Alternative electrolyte compositions for aluminium electrolysis

AbstractThe traditional electrolyte for aluminium electrolysis is based on molten cryolite (Na3AlF6), acting as solvent for the raw material, alumina (Al2O3). Over the years, there has been a trend to increase the content of excess aluminium fluoride (AlF3) to the cryolite-based electrolyte in order to enhance the current efficiency of the process. In most cases, one has ended up at 11–13 wt% excess AlF3 because higher contents make it difficult to control the heat balance of the process. This problem may be overcome if sensors are developed that will allow online control of electrolyte temperature and composition, and we may then see a surge towards still higher AlF3 contents. In the development of new anode materials to replace the carbon anode with inert, oxygen-evolving anodes, focus is on anode corrosion, and a low electrolyte temperature is then highly desirable. While the conventional process operates at around 960°C, electrolyte temperatures as low as 750°C are being tested. This is achieved by ha...