Study On The Electrochemical Behavior Of Niobium Ions In Molten Salt

Metallic niobium has characteristics of small thermal neutron capture area and high melting point,and is a vital metal material in the development of modern science and technology.At present,the production process of metallic niobium has problems such as complicated process,large energy consumption,environmental pollution and difficult to control product quality.These deficiencies also lead to the high price of metallic niobium,which limits its applications in various fields.Based on the above problems,in the new extraction technology of metal niobium,molten salt electrolytic process has become the focus of attention.During the electrolysis process,due to the interaction between anions/cations in the electrolyte and niobium ions,the existence states of niobium ions is different,which in turn affects the electrolytic products and efficiency.This paper focused on the molten salt electrolytic niobium technology,mainly studied the interaction between electrolyte anion and niobium ion,and explored its influence by means of electrochemical and chemical analysis,so as to provide theoretical support for the short process and low cost electrolytic preparation of niobium metal.The work of this paper mainly includes the following three parts:Firstly,the electrochemical behaviors of niobium ions in KCl-Na Cl molten salt was systematically studied.Secondly,the effect of fluoride ions on the reduction process of niobium ions in KCl-Na Cl molten salt was investigated.Thirdly,the electrochemical behavior of niobium ions in different concentrations of fluoride ions in Al Cl₃-Na Cl molten salts was investigated.The study found that,firstly,the electrode reduction process of niobium ions in KCl-Na Cl molten salt at 750?was a quasi-reversible three-step reaction Nb?V??Nb?III??Nb?I??Nb.The cyclic voltammetry,square wave voltammetry and chronopotentiometry were used to prove that the electrode reduction process of Nb?V?was controlled by diffusion,and the diffusion coefficient was calculated.In addition,the nucleation mode of niobium ions was determined by the chronoamperometry as transient nucleation.Secondly,Na F was added to the main salt of KCl-Na Cl by adding salt in situ,and the change of electrochemical reduction of niobium ion by fluoride ion was tested.The amount of Na F added was based on the molar concentration ratio of different fluoride ions to niobium ions,that is,[F^-]/[Nbⁿ⁺]was equal to 1.0,2.0,3.0,5.0,and10.0,respectively.Studies have shown that the electrode reduction process of Nb?V?ions is shortened from Nb?V??Nb?III??Nb?I??Nb to Nb?V??Nb?III??Nb when[F^-]/[Nbⁿ⁺]was equal to 1.0.With the increase of fluoride ion concentration,when[F^-]/[Nbⁿ⁺]is greater than or equal to 5.0,the concentration of niobium ions with high-valence increased,and the electrode reduction process of Nb?V?ions was transformed into Nb?V??Nb?IV??Nb.In addition,when[F^-]/[Nbⁿ⁺]was less than or equal to 5.0,with the addition of Na F in the molten salt,the reduction reaction potential of the niobium ion electrode moved forward.Thirdly,in the low-temperature molten salt of Al Cl₃-Na Cl,as the fluoride ion concentration increased,the reduction step for niobium ions changed.When it free of Na F in the molten salt,the electrode reduction process of Nb?V?ions was:Nb?V??Nb?II??Nb?I??Nb.When[F^-]/[Nbⁿ⁺]was equal to 1.0,the electrode reduction process was transformed into a two-step reaction of Nb?V??Nb?III??Nb.When[F^-]/[Nbⁿ⁺]was equal to 2.0,the electrode reduction process was Nb?V??Nb?IV??Nb?II??Nb.Moreover,the electrode reduction process is shortened to Nb?V??Nb?III??Nb when[F^-]/[Nbⁿ⁺]was greater than or equal to 3.0.In addition was also found that,the reduction potentials moved forward as the fluoride ion concentration increased.The significance of this work is to find a way to design electrolytes based on performance requirements in rare metal molten salt electrolysis processes to accelerate the selection and efficient determination of electrolyte components;to lay the foundation for the genetic mechanism of the interaction of rare metal ions and electrolytes.It provided an important support for the further construction of the database of metal ion and electrolyte interactions.