Calcining boehmite instead of gibbsite to smelter grade alumina would result in significant energy savings. Until now attempts to produce boehmite from the Bayer process have concentrated on the direct crystallisation of boehmite from green Bayer liquors. These have not been adopted industrially due to the slow precipitation kinetics and the presumed unsuitability of the particle characteristics for subsequent calcination. We have investigated hydrothermally produced boehmite from product hydrate. It was found that although this product maintained good morphology and had low soda content, its overall lack of strength after calcination made it unsuitable as a smelter feed.
In this paper we present an alternative method for producing boehmite that maintains the physical characteristics of current smelter grade alumina, including strength. The method involves rapid reversion (dissolution and re-precipitation) of gibbsite in spent liquor at high volume fraction. Some issues remain to be addressed, especially those related to water balance and soda content in the product boehmite.