Environmental Engineering Reference
In-Depth Information
Figure 11.15
D-R adsorption isotherm for Tartrazine (pH = 2.0) - Hen Feather (0.01
g/25mL) system at different temperatures.
Table 11.4
Thermodynamic parameters for the uptake of Azo Dyes.
Adsorbent
-ΔG
(kJ mol
-1
)
ΔH
(kJ
mol
-1
)
ΔS
(JK
-1
mol
-1
)
30 C 0C 0C
Amaranth - Hen Feather
17.96
19.40
20.66
22.75
11.00
Tartrazine - Hen Feather
30.47
31.62
33.04
8.50
74.16
11.5.3.5 Thermodynamic Parameters
The theory presented above indicates that thermodynamic dependency
and various thermodynamic parameters of the adsorption of Azo dyes over
Hen Feather can be evaluated by using Langmuir adsorption constant 'b.
The values of free energy (ΔG ), enthalpy change (ΔH ) and change in
entropy (ΔS ) are calculated and presented in Table 11.4.
For all the Azo dyes ΔG values are negative, indicating that the sorp-
tion process brings a decrease in Gibbs free energy and that the adsorption
process is feasible and spontaneous at all the temperatures. Equilibrium
experiments performed for the adsorption of Amaranth and Tartrazine
over Hen Feathers at different temperatures (30, 40 and 50 C) show an
increase in the amount of dye adsorbed, implying an endothermic nature
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