358 19 · SEPARATING MIXTURES
BOX 19.3
Zeolites
Some aluminosilicates are known as zeolites. Zeolites
are part of a class of compounds known as molecular
sievesand consist of an aluminosilicate frame with
group 1 or 2 cations trapped inside tunnels or cages.
In addition to their ability to act as ion exchangers,
they can selectively remove small molecules, such as
water, from mixtures – hence the term ‘molecular
sieves’ (Fig. 19.14).Fig. 19.14Cage structure of a
typical zeolite.Fig. 19.15Steps in solvent extraction.