Adsorption of Fe(III), Co(II) and Zn(II) onto particulates in fresh waters on the basis of the surface complexation model II. Stabilities of metal species dissolved in fresh waters

Particulates, fine sediments and residue from evaporation of the filtrate from fresh waters were sequentially extracted with several reagents, and concentrations of iron, manganese, cobalt and zinc were determined. Iron(III) and Co(II) in particulates were similar to those in fine sediments in both their contents and chemical forms. Concentrations of Zn(II) and Mn in particulates were higher than those found in fine sediment, and considerably different in their chemical speciation. The difference between Fe and Mn may be due to the difference in their oxidation potentials. The difference between Co and Zn may depend on their affinity for Fe or Mn oxides. Distributions of Fe(III), Co(II) and Zn(II) between particulates and water were determined and compared with those predicted on the basis of the surface complexation model. These results are generally consistent with theories that metal species dissolved in water exist as free ions or are considerably less stable than their surface complexes on particulates.