Siberian Federal University, Krasnoyarsk, Russia

Y. G. Mikhalev, Professor of the Physical and Inorganic Chemistry Department
P. V. Polyakov, Consultant-Professor of the Metallurgy of Non-ferrous Metals Department
A. S. Yasinskiy, Senior Lecturer of the Metallurgy of Non-ferrous Metals Department, e-mail: ayasinskiykrsk@gmail.com
A. A. Polyakov, Post-Graduate Student of the Metallurgy of Non-ferrous Metals Department

The results of simulation of the current distribution on the active surface of the carbon anode, the subsystem of the aluminum reduction cell, are presented. The anode, like the cell itself, is a dissipative structure and, therefore, it is very sensitive to boundary conditions. Local unevenness of its composition and violation of the interaction conditions with the electrolyte lead to technological “disorders”, for example, to the distortion of the surface relief. Such violations are conventionally divided into three types: “typical spike” — the formation of a cylindrical or conical shape at anodes; “lagging” — protrusions at the base of an anode of rectangular cross-section or unevenness, occupying up to 50–60% of the anode area; “overglow” — a violation at the anode bottom (ball, mushroom, etc.) that occurs at any face of the immersed anode block. One of the main dangers of spike formation is a significant reduction in current efficiency. On the basis of model representations, considering the problem as onedimensional, the influence of alumina concentration distribution and the presence of carbon dust under the bottom of the anode block on the anodic current density distribution and on the “consumption” of the anode is analyzed. The model is based on the expressions given in the literature which combine together: anodic overvoltage, equal to the sum of the activation and the concentration components; the anodic current density, the alumina concentration in the melt and the voltage drop in the anode-cathode space at various technological parameters and the electrolyte physicochemical properties. The model allows predicting local consumption rate of the anode and the spike growth rate. The time calculated before the appearance of the spike shorting the anode to the cathode is about 2 days, which confirms adequacy of the model. To suppress the spikes formation and growth it is recommended to increase the velocity of alumina transport, changing the conditions of its inflow in the anode-cathode space and to reduce the content of carbon dust, aligning the reactivity of the coke-binder and coke-filler, selecting the optimum baking temperature.

1. Yanko E. A. Anodes of aluminum electrolyzers. Moscow : Ore and Metals, 2001. 672 p.
2. Martel A. Spike detection using advanced analytics and data analysis. Light Metals. 2018. pp. 485–490.
3. Thonstad J., Fellner P., Haarberg G. M., Hives J., Kvande H., Sterten A. Aluminium Electrolysis. Fundamentals of Hall-Heroult Process. 3^rd ed. Düsseldorf : Aluminium-Verlag Marketing & Kommunikation GmbH, 2001. 359 p.
4. Mikhalev Yu. G., Polyakov P. V., Yasinskiy A. S., Shakhray S. G., Bezrukikh A. I., Zavadyak A. V. Causes of technological disturbances in anode processes. A review of the research of Russian and foreign experimenters. Zhurnal Sibirskogo federalnogo universiteta. Seriya: tekhnika i tekhnologii. No. 10 (5). pp. 593–606.
5. Polyakov P. V., Vlasov A. A., Mikhalev Yu. G., Yanov V. V. About formation of cones on the base of the burnt anode of aluminum electrolysers. Metallurg. 2016. No. 10. pp. 79–83.
6. Vetyukov M. M., Chuvilyaev R. G. Behavior of coal “foam” in the electrolysis of cryolite-alumina melts. Izvestiya vuzov. Tsvetnaya metallurgiya. 1964. No. 6. pp. 74–81.
7. Pietrzyk S., Thonstad J. Influence of carbon dust in the electrolyte on aluminium electrolysis parameters. ICSOBA Proceedings 2015. Available at: icsoba.org/sites/default/files/2015paper/aluminiumpapers/AL17%20-%20Influence%20of%20carbon%20dust%20in%20the%20electrolyte%20on%20aluminium%20electrolysis%20parameters.pdf (accessed: 30.07.2018).
8. Bugnion, Fischer J.-C. Carbon dust in electrolysis pots — effect on the electrical resistivity of cryolite bath. Aluminium. 2016. No. 1–2. pp. 44–47.
9. Bjørn M., Halvor K., Asbjørn S. Experience and challenges with amperage increase in hydro aluminium potlines. Light Metalls. 2007. Vol. 2. pp. 263–268.
10. Grjotheim K., Kvande H. Introduction to aluminium electrolysis. Understanding the hall-Heroult process. Düsseldorf : Aluminium-Verlag, 1993. 260 р.
11. Warren Haupin. Interpreting the components of cell voltage. Light Metals. 1998. pp. 531–537.
12. Vetyukov M. M., Tsyplakov A. M., Shkolnikov S. N. Electrometallurgy of aluminum and magnesium: a textbook for high schools. Moscow : Metallurgiya, 1987. 320 p.
13. Solheim A., Rolseth S., Skybakmoem E. Liquidus temperature and alumina solubility in the system Na₃AlF₆ – AlF₃ – LiF – CaF₂ – MgF₂. Light Metals. 1995. pp. 451–460.
14. Hives J., Thonstad J., Sterten A. Electrical conductivity of molten cryolite — based mixtures obtained with a tube-type cell made of perolytic boron nitride. Light Metals. 1994. pp. 187–194.