ABSTRACT
The efficiency of unmodified (UMGK) and modified (MGK) Garcinia kola pod husk were investigated as adsorbents for removal of Cr(III), Pb(II) and Cd(II) from aqueous solution. Parameters of importance such as pH, adsorbent dosage, initial metal ion concentration, contact time, temperature, and co ions were conducted in batch process to assess sorption capacities of the adsorbent. The adsorption process was optimum for the Cr(III) at pH 6, pH 4 for Pb(II) and pH 6 for Cd(II) in which MGK showed higher sorption capacity 6.0639,5.4981 and 6.1206 respectively from the metal ion. The adsorbent dosage was a determining factor of efficiency in the adsorption pores. In all the three metal ions, increase in dosage increased adsorbent efficiency for both MGK and UMGK. The effect of varying the metal ion concentration showed that the MGK had high sorption capacities as compared to the UMGK while the contact time showed progressive sorption capacities until equilibrium was attained between 90 mins. The effect of temperature indicated that the adsorption process will decrease with increase in temperature for both UMGK and MGK pod husk. The effect of co ions in the batch process indicated a decrease in sorption capacities of the adsorbent. The FTIR analysis revealed some functional group that are possible site of adsorption for the UMGK and the MGK modified spectra introduced an adjusted thiol group. The SEM images correspond to a good surface coverage of the adsorbent. The equilibrium data was analyzed using Languimur and Freudlich isotherm models. The equilibrium indicated the following order of fit for the isotherms Freudlich> Languimur. The pseudo first order and pseudo second order model were used to analyze the kinetics of the adsorption process. The pseudo second order gave the best interpretation of the experimental data. Generally, the UMGK results obtained showed a good sorption capacity and removal efficiency but the MGK had a better sorption capacity. The adsorbent showed affinity for the metal ion in the order Cd (II)> Cr(III)> Pb(II).
TABLE
OF CONTENTS
Title page
i
Declaration
ii
Certification
iii
Dedication
iv
Acknowledgement
v
Table of contents
vi
List of tables
x
List of figures
xi
Abstract
xiii
CHAPTER 1: INTRODUCTION
1.1 Background
to the Study 1
1.2 Chemical
Modification of Adsorbent
2
1.3 Statement
of the Problem 2
1.4 Aim
and Objectives of the Study 2
1.5 Justification
of the Study 3
1.6 Scope
and Limitations of the Study 3
CHAPTER 2: LITERATURE REVIEW
2.1 Origin and Geographical Distribution
of Garcinia Kola
4
2.1.1
Uses of Garcinia kola
4
2.1.2
Pharmacological activity of Garcinia
Kola
4
2.1.3
Description of Garcinia Kola pod husk
and chemical constituent of Garcinia Kola 5
2.2 Heavy Metals
5
2.3 Toxicity of
Heavy Metals
6
2.3.1 Nickel
6
2.3.2 Lead
7
2.3.3 Mercury
8
2.3.4 Arsenic
8
2.3.5 Cadmium
8
2.3.6 Chromium
9
2.3.7 Copper
9
2.4 Methods for Heavy Metal Removal
10
2.4.1
Precipitation
10
2.4.2
Distilation
10
2.4.3 Reverse osmosis
10
2.4.4 Solvent extraction
10
2.4.5 Ion
–exchange 11
2.4.6
Electrodialysis
11
2.4.7 Ultra filtration 11
2.4.8 Phytoremediation
11
2.5 Sorption
Process
11
2.5.1 Adsorption
11
2.5.2
Biosorption process
13
2.5.3 Biosorption mechanism
14
2.6 Desorption Process
15
2.7 Adsorbents
15
2.8 Biosorbents
16
2.8.1 Plant extracts evaluated as biosorbents by other
authors
16
2.9 Factors Affecting Biosorption Capacity of Metal
Ions
20
2.9.1 pH
20
2.9.2 Dosage
20
2.9.3 Temperature 21
2.9.4 Initial concentration of metal ions
21
2.9.5 Contact time 21
2.10 Adsorption Isotherms and Kinetic Models
21
2.10.1 Equillibrium
isotherm and kinetic models 21
2.10.2 Languimur adsorption isotherm
21
2.10.3 Freudlich adsorption isotherm 22
2.10.4 Dubnin –Radushkevic (D –R) isotherm
23
2.10.5 Kinetics models
23
2.10.6 Pseudo first order
24
2.10.7 Pseudo second order
24
CHAPTER 3: MATERIALS AND METHODS
3.1 Chemicals and Reagents
25
3.2 Glassware and Apparatus
25
3.3 Sample Collection Processing and Preparation of
Adsorbent 25
3.3.1 Chemical activation of the adsorbent 26
3.3.2 Chemical modification of adsorbent
26
3.4 Preparation of Metal Ion Solutions 26
3.5 Instrumentation
27
3.5.1 Fourier-Transform
Infrared Spectroscopy ( FTIR) sample preparation 27
3.5.2 Scanning Electron Microscope (SEM)
analysis preparation 27
3.6 Batch Biosorption Experiments
28
3.6.1 Determination
of the effect of pH in the adsorption of Cr3+, Pb2+ and Cd2+ ions onto Garcinia kola pod husk
28
3.6.2
Determination of the effect of adsorbent
dosage on the adsorption of Cr3+,
Pb2+ and
Cd2+ ions
onto Garcinia kola pod husk.
