Vaporization of Fluorides from Aluminium Cells, Part II: Treatment of Spent Potlining in a Laboratory Furnace

Today, spent potlining (SPL) from the aluminium industry is mainly sent to landfills. From a circular economy perspective, and with limited availability for landfill sites in the future, the industry is looking into ways of cleaning the SPL to produce saleable products. Vacuum vaporization was investigated to determine its applicability for removing fluorides from the graphite-rich first-cut SPL. It was demonstrated that vacuum vaporization at elevated temperatures is suitable for the removal of fluorides. The condensate generally contains cryolite and NaF only, in accordance with thermodynamic theory. At the temperatures used, it was impossible to remove CaF2 or alumina from the SPL, due to the low vapour pressure of these compounds. The holding time at elevated temperature and vacuum affected the amount of electrolyte removed. The findings comply with the theory for vaporization of fluoride mixtures.