Clay Mineralogy

Topic 3: Clay Mineralogy

Hassan Z. Harraz [email protected] 2013- 2014

1 Prof. Dr. H.Z. Harraz Presentation Clay Mnerals

OUTLİNE OF TOPIC 3:     

      

4 May 2016

ORIGIN OF CLAY MINERALS CLAY MINERALS ATOMIC STRUCTURE Basic Structural Units TYPES OF CLAY MINERALS: 1) Silicate Clays (crystalline): a) Kaolinite b) Halloysite c) Smectite d) Illite e) Vermiculite f) Chlorite g) Attapulgite (Chain Structure Clay Minerals) h) Mixed Layer Clays 2) Sesquioxide/oxidic clays 3) Amorphous clays (non-crystalline) “Activity” of silicate clays Generalized Chemical Weathering Chemical Weathering Products Uses of Clay Clay Fabric IDENTIFIED CLAY MINERALS SPECIAL TERMS

Prof. Dr. H.Z. Harraz Presentation Clay Mnerals

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Elements of Earth 8-35 km crust

% by weight in crust

12500 km dia

O Si Al Fe Ca Na K Mg other

= 49.2 = 25.7 = 7.5 = 4.7 = 3.4 = 2.6 = 2.4 = 1.9 = 2.6

82.4%

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Soil Formation Parent Rock

~ formed by one of these three different processes 1) Igneous: formed by cooling of molten magma (lava) e.g., Granite, Basalt

Residual soil

Transported soil

~ in situ weathering (by physical & ~ weathered and transported chemical agents) of parent rock far away

2) Sedimentary: formed by gradual deposition, and in layers e.g., Sandstone, limestone, shale

3) Metamorphic: formed Transported by:

Special name:

 Wind

“Aeolian”

 Sea (salt water)

“Marine”

 Lake (fresh water)

“Lacustrine”

 River

“Alluvial”

 Ice

“Glacial”

by alteration of igneous & sedimentary rocks by pressure/temperature e.g., schist, marble

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Origin of Clay Minerals  “The contact of rocks and water produces clays, either at or near the surface of the earth” (from Velde, 1995). Rock +Water  Clay  For example,  The CO2 gas can dissolve in water and form carbonic acid, which will become hydrogen ions H+ and bicarbonate ions, and make water slightly acidic. CO2 + H2O  H2CO3  H+ + HCO3 The acidic water will react with the rock surfaces and tend to dissolve the K ion and silica from the feldspar. Finally, the feldspar is transformed into kaolinite. Feldspar + hydrogen ions + water  clay (kaolinite) + cations, dissolved + silica

2KAlSi3O8 + 2H+ + H2O  Al2Si2O5(OH)4 + 2K+ + 4SiO2 Note that:  The hydrogen ion displaces the cations. The alternation of feldspar into kaolinite is very common in the decomposed granite.  The clay minerals are common in the filling materials of joints and faults (fault gouge, seam) in the rock mass.

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Prof. Dr. H.Z. Harraz Presentation Clay Minerals

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CLAY MINERALS  Clay minerals exhibit colloidal behaviour. That is, their surface forces have greater influence than the negligible gravitational forces.  Clay is a particle size  i.e., Micelle: meaning particle of silicate clay  Clay particles are smaller than 2 microns. Their shapes can be studied by an electron microscope.  Predominant make-up is Secondary minerals  Clay minerals are Phyllosilicate minerals  Composed of tetrahedral and octahedral “sandwiches”  Tetrahedron: central cation (Si+4, Al+3) surrounded by 4 oxygens  Octahedron: central cation (Al+3,Fe+2, Mg+2) surrounded by 6 oxygens (or hydroxyls)  Sheets combine to form layers  Layers are separated by interlayer space  Water, adsorbed cations

 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. 4 May 2016


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A Clay Particle

Plate-like or Flaky Shape

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Basic Structural Units oxygen

Silicon tetrahedron

Clay minerals are made of two distinct structural units

silicon

Tetrahedron

and Tetrahedral sheets

Aluminium Octahedron

Connected tetrahedra, sharing oxygens

hydroxyl or oxygen

SEM view of clay All have layers of Si tetrahedra and layers of Al, Fe, Mg octahedra, similar to gibbsite or brucite

aluminium or magnesium

Octahedron and Octahedral Sheets

Connected octahedra, sharing oxygens or hydroxyls

All clay mineral are made of different combinations of the above two sheets: tetrahedral sheet and octahedral sheet.

