Studies on Arsenic (III) biosorption from aqueous solution by glutaraldehyde cross-linked chitosan beads

Research Journal of Chemistry and Environment______________________________________ Vol. 18 (4) April (2014) Res. J. Chem. Environ.

62

Studies on Arsenic (III) biosorption from aqueous solution by glutaraldehyde cross-linked chitosan beads

Madala Suguna1* and Nadavala Siva Kumar

2

1. Biopolymers and Thermo physical Laboratories, Department of Chemistry, Sri Venkateswara University, Tirupati – 517 502, A.P., INDIA

2. Department of Biological and Agricultural Engineering Faculty of Engineering, University Putra Malaysia, Serdang,

Selangor Darul Ehsan, MALAYSIA

*[email protected]

Abstract In the present work, the ability of glutaraldehyde

cross-linked chitosan beads (GCC beads) as synthetic

adsorbent for adsorptive removal of As(III) from

aqueous solutions is reported. GCC beads are

synthesized by homogenous reaction of medium

molecular weight chitosan in aqueous acetic acid

solution with glutaraldehyde as cross linking agent.

The biosorbent has been characterized by BET and

FTIR techniques. The effects of experimental variable

parameters such as pH, concentration of metal ion,

amount of adsorbent, contact time and temperature on

adsorption have been investigated. The optimum

solution pH for adsorption of As(III) from aqueous

solutions has been found to be pH 7.0.

Based on R2 and error function values, it is observed

that the kinetic data are better fitted to pseudo-

second-order kinetic and chemisorption models. The

experimental data have been analyzed using

Langmuir and Freundlich adsorption isotherm

models. The monolayer biosorption capacity of GCC

beads as obtained from Langmuir isotherm at 350C is

found to be 68.5 mg/g. The thermodynamic process is

endothermic in nature and spontaneous. These studies

consider the possibility of using GCC beads as cost

effective adsorbent for the removal of As(III) from

aqueous medium. So GCC beads could be an

alternative for more costly adsorbents used for As(III)

removal.

Keywords: Biosorption, Arsenic(III), GCC beads,

Kinetics, Isotherms, Thermodynamics.

Introduction Heavy metals, due to their non-degradable, persistent and

accumulative nature are toxic when present in trace

amounts. Some heavy metals like As, Pb, Cd and Hg are

more toxic even at trace quantities also1. Arsenic is present

in water as a result of both natural and anthropogenic

activities. Arsenic occurs in ground and surface waters in

organic and inorganic forms, though the organic form is

uncommon. Inorganic arsenic can occur in the environment

in several forms2. Arsenic may exist in groundwater both in

+3 and +5 oxidation states depending upon the prevalent

redox conditions. The toxicity of arsenic depends on its

binding form. Inorganic forms of arsenic are more toxic

than organic species. As(III) is more toxic in biological

systems than As(V)3. As(V) can replace phosphate in

several biochemical reactions whereas As(III) may react

with critical thiols in proteins and may inhibit their

activity4,5

.

Arsenic is mobilized through a combination of natural

processes such as weathering reactions, biological activity

and volcanic emissions as well as through a range of

anthropogenic activities such as gold mining, non-ferrous

smelting, petroleum-refining, combustion of fossil fuel in

power plants and the use of arsenical pesticides and

herbicides6.

In recent years arsenic contamination of water and ground

water has become a major concern on a global scale. In

India many districts of West Bengal are facing the problem

of arsenic contamination of ground water7. Usually arsenic

reaches the body through drinking water and contaminated

food with arsenic and causes increased risk of cancer on the

skin, in lungs, liver, kidney and bladder. Consumption of

arsenic also leads to disturbance of the cardiovascular and

nervous system functioning and eventually leading to life

threat8. Arsenic contamination has been acknowledged as a

major public health issue. These serious health effects of

arsenic have alerted the World Health Organization (WHO)

and the United States Environmental Protection Agency

(USEPA) to reduce the drinking water arsenic standard

from 0.05 to 0.01 mg/L9. Drinking water arsenic

concentrations greater than 10 ppb pose a significant health

problem across the World10

.

