Environmental Engineering Reference
In-Depth Information
ions and helps in determining entropy of activation using the following
expression:
The entropy of activation ΔS can be calculated by using the following
equation:
S
R
(11.21)
2
D
(.
272
d
kT/h
)exp
o
where d is the average distance between two successive sites of the adsor-
bent, k is the Boltzmann constant (J. K -1 ), h is the Plank's constant (J. K -1 ),
T is the temperature (K) and R is the Universal Gas Constant (J. K -1 .mol -1 ).
Usually the distance between two successive sites of the adsorbent is taken
as 5 × 10 -8 cm [92]. The value of change in entropy (ΔS) plays an impor-
tant role in diagnosing the change in the internal structure of the adsor-
bent after the adsorption of the dye. The negative value of ΔS indicates
no change in the internal structure of the adsorbents, while positive value
suggests some change in the internal structure of the adsorbent, which may
affect the adsorbing ability of the adsorbent.
11.6.2 Experimental Methodology
In all the adsorption experiments 25 mL dye solution of known concen-
tration is taken in a 100 mL graduated volumetric flask at a fixed pH and
amount of adsorbent. The mixture is then shaken on a mechanical agitator
and after a fixed interval of time, the solution is withdrawn and uptake of
the dye is analyzed spectrophotometrically.
11.6.3
Results and Discussions
11.6.3.1
Effect of Contact Time
The uptake of the dye molecules by the Hen Feather and time of establish-
ment of equilibrium suggest the effectiveness of this material for wastewa-
ter treatment. In order to determine the equilibrium time for maximum
dye uptake, a contact time study is carried out. For the contact time studies
of the adsorption over Hen Feathers, it is observed that at temperatures
30, 40 and 50 C the adsorption of the Amaranth is faster in the case of low
concentration of the dye solution and equilibrium is established in about
2 hours, while at higher concentration the equilibration time is around 3
hours. In both the concentration ranges the amount of adsorbate increases
with increasing temperatures. A careful inspection suggests that at 30, 40
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