TABLE OF CONTENTS

Title page ……………………………………………………………..………………………..….i
Declaration…….…………………………………….………………………….……………….…ii
Certification ………………………………………………………………………………………iii
Dedication …………………………………………………………………………………………iv
Acknowledgement …………………………………………………………………………………v
Abstract ……………………………………………………………………………………………vi
List of Figures …………………………………………………………………………………….xi
List of Tables ……………………………………………………………………………….xii-xiii
Notations and Abbreviations ………………………………………………………….…….xiv-xvi
Key Words ……………………………………………………………………………………..xvii
Table of Contents …………………………………….………………………………….xviii-xxiv
CHAPTER ONE
INTRODUCTION
1.1 Background of Study ……………………………………………………………………..1
1.1.1 Hazards of Heavy Metals Contamination ……………………………………………………..3
1.2 Statement of Problem ……………………………………………………………………..5
1.3 Objectives of Study ……………………………………………………………………….6
1.4 Significant of Study ………………………………………………………………………7
1.5 Scope of Study ……………………………………………………………………………7
1.6 Research Questions ……………………………………………………………………….8
CHAPTER TWO
LITERATURE REVIEW
1.7 Pollution …………………………………………………………………………………..9
1.7.1 Heavy Metal Pollution …………………………………………………………………9-10
xix
1.7.2 Industrial and Agricultural Pollution ………………………………………………..10-11
1.7.3 Air Pollution ………………………………………………………………………………..12
1.7.4 Water Pollution ………………………………………………………………………….12
1.7.4.1 Sea and Ocean Pollution ……………………………………………………………..12-13
1.7.4.2 Ground Water Pollution ………………………………………………………………….13
1.8 Heavy Metals in the Environment ……………………………………………………13-14
1.8.1 Need for the Removal of Heavy Metals …………………………………………………14
1.8.2 Biosorption ………………………………………………………………………….14-16
1.9 Toxocological Aspect of Heavy Metals ……………………………………………..16-17
1.9.1 Lead, Pb …………………………………………………………………………………17
1.9.1.1 Sources of Lead….. ………………………………………………………………….18-19
1.9.1.2 Health Effects of Lead …………………………………………………………………..19
1.9.2 Cadmium, Cd ……………………………………………………………………………20
2.3.2.1 Health Effect of Cadmium ………………………………………………………………21
2.3.2.2 Environmental Effect of Cadmium………………………………………………………22
2.3.2.3 Exposure to Cadmium……………………………………………………………………22
2.3.2.4 Toxicity of Cadmium…………………………………………………………………22-23
2.3.3 Copper, Cu……………………………………………………………………………23-24
2.3.3.1 Copper in Human Health…………………………………………………………..…23-24
2.3.3.2 Copper in the Environment………………………………………………………………25
2.3.4 Cobalt, Co…………………………………………………………………………….25-26
2.3.4.1 Health Effect of Cobalt……………………………………………………………….26-27
2.3.4.2 Environmental Effect of Cobalt…………………………………………………………27
2.3.5 Effect of Heavy Metals on Aquatic Organisms………………………………………27-28
2.3.6 Irrigation Effects of Heavy Metals………………………………………………………29
2.4 Conventional Methods for the Removal of Heavy Metals………………………………29
xx
2.4.1 Chemical Precipitation……………………………………………………………….29-30
2.4.2 Xanthate Process………………………………………………………………………30-31
2.4.3 Solvent Extraction……………………………………………………………………….31
2.4.4 Membrane Process……………………………………………………………………….41
2.4.5 Evaporation………………………………………………………………………………32
2.4.6 Cementation…………………………………………………………………………..32-33
2.4.7 Ion -exchange………………………………………………………………………….…33
2.4.8 Electro-deposition……………………………………………………………………….33
2.4.9 Phytoremediation…………………………………………………………………………34
2.4.10 Adsorption……………………………………………………………………………34-35
2.5 Disadvantages of Conventional Methods for the Treatment of Wastewater Containing
Heavy Metals…………………………………………………………………………….35
2.6 Adsorption Isotherms…………………………………………………………………35-36
2.6.1 Adsorption Kinetics…………………………………………………………………..36-37
2.7 Desorption……………………………………………………………………………37-38
2.8 Removal of Heavy Metals by Activated Carbon…………………………………….38-39
2.9 Removal of Heavy Metals from Aqueous Solutions by Low Cost Adsorbent………39-40
2.10 Biosorption of Heavy Metals by Dried Plant Parts Powder…………………………40-41
2.10.1 Biosorbents……………………………………………………………………………41-42
2.10.1.1 Bacteria…………………………………………………………………………………42
2.10.1.2 Algae……………………………………………………………………………………42
2.10.1.3 Fungi and Yeast…………………………………………………………………..…42-43
xxi
2.10.1.4 Clay and Fly Ash……………………………………………………………………….43
2.10.1.5 Zeolites………………………………………………………………………………….43
2.10.1.6 Peat Moss……………………………………………………………………………43-44
