Over the last 25 years the capacity of the Alcan Gove alumina refinery has increased from its original 1.0 Mt/y to approximately 2.0 Mt/y mainly through liquor productivity and flow increases. Gove bauxite, like other Australian bauxites, has high organic impurities. Consequently, Alcan Gove has been obliged to purge caustic to control impurities, such as sodium oxalate that has a detrimental affect on product quality. As a result, other organic and inorganic impurities have remained at acceptable levels. This purge of sodium oxalate, apart from the high cost of sodium hydroxide, has made the rehabilitation of the red mud disposal area more demanding.
Therefore, it was decided in the early 1990s to investigate environmentally acceptable means of controlling and destroying these liquor impurities.
Processes that were available at that time were not suitable/adaptable to the Gove situation. After a detailed literature survey was carried out to review all existing processes, the potential solutions were narrowed down to the following two possible options:
1. Combustion of liquor organics at high temperatures
2. Wet oxidation at high temperatures and pressures (similar to installations that have operated in the paper industry).
Laboratory scale trials were carried out for both liquor calcination and wet oxidation, and heat and mass balances were modelled for these scenarios.
After a thorough review, Alcan concluded that the ‘Solid Liquid Calcination’ process was the most appropriate option.
Details of the studies carried out for Alcan Gove are presented in this paper.