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The basic theory for the behaviour of impurity elementsImpurity elements in aluminiumAluminium electrolysis cells is reviewed, with emphasis on the difference between noble and non-noble elements. Noble elements are transferred from bath to metalMetals by diffusion and reaction at the metalMetals-bath interface, while non-noble elements in bath and metalMetals are at equilibrium. A general expression for theCo-variation co-variation between the concentration of sodium and other trace elements in the produced metalMetals was derived. This co-variationCo-variation can be used for control purposes, provided that the methods for sampling and analysis are good enough. Non-noble elements can be removed by oxidationOxidation, but this is not possible with noble elements. Noble impuritiesImpurities are expected to become an increasing challenge in the future, since the concentrations in the raw materials are increasing, and because the ratio between recycled metalMetals (alloys) and primary metalMetals is increasing. Therefore, new methods are needed for the removalRemoval of noble impuritiesImpurities. It may be possible to reduce impuritiesImpurities by removing the fine fraction from the aluminaAlumina and by electrolytic separation of aluminiumAluminium and noble elements in scrap.

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Theoretical Basis for Future Control of Impurity Elements in the Hall-Héroult Process

  • 会议论文

  • 发表日期：

    2025年

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  • Asbjørn Solheim,
  • Ole S. Kjos,
  • Sverre Rolseth,
  • Egil Skybakmoen

摘要

The basic theory for the behaviour of impurity elementsImpurity elements in aluminiumAluminium electrolysis cells is reviewed, with emphasis on the difference between noble and non-noble elements. Noble elements are transferred from bath to metalMetals by diffusion and reaction at the metalMetals-bath interface, while non-noble elements in bath and metalMetals are at equilibrium. A general expression for theCo-variation co-variation between the concentration of sodium and other trace elements in the produced metalMetals was derived. This co-variationCo-variation can be used for control purposes, provided that the methods for sampling and analysis are good enough. Non-noble elements can be removed by oxidationOxidation, but this is not possible with noble elements. Noble impuritiesImpurities are expected to become an increasing challenge in the future, since the concentrations in the raw materials are increasing, and because the ratio between recycled metalMetals (alloys) and primary metalMetals is increasing. Therefore, new methods are needed for the removalRemoval of noble impuritiesImpurities. It may be possible to reduce impuritiesImpurities by removing the fine fraction from the aluminaAlumina and by electrolytic separation of aluminiumAluminium and noble elements in scrap.