Abstract
In natural environments the interaction between existing dissimilar colloids can affect the metal adsorption on the colloids and result in the deviation from the additivity of the adsorption models for single colloid. This effect was studied with goethite and humic acid (HA) as sorbents and H+, Cu2+ and UO22+ as adsorbing ions. Due to the interaction of HA and goethite (i.e. the adsorption of HA on goethite), H+ was released from adsorbed HA molecules and negative charges were induced on HA at relatively low pH. On the other hand, at relatively high pH, H+ coadsorbed on the goethite surface with HA and net positive charges were induced. As for Cu2+ and UO22+, the adsorption of the former was enhanced in the ternary system possibly because of the aforementioned charge regulation between HA and goethite, and the latter diminished by the direct competition between HA and UO22+ for the surface sites of goethite.
