ازالة المواد البترولية من المياه باستخدام الزيوليت الطبيعى

Chemical compositions[/u
[u]zeolite
High selectional absorption
Cation exchange
Content of biogenous and trace elements
Reversible dehydration and hydration

Sio2=73.42%
Al2o3=12.43%
Fe2o3=1.05%
Feo= 0.31%
Tio2=0.12%
Cao= 2.94%
Mgo=0.85%
Mno=0.042%
P2o5=0.04%
Na2o=0.24%
K2o=2.61%
So3=0.03%
S=2.79%
H2o+=3.94%
H2o-=5.12%
Sn=2.0ppm
Hg=0.01ppm
Cu=10.0ppm
Pb=32.0ppm
Zn=88ppm
Ni=1ppm
Co=1ppm
Cd=1ppm
As=20ppm
Ba=850ppm

Exchange capacity of zeolite raw material
Partial=0.7mol/l
Total = 1.4mol/l
Average mineral composition of zeolite raw materials
Clinoptilolite=55-60%
Am.glass = 15-18%
Potassium feldspar=11-13%
Silica= 2-3%
Cristobalite=4-8%
Mica=1%
Other minerals=2%



Average chemical composition of zeolite raw materials
Sio2=70%
Al2o3=12%
Tio2=0.2%
Fe2o3=1.0%
Mgo=0.8%
Cao=3.0%
Na2o=1.0%
K2o=2.5%
H2o at 350c=3%
Porosity=30-40%
Absorption capacity=15-20%
Exchange capacity=1.3mol/kg/l

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.

Zeolites are widely used in industry for water purification, as catalysts

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 areanalcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite, and stilbite.

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

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

the pores in many zeolites are not cylindrical.

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 thehydrothermal method is very stable. Also 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

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

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.

Molecular Sieve Effect

Molecules which can penetrate the pore system are usually strongly adsorbed in the micropores.

This strong adsorption is due to a significant decrease of the interaction potential (Lennard-Jones) when two surfaces are brought closely together as in microporous materials.

The potentials on top of the surfaces overlap which leads to a decrease of the potential

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.

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.



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.


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.

Zeolite usually contain cations (e.g., Na+, K+, or NH4+) after the synthesis.
These cations are required to balance the negative net-charge caused by

trivalent aluminum cations which are coordinated tetrahedrally by oxygen anions.

By exposing a sodium containing zeolite to a solution containing other cations, the sodlium ions can be exchanged by these other cations provided they are not excluded from the pores due tho their size (including the water molecules coordinating the respective cations).

Zeolites thus can be used as ion-exchangers to remove cationic species from aqueous solutions by replacing them by sodium cations.

This principle is used for example to soften water where Ca2+ and Mg2+ are removed from the water.

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

Acidity

As already mentioned protonated zeolites have acidic properties.

The protons which balance the negative charge of a zeolite framework are not strongly bound to the framework and are able to move within the pores and react with molecules which penetrate into the zeolite pore system.

A protonated zeolite thus can act as a Bronsted acid. Furthermore, Lewis acidity can be caused by cations within the pores.

ODOR PH CONTROL ABSORBENT INDUSTRIAL ZEOLITE

Natural Zeolites are the least-known treasures for environmental pollution control, separation science and technology.

Natural zeolites are volcanic minerals with unique characteristics. Their chemical structure classifies them as hydrated aluminum silicates, comprised of hydrogen, oxygen, aluminum, and silicon, arranged in an interconnecting lattice structure.

The arrangement of these elements in a zeolite crystal gives rise to a honeycomb framework with consistent diameter connecting channels that vary in size depending on the type of zeolite mineral.

This unique structure makes zeolites different from "other" aluminum silicates (kaolin, bentonite, etc.) due to the following special properties:

Oil Absorbents (Zeolite granules can be used as oil absorbents. )

• Gas adsorption: the ability to selectively adsorb molecules of gases and vapors;
• Water absorption/desorption: the ability to reversibly absorb/desorb water without any chemical or physical change in the zeolite matrix;

• Ion exchange: the ability to exchange inherent cations for other cations on a basis of ion selectivity.

• Oils, Acids, Hazardous Materials, Animal Fluids, Grease, Cooking Oils, Brake Fluid, Liquid Pesticides, Antifreeze, Power Steering Fluids, Transmission Fluid, Gasoline, Diesel Fuel, Battery Acids, Chemical Spills, Solvents, Paint Thinner, Petroleum Distillates, Hydraulic Fluid, Bio-Hazardous Waste, etc.

WASTEWATER TREATMENT AND SEWAGE

Ammonia is a major issue for the treatment of municipal wastewater.

Ammonia levels in municipal wastewaters can be reduced to 10-15 ppm through traditional primary and secondary treatment facilities.

Final circulation in the tertiary treatment stage is accomplished with polishing filters containing Laumontite, a popular form of natural zeolite.

The zeolites lower the level of ammonium to non-toxic, acceptable levels.

The zeolite beds can be regenerated and recycled indefinitely.

Significant properties include:

• High cation exchange capacity

• Selectivity for ammonium cations

• Regeneration capability

The size of zeolite used in wastewater polishing filter columns varies according to the design. A size specification of -20 to +35 Tyler mesh is typical for this application.

