Study On Electrochemical Reduction Mechanism Of Vanadium Ions In LiCl-KCl Molten Salt System

Metal vanadium has a wide range of applications in alloys,batteries,chemical industry,aerospace and other fields due to its excellent physical and chemical properties.At present,the preparation process of metal vanadium has problems such as long process,high energy consumption and low product purity,which result in high cost of metal vanadium and limit its application in various fields.Among the various extraction technologies of metal vanadium,molten salt electrolysis is a process with great development potential and application prospects.In the extraction of vanadium by molten salt electrolysis,due to the various valence states of vanadium ions and the coordination behavior of electrolyte ions and vanadium ions,the existence of vanadium ions is complicated,which affects the electrolysis products and current efficiency.In addition,the electrode material is also a hot spot in the electrolysis process.Using liquid cathode to replace the traditional inert cathode is an efficient method to promote the cathode deposition of vanadium ions.This paper focuses on the key scientific issues involving current efficiency and product morphology in molten salt electrolysis extraction of metallic vanadium.The redox mechanism of vanadium ions on solid and liquid metal electrodes in LiCl-KCl molten salt system is studied,and the relationship between electrolyte ions and vanadium ions is explored,and its influence is researched through various electrochemical analysis methods.It provides theoretical support for the short-flow and low-cost molten salt electrolytic preparation of vanadium metal.The specific work of this paper includes the following three parts:Firstly,the electrode reduction process of V（Ⅲ）in LiCl-KCl molten salt on tungsten electrode is studied by transient electrochemical analysis techniques.It is found that the reduction step of vanadium ions in LiCl-KCl molten salt at 450℃is a reversible three steps process:V（Ⅲ）→V（II）→V and V（Ⅲ）→V.Meanwhile,the reduction processes are all controlled by diffusion,and the diffusion coefficients are obtained.In addition,through the fitting of data,the nucleation models of vanadium ions with different valence states on the electrode surface are analyzed.Secondly,the effect of electrode materials on the mechanism of vanadium ions reduction is investigated.The results show that the reduction peak of vanadium ions can be observed within the potential window of the liquid zinc electrode.The reduction peak of V（Ⅲ）→V cannot be observed because it is too close to the alkali metal precipitation potential due to the depolarization of liquid electrodes,which is different from the results of solid state electrodes.The deposition of metallic vanadium on the liquid zinc electrode is achieved by potentiostatic electrolysis,and then the distribution of elements in the product is analyzed.The vanadium and zinc are separated by vacuum distillation to obtain metal vanadium.Thirdly,the effect of fluoride ions on the electrode reduction process of V（Ⅲ）is investigated by adjusting the electrolyte composition.The research shows that V（Ⅲ）forms a regular octahedral coordination compound VCl_iF_6-i^3- with fluoride ions in the melt.The result of electrochemical analysis shows that the introduction of fluoride ions into the molten salt would lead to a new reduction step VCl_iF_6-i^3-→V²⁺,and the mass transfer process is also affected.At the same time,with the increase of the fluoride ions concentration in the molten salt,the particle size of the deposited products would decrease.The significance of this paper is to reveal the influence of electrolyte composition and electrode materials on the electrochemical reduction mechanism of vanadium ions during vanadium electrolytic deposition,and to provide theoretical basis and data support for exploring the common basic mechanism of the interaction between rare metal ions with various valence states and electrolytes ions.