| dc.description.abstract | Ion exchangers are insoluble granular substances which have in their
molecular structure acidic or basic radicals that can exchange, without any apparent
modification in their physical appearance and without deterioration or solubilization,
the positive or negative ions fixed on these radicals for ions of the same sign in
solution in the liquid in contact with them. This process, know as ion exchange,
enables the ionic composition of the liquid being treated to be modified without
changing the total number of ions in the liquid before the exchange.
The first ion exchange substances were natural earths (zeolites); they were
followed by synthetic inorganic compounds (alluminosilicates) and organic
compounds; the latter materials are used today almost exclusively under the name of
resins. This term has been wrongly extended to cover any kind of exchanger. They are
either in the form of granules, as is usually the case, or in the form of beads.
There are two categories: the resins of the gel type and those of macro-porous
or loosely cross-linked type. The basic structure is identical: the macro-molecular structure is obtained in both cases by copolimerization of, e.g., styrene and
divinylbenzene. The difference between them lies in their porosity. | en_US |
