Research On Corrosion Resistance Of Cu-Ni-Fe Anodes To Potassium Cryolite Melts In Low Temperature Aluminum Electrolysis

The aluminum electrolysis industry belongs to the industry with high energy consumption and high pollution.Especially,when the primary aluminum is produced by Hall-Heroult electrolysis,the production process consumes more energy and emits more polluted gas.Under the increasing environmental pressure,low temperature aluminum electrolysis has become the focus of modern aluminum industry.Generally,the research on low temperature aluminum electrolysis has two aspects:inert electrode and electrolyte system.The combination of them can achieve the purposes of reducing energy consumption and pollution.Therefore,low temperature aluminum electrolysis will have great development potential in the future.With the development of inert anodes,alloy electrodes or ceramic composite electrode materials have been widely used instead of carbon electrodes.In addition,due to the high solubility of alumina,potassium cryolite has attracted the wide attention of researchers.Therefore,the effects of the addition of LiF and NaCl on the liquidus temperature and the solubility of Al₂O₃ in the potassium cryolite electrolyte system of K₃AIF₆-Na₃AIF₆-AlF₃(w(KR)=50 wt%,w(AlF₃)=22 wt%,KR=K₃AlF₆/(K₃AlF₆+Na₃AlF₆))were investigated.The electrolytic corrosion behavior of Cu-Ni-Fe inert alloy anode in the electrolyte system was studied.The main research results are as follows:When LiF content is 0-4 wt%,NaCl content is 0-4 wt%,the liquidus temperature of K₃AlF₆-Na₃AlF₆-AlF₃ was studied.At last,the influence law of LiF and NaCl on the liquidus temperature of K₃AlF₆-Na₃AlF₆-AlF₃ system was found.In the scope of research,the liquidus temperature of the electrolyte system is 770?841?,which can meet the needs of low temperature aluminum electrolysis.The isotherm plot and the regression equation with a correlation coefficient of 0.994 were obtained by fitting the experimental data.When LiF content is 0?4 wt%,NaCl content is 0?4 wt%,the solubility of Al₂O₃ in K₃AlF₆Na₃AlF₆-AlF₃ was studied.Consequently,the influence law of LiF and NaCl on the solubility of Al₂O₃ in K3AIF6-Na3AlF6-AlF₃ system was revealed.The isosolubility diagram and regression equation with a correlation coefficient of 0.904 were obtained by fitting the experimental data.The results show that the solubility of Al₂O₃ in the electrolyte system is more than 4 wt%,which can meet the requirements of low temperature aluminum electrolysis.Cu-Nu-Fe alloys with different compositions were prepared by cold pressing and sintering process,and the best alloy was obtained as Cu-20Ni-15Fe.The static corrosion rate of the alloy in the potassium cryolite electrolyte at 861? was 6.61 cm/a.While the static corrosion rate at 790? was 3.49 cm/a.The electrolytic corrosion behavior of Cu-20Ni-15Fe inert alloy anode was studied for 10 h.The variation of the cell voltage ranged from 2 to 4 V.The corrosion rates of the anode under the three molten salt systems were 5.41,3.63,and 2.56 cm/a,respectively.The corrosion rate of Cu-20Ni-15Fe anode in the molten salt system without Al₂O₃ is as high as 13.85 cm/a,while the corrosion rate is only 1.98 cm/a when in K₃AlF₆-Na₃AlF₆-(22 wt%)AlF₃-(4 wt%)NaCl-(4 wt%)LiF molten salt with saturated Al₂O₃,the corrosion resistance of the anode in the potassium cryolite system satisfies the requirements of low temperature aluminum electrolysis.