ABSTRACT
Activated carbon prepared from plantain peel is used to adsorb selected heavy metals such as copper, cadmium and chromium. Heavy metals are toxic and may be found in both surface and underground water. Plantain peel which is an agricultural wastes comprising mostly of cellulose materials was activated with three activating agents (0.10M H3PO4, 0.10M NaOH and 0.10M ZnCl2 ), then latter used for the removal of these toxic metals from their aqueous solutions. Activation of plantain peel with 0.10M H3PO4 and 0.10M NaOH solutions resulted to a two-fold increase in the amounts of adsorbed Cd2+, Cr6+ and Cu2+ compared to activation with 0.10M ZnCl2.The effects of varying the particle sizes, the type of activating agents as modifiers, adsorbent dosage, agitation time, agitation speed, pH as well as initial concentration of the metal ions on the adsorption capacity of the activated carbons were determined. The linearization of equilibrium isotherms data for Langmuir and Freundlich models were obeyed over the entire range of the concentration studied, while the metal sorption closely followed Langmuir model and Freundlich model. The Langmuir isotherm has R2 values of 0.9557 for Cd2+, 0.9924 for Cr2+ and 0.9954 for Cu2+ which indicated that the adsorption behaviour was homogenously distributed. The RL value indicated favorability of adsorption capacity by adsorbent since RL value fall within 0 to 1.The characterization by FTIR showed absorbance peaks of aldehyde, amide, alkyl, hydroxyl and carboxylic functional group. Hence, these functional groups are responsible for the adsorption and activation process has an enhanced factor on the adsorption of the selected metals. The optimum conditions for the adsorption of Cd2+, Cr6+ and Cu2+ onto the activated carbon are 2.5 g of the adsorbent dosage of particle size 75 μm, 20.0 mg/dm3 of the adsorbate concentration at 60 min agitation time carried out at 150 rpm agitation speeds. At the optimum conditions the highest percentage of the metal ions adsorbed were Cr6+ (97.2%), followed by Cu2+ (90.2%) and the least was Cd2+ (53.9%).
TABLE OF CONTENTS
Declaration ii
Certification iii
Dedication iv
Acknowledgment v
Abstract vi
List of Tables vii
List of figures viii
List of Appendices ix
List of Abbreviations x
CHAPTER ONE 1
1.0 INTRODUCTION 1
1.1 Background to the Study 1
1.2 Activated Carbon 2
1.3 Plantain Peel 3
1.4 Justification for the Research 3
1.4 Aim and Objectives 4
CHAPTER TWO 5
2.0 LITERATURES REVIEW 5
2.1 Other Uses of Activated Carbon Metals Adsorption 6
2.2 Carbonization and Activation Processes 7
2.3 Elemental Analysis 8
2.4 Earlier Studies on the use of Activated Carbon from Agricultural Waste 8
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2.5 Theory of Adsorption Isotherms 10
2.6 Heavy Metals as a Source of Pollution 12
2.6.1 Sources and Toxicity of Selected Heavy Metals 13
2.6.1.1 Cadmium 13
2.6.1.2 Copper 14
2.6.1.3 Chromium 15
2.7 Treatment of Industrial Effluents with Activated Carbon 15
2.7.1 Adsorbent from Plants for Treatment of Effluents 16
2.7.2Adsorbent from Fungi and Biomass for Treatment of Effluent 17
2.8 Preparation of Activated Carbon 18
2.9 Activating Agents 19
2.10 Definitions and Processes of Adsorption 19
2.11 Factor Affecting the Extent of Adsorption 20
CHAPTER THREE 21
3.0 MATERIALS AND METHODS 21
3.1 Sample Collection, Identification and Treatment 21
3.2 Reagent 21
3.3 Carbonization Process 21
3.4 Activation 21
3.5 Characterization Studies 22
3.5.1 Moisture and Dry Mater Content Determination 22
3.5.2 Ash Content Determination 22
3.5.3 pH Determination 23
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3.5.4 Bulk Density 23
3.5.5 Elemental Analysis 24
3.5.6 FTIR Analysis 24
3.5.7 Density of Carbonized Material 25
3.5.8 Determination of Surface Area 25
3.6 Preparation of Standard Solutions of Cd2+ , Cr6+ and Cu2+ 26
3.6.1 Chromium Stock Solution (1000 mg/dm3) 26
3.6.2 Cadmium Stock Solution (1000 mg/dm3) 26
3.6.3 Copper Stock Solution (1000 mg/dm3) 26
3.6.4 Working Solution of Cd2+, Cr6+ and Cu2+ 26
3.6.5 1M H3PO4 26
3.6.6 0.1M NaOH 27
3.6.7 0.1M ZnCl2 27
3.7 Adsorption Experiments 27
3.7.1 Effect of Initial Concentrations of Cd2+ , Cr6+ and Cu2+ on the Adsorption 28
3.7.2 Effect of Adsorbent Dosage on the Removal of Heavy Metals 29
