Reduction And Extraction Of Ce And Sm In LiF-KF Molten Salt/Liquid Bi(Zn)-Li System And Its On-Line Monitoring

The development of nuclear energy is conducive to resource conservation and environmental protection,and is an inevitable requirement for our country to implement the sustainable development strategy.The reprocessing of spent fuel has become one of the main issues restricting the development of nuclear energy.Dry reprocessing technology for spent nuclear fuel has unique advantages in preventing nuclear proliferation and reducing strong radiation.Among them,molten salt/liquid metal reduction and extraction technology has received extensive attention.In this work,LiF-KF molten salt and liquid metal Bi（Zn）-Lialloy were used as the two-phase medium for extraction.The reduction-extraction mechanism and reaction kinetics of rare earth ions were investigated on the two-phase interface of LiF-KF and Bi（Zn）-Li.And online monitoring of its reduction and extraction process was carried out through electrochemical methods.Details are as follows:（1）In order to electrochemically monitoring the extraction process online,the electrochemical behavior of Ce（Ⅲ）and Sm（Ⅲ）ions on inert Mo electrode was firstly studied in LiF-KF eutectic molten salt.The reduction process of Ce（Ⅲ）on Mo electrode was found to be three electrons transfer in one step,and the reduction process of Sm（Ⅲ）on Mo electrode is a two-step reaction.Then,the linear relationship between peak currents and Ce（III）ion concentrations was measured by SWV,and the standard working curves of Ce（III）in the temperature range of 823 K to 973 K were obtained.At the same time,the standard working curve of Sm（III）at 923 K was obtained by the same method.（2）First,the extractant（Bi-Lialloy）was prepared by electrolysis in a molten salt medium,and the alloy composition was characterized.Then,in the molten salt（LiF-KF）/liquid metal（Bi-Li）system,the Ce（Ⅲ）ion was reduced and extracted from molten salt,and the process was monitored in real time by SWV.The effect of the content of lithium and temperature on the reduction and extraction of Ce was investigated.The results showed that the final extraction rate is 98.34%at 923 K and the Licontent of 2.60 wt%in Bi-Lialloy,and the distribution coefficient could reach 203.39.In the temperature range of 823 K～973 K,the reductive extraction of Ce in the first 3 h was found to be a quasi-first order reaction.The rate constant increases gradually with the increasing temperature.The extraction products were analyzed by XRD,SEM and EDS,and the results indicated the Bi Ce phase existed in the liquid Bi metal.At 923 K and Licontent of 2.60 wt%in the Bi-Lialloy,Sm was reduced and extracted from molten salt and the process was monitored online,the extraction rate was 97.86%,and the partition coefficient was 157.9.The results showed that the process accorded with the quasi-first order reaction.The characterization results of the extracted products indicated the presence of Bi Sm phase in the liquid Bi metal.Comparison of the reductive extraction of Ce and Sm under the same conditions,the extraction rate and distribution coefficient of Ce were found to be higher than that of Sm.（3）In the two-phase medium of LiF-KF molten salt and liquid metal Zn-Lialloy,Ce（Ⅲ）ion was extracted from the molten salt and the extraction process was monitored online using SWV.The results showed that when the temperature is 923 K and the Licontent of the Zn-Lialloy is3.24 wt%,the extraction rate is larger,which is 98.32%,and the partition coefficient reaches200.53,and the reduction extraction results were compared with those using Bi-Lias reductant.The extraction products were analyzed by XRD,SEM and EDS,and the results showed that there was Ce Zn₁₁ phase in the liquid Zn metal.Sm was reduced and extracted and the process was monitored online at 923 K and Licontent of 3.24 wt%in the Zn-Lialloy.The extraction rate of Sm was 96.67%,and the partition coefficient was 99.36.The extraction products were analyzed by XRD,SEM and EDS,and the results showed that there was Sm₂Zn₁₇ alloy phase in the liquid Zn metal.The kinetic parameters of the extraction process using Zn-Lialloy and Bi-Lialloy as reductant were compared and analyzed.