ABSTRACT
Heavy metals which are directly discharged into receiving water bodies pollute and make them unsafe for use because of their extreme harmful effects on man. Adsorption is one of the effective methods for the removal of heavy metal ions from waste water. This work investigates the potential of a cheap and readily available adsorbent, the seeds of velvet tamarind in adsorbing Pb2+, Cu2+ and Fe2+ from aqueous solution. The effects of various parameters such as adsorbent dose, temperature, initial concentration, pH and contact time for adsorption of lead, copper and iron ions from aqueous solutions by tamarind seeds were examined. The experimental equilibrium adsorption data were tested using the Langmuir, Freundlich, Halsey and Harkins-Jura equations and their constants and correlation coefficients determined. Freundlich model showed the best fit to the experimental data as assessed from the high R2 values. The adsorption isotherm results showed the following order of fitting:Freundlich > Halsey >Harkins-Jura > Langmuir.The result of the thermodynamic study showed the sorption process to be spontaneous. Adsorption kinetic data were studied using pseudo-first and pseudo-second order models. The results indicated that the pseudo-second order model gives better interpretation to the adsorption data. The experimental results show that velvet tamarind seed has a significant capacity for removal of lead, iron and copper ions from waste water streams.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents
vi
List of Tables x
List of Figures xi
Abstract xii
CHAPTER 1: INTRODUCTION 1
1.1
Background of the Study 1
1.2
Statement of the Problem 4 1.3 Aim of the Study 4 1.4
Objectives of the Study 4
1.5
Justification of the Study 5 1.5 Scope and Limitation of the
Study 5
CHAPTER 2: LITERATURE REVIEW 6
2.1 Brief History of African Velvet Tamarind (Dialium guineense) 6
2.2 Cultivation and Propagation 8
2.2.1 Chemical composition of fruit and seeds 8
2.2.2 Health benefits of velvet tamarind 9
2.3 Metal Uptake Ability of (Dialium guineense) 9
2.4 Heavy Metal Pollution 10
2.4.1 Toxicity and sources of heavy metal contamination
10
2.5
Methods of Heavy Metal Removal 11
2.5.1 Techniques for the treatment of heavy metals 12
2.5.2 Newest adsorption technology 14
2.6 Mechanism of Biosorption 15
2.6.1 Agricultural waste materials as adsorbents
for
heavy metal removal 16
2.7 Utilization of Atomic Absorption Spectrometry
18
2.7.1 Basic principles of atomic absorption
spectrometry 18
2.8 Mechanism of Adsorption Theory 19
2.9 Factors Influencing Heavy Metal Removal by
Adsorption 23
2.10 Recovery and Desorption Study 25
2.11 Feasibility of Adsorption 26
2.12 Some Toxic Heavy Metals in the
Environment 27
2.12.1 Lead poisoning 27
2.12.2 Copper poisoning 28
2.12.3 Iron poisoning 29
2.12.4 Zinc poisoning 30
2.12.5 Cadmium poisoning 31
2.13 Adsorption Isotherm 32
2.14 Kinetic Study 37
2.15 Thermodynamic Study 38
CHAPTER 3: MATERIALS AND METHODS 40
3.1.1 Reagents used 40
3.1.2 Instruments used 40
3.1.3 Apparatus used 40
3.2 Adsorbent Collection and Preparation 41
3.3 Adsorbate Preparation 41
3.4 Batch Adsorption Experiments 42
3.5 Data Analysis
CHAPTER 4: RESULTS AND DISCUSSION 45
4.2 Fourier Transform Infrared Spectroscopy
FTIR Analysis 45
4.3
Effect of Contact Time on Adsorption of the Metal Ions by
Tamarind
Seeds 46
4.4
Kinetic Adsorption 47
4.5
Effect of Adsorbent Dosage on Adsorption of the
Metal Ions by Velvet Tamarind Seeds 49
4.6 Effect of pH on
Adsorption of the Metal Ions by
Velvet Tamarind Seeds 51
4.7 Effect of Temperature on
Adsorption of the Metal Ions by
Velvet Tamarind Seeds 52
4.8 Effect of Initial Metal Ions on Adsorption of the
Metal
Ions by Velvet Tamarind Seeds 53
4.9 Adsorption Isotherms 54
4.9.1 Langmuir and Freundlich isotherm models 54
4.9.2 Harkins-Jura isotherm model 59
4.9.3 Halsey isotherm model 60
4.13 Thermodynamic Study 62
CHAPTER 5: CONCLUSION AND
RECOMMENDATION 67
5.2
Conclusion 67
5.3
Recommendation 68
References 69
Appendices
LIST OF TABLES
2.1: Physicochemical
properties of tamarind seed 10
4.1: Physicochemical Properties of Tamarind
Seed 47
4.2: IR Interpretation 48
4.3: Kinetic Rate Constant for Pseudo-first
Order Reaction at 30OC 53
4.4: Kinetic Rate Constant for Pseudo-second
