zeolites, types, nature, synthetic, processes, Deposits and properties;Physical characteristics of some naturally occurring zeolites; molecular sieves;Adsorption and related molecular sieving; zeolite catalysts

1. Lecture 5: ZEOLITES
A short series of lectures prepared for
the Second Levels of Geology, Tanta
University
2016- 2017
by
Hassan Z. Harraz
hharraz2006@yahoo.com

2. Notice
©2017 Prof. H.Z. Harraz
Notice – Information and figures in these slides
were collected from a wide range of sources
including but not limited to publications from the
USGS and pictures from internet sources dealing
with Minerals Data.
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3. ZEOLITES
• Some aluminosilicates lose water when heated to forms a porous structure with
a large surface area.
• These aluminosilicates are called ZEOLITES.
• Zeolites are also known as Permutits.

4. What are zeolites?
• Zeolites are hydrated aluminosilicate minerals made from interlinked
tetrahedra of alumina (AlO4) and silica (SiO4).
• In simpler words, they're solids with a relatively open, three-dimensional
crystal structure built from the elements aluminum, oxygen, and silicon,
with alkali or alkaline-Earth metals (such as sodium, potassium, and
magnesium) plus water molecules trapped in the gaps between them.
• Zeolites form with many different crystalline structures, which have large
open pores (sometimes referred to as cavities) in a very regular
arrangement and roughly the same size as small molecules.
• There are about 40 naturally occurring zeolites, forming in both volcanic
and sedimentary rocks; according to the US Geological Survey, the most
commonly mined forms include chabazite, clinoptilolite, and mordenite.
• Dozens more artificial, synthetic zeolites (around 150) have been designed
for specific purposes, the best known of which are zeolite A (commonly
used as a laundry detergent), zeolites X and Y (two different types of
faujasites, used for catalytic cracking), and the petroleum catalyst ZSM-5 (a
branded name for pentasil-zeolite).
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5. Zeolites
• The general chemical composition of a zeolite is:
Mn
x/nSi1-xAlxO2 · yH2O
Where M = e.g. Na+, K+, Li+, Ag+, NH4+, H+, Ca2+, Ba2+…
 This means that the Si/Al ratio is larger than 1 and that x is smaller than 0.5
 This rule is not always obeyed! (High aluminium e.g. Si/Al = 0.5)
 High silica and pure silica zeolites have been synthesized
Characteristics of zeolites:
1)Tectosilicates, i.e. three dimensional structure built from tetrahedra. Some silicon atoms have
been replaced by aluminium, i.e. the (Si+Al)/O = ½. (Tetrahedra usually denoted T-atoms).
2)Loewensteins rule imposes a limit to the amount of aluminium which may be substituted into
the framework: Number of Al-O-Al may be present in tectosilicates. This means that only half of
the silicon atoms may be substituted by aluminium.
3)Open framework structure built from TO4-tetrahedra, containing pores and voids. The structure
and porosity is periodic (i.e. crystalline materials). The pores have molecular dimensions.
4)Counter ions (cations) are present in order to compensate for the negative framework charge
created by aluminium substitution. The counter ions are situated in the pores and voids, and are
usually mobile.
5)In the voids and pores are also water molecules (zeolitic water). One measure of the porosity is
the amount of adsorbed water. The water molecules are also present in the pores and voids,
and may (in many cases) be removed by heating and readsorbed at lower temperatures.
6)Zeolites have a porous structure that can accommodate a wide variety of cations, such as Na+,
K+, Ca2+, Mg2+ and others.
7)These positive ions are rather loosely held and can readily be exchanged for others in a contact
solution.
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6. Name Structure Formulae
Analcime NaAlSi2O6·H2O
Chabazite (Ca0.5,Na,K)4[Al4Si8O24]•12H2O
Clinoptilolite (Na,K,Ca)2-3Al3(Al,Si)2Si13O36•12(H2O)
Hulandite (Ca,Na)2-3Al3(Al,Si)2Si13O36·12H2O
Natrolite Na2Al2Si3O10·2H2O
Phillipsite (Na,K,Ca)1-2(Si,Al)8O16•6(H2O)
Stilbite NaCa4(Si27Al9)O72·28(H2O)
Thomsonite NaCa2Al5Si5O20·6H2O
Mordenite (Ca,Na2,K2)Al2Si10O24•7(H2O)
Erionite (Ca,K2,Na2)2[Al4Si14O36]•15(H2O)
Ferrierite (Na,K)2Mg(Si,Al)18O36•9(H2O)
Some of the more common
mineral zeolites are
Microporous and
mesoporous materials
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7. Types of Zeolite
Zeolites are of two types:
1) Natural zeolite :
 Natural zeolite are non-porous.
 for example, natrolite ,Na2O.Al2O3.xSiO2.yH2O.
2) Synthetic zeolite :
 Synthetic zeolite are porous and posses get structure.
 They are prepared by heating together china clay, feldspar and soda ash.
 such zeolites possess higher exchange capacity per unit weight than
natural zeolites.

