The variable valence rare earth elements are difficult to separate due to their similar properties and intermediate valence states in molten salts. In order to realize their efficient and selectivity separation, the properties and separation methods of Sm, Yb, and Eu have been investigated in a low-temperature AlCl-NaCl molten salt. It has been found that the oxidation reactions of different Ln(II) to Ln(III) have different potentials. The Ln(II)/Ln(III) reaction is also irreversible when the AlCl content is less than 50 mol%, Ln(III) exists in the form of LnCl precipitation. Therefore, selectively modulating the valence of Sm, Yb, and Eu by electrochemical methods can achieve their separation. The LnCl produced from the Ln(II) electro-oxidation precipitates and separates from the other unoxidized soluble Ln(II) in AlCl-NaCl melt. The efficient separation of Ln(II) in AlCl-NaCl can be achieved by pulse potentiostatic electrolysis. Under these conditions, the separation factors of Sm-Eu, Sm-Yb, and Yb-Eu can reach 10. The maximum removal of Ln(II) exceeded 99 % with a maximum current efficiency of more than 90 %. Most importantly, the separation of variable valence rare earth elements has been realized in a low-temperature AlCl-NaCl melt.

中文翻译：

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低温熔盐AlCl3-NaCl中选择性电氧化分离Sm、Yb和Eu

变价稀土元素由于性质相似且在熔盐中处于中间价态而难以分离。为了实现Sm、Yb和Eu的高效选择性分离，在低温AlCl-NaCl熔盐中研究了Sm、Yb和Eu的性质和分离方法。研究发现不同的Ln(II)到Ln(III)的氧化反应具有不同的电位。当AlCl含量低于50 mol%时，Ln(II)/Ln(III)反应也是不可逆的，Ln(III)以LnCl沉淀的形式存在。因此，通过电化学方法选择性调节Sm、Yb和Eu的价态可以实现它们的分离。 Ln(II) 电氧化产生的 LnCl 沉淀并与 AlCl-NaCl 熔体中其他未氧化的可溶性 Ln(II) 分离。脉冲恒电位电解可以实现AlCl-NaCl中Ln(II)的高效分离。在此条件下，Sm-Eu、Sm-Yb、Yb-Eu的分离因子可达10。Ln(II)的最大去除率超过99%，最大电流效率超过90%。最重要的是，在低温AlCl-NaCl熔体中实现了变价稀土元素的分离。