Carbon anodes in aluminium electrolysis cells. Factors affecting anode potential and carbon consumption

摘要

The Hall-Heroult process today represents the only commercial way of making aluminium. The principles of the Hall-Heroult cells involve electrochemical decomposition of alumina (Al2O3). A cryolite (Na3AlF6) based melt serves as the solvent for the oxide. Additives are used to optimize the physical and chemical properties of the electrolyte. The present work concerns the issues of carbon consumption in general, and the formation of carbon dust in particular. One way to determine the electrochemical reactivity is in terms of overvoltage (or polarization potential), high electrochemical reactivity results in a low overvoltage. The main part of the experimental work in this study has been concentrated with determination of anode potentials, and recordings of the potential versus current density dependence (including steady-state potential versus current determinations and a.c. impedance measurements). Important parameters which have been selected for investigation are impurities in the anode paste, composition of the paste (dry aggregate recipe, binder content) and heat treatment of the anode. In addition, operational parameters, such as electrolysis temperature and bath composition, are investigated. Carbon consumption measurements, which are partly determined by the electrochemical consumption process, and partly by chemical oxidation processes, are also performed with respect to the mentioned parameters. By additional supply of CO(sub 2) reactivity results and different physical material properties, a solid basis should exist for approaching an understanding of some important factors governing the carbon reactivity, the consumption rates of carbon, and the dust formation in aluminium electrolysis cells. 164 refs., 73 figs., 37 tabs.