An important stage of the Bayer process leads to the formation of gibbsite particles (Al(OH)(3)) mostly grown by agglomeration (aggregation and crystal growth). In this work, a population balance model is developed to account for experimental data generated in a constant supersaturation crystallizer. The objective is to quantify the effect of the seed concentration on the agglomeration kinetics. The population balance equation is discretized and solved with the method of classes. Several classical agglomeration and fragmentation kernels are tested. The size-independent agglomeration kernel taken alone results in the most suitable description of the experiments. The kinetic constant must then strongly decrease with the seed mass. The hypothesis of an agglomeration kernel independent of the seed mass combined with a fragmentation kernel increasing with the seed mass is also tested. Results are compared and discussed with the previous ones drawn from the literature.