The Study On Extraction And Separation Of Praseodymium,Gadolinium And Erbium Frommolten Salts On Cu And Mg Electrode

Non-aqueous reprocessing of nuclear fuel is one of the important technologies to ensure continued use of nuclear fuel.The technology is that actinide element and rare-earth element(neutron poison)were separated and extracted by molten salt electrolysis to enable the re-use of nuclear fuel.In this paper,rare earth Pr,Gd and Er were selected as the research objects,and the rare earth elements were extracted and separated on active Mg and Cu electrode by molten salt electrolysis.The electrochemical behavior of rare earth under different electrodes,kinetic process and thermodynamics parameters were studied.The experimental results provided some useful theoretical foundation and experiment basis for the reprocessing of spent nuclear fuel.The electrochemical behavior of Pr(Ⅲ),Gd(Ⅲ)and Er(Ⅲ)ions on Cu electrodes has been investigated by cyclic voltammetry,square wave voltammetry and open circuit potential.For the deposit of Pr(Ⅲ)ion,the reduction of Pr(Ⅲ)ion is a one-step process involving three electrons.On the basis of the open circuit potential curves at different temperatures,the Gibbs free energy,enthalpy change and entropy change of Cu6 Pr were calculated.To extract rare earth element Pr,potentiostatic electrolysis was performed on Cu electrode,and the concentration of Pr(Ⅲ)ion was monitored by ICP-AES at different electrolysis durations.Finally,the extraction efficiency reached 99.8%.For the deposit of Gd(Ⅲ)ion,the reduction of Gd(Ⅲ)ion is also a one-step process involving three electrons.The Gibbs free energy of formation of Cu7 Gd,Cu6Gd,Cu5 Gd,Cu9Gd2,Cu2 Gd and Cu Gd was calculated by open circuit potential.Potentiostatic electrolysis was performed on Cu electrode,and the concentration of Gd(Ⅲ)ion was monitored by ICP-AES at different electrolysis durations Finally,the extraction efficiency reached 99.7%.For the deposit of Er(Ⅲ)ion,three kinds of intermetallic compounds(Cu5Er、Cu2Er and Cu Er)were detected.Potentiostatic electrolysis was performed on Cu electrode,and the extraction efficiency reached 99.6%.Furthermore,the electrochemical behavior of Pr Cl3 and Er Cl3 on Mg electrode was studied.Intermetallic compounds Mg3 Pr and Mg24Er5 were obtained by XRD and EDS.Due to open circuit potential,the potential difference value of two rare earths on Mg electrode is 0.12 V.The separation efficiency was calculated as 95.3%.