METALS REMOVAL - MINE WASTEWATER TREATMENT

Zeolites are highly selective scavengers of a variety of metal cations that can be removed from liquid effluents through the process of ion-exchange.

These cations include lead, silver, cadmium, cobalt, zinc, copper, mercury, magnesium, iron, aluminum, chromium and others. Laumontite water polishing treatment systems are applicable in industries such as mining, electroplating and electronics.

Significant properties include:

• High cation exchange capacity
• Selectivity for many metals
• Low cost relative to resins or synthetic zeolites
• Capacity for regeneration

POLLUTION CONTROL

Natural zeolites are an adsorbent of choice for many cost effective air pollution control technologies treating the hazardous air pollutants (HAP) and listed volatile organic compounds (VOC).

The need for technologically improved air purification systems has been indicated by keen client interest in the use of zeolites in controlling indoor air pollutants or "sick building syndrome".

Existing filtration systems typically contain activated carbon as the adsorbent media.

Because most grades of activated carbon contain large internal pores, they tend to trap a wide variety of larger molecules.

Zeolites, on the other hand, contain a very small internal pores, in all cases from 3 to 5 angstroms.

For this reason zeolite is a highly selective adsorbent of specific gas-phase molecules and elements.

Many of the identified indoor air pollutants, including formaldehyde, chloroform, ammonia and carbon monoxide, are in a size range that is most effectively sieved by zeolite.

Many promising zeolite and zeolite/carbon air purification and odor controlling systems are being developed to meet the need.

Beneficial qualities include:

• Selectivity for pollutant gases of concern

• Inexpensive relative to other molecular sieves

MODIFIED NATURAL ZEOLITES

A variety of products have been formulated wherein zeolites are pelletized and/or activated for utilization in specific applications.

Some of these products include:

• Manganese coated zeolites used in home water softening and purification units

• Air dryers for compressed air brake systems

• Insulated window desiccants

• General packaging and food desiccants

• Moisture absorbents in automotive mufflers

• Moisture absorbents in refrigeration systems


zeolite particulate can be dispersed on water to encapsulate surface oil where it can be efficiently “skimmed” after it has been encapsulated.

The surface oil or the coagulated mass can be allowed to settle to the bottom where it will not leach out into the water.

Reportedly, the zeolite is not flammable after absorbing the oil or gas. After certain preparation and activation a zeolite can be made to float on water and can be used for marine and inland waterway oil spills cleanup.

Water Softener

Zeolites are minerals that are microporous cage-like molecules.Theses cages are interconnected forming a framework with many cavities and channels.

The zeolite is the main ingredient in a water softener and is also called resin.

A typical water softener is a mechanical device that is plumbed into your home's water supply system.

All water softeners use the same operating principle, trading minerals in a process called “ion exchange.”

The zeolite /resin carries a negative charge and the offending minerals carry a positive charge.

The positive charged mineral ions exchange places with the weaker positively charged sodium ions and are held fast in the zeolite until they themselves are knocked off during the recharge cycle.

After recharging, the zeolite is cleaned of the bad minerals and reunited with its slightly positive friend the sodium ion and ready to attract more minerals in the water stream.

The essential part of a water softener is the mineral tank that holds the negatively charged resin/zeolite beads.

Calcium, magnesium and sodium (the minerals that make your water hard) carry positive charges with sodium holding the weaker charge of the three.As the water moves through the tank, the minerals will displace the weaker charged sodium ions and become entrapped in the zeolite.

If all is working correctly, after the zeolite bed is completely saturated, the unit will recharge itself with a strong brine (salt) solution.

The force and strength of the solution knocks the minerals off the beads and reseats the sodium ions back into the zeolite beads.


Wastewater Treatment

Removal of Heavy Metals

Many toxic heavy metals have been discharged into the environment as industrial wastes, causing serious soil and water pollution. Pb+2, Cu+2, Fe+3, and Cr+3 are especially common metals that tend to accumulate in organisms, causing numerous diseases and disorders.

They are also common groundwater contaminants at industrial and military installations.

Numerous processes exist for removing dissolved heavy metals, including ion exchange, precipitation, phytoextraction, ultra filtration, reverse osmosis, and electro dialysis.

The use of alternative low-cost materials such as zeolites as potential sorbents for the removal of heavy metals has been emphasized recently.

Various treatment processes are available, among which ion exchange is considered to be cost-effective if low-cost ion exchangers such as zeolites are used.

The structures of zeolites consist of three-dimensional frameworks of SiO4 and AlO4 tetrahedra.

The aluminum ion is small enough to occupy the position in the center of the tetrahedron of four oxygen atoms, and the isomorphous replacement of Si4+ by Al3+ produces a negative charge in the lattice.

The net negative charge is balanced by the exchangeable cation (sodium, potassium, or calcium).

These cations are exchangeable with certain cations in solutions such as lead, cadmium, zinc, and manganese.

The fact that zeolite exchangeable ions are relatively innocuous (sodium, calcium, and potassium ions) makes them particularly suitable for removing undesirable heavy metal ions from industrial effluent waters.