Research Article Open Access
Adsorption of Rhodamine-B Dye from an Aqueous Solution by Biomass Pine Apple Peel: Kinetics, Equilibrium and Thermodynamic Studies
N Ramulu1, V Thirumurugan1*, S Krishnaveni1 and R Rajajeyaganthan2
1AVVM Sri pushpam college,(Autonomous) poondi, Tamilnadu, India.
2M Kumarasamy college of Engineering, Karur, Tamilnadu, India.
*Corresponding author: V Thirumurugan, AVVM Sri Pushpam college,(Autonomous) poondi, Thanjavur-613501,Tamilnadu, India.;E-mail: @
Received: June 16, 2016; Accepted: June 30, 2016; Published: July 15, 2016
Citation: MRamulu N,Thirumurugan V , Krishnaveni S, Rajajeyaganthan R (2016) Adsorption of Rhodamine-B Dye from an Aqueous Solution by Biomass Pine Apple Peel: Kinetics, Equilibrium and Thermodynamic Studies. SOJ Mater Sci Eng 4(2): 1-9.
AbstractTop
Today there are lots of dyes available commercially. They are used in many industries such as paper, rubber, plastic, cosmetics and especially Textiles. Many methods have been proposed in order to remove color from waste water among which adsorption is more acceptable due to the ability for its use in the large scale. The objectives of this study were to investigate pine apple peel as on inexpensive adsorbent for removal of Rhodamine-B dye from aqueous solution. In this study the effect of pH, initial concentration, contact time and amount of adsorbent where optimized in order to investigate the mechanism of adsorption process. Several kinetic models including lagergren,s pseudo first order, lagergren,s pseudo second order, Intra particle diffusion, Elvoich model, Natarajan and Khalf model, Bhattarcharya and Venkobechar model were used. In addition equilibrium data were fitted on Langmuir, Freundlich, Temkin, Dubihin-Radhushkevich.The kinetic study on Rhodamine-B dye suggest that the adsorption follows pseudo second order kinetics. Adsorption follows the Freundlich isotherm model than other models. The thermodynamic study on Rhodamine-B reveals that the reaction is spontaneous and endothermic. The study reveals that the biomass pine apple peel proved to be an effective alternative and environmentally benign adsorbent for Rhodamine-B removal from aqueous solution.

Keywords: Rhodamine-B; Pine apple peel; Adsorption; Kinetics; Isotherm; Thermodynamics
Introduction
Industrial wastewater is considered as one of the major pollutants of the environment [1]. Colored wastewater is produced by various industries, such as textile, dyeing, pharmaceutical, food, cosmetics and healthcare, paper and leather industries [2, 3]. Many dyes and their breakdown products may be toxic for living organisms. Therefore decolorization of dyes is important before the discharge of effluent. Removal of dye has been attempted extensively using physico-chemical methods such as coagulation, ultra-filtration, electro-chemical adsorption, photo oxidation, activated carbon adsorption, etc [5]. But thesetechnologies are not efficient, satisfactory and also cost effective [4]. Adsorption has been shown to be one of the most promising and extensively used methods for the removal of both inorganic and organic pollutants from contaminated water [6, 7]. Use of low cost, easily available biomaterials for the adsorption of dyes is practiced as an alternative method and several botanical, low cost materials have directly been used as an adsorbent for removal of dyes from wastewater [8, 9]. Now days, agricultural waste materials are receiving much more attention as adsorbents for the removal of dyes from waste water due to its low cost and good availability. In the present study, pine apple peel (PAP) has been used as an adsorbent whose results showed good absorption in Rhodamine-B dye aqueous solution [10].
Material And Methods
Preparation of an adsorbent
Pineapple biomass was obtained from fruit market in Thanjavur. The pineapples were peeled of using peeler. The peeled pineapple peels (PAP) were washed using tap water followed by double distilled water. After washing the peel pieces were dried under sun light for 72 hours to remove moisture content present. The dried PAP pieces were washing repeatedly with hot water (700 C) to remove any soluble matter present and dried in oven at 850 C for 48 hours. The dried PAP were powdered and sieved through 100 mesh sieves and stored air tight polythene bottles for adsorption experiments.
Figure 1:
The experiment was carried out by the batch adsorption method in the Erlenmeyer flasks for a predetermined period using orbital shaker. In the adsorption, parameters such as PH, Initial dye concentration, equilibrium time fixation were studied for optimization. The kinetic studies and isotherm study were carried out at different dye concentration 200ppm, 250ppm, 300ppm, 350ppm, 400ppm and 450ppm. By keeping temperature constant, at 150 rpm for 2 and half an hours. The mechanism of adsorption was investigated by Lagergren,s pseudo first order, pseudo-second order, Natarajan and Khalf first order, Bhattacharya and Venkobechar first order, Elvoich and Intra particle diffusion models. The isotherm study results were fitted in Langmuir, Freundlich, Temkin, Dubihin-Radushkevich isotherms. The thermodynamics study carried out at three different temperatures 310,320 and 330K. The measurement of absorbance of colour was done Spectrophotometrically. The equilibrium adsorption capacity was evaluated using the equation