The conventional removal methods for arsenic and other

heavy metals from drinking water and waste waters include

reverse osmosis, chemical precipitation, solvent extraction,

filtration, ion-exchange, phytoremediation, electro dialysis,

electro flotation, chemical oxidation or reduction,

coagulation and adsorption. The methods available for the

removal of arsenic have adequately been reviewed by

Mohan and Pittman11

. Although flotation12

, precipitation

with sulfide13

, coagulation14

and filtration and ion

exchange15

have been used for arsenic removal, there exist

certain disadvantages as those could produce large amounts

of toxic sludge which requires further treatment before

disposal in to the environment.

Among the various waste water treatment techniques,

biosorption of heavy metals is a promising alternative

method due to its high selectivity and easy handling. The

major advantages of the biosorption technology are its


63

effectiveness in reducing the concentration of heavy metal

ions to very low levels and the use of inexpensive

biosorbent materials16

. A number of researchers have

studied the adsorption of As(III) on different sorbents such

as iron hydroxide coated alumina17

, activated alumina18

,

iron oxide coated cement19

, granular ferric hydroxide20

,

iron (III) loaded chelating resin21

, Zr (IV) - loaded

chelating resin22

, chitosan coated biosorbent8 and iron-

chitosan composite23

are used as adsorbents for the removal

of arsenic from aqueous environment.

Over the past couple of decades, biosorption has drawn

more attention of the scientists due to the diversity of the

available sorbent material such as fungal or bacterial

biomass and alginate or chitosan biopolymers. Chitosan is

an alkaline deacetylated product of chitin. The amine

groups on chitosan are much more reactive than the

acetamide groups on chitin24

. Yang and Zall25

have

reported that chitosan has the highest chelating ability in

comparison with other natural polymers obtained from

seafood wastes and natural substances like bark, activated

sludge and the synthetic polymers. But in natural form it is

soft and has a tendency in aqueous solution to agglomerate

or to form a gel. In addition, the active binding sites are not

readily available for sorption in its natural form thereby

reducing sorption capacity. Therefore chitosan is

chemically crosslinked with glutaraldehyde to improve

chemical and mechanical resistance and to improve metal

sorption capacity.

The main objectives of this study are to prepare

glutaraldehyde cross-linked chitosan beads to remove

As(III) ions from aqueous solution. The effects of contact

time, solution pH, concentration of metal ions, temperature

and amount of biomass on the extent of adsorption are also

studied. The kinetic data are checked for the pseudo-first-

order, pseudo-second-order, chemisorption, Weber-Morris

model, Boyd model, fractionary order reaction kinetic

models and the rate constants are evaluated. The

equilibrium data are fitted to Langmuir, Freundlich and

Sips isotherm models. In addition, the biosorbent is

characterized by BET and FTIR analysis to examine the

metal accumulation due to the presence of different

functional groups on biosorbent. The obtained results may

provide useful data for future scale up using this material as

a low cost and promising adsorbent for the removal of

As(III) from aqueous solutions.

Material and Methods Chemicals and equipment: All the chemicals used in the

study were of analytical grade and used without further

purification. Chitosan with molecular weight 9.9 ×105

g/mol was purchased from Sigma-Aldrich, St. Louis, MO,

U.S.A. Deionized double-distilled water was used for the

preparation of standard solutions. An adsorbate stock

solution of 1000 mg/L of arsenic (III) was prepared by

dissolving As2O3 (Sigma–Aldrich) in deionized double-

distilled water. The range of concentrations prepared from

stock solution varied from 100 to 400 mg/L. The pH of the

solution was measured with a Digisun electronics digital

pH meter (Model: 2001, Hyderabad, India) using solid

electrode calibrated with a standard buffer solutions of pH

4.0, 7.0 and 9.2. FTIR spectrometer (Thermo-Nicolet FTIR,

Nicolet IR-200, USA) was used for the IR spectral studies

(4000–400 cm−1

) of adsorbent. The metal As(III)

concentrations in the samples were determined using

atomic absorption spectrophotometer (AAS; Model AA

6300, Shimadzu, Japan) with arsenic hollow cathode lamp.

Absorbance was measured at wavelength of 193.7 nm

using 12 mA lamp current and a spectral slit width of 0.7

nm. The signals were registered using a Canon LBP-2900B

Laser Printer.