28
3.6.3
Determination of the effect of initial
metal ion concentration on the adsorption of Cr3+,
Pb2+ and Cd2+ ions
onto Garcinia kola pod husk
29
3.6.4 Determination of the
effect of contact time on the
adsorption of Cr3+, Pb2+
and Cd2+
ions
onto Garcinia kola pod husk
29
3.6.5 Determination of the
effect of temperature on the
adsorption of Cr3+, Pb2+
and Cd2+
ions
onto Garcinia kola pod husk
30
3.6.6 Determination of the
effect of co - ions on the
adsorption of Cr3+, Pb2+
and Cd2+ ions
onto Garcinia kola pod
husk.
30
3.7 Data Analysis
31
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Effect of Modification
By Mercaptoacetic Acid on the Garcinia
kola Pod Husk 32
4.1.1 Fourier-Transform Infrared Spectroscopy ( FTIR)
32
4.1.2 Scanning Electron
Microscope (SEM)
36
4.2 Effect of pH
on the Adsorption of the Metal Ions by Unmodified and Modified Garcinia Kola Pod Husk.
39
4.3 Effect of Adsorption Dosage on the Adsorption of the Metal Ions by Unmodified
and Modified Garcinia Kola Pod Husk.
42
4.4 Effect of Initial Metal Ion Concentration on
the Adsorption of the Metal Ions by Unmodified and Modified Garcinia Kola Pod Husk.
45
4.5 Effect of Contact Time on the Adsorption of the
Metal Ions by Unmodified and Modified Garcinia
Kola Pod Husk.
48
4.6 Effect of Temperature on the Adsorption of the
Metal Ions by Unmodified and Modified Garcinia
Kola Pod Husk.
52
4.7 Effect of Co - Ions on the Adsorption of the
Metal Ions by Unmodified and Modified Garcinia
Kola Pod Husk.
55
4.8 Adsorption Isotherms and Kinetic
Models
58
4.8.1 Langmuir isotherm model
59
4.8.2 Freudlich isotherm model 61
4.9 Kinetic models
64
4.9.1 Pseudo first order 64
4.9.2 Pseudo second order
66
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion
68
5.2 Recommendations
68
REFERENCES
APPENDICES
LIST OF
TABLES
Tables
Pages
2.1 Difference Between Physisorption and Chemisorption
13
4(a) Characteristic Adsorption Band in the FTIR
Spectra of UMGK and MGK Pod
Husk
35
4(b) Characteristic Adsorption Band in the FTIR
Spectra of (UMGK + Cr3+ ) and
(MGK + Cr3+ ) Pod Husk 36
4.1.1 Equilibrium sorption capacities [qe(mg/g)] of Cr3+, Pb2+
and Cd2+ ions onto
Unmodified and Modified pod husk for the effect of pH 41
4.1.2 Removal Efficiency (%R) of Cr3+,
Pb2+ and Cd2+ ions
onto Unmodified and
Modified pod husk for the effect of pH 41
4.2.1 Equilibrium sorption capacities [qe(mg/g)] of Cr3+, Pb2+
and Cd2+ ions onto
Unmodified
and Modified pod husk for the effect of adsorbent dosage 44
4.2.2 Removal Efficiency (%R) of Cr3+,
Pb2+ and Cd2+ ions
onto Unmodified and
Modified pod husk for the effect of adsorbent dosage
44
4.3.1 Equilibrium sorption capacities [qe(mg/g)] of Cr3+, Pb2+
and Cd2+ ions onto
Unmodified and Modified pod husk
for the effect of initial metal ion concentration 47
4.3.2 Removal Efficiency (%R) of Cr3+,
Pb2+ and Cd2+ ions
onto Unmodified and
Modified pod husk for the effect of Initial Metal Ion concentration 47
4.4.1 Equilibrium sorption capacities [qe(mg/g)] of Cr3+, Pb2+
and Cd2+ ions onto
Unmodified and Modified pod husk for the effect of
contact time
50
4.4.2 Removal Efficiency (%R) of Cr3+,
Pb2+ and Cd2+ ions
onto Unmodified and
Modified pod husk for the effect
of contact time
51
4.5.1 Equilibrium sorption capacities [qe(mg/g)] of Cr3+, Pb2+
and Cd2+ ions onto
Unmodified and Modified pod husk for the effect of
temperature 54
4.5.2 Removal Efficiency (%R) of Cr3+,
