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ABSTRACT
Adsorption and kinetic modelling of heavy metals uptake from wastewater effluents using indigenous cellulose based waste biomass, such as nipa palm nut (NPN), palmyra palm nut (PPN), oil palm empty fruit bunch (EFB), oil palm fibre (OPF), and oil palm shell (OPS), as potential raw materials for the preparation of activated carbons was studied. Full factorial design of experiments was used to correlate the preparation variables (activation temperature, activation time and acid impregnation ratio) to the lead and copper uptake from aqueous solution. Minitab Release 11.21 was used for statistical analysis. The optimum conditions for preparing activated carbon from NPN for Pb2+ adsorption were as follows: activation temperature of 5000C, activation time of 1hr and acid impregnation ratio of 2:1, which resulted in 99.82% uptake of Pb2+ and 30.20% of activated carbon yield. Different results were obtained for other adsorbents. The experimental results obtained agreed satisfactorily with the model predictions. Proximate analysis was carried out in order to determine the ash content, fixed carbon, volatile matter and moisture content of the raw materials and activated carbons produced under optimum conditions. Bulk density, pH, iodine number and surface area of the activated carbons were also determined. The Fourier Transform Infrared Spectra of the activated carbons indicated the presence of hydroxyl, carboxyl, lactones, phenols and amino groups which are important sorption sites. The results of adsorption studies showed that activated carbons produced from OPS and NPN are the most efficient adsorbents for the removal of Pb2+ from aqueous solutions while NPN and PPN are the most efficient for Cu2+ removal. The amount of Pb2+ and Cu2+ adsorbed was found to be dependent on adsorbent dosage, pH, initial ion concentration, particle size, contact time and temperature. Equilibrium data fitted well to the Freundlich, Langmuir and Tempkin models. The equilibrium data was best described by Freundlich model. The kinetic data obeyed the pseudo first-order, pseudo second-order, Elovich and Bhattachanya-Venkobachor models. Pseudo second-order best described the kinetics of the adsorption process. The determined negative free energy changes (∆G) and positive entropy changes (∆S) indicate the feasibility and spontaneous nature of the adsorption process. The positive values of enthalpy change (∆H) suggest that the adsorption process is endothermic. A mini packed bed adsorption column was fabricated and used for continuous adsorption study. The column experiments showed that adsorption efficiency increased with increase in the influent concentration and bed depth and decreased with increasing flow rate. Column adsorption kinetics was described with Thomas and Yoon and Nelson models and the kinetic constants. The comparison of the experimental breakthrough curves to the breakthrough profiles calculated by Yoon and Nelson method showed a satisfactory fit for all the adsorbents.
TABLE OF CONTENTS
Title page – – – – – – – – – i
Certification – – – – – – – – – ii
Approval page – – – – – – – – iii
Dedication – – – – – – – – – iv
Acknowledgement – – – – – – – – v
Abstract – `- – – – – – – – vi
Table of contents – – – – – – – – vii
List of table – – – – – – – – – xiii
List of figures – – – – – – – – xxv
Nomenclature – – – – – – –
xxxvii
CHAPTER ONE INTRODUCTION
1.1 Background of the Study – – – – – – 1
1.2 Motivation for the work – – – – – – 5
1.3 Aims and Objectives – – – – – – – 6
1.4 Significance of the Study – – – – – – 7
1.5 Scope and Limitations- – – – – – – 8
CHAPTER TWO LITERATURE REVIEW
2.1 Activated Carbon
2.1.1 Introduction – – – – – – – 9
2.1.2 Activated Carbon and its surface structure – – – 10
