Non silicate Clays

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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.

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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.

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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

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HUMUS

• CEC 300-700 meq/100 g soilcmol 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

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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.

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Clay mineral-Clay humus
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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

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Geographic distribution of Mineral Clays

• Midwest
• Prairie land MONTMORILLONITE, ILLITE, SMECTITES
• Southeast
• Subtropical- tropical KEOLINITE, Amorphous
  mineral clays Fe/Al oxides

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Genesis and Geographic of mineral clays

• Weathering
• Physical and chemical alteration
• Chemical decomposition-recrystallization
• Alteration Changes of particle size, and broken
  edges. Weathered 21
• Recrystallization Complete breakdown of clay
  structures and re-crystallization of a new
  structure. 11 from 21

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How ions interact with colloids

• Cations (POSITIVE CHARGES)
• Anions (NEGATIVE CHARGES)
• Implications?

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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?

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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

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Exchange Reactions

• Principles governing this phenomena
• Reversibility
• Ratio Law
• Cation selectivity
• Al 3 gt Ca 2 gt Mg 2 gt K NH4 gt Na

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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!

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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

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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

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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

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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

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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

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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