Transcript DASAR ILMU TANAH CIRI-CIRI KOLOID TANAH

CIRI-CIRI
KOLOID LIAT
&
KOLOID ORGANIK
TANAH
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Properties of Clay and
Organic Colloids
1.
2.
3.
4.
5.
6.
Introduction
Properties of Colloids
Types of Colloids
Structure of Colloids
Sources of Charge on Colloids
Reactions of Soil Colloids
Koloid Liat dan Koloid Organik
1. Soil colloids are organic and inorganic matter with
very small particle size and a correspondingly large
surface area.
2. Organic materials = Koloid humus
Fraksi Koloid
3. Inorganic materials = Koloid Liat
4. Their small size, large surface area, and electrically
charged surface give them the advantage of being
highly reactive.
5. Their presence in soil give soil very large surface
area.
}
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Ciri-ciri Umum Koloid
1.
Size- Colloids are generally defined
be less than 2 m in diameter.
to
2.
Surface area- The smaller the particle size in
a given mass of soil, the greater the surface
area.
3.
Surface Charge- Soil colloids carry positive or
negative electrostatic charges.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Ciri-ciri Umum Koloid
4.
Adsorption of ions- Negatively charged soil
colloids attract positively charged ions (cations e.g
Al3+, Ca2+, Mg2+, K+, Na+, H+, etc) while positively
charged colloids attract negatively charged ions
(anions e.g NO3-, SO42-, Cl-, etc).
5.
Adsorption of water- Colloids attract and hold
large number of water molecules due to the polar
nature of water molecules.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Clay Crystal (Micelle)
1. A clay unit has different
layers
2. Each Layer is made up of
sheets
3. Each colloid particle
(micelle) attracts
thousands of cations to
the colloid surface by
electrostatic attraction.
4.
Some cations will break
away from the swarm on
the surface and be
replaced by other cations
of equal charge in a
process called “Cation
Exchange” process.
5.
The cations and anions
involved in the process
are called exchangeable
ions
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Kelas Koloid Tanah
Soils contain different types of colloids, each with its
particular composition, structure, and properties.
The four main groups of colloids are as follows:
1.
2.
3.
4.
Crystalline silicate colloids
Noncrystalline silicate colloids
Iron and Aluminum Oxide colloids
Organic Colloids
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Koloid Silikat Kristalin
1.
The predominant type of colloids in
most soils is the crystalline silicate type
2.
These colloids have a layered structure
(like pages of a book) -phyllosilicates.
3.
Each layer consists of two to four sheets
of closely packed and tightly bonded
O2, Si, and Al atoms.
4.
Their structure make them negatively
charged.
5.
Members of this group differ in particle
shape, and adsorption of water and
ions.
6.
Contoh: Kaolinite, Smectite, Mica, dll.
Kaolinite
Mica
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Struktur Umum Koloid Silikat Kristalin
Single silica tetrahedral structure
Silica tetrahedral sheet
Single Al/Mg Octahedral structure
Al octahedral sheet
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Figure 1. Silicon tetrahedron structure showing
a silicon ion in coordination with four oxygen
ions to form a tetrahedral structure.
Figure 3. Silicon tetrahedron sheet
in figure 2 turned upside down
toward figure 3 (the Aluminum
octahedral sheet)
Figure 2. Silicon tetrahedron sheet showing one
plane of oxygen ions bonded to two silicon ions in
two directions to form a sheet of silicon tetrahedrons
with unbalanced charges on the apical O ions.
Figure 4. The structure of kaolinite (~0.7
nm thick from the bottom oxygen to the top
oxygen) showing apical oxygen ions of a
silicon tetrahedral sheet bonded with the
octahedral sheet to form a 1:1 layer
mineral.
Figure 3. Aluminum octahedral structure
showing aluminum in coordination with
six oxygen ions.
Figure 5. The basic structure of 2:1 clay
minerals showing two silicon tetrahedral
layers on top and bottom and one
aluminum octahedral layer in the middle of
the structure
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Blok-blok Tetra dan Okta saling bersambungan membentuk bidang Si dan Al
(Mg) yang berselang seling dengan bidang O2 dan OH.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Susunan lembaran-lembaran dalam liat koloid
Kaolinite (Si4Al4O10(OH)8)- One sheet of tetrahedron bonded to
one sheet of octahedron
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Mica (muscovite)
Vermiculite
Smectite
2:1:1. Chlorite
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Koloid Silikat Non-Kristalin
• These clays consist of tightly bonded O2, Si, and
Al atoms, but they do not have ordered,
crystalline sheets.
– Examples = Allophane, immogolite
– These group of colloids are highly charged, and are
formed from volcanic ash.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Oksida Fe dan Al
1. These colloids are found in highly weathered
tropical environments.
