兰州大学机构库 >核科学与技术学院
酰胺功能化离子液体的合成及其对U(Ⅵ)和Th(Ⅳ)的自组装萃取
Alternative TitleSYNTHESIS OF FUNCTIONAL AMIDE-BASED EXTRACTANTS AND APPLICATION ON U(VI) AND TH(IV) SELF-ASSEMBLY EXTRACTION
张芳
Subtype博士
Thesis Advisor刘斌 ; 严则义
2023-06-03
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name理学博士
Degree Discipline放射化学
Keyword钍,铀,功能性离子液体,酰胺类萃取剂,自组装萃取 Thorium, Uranium, Functional ionic liquids, Amide-based extractants, selfassembly extraction
Abstract

核能作为清洁能源,对于能源的可持续发展具有重要意义。核能的安全稳定运行,离不开核燃料循环技术的发展。在核燃料循环体系中,从前端开采到乏燃料后处理环节,溶剂萃取法在放射性元素(如铀、钍等)的纯化分离过程中起关键作用。然而,萃取剂配体以及萃取分离方法在应用过程中却不断暴露出一些短板或弊端。比如,在前端铀矿浸出液中为干扰离子增加多余步骤,成本增加的同时产生多余有机废液和酸性废液;在萃取步骤后往往需要反萃取步骤,造成分离流程复杂,试剂大量消耗;在乏燃料后处理环节中分离镧系/锕系元素时选择性较差等。这些问题有待通过新型萃取剂及萃取流程的开发得到缓解或解决。此外,为满足经济性及绿色环保的要求,开发符合“CHON”原则的萃取剂成为促进核能绿色发展的重要原则。

本论文针对当前核燃料循环体系中,前端铀矿浸出液和后端乏燃料后处理环节中存在的问题,开发了新型的功能性离子液体,并将其应用于核燃料循环的萃取流程中。论文深度调研了离子液体在分离领域的应用及研究进展,对季铵型离子液体在核燃料循环多个环节中的分离应用进行了剖析,以此为研究导向,针对存在的问题,设计合成了两大类离子液体,其中阳离子为应用广泛的阳离子表面活性剂,阴离子分别为具有丰富配位点的二甘醇酰胺酸及琥珀酰胺酸。

使用合成的二甘醇酸酰胺类离子液体[DODMA]+[DRDGA]-与琥珀酰胺类离子液体[DODMA]+[DRSCA]-,分别研究了其对钍离子的自组装萃取分离,发展了一体化的萃取-固化策略。在高酸度条件下,功能离子液体萃取钍后通过自组装过程以固相的形式聚集在两相界面处,同步实现了萃取-固化的一步操作,省略了后续的洗脱、沉淀过程,极大的简化了分离流程。在静态与振荡两种条件下,自组装聚集体均能够富集超过99%的Th(IV)。利用SEM、EDX、XPS、FT-IR等表征手段分析了固体的形貌与结构组成,证实了该固化是自组装驱动的过程。用ESI-HRMs和斜率分析推导出该萃取过程为阴离子交换与配体交换共同作用,萃取产物分别为[DODMA]+[DGA⋅Th(NO3)4]-和[DODMA]+[SCA⋅Th(NO3)4]-。离子液体的阴离子以及络阴离子Th(NO3)5-参与了萃取过程,阳离子触发了随后的固化过程。另外,在干扰离子存在的混合溶液中,以上两种离子液体均对Th(IV)表现出优异的选择性和很高的回收率。

针对从铀矿浸出液中分离铀的实际需求,探究了两种离子液在硫酸体系中对U(VI)的萃取行为。结果表明,通过功能性离子液所提出的自组装萃取策略,对铀矿浸出液中的U(VI)也具有很好的萃取效果(>99%)。通过表征和分析自组装固体,证实了萃取产物分别为[DODMA]+[DGA∙UO2SO4]-和[DODMA]+[SCA∙ UO2SO4]-,且离子液体的阴、阳离子以及络阴离子[UO2(SO4)2]2-参与了自组装萃取过程。有趣的是,当萃取条件从高浓度硝酸体系转变为低浓度硫酸体系后,两种离子液的选择性发生了反转,由萃取Th(IV)转向到萃取U(VI)。在模拟以及真实的铀矿浸出液中,两种离子液体均表现出对U(VI)的优异选择性。

综上所述,合成的自组装萃取剂二甘醇酸酰胺类离子液体[DODMA]+[DRDGA]-与琥珀酰胺类离子液[DODMA]+[DRSCA]-,分别在硝酸体系和硫酸体系下对钍和铀展现出优异的选择性萃取效果,表明了其在铀矿浸出液的纯化和乏燃料后处理环节具备一定的应用潜力。论文的研究成果将为复杂体系中目标核素的分离纯化提供新的视角与思路。

