Effect of environmental conditions on the sorption of uranium on Fe3O4@MnO2 hollow spheres

Herein, the hydrothermal method was adopted to synthesize Fe3O4@MnO2 hollow spheres for the removal of U(VI) from aqueous solution. The effects of contact time, pH, ionic strength, solid content and temperature were investigated by using a batch technique. The sorption of U(VI) was dependent on ionic strength at pH < 7, suggesting that electrostatic interaction and/or outer-sphere surface complexation was the predominant sequestration mechanism within this pH range. In contrast, the ignorable effect of ionic strength on the sorption behaviors at pH > 7 pointed to the occurrence of inner-sphere surface complexation. Typical sorption isotherms (Langmuir, Freundlich, Dubinin-Raduskevich) were determined for the mechanism of sorption process. The maximum sorption amount of U(VI) on Fe3O4@MnO2 hollow spheres reached to 13.95 mg/g at 293 K. The thermo-dynamic parameters were calculated from the temperature isotherms, and the results suggested that U(VI) sorption on Fe3O4@MnO2 hollow spheres was a spontaneous and endothermic process. The results might be important for the application for U(VI) pollution management.