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The Solid Phase

The Solid Phase. Inorganic components : soil minerals Organic components : soil organic matter Inorganic components : Primary minerals: The sand and silt fractions consist largely of primary minerals.

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The Solid Phase

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  1. The Solid Phase • Inorganic components: soil minerals • Organic components: soil organic matter • Inorganic components: • Primary minerals: • The sand and silt fractions consist largely of primary minerals. • Primary minerals are formed at elevated temperatures and inherited unchanged from igneous and metamorphic rocks, sometimes through a sedimentary cycle. • The most abundant primary minerals in soils: quartz(SiO2) and feldspars (MAlSi3O8) • Micas, pyroxenes, amphiboles, and olivine are in smaller quantities.

  2. The Solid Phase(續) • Second minerals: • Minerals of the clay fraction of soils are largely secondary. • Secondary minerals are formed by low temperature reaction and either inherited from sedimentary rocks or formed directly by weathering. • Common secondary minerals in soils include the carbonate, the sulfur minerals, and the layer silicates, the various oxides.

  3. Crystal chemistry of silicates • Internal bonding in silicates is predominantly ionic. As a result, forces are undirected and ionic size plays an important part in determining crystal structure.

  4. O O O Si Si Si O O O O O O O O O O Si Si O O O • 鏈狀矽酸鹽 (chain structures)- Inosilicates 單鏈 (single chain) e.g.輝石類 (Pyroxenes) e.g.MgSiO3 (SiO3)n 雙鏈 (Double Chains)- e.g.角閃石類 (amphiboles)

  5. O O O O Si Si O O O O Si Si O O Si Si Ring 環狀矽酸鹽 (Cyclic structures)- Cyclosilicates e.g.電氣石 (Tourmaline) 綠寶石 (Beryl) Be3Al2(SiO3)6

  6. Layer silicates 層狀矽酸鹽(Sheet structure)- Phyllosilicates (a)為鏈狀構造之 two-dimensional extension (b)雲母類、綠泥石 (砂粒及坋粒部) 、黏土礦物 (黏粒部) 。 (c)基本架構 (unit structure) Tetrahedral layer (四面體層) :由矽四面體所構成之層狀構造。 Octahedral layer (八面體層) :由鋁八面體 (Aluminum Octahedron) 所構成之層狀構造。 Dioctahedral:鋁原子只佔有2/3之 Octahedral position Trioctahedral:所有之 Octahedral position 均被佔滿。 [Al2(OH)6]n [Mg3(OH)6]n

  7. 四面體層 八面體層 unit cell 四面體層 K+ K+ (d)層狀之矽酸鹽通常由四面體層和八面體層延著垂直c之方向堆積而成。 (e) e.g.雲母類 白雲母(muscovite) 黑雲母(biotite)

  8. 同位置換 (Isomorphous substitution) 在結晶格子中以 一元素取代另一元素而不改變結晶構造,通常大小相近之離子 (即配位數相同) 可互相取代,但電荷並不一定相同,而取代所造成之電荷不平衡可由其他陽離子來中和。 e.g. Al3+(Ⅳ) 取代 Si4+(Ⅳ) Mg2+(Ⅵ) 取代 Fe3+(Ⅵ) 或者 Al3+(Ⅵ)

  9. Si O O Si Si Si O O O O O Si Si 四面體累積架構矽酸鹽 (Framework Structures) 3-dimensional Tectosilicates 此類的矽酸鹽礦物最重要為 Silica (矽酸) 和 feldspars (長石類) 矽酸最重要為石英 (quartz)

  10. 黏粒部之礦物 主要為層狀的矽酸鹽,可由初級之層狀的矽酸鹽 (雲母類和綠泥石類) 稍微改變而來。或由土壤之生成過程中而生成之次級層狀矽酸鹽 高嶺石類 (Kaolins) 水化雲母類 (hydrous micas):包括 illite (伊來石) 和 Vermiculite (蛭石) 蒙特石類 (Smectites)

  11. Crystal: an arrangement of ions or atoms that is repeated at regular intervals in three dimensions. • Unit cell: the smallest repeating three-dimensional array of a crystal. • Formula unit: The chemical composition of layer silicate minerals is normally expressed as one halfof a unit cell in order to simplify the chemical formulas. Formula unit=1/2 unit cell

  12. Layer Charge The magnitude of charge per formula unit, when balanced by cations external to the unit layer.

  13. 高嶺石類 (kaolins) 1:1 layer silicates 1. 基本構造 1:1 層狀 (由一四面體層和八面體層共用一些 O 原子而形成) 2. Unit Formula 組成 Si2ⅣO5Al2Ⅵ(OH)4 3. Lamella 間以 H-bonding 鍵結 c-spacing = 7.2Å (0.72 nm)

  14. 高嶺石類 (kaolins) (續) 4. 土壤中最常見之二種為 Kaolinite 和 Halloysite 5. 高嶺石類為非膨脹性礦物 非常少之同位置換  非常低的 net negative charge主要之負電荷之來源為結晶邊緣 (edge) 之未滿足之 O 或 OH 之價數 CEC: 10 ~100 mmoles(+)·kg-1 6. Surface Area 10 ~ 20×103 m2·kg-1 (no internal surface)