2.1.3 Production of Activated Carbon – – – – 11
2.1.3.1 Physical Activation – – – – 11
2.1.3.2 Chemical Activation – – – – 13
2.1.3.3 Previous Works on Preparation of Activated Carbons 15
2.1.4 Properties of Activated Carbon – – – – 21
2.1.4.1 Ash Content – – – – – 21
2.1.4.2 Moisture – – – – – – 21
2.1.4.3 Apparent Density – – – – 21
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2.1.4.4 Bulk Density – – – – – 21
2.1.4.5 Hardness/Abrasion number – – – 21
2.1.4.6 Particle Size Distribution – – – 22
2.1.4.7 Surface Area – – – – – 22
2.1.4.8 Pore Volume – – – – – 22
2.1.4.9 Iodine Number – – – – – 22
2.1.4.10 Molasses Number – – – – 22
2.1.4.11 Methylene Blue – – – – – 23
2.1.5 Classification of Activated Carbon – – – – 23
2.1.5.1 Powdered activated Carbon (PAC) – – 23
2.1.5.2 Granular Activated Carbon (GAC) – – 23
2.1.5.3 Pelleted Activated Carbon – – – 24
2.1.2.4 Impregnated Carbon – – – – 24
2.1.5.5 Polymers Coated Carbon – – – – 24
2.2 Wastewater – – – – – – – – 24
2.2.1 Pollutants in Water – – – – – – 25
2.3 Heavy Metals – – – – – – – 26
2.3.1 Definitions – – – – – – – 26
2.3.2 Heavy Metals and Living Organisms – – – 27
2.3.3 Heavy Metal Pollution – – – – – 28
2.4 Other Adsorbents – – – – – – – 30
2.4.1 Molecular sieves – – – – – – 30
2.4.2 Silica gel – – – – – – – 30
2.4.3 Activated alumina – – – – – – 30
2.5 Adsorption – – – – – – – – 31
2.5.1 Factor affecting the rate of Adsorption- – – – 32
2.5.2 Adsorption Equilibrium – – – – – 33
2.5.3 Adsorption Isotherm – – – – – – 34
2.5.3.1 Langmuir Isotherm – – – – – 34
2.5.3.2: Freundlich Isotherm – – – – – 36
2.5.3.3: Temkin Isotherm – – – – – 36
2.5.3.4 Dubinin – Radushkevich (DR) Isotherm – – 37
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2.5.3.5 BET Isotherm – – – – – 39
2.5.3.6 Redlich-Peterson Isotherm – – – – 40
2.5.4 Adsorption Kinetics – – – – – – 40
2.5.4.1 First-order kinetics – – – – – 40
2.5.4.2 Pseudo First – order Kinetics – – – 41
2.5.4.3 Second-order Kinetics – – – – 41
2.5.4.4 Pseudo second- order model – – – – 41
2.5.4.5 Elovich Equation – – – – – 42
2.5.4.6 The Intra-particle Diffusion Model – – 43
2.5.4.7 Bhattacharya – Venkobachor Model – – 43
2.5.4.8 Power Function Equation – – – – 43
2.5.5 Adsorption Thermodynamics – – – – – 44
2.5.6 Competitive Adsorption – – – – – 45
2.5.7 Activated Carbon Adsorption Application – – – 49
2.5.7.1 Liquid Phase Applications of activated carbon – 49
2.5.7.2 Gas-Phase Applications – – – – 51
2.5.7.3 Catalysis – – – – – – 52
2.5.7.4 Activated Carbons Adsorption in Nuclear Technology 52
2.5.7.5 Activated Carbon Adsorption in Vacuum Technology 52
2.5.7.6 Medicinal Application of Activated Carbon Adsorption 52
2.5.8 Fixed Bed Adsorption – – – – – – 53
2.5.8.1 Basic Design Considerations – – – – 53
2.5.8.2 Predictive Models – – – – – 55
2.5.8.3 Surface Reaction Models – – – – 56
2.5.9 Activated Carbon Regeneration and Reactivation – – 62
2.6 Agricultural Waste Biomass – – – – – – 63
2.6.1 Oil Palm Wastes – – – – – – 63
2.6.1.1 Oil Palm Shell (OPS) – – – – 64
2.6.1.2 Oil Palm Fibre (OPF) – – – – 64
2.6.1.3 Empty Fruit Bunch (EFB) – – – – 64
2.6.2 Palmyra Palm – – – – – – – 65
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2.6.3 Nipa Palm – – – – – – – 66
2.7 Factorial Design – – – – – – – – 68
2.7.1 Full Factorial Experiments and Fractional Factorial Experiments 68
CHAPTER THREE MATERIALS AND METHODS
3.1 Sourcing and Pre-treatment of Raw Materials – – – – 70
3.2 Production of Activated Carbon – – – – – 70
3.3 Characterization of Activated Carbon – – – – – 73
3.3.1 Determination of pH of Activated Carbon – – – 73
3.3.2 Determination of moisture content of the raw materials and activated
carbon – – – – – – – – 73
3.3.3 Determination of Ash Content – – – – 73
