Zeolite

What is zeolite?

Zeolite is a type of natural mineral and rock, forming unique crystals in their shape and properties with aluminium silicate known as molecular sieves. These minerals are characterized by a relatively small specific weight, due to the spread of voids that make up from 35% to 50% of the crystal size. Zeolite is characterized by a three-dimensional hive-like network structure consisting of layers, channels and continuous gaps in which positive ions and water molecules are concentrated.

                    

The ions in the structure of zeolites can be exchanged easily and easily with nutrients without affecting their structure in the so-called positive ion exchange (Cation Exchange) feature. Water molecules can also be lost and acquired with the same ease, which gives zeolites a hydration-dehydration property.

Uses of zeolite

Zeolite in plant production:

Zeolite is used in various horticultural and field crops, green landscapes, and protected crops, to provide the following benefits:

  •  Enriched and improved soil:This is due to its ability to keep potassium, nitrogen and other positive elements in the soil and prevent its loss so that the plant can benefit from them as needed.
  • Fertilizer and source of nutritional elements: Zeolite contains a group of fertilizer elements according to the following table:

 

TRACE ELEMENT

MACRO ELEMENT

SO3

Wt%

Cl

Wt%

ZnO

Wt%

CuO

Wt%

SiO2

Wt%

Al2O3

Wt%

MgO

Wt%

P2O5

Wt%

K2O

Wt%

CaO

Wt%

Fe2O3

Wt %

0.158

0.0280

0.0118

0.0147

41.5

12.9

9.83

0.452

1.94

11.2

11.5

 

 

  • Increasing the soil water capacity: the zeolite property of absorbing and losing water that causes it to absorb excess water from the soil and then slowly works to provide the plant with it, which helps the plant to adapt to the dry or humid environment as it maintains a constant level of moisture and reduces dryness and limits Disease infection, especially root rot.
  • Encouraging root growth: As a result of the ability of zeolites to raise the temperature of the root zone and improve soil properties, it is used in nurseries and rooting processes for different types of seedlings such as trees, palm trees, etc., to improve the rooting process and the growth and spread of the root system and also helps to early production.
  • Improving storage conditions for agricultural crops: As a result of the ability of zeolites to absorb excess moisture, harmful gases, toxins, etc., it has been used in the storage of different fruits and crops, to prolong the storage period and to preserve the freshness and quality of the fruits and crops stored.

 

Zeolite in animal production:

Zeolite is used in most animal species, such as poultry, cows, sheep, goats, horses, fish, etc., within the following ranges:

  • Food additive: Zeolite was added to feed mixtures to increase the efficiency of food transformation, increase production of meat, milk, etc., and protect animals from the impact of toxic materials caused by disease-causing organisms and reduce deaths, and to prevent fodder rot, etc.
  • Bedding for animals: By using zeolites as a floor bedding in animal stables, it reduces the release of unpleasant smells such as ammonia and others, and prevents the spread of diseases resulting from animals coming into contact with other animal waste in the same enclosure and others.
  • Production of animal manure: The addition of zeolite to organic fertilizers during fermentation processes, preserves nutrients such as nitrogen from loss, and prevents the release of toxic and unpleasant gases, which increases the efficiency of the use of organic fertilizer.

 

Unique Zeolite properties

  1. Cation Exchange Capacity:

Zeolite has the highest ion exchange capacity between minerals, reaching more than three times the capacity of ion exchange for clay.This feature helps to load zeolites with important nutrients to the plant, and in a way that reduces their loss, as the zeolite slowly releases it to the plant and lasts in the soil for long time, which helps to increase the availability of the elements to the plant and the ability of the plant to benefit from it.

   

  1. Absorption and water holding capacity:

It is the absorption and maintenance of water and moisture from the surrounding medium, and the retention capacity is one of the highest proportions. This capacity reaches more than 45% of its weight, and the property of adsorption and absorption of water inside the crystal building is added to it and is not lost even when the temperature rises, and this capacity reaches 15%, to become the total capacity of zeolite is more than 60% by weight of water.This feature reduces water consumption in agriculture by up to 50% and works to separate irrigation periods.

              

 

  1. The ability to absorb toxins and heavy elements from the surrounding medium

It is a property that enables zeolites to capture and retain toxins and heavy elements, both those caused by pathogenic microorganisms, or those emanating from various chemical reactions, etc., and this property is of great importance in neutralizing the impact of these toxins and heavy elements and preventing and reducing their impact, whether on plants or animals, Which increases its growth and prosperity.

