Transport of barrel and spherical shaped colloids in unsaturated porous media

Knappenberger, Thorsten; Aramrak, Surachet; Flury, Markus

doi:10.1016/j.jconhyd.2015.07.007

Cited by 34 publications

(22 citation statements)

References 43 publications

(63 reference statements)

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“…For a large particle in a deposition matrix (Figure a), the surface topography was categorized as flat, convex, or concave. The overall deposition behaviour was distinctly observed and was consistent with the results of the synthetic‐based colloid transport experiment (Knappenberger et al, ), namely, concave > flat > convex. Additionally, similar‐sized colloids were aggregated at different scales, including separation (Figure b), medium‐scale aggregation (Figure c), and large‐scale aggregation (Figure d).…”

Section: Resultssupporting

confidence: 85%

“…Thus, when a coastal aquifer is polluted by highly concentrated heavy metals, the environmental impact is relatively in situ over a certain period. Additionally, the colloids in seawater–freshwater interaction zones are important facilitators of heavy metal migration when they are released from the secondary energy minimum (Knappenberger et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…A small fraction of the colloid was coated with platinum to visualize colloid aggregation. Three types of colloid occurrence were randomly chosen for more detailed investigation: (a) for fine colloids retained on large colloids, the roughness and the topography of each large colloid surface were categorized as smooth or rough and flat, convex, or concave (Knappenberger, Aramrak, & Flury, ) to evaluate the deposition states of fine colloids; (b) the homogeneous aggregates in clusters of multiple colloids were characterized; and (c) separate particles were characterized.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…In the calculation, colloidal particles were supposed as sphere, whereas the sand particle surfaces were supposed as plate. The sphere–plate double‐layer interaction energy was expressed as (Gregory, ; Knappenberger et al, )

Δ G_{el} = 64 italicπrε {(\frac{kT}{ez})}^{2} γ_{1} γ_{2} exp ((), - italicκh)

the van der Waals interaction energy as (Gregory, ; Knappenberger et al, )

Δ G_{vdW} = - \frac{Ar}{6 h} ([], 1 - ((), \frac{5.32 h}{λ}) ln ((), 1 + \frac{λ}{5.32 h}))

the Debye length as

κ^{- 1} = \sqrt{\frac{ε_{0} εkT}{2 N_{normalA} e^{2} I}}

and the total interaction energy as

Δ G_{TOT} = Δ G_{el} + Δ G_{vdW}

where r is the colloid radius; ε is the electromagnetic permittivity of the medium, which was taken as ε = 70 (Gavish & Promislow, ); k is the Boltzmann constant; T is the absolute temperature; e is the electron charge; z is the ion valence; γ 1 and γ 2 are the surface potentials; κ is the inverse Debye length; h is the separation distance; A is the Hamaker constant, which was taken as A 132 = 7.59 × 10 −20 J between silica sand and silica colloid (Bergström, ); λ is the length of interaction; I is the ionic strength of the electrolyte; and N A is the Avogadro number. Meanwhile, the thickness of the double layer is given as being approximately 1.5 κ −1 (Stojek, ).…”

Section: Experimental Methodsmentioning

confidence: 99%

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Modelling of colloidal particle and heavy metal transfer behaviours during seawater intrusion and refreshing processes

Tan

Dai

Zhou

et al. 2017

Hydrological Processes

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The proper management of coastal aquifers commonly requires an understanding of regional mass flow and complete seawater-freshwater circulation. In this study, time series observations of seawater intrusion and refreshing were conducted using a column experiment based on natural flow conditions in coastal groundwater and a sampled medium from a coastal sandy aquifer without chemical treatment. Ranges of hydrodynamic and hydrochemical variables were tested and

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Section: Resultssupporting

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Δ G_{el} = 64 italicπrε {(\frac{kT}{ez})}^{2} γ_{1} γ_{2} exp ((), - italicκh)

the van der Waals interaction energy as (Gregory, ; Knappenberger et al, )

Δ G_{vdW} = - \frac{Ar}{6 h} ([], 1 - ((), \frac{5.32 h}{λ}) ln ((), 1 + \frac{λ}{5.32 h}))

the Debye length as

κ^{- 1} = \sqrt{\frac{ε_{0} εkT}{2 N_{normalA} e^{2} I}}

and the total interaction energy as

Δ G_{TOT} = Δ G_{el} + Δ G_{vdW}

Section: Experimental Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Modelling of colloidal particle and heavy metal transfer behaviours during seawater intrusion and refreshing processes

Tan

Dai

Zhou

et al. 2017

Hydrological Processes

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“…4). Further drainage and film thinning reduces liquid speed and shear forces, leaving the gathered material on particle surfaces (Torkzaban and Bradford, 2016; Knappenberger et al, 2015). Multiple wetting and drying events increase aggregate surface roughness, which further facilitates the accumulation of fine debris and microbial colonization on the surfaces (Bradford and Torkzaban, 2015).…”

Section: Resultsmentioning

confidence: 99%

Sandy Soil Microaggregates: Rethinking Our Understanding of Hydraulic Function

Paradiś

Brueck

Meisenheimer

et al. 2017

Vadose Zone Journal

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Core Ideas Sandy soil microaggregates are comprised of a solid sand core encrusted with fines. Thick films control a significant proportion of water retention in coarse sandy soil. Three water pools drain sequentially: capillary water, thick films, and adsorptive films. Film seepage rates should be considered when irrigating sandy soil. This study investigated the peculiar structure of microaggregates in coarse sandy soils that exhibit only external porosity and investigated their control on soil hydrology. The microstructure underpins a hydrologic existence that differs from finer textured soils where aggregates have internal porosity. Understanding the impact of these microaggregates on soil hydrology will permit improved agricultural irrigation management and estimates associated with ecosystem capacity and resiliency. Microstructure was investigated using a digital microscope, and aspects of the structure were quantified by sedimentation and computed microtomography. Sandy soil microaggregates were observed to be comprised of a solid sand‐grain core that is coated with fines, presumably cemented by organic media. This microstructure leads to three distinct water pools during drainage: capillary water, followed by thick films (1–20 μm) enveloping the outer surfaces of the crusted microaggregates, followed by adsorbed thin films (<1 μm). The characteristics of the thick films were investigated using an analytical model. These films may provide as much as 10 to 40% saturation in the range of plant‐available water. Using lubrication theory, it was predicted that thick film drainage follows a power law function with an exponent of 2. Thick films may also have a role in the geochemical evolution of soils and in ecosystem function because they provide contiguous water and gas phases at relatively high moisture contents. And, because the rough outer crust of these microaggregates can provide good niches for microbial activity, biofilm physics will dominate thick film processes, and consequently hydrologic, biologic, and geochemical functions for coarse sandy soils.

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

Flury

Aramrak

2017

Water Resources Research

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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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Transport of barrel and spherical shaped colloids in unsaturated porous media

Cited by 34 publications

References 43 publications

Modelling of colloidal particle and heavy metal transfer behaviours during seawater intrusion and refreshing processes

Modelling of colloidal particle and heavy metal transfer behaviours during seawater intrusion and refreshing processes

Sandy Soil Microaggregates: Rethinking Our Understanding of Hydraulic Function

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

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