Electrorefining Of Al-RE(La,Gd) Alloys In LiCl-KCl Melts

Nuclear energy is a clean,safe and efficient energy source,and spent fuel reprocessing is a key step in ensuring the sustainable development of nuclear energy.Molten salt electrorefining is considered to be one of the most promising spent fuel dry reprocessing processes.Therefore,this work studies the electrorefining of Al-RE(La,Gd)alloys in LiCl-KCl melts,including the electrochemical behavior of rare earth elements on different electrodes,the anodic dissolution of Al-RE alloys,and electrorefining of Al-RE(La,Gd)alloys.The detailed is as follows:1.The electrochemical behaviors of La(III)and Gd(III)on an inert W electrode were investigated by a series of electrochemical methods in LiCl-KCl melts.The reduction mechanisms of La(III)and Gd(III)on the inert electrode were found to be one-step process with three electrons exchanged.Subsequently,the electrochemical behaviors of La(III)and Gd(III)on a reactive Al electrode were studied by cyclic voltammetry and square wave voltammetry.The electrochemical signals of Al-La and Al-Gd were observed at-1.65 V and-1.50 V,respectively.The deposition potentials of La(III)and Gd(III)shift towards positive,which indicated that that underpotential deposition 0f La(III)and Gd(III)occur on Al electrode.2.The anodic dissolution of Al-RE(La,Gd)alloys in LiCl-KCl melts were studied by cyclic voltammetry,anodic stripping voltammetry and polarization curve method at 773 K.With the two alloys as the working electrodes,the dissolution potential and dissolution orders of the different phases in the alloys were determined by cyclic voltammetry.The results showed that the phase with more negative potential in the alloy dissolves firstly.The anodic dissolution process of Al-RE(La,Gd)alloy in LiCl-KCl molten salt was studied by cyclic voltammetry,anodic stripping voltammetry and polarization curve method at 773 K.The dissolution potential and dissolution order of the different phases in the alloy were determined by cyclic voltammetry.The results showed that phases with negative potentials in the alloys would dissolve firstly.The corrosion potential of Al-La alloy was determined by Tafel curve.The exchange current density of Al11La3 dissolving and the diffusion coefficient of La in Al-La alloy were calculated.The anodic dissolution process of Al-La alloy was also monitored by square wave voltammetry which proved that the dissolution orders of different phases in the alloy was found to be La>Al-La>Al.Finally,XRD and SEM-EDS were applied to characterize the anodic dissolved products.The results showed that the anodic dissolution of Al-RE occurred on the surface of the alloys and the intermetallic compounds were completely dissolved.3.The electrolytic refining processes of two Al-RE(La,Gd)alloys in LiCl-KCl melts were performed under different conditions,such as potentiostatic and galvanostatic electrorefining.The current efficiency of the electrorefining process was calculated according to the mass change before and after the anodic dissolution and cathodic deposition.The results indicated that the anodic current efficiency was low by potentiostaic electrolysis and the cathodic product could not be obtained.However,the cathodic current efficiency could reach 71% by galvanostatic electrolysis when the applied current was between 0.1 A and 0.3 A.Finally,the anodic residues after electrorefining of Al-RE(La,Gd)alloys were analyzed by SEM-EDS.