2.5. Effect of contact time
Results depicted in Fig. 1 clearly show that the adsorption of methylene blue onto DPLP reached
equilibrium in 160 min. Adsorption first followed linear rising in which instantaneous, extremely fast
uptake takes place, and then a stationary state was observed. The fast initial uptake was due to
accumulation of methylene blue on surfaces of DPLP adsorbents which is a rapid step. It was concluded
that 160 min was sufficient for adsorption to attain equilibrium.