LOGO
Cation Exchange And It’s Role On Soil Behavior
Presented by Sh.Maghami
Instructor :
Dr.Nikoodel
Autumn ,1391
Contents
Chapter 1) Introduction
• Deffinitions
• Why do soils have CEC
• Basics of Clay content & CEC
Chapter 2) Clay Structure
•
•
•
•
How do clays Have a CEC
Isomorphous substitution
Foundations and differences of Clays structures
Some properties of clay minerals
Chapter 3) Surface Properties
• Surface Properties Relations
Chapter 4) Engineering Properties
• The physical properties affected by surface phenomenones
Cation Exchange
What expect you to know
How the soil properties
could related to each other
How CEC effect
on soil properties ?
What properties affected ?
What is the relation
of surface properties
of the soil
Cation Exchange &
Cation Echange Capacity (CEC)
Cation
CEC Agents and what
Is their relationship
to soil
Describing the clay structures
and the differences between those .
Chapter 1
INTRODUCTION
 Definitions
Cation Exchange
Cation Exchange Capacity
Why do soils have CEC
Definitions
Soil colloids will attract and hold positively
charged ions to their surface Replacement
of one ion for another from solution
Cation Exchange
For every cation that is adsorbed, one goes back into soil solution
In soil science the maximum quantity of
total cations , of any class, that a soil is
Cation Exchange Capacity
capable of holding, at a given pH
(CEC)
value, available for exchange with the
soil solution (meq+/100g)
Why do soils have CEC ?
The cation exchange capacity (CEC) of the soil is determined by
the amount of clay and/or humus that is present .
Clay & Humus : Cation warehouse or reservoir of the soil
Sandy soils with very little OM
Clay soils with high levels of OM
Low CEC
much greater capacity
to hold cations .
(negative soil particles attract the positive cations)
Sand
Clay
Si2O4
SiAlO4-
No charge.
Does not retain cations
Negative charge.
Attracts and retains cations
CLAY STRUCTURE
How do clays Have a CEC
Isomorphous substitution
Foundations and differences of Clays structures
1:1 Clays
2:1 Clays
Some properties of clay minerals
Why do clays have a CEC?
If the mineral was pure silica and
oxygen (Quartz), the particle would
not have any charge.
Figure 1 ) SiO 2 Structure
Isomorphous substitution
 However, clay minerals could contain aluminum as well as silica.
They have a net negative charge because of :
 the substitution of silica (Si4+) by aluminum (Al3+)
 in the clay. This replacement of silica by aluminum in the clay
mineral’s structure is called “isomorphous substitution”, and the
result is clays with negative surface charge
Figure 2)
Tetrahedron - SiO4
Octahedron - Al(OH)6
How clays are forming basically ?
Sharing of O or OH groups
Sheets and unit layers
(a) Tetrahedral sheet
(b) Octahedral sheet
Si
Al
Figure 3) Sheets Formation
How clays are forming basically ?
Exposed Oxygen
Si
Shared Oxygen
Hydrogen
Balance Oxygen Charge
Figure 4) Clays unit structure
Al
Clay Types
 A) 1:1 Type Minerals
Si
Mostly Kaolinite
Al
7Ao
Si
Al
Hydrogen bonding between layers. This gives 1:1
type minerals a very rigid structure .
 Well crystallized
Low cation adsorption
Little isomorphous substitution
Larger particle size (0.1 - 5 m m)
Figure 5) 1:1 clays
Fixed lattice type
 No interlayer activity
 No shrink-swell
 Only external surface
Clay Types
 B) 2:1 Type Minerals
1. Expanding lattice

Smectite group

Mostly Montmorillonite
Si
18Ao
Al
Si
Mg
H2O
Si
Al
Si
 Freely expanding
 Water in interlayer
 Large shrink-swell
 Small size
 Poorly crystallized
Large internal surface
Isomorphous substitution
 Large cation adsorption
 Adsorbed cations in interlayer
Ca
Figure 6) 2:1 expanding clays
Clay Types
- - - Si- - - -
 2. Non-expanding lattice
Fine-grained micas or illite
10Ao
Al
Si

K K K K K K K
- - - -Si - - -
Some distribution of Al for Si in the tetrahedral
layers leads to permanent net negative charge
Al+3 and K+ substitute for Si+4 (tetrahedral sheet)
weathering at edges = release of
Al
K+
Si
very limited expansion
medium cation adsorption
limited internal surface
properties between kaolinite and vermiculite
-------
Figure 7) 2:1 non expanding clays
Clay Types
 Chlorites :
 Mg replace K+ of illite
 Similar to illite
 Vermiculite :
 similar to Smectite
 more structured
=> limited expansion
 Rather large cation
adsorption
Figure 8) Clays comparison
Table 1) Summary of Properties :
Major Clay
particles
properties
differences
Size (um)
Surface Area (m2/g)
External
Internal
Interlayer
Spacing (nm)
Cation
Sorption
Kaolinite
0.1-5.0
10-50
-
0.7
5-15
Smectite
<1.0
70-150
500-700
1.0-2.0
85-110
Vermiculite
0.1- 5.0
50-100
450-600
1.0-1.4
100-120
Illite
0.1-2.0
50-100
5-100
1.0
15-40
coatings
-
-
-
100-300
Humus
What happens in soil
R-H+
R-H+
R-H+
+ 4 Na+
R-H+
R-Na+
R-Na+
+ 4 H+
R-Na+
R-Na+
Figure 9) what happens in soil
Conclusion
From the previous discussion , it is obvious that the amount and type
of clay in the soil determines cation exchange capacity.
