The use of liquid ion exchangers enables selective separations of, e.g., metal ions or acids, by reactive extraction processes. For the simulation of countercurrent column performance, three major points have to be tackled: The first step is a description of reactive equilibria, based on Gibbs energy modeling, taking into account complexation of organic species and dissociation reactions of the aqueous phase (often containing electrolytes). In addition to physical extraction, the overall mass transfer must be determined taking into account diffusional and/or chemical reaction resistances. Finally, the column hydrodynamics have to be considered, where the state of the art is to consider the deviation from plug flow with one parameter (e.g., the axial dispersion coefficient). The development of droplet population methods and the helpful information from CFD-calculations for the improvement of the physical understanding of complex flows is discussed. The use of lab-scale equipment to estimate all necessary design parameters, with a minimum of effort involved, is also presented.