Kinetics and mechanism of Sr(II) adsorption by Al-Fe2O3: Evidence from XPS analysis

The Al-Fe2O3 with different aluminum contents were synthesized by heating Al-substituted goethite and were characterized by FESEM, XRD, FT-IR and XPS techniques. The characteristic results showed that the Fe3+ ion in hematite was partly substituted by Al3+ ion, leading to the change of crystal structure. The batch experiments indicated that the adsorptions of Sr(II) on Al-Fe2O3 slowly increased with increasing pH starting from 2 to 11. The pseudo-second-order kinetic and the Langmuir model gave the better fits to the adsorption kinetics and isotherms, respectively. The thermodynamic parameters indicated that the adsorption of Sr(II) on Fe2O3 was an endothermic and spontaneous process. The XPS analysis demonstrated that the oxygen-containing functional groups were responsible for the Sr(II) adsorption. These findings indicated that Al-Fe2O3 may be a valuable candidate for pre-concentration and solidification of radionuclides from aqueous solutions.