2.10.1.7 Agricultural Based Biosorbents……………………………………………………..44-45
2.10.2 Mechanism of Biosorption……………………………………………………………….46
2.10.3 Factors Affecting Biosorption……………………………………………………………46
2.10.3.1 Effect of pH……………………………………………………………………………..47
2.10.3.2 Effect of Temperature…………………………………………………………………..48
2.10.3.3 Effect of Adsorbent Dose……………………………………………………………….48
2.10.3.4 Effect of Metal Ion Concentration………………………………………………………48
2.10.3.5 Effect of Contact Time………………………………………………………………….49
2.10.3.6 Effect of Presence of Other Cations………………………………………………….…49
2.10.3.7 Effect of Biomass Type……………………………………………………………..49-50
2.10.3.8 Efeect of Presence of Anions (Ligands)………………………………………………..50
2.10.4 Advantages of Biosorption Procees Over Conventional Methods……………………50-51
2.11.0 Adansonia digitata Plant (Baobab)……………………………………………………….52
2.11.1 Identification and Biological Description of Adansonia digitata Plant…………………..52
2.11.2 Uses of Adansonia digitata Plant……………………………………………………52-53
CHAPTER THREE
MATERIALS AND METHODS
3.1 Apparatus and Chemicals ……………………………………………………………54-55
3.2 Preparation of Aqueous Solutions of the Metal Ions……………………………………55
xxii
3.2.1 Preparation of 1000 mg/L of Pb(NO3)2 Aqueous Solution……………………………….55
3.2.2 Preparation of 1000 mg/L of Cd(NO3)2.4H2O Aqueous Solution………………………..55
3.2.3 Preparation of 1000 mg/L of Cu(NO3)2.3H2O Aqueous Solution……………………….56
3.2.4 Preparation of 1000 mg/L of Co(NO3)2.6H2O Aqueous Solution……………………….56
3.2.5 Preparation of 0.1 M HCl Solution………………………………………………………56
3.2.6 Preparation of 0.1 M NaOH Solution……………………………………………………56
3.2.7 Preparation of 25 % ZnCl2 Solution…………………………………………………..…56
3.3 Sample Collection and Preparation…………………………………………………..56-57
3.3.1 Carbonization of the Adsorbent……………………………………………………….…57
3.3.2 Activation of the Carbonized Adsorbent…………………………………………………58
3.4 Characterization of the Adsorbents………………………………………………………58
3.4.1 Determination of Moisture Content of the Adsorbent……………………………….58-59
3.4.2 Determination of Ash Content and Volatile Matter of the Adsorbents………………….59
3.4.3 Fixed Carbon Determination of the Adsorbents………………………………………..59
3.4.4 Determination of Pore Volume of the Adsorbents……………………………………59-60
3.4.5 Determination of Bulk Density and Porosity of the Adsorbents …………………….60-61
3.4.6 Determination of pH and Conductivity of the Adsorbents………………. …………….61
3.4.7 Fourier Transform Infrared (FTIR) Spectroscopic Analysis……………………………61
3.4.8 Scanning Electron Microscopic Analysis ………………………………………………61
3.5 Batch Adsorption Experiment………………………………………………………..61-62
3.5.1 Effect of pH on Adsorption………………………………………………………………62
3.5.2 Effect of Initial Concentration of the Metal Ion on Adsorption………………………62-63
xxiii
3.5.3 Effect of Contact Time on Adsorption…………………………………………………..63
3.5.4 Effect of Adsorbent Dosage on Adsorption……………………………………………..63
3.5.5 Effect of Particle Size on Adsorption…………………………………………….………63
3.5.6 Effect Carbonization Temperature and Activation on Adsorption………………………64
3.5.7 Competitive Adsorption of the Metal Ions………………………………………………64
3.5.8 Desorption Experiment………………………………………………………………64-65
3.6 Metal Analysis……………………………………………………………………….…..65
3.6.1 Data Analysis…………………………………………………………………………65-66
3.6.2 Adsorption Isotherms…………………………………………………………………66-69
3.6.3 Adsorption Kinetics………………………………………………………………..…69-70
3.6.4 Batch Desorption Analysis………………………………………………………………70
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Characteristics of the Adsorbents ……………………………………………….…71-772
4.2 Infrared Spectroscopic Studies ………………………………………………………72-76
4.2.1 The FTIR of ADSAC Before Adsorption ………………………………………….……77
4.2.2 The FTIR of ADSAC After Adsorption …………………………………………………77
4.2.3 The FTIR of ADRP Before and After Adsorption ………………………………………78
4.3 Scanning Electron Microscopic Studies of the Adsorbents …………………………78-82
4.4 Batch mode Adsorption Studies …………………………………………………………83
4.4.1 Effect of pH Solution on Adsorption …………………………………………………83-85
4.4.2 Effect of Initial Metal Ion Concentration…………………………………………….85-87
xxiv
4.4.3 Effect of Adsorbent Dose…………………………………………………………….87-89
