Environmental Engineering Reference
In-Depth Information
adsorbents, Fe-ACF and ACF. The loading of arsenic on Fe-CNF is approximately 10× and
8× larger than ACF and Fe-ACF, respectively.
Generally, carbon-iron-based adsorbents have exhibited large arsenic loading capacities
compared with other adsorbents. From the equilibrium isotherms presented in Figure 36.11,
one may note that the loading of arsenic ions on Fe-CNF is 0.6-14 mg/g, corresponding to
aqueous-phase arsenic concentrations between 0.2 and 40 ppm at pH 6.5. These values are
comparable to 10 mg/g on FePO
4
(amorphous and crystalline) corresponding to 0.5-100 mg/l
of arsenic at pH 6.0-6.7, 4.5 mg/g on the GAC-based iron containing adsorbent at pH 5.0,
6.5 mg/g obtained for the cationic surfactant-modiied PAC corresponding to 10 ppm of arse-
nic in water, and 1-4 mg/g on laterite and iron-modiied AC corresponding to 0-4 ppm of arse-
nic in water at pH 8.18. In most of the other studies reported in the literature, arsenic loading is
lower than that reported here. Some examples include arsenic loading of 2.4 mg/g obtained for
coconut shell carbon, corresponding to 0-200 mg/l As concentration at pH 5; 0.02 mg/g loading
obtained on Fe
3+
-impregnated carbon at 3.2 ppm arsenic concentration and pH 7.0;
1.9 2 m g /g
loading for GAC-Fe-H
2
O
2
at 0-30 mg/l and pH 4.2;
and 0.036 mg/g loading for AC impreg-
nated with Fe
2+
and Fe
3+
at 0.3 ppm and pH 6.5-8.5.
There are very few studies with higher
arsenic loading, such as 51.3 mg/g at
pH 6.0 and 43.6 mg/g at pH 8.0 for iron-modiied AC, cor-
responding to 20 mg/l of aqueous-phase concentration; 37.46 mg/g at pH 5.0 for FeO/AC, cor-
responding to 37.46 mg/l of arsenic in water;
and 26 mg/g at pH 7.6-8.0 for hydrous FeO-GAC,
corresponding to 0.3 ppm of arsenic in water [41]. In general, variation in the arsenic loading
on the adsorbents is because of different types of carbon, surface functional groups, textural
properties, the amount of iron loaded, and operating conditions, including pH.
Similar to the case of the adsorbents developed for luorides, Fe-CNF was also tested
under low conditions to ascertain its arsenic uptake (mg/g) compared with the equilib-
rium loadings under batch conditions, and determine its potential applications as a mate-
rial for water puriiers. Figure 36.12 describes the breakthrough data for different inlet
1.0
0.8
0.6
0.4
As(V) concentration (mg/l)
40
15
5
0.2
0.0
0
100
200
300
Time (min)
FIGURE 36.12
Breakthrough data for varying inlet As(V) concentration (
W
Fe-CNF
= 3 g,
Q
= 0.01 l/min, pH 6.5,
T
= 303 K). (From
A. Gupta et al.,
I&EC Res.
, 49, 7074, 2010.)
