Chapter 8
Soil colloidal chemistry and soil
surface reaction
一,Surface types of the soil colloid
（一） Siloxane surface
（二） Hydrous oxide surface
（三） Organic matter surface
Section 1 Soil colloidal surface nature
二,The specific surface area and surface
area of the soil colloid
(一 ) Surface area of the soil colloid
表 8－ 1 土壤中常见粘土矿物的比表面积（ m2·g -1）
胶体成分 内表面积 外表面积 总表面积蒙脱石蛭 石水云母高岭石埃洛石水化埃洛石水铝英石
700-750
400-750
0-5
0
0
400
130-400
15-150
1-50
90-150
5-40
10-45
25-30
130-400
700-850
400-800
90-150
5-40
10-45
430
260-800
The specific surface area of main soils in China
Latosol 60－ 80m2?g-1
Red soil 100－ 150m2?g-1
Yellow brown earth 200－ 300m2?g-1
(二 ) Measurement method of the specific
surface area
1,Instrument method
2,Adsorbed method,nitrogen,glycerine
etc.、
三,Surface charge and potential of soil
（一） Cause and categories of the soil charge
1,Permanent charge-The net negative (or positive)
charge of clay particles inherent in the crystal structure of
the particle; not affected by changes in pH or by ion-
exchange reactions.
2,Variable charge- pH dependent charge
Zero point of charge (ZPC) –The pH value of a solution
in equilibrium with a variable charge material or mixture
of materials whose net charge from all sources is zero.
Cause of variable charge:
A,Dissociation of hydrous alumino-silicate
B,Removal of H+ ions from OH groups on
various types of mineral surface.
C,The dissociation of hyogen ions (H+) from
the functional associated with soil organic matter.
D,The oxides and hydrous oxides of iron and
aluminium,the short-range order aluminosilicates and
the edge face of clay minerals can all give rise to
variable charge in this way.
（二） The charge quantity of the soil
1,The soil charges exist in parts of soil
colloid
2,The composition of soil colloid
3,The interaction of soil colloid
Affect the factors of charge quantity of the soil:
C,pH value
B,Types of soil colloid
A,Texture
The electric double layer:
The actual distribution of cations in a system is considered to grade
continuously from a high concentration near the colloid surface to a
considerably lower concentration in the bulk solution,This type of
distribution is known as a diffuse double layer,
（ 三） The surface potential of soil colloid
图 8－ 2 双电层模型胶体微粒胶粒胶核双电层决定电位离子层（内）
补偿离子层（外）
非活性离子层扩散层
Boltzmann equation
Cx=Coexp( )
Gouy（ 1910） and Chapman（ 1913） put forward model of
electric double layer:?
x=?o exp(-k·x)
Where?o is surface potential; k is constant,
under 25° C:
k＝ 3× 107 Z ·Co
1/K is called by the thickness of diffusion
double layer
1879年 1910年
1924年 1947年
Section 2 adsorption and exchange
reaction of cation in soil colloid
一,Definition of ion adsorption
Adsorption-The process by which atoms,molecules,or
ions are take up from the soil solution or soil atmosphere
and retained on the surfaces of solids by chemical or
physical binding.
Adsorption can be divided into positive adsorption and
negative Adsorption.
二,Electrostatic Adsorption of the cation
Most soils,especially those in temperate regions,
as a result of the predominance of the permanent
negative charge on 2:1 clay minerals and the negative
charge on organic matter,carry an overall net
negative charge.
M3+>M2+>M+
Al3＋ >Mn2＋ >Ca2＋ >K+
Rb+>NH4+>K+>Na+>Li+
Table8－ 2 Ion radius with adsorptive force
Monovalent ions Li+ Na+ K+ NH+4 Rb+
离子的真实半径 (nm) 0.078 0.098 0.133 0.143 0.149
离子的水合半径 (nm) 1.008 0.790 0.537 0.532 0.509
Strong Weak
三,Cation exchange
（一） Cation exchange function
The exchange of one positive ion by another
is called cation exchange function.
Cation exchange takes place on the surfaces
of clay and humus colloids as well as on the
surface of plant roots.
（ 1） Cation exchange reactions are
reversible processes.
（ 2） Exchange between ions of different
valencies has to take into account the fact
that ions are exchanged by the same
number of equivalents of other ions.
（ 3） Cation exchange is controlled by mass
action law,
Characteristic of cation exchange
The highest CEC values are observed for
humic colloids and swelling 2:1 clay minerals;
however,soils themselves may contain only a
relatively small percentage of these materials
and thus have much lower CEC values.
CEC <10 10~20 >20
Protect nutrient
ability
Low Middle High
(二 ) Cation exchange capacity (CEC):
The sum total of exchangeable cations that a
soil can adsorb,expressed in centimoles of charge
per kilogram of soil (cmol(+)kg-1 ） or millimoles
of charge per kilogram of soil.