4.4.4 Effect of Contact Time …………..………………………………………………….89-91
4.4.5 Effect of Particle Size ……………………………………………………………..…91-92
4.4.6 Effect of Carbonization Temperature and Activation on Adsorption ……………….93-94
4.4.7 Competitive Adsorption of Pb(II), Cd(II), Cu(II) and Co(II) by Adansonia digitata plant
parts ………………………………………………………………………………….94-95
4.4.8 Adsorption Isotherms ………………………………………………………………96-118
4.4.9 Adsorption Kinetics ………………………………….……………………………119-135
4.4.10 Desorption Studies …………………………………………………………………136-137
CONCLUSION ………………………………………………………………………..…138-140
REFERENCES …………………………………………………………………………..141-152
APPENDIX ……………………………………………………………………………….153-

CHAPTER ONE

NTRODUCTION
1.1 Background of the study
The amount of heavy metals released to the environment has been increasing
significantly resulting from industrial activities and technology development1. Contaminations
by heavy metals exist in aqueous waste streams of many industries such as metal purification,
metal finishing, chemical manufacturing, mining operations, smelting, battery manufacturing,
and electroplating. As a result of industrial activities and technological development, the amount
of heavy metals discharged into streams and rivers by industrial and municipal wastewater have
been increasing incessantly2.
Heavy metals are member of a loosely-defined subset of elements that exhibit metallic
properties, which mainly includes the transition metals, some metalloids, lanthanides, and
actinides. Certain heavy metals such as iron (Fe), copper (Cu), zinc (Zn), and manganese (Mn)
are required by humans for normal biological functioning. However, heavy metals such as
mercury, lead, cadmium, cobalt are toxic to organisms. Most of the health disorders are linked
with specific tendency of heavy metals to bioaccumulate in living tissues and their disruptive
integration into normal biochemical processes3.
Increased use of metals and chemicals in the process industries has resulted in generation
of large quantities of effluent that contains high level of toxic heavy metals and their presence
poses environmental disposal problems due to their non-degradable and persistence nature.
Soil particles tend to have a variety of charged sites on their surfaces, some are positive while
some are negative. The negative charges of these soil particles tend to attract and bind the
positively charged metal cations, preventing them from becoming soluble in water. The soluble
form of metals is more dangerous because it is easily transported, hence more readily available to
plants and animals.
Metal behaviour in the aquatic environment is similar to that outside a water body.
Sediments at the bed of streams, lakes and rivers exhibit the same binding characteristics as soil
particles mentioned earlier. Hence, many heavy metals tend to be sequestered at the bottom of
water bodies. Yet, some of these heavy metals will dissolve. The aquatic environment is more
susceptible to the harmful effects of heavy metal pollution. Metal ions in the environment
bioaccumulate and are biomagnified along the food chain. The effect of heavy metals is more
2
pronounced in animals at higher trophic levels4. Some metals may be either beneficial or toxic,
depending on concentration.
Lead (Pb) is the most significant toxic of the heavy metals and its effects are of a
toxicological and neurotoxic nature including irreversible brain damage in humans. Inorganic
forms of lead typically affect the central nervous system, peripheral nervous system, and
hematopoietic, gastrointestinal, cardiovascular, and reproductive systems. Organic lead toxicity
predominantly tends to affect the central nervous system. Other hazardous effects of lead are
visual disturbances, convulsions, loss of cognitive ability, antisocial behavior, constipation,
anemia, tenderness, nausea, vomiting, severe abdominal pain, and gradual paralysis in the
muscles5. However, human activity has resulted in atmospheric Lead, mainly as PbSO4 and
PbCO3. Industries such as coating, paint, lead smelting and mining generate large quantities of
wastewater containing various concentrations of lead.
