Growth and dissolution rates of potassium chloride in pure aqueous solutions were measured in a fluidized bed crystallizer. Within the experimental uncertainty, the growth rates are nearly first-order relatively to the thermodynamic driving force. The coefficient of the overall kinetic equation was found to decrease with the residence time in the crystallizer, until a steady-state mode of growth is reached. The size of the seeds and the porosity of the fluidized bed have little influence on the steady growth of KCI crystals, but affect the dissolution and, to a lesser extent, the initial stages of growth. The diffusive nature of dissolution is well illustrated by an activation energy of 8.5 +/- 1.0 kJ mol(-1). The corresponding values pertaining to growth experiments with 5 and 20 min of residence time were (23.9 +/- 4.4 and 39.1 +/- 1.7) kJ mol(-1), respectively, thus indicating a significant role of the diffusional mass transfer step during the early contact of the seeds with the solution. As the growth rates approach a constant value, the importance of this step decreases relatively to the surface-reaction contribution. The linear correlation between growth rates and driving force suggests, therefore, a growth process controlled by a direct integration mechanism. (c) 2006 Elsevier B.V. All rights reserved.