Pb2+ and Cd2+ ions
onto Unmodified and
Modified pod husk for the effect
of temperature
54
4.6
Langmuir Isotherm Constants
60
4.7
Freudlich Isotherm Constants
63
4.8 Pseudo
First Order Kinetics Constants
65
4.9 Pseudo Second Order Kinetics Constants
67
LIST
OF FIGURES
Figures
Pages
2.1 Garcinia Kola Pod
5
2.2
Mechanism of Adsorption 15
4(a) Unmodified Garcinia Kola
Pod Husk FTIR
33
4(b) Modified Garcinia Kola Pod
Husk FTIR
34
4(c) Unmodified Garcinia Kola Pod
Husk + Cr3+ FTIR
34
4(d) Modified Garcinia Kola
Pod Husk + Cr3+ FTIR
35
4(e) Unmodified Garcinia Kola
Pod Husk SEM
37
4(f) Unmodified Garcinia Kola
Pod Husk + Cr3+ SEM
37
4(g)
Modified Garcinia Kola
Pod Husk SEM
38
4(h)
Modified Garcinia Kola
Pod Husk + Cr3+ SEM
38
4.1 Plot of Adsorption Capacity versus pH for
Unmodified Garcinia Kola Pod Husk.
40
4.2 Plot of Adsorption Capacity versus pH for
Modified Garcinia Kola Pod Husk.
40
4.3 Plot of Adsorption Capacity
versus Adsorbent Dosage for Unmodified Garcinia
Kola Pod Husk.
43
4.4 Plot of adsorption capacity versus
Adsorbent Dosage for Modified Garcinia Kola
Pod Husk 43
4.5 Plot of Adsorption Capacity versus Initial
Metal Ion Concentration for Unmodified
Garcinia
Kola Pod Husk 46
4.6 Plot of Adsorption Capacity versus Initial
Metal Ion Concentration for Modified
Garcinia
Kola Pod Husk
46
4.7 Plot of Adsorption Capacity versus Contact
Time for unmodified Garcinia kola
Pod husk 49
4.8 Plot of Adsorption Capacity versus Contact Time
For Modified Garcinia Kola
Pod Husk. 49
4.9 Plot of Adsorption Capacity versus
Temperature for Unmodified Garcinia Kola
Pod Husk 53
4.10 Plot of Adsorption Capacity versus
Temperature for Modified Garcinia Kola
Pod Husk 53
4.11(a)
Plot of percentage removal vs Cr(III)
+ Co Ions for UMGK and MGK pod husk
56
4.11(b)
Plot of percentage removal vs Pb(II)
+ Co Ions for UMGK and MGK pod husk
56
4.11(c)
Plot of percentage removal vs Cd(II)
+ Co Ions for UMGK and MGK pod husk
57
4.12
Adsorption Isotherm graph
58
4.13
Langmuir Isotherm Plot of Ce/qe vs
Ce for Adsorption of Metal Ions onto
UMGK Pod Husk
59
4.14 Langmuir
Isotherm Plot of Ce/qe vs Ce for Adsorption of Metal Ions onto MGK
Pod Husk
60
4.15 Freundlich
Isotherm Plot of log qe vs log Ce for
Adsorption of Metal Ions onto
UMGK
Pod Husk 62
4.16 Freundlich
Isotherm Plot of log qe vs log Ce for Adsorption of Metal Ions onto
MGK
Pod Husk
62
4.17 Pseudo
First Order Kinetics Plot of In (qe- qt) vs Time (min) for Adsorption of
Metal Ions onto UMGK Pod Husk
64
4.18 Pseudo
First Order Kinetics Plot of In (qe- qt) vs Time (min) for Adsorption
of
Metal
Ions onto MGK Pod Husk
65
4.19 Pseudo
Second Order Kinetics Plot of t/qt vs Time (min) for Adsorption
of Metal
Ions onto UMGK Pod Husk
66
4.20 Pseudo
Second Order Kinetics Plot of t/qt vs Time (min) for Adsorption
of Metal
Ions
onto MGK Pod Husk
67
CHAPTER 1
INTRODUCTION
1.1
BACKGROUND TO THE STUDY
Environmental
pollution by heavy metals through
indiscriminate dumping of metallic compounds, Accidental discharge, Industrialization, Urbanization, Mining of
metallic ores, has been of great concern . Discharging waste materials
containing heavy metals into the environment affects human beings, plants and
animals even at low concentration. The contamination of the environment by
heavy metals is not a recent problem, but its management and prevention is
still a global issue (Monachese et al.,
2012).