Other Abstract

As one of clean energy, nuclear energy is of great significance to the sustainable development of energy resources. The safety and stability of nuclear energy operation highly depend on the development in nuclear fuel cycle technologies. In the nuclear fuel cycle, solvent extraction plays a key role in the purification and separation of radioactive elements (such as uranium, thorium, etc.) from front-end mining to spent fuel reprocessing. However, shortcomings and drawbacks exist in the application of the extractant as wellas extraction methods. For instance, mult-steps are inevitable in separating the interfering ions in the front-end uranium leaching process, leading to tremendous wastes and extra costs. The usually required back-extraction precess complicated the separation process meanwhile a consumption of reagents. In spent fuel reprocessing, the selectivity in lanthanide/actinide elements by extraction is usually poor, etc. These problems may be improved or solved by the development of new extractants and extraction process. In addition, in order to meet the future economic and “green” requirements, the extractant in line with the "CHON" principle will certainly be more conducive to the future development.

In the present thesis, new functional ionic liquids are synthesized and applied in the scenario of nuclear fuel cycle system, to address some current problems in both front-end uranium leaching process and the back-end spent fuel reprocessing. Frontier studies of ionic liquids in separating usages were thoroughly summarized, and two major types of ionic liquids are designed and synthesized. The cation is a widely used cationic surfactant, and the anion is diglycolic amide acid/succinic amide acid with abundant coordination sites, respectively.

The synthesized diethylene glycol amide ionic liquid [DODMA]+[DRDGA]- and succinic amide ionic liquid [DODMA]+[DRSCA]- were firstly applied in the separation of thorium from nitric acid systems via the self-assembly extraction stratigy. Under high acidity conditions, the functional ionic liquids not only extracted thorium but self-assembly aggregated in forming solid phase at the extraction interface. The one-step separation and solidification may spare the subsequent elution and precipitation processes and greatly simplifying the separation process in the current prosedure. The self-assembled aggregates enriched more than 99% of Th(IV) in both static and shaking conditions. The morphology and structural composition of the self-assembled solids were comprehensively analyzed by SEM, EDX, XPS and FT-IR, etc, comfirming the presence of incorporated Th(IV). The extraction mechanism was anion/ligand exchange, revealed via the results from ESI-HRMs and slope analysis. The extraction products were confirmed to be [DODMA]+[DGA⋅Th(NO3)4]- and [DMA]+[SCA⋅Th(NO3)4]-, respectively. Both anions and cations of the ionic solution as well as the complex anion Th(NO3)5- were involved in the self-assembly extraction process. In addition, both ionic liquids showed excellent selectivity for Th(IV) in the presence of interfering ions.

As for the application scenario of uranium extraction from uranium ore leach solution, the extraction behavior of two ionic liquids for U(VI) in sulfuric acid system was further explored. The results show that the functional ionic liquids showed high extraction effect (>99%) on U(VI) by self-assembly extraction. According to the characterization and analysis of the self-assembled solids, the extraction products were [DMA]+[DGA∙UO2SO4]- and [DMA]+[SCA∙ UO2SO4]-, respectively, and the anions and cations of the ionic liquid as well as the complex anion [UO2(SO4)2]2- were involved in the self-assembled extraction process. Interestingly, the selectivity of both ionic liquids shifted from Th(IV) to U(VI) when the extraction conditions changed from nitric acid system to sulfuric acid system. Both ionic liquids exhibited excellent selectivity for U(VI) in both simulated and real uranium leaching solutions.

Over all, the synthesized self-assembled extractants diethylene glycol amide-based ionic liquids [DODMA]+[DRDGA]- and succinimide-based ionic liquids [DODMA]+[DRSCA]- showed excellent selective extraction to thorium (IV) and uranium (VI) in nitric acid and sulfuric acid systems, respectively. The extractants as well as the self-assembly extraction show a potential in uranium leaching and spent fuel reprocessing. The results may provide further perspectives and inspirations for the separation strategy of target nuclides in complex systems.

Subject Area放射化学
MOST Discipline Catalogue无机化学
URL查看原文
Language中文
Other Code262010_120190902570
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/539751
Collection核科学与技术学院
Affiliation
兰州大学核科学与技术学院
Recommended Citation
GB/T 7714
张芳. 酰胺功能化离子液体的合成及其对U(Ⅵ)和Th(Ⅳ)的自组装萃取[D]. 兰州. 兰州大学,2023.
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