8. Zeolite stability fields
• All zeolites are formed in aqueous solution. The water molecules
act as “templates”, which are necessary in order to form a porous
structure.
• Most zeolites are formed from basic solution (exceptions are
fluoride syntheses) which favours four coordinated aluminium.
• Zeolites are formed in the low temperature end of the
hydrothermal synthesis (70- 300oC) due to the open structure and
high water content. Higher temperatures often gives denser
materials.
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9.  Inorganic, crystalline, aluminosilicate materials.
 Natural aluminosilicate minerals with crystal three-dimensional structure.
 Hydrated cations are located inside framework structure and weakly bound with structure.
 Zeolites have different dimensions of pores and channels responsible for their physical and
chemical properties.
 Chemically and thermally stable.
 Zeolite Formed from weathering, dissolution and reprecipitation in fine grained high silica
igneous rocks or sedimentary deposits derived from them- Generally looking for tuffs or glassy
volcanic flows.
 Zeolites transform to other minerals under weathering, hydrothermal alteration or metamorphic
conditions
 Advantages of these natural minerals are their large deposits on the Earth, easiness of
exploitation and mostly unnecessary treatment for practical application. The most important
deposits are in the United States, Mexico, Ukraine, Slovakia, Italy, Greece, Turkey, Russia,
Serbia, Romania, Bulgaria, Georgia, Armenia, Cuba and Croatia.. Currently, the world’s annual
production of natural zeolite is ~4 million tons.
 ~50 different minerals of zeolites are discovered in nature, but some of them have commercial
valuable. Many natural zeolites are synthesized in laboratory.
 Difference between natural zeolite minerals is manifested in content of hydrated cations which
occupied pores and channels, ratio of Si/Al in structure and number of water molecules
Deposits and properties
NATURAL ZEOLITES
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10. • Zeolites: Tectosilicates, a crystalline structure characterized by a framework of
linked tetrahedra, each consisting of four O atoms surrounded by a cation.
• This framework open cavities in the form of channels and cages. These
channels are usually occupied by H2O, but large enough to allow the passage of
guest species.
• Zeolites are the aluminosilicate members of the family of microporous solids
known as "molecular sieves" mainly consisting of Si, Al, O, and metals including
Ti, Sn, Zn, and so on.
• 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 eight 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.
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11. What are zeolites used for?
• The cage-like structure of zeolites makes them useful in all sorts of ways. One of the biggest everyday uses for
zeolites is in water softeners and water filters. In ion-exchange water softeners, for example, hard water (rich
in calcium and magnesium ions) is piped through a column filled with sodium-containing zeolites. The zeolites
trap the calcium and magnesium ions and release sodium ions in their place, so the water becomes softer but
richer in sodium. Many everyday laundry and dishwasher detergents contain zeolites to remove calcium and
magnesium and soften water so they work more effectively.
• Two other very common, everyday uses of zeolites are in odor control and pet litter; in both, the porous
crystalline structure of the zeolites helps by trapping unwanted liquids and odor molecules. This simple idea, so
effective in our homes, has much more important uses outside them: zeolites have proved extremely effective at
removing radioactive particles from nuclear waste and cleaning up soils contaminated with toxic heavy metals.
(Following the Fukushima nuclear disaster in Japan in 2011, rice farmers spread zeolites on their fields in an
attempt to trap any lingering radioactive contaminants). The many other uses for zeolites including concrete
production, soil-conditioners, and animal food.
 About 80% of Zeolite Use:
 Animal Feed
 Pet Liter
 Water Purification
 Odor Control
 Other Uses:
 Fungacide or pesticide carrier
 Oil absorbent / Desiccant
 Catalyst
 Horticulture
 Aquaculture (keeps water clean in the presence of overpopulation)
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12. What special properties do zeolites have?
Zeolites are very stable solids that resist the kinds of environmental conditions that challenge
