Finding the most appropriate governing equation under different environmental conditions is the most important step for both designing sorption systems and pollutant transport modeling. In this study, the second order model based on the sorbent concentration is theoretically and experimentally investigated. A circular flume was used for the sorption of cadmium by zeolite to simulate the natural conditions. The results indicate that the various equations proposed by different researchers for the sorption are the same and the differences are only due to the linearization and parameter definition methods. The results also state that linear R2 could not be used unaccompanied to determine the best linearization method and it should be used with the sum of square error (SSE). Comparison between seven linearization methods with current data showed that the methods of Sobkowsk and Czerwinski, Ritchie and Blanchard are the best linearization methods for linearization of the second order kinetic equations. Finally it was found that the sorption capacity should be experimentally measured.