Another element of interest is copper; copper (Cu) is a chemical element, a soft reddishbrown
metal used for making electric wires, pipes, etc. it is also beneficial to organisms. The
American Medical Association has recommended 1.2 – 1.3 mg/day as the dietary requirements
for Copper. On the average, drinking water accounts for less than 5 % of our daily copper intake.
The U.S. Environmental Protection Agency (U.S. EPA) has determined that copper level in
drinking water should not exceed 1300 ug/L. In 1974, congress passed the safe drinking water
Act. This law requires Environmental Protection Agency (EPA) to determine safe levels of
chemicals in drinking water which may cause health problems. The Maximum Contamination
Level Goals (MCLG) for copper has been set at 1.3 parts per million (ppm) because,
Environmental Protection Agency believes that this level of protection would not cause any of
the potential health problems resulting from excess level of Cu6. Short periods of exposure can
cause gastrointestinal disturbance, including nausea and vomiting while Long-term exposure to
copper can cause irritation of the nose, mouth and eyes and it causes headaches, stomachaches,
dizziness and diarrhea. Use of water that exceeds the maximum Level of copper over many years
could cause liver or kidney damage.
Cadmium (Cd) is present in air in the form of particles in which cadmium oxide is
probably an important constituent. Cigarette smoking increases cadmium concentrations inside
houses. The average daily exposure from cigarette smoking (20 cigarettes a day) is 2 to 4 μg of
cadmium. Cadmium concentrations in unpolluted natural waters are usually below 1 μg/dm3.
Contamination of drinking water may occur as a result of the presence of cadmium as an
3
impurity in the zinc of galvanized pipes or cadmium-containing solders in fittings, water heaters,
water coolers and taps. Food is the main source of cadmium intake for non-occupationally
exposed people. Crops grown in polluted soil or irrigated with polluted water may contain
increased concentration of Cd(II). Levels of Cd(II) concentrations in fruit, meat and vegetables
are usually below 10 μg/kg, in liver 10–100 μg/kg and in kidney 100 – 1000 μg/kg. Cadmium
concentrations in tissues increase with age. Both kidney and liver act as cadmium stores, 50–85
% is stored in kidney and liver, 30–60 % being stored in the kidney alone7.
Cobalt (Co) is used in many alloys (superalloys for parts in gas turbine aircraft engines,
corrosion resistant alloys, high-speed steels, cemented carbides), in magnets and magnetic
recording media, as catalysts for the petroleum and chemical industries, as drying agents for
paints and inks. Cobalt blue is an important part of artists’ palette and is used by craft workers in
porcelain, pottery, stained glass, tiles and enamel jewelers. The radioactive isotopes, cobalt-60, is
used in medical treatment and also to irradiate food, in order to preserve the food and protect the
consumer. As cobalt is widely dispersed in the environment humans may be exposed to it by
breathing air, drinking water and eating food that contains cobalt. Skin contact with soil or water
that contains cobalt may also enhance exposure. Cobalt is not often freely available in the
environment, but when cobalt particles are not bound to soil or sediment particles the uptake by
plants and animals is higher and accumulation in plants and animals may occur8.
1.1.1 Hazards of Heavy Metal Contamination
The main threats to human health from heavy metals are associated with exposure to
lead, cadmium, mercury, copper, cobalt and arsenic. These metals have been extensively studied
and their effects on human health regularly reviewed by international bodies such as the World
Health Organization (WHO). Heavy metals have been used by humans for thousands of years.
Although several adverse health effects of heavy metals have been known for a long time,
exposure to heavy metals continues, and is even increasing in some parts of the world, in
particular in less developed countries, though its contaminant have declined in most developed
countries over the last 100 years. For example, Cadmium compounds which are currently used in
re-chargeable nickel–cadmium batteries have increased dramatically during the 20th century, one
reason being that cadmium-containing products are rarely re-cycled, but often dumped together
with household waste. Also, cigarette smoking is a major source of cadmium exposure, while in
non-smokers; food is the most important source of cadmium exposure. Recent data indicate that
4
adverse health effects of heavy metals exposure may occur at lower exposure levels, primarily in
the form of kidney damage but possibly also bone effects and fractures9. Many individuals
already exceed these exposure levels and the margin is very narrow for large groups. Therefore,
measures should be taken to reduce heavy metals exposure in the general population in order to
minimize the risk of adverse health effects. The general population is primarily exposed to
mercury via food, fish being a major source of methyl mercury exposure, and dental amalgam.
