Natural Zeolite

WHAT IS ZEOLITE?

Zeolites are a family of crystalline aluminosilicate minerals. The first zeolite was described in 1756 by Cronstedt, a Swedish mineralogist who coined the name from two Greek words meaning ‘boiling stones’, referring to the evolution of steam when the rock is heated. About fifty natural zeolites are now known and more than one hundred and fifty have been synthesised for specific applications such as industrial catalysis or as detergent builders. Clinoptilolite is a naturally occurring zeolite, formed by the devitrification of volcanic ash in lake and marine waters millions of years ago. It is the most researched of all zeolites and is widely regarded as the most useful.
In common with other zeolites, clinoptilolite has a cage-like structure consisting of SiO4 and AlO4 tetrahedra joined by shared oxygen atoms. The negative charges of the AlO4 units are balanced by the presence of exchangeable cations notably calcium, Magnesium, sodium, potassium and iron. These ions can be readily displaced by other substances, for example heavy metals and ammonium ions. This phenomenon is known as cation exchange, and it is the very high cation exchange capacity of clinoptilolite which provides many of its very useful properties. Clinoptilolite is also known to be a powerful adsorbent of certain gases, such as hydrogen sulphide and sulphur dioxide.

Being a naturally occurring mineral, the precise composition of clinoptilolite is subject to a degree of variation. However, an approximate empirical formula is