Lecture 11 CEC, Flocculation, Iron, Aluminum

Lecture 11 CEC, Flocculation, Iron, Aluminum - Mineral...

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Unformatted text preview: Mineral Colloids Continued Na + K + K + Na + K + K + K + Cation Exchange Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Colloid Soil Solution Factors Determining Cation Preference 1. Concentration 2. Charge (+1, +2,+3) 3. Size Mineral Cation Exchange Capacity The total quantity of cations a clay can adsorb. Equal to the amount of charge Units are cmol c /kg soil Range: 0 - 180 cmol c /kg Related directly to the amount of Isomorphous substitution K H O H H O + 1. Kaolinite 1. Has low CEC Reason: limited isomorphous substitution 2. Is non-expanding Reason: layers are glued shut by hydrogen bonds 3. Cation adsorption is on the outer mineral surfaces Reason: layers are glued shut by hydrogen bonds 2. Smectite 1. Has high CEC Reason: abundant isomorphous substitution (Mg for Al) 2. Is highly expanding 3. Cation adsorption is in the interlayers of mineral Reason: layers are not glued shut by hydrogen bonds Allowing easy movement of water and hydrated cations to the interlayer regions Reason: layers are not glued shut by hydrogen bonds Allowing easy movement of water and hydrated cations to the interlayer regions 3. Vermiculite 1. Has high CEC Reason: abundant isomorphous substitution (Al for Si) 2. Is moderately expanding 3. Cation adsorption is in the interlayers of mineral Reason: layers are not glued shut by hydrogen bonds Reason: layers are not glued shut by hydrogen bonds, but interlayer cations are very close to the source of the negative charge (the tetrahedra) holding the layers together. 3. Illite 1. Has low CEC Reason: abundant isomorphous substitution (Al for Si),...
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Lecture 11 CEC, Flocculation, Iron, Aluminum - Mineral...

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