The packed bed reactor theory was applied to define the mass transfer mechanism between the liquid and the solid phase for Pb and Zn removal from binary solutions at different flow rates. The typical breakthrough curves were converted into the derived form, from whose maximum the inflection point was successfully determined. Up to the inflection point, the mass transfer through the liquid phase is the slowest process and controls the overall rate due to available exchangeable sites in zeolite particles. The quantity of (Pb + Zn) ions increases linearly from the beginning of the experiment to the inflection point. After inflection, the mass transfer through the boundary layer of the zeolite particle becomes more significant and controls the overall process rate. The Advection-Dispersion-Reaction (ADR) model has been applied, and parameters DL, trnin and kf have been calculated for different experimental conditions. It has been found that parameter tmin corresponds to experimentally determined inflection time on the breakthrough curve. This confirms the successful application of the ADR model in definition of mass transfer mechanism in the packed bed. (C) 2016 Elsevier B.V. All rights reserved.