High-efficiency Magnesium-based Sorbent For The Removal Of U(?):Preparetion And Adsorption Performance

Uranium is a chemical element with symbol U and atomic number 92.Uranium is a toxic and radioactive water pollutant.Uranium is usually found in the aqueous streams as uranyl ion?hexavalent oxidation state?and its complexes causing serious pollution to the environment and endangering the human health.There is a series of nuclear processes may cause radioactive contamination,such as nuclear power plant spent fuel,uranium mining,nuclear tests,nuclear power plant accidents and various types of nuclear facilities are likely to discharge waste water containing high-level radioactive material.Uranium contamination poses a threat both to surface and ground water resources and is a risk factor for human health.Therefore,the removal of uranium???ion from aqueous is conducive to reducing the uranium contamination,maintaining the natural balance,and promoting the recovery of uranium resources.In this thesis,a variety of magnesium-based?Mg-based?materials with uranium enrichment properties were prepared and applied to uranium adsorption in water.The adsorption mechanism of uranium by different materials was analyzed deeply.The effects of chemical composition,structures and interface properties of Mg-based materials on the adsorption were investigated.Magnesium oxide particles with different morphologies have been synthesized by using different precursors of magnesium,and urea as precipitating agent.The as-prepared samples,and the magnesium oxide materials before and after adsorption of U???,which were characterized by means of X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?,and energy dispersive X-ray spectroscopy?EDX?,TG and DSC thermal analysis and so on.After calcination,the samples prepared using different precursors of magnesium were completely converted to cubic MgO.The results show that the MgO sheets were composed of large numbers of micro crystalline grains,and the microcrystal size distribution is in the range of 5 to25 nm.The treatment of uranium-containing wastewater with magnesium oxide was studied under static state in the laboratory,and also the effects of adsorption time,pH value of wastewater and temperature were discussed.Through the investigation of adsorption thermodynamics and adsorption kinetics,the adsorption capacity of the three types of MgO particles for uranium more than 1600 mg g^-1,the optimum pH was 3.0–4.0,and the thermodynamic parameter calculation results indicate that the adsorption process is a spontaneous endothermic process.The removal of uranium from aqueous solution by hydromagnesite and its calcination products was investigated.Through the study,we found that the adsorption capacities of hydromagnesite,magnesium carbonate and magnesium oxide for uranium could reach 342.96 mg g^-1,493.79 mg g^-1,2154.14 mg g^-1,respectively.The high temperature will reduce the activity of magnesium oxide,resulting in the adsorption capacity decrease.The results indicate that the optimum pH for the heat-treated samples was 3.0 to 4.5 and for hydromagnesite 6.0 to 7.0.Thermodynamic parameters such as?G,?H and?S,indicated that the adsorption processes are spontaneous and endothermic.In order to optimize the properties of magnesium oxide,we prepared porous magnesium oxide?MP-MgO?by sol-gel and in-situ carbonization method and using Mg?NO₃?₂ as precursor along with P123 as soft template.The BET surface area,and total pore volume of MP-MgO were found to be 14.76 m² g,0.15 cm³ g^-1,respectively.The adsorption behavior of U???by the porous MgO was studied by static adsorption experiments,and also the effects of adsorption time,pH of wastewater and U???concentration were discussed.The results indicated that the optimum pH for MP-MgO was 3.0 to 4.5,the removal of uranium in this case was mainly due to surface complexation.Through the study,we found that the adsorption capacity of MP-MgO for uranium was more than 2500 mg g^-1,the adsorption equilibrium time was about150 min.Moreover,the kinetic study showed that the process followed the pseudo-first-order model,and the adsorption process was spontaneous and endothermic.