340
solid-to-liquid ratio on the biosorption capacity confirms that an increase in biosorbent concentration rapidly increases the adsorption rate. Sorption capacity of mango
peel waste with varying mass for the sorption of Cd
2+
and Pb
2+
of constant initial
concentration reveals a mere 0.5–2.5 g L-1 increase in biosorbent mass showed
rapid intake of both the ions.
However, further increase in the mass of mango peel waste did not show any
significant increase in the biosorption of the metals. Although, initially, more biosorbent means more active sites for heavy metal uptake, a saturation point will be
reached where there are excess active sites for limited number of metal ions (Iqbal
et al. 2009b). This was also shown in a study of the adsorption of Pb
2+
by modified
orange peels. The Pb
2+
removal rate increases with the increase in the biosorbent
until a saturation point and gave a maximum removal of 90% (Xuan et al. 2006).
13.5 Adsorption Models
The effect of time on adsorption capacity was studied to determine the adsorption
kinetics to enhance the understanding of the dynamics of the metallic cations on the
fruit cortexes. Al-Qahtani reported that the metal ion adsorption was rapid and can
be achieved at full capacity within 60 min. A pseudo-second-order model was suggested for the kinetics data. The rate of reaction was found to be proportional to the
square of the number of remaining free surface sites (Al-Qahtani 2016).
The equation for model (Ho and McKay 1999) is as follows:
t
q
k q
t
q
t
e
e
=
+
1
2
2
(13.6)
where k 2 (g/(mg min)) is a pseudo-second-order rate constant, q e is the adsorption
capacity (mg/g), and t is the time taken for adsorption. It was found that
t
q t
and t
are linear and
1
q e
is the slope intersecting at
1
2
2
k q e
. All linear graphs were obtained
for kiwi, tangerine, and banana cortex as per a pseudo-second-order model, suggesting chemical adsorption as the mechanism (Feng et al. 2009a, b).
Adsorption kinetics for modified orange peel also showed a pseudo-secondorder kinetic model suggesting that the rate-limiting step is the chemical sorption
that involves the forces of the valence. The sharing/exchange of electrons between
the metallic cations and the fruit cortexes gives the best correlation data for the
heavy metal ions (Feng et al. 2011). Citrus sinensis peel also showed a pseudosecond- order adsorption kinetics with adsorption capacity higher than that of sawdust (Khan et al. 2013).
It is often important to study the adsorption kinetics to gain control of the efficiency of the adsorbent. This is because complex kinetics is involved in the
S. Ganesan
solid-to-liquid ratio on the biosorption capacity confirms that an increase in biosorbent concentration rapidly increases the adsorption rate. Sorption capacity of mango
peel waste with varying mass for the sorption of Cd
2+
and Pb
2+
of constant initial
concentration reveals a mere 0.5–2.5 g L-1 increase in biosorbent mass showed
rapid intake of both the ions.
However, further increase in the mass of mango peel waste did not show any
significant increase in the biosorption of the metals. Although, initially, more biosorbent means more active sites for heavy metal uptake, a saturation point will be
reached where there are excess active sites for limited number of metal ions (Iqbal
et al. 2009b). This was also shown in a study of the adsorption of Pb
2+
by modified
orange peels. The Pb
2+
removal rate increases with the increase in the biosorbent
until a saturation point and gave a maximum removal of 90% (Xuan et al. 2006).
13.5 Adsorption Models
The effect of time on adsorption capacity was studied to determine the adsorption
kinetics to enhance the understanding of the dynamics of the metallic cations on the
fruit cortexes. Al-Qahtani reported that the metal ion adsorption was rapid and can
be achieved at full capacity within 60 min. A pseudo-second-order model was suggested for the kinetics data. The rate of reaction was found to be proportional to the
square of the number of remaining free surface sites (Al-Qahtani 2016).
The equation for model (Ho and McKay 1999) is as follows:
t
q
k q
t
q
t
e
e
=
+
1
2
2
(13.6)
where k 2 (g/(mg min)) is a pseudo-second-order rate constant, q e is the adsorption
capacity (mg/g), and t is the time taken for adsorption. It was found that
t
q t
and t
are linear and
1
q e
is the slope intersecting at
1
2
2
k q e
. All linear graphs were obtained
for kiwi, tangerine, and banana cortex as per a pseudo-second-order model, suggesting chemical adsorption as the mechanism (Feng et al. 2009a, b).
Adsorption kinetics for modified orange peel also showed a pseudo-secondorder kinetic model suggesting that the rate-limiting step is the chemical sorption
that involves the forces of the valence. The sharing/exchange of electrons between
the metallic cations and the fruit cortexes gives the best correlation data for the
heavy metal ions (Feng et al. 2011). Citrus sinensis peel also showed a pseudosecond- order adsorption kinetics with adsorption capacity higher than that of sawdust (Khan et al. 2013).
It is often important to study the adsorption kinetics to gain control of the efficiency of the adsorbent. This is because complex kinetics is involved in the
S. Ganesan