Affect the factors of CEC of the soil:
（ 1） Texture
（ 2） Organic matter OM %? CEC
（ 3） The types of colloid
montmorillonite ＞ kaolinite
（ 4） pH value
Texture Sand Sandy
loam
Silt Clay
CEC 1~5 7~8 15~18 25~30
Table 8-3 The CEC of soil colloids of different types
Soil colloids CEC[cmol(+).kg-1]
腐殖质蛭 石蒙脱石伊利石高岭石倍半氧化物
200
100-150
70-95
10-40
3-15
2-4
2,The base saturation
（ 1） Basic cations with acidic cations
The exchange sites in soils are dominated
by a relatively small number of different
cations,which can be categorized into two
groups,the basic cation or exchangeable bases,
Ca2+,Mg2+,K+,and Na+,and the acidic cations,
H+ and Al3+.
（ 2） Base saturation percentage (BSP)
Base saturation percentage (BSP) –The ratio of the
quantity of exchangeable bases to the cation exchange
capacity。
The soil of base saturation is neutral or alkaline reaction,
The soil of base unsaturation is acid reaction.
Base saturation (%) = (∑Ca,Mg,K,Na/Cation Exchange Capacity)× 100
(四 ) Availability of exchangeable ions
（ 1） Base saturation percentage
（ 2） The complementary ions effect in soil
（ 3） The types of clay minerals
Table 8-5 Availability of complementary
ions with exchangeable Ca
土壤 交换性阳离子组成小麦幼苗干重 (g)
小麦幼苗吸钙量
(mg)
A
B
C
40%Ca+60%H
40%Ca+60%Mg
40%Ca+60%Na
2.80
2.79
2.34
11.15
7.83
4.36
四,Specific adsorption of cation
（ 一） Mechanism of specific adsorption of cation
The strong adsorption of ions or
molecules on a surface,Specifically
adsorbed materials are not readily
removed by ion exchange.
产生阳离子专性吸附的土壤胶体物质主要是铁、铝、锰等的氧化物及其水合物。
(二 ) Affect the factors of specific
adsorption of cation
1,pH value
2,The types of soil colloid
(三） Reality significance of specific
adsorption of cation
1,Enrichment of micro-heavy metal
ions
2,Control the concentration of heavy
metal in soil solution
Section 3 Adsorption and exchange
of anion in soil colloid
（ 一 ） Adsorption of anion
1,Easy Adsorbed anion
H2PO4- HPO42- PO43-
HsiO3- SiO32- C2O42-
2,The weakly adsorbed anion
Cl- NO3- NO2-
3,Middle types of anions
SO42- CO32-
Anion is adsorbed in soil colloid:
F- > H2PO4- > HCO3- > HBO3- > SO42- > Cl - > NO3-
（ 二 ） Anion negative adsorption
(三 ) Specific adsorption of Anion
Soil colloidal chemistry and soil
surface reaction
一,Surface types of the soil colloid
（一） Siloxane surface
（二） Hydrous oxide surface
（三） Organic matter surface
Section 1 Soil colloidal surface nature
二,The specific surface area and surface
area of the soil colloid
(一 ) Surface area of the soil colloid
表 8－ 1 土壤中常见粘土矿物的比表面积（ m2·g -1）
胶体成分 内表面积 外表面积 总表面积蒙脱石蛭 石水云母高岭石埃洛石水化埃洛石水铝英石
700-750
400-750
0-5
0
0
400
130-400
15-150
1-50
90-150
5-40
10-45
25-30
130-400
700-850
400-800
90-150
5-40
10-45
430
260-800
The specific surface area of main soils in China
Latosol 60－ 80m2?g-1
Red soil 100－ 150m2?g-1
Yellow brown earth 200－ 300m2?g-1
(二 ) Measurement method of the specific
surface area
1,Instrument method
2,Adsorbed method,nitrogen,glycerine
etc.、
三,Surface charge and potential of soil
（一） Cause and categories of the soil charge
1,Permanent charge-The net negative (or positive)
charge of clay particles inherent in the crystal structure of
the particle; not affected by changes in pH or by ion-
exchange reactions.
2,Variable charge- pH dependent charge
Zero point of charge (ZPC) –The pH value of a solution
in equilibrium with a variable charge material or mixture
of materials whose net charge from all sources is zero.
Cause of variable charge:
A,Dissociation of hydrous alumino-silicate
B,Removal of H+ ions from OH groups on
various types of mineral surface.
C,The dissociation of hyogen ions (H+) from
the functional associated with soil organic matter.
D,The oxides and hydrous oxides of iron and
aluminium,the short-range order aluminosilicates and
the edge face of clay minerals can all give rise to
variable charge in this way.
（二） The charge quantity of the soil
1,The soil charges exist in parts of soil
colloid
2,The composition of soil colloid
3,The interaction of soil colloid
Affect the factors of charge quantity of the soil:
C,pH value
B,Types of soil colloid
A,Texture
The electric double layer:
The actual distribution of cations in a system is considered to grade
continuously from a high concentration near the colloid surface to a
considerably lower concentration in the bulk solution,This type of
distribution is known as a diffuse double layer,
（ 三） The surface potential of soil colloid
图 8－ 2 双电层模型胶体微粒胶粒胶核双电层决定电位离子层（内）
补偿离子层（外）
非活性离子层扩散层
Boltzmann equation
Cx=Coexp( )
Gouy（ 1910） and Chapman（ 1913） put forward model of
electric double layer:?
x=?o exp(-k·x)
Where?o is surface potential; k is constant,
under 25° C:
k＝ 3× 107 Z ·Co
1/K is called by the thickness of diffusion
double layer
1879年 1910年
1924年 1947年
Section 2 adsorption and exchange
reaction of cation in soil colloid
一,Definition of ion adsorption
Adsorption-The process by which atoms,molecules,or
ions are take up from the soil solution or soil atmosphere
and retained on the surfaces of solids by chemical or
physical binding.
