Intraparticle diffusion model describes three stages of metal
adsorption process by adsorbents. In the first stage, adsorption takes
place on exterior surface of adsorbent until the exterior surface is
saturatedbymetal ions. The second stage takes place by entering the
adsorbed metal ions into pores of adsorbents within the particle.
When the metal ions diffused into adsorbent pores, the diffusion
resistance increased due to crowding, and consequently the