Electrochemical Reduction And Molten Salt/Liquid Metal Separation Extraction Praseodymium From Chloride Molten Salts

The nuclear power, having safety, cleanability and high efficiency, has been paid more attention. But some radioactive products of its spent fuel have huge potential hazards to biological and environment on the earth. Meanwhile, most of materials in the spent fuel can be recycled, such as lanthanides. So it is of great importance to manage spent fuel correctly. Thus,the two method of spent fuel dry processing methods, i.e. molten salt electrolysis and molten salt/liquid metal extraction were used to separate praseodymium from chloride molten salts in this thesis as follow:(1) The electrolysis in the molten salts: The electrochemical behaviour of praseodymium(?)was studied in the eutectic LiCl-KCI at different temperatures on a Ni electrode. Transient electrochemical techniques were used in order to study the reaction mechanism and the transport parameters of electroactive species on a Ni electrode. It has been found that Pr(?) ions were reduced to metal praseodymium in one step at -2.15V (vs Ag+/Ag). Four cathodic peaks were observed at -2.02V, -1.8V, -1.45V, -1.05V, respectively. The results showed that the Pr(?)/Pr(0)electrochemical system is reversible. Mass transport towards the electrode is a simple diffusion controlled process, and the diffusion coefficient of Pr(?) ions has also been calculated. The Pr-Ni alloys were prepared by potentiostatic electrolysis and characterized by XRD, SEM-EDS.The results showed that the intermetallic compounds, PrNi2, PrNi3, Pr2Ni7 and PrNis were produced, respectively. The alloying thermal effect of Pr deposited on a Ni electrode to form PrNi2 was calculated about -83.9kJ mol-1, and temperature electrode surface electrodes can reach 1903.9 K in instantaneous.(2) Molten salts/liquid metal extraction separation: the first the Al-Li alloys were prepared by electrolysis on a liquid Al electrode. Then the extraction was conducted in LiCl-KCI eutectic salts/liquid Al-Li alloys. The effects of extraction temperature, aluminum content, electrolysis time, stirring time on distribution coefficients were studied and found that increasing temperature,the amount of reductant and rare earth chloride, lengthening stirring time can improve the distribution coefficients. The extraction in multicomponent rare earth chlorides were explored and found that the distribution coefficient of light rare earth elements is higher than the one of heavy rare earth elements. Meanwhile, the rare earth element Sm with valence change was extracted from LiCl-KCl salts/liquid Al-Li alloys. The results showed that the distncoefficient of Sm is higher than that of Pr, the separation factor of Sm can reach 23.30.