qe=(Co-Ce) V/m------(1)

Where qe (mg/g) is the equilibrium adsorption capacity, Co and Ce is the initial and equilibrium concentrations (mg/L) of Rhodamine-B dye solution. V is the volume and m is the weight of adsorbent.
Results And Discussion
Effect of pH: Initial pH of dye can influence the adsorption of it on the surface. In the present study pH 1-10 was used to observe the better adsorption with initial concentration of dye 250ppm with 1 g/L PAP as adsorbent dosage. The reaction mixture was agitated for 1 hr at 310K with agitating speed ss150rpm.The most favorable adsorption was seen at basic pH 8, with 107.9 mg/g uptake of dye adsorption. It was shown in the Figure 1.

The surface of the adsorbent which may be negatively charged at higher pH,which favored for adsorption of the positively charged dye cations through electrostatic force of attraction. The adsorption of PAP to adsorbent consequently increased with an increase of pH values [11, 12]. So, optimum pH was 8.
Effect of biosorbent dosage
At optimum pH the biosorbent dose were increased from 0.5 g/L at intervals of 0.5g/L up to 5.5g.The reaction mixture was agitated for 1hr at 310K with agitating speed 150 rpm. The percentage of removal efficiency was found high at 4 g/L. So, optimum biosorbent dose was 4 g/L. It was shown in Figure 2.

Equilibrium time fixation:At optimum pH 8 and biosorbent dose 4 g/L the reaction mixture was agitated for 2 and half an hour with regular time intervals of 15 minutes at 310K. The maximum adsorption was found at 120 minutes. After that there is no increase in adsorption. It was shown in Figure 3.
Kinetic study of adsorption
The kinetics of Rhodamine-B adsorption by using PAP was studied at different time intervals and different initial concentration of dye. The kinetic parameters are helpful for theprediction of adsorption rate, give important information for designing and modeling the adsorption process [13].

The mechanism of kinetics was investigated by Natarajan and khalf first order, Elvoich model, Bhattacharya and Venkobechar first order, Lagergren,s pseudo first order, pseudo second order and intra particle diffusion models. The study was carried at different time intervals up to equilibrium time and at different ppm at 310K are shown in Table 1.

