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Non silicate Clays

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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Non silicate 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

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