What is Zeolite?
Zeolites are micro porous minerals which are formed by the devitrification of volcanic ash over millions of years. The molecular structure of the ash is slowly transformed, under the right geological conditions, into the regular crystalline structure which gives zeolites their unique characteristics.
There are many types of natural zeolite, but they all have a similar structure and share roughly the same physical and chemical properties, although there are differences between the different types of zeolite.
All zeolites have a three dimensional ‘cage-like’ structure which contains channels of a specific diameter. This framework is made of SiO4 and AlO4 tetrahedra in slightly differing configurations which correspond to the specific types of zeolite.
There are about 50 different natural zeolite structures which have been identified, each with a slightly different Si:Al:O ratio, and therefore a slightly different pore size and ion exchange capacity.
The aluminium atoms within the framework carry a negative charge which gives the zeolite its natural ion exchange capacity, and each individual negative charge is balanced by the presence of an interchangeable cation.
The most commonly occuring cations are sodium, potassium, calcium and magnesium but many other elements can also be present at varying levels depending on how and where the zeolite was formed. This mix of cations is different for every natural zeolite deposit and it is an important characteristic of the zeolite.
Types of natural zeolite
There are several types of natural zeolite, but they all have a very similar structure and exhibit almost the same physical and chemical properties, although there are important differences between each type. The most common zeolites are:
Clinoptilolite
The most widely commercialised natural zeolite type is called clinoptilolite. It has a high ion exchange capacity and porosity and is found in relatively pure form in several different countries. The purest clinoptilolite ever found comes from Turkey and has a purity of between 92 and 96%.
Chabasite
Another favoured zeolite type is chabasite which has an even higher ion exchange capacity and larger pore size, but it is much less common than clinoptilolite and most chabasite deposits have much lower purity. The purest chabasite deposits found in Europe are only around 60% pure.
Main applications
The combination of a rigid structure with high porosity and natural ion exchange capacity is what gives zeolites such a wide range of potential uses. It is already widely used in agriculture both as a soil additive and as an animal feed additive.
It is also used in almost every possible water treatment application from sewage treatment to swimming pool filters. Zeolite granules have been described as “the worlds smallest water filter”.
