Hen Feather: A Remarkable Adsorbent for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 441

of the sorption process for all four adsorption systems. The endother-
mic nature of the adsorption process is further confirmed by the posi-
tive values of ΔH obtained in each case. The positive values of entropy
change (ΔS ) for these adsorption systems show decreased randomness at
the interface and no considerable change in the internal structure of the
adsorbents. Thus, values of ΔG , ΔH and ΔS confirm the spontaneous
and endothermic nature of the adsorption process for both dye-adsorbent
systems.

11.5.3.6 Favorability of the Processes

By applying the Weber-Chakravorti equation (Equation 11.10) to both the
adsorption systems, the separation factor 'r' is calculated for each system.
It is evident from Table 11.3 that the value of the Langmuir constant 'b' is
positive and so is the dye initial concentration (C o ). Therefore the denomi-
nator of Equation 11.10 will always be greater than unity and the value of
separation factor 'r' will stand between zero to unity. This indicates favor-
ability of the adsorption process for both the Azo dye-adsorbent systems
at all temperatures.

11.6 Kinetics Measurements

The main focus of the present work is to couple kinetic studies with the
adsorption process so that on the basis of the results obtained, a deeper
understanding of the ongoing adsorption process can be developed,
thereby unfolding many hidden intricacies of the adsorption of Azo
dyes over Hen Feathers. The principal application of teaming adsorption
technique with kinetic studies includes deriving necessary information
about the order and mechanism of the process through which the accu-
mulation of the dye takes place over the surface of the adsorbent mate-
rial, and also determining various other kinetic parameters and sorption
characteristics of the adsorbents. The purpose of carrying out chemical
kinetic study of any adsorption process is to observe the influence of dif-
ferent experimental conditions over rate of adsorption and adsorption
mechanism. In order to determine the rate-controlling steps, the kinetic
behavior of the overall adsorption and mechanism of the present ongo-
ing adsorption processes finite bath method has been chosen. The mod-
els describing the order of the reaction have also been analyzed along
with detailed quantitative investigations of the mechanisms involved in
the present adsorption processes.