many other materials. High temperatures don't bother them because they have relatively high
melting points (over 1000°C), and they don't burn. They also resist high pressures, don't
dissolve in water or other inorganic solvents, and don't oxidize in the air. They're not believed
to cause health problems through, for example, skin contact or inhalation, though in fibrous
form, they may have carcinogenic (cancer-causing) effects. Since they're unreactive and based
on naturally occurring minerals, they're not believed to have any harmful environmental
impacts. Although zeolites might sound incredibly boring, their stable and unreactive nature
isn't what makes them useful.
The most interesting thing about zeolites is their open, cage-like, "framework" structure and
the way it can trap other molecules inside it. This is how water molecules and alkali or alkaline-
Earth metal ions (positively charged atoms with too few electrons, sometimes called cations)
become a part of zeolite crystals-although they don't necessarily remain there permanently.
Zeolites can exchange other positively charged ions for the metal ions originally trapped inside
them (technically this is known as cation exchange) and, as Cronstedt found over 250 years
ago, they can gain or lose their water molecules very easily too (this is called reversible
dehydration). Zeolites have regular openings in them of fixed size, which let small molecules
pass straight through but trap larger ones; that's why they're sometimes referred to as
molecular sieves. Unlike natural zeolites, which occur in random forms and mixed sizes,
synthetic zeolites are manufactured in very precise and uniform sizes (typically from about 1μm
to 1mm) to suit a particular application; in other words, they're made a certain size to trap
molecules of a certain (smaller) size inside them.
Although all zeolites are aluminosilicates, some contain more alumina, while others contain
more silica. Alumina-rich zeolites are attracted to polar molecules such as water, while silica-
rich zeolites work better with nonpolar molecules.
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13. Physical characteristics of some naturally occurring zeolites
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14. Physical characteristics of some naturally occurring zeolites
Zeolites are microporous, aluminosilicate Tectosilicates minerals commonly used as commercial
adsorbents and catalysts.
A major application of the zeolites in catalysis: Zeolite is in acid catalyzed reactions such as
alkylation, acylation, electrophilic aromatic substitution, cyclization, isomerization and condensation.
Actually a family of related mineral structures with very high internal surface area:
 It can act as a molecular sieve by grabbing some small molecules while letting larger ones pass
High surface area provides a big surface area to stage reactions – makes a great catalyst.
Zeolites have relatively large CEC and are useful for a variety of environmental remediation
processes.
 APPLICATION of natural zeolites is based on or more of the following properties:
 cation exchange
 ion-exchangers
 Adsorption and related molecular sieving
 water softeners
 dehydration and rehydration
 biological activity
 Excellent catalysts /catalytic
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15.  the ability to exchange inherent cations for other cations on a basis of ion
selectivity
 high cation exchange capacity for heavy 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, aluminium, chromium and others. Some natural zeolites are applicable
in industries such as mining, electroplating and electronics. Giant industrial
houses, like IBM, have deployed this application for treatment of
wastewater containing heavy metals.
 selectivity for ammonium cations, the natural zeolites lower the level of
ammonium in wastewaters and sewages to non-toxic, acceptable levels.
The zeolite beds can be regenerated and recycled indefinitely.
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Cation exchange
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16. Adsorption and related molecular sieving
 The adsorption process is fully reversible and of purely physical nature. The structure
of the zeolite is unchanged during the adsorption process and its later regeneration.
 The adsorption on molecular sieves is therefore dependent on the following physical
molecular properties:
 Size and Shape; molecules or ions larger than the pore opening of the zeolite can
