16
possesses. When ash is present in excess, it could lead to the blockage of the
pores on the activated carbon so that there is not enough space for the surface
area of the carbon (Schröder et al. 2007). Ash content rises with continuous
change in concentration of activating agent as this result in decrease of the
organic compounds of activated carbon. Nevertheless, there is a relatively fixed
amount for the content of an inorganic compound in activated carbon (Maulina
and Iriansyah 2018). Activated carbon ranges of 1 to 12% ash content have
been reported based on raw material variation used as a precursor in synthesis.
The weight difference between the initial and final mass of the carbon is used
in calculating the ash content of activated carbon in mass per gram. Standard
test method (ASTM D2866–83) can be used in estimating the totality of the
ash content in activated carbon.
(iii) pH of activated carbon: pH is a significant factor that must be considered for
effective adsorption process. It affects the binding forces around the surface
morphology and charges of the activated carbon (Boehm 1994). Non-carbon
atoms such as nitrogen, oxygen, and sulfur found on activated carbon surface
affect the surface acidity and the whole adsorption process (Zhang et al. 2005).
For the adsorption process to be effective, pH must be controlled before and
after process activation. For example, the necessity for pH in metal adsorption
could be traceable to the ionic charge of the functional groups on the adsorbent
and the chemistry of the metal solution (Attia et al. 2010). The standard test
method (ASTMD3838–80) is usually used for the determination of pH in activated carbon.
(iv) Volatile matter: Gases and vapor driven off during thermal decomposition of
coal are usually referred to as volatile matter. The increase in activator
concentration causes a decrease in a number of volatile matters in the activated
carbon. This can be clearly explained in that activators bring about change in
the structure and quality of activated carbon. Also, the carbon activator discharges substances that are volatile and causes micropore structure in activated
carbon (Maulina and Iriansyah 2018). Non-carbon compound attached to the
activated carbon surface area is drastically reduced when the activator is
impregnated, while their entrance becomes feasible through the pores of the
coal. Therefore, the pore surface is cleansed and enlarged due to the presence
of the activator. The standard test method (ASTMD8832–98) is usually used
for the determination of volatile matter in activated carbon.
1.7 Adsorption Mechanism of Activated Carbon
Adsorption is receiving great attention as a method for removal of heavy metals
from polluted media, especially those contaminated with wastewater. Adsorption
depends on the extent of mass transfer between the two phases involved (liquid and
solid phase) (Azimi et al. 2017). The adsorption of heavy metal contaminants
ion onto an adsorbent (i.e., activated carbon) consists of three main steps namely:
B. Oladipo et al.
possesses. When ash is present in excess, it could lead to the blockage of the
pores on the activated carbon so that there is not enough space for the surface
area of the carbon (Schröder et al. 2007). Ash content rises with continuous
change in concentration of activating agent as this result in decrease of the
organic compounds of activated carbon. Nevertheless, there is a relatively fixed
amount for the content of an inorganic compound in activated carbon (Maulina
and Iriansyah 2018). Activated carbon ranges of 1 to 12% ash content have
been reported based on raw material variation used as a precursor in synthesis.
The weight difference between the initial and final mass of the carbon is used
in calculating the ash content of activated carbon in mass per gram. Standard
test method (ASTM D2866–83) can be used in estimating the totality of the
ash content in activated carbon.
(iii) pH of activated carbon: pH is a significant factor that must be considered for
effective adsorption process. It affects the binding forces around the surface
morphology and charges of the activated carbon (Boehm 1994). Non-carbon
atoms such as nitrogen, oxygen, and sulfur found on activated carbon surface
affect the surface acidity and the whole adsorption process (Zhang et al. 2005).
For the adsorption process to be effective, pH must be controlled before and
after process activation. For example, the necessity for pH in metal adsorption
could be traceable to the ionic charge of the functional groups on the adsorbent
and the chemistry of the metal solution (Attia et al. 2010). The standard test
method (ASTMD3838–80) is usually used for the determination of pH in activated carbon.
(iv) Volatile matter: Gases and vapor driven off during thermal decomposition of
coal are usually referred to as volatile matter. The increase in activator
concentration causes a decrease in a number of volatile matters in the activated
carbon. This can be clearly explained in that activators bring about change in
the structure and quality of activated carbon. Also, the carbon activator discharges substances that are volatile and causes micropore structure in activated
carbon (Maulina and Iriansyah 2018). Non-carbon compound attached to the
activated carbon surface area is drastically reduced when the activator is
impregnated, while their entrance becomes feasible through the pores of the
coal. Therefore, the pore surface is cleansed and enlarged due to the presence
of the activator. The standard test method (ASTMD8832–98) is usually used
for the determination of volatile matter in activated carbon.
1.7 Adsorption Mechanism of Activated Carbon
Adsorption is receiving great attention as a method for removal of heavy metals
from polluted media, especially those contaminated with wastewater. Adsorption
depends on the extent of mass transfer between the two phases involved (liquid and
solid phase) (Azimi et al. 2017). The adsorption of heavy metal contaminants
ion onto an adsorbent (i.e., activated carbon) consists of three main steps namely:
B. Oladipo et al.