52
3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …
3.2.6 Data Assessment Theory
3.2.6.1 Isotherm
Adsorption isotherms are essential in achieving the binding process mechanism.
Basically, an adsorbent’s binding capability can be derived from isotherms such as the
model Langmuir, Freundlich, Temkin and DKR. Model constants are measurements
of adsorbent binding power for the metal ions being studied.
The Langmuir model assumes binding occurs at common homogeneous binding
sites of the adsorbent and monolayer binding, and maximal adsorption occurs when
adsorbed molecules form a saturation layer on the adsorbent surface [10]. The linear
form of this model is defined in 3.4.
C e
q e
=
C e
Q m
+
1
Q m K L
(Linear form)
(3.4)
The Langmuir constant Q m (mmol/g) represents the maximum capacity to adsorb,
and K L (L/mmol) refers to the adsorption bonding strength. The K L represents the
degree of binding affinity that the metal ions have to the adsorbent. Higher K L values
suggest much stronger metal ion binding affinities [11]. The Langmuir model parameters can be found from the slope and intercepts of C e /q e versus C e. The essential
characteristics of the Langmuir model can be seen in respect to a dimensionless
constant known as the separation factor (R L ) that is applied in verifying if an adsorption process is favourable [12], as seen in 3.5. The R L command, R L = 1 and R L
command between 0 and 1, respectively, means unfavourable, linear and favourable.
R L =
1
1 + K L C o
(3.5)
The Freundlich isotherm is focused on the relation of balance between heterogeneous surfaces. This isotherm is based on the postulation that the adsorption sites
are spread-out exponentially with regard to adsorption heat, it also implies that the
stronger adsorption sites are first saturated and the adsorption strength decreases with
increased occupation of the site [11]. This model is explained in the linear form in
3.6.
log q e = log K F +
1
n
log C e (Linear form)
(3.6)
K F and n are constant representing the respective adsorption capability and adsorption strength. The higher the K L values, the higher the possibility of more reactive
definition of the adsorbent [13]. This model’s parameters can be estimated from the
slope and intercepts log q e against log C e plot. Under normal binding conditions, n
values should be within the limit of 1–10 [14].
3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …
3.2.6 Data Assessment Theory
3.2.6.1 Isotherm
Adsorption isotherms are essential in achieving the binding process mechanism.
Basically, an adsorbent’s binding capability can be derived from isotherms such as the
model Langmuir, Freundlich, Temkin and DKR. Model constants are measurements
of adsorbent binding power for the metal ions being studied.
The Langmuir model assumes binding occurs at common homogeneous binding
sites of the adsorbent and monolayer binding, and maximal adsorption occurs when
adsorbed molecules form a saturation layer on the adsorbent surface [10]. The linear
form of this model is defined in 3.4.
C e
q e
=
C e
Q m
+
1
Q m K L
(Linear form)
(3.4)
The Langmuir constant Q m (mmol/g) represents the maximum capacity to adsorb,
and K L (L/mmol) refers to the adsorption bonding strength. The K L represents the
degree of binding affinity that the metal ions have to the adsorbent. Higher K L values
suggest much stronger metal ion binding affinities [11]. The Langmuir model parameters can be found from the slope and intercepts of C e /q e versus C e. The essential
characteristics of the Langmuir model can be seen in respect to a dimensionless
constant known as the separation factor (R L ) that is applied in verifying if an adsorption process is favourable [12], as seen in 3.5. The R L command, R L = 1 and R L
command between 0 and 1, respectively, means unfavourable, linear and favourable.
R L =
1
1 + K L C o
(3.5)
The Freundlich isotherm is focused on the relation of balance between heterogeneous surfaces. This isotherm is based on the postulation that the adsorption sites
are spread-out exponentially with regard to adsorption heat, it also implies that the
stronger adsorption sites are first saturated and the adsorption strength decreases with
increased occupation of the site [11]. This model is explained in the linear form in
3.6.
log q e = log K F +
1
n
log C e (Linear form)
(3.6)
K F and n are constant representing the respective adsorption capability and adsorption strength. The higher the K L values, the higher the possibility of more reactive
definition of the adsorbent [13]. This model’s parameters can be estimated from the
slope and intercepts log q e against log C e plot. Under normal binding conditions, n
values should be within the limit of 1–10 [14].