Natural zeolites are environmentally and economically acceptable hydrated
aluminosilicate materials with exceptional io
n-exchange and sorption properties. Their
effectiveness in different technological processes depends on their physical-chemical
properties that are tightly connected to their geological deposits. The unique tree-
dimensional porous structure gives natural zeolites various application possibilities.
Because of the excess of the negative charge on the surface of zeolite, which results from isomorphic replacement of silicon by aluminum
in the primary structural units, natural zeolites belong to the group of cationic exchangers. Numerous studies so far have confirmed their excellent performance on the removal of metal cations from wastewaters.
However, zeolites can be chemically modified by inorganic salts or organic surfactants,
which are adsorbed on the surface and lead to the generation of positively charged oxi-
hydroxides or surfactant micelles, and which enables the zeolite to bind also anions, like arsenates or chromates, in stable or lessstable complexes. Natural zeolites have
advantages over other cation exchange materials such as commonly used organic resins,
because they are cheap, they exhibit excellent selectivity for different cations at low
temperatures, which is accompanied with a release of non-toxic exchangeable cations (K+
, Na+
, Ca2+ and Mg2+) to the environment, they are compact in size and they allow simple
and cheap maintenance in the full-scale applications. The efficiency of water treatment by using natural and modified zeolites depends on the type and quantity of the used zeolite, the size distribution of zeolite particles, the initial concentration of contaminants (cation/anion), pH value of solution, ionic strength of solution, temperature, pressure, contact time of system zeolite/solution and the presence of other organic compounds and anions. For water treatment with natural zeolites, standard procedures are used,