Electrodeposition Of Rare Earth Metal Neodymium In Solvated Ionic Liquid At Room Temperature

Metal neodymium is an important rare earth element and is mainly used to prepare neodymium iron boron permanent magnet materials.Industrially,the production of metal neodymium uses molten salt electrolysis,which has the disadvantages of high temperature and high energy consumption.As a low-temperature green solvent,ionic liquid can be well applied to room temperature electrodeposition of active metals.In this thesis,the electrochemical deposition process and mechanism of Nd in ionic liquids are studied based on the purpose of preparing rare earth neodymium by low temperature electrolysis.The electrolyte used in the electrochemical deposition process and mechanism research is a new lithium-containing solvated ionic liquid composed of 1,3-dimethyl-2-imidazolinone(DMI)and 0.5 mo l/L lithium nitrate.First,the physical and chemical properties of the system at room temperature were studied using the Archimedes method,capillary method,and fixed conductance cell constant method.Second,neodymium triflate Nd(CF3SO3)3 was used as the raw material.Electrochemical methods such as chronoamperometry and potentiostatic method were used to analyze the electrochemical reduction mechanism and electrodeposition behavior of Nd(Ⅲ)in this electrolyte system.According to 7LiNMR analysis,the DMI/LiNO3 binary lithium-co1taining solvated ionic liquid electrolyte system is composed of a cation[Li(DMI)n]+ and an anion NO3-.At room temperature,the conductivity of this system is in the range of 1～6 mS·cm-1,and the relationship between conductivity and temperature is in accordance with the VTF equation and the Arrhenius equation:lnσ=1.98-2476.67/T.The viscosity is in the range of 14～70 mPa·s.and the relationship between viscosity and temperature is consistent with the VTF equation and the Arrhenius equation:ln η=7.69+1727.7/T;The density is in the range of 1.08～1.14 g·cm-3,and the relationship between density and temperature is linear:ρ=-7.6428×10-4T+1.3612.The electrochemical window of the system is about 4.5 V(vs.Pt).Cyclic voltammetry and chronoamperometry were used to study the electrochemical reduction behavior and mechanism of Nd(Ⅲ)in DMI-LiNO3-Nd(CF3SO3)3 electrolyte system.Cyclic voltammetry studies show that the electrochemical reduction of the cathode is an irreversible reaction to obtain three electrons in one step.The process is controlled by diffusion.The reduction mechanism is Nd(Ⅲ)+3e-=Nd,where the average mass transfer coefficient is 0.087 and the diffusion coefficient is 4.16×10-12 cm2/s.The chro no ampero metry study shows that the deposition process of the cathode is controlled by diffusion,and its diffusion coefficient is 4.05×10-12 cm2/s,which is close to the cyclic voltammetry result,and the nucleation process of metal neodymium on the electrode conforms to three-dimensional instantaneous nucleation growth mechanism.Electroplating of Nd(Ⅲ)in DMI-LiNO3-Nd(CF3SO3)3 electrolyte system was performed by potentiostatic electrolysis,and the obtained coatings were characterized.XRD and SEM-EDS analysis showed that the coating contained elemental neodymium,metal neodymium mainly exists in the form of Nd and Al-Nd.XPS analysis shows that neodymium exists in the form of simple substance.During the research,the effects of deposition potential,deposition time and deposition temperature on the morphology of the coating were investigated,and the better electrodeposition process conditions were obtained:deposition potential-3.2 V(vs.Pt),deposition time greater than 2 h,and deposition temperature at around 323 K.