Clays as Colloids

R. F. Giese

Geology

glgclay@acsu.buffalo.edu

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Meaning of “clay”

• Engineering– small particles of any material

• Geological– small particles of layer silicate minerals

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Outline

• Uses.

• Structure.

• Chemistry.

• Surface properties.

• Stability of clay-water systems

• Landslide

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Importance of clays• Industrial

– thickeners (paints, drilling muds)– catalysts (cracking of hydrocarbons)– fillers (rubber, plastics)– adsorbents

• Geological– alteration products of rock– formation of hydrocarbons

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Importance of clays

• Scientific– large surface area– known surface structure– nano-composites– insulators– designer surfaces

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Clay Minerals

• Layer silicates

• Silicates are oxides of silicon and other elements:

• Aluminum, magnesium, iron, calcium, sodium

• Oxygen (anion) is larger than the other elements (cations)

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Origin and calculation of the layer charge for 2:1 clay minerals.

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Kaolinite: TEM replica

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Kaolinite: TEM

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Halloysite: TEM

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Micas

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Smectites

Vermiculites

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Organo-clays

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Montmorillonite: TEM replica

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Montmorillonite: TEM

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Allophane

TEM replica

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Allophane

TEM replica

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Surface tension measurements

• Single crystals (micas)

• oriented films (smectites)

• thin layer wicking (kaolinite)

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Generalities for clays

2

2

2

35 45mJ/m

0 3mJ/m

5 45mJ/m

LW

$

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For all natural clays:

difference between hydrophobic and hydrophilic

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Natural and modified clay materials

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Coverage of talc by a long chain amine (in wt%)

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0 5 10 15

Chain length

0

5

10

15

20

25

30

35

40

-n-alkyl ammonium cations

Coverage of smectite by organic matter

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Interactions in water

• Flocculation

• Adsorption

• DLVO versus XDLVO

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F r e e E n e r g y o f I n t e r a c t i o n :

1 2 1 1 2

1 1 2 2 1 2 1 2

2

4

A B A BG

$ $ $ $

1 2 1 1 2

1 2 1 2

2

2 2

L W L W

L W L W L W L W

G

21 2 1

1l n 1 e x p

2E LG R

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XDLVO plot

-1000

0

1000

2000

3000

4000

5000

6000

0 10 20 30 40 50 60

Distance (A)

De

lta

G (

kT

)

Series1

Series2

Series3

Series4

Series5

Series6

Series7

Montmorillonite: XDLVO

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Stability of montmorillonite

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Quick clays

• Clays deposited in marine environment

• sea level drops

• rain leaches out the salty pore water

• attraction between particles is weakened

• soil becomes unstable

• Canada, Scandinavia