ABSTRACT
The removal of Pb(II) ions from aqueous model solution using zeolite has been
investigated under different operational parameters like heavy metal ion
concentration, adsorbent amount and particle size. The zeolite used was
synthesized and characterized using SEM and XRD analysis. The equilibrium
adsorption capacity of zeolite used for lead removal were measured and the
experimental data analyzed by means of Freundlich and Langmuir isotherm
models. The adsorption efficiency of Zeolite in removing Pb2+ ions at room
temperature and 60 minute agitation time at pH<10 was 98%. The results also
show that the adsorbent with the lowest particle size of 53.6μm had the highest
adsorption efficiency(98.33%) The concentration of metal ions were measured by
Atomic Absorption Spectroscopy (AAS). Overall, the results showed that synthetic
zeolite could be considered as a potential adsorbent for lead removal from aqueous
solutions.
TABLE OF CONTENTS
Title Page .. .. .. .. .. .. .. .. .. .. .. i
Certification .. .. .. .. .. .. .. .. .. .. ii
Dedication …. .. .. .. .. .. .. .. .. .. iii
Acknowledgment .. .. .. .. .. .. .. .. .. iv
Table of Contents .. .. .. .. .. .. .. .. .. v
List of Tables .. .. .. .. .. .. .. .. .. .. viii
List of Figures .. .. .. .. .. .. .. .. .. .. ix
List of Symbols .. .. .. .. .. .. .. .. .. .. x
List of Abbreviation …. .. .. .. .. .. .. .. .. xi
Abstract .. .. .. .. .. .. .. .. .. .. .. xii
CHAPTER ONE: INTRODUCTION
1.0 Background of Study .. .. .. .. .. .. .. .. 4
1.1 Heavy Metal Toxicity.. .. .. .. .. .. .. .. 4
1.2 Methods of Heavy Metal Removal .. .. .. .. .. .. 5
1.3 Types of Heavy Metal Adsorbents . .. .. .. .. .. 5
1.3.1 Zeolite .. .. .. .. .. .. .. .. .. .. 6
1.3.2 Use of Synthetic Zeolite for Wastewater Treatment .. .. .. 8
1.3.3 Mechanisms of Heavy Metal Removal from Industrial Waste Water .. .. 10
1.4 Adsorption .. .. .. .. .. .. .. .. .. .. 11
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1.4.1 Adsorption Isotherms .. .. .. .. .. .. .. .. 12
1.5 Statement of the Problem .. .. .. .. .. .. .. .. 13
1.6 Objective of Study .. . .. .. .. .. .. .. .. 14
1.7 Justification of the Study .. .. .. .. .. .. .. .. 14
CHAPTER TWO
2.0 Literature Review .. .. .. .. .. .. .. .. .. 15
2.1 A Review of Zeolite Types used as Adsorbents .. .. .. .. 15
2.2 Adsorption of Heavy Metals using Zeolite .. .. .. .. .. 23
CHAPTER THREE
3.0 Reagents .. .. .. .. .. .. .. .. .. .. 29
3.1 Instrument/Apparati .. .. .. .. .. .. .. .. 29
3.2 Methods .. .. .. .. .. .. .. .. .. .. 30
3.2.0 Zeolite Synthesis .. .. .. .. .. .. .. .. .. 30
3.2.1 Preparation of Synthesis Gel .. .. .. .. .. .. .. 30
3.2.2 Crystallization Gel .. .. .. .. .. .. .. .. 30
3.2.3 Crystallization .. .. .. .. .. .. .. .. .. 31
3.2.4 Product Recovery …. .. .. .. .. .. .. .. 31
3.2.5 Product Characterization .. .. .. .. .. .. .. 31
3.2.6 Heavy Metal Determination .. .. .. .. .. .. .. 31
3.3 Freundlich and Langmuir Models .. .. .. .. .. .. 32
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CHAPTER FOUR
4.0 Results and Discussion .. .. .. .. .. .. .. .. 35
4.1 Synthesis of Adsorbent .. .. .. .. .. .. .. .. 35
4.2 Characterization of Adsorbent .. .. .. .. .. .. .. 36
4.3 Adsorption of Heavy Metal Ion .. .. .. .. .. .. .. 37
4.3.1 Effect of Heavy Metal Ion Concentration .. .. .. .. .. 37
4.3.2 Effect of Adsorbent Dosage .. .. .. .. .. .. .. 40
4.3.3 Effect of Particle Size on Adsorption .. .. .. .. .. .. 41
4.4 Adsorption Isotherms .. .. .. .. .. .. .. .. 43
CHAPTER FIVE
5.0 Conclusion .. .. .. .. .. .. .. .. .. .. 47
REFERENCES
APPENDIX
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CHAPTER ONE
INTRODUCTION
In developing countries, rapid growth of urbanization and industrialization
has generated large volume of waste containing toxic heavy metals. Heavy metal
contamination exists in aqueous waste water streams of many industries such as
