Abstract
Electrochemical behaviour of sulphate under anodic polarization in molten sodium chloride, cryolite and sodium fluoride was investigated by cyclic voltammetry and chronopotentiometry at the temperatures of 820°C, 1010°C, and 1000°C, respectively. Using a platinum working electrode, two waves were observed on the chronopotentiograms in the systems: NaCl-Na2SO4 and Na3AlF6-Na2SO4. The first wave was attributed to the formation of oxygen. The second wave probably originated from the reaction of oxygen with platinum, or from oxidation of SO3 decomposition products. Three waves were observed for the anodic process of sulphate ions dissolved in molten sodium fluoride. The first wave was attributed to the formation of oxygen. The second and the third wave were attributed to the formation of PtO and PtO2. This conclusion was supported by cyclic voltammetry experiments of the in-situ formed sulphide in molten NaCl at 820°C and by chronopotentiometry on a gold working electrode in the system NaCl-Na2SO4, where no anodic wave was observed.
Similar content being viewed by others
References
Ambrová, M., Danielik, V., Fellner, P., & Thonstad, J. (2006). The cathode process in sodium chloride melts containing sulphate. Electrochimica Acta, 51, 5825–5828. DOI: 10.1016/j.electacta.2006.03.018.
Arvia, A. J., Calandra, A. J., & Videla, H. A. (1968). Kinetics of oxygen formation and dissolution on platinum electrodes in the electrolysis of molten potassium bisulphate. Electrochimica Acta, 13, 167–182. DOI: 10.1016/0013-4686(68)80019-2.
Baudo, G., Tamba, A., & Bombara, G. (1970). An electrochemical investigation of corrosion of ferritic steels in molten sulfates. Corrosion-NACE, 26, 193–199.
Burnakin, V. V., Polyakov, P. V., Zalivnoi, V. I., Popkova, R. K., & Mozhaev, V. M. (1982a). Behaviour of sulphate ion in cryolite-alumina melts. Soviet Journal of Non-Ferrous Metals, 10, 279–285.
Burnakin, V. V., Mozhaev, V. M., Kryukovskiy, V. A., Polyakov, P. V., & Schipok, S. N. (1982b). Study of the mass transport between bulk of the electrolyte and the electrodes of aluminium electrolysis cells by the low-temperature modelling. Tsvetnaya Metallurgiya, 4, 46–50. (in Russian)
Burnakin, V. V., Popkova, R. K., Zalivnoi, V. I., Polyakov, P. V., & Kolosova, V. I. (1983). Behaviour of sulphate during the electrolysis of aluminium. Soviet Journal of Non-Ferrous Metals, 11, 282–285.
Burrows, B. W., & Hills, G. J. (1970). Electrochemical studies of molten alkali sulphates. Electrochimica Acta, 15, 445–458. DOI: 10.1016/0013-4686(70)87004-9.
Cutler, A. J. B., Hart, A. B., Foutain, M. J., & Holland, N. H. (1967). Corrosion and deposits from combustion gases, ASME Publication No. 67-WA/CD-4. New York, NY, USA: ASME.
Fang, W. C., & Rapp, R. A. (1983). Electrochemical reactions in a pure Na2SO4 melt. Journal of the Electrochemical Society, 130, 2335–2341. DOI: 10.1149/1.2119581.
Gul’din, I. T., & Buzhinskaya, A. V. (1965). Anodic process during discharge of sulfate ions from fused salts on a carbon anode. Soviet Electrochemistry, 1, 634–637. Translated from Elektrokhimiya, 1, 716–719.
Hay, S. J. (2002). The formation and fate of carbonyl sulfide (COS) gas in aluminium smelting. Ph.D. thesis, University of Auckland, Auckland, New Zealand.
Hay, S. J., Hyland, M. M., Metson, J. B., & Bade, O. M. (2001). Reducing carbonyl sulfide emissions in aluminium smelting. In Proceedings of the 11th International Aluminium Symposium, 19–22 September 2001 (pp. 231–241). Trondheim-Bergen, Norway: NTNU.
Hyland, M. M., Welch, B. J., & Metson, J. B. (2000). Changing knowledge and practices towards minimizing fluorine and sulphur emissions from aluminium reduction cells. Light Metals, 2000, 333–338.
Johnson, K. E., & Laitinen, H. A. (1963). Electrochemistry and reactions in molten Li2SO4-Na2SO4-K2SO4. Journal of the Electrochemical Society, 110, 314–318. DOI: 10.1149/1.2425739.
Liu, C. H. (1962). Electrode potentials in molten lithium sulphate-potassium sulphate eutectic. The Journal of Physical Chemistry, 66, 164–166. DOI: 10.1021/j100807a038.
Ødegård, R., Roenning, S., Sterten, Å., & Thonstad, J. (1985). Sulfur containing compounds in the anode gas from aluminum cells: A laboratory investigation. Light Metals, 1985, 661–670.
Sequeira, C. A. C., & Hocking, M. G. (1978). Polarization measurements on solid platinum-molten sodium sulphate-sodium chloride interfaces. Electrochimica Acta, 23, 381–388. DOI: 10.1016/0013-4686(78)80078-4.
Thonstad, J., Fellner, P., Haarberg, G. M., Híveš, J., Kvande, H., & Sterten, Å. (2001). Some effects of electrolyte impurities. In K. Grjotheim, & M. Krohn (Eds.), Aluminium electrolysis: Fundamentals of the Hall-Héroult process (3rd ed., Chapter 10.1., pp. 272–273). Düsseldorf, Germany: Aluminium Verlag.
Warner, N. A., & Ingraham, T. R. (1960). Decomposition pressures of ferric sulphate and aluminum sulphate. Canadian Journal of Chemistry, 38, 2196–2202. DOI: 10.1139/v60-297.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Ambrová, M., Fellner, P. & Thonstad, J. Anodic reactions of sulphate in molten salts. Chem. Pap. 64, 8–14 (2010). https://doi.org/10.2478/s11696-009-0099-2
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.2478/s11696-009-0099-2