Alkali and earth alkaline metal contents in the aluminium cathode in aluminium electrolysis

The contents of sodium, lithium, calcium and magnesium in aluminium in cont act with NaF-AlF3-based melts in laboratory and in industrial aluminium cel ls were investigated in the temperature range 950-1030 degrees C. The exper imental data were compared with a thermodynamic model. It was found that th e addition of alumina or CaF2 to the NaF-AlF3 melts has only a minor effect on the equilibrium content of sodium in aluminium. Cathodic polarization e nhances the content of sodium in aluminium. However, polarization has a sma ller effect on the concentrations of lithium, calcium and magnesium in alum inium in industrial cells.