Simulation of the migration of colloidal particles in porous media: application to the transport of contaminants

A mechanisms of particle transport of contaminants is examined. Contaminants are carried out by migrating colloidal particles on which they are assumed to be sorbed. Both hydrodynamic dispersion of particles and adsorption of contaminants are taken into account. Migration of particles is simulated by a random walk procedure. The porous medium is homogeneous and isotropic; it is seen as a 3D network of randomly orientated pores. Simulations are performed with dilute and concentrated suspensions; in this later case a non-Newtonian behaviour described by a Bingham law is considered. The simulations show that the dispersion of colloidal particles in a porous medium obeys a anomalous diffusion law as soon as molecular diffusion ceases to occur. The residence time distribution of particles have got a long tail of dispersion. This anomalous process added to the adsorption of contaminants imply: (i) that contaminant migration to the underground water is faster than in solution, and (ii) that particles and subsequently sorbed contaminants can be trapped during a very long period inside the porous medium.