KINETICS OF BOEHMITE PRECIPITATION FROM SUPERSATURATED SODIUM ALUMINATE SOLUTIONS WITH ETHANOL-WATER SOLVENT

Boehmite was prepared from supersaturated sodium aluminates solutions with ethanol-water solvent. The results of thermogravimetric analyzer and XRD showed that the product was mixture of boehmite and gibbsite, and the mass ratio of gibbiste and boehmite varied greatly with different process conditions. This work presents the effects of mass ratio of ethanol and temperature on the precipitation rate and phase compositions of alumina hydrate. The ratio of AlOOH in the product increased significantly with the increase of mass ratio of ethanol because the precipitation of gibbsite was restrained. When the solvent was pure ethanol, the ratio of AlOOH in the product reaches the peak of 90%. Ethanol reduces the free caustic concentration and increases initial supersaturation coefficient significantly. The boehmite activation energy of precipitation in ethanol solvent was 13.7 kJ/mol, indicated that ethanol reduces effectively energy barrier of boehmite from sodium aluminate solutions and it was controlled by diffusion process