Filtration of micron-sized particles in granular media revealed by x-ray computed tomography

We investigate the deep-bed filtration of micron-sized hematite particles suspended in distilled water during flow in siliceous granular porous media, where particle retention is mostly due to surface (van der Waals and electrostatic) interactions. We show that x-ray computed tomography enables three-dimensional images of the filtration process to be generated. The one-dimensional filtrate concentration profiles obtained by averaging the images over sections perpendicular to the flow direction are rapidly decaying functions of the distance from the porous medium inlet and slide upward in the course of time, consistently with the filtration model presented by Herzig et al. [Ind. Eng. Chem. 62, 8 (1970)]. Finally, the filtration coefficient is found to decrease rapidly as a function of time: This indicates that the attractive interaction responsible for the retention of the hematite particles is strongly attenuated as the particles accumulate of the pore surfaces.