Modeling migration of radionuclides in porous rock in the presence of colloids: effects of kinetic interactions

[[abstract]]The model for coupled colloid and radionuclide migration is presented in this paper. Radionuclides are distributed among in the liquid phase, the solid matrix, mobile and immobile colloids. The transport mechanisms for radionuclides are considered as advection, dispersion, radioactive decay and an adsorption-desorption interaction with the solid matrix or colloids. The colloids migrate in the groundwater system with advection, dispersion and adsorption-desorption interaction with the solid matrix. Furthermore, the transport properties of radionuclides may differ from those of colloids. Detail mathematical formulations for the adsorption-desorption interaction mechanisms are included in this model. The sorption interaction processes can be described by equilibrium and kinetic models. Under an equilibrium assumption, three different adsorption isotherms can be employed, those that are linear, Freundlich (modified Freundlich) and Langmuir isotherms. For a kinetic interaction mechanism, the nonlinear relationship with a maximum adsorption capacity and linear relationship between free species and adsorbents can be applied in modeling the transport processes of radionuclides and colloids. An analytical solution can be obtained under the simplified linear equilibrium interaction mechanism. Using this analytical solution, the parameters for colloid-facilitated radionuclide migration such as colloid concentration, velocity ratios (colloid velocity to water velocity), dispersion and distribution coefficients among different species can be investigated numerically. Colloids in the liquid phase act as mobile vehicles to enhance the migration of radionuclides, however, the solid matrix and immobile colloids play a role in retardation[[fileno]]2060101010009[[department]]工程與系統科學