lutes interact with adsorbents, and is critical in optimizing the
use of adsorbents. The Langmuir [19], the Freundlich [20] and the
Temkin [21] were employed in the present study. The linearized
forms of the three isotherms are
1
qe
= 1
KaqmCe
+ 1
qm
(4)
ln qe = ln KF + 1
n
ln Ce (5)
qe = B ln A + B ln Ce (6)
where B = RT/b.The Langmuir constants qm (mg/g) and Ka (L/mg)
are Langmuir constants related to adsorption capacity and energy
of adsorption, respectively. The constants qm and Ka can be calculated
from the plot between 1/qe versus 1/Ce (Eq. (4)). Ce (mg/L)
and qe (mg/g) are the equilibrium concentration, and the amount of
dye adsorbed at equilibrium, respectively. Similarly the Freundlich
isotherm constants KF and 1/n can be calculated from the plot of
ln (qe) versus ln (Ce) (Eq. (5)). KF and n are the Freundlich constants,
which are indicators of adsorption capacity and adsorption intensity,
respectively [22]. The Temkin isotherm [21] has generally been
applied in the form given by Eq. (6). Therefore, by plotting qe versus
ln Ce (Eq. (6)), enables the determination of the constants A and B.
B is the Temkin constant related to heat of sorption (J/mol), A is the
Temkin isotherm constant (L/g), R the gas constant (8.314 J/mol K),
b is Temkin isotherm constant and T the absolute temperature (K).