metal plating facilities, mining operations, tanneries etc1. Environmental pollution
due to these toxic metals have been of major concern to environmental engineers;
the ions from these heavy metals cause damage to humans e.g. cadmium poisoning
causes acute chronic disorders such as renal damage and hypertension, problem in
Haemoglobin synthesis, kidney, gastrointestinal tract, joints and reproductive
disorders. Acute or chronic dosage results in damage of the nervous system2.
Within the body, lead is absorbed and stored in the bones, blood, and tissues. It
does not stay there permanently, rather it is stored there as a source of continual
internal exposure 3. As time goes by, the bones demineralize and the internal
exposures may increase as a result of larger releases of lead from the bone tissue.
There is also concern that lead may mobilize from the bone among women
undergoing menopause4. Post menopausal women have been found to have higher
blood lead levels than pre-menopausal women5.
Lead poisoning occurs if a person is exposed to very high levels of lead over
a short period of time. When this happens, a person may feel abdominal pain,
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constipated, tired, headachy, irritable, loss of appetite, memory loss, pain or
tingling in the hands and/or feet and weak.
Generally, lend affects children more that it does adults. Children tend to
show signs of sever lead toxicity at lower levels than adults. Neurological effects
and mental retardation have also occurred in children whose parents may have jobrelated
lead exposure6. The health effects from prolonged exposure to lead
included abdominal pain, depression, forgetfulness among others. Also, the
Department of Health and Human Services (DHHS), Environmental Protection
Agency (EPA), and the International Agency for Research on cancer (IARC) have
determined that lead is probably cancer-causing in human7.
Exposure to chromium results in asthma, chronic bronchitis, chronic
irritation, chronic pharyngitis, chronic rhinitis, congestion and hyperemia, polyps
of the upper respiratory tract, tracheobronchitis, and ulceration of the nasal mucosa
with possible septal perforation though zinc is considered to be relatively nontoxic,
particularly if taken only. However, manifestations of overt toxicity symptoms
(nausea, vomiting, epigastric pain, lethargy and fatique) will occur with extremely
high intakes 8.
Arsenic and mercury are other heavy metals that are highly toxic even on
minimal exposure. Arsenic is classified as a metalloid usually found combined
with oxygen, chlorine, and sulphur. Exposure to arsenic include sore throat and
15
irritated lungs as much as skin effects. Longer exposure at lower concentrations
can lead to circulatory and peripheral nervous disorders as well as high risk of lung
cancer 9. Health effect of mercury include hydrargyria or mercurialism. Elemental
mercury does cause damage by blocking blood vessels, damage to the brain,
kidneys and lungs 10. Mercury poisoning can result in several diseases, including
acrodynia (pink disease)11, Hunter–Russell syndrome and minamata disease
chronic exposure to excessive manganese levels can lead to variety of psychiatric
and motor disturbances, termed manganism. Generally, exposure to ambient
manganese air concentrations in excess of 5 micrograms Mn/m3 can lead to Mninduced
symptoms 12.
Adsorption of these metal ions from industrial effluent before discharged
into the environment is of great importance so as to control the risk and
endangerment they cause. To achieve this i.e. elimination or adsorption of heavy
metals from industrial effluents, adsorbents such as zeolites are employed for
effective adsorption of heavy metals from waste water or industrial effluents so as
to free the effluents of the heavy metal ions such as Pb ions, Cd ions, Cr ions etc
before they are discharged or released into the environment13.
