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4.1 Basic Principles of Adsorption and Ion Exchange 259

Figure 4.10 Polyacrilic matrix (cross-linked polymethacrylate).

Table 4.11
Functional groups of standard ion-exchange resins (IAEA, 2002;
Helffercih, 1962)

Type Functional group
xchangers) Strongly acidic (cation e SO 3 –
Weakly acidic (cation exchangers) COO –
xchangers) Other acidic (cation e PO 3 2–
HPO 2 –
AsO 3 2–
SeO 3 –
Strongly basic (anion e xchangers) [N(CH 3 ) ] 3
[N(CH 3 ) C H 2 4 OH]
2
Weakly basic (anion exchangers) NH 3
R –NH 1 2 R 2

define the chemical behavior and the specific applications of the resin. Generally resins ,
can be typified into strong or weak acid cation exchangers and strong or weak base anion
exchangers (Table 4.11).
Strong acid cation r esins : These resins are highly ionized in both the acid (R SO H)
3
and salt (R SO Na) form and behave like strong acids. They can convert a metal salt into
3
the corresponding acid by the reaction
2(RSO H N l C i (RSO )N 2Hl C 2 4

,
i
)
3
Na and H ions are highly exchangeable over the entire pH range. Depending on the spe-
cific usage, these resins are used either in the hydrogen or in the sodium form. For e xam-
ple, the sodium form is preferred if water softening (calcium and magnesium remo al) is v
the desired action (Table 4.12). The resins can be regenerated by treatment with the appro-
priate solution (a strong acid for the hydrogen form or a sodium chloride solution for the
sodium form). The treatment with hydrochloric acid (HCl) results in a concentrated nickel
chloride (NiCl) solution according to the previous chemical equation.
Weak acid cation resins : Here, the ionic group is a carboxylic acid ( COOH) and these
v
resins behae as if they were weak organic acids. They hae a much higher afinity than v f
strong acid resins for hydrogen ions. Therefore, fewer amounts of acids are required in