Hen Feather: A Remarkable Adsorbent for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 442

11.6.1 Theory of Kinetic Measurements

11.6.1.1 Effect of Contact Time

Contact time studies are used to monitor the influence of system param-
eters on the rate of adsorption of the dye on the adsorbent. They also help
in determining the time of equilibrium attainment, i.e., the time beyond
which no further significant adsorption takes place over the surface of
adsorbent, rate-determining step of the process. Thus, equilibrium tests are
carried out to ascertain the time at which complete saturation of adsorbent
occurs and steady rate is reached.
Under the contact time study, uptake capacity of the adsorbent is deter-
mined at different temperatures, fixed amount of adsorbent, definite con-
centration of the dye and constant pH. When the equilibrium is reached,
the solution is filtered and dye uptake (q e ) is calculated using the following
equation:

(C C ) V

W

(11.11)

q

o e

e

where C e is the concentration of the dye at equilibrium in mol/L, C o
is the initial concentration in mol/L, V is volume in liters and W is the
mass (g) of the adsorbent taken in the reaction flask.

11.6.1.2 Rate Constant Study

Kinetics of any adsorption process is helpful in determining the efficacy of
the adsorbent material for a particular dye and efficiency of the ongoing
adsorption process. The monitoring of kinetics of the adsorption process is
useful in ascertaining the rate-determining step, order of the process and
value of rate constant. These parameters mainly provide information about
the rapidity of the adsorption. A literature survey confirms that there are
several models and methods which can be used for calculating the rate and
rate-determining step of any adsorption process. However, in the present
cases, the determination of specific rate constant of adsorption of dyes on
each adsorbent has been made by using Lagergren's pseudo-first-order rate
expression [83]. The verification of the model has been done by calculating
the regression coefficients of the best-fit straight lines.
The adsorption of the dye molecules from the aqueous phase to a solid
phase can be considered a reversible process in which equilibrium is estab-
lished between the dye in the solution and dye at the surface of adsor-
bent at equilibrium. The kinetics of such type of adsorption is described