Study On The Mechanism Of Carbon Pollution And The Preparation Of Carbon Materials In Deoxidation Of Titanium Dioxide By Electrochemical Process

In the past 20 years,since FFC Cambridge process was proposed,the research on the preparation of titanium by electrochemical process has been very active,and some achievements have been made.However,due to the strong combination energy between titanium and oxygen,the problem of low current efficiency in the preparation of titanium by direct electrolytic deoxidization of titanium oxide has not been effectively solved.In addition to the high combination energy of titanium and oxygen,there are many factors that directly affect the current efficiency of the electrolysis process.Therefore,while studying how to solve the problem of high titanium-oxygen binding energy,understanding other influencing factors is also the key to further breakthroughs in the molten salt electrolysis process.Here,in this paper,the carbon contamination mechanism in the process of FFC,recycling of carbon materials and effective ways to solve the problem of carbon contamination were studied,aiming at the problems caused by the use of graphite anode in FFC process such as excessive carbon content of metal products,molten salt pollution and short circuit of electrolytic cells,etc.,which lead to lower process current efficiency.The main conclusions of the paper are as follows:(1)During the preparation of titanium metal by electrolysis of TiO₂ in molten CaCl₂,when graphite material is used as the anode,a certain amount of CO₂ is generated in the anode and dissolved in the molten salt,and reacts with O^2-in the molten salt to form CO₃^2-ions.The decomposition voltage of CO₃^2-ion is lower than electrolytic voltage of TiO₂.Therefore,CO₃^2-ion will be electrolyzed to produce carbon materials at the cathode,including graphite,graphene,carbon nanotubes,carbon fiber and other small carbon products with large specific surface area,and the carbon deposition process has been accompanied by the titanium oxide electrolytic deoxidation process until the end of deoxidation.That is,when graphite material is used as the anode in the process of preparing metal titanium by the FFC process,part of the anode carbon will participate in the side reaction of the TiO₂ deoxidation process,and as the time increases,the greater the consumption.Finally,the consumed carbon will eventually be transferred to the cathode to precipitate or form CO₃^2-ions in molten salt,which will cause the pollution of cathode products(forming Ti C)and molten salt,current short circuit,reduce current efficiency of the electrolysis process.(2)It is proved that CaCl₂ based molten salt electrolysis system can realize high-value utilization of CO₂ into carbon materials.It is found that 8RuO₂·2TiO₂ inert anode has better stability and corrosion resistance than other anodes materials.When Ni,Co and Fe are used as cathodes respectively,it is found that metal cathodes can promote the deposition of carbon on the electrode surface during electrolysis,but the effect is not obvious.The effects of metal oxides such as Fe₂O₃,Ni O and Co O on the preparation of the high valuable carbon in high temperature molten salt with graphite as cathode were studied.The results show that the graphitization degree of the carbon material is the highest and have the most significant catalytic effect on carbon deposition when Fe O is added into the molten salt.In the molten salt of CaCl₂-NaCl-CaO-Li₂SO₄,sulfur doped graphite flakes were successfully prepared.Li⁺can improve the graphitization degree of the carbon materials.Sulfur doping is affected by temperature.At different temperatures,the morphology of the products are different.With the increase of temperature,the product morphology gradually changes in the order of rod,sheet,particle and tube.The rod structure is composed of finer carbon rod or ultra-thin graphite sheet.The carbon ball is composed of smaller carbon particles.The sheet structure is composed of ultra-thin graphite sheets.(3)Based on the basic research of FFC process carbon pollution and carbon high-value utilization,the idea of using composite electrode in the same cell to solve C pollution and realize carbon utilization was proposed.One pair of electrodes(graphite anode and titanium oxide cathode)is used to deoxidize of titanium oxide,and the other pair of electrodes(inert anode and graphite cathode)is used for the electrochemical reduction of carbonate ions.According to the theoretical analysis of the influence of the compound electric field on the movement track of CO₃^2-ion and O^2-ion in molten salt when two pairs of electrodes are placed at different positions,it is found that the closer the position of the cathode of one pair of electrodes is to the anode of the other pair of electrodes,the more favorable the carbon pollution is to be reduced.However,the experimental results show that when the composite electrode is used to deoxidize of titanium oxide and utilization of CO₂ simultaneously in the same cell to prepare high-quality carbon materials,the molten salt pollution and the pollution of titanium are more serious than that in the single electrode system.The main reason is that the precipitated carbon material is easy to fall into the molten salt due to its small particle size,large specific surface area and fluffy porosity,which is dispersed in the whole molten salt driven by the moving ions in the molten salt.Moreover,due to the effect of composite electric field,the carbon pollution of titanium metal much more serious due to better dynamic conditions.Therefore,it is the premise that the composite electrode system can realize the simultaneous electrolysis deoxidation and CO₂ utilization to prevent carbon from falling off the electrode and falling into the molten salt.Much further research is needed.