الزيوليت الطبيعى والصناعى واستخداماته

Zeolite

technolab el-bahaa group

general.dr

bahaa badr

chemical advisor

01229834104

The microporous molecular structure of a zeolite, ZSM-5

Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents.[1]

The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been adsorbed by the material.

Based on this, he called the material zeolite, from the Greek ζέω (zéō), meaning "to boil" and λίθος (líthos), meaning "stone".[2]

As of October 2012, 206 unique zeolite frameworks have been identified, and over 40 naturally occurring zeolite frameworks are known.[3][4]

Zeolites are widely used in industry for water purification, as catalysts, for the preparation of advanced materials and in nuclear reprocessing.

They are used to extract nitrogen from air to increase oxygen content for both industrial and medical purposes.

Their biggest use is in the production of laundry detergents.

They are also used in medicine and in agriculture.

Properties and occurrence

A form of thomsonite (one of the rarest zeolites) from India
Zeolites have a porous structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others.

These positive ions are rather loosely held and can readily be exchanged for others in a contact solution.

Some of the more common mineral zeolites are analcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite, and stilbite. An example mineral formula is:

Na2Al2Si3O10·2H2O, the formula for natrolite.

Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater.

Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins.

Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, or other zeolites.

For this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential.

Zeolites are the aluminosilicate members of the family of microporous solids known as "molecular sieves."

The term molecular sieve refers to a particular property of these materials, i.e., the ability to selectively sort molecules based primarily on a size exclusion process.

This is due to a very regular pore structure of molecular dimensions.

The maximum size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the dimensions of the channels.

These are conventionally defined by the ring size of the aperture, where, for example, the term "8-ring" refers to a closed loop that is built from 8 tetrahedrally coordinated silicon (or aluminium) atoms and 8 oxygen atoms.

These rings are not always perfectly symmetrical due to a variety of effects, including strain induced by the bonding between units that are needed to produce the overall structure, or coordination of some of the oxygen atoms of the rings to cations within the structure.

Therefore, the pores in many zeolites are not cylindrical.

Zeolites transform to other minerals under weathering, hydrothermal alteration or metamorphic conditions. Some examples:[5]

The sequence of silica-rich volcanic rocks commonly progresses from:

Clay → quartz → mordenite–heulandite → epistilbite → stilbite → thomsonite–mesolite-scolecite → chabazite → calcite.

The sequence of silica-poor volcanic rocks commonly progresses from:

Cowlesite → levyne–offretite → analcime → thomsonite–mesolite-scolecite → chabazite → calcite.

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Sources

Natrolith from Poland

Conventional open pit mining techniques are used to mine natural zeolites.

The overburden is removed to allow access to the ore.

The ore may be blasted or stripped for processing by using tractors equipped with ripper blades and front-end loaders.

In processing, the ore is crushed, dried, and milled.

The milled ore may be air-classified as to particle size and shipped in bags or bulk.

The crushed product may be screened to remove fine material when a granular product is required, and some pelletized products are produced from fine material.

Currently, the world’s annual production of natural zeolite is about 3 million tonnes.

The major producers in 2010 were China (2 million tonnes), South Korea (210,000 t), Japan (150,000 t), Jordan (140,000 t), Turkey (100,000 t) Slovakia (85,000 t) and the United States (59,000 t).[6]

The ready availability of zeolite-rich rock at low cost and the shortage of competing minerals and rocks are probably the most important factors for its large-scale use.

According to the United States Geological Survey, it is likely that a significant percentage of the material sold as zeolites in some countries is ground or sawn volcanic tuff that contains only a small amount of zeolites.

Some examples of such usage are dimension stone (as an altered volcanic tuff), lightweight aggregate, pozzolanic cement, and soil conditioners.[7]

Synthetic zeolite

There are several types of synthetic zeolites that form by a process of slow crystallization of a silica-alumina gel in the presence of alkalis and organic templates.

One of the important processes used to carry out zeolite synthesis is sol-gel processing.

The product properties depend on reaction mixture composition, pH of the system, operating temperature, pre-reaction 'seeding' time, reaction time as well as the templates used.

In sol-gel process, other elements (metals, metal oxides) can be easily incorporated.

The silicalite sol formed by the hydrothermal method is very stable.

The ease of scaling up this process makes it a favorite route for zeolite synthesis.
Synthetic zeolites hold some key advantages over their natural analogs.

The synthetics can, of course, be manufactured in a uniform, phase-pure state.

It is also possible to manufacture desirable zeolite structures which do not appear in nature.

Zeolite A is a well-known example.

Since the principal raw materials used to manufacture zeolites are silica and alumina, which are among the most abundant mineral components on earth, the potential to supply zeolites is virtually unlimited.