Preparation of glutaraldehyde cross-linked chitosan

beads: The glutaraldehyde cross-linked chitosan beads

(GCC beads) were prepared as follows:26

Chitosan solution

was prepared by dissolving 2.0 g of chitosan flakes in 60

ml of 5% (v/v) acetic acid solution. The chitosan solution

was sprayed into a precipitation bath containing 500 mL of

0.5 M NaOH which neutralizes the acetic acid within the

chitosan gel and thereby coagulates the chitosan gel to

spherical uniform chitosan gel beads. A magnetic stirrer

was used in stirring the aqueous NaOH solution. The wet

chitosan gel beads were extensively rinsed with distilled

water to remove any residual NaOH, filtered out and finally

air-dried in order to remove the water from the pore

structures.

Freshly prepared wet chitosan beads were suspended in

0.025 M glutaraldehyde solution to obtain a ratio of 1:1

with chitosan. The chitosan beads in resulting

glutaraldehyde solution are kept standing for 24 h at the

range of room temperature is 20-25oC. After 24 h the cross-

linked chitosan beads were intensively washed with

distilled water to remove excess glutaraldehyde, filtered

and air-dried at room temperature.

Batch studies: Batch adsorption studies were carried out

by adding 100 mg of GCC beads to 100 mL of metal

solution taken in a 125 mL Erlenmeyer flask. The

equilibration (shaking) time was 4 h at an agitation speed of

200 rpm on a Lab line rotatory shaker. The initial pH was

adjusted with solution of 0.1M HCl or 0.1M NaOH.

Equilibrium isotherm measurements were carried out by

keeping the solution volume (100 mL) and amount of GCC

beads was kept constant by varying the concentration of

As(III) ions. For kinetic studies, samples were withdrawn at

periodic time intervals and filtered by using Whatmann No.

42 filter paper.

Atomic absorption spectrophotometer was used for the

determination of As(III) before and after adsorption. The

effects of contact time, metal ion concentration, adsorbent

dose, effect of pH and effect of temperature are studied.

The adsorption on the glassware was found to be negligible

and was determined by running blank experiments. Each


64

experiment was repeated at least three times and mean

values were taken. Based on mass balance, the amount

adsorbed per unit mass of adsorbent (Qe) is obtained using

the following equation:

i ee

C CQ v

m (1)

where Qe (mg/g) is the adsorption capacity at equilibrium,

Ci and Ce denote respectively the initial and equilibrium

concentrations of metal ion (mg/L), V is volume of the

solution (L) and m is the mass of the adsorbent (g). The

effect of pH on adsorption was studied by carrying out the

experiment at different pH values, keeping the

concentration, volume of adsorbate solution and amount of

adsorbent constant. The effects of adsorbent dose on

adsorption of metal ions were studied by agitating 100 mL

of 100 mg/L metal solution with different amounts of

adsorbent.

Statistical evaluation of the kinetic parameters 1. Marquardt’s percent standard déviation (MPSD): The MPSD error function

27 is employed in this study to

find out suitable kinetic model to represent the

experimental data. The MPSD error function has been used

previously by a number of researchers in the field26

.

2

mod exp

exp

1% 100х .

1

pi el i

error

i i

q qF

q p (2)

where qimodel is each value of q predicted by the fitted

model and qiexp is each value of q measured experimentally

and p is the number of experiments performed.

2. The sum of the squares of the errors (SSE): The SSE

is defined as:

SSE = 2

exp model

1

( )p

i i

i

q q (3)

3. The hybrid fractional error function (HYBRID): This

error function was developed in order to improve the fit of

the SSE method at low concentration values28

:

HYBRID = exp model

1 exp

( )100

p-n

pi i

i i

q q

q (4)

Adsorption kinetics Adsorption kinetic study is important in treatment of

aqueous solutions as it provides valuable information on

reaction path-ways and in the mechanism of adsorption

reactions. Many kinetic models were developed to find out

kinetic adsorption constants.

1. First-order kinetics: Regarding kinetic modeling of As

(III) biosorption, the pseudo first order rate expression is

given by

1log( ) log2.303

e t e

kQ Q Q t

(5)

where Qe and Qt are the amounts of metal ion adsorbed per

unit mass of adsorbent at equilibrium and at time t (min). k1

is the rate constant of adsorption.