Basic Unit-Silica Tetrahedra Tetrahedral Sheet

(Si2O10)-4

1 Si

Replace four Oxygen with hydroxyls or combine with positive union

4O

 

Tetrahedron

Plural: Tetrahedra



Several tetrahedrons joined together form a tetrahedral sheet. Here is a tetrahedral sheet, formed by connecting several tetrahedons. Note the hexagonal holes in the sheets.

hexagonal hole (Holtz and Kovacs, 1981)

Basic Unit-Octahedral Sheet 1 Cation

6 O or OH Gibbsite sheet: Al3+ Al2(OH)6, 2/3 cationic spaces are filled One OH is surrounded by 2 Al: Dioctahedral sheet

Different cations

Brucite sheet: Mg2+ Mg3(OH)6, all cationic spaces are filled One OH is surrounded by 3 Mg: Trioctahedral sheet 13 (Holtz and Kovacs, 1981)

Tetrahedral & Octahedral Sheets For simplicity, let’s represent silica tetrahedral sheet by: Si and alumina octahedral sheet by:

Al

Mitchell, 1993

Different Clay Minerals

 All clay mineral are made of different combinations of the above two sheets: tetrahedral sheet and octahedral sheet.  Different combinations of tetrahedral and octahedral sheets form different clay minerals:

1:1 phyllosilicate Clay Mineral (e.g., kaolinite, halloysite)

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2:1 phyllosilicate Clay Mineral (e.g., montmorillonite, illite)


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TYPES OF CLAY MINERALS 1) Silicate Clays (crystalline) 2) Sesquioxide/oxidic clays 3) Amorphous clays (non-crystalline)

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1) Silicate Clays (crystalline) Different types of silicate clays are composed of sandwiches (combinations) of layers with various substances in their interlayer space.

2:1 two tetrahedral sheets to one octahedral sheet

1:1 one tetrahedron sheet to one octahedral sheet

Mitchell, 1993

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a) Kaolinite Typically 70100 layers

Al Si Al

layer

0.72 nm

Si joined by strong H-bond no easy separation

Al Si Al Si

joined by oxygen sharing

a) Kaolinite  1:1 phyllosilicate Minerals  Si4Al4O10(OH)8  Platy shape  The bonding between layers are van der Waals forces and hydrogen bonds (strong bonding).  There is no interlayer swelling  Width: 0.1~ 4m  Thickness: 0.05~2 m  Hydrogen bonds in interlayer space  strong  Nonexpandable  Low cation exchange capacity (CEC)  Particles can grow very large (0.2 – 2 µm)  Effective surface area = 10 – 30 m2/g  External surface only  Kaolinite is used for making paper, paint, pottery and pharmaceutical industries 4 May 2016


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a) Kaolinite

 Mineral particles of the kaolinite subgroup consists of the basic units stacked in the c direction.  The bonding between successive layers is by both van der Waals forces and hydrogen bonds.  Kaolinite is the purest of clays, meaning that it varies little in composition. It also does not absorb water and does not expand when it comes in contact with water. Thus, kaolinite is the preferred type of clay for the ceramic industry.

Kaolinite grades

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17 m Kaolinite "booklets", platelet Trovey, 1971 ( from Mitchell, 1993)

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 Clays are categorized into six groups: 1) Kaolin or china clay: white, claylike material composed mainly of kaolinite industrial applications: paper coating and filling, refractories, fiberglass and insulation, rubber, paint, ceramics, and chemicals 2) Ball clay: kaolin with small amount of impurities industrial application: dinnerware, floor tile, pottery, sanitary ware. 3) Fire clays: kaolin with substantial impurities (diaspore, flint) industrial applications: refractories 4) Bentonite: clay composed of smectite minerals, usually montmorillonite industrial applications: drilling muds, foundry sands 5) Fuller’s earth: nonplastic clay high in magnesia, a similar to bentonite industrial applications: absorbents 6) Shale: laminated sedimentary rock consisting mainly of clay minerals mud industrial application: raw material in cement and brick manufacturing Prof. Dr. H.Z. Harraz Presentation Clay Minerals

