Dubinin Radushkevich Isotherm Model

The values for the theoretical saturation capacity and that of b which is a constant connected with the mean free energy of adsorption per mole of adsorbate were determined from the slopes and y intercepts of the linearly regressed lines

Fig. 28 The linearised D-R isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 17.5 g/L
Fig. 29 The linearised D-R isotherm for RR158 on CAC's. Experimental conditions: room temperature, 200 rpm, adsorbent dosage = 20 g/L

illustrated in Figs. 24, 25, 26, 27, 28 and 29. A summary of the results obtained is tabulated in Table 8. The R2 values were greater than 0.945 for varying initial concentration of dye solution for fixed amount of adsorbent of 10 g/L, greater than 0.899 for adsorbent dosage of 12.5 g/L, greater than 0.916 for adsorbent dosage of

Table 8 Summary of results obtained for values of Dubinin-Radushkevich constants

Dye concentration R2 values kad qs (mg/g) R2 values kad qs (mg/g)

Table 8 Summary of results obtained for values of Dubinin-Radushkevich constants

Dye concentration R2 values kad qs (mg/g) R2 values kad qs (mg/g)

(mg/L)

Adsorbent

dosage: 7.5 g/L

Adsorbent

dosage: 15 g/L

20

0.004

0.06700

0.1579

0.934

-0.00012

0.0280

40

0.827

-0.09700

0.2245

0.936

-0.00019

0.2365

60

0.524

-0.02600

1.2105

0.998

-0.00038

0.3423

80

0.890

-0.01100

1.5008

0.997

-0.00100

0.0850

100

0.848

-0.04400

0.6263

0.916

-0.00300

0.0325

120

0.769

-0.03400

1.3034

0.988

-0.00300

0.2131

Adsorbent

dosage: 10 g/L

Adsorbent

dosage: 17.5

g/L

20

0.997

-0.00011

0.0316

0.900

-0.00004

0.0692

40

0.945

-0.00100

0.0002

0.958

-0.00023

0.0872

60

0.961

-0.00200

0.0024

0.997

-0.00046

0.2302

80

0.997

-0.00100

0.1673

0.994

-0.00100

0.2101

100

0.998

-0.00100

0.9305

0.998

-0.00200

0.1643

120

0.998

-0.00200

0.6011

0.984

-0.00400

0.0976

Adsorbent

dosage: 12.5

g/L

Adsorbent

dosage: 20 g/L

20

0.990

-0.00013

0.0301

0.945

-0.00002

0.6213

40

0.966

-0.00093

0.0660

0.803

-0.00017

0.2539

60

0.998

-0.00100

0.0630

0.982

-0.00028

0.8411

80

0.899

-0.01300

0.0000

0.909

-0.00100

0.2587

100

0.992

-0.00100

0.3420

0.996

-0.00100

0.6163

120

0.999

-0.01000

0.0035

0.995

-0.00200

0.8163

15 g/L, higher than 0.900 for adsorbent dosage of 17.5 g/L and higher than 0.909 for adsorbent dosage of 20 g/L. While for adsorbent dosage of 7.5 g/L, the R2 values varied between 0.004 and 0.890 indicating that the D-R model fitted well at high dosages of adsorbent, it was not a good model at low dosages of adsorbent for the adsorption process. The values of e2 were in the range of 11.91 and 17.96 kJ/mol for dye concentration of 20 mg/L with 7.5 g/L of adsorbent. For an adsorption process with e2 between 8 and 16 kJ/mol, the process is known to follow chemical ion exchange while the process is likely to be considered as physical adsorption with e2 less than 8 kJ/mol. Therefore, the adsorption of RR158 by CAC's in the present study was considered to be influenced physically for initial dye concentration of 40, 60, 80, 100 and 120 mg/L as e2 values were below 8 kJ/mol whereas at lower initial concentrations of 20 mg/L, the adsorption process was influenced by chemisorption.

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  • jennifer
    What is qs in DR isotherm?
    2 years ago

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