The general population does not face a significant health risk from methyl mercury, although
certain groups with high fish consumption may attain blood levels associated with a low risk of
neurological damage to adults. Since there is a risk to the fetus in particular, pregnant women
should avoid a high intake of certain fish, such as shark, swordfish and tuna; fish (such as pike,
walleye and bass) taken from polluted fresh waters should especially be avoided. There has been
a debate on the safety of dental amalgams and claims have been made that mercury from
amalgam may cause a variety of diseases. However, there are no studies so far that have been
able to show any associations between amalgam fillings and ill health.
The general population is also exposed to lead from air and food in roughly equal
proportions. During the last century, lead exposure to ambient air has caused considerable
pollution, mainly due to lead emissions from petrol. Children are particularly susceptible to lead
exposure due to high gastrointestinal uptake and the permeable blood–brain barrier. Blood levels
in children should be reduced below the levels so far considered acceptable, recent data
indicating that there may be neurotoxin effects of lead at lower levels of exposure. Although lead
in petrol has dramatically decreased over the last decades, thereby reducing environmental
exposure, phasing out any remaining uses of lead additives in motor fuels should be encouraged.
The use of lead-based paints should be abandoned, and lead should not be used in food
containers. In particular, the public should be aware of glazed food containers, which may leach
lead into food.
Exposure to arsenic is also mainly via intake of food and drinking water, food being the
most important source in most populations. Long-term exposure to arsenic in drinking-water is
mainly related to increased risks of skin cancer, but also some other cancers, as well as other skin
lesions such as hyperkeratosis and pigmentation changes. Occupational exposure to arsenic,
primarily by inhalation, is usually associated with lung cancer. Clear exposure–response
relationships and high risks have been observed.
5
Biosorption is presented as an alternative to traditional physicochemical means for
removing toxic metals from ground-waters and wastewater. It is a relatively new process that has
proven very promising in the removal of contaminants from aqueous solutions. It has been
shown to be an economically feasible alternative method for removing heavy metals.
Mechanisms involved in the biosorption process include chemisorptions, complexation, ion
exchange, microprecipitation, hydroxide condensation onto the biosurface and surface
adsorption. The phenomenon of biosorption has been described in a wide range of non-living
biomass like nile rose plant powder and ceramics10.
In this study, the adsorption of heavy metals onto biomaterials derived from Adansonia
digitata plant commonly known as baobab was investigated. Often referred to as grotesque by
some authors, the main stem of larger baobab (Adansonia digitata) trees may reach enormous
proportions of up to 28 metres. The massive squat cylindrical trunk gives rise to thick tapering
branches resembling a root-system, which is why it has often been referred to as the upside-down
tree. The stem is covered with a bark layer, which is 50-100 mm thick. The bark is greyish
brown and normally smooth. The leaves are hand-sized and divided into 5-7 finger-like leaflets.
Being deciduous, the leaves are dropped during the winter/harmattan and appear again in late
spring or early summer/rain11.
The usefulness of the biomass of many plant materials in removing metal ions from aqueous
solution have been investigated by several researchers and all have shown that the plant base
adsorbents have the potential of being used as cheap source of biosorbent for metal ions,12,13,14,15.
However, no such work has been reported for Adansonia digitata to our knowledge.
1.2 Statement of problem
Heavy metals released by a number of industrial processes are major pollutants in marine,
ground, industrial and even treated wastewaters. A high degree of industrialization and
urbanization has substantially enhanced the degradation of our aquatic environment through the
discharge of industrial wastewaters and domestic wastes. The presence of heavy metals in water,
even at very low concentrations, is highly undesirable. The problem of heavy metal pollution in
water needs continuous monitoring and surveillance as these elements do not degrade and tend to
biomagnify in man through food chain.
This environmental problem has led to extensive research into developing effective alternative
technologies for the removal of these potentially damaging substances from effluents and
6
industrial wastewaters. Moreover, recovery of heavy metals from industrial waste streams is
becoming increasingly important to neutralize the hazard from the industrial waste harmful to
plant and animal life. Hence there is a need to remove the heavy metals from the industrial
wastewater before disposal.
