Fe3O4/chitosan magnetic microspheres were prepared with inverse-phase suspension dispersion method. It was modified through the reaction with poly(ethyleneimine) to increase the content of amine group of the adsorbent. The samples were characterized by X-ray diffraction (XRD)

FT-IR

and thermogravimetric analysis (TGA). Adsorp- tion performance of the modified chitosan microspheres toward Hg2+ and UO22+ was investigated. The results showed that the concentration of amine group of the adsorbent was 6.47 mmol/g. The adsorption rate was fast due to their small size (15—30 μm). Selective separation of Hg2+ and UO22+ was achieved at pH<3.This was due to the fact that Hg2+ was able to form complexing anion (HgCl3-) with Cl- and adsorb onto the modified chitosan adsorbent through ion-exchange mechanism

but UO22+ could not. The maximum adsorption capacity (qm) was 2.19 mmol/g for Hg2+ and 1.38 mmol/g for UO22+. The adsorption rate constant calculated by Lagergrent equation was 0.087 min-1 for Hg2+

0.055 min-1 for UO22+. More than 90% desorption efficiency for UO22+ and Hg2+ was achieved using 1 mol/L H2SO4 and for UO22+ using 2 mol/L HCl.