ABSTRACT
The need to clean-up heavy metals that contaminate water cannot be over emphasized. This
paper examined the kinetics of lead adsorption using activated rice husk ash. The influences of
contact time, adsorbent dose, pH and temperature on adsorption were investigated. From the
results obtained, by analyzing the effect of contact time, it was discovered that maximum
adsorption of about 90 % removal efficiency took 240 minutes using 0.2g of adsorbent. While in
testing for the effect of adsorbent dose, the study found that for 180 minutesusing a dose of 0.4g
of adsorbent, 90 % removal efficiency was obtained at pH 3.0.It was also discovered that the
amount of lead ion adsorbed per gram of the adsorbent increased with decreasing concentration
of lead (Pb) and that the percentage efficiency of adsorption increased with decreasing
temperature. The two theoretical adsorption isotherms, namely, Langmuir and Freundlich were
used to describe the experimental results. The Langmuir adsorption isotherm best fittted the
model for the study with its correlation coefficient R2of 0.982. The adsorption of lead (Pb)
followed the first order kinetics with the correlation R2 of 0.985 and was found to be pH
dependent with a maximum value at pH 3.0. Based on the findings, the study therefore
recommended that Industries, governments and individual households should consider the use of
rice husk ash in wastewater treatment due to its high efficiency and relative cost effectiveness.
TABLE OF CONTENTS
Title Page ………………………………………………………………………………………..ii
Certification Page………………………………………….
……………..………………..…….iiiApproval Page
………………….……………………………………. ……………..………….iv
Dedication ………………………………………………………………………..……….…v
Acknowledgment …………………………………………………………………………….…vi
Abstract…………………………………………………………………………………………vii
Table of Contents……………………………………………………………………………. ….viii
List of Table ……………………………………………………………………………………xii
List of Plates ………………………………………………………………………..…………xiv
List of Figures ………………………………………………………………………….xiii
CHAPTER ONE:
INTRODUCTION
1.1 Background of Study ……………………………………………… …………………….1
1.2 Research Problem ………………………………………………………………..………6
1.4 Research Objective …………………………………………………………….……..6
1.5 Scope and Limitation…………………………………………..…………………………7
CHAPTER TWO
LITERATURE REVIEW
ix
2.1 Adsorption……………………………………………………………………………….8
2.2 Types of Adsorption
2.2.1 Physical Adsorption……………………………………………………………….9
2.2.2 Chemisorption……………………………………………………………………….9
2.3 FACTORS AFFECTING ADSORPTION
2.3.1 Particle size of Adsorbent…………………………………………………………11
2.3.2 Surface Area……………………………………..………………………………11
2.3.3 Temperature…………………….….………………………………………………12
2.3.4 pH………………………………………………………………………………..13
2.3.5 Solubility of Solute………………………………………………………………. 14
2.4 Rice Production and Availability of Rice Husk in the world and in west Africa
……………………. …………………………………………………………………….14
2.5 Adsorbent…………………………………………….…………………………………. 18
2.6 Adsorption Isotherms
2.6.1 Langmuir Adsorption Isotherm……………………………….…………………22
2.6.2 Freundlich Adsorption Isotherm………..…………………..……………….… 24
2.7. EXISTING KINETICS
2.7.1 Pseudo First Order Kinetics………………………………………………………25
2.7.2 Pseudo Second Order Kinetics…………………………………………….…….26
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CHAPTER THREE
METHODOLOGY
3.1 Collection of Sample……………………………………………………………………..27
3.2 Activation of Rice Husk Ash……….……………………………………………………28
3.3 Preparation of Metal Solution………………………………………………………..….30
3.4 Batch Adsorption of Lead by RHA……….……………………………………………..31
CHAPTER FOUR
DISCUSSION
4.1 Characteristic of Incinerated Rice husk Ash…………….……………………………………….35
4.2 Effect of Contact Time on the Adsorption rate……………… …………………………..39
4.3 Effect of pH ……………………………………………………………………………..41
4.4 Effect of Initial Concentration of Lead on the Removal Per % and
Adsorption……………………………………………………………………………………..…43
4.5 Effect of Temperature………………………………………………………………………..46
4.6 Effect of Adsorbent Dose……………………………………………………. ………….48
4.7 Determination of Suitable Isotherm…………….…………………….………………….49
4.8 Determination of Suitable Kinetics Model……………………..………………………..56
4.9 Coefficient Correlation of Adsorption Isotherms..…………………………………..60-61
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 Conclusion……………………………………………………………………………….63
xi
5.2 Recommendation…………………………………………………………………………63
Reference…………………….…………………………………..……………………..……64 -69
Appendix…………………………………………………………………………………….69-90
