Kinetic, Equilibrium and Thermodynamic Studies on Removal of Cr(VI) by Modified Activated Carbon...

Coromandal Journal of Science,

Vol. 1, No. 1, December 2012. pp.30-39.

Kinetic, Equilibrium and Thermodynamic Studies on Removal of Cr(VI) by

Modified Activated Carbon Prepared from Ricinus Communis Seed Shell

P. Thamilarasu1, R. Sharmila

2 and K. Karunakaran

3

1Department of Chemistry, AMS Engineering College, Namakkal. 3Department of Chemistry, Sona College of Technology, Salem.

Email [email protected], [email protected]

ABSTRACT

Removal of hexavalent chromium ions from aqueous solutions by using modified activated carbon prepared

from Ricinus Communis seed shell was studied. It was carbonized and activated by treating with concentrated

sulphuric acid followed by heating for 5 hours at 500oC. Then, it was modified by the polymerization of

activated carbon with pyrrole solution. Batch adsorption experiments were carried out as a function of pH,

contact time, initial concentration of the adsorbate, adsorbent dosage and temperature. The experimental data

was fitted well to the Freundlich isotherm. Thermodynamic parameters such as ∆Ho, ∆S

o, and ∆G

o were

calculated, which indicate that the adsorption was spontaneous and endothermic nature. Adsorbent used in this

study, characterized by FT-IR and SEM before and after the adsorption of hexavalent chromium ions.

Keywords— Adsorption, Isotherm, Chromium and modified Ricinus Communis seed shell.

1. INTRODUCTION

The pollution by heavy metals has received wide spread

attention in the recent years [1], due to the toxicological

importance in the ecosystem, agriculture and human

health. Concerning over this problem has led to the

development of alternative technologies for effecting the

removal of these pollutants from aqueous effluents. The

use of low-cost and waste biomaterials as adsorbents of

dissolved metal ions has been shown to provide economic

solutions to this global problem [2]. In this context, our

adsorbent (Ppy/RRC : Polypyrrole coated Ricinus

Communis seed shell activated carbon) can be used as an

effective and environmentally friendly adsorbent for the

treatment of Cr(VI) containing wastewaters.

Chromium is a highly toxic pollutant generated from

many industrial processes such as leather tanning

processes, electroplating, and manufacturing of dye, paint

and paper. Chromium exists in the aquatic environment

mainly in two states; trivalent Chromium and hexavalent

Chromium. Hexavalent chromium is primarily present in

the form of chromate and dichromate ions[3]. The

USEPA has set the maximum contaminate level for

chromium in drinking water at 0.1mg/L. These standards

are based on the total concentration of the trivalent and

hexavalent forms of dissolved chromium. Chromium has

the potential to cause the following health effects from

long-term exposures at levels above the MCL: damage to

liver, kidney circulatory and nerve tissues; dermatitis.

Furthermore, chromium has serious effects on the health

of human being [4].

Conventional methods for removing dissolved heavy

metal ions include chemical precipitation, chemical

oxidation and reduction, ion exchange, filtration,

electrochemical treatment and evaporative recovery.

However, these high technology processes have

significant disadvantages, including incomplete metal

removal, requirements for expensive equipment and

monitoring systems, high reagent or energy requirements

or generation of toxic sludge or other waste products that

require disposal [5].

Adsorption on activated carbon has been found to be an

effective process for Cr(VI) removal, but it is too

expensive. Natural materials that are available in large

quantities, or certain waste products from industrial or

agricultural operations, may have potential as inexpensive

sorbents. Due to their low cost, after these materials have

been expended, they can be disposed of without

expensive regeneration. Most of the low cost sorbents

have the limitation of low sportive capacity and thereby

for the same degree of treatment, which poses disposal

problems. Therefore, there is need to explore low cost as

our biosorbent having high contaminant sorption capacity

[6]. Consequently numerous low cost alternatives have

been studied including Beech sawdust[7], eucalyptus

bark[8], green algae[9], seaweeds[10], coir pitch[11],

peanut husks carbon[12], Zeolite tuff [13], activated

carbon fabric cloth[14], bagasse fly ash[15], activated

Kinetic, Equilibrium and Thermodynamic Studies on Removal of Cr(VI) by Modified Activated Carbon Prepared ... 31

slag [16] etc. New economical, easily available and

highly effective adsorbents are still needed. Generally,

biosorptive processes can reduce capital costs by 20%,

operational costs by 36% an total treatment costs by 28%,

compared with the conventional systems [17].

