Development Of Macroporous Silica-based Adsorbents And Study On Their Applicability To Radioactive Contaminated Wastewater Treatment

Nuclear power plants provide clean energy for humans, while a significant amount of contaminated liquid waste is generated during utilizing nuclear energy. Decontamination of radioactive wastewater by effective removing of radionuclides is one of the important issues in the world to protect the ecological environment. The decontamination method strongly depends on the type of radioactive wastewater. In this study, the radioactive wastewater caused by the nuclear accident and also another radioactive wastewater from the leakage of reprocessing facilities have been studied. The thesis focuses on development of macroporous silica-based titanate inorganic adsorbent and study on its applicability to removal of Sr2+ from nuclear wastewater accident. In addition, the silica-based organic/inorganic hybrid macromolecule adsorbent has been prepared. The characteristics of the adsorbents for various radionuclides(Cs, TRU etc.) removal from different types of wastewater(acid and sea water system) were also studied.Column technique has becomes widely used for radioactive wastewater treatment. Compared to traditional resin materials, macroporous silica-based composite materials show that the adsorption process is rapid, which significantly improve application efficiency in engineering.A large amount of contaminated wastewater was generated from the nuclear accident at Fukushima NPP-1 caused by the Great East Japan Earthquake. The decontamination of wastewater is conducted by the advanced liquid processing system(ALPS) and is expected to take over 20 years. Compared to other nuclides, selective removal of 90 Sr is a complex and challenging task especially in presence of competing cations(Ca2+,Mg2+, Na+) and effluent with neutral p H. The thesis aims at removing Sr2+ from nuclear accident wastewater by simulating Fukushima wastewater. The silica-based potassium hexatitanate K2Ti6O13/Si O2 adsorbent was prepared by the sol-gel procedure. X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS) reflected that K2Ti6O13 was successfully loaded into the pores of the macroporous silica-based support(Si O2) particles. The results of EDS of the adsorbents before and after adsorption of Sr2+ show that there was ion-exchange reaction between K+ and Sr2+. The study found that ion-exchange ratio can reach up 58.5 ~ 78.8% and the uptake reached more than 83% within 60 min in 298 K. These results indicate that nano-materials have a huge advantage in ion-exchange reaction. Hot column filled with K2Ti6O13/Si O2 test shows that the adsorbent can be used to remove Sr2+ very quickly and efficiently from high salty Fukushima wastewater. In addition, the effect of competing ions on the adsorption process was evaluated and the adsorbent can be extended to general nuclear wastewater accident.In order to remove Cs+ from radioactive wastewater of the leakage of reprocessing facilities,1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-Calix[4]arene(Calix[4]areneR14) modified with dodecyl benzenesulfonic acid(DBS) was impregnated into the pores of silica-based support(Si O2-P) and(Calix[4] + dodecanol + DBS)/Si O2-P was prepared.(Calix[4] + dodecanol + DBS)/Si O2-P displayed a higher selectivity for Cs+ in the range of 0.5 ~ 3 M HNO3. The adsorbent containing DBS is better than(Calix[4] + dodecanol)/Si O2-P by the reason of the shortcoming about only having a higher selectivity for Cs+ in higher concentration of HNO3. DBS as a counter anion in low concentration of HNO3 promoted reaction rate. The results indicate that the adsorbent containing DBS can quickly and effectively remove Cs+ from low-acid leakage of radioactive wastewater. In addition, some effect factors on chemical and γ-ray radiation stability were examined. It was confirmed that DBS can effectively reduce the degradation of Calix[4]arene-R14.In order to remove TRU elements from contaminated sea water, the adsorption behaviors of trivalent rare earth elements on TODGA/Si O2-P in Na Cl solution were investigated. Uptake of trivalent elements was getting gradually increase with increasing of Cl- concentration. The adsorption reaction was very fast even in 0.6 M Na Cl. Some factors which affect chemistry and γ-ray radiation stability were also examined. Na Cl system increased the risk of radiolysis of TODGA/Si O2-P.