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1.0 BACKGROUND OF STUDY
1.1 HEAVY METAL TOXICITY
Heavy metal is a metal with a fairly high relative atomic mass, and specific
gravity greater than 5.0 especially those that are significantly toxic (e.g., lead,
cadmium, mercury).They persist in the environment and can accumulate in plant
and animal tissues. Mining and industrial wastes and sewage sludge are potential
sources of heavy metal pollution16.
With the rapid development of industries such as metal plating facilities,
mining operations, fertilizer industries, tanneries, batteries, paper industries and
pesticides etc, heavy metal wastewaters are directly or indirectly discharged into
the environment increasingly, especially in developing countries such as Nigeria.
Unlike organic contaminants, heavy metals are not biodegradable and tend to
accumulate in living organisms and many heavy metal ions are known to be toxic
or carcinogenic. Toxic heavy metals of particular concern in the treatment of
industrial waste waters include zinc, copper, nickel, mercury, cadmium, lead and
chromium.
Now-a-days heavy metals are the environmental priority pollutants and are
becoming one of the most serious environmental problems. So these toxic heavy
metals should be removed from industrial waste water or effluents to protect the
people and the environment.
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1.2 METHODS OF HEAVY METAL REMOVAL
Many methods that are been used to remove heavy metal ions include
chemical precipitation17, sulfide precipitation18 investigated pyrite and synthetic
iron sulphide for removal of lead and copper. Ion-exchange processes have been
widely employed to remove heavy metals from effluents due to their many
advantages, such as high treatment capacity, high removal efficiency and fast
kinetics19-21.
Adsorption additives22, tannic acids23, magnesium24, surfactants25 and
activated carbon composite could be effective adsorbents for heavy metals.
Agricultural waste materials as potential adsorbent for sequestering heavy metal
ions from aqueous solutions26, membrane filtration27, nanofiltration (NF) used for
nickel28,29 performed a new working system of investigate the removal of
hexavalent chromium ions using electrolysis electrochemical treatment
technologies, etc30 studied the performance of an electrochemical treatment
technologies system with aluminum electrodes for removal of metal ions from
water.
1.3 TYPES OF HEAVY METAL ADSORBENTS
Various types of adsorbent used in heavy metal removal are activated
carbon31, clay minerals32,33, biomaterials34, zeolites35,36, and some industrial solid
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wastes37,38 have been widely used as adsorbents for adsorption of ions and organics
in waste water treatment.
Adsorption is now recognized as an effective and economic method for
heavy metal removal in waste water treatment. The adsorption process offer
flexibility in design and operation and in many cases will produce high-quality
treated effluent. In addition, because adsorption is sometimes reversible,
adsorbents can be regenerated by suitable desorption process. In this work, zeolite
will be used as the adsorbent in removal of lead ions from simulated waste water.
1.3.1 Zeolites
Zeolites are microporous, alumino silicate minerals commonly used as
commercial adsorbents39. Some zeolites occur naturally while others are synthetic.
Zeolite has a three-dimensional structure with pores.
The zeolite history began with the discovery of stilbite by Crönstedt, a Swedish
mineralogist in year 1756. Upon heating the zeolite released occluded water, which
gave the materials their general name, zeolite, after the Greek words, “ξειv” (zeo) ,
to boil, and “λιϑoς” (lithos), stone. A representative empirical formula of a zeolite
is
M2/nO . Al2O3 . xSiO2. yH2O
where M represents the exchangeable cation of valence n. M is generally a Group I
or II ion, although other metal, non-metal and organic cations may also balance the
19
negative charge created by the presence of Al in the structure. The framework may
contain cages and channels of discrete size, which are normally occupied by water.
It consists of silicon, aluminium and oxygen ions. The silicon ions are neutrally
charged in the crystal structure. Aluminium ions create negative places. To keep
the cargo in balance, a counter ion (Na+, K+) or a proton (H+) is present in the
pores. One type of zeolite have just as large pores through the entire crystal
structures. All natural zeolites contain aluminium and are hydrophilic in nature40.