New economical, easily available and highly effective

adsorbents are still needed. A through literature survey

indicated that Ricinus Communis has not been used as

adsorbent for remove of chromium thus far. The common

name of Ricinus Communis carbon is castor and belongs

to the family Euphorbiaceae. It is commonly cultivated in

dry lands along with ground nuts in most process of India.

The Pericarb is removed from the seed before going for

the castor oil extraction. It is one of the agricultural waste

and used as fuel to a small extent. Ricinus Communis

Seed Shell activated carbons as an adsorbent is a low-cost

material was used for the removal of Cr(VI) in

wastewater. In the present work, values of well known

thermodynamic functions and isotherm studies have been

performed to elucidate the equilibrium adsorption

behavior of Cr(VI) at different temperatures. In addition,

the effect of agitation time, pH and temperature on the

adsorption has been investigated.

2. MATERIALS AND METHODS

2.1 Preparation of Adsorbent

Activated carbons were prepared from Ricinus Communis

seed shell (CCC). The raw material was procured from

local vendor. The material was washed in hot distilled

water to remove earthy matter, cut into small pieces and

dried. The activated carbon was prepared from the above

material impregnated with concentrated sulphuric acid.

For impregnation, a ratio of acid volume to weight 1: 1

was employed. After that, the charred material was

washed several times in distilled water until the pH of the

washings becomes neutral. Then the material was dried

and carbonized at 500oC using muffle furnace. Finally,

the activated material was ground and sieved in to 180 –

300 micron using standard sieves.

Pyrrole used as a monomer for the preparation of

Ppy/RCC. In order to prepare Ppy/RCC, 5.0 g RCC was

immersed in 50 mL of 0.2M freshly prepared pyrrole

solution for 12 hours before polymerization. Then 50 mL

of 0.5 M ferricchloride-oxidant solution was gradually

added into the mixture and then the reaction was allowed

to continue for another 2 hours at room temperature. The

coated RCC polymer filtered, washed in distilled water

and then dried at 60oC in a hot air oven and sieved again

before use. All the reagents used for this study are

commercially available Analar grade (Merck, SRL, India

and SD-fine, India).

2.2 Adsorbate

A stock solution of the adsorbate was prepared by

dissolving the exact calculated quantity of Potassium

dichromate in doubly distilled water. Double distilled

water was used through out the experiments.

2.3 Experimental Methods

2.3.1 Batch Mode Studies

50ml of Cr(VI) known concentration of solution was

taken in a 100ml screw-cap conical flask with 50mg of

adsorbent and was agitated at 120rpm in a thermostatic

shaker water batch at 30oC for a 60minutes of contact

time. Then, the solution was centrifuged. The remaining

concentration of Cr(VI) was measured by using UV-

Visible spectrophotometer(systronics 169) with 1,5

diphenyl carbazide in acid medium. The amount of

Cr(VI) adsorbed in mg g-1 at time t was computed by

using the following equation[18].

qt = (Co - Ct ) V/ M (1)

Where, Co = Initial concentration of Cr(VI) ;Ct =

Concentration at a given time t

V = Volume of the Cr(VI) solution in L and M = Weight

of activated carbon in g.

The percentage of removal Cr(VI) ions in solution was

calculated by using the following equation,

R(%) = Co - Ct / Co X 100 (2)

3. RESULT AND DISCUSSION

3.1 Adsorbent Characterization

All the parameters were analyzed using standard testing

methods [18]. Activated carbons are widely used

adsorbent due to its high adsorption capacity, high surface

area, micro porous structure and high degree of surface

respectively. The chemical nature and pore structure

usually determine the sorption activity. Some important

physico-chemical characteristics of RCC and Ppy/RCC

are given in Table 1. The lower ash content values

attributed to lower inorganic content and higher fixed

carbon. The high surface area is considered to be most

suitable for adsorption of adsorbates in aqueous solution.

The lower bulk density value indicates the highly

branched and porous carbon with more void space. Acid

soluble matter content was found higher in the carbon

because of incorporated carbonate groups in the pores.

