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Thermodynamic and thermochemical investigation of the deposits formed on the cathode surface of aluminum electrolysis cells

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Abstract

The efficiency of the Hall-Héroult process is influenced by the formation of solid or solid–liquid deposits on the cathode block surface. These deposits have a high electrical and thermal resistivity. Hence, they disturb the electrical current path at the aluminum and cathode block interface. The phase diagrams of deposits with a typical composition were calculated by thermodynamic equilibrium, and the results were confirmed by differential scanning calorimetry measurements. The ledge toe is mainly composed by Na3AlF6(ss), Al2O3(s), and liquid bath in industrial cells. The liquid fraction in the deposits at temperature lower than 933 °C is due to the presence of Na5Al3F14, Na2Ca3Al2F14, and NaCaAlF6 and depends on [Al2O3], [CaF2] and the cryolite ratio (CR). The side ledge in industrial cell contains liquid phase when the CR is lower than 2.8. The sludge contains Al2O3(s) and liquid bath. The ledge toe grows when the local temperature is lower than the solidification temperature of Na3AlF6.

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Acknowledgements

The authors are grateful to the employees of the “Centre de Caractérisation des Matériaux” for their help with the various characterization devices and to the chemist, Mr. Carl St-Louis, who helped to elaborate the DSC method. The authors also thank Alireza Hekmat and Lynne Davies for manuscript revision and correction. This work is financed and supported by Rio Tinto Alcan, “Conseil de Recherches en Sciences Naturelles et en Génie du Canada” (CRSNG) and “Fonds de Recherche du Québec-Nature et Technologies” (FRQNT).

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Authors and Affiliations

  1. Department of Chemical Engineering and Biotechnological Engineering, Université de Sherbrooke, C1 - Pavillon J. Armand Bombardier, 2500 Boulevard de l’Université, Sherbrooke, QC, J1K 2R1, Canada

    François Allard, Gervais Soucy & Martin Désilets

  2. Rio Tinto Alcan (Arvida Research and Development Centre), 1955 Boulevard Mellon, Jonquière, QC, G7S 4K8, Canada

    Loig Rivoaland

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  1. François Allard
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  2. Gervais Soucy
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  3. Loig Rivoaland
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  4. Martin Désilets
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Correspondence to Gervais Soucy.

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Allard, F., Soucy, G., Rivoaland, L. et al. Thermodynamic and thermochemical investigation of the deposits formed on the cathode surface of aluminum electrolysis cells. J Therm Anal Calorim 119, 1303–1314 (2015). https://doi.org/10.1007/s10973-014-4288-z

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  • DOI: https://doi.org/10.1007/s10973-014-4288-z

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