  15. 蛭石(vermiculite) 黑雲母(biotite) [(OH)4(Al2Si6)Ⅳ(MgFe)6ⅥO20]2-2K+ [(OH)4(AlxSi8-x)Ⅳ(MgFe)6ⅥO20]x-·Mg2+ , X<2 CEC: 1200 ~ 1500 m moles (+) ·kg-1 • c-spacing ~ 1.4-1.5 nm Trioctahedral 加熱脫水後1.0 nm • c-spacing ~ 1.0 nm • 有限度膨脹之礦物 • CEC: 200 ~ 400 m moles (+) ·kg-1 • 較雲母類有較少之負電荷,因同位置換少。 • Surface Area: 70 ~120×103 m3·kg-1 • 有較高含量之結晶水。 伊來石(illite) hydrous mica [(OH)4(AlxSi8-x)ⅣAl4ⅥO20]x-K+ 白雲母(muscovite) [(OH)4(Al2Si6)ⅣAl4ⅥO20]2-2K+ Dioctahedral H3O+ • c-spacing 1.0 nm • c-spacing 1.0 nm • CEC: 200 ~ 400 m moles (+) ·kg-1 • Surface Area: 70 ~120×103 m3·kg-1 • 層間鍵結較白雲母弱,層之排列較不規則。 Vermiculites & Micas

  16. Vermiculite. n=0.6-0.9

  17. 蒙特石類 (Smectites) 1. 為2:1層狀構造,類似於水化雲母類,但其有較大之組成變化,因同位置換可發生於四面體層和八面體層。 2. 此類礦物之負電荷由 Ca2+,Mg2+,K+,Na+ 等離子在層間中和之,但無高度之方向性。 3. Interlamellar 之鍵結弱而且決定於存在陽離子之水合程度,而 c-spacing 可由1 nm ~ > 4 nm。 4. 由於層間可存在水合陽離子或極性分子(如:glycerol)  膨脹性礦物 (Expanding clays) 。

  18. 蒙特石類 (Smectites) (續) 5. 比表面積相當大(有相當大之內表面積)。 6. Layer charge 0.25~0.6 per formula unit. 7. 在土壤中常見有蒙特石(Montmorillonite、 Beidellite 和 Nontronite。 CEC: 800 ~ 1200 m moles (+)·kg -1 Surface Area: 600 - 800×103 m2·kg -1

  19. Fig. 4.7 Schematic structure of montmorillonite. (From F. E. Bear (Ed.), Chemistry of the Soil. ACS Monograph Series No. 160. 1964.) x=0.25-0.6

  20. 2:1:1 Layer Silicates

  21. 其他之礦物與無定形物質(非結晶性)-存在於黏粒部分其他之礦物與無定形物質(非結晶性)-存在於黏粒部分 • 碳酸鈣 (CaCO3, Calcite) -乾燥地區,高 pH 之土壤 • 游離氧化物 (Free Oxides) • 矽酸 (Silica) 新近堆積之火山灰形成的土壤中常有無定形之二氧化矽,如在紐西蘭、日本、夏威夷、台灣陽明山。此類土壤中大部分黏粒成分,皆以氧化矽與氧化鋁組成之非結晶性礦物,稱之為鋁英石 (Allophane) ,其化學組成份不一定,其 SiO2/Al2O3≌ 1/2。

  22. 其他之礦物與無定形物質(非結晶性)-存在於黏粒部分 (續) • 氧化鐵 (Iron Oxides) 1.黃至紅褐色之鐵氧化物是非常明顯地存在高風化之熱帶土壤。 2.氧化鐵在土壤中最常見為 Goethite (α-FeOOH) 針鐵礦(水合 結晶性礦物)。 3.在高溫熱帶土壤之表層,Goethite 可轉變成 Hematite (α-Fe2O3,赤鐵礦)

  23. 氧化鋁 (Aluminum Oxides) 1.氧化鋁之(不明顯)灰白色,在土壤中不易顯出。 2.在土壤中主要之結晶氧化鋁為Gibbsite(水鋁氧,γ-Al(OH)3)。 3.非結晶性之 Al(OH)3 可沉積於黏土礦物之層片間(尤其是蛭石)或 coating 在黏粒之表面。 4.在熱帶經強烈風化作用之情況下,氧化鋁及鐵兩者皆會聚積。同時其存在可顯著影響所形成之土壤物理及化學性質。

  24. 表面電荷 • 重要性:黏粒或氧化物之表面電荷決定溶質(陰陽離子)被土壤所吸附----影響肥料,農藥在土壤中之行為。 • 電荷之分類: • 永久電荷 (Permanent charge) :由同位置換而造成---負電荷。 • pH-依賴電荷 (pH-dependent charge) :發生於黏粒之邊緣面(edge faces) 或水合鐵鋁氧化物之表面---可能為正電荷或負電荷,其電荷之大小或正負決定於溶液之 pH。 • 陽離子交換容量 (Cation Exchange Capacity, CEC) • 單位重量之土壤(或黏粒)所吸附之”可交換”陽離子當量或莫耳數。 • 單位:meq/100g soil (clay) mmol(+)/kg soil (clay)

  25. FIGURE 5.11. Representation of pH-dependent charge at kaolinite edges. (By permission from R. K. Schofield and H. R. Samson. 1953 Clay Miner Bull. 2:45.)

  26. X-ray diffraction

  27. Surface Area Measurements • Water vapor adsorption – internal & External • N2-gas adsorption (BET Eq.) – External • Retention of polar molecules – internal & external • Ethylene glycol • glycerol • EGME (ethylene glycol monoethyl ether)

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