Sodium and potassium content may be due to the

presence of mineral sodium and potassium in the RCC

seed shell [19]. Based on the some characteristics of

adsorbents, Ppy/RCC is more preferable for removal of

heavy metals than RCC.

32 Coromandal Journal of Science, Vol. 1, No. 1, December 2012.

Table 1: Characteristics of Activated Carbon

S.

No. Parameter RCC Ppy/RCC

1 pH 7.70 8.13

2 pHzpc 5.86 5.97

3 Moisture content (%) 3.00 2.70

4 Bulk density (g/mL) 0.44 0.38

5 Solubility in water (%) 0.93 0.65

6 Solubility in 0.25 M HCl (%) 4.23 2.14

7 Porosity (%) 70.94 78.40

8 Specific gravity 1.64 1.76

9 Volatile matter (%) 4.54 3.82

10 Ash content (%) 7.52 6.68

11 Fixed carbon (%) 84.94 86.80

12 Sodium (mg/L) 62.00 58.00

13 Potassium (mg/L) 2.80 2.60

14

Phenol adsorption capacity

(%) 19.14 26.32

15 Conductivity (mS/cm) 1.95 1.97

16 Surface area (m2/g) 558 572

17 Iodine number (m2/g) 466 453

3.2 Effect of Adsorbent Dosage, pH and Agitation

Time

These experiments are done by using 25mg to 300mg of

adsorbents, 50ml of 10ppm of Cr(VI) solution and

agitation of various time intervals. The results indicate

that the optimum dose is fixed as 50mg due the quantity

of Cr(VI) uptake more [20], the optimum pH is fixed as 2

due to maximum removal of Cr(VI) and the optimum

agitation time is fixed as 60 minutes due to after this time

removal of Cr(VI) was constant [21].

3.3 Effect of Initial Concentration on Temperature

In this investigation, 50 mg of adsorbents (Ppy/RCC) was

treated with 50ml of Cr(VI) solutions containing different

concentration. Sorption experiments were carried out at

the most suitable pH 2 for each sorbent. In Table 2, at

30oC, When the initial Cr(VI) ion concentration increased

from 2 to 10 mgL-1, Cr(VI) adsorption removal slightly

decreased from 89.50 to 88.19% and the uptake capacity

of Ppy/RCC was increased. The increase in uptake

capacity with the increase of Cr(VI) ion concentration is

due to higher availability of Cr(VI) ions in the solution for

the adsorption. Moreover, higher initial Cr(VI)

concentration increased driving force to overcome all

mass transfer resistance of metal ions between the

aqueous and solid phases resulting in higher probability of

collision between Cr(VI) ions and adsorbent. This also

results in higher metal uptake [22].

The rise in adsorption capacity with temperature is

because of rise in the kinetic energy of sorbent particles.

Thus the collision frequency between adsorbent and

adsorb ate increases, which results in the enhanced

sorption on to the surface of the adsorbent. Secondly, at

high temperature due to bond rupture of functional groups

on adsorbent surface there more, be an increase in number

of active sorption sites, which may also lead to enhanced

sorption with the rise in temperature.

3.4 Adsorption Isotherms

Isotherms are mathematical relationships used to describe

the adsorption behaviour of a particular adsorbent-

adsorbate combination. They help in modeling adsorption

behaviour and in calculating the adsorption capacity of

materials. Three adsorption isotherms are the Langmuir,

Freundlich and Tempkin isotherms.

Linear form of the rearranged Langmuir model [23] is

00.

1

Q

C

bQq

C e

Le

e+=

(3)

The constants Q0 and bL can be calculated from the slope

and intercept of the plot of Ce/qe versus Ce.

