Hen Feather: A Remarkable Adsorbent for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 448

for the adsorption of Tartrazine and the half-life of each process is found to
decrease with increase in temperature (Table 11.6).
In all the above-mentioned cases the rate of removal of dye decreases
with time, which may be due to aggregation of dye molecules around the
adsorbent. This aggregation disallows the migration of adsorbate, as the
adsorption sites get filled up, and also because resistance to diffusion of dye
molecules in the adsorbent increases.

11.6.3.2 Rate Constant Study

In order to identify the order of the reaction for the adsorption of the Azo
dyes, Lagergren's pseudo-first-order rate equations have been applied and
order of the ongoing adsorption process is ascertained on the basis of com-
parison of regression constant values of the best-fit straight lines.
For the Hen Feather adsorption of Azo dyes-Amaranth (Figure 11.16)
and Tartrazine (Figure 11.17), the R 2 values are found closer to unity in the
case of Lagergren's pseudo-first-order. It is therefore concluded that dyes
Amaranth and Tartrazine exhibit pseudo-first-order kinetics for adsorp-
tion over Hen Feather. A higher molecular weight of Amaranth (Molecular
Weight = 604.48) and Tartrazine (Molecular Weight = 534.4) may be the
possible reason for lower order in these cases.
In the case of systems following first order kinetics the values of
rate constants presented in Table 11.7 follow the order Amaranth-Hen
Feather > Tartrazine-Hen Feather, which may be due to more numbers
of attachment sites (-SO 3 - ) with Amaranth. Moreover, no significant

Table 11.6 Effect of adsorbent amount on rate of adsorption of Azo Dyes over
Hen Feathers and half life of the process at different temperatures.

Dye Amount of

Adsorbent (g)

Rate Constant
(per hour)

Half Life (Hour)

30°C 40°C 50°C 30°C 40°C 50°C

Amaranth 0.005 0.014 0.017 0.019 48.28 41.35 35.88

0.01 0.031 0.034 0.038 22.33 20.46 18.35

0.025 0.042 0.045 0.054 16.46 15.32 12.76

0.05 0.049 0.054 0.066 14.12 12.76 10.50

Tartrazine 0.005 0.019 0.021 0.027 37.41 32.62 25.86

0.01 0.034 0.037 0.041 20.31 18.83 17.00

0.015 0.048 0.052 0.062 14.32 13.29 11.19

0.02 0.087 0.107 0.263 7.92 6.47 2.63