Development of Ion Exchange Concept Materials and Methods

The main stages in the development of ion exchange are shown in Table 1 and 2. Ion exchange gradually became an important separation method in water treatment, waste water puriRcation, analytical chemistry, medicine, the food industry and many other areas of application.

The Rrst systematic studies of ion exchange occurring in natural inorganic materials were performed during the period 1850-80, clays, sands and zeolites became objects of investigation and it was shown that soil treated with ammonium salts absorbs these ions, releasing an equivalent amount of calcium ions. Later, some natural materials found application for puriRcation of water as well as for other purposes. At that time, the evidence for existence of ions in solution had not yet been elucidated and the concept of a double electric layer had not yet been proposed. Despite this the stoichiometry of ion exchange and its connection with aluminosilicates present in the soil were established. It was demonstrated that the degree of exchange increased up to a limiting value with the

Sherrington DC and Hodge P (eds) (1988) Synthesis and Separations Using Functional Polymers. New York: Wiley.

Thomas JM and Thomas WJ (1996) Principles and Practice of Heterogeneous Catalysis. New York: VCH Publishers.

increase of concentration of salt solution, while the influence of temperature on ion exchange was shown to be less signiRcant.

At the beginning of the twentieth century complementary investigations in the areas of synthesis and application of ion exchangers took place. Industrial production of synthetic amorphous aluminosili-cate ion exchange materials was started. These materials (permutites) were used for water softening and in the treatment of sugar syrups. In the Rrst artiRcial sodium aluminosilicates a substitution of sodium to calcium occurred, but the ion exchanger could be regenerated in a column by treatment with saturated sodium chloride solution.

Ion exchange materials can also be obtained by oxidation and sulfonation of coals. Some types of charcoal, soft and hard brown coals, are suitable for this purpose. They can be converted into cation exchangers after treatment with fuming sulfuric acid. As a result, sulfonic and carboxylic groups (resulting from oxidation) are introduced into the coal structure, playing the role of Rxed ions. Furthermore, the coal is transformed to a gel due to polycondensation reactions. The total exchange capacity of such materials is about 1.5 meq g-1.

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