Linear form of Freundlich equation [24] is

efe Cn

kq log1

loglog +=

(4)

where, qe is the amount of metal ions adsorbed per unit

mass of adsorbent (mg/g), Ce is the final concentration of

Cr(VI) in solution (mg/L), Qo and bL are the Langmuir

constants related to the monolayer adsorption capacity

(mg/g) and energy of adsorption(L/mg), kf and n are the

empirical constants of the Freundlich isotherm measuring

Table 2: Equilibrium Parameters for the Removal of Cr(VI) by Ppy/RCC

Initial conc.

of Cr(VI)

(Co), mg/L

Equilibrium

conc. of Cr(VI) (Ce),

mg/L

Quantity of Cr(VI)

adsorbed at

equilibrium (qe), mg/g

Cr(VI) removal (%)

by Ppy/RCC

30oC 40oC 50oC 30oC 40oC 50oC 30oC 40oC 50oC

2 0.210 0.184 0.081 1.790 1.816 1.919 89.50 90.80 95.96

4 0.456 0.411 0.202 3.544 3.589 3.798 88.60 89.73 94.95

6 0.687 0.620 0.359 5.313 5.380 5.641 88.55 89.67 94.01

8 0.934 0.843 0.652 7.066 7.157 7.348 88.32 89.47 91.85

10 1.181 1.104 0.934 8.819 8.896 9.066 88.19 88.96 90.66


the adsorption capacity (mg1-1/n

L1/n g-1) and intensity of

adsorption respectively.

The essential characteristics of the Langmuir equation can

be described by dimensionless equilibrium parameter RL,

RL = 1/ (1+bL.C0) (5)

Where, bL = Langmuir constant ,Co -= Initial

concentration of Cr(VI) (mg/L)The value of RL indicates

the shape of the isotherms to be either unfavorable

(RL>1), linear (RL = 1), favorable (0< RL,<1) or

irreversible (RL=0). Based on RL values, adsorption is

favorable one.

The Langmuir and Freundlich isotherm for the removal of

Cr (VI) from aqueous solution by activated carbon

prepared from Ricinus Communis seed shell were shown

in Figure 1 and 2. The correlation coefficients, constants

of Langmuir and Freundlich isotherms were presented in

Table 3. Form the Table 3; it was observed that

correlation coefficients of Freundlich isotherm are higher

than the correlation coefficients of Langmuir isotherm.

This indicates that Freundlich isotherm is fitted well with

the experimental data of the present system. The good

agreement of Freundlich isotherm indicates that the

surface of the activated carbon prepared from Ricinus

Communis seed shell is highly heterogeneous [25].

3.5 Thermodynamics Studies

The standard free energy change, enthalpy and entropy

changes along with equilibrium constants were computed

[26] and are given in Table 4. The results in Table 4

indicate that standard free energy values are negative

which mean that the reaction is spontaneous. The values

of enthalpy of an adsorption process may be used to

distinguish between physical and chemical adsorption.

Enthalpy change values range from 41 to 10 KJ/mol,

based on this values adsorption of Cr(VI) by RCC could

be a physical adsorption process. Positive values of

standard enthalpy change suggest that the process is

endothermic nature. The standard entropy change values

for the adsorption suggests a high degree of disorderness

at the solid-liquid interface during the adsorption of

Cr(VI) onto Ppy/RCC[27].

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0.04

0.06

0.08

0.10

0.12

0.14

Ce/qe (g/L)

Ce (mg/L)

300C

400C

500C

Fig. 1: Langmuir Isotherm for the Adsorption of Cr(VI) on Ppy/RCC

Table 3: Results of Isotherm Models for the Adsorption of Cr(VI) on Ppy/RCC

Temp.

(ºC)

Langmuir Isotherm Freundlich Isotherm

Correlation coefficient Constants Correlation coefficient Constants

r2 Qo (mg/g) bL (L/mg) r2 kf n

30 0.886 65.359 0.130 0.999 7.497 1.081

40 0.919 46.511 0.213 0.999 8.199 1.114

50 0.995 13.793 1.918 0.995 9.876 1.593


3.6 Kinetics of Adsorption Studies

The kinetic results obtained from batch experiments were

analyzed using different kinetics models such as

Lagergren pseudo first-order [28], pseudo second-order

[29] models.

The integrated form of the pseudo first-order kinetic

model is

tk

qqq ete303.2

log)log( 1−=−

(6)

Hence, a linear trace is expected between the two

parameters, log(qe-qt) and t, provided the adsorption

follows first order kinetics. The values of k1 and qe can be

determined from the slope and intercept.

The adsorption may also be described by pseudo-second

order kinetic model if the adsorption does not follow the

first order kinetics.

