Preparation Of Modified Amidoxime Polyacrylonitrile Fibers And Their Adsorption Properties For Uranium (Ⅵ)

With the rapid development of nuclear energy,a large amount of uranium-containing wastewater will be produced,which must be effectively treated to meet the discharge requirements.Therefore,the treatment of uranium-containing wastewater is of great significance for the sustainable development and environmental safety of nuclear energy.In this paper,amidoxime polyacrylonitrile fiber prepared by wet spinning was further modified to improve its adsorption property of uranium,in order to obtain better performance of uranium-containing wastewater treatment adsorption material.In this paper,the amidoxime polyacrylonitrile fiber prepared by our research group was used as raw material,which was treated with alkali and further modified with hydroxylamine,and the active functional group was grafted to the surface of the fiber,and two kinds of uranium adsorption functional materials were developed.The effects of solid-liquid ratio,p H,adsorption time,temperature,and initial uranium concentration on adsorption properties were investigated during the static adsorption process.The desorption effects of different desorption agents and the recycling properties of fibers were investigated.Through dynamic adsorption experiments,the penetration curve was obtained to explore the relationship between penetration time,adsorption bed height,and initial uranium concentration.Scanning electron microscopy,Fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy was used to characterize the two materials before and after the adsorption of uranium,and the adsorption mechanism was analyzed.Finally,kinetic model fitting,adsorption isotherm model fitting,and thermodynamic calculation were carried out to study the adsorption processes of two uranium adsorption functional materials.The carboxyl group was grafted onto the surface of amidoxime polyacrylonitrile fiber to improve its adsorption performance,and the adsorption performance and morphology of the fiber under different modification temperatures,Na OH concentration,and modification time were investigated.The results of the static adsorption experiment show that the maximum adsorption capacity is 813.1 mg·g^-1 when p H=5.5 and C₀=100 mg·L^-1.It indicates that the grafting of the carboxyl group improves the adsorption performance of fiber on U（Ⅵ）because the O of the carboxyl group and the N of the amidoxime group can provide the electron pairs coordinated with U（Ⅵ）.However,in the adsorption and desorption cycle experiment,it was found that the recycling performance of PAN-PAO-OH fiber was not ideal,and the adsorption rate decreased to 43.2%.Therefore,hydroxylamine hydrochloride was used to further modify it,and the amidoxime functional group with better stability was grafted on its surface.When p H=5.5 and C₀=100 mg·L^-1,the maximum uranium adsorption capacity of the fiber grafted with amidoxime group is 908.7 mg·g^-1.The graft of amidoxime group on the surface of the fiber improves the adsorption performance of U（Ⅵ）,because C=N-OH and C-NH₂ in the amidoxime group provide electron pairs to U（Ⅵ）to form a complex.PAN-PAO-OH-AO fiber also showed good reuse performance in the adsorption and desorption cycle experiments,with an adsorption rate of more than 77.3%in six adsorption and desorption cycles.The efficiency of the column can be improved by decreasing the initial uranium concentration and increasing the adsorption bed height.The kinetic fitting results show that the two fibers conform to the pseudo-second-order kinetics model.The thermodynamic fitting results show that the adsorption process of the two fibers is spontaneous endothermic.The surface energy of PAN-PAO-OH fiber is not uniform,and the carboxyl group and amine oxime group synergistic adsorption make the adsorption process conform to the Freundlich model,while the PAN-PAO-OH-AO fiber adsorption process with uniform surface energy conforms to Langmuir adsorption model.