Marine Algae Biomass for Removal of Heavy Metal Ions 25.5 Modeling of Biosorption in Batch Conditions 633
Part D | 25.5
In addition, the variation of the Langmuir constant
(K L / with temperature indicates whether the biosorption process is exothermic or endothermic. Thus, the
decrease of K L value with temperature rise signifies
the exothermicity of the biosorption process (physical
biosorption), while the decrease of K L with temperature
indicates that the biosorption process need supplementary (thermal) energy (is endothermic), leading to
chemosorption. These observations are very useful in
the optimum design of biosorption systems. Thus, in the
case of physical biosorption, the bonds between heavy
metals and active sites of biosorbent are weak, and desorption occurs simply, by treating the loaded biosorbent
with water. In the case of chemosorption, the bonds between heavy metals and active sites of biosorbent are
stronger, and for desorption are needed more aggressive
chemical reagents (mineral acids, complexing agents,
etc.).
In order to appreciate the nature – physical or
chemical – of the biosorption process, the Dubinin–
Raduskevich model (Table 25.7) is more adequate for
the analysis of equilibrium biosorption data. This model
takes into account the energetically nonuniform surface
of biosorbent, and the model parameters (q
DR
max and ˇ)
are obtained from the graphical representation of ln q e
versus "
2 . Using the value of ˇ, the mean biosorption
energy (E, kJ=mol) can be calculated using the following equation,
E D
1
p
2ˇ
:
(25.4)
The mean energy of biosorption (E, kJ=mol) gives information about the biosorption mechanism. Therefore,
if the biosorption process has a mean energy of biosorption in the range of 116 kJ=mol, then it indicates that
the physical electrostatic interactions are potentially
involved in the biosorption mechanism [25.32, 143].
Some values of the Dubinin–Raduskevich model parameters obtained for biosorption of heavy metal ions
onto marine algae biomass are given in Table 25.9.
One of the main advantages of the Dubinin–
Raduskevich model is that it is temperature dependent.
If the biosorption data at different temperatures are
graphical represented, all the suitable data shall in general lay on the same characteristic curve. This curve can
be used to measure the applicability of the Dubinin–
Raduskevich model in analysis of the biosorption equilibrium data, together with the value of correlation
coefficient. When the fitting procedure gives high correlation coefficient, but the analyzed data does not lie in
the same characteristic curve, the validity of calculated
parameters is questionable. Anyway, the characteristic
curve for a given biosorption systems cannot be examined if the experiments were performed for a single
value of temperature [25.18].
The other isotherm models presented in Table 25.7,
even commonly appearing in the biosorption literature,
have a much lower applicability in the analysis of equilibrium experimental data. This is mainly determined
by the fact that these models do not always reflect the
physicochemical principles of the biosorption process,
and in most of the cases, are not well understood. From
the practical point of view, they are just mathematical
models that describe the experimentally observed relation between amount of heavy metal retained on weight
unit of biosorbent (q e ) and its equilibrium concentration
from solution (c e ), without to offer information about
biosorption mechanism, or taking into account the influence of the experimental parameters.
Most of biosorption studies of heavy metal ions by
diverse kinds of biosorbents, including marine algae
biomass, have been performed on the single metal uptake. In contrast to this ideal situation, the real wastewater commonly contain a mixture of metal ions, and
therefore the modeling of multimetal biosorption systems is essential in the design of treatment systems.
The biosorption of heavy metal ions in real systems
that contain more than one component (multicomponent systems) involves the study of the biosorption
equilibrium in conditions of competition between different types of heavy metal ions, and are required
for better understanding of the system and for design
purpose.
Only few isotherm models have been developed to
describe the biosorption equilibrium in such systems.
The most used multimetal biosorption models applied
for the modeling of biosorption equilibrium are listed
in Table 25.7. These models range from simple equations associated with the individual isotherm parameters (nonmodified biosorption models) to more complex
models; exploiting the individual isotherm parameters along with correction factors (modified biosorption
models) [25.144].
