Kinetic Modelling 491 Pseudo First Order

The adsorption kinetics was investigated for better understanding of the dynamics of adsorption of RR158 onto CAC's and obtaining predictive models that allow estimations of the amount of dye adsorbed with the treatment time. The linearised forms of the models are illustrated in Figs. 36, 37, 38, 39, 40 and 41. A summary of the results for the pseudo first order parameters with the correlation coefficients

Fig. 36 The linearized pseudo first order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 7.5 g/L; pH: 2
Fig. 37 The linearized pseudo first order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 10 g/L; pH: 2

is tabulated in Table 10. The correlation coefficients, R2 for the first-order kinetic model obtained at the studied concentrations were in the range of 0.002 and 0.416. These low values indicated that the experimental data were not well fitted to the aforementioned model. This may be due to the stirring speed used in the present work (200 rpm) which reduced the film boundary layer [2]. It was also observed

Fig. 38 The linearized pseudo first order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 12.5 g/L; pH: 2
Fig. 39 The linearized pseudo first order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 15 g/L; pH: 2

that qt values computed from this model deviated considerably from the experimental qt values which indicated that pseudo-first order equation might not be sufficient to describe the mechanism of RR158 and CAC's interactions [11]. The

Fig. 40 The linearized pseudo first order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 17.5 g/L; pH: 2
Fig. 41 The linearized pseudo first order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 20 g/L; pH: 2

calculated qt values were lower compared to the experimental qt values at the various initial dye concentrations and adsorbent dosages. Also, as initial dye concentration increased at a constant dosage of adsorbent, the theoretical qt values increased such as for adsorbent dosage of 15 g/L, theoretical qt values increased from 0.2399 to 1.1885 mg/g for increase in dye concentration from 20 to 120 mg/L.

Table 10

Summary of values of rate constant and theoretical q, values of pseudo first order model

Dye concentration (mg/L)

value

(min-1)

Theoretical qt (mg/g)

Experimental qt (mg/g)

value

(min-1)

Theoretical qt (mg/g)

Experimental qt (mg/g)

20

Adsorbent dosage: 7.5 g/L 0.005 -0.0023

0.1675

0.348

Adsorbent dosage: 15 g/L 0.084 -0.0069

0.2399

0.293

40

0.086

-0.0115

0.0703

0.668

0.134

0.0046

0.6457

0.937

60

0.104

-0.0138

0.0778

1.881

0.002

0.0690

1.3772

1.378

80

0.264

0.0253

0.0188

1.941

0.002

0.0290

1.0186

1.019

100

0.048

-0.0069

0.1637

2.296

0.288

0.0161

1.1885

1.652

120

0.274

0.0161

0.0811

4.407

-

-

-

1.307

20

Adsorbent dosage: 10 g/L 0.423 0.0115

0.2904

0.394

Adsorbent dosage: 17.5 g/L 0.210 -0.0069

0.9098

0.698

40

0.246

0.0184

0.4592

0.444

0.234

-0.0023

0.6339

0.911

60

0.086

0.0211

0.6669

0.667

0.032

0.0069

0.2642

1.022

80

0.071

-0.0046

0.5848

1.533

0.058

0.0069

0.7096

1.076

100

0.375

0.0046

1.6368

2.894

0.052

0.0046

0.9594

1.130

120

0.007

0.0023

0.6592

3.311

0.021

-0.0069

0.3882

0.876

20

Adsorbent dosage: 12.5 g/L 0.248 -0.0092

0.1963

0.391

Adsorbent dosage: 20 g/L 0.272 0.0069

1.3489

1.770

40

0.296

0.0161

1.1534

1.422

0.461

0.0046

1.3489

2.533

60

0.215

0.0516

1.1194

1.120

0.143

0.0115

1.6406

3.289

80

0.177

-0.0023

0.6295

0.809

0.535

0.0069

4.0551

3.459

100

0.019

-0.0046

0.4426

1.498

0.375

0.0184

1.5453

2.556

120

0.228

0.0147

1.2677

1.267

0.256

0.0345

4.0551

4.052

Fig. 42 The linearized pseudo second order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 7.5 g/L; pH: 2
Fig. 43 The linearized pseudo second order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 10 g/L; pH: 2

It was also noticed that at adsorbent dosage of 17.5 g/L, the calculated qt values decreased as dye concentration increased which might be due to the use of insufficiently pretreated coconut shells.

Fig. 44 The linearized pseudo second order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 12.5 g/L; pH: 2
Fig. 45 The linearized pseudo second order kinetics of RR158 by CAC's. Experimental conditions: room temperature; agitation rate: 200 rpm; biomass dosage: 15 g/L; pH: 2
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