Two-Stage Process for Precipitating Coarse Boehmite from Sodium Aluminate Solution

To increase the precipitation rate significantly and obtain sandy alumina, a two-stage seeded precipitation process for preparing coarse boehmite was studied. In the first stage, which involved gibbsite precipitation, the fresh fine gibbsite, along with the active seed of less than 20 g L−1, acted as seed. An estimated 70% precipitation rate was achieved in the concentrated sodium aluminate solution at 45°C for ~20 h. In the second stage, which involved boehmite precipitation, the fine gibbsite played a dual function in dissolution and as seed. After gibbsite was dissolved into the solution and boehmite was precipitated, uniform coarse boehmite was precipitated from sodium aluminate solution at 95°C for ~20 h. Extending the duration and adding boehmite as seed benefitted the formation of coarse boehmite and the transformation of gibbsite into boehmite. Finally, a precipitation process that remarkably increased the precipitation rate was presented.