] H. Eccles and S. Hunt, Immobilization of Ions By
Biosorption,Ellis Horwood Limited, Chichester, UK, 1986.
[20] O. M. M. Freitas, R. J. E. Martins, C. M. Delerue-Matos,
andR. A. R. Boaventura, “Removal of Cd(II), Zn(II) and Pb(II)from
aqueous solutions by brown marine macro algae: kineticmodelling,”
Journal of Hazardous Materials, vol. 153, no. 1-2, pp.493–501,
2008.
[21] G. Tan and D. Xiao, “Adsorption of cadmium ion from
aqueoussolution by ground wheat stems,” Journal of Hazardous
Materi-als, vol. 164, no. 2-3, pp. 1359–1363, 2009.
[22] L. Nouri, I. Ghodbane, O. Hamdaoui, and M. Chiha,
“Batchsorption dynamics and equilibrium for the removal of
cadmiumions from aqueous phase using wheat bran,” Journal of
Haz-ardous Materials, vol. 149, no. 1, pp. 115–125, 2007.
[23] J. Zeldowitwch, “Urben den mechanismus der
katalytischenoxydation von CO and MnO
2
,” Acta Physicochimica USSR, vol.1, pp. 449–464, 1934.
[24] S. Lagergren, “Zur theorie der sogenannten adsortion
gelosterstoffe, Kungliga Svenska Vetenskapsakademiens,”
Handlingar,Band, vol. 24, no. 1, pp. 1–34, 1898.
[25] Y.-S. Ho, “Citation review of Lagergren kinetic rate
equation onadsorption reactions,” Scientometrics, vol. 59, no. 1,
pp. 171–177,2004.
[26] Y. S. Ho and G. McKay, “Sorption of dye from aqueous
solutionby peat,” Chemical Engineering Journal, vol. 70, no. 2, pp.
115–124, 1998.
[27] Y.-S. Ho, “Review of second-order models for
adsorptionsystems,” Journal of HazardousMaterials, vol. 136, no. 3,
pp. 681–689, 2006.
[28] C. W. Cheung, J. F. Porter, and G. McKay, “Elovich
equationand modified second-order equation for sorption of
cadmiumions onto bone char,” Journal of Chemical Technology
andBiotechnology, vol. 75, no. 11, pp. 963–970, 2000.
[29] C. W. Cheung, J. F. Porter, and G. Mckay, “Sorption
kineticanalysis for the removal of cadmium ions from effluents
usingbone char,”Water Research, vol. 35, no. 3, pp. 605–612,
2001.
[30] W. J. Weber and J. C. Morris, “Advances in water
pollutionresearch: removal of biologically resistant pollutant from
wastewater by adsorption,” in International Conference on
WaterPollution Syposium, pp. 231–236, Pergamon Press, 1962.
[31] I. Langmuir, “The adsorption of gases on plane surfaces
ofglass,mica and platinum,”The Journal of the
AmericanChemicalSociety, vol. 40, no. 9, pp. 1361–1403, 1918.
[32] H. M. F. Freundlich, “Uber die adsorptio nin losungen,”
Zeit-schrift Fur Physikalische Chemie A, vol. 57, pp. 385–470,
1906.
[33] M. Temkin, “Die gas adsorption und der nernstsche
warme-satz,” Acta Physicochimica USSR, vol. 1, pp. 36–52, 1934.
[34] W. D. Harkins and G. Jura, “Surfaces of solids. XIII. A
vaporadsorption method for the determination of the area of a
solidwithout the assumption of a molecular area, and the
areasoccupied by nitrogen and other molecules on the surface of
asolid,” Journal of the American Chemical Society, vol. 66, no.
8,pp. 1366–1373, 1944.
[35] M. M. Dubinin and L. V. Radushkevich, “On the
characteristiccurve equation for active charcoals,” Doklay Akademii
Nauk,vol. 15, pp. 327–329, 1947.
[36] K. R. Hall, L. C. Eagleton, A. Acrivos, and T.
