| BackgroundIodine-131(half-life T1/2=8.04 d)is one of the main nuclides in the radioactive wastewater of nuclear medicine.The conventional processing method is the delay and decay method.The radioactive wastewater in the decay tank decays to meet the emission requirements and then discharges.The process is simple and easy to operate.In recent years,nuclear medicine has developed rapidly in china,as the amount of radioactive wastewater increases and accumulates,the volume requirements of the decay tanks are increasing,and there is a potential risk of excessive discharge of radioactive wastewater.Thus,it is of great significance to study new materials and methods for the treatment of wastewater containing iodine-131 to ensure the discharge of radioactive wastewater in hospitals to meet the standard.In this paper,we mainly designed and synthesized magnetic materials for efficient adsorption of iodine,and carried out the technical research on magnetic separation of iodine.Layered double hydroxide(LDH)has been widely used as an adsorbent for the removal of numerous ionic contaminants,due to the advantages of its unique layered structure,antiradiation,simple synthesis,and low cost.However,LDH usually exists in powdered form,which limits its seperation and recycle from the reaction system quickly.Due to the advantages of magnetic materials,can be simply and quickly separated from aqueous solutions via an external magnetic field.Magnetic LDH composites were prepared by combining LDH materials with magnetic materials,if iodine can be effectively separated,the storage time of waste liquid can be shortened and the storage volume of waste can be reduced,which provides a new idea for the treatment of iodine-containing wastewater in hospital.ObjectiveIn order to remove iodide(I-)efficiently,rapidly and simply,a magnetic LDH composite was prepared in this study.The adsorption performance and mechanism of the material were investigated,which provided the experimental and theoretical basis for its application in the treatment of medical iodine-containing wastewater.MethodsA novel calcined magnetite-activated carbon/MgAl-layered double hydroxide composites(MAC/MgAl-LDO)was prepared by using the magnetic properties of Fe3O4,the carrier characteristics of activated carbon(AC)and the "memory effect" of the layered structure of MgAl-LDH.The adsorption behavior of I' on MAC/MgAl-LDO was studied.The experimental method routes were as follows:(1)Fe3O4 was loaded on AC to prepare magnetic activated carbon(MAC)by chemical co-precipitation method,and then MgAl-LDH was loaded on MAC by co-precipitation method.After calcination,MAC/MgAl-LDO were prepared to optimize and study the preparation conditions of MAC/MgAl-LDO.(2)The material morphology,specific surface area,chemical composition,charge change,and magnetic properties were characterized and analyzed by the scanning electron microscope(SEM),high resolution transmission electron microscope(HRTEM),brunauer-emmett-teller(BET),X-ray photoelectron spectroscopy(XPS),fourier transfer infrared spectrum(FT-IR),X-ray diffraction(XRD),zeta potential analysis,and vibratin sample magnetometer(VSM).(3)The effects of adsorbent dosage,pH value,adsorption time,initial I-concentration,and temperature on the adsorption of I-were surveyed.The adsorption kinetics,adsorption isotherm and thermodynamic models were established to study the adsorption mechanism.In addition,the ion selectivity and reusability of MAC/MgAl-LDO were verified.The adsorption properties were compared with those of the components in MAC/MgAl-LDO.Results(1)Through the optimization experiment,MAC/MgAl-LDO was prepared when the mass ratio of AC:Fe3O4:MgAl-LDH was 1:1:2.4,the reaction time was 3 h,and the calcination temperature was 500?.(2)The spherical Fe3O4 particles and flake MgAl-LDH were loaded on AC,and MAC/MgAl-LDO was successfully synthesized after calcination.The specific surface area of MAC/MgAl-LDO was 102.12 cm3 g-1;The results of FT-IR showed that most of the interlayer CO32-disappeared due to calcination at high temperatures.XRD results showed that the diffraction peaks of MgAl-LDH at(003)and(006)crystal planes disappeared after calcination at high temperatures.After adsorption of I-,the diffraction peaks appeared again.At the same time,After adsorption of I-,the content I-accounts for 1.2%of all elements for MAC/MgAl-LDO.These results verified that the adsorption mechanism of MAC/MgAl-LDO for I-was mainly the reconstruction of MgAl-LDH layered structure,which was corresponding to the "memory effect" of LDH.VSM results showed that MAC/MgAl-LDO has superparamagnetism with saturation magnetization of 20.12 emu g-1 and could be rapidly separated from the aqueous solution in the existence of the external magnetic field.(3)The adsorption experiment showed that the optimum adsorption pH of MAC/MgAl-LDO was 9;The adsorption behavior conformed to the pseudo-second-order kinetic model.The intraparticle diffusion model and Boyd model further indicated that the adsorption rate was dominated by liquid film diffusion.The adsorption behavior conformed to the Langmuir model of monolayer adsorption;The negative values of thermodynamic parameters enthalpy change(?H0)and gibbs free energy(?G0)indicated that the adsorption was a spontaneous exothermic process;Ion selectivity indicated that the coexisting ions at low concentrations had little effect on the adsorption of I-by MAC/MgAl-LDO;MAC/MgAl-LDO was repeatedly used for five times of adsorption,and the fifth adsorption efficiency could still reach above 81%;Compared with the adsorption performance of various component materials,it was found that the mechanism of MAC/MgAl-LDO for I-adsorption was mainly the "memory effect" of MgAl-LDH.ConclusionIn this study,MAC/MgAl-LDO was successfully prepared with AC as the carrier.The material had high adsorption efficiency for and good reusability,which realized the simple and rapid separation and recovery of I-from the simulated wastewater system.This study provides experimental and theoretical basis for the magnetic separation of I-from medical iodine-containing wastewater. |
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