Environmental Engineering Reference
In-Depth Information
standard (initial luoride concentration = 10 mg/L; adsorbent dose = 3 g/L). Interestingly,
the coexisting anions had no signiicant effect on luoride adsorption and thus suitable
for practical application. A novel Fe(III)-loaded ligand-exchange cotton cellulose (Fe(III)
LECCA) was synthesized and used for luoride removal from drinking water [105]. The
luoride uptake capacity of the material was tested as a function of pH, reaction time, tem-
perature, co-ions, and flow rate, in batch and continuous mode. The studies indicated that
the adsorbent is good in removing luoride from water and showed a maximum equilib-
rium adsorption capacity of 18.55 mg/g at a temperature of 25°C. The regeneration poten-
tial of the adsorbent bed packed in column was tested in continuous mode using 1 M
NaOH solution as an eluent at room temperature. The results revealed that >98% adsorbed
luoride was eluted. Interestingly, there was a slight increase in the adsorption capacity
of Fe(III)LECCA with each regeneration cycle. This has been attributed to the formation
of colloidal ferric hydroxide due to the reaction between loaded iron and NaOH. The
adsorption mechanism was studied using FT-IR spectroscopy and by chemical analysis. A
ligand-exchange mechanism (X ≡ Fe(III)-L + F
−
→ X ≡ Fe(III)-F + L
−
; X: cellulose, L: anion
ligands) was proposed for the removal of luoride in water.
Chitosan is another interesting biopolymer extensively used in water and wastewater
puriication. Chitosan can be shaped to several forms, including membranes, gel beads,
microspheres, films, etc. [106-108]. It is able to provide a ratio of surface area to mass that
enhances the adsorption capacity and reduces the hydrodynamic limitation effects, such
as column clogging and friction loss [109]. Owing to these attractive properties, many
investigations have been performed using chitosan as supporting material. A detailed
review on the use of chitosan and its composites as luoride-removing media is available
elsewhere [110].
19.4.2.2 Synthetic Polymers as Support Matrix
Swain et al. [111] have synthesized a novel composite (FZCA) by impregnating micro-
particles/NPs of a binary metal oxide (Fe(III)-Zr(IV)) in an alginate matrix, a polysac-
charide composed of different proportions of β-d-mannuronic acid and α-l-guluronic
acid units, linked by β-1-4 and α-1-4 bonds. The synthesized material was tested for
luoride uptake as a function of the initial concentration of luoride, contact time, pH,
and temperature. The maximum luoride uptake was reported to be 0.981 mg/g and it
was observed at pH 6. The average diameter of the composite beads was 3 mm, and
the average particle size of the impregnated Fe-Zr particles varied between 70.89 and
477.7 nm. The material was regenerated using NaOH as the eluent (pH 12) and found
to be effective for several cycles of adsorption. Wu et al. [112] prepared a new granu-
lar adsorbent by immobilizing a nanoscale trimetal hydroxide of Fe-Al-Ce (FAC) in
porous polyvinyl alcohol (PVA) via cross-linking with boric acid. Various optimization
studies were conducted to check the feasibility of using PVA as a support matrix for
FAC. The effects of the concentration of PVA and FAC on the mechanical stability and
luoride adsorption capacity were also investigated. The luoride adsorption capacity
of the composite was increased with FAC concentration and decreased with PVA con-
centration. An FAC concentration of 12% and a PVA concentration of 7.5% were found
to be the optimum values. The granules showed a luoride adsorption capacity of 4.46
mg/g at a pH of 6.5 and an initial luoride concentration of 19 mg/L. In another attempt,
Zhao et al. [113] have used the extrusion method to granulize FAC using cross-linked
PVA as the binder. The schematic diagram of the steps employed during extrusion is
depicted in Figure 19.6. The stability and luoride uptake capacity of the granules were