Order Reaction at 30OC 53
4.5: Langmuir and Freundlich Isotherm Values
for Adsorption of Cu(II)
Fe(II) and Pb(II) Ions 64
4.6: Halsey and Harkins- Isotherm Values for
Adsorption of Cu(II)
Fe(II) and Pb(II) Ions 67
4.7: Activation Energies (Ea), InA for the
Arrhenius plot 70
4.8: Transition State Plot at 30OC 71
4.9: Transition State Plot at 40OC 71
4.10: Transition State Plot at 50OC 71
4.11: Transition State Plot at 60OC 72
4.12: Transition State Plot at 70OC 72
4.13:
Transition State Plot at 80OC 72
LIST OF FIGURES
4.1:
Effect of Contact Time on Adsorption of the Metal Ions by the
Adsorbent 50
4.2: Pseudo-first Order Plot for Adsorption of
the Metal Ions 52
4.3: Pseudo-second Order Plot for Adsorption
of the Metal Ions 52
4.4: Effect of Adsorbent Dosage on Adsorption
of the Metal Ions by the
Adsorbent 55
4.5: Effect of pH on Adsorption of the Metal
Ions by the Adsorbent 57
4.6: Effect of Temperature on the Amount
Adsorbed
onto the Adsorbent 58
4.7: Variation of Amount Adsorbed with Initial
Metal Ion Concentration
for the Adsorption Process 60
4.8: Langmuir Adsorption Isotherm Plots of
Fe(II), Cu(II)and Pb(II) Ions by
Tamarind Seeds 63
4.9: Freundlich Adsorption Isotherm Plots of
Cu(II), Fe(II)and Pb(II) Ions
by Tamarind Seeds 64
4.10: Harkins-Jura Isotherm Plots
of Fe(II), Cu(II) and Pb(II)Ions by
Tamarind Seeds 66
4.11: Halsey Isotherm Plots of Pb(II), Cu(II)
and Fe(II) Ions by Tamarind
Seeds 67
4.12: Van’t Hoff Plots for Adsorption of the
Metal Ions onto the Adsorbent at
30OC, 40OC, 50OC, 60OC, 70OC
and 80OC 69
4.13: Transition State Plots for Adsorption of
the Metal Ions onto the
Adsorbent at 30OC, 40OC, 50OC, 60OC,
70OC and 80OC 70
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Heavy metal toxicity is a cause of concern to
man and his environment. It is well known that heavy metals are very toxic
elements and their discharge into the receiving water bodies causes detrimental
effects on human health and environment (Sud et al., 2008). Due to the uncontrolled, increasing
development in agriculture, industry, commerce, hospital and health-care
facilities, many industrial activities are consuming significant quantities of
toxic chemicals and generating a large amount of hazardous wastes. An increase
in the use of metals and chemicals in these industries has resulted in
accumulation of large quantities of effluents that contain high levels of toxic
heavy metals and their presence is life threatening due to their non-degradability.
Heavy metals once introduced into the environment are difficult to be destroyed
or degraded technically or mechanically into harmless end- products. They
persist over time in all parts of the environment including the food we eat and
the water we drink causing pollution of air, soils and water (Apha, 1985).
Almost all heavy metals are highly toxic when their concentrations exceed their
permissible limit in the ecosystem. High concentration of heavy metals may accumulate in the human body
once present in human food chain and possibly in effect, cause severe health
problems if they exceed the permitted concentration (Babel and Kurniawan, 2011). These heavy metals are of
specific concern due to their toxicity, bio-accumulating tendency and
persistency in nature, hence, the need to reduce their bioavailability,
mobility and toxicity. But just as heavy metals have their negative effects,
they also have positive effects. For instance, in small quantities, certain
heavy metals are nutritionally essential for healthy life such as Fe, Cu, Zn and
so on. These elements, or some form of them, are commonly found in foodstuff
such as fruits, vegetables and in commercially available multivitamin products.
Heavy metals are also common in industrial applications such as in the
manufacture of pesticides, batteries, alloys, electroplated metal parts,
textile dyes, steel and mining, refining ores, fertilizer industries, paper
industries and so forth. Many of these products are in our homes and actually
add to our quality of life when properly used. But the truth is that their
negative effect is a severe headache to mankind. Hence, the need for reduction
or better still the removal of heavy metals by cheap materials and simple
methods such as adsorption.
