| The development and utilization of uranium resources have a greater impact on the environment,and the treatment costs are relatively high.It is of great significance to find suitable methods to treat uranium pollution and fully recycle uranium.In this paper,we use the polyacrylonitrile-amidoxime polyacrylonitrile(PAN-PAO)mixed fiber obtained by wet spinning to explore the influencing factors of the uranyl adsorption process in different uranium solutions,and try a variety of desorbents for adsorption-desorption cycle experiment.Through Fourier transform infrared spectroscopy(FT-IR),scanning electron microscope(SEM),X-ray energy dispersive spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),thermal weight loss analyzer(TGA)and X-ray diffraction(XRD)analyzed the changes of chemical structure and surface morphology before and after fiber adsorption and desorption.This thesis explored the influence of five factors of p H value,adsorption time,solid-liquid ratio,temperature and initial uranium concentration on the adsorption process of uranyl in the solution.It is found that the optimal adsorption p H is 7 under the condition of298 K in a higher concentration of uranium-containing solution,the adsorption capacity is100.15mg/g,and the adsorption equilibrium is reached after 2880 min.At the same time,the adsorption effect becomes better as the temperature increases,and the adsorption capacity of the fiber increases slowly as the initial uranium concentration increases.The optimal p H for adsorption in low-concentration uranium-containing solutions is 4,and the adsorption equilibrium time is 360 min.The adsorption equilibrium time in the low-concentration real uranium-containing waste liquid is 1440 min.A variety of kinetic and thermodynamic models are used to fit and analyze the adsorption performance and mechanism of PAN-PAO fiber to uranyl ions.The results show that the quasi-second-order kinetic model,intraparticle diffusion model,liquid film diffusion model and Langmuir model can explain the adsorption process well.The adsorption process is a spontaneous chemical adsorption process controlled by entropy increase.The experiment selected eight kinds of desorbents: hydrochloric acid,nitric acid,tartaric acid,potassium hydroxide,sodium carbonate,sodium bicarbonate,potassium bicarbonate and sodium carbonate + hydrogen peroxide mixture to carry out experimental research on the adsorption-desorption cycle of uranium solution under different conditions.Due to the relatively low surface uranium content of the fiber after the first adsorption in a higher concentration uranium solution,the desorption rate of various desorption agents is less than70%.The capacity of the fiber increases when it is adsorbed again after the action of various desorbents,the acid and base are the most obvious.After XPS,XRD and other characterization analysis,it is confirmed that the fiber has a carboxyl group due to the hydrolysis of the desorbent to enhance the adsorption effect.After performing 6adsorption-desorption cycles in a higher concentration uranium-containing solution,it was found that various desorbents reached the desorption equilibrium at 360 min.The desorption rate of each desorbent gradually increased before the fourth cycle,and then began to gradually decline.The desorbents that still maintain good desorption ability after 6 cycles are 0.05 M hydrochloric acid,0.05 M nitric acid,0.5M tartaric acid,1M sodium carbonate,1M sodium bicarbonate,1M potassium bicarbonate and 1M sodium carbonate + 0.1M hydrogen peroxide.The desorption rate of them are maintained above 90%.The adsorption-desorption cycle experiment was carried out on the low-concentration uranium-containing solution using desorbents with better desorption effect.The results showed that the desorption effect of various desorption agents is small,and the desorption rate can be maintained above 90% after6 cycles,showing a good desorption effect.For the real uranium-containing waste liquid,after comprehensive comparison,the desorption effect of 0.5M hydrochloric acid is better,but in consideration of reducing the corrosion of containers and the use of acid in the nuclear fuel cycle system,it is more feasible to use 0.5M nitric acid for desorption. |
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