mineral colloids continued. na + k + k + na + k + k + k + cation exchange na +
TRANSCRIPT
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