The linearized form of Natarajan and Khalf first order kinetics is presented as
log (C0/Ct)= (K/2.303)t-----------(2)
Where C0and Ct are concentration of Rhodamine-B dye (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 C0/Ct) against t which was given in Table 2 and Figure 4. The R2, value from 0.849 to 0.866 (Table 5) and also does not fit for whole range of contact time so, it does not follow first order kinetics.
Figure 1:
Figure 2:
Figure 3:
Table 1:

Time\ppm

200

250

300

350

400

450

Ct

qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

15

94.2

26.45

118.6

32.85

142.0

39.50

168.2

45.45

194.2

51.45

220.3

57.43

30

70.7

32.33

89.8

40.05

108.6

47.84

129.6

55.10

150.8

62.29

172.5

69.38

45

60.3

34.92

77.2

43.20

94.2

51.45

112.9

59.28

132.0

67.00

151.6

74.60

60

54.5

36.37

70.2

44.96

86.2

53.46

103.5

61.62

122.6

69.34

139.9

77.52

75

50.8

37.36

65.6

46.10

81.0

54.75

97.5

63.12

114.7

71.32

132.5

79.38

90

48.2

37.96

62.5

46.88

77.4

55.64

93.4

64.15

110.0

72.49

127.3

80.67

105

46.3

38.43

60.2

47.46

74.8

56.30

90.4

64.91

106.6

73.34

123.5

81.62

120

44.8

38.8

58.4

47.90

72.8

56.80

88.0

65.50

104.0

74.00

120.6

82.34

135

44.8

38.8

58.4

47.90

72.8

56.80

88.0

65.50

104.0

74.00

120.6

82.34

150

44.8

38.8

58.4

47.90

72.8

56.60

88.0

65.50

104.0

74.00

120.6

82.34

165

44.8

38.8

58.4

47.90

72.8

56.60

88.0

65.50

104.0

74.00

120.6

82.34

Table 2:

Time

200 ppm

250 ppm

300 ppm

350 ppm

400 ppm

450 ppm

Log Co/Ct

Log Co/Ct

Log Co/Ct

Log Co/Ct

Log Co/Ct

Log Co/Ct

15

0.327

0.3239

0.3248

0.3183

0.3138

0.3102

30

0.4517

0.4447

0.4413

0.4315

0.4237

0.4164

45

0.5205

0.5103

0.5031

0.4914

0.4815

0.4725

60

0.5644

0.5516

0.5416

0.5291

0.5136

0.5074

75

0.5955

0.581

0.5686

0.5551

0.5425

0.531

90

0.6183

0.6021

0.5884

0.5737

0.5607

0.5484

105

0.6356

0.6183

0.6032

0.5879

0.5743

0.5615

120

0.6498

0.6315

0.615

0.5996

0.585

0.5719

Table 3:

Time

200ppm

250 ppm

300 ppm

350 ppm

400 ppm

450 ppm

Log 1-u(T)

log-u(T)

log-u(T)

log-u(T)

log-u(T)

log-u(T)

15

-0.4972

-0.5028

-0.5163

-0.5141

-0.5161

-0.519

30

-0.7781

-0.7854

-0.8024

-0.7992

-0.8011

-0.8024

45

-1.0000

-1.0083

-1.026

-1.022

-1.0241

-1.0264

60

-1.2034

-1.2104

-1.2292

-1.2277

-1.202

-1.2321

75

-1.4157

-1.4248

-1.4425

-1.4401

-1.4425

-1.4425

90

-1.6656

-1.6696

-1.6947

-1.6861

-1.6925

-1.6925

105

-2.0223

-2.0269

-2.0969

-2.0362

-2.0555

-2.0555

Table 4:

logt

qt

qt

qt

qt

qt

qt

1.1761

26.45

32.85

39.5

45.45

51.45

57.43

1.4471

32.33

40.05

47.84

55.1

62.29

69.38

1.6532

34.92

43.2

51.45

59.28

67

74.6

1.7782

36.37

44.96

53.46

61.62

69.34

77.52

1.8751

37.31

46.1

54.75

63.12

71.32

79.38

1.9542

37.96

46.88

55.64

64.15

72.49

80.67

2.0212

38.43

47.46

56.3

64.91

73.34

81.62

2.0792

38.8

47.9

56.8

65.5

74

82.34

Bhattacharya and Venkobechar models
The linearized form of Bhattacharya and Venkobechar first order kinetic equation is presented as
log[1-u(T)] = -(K/2.303)t ------------------(3)
Where u (T) = [(Co-Ct) / (Co-Ce)]