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Lead-based compounds have been a major source of environmental contamination during these
past decades. Lead has been reported to affect human health and as a possible cause of human
cancer (Lin et al., 1996). Due to developments in technology, environmental pollution has
become one of the most important contemporary problems. Industrial effluents have a great
potential to cause lakes, streams, rivers and sea pollution. The ever increasing industrialization
has increased discharge of heavy metals into the environment. Heavy metals contamination
exists in aqueous waste streams of many industries, such as metal finishing, electroplating,
metallurgical work, mining, chemical manufacturing, pesticides, fertilizers, dyes, pigments,
tanning and battery manufacturing industries (Kang et al.; 2007; Lesmana et al.; 2009). Heavy
metals have been reported as priority pollutants, due to their mobility in natural water
ecosystems. Their presence have caused severe environmental problems due to their toxicity
even at low concentrations and insusceptibility to the environment. These heavy metals are nonbiodegradable
and tend to accumulate in living organisms, causing various diseases and
disorders. For instance, cadmium exposes human health to severe risks, as it can aggravate
cancer, bone damage, vomiting, diarrhea, kidney damage, mucous membrane destruction, and
affect the production of progesterone and testosterone (Godt et al., 2006). So far, a number of
efficient methods have been suggested by researchers for the removal of heavy metals among
which are chemical precipitation, ion exchange, reverse osmosis, electrodialysis, ultrafiltration,
nanofiltration, coagulation, flocculation, floatation, etc. However, these methods have several
disadvantages such as high reagent requirement, unpredictable metal ion removal, generation of
2
toxic sludge etc. Adsorption process, being very simple, economical, effective and versatile has
become the most preferred method for removal of toxic contaminants from wastewater. Table
1.1 shows the comparism using adsorption process with other conventional method.
Table 1.1: Comparison among wastewater treatment technologies. [Luqman
Chuah Abdullah et al., (2010)].
Physical and/or chemical
process
Advantages Disadvantages
Oxidation
Rapid process for dye removal.
High energy costs and formation
by products.
Ion-exchange
Good removal of a wide range of
metals and dyes.
Absorbent requires
regeneration or disposal.
Membrane filtration
technologies
Good removes of heavy metals
and dyes.
Concentrated sludge production,
expensive
Coagulation/flocculation
Economically feasible
High sludge production and
formation of large particles
Electrochemical treatment
Rapid process and effective for
certain metal ions
High energy costs and formation
of by-products
Ozonation Applied in gaseous state:alteration
of volume
Short half life
Photochemical No sludge
production
Formation of byproducts
Irradiation Effective at lab
scale
Required a lot of
dissolved O2
Biological treatment Feasible in removing some
metals and dyes
Technology yet to be
established and commercialized
Adsorption (i) The high cost of AC limits its
use in adsorption
(ii) Many varieties of low-cost
adsorbents have been developed
and tested to remove heavy
metal ions
(iii) Biosorption is a relatively
new process that has proven very
promising for the removal of
heavy metal from wastewater
(i) Removal of heavy metals
from low wastewater
concentration
(ii) Adsorption efficiency
depends on the type of
adsorbents
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On the other hand, lead (Pb) has been as one of the three most toxic heavy metals that have
dormant long-term negative impacts on health, causing hepatitis, anemia, nephritic syndrome,
brain damage, mental deficiency, anorexia, vomiting, malaise and encephalopathy (Deng et al.;
2006). Also, zinc poisoning can cause to nausea, vomiting, loss of appetite, abdominal cramps,
diarrhea, headaches, anemia, damage to the pancreas, and decrease in levels of high-density
lipoprotein (HDL) cholesterol. Conventional methods for heavy metal removal from water
include ion exchange, reduction, precipitation, evaporation, electrochemical treatment,
membrane filtration, reverse osmosis, electrodialysis and carbon adsorption. Most of these
methods may be expensive or ineffective when metals are dissolved at relatively low
concentrations (Volesky, 1990).
