Extraction Of Sm By Electrochemical Codeposition Of Zn And Sm And Study On The Chlorination Effect Of ZnCl₂ On Sm₂O₃

Electrochemical separation of lanthanide and actinide has attracted increasing attention in the field of molten salt electrolysis.Therefore,acquisition of the basic electrochemical data of lanthanide and actinide in the molten salt is a basic research work of molten salt electrolysis and separation lanthanide and actinide.In this thesis,the electrochemical behavior and extraction of Sm by co–deposition method in LiCl–KCl melts were studied.MOX fuel is oxide fuel.To dissolve MOX fuel into the melt,HCl–Cl₂ mixed gas should be introduced.In this paper,chloride is used as both chlorinating agent and alloying elements to extract the oxide fuel.Therefore,except SmCl₃ as a raw material,extraction of Sm from Sm₂O₃ was also attempted in LiCl–KCl molten salts.Meanwhile,the chlorination effect of ZnCl₂?MgCl₂,Al Cl₃? on Sm₂O₃ was explored,which provides the basic data and effective extraction method for the separation and extraction of lanthanide.In the first section of this thesis,the codeposition mechanism of Zn???and Sm???ions was explored via cyclic voltammtery,square wave voltammtery,chronopotentiometry and open circuit chronopotentiometry in LiCl–KCl–ZnCl₂–SmCl₃ melt.Moreover,the electrochemical behavior of Zn???was first investigated in LiCl–KCl molten salts.The results showed that the reduction of Zn???to Zn?0? was consisted of one step,and the reduction reaction is quasi–reversible.The reduction of Zn???to Zn?0? is controlled by diffusion process.The reduction reaction is considered to be a reversible reaction in lower scanning speed,and the diffusion coefficient of Zn???ions in the melts was 1.28×10^-5cm²·s^-1.When the electrode potential is–1.56,–2.16 and–2.29 V,three kinds of Zn–Sm intermetallic compounds were detected.The electrochemical extraction of samarium was carried out in LiCl–KCl–ZnCl₂ melts at 773 K by potentiostatic electrolysis,and the extraction efficiency was about 99.87%.Zn–Sm bulk alloy was obtained by galvanostatic electrolysis.The microstructure and micro–zone chemical analysis of Zn–Sm alloy were characterized by X–ray diffraction?XRD?and scanning electron microscopy?SEM?with energy dispersive spectrometry?EDS?,respectively.In the second section of this thesis,the electrochemical behavior of Sm₂O₃ and chlorination effect was investigated via cyclic voltammtery,square wave vo1tammtery,chronopotentiometry and open circuit chronopotentiometry in LiCl–KCl–ZnCl₂?MgCl₂,AlCl₃?molten salts.By contrast the solubility of Sm₂O₃ in LiCl–KCl–ZnCl₂?MgCl₂,AlCl₃? molten salts at various temperatures,it is found that the chlorination effects of ZnCl₂ and MgCl₂ on Sm₂O₃ are much weaker than that of AlCl₃ on Sm₂O₃.The solubility of Sm₂O₃ in LiCl–KCl–AlCl₃ molten salts increases with temperture,and reaches the maximum at 923 K.The reacted mixture of ZnCl₂?MgCl₂,AlCl₃? and Sm₂O₃ was characterized by XRD.The results showed that new compounds?SmOCl,SmCl₃ and ZnO,MgO,and Al₂O₃? were appeared,which proved that ZnCl₂,MgCl₂ and Al Cl₃ have chlorination effect on Sm₂O₃.The chlorination effects ZnCl₂ and MgCl₂on Sm₂O₃are weak and incomplete,while the chlorination effect of AlCl₃ is relatively strong.