In this study, the population balance model was used to simulate the steady axial profile of the drop size distribution along the extraction column. Based on the population balance model, a dynamic interaction mass transfer model for simulation of the mass transfer process within extraction columns was developed with only one parameter that needs to be optimized. In comparison with conventional mass transfer models, the dynamic interaction mass transfer model has a theoretical basis and is less empirical because the influence of drop breakage and drop coalescence on the drop size distribution and the mass transfer process were carefully considered. (c) 2006 Elsevier Ltd. All rights reserved.