2. Fractionary order: Pseudo-first and pseudo–second–

order kinetic models are being used for most adsorption

kinetic works, determination of kinetic parameters, possible

change of the adsorption rates as function of initial

concentration and adsorption time. An alternative

fractionary order kinetic equation proposed by Avrami29,30

is used to analyze the present data:

α 1 exp[ ( )]n

AVk t (6)

where α is adsorption fraction (qt /qe) at time t, kAV is the

Avrami kinetic constant (min-1

) and n is a fractionary

reaction order.

3. Second order kinetics: Experimental data are also

analyzed in terms of pseudo-second-order kinetic model

which is given by the following equation:

2

2

1 1

t e e

tt

Q k Q Q (7)

where k2 (g/mg/min) is the rate constant of the second-

order equation, Qt (mg/g) is the amount adsorbed at time t

(min) and Qe is the amount adsorbed at equilibrium (mg/g).

4. Chemisorption: The Elovich equation is commonly

used to determine the kinetics of chemisorption of gases

onto heterogeneous solids and in recent years, this equation

has been found to be valid to describe the sorption of

pollutants from aqueous solution31

. The equation has been

applied satisfactorily to some chemisorption processes and

has been found to cover a wide range of slow adsorption

rates. The Elovich equation could be written in the

following form:

1 1ln( ) ln( )

β βtQ t

(8)

where α is adsorption rate (mg/g/min) and β is related to

the extent of surface coverage and the active energy

involved in chemisorption (g/min).


65

5. Weber-Morris method: In the case of batch mode

operation, there is a possibility of transport of sorbate

species into the pores of sorbent which denotes the rate

controlling step. An intra particle diffusion model proposed

by Weber-Morris could be written as follows:

1/ 2Q k t C

t id (9)

where Qt (mg/L) is the amount adsorbed at time t (min), kid

(mg/g min-1/2

) is the rate constant of intraparticle diffusion.

C is the value of intercept which gives an idea about the

boundary layer thickness i.e. larger is the intercept, greater

is the boundary layer effect.

6. Boyd model: Boyd model32

is applied to check that

sorption proceeds via film diffusion or intraparticle

diffusion mechanism and can be written in the following

form:

2(1 - ) exp(-6

)t

F B

(10)

where F = qt/qe; qe is the amount of metal ions adsorbed at

equilibrium (mg/g), qt represents the amount of ions

adsorbed at any time t (min) and Bt is a mathematical

function of F. Eq. 10 can be rearranged by taking the

natural logarithm to obtain the equation:

tB = -0.4977 - ln(1 - F)

(11)

Adsorption isotherms Langmuir isotherm: Langmuir model is generally used to

describe equilibrium adsorption data. This is valid for

monolayer sorption on to a surface with a finite number of

identical sites which is given by:

e

e

o

bC

bCQQ

1e

(12)

where Q0 is the maximum amount of the metal ion

adsorbed per unit weight of GCC beads to form a complete

monolayer on the surfaces at equilibrium concentration and

b is related to affinity of the binding site.

Freundlich isotherm: A widely used empirical Freudlich

equation, based on sorption on a heterogeneous surface is

given by:

nef CKQ1

e (13)

where Kf and n are Freundlich constants, Kf and 1/n

indicate the adsorption capacity and adsorption intensity

respectively.

At low sorbate concentration it effectively reduces to a

Freundlich isotherm while at high sorbate concentration it

predicts a monolayer adsorption capacity characteristic of

the Langmuir isotherm.

Thermodynamic parameters: Based on fundamental

thermodynamics concepts, it is assumed that in an isolated

system, energy cannot be gained or lost and the entropy

change is the only driving force. In environmental

engineering practice, both energy and entropy factors must

be considered to determine the process occurrence

spontaneously. The thermodynamic parameters such as the

enthalpy change (ΔH0), the entropy change (ΔS

0) and the

free energy changes of the sorption (ΔG0) are calculated

using the following well-known relations33

:

0Δ ln LG RT K

(14) 0 0 0Δ ΔH ΔSG T (15)

0 0Δ ΔL

S HlnK

R RT (16)

where R is gas constant and KL is Langmuir constant.

