Colloid Mobilization and Transport during Capillary Fringe Fluctuations

Aramrak, Surachet; Flury, Markus; Harsh, James B.; Zollars, Richard L.

doi:10.1021/es501797y

Cited by 25 publications

(31 citation statements)

References 49 publications

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“…These processes should be validated by directly observing fluorescent colloids in porous media in a glass chamber using a confocal microscope. 31 Effect of Flow Path Permeability. By monitoring colloid mobilization in different flow paths within the same soil core, we established the link between flow path permeability and colloid mobilization in response to increasing drying duration.…”

Section: ■ Discussionmentioning

confidence: 99%

Colloid Mobilization in a Fractured Soil during Dry–Wet Cycles: Role of Drying Duration and Flow Path Permeability

Mohanty

Saiers

Ryan

2015

Environ. Sci. Technol.

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In subsurface soils, colloids are mobilized by infiltrating rainwater, but the source of colloids and the process by which colloids are generated between rainfalls are not clear. We examined the effect of drying duration and the spatial variation of soil permeability on the mobilization of in situ colloids in intact soil cores (fractured and heavily weathered saprolite) during dry-wet cycles. Measuring water flux at multiple sampling ports at the core base, we found that water drained through flow paths of different permeability. The duration of antecedent drying cycles affected the amount of mobilized colloids, particularly in high-flux ports that received water from soil regions with a large number of macro- and mesopores. In these ports, the amount of mobilized colloids increased with increased drying duration up to 2.5 days. For drying durations greater than 2.5 days, the amount of mobilized colloids decreased. In contrast, increasing drying duration had a limited effect on colloid mobilization in low-flux ports, which presumably received water from soil regions with fewer macro- and mesopores. On the basis of these results, we attribute this dependence of colloid mobilization upon drying duration to colloid generation from dry pore walls and distribution of colloids in flow paths, which appear to be sensitive to the moisture content of soil after drying and flow path permeability. The results are useful for improving the understanding of colloid mobilization during fluctuating weather conditions.

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Section: ■ Discussionmentioning

confidence: 99%

Colloid Mobilization in a Fractured Soil during Dry–Wet Cycles: Role of Drying Duration and Flow Path Permeability

Mohanty

Saiers

Ryan

2015

Environ. Sci. Technol.

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“…As the air‐water interface is a mobile boundary, colloids that are attached to the air‐water interface by capillary forces can freely move around [ Kralchevsky et al ., ; Gao et al ., ; Lazouskaya et al ., ; Aramrak et al ., ]. This movement can be driven by hydrodynamic forces, Brownian motion, or by surface tension‐driven forces.…”

Section: Interactions Of Colloids and Air‐water Interfacesmentioning

confidence: 99%

“…In general, column transport experiments yield breakthrough curves and depth profiles of colloids, and these data can then be analyzed to quantify colloid retention and mobilization for varying initial and boundary conditions. In some cases, bright‐field and confocal microscopy was combined with column experiments to provide pore‐scale information on colloid interactions with interfaces [ Zevi et al ., ; Aramrak et al ., ]. Key findings of unsaturated flow studies are summarized in Table .…”

Section: Colloid Transport In Unsaturated Porous Mediamentioning

confidence: 99%

Role of air‐water interfaces in colloid transport in porous media: A review

Flury

Aramrak

2017

Water Resources Research

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103

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Air‐water interfaces play an important role in unsaturated porous media, giving rise to phenomena like capillarity. Less recognized and understood are interactions of colloids with the air‐water interface in porous media and the implications of these interactions for fate and transport of colloids. In this review, we discuss how colloids, both suspended in the aqueous phase and attached at pore walls, interact with air‐water interfaces in porous media. We discuss the theory of colloid/air‐water interface interactions, based on the different forces acting between colloids and the air‐water interface (DLVO, hydrophobic, capillary forces) and based on thermodynamic considerations (Gibbs free energy). Subsurface colloids are usually electrostatically repelled from the air‐water interface because most subsurface colloids and the air‐water are negatively charged. However, hydrophobic interactions can lead to attraction to the air‐water interface. When colloids are at the air‐water interface, capillary forces are usually dominant over other forces. Moving air‐water interfaces are effective in mobilizing and transporting colloids from surfaces. Thermodynamic considerations show that, for a colloid, the air‐water interface is the favored state as compared with the suspension phase, except for hydrophilic colloids in the nanometer size range. Experimental evidence indicates that colloid mobilization in soils often occurs through macropores, although matrix transport is also prevalent in absence of macropores. Moving air‐water interfaces, e.g., occurring during infiltration, imbibition, or drainage, have been shown to scour colloids from surfaces and translocate colloids. Colloids can also be pinned to surfaces by thin water films and capillary menisci at the air‐water‐solid interface line, causing colloid retention and immobilization. Air‐water interfaces thus can both mobilize or immobilize colloids in porous media, depending on hydrodynamics and colloid and surface chemistry.

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“…The matrix in contact with an AWI could experience a capillary stress and be deformed (such as cracking and shrink) (Majdalani et al 2008;Mohanty et al 2015a), and the deformation of the matrix is a kind of weakening process. This weakening effect on pore walls could generate mounts of colloidal particles (Aramrak et al 2011(Aramrak et al , 2014Michel et al 2010). When the infiltration was resumed, the TPs were easily to be mobilized from a weakened tailing matrix, which resulted in a large initial peak concentration.…”

Section: Particle Mobilization and Transportmentioning

confidence: 99%

Drying–wetting cycles facilitated mobilization and transport of metal-rich colloidal particles from exposed mine tailing into soil in a gold mining region along the Silk Road

2016

Environ Earth Sci

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Exposed mine tailings could release substantial amounts of toxic metal-rich colloidal particles into soils during drying-wetting (D-W) cycles, but the mechanisms are still incompletely understood. In this study, two-layered (tailings above and soils below) packed columns were set to explore the effects of D-W cycles on tailing particle (TP) mobilization and transport in soil, and the mediating effect of TPs on the release and transport of heavy metals (Pb and Cu) was also examined. Results show that D-W cycles enhanced colloidal TP (approximately 190-712 nm) release from the column. The enhancing effect depends on duration of drying period, being slight for short-term drying (1, 3, 7, and 14 days) and significant for long-term drying (30, 60, and 90 days). The most interesting observation is the concentration valley of the effluent TPs during wetting event after 7-and 14-day drying. Based on these results, the dependence of TP mobilization and transport upon drying duration can be attributed to a combined action of different particle generation mechanisms during different drying periods, which appears to be relevant to the pore water content. The release and transport of Pb and Cu from the tailings into soil were dominantly mediated by the TPs and significantly enhanced by D-W cycles. These findings improve the understanding of TPs mobilization and transport in soil under fluctuating weather conditions.

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Colloid Mobilization and Transport during Capillary Fringe Fluctuations

Cited by 25 publications

References 49 publications

Colloid Mobilization in a Fractured Soil during Dry–Wet Cycles: Role of Drying Duration and Flow Path Permeability

Colloid Mobilization in a Fractured Soil during Dry–Wet Cycles: Role of Drying Duration and Flow Path Permeability

Role of air‐water interfaces in colloid transport in porous media: A review

Drying–wetting cycles facilitated mobilization and transport of metal-rich colloidal particles from exposed mine tailing into soil in a gold mining region along the Silk Road

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