3.7.3 Effect of Agitation Time on the Removal of Cd2+ , Cr6+ and Cu2+ 29
3.7.4 Effect of Particle Sizes on the Adsorption Rate of Selected Metals 29
3.7.5 Effect of Activating Agents on the Adsorption Rate of Selected Metals 29
3.7.6 Effect of Agitation Speed on the Adsorption Efficiency of Heavy Metals 30
3.8 Atomic Absorption Spectrometry 30
3.9 Adsorption Modeling of Heavy Metal Ions 30
3.9.1 Langmuir Isotherm Model 31
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3.9.2 Freundlich Isotherm Model 32
CHAPTER FOUR 34
4.0 RESULTS 34
4.1 Physicochemical Properties 34
4.2 Characterization of the Adsorbent 35
4.2.1 Fourier Transform Infrared Analysis 35
4.3 Adsorption Experiment 40
4.3.1 Effect of Agitation Time on the Adsorption of Selected Metal 40
4.3.2 Effect of Adsorbent Dosage on the Adsorption of Selected Metal 41
4.3.3 The Effect of Particle Sizes on the Removal of Selected Metals Ions 44
4.3.4 Effect of Agitation Speed on the Adsorption Selected Metals 45
4.3.5 Effect of pH on the Removal of Heavy Metals 46
4.3.6 Effect of Activating Agents on the Adsorption of Selected Metal 47
4.3.7 Effect of Initial Concentration on the Cd2+ , Cr6+ and Cu2+ Adsorption 48
4.3.8 The Langmuir and Freundlich Isotherms Modeling for Metals Uptake 50
CHAPTER FIVE 60
5.0 DISCUSSION 60
5.1.1 Dry Matter and Moisture Content 60
5.1.2 Ash Content of Plantain Peels Samples 60
5.1.3 pH of Raw and Carbonized Sample 61
5.1.4 Carbonized Sample and Bulk Densities Peel 61
5.1.5 Surface Area of Plantain Peel 62
5.2 Fourier Transform Infrared Analysis 62
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5.3 Elemental Composition of Plantain Peel by Neutron Activation Analysis NAA 63
5.4 Effect of Agitation Time on the Adsorption of Selected Heavy Metals 63
5.5 Effect of Adsorbent Dosage on the Adsorption of Selected Metals 64 5.6 Effect of Particle Sizes on the Removal of Selected Metals Cd2+, Cr6+ and Cu2+ 64
5.7 Effect of Agitation Speed on the Adsorption of Selected Metals 65
5.8 Effect of pH on the Removal of Heavy Metals 66
5.9 Effect of Activating Agents on the Adsorption of Selected Heavy Metals 67
5.10 Effect of Initial Concentration on the Adsorption of Selected Metals 68
5.11 The Langmuir and Freundlich Isotherms Modeling for Metals Uptake 69
5.12 Separation Factor RL 70
CHAPTER SIX 72
6.0 SUMMARY, CONCLUSION AND RECOMMENDATION 72
6.1 Summary 72
6.2 Conclusion 72
6.3 Recommendation 73
REFERENCES 74
APPENDICES 88
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CHAPTER ONE
1.0 Introduction
1.1 Background to the Study
Heavy metals are environmental pollutants that can be derived from various sources including lead in petrol, industrial effluents, purification of metals, smelting of ores, preparation of nuclear fuels and electroplating (Al-Omair and El-Sharkawy, 2001; Shikurrullahet al., 2006). These metals are any elements in the d-block of the periodic table, usually referred to as transition metal (Ahmad et al., 2006). Some are known to be harmful to both human and other living forms, with their accumulation over period of time causing damage to kidney, liver, lung, and reproductive system (Anwar, et al., 2010; James et al., 2007; Gimbaet al., 2004). They percolate into soil, underground water and surface water. Unlike organic pollutants, heavy metals are not biodegradable and are thus considered a challenge for remediation.
Many nations including Nigeria have set up bodies concerned with the protection of the environment from degradation. In Nigeria for instance, we have the National Environmental Standards and Regulation Enforcement Agency (NESREA). Its duties range from enactment of laws granted to them by empowering body, to the implementation of these laws. It also ensure that wastes from industries are treated to remove the hazardous chemicals before they are introduced into environment and water bodies such as rivers, lakes etc. (Mayflor, 2009). Accordingly, many studies have been carried out on removal of heavy metals using ion exchange, reverse osmosis, chemical precipitation, electro-dialysis, electrolytic extraction and coagulation techniques. However, a number of these are too expensive or incapable of meeting treatment objectives. Adsorption on the other hand, has been shown to be potentially viable alternative with adsorption using activated carbon is the most common method.
