Marsac Rémi, Réal Florent, Banik Nidhu Lal, Pédrot Mathieu, Pourret Olivier, Vallet Valérie
Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042, Rennes Cedex, France.
Dalton Trans. 2017 Oct 10;46(39):13553-13561. doi: 10.1039/c7dt02251d.
The prediction of cerium (Ce) aqueous speciation is relevant in many research fields. Indeed, Ce compounds are used for many industrial applications, which may require the control of Ce aqueous chemistry for their synthesis. The aquatic geochemistry of Ce is also of interest. Due to its growing industrial use and its release into the environment, Ce is now considered as an emerging contaminant. Cerium is also used as a proxy of (paleo)redox conditions due to the Ce(iv)/Ce(iii) redox transition. Finally, Ce(iv) is often presented as a relevant analogue of tetravalent actinides (An(iv)). In the present study, quantum chemical calculations were conducted to highlight the similarities between the structures of Ce(iv) and tetravalent actinide (An(iv); An = Th, Pa, U, Np, Pu) aqua-ions, especially Pu(iv). The current knowledge of An(iv) hydrolysis, solubility and colloid formation in water was briefly reviewed but important discrepancies were observed in the available data for Ce(iv). Therefore, new estimations of the hydrolysis constants of Ce(iv) and the solubility of Ce(iv)-(hydr)oxides are proposed, by analogy with Pu(iv). By plotting pH-Eh (Pourbaix) diagrams, we showed that the pH values corresponding to the onset of Ce(iv) species formation (i.e. Ce(iv)-(hydr)oxide or dissolved Ce(iv)) agreed with various experimental results. Although further experimental studies are required to obtain a more accurate thermodynamic database, the present work might yet help to predict more accurately the Ce chemical behavior in aqueous solution.
铈（Ce）水相形态的预测在许多研究领域都具有重要意义。事实上，铈化合物被用于许多工业应用中，这些应用在合成过程中可能需要对铈的水相化学进行控制。铈的水生地球化学也备受关注。由于其在工业中的使用不断增加且会释放到环境中，铈现在被视为一种新兴污染物。由于Ce(IV)/Ce(III)的氧化还原转变，铈还被用作（古）氧化还原条件的替代指标。最后，Ce(IV)常被视为四价锕系元素（An(IV)）的相关类似物。在本研究中，进行了量子化学计算，以突出Ce(IV)与四价锕系元素（An(IV)；An = Th、Pa、U、Np、Pu）水合离子结构之间的相似性，特别是Pu(IV)。本文简要回顾了目前关于An(IV)在水中水解、溶解度和胶体形成的知识，但在Ce(IV)的现有数据中观察到了重要差异。因此，通过与Pu(IV)类比，提出了Ce(IV)水解常数和Ce(IV) -（氢）氧化物溶解度的新估计值。通过绘制pH - Eh（Pourbaix）图，我们表明与Ce(IV)物种形成开始（即Ce(IV) -（氢）氧化物或溶解的Ce(IV)）相对应的pH值与各种实验结果一致。尽管需要进一步的实验研究来获得更准确的热力学数据库，但目前的工作仍可能有助于更准确地预测铈在水溶液中的化学行为。
