What
is Active Carbon? What are its qualities? What is the difference
between physical carbon adsorption, chemical adsorption, and
what affects the adsorption capabilities?
Removal of chlorine and organic matter is done effectively
by active carbon as a function of time, contact and cloudiness
of the water.
The right combination of particles in different sizes will
allow adsorption of a large range of polluters.
Enlarging the carbon's surface area bigger (creating cracks
and branched channels) is done by exposing the carbon to high
temperatures and steam in anaerobic conditions. Enlarging
the carbons surface area provides the carbon high adsorption
ability and allows the negative ions of the polluters to adsorb
to the carbon's positive charged surface.
The adsorption and absorption capabilities of the carbon
is affected of many factors, but basically affected of:
- The raw material's source
- The division of the pores capacity inside the carbon
There are two types
of adsorption:
Physical Adsorption: In this process, the
adsorbed materials are located on the pores' surface area
and are drawn with low electrostatic forces (Van der Vals).
This adsorption produces a small amount of heat. An example
of physical adsorption: is removal of organic materials.
Chemical Adsorption: In this type of adsorption
there's a chemical interaction between the adsorbed material
and the active carbon. This adsorption produces a large amount
of heat. An example of chemical adsorption is the removal
of inorganic compounds and formaldehyde. Organic apolaric
materials are absorbed quickly on the active carbon. The more
soluble the material is, the less its capability to adsorb,
and that's why variables such as temperature and pH which
affect its solubility, indirectly affect its adsorption.
Adsorption Capabilities
Since pores in different sizes adsorb different sized molecules,
loading tests are done:
A. IODIN NUMBER: The results of this test
give indication to the effectiveness of the adsorption of
small molecules on the general surface area of the carbon.
B. MOLLASSES NUMBER: Gives information of
large molecules adsorption capabilities.
C. TANIN NUMBER: This value helps in the
assessment of carbon's capabilities in removing odours and
flavours from water.
Active Carbon's features:
- Density Bulk
- Content Ash Total - To determine the amount of the mineral
materials in the carbon
- Hardness/Wear
- Volume Pore Total (ml/g) A large amount of pores shows
a high effectiveness of adsorption.
- Radius Pore: The average radius is measured in Microns
and changes by the carbon's type.
The pore volume segmentation: Each carbon type has a different
segmentation:
MICROPORES, MESOPORES and MACROPORES. Carbon that adsorbs
different types of gas molecules is characterized with MICROPORES.
Carbon that is recommended for dichloride is characterized
with MESOPORES.
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