Heavy metals are stable elements that the body
cannot metabolize; hence they are passed
into the food chain ( Dubey and Shiwani, 2012).
Metals such as cadmium (Cd), chromium (Cr),
copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) are associated
with environmental pollution and toxicity problems (O’Connell et al, 2008). At low concentrations, these metals can be toxic to
living organisms.
Exposure to heavy metals causes serious health effects including
organ damage, nervous system damage, reduced growth and development, cancer,
and in extreme cases, death (Shokri et
al, 2016) .
Their persistence in the environment (soil, air, water) has
serious ecological impact which range from bioconcentration ,biomagnification,
and bioaccumulation of heavy metals in the tissues of living organisms.
The removal of these heavy metals has not been cost effective
and non biodegradable hence the need for low cost efficient technique.
Several techniques have been investigated in the removal of heavy metals from
wastewaters; Distillation, Reverse osmosis, Electro-dialysis, Evaporation, Chemical
precipitation, Ion-exchange, Ultra-filtration, Nano-filtration, Flocculation
and Coagulation are some of the methods frequently used in the treatment of
wastewaters containing heavy metals, (Chukwu, 2017) .These techniques have
their own limitations such as less efficiency, sensitive operating conditions
and production of secondary sludge requiring further costly disposal (Ahluwalia
and Goyal, 2005). Scientists have shown in recent research that agricultural by products such as algae, fungi have the potential to sequester
heavy metals from aqueous solution; more also it follows a biosorption
mechanism
The
major constituent of these agricultural
by-products are usually lignin and cellulose and may also include other polar
functional groups of lignin such as alcohols, aldehydes, ketones, carboxylic,
phenolic and ether groups (Chinedu et al,
2012). These groups have the ability to bind heavy metal ions to a large extent
by donation of an electron pair from these groups to form complexes with the
metal ions in solution (Pagnanelli et al.,
2003).
1.2
CHEMICAL
MODIFICATION OF ADSORBENTS
The chemical modification of agricultural wastes used as
biosorbent solves the problem of low adsorption capacity, biological oxygen
demand, chemical oxygen demand and total organic carbon due to the removal of soluble organic compounds contained in the
agricultural waste.
Consequently, For an increased
pollutant-removing capacity, agricultural by products are chemically treated or
modified with chemical reagents in low-cost solutions such as acids or bases (Schwantes
et al., 2014). Other modifying agents
includes mineral acid (thioglycolic acid) ,organic compound (ethylene diamine
tetraacetatic acid EDTA, Methanol, Formaldehyde) aromatic compounds and
oxidizing agents (hydrogen peroxide)
The modification of agricultural by
products increases its porosity and introduces some functional group that binds
readily with the metal ion.
1.3
STATEMENT
OF THE PROBLEM
The release of heavy metals to the
environment has contributed to environmental pollution. The problem posed by
the presence of heavy metal ions in aquatic medium can be solved using low cost
agricultural waste products thereby converting waste to wealth. The use of
other methods to remove metal ions is costly as most developing countries may
not afford or maintain such methods.
1.4
AIMS
AND OBJECTIVE OF STUDY
The
present study is aimed at assessing the ability of garcinia kola pod
husk to remove toxic heavy metal ions such as Cr3+, Cd2+and
Pb2+ from aqueous medium . In order to achieve this aim, the
following objective were adopted
I.
Investigate the sorption capacity of
unmodified and chemically modified garcinia kola pod husk in the removal
of metal ions
II.
Study the effect of various operating factors
such as pH, dosage, concentration, contact time, temperature and co-ions on the adsorption process
III.
Determine the most suitable adsorption
isotherms for the adsorption process
IV.
Determine the best fitted kinetic and intra
particle diffusion model for the adsorption of the studied heavy metals.
1.5 JUSTIFICATION OF THE STUDY
The presence of pollutants in the environment is a
major concern especially in water bodies and the food chain. The toxic nature
of heavy metals in the environment is a threat to the ecosystem considering the
fact that they do not readily biodegrade into harmless end products. Other
conventional methods that are cost effective
have been used by researchers to eliminate heavy metal ions but they are
not environmentally friendly, hence the
need for a more eco-friendly method for
eliminating heavy metals from aqueous medium
has necessitated this research.
In this research,
garcinia kola pod husk an agricultural waste is being tested for its
potential to sequester metal ions from aqueous medium. This biosorbent is
readily available, economically feasible and above all biodegradable.
1.6 SCOPE AND
LIMITATIONS OF THE STUDY
The study focuses on
investigating the efficiency of using Garcinia
Kola in removal of Cr3+, Cd2+and
Pb2+ heavy metal ions from
aqueous medium. This research involves a comparative study of the modified and
unmodified Garcinia Kola as adsorbent. The materials used were based on
availability. The limitations that as encountered was non steady power supply
and lack of funding.
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