Colloid Deposit Morphology and Clogging in Porous Media: Fundamental Insights Through Investigation of Deposit Fractal Dimension

Abstract

Experiments reveal a wide discrepancy between the permeability of porous media containing colloid deposits and the available predictive equations. Evidence suggests that this discrepancy results, in part, from the predictive equations failing to account for colloid deposit morphology. This article reports a series of experiments using static light scattering (SLS) to characterize colloid deposit morphology within refractive index matched (RIM) porous media during flow through a column. Real time measurements of permeability, specific deposit, deposit fractal dimension, and deposit radius of gyration, at different vertical positions, were conducted with initially clean porous media at various ionic strengths and fluid velocities. Decreased permeability (i.e., increased clogging) corresponded with higher specific deposit, lower fractal dimension, and smaller radius of gyration. During deposition, fractal dimension, radius of gyration, and permeability decreased with increasing specific deposit. During flushing with colloid-free fluid, these trends reversed, with increased fractal dimension, radius of gyration, and permeability. These observations suggest a deposition scenario in which large and uniform aggregates become deposits, which reduce porosity, lead to higher fluid shear forces, which then decompose the deposits, filling the pore space with small and dendritic fragments of aggregate.

Solute mixing regulates heterogeneity of mineral precipitation in porous media

“…These observations and the results of pore-scale flow simulations (Figures 3 and S6) suggest that the flow field reorganized as a result of the evolving pore structure, thus yielding solute mixing and precipitation slightly beyond the initial mixing interface. This pattern of evolution of the pore geometry results from the spatial confinement associated with packing of the porous medium and is qualitatively similar to the patterns of pore clogging resulting from the deposition of colloidal particles [Chen et al, 2009;Roth et al, 2015]. However, here the CaCO 3 deposits grew on grain surfaces, while colloidal deposits are strongly biased to the flow direction and to grain contacts, indicating that direct precipitation on grain surfaces was the primary mechanism of CaCO 3 accumulation.…”

“…Precipitation was rather uniform along the flow direction, with slightly more deposits near the inlet, whereas considerable variation was observed along the y direction ( Figure S4). This pattern of evolution of the pore geometry results from the spatial confinement associated with packing of the porous medium and is qualitatively similar to the patterns of pore clogging resulting from the deposition of colloidal particles [Chen et al, 2009;Roth et al, 2015]. This pattern of evolution of the pore geometry results from the spatial confinement associated with packing of the porous medium and is qualitatively similar to the patterns of pore clogging resulting from the deposition of colloidal particles [Chen et al, 2009;Roth et al, 2015].…”

Continuum-based models and concepts for the transport of nanoparticles in saturated porous media: A state-of-the-science review

“…X-ray computed tomography (XCT) has also been shown to have the potential for imaging the attached phase of NP, but its application at bulk scale is challenging because of interference at the grain/void interface and being limited to high electron density materials with high X-ray contrast [30]. Real-time monitoring of the attached phase of particles has been achieved by Roth et al [377] via static light scattering (SLS) yielding important parameters such as permeability, the radius of gyration (analogous to the hydrodynamic radius), and the fractal dimension of deposited aggregates. SLS can obtain very small length scales (voxel resolution as low as 50 nm) at significantly lower cost than alternatives such as X-ray microtomography.…”

Aggregation and sedimentation of shattered graphene oxide nanoparticles in dynamic environments: a solid-body rotational approach

“…To investigate such systems, we used a slow rotating cylinder in which these impacts are simulated by slow continuous revolutions of the cylinder. This simple apparatus allows monitoring the particle size dynamics during aggregation which is cumbersome or impossible in other experimental approaches used for studying the NP fate, such as packed column experiments 45 or mesocosm tests. 46 Rolling cylinders have been used extensively in marine science to mimic the natural condition of marine snow aggregate formation.…”