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1.Silicate Clays

kaolinite

Kaolinite • Kaolinite clays have long been used in the ceramic industry, especially in fine porcelains, because they can be easily molded, have a fine texture, and are white when fired. • These clays are also used as a filler in making paper.  good road base  good foundation  good for pottery; China clay (porcelain)  easy to cultivate, but need manure or fertilizer  Dominant clay mineral in highly weathered soils 4 May 2016


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Kaolinite grades

Clays are categorized into six groups: 1) Kaolin or china clay: white, claylike material composed mainly of kaolinite industrial applications: paper coating and filling, refractories, fiberglass and insulation, rubber, paint, ceramics, and chemicals 2) Ball clay: kaolin with small amount of impurities industrial application: dinnerware, floor tile, pottery, sanitary ware. 3) Fire clays: kaolin with substantial impurities (diaspore, flint) industrial applications: refractories 4) Bentonite: clay composed of smectite minerals, usually montmorillonite industrial applications: drilling muds, foundry sands 5) Fuller’s earth: nonplastic clay high in magnesia, a similar to bentonite industrial applications: absorbents 6) Shale: laminated sedimentary rock consisting mainly of clay minerals mud industrial application: raw material in cement and brick manufacturing

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China Clay processing Blunging :The kaolin is mixed with water and chemical dispersants, which puts the clay particles in suspension (slurry). De-gritting: The slurried kaolin is usually transported through pipelines to degritting facilities (rakes), where sand, mica and other impurities are extracted with the help of gravity. Centrifuging: The centrifuge separates the fine kaolin particles from coarse particles.Fine particles, still in the form of a slurry, move on for further processing.

De-gritting (rake) tables

China Clay processing (cont.) Brightness enhancement: Undesirable colors are removed through one or more processes including bleaching, magnetic separation, flocculation, ozonation, flotation, and oxidation, which will remove iron oxides, titanium oxides, organic, and other undesirable materials. Delamination :For customers who want a delaminated clay product suited for lightweight coating applications, coarse kaolinite particles are used as starting material. Delamination occurs as the coarse particles of kaolin which when magnified appear as "booklets" are broken into thin platelets by mechanical milling. Filtering and drying :Large rotary vacuum filters remove water from the slurried kaolin. Large gas-fired spray dryers remove and evaporate the remaining moisture.

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b) Halloysite • 1:1 phyllosilicate Minerals • Si4Al4O10(OH)8·4H2O • A single layer of water between unit layers. • kaolinite family; hydrated and tubular structure while it is hydrated • The basal spacing is 10.1 Å for hydrated halloysite and 7.2 Å for dehydrated halloysite.

Trovey, 1971 ( from Mitchell, 1993)

2 m

• If the temperature is over 50 °C or the relative humidity is lower than 50%, the hydrated halloysite will lose its interlayer water (Irfan, 1966). Note that this process is irreversible and will affect the results of soil classifications (GSD and Atterberg limits) and compaction tests. • There is no interlayer swelling.

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c) Montmorillonite  also called smectite; expands on contact with water Si Al Si

easily separated by water

Si Al Si

A highly reactive (expansive) clay swells on contact with water

0.96 nm

(OH)4Al4Si8O20.nH2O high affinity to water

Bentonite:

joined by weak van der Waal’s bond

Si Al Si

 montmorillonite family  used as drilling mud, in slurry trench walls, stopping leaks

c) Montmorillonite  Montmorillonite or smectite is family of expansible 2:1 phyllosilicate clays having permanent layer charge because of the isomorphous substitution in either the octahedral sheet (typically from the substitution of low charge species such as Mg2+ , Fe2+, or Mn2+ for Al3+)  The most common smectite clay is Montmorillinite, with a general chemical formula : (0.5Ca,Na)(Al,Mg,Fe)4(Si,Al)8O20(OH)4.nH2O  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).  Montmorillinite is the main constituent of bentonite, derived by weathering of volcanic ash. Bentonite has the unsual property gives rise to interesting industrial used. Montmorillinite can expand by several times its original volume when it comes in contact with water. This makes it useful as a drilling mud (to keep drill holes open), in slurry trench walls, stopping leaks and to plug leaks in soil, rocks, and dams.  Most important is as drilling mud in which the montmorillonite is used to give the fluid viscosity several times that of water. It is also used for stopping leakage in soil, rocks, and dams.  Montmorillinite, however, is a dangerous type of clay to encounter if it is found in tunnels or road cuts. Because of its expandable nature, it can lead to serious slope or wall failures.

