Purification of Graphite by Thermal Vacuum Treatment of Spent Potlining

The aluminium industry is striving towards a lower environmental footprint, and the management of spent potlining (SPL) is high on the agenda. The reuse and recycling alternatives of SPL are limited primarily due to its content of sodium, fluorides and cyanide. In this work, a thermal vacuum process for the purification of first cut SPL has been tested. The process consists of a vacuum furnace and an off-gas condensation system. Small scale trials using 1000 g first cut SPL samples were carried out, with varying particle sizes and furnace temperatures. All tests demonstrated significant distillation of sodium fluoride and cryolite. The remaining residues contained up to 91% graphite, with minor amounts of contaminants such as aluminium oxide and calcium fluoride. Conclusively, the vacuum treatment process shows great potential for reuse of the challenging material of first cut SPL.