Ce is equilibrium Rhodamine-B 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, which was shown in Table3 and Figure 5. The R2 value is found to be from 0.954 to 0.993. (Table 5)
ELVOICH MODEL
The linearized form of Elvoich kinetic equation is presented as [14]
qt = 1/β ln (α, β)] + log t/ β ----------------------(4)
Where α and β are constants calculated from Table 4 and from the intercepts and slopes plot qt against log t shown in Figure 6.The constant β is related to the extent of surface coverage. The simple Elvoich models used to describe second order kinetics, assuming of that the actual solid surface is energetically heterogeneous. The Elvoich model has R2 =0.961 to 0.964 for adsorbents under study. Where α is initial adsorption rate 1 (mg/g /min) and β is related to the extent of the surface coverage and the activation energy for chemisorptions (g mg-1). The initial adsorption rate, decreased from -0.7885 to -0.7261 while increasing the initial dye concentration from 200 to 450. It was shown in Figure 6 and table 4 and 5.
Pseudo first order kinetics
The kinetic data were treated with the following Lagergren,s pseudo first order rate equation [15] for 250 ppm. Activation energy for chemisorptions (g mg-1).The initial adsorption ratedecreased from -0.7855 to -0.7261, while increasing the initial dye concentration from 200 to 450 ppm.
log (qe-qt) = log qe-K1 t/(2.303)-----------------(5)
Where qt and qe are the amount adsorbed at time t and at equilibrium (mg/g) and K1 is pseudo first order rate constant for the adsorption process (min-1). The plot of log (qe-qt) versus t was shown. (Table 6 Figure 7)
Pseudo second order kinetics
The pseudo second order model can be represented in the following form [16, 17]

t/ qt = 1/ K2 qe 2 +1. t/ q,e ----------------------------------------(6)
Where K2 is the pseudo second order rate constant (g/ mg.min).The plots of t versus t/qt result was shown in Table 7 and Figure 9 for 250ppm. From the above results pseudo first order has R2 value was 0.997 and pseudo second order kinetics has R2 value was 1.0000.for first order qe experimental is 26.06 mg/g where as qe theoretical is 47.90 mg/g but for second order qe is experimental is 52.63 and qe theoretical is 47.90 mg/g .So for the second order only qe experimental and qe theoretical (mg/g) values are nearly same. From this, it clearly indicates that pseudo second order better fitted than pseudo first order.
Table 5:

Rhodamine B

Natarajan and khalf model

Bhattacharya and Venkobechar model

Elvoich model

K (min-1)

R2

K (min-1)

R2

α (mg/g/min)

β (g/mg)

R2

200

0.004606

0.866

0.0368

0.992

-0.7855

0.0747

0.964

250

0.004606

0.861

0.0368

0.993

-0.7631

0.0613

0.963

300

0.004606

0.854

0.0368

0.988

-0.8035

0.0534

0.961

350

0.004606

0.853

0.0368

0.993

-0.7520

0.0467

0.962

400

0.004606

0.855

0.0368

0.991

-0.7339

0.0409

0.964

450

0.004606

0.849

0.0276

0.954

-0.7261

0.0370

0.960

Table 6:

Time

Log(qe-qt)

15

1.1775

30

0.8949

45

0.6721

60

0.4684

75

0.4684

90

0.0086

105

-0.3566

Table 6a:

K1

-0.015

qe(experimental)

23.77

R2

0.997

qe (theoretical)

47.40

Table 7:

Time

t/qt

15

0.4566

30

0.7491

45

1.0417

60

1.3345

75

1.6269

90

1.9198

105

2.2124

120

2.5052

Table 7a:

K1

0.0002

qe (experimental)