Another zeolite uses

Zeolite is used in various fields other than the agricultural one. In the field of water purification, zeolite has been used with wastewater, swamps, groundwater and fish ponds to filter and purify water and to remove organic pollutants from it.

In the industrial field, such as the petroleum, paper, plastic, and chemical industries, etc., zeolites have been used as a catalyst for chemical reactions, as a control for bacterial growth, and in the processes of filtering and absorption, among others.

In the field of construction, zeolites were used in walls and floors, and in decoration and sculptures, as insulation, for drying, as a filler, for deodorization and as a raw material for all uses.

Zeolites are microporous crystalline solids with well-defined structures. Generally they contain silicon, aluminium and oxygen in their framework and cations, water and/or other molecules wthin their pores. Many occur naturally as minerals, and are extensively mined in many parts of the world. Others are synthetic, and are made commercially for specific uses, or produced by research scientists trying to understand more about their chemistry.

Because of their unique porous properties, zeolites are used in a variety of applications with a global market of several million tonnes per annum. In the western world, major uses are in petrochemical cracking, ion-exchange (water softening and purification), and in the separation and removal of gases and solvents. Other applications are in agriculture, animal husbandry and construction. They are often also referred to as molecular sieves.

                                                         

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Structural formula

 

 

 

 

 

 

 

A defining feature of zeolites is that their frameworks are made up of 4-connected networks of atoms. One way of thinking about this is in terms of tetrahedra, with a silicon atom in the middle and oxygen atoms at the corners. These tetrahedra can then link together by their corners (see illustration) to from a rich variety of beautiful structures. The framework structure may contain linked cages, cavities or channels, which are of the right size to allow small molecules to enter - i.e. the limiting pore sizes are roughly between 3 and 10 Å in diameter.

In all, over 130 different framework structures are now known. In addition to having silicon or aluminium as the tetrahedral atom, other compositions have also been synthesised, including the growing category of microporous aluminophosphates, known as ALPOs.

 

                                                                

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Catalysis

 

 

Zeolites have the ability to act as catalysts for chemical reactions which take place within the internal cavities. 
An import
ant class of reactions is that catalysed by hydrogen-exchanged zeolites, whose framework-bound protons give rise to very high acidity. This is exploited in many organic reactions, including crude oil cracking, isomerisation and fuel synthesis. Zeolites canalso serve as oxidation or reduction catalysts, often after metals have been introduced into the framework. Examplesare the use of titanium ZSM-5 in the production of caprolactam, and copper zeolites in NOx decomposition.

Underpinning all these types of reaction is the unique microporous nature of zeolites, where the shape and size of a particular pore system exerts a steric influence on the reaction, controlling the access of reactants and products. Thus zeolites are often said to act as shape-selective catalysts. Increasingly, attention has focused on fine-tuning the properties of zeolite catalysts in order to carry out very specific syntheses of high-value chemicals e.g. pharmaceuticals and cosmetics.

 

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Adsorption and Separation

 

 

 

 

     

 

 

The shape-selective properties of zeolites are also the basis for their use in   molecular adsorption. The ability preferentially to adsorb certain molecules, while excluding others, has opened up a wide range of molecular sieving applications. Sometimes it is simply a matter of the size and shape of pores controlling access into the zeolite. In other cases different types of molecule enter the zeolite, but some diffuse through the channels more quickly, leaving others stuck behind, as in the purification of para-xylene. As shown in the picture on the left, the shape of para-xylene means that it can diffuse freely in the channels of silicalite while the other isomers get stuck.

Cation-containing zeolites are extensively used as desiccants due to their high affinity for water, and also find application in gas separation, where molecules are differentiated on the basis of their electrostatic interactions with the metal ions. Conversely, hydrophobic silica zeolites preferentially absorb organic solvents. Zeolites can thus separate molecules based on differences of size, shape and polarity.

 

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Zeolites and the Environment

 

 

 

 

Zeolites contribute to a cleaner, safer environment in a great number of ways. In fact nearly every application of zeolites has been driven by environmental concerns, or plays a significant role in reducing toxic waste and energy consumption.In powder detergents, zeolites replaced harmful phosphate builders, now banned in many parts of the world because of water pollution risks. Catalysts, by definition, make a chemical process more efficient, thus saving energy and indirectly reducing pollution. Moreover, processes can be carried out in fewer steps, miminising unecessary waste and by-products. As solid acids, zeolites reduce the need for corrosive liquid acids, and as redox catalysts and sorbents, they can remove atmospheric pollutants, such as engine exahust gases and ozone-depleting CFCs. Zeolites can also be used to separate harmful organics from water, and in removing heavy metal ions, including those produced by nuclear fission, from water.

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