Transport laws of contaminant in porous media considering non-equilibrium adsorption under cyclic injection

According to the classical equations for contaminant transport considering the effect of adsorption and desorption, a theoretical model for non-equilibrium adsorption is obtained by regarding the Freundlich linear isotherm as an adsorption and desorption process. Then, the relevant expressions for the cumulative mass fraction and the relative concentration are given correspondingly. The transport laws of contaminant are analyzed by Comsol Multiphysics for the cyclic injection of the trigonometric function and Gauss pulse function. The results show that there is an obvious impact on the adsorption capacity of contaminant due to the difference between the constant of adsorption and desorption. The adsorption amount increases with the increase of the difference. On the other hand, with the increase of the dispersivity, the peak of breakthrough curve has a decreasing trend at first and then increases. Also, the penetration process increases with the increase of the dispersivity. In addition, there is a critical value of injection time, below which the breakthrough peak increases with the increase of the injection time. Beyond this threshold, it maintains a steady state and is equal to the injection concentration of pollutant.