固、液双阴极熔盐电解分离铀、稀土元素及分离产物与熔盐的相互作用

Electrolytic separation of uranium and rare earth element as well as the dissolution loss of alloys obtained by electrolysis dissolution into molten salts were studied on solid and liquid electrodes in order to improve separation efficiency and recovery rate of uranium and rare earth elements from spent nuclear fuel reprocessing. First, the electrochemical behaviors of uranium and rare earth ions were explored in order to build the galvanic series of uranium and rare earth on solid and liquid cathodes in molten salts. The study on dynamics, thermodynamics as well as the electrochemical mechanism of under-potential deposition were carried out in the processing of separation of uranium and rare earth in molten salts to explore the laws of high efficient separation and improve the separation factor. And then, the dissolution behaviors of dissolution loss, valence state of deposits (U-M, RE-M) dissolved in molten salts as well as the effects of cathodic polarization on dissolution behavior of deposits dissolved in molten salts were investigated to explore the dissolution mechanism and interaction law between deposits and molten salts. Based on the above results, the essence of difference of extraction efficiency (extraction rate) at different electrode was revealed. Last, competition reaction occurred on double cathodes was studied by galvanostatic/potentiostatic electrolysis at double cathodes selected based on above results to explore electrochemical mechanism for high efficiency separation of uranium and rare earth elements. The studies above can provide fundamental data for electrolytic separation of uranium and rare for the dry reprocessing.

本项目针对乏燃料干法后处理中铀、稀土元素的高效分离和回收问题，拟开展在固、液阴极上熔盐电解分离以及分离产物在熔盐中溶解损失的研究工作。首先研究铀、稀土离子在固、液阴极上的电化学行为，建立铀、稀土元素在固、液态阴极上的电位序；研究熔盐电解分离铀、稀土过程的动力学、热力学及欠电位沉积的电化学机理，探索高效分离铀、稀土元素的规律；同时研究分离产物在熔盐中的溶解损失、溶解后的价态等溶解行为及阴极极化对溶解行为的影响，探索分离产物在熔盐中的溶解机理和相互作用规律。通过以上三方面的研究以揭示固、液电极提取效率（提取速率、提取率）不同的本质问题。最后，采用筛选的双阴极进行恒电流/恒电位电解，研究双阴极上的竞争反应、双阴极电解分离铀、稀土元素的电化学机制，以期达到高效分离和回收铀、稀土的目的，为干法后处理分离铀、稀土元素和筛选固、液金属电极提供基础数据。

本项目针对乏燃料干法后处理过程中铀、稀土元素的高效分离和回收问题，开展了固、液阴极上熔盐电解提取分离以及提取产物在熔盐中溶解损失的研究工作。（1）研究了铀、稀土离子在LiCl-KCl熔盐中固、液电极上的电化学行为，结果表明，U和稀土（RE）在固、液活性电极上均发生欠电位沉积，是由于生成金属间化合物，计算了高温条件下U(RE)-Cu 、RE-Bi(Zn)金属间化合物的生成吉布斯自由能、生成焓等热力学数据；并建立了铀、稀土元素在固、液态电极上的电位序。（2）对比分析了RE在固态Cu和液态Zn电极上的动力学和热力学性质，发现富Zn化合物TbZn12/Tb(III)电对的交换电流密度均大于富Cu化合物TbCu5/Tb(III)的交换电流密度，而TbZn12/Tb(III)电极反应的活化能小，所以Tb(III)在Zn电极上比Cu电极上的反应速度更快；热力学研究结果与动力学相同。RE在固态Cu和液态Zn电极上的提取率均大于90%。（3） 研究了固、液双阴极电解提取RE，发现采用双阴极恒电流电解时，沉积电位始终比单阴极Zn上的电位更负，而比单阴极Cu电极上的电位更正，但更接近Zn电极电位。在双阴极体系中，只有少量的Y被沉积在Cu电极上，而大部分Y主要在Zn电极上沉积。（4）研究了固、液电极材料和提取产物与熔盐的相互作用，实验结果表明，极化条件下，即电解提取过程中可有效抑制电极材料和提取产物的自溶解。