kinetics of adsorption of crystal violet from aqueous ... · kinetics of adsorption of crystal...

INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 6, 2011

© 2011 Satish Patil et al., licensee IPA- Open access - Distributed under Creative Commons Attribution License 2.0

Research article ISSN 0976 – 4402

Received on December, 2010 Published on March 2011 1123

Kinetics of adsorption of crystal violet from aqueous solutions using

different natural materials Satish Patil

1, Vaijanta Deshmukh

2, Sameer Renukdas

2, Naseema Patel

2

1 -Department of Chemistry, A.P.Science College, Nagothane – 402106 (MS), India.

2- Research guide, Department of Chemistry, Yashwant Mahavidyalaya, Nanded – 431602

(MS), India.

[email protected]

doi:10.6088/ijes.00106020007

ABSTRACT

Adsorption studies of Crystal Violet (CV) on different natural materials were carried out by

batch experiments. The parameter studied includes initial dye concentration, adsorbent dose,

pH, contact time, agitation speed, particle size of adsorbent and temperature. The linear

regression coefficient R2 was used to elucidate the best fitting isotherm model. All isotherm

models, Langmuir (R2 = 0.982 to 0.999), Temkin (R

2 = 0.973 to 0.998) and Freundlich (R

2 =

0.98 to 0.998 and n = 1.886 to 2.294) were found to be best fitting models. The monolayer

(maximum) adsorption capacities (qm) were found to be between 142.857 to 250 mg/g for

natural adsorbents under study. Lagergen pseudo -second order model best fits the kinetics of

adsorption. The correlation coefficient R2 for second order adsorption model has very high

values of R2 for all absorbents (R

2 ≈ 0.998) and qe(the) values are in good agreement with with

qe(exp) showed that adsorption of CV on these natural materials follwed second order kinetics

and chemosorption playing role in rate determining step. Intra particle diffusion plot showed

boundary layer effect and larger intercepts indicates greater contribution of surface sorption

in rate determining step. pH was found to be an important factor in controlling the adsorption

of cationic dye. Adsorption of CV on adsorbents was found to increase on increasing pH,

increasing temperature and decreasing particle size. Thermodynamic analysis showed that

adsorption was favourable and spontaneous, endothermic physical adsorption and increased

disorder and randomness at the solid- solution interface of CV with biosorbents. Mangrove

plant leaf powder was found have excellent adsorption capacity towards CV than other

natural materials under study.

Keywords: Adsorption isotherm, Crystal violet (CV), biosorbents, kinetic and

thermodynamic parameters.

1. Introduction

Textile industry uses large volumes of water in wet processing operations and thereby,

generates substantial quantities of wastewater containing large amounts of dissolved

dyestuffs and other products, such as dispersing agents, dye bath carriers, salts, emulsifiers,

leveling agents and heavy metals1. Majority of this dyes are synthetic in nature and are

usually composed of aromatic rings in their structure, inert and non-biodegradable when

discharged into waste streams. Colored dyes are not only aesthetic, carcinogenic but also

hinder light penetration and disturb life processes of living organisms in water. Therefore, the

removal of such colored agents from aqueous effluents is necessary. Crystal violet (CV), a

basic dye, is most widely used for the dyeing of cotton, wool, silk, nylon, paper, leather etc.,

among all other dyes of its category. In fact, basic dyes, such as crystal violet, are the

Kinetics of adsorption of crystal violet from aqueous solutions using different natural materials

Satish Patil, Vaijanta Deshmukh, Sameer Renukdas , Naseema Patel

International Journal of Environmental Sciences Volume 1 No.6, 2011 1124

brightest class of soluble dyes whose tinctorial values are very high; less than 1 mg/L of the

dye produces an obvious coloration. Hence, it is needed to remove these dyes from textile

effluent before it is discharged into receiving water bodies. The studies have been performed

in order to remove color and other contaminations using various types of methods include

adsorption4, coagulation

5, nano-filtration and ozonalysis

6, membrane filtration

7, oxidation

process8 etc., in which adsorption is most useful due to its efficiency and visibility. Although,

activated carbon adsorption appears to be the one of the most widely used techniques for dye

removal, but in view of the high cost and regeneration problems, there has been a constant

search for alternate low cost adsorbents. The adsorbents were prepared from natural materials

such as plant roots, leaf and seed like neem leaf powder10,11

, gulmohar plant leaf powder12

,

shells of hazelnut and almond13

, shells of lentil, wheat and rice14

, orange peel15

, Banana

peel16

, guava leaf powder17

used for removal of color.