Results and Discussion Characterization of the biosorbent: FTIR spectra of GCC

beads, before and after adsorption of metal ions are shown

in fig. 1. The spectra display a number of peaks, indicating

the complex nature of the material examined. The broad

and intense absorption peaks around 3400 cm-1

were

indicative of the existence of bounded hydroxyl groups (-

OH) or amine (-NH) groups of the biomass (3400–3436

cm-1

). The peaks observed at 2920 cm-1

could be assigned

to the C-H group. The spectrum of glutaraldehyde cross

linked chitosan displayed the intense peak at 1642.9 cm-1

which can be due to the N=C stretching of the imine group.

This clearly indicates the cross linking reaction with

glutaraldehyde. The intense bands at 1070 cm-1

are

assigned to the C-O of alcohols and carboxylic acids. This

figure reveals that all functional groups are actually present

in chitosan that are intact even after cross linked with

glutaraldehyde and are available for interaction with the

metal ions. The intensity of transmittance of peaks is

relatively more in the case of metal-ions-loaded GCC beads

compared with unloaded GCC beads. This higher intensity

may be attributed to the presence of a lesser number of

functional groups in the loaded GCC beads i.e. some

functional groups are binded with metal ions.

Surface Area Analysis: Surface area, pore volume, pore

diameter and porosity of the GCC beads were determined

on the basis of the BET (Brunauer, Emmett and Teller)

instrument (Micromeritirics ASAP-2000, USA). Surface

area is measured by assuming that the adsorbed nitrogen

forms a monolayer and posses a molecular cross sectional

area of 16.2 A˚2/molecule. The isotherm plots were used to

calculate the specific surface area (N2/BET method) and


66

average pore diameter of GCC beads while micropore

volume is calculated from the volume of nitrogen adsorbed

at p/po 1.2. The shape of the adsorbent is nearly spherical

with particle diameter ranging from 100–150 mm. The

sorbent material shows an average surface area of 121.6

m2/g, pore volume of 0.36 cm

3/g, pore diameter 32.8 nm

and porosity of 50.12%.

Effect of pH: The pH of the solution is an important

variable parameter which governs metal adsorption. The

effects of pH on metal biosorption have earlier been studied

by many researches and the results indicate that pH of the

solution can significantly influence the biosorption23,34

. The

variation of adsorption capacity of GCC beads with pH for

As(III) is graphically presented in fig. 2. In order to

evaluate the influence of this parameter on the adsorption

of As(III), the experiments were carried out in the pH range

of initial pH 2-9. The free amino groups (-NH2) in chitosan

(Ch-) exist in equilibrium with the protanated amino group

in presence of acidic aqueous solution.

Ch-NH2 + H2O ↔ Ch-NH3+ + OH

-

The removal of As (III) increases as the pH of the system

increases and reaches maximum at pH 7.0 followed by a

sharp decrease in the extent of adsorption up to pH 9.0. As

(III) exists in non-ionic (H3AsO3) and anionic (H2AsO3-)

forms in the pH range of 2.0-9.0 and 10-12 respectively35

.

In acidic conditions the surface of GCC beads is highly

protanated and such a situation is not favorable for the

removal of As(III). When pH increases, the degree of

protanation of the adsorbent surface decreases.

Therefore, the adsorption of As(III) would be less strongly

influenced by charge repulsive forces. Given adsorbing

species are uncharged, adsorption will occur most readily

on all surface sites36

. In alkaline medium the negative

charged adsorbate species start dominating and the surface

of the adsorbent also acquires negative charge. Hence

repulsive forces exist between adsorbent and adsorbate

resulting in a decrease of adsorption.

Effect of contact time: The effect of contact time on the

extent of adsorption of As(III) on GCC beads at different

concentrations was studied. The extent of adsorption

increased with time and attained equilibrium for all the

concentrations of As(III) studied (100, 200, 300, 400 mg/L)

at 180 min. After this equilibrium period, the amount of

metal adsorbed did not change significantly with time

indicating that this time is sufficient to attain equilibrium

for the maximum removal of As(III) from aqueous

solutions by GCC beads.

