The intraparticle diffusion model is according to the equationdescribed in previous report [21]. Here, Kpi(mg g−1min0.5) denotes the intraparticle diffusion rate constant. Kpi and Ci, determined from the slope and intercept of the plots of qt versus t 0.5, are shown in Table 3. This model is used to determine the adsorption mechanism and dope out the rate controlling step. Usually, the controlling step of an adsorption process include (1) film diffusion, (2) intra-particle diffusion, (3) adsorption of adsorbate on the interior surface of adsorbents [22], (4) the combination of the above step. Here, the plot of qt versus t 0.5was a straight line which did not pass trough the origin. This result implied that the intraparticle diffusion was not the only rate controlling step.