Environmental Engineering Reference
In-Depth Information
for luoride removal from drinking water. The luoride adsorption capacity of alum sludge
was 5.35 mg/g and the maximum luoride adsorption occurs at pH of 5.5-6.5. Cengeloglu
et al. (2002) have extensively studied the potential of red mud as such and activated with
acid for luoride removal from drinking water. Red mud is a strongly alkaline waste pro-
duced during the aluminum ore processing. It was observed that red mud has an appre-
ciable luoride adsorption capacity, which can be further improved by treatment with acid.
However, the maximum luoride adsorption occurs at pH 5.5, and the maximum luoride
adsorption capacities were found to be 3.12 and 6.29 mg/g for as is and acid-activated
mud, respectively. Mahramanlioglu et al. (2002) have reported on acid-treated spent bleach
earth, a solid waste generated from the edible oil processing industry for luoride removal
from drinking water. The maximum luoride adsorption was observed at pH 3.5, and its
luoride adsorption capacity was 7.75 mg/g.
Nigussie et al. (2007) have reported an aluminum sulfate manufacturing process waste
as low-cost material generated for removal of excess luoride from water. The material
exhibits fast kinetics with adsorption capacity of 332.5 mg/g at an initial luoride concen-
tration of 100-550 mg/L. Tor et al. (2009) have also studied granular red mud for luoride
sorption capacity in batch and column adsorption experiments with maximum adsorp-
tion occurs at pH of 4.7 and the adsorption capacity was 0.851 mg/g. The exhausted
ixed-bed column was regenerated by treating with mild alkali to desorb the luoride
and desorption eficiency of 87%-46% was achieved from the irst to fourth cycle. Kemer
et al. (2009) reported that precipitated waste mud (p-WM), which was obtained as a by-
product from a Cu-Zn mine (Çayeli, Rize, Turkey), is a promising material to remove
excess luoride from water and wastewater. Maximum luoride uptake was obtained at
27.2 mg/g with p-WM. The results have demonstrated that the p-WM can be used as a
low-cost, highly effective, and readily available adsorbent for removal of luoride from
aqueous solutions.
17.7.7 Biopolymer-Based Adsorbents
Extensive efforts have also been made to develop deluoridation media based on bio-
polymers, viz. chitin and chitosan. Ma et al. (2007) have reported magnetic chitosan
particles prepared by a coprecipitation method. The authors claimed excellent luoride
removal capacity of 22.49 mg/g for magnetic chitosan particles at neutral pH, and there-
fore, can be used as a potential adsorbent for deluoridation of water and wastewater.
Regeneration studies show that loaded luoride magnetic particles were recovered by
0.8-1.0 M NaOH solution, and the regenerated adsorbent retained the adsorption capac-
ity up to 98%-99% of the fresh adsorbent. Kamble et al. (2007) have studied the poten-
tial of chitin, chitosan, and lanthanum (La)-incorporated chitosan as adsorbents for the
removal of excess luoride from drinking water. Lanthanum chitosan adsorbents show
excellent removal of luoride from water, which is signiicantly higher than unmodi-
ied biopolymers. However, it was observed that the presence of anions, viz. carbonate
and bicarbonate, has a deleterious effect on the adsorption of luoride. The adsorption
capacity of 20% La-chitosan was 3.1 mg/g at pH 5 and the material can be regenerated
e a s i ly.
Sahlia et al. (2007) reported removal of luoride from water by adsorption on chitosan.
Sundaram et al. (2008) synthesized a bioinorganic composite namely nano-HAp/chitosan
(n-HApC) and evaluated its performance for removal of luoride. Deluoridation capacity
of the n-HApC composite was observed to be 1.560 mg/g, which is slightly higher than
nano-HAp (n-HAp) having a deluoridation capacity of 1.296 mg/g. Field trials were also
