Fluid flow and colloid transport experiment in single-porosity sample; tracking of colloid transport behavior in a saturated micromodel

Abstract

Release of colloids and their subsequent transport into the subsurface environments takes place during a wide range of applications such as industrial, energy storage, and agricultural activities. Therefore, processes contributing to transport, attachment, and re-mobilization of colloids in porous media are attracting attention. A fraction of the released colloids may cross the soil vadose zone to reach the saturated groundwater. In this study, we explored colloid transport in a micromodel with high repulsion energy barrier where colloid retention is assumed to be low. Three major shortcomings were improved: pore space domain size, imaging resolution, and speed of imaging. The flow path of 1357 colloids with a size of 4 µm were tracked and these enabled precise determination of individual colloid transport mechanism as well as the integrated behavior of the system. Our direct observations have shown that even under unfavorable attachment conditions (defined based on the DLVO theory) colloids deposition occurred which was mainly due to the local flow velocity fluctuations and grain surface heterogeneity. Using the information from collective trajectories, we have quantified the contribution of differently behaved colloids in the observed breakthrough curve which show an integrated, macroscopic, behavior of the system and is often the only available information when performing column or field scale experiments to explore colloid transport in porous media. Furthermore, we have shown that attachment and remobilization of colloids increased the dispersion coefficient, and consequently the dispersivity value of the media.