Environmental Engineering Reference
In-Depth Information
11.5.2 Experimental Methodology
For the verification of isotherm models batch adsorption has been per-
formed over Hen Feather for both the Azo dyes by taking 25 mL of the dye
solution of known concentration and definite pH, in a 100 mL volumetric
flask at 30, 40 and 50 C. A fixed amount of the Hen Feather is now added
into the solution and adsorption is monitored after gradually mixing the
dye-adsorbent mixture in a mechanical shaker for about 24 hours. After
24 hours these solutions are filtered with Whatman filter paper (No. 41)
and the amount of the dye uptake is analyzed spectrophotometerically at
definite wavelengths, λ
max
corresponding to the dye. The complete experi-
mental procedure involved in the study has already been explained in the
previous chapter. The data obtained is then applied to various isothermal
models and the best-fit straight lines are ascertained in each adsorption
model.
11.5.3
Results and Discussions
11.5.3.1
Langmuir Isotherm Model
For the verification of the Langmuir isotherm model 1/C
e
versus 1/q
e
graphs have been plotted for the data obtained during adsorption of both
the Azo dyes at temperatures 30, 40 and 50 C. The Langmuir plots for the
adsorption systems Amaranth-Hen Feather and Tartrazine-Hen Feather
are presented in Figures 11.8 and 11.9, respectively. In all the cases, straight
lines with appreciable R
2
values are obtained at all the temperatures, thereby
indicating verification of the Langmuir adsorption model and involvement
of monolayer adsorption in each case. These straight lines are helpful in
calculating the Langmuir constant 'b' and the number of moles of the dye
adsorbed per unit weight of the adsorbent (q
o
) through their slopes and
intercepts, respectively (Table 11.3).
11.5.3.2
Freundlich Isotherm Model
The linear plots of log C
e
versus log q
e
at temperatures 30, 40 and 50 C
give straight lines with regression coefficient value close to unity. This
clearly reveals that adsorption of Azo dyes on Hen Feathers (Figures 11.10
and 11.11) follows the Freundlich model at all the temperatures. With the
help of these Freundlich linear adsorption isotherm plots, Freundlich con-
stants are evaluated. The values of K
F
and n derived from the intercepts and
slopes of straight lines obtained are collectively listed in Table 11.3.
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