Application of Complex-Forming Reaction to Separation of Rare Earth element by Ionic Exchanger

为了提高溶剂萃取中稀土金属离子的分离效果，研究了在水相中加入螯合剂对Ce、Pr和Nd的分离效果。本研究考虑的萃取剂为D2EHPA(二（2-乙基己基磷酸）和HEH (EHP)（2-乙基己基磷酸氢酯），并在水相中加入螯合剂DTPA（五乙酸二乙烯三胺）。在这样的体系中，萃取被认为取决于水相中络合物形成和离子与萃取剂在有机相中的结合之间的相对强度。在D2EHPA萃取过程中，螯合剂DTPA在整个pH范围内的存在对萃取的影响很小，这可能是由于D2EHPA与所讨论的金属离子具有很强的亲和力。稀土金属离子在水相中形成DTPA配合物，显著提高了HEH （EHP）溶剂萃取中稀土离子的分离效果。在较高的pH值下，离子的萃取量依次为Ce、Pr和Nd，且在较高的pH值范围内有利于分离。此外，根据络合离子在水相中的稳定性，发现萃取离子在水相中向有机物转移时受到不同程度的抑制。结果表明，在水相中加入螯合剂可以有效地使Ce、Pr和Nd离子在萃取平衡中相互分离，并将离子转移到有机相中。

In order to improve the separation of rare earth metal ions in the solvent extraction, the addition of a chelating reagent in the aqueous phase was investigated for Ce, Pr, and Nd. The extractants considered in this work were D2EHPA (di(2-ethylhexyl phosphorous acid) and HEH (EHP) (2-ethylhexyl hydrogen 2-ethylhexyl phosphonate) and a chelating reagent DTPA (diethylene triamine pentaacetate) was added into the aqueous phase. In such systems the extraction is considered to be depending on the relative strength between complex-forming in aqueous phase and the combination of the ion with the extractant in the organic phase.In the extraction with D2EHPA, the extraction was onli slightly affected by the presence of the chelating reagent, DTPA over the whole range of pH probably due to strong affinity between D2EHPA and metal ions in question.The formation of DTPA complex of the rare earth metal ions in the aqueous phase significantly enhanced the separation of the ions in the solvent extraction using HEH (EHP). At higher pH, the extractoin of the ions was higher in the order of Ce, Pr and Nd and the separation was promoted in high pH range.Also in the transfer of the extracted ions from the aqueous phase to the organic was found to be suppressed to different extent according to the stability of the complex ions in the aqueous phase.The addition of chelating reagent in the aqueous phase was shown to be effective in mutual separation of Ce, Pr and Nd ions both in equilibrium of extraction and in the transfer of the ions into the organic phase.