Zeolites are widely used in industries for water purification, as catalysts, for
the preparation of advanced materials and in nuclear processing. Their biggest use
is in the production of laundry detergents. Zeolites are also used in medicine and in
agriculture.
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 Analcine, Chabazite, Clinoptiloite,
Heulandites, 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
ground water. Zeolites also crystallize in post-depositional environments over
periods ranging from thousands to millions of years in shallow marine basins.
20
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.
1.3.2 Use of Synthetic Zeolite for Wastewater Treatment
The use of synthetic zeolite for the environmental protection is stimulated by
its good physico-chemical properties e.g. selective sorption,its non-toxic nature
and availability. A great deal of research on zeolite has focused on a wide range of
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applications including waste water treatment or purification with emphasis on the
ammonia and heavy metal removal41, removal of radioactive 137Cs and 90Sr from
low-level waste streams of nuclear installations42, and recently also for the removal
of organic pollutants, like hydrochloroflourocarbons (HCFCs) from petroleum
products from water43. They can be used as barriers to contaminant migration or as
binders in waste solidification systems.
There are increasing demands for healthier environment, with the emphasis
on high-quality drinking water and on the removal of contaminants from industrial,
agricultural and municipal waste waters. Most technologies using zeolites for water
and soil purification are based on the unique cation-exchange behaviour of zeolites
through which dissolved cations are removed from water or soil by exchanging
with cations in zeolites exchange sites. The most common cation in waters
affecting human and animal health is NH4
+. It can be replaced with biologically
accepted cations, like Na+, K+ or Ca2+ in the zeolite. Ammonia removal is very
important to prevent oxygen depletion and algae bloom and due to its extreme
toxicity to most fish species44. Additionally, it has detrimental effects on
disinfection of water supplies and corrosive action on certain metals and
construction materials. Nitric oxides, nitrates and ammonia/ammonium are very
soluble in water and can quickly end up in ground and drinking water. Some
naturally occurring zeolite such as chabazite and clinoptilolite showed the best
22
results for ammonia removal. Heavy metals are well known for their toxicity and
their disposal is a significant industrial waste problem. Pb2+, Cu2+, Fe3+, Cd2+ and
Cr3+ are especially common metals in industrial wastes that tend to accumulate in
organisms, causing numerous diseases and disorders45.
1.3.3 Mechanisms of Heavy Metal Removal from Industrial Waste Water
The contamination with heavy metals exists in aqueous waste streams of
many industries such as metal plating industries, dyes and textile industries, mining
operations etc. The amount of heavy metal waste is increasing on yearly basis; they
tend to accumulate in living organisms. Treatment processes for the removal of
heavy metals from waste water include coagulation, carbon adsorption, ion
exchange, reverse Osmosis etc46. The sorption processes are the most attractive
since their application is simple, and they require mild operating conditions. The
limiting factor could be the regeneration of the sorbing materials.
The sorption of heavy metals by zeolites is a complex process because of the
inner and outer charged surfaces, imperfections on the surfaces, mineralogical
heterogeneity among others that can also contribute to the overall sorption
capacity. The extensive research of adsorption isotherms revealed that ion
exchange or chemisorptions on zeolites governs the immobilization of metal
cations especially in natural zeolites tuffs47.
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Following the ion exchange mechanism, ions present in the pores of zeolite
crystalline lattices, like Na+, K+, Ca2+ etc are substituted by metal ions from the
solution. The chemisorption always results in the formation of stable inner-sphere
or outer-sphere complexes, where functional groups on the zeolite framework
(mainly OH-) form strong chemical bonds with the metal ions. In clinoptilolite and
the majority of zeolites, ion-exchange processes generally dominate over
chemisorption. The sorption of heavy metal by the zeolite is directly related to the
charge of the zeolite framework, i.e the quantity of aluminium present in the
zeolite framework, the nature and concentration of the cationic species, the size
and distribution of zeolite tuff particles, the solvent and the temperature.48
1.4 ADSORPTION
Adsorption refers to the adhesion of atoms, ions or molecules from a gas,
liquid or dissolved solid to a surface 49. This process creates a film of the adsorbate
on the surface of the adsorbent. This process differs from absorption in which a
fluid (the absorbate) permeates or is dissolved by a liquid or solid (the absorbent)50.