Effect of adsorbent dosage: One of the parameters that

strongly affect the biosorption capacity is the amount of the

biosorbent. Quantity of biomass can influence the extent of

metal uptake from solution. The dependence of metal

sorption on dose is studied by varying the amount of

adsorbents from 0.05 to 0.5g while keeping other

parameters (pH and contact time) constants. The effect of

adsorbent dose on the extent of adsorption is studied and it

is noticed that the extent of removal of metal ions increases

with an increase in the amount of adsorbent. The removal

efficiency increases up to an optimum dose, beyond which

the increase in removal efficiency becomes negligible for a

given initial concentration. This is to be expected because

for a given fixed initial solute concentration, increasing the

adsorbent dose provides a greater surface area or adsorption

sites. The results indicate that the GCC beads remove 89 %

of As(III) as shown in fig. 3.

Adsorption kinetics: For the pseudo-first-order rate

constant k1, fractionary order constant kav are obtained from

plots of ln(qe-qt) vs. t and ln[-ln(1-Qe/Qt)] against time (t)

for As(III) analyzed. Approximately, linear fits are

observed. The kinetic models are used to fit experimental

data by non linear regression, using three different error

functions. The correlation coefficient, rate constant k1

and error function values have been calculated and are

summarized in table 1.

The pseudo-second order sorption rate constants k2 of

As(III) are calculated from the slopes of the plots of t/Qt vs.

t (Figure not shown). Equilibrium adsorption capacity Qe

along with the correlation coefficients for As(III)

adsorption on GCC beads is shown in table 1. It may be

concluded that the data are well fitted to pseudo-second-

order kinetic model on the basis of higher R2 values, the

low error function values and the calculated Qe (cal) values

are closer to the experimental data than the calculated

values of pseudo-first-order kinetic model. The error

function evaluates the differences associated with each

individual point fitted by the model in relation to each

experimental point measured. This observation supports the

contention that the adsorption of As(III) on GCC beads

follows pseudo-second-order kinetic model.

Weber-Morris method: If the plots of Qe vs. t1/2

are linear

and pass through the origin, it indicates that intraparticle

diffusion alone determines the overall rate of adsorption.

The intraparticle diffusion rate constant kid, correlation

coefficient and error function values are given in table 1.

However, the linear plots could not pass through the origin,

indicating that the intra particle diffusion is not the only

rate determining factor. This indicates that the mechanism

of metal ions adsorption by GCC beads is complex and

both, the surface adsorption as well as intraparticle

diffusion contribute to the rate determining step.

Chemisorption: The plots of ln (t) vs. Qt are presented in

fig. 4. The values of α, β and error function values are

given in table 1. The plots are linear and with good

correlation coefficients and low error function values. The

equilibrium concentrations, calculated from this model are

closely related with experimental equilibrium concentration

values. This suggests that the sorption system studied


67

belongs to the pseudo-second-order kinetic model based on

the assumption that the rate determining step may

bechemisorption, involving valence forces through sharing

or exchange of electrons between adsorbent and adsorbate.

Boyd model: The Boyd model plots of Bt vs. t at different

initial concentrations of As(III) are shown in fig. 5. The

plots showed that the adsorption process is controlled by

film diffusion that means adsorption mechanism was

governed by external mass transport. Adsorbate ions travel

towards the external surface of the adsorbent.

Adsorption isotherms: Q0 and b are determined from the

linear plots of 1/Ce vs. 1/Qe. The linearized Langmuir

adsorption isotherms of As(III) ions obtained at the

temperatures of 25, 30 and 350C are shown in fig. 6. The

values of the parameters and correlation coefficient (R2) of

As(III) are summarized in table 2.

It is noted that the Langmuir isotherm model exhibits better

fit to the sorption data of As(III) over the Freundlich

isotherm model. The value of Q0 determined from the

Langmuir model increases with increase in temperature,

thereby confirming that the process of adsorption is

endothermic. Comparing the monolayer adsorption

capacity of GCC for As(III) obtained in the present study

with those included in table 3 indicates that the GCC beads

show higher adsorption capacity compared with many of

the adsorbents reported in literature. This observation

clearly demonstrates the enhancement in the uptake of

As(III) as a result of chitosan cross linking with

glutaraldehyde.

Freundlich isotherm constants n and Kf for As(III) are

calculated at different temperatures (25, 30 and 350C) from

the slope and intercept as shown in fig. 7 and presented in

table 2. The R2 values of Freundlich isotherm from table 2

indicate that this model has not been able to adequately

describe the relationship between the amounts of As(III)

adsorbed by the biomass and its equilibrium concentration

in the solution. The adsorption capacity, Kf was found to

increase with an increase in temperature which suggests

that adsorption process is endothermic in nature.

