Conclusions

The area of organic ion exchangers remains a very active one with intensive technical and scientific work on both conventional resins and entirely novel systems. Thus, organic ion exchangers with different morphologies of their three-dimensional networks and base and acid groups with various chemical structures have been prepared.

There is also a growing interest in the development of selective chelating ion exchangers for the possible application of these resins in analytical chemistry, metal recovery and wastewater treatment. The latter two applications have a great importance in economic and ecological domains. Requirements of the properties of these ion exchangers include high capacity, high selectivity and fast kinetics. Most of the

— CH2 —NH —(C2H4 —NH) —H — CH2 — NH — (C2H4 — NH) — H

base J I

amine groups (free base form)

isothiouronium group (free base form)

h h amine groups (salt form)

isothiouronium group (salt form)

Figure 16 Chemical structure dependence of amine and isothiouronium groups on the pH of aqueous medium.

commercial resins show a high capacity but a poor selectivity towards metal ions.

The combination of the physical strength of an inorganic support with the higher ion exchange capacity and kinetics of the organic ion exchangers could, in the future, lead to an interesting class of ion exchangers with special applications.

See also: II/Ion Exchange: Historical Development; Inorganic Ion Exchangers; Organic Membranes; Theory of Ion Exchange.

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