冠醚插层对α相磷酸锆吸附铯性能的影响机理

Development of inorganic ion exchangers for separation of high release heat, long half-life fission nuclide from high level waste liquid is an important content in advanced nuclear fuel cycle system. α phase layered zirconium phosphate is a potential inorganic ion exchange agent used to treatment of high level waste liquid. Our previous study has indicated that a part of the layered structure of zirconium phosphate deformed in a strong acid system. The stability of the layer structure has a significant effect on the selectivity of fission nuclides and the applicability of the material in the high-level radioactive waste liquid system. In this work, the changes of structure stability of zirconium phosphate layer with acidity and salinity in high radiation system are systematically studied from the point of view of apparent electrical property and microstructure change. On this basis, the crown ethers compounds used as guest molecule are embedded in α phase zirconium phosphate interlayer to support their layer structure. To explain the reason that why the guest molecular intercalation of crown ethers can improve the stability of zirconium phosphate materials in complex systems, the intercalation mechanism of crown ether guest macromolecules and the relationship between guest molecular size and the structure stability of host material layer are studied. In addition, to evaluate the adsorption ability of zirconium phosphate intercalated by crown ether compounds, a batch of adsorption experiments are carried out to removal of cesium ions form the stimulated high level liquid waste, and the interaction between the adsorbent and adsorbate is determined by various spectroscopy technologies. This research results are expected to provide theoretical and technical support for the structural design of fissile element separation materials in radioactive waste liquid.

研制用于分离高放废液中高释热、长半衰期裂变核素的无机离子交换剂是先进核燃料循环体系中一项重要研究内容。α相层状磷酸锆是极具潜力的用于高放废液中无机离子交换剂。前期研究发现在强酸、高盐度的复杂体系中磷酸锆的层状结构部分会发生扭曲变形。材料层结构的稳定性对裂变核素的选择性及其在高放体系中的适用性影响显著。本项目拟从材料宏观、表观电性及微观结构变化等多角度，系统给出在高放体系中α相磷酸锆层结构的稳定性随酸度、盐度的变化规律；在此基础上将冠醚类大环化合物插入α相磷酸锆层间对其层结构进行支撑和修饰，通过研究客体分子插层机制及其与主体材料层结构稳定性之间的关系，揭示冠醚类客体分子插层为何能提高α相磷酸锆在复杂体系中的稳定性；进一步开展冠醚插层α相磷酸锆对铯离子的吸附实验，阐明其对复杂体系中裂变铯的选择性及相互作用机理。研究成果可望为放射性废液中裂变元素分离材料的结构设计提供理论与技术支持.

137Cs是高放废液中的主要释热核素，若将其分离提取不仅可有效降低高放废液的放射性强度及后期处理成本，而且可实现该类有价值核素的回收利用。α相磷酸锆具有典型的2D层状结、良好的稳定性和离子交换性能，其对137Cs呈现优良的交换性能。但该类材料在强酸体系中稳定性差、缺乏选择性以及吸附容量低等，限制了其在高放废液减容降级中的应用。本项目以强酸性高放废液体系中137Cs的高效分离为目标，创新性将功能客体分子嵌入磷酸锆的层间，一方面通过主客体之间形成强的相互作用达到对主体层结构的支撑，提升其稳定性；另一方面，功能客体分子本身对Cs+特异络合能力，使材料稳定性提升的同时实现了在复杂体系对Cs+的选择性吸附。获得以下具有意义的研究结果：1）采用预撑插层成功的将冠醚引入磷酸锆的层间，获得新型的磷酸锆复合材料，且冠醚插层后未引起主体材料的形貌及物相明显的变化，但由于层间客体的存在使主体材料的层间距增大；2）对获得磷酸锆复合材料的稳定性考察表明，通过客体分子插层组装有效的提升了主体磷酸锆材料的稳定性，反应中主客体之间形成强的相互作用，使层间客体分子对层板支撑同时抑制了层板的扭曲变形，该材料在强酸体系0.5mol L-1硝酸呈现良好稳定性；3）对获得磷酸锆材料的吸附性能研究表明：功能性客体分子插层增强磷酸锆材料对Cs的选择性吸附容量。但插层方法及客体分子类型的不同导致获得的磷/膦酸锆材料对Cs吸附效果存在差异，其中客体21冠7由于本身对Cs强烈的的络合能力，使获得21冠7插层磷酸锆对Cs展现良好的选择性吸附，对Cs的最大吸附容量远高于传统的ZrP材料。基于该研究成果不仅为应用于复杂体系中分离材料性能的改进提供了新的方法，也为其他领域功能性材料的设计、开发提供新的研究思路。