Adsorption is a surface-based process while absorption involves the whole volume
of the material. The term sorption encompasses both processes, while desorption is
the reverse of it. Adsorption is a surface phenomenon. Adsorption is present in
many natural, physical, biological and chemical systems, and is widely applied in
industrial processes such as activated charcoal, capturing and using waste heat to
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provide cold water for air conditioning and other process requirements (adsorption
chillers), synthetic resins and water purification. The word “adsorption” was
coined in 1881 by German physicist Heinrich Kayser 51.
1.4.1 Adsorption Isotherms
Adsorption is usually described through isotherm, that is, the amount of
adsorbate on the adsorbent as a function of its pressure (if gas) or concentration (if
liquid) at constant temperatures. The quantity adsorbed is nearly always
normalized by the mass of the adsorbent to allow comparison of different
materials.
The equilibrium distribution of metal ions between the sorbent and the
solution is important in determining the maximum sorption capacity. Several
isotherm models are available to describe the equilibrium sorption distribution in
which two models are used to fit the experimental data: Langmuir and Freundlich
models. The linear form of Langmuir model52 is given as:
ıı ıı ı = ı1
ııı ıı. ııı+ ıı
ııı ıı
Where qe is metal concentration on the zeolite at equilibrium (mg of metal
ion/g of zeolite), Qmax (mg/g) and KL (1/mg) are Langmuir constants related to the
maximum adsorption capacity corresponding to complete coverage of available
adsorption sites and a measure of adsorption energy (equilibrium adsorption
25
constant) respectively. These constants are found from the slope and intercept of
Ce/qe Vs Ce linear plot so that Qmax = 1/slope and KL = slope/intercept.
The linear form of the Freundlich model53 is given as:
lnqe = In KF + (1/n) In Ce
Where KF and n are Freundlich constants determined from the slope and intercept
of plotting In qe vs In Ce.
Amount of metal ion adsorbed on zeolite is calculated at the difference between
initial and final concentrations at equilibrium.
qe = (Ci-Ce)/S
Where qe is the ion concentration adsorbed on the zeolite at equilibrium (mg of
ion/g of zeolite). Ci is the initial concentration of ions in the solution (mg/L). The
slurry concentration, S, is expressed by :
S = m/v
Where v is the initial volume of ions solution used (L) and m is the mass of zeolite
used (g). The percent adsorption (%) is calculated using the equation.
% adsorption = (Ci -Ce/Ci) x 100%
1.5 STATEMENT OF PROBLEMS
With the rapid development of industries such as metal plating facilities,
mining operations, fertilizer industries, tanneries, batteries, paper and pesticide
industries, heavy metal wastewaters are directly or indirectly discharged into the
environment increasingly, especially in developing countries such as Nigeria.
26
Unlike organic contaminants, heavy metals are not biodegradable and tend to
accumulate in living organisms and many heavy metal ions are known to be toxic
or carcinogenic.
Despite the very useful collection of verified synthesis of zeolite materials,
recipes for zeolite synthesis are often difficult to follow.
1.6 OBJECTIVE OF THE STUDY
The aim of the research is to study the adsorption capacity of synthetic
zeolite synthesized from aluminosilicate solutions and gels. To achieve this, a
study was carried out with the following objectives:
i. To synthesize zeolite X from sodium aluminosilicate solution via
hydrothermal sol gel process.
ii. To characterize the synthesized zeolite via Scanning Electron Microscopy
and X-ray diffraction.
iii. To evaluate the potential of the produced synthetic zeolite on its capacity as
an adsorbent for adsorption of Pb ions from waste water
1.7 JUSTIFICATION OF THE STUDY
The hydrothermal approach used to synthesize the zeolitic adsorbent not
only proffered acheaper route and lower reaction time for synthesis, it also gave
high yield of the product with high purity hence its efficacy in removal of metallic
lead ions in waste water.
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