3.3.4 Determination of Bulk Density of Activated Carbon – 73
3.3.5 Determination of Iodine Number of Activated Carbon – 74
3.3.6 Determination of volatile content of raw materials and activated
carbon – – – – – – – 74
3.3.7 Determination of percentage fixed carbon – – – 75
3.3.8 Determination of surface area – – – – 75
3.3.9 Fourier Transform Infrared (FTIR) Spectrometer – – 75
3.4 Adsorbate preparation and batch adsorption studies – – – 75
3.4.1 Effects of particle size – – – – – 76
3.4.2 Effect of Adsorbent dosage – – – – – 76
3.4.3 Effect of pH – – – – – – – 76
3.4.4 Effect of contact time – – – – – – 77
3.4.5 Effect of temperature – – – – – – 77
3.4.6 Effects of initial ion concentration – – – – 77 3.4.7 Competitive Adsorption of Pb2+ and Cu2+ – – – 77 3.5 Fractional factorial design of experiment for the adsorption of Pb2+ and Cu2+ 77
3.6 Column Studies – – – – – – – – 79
3.6.1 Construction of fixed bed adsorption column – – – 79
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CHAPTER FOUR RESULTS AND DISCUSSIONS
4.1 Yield of activated carbons – – – – – – 84
4.2 Characterization of activate carbons – – – – – 86
4.2.1 Proximate Analysis – – – – – – 86
4.2.1.1 Ash Content – – – – – – 86
4.2.1.2 Moisture content – – – – – 87
4.2.1.3 Volatile matter – – – – – 87
4.2.1.4 Fixed carbon – – – – – – 87
4.2.2 Bulk density – – – – – – – 87
4.2.3 Iodine number – – – – – – – 88
4.2.4 pH – – – – – – – – 88
4.2.5 Surface area – – – – – – – 88
4.2.6 Fourier transform infrared spectrometer (FTIR) – – 89
4.3 Production of activated carbon using 23 full factorial design – – 95
4.4 Batch adsorption studies – – – – – – 105
4.4.1 Effects of adsorption dosage on the adsorption process – – 105
4.4.2 Effects of particle size on the adsorption process – – 107
4.4.3 Effects of pH on the adsorption process – – – – 110
4.4.4. Effects of initial ion concentration process – – – 113
4.4.5 Effects of contact time on the adsorption process – – – 116
4.4.6 Effects of temperature on the adsorption process – – – 119
4.4.7 Competitive adsorption of Pb2+ and Cu2+ on the adsorbents – 119 4.4.8 Fractional Factorial design of experiment for the adsorption of Pb2+ and Cu2+on the adsorbents – – – – – – 121
4.5 Isotherm studies – – – – – – – – 130
4.5.1 Langmuir isotherm model – – – – – 130
4.5.2 Freundlich isotherm model – – – – – 133
4.5.3 Temkin isotherm – – – – – – 136
4.5.4 Dubinin-Radusherich isotherm model – – – – 139
4.6 Kinetic studies – – – – – – – – 149
4.6.1 First-order kinetic model – – – – – 149
4.6.2 Pseudo first-order kinetic model – – – – 152
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4.6.3 Pseudo second-order kinetic model – – – – 155
4.6.4 Second-order kinetic model – – – – – 158
4.6.5 Elovich kinetic model – – – – – 161
4.6.6 Intraparticle diffusion kinetic model – – – – 164
4.6.7 Bhattacharya – Venkobachor kinetic model – – – 167
4.7 Thermodynamics study – – – – – – – 181
4.7.1 Activation Energy – – – – – – 181
4.7.2 Thermodynamics properties – – – – – 182
4.8 Column Studies – – – – – – – – 186
4.8.1 Breakthrough curves – – – – – – 186
4.8.1.1 Effect of flow rate on breakthrough curves – – – 186
4.8.1.2 Effect of bed height on breakthrough curves – – – 189
4.8.1.3 Effect of initial ion concentration – – – – 192
4.8.2 Column kinetic study – – – – – – 195
4.8.2.1 Thomas model – – – – – – 195
4.8.2.2 Yoon and Nelson model – – – – – 202 4.8.3 Modelling the behaviour of Pb2+ and Cu2+ in a fixed bed adsorption
column – – – – – – – 212
CHAPTER FIVE CONCLUSION AND RECOMMENDATIONS
5.1 Contribution to knowledge – – – – – – 215
5.2 Conclusions – – – – – – – – 216
5.3 Suggestions for further research – – – – – – 217
REFERENCES – – – – – – – – 218
Appendix A: Calibration curve for Pb (II) and Cu (II) – – – 234
