Aluminium is produced in the Hall-Héroult reduction cell where aluminium oxide is the raw material that is continuously fed to the cell and is reduced at the cathode, creating aluminium. The bath or electrolyte contains a mixture of cryolite (sodium hexafluoraluminate), aluminium fluoride and calcium fluoride.
The ratio between aluminium fluoride and sodium fluoride in the electrolyte is of importance for the properties of the electrolyte. Aluminium oxide contains a small amount of sodium oxide, and when this sodium oxide is fed to the electrolyte, the chemical composition of the electrolyte changes over time. Aluminium fluoride will then have to be fed to the cell in order to maintain the correct composition of the electrolyte and this generates a surplus of electrolyte that will have to be removed from the reduction cell from time to time. This electrolyte can be sold to opening aluminium plants.
For several years, the aluminium industry has expanded enough to absorb most of the surplus electrolyte, but this market is now saturated, and the only option today is recovery or deposition. Deposition is not a preferred solution for an industry working towards a more circular economy.
In the BADELand project, two thermodynamically promising processes for recovering the aluminium fluoride from the surplus electrolyte are proposed. Aluminium fluoride is a high value product and is today produced using a raw material (CaF2) identified as critical by EU. Avoiding the use of critical raw materials is favourable. The other side products of the processes might also turn out sellable if they are separable from each other through hydrometallurgical processes. In the project, the two processes will first be investigated experimentally in a laboratory, and the most promising process will be scaled up in a pilot line. The objective of the project is to get rid of a waste problem while creating products of value.
SINTEF Helgeland and SINTEF Industry contribute as project leader, with knowledge and laboratory experiments within hydro and pyro metallurgy.