Vermeulen,“Pore- and solid-diffusion kinetics in fixed-bed
adsorptionunder constant-pattern conditions,” Industrial and
EngineeringChemistry Fundamentals, vol. 5, no. 2, pp. 212–223,
1966.
[37] I. A. Rahman and J. Ismail, “Preparation and
characterizationof a spherical gel from a low-cost material,”
Journal of MaterialsChemistry, vol. 3, no. 9, pp. 931–934,
1993.
[38] J. Anwar, U. Shafique,W.-U.Waheed-Uz-Zaman,M. Salman,
A.Dar, and S. Anwar, “Removal of Pb(II) and Cd(II) from waterby
adsorption on peels of banana,” Bioresource Technology, vol.101,
no. 6, pp. 1752–1755, 2010.
[39] C. Theivarasu, S. Mylsamy, and N. Sivakumar, “Removal
ofmalachite green from aqueous solution by activated
carbondeveloped from cocoa (Theobroma cacao) shell: kinetic
andequilibrium studies,” Oriental Journal of Chemistry, vol. 27,
no.3, pp. 1083–1091, 2011.
[40] V. B. H. Dang, H. D. Doan, T. Dang-Vu, and A. Lohi,
“Equilib-rium and kinetics of biosorption of cadmium(II) and
copper(II)ions by wheat straw,” Bioresource Technology, vol. 100,
no. 1, pp.211–219, 2009.
[41] M. Iqbal and R. G. J. Edyvean, “Alginate coated loofa
spongediscs for the removal of cadmium from aqueous
solutions,”Biotechnology Letters, vol. 26, no. 2, pp. 165–169,
2004.
[42] E. W. Shin and R. M. Rowell, “Cadmium ion sorption
ontolignocellulosic biosorbent modified by sulfonation: the
originof sorption capacity improvement,” Chemosphere, vol. 60, no.
8,pp. 1054–1061, 2005.
[43] N. Jamil, M. A. Munawar, S. Babar, and S. T.
Muntaha,“Biosorption of Hg (II) and Cd (II) from waste water by
usingZeaMayswaste,” Journal of the Chemical Society of Pakistan,
vol.31, no. 3, pp. 362–369, 2009.
-
12 Journal of Applied Chemistry
[44] Y.-S. Ho and A. E. Ofomaja, “Biosorption thermodynamics
ofcadmium on coconut copra meal as biosorbent,”
BiochemicalEngineering Journal, vol. 30, no. 2, pp. 117–123,
2006.
[45] M. O. Omorogie, J. O. Babalola, E. I. Unuabonah, and J.
R.Gong, “Kinetics and thermodynamics of heavy metal
ionssequestration onto novel Nauclea diderrichii seed
biomass,”Bioresource Technology, vol. 118, pp. 576–579, 2012.
[46] H. S. Ibrahim, N. S. Ammar, M. Soylak, and M.
Ibrahim,“Removal of Cd(II) and Pb(II) from aqueous solution
usingdried water hyacinth as a biosorbent,” Spectrochimica Acta
PartA, vol. 96, pp. 413–420, 2012.
[47] A. Saeed, M. W. Akhter, and M. Iqbal, “Removal and
recoveryof heavy metals from aqueous solution using papaya wood asa
new biosorbent,” Separation and Purification Technology, vol.45,
no. 1, pp. 25–31, 2005.
[48] J.-M. Luo, X. Xiao, and S.-L. Luo, “Biosorption of
cadmium(II)from aqueous solutions by industrial fungus Rhizopus
cohnii,”Transactions of Nonferrous Metals Society of China, vol.
20, no.6, pp. 1104–1111, 2010.
-
Submit your manuscripts athttp://www.hindawi.com
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation http://www.hindawi.com Volume
2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Journal of
Chemistry
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttp://www.hindawi.com
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing
Corporationhttp://www.hindawi.com Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
The Scientific World JournalHindawi Publishing Corporation
http://www.hindawi.com Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Chromatography Research International
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Journal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Quantum Chemistry
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation http://www.hindawi.com Volume
2014
Hindawi Publishing Corporationhttp://www.hindawi.com Volume
2014
CatalystsJournal of