100
4.5 Biosorbent Composites of Montmorillonite
Biosourced sorbents such as algae, bacteria, cellulose, or residue of cereals are
focused in recent studies. Lignocellulose, which includes lignin, hemicellulose, and
cellulose, is low cost and an efficient adsorbent for heavy metals (Ngah and Hanafiah
2008; Zhong et al. 2012; Mahmood-ul-Hassan et al. 2018). Bunhu and Tichagwa
fabricated lignocellulose–montmorillonite composite by in situ intercalative polymerization using methacryloxypropyltrimethoxysilane and investigated competitive
adsorption of methyl orange from aqueous solution in the presence of Cd(II) and
Pb(II) ions. It was observed that methyl orange adsorption onto composite increased
in the presence of those heavy metal ions. This situation was attributed to existence
of new active sites sourced from heavy metals (Bunhu and Tichagwa 2012). In fact,
the enhancement of methyl orange adsorption can be better explained by the possible formation of ternary surface–metal–methyl orange complexation via metal
bridge on the composite sorbent.
Cr(VI) uptake using cellulose–montmorillonite composite as an adsorbent was
studied by Kumar et al. High adsorption capacity of adsorbent was explained considering the pH dependency of Cr(VI) species and surface of adsorbent. Because the
formation of Cr(VI) species depends on the pH of solution, in this study the favorable pH for the Cr(VI) adsorption was determined to be the pHs between 3.8 and
5.5. In this pH range, HCrO 4
−
species is dominant, and the author suggested that the
ion pair formed between negatively charged Cr(VI) and the positively charged cellulose–montmorillonite composite. High determination coefficients were yielded
for both linearized Langmuir and Freundlich models. The kinetics of Cr(VI) adsorption fitted second-order model, and the adsorbent were reused for tenfold cycles
(Kumar et al. 2012).
Bacteria are considered as efficient biosorbents for heavy metals. Thus, bacteria
can affect mobility and speciation of heavy metals in environmental systems. The
characteristics and mechanisms of competitive adsorption of Pb(II) and Cd(II) on
Pseudomonas putida–montmorillonite composite were inspected by Du et al. Du
et al. observed that when the adsorption of Cd(II) and Pb(II) mixture was performed,
the maximum adsorption capacity of composite for both ions decreased. This situation was explained by the authors by the fact that Cd and Pb were bound to same
types of adsorption sites on the sorbent. Du et al. also declared that bacteria–clay
composites showed different behavior in competitive adsorption with respect to
competitive adsorption on individual clay and bacteria (Du et al. 2016a).
As known clays, bacteria and humic substances are soil components. In a continuing work, Du et al. tried Cd(II) adsorption on montmorillonite–humic acid–
Pseudomonas putida composite in order to provide better understanding of the
biogeochemical cycling and fate of heavy metals in natural soils and sediments. As
a result, Du et al. observed that the Cd(II) adsorption on ternary composite decreased
with respect to the adsorption on individual and/or binary components, and the
J. Hızal and M. Yılmazoğlu
4.5 Biosorbent Composites of Montmorillonite
Biosourced sorbents such as algae, bacteria, cellulose, or residue of cereals are
focused in recent studies. Lignocellulose, which includes lignin, hemicellulose, and
cellulose, is low cost and an efficient adsorbent for heavy metals (Ngah and Hanafiah
2008; Zhong et al. 2012; Mahmood-ul-Hassan et al. 2018). Bunhu and Tichagwa
fabricated lignocellulose–montmorillonite composite by in situ intercalative polymerization using methacryloxypropyltrimethoxysilane and investigated competitive
adsorption of methyl orange from aqueous solution in the presence of Cd(II) and
Pb(II) ions. It was observed that methyl orange adsorption onto composite increased
in the presence of those heavy metal ions. This situation was attributed to existence
of new active sites sourced from heavy metals (Bunhu and Tichagwa 2012). In fact,
the enhancement of methyl orange adsorption can be better explained by the possible formation of ternary surface–metal–methyl orange complexation via metal
bridge on the composite sorbent.
Cr(VI) uptake using cellulose–montmorillonite composite as an adsorbent was
studied by Kumar et al. High adsorption capacity of adsorbent was explained considering the pH dependency of Cr(VI) species and surface of adsorbent. Because the
formation of Cr(VI) species depends on the pH of solution, in this study the favorable pH for the Cr(VI) adsorption was determined to be the pHs between 3.8 and
5.5. In this pH range, HCrO 4
−
species is dominant, and the author suggested that the
ion pair formed between negatively charged Cr(VI) and the positively charged cellulose–montmorillonite composite. High determination coefficients were yielded
for both linearized Langmuir and Freundlich models. The kinetics of Cr(VI) adsorption fitted second-order model, and the adsorbent were reused for tenfold cycles
(Kumar et al. 2012).
Bacteria are considered as efficient biosorbents for heavy metals. Thus, bacteria
can affect mobility and speciation of heavy metals in environmental systems. The
characteristics and mechanisms of competitive adsorption of Pb(II) and Cd(II) on
Pseudomonas putida–montmorillonite composite were inspected by Du et al. Du
et al. observed that when the adsorption of Cd(II) and Pb(II) mixture was performed,
the maximum adsorption capacity of composite for both ions decreased. This situation was explained by the authors by the fact that Cd and Pb were bound to same
types of adsorption sites on the sorbent. Du et al. also declared that bacteria–clay
composites showed different behavior in competitive adsorption with respect to
competitive adsorption on individual clay and bacteria (Du et al. 2016a).
As known clays, bacteria and humic substances are soil components. In a continuing work, Du et al. tried Cd(II) adsorption on montmorillonite–humic acid–
Pseudomonas putida composite in order to provide better understanding of the
biogeochemical cycling and fate of heavy metals in natural soils and sediments. As
a result, Du et al. observed that the Cd(II) adsorption on ternary composite decreased
with respect to the adsorption on individual and/or binary components, and the
J. Hızal and M. Yılmazoğlu