Zeolites

Zeolite minerals were recognized over 200 years ago, but until recently were thought to be quite rare. The name in Greek means "boiling rock" and was given because of the mineral's ability to absorb water, which is readily given off when the mineral is heated. Appreciation of zeolite's several unique qualities led to the successful synthesis of several varieties in the 1950's, and a substantial industry has been built over the use of synthetic zeolites as ion exchange agents, desiccants, catalylists in petroleum refining, adsorbents for gas separations, and carriers in detergents.

By the early 1970's, geologists began to realize that natural zeolites are in fact quite common and wide spread. Since that time natural zeolites have gradually gained acceptance as an industrial commodity used for odor control, water purification, cattle feed supplements, and fertilizer additives.

Natural zeolites are crystalline hydrated aluminosilicates of the alkalis and alkaline earths generally found in volcaniclastic sediments originally rich in volcanic glass, which was subjected to natural geologic alteration processes. Their usefulness is based on both their chemical composition and their physical form. They have a framework structure that encloses interconnected cavities occupied by relatively large cations and water molecules. The cations, chiefly sodium, potassium, and calcium, as well as the water, have considerable freedom of movement within the structure and give the zeolites their cation exchange and reversible dehydration properties. The porous framework of the zeolites enables them to act as molecular sieves for separation of mixtures according to the size and shape of the molecular compounds in the mixture.

Natural zeolites vary in composition and quality from one deposit to another, so they are not as consistent in their characteristics as the various synthetics. They are however much lower in cost, more resistant to attrition, and some have qualities that have not yet been achieved by any synthetic.