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Lecture 11 Clay Minerals

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Iron staining is often a good indicator of disturbed acid sulfate soils. When acid sulfate soils are disturbed and undergo oxidation, the sulfuric acid ... – PowerPoint PPT presentation

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Title: Lecture 11 Clay Minerals


1
Lecture 11Clay Minerals
  • Clay and organic matter in the soil provide the
    negative absorptive sites or Cation Exchange
    Capacity (CEC)

2
Organic matter as a source of negative charge
  • 1. Soil Humus - SOM
  • R-CO OH lt---gt R-CO-O- H
  • This charge is pH dependent or as the pH
    increases more OH- is available and therefore
    more CEC and conversely acid soils have a lower
    CEC from OM.

Acid soil (neutral molecule)
Deprotonates
Raise the pH
Anion CEC site
OH- or O- Ca or K
3
Clay minerals as a source of negative charge
4
Clay as a source of negative charge
  • 2. Source 1
  • 1) broken bonds at edge of clay mineral

5
Edge Effects are pH Dependent
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7
Source 2
  • 2) internal charge not satisfied because of ionic
    substitution -called Isomorphous Substitution
  • Al 3 for Si 4 or Mg2 for Al 3 or Zn2
    for Al3

No substitution Zn for Al
Neutral -1 charge
8
Silicate Clay Minerals
  • Aluminosilicates have a definite crystalline
    structure. Formed by the alteration of existing
    minerals or by synthesis from elements.
  • lt .002 mm in size (only seen with aid of electron
    microscope)
  • Two basic kinds of clay minerals 1 1 and 2
    1

9
Basic Building Blocks for Clay Minerals
  • Silicon - Oxygen Tetrahedron
  • SiO4-4
  • Repeat Unit (Si2O5)-2

10
Basic Building Blocks - 2
Al(OH)3
  • Aluminum Octahedral (Gibbsite Sheet)
  • Al(OH)6-3 Repeat Unit Al2(OH)42

11
Types of Clay Minerals
  • 1) Kaolinite a 1 1 clay mineral - 1 silica
    sheet and 1 gibbsite sheet
  • .000000072 cm thick

Si
Al
Properties 1) LARGE PARTICLES LOW CEC - 3-15
MEQ/100G 2) RIGIDLY FIXED- LOW SHRINK SWELL
12

11 layer
Basal O
Apical O, OH
13
2 1 CLAY MINERALS
  • 1. Hydrous Mica or Illite
  • replacement of Si4 with Al3 in 25 of
    tetrahedrals, each substitution leaves 1 neg
    charge site also K ions are a bridge between
    layers and hold them tightly together

Properties 1) non-expanding 2) Low CEC 30 meq/100
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15
kaolinite
illite
humus (fulvic acid)
mont- morillonite
16
2. Vermiculite
  • Same as Illite with all the K ions removed

Properties 1) expanding - large shrink swell 2)
High CEC150meq/100g
17
3. Smectite or Montmorillonite
  • Mg replaces Al in Octahedral layer
  • Properties 1) expanding (common clay found in
    Minnesotas soils.
  • 2) CEC 80-150 meq/100g

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20
Go To Clay Minerals Web Page
  • http//www.soils.wisc.edu/virtual_museum/

21
Dyad
  • Where have you had contact with a clay ?

22
Sheets and Layers
11 non-expanding
21 non-expanding
21 expanding
Al sheet
Si sheet







Al sheet
Si sheet
Al sheet
Si sheet





Al sheet


Si sheet
kaolinite
illite
smectite and vermiculite
23
Clay Minerals Comparison
24
The End
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