Mineral Colloids Continued

Na+

K+

K+Na+

K+K+

K+

Cation Exchange

Na+ Na+ Na+

Na+ Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+Na+

Na+

Na+

Na+

Na+

ColloidSoil Solution

Factors Determining Cation Preference

1. Concentration

2. Charge (+1, +2,+3)

3. Size

Mineral Cation Exchange Capacity

The total quantity of cations aclay can adsorb.

Equal to the amount of charge

Units are cmolc/kg soil

Range: 0 - 180 cmolc/kg

Related directly to the amount of Isomorphous substitution

K

HH

O

HH

O

HH

O

H H

O

+

1. Kaolinite

1. Has low CEC

Reason: limited isomorphous substitution

2. Is non-expanding

Reason: layers are “glued” shut by hydrogen bonds

3. Cation adsorption is on the outer mineral surfaces

Reason: layers are “glued” shut by hydrogen bonds

2. Smectite

1. Has high CEC

Reason: abundant isomorphous substitution (Mg for Al)

2. Is highly expanding

3. Cation adsorption is in the interlayers of mineral

Reason: layers are not “glued” shut by hydrogen bondsAllowing easy movement of water and hydrated cationsto the interlayer regions

Reason: layers are not “glued” shut by hydrogen bondsAllowing easy movement of water and hydrated cationsto the interlayer regions

3. Vermiculite

1. Has high CEC

Reason: abundant isomorphous substitution (Al for Si)

2. Is moderately expanding

3. Cation adsorption is in the interlayers of mineral

Reason: layers are not “glued” shut by hydrogen bonds

Reason: layers are not “glued” shut by hydrogen bonds,but interlayer cations are very close to the source of the negative charge (the tetrahedra) holding the layers together.

3. Illite

1. Has low CEC

Reason: abundant isomorphous substitution (Al for Si),but potassium ions fit well in cavities on the surface ofthe interlayers, holding them tightly together.

2. Is non-expanding

3. Cation adsorption is mostly on external mineral surfaces

Reason: potassium ions fit well in cavities on the surface ofthe interlayers, holding them tightly together.

Reason: potassium ions fit well in cavities on the surface ofthe interlayers, holding them tightly together.

K K KClay Layer

Clay Layer

MineralsMinerals

Kaolinite Smectite Vermiculite illite

1:1None2 – 5

2:1 High80 - 120

2:1 Limited100 – 160

2:1None 20-40

MineralExpansionCEC (cmol/kg)

Octahedralsubstitution

tetrahedralsubstitution

{tetrahedralsubstitution

Bt horizon

E horizon

A horizon

B horizon(Illuvial)

(Elluvial)

Bt horizonBt horizon

t = accumulation of silicate clays formedin place or translocated from above

Soils and Clays

Implications of Negative Charge sites.

Important Cations: H+, Ca2+, Mg2+, Zn2+, Mn2+, K+, NH4+, Cu2+

reserve

Ca2+ Mg2+Zn2+

Cu2+

Ca2+

Ca2+

Ca2+

Ca2+

Na+

K+

K+

K+

K+

K+

Na+

K+

Na+

Na+

Na+

Root

H+H+

H+

H+

Flocculation and Dispersion

Na+ Na+

Ca2+

Particles with a Single Charge

- - - - - -

- - - - - -

Clay-Sized Particles

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+ Na+ Na+ Na+

- - - - - -

- - - - - -

Al3+ Al3+ Al3+ Al3+

Dispersed Flocculated

- -

- -

- -

- -

- -

- -

- -

-

Hig

h ca

tion

co

nce

ntr

atio

n

Am

bie

nt c

on

cen

tra

tion

- -

- -

- -

- -

- -

- -

- -

-

Ambient solution cation concentration

- - - - - - - - - - - - - - -

- -

- -

- -

- -

- -

- -

- -

-

- - - - - - - - - - - - - - -

Cations satisfying charge on both negatively charged colloids

Aids in development of soil structureIncreases infiltration of water at the soil surfaceCan increase hydraulic conductivityIncreases movement of gases (O2)Aids in root penetration

Flocculation

A Practical Matter for Flocculation

Wastewater Constituents

Pathogenic organisms: bacteria, protozoa, virusesNon-pathogenic bacteria (> 100,000 / ml for sewage)

Organic (carbon) particles: feces, food, plant material, humusSoluble Organics (carbon): pesticides, poisons, paints, drugs

Soluble Inorganic Chemicals: nutrients (N and P), metals

Inorganic particles: sand, silts, clays

Organic and inorganic particles

Higher turbidity levels are often associated with higher levels of viruses, parasites and bacteria.

