Simulation of Colloid Transport and Retention Using a Pore‐Network Model With Roughness and Chemical Heterogeneity on Pore Surfaces

Abstract

Colloid transport and retention in porous media is a common phenomenon in both nature and industry. However, many questions remain on how to obtain colloid transport and retention parameters. Previous work usually assumed constant transport parameters in a medium under a given physicochemical condition. In this study, pore‐network modeling is employed to upscale colloid transport and retention from the pore‐scale to the macro‐scale. The pore‐scale transport parameters including the collection efficiency (η), the sticking efficiency (α), and the fraction of the solid‐water interface that contributes to the colloid attachment (Sf) are obtained using numerical simulation and probability analysis for each pore throat. The influence of roughness and charge heterogeneity on the distribution of pore‐scale parameters is discussed. Breakthrough curves and the retention profiles under different roughness and charge heterogeneity conditions are also analyzed. Results show that pore‐scale parameters η, α, and Sf have various distributions in porous media that may not be accurately described using single‐valued effective parameters. The value of η decreases with velocity and exhibits a wide distribution under low‐velocity conditions. The parameter α tends to decrease with the colloid size and the pore water velocity and increased with the charge heterogeneity fraction. Nanoscale roughness alters α in a non‐monotonic fashion but tends to increase for lower roughness fractions and zeta potential. Microscopic roughness increases values of α for colloids that would otherwise be susceptible to hydrodynamic removal. Breakthrough curves and retention profiles show that more retention occurs for smaller particles, which reflects the influence of blocking.

Colloid Transport and Retention in Constricted Tube Pore Spaces With Diverse Geometries and Orientations

“…Therefore, obtaining the collection efficiency η , as we did in this study, is a crucial step in quantifying colloid attachment also in the presence of repulsive barriers. Recent research on cylindrical pore throats (Lin et al., 2021, 2022) has shown that not only is η highly sensitive to fluid velocity, colloid size, and pore size, in agreement with our study, but so is the sticking efficiency for characterizing attachment through energy barriers. Since the fluid velocity and the ratio of colloid radius to pore radius changes drastically within a single constricted tube pore, and since pore shapes are heterogeneous in real soils, future research is necessary to elucidate the effects of pore throat geometry and orientation on the sticking efficiency.…”

“…In such a case, nanoscale charge heterogeneity may also facilitate attachment under mean-field repulsive conditions, but is beyond the scope of this study, though we note that numerical models that consider this are available for other pore geometries (e.g., Johnson, 2020;Rasmuson, VanNess, et al, 2019). Possible attachment through energy barriers may be characterized by combining the collection efficiency with a sticking efficiency parameter (Lin et al, 2021(Lin et al, , 2022, which is at least in the first order independent of the collection efficiency. Thus, we only simulate purely attractive DLVO potentials, representing favorable attachment conditions, to obtain the collection efficiency (Molnar et al, 2015).…”

Modeling the Transport and Retention of Nanoparticles in a Single Partially Saturated Pore in Soil

“…The formulations for 1D-averaged deposition rate coefficients at SWI, AWI, and AWS proposed in this study are applicable only for partially drained pores. For fully saturated pores, the deposition rate coefficients at SWI can be calculated using the formulations proposed by Seetha et al (2017), or by following the approach of Lin et al (2021Lin et al ( , 2022.…”

The effect of kaolinite on ferrihydrite colloid migration in soil: molecular-scale mechanism study

“…Some models have shown that the inhibition of colloid migration increases with solid surface roughness. 16,17 Most previous studies have focused on the migration of colloids in columns of glass beads or quartz sand that were employed as models for naturally occurring transport solids, and show that those columns do not normally hinder the migration of well-dispersed colloids. 11,12,18 Nonetheless, natural porous media are composed of distinct mineral constituents with surface characteristics that are much more complicated than those of quartz sand or glass beads, and those characteristics have different effects on colloid transport.…”