摘要/Abstract
镎(Np)和钚(Pu)是核能领域两种重要的锕系元素, 其在水溶液中的配位化学对于了解和控制其在水环境中的种态分布和迁移行为具有重要意义. Review了近十几年来国内外Np和Pu与环境中常见无机阴离子在水溶液中的配位化学研究进展, 重点阐述了不同价态Np/Pu离子与OH–、 $CO_3^{2-}$、 $SO_4^{2-}$、Cl–、 $NO_3^-$、F–、 $PO_4^{3-}$等阴离子之间形成的配位物种和配位热力学信息, 并对该领域存在的关键科学问题和未来发展方向进行了分析和展望.
关键词: 镎, 钚, 环境, 无机阴离子, 配位化学, 热力学
Neptunium (Np) and plutonium (Pu) are two important actinides in nuclear industry. They can be generated through neutron capture of uranium (U) in reactors or decay from other transuranic elements. Representative isotopes of Np and Pu such as 237Np and 239Pu have long half-lives and possess high radiotoxicity, therefore may impose great hazard to biological system if they are released into the environment. The rich redox chemistry of Np and Pu further adds complexity of their chemical behavior in the environment. The coordination chemistry of Np and Pu in aqueous solution is of great significance to help understand and control their speciation distribution and migration behaviors in aqua environment. This article reviews the advances in coordination chemistry of Np and Pu with several common inorganic anions (OH–, $CO_3^{2-}$, $SO_4^{2-}$, Cl–, $NO_3^-$, F–, $PO_4^{3-}$) in aqueous solution, especially the speciation and coordination thermodynamics between Np/Pu in different oxidation states and these anions. In general, Np and Pu ions in the same oxidation state exhibit similar coordination behavior (species, structure, stability constants, etc.) when coordinating with the same anion. The coordination strength for Np/Pu ions in different oxidation states with the same anion ligand is roughly in the order of IV>III, VI>V. For the coordination of Np/Pu ions with different anions, the strength sequences are OH–>F–> ${H_2}PO_4^-$> $NO_3^-$>Cl– for monovalent anions and $CO_3^{2-}$> $HPO_4^{2-}$> $SO_4^{2-}$ for divalent anions. Factors such as instability of Np/Pu ions in some oxidation states, weak complexation, and low solubility of the complexes in the aqueous solution cause difficulties in obtaining precise and reliable coordination parameters for these ions experimentally. Moreover, the coordination parameters determined by different methods may vary with each other. To obtain more reliable parameters for the coordination of Np/Pu ions with these anions in the future, the use of more advanced characterization methods and the assistance of theoretical computation may provide strong support.
Key words: neptunium, plutonium, environment, inorganic anion, coordination chemistry, thermodynamics
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