Freundlich Model

The values of the Freundlich constants determined from the graphs displayed in Figs. 18, 19, 20, 21, 22 and 23 are given in Table 7. The high correlation

Table 7 Langmuir and Freundlich constants of RR158 adsorption on CAC's

Dye concentration (mg/L)

Langmuir

Freundlich

qmax

qmax

Table 7 Langmuir and Freundlich constants of RR158 adsorption on CAC's

20

Adsorbent dosage: 0.990 0.0017

7.5 g/L 0.0525

0.488

0.827

20.28

0.049

3.76E+25

40

0.990

0.0543

0.0301

0.454

0.997

9.065

0.110

8.81E+13

60

1.000

0.3719

0.0271

0.380

0.999

3.573

0.280

1.62E+06

80

1.000

0.3349

0.0185

0.404

0.999

4.573

0.219

3.89E+08

100

1.000

0.3100

0.0133

0.429

0.998

5.621

0.178

1.79E+11

120

1.000

0.9381

0.0134

0.383

0.998

3.233

0.309

1.06E+07

20

Adsorbent dosage: 0.999 0.0604

10 g/L 0.0738

0.404

0.999

4.702

0.213

1.82E+05

40

0.841

0.0139

0.0288

0.464

0.953

14.37

0.070

8.99E+21

60

0.922

0.0396

0.0197

0.459

0.973

10.81

0.093

3.76E+18

80

0.999

0.2838

0.0180

0.410

0.998

4.456

0.224

2.29E+08

100

1.000

0.9074

0.0194

0.340

0.999

2.406

0.416

9.39E+04

120

0.999

0.7168

0.0133

0.385

0.999

3.233

0.309

8.45E+06

20

Adsorbent dosage: 0.966 0.0595

12.5 g/L 0.0693

0.419

0.998

4.295

0.233

7.76E+04

60

0.564

0.3227

0.0321

0.342

-

-

-

-

80

0.844

0.0030

0.0136

0.479

0.915

26.31

0.038

1.08E+49

100

0.977

0.4172

0.0161

0.383

0.990

3.419

0.292

6.08E+06

120

0.945

0.0538

0.0101

0.451

0.972

10.8

0.093

7.89E+21

20

Adsorbent dosage: 0.988 0.0481

15 g/L 0.0685

0.422

0.964

4.297

0.233

6.62E+04

40

0.997

0.0958

0.0398

0.386

0.958

3.823

0.262

2.74E+05

60

1.000

0.3361

0.0327

0.337

0.999

2.445

0.409

1.17E+04

80

1.000

0.1627

0.0178

0.412

0.998

4.814

0.208

6.17E+08

100

0.975

0.0884

0.0136

0.424

0.536

3.339

0.299

2.93E+06

120

0.999

0.3141

0.0129

0.392

0.983

3.820

0.262

6.00E+07

20

Adsorbent dosage: 0.997 0.0830

17.5 g/L 0.1075

0.317

0.885

2.044

0.489

79

40

0.966

0.1112

0.0467

0.349

0.977

3.079

0.325

1.66E+04

60

1.000

0.2931

0.0325

0.339

0.998

2.446

0.409

1.02E+04

80

1.000

0.2558

0.0203

0.382

0.997

3.297

0.303

1.01E+06

100

0.999

0.2348

0.0160

0.384

0.999

3.854

0.259

2.29E+07

120

0.999

0.1893

0.0119

0.412

0.990

4.934

0.203

8.82E+09

20

Adsorbent dosage: 0.996 0.5076

20 g/L 0.1391

0.264

0.982

1.330

0.752

38

40

0.999

0.2759

0.0478

0.343

0.916

2.741

0.365

1.28E+04

60

0.983

0.8389

0.0377

0.306

0.902

2.130

0.469

6.87E+03

80

0.999

0.3266

0.0191

0.396

0.950

4.208

0.238

8.52E+07

100

0.999

0.7278

0.0178

0.359

0.998

3.204

0.312

2.96E+06

120

1.000

0.9728

0.0133

0.385

0.999

3.202

0.312

9.82E+06

Fig. 18 The linearised Freundlich isotherm for RR158 on CAC's. Experimental conditions: at room temperature, 200 rpm, adsorbent dosage = 7.5 g/L
Fig. 19 The linearised Freundlich isotherm for RR158 on CAC's. Experimental conditions: at room temperature, 200 rpm, adsorbent dosage = 10 g/L

coefficients of the linearised Freundlich models obtained imply that heterogeneous surface conditions may co-exist within the monolayer adsorption under the applied experimental conditions. Hence, the overall adsorption of RR158 on the biomass is complex, involving more than one mechanism, such as ion exchange, surface complexation and electrostatic attraction [5].

Dosage Models
Fig. 20 The linearised Freundlich isotherm for RR158 on CAC's. Experimental conditions: at room temperature, 200 rpm, adsorbent dosage = 12.5 g/L
Dosage Models
Fig. 21 The linearised Freundlich isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 15 g/L

The constants of the Freundlich isotherm, KF were in the range of 79 to 3.76 E+21. High values of these parameters at pH 2 showed easy separation of RR158 from the aqueous solution [17]. The values of the Freundlich constants showed a relatively easy uptake of RR1528 with high adsorptive capacity of CAC's.

Fig. 22 The linearised Freundlich isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 17.5 g/L
Fig. 23 The linearised Freundlich isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 20 g/L

The values of n for the present work were in the range of 2-10 hence indicating that adsorption is beneficial and the values of 1/n less than 1 generally indicated that adsorption capacity was only slightly suppressed at lower equilibrium concentrations. However, there were some exceptions such that at constant dosage of CAC's and a dye solution of 20 mg/L, n was 20.28.

Fig. 24 The linearised D-R isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 7.5 g/L
Biomass Adsorbent
Fig. 25 The linearised D-R isotherm for RR158 on CAC's. Experimental conditions: at room temperature, 200 rpm, adsorbent dosage = 10 g/L
Fig. 26 The linearised D-R isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 12.5 g/L
Fig. 27 The linearised D-R isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 15 g/L
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