Appendix B: Tables of the percentage yield of activated carbons – – 236
Appendix C: FTIR spectra of the activated carbons – – – – 237
Appendix D: Contour and 3D surface plots for the optimization
of production of the activated carbons – – – – – 240
Appendix E: Contour and 3D surface plots for the optimization of adsorption of
Pb2+ and Cu2+ on the adsorbents – – – – – 246
xiii
Appendix F: Effects of variables on the adsorption of Pb2+ and Cu2+ – 253
Appendix G: Isotherm data for Pb2+ and Cu2+ adsorption on the adsorbents 268 Appendix H: Kinetic data for Pb2+ and Cu2+ adsorption on the adsorbents 276 Appendix I: Thermodynamic data for the adsorption of Pb2+ and Cu2+ – 284
APPENDIX J: Kinetic parameters for column studies – – – 287
APPENDIX K: Relevant publications – – – – – 298
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Industrial wastewater represents the main source of environmental pollution
with heavy metals, e.g. Cu, Pb, Fe, Cd, Mn, etc. Such metal may be discharged into the
wastewater from various industries, including metal plating, storage batteries, alloy
industries, dying, textile, fertilizers and other chemical industries. The progressive
increase of industrial technology result in continuous increase of pollution, so that a
great effort has been devoted for minimizing these hazardous pollutants and therefore
avoiding their dangerous effects on animals, plants and humans (Al-Omair and El-
Sharkawy, 2001)
Heavy metal ions are reported as priority pollutants, due to their mobility in
natural water ecosystems and due to their toxicity (Volesky and Holan, 1995). These
heavy metals are not biodegradable and their presence in streams and lakes leads to
bioaccumulation in living organisms causing health problems in animals, plants, and
human beings (Ong et al, 2007)
Lead is a pollutant that is present in drinking water and in air. In air, it is
derived from lead emissions from automobiles because it is used as an anti knocking
agent in the form of lead tetraethyl in gasoline. In water, lead is released in effluent
from lead treatment and recovery industries, especially from lead battery manufacturing
units. Lead is toxic to living organisms and if released into the environment can both
accumulate and enter the food chain. Lead is known to cause mental retardations,
reduces haemoglobin production necessary for oxygen transport and it interferes with
normal cellular metabolism (Qaiser et al, 2007). Lead has damaging effects on body
nervous system. It reduces 1.Q Level in children. Lead is used as industrial raw
materials in the manufacture of storage batteries, pigments, leaded glass, fuel,
photographic materials, matches and explosives (Raji and Anirudhan, 1997). For
drinking water, the maximum permissible limit of lead is 0.1mg/l (WHO, 1971). The
maximum concentration allowed for discharge into inland water is less than 1mg/l
(FEPA, 1991).
Copper is one of the few metallic elements found in the earth’s crust. It
constitutes 70mg/kg of the earth’s crust, occurring as a constituent of several ores like
chalcopyrite (CuFeS2 ), which is about 50% of total world copper deposits ( Maheswari
et al, 2008 ). Copper is an essential nutrient to all higher plants and animals. In humans,
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it is found primarily in the blood stream as a cofactor in various enzymes and in Cu
based pigments. Copper is metal that has a wide range of applications due to its good
properties. It is used in electronics, for production of wires, sheets, tubes, and also to
form alloys (Antonijevic and Petrovic, 2008). Since copper is a widely used material,
there are many actual or potential sources of copper pollution. Copper may be found as
a contaminant in food, especially shellfish, liver, mushrooms, nuts, and chocolate.
