Three kinetic models; pseudo first and second order and intra particle diffusion, are mostly used to describe the adsorption kinetics
However, it was noticed that the pseudo first order and intra particle diffusion models did not fit well to this study (data not
shown) in agreement with literature
Thus, kinetic data was best explained by pseudo-second order model (Ho & McKay, 1998) as shown in Fig. 4b. This model is given as under by Eq. (8).
where qt is the adsorption capacity (mg/g) at any time t, and k2 (g/mg min) is the second order rate constant.
Pseudo second order model was applied by plotting t/qt vs. t, and model parameters; rate constant (k2) and initial adsorption rate (h = k2q2e ), were calculated from the intercept of plot.
These parameters are given in Table 3. The values of R2 for two dye concentration levels were calculated as 0.999 which showed the adequacy of this model to describe kinetic data.