Finally, zeolite manufacturing processes engineered by man require significantly less time than the 50 to 50,000 years prescribed by nature.

Disadvantages include the inability to create crystals with dimensions of a comparable size to their natural counterparts.

Uses

Commercial and domestic

Zeolites are widely used as ion-exchange beds in domestic and commercial water purification, softening, and other applications.

In chemistry, zeolites are used to separate molecules (only molecules of certain sizes and shapes can pass through), and as traps for molecules so they can be analyzed.

Zeolites have the potential of providing precise and specific separation of gases including the removal of H2O, CO2 and SO2 from low-grade natural gas streams.

Other separations include noble gases, N2, O2, freon and formaldehyde.

However, at present, the true potential to improve the handling of such gases in this manner remains unknown.

On-Board Oxygen Generating Systems (OBOGS) use zeolites to remove nitrogen from compressed air in order to supply oxygen for aircrews at high altitudes.[8]

Petrochemical industry

Synthetic zeolites are widely used as catalysts in the petrochemical industry, for instance in fluid catalytic cracking and hydrocracking.

Zeolites confine molecules in small spaces, which causes changes in their structure and reactivity.

The hydrogen form of zeolites (prepared by ion-exchange) are powerful solid-state acids, and can facilitate a host of acid-catalyzed reactions, such as isomerisation, alkylation, and cracking.

The specific activation modality of most zeolitic catalysts used in petrochemical applications involves quantum-chemical Lewis acid site reactions.

[citation needed]

Catalytic cracking uses reactor and a regenerator.

Feed is injected onto hot, fluidized catalyst where large gasoil molecules are broken into smaller gasoline molecules and olefins.

The vapor-phase products are separated from the catalyst and distilled into various products.

The catalyst is circulated to a regenerator where air is used to burn coke off the surface of the catalyst that was formed as a byproduct in the cracking process.

The hot regenerated catalyst is then circulated back to the reactor to complete its cycle.

Nuclear industry

Zeolites have uses in advanced reprocessing methods, where their micro-porous ability to capture some ions while allowing others to pass freely, allowing many fission products to be efficiently removed from nuclear waste and permanently trapped.

Equally important are the mineral properties of zeolites.

Their alumino-silicate construction is extremely durable and resistant to radiation even in porous form.

Additionally, once they are loaded with trapped fission products, the zeolite-waste combination can be hot pressed into an extremely durable ceramic form, closing the pores and trapping the waste in a solid stone block.

This is a waste form factor that greatly reduces its hazard compared to conventional reprocessing systems.

Zeolites are also used in the management of leaks of radioactive materials.

For example, in the aftermath of the Fukushima Daiichi nuclear disaster, sandbags of zeolite were dropped into the seawater near the power plant to adsorb radioactive caesium which was present in high levels.[9]

Biogas Industry

The German group Fraunhofer e.V. announced that they had developed a zeolite

substance for use in the biogas industry for long-term storage of energy at a density 4x more than water.[10]

Ultimately, the goal is to be able to store heat both in industrial installations and in small combined heat and power plants such as those used in larger residential buildings.

Heating and refrigeration

Zeolites can be used as solar thermal collectors and for adsorption refrigeration.

In these applications, their high heat of adsorption and ability to hydrate and dehydrate while maintaining structural stability is exploited.

This hygroscopic property coupled with an inherent exothermic (energy releasing) reaction when transitioning from a dehydrated to a hydrated form make natural zeolites useful in harvesting waste heat and solar heat energy.

Zeolites are also used as a molecular sieve in cryosorption style vacuum pumps.[11]

Detergents

The largest single use for zeolite is the global laundry detergent market.

This amounted to 1.44 million metric tons per year of anhydrous zeolite A in 1992.[

Construction

Synthetic zeolite is also being used as an additive in the production process of warm mix asphalt concrete.

The development of this application started in Germany in the 1990s.

It helps by decreasing the temperature level during manufacture and laying of asphalt concrete, resulting in lower consumption of fossil fuels, thus releasing less carbon dioxide, aerosols, and vapours. Other than that, the use of synthetic zeolite in hot mixed asphalt leads to easier compaction and, to a certain degree, allows cold weather paving and longer hauls.

When added to Portland cement as a pozzolan, it can reduce chloride permeability and improve workability.

It reduces weight and helps moderate water content while allowing for slower drying which improves break strength.[12]

When added to lime mortar, synthetic zeolites can act simultaneously as pozzolanic material and water reservoir.[13]

[Gemstones

Pollucite – rough and facetted.

