r - The Hong Kong Polytechnic University

The Freundlich model can be expressed as (Do 1998)
1
ln qe = ln KF + ln Ce
(4)
n
where K F (mg g -1 ) is the Freundlich constants related to the adsorption capacity and intensity, and n is the
heterogeneity factor.
The D-R model can be written as (Do 1998)
2
ln qe
= ln qm
− kε
(5)
where q m (mol g -1 )is the maximum adsorption capacity, k the model constant related to the free adsorption
energy and ε is the Polanyi potential related to the equilibrium concentration as follows
⎛ 1 ⎞
ε = RT ln ⎜1+
⎟
⎝ Ce
⎠
where the unit of C e should be translated into mol L -1 .The mean free energy of adsorption E is calculated by
E
1
=− (7)
2k
In general, the adsorption is physical adsorption when |E| is between 1.0 and 8.0 kJ mol -1 , while, the adsorption
mechanism is basically surface adsorption by ion exchange when |E| is between 8.0 and 16.0 kJ mol -1
(Kilislioglu and Bilgin 2003; Özcan et al. 2006).
Figures 5-7 show the fitting curves simulated by the above three isotherm models and the isothermal parameters
for Ni(II) and Mn(II) adsorption on loess soil are presented in Table 4. The Langmuir, Freundlich and D-R
models were all found to fit the test data very well according to their high coefficients of determination. The
D-R model showed a relatively better fit with the test results for its highest coefficients.
(6)
Fiurge 4 The adsorption isotherms of Ni(II) and
Mn(II) on loess
Figure 6 Fitting curves of Ni(II) and Mn(II)
adsorption on loess with Freundlich model
Figure 5 Fitting curves of Ni(II) and Mn(II)
adsorption on loess with Langmuir model
Figure 7 Fitting curves of Ni(II) and Mn(II)
adsorption on loess with D-R model
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