In the present study different leaf, fruit and bark materials were tested as adsorbents for

adsorption of CV from wastewater.

2. Materials and methods

2.1 Adsorbents

Adsorbents used in the present study are-

1. Mangrove plant (Sonneratia Apetala ) leaf powder ( MPLP)

2. Mangrove plant (Sonneratia Apetala ) fruit powder ( MPFP)

3. Mango ( Mangifera Indica) leaf powder (MLP)

4. Tamarind ( Tamarindus indica) fruit shell powder (TFSP)

5. Teak tree ( Tectona Grandis) bark powder (TTBP)

6. Almond tree (Terminialia cattapa) bark powder (ATBP)

Mature materials of all above biosorbents were collected from Konkan region of Maharashtra

state in India and washed thoroughly with distilled water to remove dust and other impurities.

Washed materials were dried for 10 days in sunlight. Dried materials were grounded in a

domestic mixer- grinder after removing non required parts separately. After grinding, the

powders were again washed and dried. Different sized powders of each adsorbent were

obtained by passing the powders through Jayant’s sieves and stored in plastic bottle

containers for further use.

2.2 Synthetic textile dye solution

Crystal Violet (CV), a monovalent cationic basic dye with Molecular Formula C25H30N3Cl. In

dye classification it is classified as C.I. 42555 and Class: basic dye 3. It has a molecular

weight of 407.98 g/mol, used in this study was supplied by Merck, India.

Structure of crystal violet molecule is,

A stock solution of CV 1000 mg/l was prepared in double- distilled water and the

experimental solutions of the desired concentration were obtained by successive dilutions.




2.3 Methods

Standard solution (5 mg/l) of the CV was taken and absorbance was determined at different

wavelengths using Equiptronics single beam u.v. visible spectrophotometer to obtain a plot of

absorbance verses wavelength. The wavelength corresponding to the maximum absorbance

(λmax= 580 nm) as determined from the plot, was noted and this wavelength was used for

measuring the absorbance in the present study. pH of solutions were adjusted using 1M HCl

and 1M NaOH by Equiptronics pH- meter.

The efficiency of adsorbents is evaluated by conducting laboratory batch mode studies.

Specific amounts (25mg) of adsorbents were shaken in 25 ml aqueous solution of dye of

varying concentration for different time periods at natural pH (≈ 7) and temperature (≈ 303K).

At the end of pre-determined time intervals, adsorbent was removed by centrifugation at

10000 rpm and supernant was analyzed for the residual concentration of CV,

spectrophotometrically at 580 nm wavelength.

Also variation in pH, adsorbent dose, particle size, agitation speed and temperature were

studied.

2.3.1 Effect of contact time

25 mg of adsorbent of ≥ 120 mesh size with 25 ml of dye solution was kept constant for

batch experiments with an initial dye concentration of 200 mg/l (for MPLP, MPFP, MLP)

and 125 mg/l (TFSP, TTBP, ATBP) were performed at nearly 303K on a oscillator at 230

rpm for 10, 20, 30, 40, 50,60 and 70 minutes at pH = 7. Then optimum contact time was

identified for further batch experimental study.

2.3.2 Effect of adsorbent dosage

Initial dye concentration of 400 mg/l were used in conjunction with adsorbent dose of 1, 2, 3,

4, 5, and 6 g/l . Contact time, pH, agitation speed, temperature and particle size of 60 minutes,

7, 230 rpm, 303K and ≥ 120 mesh respectively were kept constant.

2.3.3 Effect of initial dye concentration

Initial dye concentration of 50, 75, 100, 125, 150, 175 and 200 mg/l were used in conjunction

with adsorbent dose of 1 g/l . Contact time, pH, agitation speed, temperature and particle size

of 60 minutes, 7, 230 rpm, 303K and ≥ 120 mesh respectively were kept constant.




2.3.4 Effect of pH

Initial PH of dye solutions were adjusted to 3, 4.3, 7, 9 and 11 for 100 mg/l concentration.

Contact time, adsorbent dose, agitation speed, temperature and particle size of 60 minutes, 1

g/l, 230 rpm, 303K and ≥ 120 mesh respectively were kept constant.