52.63

R2

1

qetheoretical)

47.90

Table 8:

t1/2

qt

3.873

32.85

5.4772

40.05

6.7082

43.2

7.746

44.96

8.6603

46.1

9.4868

46.88

10.247

47.46

10.9544

47.9

Table 8a:

K diff

1.9648

C

28.10

R2

0.8865

Table 9:

Ce

Ce/qe

44.8

1.1217

58.4

1.2192

72.8

1.2817

88

1.3435

104

1.4045

120.6

1.4645

Table 9a:

qmax

250

KL

0.00421

RL

0.3458

R2

0.984

Table 10:

log Ce

log qe

1.6513

1.5658

1.7664

1.6803

1.8621

1.7543

1.9444

1.8162

2.017

1.8692

2.0813

1.9157

Table 10a:

1/nf

            0.8021

              nf

           1.2467

              R2

           0.9956

              Kf

           1.7924

Table 11:

logCe

Qe

1.6513

36.8

1.7664

47.9

1.8621

56.8

1.9444

65.5

2.0170

74.0

2.0813

82.35

Table 11a:

R2

0.9940

bt

24.24

At

0.0483

B

106.32

Table 12:

2

log qe

609.6

1.5658

360.24

1.6803

231.95

1.7543

158.50

1.8162

114.28

1.8698

85.56

1.9157

Intra particle diffusion
According to Weber and Morris the intra particle diffusion constant (Ki) is given by the following equation [17] for 250ppm.
qt= Ki t ½ -----------------------(7)
The intra particle diffusion would be the controlling step if this line passed through the origin .when the plots do not pass through the origin. This is indicative of some degree of boundary layers control and this further show that the intra particle diffusion is not the only rate controlling step but also other processes may control the rate of adsorption [18].
Ki (mg/g/min1/2) values can be determined from Table 8 and from the Figure 9, slope of plot qt against t1/2 .The R2 value was 0.8865.
Adsorption isotherm
Equilibrium isotherm equations are used to describe the experimental adsorption data. The parameters obtained from the different models provide important information on the adsorption mechanism and the surface properties and affinities of the adsorbent. Linear regression is frequently used to determine the best fitting isotherm and the applicability of isotherm equation is compared by judging the correlation co-efficient.
Langmuir isotherm
The Langmuir equation [18] is expressed as
Ce/qe = (1/KL qm) + (1 qm) Ce----------------------(8)
Where qm is monolayer adsorption capacity (mg/g)KL is Langmuir isotherm constant related to the affinity of the binding sites and the energy of adsorption(l/mg). The values are the qm and KL can be calculated by plotting Ce/qe versus Ce. The dimensionless constant separation factor is RL[19]
RL =1/ (1+KL Ce) ---------------------- (9)
The RL value indicates the type of isotherm to be either unfavorable(RL1), linear(RL =1),favorable (0< RL< 1)or is reversible (RL=0) [20, 21]. It was shown in figure 10 and table 9. The R2 value was 0.9847 and RL is 0.34548 . So this isotherm is
Table 13: 310K Temperature.

 

