Surfactant-modified adsorbents for the removal of toxic anions in

water

BY

OLANIYI, OLARONKE TEMITOPE

RUN/CHE/14/5842

A DISSERTATION SUBMITTED TO THE DEPARTMENT OF CHEMICAL

SCIENCES, REDEEMER’S UNIVERSITY, EDE, OSUN STATE, IN PARTIAL

FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTERS OF

SCIENCE DEGREE (M.Sc) IN ENVIRONMENTAL AND ANALYTICAL

CHEMISTRY.

JULY, 2016

CERTIFICATION

This is to certify that this dissertation ―Surfactant-Modified Adsorbent for the removal of Toxic

Anions in Water” was written by OLANIYI, OLARONKE TEMITOPE (RUN/CHE/14/5842)

for M.Sc.Environmental and Analytical Chemistry in the Department of Chemical Sciences,

Redeemer’s University, Ede, Osun State.

…………………………………………

Supervisor

Dr. E. I. Unuabonah

B.Sc (Benin), M.Sc, PhD (Ibadan)

…………………………………………

Head of Department

Prof. O. G. Adeyemi

B.Sc, M.Sc, PhD (Ilorin)

…………………………………………

External Supervisor

Prof. B. I. Olu-Owolabi

B.Sc, M.Sc, PhD (Ibadan)

DEDICATION

This dissertation is dedicated to God Almighty and my family.

ACKNOWLEDGEMENT

I acknowledge God for seeing me through from the beginning to the end of this dissertation and

beyond. I also acknowledge the Vice Chancellor, Redeemer’s University, Prof. Z. D. Adeyewa.

I express my profound gratitude to The World Academy of Sciences (TWAS) for the scholarship

given to me to pursue this programme. Special gratitude to Prof. E. A. Ofomaja and all members

of the Biosorption and Water Treatment Laboratory, Vaal University of Technology. The HOD

and laboratory staff of Chemical Science Laboratory, Adekunle Ajasin University. Special

thanks to Prof. Andreas Taubert and Dr. Christian Guenter for their input to the success of this

work.

I cannot but say a big ―Thank you‖ to the members of Environmental and Chemical Process

Research Group, in the Department of Chemical Sciences, under the able leadership of Dr. E. I.

Unuabonah, other members of the advisory team; Dr. F. O. Agunbiade, Dr. M. O. Omorogie,

Dr. A. Adewuyi, Dr. O. M. Kolawole and Dr. C. P. Okoli for their prayers and support. My

gratitude also goes to Engr. Samuel for his support during the period of this project.

Also, I say ―Thank you‖ to the Department of Chemical Sciences, under the able leadership of

Prof. O. G. Adeyemi for their support. I also acknowledge my parents, Engr. and Mrs. Olaniran

Olaniyi for their love and support, my siblings Olayinka and Olawande for their prayers and

support. I also thank my friends and my course mates; Alfred, Thompson, Koko, Lekan,

Leonard, Chidinma, Jibola, Tolu, Kemi, Victor, Kenny, who instilled in me words of

encouragement. For those unmentioned here, I say thank you.

TABLE OF CONTENTS

Title Page………………………………………………………………………………………..…

i

Certification

Page………………………………………………………………………………….ii

Dedication…………………...……………………………………………………………………iii

Acknowledgement……………………………………………………………………………..…iv

Table of Contents……………………………………………………………………………….…v

List of Figures………………………………………………………………………...………..…ix

List of

Tables………………………………………………………………………..…………….xi

Abstract…………………………………………………………………………….…………….xii

CHAPTER ONE

1.0 Introduction.............................................................................................................................. 1

1.1 Statement of Problem………………………………………………………………………….2

1.2 Aim and Objectives……………………………………………………………………………3

CHAPTER TWO

2.0 Literature Review…………………………………………………………………………......4

2.1 Water

Pollution………………………………………………………………………………...4

2.2 Anions as water

contaminants…………………………………………………………………5

2.2.1 Fluoride……………………………………………………………………………...5

2.2.2

Nitrate………………………………………………………………………………..6

2.2.3

Perchlorate…...............................................................................................................7

