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Colloid Transport and Colloid-Facilitated Transport in Groundwater

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Colloid Transport and Colloid-Facilitated Transport in Groundwater Introduction DLVO Theory Stabilization/Transport/Aggregation/Filtration Applications – PowerPoint PPT presentation

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Title: Colloid Transport and Colloid-Facilitated Transport in Groundwater


1
Colloid Transport and Colloid-Facilitated
Transport in Groundwater
  • Introduction
  • DLVO Theory
  • Stabilization/Transport/Aggregation/Filtration
  • Applications
  • Special Case CFT the Vadose Zone

B.C. Williams, 2002
2
Colloids Defined
  • Particles with diameters lt 10 micron, lt 0.45 µ
  • Mineral detrital(as deposited) or autigenic
    (from matrix)
  • Layer silicates
  • Silica Rich Particles
  • Iron oxides
  • Organic e.g. humic macromolecules
  • Humic macromolecules
  • Biocolloids bacteria and viruses

3
(No Transcript)
4
Groundwater Transport in General
  • Usual conceptual model for groundwater transport
    as follows
  • Dissolved phase
  • Adsorbed phase (onto soil/rock matrix)
  • How a given chemical partitions into these two
    phases is represented by the partition
    coefficient, Kd.

5
Groundwater Transport Including
Colloid-Facilitated Transport
  • Three phases
  • Dissolved phase
  • Adsorbed phase (onto soil/rock matrix)
  • Adsorbed onto mobile particles

6
Colloid-Facilitated Groundwater Transport
Solid matrix
mobile colloid
Adsorbed
Dissolved
7
DLVO Theory Derjaguin, Landau, Verwey, Overbeek
  • The stability of a homogeneous colloidal
    suspension depends upon (stabilitydispersed)
  • Van der Waals attractive forces (promote
    aggregation)
  • Electrostatic repulsive forces that drive
    particles apart
  • If electrostatic dominates, particles are
    electrostatically stabilized (dispersed)

8
DLVO - stabilized
  • Colloids are stabilized (in suspension) when
  • Double layers expand (by decreasing electrolyte
    concentration, decreasing ionic strength
  • Net particle charge ? 0
  • Colloids coagulate/aggregate when
  • Double layer shrinks because of increasing ionic
    strength

9
Challenges to DLVO
  • Hot controversy in literature on whether spheres
    of like charge always repel. Experimental
    evidence that colloidal electrostatic
    interactions include a long-ranged attractive
    component.
  • http//griergroup.uchicago.edu/grier/leshouches2/
    leshouches2.html
  • http//griergroup.uchicago.edu/grier/comment3b/

10
Stabilization and sorbable species
  • Sorbed species can influence surface charge, and
    therefore stability (end of DLVO discussion)
  • Sorbed species can also be mobilized if the
    colloid is mobilized through the soil/rock matrix
    (colloid-facilitated transport!)

11
Colloid Transport in General (Saturated and
Unsaturated GW)
  • Detachment / Mobilization / Suspension
  • Stabilization
  • Transport
  • Aggregation / Filtration / Straining

12
Detachment/Mobilization/ Suspension
  • Colloids can detach from matrix
  • Biogeochemical weathering
  • Precipitation from solution (thermodyn)
  • Biocolloids or humics flushed from shallow zones
  • If cementing agents dissolve
  • If stable aggregates deflocculate

13
Transport
  • More likely if colloid is neg. charged, because
    most soil/rock matrices are neg.
  • Transport optimal if
  • Slow interpore transport rate few collisions
    with side surfaces
  • High velocities in preferential pathways
  • In preferential pathways, may have faster travel
    times than ambient gw flows

14
Stabilization/Aggregation
  • Aggregation occurs when double layer shrinks due
    to increasing ionic strength (slide 6)

15
Filtering / Straining
  • Physical filtering due to size, geometry
  • Physicochemical straining surface chemical
    attraction to matrix
  • Cementation agents (iron oxides, carbonates,
    silica)

16
Applications
  • Many engineering ramifications of passage versus
    filtration
  • Colloid-facilitated transport how a
    low-solubility (strongly-sorbed!) contaminant can
    travel miles from the source

17
Engineering Applications
  • Wastewater sand filters removal is good,
    too-small particles clog
  • Roads clogging of drain filters ? force buildup
    ? failure
  • Dams matrix piping ? erosion ? 26 of earth dam
    failures
  • ref Reddi, 1997

18
Engineering Applications, cont.
  • Petroleum Extraction permeability reduction
    termed formation damage
  • Slurry Walls very fines filtered by fines is
    considered good
  • Lining of Lakes/Reservoirs ditto
  • ref Reddi, 1997

19
Colloid-Facilitated Transport
  • When a highly sorptive contaminant (constituent)
    is adsorbed onto colloids
  • Contaminant of interest must have as high or
    higher affinity to sorb as other possible
    constituents
  • Colloid may have patches of surface coatings
    (ferric, aluminum or manganese oxyhydroxides)
    that are best sites

20
Colloid Transport in the Unsaturated Zone
  • Colloids may be strained, or retarded, if
    moisture content reduced so that water films have
    thickness less than colloid diameter
  • Colloids may sorb to the air/water interface
  • Called partitioning same Kd.concept

21
Colloid Transport in the Unsaturated Zone Ongoing
Research
  • Film Straining of Colloids
  • http//www.lbl.gov/jwan/film_straining/film_strai
    ning.html
  • http//www.lbl.gov/jwan/particles_film/particles_
    film.html
  • Colloids Sorbing to the Air-Water Interface
  • http//www.lbl.gov/jwan/colloid_partition/colloid
    _partitioning.html

22
References
  • Johnson, P.R., Sun, N., and Elimelech, M., 1996.
    Colloid Transport in Geochemically
    Heterogeneous Porous Media, Environmental
    Science and Technology, 30, 3284-3293. 
  • Reddi, L. N., 1997. Particle Transport in Soils
    Review of Significant Processes in Infrastructure
    Systems. J. Infrastructure Systems. 3, 78-86.
  •  McCarthy, J.F., Zachara, J.M., 1989.
    Subsurface Transport of Contaminants.
    Environmental Science and Technology, 23,
    496-502.
  • Wan, J. T.K. Tokunaga, 1998. "Measuring
    partition coefficients of colloids at air-water
    interfaces", Environ. Sci. Technol, 32,
    p3293-3298,
  • Wan, J., Wilson, J.L., 1994. Colloid transport
    in unsaturated porous media. Water Resources
    Research. 30, 857-864.

23
Acknowledgements
  • Jason Shira, MS Student
  • George Redden, INEEL
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