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The Soil Solid Fraction

The Soil Solid Fraction. Solids. Pores. From where do mineral particles originate?. Rocks and Minerals. Rock Dominant Mineral. Limestone Calcite Sandstone Quartz Shale Clays Granite Quartz/Feldspars Basalt Quartz/Feldspars. Weathering. Physical: changing the size and shape of

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The Soil Solid Fraction

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  1. The Soil Solid Fraction

  2. Solids Pores

  3. From where do mineral particles originate?

  4. Rocks and Minerals Rock Dominant Mineral Limestone Calcite Sandstone Quartz Shale Clays Granite Quartz/Feldspars Basalt Quartz/Feldspars

  5. Weathering Physical: changing the size and shape of Rocks or mineral particles without altering their chemical composition Chemical: altering a mineral particle’s chemical composition.

  6. Weathering Destruction and Synthesis } Physical: freezing and thawing plants and biota wind, rain, abrasion Reduce Size Chemical: hydration hydrolysis oxidation/reduction acids dissolution } Chemical Alteration

  7. Granite Minerals: quartz, feldspars, biotite

  8. Rocks breakdown (weather) by physical means Primary Minerals Primary minerals (e.g. quartz, feldspars) are dominated by Si, Al, O Primary minerals breakdown (weather) principally by chemical means Secondary Minerals Silicate clays Iron oxides Aluminum oxides Silicate clay minerals are dominated by Si, Al, O

  9. Primary Minerals Quartz SiO2 Feldspar KAlSi3O8 Biotite KMg3AlSi3O10(OH)2 Albite NaAlSi3O8 Muscovite KAl3Si3O10(OH)2 Aluminum and Silicon

  10. Chemical Alteration and Reorganization Primary Minerals Quartz SiO2 Feldspar KAlSi3O8 Biotite KMg3AlSi3O10(OH)2 Albite NaAlSi3O8 Muscovite KAl3Si3O10(OH)2 Secondary Minerals Chemical weathering Crystalline Aluminosilcate Clays Dominated by Aluminum, Silicon, Oxygen

  11. Silicate Clays

  12. Silicate Clays Colloidal • Small (< 1 micron) • Large surface area • Highly reactive

  13. Constituents of Silicate Clays Aluminosilicates Si4+ Al3+ O2- OH- These 4 ions are arranged together to form crystals with a number of important properties related to soil reactivity.

  14. Ions: what are they?

  15. Silicate Clay minerals are crystalline and formed by specific arrangement of ionic forms of Si, Al, and O Ions are stable forms of elements that possess an electrical charge. Cations are elements that have lost electrons to become (+) charged Anions are elements that have gained electrons to become (-) charged.

  16. Elements Electrons (-) Elements in the periodic table have equal numbers of protons and electrons. They are electrically neutral Protons (+)

  17. Ions Ions are stable forms of elements that acquire an electrical charge by gainingor losing electrons Elemental Sodium (Na) 11 protons (+), 11 electrons (-) 11 protons (+), 10 electrons (-) Sodium ion (Na+) By losing an electron, sodium has more protons than electrons and becomes positively charged. Na - 1e- = Na+

  18. e- e- e- e- e- e- e- e- e- e- Sodium Na (11 electrons) + e- Na Na+ 11 protons

  19. 2Na + 2H20 2Na+ + 2 OH- + H2

  20. Ions Ions are stable forms of elements that acquire an electrical charge by gaining or losing electrons Elemental Chlorine (Cl) 17 protons (+), 17 electrons (-) 17 protons (+), 18 electrons (-) Chloride ion (Cl-) By gaining an electron, chlorine has more electrons than protons and becomes negatively charged. Cl + 1e- = Cl-

  21. e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- Chlorine _ e- Cl Cl- 17 protons

  22. Elements that lose electrons and become positively charged are called cations. Na+, K+, Ca2+, Mg2+, Cu2+, Fe3+ Elements that gain electrons and become negatively charged are called anions. Cl-, Br-, F-, I- CO32-, SO42-, PO4-3 oxoanions

  23. Electrostatic Attraction + + + + + + + + + - - - - - - - - - Na+ Cl-

  24. Salts Salts are formed by combining cations and anions to form solids that have no charge. Cations: K+, Na+, Mg2+, Ca2+ Anions: Cl-, CO3-2, SO4-2 K+ + Cl- = KCl Na+ + Cl- = NaCl KCl, NaCl, MgCl2, CaCO3, CaSO4

  25. Water Ca+2 and CO3-2 Water Ca+2 and SO4-2 Conversely, if solid salts are mixed with water they dissolve and the ions go into solution solution solid KCl K+ + Cl- NaCl Na+ + Cl- CaCO3 CaSO4

  26. Dissolution Cl- Cl Cl Na Cl Cl NaCl Na+

  27. Building a Crystal with Cations and Anions

  28. Crystalline Mineral Colloids Aluminosilicates Cations and Anions Si4+ Al3+ O2- OH-

  29. Building Blocks for Silicate Clays Silicon Tetrahedron Aluminum octahedron hydroxide (OH-) oxygen Aluminum (Al3+) silicon (Si4+)

  30. Graphite Diamond Oxygen (O2-) Hydroxide (OH-) silicon (Si4+) Aluminum (Al3+) Fundamental Building Blocks Silicon Tetrahedron Aluminum Octahedron Crystalline Minerals

  31. Tetrahedra and OctahedraSharing the Oxygens Linkage of thousands of silica tetrahedra and aluminum octahedra O { Tetrahedra Si O, OH { octahedra Al OH 1:1 Mineral

  32. 2:1 mineral { Tetrahedra { octahedra { Tetrahedra

  33. 1:1 minerals 2:1 minerals

  34. Layers and Interlayers Layer interlayers

  35. Electrical Properties of Soil Minerals

  36. Charge Balance Si4+ O2- Al3+ OH- = Positive charge Negative charge Al3+ Si4+ OH- O2-

  37. Positive Charge Al3+Si4+ Negative Charge O2-OH- Uncharged silicate clay minerals Talc Pyrophillite AlSi2O5OH. +3 5 x (-2) = -10 2 x (+4) = +8 -1 Total = zero

  38. Isomorphous Substitution Substitution of lower-charge cations for higher charge cations during mineral formation. Al3+ for Si4+ in tetrahedra Mg2+ for Al3+ in octahedra The result is a deficit of positive charge or a surplus of negative charge in the mineral structure.

  39. Positive Charge = Negative Charge Tetrahedral Substitution Al3+ for Si4+

  40. Positive Charge = Negative Charge Octahedral Substitution Mg2+ for Al3+

  41. Tetrahedral Substitution Al3+ for Si4+ Octahedral Substitution Mg2+ for Al3+

  42. Na+ Charge Na+ Na+ Na+ Na+ Na+ Na+

  43. K+ Cation Exchange K+ Na+ K+ Na+ K+ K+ Na+ Na+ Na+ Na+ Na+

  44. Implications of Negative Charge sites. Important Cations: H+, Ca2+, Mg2+, Zn2+, Mn2+, K+, NH4+, Cu2+ reserve Paraquat, Diquat, Triazines Pyridine, quinoline, arcidine

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