2.3.5 Effect of particle size

Three different sized particles of ≥ 120, 120 ≤ 85 and 85 ≤ 60 mesh were used in conjunction

with 150 mg/l dye concentration. Contact time, adsorbent dose, agitation speed, temperature

and pH of 60 minutes, 1 g/l, 230 rpm, 303K and 7 respectively were kept constant.

2.3.6 Effect of agitation speed

100, 170 and 230 rpm agitation speeds were used in conjunction with initial dye

concentration of 150 mg/l. Adsorbent dose, pH, temperature, contact time and particle size of

1 g/l, 7, 303K, 60 minutes and ≥ 120 mesh respectively were kept constant.

2.3.7 Effect of temperature

303K, 313K and 323K temperatures were used in conjunction with 200 mg/l dye

concentration. Contact time, adsorbent dose, agitation speed, particle size and pH of 60

minutes, 1 g/l, 230 rpm, ≥ 120 mesh and 7 respectively were kept constant.

3. Results and Discussions

3.1 Effect of contact time

Effect of contact time on adsorption of CV is presented in Figures 1 and 2. Uptake of CV was

rapid in first 10 minutes and after 60 minutes amount of dye adsorbed was almost constant.

The dye uptake process appears to be rapid in first 10 minutes and nearly 40 to 70% of total

dye uptake appears to have been adsorbed in this duration depending upon the adsorption

ability of different adsorbents. The initial rapid phase may also be due to the increased

number of vacant sites available at the initial stage. Later on the process becomes relatively

slower and equilibrium conditions are reached within 50 to 60 minutes. At this point, the

amount of the dye desorbing from the adsorbent is in a state of dynamic equilibrium with the

amount of the dye being adsorbed onto the adsorbents. The time required to attain this state

of equilibrium is termed the equilibrium time, and the amount of dye adsorbed at the

equilibrium time reflects the maximum adsorption capacity of the adsorbent under those

operating conditions.Therefore, further batch experiments were carried out at 60 minutes

optimum contact time.

The mechanism of adsorption was investigated by pseudo - first order, pseudo- second order,

Natarajan and Khalaf first order, Bhattacharya and Venkobachar first order, Intraparticle

diffusion and models.

The Lagergen (Singh et al., 1998) pseudo- first order rate expression is given as

log (qe - qt) = log qe – (k1 / 2.303) t (1)




Where qe and qt are amounts of dye adsorbed (mg /g) on adsorbent at equilibrium and at time

t, respectively and k1 is rate constant of pseudo first order adsorption (min-1

). The slope and

intercept values of plot log (qe - qt) against t , Figures 3 was used to determine pseudo first

order rate constant (k1) and theoretical amount of dye adsorbed per unit mass of adsorbent

qe(the), respectively. qe(the)were compared with the qe(exp) values in Table(1). qe(exp) values do

not agree with calculated values i.e. qe(the) values. This shows that the adsorption of the CV

onto adsorbents under study is not the first-order kinetics (Ho and Mckay, 1999).

The Langergen pseudo- second order kinetic model (Ho and Mckay, 1999) is given as

t/qt = 1/(k2qe2) + t/qe (2)

Where k2 is rate constant of second order adsorption (g /mg/ min). The slopes and intercepts

of plot of t/qt against t , Figure 4, were used to determine qe(the) and k2 respectively. The

pseudo second order parameters, qe(the), h and k2 obtained from the plot are represented in

Table (1).

Where h is initial adsorption rate (mg g-1

.min), h = k2 qe2 .

The second order rate constant (k2) was 0.00112 to 0.002564 mg/gm /min and in addition the

experimental and theoretical equilibrium uptake values i.e. qe(exp) and qe(the) were found to

have good agreement between them and the highly linear plot with correlation coefficient (R2

≥ 0.998) for all the adsorbents showed that pseudo second order adsorption equation of

Langergen fit well with whole range of contact time and dye adsorption process appears to be

controlled by chemisorptions playing a significant role in the rate determining step. This

indicates the adsorption of CV on these adsorbents is second order kinetics.

Figure 1: Effect of contact time on adsorption of CV.




Figure 2: Effect of initial dye concentration and contact time on % removal of CV

Figure 3: Pseudo first order plot of effect of contact time on adsorption of CV.

Figure 4: Pseudo second order plot of effect of contact time on adsorption of CV.




