Cryptand Cages for Anion Selective Encapsulation for Nuclear Waste

乏燃料的再处理和历史核设施的退役产生了复杂的废料混合物，需要使其安全地长期储存和最终处置。一些最困难的废物流是那些含有含氧阴离子的有毒和放射性元素，例如高锝酸盐，亚硒酸盐，硒酸盐，铬酸盐，铬酸盐，碘酸盐，溴酸盐。我们提出了一种具有成本效益的去除策略的基础上，一种新的选择性封装过程中使用自组装穴状笼。对常见阴离子（具有不同电荷和形态）的初步研究表明，回收速度快，将阴离子浓度从1000 ppm降至<0.1 ppm。这项研究于2018年发表在高影响力期刊Angewandte Chemie上，专利保护正在进行中。去除可以被设计成在极端环境、高酸性溶液和高离子强度下工作，从而在溶液中或作为结晶沉淀物产生阴离子的稳定包封。这对于有待玻璃化的液体高放射性废物具有优势，因为阴离子将稳定在高放射性液体中。我们的研究愿景是通过基于阴离子电荷和形态学的穴状配体笼固定来实现控制去除。因此，我们需要确定控制包封和沉淀的因素：穴状配体的性质（其设计的变化如何反映在包封中），复合笼的金属中心，液体介质的条件（pH值，离子强度）和释放动力学。为了定义这种复杂的关系，我们将采用多学科的方法，汇集了计算筛选，实验合成和表征的力量。这将加速可持续和低成本的封装策略的发展，减少环境影响，提高废物形式的性能。我们的目标是支持我们的假设，并实现以下目标：（1）合成基于以前报道的配体，但调节给体原子的性质和空腔的大小，与一系列的金属中心，以确定控制阴离子选择性的因素;（2）确定笼和阴离子之间的相互作用以延迟动力学释放;（3）使用综合实验和建模产生靶结构的原子模型，并表征其稳定性、形态和组成。

The reprocessing of spent fuels and the decommissioning of historical nuclear facilities generates a complex mixture of waste material that needs to rendered safe for long term storage and ultimate disposal. Some of the most difficult waste streams are those that contain oxyanions of toxic and radioactive elements, e.g. pertechnetate, selenite, selenate, chromate, molybdate, iodate, bromate.We propose a cost-effective removal strategy based on a novel selective encapsulation process using self-assembled cryptand cages. A pilot study on common anions (with different charge and morphology) demonstrated a fast recovery, reducing anions concentration from 1000 to <0.1ppm. This research was published in the high-impact journal Angewandte Chemie in 2018, and patent protection is under way. The removal can be engineered to work in extreme environments, highly acidic solutions and high ionic strength, producing stable encapsulation of anions either in solution or as crystalline precipitates. This has an advantage for liquid high-level waste pending vitrification, as the anions will be stabilized within the highly radioactive liquor. Our research vision is to attain controlled removal via immobilization using cryptand cages based on anion charge and morphology. Thus we need to determine the factors controlling the encapsulation and the precipitation: the nature of the cryptand (how changes in its design reflect in encapsulation), the metal center for the complex cage, the conditions of the liquid media (pH, ionic strength), and the kinetics of release. To define this complex relationship, we will employ a multidisciplinary approach that brings together the power of computational screening, experimental synthesis and characterization. This will accelerate the development of sustainable and cost-effective encapsulation strategies, reduce environmental impact and enhance waste form performance.We aim to support our hypothesis and to achieve the following objectives: (1) to synthetize ligands based on those previously reported but modulate the nature of the donor atoms and the size of the cavity, with a range of metal center to determine the factors controlling anion selectivity; (2) to identify the interactions between the cage and the anion to retard kinetic release; (3) to produce atomistic models of target structures using integrated experiments and modelling, and to characterize their stability, morphology, and composition.