not be adsorbed, smaller molecules or ions can.
 Molecular Polarity; due the charge on outer and inner zeolitic surface particle,
molecules with large polarity or polarizability can be adsorbed preferentially under
identical conditions.
 this property is used for selective absorption of organic molecules and for absorption
of radioactive ions (absorber of Sr and Cs radioisotopes in the nuclear industry and
for clean up of nuclear accidents - applied in the Chernobyl disaster).
 adsorption process on zeolite is used to remove polar H2O, H2S, and CO2 from natural
gas and developed a zeolite-adsorption process for purifying methane produced in a
landfill.
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17. Adsorption Ion exchange Catalytic activity
Adsorption in zeolites is significantly different from adsorption in
e.g. silica gel or active coal, which have a broad size distribution of
pore sizes, and where the size of the pores are in the range of 10 nm.
In zeolites the porosity is determined by the crystalline structure, i.e.
the pores are arrnged in a regular fashion with only one (or a few)
discrete pore sizes. Also the pores have molecular dimensions.
The implication of this is the use of zeolites as adsorbants and
molecular sieves.
Mainly used for water adsorption (very low equilibrium water
vapour pressure) Gas (hydrogen?) storage materials
Molecular sieving effect due to size limitation imposed by
framework structure and cation size and position.
Also weaker interactions:
N2-O2 separation
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18. Dehydration and rehydration
 Natural zeolites may hold water up to 60% of their weight due to a
high porosity of the crystalline structure. Water molecules in the pores
could be easily evaporated or reabsorbed without damage to such
structures.
 Zeolites assure a permanent water reservoir, providing prolonged
moisture during dry periods; they also promote a rapid rewetting and
improve the lateral spread of water into the root zone during
irrigation. This results in a saving in the quantity of water needed for
irrigation.
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19. Biological activity
natural zeolite has been shown to exhibit diverse biological activities
and has been used successfully for the treatment in medical therapy
 promotes better plant growth by improving the value of fertilizer, helps
preventing the plant from burning, that can be caused by over use of
fertilizer, by trapping and slowly releasing valuable nutrients
 as additive in concentrated animal growing facilities improve feed
conversion, reduce airborne ammonia up to 80%, act as a mycotoxin
binder, and improve bone density, it can be used in general odour
elimination for all animal odours
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20.  modifying the surface of clinoptilolite with long-chain quaternary amines
allowed it to adsorb benzene, toluene, and xylene in the presence of water
 surface modified natural zeolites remove toxic compounds from animal food
 natural zeolite can be treated further with additional amine to produce
anion exchangers capable of taking up chromate, arsenate, selenate, and
other metal oxyanions from aqueous solutions
Surface modification of natural zeolites
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21. Nanoporous Materials
• Nanoporous materials consist of a regular organic or inorganic
framework supporting a regular, porous structure.
• Pores are by definition roughly in the nanometre range, that is
between 1x10-7 and 0.2x10-9 m.
Subdivisions:
• Nanoporous materials can be subdivided into 3 categories, set out
by IUPAC:
Microporous materials: Such as Zeolites, 0.2–2nm
Mesoporous materials: 2–50nm
Macroporous materials: 50–1000nm
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22. USESOFZEOLITES AS MOLECULAR SIEVES
- Used as molecular sieves where they can retain molecules that can fit into their
molecular cavities.
- Is to separate straight-chain hydrocarbons from branched-chain hydrocarbons
in gas chromatography.
AS ION EXCHANGERS
- Used in exchange (ions) columns where the ions in zeolites can be exchanged with other ions.
-This process needs Soften Hard Water. When hard water containing Ca2+ and Mg2+ ions will
pass through zeolite, then the Ca2+ and Mg2+ ions will be replaced with Na2+ ions
Na2Z + Ca2+ (aq) <--> CaZ + 2Na+
AS CATAYLST
- Have the ability to act as catalyst for chemical reactions
which take place within internal cavities.
- Used in many organic reactions

