Kinetics of boehmite precipitation from supersaturated sodium aluminate solutions

This work presents the effect of the most important parameters, the precipitation temperature, the sodium hydroxide concentration and the initial seed ratio (SR) in the solution, on the boehmite precipitation from supersaturated sodium aluminate solutions. A kinetic model that describes the experimental data was developed. According to that model, boehmite precipitation follows second order reaction kinetics and has activation energy of 89 kJ/mol. The orders of the precipitation reaction with respect to the initial sodium hydroxide concentration and the initial seed ratio are estimated to be −1.8 and 0.54, respectively. The most important result is that the boehmite precipitation reaches an apparent equilibrium stage at which the alumina concentration is much higher compared to the value of the boehmite solubility under the same experimental conditions. The results reveal that the boehmite precipitation is a self-decelerated process and the observed kinetic inhibitions are related to the sodium hydroxide concentration in the supersaturated solution. Finally, a mechanistic interpretation of the experimental data is presented based on the concept of the surface precipitation of boehmite on the active sites of the boehmite seed.