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c) Montmorillonite Film-like shape. There is extensive isomorphous substitution for silicon and aluminum by other cations, which results in charge deficiencies of clay particles. Always negative due to isomorphous substitution Layers weakly held together by weak O-O bonds or cation-O bonds Cations adsorbed in interlayer space Interlayer cations hold layers together:  In dry soils, bonding force is strong and hard clods form; deep cracks  In wet soils, water is drawn into interlayer space and clay swells.

n·H2O+cations

n·H2O and cations exist between unit layers, and the basal spacing is from 9.6 Å to  (after swelling). Maximum Swelling The interlayer bonding is by van der Waals forces and by cations which balance charge deficiencies (weak bonding).

(Holtz and Kovacs, 1981)

5 m

There exists interlayer swelling, which is very important to engineering practice (expansive clay). High Cation Exchange Capacity (CEC) High effective surface area = 650 – 800 m2/g  Internal surface area >> external Expandable……..Most expandable of all clays  Width: 1 or 2 m  Thickness: 10 Å

….. About ~1/100 width

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Swelling Clays The interlayer in montmorillonite or smectites is not only hydrated, but it is also expansible; that is, the separation between individual smectite sheets varies with the amount of water present in the soil. Because of this, they are often referred to as "swelling clays". Soils having high concentrations of smectites can undergo as much as a 30% volume change due to wetting and drying or these soils have a high shrink/swell potential and upon drying will form deep cracks.

Bentonite 4 May 2016


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Main difference- ions that make up the middle of the sandwich

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig. 2.19b 4 May 2016


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Cat-litter in action

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Box 02.04.f1

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d) Illite

Si Al Si

joined by K+ ions

Si Al Si

fit into the hexagonal holes in Si-sheet

Si Al Si


7.5 m

0.96 nm

d) Illite (Fine-grained micas, mica-like minerals)  Illite is the most common clay mineral, often composing more than 50 percent of the clay-mineral suite in the deep sea.  They are characteristic of weathering in temperate climates or in high altitudes in the tropics, and typically reach the ocean via rivers and wind transport.  Illite type clays are formed from weathering of K and Al-rich rocks under high pH conditions. Thus, they form by alteration of minerals like muscovite and feldspar. Illite clays are the main constituent of shales.  The Illite clays have a structure similar to that of muscovite, but is typically deficient in alkalies, with less Al substitution for Si. Thus, the general formula for the illites is:

Si8(Al,Mg, Fe)4~6O20(OH)4·(K,H2O)2 OR KyAl4(Si8-y,Aly)O20(OH)4 , usually with 1 < y < 1.5, but always with y < 2.  Because of possible charge imbalance, Ca and Mg can also sometimes substitute for K.  The K, Ca, or Mg interlayer cations prevent the entrance of H2O into the structure.  Thus, the illite clays are non-expanding clays. 1) Fewer of Si4+positions are filled by Al3+ in the illite. 2) There is some randomness in the stacking of layers in illite. 3) There is less potassium in illite. Well-organized illite contains 9-10% K2O. 4) Illite particles are much smaller than mica particles. 5) Ferric ion Fe3+

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d) Illite (Fine-grained micas, mica-like minerals)  2:1 phyllosilicate Minerals  Flaky shape.  The basic structure is very similar to the mica, so it is sometimes referred to as hydrous mica. Illite is the chief constituent in many shales.  Some of the Si4+ in the tetrahedral sheet are replaced by the Al3+, and some of the Al3+ in the octahedral sheet are substituted by the Mg2+ or Fe3+. Those are the origins of charge deficiencies.  The charge deficiency is balanced by the potassium ion between layers. Note that the potassium atom can exactly fit into the hexagonal hole in the tetrahedral sheet and form a strong interlayer bonding.  The basal spacing is fixed at 10 Å in the presence of polar liquids (no interlayer swelling).  Width: 0.1~ several m  Thickness: ~ 30 Å  As mica crystallizes from magma:  Isomorphous substitution of Al+3 for Si+4 in tetrahedra  high net negative charge  K+ ions in interlayer space (Strongly binds layers)  Non-expandable  Minimum Swelling  Surface area 70 -175 m2/g

