As shown in Table 3, the high diffusion rate in the initial stages (kp1) is the instantaneous adsorption or external surface adsorption and the decrease rate in the second stage (kp2) where intraparticle diffusion is rate-limiting, the lowest rate at the third step (kp3) is the final equilibrium stage where intraparticle diffusion started to slow down due to the extremely low adsorbate concentrations left in the solutions