The nucleation, growth, and agglomeration of monosodium aluminate hydrate (MAH) crystallization in concentrated sodium aluminate solutions were investigated in a steady-state mixed-suspension-mixed-product-removal (MSMPR) crystallizer, and the mechanism was analyzed in detail. The crystal growth was diffusion- and surface-integration-controlled, and the secondary nucleation, as a result of crystal-agitator and crystal-crystallizer collisions, was determined further. The agglomeration kernel, expressed in terms of mean residence time, growth rate, and suspension density, was found to have a positive order of about 0.52 in the suspension density, indicating that the agglomeration kernel increased at higher frequencies of collisions between particles. The growth rate of MAH was found to be higher than that of gibbsite in active NaAl(OH)(4)-NaHCO3 systems, but the nucleation rate of MAH was lower than that of gibbsite in seeded-hydrolysis processes.