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      

       

e) Vermiculite Vermiculite is a 2:1 phyllosilicate clay mineral The octahedral sheet is brucite. Octahedral ions are Al, Mg, Fe The basal spacing is from 10 Å to 14 Å. It contains exchangeable cations such as Ca2+ and Mg2+ and two layers of water within interlayers. It can be an excellent insulation material after dehydrated. It is generally regarded as a weathering product of micas (Forms from alteration of mica):  Weathering removes some K+ ions  Replaced by hydrated cations in interlayer space Water molecules and cations bridge layers, so not as expandable as smectites Still have very high net negative charge High Cation Exchange Capacity (CEC) (highest of all clays) Expandable Surface area 600 – 800 m2/g  Internal >> external Vermiculite is similar to montmorillonite, a 2:1 mineral, but it has only two interlayers of water. After it is dried at high temperature, which removes the interlayer water, expanded” vermiculite makes an excellent insulation material. Vermiculite is also hydrated and somewhat expansible though less so than smectite because of its relatively high charge.

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Vermiculite

Mitchell, 1993

Illite

Vermiculite

Vermiculite possesses the special property of expanding to between six and twenty times its original volume when heated to ~1,000oC. This process, called exfoliation, liberates bound water from between the mica-like layers of the mineral and literally expands the layers apart at right angles to the cleavage plane. Vermiculite is used to loosen and aerate soil mixes. Mixed with soil, it improves water retention and fertilizer release, making it ideal for starting seeds. Also used as a medium for winter storage of bulbs and flower tubers.

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f) Chlorite  2:1 phyllosilicate Minerals  Central cations in octahedral sheets is Fe or Mg  Interlayer space occupied by a stable, positively charged octahedral sheet.  Non-expandable.  Minimum Swelling.  70 -100 m2/g surface area

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Gibbsite or brucite


The basal spacing is fixed at 14 Å

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g) Attapulgite (Chain Structure Clay Minerals) Attapulgite

• chain structure (no sheets); needlelike appearance • They have lath-like or thread-like morphologies.

• The particle diameters are from 50 to 100 Å and the length is up to 4 to 5 m. • Attapulgite is useful as a drilling mud in saline environment due to its high stability


4.7 m

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h) Mixed Layer Clays •

•

•

Different types of clay minerals have similar structures (tetrahedral and octahedral sheets) so that interstratification of layers of different clay minerals can be observed. Most than one type of clay mineral is usually found in most soils. Because of the great similarity in crystal structure among the different minerals, interstratification of two or more layer types often occurs within a single particle In general, the mixed layer clays are composed of interstratification of expanded waterbearing layers and non-water-bearing layers. Montmorillonite-illite is most common, and chlorite-vermiculite and chlorite-montmorillonite are often found. (Mitchell, 1993)

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2) Sesquioxides / Oxidic Clays  Ultimate weathering products  Ultisols and Oxisols  Very stable; persist indefinitely  Yellow, red, brown  Fe or Al as central cations  Lack negative charge  Don’t retain adsorbed cations  Non-expandable  Low cation exchange capacity (CEC)  Low fertility:  Often are net positive  Often have enough Al or Mn to be toxic to plants  High capacity to fix phosphorous so it is not available to plants  Highly weathered so no more nutrients to release in weathering 4 May 2016


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Ultisol profile 

In heavily leached soils, sheets decompose into component Si tetrahedral and Al octahedral. 

