Investigation Of Graphite Anode Gas In CaCl₂ Molten Salt

Preparation of high melting point metals by electrochemical reduction in calcium chloride molten salt system is one of the hot topics.At present,graphite is still used as anode material in this method.But,when graphite is used as anode,there is CO2 in the anode gas.And CO2 is easily captured by O2-from the cathode and dissolved in molten salt as CO32-.Due to the decomposition voltage of CO32-is lower than that of metal oxide.Therefore,CO32-is easily reduced to C,which reduces the current efficiency,causes pollution,and even leads to short circuit.In particular,this problem of electrolysis of oxides in CaCl2 molten salts is more prominent.However,for many years,in the field of calcium chloride molten salt electrolytic oxide,researchers have been focusing on how to change the structure of cathode chip to prepare porous cathode and how to increase electrolysis rate by adding CaO to molten salt to reduce cathodic reduction overpotential and so on.There is little research on graphite anode gas.Therefore,the effect of anodic gas on tantalum pentoxide electrolysis in CaCl2 molten salt are studied with tantalum pentoxide as cathode and graphite as anode.In this paper,the anodic gas composition of electrolytic metal oxides in CaCl2 molten salt and CaCl2-lwt%CaO molten salt system was studied by thermodynamic calculation,cyclic voltammetry and gas chromatography.The effect of anode gas on cathodic electrolysis was studied by two gas carrying modes of top blowing and bubble flowing in two molten salt systems respectively,Ar and CO2 as carrier gas.The results show that the anode gas in the two kinds of molten salt systems is a mixture of CO and CO2.CaO promoted the absorption of CO2 in anode gas by CaCl2 molten salt.Two blowing modes,top blowing and bubble blowing,have little effect on electrolytic metal oxides.When the concentuation of CO32-in molten salt is too high,the electrolysis efficiency will be reduced and impurities will be introduced into the cathode.