Table 1

Values of the parameters of kinetic models for As(III) on GCC beads

Parameter Initial concentration of As(III) (mg L-1

)

100 200 300 400

Pseudo-first-order-kinetic model

k1 (min–1

) 0.007 0.005 0.003 0.003

R2 0.967 0.987 0.974 0.971

Qe,(cal) (mg g-1

) 19.98 17.90 19.01 27.35

Qe,(exp) (mg g-1

) 37.66 55.61 90.63 130.37

MPSD (%) 79.0 81.0 84.0 90.0

HYBRID 469.0 692.0 790.0 753.0

SSE 323.0 1483 5129 10606

Pseudo-second-order-kinetic model

k2 g mg-1

min-1

0.001 0.001 0.001 0.001

R2 0.999 0.997 0.995 0.995

Qe, (cal) (mg g-1

) 41.5 59.2 94.3 137.0

MPSD (%) 1.1 0.2 0.9 1.6

HYBRID 38.7 0.03 0.83 3.26

SSE 14.6 0.017 0.75 4.25

Weber-Morris

kid mg g-1

min-1

1.378 1.355 1.743 2.500

R2 0.912 0.982 0.933 0.912

Qe, (cal) (mg g-1

) 37.63 54.68 88.32 126.7

MPSD (%) 2.2×103 0.017 0.025 0.014

HYBRID 7.9 16.00 25.00 28.00

SSE 0.97 0.86 5.32 13.24

Chemisorption

α (mg g-1

min-1

) 10.4 186.8 3.4 × 103 5 × 10

3

β (g mg-1

) 0.15 0.15 0.13 0.11

R2 0.977 0.967 0.875 0.833

MPSD (%) 2.3 0.4 1.7 2.0

HYBRID 1.9 0.1 2.7 5.4

SSE 0.7 0.05 2.4 7.1


68

Table 2

Langmuir and Freundlich isotherms constants for adsorption of As(III) on GCC beads at different temperatures.

Temperature K Langmuir Freundlich

Q0 b R

2 Kf n R

2

298 55.9 0.045 0.994 1.12 1.42 0.966

303 60.6 0.034 0.997 3.32 1.55 0.976

308 68.5 0.022 0.993 4.22 1.71 0.936

Table 3

Comparison of maximum adsorption capacity (mg g-1

) of GCC beads for As(III) on different adsorbents

* Present study

Table 4

Values of thermodynamic parameters for the adsorption of As(III) on GCC beads.

Δ H0

(kJ mol-1

)

Δ S0

(J mol-1

K-1

)

Temperature

(K) -ΔG

0 (kJ mol

-1) R

2

39.09 0.135

298 2.36

0.998 303 1.82

308 1.02

Wave numbers (cm

-1)

Fig. 1: FTIR spectra of GCC beads (a) Pure GCC beads (b) loaded with As(III).

Biosorbent Adsorption capacity (mg g-1

) pH

Iron oxide coated sand7

28.57 μg g-1

7.5

Alumina Coated chitosan8

56.50 4.0

Iron hydroxide coated Alumina17

7.64 6.6-6.7

Granular Ferric hydroxide20

2.30 8.0-9.0

Iron(III)-loaded chelating resin21

62.93 9.0

Zr(IV)-loaded chelating resin22

49.15 9.0

Iron coated chitosan23

22.47 7.0

FeS-coated sand37

10.7 7.0

Iron doped phenolic resin38

13.0 6.5

Chitosan Coated Sand39

17.0 7.0

Macrofungus (Inonotus hispidus)40

51.9 6.0

Algae (Maugeotia genuflexa) biomass41

57.48 6.0

Lichen (Xanthoria parietina) biomass42

63.8 6.0

Green algae(Ulothrix cylindricum) biomass43

67.2 6.0

Glutaraldehyde cross-linked chitosan beads*

68.5 7.0


69

1 2 3 4 5 6 7 8 9 100

5

10

15

20

25

30

35

40

Ad

sorp

tion

cap

acit

y (m

g/g)

pH Fig. 2: Effect of pH for adsorption of As(III) on GCC

beads. Experimental conditions: initial concentration

= 100 mg/L; contact time = 4h;

agitation rate = 200 rpm.

