Crystallization kinetics and crystallization process of pseudoboehmite from ammonium aluminum sulfate solution

Abstract

In this work, the crystallization kinetics of pseudoboehmite was studied by intermittent crystallization method. The kinetic model of pseudoboehmite process was established based on particle number equilibrium. The results show that the nucleation is mainly caused by crystal collision, the main speed control step is diffusion process, and the enlargement of crystals mainly originates from the growth. Reducing the temperature of system can obtain pseudoboehmite crystals which have larger particle size and more uniform particle size distribution. Two parallel octahedral units connected by hydroxyl groups are preferentially stacked along the (020) crystal plane. Excessive interlayer water molecules between (020) crystal planes lead to an increase in the interlayer distance. The increased distance between (020) layers will weaken the hydrogen bond between layers, as well as the electrostatic forces and van der Waals forces, resulting in the formation of folded layers with holes. Finally, the irregularly sheets of pseudoboehmite are stacked to form porous spherical structures.