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Clay mineralogy sivakugan
- 1. N. Sivakugan Clay Mineralogy Duration = 15 mins.
- 2. Elements of Earth % by weight in crust O = 49.2 Si = 25.7 Al = 7.5 Fe = 4.7 Ca = 3.4 Na = 2.6 K = 2.4 Mg = 1.9 other = 2.6 12500 km dia 8-35 km crust 82.4%
- 3. Soil Formation Residual soil Transported soil ~ in situ weathering (by physical & chemical agents) of parent rock ~ weathered and transported far away by wind, water and ice. Parent Rock
- 4. Parent Rock ~ formed by one of these three different processes igneous sedimentary metamorphic formed by cooling of molten magma (lava) formed by gradual deposition, and in layers formed by alteration of igneous & sedimentary rocks by pressure/temperature e.g., limestone, shale e.g., marble e.g., granite
- 5. Residual Soils Formed by in situ weathering of parent rock
- 9. Tetrahedral Sheet Several tetrahedrons joined together form a tetrahedral sheet. tetrahedron hexagonal hole
- 10. Tetrahedral & Octahedral Sheets For simplicity, let’s represent silica tetrahedral sheet by: Si and alumina octahedral sheet by: Al
- 11. Different Clay Minerals Different combinations of tetrahedral and octahedral sheets form different clay minerals: 1:1 Clay Mineral (e.g., kaolinite, halloysite):
- 12. Different Clay Minerals Different combinations of tetrahedral and octahedral sheets form different clay minerals: 2:1 Clay Mineral (e.g., montmorillonite, illite)
- 13. Kaolinite Typically 70-100 layers Si Al Si Al Si Al Si Al joined by strong H-bond no easy separation 0.72 nm joined by oxygen sharing
- 17. Illite fit into the hexagonal holes in Si-sheet Si Al Si Si Al Si Si Al Si 0.96 nm joined by K + ions
- 19. A Clay Particle Plate-like or Flaky Shape
- 20. Clay Fabric Flocculated Dispersed edge-to-face contact face-to-face contact
- 25. Casagrande’s PI-LL Chart montmorillonite illite kaolinite chlorite halloysite
- 26. Special Terms
- 30. A Comparison 20-30 80 Chlorite 80-120 800 Montmorillonite 20-30 80-100 Illite 3-10 10-20 Kaolinite C.E.C (meq/100g) Specific surface (m 2 /g) Mineral
- 33. Clay Particle in Water free water double layer water - - - - - - - - - - - - - - adsorbed water 50 nm 1nm
Notas del editor
- Clay minerals exhibit colloidal behaviour. That is, their surface forces have greater influence than the negligible gravitational forces.
- Geotechnical engineers are interested mainly in the top 100 metres of the earth crust. As you can see from the table, 82% of the elements are oxygen, silicon and aluminium.
- All clay minerals are made of two distinct building blocks: tetrahedrons and octahedrons. The tetrahedron on the left has oxygen atoms at the corners, and there is a silicon in the centre. Octahedron has six oxygen or hydroxyl atoms in the corners, and an aluminium or magnesium ion at the centre.
- Here is a tetrahedral sheet, formed by connecting several tetrahedons. Note the hexagonal holes in the sheets.
- The green and yellow blocks represent the tetrahedra and octahedra sheets respectively. The octahedral sheet containing aluminium is also called gibbsite. Sometimes, Al 3+ ions are substituted by Mg 2+ and the octahedral sheet is called brucite.
- All clay mineral are made of different combinations of the above two sheets: tetrahedral sheet and octahedral sheet.
- Kaolinite is used for making paper, paint and in pharmaceutical industry. A nanometer is 10 -9 metres.
- Attapulgite has no sheets. It has a chain structure, and therefore looks like rods or needles.
- The term fabric is used to describe the geometric arrangement of the clay particles. Flocculated and Dispersed are the two extreme cases. Flocculated fabric gives higher strength and stiffness.
- Clay particles are smaller than 2 microns. Their shapes can be studied by an electron microscope.
- The clay particle derives its net negative charge from the isomorphous substitution and broken bonds at the boundaries.
- The negatively charged clay particles can attract cations from the water. These cations can be freely exchanged with other cations present in the water. For example Al 3+ can replace Ca 2+ and Ca 2+ can replace Mg 2+ .
- The negatively charged faces of clay particles attract cations in the water. The concentration of the cations decreases exponentially with the increasing distance from the clay particle. The negatively charged clay surface and the positively charged cations near the particle form two distinct layers, known as “electric double layer” or simply “double layer”.