The linearized form of Natarajan and Khalaf first order kinetic equation is presented as

log (Co/Ct) = (K /2.303) t (3)

Where Co and Ct are concentrations of CV (mg/l) at time zero and time t respectively. K is

first order adsorption rate constant (min-1

), which was calculated from slope of the plot

log(Co/Ct) against t, Figure 5, Table (2).

The lineaized form of Bhattacharya and Venkobachar first order kinetic equation is presented

as log [ 1 – U(T) ] = - (k /2.303) t (4)

Where U (T) = [(Co-Ct) / (Co-Ce)]

Ce is equilibrium MB concentration (mg/ l)

K is first order adsorption rate constant (min-1) which was calculated from slope of the plot

log [ 1 – U(T)] against t, Figure 6 , Table (2).

Figure 5: Natarajan and Khalaf first order plot of effect of contact time on adsorption of CV.

Figure 6: Bhattacharya and Venkobachar first order plot of effect of contact time on

adsorption of CV.




Natarajan and Khalaf first order and Bhattacharya and Venkobachar first order kinetic

models does not fit well with whole range of contact time and is generally applicable for

initial stage of adsorption Correlation coefficient values were high enough for all adsorbents

for Natarajan and Khalaf (R2 = 0.971 to 0.998) as well as Bhattacharya and Venkobachar (R

2

= 0.976 to 0.993) first order equations upto 50 minutes but once the equilibrium is reached

amount of dye adsorbed remains constant and thus showed non linearity.

Adsorption of the dye by adsorbent includes transport of solute from aqueous to surface of

solid and diffusion of solute into the interior of pores, which is generally a slow and rate

determining process.

According to Weber and Morris, the intra particle diffusion rate constant (Ki) is given by the

following equation qt = Ki t 1/2

(5)

Ki (mg/ g /min1/2

) values, Table (2) can be determined from the slope of the plot qt against t 1/2

, Figure 7 showed a linear relationship but they do not pass through origin. This is due

boundary layer effect. The larger the intercept, the greater the contribution of surface sorption

in rate determining step.. Initial portion is attributed to the liquid film mass transfer and linear

portion to the intra particle diffusion.

The linearized form of Elovich kinetic equation is presented as

qt =1/ β [ln(αβ)] + ln t /β (6)

Where α and β are the constants calculated, Table (2) from the intercepts and slopes of plot qt

against ln t, Figure 8. The constant β is related to the extent of surface coverage. The simple

Elovich modelis used to describe second-order kinetic, assuming that the actual solid surface

is energetically heterogeneous. This Elovich kinetic model has R2

= 0.98 to 989 for

adsorbents under study.

Figure 7: Intra particle diffusion plot of effect of contact time on adsorption of CV




Figure 8: Elovich plot of effect of contact time on adsorption of CV

3.2 Effect of adsorbent dosage

The adsorption of CV was studied by varying the adsorbent dosage. The percentage of

adsorption increased with increase in dosage of adsorbent but amount of dye adsorbed per

unit mass of adsorbent decreased with increased in adsorbent dose from 1 to 6 g/l. Figures 9

and 10.As amount of adsorbent increases, number of active sides available for adsorption also

increases thus % removal also increases but as all active sides may not be available during

adsorption due to overlapping between the active sides themselves and thus amount adsorbed

mg/g of adsorbent decreases. Thus, the adsorption of dye increased with the sorbent dosage

and reached an equilibrium value after certain sorbent dosage (3 to 4 g/l) for most of the

adsorbents.

Figure 9: Effect of adsorbent dosage on % removal of CV




Figure 10: Effect of adsorbent dosage on amount adsorbed (mg/g) of CV.

3.3 Effect of initial dye concentration

Percentage sorption decreased but amount of CV adsorbed per unit mass of adsorbent (mg /g)

increased with increase in CV concentration from 50 to 200 mg /l, Figures 11 and 12. The

initial concentration provides an important driving force to overcome all mass transfer

resistances of the CV between the aqueous and solid phases. Therefore, a higher initial dye

concentration of dye will enhance the sorption process.

Figure 11: Effect of initial dye concentration on adsorption of CV.




