Environmental Engineering Reference
In-Depth Information
and endothermic. In a regeneration study, 89% of luoride could be desorbed from loaded
sample using 1 M NaOH.
Sivasankar et al. (2012) used
Tamarindus indica
fruit shells (TIFSs), a natural compound
rich in calcium, to develop a new adsorbent. The material was impregnated with ammo-
nium carbonate followed by carbonization, leading to ammonium carbonate activated
ACA-TIFS carbon. The resulting materials and carbon arising from virgin fruit shells
V-TIFS were characterized and examined as adsorbents for the removal of luoride anions
from groundwater samples. The luoride-scavenging ability of TIFS carbons was attrib-
uted to naturally dispersed calcium compounds. X-ray diffraction showed that TIFS car-
bon contained a mixture of calcium oxalate and calcium carbonate. The luoride removal
of TIFS carbons was found to be 91% and 83% at a pH 7.05 for V-TIFS and ACA-TIFS car-
bons, respectively. The practical applicability of TIFS carbons using groundwater samples
was also examined and found satisfactory. The luoride removal was better in groundwa-
ter without hydrogen carbonate ions than those containing the ions.
Pumice stone that is functionalized by the cationic surfactant hexadecyltrimethyl ammo-
nium (HDTMA) is used as an adsorbent for the removal of luoride from drinking water
by Asgari et al. (2012). The effects of HDTMA loading, pH (3-10), reaction time (5-60 min),
and the adsorbent dosage (0.15-2.5 g/L) were investigated as a function of luoride removal
from water through different designed experiments. The results revealed that surfactant-
modiied pumice exhibited the optimal performance at dose 0.5 g/L, pH 6, and it was
reported to remove >96% of luoride from a solution containing 10 mg/L luoride after
30 min of equilibration time.
17.7.8.1 Nanomaterials for Fluoride Removal
Nanoscience and nanotechnology have arisen as a promising approach in the past decade
for various environmental applications. Use of nanomaterials as adsorbents for water
treatment is gaining wide attention recently owing to their higher surface area. CNTs as
well as other nanoforms of carbons also have appeal in water treatment. Their interesting
properties owing to small size, large surface area, high mechanical strength, and remark-
able electrical conductivities make them potential materials for a wide range of promising
applications. Li et al. (2001) used CNTs as support for depositing Al
2
O
3
and discovered the
possibility of Al
2
O
3
/CNTs for removing luoride from water. The adsorption isotherms
inferred that the best luoride adsorption on Al
2
O
3
/CNTs was observed in the pH range
5.0-9.0. The adsorption capacity for Al
2
O
3
/CNTs was reported to be about 13.5× higher than
that of AC-300 carbon, about four times higher than that of Al
2
O
3
at an equilibrium luoride
concentration of 12 mg/L. The luoride adsorption for Al
2
O
3
/CNTs at pH 6.0 was reported
to reach 28.7 mg/g at an equilibrium concentration of 50 mg/L. Aligned CNTs (ACNTs)
were prepared by catalytic decomposition of xylene using ferrocene as a catalyst, and their
performance was tested for luoride removal from water (Li et al., 2003a). Both the surface
and inner cavities of ACNTs were found to be easily available for luoride sorption. A wide
pH range of 3-9 was found optimal for luoride removal. A high surface area of the adsor-
bent was reported to favor the sorption rate and adsorption capacity, while microporous
diffusion in larger adsorbent particles was observed to take place slowly. Application of
nanoparticles has potential for adsorption-based water treatment technologies. The maxi-
mum adsorption capacity of ACNTs was observed at pH 7.0 with 4.5 mg/g luoride uptake
at an equilibrium luoride concentration of 15 mg/L. CNTs were modiied with alumina,
and the synthesized adsorbent was studied for deluoridation from water and the effects
of calcination temperature, alumina loading, and pH on luoride removal capacity were
