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Non Silicate Colloids. Modified crystalline structures, and they commonly have neither tetrahedral nor octahedral sheets in their composition. Very little isomorphous subst. Charges from either removal or addition of H ions to the surface of the oxy-hydroxyl groups. . Typical Non Silicate Amorphous Clays.
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1. Non silicate Clays Amorphous clays
A = without
morphous = shape
Small structures, from mineral source
Humus
Organic matter
Large non crystalline structures (CHON)
Very difficult to identify a typical structure
2. Non Silicate Colloids Modified crystalline structures, and they commonly have neither tetrahedral nor octahedral sheets in their composition.
Very little isomorphous subst.
Charges from either removal or addition of H+ ions to the surface of the oxy-hydroxyl groups.
3. Typical Non Silicate Amorphous Clays Iron and Aluminum Oxides
Gibbsite [Al(OH)3] Oxisols and Ultisols
Goethite (FeOOH) yellow brown soils
Hematite (Fe2O3) red soils
Allophane and Imogolite Volcanic
Si(OH)x and Al(OH)x
In many soils clay silicates are mixed with non silicates clays. They may form external coating, and may alter typical behavior of clays.
4. Typical Non Silicate Humus Clays Humic substances
Humus: Humic acid, Fulvic acid, and Humin
Humus includes sugar amines, nucleic acids, phospholipids, vitamins, polysaccharides and many other unclassified compounds
Very complex series of carbon chains and ring structures
Numerous active functional groups (-COO-, NH2+ )
Very large specific surface area and charges
5. HUMUS CEC 300-700 meq/100 g soil=cmol kg-1 soil
Nutrients
Capacity to chelate metals
Nutrients and toxicity
Very large specific surface area
Increase water holding capacity
Soil aggregation
Source of N,S,P
6. Humus is part of the soil In most soils, humus substances are mixed with silicates clays. They may form external coating, and will alter typical behavior of clays.
Sometimes overwhelming the typical response.
7. Clay mineral-Clay humus
8. Review from last class Non silicate colloids
Non crystalline structures
Amorphous
Mineral and organic
Mineral
Al/Fe oxides - implications
Allophane and Imogolite - implications
Humus
Fulvic, Humic, Humin
Very complex
Functional groups
Implications
9. Geographic distribution of Mineral Clays Midwest
Prairie land MONTMORILLONITE, ILLITE, SMECTITES
Southeast
Subtropical- tropical KEOLINITE, Amorphous mineral clays Fe/Al oxides
10. Genesis and Geographic of mineral clays Weathering
Physical and chemical alteration
Chemical decomposition-recrystallization
Alteration: Changes of particle size, and broken edges. Weathered 2:1
Recrystallization: Complete breakdown of clay structures and re-crystallization of a new structure. 1;1 from 2:1
11. How ions interact with colloids Cations (POSITIVE CHARGES)
Anions (NEGATIVE CHARGES)
Implications?
12. Cations Positive charge
Attract and attract to positive
charge on colloids
Most common ions
K+, Mg2+, Ca2+, NH4+, Al3+, H+
Cation exchange capacity CEC
Sum of total cations that a given soil can absorb
How this exchange works out?
13. Anions Negative charges
Attracted to the positive charge on colloids
Most common anions
NO3-, HCO3-, OH-, SO4-
Anion exchange capacity AEC
Sum of total anions that a given soil can absorb
14. Exchange Reactions Principles governing this phenomena
Reversibility
Ratio Law
Cation selectivity
Al 3+ > Ca 2+ > Mg 2+ > K + = NH4 + > Na +
15. CEC Units : Number of moles / equivalent of + charges absorbed per unit of mass.
meq/100 g soil
cmol/kg soil (METRIC)
WE WILL NOT USE THIS UNIT IN THIS CLASS.
meq/100 g soil = cmol/kg soil
Nutrient availability in the soil system.
Before going into CEC
We need to understand the chemical definition of meq!
16. meq? Chemical Unit: Is the amount of ion required to cancel out the electrical charge of an opposite charged ion.
Amount of substance it takes to combine with a mole of H ion.
EQUIVALENT, in chemistry, the proportion of an element which will combine with or replace unit weight of hydrogen. When multiplied by the valency it gives the atomic weight.
Equiv = gram-atomic weight/valence
Valence= # of equivalents in one mole of a given ion
Equiv-w = g/mol /equiv/mol = g/equiv
meq = Equiv/1000
17. meq? Equiv-w = g-atomic Wt/valence
Valence= # of equiv in one mole
of a given ion
Equiv-w = g/mol /equiv/mol
= g/equiv
if meq = equiv/1000
And mg = g/1000
Equiv-g = meq-mg
18. Example How many equivalent-w are needed to neutralized hydrogen?
MW: 1 g/mol
Valence: 1 equiv/mol
Ca equv = 1 g/mol / 1 equiv/mol
Ca equiv = 1 g/equiv
= 1 mg/meq
19. Example How many equivalent-w are needed to neutralized Calcium?
MW: 40 g/mol
Valence: 2 equiv/mol
Ca equv = 40 g/mol / 2 equiv/mol
Ca equiv = 20 g/Equiv
= 20 mg/meq
20. Example How many equivalent-w are needed to neutralized Aluminum?
MW: 27 g/mol
Valence: 3 equiv/mol
Ca equv = 27 g/mol / 3 equiv/mol
Ca equiv = 9 g/Equiv
= 9 mg/meq
21. Example How many equivalent-w are needed to neutralized ammonium?
MW: 18 g/mol
Valence: 1 equiv/mol
Ca equv = 18 g/mol / 1 equiv/mol
Ca equiv = 18 g/Equiv
= 18 mg/meq