2.2.4 Phosphate……………………………………………...…………………………….8

2.3 Water treatment techniques of anions…………………………………………………………9

2.3.1 Chemical

coagulation/flocculation…………………………………………………..9

2.3.2 Reverse osmosis……………………………………………………………………10

2.3.3 Electro-

dialysis……………………………………………………………………..11

2.3.4 Ion

exchange………………………………………………………………………..12

2.4 Adsorption…………………………………………………………………………………....13

2.4.1 Types of adsorption……………………………………………………………...…13

2.4.2 Modes of operation of adsorption………………………………………………….14

2.4.3

Adsorbents………………………………………………………………………….15 2.4.4

Low cost adsorbents………………………………………………………………..16

2.4.4.1 Red Mud……………………………………………………………….…16

2.4.4.2 Chitin and Chitosan………………………………………………………17

2.4.4.3 Rice Husk……………………………………………………………...…19

2.4.4.4 Fly Ash…………………………………………………………………...21

2.4.5 Clay

minerals……………………………………………………………………….22

2.4.5.1 Zeolite…………………………………………………………………....24

2.4.5.2 Bentonite…………………………………………………………………25

2.4.5.3 Montmorillonite………………………………………………………….27

2.4.5.4 Kaolinite………………………………………………………………….30

CHAPTER THREE

3.0 Materials and Methods…………………………………………………………………….....34

3.1 Materials and

Equipment…………………………………………………………….……….34

3.2 Methods……………………..…………………………………………………………..……34

3.2.1 Preparation of hybrid clay adsorbent (furnace-

calcined)…………………..…….....34

3.2.2 Preparation of hybrid clay adsorbent (vacuum-

calcined)…………………..…….....35

3.2.3 Preparation of modified hyca adsorbents…………………..……………..……......36

3.2.3.1 Synthesis of N-1-Napthylethylenediaminedihydrochloride

modified adsorbent (NEDD)………………………………………….…36

3.2.3.2 Synthesis of Ortho-Phenylenediamine modified adsorbent

(OP)………..37

3.3 Characterization of modified

adsorbents……………………………………………………..37

3.4 Determination of pHpzc (point of zero charge) of the

adsorbents……………………………..37

3.5 Preparation of standard reagents……………………………………………………………..38

3.6 Adsorption

studies……………………………………………………………………………39

3.6.1 Adsorption isotherm

studies……………………….….……………………………39

3.6.1.1 Freundlich

isotherm………………………………………………………39

3.6.1.2 Brouers-Sotolongo isotherm……………………….…………………….40

3.6.1.3 Jovanovic isotherm……………………………………………..………..40

3.6.2 Adsorption of phosphate……………………………………………………..…….41

3.6.3 Adsorption of nitrate and

fluoride……………………………………….………….42

CHAPTER FOUR

4.0 Results and

Discussion………………………………………………………...……………..43

4.1 Physicochemical Characterization……………………………...……………………………43

4.1.1 Fourier Transform Infrared Characterization

(FTIR)……………………………....43

4.1.2 pHpzc Characterization (Point of Zero

Charge)……………………………………..51

4.2 Adsorption of Phosphate……………………………………………………………….…….53

4.3 Adsorption of Nitrate and Phosphate………………………………………………………...65

4.3.1 Adsorption of Nitrate………………………………………………………………65

4.3.2 Adsorption of Fluoride………………………………………………………….….66

CHAPTER FIVE

5.1 Conclusion and

Recommendation…………………………………………………………....67

REFERENCES……………………………………………………………………....…………..69

APPENDIX………………………………………………………..………………….………….80

LIST OF FIGURES

Figure 2.1: The process of reverse

osmosis………………………………………………………11

Figure 2.2: Mineralogical classification associated with clay minerals…………………………23

Figure 2.3: Structure of

zeolite…………………………………………………………………...24

Figure 2.4: Structure of

bentonite………………………………………………………………...25

Figure 2.5: Structure of

montmorillonite………………………………………………………....27

Figure 2.6: Structure of

kaolinite………………………………………………………………....31

Figure 3.1: Phosphate calibration

curve……………………………………………………..……42

Figure 4.1: Fourier Transform Infrared spectra of N-1-Napthylethylenediamine

dihydrochloride modified HYCA adsorbent under Vacuum (NEDD-VCHYCA)…..44

Figure 4.2: Fourier Transform Infrared spectra of Ortho-phenylenediamine-modified

