An Inverted Aluminum Electrolysis Cell Using a High Density Electrolyte and an Inert Anode - A Test of the Concept

Abstract

For the application of inert, oxygen-evolving anodes in low-temperature electrolytes for aluminum electrolysis, the dissolution rate of the raw material alumina may be critical. It may then be desirable to maintain a content of excess alumina in the electrolyte. Experiments were carried out in a fluoride electrolyte with density higher than that of liquid aluminum, whereby the metal produced collected on top of the electrolyte. The electrolyte composition in weight-% was: NaF: 18, AlF3: 48, CaF2: 16 and BaF2: 18. Fine-grained alumina was fed to the electrolyte in excess of the solubility limit. The excess alumina was kept in suspension by the gas-induced convection created by the oxygen gas generated at the anode. A vertically arranged slab of TiB2 was used as cathode, while platinum, tin oxide and nickel-ferrite were tested as inert, oxygen-evolving anode materials. In one day experiments, current efficiencies in the range of 72- 92 % were achieved.