【作者】 刘琦；

【导师】 王君；

【作者基本信息】 哈尔滨工程大学 ， 材料学， 2016， 博士

【摘要】 核能作为一种安全、清洁、可持续发展的新能源,已被社会所认可。然而核能的可持续发展取决于核燃料铀的持续供应,目前核电反应中所用燃料铀都来自于陆地铀,我国属于贫铀国家,陆地铀匮乏,现已探明的有利用价值的铀储存量只能维持现有核电装机容量运行30年,未来我国核电所需的燃料铀将完全依赖于进口。海水中含有丰富的铀资源,是陆地铀储量的千余倍,开发海洋中的铀资源,能够持续的为核电站提供充足的核燃料,缓解未来所面临的能源危机,因此开展海水提铀具有重要意义。本文针对海洋中低浓度铀的提取,设计开发了多种以Fe₃O₄和CoFe₂O₄为磁性基质的有机功能化的复合吸附材料,系统地考察了pH值、初始铀溶液浓度、吸附时间对铀酰离子吸附性能的影响,通过拟合热力学方程和动力学方程研究了磁性铀吸附材料的吸附过程,同时开展了模拟海水吸附实验和离子竞争实验。采用溶剂热法一步制备Fe₃O₄@C磁性纳米材料,再利用酮肟对Fe₃O₄@C的表面进行修饰制备有机/无机复合磁性吸附剂Fe₃O₄@C-ketoxime。该复合材料的饱和磁化强度为30.33 emu/g,具有很好的磁响应性和再分散性,易于磁性分离和回收。Fe₃O₄@C-ketoxime的最佳吸附pH为6,吸附平衡时间为60 min。两种吸附剂均符合准二级动力学方程和Langmuir等温吸附模型,吸附剂对铀酰离子的吸附主要是化学吸附。Fe₃O₄@C与Fe₃O₄@C-ketoxime对铀的吸附属于吸热、自发的。对比Fe₃O₄@C与Fe₃O₄@C-ketoxime对铀的吸附性能表明,酮肟的加入提高了磁性纳米材料对铀酰离子的吸附性能和选择性,这主要是因为酮肟含有-OH键上氧原子的孤对电子与铀酰离子的络合作用。通过3-氨丙基甲氧基硅烷对磁性四氧化三铁表面修饰,制得表面具有氨基功能基团的Fe₃O₄-APTMS磁性吸附剂。Fe₃O₄-APTMS吸附的最佳pH值为6,最佳吸附时间为60 min,25 ^oC达到吸附平衡时饱和吸附容量为160.8 mg/g。脱附实验结果表明Fe₃O₄-APTMS磁性吸附材料在NaOH溶液中脱附率很高且有良好的再生性。Fe₃O₄-APTMS对U（VI）的吸附过程更符合Langmuir等温吸附模型,是一个自发吸热的反应过程。对核壳结构的Fe₃O₄@SiO₂有机功能化修饰合成了Fe₃O₄@SiO₂-PEI磁性吸附材料。Fe₃O₄@SiO₂-PEI为球状颗粒,且分散性良好,粒径为260³00 nm。Fe₃O₄@SiO₂-PEI具有良好的磁响应性,饱和磁化强度为56.76 emu/g。pH值在5-7之间Fe₃O₄@SiO₂-PEI吸附性能最佳,吸附时间为240 min,吸附达到平衡时饱和吸附容量为278.16 mg/g。Fe₃O₄@SiO₂-PEI对U（VI）的吸附过程更符合准二级动力学方程和Langmuir等温吸附模型。模拟海水吸附实验表明当含铀海水中的铀浓度<30μg/L时,去除率均在90%以上,在模拟海水条件下Fe₃O₄@SiO₂-PEI对铀离子仍保持很好的吸附性能。同时在竞争阳离子存在的条件下,该吸附剂对铀酰离子的选择性最好。利用水热法在MWCNTs表面负载CoFe₂O₄纳米粒子合成了具有较高磁响应性的CoFe₂O₄@MWCNTs吸附剂,并通过PPy对CoFe₂O₄@MWCNTs表面修饰得到CoFe₂O₄@MWCNTs-PPy磁性吸附剂。吸附实验表明经过聚吡咯修饰后吸附剂的吸附最佳pH为7.0,CoFe₂O₄@MWCNTs-PPy吸附剂最佳pH更接近实际海水pH值,且pH在8左右时,吸附容量值为104 mg/g,仍然保持较高的吸附容量,更适合海水提铀。0.5 mol/L的NaHCO₃对CoFe₂O₄@MWCNTs-PPy和CoFe₂O₄@MWCNTs两种吸附剂脱附效果最佳,3次吸附循环后,吸附容量仍保持100 mg/g左右。更多还原

