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pH dependent sites
ionization of hydrogen
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chlorite
2:2 non-expanding clay
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illite
2:1 non-expanding clay
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kaolinite
1:1 non-expanding clay
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soil nitrogen component
percent organic matter
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amorphous soil compound
allophane
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octahedron
eight-sided clay structure
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vermiculite
2:1 limited expanding clay
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Al/Fe oxide clays
tropical clays
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montmorillonite
2:1 highly expanding clay
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tetrahedron
four-sided structure
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space between tetrahedral and octahedral sheets
interlayer
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The area right next to the atoms, on the edge of the interlayer
- internal surface area
- they repel so water, other cations come in
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the storehouse where nutrients are adsorbed
cation exchange capacity
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Name the 5 silicate clays we studied
- kaolinite
- montmorillonite
- illite
- vermiculite
- chlorite
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what are some non-silicate colloids?
- oxide/hydroxide clays (tropical)
- amorphous materials (noncrystalline, volcanic ash, lava)
- humus
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as a pH nears 7, what happens to the ionization amount?
- it's greater
- we're talking about how close H is to O. The lower the pH, the tighter the bond between H and O
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isomorphous (ionic) substitution
- in tetrahedral or octahedral sheets
- referred to as constant or permanent negative sites (not affected by pH)
- in octahedral, the most common sub is Mg
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the number of negative charges determines what?
CEC
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What elements are most common in silicate clays?
- Si4+
- Al3+
- Fe 3+
- Mg 2+
- Zn 2+
- Fe 2+
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The lower the pH...
- the higher amounts of H
- also the more acidic
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4 key things to remember about kaolinite
- 1. 1:1 clay structure (1 tetra, 1 octa)
- 2. No substitution in tetra or octa sheets
- 3. Non-expanding
- 4. Low CEC
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expansion of clays occurs where?
- interlayer
- if H moves into the interlayer, it's going to be attracted to the top and bottom of the sheet, oxygens are tightly held so there's no expansion
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4 key things to remember about montmorillonite
- 1. 2:1 clay structure
- 2. ionic substitution in tetra and octa sheets - but mostly octa
- 3. highly expanding clay
- 4. High CEC
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4 key things to remember about Illite?
- 1. 2:1 clay structure
- 2. Ionic sub in the tetrahedral sheet (sub Al3+ for Si4+)
- 3. Non-expanding clay
- 4. Moderate CEC
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Vermiculite - 5 things
- 1. 2:1 clay
- 2. ionic subs in tetra and octa (little more in tetra)
- 3. interlayer space contains strongly adsorbed hydroxyions of Mg (mainly) and Al
- 4. limited expanding clay
- 5. very high CEC
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common sub in tetrahedral sheet?
Al for Si
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common sub in octahedral?
Mg for Al
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5 things to remember about Chlorite
- 1. 2:2 structure
- 2. Ionic substitution in octahedral layer
- 3. Mg-dominated octahedral sheet in interlayer
- 4. Non-expanding
- 5. Low to moderate CEC
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5 things to know about humus?
- 1. non crystalline
- 2. CHO framework
- 3. Large number of negative sites (compared to clays)
- 4. pH dependent sites (H moves away from O)
- 5. Very high CEC
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Oxide-hydroxide clays
- sesquioxides
- crystalline or amorphous
- nonsticky, nonplastic, noncohesive (well-drained clays)
- small negative charge (CEC)
- small positive charge (AEC)
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Amorphous inorganic compounds
- Noncrystalline
- some oxide clays
- allophane & imoglite
- positive and negative sites
- origin - volcanic compounds and some igneous rocks
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CEC calculations are based on
- clay content
- type of clay
- humus content
- PH
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CEC summation method
- summation of all cations adsorbed on soil colloid
- method used on mo soil testing report
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Base-forming cations (raises pH)
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Acidic cations (lower pH)
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