Electrochemical Behavior Of Tb(?) On Diffirent Electrodes And Preparation Of Tb-M(M=Bi,Cu,Al) Alloys In Melts System

Spent fuel reprocessing is the key to the sustainable development of nuclear energy production.Molten salt electrolysis is the main step in dry reprocessing process.Terbium is a typical fission product and difficult to be separated from actinides.Therefore,the electrochemical behaviors of Tb(?)were studied on different electrodes(liquid Bi electrode,Bi film electrode and solid,state Cu electrode)in LiCl-KCl molten salts.The thermodynamic properties of Tb-M(M=Bi,Cu)intermetallic compounds were estimated and Tb-M(M=Bi,Cu)alloys were also formed.Meanwhile,the effect of AIF3 on the dissolution of Tb4O7 was investigated and the Tb-Al alloys were prepared by direct electrolysis in NaCl-KCl-AlF3-Tb4O7 molten salts.The detailed were as follows:1.The electrochemical reactions of Tb(?)were investigated on liquid Bi electrode and Bi film electrode in LiCl-KCl eutectic by a series of electrochemical techniques.On the both electrodes,the redox potentials of Tb(?)/Tb couple were observed at less negative potential values than that on W electrode,which indicated underpotential deposition of Tb(?)occurring on the both Bi electrodes.On Bi pool electrode,the result of cyclic voltammetry suggested that the electrochemical reaction of Tb(?)to Tbin liquid Bi was a quasi-reversible and diffusion-controlled process.The activities and partial molar Gibbs energies of Tb in Tb-Bi alloys and the standard Gibbs free energies,enthalpies and entropies of formation for different Tb-Bi intermetallic compounds were estimated by electromotive force(emf)measurement in the temperature range from 673 to 873 K.Moreover,the electrochemical preparation of Tb-Bi alloys was performed by galvanostatic electrolysis at 0.02 A and 0.05 A,respectively,in LiCl-KCl-TbCl3 melts on liquid Bi electrode.The Tb-Bi alloys were characterized by X-ray diffraction(XRD)and scanning electronic microscopy(SEM).XRD showed that Tb-Bi alloys were comprised of TbBi phase.2.The electrochemical behaviors of Tb(?)were studied on Cu electrode in LiCl-KCl melts by a variety of electrochemical techniques.From the results of cyclic voltammetry and square wave voltammetry show that three reduction signals corresponded to the formation of Cu-Tb intermetallic compounds.Moreover,the thermodynamic properties,such as activities of Tb in Tb-Bi alloys and the standard Gibbs free energies of formation for different Cu-Tb intermetallic compounds were evaluated by emf measurement.And the enthalpies and entropies of formation for each Cu-Tb intermetallic compound were also calculated according to the change of standard Gibbs free energies with temperatures.The electrochemical preparation of Cu-Tb alloys was performed by galvanostatic electrolysis at 0.097 A in LiCl-KCl-TbCl3 melts on Cu electrode.The Cu-Tb alloys were characterized by XRD and SEM-EDS.The results showed that Cu-Tb alloys were comprised of CuTb and Cu2Tb phases.3.The effect of AIF3 on the dissolution of Tb4O7 was firstly studied by analyzing the supernatant and bottom salts in NaCl-KCl-AlF3-Tb4O7 system.XRD results revealed that Tb4O7 was fluorinated by AIF3 to form TbF3.The electrochemical behavior of the NaCl-KCl-AlF3-Tb4O7 system was investigated on Mo electrode.The results of cyclic voltammetry,square wave voltammetry,chronopotentiometry and open circuit chronopotentiometry indicated that the under-potential deposition of Tb(?)occurred on pre-deposited Al.The formation of Al-Tb alloys was carried out by galvanostatic electrolysis under different conditions.These samples were characterized by XRD and SEM-EDS.The Al-Tb alloy obtained by galvanostatic electrolysis at 2.5 A consisted of Al and Al3Tb phases.