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Soil Sorption Properties

Soil Sorption Properties. Ability of soil to bind various substances from the dispersion medium Polydisperse system is a mixture of particles of various shapes and sizes mixed with organic substances. Soil Colloids. Mineral Colloids Clay minerals Primary silicates

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Soil Sorption Properties

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  1. Soil Sorption Properties • Ability of soil to bind various substances from the dispersion medium • Polydisperse system is a mixture of particles of various shapes and sizes mixed with organic substances

  2. Soil Colloids • Mineral Colloids • Clay minerals • Primary silicates • Insoluble phosphates of Al, Fe • Polymeric silicic acids (H2SiO3) • Hydrated oxides (Al, Fe, Mn), sesquioxides • Organic Colloids • Humic substances • Protein, lignin • Combined Colloids – Organo-mineral complexes

  3. Soil Colloids • Electronegative – ACIDOIDS • Negatively charged • Adsorption of cations • (Clay minerals, humic substances, H2SiO3) →most of the soil colloids • Electropositive – BASOIDS • Positively charged • Adsorption of anions • (hydrates of sesquioxides) • Ampholyte – AMPHOLYTOIDES • (hydrated polymers of sesquioxides)

  4. Origin of Soil Colloid Charge • Permanent • isomorphic substitutions in the crystal lattice of clay minerals • Octahedron : Al3+→ Fe2+, Tetrahedron: Si4+ → Al3+ • Variable • pH-dependent charge • Is formed by the dissociation of carboxyl groups • negative charge increases with increasing of soil pH

  5. Soil Sorption Complexes • Soil Sorption Complexes – mineral, organic, organo-mineral • C.E.C.- (Cation Exchange Capacity) (amount of cations which a soil is able to attract at pH 7, or another suitable pH) • Effective (how much available binding sites the soil provides at the given pH) • Potential (The highest C.E.C. value which soil can achieve due to pH increase)

  6. Soil Sorption Complexes Acid Cations Base Cations Ca2+ H+ - K+ - - - H+ - - - - - - Na+ H+ Mg2+ Al3+

  7. Methods for C.E.C. Determination • The diverse range of methods • Index Ion Method (The sorption complex is saturated by the index ions → index ions are displaced and their concentration is determined) • Saturation of sorption complex by index ion • Washing of excess ions • Displacing of index ion and its determination • Mehlich method • Bower method

  8. Bower CH3COOH Ca2+ + (CH3COO)2Mg K+ Na+ Na+ + Ca2+ Na+ Na+ CH3COONa CH3COOK Na+ Na+ CH3COONa Ca2+ Mg2+ (CH3COO)2Ca Na+ Na+ Na+ Na+ NH4 + Na+ Na+ H+ washing C2H5OH + CH3COONH4 + CH3COONH4 NH4 + CH3COONa NH4 + NH4 + NH4 + Determination using AAS NH4 +

  9. 1. • Add 10ml of 1M CH3COONa (use pipette) • Let shake for 3 min • Centrifuged • Empty supernatant from the cuvette into waste 2. • Add10ml of 95% C2H5OH • Let shake for 3 min • Centrifuged • Empty supernatant from the cuvette into waste Methodology Weight 2g of soil 1. Step - Saturation (3x) 2. Step - Washing (3x) 3. Step – Displacement of index ions (3x) 4. Complete filtrate in the volumetric flask by 1M CH3COONH4 5. Measurement of index ion concentration using AAS 3. • Add 10ml of 1M CH3COONH4 • Let shake for 3 min • Centrifuged • FILTRATE SUPPERNATANT • into 50 ml volumetric flask

  10. Calculation mmol(+)/100g CNa……Concentration of Na ions (mmol/ml) V………Volume of the volumetric flask (ml) n……… Weight of soil used for the analyses (2g)

  11. Evaluation

  12. C.E.C.

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