Figure 12: Effect of initial dye concentration on % removal of CV

The Freundlich equation was employed for the adsorption of CV onto the adsorbents. The

isotherm was represented by

log qe = log Kf + 1/n log Ce (7)

Where qe is amount of CV adsorbed at equilibrium (mg/g), Ce is the equilibrium

concentration of CV in solution (mg/l), Kf and n are constant incorporating factors affecting

the adsorption capacity and intensity of adsorption respectively. The plots of log qe vs log Ce

showed good linearity (R2 = 0.98 to 0.998 ) indicating the adsorption of CV obeys the

Freundlich adsorption isotherm, Figure 13.

Figure 13: Freundlich isotherm plot of effect of initial dye concentration on adsorption of CV

The values of Kf and n given in the Table (3). Values of n between 1 to 10 indicates an

effective adsorption (Potgeiter, et al., 2005) while higher values of Kf represents an easy

uptake of adsorbate from the solution (Mahvi, et al., 2004).

The Langmuir isotherm was represented by the following equation

Ce / qe = 1/ (qm b) + Ce /qm (8)




Where qm is monolayer (maximum) adsorption capacity (mg/g) and b is Langmuir constant

related to energy of adsorption (1/mg). A linear plots of Ce / qe vs Ce suggest the

applicability of the Langmuir isotherm Figure 14 (R2= 0.982 to 0.998). The values of qm and

b were determined slop and intercepts of the plots, Table (3).

Figure 14: Langmuir isotherm plot of effect of initial dye concentration on adsorption of

CV.

The essential features of the Langmuir isotherm can be expressed in terms of dimensionless

constant separation factor, RL, which is defined by the following relation given by Hall20

RL = 1/ (1+bCo) (9)

Where Co is initial CV concentration (mg/l). RL values lies between 0.05749 to 0.308737

indicates favorable adsorption (Table 5).

The Temkin isotherm is given as

qe = B ln A + Bln Ce (10)

Where A (1/g) is the equilibrium binding constant, corresponding to the maximum binding

energy and constant B is related to heat of adsorption. A linear plots of qe against ln Ce,

Figure 15 enables the determination of the constants B and A from the slope and intercept,

Table (3).

3.4 Effect of pH

pH is one of the important factors in controlling the adsorption of dye on adsorbent. The

adsorptions of CV from 100mg /l concentration on given adsorbents were studied at pH 3, 4.3,

7, 9 and 11. The amount of dye adsorbed per unit mass of adsorbent at equilibrium (qe)

increased with increased in pH. The results, as depicted in Figure 16, reveal that the dye

uptake increases with the pH and it attains almost saturation value as the pH of the solution

becomes 7 to 11, The observed finding may be explained on the basis of the fact that when

the pH of the solution is quite low i e. 3.0, the presence of excess H+ ions compete with the

cationic dye molecules in the solution and preferably occupy the binding sites available in the

sorbent particles. As the pH of the sorbate solution increases number of H+ ions decreases




thus making the adsorption process more favorable .In the vicinity of pH value of 11.0,

optimum dye uptake is obtained. Similar results have also been reported elsewhere.

Figure 15: Temkin isotherm plot of effect of initial dye concentration on adsorption of CV

Figure 16: Effect of pH on adsorption of CV from initial concentration of 100 mg/l.

3.5 Effect of particle size

Adsorption of CV on three sized particles ≥ 120, 120 ≤ 85 and 85 ≤ 60 mesh of adsorbent

was studied for 100 mg/l concentrations of CV. The results of variation of these particle sizes

on dye adsorption are shown in Figure 17. It can be observed that as the particle size

increases the adsorption of dye decreases and hence the percentage removal of dye also

decreases. This is due to larger surface area that is associated with smaller particles. For

larger particles, the diffusion resistance to mass transfer is higher and most of the internal

surface of the particle may not be utilized for adsorption and consequently amount of dye

adsorbed is small.




3.6 Effect of agitation speed

The sorption is influenced by mass transfer parameters. The amount adsorbed at equilibrium

was found to increase with increased in agitation speed from 100, 170 and 230 rpm of an

oscillator from 150 mg/l initial CV solution. Figure 18.

Figure 17 – Effect of particle size on % removal of CV.

Figure 18: Effect of agitation speed on adsorption of CV.

This is because with low agitation speed the greater contact time is required to attend the

equilibrium. With increasing the agitation speed , the rate of diffusion of dye molecules from

bulk liquid to the liquid boundary layer surrounding the particle become higher because of an

enhancement of turbulence and a decrease of thickness of the liquid boundary layer.

