Page 130 - Industrial Wastewater Treatment, Recycling and Reuse

104 Industrial Wastewater Treatment, Recycling, and Reuse

Figure 2.7 Schematic representation of ion exchange resin bead.

In ion exchange resins, functionality of the matrix is more important than
the surface area. Although the polymer backbone is also believed to have
some role in the removal of contaminants, for all practical purposes, surface
functionality on the polymers is crucial in deciding the separation of pollut-
ant species from the solution.
The functional groups of the resin are located on the walls of the poly-
mer; this is schematically shown in Figure 2.8, along with a listing of com-
mon functional groups. On the basis of functionality, the ion exchange resins
are classified as strong acid resins, weak acid resins, strong base resins, and
weak base resins. Selection of the resin is generally made on the basis of func-
tionality and the capacity of the resin along with porosity considerations. For
example, for established water treatment using ion exchange application,
cations in the water are removed by cationic resins, and anions are removed
by anion exchange resins. The capacity of the resin from the specified class
(usually operating capacity) dictates the quantity of resin required and cost,
while the rate of exchange also dictates selection of suitable resin among the
classes, for example selecting microporous resin versus macroporous resin
from a kinetics point of view. It is to be noted that there are hundreds of
resins in each class, and selection of any resin for specific application is