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258 4. Adsorption and Ion Exchange

Figure 4.8 Cross-linked polystyrene.

Figure 4.9 Divinilbenzene (DVB).

in the matrix corresponds to 5% cross-linking. As mentioned abo the degree of cross- v e,
ylbenzene content means lo w vin linking is connected to the properties of the resin. Lo w di
ents.
cross-linking and the result is a soft resin prone to swelling in solvThen, the ion-
exchange potential is created by introducing fed ionic groups into the resin matrix. F ix or
example, in sulfonation, 8–10 –SO 3 H groups are introduced in the matrix for every 10 ben-
zene rings. The H ions contained in the –SO 3 H groups is the mobile ion or counterion
that will be exchanged in a solution with dif ferent cations.
Phenolic : There are various kinds of phenolic resins. The ones that are produced from
xchangers,
phenol–formaldehyde condensation are very weak acid e where the phenolic
ix
–OH groups are the fed-ionic groups. The formaldehyde content decides the extent of
cross-linking in the resin. On the other hand, phenolsulfonic acid resins contain both
strong acid –SO 3 H and weak acid –OH groups.
Acrylic : This resin is manuf actured from a copolymer of acrylic or methacrylic acid with
divinylbenzene (Figure 4.10). The result is a weak acid ion-exchange resin with –COOH
v , e v groups that haery little salt splitting capacity but are very efving Ca fecti e in remo v 2
and similar ions under alkaline conditions.

oups Classification based on the functional gr
On the basis of the charge of the exchangeable ions, there are cation (positi v e mobile ions)
v gati and anion (nee mobile ions) resins. Both types are manufactured from the very same
basic organic polymers. Ho the ionic groups that are introduced into the matrix
v
,
er
we