Non
Clays
Kaolinite
In addition, the type of clay also affects
cation exchange capacity. There are
three types of aluminosilicate clays in
temperate region soils:
CEC , Shrinkage & Swelling
Illite
Montmorillonite
Figure 10) CEC comparison
How tight an ion is held .
1) Ion’s hydrated radius
 • Smaller radius = tighter hold
2) Magnitude of ion’s charge
 • Higher charge = tighter hold
Al3+ > Ca2+ > Mg2+ > K+, NH4 + > Na+ > Li+
How likely an ion species is to be adsorbed is determined by its
concentration in the soil solution
Higher concentration = more adsorption
High concentration of one ion species relative to another ion species can
supersede the effect of radius and charge
Chapter 3
SURFACE PROPERTIES
Surface Properties Relations
Surface Properties Relations
 There are some important correlations between some surface
properties of soil ,that have to be obvious .
 This Properties are :
Reason of differences
1m
Montmorillonite
Area : 18 m2
Figure 11)
Area : 6 m2
CEC & SSA Relationship
 Many researchers (e.g., Farrar and Coleman 1967; De Kimpe et al. 1979; Cihacek and
Bremner 1979; Newman 1983; Tiller and Smith 1990) have found
:
 Surface Area to relate closely to Cation Exchange Capacity of soils.
 The surface activity of a clayey soil can be described in part by its CEC
or by its Specific Surface Area (Locat et al. 1984).
 Gill and Reaves (1957) presented SSA versus CEC with a correlation
coefficient of r2 = 0.95, which is similar to Mortland’s (1954) and Reeve’s
et al. (1954) findings. Farrar and Coleman (1967) presented results for
19 British Clays, which show a relatively
linear correlation between CEC and SSA.
 All of these equations can be found in Table 2 .
Table 2) Equations between CEC and SSA
Correlation Equations for Relationships Between CEC and Surface Area .
CEC=0.15SA-1.99
Southestern US Clay
Gill and Reaves (1957)
CEC=0.28SA+2
British Clay Soils
Farrar and Coleman (1967)
CEC=0.12SA+3.23
Israel soils
Banin and Amiel (1970)
CEC=0.14SA+3.6
Osaka Bay Clay
Tanaka (1999)
Figure 12) SSA versus CEC
Correlation
Correlation
Between
Between
CECCEC
andand
SSASSA
for Clay
for Osaka
Soils of
Bay
Israel.
Clay.
(after Banin
(afterand
Tanaka
Amiel
1999)
1970)
Figure 13) CF versus CEC
Relationship
Relationship
Between
between
Cation
Surface
Exchange
AreaCapacity
and Clayand
Fraction
Clay Fraction.
for
Sensitive Canadian
(after Davidson
Clays. (after
et al.Locat
1952)et al. 1984)
Total surface area of different clays
According to this chart it is expected to cation exchange capacity
have an increasing trend from montmorillonit to kaolinite .
0 50
Kaolinite
Illite
600
100
Montmorill
onite
700
0
150
100
200
Figure 16) Surface area of clays
300
400
Internal
500
600
External
700
800
900
M2/g
Figure 14) Cation activity chart
Cation Activity Chart (after Kolbuszewski et al. 1965)
Chapter 4
ENGINEERING PROPERTIES
How the surface properties affect on soil physical
properties
Introduction
 Many properties of the fine-grained soils
are attributed to cation exchange, which
is a surface phenomenon .
 By replacing the existing cations in the
exchange complex, several improvements
can be effected in the soil properties.
 These beneficial changes are in the form
of reduction in plasticity, increase in the
strength, and reduction in the
compressibility.
Figure 11) Lime Stabilization
The addition of lime to a soil supplies an excess of calcium ions, and cation
exchange can take place with divalent calcium, Ca+2 replacing all other
monovalent cations. The base exchange phenomenon has been used by
several investigators to explain the effects of chemical stabilization.
(K. Mathew 1997)
Diagram
1: Atterberg Limits
2: Dispersion
3: Hydraulic conductivity
4: Swelling Potential
5: Compressibility
6: Consoildation
Following previous session ,some
soil engineering properties
changes that found to be related
,directly or not ,with Cation
Exchange process are discussed
1 : Atterberg Limits
 Sridharan et al. (1975) tested seven natural soils containing
LL%
montmorillonite as the dominant clay mineral and showed the
relationship between the Atterberg limits and Clay Fraction (CF),
SSA and CEC. The Liquid Limit versus CEC shows somewhat of a
linear trend, as indicated in Figure 19.
