The cathode processes in aluminium electrolysis cells are discussed, with detailed descriptions of the chemical reactions and transport processes leading to loss of current efficiency with respect to aluminium. The cathode current consuming reactions can be described by (i) the aluminium formation reaction, and (ii) reduction reactions forming so-called dissolved metal species (reduced entities). The rate determining steps for the aluminium forming process are mass transport of AIF3 to the metal surface, and mass transport of NaF away from the metal surface. In commercial cells there is continuous feed of impurity species to the electrolyte, depressing the concentration of dissolved metal species to very low equilibrium values in the bulk phase of the electrolyte. However, the equilibrium values of reduced entities in the electrolyte at the metal surface are much higher than in the bulk phase. This means that polyvalent impurity species are involved in cyclic redox reactions in the electrode and gas boundary layers. The most important rate-determining steps related to these cyclic processes are (i) mass transport of reduced entities from the metal surface to a reaction plane within the cathode boundary layer, and (ii) mass transport of impurity species from the electrolyte bulk phase to the reaction plane in the cathode boundary layer. This means that there is negligible transport of dissolved metal species through the bulk of the electrolyte phase during normal operation of commercial cells.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
H. Ginsberg and H. C. Wrigge, Metall. 26 (1972) 997.
N. Jarrett, in ‘Production of Aluminium and Alumina’, (edited by A. R. Burkin), John Wiley, New York (1987) chapter 13.
H. Kvande, Mag. Alum. 26 (1989) 382.
T. G. Pearson and J. Waddington, Discuss. Faraday Soc. 1 (1947) 307.
A. Sterten, Acta Chem. Scand. 44 (1990) 873.
A. Sterten, ‘Light Metals’, (edited by E. L. Rooy), Proceedings of the 120th TMS annual meeting (1991), p. 445.
A. Sterten, J. Appl. Electrochem. 18 (1988) 473.
K. Grjotheim, C. Krohn, M. Malinovsky, K. Matiosovsky and J. Thonstad, ‘Aluminium Electrolysis. Fundamentals of the Hall-Heroult process’, 2nd ed., Aluminium-Verlag, Düsseldorf (1982).
J. Thonstad, Can. J. Chem. 43 (1965) 3429.
K. Yoshida and E. W. Dewing, Met. Trans. 3 (1972) 1817.
R. Ødegård, A. Sterten and J. Thonstad, 19B (1988) 449.
X. Wang, R. D. Peterson and N. Richards, Light Metals, (edited by E. L. Rooy), Proceedings of the 120th TMS annual meeting (1991), p. 323.
E. W. Dewing and K. Yoshida, Can. Met. Quart. 15 (1976) 299.
V. Borisoglebskii, M. M. Vetyukov and S. A. Nikiforov, Sov. Electrochem. 13 (1977) 506.
R. Ødegård, ‘Solubility and Electrochemical Behaviour of Al and Al4C3 in Cryolitic Melts’', thesis, Norwegian Institute of Technology, Trondheim, Norway (1986).
M. A. Bredig, ‘Molten Salt Chemistry’, (edited by M. Blander), Interscience Publishers, New York (1964), p. 367.
J. J. Egan and W. Freyland, Phys. Chem. 89 (1985) 381.
G. M. Haarberg, K. S. Osen, J. J. Egan, H. Heyer and W. Freyland, Ber. Bunsenges. Phys. Chem. 92 (1988) 139.
J. Liu, J.-C. Poignet, J. Appl. Electrochem. 22 (1992) 1110.
G. M. Haarberg, K. S. Osen, J. Thonstad, R. J. Heus and J. J. Egan, ibid. 137 (1990) 2777.
E. W. Dewing, Met. Trans. 22B (1991) 669.
R. Piontelli, G. Montanelli and G. Sternheim, Rev. Metall. 53 (1956) 248.
R. Piontelli, Electrochim. Metall 1 (1966) 191.
J. Thonstad and S. Rolseth, Electrochim. Acta 23 (1978) 221.
, 23 (1978) 233.
E. Sum and M. Skyllas-Kazacos, 23 (1978) 677.
W. B. Frank and L. M. Foster, J. Phys. Chem. 61 (1957) 1531.
S. K. Ratkje, H. Rajabu and T. Forland, Electrochim. Acta 37 (1992) 415.
A. Sterten, 25 (1980) 1673.
J. Thonstad, J. Electrochem. Soc. 111 (1964) 955.
H. G. Johansen, ‘Jern som forurensningselement i aluminium elektrolysen’, thesis, Department of Electrochemistry, Norwegian Institute of Technology, Trondheim, Norway (1975).
S. Rolseth and J. Thonstad, Light Metals, (edited by G. M. Bell), Proceedings of the 110th TMS annual meeting (1981), p. 289.
P. Chin, ‘The Behaviour of Impurity Species in Hall-Heroult Aluminium Cells’, Dissertation, Carnegie Mellon University, Pittsburgh, Pennsylvania (1992).
D. Bratland, K. Grjotheim, C. Krohn and K. Motzfeldt, J. Metals 19 (1967) 13.
H. Numata and J. O'M. Bockris, Met. Trans. 15B (1984) 39.
C. Szeker, Acta Technika Acad. Sci. Hung. 10 (1954) 19.
A. Kerouanton and J. Badoz-Lambling, Rev. Chim. Minerale 11 (1974) 223.
J. Gerlach and L. Deininger, Metall 33 (1979) 31.
N. I. Anufrieva, L. S. Baranova and Z. N. Balashova, Sov. J. Non-Ferrous Met. 24 (1983) 38.
About this article
Cite this article
Sterten, Å., Solli, P.A. Cathodic process and cyclic redox reactions in aluminium electrolysis cells. J Appl Electrochem 25, 809–816 (1995). https://doi.org/10.1007/BF00233898
- Metal Surface
- Mass Transport
- Current Efficiency
- Rate Determine Step
- Bulk Phase