Adsorption has been proved to be an excellent method to treat contaminated water, offering
significant advantages like low-cost, greater availability, profitability, easiness of application
and effectiveness in reducing the concentration of heavy metal ions to very low levels
(Demirbas, 2008). Thus, Cost considerations can make it expedient to use local materials,
produced in agricultural or industrial operations as adsorbents for toxics. Adsorption process is
recommended for the removal of low concentrations of metal ions in water. This process
implies the presence of an “adsorbent” solid that binds molecules by physical attractive forces,
ion exchange, and chemical binding like activated carbon. Activated carbon is the most popular
and widely used adsorbent for heavy metal removal in water treatment applications throughout
the world. Though it is prolific in use, it remained an expensive material because its cost
increased with it quality (Babel and Kurniawan, 2003).
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The table 1.2 shows the maximum level of contaminants that drinking water should not exceed
as recommended by the World Health Organization (WHO) and the National Agency for Food
and Drugs Administration and Control (NAFDAC).
Table 1.2 Guideline for drinking water by the World Health Organization (WHO,
1998) and National Agency for Food and Drugs Administration and Control (NAFDAC),
Nigeria.
No Heavy metal Max. acceptable conc.
(WHO,1998)
Max. acceptable conc.
(NAFDAC, 1998)
1 Zinc 5mg/l 5mg/l
2 Arsenic 0.01mg/l 0.0mg/l
3 Magnesium 50mg/l 30mg/l
4 Calcium 50mg/l 50mg/l
5 Cadmium 0.003 0.0mg/l
6 Lead 0.01mg/l 0.0mg/l
7 Silver 0.001mg/l 0.0mg/l
8 Mercury 0.001 0.0mg/l
Another type of adsorbent is agricultural waste materials. Agricultural waste materials are
usually generated in large quantities. Rice husk, a type of agricultural waste material, which is a
major by-product of the rice milling industry and is one of the most commonly available
lignocellulosic materials. For example, the annual rice husk produced in India is approximately
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120 million tons. Typically it is chemically composed of 20% ash, 38% cellulose, 22% lignin,
18% pentose, and 2% other organic components (James and Rao, 1986). Lignin, one of its
major components, is a natural amorphous cross-linked resin that has an aromatic threedimensional
polymer structure containing a number of functional groups such as phenolic,
hydroxyl, car boxyl, benzyl alcohol, methoxyl, and aldehyde groups (Sarkanen and Ludwig,
1971), making it potentially useful as an adsorbent material for the removal of heavy metals
from water.
1.2 RESEARCH PROBLEM
Heavy metals pose a risk of contaminating groundwater and surface water sources due to
geogenic activities, industrial and agricultural sources (Daping et al.; 2015). The removal of low
concentrations of heavy metals e.g., cadmium, lead and zinc from drinking, industrial and
irrigation water is a recurring challenge, especially in developing countries. The removal of this
heavy metals from our water and wastewater using adsorption process was proved to be an
excellent way to treat contaminated water, offering significant advantages like low-cost, greater
availability, profitability, easiness of operation and effectiveness in reducing the concentration
of heavy metal ions to very low levels (Demirbas, 2008). Thus, cost considerations, greater
availability and effectiveness has made it expedient to consider the use of local agricultural
materials like rice husks to treat contaminated water.
I.3 RESEARCH OBJECTIVE
i. To characterize rice husk ash;
ii. To investigate the effect of pH on the adsorption of lead by rice husk ash(RHA);
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iii. To investigate the effect of temperature on the adsorption of lead by rice husk
ash(RHA);
iv. To determine the effect of contact time on the adsorption of lead by rice husk ash(RHA);
and
v. To obtain the appropriate adsorption isotherm and kinetics for lead adsorption by rice
husk ash(RHA)
1.4 SCOPE AND LIMITATIONS
The scope of this research is limited to determining the adsorption properties of rice husk ash.
Several constraints were encountered during the course of the project. The constraints included
inadequate laboratory facilities, finance and poor energy supply.
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