3.7 Effect of temperature

Temperature has important effects on adsorption process. Adsorption of CV at three different

temperatures (303K, 313K and 323K) onto biosorbents was studied for 200 mg/l initial CV

concentration. The results, as depicted in Figure 19, clearly indicate that dye uptake increases

with temperature. This may be explained on the basis of the fact that increase in temperature

enhances the rate of diffusion of the adsorbate molecules across the external boundary layer

and in the internal pores of the adsorbent particles as a result of the reduced viscosity of the




solution. In addition, the mobility of sorbate molecules also increases with temperature,

thereby facilitating the formation of surface monolayers. Changing the temperature will

change the equilibrium capacity of the adsorbent for particular adsorbate.

Thermodynamic analysis:

Thermodynamic parameters such as change in free energy (∆G) (J/mole), enthalpy (∆H)

(J/mole) and entropy (∆S) (J/K/mole) were determined using following equations

Ko = Csolid /Cliquid (11)

∆G = -RTlnKo (12)

∆G = ∆H - T∆S

lnKo = -∆G/RT

lnKo = ∆S/R - ∆H/RT (13)

Where Ko is equilibrium constant, Csolid is solid phase concentration at equilibrium (mg/l),

Cliquid is liquid phase concentration at equilibrium (mg/l), T is absolute temperature in Kelvin

and R is gas constant.∆G values obtained from equation (12), ∆H and ∆S values obtained

from the slope and intercept of plot ln Ko against 1/T , Figure 20 presented in Table (4). The

negative value of ∆G indicates the adsorption is favourable and spontaneous. ∆G values

increases with increase in temperature.

Figure 19: Effect of temperature on adsorption of CV

The low positive values of ∆H indicate endothermic nature of adsorption. The positive values

of ∆S indicate the increased disorder and randomness at the solid solution interface of CV

with the adsorbent. The adsorbed water molecules, which were displaced by adsorbate

molecules, gain more translational energy than is lost by the adsorbate molecules, thus

allowing prevalence of randomness in the system. The increase of adsorption capacity of the

adsorbent at higher temperatures was due to enlargement of pore size and activation of

adsorbent surface.




Table 1: Effect of contact time on adsorption of CV

Pseudo -first order model Pseudo -second order model

Adsorbe

nt

Initial

CV

Conc.

(mg/l

)

qe(exp

)

(mg/

g)

K1

(min-1

)

qe(the)

(mg/g

)

R2

qe(exp)

(mg/g

)

K2

(g/mg/

min)

qe(the)

(mg/g)

h

(mg/g .

min)

R2

MPLP 200

155

0.03684

8

52.72

3 0.993

155 0.0012

166.666

7

33.3333

3

0.99

8

MPFP 200

149

0.04375

7

56.23

4 0.982

149

0.00112

5

166.666

7 31.25

0.99

8

MLP 200

136

0.03915

1

44.77

1 0.976

136

0.00112

5

166.666

7 31.25

0.99

8

TFSP 125

78

0.05296

9

48.75

3 0.989

78

0.00130

1

90.9090

9

10.7526

9

0.99

8

TTBP 125

107.

5

0.05527

2

42.75

6 0.976

107.5

0.00182

9 125

28.5714

3

0.99

9

ATBP 125

91

0.05296

9

32.73

4 0.981

91

0.00256

4 100

25.6410

3

0.99

9

Table 2: Effect of contact time on adsorption of CV

Intra particle diffusion

model Elovich Model

Natarajan and

Khalaf model

Bhattacharya and

Venkobachar

model

Adsorb

ent

Initial

CV

Conc.

(mg/l)

Ki

(mg/g

/min1/

2)

A

(mg/g) R2

α

(mg/g/mi

n)

