Study On Electrochemical Extraction And Alloy Formation Mechanism Of Rare Earth Element Gd

With the extensive application of nuclear energy,spent fuel reprocessing has become one of the key issues constraining the sustainable development of nuclear energy.Molten salts,such as fused chlorides and fluorides which have attributes of high radiation and thermal resistance,low neutron cross-section and high solubility of fuel components,have been widely investigated for deposition of metals,to reduce the amount and long-term hazards of nuclear,especially for extracting the lanthanides elements.In this paper,the electrochemical behavior and thermodynamic properties of GdCl3 were studied in LiCl–KCl melt on both Al and Mg electrodes.To find an effective method for separation of lanthanides,the cathode depolarization values and the theoretical extraction efficiency of Gd on both Mg and Al electrodes were assessed.Extraction of Gd was carried on active electrodes to calculate the practical extraction efficiency.In the first part of this paper,the electrochemical behavior and thermodynamic properties of GdCl₃ were studied by cyclic voltammetry,square wave voltammetry and open circuit chronopotentiometry in LiCl–KCl melt on both Mo and Al electrodes.The equilibrium potentials and standard apparent potentials of Gd?III?/Gd?0?system were determined in different temperature ranges.Moreover,the activity coefficients of GdCl₃ were calculated at different temperatures.Depolarization values were calculated by steady state polarization test,and the theoretical extraction efficiency was obtained.Potentiostatic electrolysis was conducted to extract gadolinium from LiCl–KCl–GdCl₃ melt on Al electrodes.The extraction efficiency is about 94.1%.Al₃Gd phase was identified by X-ray diffraction?XRD?in the deposit.In the second part of this paper,the electrochemical co-reduction process of Gd?III?and Al?III?and the preparation of Al–Li–Gd alloys were studied in LiCl–KCl–AlCl₃–GdCl₃molten salt at 773 K.The results of cyclic voltammograms,square wave voltammograms and chronopotentiogram indicated that the underpotential deposition?UPD?of Gd?III?on pre-deposited Al forms two Al–Gd intermetallic compounds at about–1.39 and–1.46 V.Al₂Gd and Al₂Gd₃ phases were identified by X-ray diffraction?XRD?in the deposits obtained via galvanostatic electrolysis.Al–Gd alloys with different phases can be obtained by adjusting the concentration of AlCl₃.In the third part of this paper,the electrochemical behavior and thermodynamic properties of GdCl₃ were studied in LiCl–KCl melt on Mg electrode.Open circuit chronopotentiograms were investigated to determine the equilibrium potentials and standard apparent potentials of Gd?III?/Gd?0?system.Depolarization values were obtained by steady state polarization test,and the theoretical extraction efficiency was calculated.Potentiostatic electrolysis was conducted to extract gadolinium from LiCl–KCl–Gd Cl₃ melt on Mg electrodes,the extraction efficiency is about 97.9%.The electrochemical extraction of rare earth element Gd was realized by galvanostatic electrolysis.