The linearised form of the pseudo second-order model is

tqqkq

t

eet

112

2

+=

(7)

A plot of t/qt and t should give a linear relationship if the

adsorption follows second order, qe and k2 can be

calculated from the slope and intercept of the plot.

where qe and qt are the amounts of Cr(VI) adsorbed on

adsorbent (mg/g) at equilibrium and time t (min), k1 is the

pseudo-first order rate constant (min-1) and k2 is the

pseudo-second order the rate constant (g mg-1 min

-1).

Figure 3, 4 shows the pseudo-first and pseudo-second

order model the removal of Cr(VI) from aqueous solution

by activated carbon prepared from Ricinus Communis

seed shell. The pseudo-first (k1), pseudo-second order rate

constants (k2) and correlation coefficients were shown in

the Table 5. A good agreement between the calculated

and experimental results was found in pseudo-second

order model. The experimental data for the adsorption of

Cr(VI) with high correlation co-efficient (r2 = 0.999) in

pseudo-second order model. It is also to be noted that the

-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

log qe

log Ce

300C

400C

500C

Fig. 2: Freundlich Isotherm for the Adsorption of Cr(VI) on Ppy/RCC

Table 4: Thermodynamic Parameters for the Adsorption of Cr(VI) on Ppy/RCC

Co, mg/L Ko ∆Go (kJ mol-1) ∆Ho ∆So

30oC 40oC 50oC 30oC 40oC 50oC (kJ mol-1) (J K-1 mol-1)

2 8.524 9.870 23.752 -5.398 -5.958 -8.507 41.362 153.327

4 7.772 8.732 18.802 -5.166 -5.639 -7.879 35.625 133.732

6 7.734 8.677 15.694 -5.153 -5.623 -7.394 28.542 110.556

8 7.562 8.493 11.266 -5.096 -5.567 -6.504 16.154 69.895

10 7.465 8.060 9.702 -5.064 -5.431 -6.102 10.609 51.568


experimental adsorption capacities (qe) are very close to

the adsorption capacities calculated by the pseudo-second

order kinetic model [30]; these values are also furnished

in Table 5.

Table 5: Pseudo-First and Second Order Constants for the Adsorption of Cr(VI) on Ppy/RCC

Co

(mg/L)

qe(exp)

(mg/g)

pseudo-first order kinetic model pseudo-second order kinetic model

qe(cal)

(mg/g)

k1

(min-1) r2

qe(cal)

(mg/g)

k2

(g mg-1 min-1) r2

2 1.790 0.818 0.046 0.988 1.807 0.721 0.999

4 3.544 0.119 0.043 0.993 3.558 0.795 0.999

6 5.313 0.242 0.102 0.933 5.327 1.144 0.999

8 7.066 0.220 0.058 0.904 7.092 0.560 0.999

10 8.819 0.209 0.065 0.967 8.842 0.649 0.999

10 20 30 40 50

-3.4

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2

-2.0

-1.8

-1.6

-1.4

-1.2

-1.0

log (qe - qt)

t (min)

2 mg/L

4 mg/L

6 mg/L

8 mg/L

10 mg/L

Fig. 3: Pseudo-First Order Kinetic Model for the Adsorption of Cr(VI) on Ppy/RCC

10 20 30 40 50 60

0

5

10

15

20

25

30

35

t/qt (min g mg-1)

t (min)

2 mg/L

4 mg/L

6 mg/L

8 mg/L

10 mg/L

Fig. 4: Pseudo-Second Order Kinetic Model for the Adsorption of Cr(VI) on Ppy/RCC


3.7 Fourier Transform Infrared Spectroscopy

(FTIR) Investigations

The adsorption capacity of activated carbon depends upon

porosity as well as the chemical reactivity of functional

groups at the surface. This reactivity creates an

imbalance between forces at the surface as compared to

those within the body, thus leading to molecular

adsorption by the vander waals force. To find out the

nature and type of adsorption, FTIR spectra of Ppy/RCC

are taken before and after adsorption of Cr(VI) which are

shown in Figures 5a and 5b.

The Ppy/RCC spectrum at 3914-3383 cm-1 indicated the

presence of –OH groups of activated carbons. The

aromatic –CH stretching observed at wave number from

3100-3000cm-1.A peak at 2857-2686 cm

-1 indicated the

presence of -CH and –CO stretching group of aldehydes.