As

0

10

20

30

40

50

60

70

80

90

100

0 0.1 0.2 0.3 0.4 0.5 0.6

Amount of adsorbent (g/L)

Percen

t rem

ov

al

Fig. 3: Effect of adsorbent dose on percent removal of

As(III) on GCC beads. Experimental conditions: for

As(III): initial concentration = 100 mg/L;

contact time = 4h; pH 7.0.

Elovich

0

20

40

60

80

100

120

140

2 3 4 5 6

Ln (t)

Ad

sorp

tio

n c

ap

acit

y (

mg

/g)

100 mg/L

200 mg/L

300 mg/L

400 mg/L

Fig. 4: Elovich model for adsorption of As(III) on

GCC beads. Experimental conditions: for As(III): pH

7.0; initial concentration = 100 mg/L;

biosorbent dosage = 0.1g/0.1L.

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

Time (min)

Bt

100 mg/L

200 mg/L

300 mg/L

400 mg/L

Fig. 5: Boyd model for adsorption As(III) on GCC

beads. Experimental conditions: for As(III): pH 7.0;

initial concentration = 100 mg/L;


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

1/Ce

1/Q

e

As-308 K

As-303 K

As-298 K

Fig. 6: Langmuir isotherms for adsorption of As(III)

on GCC beads. Experimental conditions: for As(III):

pH 7.0; initial concentration = 100 mg/L;

biosorbent dosage =0.1g/0.1L.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.5 1 1.5 2

Log Ce

Lo

g Q

e

As-308 K

As-303 K

As-298 K

Fig. 7: Freundlich isotherms for adsorption of As(III)

on GCC beads. Experimental conditions: for As(III):

pH 7.0; initial concentration = 100 mg/L;



70

The values of n between 1 and 10 (i.e. 1/n less than

1) represent a favorable sorption37

. For the present study

the values of n also follows the same trend. Higher is the

value of 1/n, higher will be the affinity between the

adsorbate and adsorbent to reveal heterogeneity of the

adsorbent sites.

Thermodynamics: The values of ΔG

0 for sorption of As

(III) on GCC beads at different temperatures are given in

table 4. The negative values of ΔG0 indicate feasibility and

spontaneity of the process of removal of metal ions by

adsorption on the GCC beads. The values of ΔH0 and ΔS

0

are determined from the slope and intercept of the plot of ln

KL vs. 1/T (Figure not shown). From table 4 it is clear that

the positive value of enthalpy indicates that the process of

removal of As(III) is endothermic in nature.

Conclusion

In this study, the use of GCC beads as a biosorbent has

been successfully examined in the removal of As (III) ions

from aqueous solution. The following conclusions are made

based on the results of the present study:

The kinetics of As(III) ions biosorption on glutaraldehyde

cross-linked chitosan beads depends on the experimental

conditions particularly medium pH, initial metal ion

concentration, biosorbent dosage, contact time and

temperature. As the pH increased, the metal biosorption

capacity increased significantly up to pH 7.0. The

equilibrium data were fitted very well to the Langmuir

isotherm model. The maximum monolayer biosorption

capacity of GCC beads was found to be 68.5 mg/g.

Comparing the equilibrium capacities of the kinetic models

with the experimental and calculated equilibrium capacities

of the biosorbent, second order equation seems to give a

best fit of the experimental data. The rate determining step

may be chemisorption, involving valence forces through

sharing or exchange of electrons between adsorbent and

adsorbate. This suggests that rate limiting step is a chemical

adsorption phenomenon. Based on the thermodynamic

constants ΔG0, ΔH

0 and ΔS

0, biosorption of As(III) on

GCC beads is an endothermic and spontaneous process.

Studies conducted using synthetic metal ion solutions

revealed the practical application of the glutaraldehyde

cross-linked chitosan as a potential biosorbent for the

removal of As(III) from aqueous medium.

Acknowledgement

Madala Suguna is thankful to DST, New Delhi, India for

the award of Women Scientist and the financial support of

this research project, SR/WOS-A/CS-76/2011/.

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(Received 19th December 2013, accepted 12

th February

2014)

Studies on Arsenic (III) biosorption from aqueous solution by glutaraldehyde cross-linked chitosan beads

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