Špadina Mario, Bohinc Klemen, Zemb Thomas, Dufrêche Jean-François
ICSM, CEA, CNRS, ENSCM, University of Montpellier , 34199 Marcoule , France.
Faculty of Health Sciences , University of Ljubljana , 1000 Ljubljana , Slovenia.
Langmuir. 2019 Feb 26;35(8):3215-3230. doi: 10.1021/acs.langmuir.8b03846. Epub 2019 Feb 15.
We propose the statistical thermodynamic model for the prediction of the liquid-liquid extraction efficiency in the case of rare-earth metal cations using the common bis(2-ethyl-hexyl)phosphoric acid (HDEHP) extractant. In this soft matter-based approach, the solutes are modeled as colloids. The leading terms in free-energy representation account for: the complexation, the formation of a highly curved extractant film, lateral interactions between the different extractant head groups in the film, configurational entropy of ions and water molecules, the dimerization, and the acidity of the HDEHP extractant. We provided a full framework for the multicomponent study of extraction systems. By taking into account these different contributions, we are able to establish the relation between the extraction and general complexation at any pH in the system. This further allowed us to rationalize the well-defined optimum in the extraction engineering design. Calculations show that there are multiple extraction regimes even in the case of lanthanide/acid system only. Each of these regimes is controlled by the formation of different species in the solvent phase, ranging from multiple metal cation-filled aggregates (at the low acid concentrations in the aqueous phase), to the pure acid-filled aggregates (at the high acid concentrations in the aqueous phase). These results are contrary to a long-standing opinion that liquid-liquid extraction can be modeled with only a few species. Therefore, a traditional multiple equilibria approach is abandoned in favor of polydisperse spherical aggregate formations, which are in dynamic equilibrium.
我们提出了一种统计热力学模型，用于预测使用常见的双（2-乙基己基）磷酸（HDEHP）萃取剂萃取稀土金属阳离子时的液-液萃取效率。在这种基于软物质的方法中，溶质被建模为胶体。自由能表示中的主要项包括：络合作用、高度弯曲的萃取剂膜的形成、膜中不同萃取剂头部基团之间的横向相互作用、离子和水分子的构型熵、二聚作用以及HDEHP萃取剂的酸度。我们为萃取体系的多组分研究提供了一个完整的框架。通过考虑这些不同的贡献，我们能够建立系统中任何pH值下萃取与一般络合之间的关系。这进一步使我们能够在萃取工程设计中合理化明确的最佳条件。计算表明，即使仅在镧系元素/酸体系中，也存在多种萃取机制。这些机制中的每一种都由溶剂相中不同物种的形成所控制，范围从多个金属阳离子填充的聚集体（在水相中低酸浓度时）到纯酸填充的聚集体（在水相中高酸浓度时）。这些结果与长期以来认为液-液萃取仅能用少数物种建模的观点相反。因此，摒弃了传统的多重平衡方法，转而支持处于动态平衡的多分散球形聚集体的形成。
