Preparation Of Functionalized Amidoxime-based Ion Exchange Fiber For Highly Efficient Purification Of Uranium-Containing Wastewater

The demand for uranium resources is on the increase with the rapid development of the global nuclear power industry,which leads to the increasing exploitation quantity of uranium mines.A large number of uranium-containing wastewater with different types have been produced from uranium mining to nuclear component manufacturing,the potential risks and threats to human health and the natural environment are increasing.Therefore,the problem about how to properly and effectively purify uranium-containing wastewater has received tremendous attention.Strategies for the extraction of U?VI?include chemical precipitation,biological/electrochemical reduction and adsorption methods,etc.Adsorption method has been considered as one kind of highly efficient way to extract U?VI?due to the low cost,wide adaptability and environment-friendliness.There are many factors to affect the purification effect of uranium-containing wastewater,and the performance of adsorbents is the most crucial.Ion exchange fibers possess some advantages,such as large specific surface area,fast adsorption/desorption rate and outstanding cycle regeneration performance,which have attracted wide attention of researchers.In this thesis,amidoxime-based ion exchange fibers?AO-PANF?,polyamine/amidoxime groups modified polyacrylonitrile-based bifunctional ion exchange fibers?PANF-P₄-A₆?and carboxyl/amidoxime groups modified loofah-based ion exchange fibers?LC-CA₂-AO₄?have beenpreparedthroughasimplehydrothermalmethod.Inaddition,the morphology,structure and component of as-prepared materials have been tested and further analyzed.The fibers are used to treat the uranium-containing wastewater in the presence of fluoride and chlorine with high concentration,real uranium mine water and wastewater from nuclear component manufacturing.The deep purification of different kinds of uranium-containing wastewater has been realized.The main contents are as follows:?1?AO-PANF is prepared with a simple hydrothermal method.By analyzing the results of scanning electron microscopy?SEM?,it is indicated that the surface of the fibers are rough after modified by NH₂OH HCl.The results of fourier transform infrared spectroscopy?FTIR?and energy dispersive spectroscopy?EDX?show that AO-PANF adsorbs uranium through the chelation between amino groups and UO₂F₄^2-.When the concentration of NH₂OH HCl solution is 10.0 g L^-1,the conversion rate of cyano groups on fibers is 22.3%and the adsorption capacity of AO-PANF to uranium reaches up to the maximum.In addition,the concentration of fluoride ion has a greater impact on the adsorption performance of AO-PANF to uranium.?2?PANF-P₄-A₆ has been prepared with hydrothermal method,where glycol is used as oxidant,ethanediamine and NH₂OH HCl are used as modification reagent.The analysis results of SEM show that the surface of fibers become rough after grafted by EDA and NH₂OH HCl.By analyzing the results of EDX and FTIR,PANF-P₄-A₆ purifies uranium-containing wastewater by capturing UO₂²⁺in wastewater.The analysis data of thermogravimetric show that the thermal stability of the modified fiber is slightly reduced.When the dosage of EDA and NH₂OH HCl is 40 mL and 1.40 g,respectively,the adsorption capacity of PANF-P₄-A₆ to uranium reaches up to 200.1 mg g^-1.In addition,the result of adsorption/desorption test indicates that 0.50 mol L^-1 HCl solution can effectively regenerate uranium on the PANF-P₄-A₆,and the adsorption capacity of fibers have a slight decrease after eight times cyclic regeneration experiments.More importantly,PANF-P₄-A₆ exhibits higher removal efficiency?99.8%?and distribution coefficient(K_d,1779 mL g^-1)to uranium in real uranium mine water,which has low concentration of uranium and much competitive ions.?3?The adsorption capacity of fibers to uranium is improved by introducing carboxyl and amidoxime groups under the condition that the 3D-network structure of natural loofah fiber is not changed.The LC-CA₂-AO₄ has been successfully prepared with simple chemical graft method and we further discuss the effect of fiber properties with different grafting time.By analyzing the results of SEM,it is concluded that the presence of arboxyl and amidoxime groups aggravate the surface roughness of ion exchange fiber.The analysis results of EDX,XPS and FTIR indicate that LC-CA₂-AO₄ contain-OH,-COOH,-CN and-?NH₂?C=NOH groups and the uranium is successfully captured from wastwater.The data of batch experiments show that when the modification time of itaconic/acrylonitrile and NH₂OH HCl are 2 h and 4 h,respectively,the adsorption capacity of LC-CA₂-AO₄ to uranium is up to454.5 mg g^-1.In addition,the results of adsorption/desorption experiments show that uranium on the LC-CA₂-AO₄ can be effectively regenerated by 0.50 mol L^-1 HCl solution and the adsorption capacity of fibers do not present obvious decrease while it is used to purify the wastewater circularly.It is noteworthy that LC-CA₂-AO₄ exhibits high removal efficiency?99.8%?to uranium in real uranium mine water,which contains low concentration of uranium and much competitive ions.?4?The chemical precipitation is used to remove uranium from the real nuclear wastwater with precipitator?sodium dihydrogen phosphate?and crystal aid?glycol?.Afterwards,the supernatant is further purified with ion exchange method.The total removal rate of uranium is higher than 99.8%and the remaining concentration of uranium is 75.0?g L^-1after two-step purification.The results show that the purpose of deep purification of real wastewater is realized with chemical precipitation and ion exchange method.?5?The economics and the practical applicability to deep purification process of uranium-containing wastewater are assessed.The results of the budget to deep purification process for uranium-containing wastewater show that the daily energy consumption is 5.0¹3.0 kWh.Furthermore,the cost of treatment to per ton uranium-containing wastewater is about 2.88³.83 yuan?excluding personnel costs?.With regard to the high-salt uranium-containing wastewater,a deep purification process on the basis of chemical deposition and ion exchange methods is proposed with lower cost and higher feasibility.In this thesis,the ion exchange fibers are designed with chemical modification methods and we further investigate the effects of the corresponding composition,structure and morphology on the adsorption properties to uranium.According to the acquired experimental results,the as-prepared three materials exhibit excellent adsorption properties to uranium,further illustrating that the preparation methods of ion exchange fibers and the design ideas of deep purification process to uranium-containing wastewater can provide a theoretical reference for the purification of various uranium-containing wastewater and the extraction of uranium in water in the future.