【Abstract】 Nuclear power is considered as a safe,clean and sustainable new energy.The sustainable development of nuclear energy depends on continuous supply of nuclear fuel,which used in nuclear reactions comes from uranium mine in land.China belongs to the depleted uranium country and the land is lack of uranium mine.Researches proved uranium reserves in China can only maintain the existing nuclear power installed capacity for 30 years.Nuclear fuel resource will depend on import in the future.The abundant uranium source in seawater has attracted increasing attention,because it is about thousand times as those in land.It is important to exploit uranium from marine environments to provide enough fuel for nuclear power and relieve the energy crisis.By taken into consideration of low concentration uranium in seawater,magnetic organic functional composite adsorbents based on Fe₃O₄ and CoFe₂O₄were synthesized.Effects of pH,initial uranium concentration and contact time on adsorption were investigated.The thermodynamics and dynamics behaviors between uranium and magnetic adsorbents in the adsorption process were studied by fitting the thermodynamic and dynamic models.Simulated seawater adsorption experiment and ions competition adsorption experiment were carried out at the same time.Carbon coated iron oxide（Fe₃O₄@C）was synthesized by one-step solvothermal reaction.Ketoxime-functionalized carbon coated iron oxide（Fe₃O₄@C–KO）was fabricated through surface functionalization of Fe₃O₄@C with ketoxime.The saturation magnetization of the composites is 30.33 emu/g,showing good magnetic response and dispersion in solution.The adsorption process was completed in 60 minutes when the optimum pH was 6.0.The adsorption experiment data revealed that the process followed pseudo-second-order kinetic model and the adsorption of uranium（VI）was well-described by the Langmuir isotherm.Thermodynamic parameters further showed that the sorption was an endothermic and spontaneous process.Comparing with Fe₃O₄@C,Fe₃O₄@C–KO is a powerful and promising sorbent for the efficient extraction of uranium（VI）because of the chelation between uranyl ion and-OH in ketoxime.The amino-functionalized magnetic Fe₃O₄ nanoparticles（Fe₃O₄-APTMS）were prepared via encapsulation of Fe₃O₄ nanoparticles with（3-aminopropyl）trimethoxysilane.The adsorption results showed the optimum pH value was 6.0 and optimum contact time was 60min.The saturated adsorption capacity of uranium by Fe₃O₄-APTMS was 160.8 mg/g at 25^oC.In addition,the adsorption-desorption experiment in NaOH solution showed that Fe₃O₄-APTMS exhibited high regeneration and reusability.The adsorption of uranium（VI）is well-described by the Langmuir isotherm and the adsorption process is spontaneous endothermic.The surface modified Fe₃O₄@SiO₂ magnetic materials with a core-shell structure were prepared.Fe₃O₄@SiO₂-PEI magnetic particles form a spherical shape with a diameter of about 260-300 nm.The saturation magnetization of the composite materials was 56.76 emu/g.The equilibrium adsorption capacity was 278.16 mg/g at optimum pH 7.0 after 240 min.The adsorption process was best described by a pseudo-second-order kinetic model.The uranium sorption equilibrium data fitted well with the Langmuir sorption isotherm model.Simulated seawater adsorption experiments showed that the removal rates were more than 90%when the concentration of uranium was less than 30μg/L,proving that Fe₃O₄@SiO₂-PEI remained good adsorption performance.Ions competition adsorption experiment showed those adsorbents had the high selectivity for uranium ions in the presence of many competitive cations.Cobalt ferrite/multiwalled carbon nanotubes（CoFe₂O₄@MWCNTs）with magnetic responsiveness performance were successfully synthesized by a hydrothermal method,Polypyrrole/Cobalt ferrite/multiwalled carbon nanotubes adsorbents were obtained after surface modification with Polypyrrole.Batch adsorption experiments revealed that the optimum pH of CoFe₂O₄@MWCNTs-PPy was 7.0,which was close to pH value of seawater.When the pH is 8.0,CoFe₂O₄@MWCNTs-PPy still had high adsorption capacity of 104 mg/g,so CoFe₂O₄@MWCNTs-PPy will be more suitable for the extraction of uranium from the seawater.0.5 mol/L NaHCO₃ was the best desorbent for both two adsorbents.The magnetic composite adsorbents still shown good adsorption properties with adsorption capacity of 100mg/g after the three times adsorption–desorption procedures.更多还原