Isotherm Classification for Sorption from Solution

Isotherms for sorption from solution have been classified by Giles, Smith, and Huitson (1974) and reviewed by other authors, for example, Hinz (2001). They are 

FIGURE 4.7 Schematic drawing of the situation for adsorption from solution open circles represent solvent molecules, and gray filled circles are solute molecules. The binding of a solute molecule to the surface, such as that indicated by the arrow, requires removal of one or several solvent molecules from the surface. 

FIGURE 4.8 Example plot of a type L isotherm and its subtypes. Continuous Une subtype 1 dashed line subtype 2 dash-dot line subtype 3 dotted fine subtype 4. 

For each group, there are subgroups mainly defined by the extent of adsorption reached. It should be noted that often, due to the nature of the systans, the experimentally accessible concentration range is limited, thus the maximum amount sorbed may be far from samration coverage. 

FIGURE 4.9 Adsorption isotherms of NOM onto hematite in NaCl 0.01 M. Lines are fittings to a modified Langmuir isotherm. (Reprinted with permission from Gu, B. et al., 1994, Environmental Science Technology, 28, no. 1,38-46. Copyright 1994 American Chemical Society.) 

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