Geoscience Reference
In-Depth Information
Fig. 5.2 Typical adsorption
isotherms described by
a Langmuir, b Freundlich,
and c BET equations (Yaron
et al.
1996
)
If a straight line is obtained when K
d
is plotted against x/m at low concentra-
tions, the Langmuir equation is applicable. However, due to the restrictive
assumptions, Langmuir isotherms usually are of minor importance in heteroge-
neous media such as the subsurface environment. Corrections therefore have been
introduced to the Langmuir equation to overcome the problems of heterogeneous
sites, coupled adsorption-desorption reactions, and adsorption of inorganic and
organic trace elements on geosorbents.
The Freundlich equation was derived empirically, based on the logarithmic
decrease in adsorption energy with increasing coverage of the adsorbent surface.
Freundlich found that adsorption data for many dilute solutions could be fit by the
expression