Adsorption process has become one of the preferred methods for
removing toxic elements from aqueous solutions as it has been found to be very
effective, economical, versatile and simple (Apkhami et al., 2010). Various conventional
treatments have been tried and applied in the past in removing heavy metals from
aqueous solutions and they include: filtration, evaporation, precipitation, ion
exchange and activated carbon. Most of these methods are no longer in use
because of their expensive and inefficient natures particularly when very low
concentrations of the metal ions are involved.
However, adsorption today is considered as one of the best methods
in treating industrial and domestic waste effluents due to its enormous
advantages including cheapness, availability, profitability, ease of operation
and efficiency in comparison with conventional methods. In order to minimize processing costs, several research
works have centered their interests on low cost adsorbents, such as
agricultural waste by-products (Samantaroy et
al., 1997). Adsorbents like the crushed seed of pawpaw has been used in
metal adsorption (Ajmal, 1998). Adsorbents from plant wastes or by-products
have been found to offer a low costs effective and eco-friendly alternatives to
conventional treatment (Mikhail et al.,
2002). Some agricultural wastes have been employed in several adsorption
studies. For instance, use of sulphuric acid-treated rice husk (Srinivasan,
1988), Magifera indica (Ajmal, 1998), fly ash (Mall and Upadhyay, 1998), bamboo
dust (Kannan and Meenakshi, 2002) and so
on.
Tamarind seed which is the adsorbent to be used in the present
study is an underutilized by-product of the tamarind pulp industry. Only a
small portion of the seed, in the form of tamarind kernel powder (TKP), is used
as a sizing material in the textile, paper and jute industries. The present
study involves investigating the potentials of tamarind seed as a biosorbent in
the removal of Pb(II), Fe(II) and Cu(II) ions from aqueous solution. Various
experimental conditions for optimum adsorption of the metal ions will be
employed while the mechanism of binding of the metals to the biosorbent sites
will be assessed using different isotherms and kinetic models.
1.2 STATEMENT OF
PROBLEM
The uncontrolled rise in
the use of heavy metals and their compounds in our industries today present a
possible human health risk. This is because heavy metals accumulate in our food
chain and are toxic in nature. Agricultural materials mainly those comprising
of cellulose materials that can adsorb heavy metal cations in aqueous solution
are used in curbing these metals (Sun and Shi, 1998). The use of plant waste
materials is increasingly becoming an important aspect in the adsorption of
heavy metal ions which hitherto pose serious disposal problems and health
threatening issues when decayed.
1.3 THE AIM OF THE STUDY
This study aims at investigating the removal
of the following toxic metal ions: Cu(II), Fe(II) and Pb(II) from aqueous
solutions using velvet tamarind seed.
1.4 OBJECTIVES
OF THE STUDY
The main objectives of the study are
to:
i)
Investigate the effects
of pH, initial metal ion concentration, temperature, dosage and contact time on
the adsorption process.
ii)
Evaluate the
thermodynamic parameters on the feasibility of the adsorption process.
iii)
Understand the likely mechanism of the
adsorption through the applicability of different kinetics and isotherm models.
iv)
Estimate the sorption capacity of tamarind
seeds in removing toxic heavy metals: Cu(II), Fe(II) and Pb(II) ions from
aqueous solutions.
1.5 JUSTIFICATION OF STUDY
Due to the toxic and harmful effects
of heavy metals, industrial waste products should be properly treated before
they are directly discharged into the water bodies. Naturally, heavy metals are
persistent in nature, highly toxic and also non-biodegradable. One of the ways
for removing harmful effects of heavy metals is through the use of agricultural
waste adsorbents due to their
inexpensiveness and effectiveness unlike the convectional methods which are
expensive, ineffective with low metal concentrations and generate large
quantities of sludge. For large scale treatment of waste water, natural plant
waste materials are used and in this case velvet tamarind seed was assessed for
its potential to adsorb the following metal ions Pb, Cu and Fe from aqueous
environment because of its availability and cheapness.
1.6
SCOPE
AND LIMITATIONS OF THE STUDY
This work will centre on
investigating the influence of adsorption parameters on the removal the choice
of heavy metal ions from solution so as to establish the optimum experimental
conditions for the sorption process. The study will also cover the
thermodynamics, kinetics and equilibrium of the adsorption process in order to
establish the feasibility and the likely mode of bonding of the metals to the
adsorbent surface.
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