CEC
Figure 15) CEC versus LL% (Sridharan et al.1975)
Figure 16) LL versus CEC
Relationship Between Cation Exchange Capacity and Liquid Limit.
(after Davidson et al. 1952)
Figure 17) PL versus CEC
 This Slide Removed For More Reviews…
Figure 18) IP versus CEC
Relationship Between Cation Exchange Capacity and Plasticity Index
(after Davidson et al. 1952)
Figure 19) SL versus CEC
Relationship Between Cation Exchange Capacity and Shrinkage Limit.
(after Davidson et al. 1952)
Shrinkage Limit
 The shrinkage of clay soils is often said to depend not only on the
amount of clay, but also on its nature (Greene-Kelly 1974).
 Montmorillonitic soils = high water adsorption = high shrinkage
(Smith 1959)
Clay %
optimum clay content (Sridharan 1998).
30 and 50 %.
Table 3) Equations between PL , LL & SA
The Plastic and Liquid limit has been highly correlated with CEC and
Specific Surface Area (Smith et al. 1985; Gill and Reaves 1957; Farrar and
Coleman 1967; Odell et al. 1960), as seen in Table 3 .
Correlation Equations for Relationships Between PL ,LL ,and SA
CEC=0.55LL-12.2
British Clay Soils
Farrar and Coleman (1967)
CEC=1.74LL-38.15
Clays from Israel
Smith et al. (1985)
CEC=3.57PL-61.3
Clays from Israel
Smith et al. (1985)
PL=0.43SAext.+16.95
African/Georgia/Missoury
Hammel et al. (1983)
PL=0.064SA+16.60
Clays from Israel
Smith et al. (1985)
2: Dispersion
 Surface area may also play a significant role in controlling the behavior
of dispersive clays through surface charge properties (e.g., Heinzen et al.
1977; Harmse et al. 1988; Sridharan et al. 1992; Bell et al. 1994).
Sodic soils are typically highly dispersive.
 Sodic soils have a high concentration of exchangeable Na+ ,therefore
much of the negative charge on the clay is neutralized by Na+, creating
a thick layer of positive charge that may prevent clay particles from
flocculating.
---------2+ 2+ 2+
2+ 2+ 2+
-------------
---------+ + + + + + + +
+ + + + + + + +
+ + + + + + + +
+ + + + + + + +
+ + + + + + + +
-------------
3: Hydraulic conductivity
 A laboratory study of the hydraulic conductivity (HC) of a marine clay
with monovalent, divalent and trivalent cations revealed large
differences in HC .
 RAO et all 1995 suggests that HC is significantly affected by the valency
and size of the adsorbed cations .
An increase in the valency of the adsorbed cations
For a constant valency
An increase in the hydrated radius of the adsorbed cations
Higher HC
Lower HC
 As per Ahmed et al (1969) and Quirk and Schofield (1955) HC is related
to exchangeable cations in the following order
 Ca = Mg > K > Na
4: Swelling Potential
 The more montmorillonite in the mixture, the more internal
surface and the surface area.
 As the surface area increases, the swelling potential increases
 De Bruyn et al. (1957) presented results and a classification of
various soils using Specific Surface Area and moisture contents.
His criteria state that soils with :
TSSA < 70 m2/g
TSSA > 300 m2/g
&
&
w % < 3%
w % > 10%
non-expansive (good) .
expansive (bad) .
Swelling
Figure 21) Swelling versus SSA
Specific Surface Area
(De Bruyn et al ,1957)
5: Compressibility
It has been established that the thickness of the double layer is sensitive
to changes in cations present on the surface (Van Olphen 1963).
The divalent and trivalent cations in the adsorbed complex of clayey soil
are known to reduce the thickness of the diffuse double layer by one-half
and one-third. respectively (Mitchell 1976)
An increase in valency leads to a reduction in compressibility , and at a
constant valency an increase in the hydrated radii of the adsorbed
cations resulted in an increase in compressibility. Further, it has been
found that preconsolidation pressure increases with valency of the
cations.(K. Mathew 1997).
Figure 22)Cc versus SSA
(De Bruyn et al ,1957)
References :
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AMY B. CERATO ;2003 ; INFLUENCE OF SPECIFIC SURFACE
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Paul K. Mathew and S. Narasimha Rao ; 1997 ; EFFECT OF LIME
ON CATION EXCHANGE CAPACITY OF MARINE CLAY .
Paul K. Mathew· and S. Narasimha Raoz ;1997 ; INFLUENCE OF
CATIONS ON COMPRESSIBILITY BEHAVIOR OF A MARINE CLAY
S. NARASIMHA RAO AND PAUL K. MATHEW ;1999 ; EFFECTS
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LOGO
Engineering Geology Department ,
Tarbiat Modares University ,Tehran
Iran .
Shahram.maghami@modares.ac.ir