Marine Algae Biomass for Removal of Heavy Metal Ions 25.7 Mechanism of Biosorption 639
Part D | 25.7
tion from the biosorption process feasibility stand-point
by providing the time intervals between the breakthroughs of the different marine algae biomass used
as biosorbents, and the magnitude of the overshoots
that inside the column translate as concentration extremes [25.4].
In the design of the biosorption process for the removal of heavy metal ions, the biosorption/desorption
performances of marine algae biomass and some of
these characteristic properties (such as mass transfer, chemical stability, etc.) should be well known.
While batch-biosorption experiments yield some basic
information, the possible applicability of biosorption
systems at the industrial level should be tested under dynamic continuous-flow conditions. The performances
assessment of biosorption systems and prediction based
on both equilibrium as well as dynamic studies eventually leads to sizing of the equipment.
25.7 Mechanism of Biosorption
The influence of any of the experimental parameters
on the efficiency of biosorption process can be quantitatively evaluates when the biosorption mechanism is
known. The binding of heavy metal ions to the functional groups of marine algae biomass can be done
by several types of elementary mechanisms, such as
ion exchange, complexation, chelation adsorption, microprecipitation, etc. [25.24]. But, the biosorption processes are quite complex, and the overall metal uptake
mechanisms are obtained by combination of different
elementary mechanisms that take place at the same
time.
As a generalization, the uptake of heavy metal ions
from aqueous solution by biosorption on marine algae
biomass can be done via two major mechanisms:
a) Ion exchange – when the heavy metal ions are
binding by ionisable functional groups (such as
carboxyl, hydroxyl, phosphate, sulfate, etc.) from
marine algae biomass surface;
b) Complexation – in this case the metal ions from
aqueous solution form complexes (even chelates)
with functional groups of biosorbents, by electron
pair interactions. The most likely electron donor
atoms in marine algae biomass are nitrogen atoms,
neutral oxygen, or sulfur atoms.
Even if, for the removal of heavy metal ions
by biosorption on marine algae biomass, numerous types of marine algae and marine algae waste
biomass were used as biosorbent in various experimental conditions; a little attention has been
paid to investigation of the biosorption mechanism.
The understanding of the metal uptake mechanisms
can help to quantify the heavy metal ions – marine algae biomass interactions that are fundamental for the evaluation of potential implementation
methodology.
The key factors that controll and characterized the
biosorption mechanism are: (i) the type of functional
groups present on the surface of biosorbent, (ii) chemical speciation of metal ions present in aqueous solution,
and (iii) characteristics of heavy metal ions solution
(such as pH, presence of other inert or competing ions,
etc.) [25.158].
25.7.1 Ion Exchange
According to Davis et al. [25.30], the ion exchange is an
important type of interactions which may occur in the
biosorption process, and that can explain many of the
observations made during the heavy metal ions uptake
experiments. It should be noted that the ion exchange
does not clearly identify the mechanism of heavy metal
ions retention on marine algae biomass. This is because
the ion exchange interactions may range from physical
(such as electrostatic or van der Waals forces) to chemical (such as ionic or covalent), but they are useful in
describing the experimental observations [25.4].
In the most general sense, the ion exchange mechanism assumes that the functional groups from the
biosorbent surface can bind the heavy metal ions from
aqueous solution, according to the reaction
R
X
C
C M
C
R
M
C
C X
C
(25.9)
where R
is the binding site from the biosorbent surface, X
C is a mobile cation (e.g., Na
C , K
C , Ca
2C ,
Mg
2C , etc.), and M
C is the heavy metal ions present
in aqueous solution.
However, a one-to-one stoichiometry is not complied with as typical two mobile ions are released upon
the binding of one divalent heavy metal ion; the ion
exchange approach is considered to be the most sim-
Part D | 25.7
tion from the biosorption process feasibility stand-point
by providing the time intervals between the breakthroughs of the different marine algae biomass used
as biosorbents, and the magnitude of the overshoots
that inside the column translate as concentration extremes [25.4].
In the design of the biosorption process for the removal of heavy metal ions, the biosorption/desorption
performances of marine algae biomass and some of
these characteristic properties (such as mass transfer, chemical stability, etc.) should be well known.
While batch-biosorption experiments yield some basic
information, the possible applicability of biosorption
systems at the industrial level should be tested under dynamic continuous-flow conditions. The performances
assessment of biosorption systems and prediction based
on both equilibrium as well as dynamic studies eventually leads to sizing of the equipment.
25.7 Mechanism of Biosorption
The influence of any of the experimental parameters
on the efficiency of biosorption process can be quantitatively evaluates when the biosorption mechanism is
known. The binding of heavy metal ions to the functional groups of marine algae biomass can be done
by several types of elementary mechanisms, such as
ion exchange, complexation, chelation adsorption, microprecipitation, etc. [25.24]. But, the biosorption processes are quite complex, and the overall metal uptake
mechanisms are obtained by combination of different
elementary mechanisms that take place at the same
time.
As a generalization, the uptake of heavy metal ions
from aqueous solution by biosorption on marine algae
biomass can be done via two major mechanisms:
a) Ion exchange – when the heavy metal ions are
binding by ionisable functional groups (such as
carboxyl, hydroxyl, phosphate, sulfate, etc.) from
marine algae biomass surface;
b) Complexation – in this case the metal ions from
aqueous solution form complexes (even chelates)
with functional groups of biosorbents, by electron
pair interactions. The most likely electron donor
atoms in marine algae biomass are nitrogen atoms,
neutral oxygen, or sulfur atoms.
Even if, for the removal of heavy metal ions
by biosorption on marine algae biomass, numerous types of marine algae and marine algae waste
biomass were used as biosorbent in various experimental conditions; a little attention has been
paid to investigation of the biosorption mechanism.
The understanding of the metal uptake mechanisms
can help to quantify the heavy metal ions – marine algae biomass interactions that are fundamental for the evaluation of potential implementation
methodology.
The key factors that controll and characterized the
biosorption mechanism are: (i) the type of functional
groups present on the surface of biosorbent, (ii) chemical speciation of metal ions present in aqueous solution,
and (iii) characteristics of heavy metal ions solution
(such as pH, presence of other inert or competing ions,
etc.) [25.158].
25.7.1 Ion Exchange
According to Davis et al. [25.30], the ion exchange is an
important type of interactions which may occur in the
biosorption process, and that can explain many of the
observations made during the heavy metal ions uptake
experiments. It should be noted that the ion exchange
does not clearly identify the mechanism of heavy metal
ions retention on marine algae biomass. This is because
the ion exchange interactions may range from physical
(such as electrostatic or van der Waals forces) to chemical (such as ionic or covalent), but they are useful in
describing the experimental observations [25.4].
In the most general sense, the ion exchange mechanism assumes that the functional groups from the
biosorbent surface can bind the heavy metal ions from
aqueous solution, according to the reaction
R
X
C
C M
C
R
M
C
C X
C
(25.9)
where R
is the binding site from the biosorbent surface, X
C is a mobile cation (e.g., Na
C , K
C , Ca
2C ,
Mg
2C , etc.), and M
C is the heavy metal ions present
in aqueous solution.
However, a one-to-one stoichiometry is not complied with as typical two mobile ions are released upon
the binding of one divalent heavy metal ion; the ion
exchange approach is considered to be the most sim-