97
composite occurred as a result of the interaction between Cu(II) ion and carboxyl
and phosphoryl groups of extracellular polymeric substance–montmorillonite composite (Fang et al. 2010). The adsorption of Th(IV) ions on polyacrylamide–montmorillonite and polyacrylamide–phytic acid-modified montmorillonite composites
was studied by Baybaş and Ulusoy. The results were compared with those of
obtained for unmodified montmorillonite. The increase in Th(IV) adsorption on
composites was explained by increase in available sites for adsorption due to fine
dispersion of the mineral particles beyond polyacrylamide chain (Baybaş and
Ulusoy 2011).
Zhu et al. studied Ni(II), Pb(II), and Cu(II) adsorption onto 2-acrylamido- 2methyl-1-propane sulfonic acid–montmorillonite intercalated composite for the
purpose of heavy metal removal from aqueous solution and exhibited that Pb(II)
ions showed high adsorption affinity onto intercalated composite, while Ni(II) and
Cu(II) adsorbed with lower affinity. When heavy metal-loaded composite was
eluted with strong acid, 96% of loaded Cu(II) was recovered (Zhu et al. 2012).
Afterward, Urbano and Rivas used same composite for the purpose of Cu(II), Cd(II),
Pb(II), and Al(III) adsorption at different pHs. It was determined that the composite
showed high affinity to adsorb all heavy metal ions at pHs 3 and 5. But the highest
adsorption capacity was obtained for Al(III) (Urbano and Rivas 2013).
As a natural polymer, chitosan, which is an excellent adsorbent for heavy metals,
is also intercalated into montmorillonite. Chitosan to montmorillonite ratio effects
on heavy metal adsorption due to forming different chemical environment (Ngah
et al. 2011). The chitosan intercalated montmorillonite has two active functional
groups: (i) amine groups which come from chitosan chain and (ii) permanent negatively charged surface and hydroxyl sides which come from montmorillonite. These
active sites allow electrostatic interaction and chemisorption (Ngah et al. 2011). At
low pH both amine groups and hydroxyl sites are in protonated form. In acidic
medium oxoanions of heavy metals can be adsorbed. Increase in pH causes withdrawing of H
+
ions from amine groups, while hydroxyl sites become deprotonated
form which allows electrostatic interaction and chemisorption of heavy metal
cations.
Epichlorohydrin cross-linked chitosan–clay composite beads were fabricated by
Tirtom et al. Ni(II) and Cd(II) removal was performed onto fabricated composite. It
was mentioned that the maximum adsorption for Ni(II) and Cd(II) occurred at pHs
6 and 4.5, respectively, and Ni(II) adsorption was higher than Cd(II) adsorption
(Tirtom et al. 2012). On the other hand, Cr(VI) chemisorption was performed onto
chitosan/montmorillonite–Fe 3 O 4 microsphere (Chen et al. 2013). The adsorption
capacity of this microsphere was higher than those of individual chitosan and montmorillonite. That the fabricated microspheres were efficient adsorbent for Cr(VI)
was declared by the authors (Chen et al. 2013).
Irani et al. used the waste linear low-density polyethylene-g-poly(acrylic acid)co-starch-organo–montmorillonite hydrogel composite, which was synthesized by
emulsion polymerization, for Pb(II) removal. It was determined that the prepared
composite had high adsorption capacity for Pb(II) ions. The adsorption showed
Langmuir character, and the kinetics of the adsorption fitted pseudo-second-order
4 Montmorillonite Clay Composite for Heavy Metal Removal from Water
composite occurred as a result of the interaction between Cu(II) ion and carboxyl
and phosphoryl groups of extracellular polymeric substance–montmorillonite composite (Fang et al. 2010). The adsorption of Th(IV) ions on polyacrylamide–montmorillonite and polyacrylamide–phytic acid-modified montmorillonite composites
was studied by Baybaş and Ulusoy. The results were compared with those of
obtained for unmodified montmorillonite. The increase in Th(IV) adsorption on
composites was explained by increase in available sites for adsorption due to fine
dispersion of the mineral particles beyond polyacrylamide chain (Baybaş and
Ulusoy 2011).
Zhu et al. studied Ni(II), Pb(II), and Cu(II) adsorption onto 2-acrylamido- 2methyl-1-propane sulfonic acid–montmorillonite intercalated composite for the
purpose of heavy metal removal from aqueous solution and exhibited that Pb(II)
ions showed high adsorption affinity onto intercalated composite, while Ni(II) and
Cu(II) adsorbed with lower affinity. When heavy metal-loaded composite was
eluted with strong acid, 96% of loaded Cu(II) was recovered (Zhu et al. 2012).
Afterward, Urbano and Rivas used same composite for the purpose of Cu(II), Cd(II),
Pb(II), and Al(III) adsorption at different pHs. It was determined that the composite
showed high affinity to adsorb all heavy metal ions at pHs 3 and 5. But the highest
adsorption capacity was obtained for Al(III) (Urbano and Rivas 2013).
As a natural polymer, chitosan, which is an excellent adsorbent for heavy metals,
is also intercalated into montmorillonite. Chitosan to montmorillonite ratio effects
on heavy metal adsorption due to forming different chemical environment (Ngah
et al. 2011). The chitosan intercalated montmorillonite has two active functional
groups: (i) amine groups which come from chitosan chain and (ii) permanent negatively charged surface and hydroxyl sides which come from montmorillonite. These
active sites allow electrostatic interaction and chemisorption (Ngah et al. 2011). At
low pH both amine groups and hydroxyl sites are in protonated form. In acidic
medium oxoanions of heavy metals can be adsorbed. Increase in pH causes withdrawing of H
+
ions from amine groups, while hydroxyl sites become deprotonated
form which allows electrostatic interaction and chemisorption of heavy metal
cations.
Epichlorohydrin cross-linked chitosan–clay composite beads were fabricated by
Tirtom et al. Ni(II) and Cd(II) removal was performed onto fabricated composite. It
was mentioned that the maximum adsorption for Ni(II) and Cd(II) occurred at pHs
6 and 4.5, respectively, and Ni(II) adsorption was higher than Cd(II) adsorption
(Tirtom et al. 2012). On the other hand, Cr(VI) chemisorption was performed onto
chitosan/montmorillonite–Fe 3 O 4 microsphere (Chen et al. 2013). The adsorption
capacity of this microsphere was higher than those of individual chitosan and montmorillonite. That the fabricated microspheres were efficient adsorbent for Cr(VI)
was declared by the authors (Chen et al. 2013).
Irani et al. used the waste linear low-density polyethylene-g-poly(acrylic acid)co-starch-organo–montmorillonite hydrogel composite, which was synthesized by
emulsion polymerization, for Pb(II) removal. It was determined that the prepared
composite had high adsorption capacity for Pb(II) ions. The adsorption showed
Langmuir character, and the kinetics of the adsorption fitted pseudo-second-order
4 Montmorillonite Clay Composite for Heavy Metal Removal from Water