Al octahedral often weather into gibbsite Al(OH)3

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3) Amorphous clays (non-crystalline, Allophanes and Imogolite)  silicates  These are structurally disordered aluminosilicates.  They are normally derived from volcanic ash materials and constitute a major component of volcanic soils.  Allophane and imogolite  The formation of imogolite and allophane occur during weathering of volcanic ash under humid, temperate or tropical climate conditions. Allophane is X-ray amorphous and has no definite composition or shape. It is composed of hollow, irregular spherical particles with diameters of 3.5 to 5.0 nm.  Allophane is often associated with clay minerals of the kaolinite group  Imogolite has the empirical formula SiAl4O10.5H2O  High internal negative charge  High cation exchange capacity (CEC)  High water-holding capacity  Surface area 100 – 1000 m2/g

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“Activity” of silicate clays refers to cation exchange capacity (CEC) Ability to retain and supply nutrients Fertility

High activity clays: Less weathered ; high effective surface area smectite, vermiculite, mica (illite), chlorite

Low activity clays: More weathered; less effective surface area kaolinite 4 May 2016


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What determines clay minerals in a given soil?

Usually a mixture Climate Parent material Degree of weathering

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Generalized Chemical Weathering 

Temperate Climates 3KAlSi3O8 + 2H+ + 12H2O  KAlSi3O10(OH)2 + 6H4SiO4 + K+ (K-feldspar) (mica/illite) (silicic acid)



Temperate Humid Climates: 2KAlSi3O8 + 2H+ + 3H2O  3Al2Si2O5(OH)4 + K+ (K-feldspar) (kaolinite)



Humid Tropical Climate: Al2Si2O5(OH)4 + 5H2O  2Al(OH)3 + 2K+ + 4H4SiO4

(kaolinite)

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(gibbsite)


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Clays: Important Chemical Weathering Products  Clay Mineral Species are a function of:  environmental conditions at the site of weathering  available cations produced by chemical degradation

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Generalized relationships: Ultisols Oxisols

Kaolinite, oxidic clays

Alfisols Mollisols

Mica, vermiculite, smectite

Vertisols Andisols

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Amorphous


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Chemical Weathering Products  As the age of sedimentary rocks increases clay mineral assemblages in the subsurface transform through diagenesis to illite + chlorite

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Uses of Clay - Drilling Mud deep oil is at high pressure

Cooling and cleaning the drill

Drilling mud slurry

“Gushers” used to be common until the use of drilling mud was implemented

Bentonite and other clays are used in the drilling of oil and water wells. The clays are turned into mud, which seals the walls of the boreholes, lubricates the drill head and removes drill cuttings. 4 May 2016


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Uses of Clay - Contaminant Removal Clay slurrys have effectively been used to remove a range of comtaminants, including P and heavy metals, and overall water clarification.

Schematic of montmorillonite absorbing Zn 4 May 2016


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Clay Fabric edge-to-face contact

face-to-face contact

Flocculated

Dispersed

 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. 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.

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Scanning Electron Microscope  common technique to see clay particles  qualitative Clay particles are smaller than 2 microns. Their shapes can be studied by an electron microscope.

plate-like structure

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2.1 X-ray diffraction

Mitchell, 1993

• The distance of atomic planes d can be determined based on the Bragg’s equation. BC+CD = n, n = 2d·sin, d = n/2 sin where n is an integer and  is the wavelength.

• Different clays minerals have various basal spacing (atomic planes). For example, the basing spacing of kaolinite is 7.2 Å. 4 May 2016


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2.2 Differential Thermal Analysis (DTA) • Differential thermal analysis (DTA) consists of simultaneously heating a test sample and a thermally inert substance at constant rate (usually about 10 ºC/min) to over 1000 ºC and continuously measuring differences in temperature and the inert material T. For example: Quartz changes from the  to  form at 573 ºC and an endothermic peak can be observed. T

• Endothermic (take up heat) or exothermic (liberate heat) reactions can take place at different heating temperatures. The mineral types can be characterized based on those signatures shown in the left figure. (from Mitchell, 1993)

Temperature (100 ºC)

2.2 DTA (Cont.) •If the sample is thermally inert, T

•If the phase transition of the sample occurs,

T Crystallize

Time t

Melt

Time t Endothermic reactions take up Exothermic reactions liberate heat from surroundings and heat to surroundings and therefore the temperature T therefore the temperature T decreases. increases. T= the temperature of the sample – the temperature of the thermally inert substance. 4 May 2016


