WHAT IS ZEOLITE?
Natural occurring zeolite is a crystalline mineral that
has been formed from volcanic ash generally over a
period of between 50 to more than 350 million years ago.
During this time there were many violent volcanic
eruptions ejecting millions of tonnes of ash into the
air which fell on both land (to form topsoil) and into
water where most was dissipated. But in the right
conditions, in a few locations, natural zeolite deposits
Zeolites are a group of naturally occurring framework
alumino-silicates with high Cation Exchange Capacities(CEC),
high adsorption and hydration-dehydration properties.
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.
Zeolites have a rigid, 3-dimensional crystalline
structure (similar to a honeycomb) consisting of a
network of interconnected tunnels and cages. Water moves
freely in and out of these pores but the zeolite
framework remains rigid. Another special aspect of this
structure is that the pore and channel sizes are nearly
uniform, allowing the crystal to act as a molecular
sieve. 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 porous zeolite is host to water molecules and ions
of potassium and calcium, as well as a variety of other
positively charged ions, but only those of appropriate
molecular size to fit into the pores are admitted
creating the "sieving" property.
One important property of zeolite is the ability to
exchange cations. This is the trading of one charged ion
for another on the crystal. One measure of this property
is the cation exchange capacity (CEC). Zeolites have
high CEC's, arising during the formation of the zeolite
from the substitution of an aluminum ion for a silicon
ion in a portion of the silicate framework (tetrahedral
units that make up the zeolite crystal). A classic
example of cation exchange is the removal of ammonia
from water and air. When a molecule of ammonia (NH3) is
hydrated, the reaction produces ammonium (NH4+), which
is readily exchanged for all or part of the calcium,
potassium and magnesium cations contained in zeolite and
adsorbed on to its stable aluminosilicate lattice.
There are nearly 50 different types of zeolites (clinoptilolite,
chabazite, phillipsite, mordenite, etc.) with varying
physical and chemical properties. Crystal structure and
chemical composition account for the primary differences.
Particle density, cation selectivity, molecular pore
size, and strength are only some of the properties that
can differ depending on the zeolite in question. For
example, clinoptilolite, the most common natural zeolite,
has 16% more void volume and pores as much as 0.2 nm
larger than analcime, another common zeolite. It is
important to know the specific type of zeolite one is
using in order to assure that it is appropriate for
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%.
The structure of each of these minerals is different but
they all have large open 'channels' in the crystal
structure that provide a large void space for the
adsorption and exchange of cations. The internal surface
area of these channels can reach as much as several
hundred square meters per gram of zeolite, making
zeolites extremely effective ion exchangers.
Other useful chemical and physical properties include:
high void volume (up to 50%),
low density (2.1-2.2 g cm-3),
excellent molecular sieve properties,
high cation exchange capacity (CEC): 150-250 cmol+ kg-1,
cation selectivity, specifically for cations like
ammonium, potassium, cesium, etc.
Zeolite is a natural, inert non-toxic substance that is
federally classified as GRAS (generally regarded as safe)
in most applications and exempted from most regulations
and reporting when used in accordance with good
agricultural practice and when comprising less than 2%
in animal feed products (40 CFR, Part 181.1001 and
Zeolite is approved by EU for usage in the swine and
poultry industry as Myco-Toxin binder.(70/524/EEC)
Zeolite is approved by FDA for usage in animal feeds as
an anti-caking agent. (CFR 582-2727)