Polished thomsonite
Thomsonites, one of the rarer zeolite minerals, have been collected as gemstones from a series of lava flows along Lake Superior in Minnesota and to a lesser degree in Michigan, U.S.A. Thomsonite nodules from these areas have eroded from basalt lava flows and are collected on beaches and by scuba divers in Lake Superior.
These thomsonite nodules have concentric rings in combinations of colors: black, white, orange, pink, red, and many shades of green. Some nodules have copper inclusions and rarely will be found with copper "eyes." When polished by a lapidary the thomsonites sometimes display a "cat's eye" effect (chatoyancy).[14]

[
Medical

Research into and development of the many biochemical and biomedical applications of zeolites, particularly the naturally occurring species heulandite, clinoptilolite and chabazite has been ongoing.[15]

Zeolite-based oxygen concentrator systems are widely used to produce medical-grade oxygen.

The zeolite is used as a molecular sieve to create purified oxygen from air using its ability to trap impurities, in a process involving the adsorption of nitrogen, leaving highly purified oxygen and up to 5% argon.

QuikClot brand hemostatic agent, which is used to stop severe bleeding,[16] contains a calcium-loaded form of zeolite.

Agriculture

In agriculture, clinoptilolite (a naturally occurring zeolite) is used as a soil treatment.

It provides a source of slowly released potassium.

If previously loaded with ammonium, the zeolite can serve a similar function in the slow release of nitrogen.

Zeolites can also act as water moderators, in which they will absorb up to 55% of their weight in water and slowly release it under the plant's demand.

This property can prevent root rot and moderate drought cycles.

What is Zeolite?

Powdered zeolite is an all natural mineral supplement made from zeolite, which is a negatively charged mineral formed from the fusion of lava and ocean water (1).

These zeolites are micronized into a powder for maximum absorption.

They can be easily consumed by mixing with any beverage.

Quality tested zeolite products have proven through numerous scientific studies to be 100% safe (2) and have been granted GRAS (Generally Recognized as Safe) status from the U.S. Food and Drug Administration (FDA) (3).

High quality zeolite products have been put through a purification and activation process to ensure the most clean and powerful product possible.

When seeking a out a powdered zeolite product I recommend that you only buy from companies that have done extensive peer reviewed scientific studies.

As a mineral, it is considered a food supplement and because of its enormous health generating properties it is also a health supplement.

What Does it do?

Through their strong negative magnetic charge and honeycomb like structure, zeolites draw in only positively charged toxins, trap them, and then safely remove them from the body (4).

According to the website www.liquidzeolite.org, consuming powdered zeolite can have these important health benefits (5):

1. Extremely safe and non-toxic

2. Removes heavy metals including mercury, cadmium, lead, arsenic, aluminium, and tin. It also removes radioactive metals like cesium and Strontium-90.

3. Removes pesticides, herbicides and dioxins by reducing the toxic load to the liver

4. Reduces viral load

5. Reduces absorption of nitrosamines, which are most commonly found in processed meats, and have been linked to pancreatic, stomach and colon cancer, as well as to Type II diabetes

6. Helps buffer body pH to a healthy alkalinity

7. Helps to buffer blood sugar

8. Helps reduce cancer risk

9. Improves nutrient absorption

10. Acts as a powerful antioxidant

11. Reduces symptoms of allergies

12. Increases immune system function by removing toxins, viruses, yeasts, bacteria and fungi which can depress immune function

13. Helps prevent premature aging

14. Extremely easy and pleasant to take

What are Zeolites ?

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 milliion 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.

Framework Structure

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.

Catalysis

Zeolites have the ability to act as catalysts for chemical reactions which take place within the internal cavities.

An important 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 can also serve as oxidation or reduction catalysts, often after metals have been introduced into the framework.

Examples are 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.

The shape of para-xylene means that it can diffuse freely in the channels of silicalite
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 by silicalite.

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.

Sodium Zeolite A, used as a water softener in detergent powder

Ion Exchange

The loosely-bound nature of extra-framework metal ions (such as in zeolite NaA, right) means that they are often readily exchanged for other types of metal when in aqueous solution.

This is exploited in a major way in water softening, where alkali metals such as sodium or potassium prefer to exchange out of the zeolite, being replaced by the "hard" calcium and magnesium ions from the water.

Many commercial washing powders thus contain substantial amounts of zeolite.

Commercial waste water containing heavy metals, and nuclear effluents containing radioactive isotopes can also be cleaned up using such zeolites.

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.

Zeolites in the UK

Zeolite science and technology has traditionally been very strong in the UK.

Partly this has been due to the scientific legacy of the late Professor Richard Barrer, the "father of zeolite science" who, during a career of over 50 years in various British universities, laid the foundations for the study of zeolites and discovered many of their important properties.

The prominence of the UK has also been associated with the strength of its chemical industry, particularly in areas where zeolites have applications, such as petrochemicals, detergents, fine chemical synthesis and nuclear processing.

Many British companies continue to have major R&D projects in these areas.

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