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Others… 1.Specific surface (Ss) 2.Cation exchange capacity (cec) 3.Plasticity chart(Casagrande’s PI-LL Chart) 5. Potassium determination Well-organized 10Å illite layers contain 9% ~ 10 % K2O. 6. Thermogravimetric analysis It is based on changes in weight caused by loss of water or CO2 or gain in oxygen. Sometimes, you cannot identify clay minerals only based on one method. 60

U-line

Plasticity Index

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montmorillonite

illite

A-line

40 30

kaolinite

20

halloysite

10

chlorite

0 0

10

20

30

40

50

60

Liquid Limit

70

80

90

100

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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

1 mm cube

10 mm cube

spec. surface = 222.2 mm2/g

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spec. surface = 2222.2 mm2/g


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Specific Surface Specific surface  surface / volume Specific surface  surface / mass Preferred Surface related force Surface related forces: van der Waals forces, capillary forces, etc. Gravational force Demonstration of capillary force between Large particle and small particle.

Example:

111 cm cube,   2.65g / cm 3 6 1 cm 2 4 2 Ss   2 . 3  10  m /g 3 3 1 cm  2.65 g / cm 111m cube,   2.65g / cm 3 6 1m 2 2 Ss   2 . 3  m /g 3 3 1m  2.65 g / cm

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Ss is inversely proportional to the particle size


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Isomorphous Substitution The clay particle derives its net negative charge from the isomorphous substitution and broken bonds at the boundaries.  substitution of Si4+ and Al3+ by other lower valence (e.g., Mg2+) cations, i.e. Lower charge cations replace higher charge cations as central cation (e.g., Mg+2 replaces Al+3).  leaves net negative charge (results in charge imbalance (net negative))

positively charged edges

+ + + _ _ _ _+ + _ negatively charged faces + _ _ _ __ + _ _ _ _ _ _ _ _ _ _ _ _ _ Clay Particle with Net negative Charge 4 May 2016


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Cation Exchange Capacity (C.E.C) known as exchangeable cations

 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) milliequivalents  The replacement power is greater for higher valence and larger cations. Al3+ > Ca2+ > Mg2+ >> NH4+ > K+ > H+ > Na+ > Li+  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 Al3+ can replace Ca2+ and Ca2+ can replace Mg2+. 4 May 2016


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A Comparison Mineral Kaolinite Illite Montmorillonite Chlorite

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Specific surface (m2/g)

C.E.C (meq/100g)

10-20 80-100 800 80

3-10 20-30 80-120 20-30


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Cation Concentration in Water

 cation concentration drops with distance from clay particle

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”.

clay particle

+

+ + + +

++ + + + + + + + + + + + + + + + + + + + + + + + + + + + ++ ++ + +

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+ - + cations + - ++ + + + + + + + + + -+ + + + + - + + + + + + + -+ + + + + + -+ + + double layer

+


+ + +

+

+ free water 63 63

+

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

-

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-

adsorbed water


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Clay Particle in Water adsorbed water -

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1nm 50 nm - double layer water -

free water


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Origins of Charge Deficiencies 1) Imperfections in the crystal lattice -Isomorphous substitution. • The cations in the octahedral or tetrahedral sheet can be replaced by different kinds of cations without change in crystal structure (similar physical size of cations). For example, Al3+ in place of Si4+ (Tetrahedral sheet) Mg2+ instead of Al3+(Octahedral sheet) unbalanced charges (charge deficiencies) • This is the main source of charge deficiencies for montmorillonite. • Only minor isomorphous substitution takes place in kaolinite. 2) Imperfections in the crystal lattice - The broken edge: • The broken edge can be positively or negatively charged. 3) Proton equilibria (pH-dependent charges):

M  OH  H   M  OH2 (Pr otonation) M  OH  OH  M  O   H 2O (Deprotonation ) • Kaolinite particles are positively charged on their edges when in a low pH environment, but negatively charged in a high pH (basic) environment. 4) Adsorbed ion charge (inner sphere complex charge and outer sphere complex charge: • Ions of outer sphere complexes do not lose their hydration spheres. The inner complexes have direct electrostatic bonding between the central atoms.

4 May 2016


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