Adsorption can be divided into positive adsorption and
negative Adsorption.
二,Electrostatic Adsorption of the cation
Most soils,especially those in temperate regions,
as a result of the predominance of the permanent
negative charge on 2:1 clay minerals and the negative
charge on organic matter,carry an overall net
negative charge.
M3+>M2+>M+
Al3＋ >Mn2＋ >Ca2＋ >K+
Rb+>NH4+>K+>Na+>Li+
Table8－ 2 Ion radius with adsorptive force
Monovalent ions Li+ Na+ K+ NH+4 Rb+
离子的真实半径 (nm) 0.078 0.098 0.133 0.143 0.149
离子的水合半径 (nm) 1.008 0.790 0.537 0.532 0.509
Strong Weak
三,Cation exchange
（一） Cation exchange function
The exchange of one positive ion by another
is called cation exchange function.
Cation exchange takes place on the surfaces
of clay and humus colloids as well as on the
surface of plant roots.
（ 1） Cation exchange reactions are
reversible processes.
（ 2） Exchange between ions of different
valencies has to take into account the fact
that ions are exchanged by the same
number of equivalents of other ions.
（ 3） Cation exchange is controlled by mass
action law,
Characteristic of cation exchange
The highest CEC values are observed for
humic colloids and swelling 2:1 clay minerals;
however,soils themselves may contain only a
relatively small percentage of these materials
and thus have much lower CEC values.
CEC <10 10~20 >20
Protect nutrient
ability
Low Middle High
(二 ) Cation exchange capacity (CEC):
The sum total of exchangeable cations that a
soil can adsorb,expressed in centimoles of charge
per kilogram of soil (cmol(+)kg-1 ） or millimoles
of charge per kilogram of soil.
Affect the factors of CEC of the soil:
（ 1） Texture
（ 2） Organic matter OM %? CEC
（ 3） The types of colloid
montmorillonite ＞ kaolinite
（ 4） pH value
Texture Sand Sandy
loam
Silt Clay
CEC 1~5 7~8 15~18 25~30
Table 8-3 The CEC of soil colloids of different types
Soil colloids CEC[cmol(+).kg-1]
腐殖质蛭 石蒙脱石伊利石高岭石倍半氧化物
200
100-150
70-95
10-40
3-15
2-4
2,The base saturation
（ 1） Basic cations with acidic cations
The exchange sites in soils are dominated
by a relatively small number of different
cations,which can be categorized into two
groups,the basic cation or exchangeable bases,
Ca2+,Mg2+,K+,and Na+,and the acidic cations,
H+ and Al3+.
（ 2） Base saturation percentage (BSP)
Base saturation percentage (BSP) –The ratio of the
quantity of exchangeable bases to the cation exchange
capacity。
The soil of base saturation is neutral or alkaline reaction,
The soil of base unsaturation is acid reaction.
Base saturation (%) = (∑Ca,Mg,K,Na/Cation Exchange Capacity)× 100
(四 ) Availability of exchangeable ions
（ 1） Base saturation percentage
（ 2） The complementary ions effect in soil
（ 3） The types of clay minerals
Table 8-5 Availability of complementary
ions with exchangeable Ca
土壤 交换性阳离子组成小麦幼苗干重 (g)
小麦幼苗吸钙量
(mg)
A
B
C
40%Ca+60%H
40%Ca+60%Mg
40%Ca+60%Na
2.80
2.79
2.34
11.15
7.83
4.36
四,Specific adsorption of cation
（ 一） Mechanism of specific adsorption of cation
The strong adsorption of ions or
molecules on a surface,Specifically
adsorbed materials are not readily
removed by ion exchange.
产生阳离子专性吸附的土壤胶体物质主要是铁、铝、锰等的氧化物及其水合物。
(二 ) Affect the factors of specific
adsorption of cation
1,pH value
2,The types of soil colloid
(三） Reality significance of specific
adsorption of cation
1,Enrichment of micro-heavy metal
ions
2,Control the concentration of heavy
metal in soil solution
Section 3 Adsorption and exchange
of anion in soil colloid
（ 一 ） Adsorption of anion
1,Easy Adsorbed anion
H2PO4- HPO42- PO43-
HsiO3- SiO32- C2O42-
2,The weakly adsorbed anion
Cl- NO3- NO2-
3,Middle types of anions
SO42- CO32-
Anion is adsorbed in soil colloid:
F- > H2PO4- > HCO3- > HBO3- > SO42- > Cl - > NO3-
（ 二 ） Anion negative adsorption
(三 ) Specific adsorption of Anion
