5.9 Desorption and Recovery
111
mass loss (following the original membrane mass). At best, it was found that the
membrane can be recovered twice, before the membrane loses its mechanical strength
to a considerable extent.
5.10 Reaction Mechanism of Chitosan
Zinc adsorption on chitosan can arise from various effects including chelation, electrostatic, hydrophobic, donor electrons and polarity [36]. The existence of hydrophilic
groups including amine (–NH 2 ) and hydroxyl (–OH) on the chitosan backbone will
make chitosan and zinc polar, since these reactive groups interact with metal ions
based on various factors including metal type, pH, deacetylated unit fraction (free
amine groups), polymer chain length, crystallinity, molecular weight, polymer conditioning, chitosan physical structure, solution pH, acid type and concentration used for
solution, solution composition, metal ion selectivity and speciation [6]. The polarized structure of chitosan and zinc metal nevertheless causes them to be engulfed by
molecules of water. The water molecules adsorbed on the adsorbent and adsorbent
surfaces (via inter- or intramolecular attachment of the hydrogen) must be separated
and the adsorbent molecules substitute the water molecules on the adsorbent surface
[37]. This method is called replacement of solvents. The amine group establishes
a coordinate attachment with the metal ions, the connection is developed between
the nitrogen free electron pairs in the amine group and the metal’s void orbitals.
The free electron doublet of nitrogen in amine groups is indeed accountable for the
adsorption of metal cations at pH close to neutrality and at a decreased pH value,
in which amine group protonation occurs; the polymer reaches cationic groups that
can adsorb anions through electrostatic interactions [6].
5.11 Conclusions
Studies of equilibrium isotherm showed that the adsorption of Zn(II) by thick chitosan
membranes can be represented by a Langmuir equation with a maximum adsorption
capacity of 2.64 mmol g
−1 of chitosan at temperatures around 3.03–313 K. The
adsorption process was also reported to be endothermic with an adsorption enthalpy
of 20 kJ mol
−1 . The Zn(II) breakthrough was influenced by the initial concentration
of Zn(II) in the solution, but chitosan membranes were designed to work better
than some other chitosan types such as beads. This is mainly attributable to the
higher adsorption capacity of the thick chitosan membranes, especially in comparison
with beads, that is correlated to much more appropriate interaction between the
adsorbate and the chitosan adsorbent while selected as a thick adsorption layer,
i.e. membrane. While operating at low initial concentrations (<0.76 mmol L
−1 ),
the membranes adsorbed the Zn(II)-ions quite completely. Additional studies have
111
mass loss (following the original membrane mass). At best, it was found that the
membrane can be recovered twice, before the membrane loses its mechanical strength
to a considerable extent.
5.10 Reaction Mechanism of Chitosan
Zinc adsorption on chitosan can arise from various effects including chelation, electrostatic, hydrophobic, donor electrons and polarity [36]. The existence of hydrophilic
groups including amine (–NH 2 ) and hydroxyl (–OH) on the chitosan backbone will
make chitosan and zinc polar, since these reactive groups interact with metal ions
based on various factors including metal type, pH, deacetylated unit fraction (free
amine groups), polymer chain length, crystallinity, molecular weight, polymer conditioning, chitosan physical structure, solution pH, acid type and concentration used for
solution, solution composition, metal ion selectivity and speciation [6]. The polarized structure of chitosan and zinc metal nevertheless causes them to be engulfed by
molecules of water. The water molecules adsorbed on the adsorbent and adsorbent
surfaces (via inter- or intramolecular attachment of the hydrogen) must be separated
and the adsorbent molecules substitute the water molecules on the adsorbent surface
[37]. This method is called replacement of solvents. The amine group establishes
a coordinate attachment with the metal ions, the connection is developed between
the nitrogen free electron pairs in the amine group and the metal’s void orbitals.
The free electron doublet of nitrogen in amine groups is indeed accountable for the
adsorption of metal cations at pH close to neutrality and at a decreased pH value,
in which amine group protonation occurs; the polymer reaches cationic groups that
can adsorb anions through electrostatic interactions [6].
5.11 Conclusions
Studies of equilibrium isotherm showed that the adsorption of Zn(II) by thick chitosan
membranes can be represented by a Langmuir equation with a maximum adsorption
capacity of 2.64 mmol g
−1 of chitosan at temperatures around 3.03–313 K. The
adsorption process was also reported to be endothermic with an adsorption enthalpy
of 20 kJ mol
−1 . The Zn(II) breakthrough was influenced by the initial concentration
of Zn(II) in the solution, but chitosan membranes were designed to work better
than some other chitosan types such as beads. This is mainly attributable to the
higher adsorption capacity of the thick chitosan membranes, especially in comparison
with beads, that is correlated to much more appropriate interaction between the
adsorbate and the chitosan adsorbent while selected as a thick adsorption layer,
i.e. membrane. While operating at low initial concentrations (<0.76 mmol L
−1 ),
the membranes adsorbed the Zn(II)-ions quite completely. Additional studies have