Copper is essential to life and health but, like all heavy metals, is potentially toxic as
well. For example, continued inhalation of copper-containing spray is linked with an
increase in lung cancer among exposed workers. For drinking water, the maximum
permissible limit of copper is1.5mg/l (WHO, 1971). The maximum concentration
allowed for discharge into inland water is less than 1mg/l (FEPA, 1991). The main
physiological processes in which copper participates in the formation of blood and
utilization of iron in haemoglobin synthesis, the synthesis and cross linking of clastin
and collagen in the aorta and major blood vessels, etc. Various disorders such as
nephritic syndrome (Mason, 1979), copper intoxication and burning injuries (Kaur, et
al, 2008), hematemesis, melena, coma and jaundice (Maheswari et al, 2008 ), have been
associated with higher concentration of copper.
Several methods such as ion exchange, solvent extraction, reverse osmosis,
precipitation, and adsorption have been proposed for the treatment of wastewater
contaminated with heavy metals (Gupta, 2003) Among several chemical and physical
methods, the adsorption onto activated carbon has been found to be superior to other
techniques in water-re-use methodology because of its capability for adsorbing a broad
range of different types of adsorbates efficiently, and its simplicity of design (Ahmad et
al, 2006). The major advantages of an adsorption system for water pollution control are
less investment in terms of initial cost and land, simple design and easy operation, and
no effect of toxic substances compared to conventional biological treatment processes
(Markovska et al, 2006).
However, commercially available activated carbons are still considered
expensive (Chakraborty et al, 2005). Consequently, many researchers have studied
cheaper substitutes, which are relatively inexpensive, and are at the same time endowed
with reasonable adsorptive capacity. These studies include the use of coal (Mohan et al,
2002), fly ash (Mohan et al, 2002; Nollet et al, 2003; Gupta, 2003; Ricou et al, 2001,
Gupta and Ali, 2004), activated clay (Wu et al, 2001), palm–fruit bunch (Nassar, 1997),
Bagasse pith (Mckay;1998), bentonite, slag and fly ash (Ramakrishna and
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Viraraghavan, 1997; Bereket et al, 1997), rice husk (Low and Lee, 1997), wood
charcoal (Keerthinarayana, and Bandyopadhyay, 1997), hazelnut shell (Kobya,2004),
coconut shell (Goel, et al 2004); peat (Brown et al, 2000; Ho and Mckay, 2000), etc
Activated carbons are versatile adsorbents (Castro et al, 2000). Activated carbons are
becoming more and more interesting on account of their excellent properties as
adsorbents, which make it possible to use them in purification and pollutant removal
from both liquid and gaseous media (Sanchez et al, 2006).
Their adsorptive properties are due to their surface area, a micro porous
structure, and a high degree of surface reactivity. Activated carbons are usually
obtained from materials with high carbon content and possess a great adsorption
capacity, which is mainly determined by their porous structure (Otero et al, 2003). The
inherent nature of the precursor or starting material, as well as the method and
conditions employed for carbon synthesis, strongly affects the final pore size
distribution and the adsorption properties of the activated carbons (Shopova et al, 1997,
Biota et al, 1997). In recent years, special emphasis on the preparation of activated
carbons from several agricultural by products has been given due to the growing
interest in low cost activated carbons from renewable, safe, copious supplies, especially
for applications concerning treatment of drinking water and wastewater (Castro et al,
2000).
