78
zirconium increase the fluoride adsorption capacity with respect to unmodified
materials (Sathish et al. 2008). The calcium impregnated on the carbon surface also
increases the adsorption capacity with respect to the unmodified material
(Hernández-Montoya et al. 2012). In our study, it was found that the presence of
oxalic acid contributes to the increase in adsorption capacity, since it increased by
only 32%. On the other hand, kinetic studies showed that in the first 15 minutes,
carbon–zirconium removed 71% of the initial fluoride concentration, and 50 minutes are required for the modified material to reach equilibrium.
We have also developed activated carbon with lanthanum. Lanthanum uses carboxyl and phenolic groups as nucleation centers to anchor on the activated carbon surface. At pH below to 9, the activated carbon–lanthanum surface has a positive
charge (Vences-Alvarez et al. 2015). In this study, the fluoride adsorption capacity
(9 mg g
−1
) was 1.8 times higher with respect to the modified carbon with zirconium
and oxalic acid.
In the arsenic removal from water, different activated carbons modified with oxyhydroxide were studied. The granular activated carbons used in this study were
bituminous carbon (F400), and agave bagasse was used as maternal precursor to
produce activated carbon, and they were chemically activated with ZnCl 2 and
H 3 PO 4 . The adsorption capacity of the carbons at arsenic concentrations in a range
of 370 μg/g at 1250 μg/g was determined. Analyses showed that the temperature did
not have a significant effect on the arsenic adsorption; however, at pH 8, arsenic
adsorption decreased 32%. In addition, the presence of SO 4
2−
, Cl
−
, and F
−
co-anions
in the solution induce a decrement in the arsenic adsorption capacity, because these
anions compete for the active sites in the adsorbent surface (Vitela-Rodriguez and
Rangel- Mendez 2013).
On the other hand, the influence of iron content on the arsenic adsorption capacity on granular activated carbons has also been studied. Characterization analysis
has shown that iron content varies from 0 to 2%; thus the point of zero charge can
be found in a range of 3–11 depending on the iron content. The surface area of the
materials varies from 388 to 1747 m
2
/g. This study shows that the point of zero
charge is the main parameter that affects the adsorption capacity of activated carbon
for the As(V) removal from water with a contribution of 52%. Thus, it was determined that the presence of iron is essential in 36% to improve the arsenic adsorption
capacity. Therefore, the optimal iron content of activated carbon to effectively
remove arsenic is about 1%, with an arsenic adsorption capacity of 2.5 mg/g
(Arcibar-Orozco et al. 2014).
An example of the metal oxide anchoring mechanism on activated carbon is
presented in Fig. 3.12. The positive lanthanum species were charged to the periphery of the graphite sheets by electrostatic interactions with oxygenated groups to
form O–La bonds. The oxygens of the oxygenated groups become nucleation centers for the growth of the crystal of La(OH) 3 by H
+
ions displacing to form a tetrahedral structure (Vences-Alvarez et al. 2015).
E. Vences-Alvarez et al.
zirconium increase the fluoride adsorption capacity with respect to unmodified
materials (Sathish et al. 2008). The calcium impregnated on the carbon surface also
increases the adsorption capacity with respect to the unmodified material
(Hernández-Montoya et al. 2012). In our study, it was found that the presence of
oxalic acid contributes to the increase in adsorption capacity, since it increased by
only 32%. On the other hand, kinetic studies showed that in the first 15 minutes,
carbon–zirconium removed 71% of the initial fluoride concentration, and 50 minutes are required for the modified material to reach equilibrium.
We have also developed activated carbon with lanthanum. Lanthanum uses carboxyl and phenolic groups as nucleation centers to anchor on the activated carbon surface. At pH below to 9, the activated carbon–lanthanum surface has a positive
charge (Vences-Alvarez et al. 2015). In this study, the fluoride adsorption capacity
(9 mg g
−1
) was 1.8 times higher with respect to the modified carbon with zirconium
and oxalic acid.
In the arsenic removal from water, different activated carbons modified with oxyhydroxide were studied. The granular activated carbons used in this study were
bituminous carbon (F400), and agave bagasse was used as maternal precursor to
produce activated carbon, and they were chemically activated with ZnCl 2 and
H 3 PO 4 . The adsorption capacity of the carbons at arsenic concentrations in a range
of 370 μg/g at 1250 μg/g was determined. Analyses showed that the temperature did
not have a significant effect on the arsenic adsorption; however, at pH 8, arsenic
adsorption decreased 32%. In addition, the presence of SO 4
2−
, Cl
−
, and F
−
co-anions
in the solution induce a decrement in the arsenic adsorption capacity, because these
anions compete for the active sites in the adsorbent surface (Vitela-Rodriguez and
Rangel- Mendez 2013).
On the other hand, the influence of iron content on the arsenic adsorption capacity on granular activated carbons has also been studied. Characterization analysis
has shown that iron content varies from 0 to 2%; thus the point of zero charge can
be found in a range of 3–11 depending on the iron content. The surface area of the
materials varies from 388 to 1747 m
2
/g. This study shows that the point of zero
charge is the main parameter that affects the adsorption capacity of activated carbon
for the As(V) removal from water with a contribution of 52%. Thus, it was determined that the presence of iron is essential in 36% to improve the arsenic adsorption
capacity. Therefore, the optimal iron content of activated carbon to effectively
remove arsenic is about 1%, with an arsenic adsorption capacity of 2.5 mg/g
(Arcibar-Orozco et al. 2014).
An example of the metal oxide anchoring mechanism on activated carbon is
presented in Fig. 3.12. The positive lanthanum species were charged to the periphery of the graphite sheets by electrostatic interactions with oxygenated groups to
form O–La bonds. The oxygens of the oxygenated groups become nucleation centers for the growth of the crystal of La(OH) 3 by H
+
ions displacing to form a tetrahedral structure (Vences-Alvarez et al. 2015).
E. Vences-Alvarez et al.