Environmental Engineering Reference
In-Depth Information
improved performance of Magnesia-amended AA (MAAA) for luoride removal. MAAA
also exhibits high removal eficiency (>95%) at neutral pH. The maximum sorption capac-
ity of luoride deduced from the Sips equation was 10.12 mg/g. Lee et al. (2010) prepared
samples of two different kinds of mesoporous alumina using aluminum tri-sec-butoxide
in the presence of either cetyl-trimethyl ammonium bromide (MA-1) or stearic acid (MA-2)
as a structure-directing agent, and tested for adsorptive removal of luoride in water.
MA-2 prepared using stearic acid exhibited a high adsorption capacity of 14.26 mg/g for
luoride, which is signiicantly higher than those of a commercial gamma alumina. More
recently, Bansiwal et al. (2010) reported the luoride removal performance of AA modiied
by incorporating copper oxide. They reported an interesting result that the optimal luo-
ride adsorption occurs at all pH ranging from 4.0 to 9.0 with 7.22 mg/g luoride adsorption
capacity. This material overcomes the drawback associated with AA showing optimal lu-
oride adsorption below pH 6.0 and low adsorption capacity. A high desorption eficiency
of 97% was also achieved by treating a luoride-loaded adsorbent with 4 M NaOH solution.
17.7.2 Bone Charcoal
Bone charcoal (bone char) has also been reported for the removal of luoride from drinking
water by adsorption. Bone char is obtained by heating bones to temperatures that remove
organics, leaving behind hydroxyapatite (HAp), Ca
10
(PO
4
)
6
(OH)
2
(Kaseva, 2006). Regeneration
of luoride-saturated bone char is also possible by reheating or by leaching with sodium
hydroxide and, ultimately, the inal product can be applied as fertilizer to household gardens.
17. 7. 3 C l a y
A wide variety of clays have been used for removal of luoride through adsorption or loc-
culation. Several clays being used for luoride removal include ground and ired clay pot,
brick chips, calcined clay, palygorskite clay, calcite, kaolin, etc. (Hamdi et al., 2009; Bårdsen
et al., 1995), and removal is highly dependent on the type of clay used and its modiica-
tions. However, since clays have low luoride removal capacity and poor hydraulic conduc-
tivity, their practical applicability for ield applications is limited.
17.7.4 Ion-Exchange Resins
Ion-exchange resins, particularly strong-base-exchange resins, have also been evaluated
for luoride removal from water (Haron et al., 1995; Castel et al., 2000); however, the pres-
ence of other anions severely interferes, which results in low effective luoride removal
capacity of such resins. Several inorganic ion exchangers, e.g., metal chloride silicates,
formed from barium or ferric chloride with silicic acid, also exchanged luoride for chlo-
ride. Cation-exchange resins impregnated with alum solution have also been reported as
effective deluoridation media. Polystyrene anion-exchange resins, in general, and strongly
basic quaternary ammonium-type resins, in particular, are known to remove luorides
from water along with other anions.
17. 7. 5 C a r b o n
Activated carbon from coal, agricultural waste, etc., is one of the most commonly used
adsorbent materials for water treatment that can effectively remove the organic as well
as inorganic pollutants. In the past few decades, the luoride removal performance of