The selection of solid wastes as precursor for activated carbon depends on the
potential for obtaining high quality activated carbon, presence of minimum inorganics,
volume and cost of raw materials and storage life of raw materials (Al-Omair and EL
Sharkawy, 2001)
Active carbons are unique and versatile adsorbents, and they are used
extensively for the removal of undesirable colour, taste, and other organic and
inorganic impurities from domestic and industrial waste water, solvent recovery, air
purification in inhabited places, restaurants, food processing, and chemical industries;
in the removal of colour from various syrups and pharmaceutical products; in air
pollution control from industrial and automobile exhausts; in the purification of many
chemical, pharmaceutical and food products; and in a variety of gas-phase
applications(Bansal and Goyal, 2005)
There are two methods of preparing activated carbons: physical and chemical
activation. The advantage of chemical activation over physical activation is that it is
performed in one step and at relatively low temperatures. The most important and
4
commonly used activating agents are phosphoric acid, zinc chloride and alkaline metal
compounds, such as KOH (Serrano-Gomez et al, 2005; Srinivasakannan and Zailani,
2004). There have been a number of works describing phosphoric acid activation of
different precursors, and some advantages of this process, in comparison with the more
studied physical activation, have been printed out (Castro et al, 2000; Girgis et al, 1994;
Philip et al, 1996). Phosphorous acid activation only involves a single heat treatment
step and activation is achieved at lower temperatures. Higher yields are obtained and
most of the phosphoric acid can be recovered after the process is completed. In
addition, the use of chemical reagents allows another degree of freedom in the choice
of process conditions (Solum et al, 1995). Johns et al (1999) have used the physical
activation procedure for the production of activated carbon using steam and carbon
dioxide. The characteristics of activated carbon depend on the physical and chemical
properties of the precursor as well as on the activation method.Apart from the starting
material and the oxidizing agent; activation time and temperature affect the structural
properties of the resulting activated carbon. Many researchers observed that BET
surface area and pore volume increased with activation and temperature (Guo and
Chong, 2002; Villegas-Pastor and Valle-Duran, 2001; Yang, and Chong, 2003)
Adsorption equilibrium is the most fundamental data on an adsorption
system (Lee et al, 2006). It is also very important in model prediction for analyzing and
designing an adsorption process. Adsorption is usually described through isotherms, that
is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or
concentration (if liquid) at constant temperature (Metcalf and Eddy, 2003). Adsorption
isotherms are developed by exposing a given amount of adsorbate in a fixed volume of
liquid to varying amounts of activated carbon.
The study of sorption kinetics in wastewater treatment is important since it
provides valuable insights into the reaction pathways and mechanism of adsorption
process (Mincera et al, 2008). A study of adsorption kinetics provides information about
the mechanism of adsorption, which is important for the efficiency of the process
(Maximova and Koumanova, 2008). Also the kinetics describes the solute uptake rate
and mass transfer resistance at the solid-solution interface.
In order to examine the mechanism of adsorption process such as mass transfer
and chemical reaction, a suitable kinetic model is needed to analyse the rate data (Ozacar,
2003). Many models such as homogeneous surface diffusion model, pore diffusion
5
model, and heterogeneous diffusion model (also known as pore and diffusion model)
have been extensively applied in batch reactors to describe the transport of adsorbates
inside the adsorbent particles (Wu et al, 2001a-c; Raven et al, 1998). These kinetic
models are useful for the design and optimisation of effluent – treatment process
(Sivakumar and Palanisamy, 2009).
The reaction rate can be calculated from the knowledge of kinetic data. However,
the changes in reaction that can be expected during the sorption process require the
knowledge of thermodynamic parameters. The three main thermodynamic parameters include enthalpy of adsorption (∆H), Gibbs free energy charge (∆G) and entropy of adsorption (∆S).
The main feature of the dynamic behaviour of fixed-bed adsorption is the history
of effluent concentration (Tien, 1994). These concentration-time curves (or their
equivalents) are commonly referred to as the breakthrough curves, and the time at which
the effluent concentration reaches the threshold value is called the breakthrough time. It
is obvious that rational design of adsorption systems should be based on accurate
predictions of breakthrough curves for specific conditions.
Although the fixed-bed mode is highly useful, its analysis is unexpectedly
complex. Fixed-bed operation is influenced by equilibrium (isotherm and capacity),
kinetic (diffusion and convention coefficients), and hydraulic (liquid hold-up, geometric
analysis, and mal-distribution) factors (Inglezakis and Poulopoulos, 2006).
1.2 Motivation for the work The contamination of water by toxic metals through the discharge of industrial
wastewater is becoming a serious environment problem in Nigeria. Heavy
metals ions are reported as priority pollutants, due to their mobility in natural
water ecosystems and due to their toxicity. The presence of these heavy metals
in streams and surface waters has been responsible for several health problems
with animals, plants and human beings. Nigeria imports large quantities of AC annually and at very high cost. Studies show that there are more than enough of the agricultural waste raw
materials available for activated carbon production to meet local demand.