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1.2 Activated Carbon
Activated carbon is an amorphous form of carbon in which a high degree of porosity has been developed during manufacturing or treatment. This high degree of porosity and associated large surface area make it an excellent adsorbent for a wide variety of heavy metals in both liquid and gaseous phases (Abram, 1973).The use of “carbon” dates back to ancient Egypt (1500BC) where it was employed for medicinal purposes. Later in ancient Greece, wood chars were used to treat host of ailments (Yehaskel, 1978). In the 18th century, an application was found for the removal of foul odors from gangrene (Al-Omair and El- Sharkawy, 2001). Subsequently, the application of charcoal was used mainly as a decolorizing agent for sugar (Sun and Xu 1997). A wide variety of agricultural by-products and agricultural wastes comprising mostly cellulose matrix were tried by different workers for removal of heavy metals from their aqueous solutions. These include pine bark (Al-Ashehet al., 2000), saw dust (Argunet al., 2007), cotton (Ozsoy and Kumbur, 2006), fibre (James et al., 2007) biomass of fungi and yeast (Kumud and Emilia, 2007), Carica papaya seed (Omeizaet al., 2011), etc. The preparations of activated carbon from agricultural wastes is motivated by cost considerations (relatively cheaper), local generation in developing countries and effectiveness in the removal of heavy metals (Loo, 1974 and Madukasiet al., 2001). This research investigated the efficiency of activated carbon produced from plantain peel in the adsorption of three selected heavy metals (cadmium, copper and chromium) from their aqueous solutions under variable factors such as: agitation speed, agitation time, particle sizes, pH, initial concentration of the adsorbate and different chemical activation among others.
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1.3 Plantain Peel
Plantain is an important staple food in many developing countries, especially in Africa. It provides food security and income for small-scale farmers who represent the majority of producers (Akyeampong, 1999). Only about 15% of the global plantain production is involved in international trade; most production is consumed domestically FAO (2005). Plantains, like banana, are believed to have originated in Southeast Asia, having been cultivated in south India by 500 BC. From here, ancient trade routes distributed it to Africa through Madagascar. By 1000 AD, plantains had spread eastward to Japan and Samoa. It arrived in the Caribbean and Latin America by 1500 AD. Since then, it has spread widely throughout the tropics Oladele and Aina (2007). The scientific names of most cultivated bananas are Musa acuminate and Musa balbisiana, depending on their genomic constitution. The plantain peel principally consists of cellulose, pectin, pigment and proteins (Microsoft Encarta, 2009; Fortier et al., 1953).
1.4 Justification for the Research
The hazardous and adverse effects caused by heavy metals present in waste waters which are released onto the environment from different industries are of significant environmental concern. Heavy metals are non-biodegradable and bio- accumulates in living organisms thereby causing various damages, diseases and disorder. Hence, attention is currently on the use of cost effective adsorbent which studies have shown to exhibit high adsorption capacity of unwanted pollutants (Ahalyaet al., 2003). The need to search for new technique for removing of heavy metals from waste waters have directed attention to adsorption based on the metal binding capacities of different agricultural waste like cassava husk, tree bark, ground nut husk, saw dust among others (Volesky and Holan, 1995). The adsorption of heavy metals is an effective method for treatment
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of effluents mainly because of following advantage features: cheaper cost, regeneration of adsorbent, high metal binding efficiency, high efficiency in dilute effluents, no additional nutrient requirement, readily available raw material and minimal usage of chemicals among others (Pattabhiet al., 2008).
1.5 Aim and Objectives
The aim of this research was to prepare activated carbon from plantain peel by using various activating agents and application for the adsorption of some selected heavy metals. The above aim would be achieved by the following objectives
1 Determination of the elemental composition of plantain peel.
2 Preparation of activated carbon from plantain peel by chemical activation method using ZnCl2, H3PO4 and NaOH as activating agents.
3 Evaluation some physicochemical properties of the adsorbent.
4 Studying the effects of contact time, adsorbent dosage, agitation time, agitation speed, pH and initial concentration on the adsorption efficiency in order to ascertain the optimum conditions as well as nature of the adsorption process of the selected heavy metals (Cu2+, Cr6+ and Cd2+) on the activated plantain peel.
5 Investigation of the adsorption efficiency of activated carbon prepared from plantain peel with variable particle sizes on adsorption of selected heavy metals.
6 Examination of the adsorption efficiency using adsorption isotherm models.
7 Determination of adsorption efficiency using RL value.
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