Study On The New Process And Mechanism Of Molten Salt Electrolysis Of High Cobalt Cemented Carbide Scrap

Tungsten is a refractory metal with excellent physical and chemical properties.It is widely used in metallurgy,electronic industry,chemical industry,mechanical cutting industry,aerospace industry and nuclear industry.It is an irreplaceable strategic resource.With the continuous reduction of tungsten resources and rising prices,European and American countries have established a strategic reserve mechanism to treat tungsten alloy scrap as a valuable secondary resource and actively carry out recycling and reuse of tungsten.Since cemented carbide is the most important application field of tungsten,and the tungsten content in cemented carbide scrap is as high as 74%?99%,it is an important secondary resource of tungsten.How to achieve the reuse of cemented carbide and obtain high-performance recycled products is a problem worthy of study.Recovery of high cobalt cemented carbide by molten salt electrolysis directly uses cemented carbide scrap as soluble anode.Tungsten and cobalt metals are reduced on the cathode.The process is short,efficient and environmentally friendly.High performance tungsten,cobalt and derived carbon products can be obtained by controlling the process parameters.In NaCl-KCl molten salt system,the dissolution behavior of hard phase tungsten carbide was studied by electrochemical method.Transient analysis methods such as anodic polarization curve method,AC impedance method,cyclic voltammetry,square wave voltammetry and chronoamperometry were used to analyze the reaction process and mechanism of molten salt electrolysis of tungsten carbide.Tungsten in tungsten carbide dissolves into molten salts in the form of ions and remains carbon in the anode.The degree of difficulty in tungsten carbide reaction is mainly determined by the applied anode potential.The average valence of tungsten dissolved into molten salts after potentiostatic electrolysis is + 6 valence,and the oxidation-reduction reaction is a reversible reaction controlled by diffusion.The effects of temperature,potential and current density on the dissolution of tungsten carbide and cathode tungsten powders were studied.The results show that the tungsten powders obtained from cathode has the purest phase and the smallest particle size with an average diameter of about 50 nm when the cell voltage is 2.4 V and the cathode current density is 10 mA/cm2.However,the dissolution efficiency of tungsten carbide is not high during this process,and the residual carbon of the anode will drift to the cathode and the tungsten powder products produce W2C by secondary reaction,which affects the purity of tungsten powder products.Adding a certain proportion of sodium tungstate into molten salt can effectively improve the anodic dissolution efficiency and current efficiency.The results of electrolysis of tungsten carbide with different contents sodium tungstate addition showed that the anodic dissolution efficiency was 4.6 times higher when the content of sodium tungstate was 2.0%,and the anodic current efficiency was increased from 7.5%to 68.9%,the cathodic current efficiency was increased from 3.2%to 67.2%.At the same time,during the electrolysis process,the oxygen released from the anode reacts with the residual carbon of tungsten carbide to form carbon oxide,which can remove carbon.When the content of sodium tungstate is 1.0%,the impurities in tungsten powders are the least.The effect of sodium tungstate on the electrochemical reaction was elucidated by analyzing the electrode reaction,which provided a new way of electron transfer and promoted the electrochemical reaction.In the process of electrode reaction,sodium tungstate mainly reduces the charge transfer resistance of the system,thus reducing the system impedance,making the reaction easier to occur.The dissolution process of high cobalt cemented carbide was predicted by analyzing the morphology and composition of anode profile.The dissolution rules of W and Co in high cobalt cemented carbide under different electrolytic conditions were revealed.At low potential or low current density,only the binder phase of cobalt in WC-15wt%Co dissolves and deposits on the cathode,while tungsten dissolves slightly,but it does not deposit on the cathode because it can not reach the deposition condition.At high potential and high current density,the cobalt in WC-15wt%Co dissolves rapidly in the form of ions in the early stage of electrolysis.The tungsten in WC-15wt%Co begins to dissolve gradually from the outer layer during the electrolysis process,and a large number of pores will be formed in WC-15wt%Co after the dissolution of cobalt and tungsten.The molten salt infiltrates into these pores to form a new reaction interface with the unreacted anode and promotes the continuous reaction.WC-15wt%Co was recovered by two-step electrolysis:the first step was to control the anode potential 0.6 V and electrolysis for 5 hours,and the pure cobalt powder with particle size less than 100 nm was obtained;the second step was to control the electrolysis current 100 mA and continue electrolysis for 5 hours,and the pure tungsten powder with particle size less than 200 nm was obtained;the anode after electrolysis was immersed in deionized water for 24 hours.The porous carbon with a specific surface area of 1093.68 m2/g and a porosity of 50.35%.Simulation and analysis of the process of remitting hard alloy by molten salt electrolysis,visually reproduce the reaction process,and obtain visualization results such as anode dissolution state,material concentration change,electric field distribution,etc.that cannot be directly observed in the experiment;The data analysis improves the accuracy of the experimental conditions,and the fundamental reason that affects the dissolution speed of different positions of the anode is that the local current density of the anode is different due to the uneven electric field;the anode has the best anode dissolution between 10 and 20 mm;The experimental conditions were developed to predict the theoretical dissolution time of cemented carbide anodes with different cobalt contents.The effects of electric field uniformity and bath depth on anode dissolution were analyzed.The conclusions of regular data were obtained and the experimental amount was reduced.