Electrochemical Behavior Of Rare Earth(Eu?Ce)in Fluoride Fused Salts And Electrochemical Extraction Of Eu

Dry reprocessing of spent fuel is an important step to realize the safe and sustainabledevelopment of nuclear energy.The main purpose of molten salt electrolysis is to separate actinides and fission products so as to realize the recovery and utilization of nuclear fuel.Among lanthanide elements,Eu is one of the fission products that are difficult to separate from other lanthanide elements,while Ce is the most abundant lanthanide element in the crust,therefore,the research of LiF-CaF₂molten salt system between the two different electrode(inert Mo,Al membrane and membrane Bi)on the electrochemical behavior,and through the liquid cathode method for extraction of rare earth elements is significant.The main research work is as follows:1.In the LiF-CaF₂molten salt system,the process of Eu(?)reduction to transfer oneelectron in the first step in the electrochemical window of inert Mo electrode was studied.The electrochemical behavior of Al(?)was studied on an inert Mo electrode,indicating that the reduction process of Al(?)is a three-step electron transfer.The Eu(?)/Eu(II)process is a quasi reversible process,and the velocity control steps are diffusion control,and the average diffusion coefficient is calculated.The electrochemical behavior of Eu(?)on Al film electrode was studied to form the Al-Eu intermetallic compound,which was basically consistent with the REDOX signal obtained by the square wave curves of different frequencies.The electrolytic extraction of rare earth ions Eu(?)by liquid Al electrode in LiF-CaF₂molten salt system was studied.The effects of different experimental conditions on the formation products and alloys were investigated.The samples were characterized by XRD and SEM-EDS.Firstly,under the condition of changing the electrolysis time,two intermetallic compounds,Al₂Eu and Al₄Eu,appeared in the product when the molten salt was electrolyzed for 6 h,and Al Li appeared when the electrolysis time was 8 h.A suitable electrolysis time of 6 h is obtained.And when the electrolysis time is 6 h,the elemental analysis shows that there may be an Al₄Eu or the coexistence of Al₂Eu and matrix Al.Then,under the condition of changing the electrolytic current,when the electrolytic current density is 0.09 A,the product is Al₄Eu,while when the current density is 0.11 A,only Al₂Eu exists,and when the current density is 0.12 A,Al Li appears.2.The electrochemical behavior of Bi(?)on inert Mo electrode and Eu(?)on Bi membrane electrode was studied in LiF-CaF₂molten salt system.The rare earth Eu(?)was extracted electrolytically through liquid Bi electrodes.Three Bi-Eu intermetallic compounds,Eu Bi₂,Eu₅Bi₃and Eu₁₁Bi₁₀,were obtained by studying the electrochemical behaviors of Eu(?)on Bi film electrode in LiF-CaF₂-Eu F₃(0.56 mol/L)-Bi Cl₃(0.54 mol/L)molten salt system.The square wave voltammetry was used to study the extraction process of the molten salt system on the liquid Bi electrode.The peak current density decreased with the increase of time.When the extraction time reached 2.5 h,the peak current density did not change with the increase of time.Eu(?)in molten salt was extracted by liquid Bi electrode electrolysis,and Bi-Eu intermetallic compounds were not obtained in the products with the electrolysis time of 4 h or 8 h.3.1123K in LiF-CaF₂studied the rare earth ions in molten salt system Ce(?)in inert Moelectrode on the electrochemistry properties,through different frequency square wave curve calculation got Ce(?)reduction process generated Ce for step three electron transfer,and Ce(?)/Ce(0)for the process of the reversible process.Ce is studied through different speed cycle volt-ampere Ce(?)/Ce(0)rate control steps for the diffusion control of the process,and calculated the Ce(?)ions under 1123K in LiF-CaF₂eutectic molten salt system diffusion coefficient of 1.77 x 10^-5cm²s^-1.Rare earth ion Ce(?)was studied on the Al film electrode electrochemical behavior,through different termination potential cyclic voltammetric curves obtained three kinds of Al-Ce intermetallic compound.