| abstract |
Alumina is carbothermically and cyclically reacted with carbon and recycled materials within a reduction zone to produce a slag layer, an overlying aluminum metal layer, and vaporization products which are passed through a vapor-permeable back-reaction zone, which comprises a feed charge mixture which is selectively connected to the reduction zone. The aluminum metal layer is initially contaminated with 20-37% of Al4C3 by weight. The vaporization products preheat and react with the feed charge mixture within the back-reaction zone to produce pre-reduction products which are selectively co-fed to the reduction zone with any unreacted portions of the feed charge mixture. The liquid/solids ratio in the back-reaction zone is limited, thereby maintaining the zone in vapor-permeable and non-slumping condition, by varying proportions of alumina fed to the back-reaction zone and to the reduction zone. The aluminum in the aluminum metal layer is selectively purified by feeding no additional carbon and by raising the reaction temperature until substantially all aluminum carbide is decomposed. |