Study On Deposition Potential Law Of The Alloys Formed By Lanthanides And Tin,Lead,Cobalt And Aluminum In Molten Salt System

With the wide application of nuclear energy,managing nuclear fuel in a safe,economic and non?proliferation manner is one of the most important issues related to the sustainable development of nuclear energy.Since most actinides are radioactive,it is difficult to study the chemical properties of actinides.Besides,extraction of actinides from spent fuel is even more difficult at present,because of the unknown deposition potentials of many actinides.However,to theoretically explore the depolarization and underpotential deposition mechanism and law of lanthanide alloys,the precipitation potential,electrochemical process and mechanism and the of lanthanides electrodeposition on tin,lead,cobalt,aluminum cathodes were studied in this paper,depending on the chemical similarities between lanthanides and actinides and the known deposition potentials of lanthanides.According to the electrochemical behavior at different temperatures and the kinetics and thermodynamics of the electrolysis process.The electrochemical process of co-deposition of alloy elements was characterized by various electrochemical methods,and the relevant electrochemical parameters were obtained.The microstructure of the alloy was investigated by XRD and SEM.It is found that the absolute value of deposition potential of elements with larger radius is obviously larger than that of elements with smaller radius,indicating the metal radius affects the deposition potential of alloy formation.Using the electrolytic deposition potential of lanthanides as the function and the atomic radius as variables,the relationship among the deposition potential,the atomic radius of lanthanides and the atomic radius of cathode was simulated.The mathematical model of the functional relationship among the deposition potential of electrolytic lanthanides deposited on the cathode,lanthanides radius,and cathode metal radius was derived,that is,E_RE-alloy=f(r₁,r₂).The deposition potential law of lanthanides on Sn,Pb,Co,Al cathodes is summarized.The mathematical function relationship between the deposition potential and lanthanide radius is further deduced to obtain the universal mathematical equation.According to the known radius of cathode metal and lanthanide,the potential value of alloy electrolysis could be predicted,and the accuracy and universality of the equation could be verified by electrochemical tests.The mathematical equation between the deposition potentials and the radius of the co-deposition of Sn and lanthanides is Y=9.11+13.85X(R²=0.998).According to this equation,the deposition potentials of Sn-Ce,Sn-Nd,Sn-Yb and Sn-Lu alloy compounds are predicted,with the error less than 0.33%compared with the experimental values.The potential predicted by the equation is used to electrolyze the Sn-Ce intermetallic compound,which is Ce Sn₃ alloy confirmed by XRD test.Based on the establishment of this mathematical equation,it is further applied to extract Nd element from a variety of elements.Potentiostatic deposition was performed based on the potential predicted by the mathematical equation,and the current changes after different times of electrolysis were recorded by square wave voltammogram.After 40 h of electrolysis,the calculated electrochemical extraction efficiency was 97.6%.In addition,XRD results show that the alloy is mainly composed of Nd Sn₃ intermetallic compounds.The electrochemical behavior of the co-reduction of Pb with La,Ce,Pr,Gd and Dy in the KCl-LiCl molten salt system is studied.Determine the deposition potential for forming Pb-La,Pb-Ce,Pb-Pr,Pb-Gd and Pb-Dy alloy compounds are determined.The deposition potential was used as a reference for alloy electrolysis to obtain La₄Pb₅,Ce_1.88Pb_2.12,Pb₃Pr and Dy_2.41Pb_1.59alloys,respectively.According to the established mathematical equation,the relationship between the atomic radius and the deposition potential is summarized,and the fitting equation is Y=45.15+66.12X(R²=0.998)after fitting the curve.The mathematical equations are not affected by temperature at 873,923,973 and 1023 K,respectively.According to the mathematical equation,the precipitation potentials of Pb-Yb and Pb-Lu alloy compounds are predicted,which are almost the same as the experimental values.The mathematical equation between the deposition potential and the radius of the co-deposition of Co and different lanthanides is Y=0.1402X-0.6457(R²=0.992).According to the measured deposition potential,the Co-Ce,Co-Pr,Co-Gd,Co-Dy and Co-Er alloy compounds are subjected to constant potential electrolysis.XRD results showe that the electrolyzed samples were Co₂Gd,Ce₅Co₁₉,Co₂Pr,Co₅Dy,Co₂Dy and Co₂Er alloys,respectively.In addition,the precipitation potential and atomic radius of the alloy compound formed by lanthanides and Cu and Ni are also conformed to the established mathematical equations.The linear equations are Y=13.044X+8.609(R²=0.994)and Y=15.817X+10.407(R²=0.996),respectively.In the study of the electrochemical behavior of Ni and Ce co-deposition,a certain correlation between the binary alloy phase diagram and deposition potential was found.By modelling the fitting relationship between the deposition potential and the content of lanthanides(C=e^(E-a)/b)and fitting through the determined deposition potential and atomic percentage,the equation after fitting is C=e^(E+2.016)/^(-0.403),R²=0.998.The un-recorded Ce₄Ni,Ce₃Ni,Ce₇Ni₃,Ce₃Ni₂,Ce₂Ni₃,Ce₃Ni₇ alloys in the phase diagram are predicted by this fitting equation.Subsequently,the relationship between the deposition potential and the atomic percentage of the alloy compounds formed by Ni and others lanthanides(La,Pr,Nd,and Gd)was further studied,which all conformed to the mathematical model of C=e^(E-a)/b.A three-dimensional phase diagrams of atom percentage,deposition potential and alloy composition is established by this equation,which can predict not only the phase diagrams of unknown alloys,but also the deposition potentials of binary alloys with non-integer ratio.The law discovered in this research is beneficial for electrolyzing out the alloy phases nonexistent in a phase diagram and deeply understanding the formation conditions of binary alloy phases.The proposed method and concept are of guiding significance to address the theoretical conundrums in phase diagram constitute.The mathematical equation between the deposition potential and radius of lanthanides and Al co-deposition is Y=26.17X+17.59,R²=0.992.According to the fitted mathematical equation,the precipitation potentials of Al-U,Al-Pu,Al-Th and Al-Np intermetallic compounds are predicted through the radius of the actinides.Compared with the results of previous reports,it has smaller error,indicating that the electrochemistry of lanthanides and actinides on active cathodes could be reasonably predicted by the fitted mathematical equation.This provides a primary model and theoretical basis for the behavior of lanthanides in electrolysis-based thermal processing.And the electrolytic deposition potential of the formed alloy at a certain temperature can be inferred from the radii of any two elements.It shows that the deposition potential of electrolytic precipitation can be deduced from the radius of any two elements at a certain temperature.The discovery of this equation will provide a concise and reliable criterion for the study of the electrolytic preparation of alloys in the periodic table.