The distribution of the metal ions between the liquid phase
and the adsorbent is a measure of the equilibrium condition in
the adsorption process and can generally be expressed in terms of
the two most popular isotherm models: Langmuir and Freundlich
isotherms.
The Langmuir isotherm model is based on the assumption of
homogeneous adsorption and its equation can be written as fol-
lows:
qe = qmKLCe
1 + KLCe
where qm (mg/g) is the maximum adsorption capacity of the adsor-
bent, KL (L/mg) is the Langmuir adsorption constant related to the
free energy of adsorption and Ce (mg/L) is the equilibrium concen-
tration.