海水中铀酰离子与酰胺类分子的配位热力学研究

With the development of the nuclear power industry, the amount of uranium resources required is increasing every year. The ocean is an important source of uranium because it contains about 4.5 billion tons of uranium, a thousand times as much as the amount of uranium in terrestrial ores. However, it is extremely difficult to extract uranium from seawater, because uranium compounds exist in extremely low concentrations as very stable carbonate complexes, and because the ocean also contains many other metal ions, some of which are in overwhelming higher concentration. Amidoxime material could potentially be used to extract uranium from seawater more efficiently. The structure of Amine is similar to amidoxime. Amines have a high binding affinity to a range of transition metal ions and are ligands ubiquitous in coordination chemistry. Yet, the coordination modes of amine complex with uranium are not well understood in marine environments. In this study, we aim to provide thermodynamic data regarding this specific type of complex that should assist in the rational design of uranium chelating agents for sequestration of uranium from seawater. To quantify and compare the binding strengths of different functional groups towards uranium, a number of thermodynamic and spectroscopic techniques can be applied to the studies of uranium complexation in seawater solution, providing fundamental information on the nature (e.g., ionic bonding vs covalency, outer sphere vs inner sphere), energetics (e.g., free energy, enthalpy, entropy and heat capacity) and structures of uranium complexes. Also, fundamental understanding of uranium complex with amines is critical to understand their transport in the environment.

随着世界核电事业的蓬勃发展，全球每年所需的铀资源量不断增加。由于陆地铀资源有限，海水提铀已经越来越具有实际应用价值。偕胺肟是海水提铀中最具有工程应用前景的材料。酰胺类化合物广泛存在自然界，与偕胺肟结构相似，海水中的酰胺化合物将影响偕胺肟材料对铀的吸附性能，需对其开展更深入的研究。本项目设计、合成与偕胺肟结构相近的酰胺分子，同时筛选环境中常见的酰胺分子，比较研究酰胺、偕胺肟分子对海水中铀酰离子及主要竞争离子的溶液配位热力学，提供关于配合物的本性（离子价、共价，外界、内界络合）、能量（自由能、热焓、热熵、热容）和溶液配位结构的基础科学信息。以定量的数据阐述酰胺化合物对偕胺肟分子海水提铀性能的影响，为改进海水提铀材料的设计与合成提供支持，同时也为研究重金属在开放水体中与有机分子的相互作用提供热力学数据。

采用光谱滴定法、电位滴定法、微量热滴定法测量了模拟海水（0.5mol·L-1 NaCl溶液）中肌肽、鹅肌肽、草甘膦、甲基草甘膦、草铵膦、环戊胺二肟酸、甲基环戊胺二肟酸、O-磷酸-L-丝氨酸、环己烷二胺四乙酸、羟乙基乙二胺三乙酸、二胺四乙酸等分子与铀酰离子在溶液中的配合物稳定常数、配位热焓，采用晶体结构结合核磁共振波谱分析了溶液中配合物结构。结果表明环戊胺二肟酸结构对铀酰离子具有强烈的配位作用，会改变铀酰离子的吸收光谱。该分子能将高价镎酰离子(NpO2+)还原到低价（Np4+），能将低价铈离子（Ce3+）氧化到高价（Ce4+），表明该分子倾向于与四价金属离子配位。在酰胺分子如肌肽、鹅肌肽存在时，铀酰离子的水解作用受到抑制，从而改变铀酰离子在溶液中的存在形态。这些小分子可能与提铀材料中的功能分子竞争铀酰离子，影响海水提铀效率。更正了乙二胺四乙酸及其衍生物与铀酰离子配位的错误认识。更正了溶液中草甘膦分子质子化反应的错误认识。这些参数为理论预测溶液中铀酰离子存在形态提供了热力学层面支持，为提铀材料结构设计提供参考。