1.3 Objectives of the study
The effluent treatment in developing countries is expensive and high cost is associated
with the dependence on imported technologies and chemicals. The indigenous development of
treatment techniques and chemicals or use of locally available non-conventional materials to
treat pollutants seems to be the solution to the increasing problem of treatment of effluents. In
this regard, there has been a focus on the use of appropriate low cost technology for the treatment
of wastewater in developing countries in recent years. Technically feasible and economically
viable pretreatment procedures with suitable biomaterials based on better understanding of the
metal biosorbent mechanism(s) are gaining importance. Activated carbon of agricultural waste
products as low cost adsorbents has been reported till now. However, there is an additional cost
involved in the conventional methods of waste water treatment, which is posing economic
difficulties necessitating research on alternate adsorbents with equivalent potential of the
conventional methods.
The objectives of this research were to:
(i) investigate the biosorption of some heavy metals by Adansonia digitata roots, stem
powder and activated carbon made from its stem.
(ii) identify the optimum conditions for the removal of the heavy metals by Adansonia
digitata plant parts.
(iii) compare the ability of Adansonia digitata activated carbon as adsorbent to activated
carbon from some plants.
(iv) investigate simultaneous removal of Pb(II), Cd(II), Cu(II), and Co(II) from mixed
aqueous solution by Adansonia digitata root, stem powder and activated carbon made
from the stem.
(v) develop adsorption kinetic models for the studied processes and
7
(vi) carry out desorption studies on the heavy metals loaded activated carbon (ADSAC).
1.4 Significance of the study
This study was to remove heavy metals [Pb(II), Cd(II), Co(II) and Cu(II)] which causes
environmental problem from aqueous solutions. These heavy metals cannot be destroyed as they
are not biodegradable. It means that the pollution of heavy metals in the environment will
continuously increase if there is no immediate action taken to remove these heavy metals. As
people or living organisms are exposed to the dangers of these heavy metals, it can be dangerous
because they tend to bioaccumulate and easily enter our bodies via food, drinking water, dermal
contact and air. It is important to study the removal of these heavy metals. This study, a
biosorption process, is a biological method of environmental control as an alternative to
conventional methods that are ineffective or extremely expensive. Natural materials such as
Adansonia digitata plant parts which are environmental friendly, easily available, and cheap is
been used in this study. With this technology (biosorption) and the use of Adansonia digitata
plant as an adsorbent, a huge success will be recorded in the treatment of waste waters.
1.5 Scope of the study
The scope is to study the removal of heavy metals, Pb(II), Cd(II), Co(II) and Cu(II) in
aqueous solution using Adansonia digitata roots powder and activated carbon made from its
stem through the biosorption process.
The following limit has been defined:
(i) Determination of functional groups on the surface of the sample that contribute to the
biosorption of heavy metals used in the study through infrared spectroscopy.
(ii) Determination of the pore sizes in the adsorbent that enhance the adsorption capacity
using scanning electron microscope (SEM).
(ii) Determination of the agitation/equilibrium time, pH, dosage, carbonization temperature,
particle size and effect of adsorbent at different initial metal concentrations.
(i) Calculation of the adsorption capacity and intensity using Langmuir, Freundlich, Temkin
and Dubinin- Radushkevich isotherm models.
(ii) Biosorption kinetic studies on the adsorption are investigated
(iii) Comparison between the Adansonia digitata activated carbon as adsorbents to activated
carbon from some plants found in literature.
8
1.6 Research questions
Heavy metals are one of the important pollutants in wastewater and it has become a
public health concern, because of its persistent nature. The toxicity of heavy metal is enhanced
through accumulation in living tissues and consequent bio-magnification in food chain. Nature
has given many things which are far better than artificial products. Then came a thought “Why
can’t we use Adansonia digitata plant parts as bioadsorbents for removing heavy metals from
aqueous solution? With this view, experimental questions were aim at answering the questions
below:
(i) Do Adansonia digitata plant parts have the ability to adsorb heavy metals from aqueous
solution?
(ii) How effective is the use of Adansonia digitata plant powder and its activated carbon as
adsorbent in the removal of heavy metals from aqueous solution?
(iii) What are the optimum conditions in the removal of heavy metals from aqueous solution
by Adansonia digitata plant?
(iv) What are the adsorption isotherm models for Adansonia digitata plant parts?
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