Chitosan hydrogel beads were studied for the adsorption of lead ions and humic acid from aqueous solutions to
examine the adsorption behaviors and mechanisms. The experiments were carried out at room temperature with
solution pH ranging from 5 to 7.5 (in near neutral pH range). Three types of batch adsorption experiments, including
single species adsorption, sequential adsorption of one species after another and co-adsorption of both species, were
investigated. The results show that: (1) adsorption of either species mainly results from the complexations between
adsorbate and functional groups at the surface of the hydrogel beads; (2) previously adsorbed species can either act as
additional binding sites for, or occupy the same binding sites as the subsequent species to be adsorbed, resulting in
enhanced or retarded adsorption of the subsequent species; and (3) for co-adsorption, metal-organic interactions play a
very important role in determining the extent of adsorption. It is concluded that multi-species adsorption can be
significantly affected by adsorbate interactions and the understanding of these interactions needs great attention in
adsorption study in the future.