6
`Activated carbons have excellent properties as adsorbents, which make it
possible to use them in purification and pollutant removal from both liquid and
gaseous media.
1.3 Aims and Objectives
In this study, the use of waste biomass of oil palm shell(OPS), palmyra palm
nut(PPN), oil palm empty fruit bunch(EFB), oil palm fibre(OPF), and nipa palm nut
(NPN) as low-cost adsorbents for the removal of toxic metals (lead and copper) from
aqueous solution is investigated. In addition, adsorption and kinetic modeling of the
uptake of these metals from aqueous solution is done.
This research will achieve the following objectives:
1. To prepare activated carbons from agricultural raw materials using full factorial
design of experiment.
2. To characterize the prepared active carbons with respect to their bulk density,
ash content, moisture content, pH, surface area, fixed carbon, iodine number,
surface characteristics, etc.
3. To investigate the effect of heat-treatment temperature, weight ratio of
phosphoric acid to precursor in the impregnation step, and carbonization time
on adsorption of heavy metal from aqueous solutions.
4. To determine the adsorptive capacity of prepared active carbons.
5. To study the influence of batch sorption specific parameters, such as initial
metal concentration, adsorbent dosage, particle size, pH, contact time and
temperature.
6. To study adsorption isotherms using four model equations – Langmuir,
Freundlich, Temkin, and Dubinin-Radushkevich equations.
7. To investigate the kinetics of heavy metal adsorption on the activated carbons
using first- order, second- order, Pseudo first- order, Pseudo second-order,
Bhattacharya-Venkobachor model, Elovich equation, and Weber-Morris intra-
particle diffusion models to test the kinetic data. 8. To determinate thermodynamics parameters such as ΔG, ΔH and ∆S as well
as energy of activation.
9. To fabricate mini packed bed adsorption column.
7
10. To study breakthrough curves using locally fabricated packed bed adsorption
column.
11. To investigate the efficiency of lead and copper removal in a packed column
with respect to experimental parameters, such as bed height, initial
concentration and flow rate.
12. To study the kinetics of lead and copper adsorption in a packed bed.
13. To model dynamic adsorption behaviour of lead and copper in packed bed
column
1.4 Significance of the Study
With the rapid development of chemical and petroleum processing industries in
Nigeria, there is a rapid increase in the amount and the variety of chemicals that are
discharged into waters. Wastewater from various industries and municipal corporations
are discharged into ground and surface water, making it unfit for human and animal
consumption. Some of the organic and inorganic compounds, when present in water,
are toxic, carcinogenic, and mutagenic, and cause several ailments in humans.
Several biological and chemical methods such as filtration, coagulation,
oxidation, solvent extraction, and reverse osmosis have been used for wastewater
treatment. However, the increase in the variety and amount of hazardous chemicals
present in lakes, rivers and ground water make these conventional methods inefficient.
Consequently, the development of new and more effective technologies becomes
essential. Adsorption onto activated carbon has been found to be superior to other
technologies.
Commercially available activated carbons are considered expensive. Also,
activated carbon is not produced in Nigeria in commercial quantity despite the
abundance of raw material like agricultural wastes. This work was undertaken to study
adsorption and kinetic modelling of heavy metals uptake from wastewater effluents
using certain indigenous cellulose based waste biomass as potential raw materials for
the preparation of activated carbons. Commercial production of activated carbon can be
started using the methodology for the preparation of activated carbon established in this
work. This will lead to the reduction in import of activated carbon into the country.
These agricultural wastes (waste biomass) impact negatively on the
environment because of indiscriminate disposal of such wastes. Hence producing
8
activated carbon from these wastes is an alternative method of waste reduction and
reuse.
The work provides data for the design of wastewater and water treatment
equipment. This study will help to improve the quality of life for people by improving
public health and providing mechanisms for environmental protection and remediation.
In the course of this study a mini-packed bed adsorption column was fabricated
and used for continuous adsorption process. The data generated in this work will serve
as reference for further research.
1.5 Scope and Limitations
The study is limited to the use of NPN, PPN, EFB, OPF, and OPS to prepare
activated carbon by chemical activation. The experimental study of adsorption is focused on the adsorption of Pb2+ and Cu2+ from aqueous solution.
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