A. A. Zagorodni Ion Exchange Materials: Properties and Applications Elsevier:2006
Book - Applets - Applet 9

Applet 9

Ion exchange isotherm and separation factor

The isotherm is shown as the red line. The broken line is the isotherm of an ion exchanger which has no preference for either counterion.

The origin and the end point of any isotherm lie in the lower left and upper right corners of the diagram because, in equilibrium, absence of one counterion in the solution requires absence of this ion in the ion exchanger.

Selectivity of the ion exchanger requires deviation of the isotherm from the diagonal. Selectivity thus necessitates a non-linear isotherm.

For any ionic composition, the separation factor is equal to the ratio of the two rectangular areas touching one another in the corresponding point on the isotherm.

The selectivity can be altered moving the green slider attached at the left side.
The right slider (grey) slider moves rectangular areas representing the separation factor for different points of the isotherm.