Study On The Preparation Of Polyacrylonitrile Amidoxime Foam And Its Adsorption To Uranyl Ion

Since the consumption of nuclear fuel during the operation of the nuclear power plant is relatively small,the remaining nuclear fuel is spent fuel,and about 95 % of the spent fuel can be reused.Radioactive nuclides in spent fuel will pollute the natural environment.On the other hand,precious uranium resources will be wasted,on the other hand,if absorbed by animals and plants including human beings,the functional tissues of animals and plants will be damaged and pathological changes will occur.If spent fuel is post-treated to extract uranium and recycled,it can not only improve the utilization rate of uranium resources,effectively alleviate the shortage of uranium resources,but also reduce the impact of radioactive waste liquid on the environment and human beings.In this experiment,an amidoxime-modified porous polyacrylonitrile foam(AOPAN foam)was prepared to adsorb uranyl ions.Using polyacrylonitrile powder as the raw material,two kinds of porous materials with different morphologies were prepared by frozen-extraction method and template method.The prepared adsorption material was characterized by using Fourier transform infrared spectroscopy(FT-IR),scanning electron microscope(SEM),thermal gravimetric analyzer(TGA),and X-ray photoelectron spectroscopy(XPS).Static adsorption was conducted to investigate the adsorption performance of the porous materials for uranyl ions under different adsorption conditions.On this basis,the adsorption thermodynamics and kinetics of the porous materials were studied.The results show that:1.The amidoxime modified polyacrylonitrile porous material(AOPAN-L)was prepared by the method of frozen-extraction following with amidoxime modification.Under the conditions that polyacrylonitrile concentration = 10 wt% and porogen content = 3 wt%,the precursor material with hierarchical pore structure can be prepared.After the amidoxime modification with hydroxylamine,the AOPAN-L with hierarchical pore structure and abundant amidoxime groups was successfully prepared.In the process of amidoxime modification,when the molar ratio of nitrile group to hydroxylamine is 1/0.5 and the modification time is 11 days,the obtained AOPAN-L has the best adsorption performance.Static adsorption experiments show that under the adsorption conditions of p H=6,initial uranyl solution concentration of 100 ppm,adsorbent dosage of 5 mg and contact time of 360 min,the foam material has the best adsorption performance and the maximum removal rate can reach 90.5%.According to the thermodynamic model fitting of the uranium adsorption process,it can be known that the adsorption process of uranyl ions by AOPAN-L conforms to the Langmuir isotherm model and belongs to the monolayer adsorption.By fitting the kinetic model of the uranium adsorption process,the analysis shows that the AOPAN-L adsorption process of uranyl ions conforms to a pseudo-second-order kinetic model and belongs to chemical adsorption.2.The amidoxime modified polyacrylonitrile porous material was also prepared by the template method following with amidoxime modification(AOPAN-M).Under the conditions that polyacrylonitrile concentration = 10 wt% and PANcontent = 3 wt%,the precursor material with hierarchical pore structure can be prepared by using cubic sugar as the template.After the amidoxime modification with hydroxylamine,the AOPAN-M with hierarchical pore structure and abundant amidoxime groups was successfully prepared.Static adsorption experiments show under the adsorption conditions that p H=7,initial uranyl solution concentration = 100 ppm,adsorbent dosage = 5 mg and contact time = 360 min,the AOPAN-M has the best adsorption performance and the maximum adsorption capacity can reach 282.91 mg/g.According to the thermodynamic model fitting of the uranium adsorption process,it can be known that the adsorption process of uranyl ions by AOPAN-M conforms to the Langmuir isotherm model and belongs to the monolayer adsorption.By fitting the kinetic model of the uranium adsorption process,the analysis shows that the AOPAN-M adsorption process of uranyl ions conforms to a quasi-second-order kinetic model and belongs to chemical adsorption.