Environmental Engineering Reference
In-Depth Information
activated carbon derived from various sources has been investigated by many research-
ers. It has been reported that activated carbon derived from various low-cost materials
exhibits good luoride removal capacity and the optimum luoride adsorption occurs at
pH <3, suggesting that the luoride adsorption is pH speciic. Sivasamy et al. (2001) inves-
tigated luoride removal from drinking water using different coal-based adsorbents such
as lignite, ine coke, and bituminous coal as a low-cost source. They reported signiicantly
high luoride adsorption capacities for these coal-based adsorbents, which are 7.09, 6.90,
and 7.44 mg/g for lignite, ine coke, and bituminous coal, respectively, as compared with
activated carbon derived from wet coconut shell carbon (3.03 mg/g), dry coconut shell car-
bon (1.08 mg/g), and dry commercial activated carbon (0.19 mg/g). In the case of lignite,
the higher deluoridation occurs at a pH range of 5.0-10.0. On the other hand, the higher
deluoridation for ine coke and bituminous coal occurs at acidic pH <4.0. Li et al. (2001)
have reported nanotubes as a support material for incorporating alumina and investi-
gated it for luoride removal from drinking water. Amorphous alumina supported on car-
bon nanotubes (CNTs) have shown the highest luoride adsorption capacity of 28.7 mg/g,
and the optimum luoride removal occurred at pH of 5.0-9.0. Kuo et al. (2004) reported
various carbonaceous materials, including six kinds of activated carbon, carbon black,
four kinds of charcoals, and bone char for luoride removal from water, and they found
that the luoride adsorption on these adsorbents depends on their speciic surface area.
The amount of luoride adsorbed on the carbonaceous materials depends on the pore size
distribution because the adsorption occurs in the pores, suggesting physical adsorption.
Among all the reported carbonaceous materials, bituminous coal exhibits higher luo-
ride adsorption capacity at pH of 4.6. Parmar et al. (2006) investigated the adsorption of
luoride on corncob powder. Powdered corncob did not show remarkable adsorption but
aluminum-treated corncobs exhibited good adsorption capacity of 18.9 mg/g at pH 5.0-
6.5. Karthikeyan and Ilango (2007) have also prepared activated carbon from the burn-
ing and carbonization of
Morringa indica
bark for luoride removal from drinking water.
This material showed luoride removal capacity of 0.17 mg/g at acidic pH. Daifullah et
al. (2007) synthesized KMnO
4
-modiied activated carbon from the steam pyrolysis of rice
husk, which is the agricultural waste, and investigated extensively for luoride removal
from water. The maximum luoride adsorption for synthesized activated carbon occurred
at a pH of 2.0, and the luoride adsorption capacity obtained was 15.5 mg/g. Sivasankar
et al. (2010) have reported luoride removal capacities of activated tamarind fruit shell
(ATFS) and ATFS modiied with MnO
2
, and found that ATFS and MTFS were effective
at pH of 6. Alagumuthu and Rajan (2010) have reported zirconium impregnated cashew
nut shell carbon for the removal of luoride from aqueous solutions at neutral pH and low
adsorbent dose. Tchomgui-Kamga et al. (2010) have synthesized charcoal adsorbents that
contain dispersed aluminum and iron oxides by impregnating wood with salt solutions
followed by carbonization at 500°C, 650°C, and 900°C. Substrates prepared at 650°C with
aluminum and iron oxides exhibited the best eficiency with a luoride sorption capac-
ity of 2.31 mg/g. More than 92% removal of luoride was achieved within 24 h from a
10 mg/L solution at neutral pH.
17.7.6 Industrial and Agricultural Waste Materials as Adsorbents
The utilization of the waste materials generated from the various industries and agricul-
tural ield as a low-cost resource is a viable option for water treatment processing. Sujana
et al. (1998) have reported the use of alum sludge, which is a waste product, generated
during the manufacture of alum from bauxite by the sulfuric acid process, as an adsorbent
