What is zeolite

Zeolite is a water-reticulated aluminosilicate of alkali and alkaline earth metals, a generic term for the zeolite family of minerals, first discovered in Europe in 1756. The mineralogist Kronsti in Sweden found a class of natural silica-aluminate ores that would boil when burned, hence the name "zeolite", which in Greek (Zeo=Boil=Boil, Lite=stone=stone) means boiling stone, or zeolite for short.

It includes more than 30 kinds of aluminosilicate minerals containing zeolite water of calcium, sodium, as well as barium and potassium. Common minerals are sodium zeolite, calcium zeolite, square zeolite, bundle zeolite, turbidite, grossular zeolite, plagioclase zeolite, filigree zeolite, etc.

The chemical formula is: MxDy[(Alx+2ysin-(x+2y)O2n)]-mH2O. where M is an alkali metal such as Na, K or other monovalent cation; D is an alkaline earth metal such as Ca, Sr, Ba, Mg or other divalent cation; M and D are commonly known as exchangeable cations. Where, x is the number of alkali metal ions, y is the number of alkaline earth metal ions, n indicates the number of silicon aluminum ions. m indicates the number of water molecules. The cations in parentheses (Si, A1) together with oxygen form a tetrahedral lattice called the structural anion.

In this structural anion, the center is a silicon (or aluminum) atom, and each silicon (or aluminum) atom is surrounded by four oxygen atoms. The individual silicon and oxygen tetrahedra are interconnected by the oxygen atoms at the apex of the tetrahedra, forming many wide pores and empty channels, which is the difference between zeolite and other shelf silicate minerals, and thus zeolite has a large specific surface area (400-800m2/g).

This lattice structure of zeolite determines its high adsorption and exchange properties. These pores and channels of zeolite can adsorb a large number of other molecules or ions, and the adsorption capacity of zeolite far exceeds that of other substances. The pores and channels of zeolite are uniform in size, with diameters between 0.3 and 1 nm. Substances smaller than this diameter can be adsorbed, while substances larger than this diameter are excluded from adsorption, and zeolite has the property of selective adsorption.

Zeolites also have a large dispersion force and electrostatic force on the surface, so their adsorption force is very large. The amount of water they contain varies with the external temperature and humidity. One of them is in the aluminum-oxygen tetrahedron because the valence electron of an oxygen atom is not neutralized, making the whole aluminum-oxygen tetrahedron with a negative charge, in order to maintain the electric neutrality, there must be a positively charged metal cation (M+) nearby to offset (usually alkali metal or alkaline earth metal ions), these cations and aluminosilicate bonding is quite weak, has a great mobility, very easy and surrounding aqueous solution of cations in the The structure of the zeolite is not destroyed after the exchange.

This structure of zeolite determines its ion exchangeability and selectivity of exchange. The residual charge resulting from the exchange of the SiO44- backbone with AlO45- isocrystals also gives the zeolite catalytic properties.