72
A. Geethakarthi
Fig. 33 Langmuir isotherm for the adsorption of dye Reactive Red 2 using SC300 for different
temperatures at 120 rpm and pH = 7.0
with increase in temperature for all the adsorbents as shown in Fig. 34 indicating that
the adsorption process was endothermic in nature. The effect of temperature on batch
adsorption studies can be correlated based on the thermodynamic studies (Fig. 34).
The apparent heat per net enthalpy (H
0 ) of adsorption is related to the Langmuir
constant (b). The Langmuir constant (b or k d ) is related to energy consumption and
the ratio of adsorption rate to desorption rate [23]. In thermodynamics equation,
change of Gibbs free energy (G
0 in kJ/mol) was calculated by using Eqs. (5.3) and
(5.4). Change in entropy (S
0 in J/Kmol) and change in enthalpy (H
0 in kJ/mol)
for the adsorption were calculated and estimated by using Eq. (5.5). K d represents
equilibrium distribution constant, and R is the universal gas constant (8.314 J/Kmol).
Fig. 34 Effect of temperature at 40 mg/L of adsorbate concentration at 120 rpm and pH = 7.0