1 / 36

N. Sivakugan

Clay Mineralogy. N. Sivakugan. Duration = 15 mins. 8-35 km crust. 82.4%. 12500 km dia. 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. Parent Rock. Soil Formation. Residual soil. Transported soil.

gavine
Download Presentation

N. Sivakugan

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Clay Mineralogy N. Sivakugan Duration = 15 mins.

  2. 8-35 km crust 82.4% 12500 km dia Elements of Earth % by weight in crust O = 49.2Si = 25.7Al = 7.5Fe = 4.7Ca = 3.4Na = 2.6K = 2.4Mg = 1.9other = 2.6

  3. Parent Rock 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.

  4. Parent Rock ~ formed by one of these three different processes sedimentary igneous metamorphic formed by gradual deposition, and in layers formed by cooling of molten magma (lava) formed by alteration of igneous & sedimentary rocks by pressure/temperature e.g., limestone, shale e.g., granite e.g., marble

  5. Residual Soils Formed by in situ weathering of parent rock

  6. Transported Soils Transported by: Special name: • wind “Aeolian” • sea (salt water) “Marine” • lake (fresh water) “Lacustrine” • river “Alluvial” • ice “Glacial”

  7. Atomic Structure

  8. hydroxyl or oxygen oxygen aluminium or magnesium silicon 0.26 nm 0.29 nm Basic Structural Units Clay minerals are made of two distinct structural units. Silicon tetrahedron Aluminium Octahedron

  9. tetrahedron hexagonal hole Tetrahedral Sheet Several tetrahedrons joined together form a tetrahedral sheet.

  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. 0.72 nm joined by strong H-bondno easy separation Al Al Al Al joined by oxygen sharing Si Si Si Si Kaolinite Typically 70-100 layers

  14. Kaolinite • used in paints, paper and in pottery and pharmaceutical industries • (OH)8Al4Si4O10 Halloysite • kaolinite family; hydrated and tubular structure • (OH)8Al4Si4O10.4H2O

  15. 0.96 nm Si Si Si Al Al Al joined by weakvan der Waal’s bond Si Si Si Montmorillonite • also called smectite; expands on contact with water easily separated by water

  16. swells on contact with water Montmorillonite • A highly reactive (expansive) clay • (OH)4Al4Si8O20.nH2O Bentonite high affinity to water • montmorillonite family • used as drilling mud, in slurry trench walls, stopping leaks

  17. joined by K+ions 0.96 nm Si Si Si Al Al Al Si Si Si Illite fit into the hexagonal holes in Si-sheet

  18. Si Al or Mg Al Others… Chlorite • A 2:1:1 (???) mineral. Vermiculite • montmorillonite family; 2 interlayers of water Attapulgite • chain structure (no sheets); needle-like appearance

  19. Plate-like or Flaky Shape A Clay Particle

  20. Clay Fabric edge-to-face contact face-to-face contact Dispersed Flocculated

  21. Clay Fabric • Electrochemical environment (i.e., pH, acidity, temperature, cations present in the water) during the time of sedimentation influence clay fabric significantly. • Clay particles tend to align perpendicular to the load applied on them.

  22. Identifying Clay Minerals

  23. plate-like structure Scanning Electron Microscope • common technique to see clay particles • qualitative

  24. Others… X-Ray Diffraction (XRD) • to identify the molecular structure and minerals present Differential Thermal Analysis (DTA) • to identify the minerals present

  25. montmorillonite illite kaolinite halloysite chlorite Casagrande’s PI-LL Chart

  26. Special Terms

  27. 1 mm cube 10 mm cube Specific Surface • surface area per unit mass (m2/g) • smaller the grain, higher the specific surface e.g., soil grain with specific gravity of 2.7 spec. surface = 222.2 mm2/g spec. surface = 2222.2 mm2/g

  28. positively charged edges + + + + _ + _ negatively charged faces _ _ _ _ + _ _ _ _ _ + _ _ _ _ _ _ _ _ _ _ _ _ Isomorphous Substitution • substitution of Si4+ and Al3+ by other lower valence (e.g., Mg2+) cations • results in charge imbalance (net negative) Clay Particle with Net negative Charge

  29. known as exchangeable cations milliequivalents Cation Exchange Capacity (c.e.c) • capacity to attract cations from the water (i.e., measure of the net negative charge of the clay particle) • measured in meq/100g (net negative charge per 100 g of clay) • The replacement power is greater for higher valence and larger cations. Al3+ > Ca2+ > Mg2+ >> NH4+ > K+ > H+ > Na+ > Li+

  30. A Comparison

  31. + + clay particle + - -- -- -- -- -- -- - + + + cations + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + double layer Cation Concentration in Water • cation concentration drops with distance from clay particle free water

  32. - -- -- -- -- -- -- - adsorbed water Adsorbed Water • A thin layer of water tightly held to particle; like a skin • 1-4 molecules of water (1 nm) thick • more viscous than free water

  33. adsorbed water - -- -- -- -- -- -- - 1nm 50 nm Clay Particle in Water free water double layerwater

  34. Practical Significance

  35. Summary - Clays • Clay particles are like plates or needles. They are negatively charged. • Clays are plastic; Silts, sands and gravels are non-plastic. • Clays exhibit high dry strength and slow dilatancy.

  36. Summary - Montmorillonite • Montmorillonites have very high specific surface, cation exchange capacity, and affinity to water. They form reactive clays. • Montmorillonites have very high liquid limit (100+), plasticity index and activity (1-7). • Bentonite (a form of Montmorillonite) is frequently used as drilling mud.

More Related