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Layer Silicate Clay Structure- basic building blocks 1. Tetrahedron - SiO 4

Layer Silicate Clay Structure- basic building blocks 1. Tetrahedron - SiO 4. Sharing of O or OH groups = sheets and unit layers (a) tetrahedral sheet                          . 2. Octahedron - Al(OH) 6. Octahedral sheet  .

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Layer Silicate Clay Structure- basic building blocks 1. Tetrahedron - SiO 4

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  1. Layer Silicate Clay Structure- basic building blocks 1. Tetrahedron - SiO4 Sharing of O or OH groups = sheets and unit layers (a) tetrahedral sheet                          

  2. 2. Octahedron - Al(OH)6 Octahedral sheet  

  3. Tetrahedral and octahedral sheets are often drawn as shownbelow   

  4. 1:1 Type Minerals kaolinite

  5. Unit layers H-bonded together • fixed lattice type • no interlayer activity • no shrink-swell • only external surface • Well crystallized • little isomorphous substitution • low cation adsorption • larger particle size • hexagonal shaped

  6. Type Minerals • Expanding lattice • (a) Smectite group (mostly, montmorillonite)

  7.  Freely expanding large internal surface water in interlayer Poorly crystallized large shrink-swell small size isomorphous substitution  adsorbed cations in interlayer offset the isomorphous substitution large cation adsorption

  8. Vermiculite Similar to smectites Except Al+3 for Si+4 in tetrahedral layer Interlayer ions are more structured (Mg+2 + H2O) Limited expansion Large cation adsorption

  9. Non-expanding lattice (a) Fine-grained micas or illite

  10. Al+3 and K+ substitute for Si+4 (tetrahedral sheet) weathering at edges = release of K+ - very limited expansion - medium cation adsorption - limited internal surface - properties between kaolinite and vermiculite

  11. Chlorites Mg-octahedral sheet replace K+ of illite properties similar to illite

  12. Summary of Properties

  13. اگر ذره رس قطري معادل رس يز داشته باشد حاوي چند لايه است ؟ رس ريز قطر 2 ميکرون (0.2 / 106) . 109 =200 nm 200 nm / (0.72) = 278 layer آيا ميتوانيد تصور کنيد که در کوچکترين ذره خاک (رس ريز) با قطر 2/0 ميکرون 278 لايه وجود داشته باشد.

  14. Source of charge on clays-  permanent or variable? 1. Permanent or constant charge (a) isomorphous substitution for example: Zn+2 for Al+3 in octahedral sheet b) both octahedral and tetrahedral sheets Mg+2, Zn+2, Cu+2, Fe+2 for Al+3 Al+3 for Si+4 (c) can form + charge - Al+3 for Mg+2 - negative charge dominates

  15. 2. Variable or pH-dependent charge (a) Dissociation of exposed OH groups (b) Occurs with humus, hydrous oxides,and broken edges of silicate clays (c) Increased pH values = more negative charge d) Protonation of O and OH groups

  16. (e) Depends on soil colloids present (f) Positive charge << negative charge in most temperate zone soils

  17. Cation Exchange 1. Process of cation replacement

  18. Cation Exchange Capacity (CEC)

  19. Units of charge per unit weight (a) centimoles of charge per kilogram of soil= cmolc/kg old units of milliequivalents per 100 grams of soil = (meq/100 g) (b) all cations are equal on a charge basis 1 cmolc/kg Na+ = 1 cmolc/kg Ca+2 = 1 cmolc/kg Al+3 (c) conversion of charge to weight 5 cmolc/kg of Ca+2 = ? g Ca+2 (5 cmolc/kg soil)(molc/100 cmolc)(mol Ca+2/2 molc)(40 g Ca+2/mol Ca+2) = 1 g Ca+2/kg soil

  20. 4. Cation exchange capacity of soils • related to components • humus » 200 cmolc/kgsmectites » 100 cmolc/kgillite » 25 cmolc/kg kaolinite » 10 cmolc/kgFe and Al oxides » 4 cmolc/kg (b) estimate soil cation exchange capacity from composition: 5 % O.M. & 20 % smectite clay 200 x 0.05 = 10 100 x 0.20 = 20 total = 30 cmolc/kg 2 % O.M. & 30 % kaolinite clay 200 x 0.02 = 4 10 x 0.30 = 3 total = 7 cmolc/kg

  21. راندمان تبادل کا تيونها غلظت نسبييا تعداد يونهاي موجود بار الکتريکييونها Na< K< Mg< Ca< Al سرعت اکتيويته يونها سرعت اکتيويته تابع شعاع هيدراته

  22. شعاع هيدراته شعاع يوني ليتيم 78/0 30/ 10 سديم 98/0 90/7 پتاسيم 33/.1 32/5 روبديم 49/1 09/5

  23. مثال ظرفيت تبادل کاتيوني خاکي که 3 درصد مواد آلي و 24 درصد رس و 36 درصد شن و 40 درصد سيلت دارد چقدر است . بافت خاک چيست CEC= 50 meq /100g کلوئيدهاي بخش معدني CEC= 200 meq /100g کلوئيدهاي بخش آلي 24 * 0.5 = 12 meq /100g 3 * 2 = 6 meq /100g 6 + 12 = 18 meq /100g

  24. مثال يک خاک چمني مطالعه شده عمق CEC Ca Mg K Na H 15-0 24.4 11.3 4.1 0.8 0.2 ? 8 ميلي اکي والان ميزان هيدروژن چقدر است ؟ ميزان کلسيم در هکتار تا عمق 15 سانتيمتري چقدر است ؟ وزن مخصوص ظاهري 5/1 گرو بر سانتي متر مکعب

  25. 10000* 0.15= 1500 m3 * 1500 kg/m3= 2250000 kg 11.3 meq for 100g *20 mgr for meq= 226 g ca for 100g = 0.226kg for 100kg (0.226kg/100kg) * 2250000 kg = 5085 kg ca /hec

  26. Clay Genesis and Distribution 1. Stages of weathering (a) alkali metals and alkaline earths dissolve (Na+, K+, Ca+2, Mg+2) (b) Si dissolves and leaches (c) continual reforming of new clay minerals Clays reflect weathering processes Young, weakly weathered soils = fine-grained mica, chlorite, vermiculite Intermediate weathering = vermiculite, smectite, kaolinite Strong weathering = kaolinite, hydrous oxides

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