23. Zeolite Process

24. Process
 For softening of water by zeolite process,hard water is percolated at a
specified rate through a bed of zeolite, kept in a cylinder.
 The hardness causing ions(Ca2+ ,Mg2+ ,etc.) are retained by the zeolite as
CaZe and MgZe ; while the outgoing water contains sodium salts.
Reactions
Na2Ze + Ca(HCO3)2  CaZe + 2NaHCO3
Na2Ze + Mg(HCO3)2  MgZe + 2NaHCO3
(Zeolite) (Hardness)
Na2Ze + CaCl2 (or CaSO4)  CaZe + 2NaCl
(or Na2SO4)
Na2Ze + MgCl2 (or MgSO4)  MgZe +
2NaCl(or Na2SO4)
(Zeolite) (Hardness)

25. Regeneration
 After some time, the zeolite is completely is completely converted into calcium
and magnesium zeolite and it ceases to soften water, i.e., it gets exhausted.
 At this stage, the supply of hard water is stopped and the exhausted zeolite is
reclaimed by treating the bed with a concentrated (10%) brine (NaCl) solution.
CaZe (or MgZe) + 2Nacl  Na2Ze + Cacl2 (or MgCl2)
(Exhausted zeolite) (Brine) (Reclaimed (Washings)
zeolite)
 The washing (containing Cacl2 and MgCl2 ) are led to drain and the
regenerated zeolite bed thus-obtained is used again for softening
purpose.

26. Limitations of process:
1. If the supply of water is turbid, the suspended matter must be removed (by
coagulation, filtration, etc.), before the water is admitted to the zeolite bed ;
otherwise the turbidity will clog the pores of zeolite bed, thereby making it
inactive.
2. If water contains large quantities of coloured ions such as Mn2+ and Fe2+,they
must be removed first, because these ions produce maganese and iron zeolite,
which cannot be easily regenerated.
3. Mineral acids, if present in water, destroy the zeolite bed and,therefore, they
must be neutralised with soda, before admitting the water to the zeolite
softening plant.

27. Advantages of process
1. It removes the hardness almost
completely and water of about 10 ppm
hardness is producted.
2. The equipment used is compact,
occupying a small space.
3. No impurities are precipitated, so there
is no danger of sludge formation in the
treatedwater at a later stage.
4. The process automatically adjust itself
for variation in hardness of incoming
water.
5. It is quite clean.
6. It requires less time for softening.
7. It requires less skill for maintenance as
well as operation.
Disadvantages of process
1. The treated-water contains more sodium
more sodium salts than in lime-soda process.
2. The method only replaces ca2+ and Mg2+ ions,
but leaves all the acidic ions ( like HCO3
- and
CO3
2-) as such in the softened water. When
such softened water (containing NaHCO3 ,
Na2CO3 ,etc.) is used in boilers for steam
generation, sodium bicarbonate decomposes
producing CO2 , which causes corrosion ;and
sodium carbonate hydrolysis to sodium
hydroxide, which causes caustic
embrittlement.
3. High turbidity water cannot be treated
efficiently by this method, because fine
impurities get deposited on the zeolite bed,
there by reacting problem for its working.

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