Environmental Engineering Reference
In-Depth Information
The organo-modified clay minerals were also used as soil-flushing agents for heavy metal-contaminated soil. natural
beidellite, Hect., and vermiculite were transformed into sH-grafted pillared clays, but difficulties were encountered to keep a
regular and significant interlayer distance until the last step [82]. The well-crystalline high-charged vermiculite of santa Olalla
(spain), after exchanging with alkyl ammonium cations and grafting of interlayer si pillars, showed the highest capacity of Cd 2+
and Pb 2+ among the three functionalized tested clay minerals. The cadmium uptake by ray-grass grown on polluted soil was
quite depressed by amendments with 0.17% or 0.5% of functionalized synthetic beidellite, but these amendments were ineffi-
cient for lead.
16.3
POlymer mOdifiCatiOn
The water-soluble polymers exhibit several advantages, such as high solubility in water, easy and cheap route of synthesis, an
adequate molecular weight and molecular weight distribution, chemical stability, high affinity for one or more metal ions, and
selectivity for the metal ion of interest [83]. However, they are difficult to be reused after the adsorption of HmI. To overcome
some of the problems associated with the reusability of water-soluble polymers as adsorbents for HmI, they have been grafted
onto water-insoluble materials such as clay minerals as supports or used in the form of hydrogels or hybrid hydrogels [84]. In
this chapter, the preparation and application of adsorbents for the removal of HmI are covered only with the functional water
soluble polymers-grafted nano-clay minerals.
16.3.1
ionic interactions
Huang et al. synthesized a novel adsorbent of BnT modified with n-2-hydroxypropyl trimethyl ammonium chloride chitosan
(HACC) [85]. The adsorption of Cd(II) onto the HACC-BnT was examined in aqueous solution with respect to the pH,
adsorbent dosage, contact time, temperature, and initial concentration. The maximum amount of Cd(II) adsorbed (q m ), as eval-
uated by the Langmuir isotherm, was 22.23 mg/g of HACC-BnT at pH 7.0 or so and 20°C, and the best desorption performance
was obtained with HnO 3 , HCl, and edTA as eluents. The change of adsorption enthalpy indicated that the adsorption of Cd(II)
onto the HACC-BnT may be carried out via cation exchange.
Humic acid (HA) was immobilized onto the amine-modified polyacrylamide/BnT composite (Am-PAA-B), which was
prepared by direct intercalation polymerization technique, and the product (HA-Am-PAA-B) was used as an adsorbent in
the removal of copper(II) ions from aqueous solutions (fig. 16.11) [86]. The adsorbent behaved like a cation exchanger, and
more than 99.0% Cu(II) ion removal was observed in the pH range 5.0-6.0. The desorption of adsorbed Cu(II) ions was
achieved by 0.1 m HCl, and four adsorption/desorption cycles were performed without a significant decrease in the adsorp-
tion capacity.
Kumar et al. reported an effective methodology for the detoxification of chromium using cellulose-mmT composite material
as the adsorbent (fig. 16.12) [87]. The interaction of surfactant-modified na-mmT with cellulose biopolymer was followed by
the subsequent adsorption of Cr(VI) from aqueous solution as bichromate anion onto the surface of the biocomposite material.
The material exhibited a maximum adsorption capacity of 22.2 mg/g in accordance with the Langmuir isotherm model. The
composite material could be regenerated using sodium hydroxide as the eluent. The adsorbent could be reused with quantitative
recovery for 10 adsorption-desorption cycles. The applicability of the method was demonstrated in the quantitative removal of
total chromium from a chrome tannery effluent sample.
16.3.2
Covalent grafting
Polyacrylamide was successfully grafted from the surfaces of the organo-modified fibrillar clay ATP via the copper-mediated
surface-initiated atom transfer radical polymerization (sI-ATRP) technique in water (fig. 16.13a) [88]. The product, polyacryl-
amide-grafted ATP (PAm--ATP), was applied preliminarily as an adsorbent in the removal of heavy metal ion (Hg(II)) and two
dyes (cationic dye: mB and anionic dye: methyl orange (mO)) from aqueous solutions. Compared with bare ATP, PAm-ATP
had much higher adsorption capacities toward Hg(II) ion because of the chelation with Hg(II) ion by formation of either mono-
amido- or diamido-Hg structures (fig. 16.13b), which provides a means of capturing Hg(II) from aqueous solution. They also
had much higher adsorption capacities toward the cationic dye mB likely due to the flotation with cationic dye of the grafted
polyacrylamide chains. However, the adsorption capacities toward the anionic dye mO did not improve from the surface graft
polymerization of acrylamide (Table 16.1).
Zhao and Chen et al. synthesized the polyacrylamide/ATP (PAm/ATP) adsorbent by grafting acrylamide (Am) onto the
silane coupling reagent-modified ATP (OATP) using solution polymerization (fig. 16.14) [89-91]. equilibrium and kinetic
adsorption data showed that PAm/ATP displays a high selectivity toward one metal in a two-component or a three-component
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