Study On Preparation Of Phosphorus-containing Functional Fibers And High-efficiency Adsorption Of Uraniumcontaining Wastewater

A large amount of complex uranium-containing low-level waste water will be produced in the process of nuclear fuel cycle.How to realize the deep purification of uranium-containing waste water and the recovery of nuclides is a scientific and technical issue that has been widely concerned by scholars at home and abroad.In this paper,natural luffa fiber and man-made polyacrylonitrile fiber are selected as substrates,and after chemical grafting,three modified fibers with phosphorus-containing groups are prepared,aiming at simulating uranium-containing waste liquid and uranium enrichment,nuclear fuel element production The real uranium-containing waste liquid produced by the process has carried out a series of static/dynamic adsorption experiments.Using adsorption thermodynamics and kinetic model calculations,combined with mesoscopic and spectroscopic characterization,the process and effect of phosphorus-containing group-modified fibers on uranium adsorption were discussed.mechanism.The main findings of the thesis are as follows:（1）Choose cheap and easy-to-obtain natural luffa fiber as the matrix material.After alkalization of 2.0 mol/L Na OH and 10%H₂O₂ to remove lignin and hemicellulose,cerium ammonium nitrate is used as the initiator,and the grafting of acrylamide onto the surface of the luffa provides a large number of amino groups and improves the hydrophilicity of the luffa.It also serves as a"bridge"for the grafting of phosphorus-containing groups.Finally,the amino-containing and the amino acid are prepared by a two-step hydrothermal method.A new type of phosphate-based bifunctional luffa fiber,named LF-A₂-M₁/P.EDS,FTIR and XPS confirmed that-NH₂ and-P=O were successfully grafted onto the luffa matrix,and the grafting rate of phosphorus-containing groups could reach 35%.It is found by SEM that amorphous deposits rich in uranium and phosphorus are covering the surface of the fiber,and XRD characteristic diffraction peaks of uranyl hydrogen phosphate appear at the same time,indicating that uranium is mainly coordinated with the phosphorus-containing groups on LF-A₂-M₁/P.It is captured from solution by way of site deposition and complexation with amino groups.LF-A₂-M₁/P has good adsorption performance in a wide pH range（5～9）,with a maximum adsorption capacity of 353.85 mg/g.Coexisting divalent cations(Ca²⁺,Mg²⁺)and monovalent anion Cl^-have little effect on the adsorption of uranium by LF-A₂-M₁/P at low pH.However,when the pH is higher（pH>6）,it has a greater impact on the adsorption of uranium by LF-A₂-M₁/P.Combined with the analysis of environmental water chemistry software,it is speculated that it is mainly due to the comprehensive effects of the uranyl ion species and the changes in the coordination priority of phosphorus-containing groups and coexisting ions under high pH conditions.Regarding the real uranium-containing waste liquid produced in the production process of nuclear fuel elements and uranium enrichment plants,without adjusting the acidity,the adsorption capacity of LF-A₂-M₁/P on uranium can reach185.6mg/g higher than all other coexistence in the system ion.（2）In order to further improve the grafting rate of phosphorus-containing groups,glycidyl methacrylate（GMA）was selected as the"anchor"for the grafting of phosphorus-containing groups,and cerium ammonium nitrate was used as the initiator.The modified luffa fiber with higher phosphorus-containing groups（grafting rate up to 43%）was synthesized by using two-step low-temperature hydrothermal method on the surface of the entanglement,which was named LFA-G-P.Its maximum adsorption capacity under the condition of pH 6 is 225.60 mg/g.The modified loofah has become rough with many obvious grooves.The appearance of C=O and P=O characteristic infrared peaks confirms the effective grafting of GMA"anchor"and phosphorus-containing functional groups on the luffa.After interacting with uranium,SEM showed that uranium was deposited on the surface of the fiber in the form of amorphous particles.XRD showed that the crystallinity of cellulose had a certain change.XPS analysis found that the peak intensity of P=O was significantly enhanced.The dynamic adsorption test showed that:Fill the chromatographic column（H=8.0 cm,D=1.5 cm）with 7.6 g LFA-G-P and treat the simulated uranium-containing waste liquid with pH=6 and 100 mg/L at a flow rate of10 m L/min.The uranium concentration in the effluent water within 1000min is below 5 ppb（far lower than the national comprehensive sewage discharge GB8978-1996 indicator of 50ppb）,continuously reaching the standard of 10L,and the penetration volume is 24 L.In this flow direction,the dynamic adsorption process of uranium by LFA-G-P can be described by Yoon-Nelson model.0.50 mol/L HCl can desorb uranium on LFA-G-P well.Research on real uranium enrichment wastewater containing uranium shows that LFA-GP still has a high removal rate（90.60%）and adsorption capacity（98.08 mg/g）for uranium even under the conditions of low uranium concentration and complex composition.（3）Polyacrylonitrile fiber（PAN）is selected as the basic material,preferably triethylenetetramine（TETA）has strong selectivity for uranyl ions and amino groups that can serve as binding sites,and phenylphosphoryl dichloride（BPOD）),which has a high adsorption amount of phosphorus-containing groups for uranium,a two-step hydrothermal method was used to rapidly prepare a PAN functionalized fiber containing both amino and phosphorus-containing groups and dual functional groups,named PANf-A-P.FT-IR analysis confirmed the successful introduction of-CN,-NH/-NH₂ and P=O groups.The XPS spectrum showed that the positions of N1s and P2p changed significantly before and after the adsorption of U（VI）,which was mainly caused by the bonding of the oxygen-containing functional groups of N and P with U（VI）.The experimental results show that PANf-A-P has good adsorption performance in a wide range of pH（5～10）,and the maximum adsorption capacity is 308.50 mg/g at pH=6.The dynamic adsorption column experiment shows that under the condition of 100 mg/L pure uranium solution,the penetration time and volume of PANf-A-P to uranium are 1560min and7.8 L,respectively,and the uranium adsorption capacity is 156 mg/g.In the multi-ion mixed solution,the penetration time and volume of PANf-A-P to uranium are 1320 min and 6.6 L,respectively,and the uranium adsorption capacity is 132 mg/g,which is a decrease of 24 mg/g.Compared with the two,the time to reach adsorption saturation in the multi-ion mixed solution is 4h earlier than that of the pure uranium solution.Within the research flow rate range,the dynamic adsorption process of PANf-A-P on uranium can be described by the Yoon-Nelson model.The obtained penetration curve of the relationship between the time and the U（VI）concentration of the effluent can provide a theoretical basis for practical engineering applications.The experimental results of real uranium enrichment waste liquid show that the adsorption capacity（72.5 mg/g）and removal rate（89.7%）of PANf-A-P fiber for U（VI）are higher than other coexisting ions in the system.To a certain extent,it shows that PANf-A-P fiber has potential application in the adsorption of U（VI）.The optimal pH of the above three fibers for uranium absorption is 6,and the two materials introduced with amino groups have a relatively wide pH adaptation range.Adsorption processes are all spontaneous and endothermic processes.The Langmuir isotherm adsorption model and the quasi-two-stage kinetic model can better simulate the adsorption process of three kinds of fibers on uranium,indicating that the single-layer chemical adsorption is dominant.The three natural/man-made fibers modified in this study,mainly containing phosphorus groups,can be successfully modified by different bridging methods.The introduction of appropriate amino groups can better improve the fiber’s adsorption capacity for uranium,and it can enrich and enrich uranium.The real complex uranium-containing waste liquid produced during the production of fuel elements has a high adsorption capacity.The preparation methods and research ideas of related materials can provide certain theoretical support for the deep purification of uranium-containing wastewater.