Zeolites

Zeolites (picture source: www.answers.com)

Zeolites are natural volcanic minerals with a number of unique characteristics. Zeolites were formed when volcanic ash was deposited in ancient alkaline lakes. The interaction of the volcanic ash with the salts in the lake water altered the ash into various zeolite materials.

In 1756, the Swedish mineralogist Axel Fredrick Cronstedt discovered that stilbite, a natural mineral, visibly lost water when heated, and he named the class of materials zeolites from the classical Greek words meaning 'boiling stones.' Zeolites were considered an obscure group of minerals with unique properties for almost 200 years, and Cronstedt was remembered primarily for discovering the element nickel.

Zeolites have an unusual crystalline structure and a unique ability to change ions. A very large number of small channel are present in its structure. These channels have typical diameters of 0.5 to 0.7 nm, only slightly larger than the diameter of a water molecule. These channels are called microporosity. Beside this there are a number of larger pores, the so-called mesoporosity. Positive ions are present in the channels, which can be exchanged for other ions.
This substitution of ions enables zeolites to selectively adsorb certain harmful or unwanted elements from soil, water and air. A classic example is the removal of calcium from hard water. Zeolites exchange sodium ions for calcium ions, which result in soft water. Zeolites also have strong affinity for certain harmful heavy metals such as lead, chromium, nickel and zinc.
In the mesopores of zeolite suspended and colloidal particles can be trapped. In these pores dissolved organic molecules are adsorbed also.

Considering all of these properties and abilities, zeolites commercial and environmental possibilities seem to be limitless. One example is the application of zeolites in landfills and at industrial sites, which can help prevent the release of a number of harmful or unwanted elements into the environment.

Click here for more information about zeolite structure and types or find more information about zeolite applications.