Selective Sorption Of Sr（Ⅱ） And Th（Ⅳ）on Surface Modified Fe₃O₄ Particles

The magnetic single-crystalline Fe₃O₄ microspheres were prepared by a solvothermal reduction method with a general size around 400 nm and were then covered with Si O2.Followingly,the surface of the Fe₃O₄-SiO₂ spheres were grafted with silane coupling agent AAAPTS.Two functional agents pyridine-2-carboxaldehyde and dioxotetrahydrofuran were coupled on respectively.Finally,two kinds of magnetic sorbents used in this thesis Fe₃O₄-SiO₂-AAAPTS-Py（abbr.Py-Fe₃O₄）and Fe₃O₄-SiO₂-AAAPTS-Di（abbr.Di-Fe₃O₄）were synthesised separately.FT-IR,XRD,SEM and VSM were used to determine the physical properties of these two magnetic materials and the characterization results gave the information of chemical components,structures,shapes and sizes,as well as the magnetic properties of the samples.The sorption of Sr（Ⅱ）on Py-Fe₃O₄ and Th（Ⅳ）on Di-Fe₃O₄ were studied as functions of solution pH,ionic strength,contacting time and temperature.The results indicated that the sorption were strongly dependent on pH and the maximum sorption of Sr（Ⅱ）on Py-Fe₃O₄ was at pH around 6,whereas the sorption of Th（Ⅳ）on Di-Fe₃O₄ reached and kept maximum when the pH value was higher than 4.Ionic strength had a big effect on the sorption of Py-Fe₃O₄ to Sr（Ⅱ）and with the increase of the concentration of background electrolyte NaNO₃ in low acidity,the sorption capacity decreased.Contacting time experiments showed that both sorption can reach equilibrium after specific hours and the kinetic process can be well fitted by pseudo second-order model.The sorption behavior of Sr（Ⅱ）and Th（Ⅳ）can be analysed by Langmuir model as well as Freundlich model.The thermodynamic parameters ΔS,ΔH and ΔG were calculated from the temperature dependent sorption isotherms.The results demonstrated that sorption process of Sr（Ⅱ）on Py-Fe₃O₄ was endothermic and with the temperature increasing,the spontaneous tendency increased.Meanwhile,Th（Ⅳ）on Di-Fe₃O₄ was spontaneous and endothermic and high temperature was advantage to sorption.