2. They consist of Fe, Mn, and Al atoms in
coordination with O2 atoms.
3. Fe and Al oxides group of colloids consist of
crystalline sheets. But there are some members in
the group that may not be crystalline.
4. Their net charge range from slightly –ve to
moderately +ve.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Struktur Koloid Oksida
1. These are octahedral
sheets with either Fe or
Al in the cation
positions.
2. They do not have
tetrahedron sheets, and
they do not have Si in
their structure.
3. They do not have
isormorphous
substitution. Eg.
Gibbsite
[Al(OH)3]shown here.
4. Other examples are
Goethite (FeOOH),
Hematite [Fe2O3], etc.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Koloid Organik
1. These colloids are not
minerals
2. They are not crystalline
3. They consist of rings and
chains of C atoms bonded
to H, O2, and N.
4. Organic colloids have a net
–ve charge.
5. Humus particles are the
smallest colloids and
exhibit very high water
adsorbing capacity.
Organic Colloid
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
StruKtur Koloid Organik
1. Consists of large organic
molecules whose
chemical composition
varies.
Structure of Humic Acid
2. Structure contains
complex series of C
chains and ring
structures with many
functional groupscarboxyl, phenolic, and
alcoholic groups.
3. -Ve or +ve charges on
the humus colloid
develop as H+ ions are
either lost or gained by
these groups.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Sumber Muatan pada Koloid Liat
1. Isomorphic Substitution - during weathering, primary minerals
dissolve and recrystalize as secondary minerals
•
During this process, one element may become substituted for
another element of similar size in the crystal structure without
changing the shape of the crystal.
•
If the two elements do not have the same ionic charge, then an
unsatisfied net charge remains at that point in the crystal.
Common substitutions are Al+3 for Si+4, Mg+2 for Al+3, and Fe+2
for Al+3, each leaving a net negative charge on the crystal. This
charge does not depend on pH, thus permanent charge or
constant charge.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Sumber Muatan pada Koloid Liat
2.
3.
Exposed hydroxyl groups (-OH-_ on the surfaces of clay
crystals. This accounts for most of the net negative charge in
Kaolinite and some of the charge in Montmorillonite,
Vermiculite and Illite.
Broken oxygen bonds at the edges of crystals. At the broken
edges of crystals, the small Al3+ and Si4+ ions are exposed to
weathering and may be lost. The remaining oxygen ions have
an unsatisfied net negative charge. This is an important source
of charge in all clays. E.g.
>SiOH2+ <------> >SiOH <--------------> >SiO- + H+
>AlOH2+ <------> >AlOH <--------------> >AlO- + H+
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Adsorption (Penjerapan) Kation
Pertukaran Kation
• Cation exchange is the exchange of cations between
the soil and the soil solution..
–
•
Cation Exchange Capacity (CEC)- sum total of
exchangeable cations that a soil can absorb
–
•
2 Na+ + Ca-clay <-------------> Na-clay + Ca2+
CEC is used as a measure of fertility, nutrient retention
capacity, and the capacity to protect groundwater from
cation contamination.
Cation Exchange Capacity is a function of:
–
–
Type and amount of clay
Humus content
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Adsorption (Penjerapan) Anion
Pertukaran Anion
Some common anions in the soil include: Cl-, HCO3-, CO32-,
NO3-, SO42-, HPO42-, OH-, F-, H2BO3-, MoO42-, etc. There
are ways that anions are retained against leaching:
1.
Attraction by exposed cations along the edges of clay
crystals and exposed cations in humus colloids.
2.
Adsorption of H2PO4-, SO42-, and MoO42- by Fe, and Al
oxides at low pH
Tropical soils, with lots of Fe, Al oxides, can have net AEC.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
Sifat Tanah yang dipengaruhi oleh Adsorpsi Ion
1. nutrient availability- Exch cations are available
for plants.
2. leaching of electrolytes- retention of
substances prevents their movement through
the soil.
3. soil pH- CEC increases with increase in pH.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt
RINGKASAN
1. The colloids in soils are both organic and inorganic.
2. The size of colloids, structure of colloids (high surface area),
and Charges of soil colloids make them the center of chemical
and physical activity in soils.
3. The –ve and +ve charge sites they have attract ions and
molecules of opposite charge.
4. The replacement of one ion for another on the colloid surface
is called cation or anion exchange reaction
5. The total number of –ve colloid charges per unit mass is
termed CEC
6. That capacity influences sorption of contaminants, nutrient
availability, and pH of soils.
SUMBER: myspace.aamu.edu/users/monday.mbila/soils/SPS251Lecture07.ppt