of t/qt
against t for pseudo-second-order model under
different temperature are shown in Fig. 9. From the
slope and intercept values, q2
and k2
were calculated
and the results are shown in Table 4. The linear plots
of t/qt
versus t show a good agreement with
experimental data giving the correlation coefficients
close to 1. Also, the calculated q2
values agree very
well with the experimental data at all temperature. This
means that the adsorption kinetics of humic acid onto
CSC obeys the pseudo-second-order kinetic model for
the entire adsorption period.
The pseudo-second-order kinetic model cannot
give a definite mechanism of adsorption. Adsorption
kinetics is usually controlled by different mechanisms,
the most general of which is the diffusion mechanism.
The intra-particle diffusion model can be defined as:
qt = k.t0.5
+ C (8)
where k is the intra-particle diffusion rate constant
(mg/g min1/2) and qt
is the amount of humic acid
adsorbed at time t (mg/g). The plot of qt
versus t
1/2
would result in a linear relationship. If the lines passed
through the origin diffusion would be the controlling
step. Otherwise, the intra-particle diffusion is involved