The most frequent use of multicomponent biosorption models is the multicomponent Langmuir model
including its modification as well as multicomponent
Freundlich models. Lee and Chang [25.60] have use
the multicomponent Langmuir and Freundlich models
to describe the simultaneous biosorption of Pb(II) and
Cu(II) ions into two types of marine algae: Spirogyra
sp. and Cladophora sp. They noticed that the co-ion
Part D | 25.5
In addition, the variation of the Langmuir constant
(K L / with temperature indicates whether the biosorption process is exothermic or endothermic. Thus, the
decrease of K L value with temperature rise signifies
the exothermicity of the biosorption process (physical
biosorption), while the decrease of K L with temperature
indicates that the biosorption process need supplementary (thermal) energy (is endothermic), leading to
chemosorption. These observations are very useful in
the optimum design of biosorption systems. Thus, in the
case of physical biosorption, the bonds between heavy
metals and active sites of biosorbent are weak, and desorption occurs simply, by treating the loaded biosorbent
with water. In the case of chemosorption, the bonds between heavy metals and active sites of biosorbent are
stronger, and for desorption are needed more aggressive
chemical reagents (mineral acids, complexing agents,
etc.).
In order to appreciate the nature – physical or
chemical – of the biosorption process, the Dubinin–
Raduskevich model (Table 25.7) is more adequate for
the analysis of equilibrium biosorption data. This model
takes into account the energetically nonuniform surface
of biosorbent, and the model parameters (q
DR
max and ˇ)
are obtained from the graphical representation of ln q e
versus "
2 . Using the value of ˇ, the mean biosorption
energy (E, kJ=mol) can be calculated using the following equation,
E D
1
p
2ˇ
:
(25.4)
The mean energy of biosorption (E, kJ=mol) gives information about the biosorption mechanism. Therefore,
if the biosorption process has a mean energy of biosorption in the range of 116 kJ=mol, then it indicates that
the physical electrostatic interactions are potentially
involved in the biosorption mechanism [25.32, 143].
Some values of the Dubinin–Raduskevich model parameters obtained for biosorption of heavy metal ions
onto marine algae biomass are given in Table 25.9.
One of the main advantages of the Dubinin–
Raduskevich model is that it is temperature dependent.
If the biosorption data at different temperatures are
graphical represented, all the suitable data shall in general lay on the same characteristic curve. This curve can
be used to measure the applicability of the Dubinin–
Raduskevich model in analysis of the biosorption equilibrium data, together with the value of correlation
coefficient. When the fitting procedure gives high correlation coefficient, but the analyzed data does not lie in
the same characteristic curve, the validity of calculated
parameters is questionable. Anyway, the characteristic
curve for a given biosorption systems cannot be examined if the experiments were performed for a single
value of temperature [25.18].
The other isotherm models presented in Table 25.7,
even commonly appearing in the biosorption literature,
have a much lower applicability in the analysis of equilibrium experimental data. This is mainly determined
by the fact that these models do not always reflect the
physicochemical principles of the biosorption process,
and in most of the cases, are not well understood. From
the practical point of view, they are just mathematical
models that describe the experimentally observed relation between amount of heavy metal retained on weight
unit of biosorbent (q e ) and its equilibrium concentration
from solution (c e ), without to offer information about
biosorption mechanism, or taking into account the influence of the experimental parameters.
Most of biosorption studies of heavy metal ions by
diverse kinds of biosorbents, including marine algae
biomass, have been performed on the single metal uptake. In contrast to this ideal situation, the real wastewater commonly contain a mixture of metal ions, and
therefore the modeling of multimetal biosorption systems is essential in the design of treatment systems.
The biosorption of heavy metal ions in real systems
that contain more than one component (multicomponent systems) involves the study of the biosorption
equilibrium in conditions of competition between different types of heavy metal ions, and are required
for better understanding of the system and for design
purpose.
Only few isotherm models have been developed to
describe the biosorption equilibrium in such systems.
The most used multimetal biosorption models applied
for the modeling of biosorption equilibrium are listed
in Table 25.7. These models range from simple equations associated with the individual isotherm parameters (nonmodified biosorption models) to more complex
models; exploiting the individual isotherm parameters along with correction factors (modified biosorption
models) [25.144].
The most frequent use of multicomponent biosorption models is the multicomponent Langmuir model
including its modification as well as multicomponent
Freundlich models. Lee and Chang [25.60] have use
the multicomponent Langmuir and Freundlich models
to describe the simultaneous biosorption of Pb(II) and
Cu(II) ions into two types of marine algae: Spirogyra
sp. and Cladophora sp. They noticed that the co-ion