Adsorption of heavy metal ions by beech sawdust - Kinetics, mechanism and equilibrium of the process

The adsorption of heavy metal ions from synthetic single ion solutions was performed by using beech sawdust. The pH value of water increases when rinsing the sawdust with distilled water. The maximum sawdust adsorption capacity was achieved at pH > 4, while at pH < 2 it gets zero. The adsorption capacity is almost equal for Cu2+ and Ni2+ (4-4.5 mg g−1), while for Zn2+ ions it is 2 mg g−1, thus exhibiting certain selectivity the first two against zinc ions. Obtained results showed that the adsorption kinetics follows the pseudo-second order reaction model. The adsorption equilibrium data show good fitting to the Langmuir equation. The adsorption occurs via an ion exchange mechanism, where mostly calcium from the sawdust cell structure was substituted by heavy metal ions.