The region from 1624-1585 cm-1 indicated the N-H

bending of primary amines and -C-C stretching of

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

Transmittance (%)

W ave number (cm-1)

Fig. 5: (a) FTIR Spectrum for Ppy/RCC Before Adsorption of Cr(VI)

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

Transmittance (%)

W ave number (cm-1)

Fig. 5: (b) FTIR Spectrum for Ppy/RCC After Adsorption of Cr(VI)


aromatic groups. The region from 1370-1350 cm-1

indicated –CH stretching of alkanes group. The regions

from 1250-1020 cm-1 and 910-665 cm

-1 indicated the

presence of –CN stretching and –NH stretching of

aliphatic amines. The region from 850-550 cm-1 indicated

the presence of –C-Cl stretching of alkyl halides.

After the adsorption of Cr(VI) on all activated carbons,

there was a small shift in wave number and some of the

wave number regions were not observed. This observation

indicated the participation of adsorption of Cr(VI) on

Ppy/RCC activated carbon [32].

3.8 Scanning Electron Microscopic (SEM) Studies

Fig. 6: (a) SEM Photograph Before Adsorption of Cr(VI) on

Ppy/RCC

Fig. 6: (b) SEM Photograph After Adsorption of Cr(VI) on

Ppy/RCC

The SEM photographs of Ppy/RCC before and after

adsorption are shown in the Figures 6a and 6b. It is

clearly stated that the presence of porous structure of the

active carbon before adsorption. They have holes and

cave type openings on the surface of the active carbon

which could definitely increased the surface area

available for adsorption. After adsorption of Cr(VI),

SEM photographs are clearly seen that the surface of

active carbons are the caves, pores and surfaces of

adsorbents was covered by adsorbate. It is evident that the

adsorbent structure is changed upon the adsorption of

Cr(VI) ions.

3.9 Comparison of Cr(VI) Removal with Different

Adsorbents

The adsorption capacity of the adsorbents for the removal

of Cr(VI) have been compared with those of others

reported in literature and the values of adsorption

capacity have been presented in Table 6. The

experimental data of the present investigation and

compared with reported values. Results of our

investigation revealed that Ppy/RCC has highest percent

removal and adsorption capacity.

Table 6: Comparison of Adsorption Capacities of Different

Adsorbents for the Removal of Cr(VI)

Adsorbents

Adsorption

capacity

(mg g-1)

References

Raw rice bran 0.07

[32]Oliveria et

al.(2005)

Riverbed sand 0.15

[33]Sharma and

Weng(2007)

Activated rice husk

carbon 0.8

[34]Bishnoi et

al.(2004)

Wollastonite 0.83 [35]Sharma(2001)

Coconut shell

powder 1.23 [36]Pino et al.(2006)

Flyash 1.4

[37]Banarjee et

al.(2004)

Activated alumina 1.6

[34]Bishnoi et

al.(2004)

Nanoiron 3.56

[38]Y.C. Sharma et

al.(2009)

Saw dust 3.6

[390]Baral et

al.(2006)

Distillary sludge 5.7

[40]Selvaraj et

al.(2003)

Ppy/RCC activated

carbon 8.8 Present study

4. CONCLUSION

Ricinus Communis seed shell activated carbon(RCC), an

agricultural waste, abundance, cheapness and

environmental friendly nature could be used as potential

adsorbent for the removal of Cr(VI) from aqueous

solution contains heavy metals and polluted water. The

Freundlich adsorption isotherm model describes the

adsorption behavior with good correlation co-efficient.

The adsorption of Cr(VI) was depended on the pH of the

solution. Based on the results, the optimum contact time

is 60 minutes and adsorbent dosage is 50 mg. The metal

ion adsorption obeyed the pseudo- second order kinetic

model. The removal of Cr(VI) is simultaneously

increased with increase in the temperature from 30oC to

50oC.


ACKNOWLEDGEMENT

The authors are thankful to the Chairman and the

Management of Sona college of Technology, Salem and

Annai Mathammal Sheela Engineering College,

Namakkal, Tamilnadu, India for providing necessary

research facilities to carryout this research.

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Kinetic, Equilibrium and Thermodynamic Studies on Removal of Cr(VI) by Modified Activated Carbon...

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