Application of Sustainable and Low-Cost Sludge-Based Adsorbents …
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3 Preparation of Adsorbents and Activation Methods
3.1 Activation Methods
Preparation of activated carbons involves two steps:
1. Carbonization of raw precursors in an inert atmosphere and
2. Activation of carbonized material.
Carbonization consists of a thermal decomposition of the carbonaceous material,
eliminating non-carbonaceous species (volatilization of the organic compounds) and
producing a fixed carbon mass developing pore structures. Volatilization of organic
compounds in the precursor is removed at lower temperatures ranging between 300
and 550 °C without inferring the production of carbon during the activation phase.
Volatilization is more enhanced in chemical activation due to the treatment of dehydrating chemical agents. Activation can be carried out by chemical or physical means.
In chemical activation, carbonization and activation are accomplished in a single step
by carrying out thermal decomposition of the raw material impregnated with certain
chemical agents. Physical activation involves gasification of the char (obtained from
carbonization of the raw material) by oxidation with steam, carbon dioxide, air or
any mixture of these gases in the temperature range from 800 to 1100 °C.
Porous carbon materials have attracted much attention in the past decades, and it is
believed that the mesoporous activated carbons hold significant potential applications
as adsorbents of large molecules [121]. Lin and Teng [67] used waste tyre char as
precursor and also employed the steam activation method. The carbon thus obtained
had a mean pore size of 50 nm and demonstrated better adsorption capacity for
methylene blue than commercial activated carbon, which was also ascribed to the
abundant mesopores of this carbon. It should be pointed out that the pore structure of
these mesoporous carbons consists of both micropores and mesopores with a broad
and disordered pore size distribution, which is an intrinsic trait of porous carbon
prepared by steam activation.
3.1.1 Physical Activation and Characterization
The thermal decomposition of the carbonaceous material through oxidation by steam,
carbon dioxide, inert gases like nitrogen within a temperature range from 800 to
1100 °C results in the formation of solids, liquids and gaseous products [34]. Karifala et al. [59] prepared pyrolysed metal sludge carbon from galvanization industry
saturated with spent mineral oil. The variation in the pyrolysis time and temperature
influenced the structural and chemical properties of the developed carbon. The waste
oil precursor provided active carbonaceous phase which was responsible for development of micropores. Moreover, it contributed to formation of new active surface
chemistry either by supplying carbon element or by reducing environment for reactions involving the inorganic compounds. The temperature was maintained between
45
3 Preparation of Adsorbents and Activation Methods
3.1 Activation Methods
Preparation of activated carbons involves two steps:
1. Carbonization of raw precursors in an inert atmosphere and
2. Activation of carbonized material.
Carbonization consists of a thermal decomposition of the carbonaceous material,
eliminating non-carbonaceous species (volatilization of the organic compounds) and
producing a fixed carbon mass developing pore structures. Volatilization of organic
compounds in the precursor is removed at lower temperatures ranging between 300
and 550 °C without inferring the production of carbon during the activation phase.
Volatilization is more enhanced in chemical activation due to the treatment of dehydrating chemical agents. Activation can be carried out by chemical or physical means.
In chemical activation, carbonization and activation are accomplished in a single step
by carrying out thermal decomposition of the raw material impregnated with certain
chemical agents. Physical activation involves gasification of the char (obtained from
carbonization of the raw material) by oxidation with steam, carbon dioxide, air or
any mixture of these gases in the temperature range from 800 to 1100 °C.
Porous carbon materials have attracted much attention in the past decades, and it is
believed that the mesoporous activated carbons hold significant potential applications
as adsorbents of large molecules [121]. Lin and Teng [67] used waste tyre char as
precursor and also employed the steam activation method. The carbon thus obtained
had a mean pore size of 50 nm and demonstrated better adsorption capacity for
methylene blue than commercial activated carbon, which was also ascribed to the
abundant mesopores of this carbon. It should be pointed out that the pore structure of
these mesoporous carbons consists of both micropores and mesopores with a broad
and disordered pore size distribution, which is an intrinsic trait of porous carbon
prepared by steam activation.
3.1.1 Physical Activation and Characterization
The thermal decomposition of the carbonaceous material through oxidation by steam,
carbon dioxide, inert gases like nitrogen within a temperature range from 800 to
1100 °C results in the formation of solids, liquids and gaseous products [34]. Karifala et al. [59] prepared pyrolysed metal sludge carbon from galvanization industry
saturated with spent mineral oil. The variation in the pyrolysis time and temperature
influenced the structural and chemical properties of the developed carbon. The waste
oil precursor provided active carbonaceous phase which was responsible for development of micropores. Moreover, it contributed to formation of new active surface
chemistry either by supplying carbon element or by reducing environment for reactions involving the inorganic compounds. The temperature was maintained between