Sorption Of U(Ⅵ)、Th(Ⅳ)and Eu(Ⅲ)on Magnetie Carboxylate-Rich Composites

Poly(sodium acrylate) and carboxylate-rich carbonaceous materials contain carboxylic groups, which has endowed sorbents with very high sorption capacities to heavy metal ions and radionuclides. The application of these carboxylate-rich materials as sorbents for the safety and reasonable treatment of radio-waste is expected. An innovative technology is the use of magnetic materials for magnetic separation of pollutants from effluents rapidly. The unique and attractive property of magnetic carrier materials, is small size, great specific surface area, high surface activity and readily be collected from sample solutions using an external magnetic field. In this work, poly(sodium acrylate)/organo-bentonite-Fe3O4(PSA/OBT-Fe3O4) magnetic superabsorbent nanocomposites were prepared and characterized. The effects on sorption (such as contact time, solid content, pH, ion strengthen, humic substances, temperature etc.) and desorption (the kind and concentration of desorbing agent, recyclability) of U(Ⅵ), Th(Ⅳ) and Eu(Ⅲ) on magnetic nanocomposites was investigated to discuss the sorption behavior and mechanism. Magnetically modified carboxylate-rich carbonaceous composite materials (10ACA-C/Fe3O4) were also prepared, characterized and applied to study the sorption capacities of Pb(Ⅱ), Ni(Ⅱ), Hg(Ⅱ) and U(Ⅵ).In the first chapter, the curren situation and the latest progress in research of hydrogels and magnetic nanoparticles were briefly reviewed.In the second chapter, the organo-bentonite-Fe3O4magnetic nanoparticles (O-BT-Fe3O4) were prepared by using co-precipitation technique, then a series of poly(sodium acrylate)/organo-bentonite-Fe3O4(PSA/OBT-Fe3O4) magnetic superabsorbent nanocomposites were prepared by copolymerization reaction of partially neutralized acrylic acid (SA) and organo-bentonite/Fe3O4(OBT-Fe3O4). The morphology, paramagnetic properties, contents, structures and surface charge properties of PSA/OBT-Fe3O4have been characterized by using SEM, FT-IR, XRD, TGA, VSM, zeta potential and ICP-AES. The experimental results showed that the nanocomposites were well responded to magnetic fields, thermodynamic stabilized and strong acid sites on surface. Swelling kinetic of the nanocomposites was measured. The water absorbency sharply increased and the equilibrium swelling was achieved after60min in distilled water and0.2%NaCl, and the higer swelling was obtained in distilled water than0.2%NaCl.The sorption percentage of Th(Ⅳ) on PSA/OBT-Fe3O42#increases with increasing adsorbent content. Sorption processes can be described accurately by the pseudo-second order rate model. The sorption of Th(Ⅳ) is affected strongly by pH and weakly by sodium ions, which indicated that the ion exchange and/or outer-sphere complexes were the main sorption species at low pH, and inner-sphere and/or surface precipitation complexes dominated at high pH range. The presence of humic substances (HA/FA) have no effect on the soption of Th(Ⅳ). Th(Ⅳ) sorption on PSA/OBT-Fe3O42#is promoted at higher temperature and sorption processes were spontaneous and endothermic. Furthermore, the PSA/OBT-Fe3O4superabsorbent could be regenerated through the desorption of Th(Ⅳ) using0.1mol/L HCI solution and the sorption capacity is still higher than3.6mmol/g after five consecutive sorption-desorption processes.The sorption of U(Ⅵ) on PSA/OBT was strongly dependent on pH and ionic strength. U(Ⅵ) sorption amount is increasing with salinity growing, inner-sphere complexes dominated U(Ⅵ) sorption on PSA/OBI. The sorption processes were strongly affected by solid-to-liquid ratio (m/V), the sorption percentage increases, decreases and then increase with solid-to-liquid ratio increases, U(Ⅵ) sorption amount is decreasing with solid-to-liquid ratio increases. IJ(Ⅵ) sorption on PSA/OBT is promoted at higher temperature and sorption processes were spontaneous and endothermic. Sorption Isotherms can be fitted accurately by the Langmuir model. FTIR spectra of before and after sorption confirmed that inner-sphere complexes formation is the major mechanism for U(VI) sorption on PSA/OBT.The sorption amount is increasing with initial Eu(Ⅲ) concentration increases until equilibrium soption was achieved, the sorption percentage of Eu(Ⅲ) on PSA/OBT-Fe3O42#decreases with initial concentration increases. Sorption isotherms can be described by the Langmuir model.In the third chapter, Carboxylate-rich carbonaceous materials were prepared using hydrothermal, followed by co-precipitation method to obtain magnetic carboxylate-rich carbons. The morphology, paramagnetic properties, contents, structures and surface charge properties of10ACA-C/Fe3O4have been characterized by TEM, FT-IR, VSM, XRD, TGA, zeta potential and BET. The experimental results showed that the composites were thermodynamic stabilized and well magnetic responsiveness. The surface charge of10ACA-C and10ACA-C/Fe3O4is negative at pH>3.0. The sorption behavior of Pb(Ⅱ), Ni(Ⅱ), Hg(Ⅱ) and U(Ⅵ) from aqueous solution to10ACA-C and10ACA-C/Fe3O4was investigated by batch experiment. The sorption capacity of Pb(Ⅱ), Ni(Ⅱ), Hg(Ⅱ) and U(Ⅵ) on10ACA-C is higher than10ACA-C/Fe3O4, and the sorption capacity of Pb(Ⅱ) and Hg(Ⅱ) on10ACA-C and10ACA-C/Fe3O4is higher than Ni(Ⅱ). Magnetic carboxylate-rich carbon is a promising sorption material for water treatment of heavy metal ions and radionuclides.The results of the present thesis confirmed that magnetic carboxylate-rich composites provides sorbent materials with many advantages like fast response, high capacity, reusability and readily be collected from sample solutions using an external magnetic field for the removal of heavy metal ions and radionuclides from aqueous solution, which indicated that magnetic carboxylate-rich composites have a good prospect in the heavy metal containing sewage as well as nuclear waste treatment.