Structure of Zeolites

Introduction

“Zeolites” are “crystalline solids” that have three dimensions. It is the crystalline form of the “aluminium silicate” that has a “micro-porous nature”. The tiny and fixed holes are found on them that help in the passing of molecules. They are also called the “molecular sieves” and the cause is that the large molecules are not able in crossing them.

Information on zeolites

“Zeolites” is categorized as a matter of “tetrahedral geometry” and the structure describes the free movement of water within these pores. The micro-pores that are seen in the zeolites at a “molecular level” are employed as “molecular sieves”. The "micro- porous zeolites" can hold the water's molecules. The pores consist of the "positively charged ions" like the cation of calcium as well as the cation within the pores.

“Zeolites” are micro-porous in nature and they are called “aluminum silicate’s three- dimensional crystalline solids”. There are three main components are needed for structural frameworks. Aluminum, silicon, and oxygen are the three main components for the creation of “structural frameworks”.

Zeolites structure

The structure of the “zeolites” proves that it has a similar composition to the most visible “clay minerals”. The reason for this matter is that both the zeolites as well as clay minerals are famous as the compounds of “alumino-silicate”. The important factor here

is that the zeolites do not contain the structures like the crystal that the clay minerals are consisted of.

Figure 1 − Structure of zeolites

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Most of the mineral clays show a feature that describes their ability to swell. They are also able to shrink when water is removed from them. In contrast, it is seen that the crystal structure of the zeolites has a “rigid nature”. The structure is famous for its networks and the networks are seen as “tiny micropores”.

Types of zeolites

The zeolites can be manufactured industrially or it can be synthesized, or it can be generated naturally. In nature, there are 50 different types of Zeolite are found but this is categorised into two main parts and they are “Natural zeolites and Synthesized zeolites”. Natural zeolites can occur in sedimentary as well as volcanic rocks. The most common example of this zeolite is “Clinoptilolite” and the ratio between “silica to alumina is 5 to 1”.

Figure 2 − “Structure of Dehydrated Zeolite”

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An example of “natural zeolite” is

$$\mathrm{"Na_{56}(AlO_{2})_{56}(SiO_{2})136.250H_{2}O(Faujasite)"}$$

The “Synthetic zeolites” are generally made by the slow crystalising process. Here a “silica-alumina gel” is important and it happens in the presence of “alkalis and organic templates”.

Zeolites’ chemical composition

All the zeolites consist of the “aluminosilicate framework” where aluminium, as well as silicon, is seen as “tetrahedrally coupled”. Four $\mathrm{O_{2}}$- are surrounded by the cations of aluminium as well as silicon (usgs, 2022). The common formula for composition is −

$$\mathrm{"Mx/n[AlO_{2}]x.(SiO_{2})y.mH_{2}O"}$$

This expression presents that zeolites consist of different “chemical components” and in the expression:

"M" is a metal, "n" refers to the "valence of the metal cation", "y" is the number of water molecules, and "y/x" refers to the ratio of "atomic Si/Al".

Zeolites properties

"Zeolites" consist of some properties and they are

• These are called solid having a highly stable nature.

• The high melting point of zeolite is “1000°C”.

• It is not able in dissolving in water as well as other inorganic compounds.

• They are not oxidised when there is oxygen within the solvents.

• It consists of a structure that looks like an “open cage” and it helps in distinguishing the trapping of potassium as well as calcium ions.

• The production of the “synthetic zeolites” happens with the presence of “uniform pore diameters”.

• “Natural zeolite” is found in the form of “non-uniform pore diameters”.

• The zeolites that are rich with alumina are attracted to polar molecules such as water.

• They have a non-reactive nature and can be derived from the minerals that exist naturally.

• They are not harmful to the environment

Zeolites applications

There are several applications of “zeolites” and they are listed below

• It is applied for water purifying in the form of “ion-exchange beds”.

• Different domestic as well as industrial applications and in softening of water this is applied.

• Zeolites are commonly used for isolating molecules in the chemistry field.

• The analysation of the molecules is done with the use of zeolites.

• They are also used as catalysts as well as sorbents.

• It is also able in providing accurate as well as precise separation of gases.

• Zeolites help in removing carbon dioxide, water, and sulphur dioxide from the “natural gas streams”.

Conclusion

“Zeolites” has a similar feature to “clay minerals” but they do not contain the same “crystal-like structure” as the minerals of clay. The structure of the zeolites has a rigid nature and they belong to the group of “hydrated minerals”. Zeolites is famous for the abilities to ion exchange and they undergo the process of hydration that is reversible. The properties of zeolites also help in differentiating the structure as well as chemical matters.

FAQs

1. How do zeolites be created?

It is made up of “aluminium, oxygen, and silicon” that gives zeolites a “crystalline solid structure”. The structure here creates a frame with channels as well as cavities. Waters, cations, and small molecules lie under the zeolites.

2. Are there any harmful effects of zeolites?

It can be harmful to the health of humans and they are categorised into “carcinogens or potential carcinogens”. An example is “erionite” which occurs naturally and can cause cancer.

3. What metals does zeolite filter?

"Lead and cadmium” are the two kinds of metals that can be filtered by zeolite. It is also effective in removing the toxic effect of the metals that are acidic in nature.