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Adsorption and Ion Exchange

4.1 BASIC PRINCIPLES OF ADSORPTION AND ION EXCHANGE

4.1.1 Adsorption materials

Activated carbon, silica gel, and alumina are the most popular adsorbent materials in
industry due to the fact that they provide large surface areas per unit weight. Activated car-
bon is produced from coconut shell, w and bone, whereas silica gel is made of
ood,
hydrated silicon dioxide. Alumina can be either mined or produced by precipitated alu-
minum oxide and hydroxide. In the follo the most important adsorbents are wing sections,
presented in detail.

Activated carbon
Activated carbon can be manufactured from carbonaceous material, including coal such as
ood,
lignite, peat, and w or nutshells such as coconut. The manuf acturing process consists
ation. vThe carbonization process includes drying and of two phases, carbonization and acti
heating, the aim being the remoal of seeral undesirable by-products from the ra v v w mate-
rial such as tar and other hydrocarbons. During the carbonization process, the material is
heated at 400–600 °C in an oxygen-deficient atmosphere that cannot support comb ustion.
Activated carbon has a very large surface area per unit weight, which makes it an ideal
absorptive material. Generally, the total surface area of activated carbon ranges between 300
and 1500 m 2 olume ranges between 0.7–1.8 cm /g, and the pore v 3 /g. Activated carbons made
from petroleum coke can have a surface area of almost 3000 m 2 /g (Knaebel, 1995).
Powdered activated carbon (PAC) : PC is made up of crushed or ground carbon parti- A
cles, 95–100% of which will pass through a designated sie v e—0.297 mm according to the
American Water Works Association Standard, or 0.177 mm according to ASTM D5158.
PAC is mainly used for biological treatment.
Granular activated carbon (GAC) : GA C is designated by mesh sizes such as 8 20, 20
40, or 8 30 for liquid-phase applications and 4 6, 4 8, or 4 10 for v -phase apor
applications. GAC is used for the remoal of toxic organic compounds from groundw v ater
w aste. and industrial w ater
Bituminous GAC : Bituminous coal has a more fully deinclud- eloped pore distrib v ution,
ing “transport pores,” and is particularly effective for water treatment. It exhibits a relatively

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