Turbidity

Primary Water Treatment

Primary Treatment

Screening, Grit Removal, Primary Settling

Bar Screen

particles larger than ¼”

Grit Chamber

Large particulates

Short time periodSand and gravelesp. storm water

V = KD2

Primary Settling Tank

Longer residence time Chemicals to promote flocculation/coagulation

Smaller Particles

Suspended solids

Solids settle to the tank bottom as “primary sludge”

Some remains as suspended solids

Al3+

Al3+

Al3+

Al3+Al3+

Al3+

Chemical Flocculation

Suspended silts, clays and organic matter areGenerally small and negatively charged.

Primary Treatment

Sludge

Suspended solids

Iron and Aluminum Iron and Aluminum Oxides/hydroxides Oxides/hydroxides

Weathering of Rocks and MineralsWeathering of Rocks and Minerals

Rocks Primary Minerals Secondary Minerals

chemical

physical chemical

QuartzMuscoviteFeldsparsbiotite

Silicate claysFe oxidesAl oxides

GraniteBasalt

soluble constituents (Ca2+, Mg2+, K+, Fe2+, Al3+, Si4+,CO3 2

-, SO4

2-)

FormationFormation

Increased Weathering

Smectites

Kaolinite

Fe, Al oxides Hot, wet climates

Iron Oxides

Release of metal ions from minerals

-SiO-Fe2+ + 2H+ <--> Fe2+ + 2OH-SI

Iron bearing silicate Free iron

Chemical weathering

Fe2+

Fe3+

oxygen

Fe(OH)3

water

Lack of oxygen

(Mobile)

Redoximorphic Features

Fe2+ Fe3+

Iron Oxides

Goethite

Hematite

Color

High soil temperature, better drained soils, rapid biomass turnover, high Fe-release rate from rocks

most frequently occurring Fe-oxidein soil and has a characteristic yellowish brown color

Bo Horizon

Bo is an oxic subsurface horizon

Less weathered, poorer drainage More weathered, better drained

Temperate Tropical

Water and Temperature

Goethite Hematite

Iron Oxides

Can possess negative, positive, zero charge

Potential interaction with cations and anions

Cl-, F-, Br-, SO42-, NO3

-, CO32-, PO4

-3

Anion Exchange

Aluminum Oxides

Al3+

Products of Extreme Weathering

Breakdown of Al-O-Si linkages

kaolinite

Si, Al

Removalby leaching

water

Al3+

Al(OH)3

Water, crystallization

Gibbsite (grayish-white color)

The principal aluminum hydroxide in soil

Products of Extreme Weathering

Al(OH)3

Gibbsite

crystalline and octahedral

Gibbsite Dominated

Products of Extreme Weathering

kaolinite

Environments

Highly weatheredLess weathered

Kaolinite Dominated

GibbsiteAl(OH)3

Aluminum Oxides

Can possess negative, positive, zero charge

Potential interaction with cations and anions

Cl-, F-, Br-, SO42-, NO3

-, CO32-, PO4

-3

Anion Exchange

Aluminum has a high affinity for phosphorus

Al3+

Al3+

Al3+

Al3+Al3+

Al3+

Chemical Flocculation

Suspended silts, clays and organic matter areGenerally small and negatively charged.

Primary Treatment

High in Al

Suspended solids

Aluminum has a high affinity for phosphorus

Both iron and aluminum oxides areprominent in highly weathered environments

Can possess negative, positive, zero charge

Both are capable of cation and anion exchange

Next: Organic Colloids