β

(g.mg-1) R2

K

(min-1) R2

K

(min-1) R2

MPLP 200 4.37 147.4

0.97

7 24.87802 0.052083

0.98

3 0.011515

0.99

7 1.077804

0.99

3

MPFP 200 5.466 126.2 0.97 25.04753 0.052521

0.98

6 0.011515

0.98

8 0.971866

0.98

2

MLP 200 5.822 89.47

0.98

5 19.63572 0.063776

0.98

1 0.006909

0.99

8 1.110046

0.97

6

TFSP 125 5.385 36.14

0.95

6 35.39472 0.067705

0.98

8 0.009212

0.98

4 0.467509

0.98

9

TTBP 125 4.551 72.57

0.94

5 15.62773 0.079936 0.98 0.018424

0.99

8 0.918897

0.97

6

ATBP 125 3.618 62.97

0.95

2 12.15542 0.100422

0.98

9 0.006909

0.97

1 1.020229

0.98

1

Table 3: Effect of initial dye concentration on adsorption of CV

Adsorbent

Freundlich isotherm

parameters Langmuir isotherm parameters Temkin isotherm parameters

Kf n R2 qm b R

2 A B R

2

MPLP 28.379 2.17865 0.98 200 0.08197 0.998 0.81427 42.24 0.998

MPFP 19.724 1.88679 0.982 250 0.08163 0.999 0.45746 46.85 0.994

MLP 18.197 2.06612 0.996 200 0.03876 0.987 0.41629 39.39 0.985

TFSP 13.614 2.1645 0.984 142.857 0.03302 0.997 0.30269 31.58 0.997

TTBP 26.122 2.1692 0.983 200 0.07042 0.997 0.71371 41.45 0.998

ATBP 19.86 2.29358 0.998 166.667 0.04478 0.982 0.49422 34.21 0.973




Figure 20: Von’t Hoff plot of effect of temperature on adsorption of CV

Table 4: Equillibrium constants and thermodynamic parameters for the adsorption of CV

Adsorbe

nt

Ko ∆G (J/mole) ∆H

(J/mole)

∆S

(J/K/mol

e) 303K 313K 323K 303K 313K 323K

MPLP 3.34783 4 5.15385 -3043.9 -3607.5 -4403.4 17509.3 67.7258

MPFP 2.8835 3.21053 3.84262 -2667.8 -3035.4 -3615 11639.6 47.1321

MLP 2.07692 2.27869 2.63636 -1841.2 -2143.2 -2603.2 9677.5 37.9285

TFSP 1.12766 1.28571 1.46914 -302.66 -653.99 -1033 10750 36.4818

TTBP 3 3.84262 5.66667 -2767.6 -3503.1 -4658.1 25798.3 94.0313

ATBP 1.75862 2.07692 2.63636 -1422.1 -1902 -2603.2 16428.5 58.8132

Table 5: Dimensionless Separation Factor (RL) calculated from Langmuir constant (b)

Initial CV

Conc.

(mg/l)

MPLP MPFP MLP TFSP TTBP ATBP

50 0.196136 0.196792 0.340368 0.377216 0.22119 0.308737

75 0.139904 0.140405 0.255951 0.287646 0.159198 0.229437

100 0.108731 0.109135 0.205086 0.23245 0.124347 0.182548

125 0.088919 0.089256 0.171086 0.195027 0.102015 0.151573

150 0.075213 0.075503 0.146757 0.167983 0.086483 0.129584

175 0.065169 0.065423 0.128485 0.147525 0.075055 0.113167

200 0.05749 0.05772 0.11426 0.13151 0.0663 0.10044

4. Conclusions

The objective of this paper was utilization of different natural materials as adsorbents for the

removal of crystal violet. Langmuir, Temkin as well as Freundlich were found to be best

fitting models with respect to R2

values. The monolayer (maximum) adsorption capacities

(qm) were found to be 142.857 to 250 mg/g for natural adsorbents under study. Lagergen




pseudo -second order model best fits the kinetics of adsorption. The correlation coefficient R2

≈ 0.998 for second order adsorption model and qe(the) values are consistent with qe(exp) showed

that pseudo second order adsorption equation of Langergen fit well with whole range of

contact time. Intra particle diffusion plot showed boundary layer effect and larger intercepts

indicates greater contribution of surface sorption in rate determining step. Adsorption was

found to increase on increasing pH, increasing temperature and decreasing particle size. ∆G,

∆H and ∆S values showed favourable, spontaneous, endothermic physical adsorption with

increased disorder and randomness at the solid- solution interface of CV with biosorbents.

Adsorption capacities of different adsorbents towards CV were found to be of the order of

MPLP > MPFP > TTBP > MLP > ATBP > TFSP.

These adsorbents have excellent adsorption capacity compared to many other non

conventional adsorbents. They can be used as a low cost attractive alternative for costly

activated carbon.

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