Time\ppm

200

250

300

350

400

450

Ct

qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

15

94.2

26.45

118.6

32.85

142.0

39.50

168.2

45.45

194.2

51.45

220.3

57.43

30

70.7

32.33

89.8

40.05

108.6

47.84

129.6

55.10

150.8

62.29

172.5

69.38

45

60.3

34.92

77.2

43.20

94.2

51.45

112.9

59.28

132.0

67.00

151.6

74.60

60

54.5

36.37

70.2

44.96

86.2

53.46

103.5

61.62

122.6

69.34

139.9

77.52

75

50.8

37.36

65.6

46.10

81.0

54.75

97.5

63.12

114.7

71.32

132.5

79.38

90

48.2

37.96

62.5

46.88

77.4

55.64

93.4

64.15

110.0

72.49

127.3

80.67

105

46.3

38.43

60.2

47.46

74.8

56.30

90.4

64.91

106.6

73.34

123.5

81.62

120

44.8

38.8

58.4

47.90

72.8

56.80

88.0

65.50

104.0

74.00

120.6

82.34

135

44.8

38.8

58.4

47.90

72.8

56.80

88.0

65.50

104.0

74.00

120.6

82.34

150

44.8

38.8

58.4

47.90

72.8

56.60

88.0

65.50

104.0

74.00

120.6

82.34

165

44.8

38.8

58.4

47.90

72.8

56.60

88.0

65.50

104.0

74.00

120.6

82.34

Table 14: 320K Temperature.

Time\ppm

200

250

300

350

400

450

Ct           qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

15

77.5

30.63

98.3

37.93

120.3

44.92

142.6

51.85

168.3

57.94

187.6

65.59

30

57.3

35.68

73.2

44.20

90.3

52.42

107.1

60.72

126.5

68.37

142.6

76.86

45

49.0

37.74

62.9

46.77

78.0

55.50

92.4

64.39

109.2

72.71

123.9

81.52

60

44.6

38.86

57.3

48.18

71.3

57.18

84.4

66.39

99.6

75.09

113.7

84.07

75

41.7

39.57

53.8

49.06

67.0

58.24

79.4

67.66

93.6

76.60

107.3

85.68

90

39.8

40.06

51.3

49.67

64.0

58.97

75.9

68.53

89.4

77.64

102.8

86.78

105

38.4

40.41

49.6

50.11

62.0

59.50

73.3

69.17

86.4

78.40

99.6

87.59

120

37.3

40.68

48.2

50.45

60.4

59.90

71.4

69.65

84.1

78.98

97.2

88.2

135

37.3

40.68

48.2

50.45

60.4

59.90

71.4

69.65

84.1

78.98

97.2

88.2

150

37.3

40.68

48.2

50.45

60.4

59.90

71.4

69.65

84.1

78.98

97.2

88.2

165

37.3

40.68

48.2

50.45

60.4

59.90

71.4

69.65

84.1

78.98

97.2

88.2

Table 15: 330K Temperature.

Time\ppm

200

250

300

350

400

450

Ct

qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

Ct

qt

15

60.3

34.93

78.2

42.95

98.6

50.40

119.5

57.62

141.8

64.54

163.6

71.60

30

44.0

39.00

58.5

47.87

72.7

56.83

88.6

65.34

105.7

73.57

122.8

81.79

45

37.8

40.56

51.0

49.76

62.5

59.38

76.4

68.39

91.4

77.16

106.6

85.86

60

34.4

41.39

48.3

50.42

57.0

60.74

69.9

70.03

83.6

79.09

97.8

88.05

75

32.4

41.91

44.4

51.39

53.7

61.58

65.8

71.05

78.8

80.30

92.3

89.42

90

31.0

42.26

42.8

51.81

51.4

62.16

63.0

71.75

75.5

81.12

88.6

90.36

105

30.0

42.51

41.5

52.12

49.7

62.58

61.0

72.25

73.1

81.72

85.8

91.04

120

29.3

42.68

38.2

52.95

48.4

62.89

59.4

72.64

71.3

82.18

83.8

91.56

135

29.3

42.68

38.2

52.95

48.4

62.89

59.4

72.64

71.3

82.18

83.8

91.56

150

29.3

42.68

38.2

52.95

48.4

62.89

59.4

72.64

71.3

82.18

83.8

91.56

165

29.3

42.68

38.2

52.95

48.4

62.89

59.4

72.64

71.3

82.18

83.8

91.56

favorable.
Freundlich Isotherm
The isotherm was represented by
log qe= log Kf + 1/n log Ce----------------------------------- (10)
Where qeis the amount of Rhodamine – B adsorbed at the equilibrium (mg/g), Ceis the equilibrium constant of Rhodamine – B in solution (mg/L) [22, 23]. Kf and 1/nf are constantincorporating factor affecting the adsorption capacity and intensity of adsorption respectively .It was shown in the Figure 11 and table 10. The R2 value is 0.9956 .It indicates good linearity and obeys the Freundlich isotherm.
Temkin isotherm
The Temkin isotherm is given as
qe= βln A + βln Ce
Table 16:

ppm

310 K

320 K

33O K

∆H
KJ/mol

∆S
J/mol

K0

∆GO

K0

∆GO

K0

∆GO

200

3.4643

-3201.40

-4.3619

-4.3619

5.8259

-4835.11

21608.09

80.04

250

3.2808

-3062.10

-4.1867

-4.1867

5.5445

-4699.29

21807.62

80.27

300

3.1203

-2933.32

-3.9669

-3.9669

5.1984

-4522.44

21209.01

77.92

350

2.9773

-2811.92

-3.9019

-3.9019

4.8923

-4355.94

19887.09

73.50

400

2.8462

-2695.85

-3.7562

-3.7562

4.6101

-4193.9

20045.05

73.55

450

2.7313

-2589.65

-3.6296

-3.6296

4.3699

-4046.12

19537.90

71.59

Table 17:

ppm

310 K

320 K

330 K

ln K0

ln K0

ln K0

200

1.2425

1.4729

1.7623

250

1.1881

1.4319

1.7128

300

1.1381

1.3779

1.6483

350

1.1091

1.3614

1.5876

400

1.0459

1.3234

1.5282

450

1.0047

1.2891

1.4747

Where At (l/g) is the equilibrium binding constant corresponding to the maximum binding energy and constant B is related to heat of adsorption [25]. A Linear plots of qe against ln Ce. Enables the determination of constant B and A from slope and intercept (table 11 and Fig 12).The R2 value is 0.994.
Dubihin – Radushkevich isotherm
The Dubihin- Radushkevich isotherm is given as
ln Q = ln Q m – K’ [ RT ln(1+(1/ce)]2E = -(2k)-0.5 ---------------- --(11)
This adsorption curve depends of the adsorbent pores. (26) The plot of lnqe vs. ᶓ2 for Rhodamine - B are shown in table 13 and figure13. The mean adsorption energy (E) gives information about the chemical and physical nature of adsorption. The R2 value is 0.955.
Thermodynamic Analysis
Thermodynamic parameters such as change in free energy ΔG (J/mole), enthalpy ΔH, (J /mole) ΔS (J/K/mole) were determined using following equations
K0 = C solid / C liquid ---------- (12)
ΔG =-RT ln K0----------------- (13)
ΔG = ΔH-TΔS___________(14)
In k0 = - ΔG/RT---------------- (15)
ln k0 = -ΔS/R-ΔH/R-------------(16)
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 a gas constant. ΔG values obtained from equation (13), It was presented in Table (14, 15, 16, 17) .
Figure 4:
Figure 5:
Figure 6:
Conclusion
The aim of this paper was utilization of natural biosorbent PAP as adsorbent for the removal of Rhodamine-B dye. Even though Bhattarchaya and Venkobechar frist order kinectic model,lagergren,s pseudo first order kinetic model gave better results ,but pseudo second order kinetic model was best fitted kinetic of adsorption . The correlation co efficient R2 = 1 for second order adsorption model and qe theoretical values are consistent with qe experimental value showed that pseudo
Figure 7:
Figure 8:
Figure 9:
Figure 10:
Figure 11:
Figure 12:
Figure 13:
second order adsorption equation fit with whole range of contact time. Among isotherms, Freundlich isotherm was found to be best fitting model with respect to R2 values. ΔG, ΔH and ΔS values showed that favorable, spontaneous and endothermic. The PAP adsorbents have excellent adsorption capacity compare to any other non conventional adsorption. So PAP can be used as a low cost attractive alternative for costly activated carbon.
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