Synthesis And Radionuclides Adsorption Performance Of Low-silica CHA Zeolite Via Interzeolite Conversion Of Natural STI Zeolite

The reserve of natural zeolites such as clinoptilolite（HEU）and stellerite（STI）is abundant.However,such natural zeolites have not yet been industrially applied.Converting them into zeolites that have been commercialized on a large scale is one of the ways to effectively utilize these resources.In this thesis,CHA zeolites with low silica-alumina ratio（denoted as low-silica CHA zeolites）were hydrothermally synthesized by using natural STI zeolite as raw materials,which expands the application field of natural STI zeolite.The factors affecting the synthesis of CHA zeolites were systematically studied,including crystallization temperature,crystallization time,and initial gel composition.On the basis of this,the optimum synthesis conditions for the synthesis of CHA zeolites from STI zeolite were obtained.The as-prepared low-silica CHA zeolites were fully characterized by powder X-ray diffraction（XRD）,scanning electron microscopy（SEM）,N₂ isothermal adsorption-desorption（BET）,and infrared spectroscopy（FT-IR）,etc.At present,our energy strategy is to gradually reduce the total consumption of fossil energy and increase the proportion of green and clean renewable energy.Nuclear energy is an emerging clean energy with the advantages of high power generation efficiency,low transportation cost,and environmental friendliness.However,nuclear energy production activities inevitably produce radionuclides and wastewater containing radionuclides.Among them,¹³⁷Cs⁺is the fission product of nuclear fuel uranium-235.Because of its high fission yield,long half-life,high gamma radiation,and high water solubility,it has become a key radionuclide in the treatment of radioactive wastewater.In this thesis,the Cs+adsorption performance of low-silica CHA zeolites synthesized by interzeolite conversion of STI zeolite has been studied,which exhibit better selectivity for Cs+,fast adsorption kinetics,high adsorption capacity（442.48 mg/g）,a broad working p H range（4-12）,and excellent removal ability for ¹³⁷Cs⁺at very low concentration（ppt grade）.The low-silica CHA zeolite obtained in this study has the advantages of high negative charge load,excellent selectivity to low concentration ¹³⁷Cs⁺in radioactive wastewater,simple treatment operation,and low cost.It is expected to be widely used in the field of radioactive wastewater treatment.