HYCA adsorbent under Vacuum (OP-VCHYCA)…………………………….…….46

Figure 4.3a: Fourier Transform Infrared spectra of N-1-Napthylethylenediamine

dihydrochloride modified HYCA adsorbent under Furnace (NEDD-FHYCA)…....47

Figure 4.3b: Fourier Transform Infrared spectra of N-1-Napthylethylenediamine

dihydrochloride modified HYCA adsorbent under Furnace (NEDD-FHYCA)…....48

Figure 4.4a: Fourier Transform Infrared spectra of Ortho-phenylenediamine

modified HYCA adsorbent under Furnace (OP-FHYCA)……………………..…..49

Figure 4.4b: Fourier Transform Infrared spectra of Ortho-phenylenediamine

modified HYCA adsorbent under Furnace (OP-FHYCA)……………………….....50

Figure 4.5: Plot of pHpzc of modified

VHYCA…………………………………………………...51

Figure 4.6: Plot of pHpzc of modified

FHYCA…………………………………………………...52

Figure 4.7: Isotherm models for adsorption of phosphate on VHYCA……………………….…59

Figure 4.8: Isotherm models for adsorption of phosphate on NEDD-VHYCA

(25)……………...59

Figure 4.9: Isotherm models for adsorption of phosphate on NEDD-VHYCA

(50)……………..60

Figure 4.10: Isotherm models for adsorption of phosphate on NEDD-VHYCA

(100)…………...60

Figure 4.11: Isotherm models for adsorption of phosphate on OP-VHYCA

(25)………………..61

Figure 4.12: Isotherm models for adsorption of phosphate on OP-VHYCA (50)……………….61

Figure 4.13: Isotherm models for adsorption of phosphate on OP-VHYCA

(100)……………….62

Figure 4.14: Isotherm models for adsorption of phosphate on NEDD-FHYCA

(25)…………….62

Figure 4.15: Isotherm models for adsorption of phosphate on NEDD-FHYCA

(50)……………..63

Figure 4.16: Isotherm models for adsorption of phosphate on OP-FHYCA

(25)………………..63

Figure 4.17: Isotherm models for adsorption of phosphate on OP-FHYCA

(50)……………..…64

Figure 4.18: Adsorption of nitrate on NEDD-VHYCA (50) and OP-VHYCA

(50)…………..…65

Figure 4.19: Adsorption of fluoride on NEDD-VHYCA (25) and OP-VHYCA

(25)…………….66

LIST OF TABLES

Table 4.1: Equilibrium isotherm analysis of the adsorption

process……………………………...56

Table 4.2: Equilibrium isotherm analysis showing the R2 and error data of the adsorption

Process………………………………………………………………………………………...…57

Table 4.3: Comparison of maximum adsorption capacity (Qm) for phosphate with other

adsorbents………………………………………………………………………...……….…..…58

ABSTRACT

An increase in water pollution has resulted to the unavailability of quality potable water to

several people in the world. This worrying environmental problem has led to the development of

various water treatment techniques. This study examined the use of surfactant modified

adsorbents for the adsorption of toxic anions in aqueous solutions.

Hybrid clay adsorbent (HYCA) was prepared in two different ways producing two materials;

vacuum-calcined hybrid clay adsorbent (VHYCA) and furnace-calcined hybrid clay adsorbent

(FHYCA). These adsorbents were enriched with Ortho-phenylenediamine (OP) and

N-1-napthylethylenediaminedihydrochloride (NEDD) through surface modification to produce

materials for toxic anions removal in aqueous solutions. Three different concentrations of the

modifiers were used; 25 mg/L, 50 mg/L and 100 mg/L. The synthesized adsorbents were

characterized using Fourier Transform Infrared spectroscopy (FTIR) and pHpzc measurement.

The pHpzc values for NEDD-VHYCA (25), NEDD-VHYCA (50), NEDD-VHYCA (100), OP-

VHYCA (25), OP-VHYCA (50), OP-VHYCA (100), NEDD-FHYCA (25), NEDD-FHYCA

(50), OP-FHYCA (25), and OP-HYCA (50) were found to be 7.31, 7.49, 7.77, 7.42, 6.73, 7.07,

6.25, 6.62, 6.75, and 7.23 respectively.

The adsorption of phosphate by the adsorbents agreed well with the Brouers-Sotolongo model

with OP-modified adsorbents been the best performing material. The maximum adsorption

capacity of OP-modified adsorbents was about 138.22 mg/g and 97.75 mg/g with correlation

coefficient of 0.9767 and 0.9773 for both FHYCA and VHYCA respectively. These adsorbents

were also applied on the removal of nitrate and fluoride in aqueous solutions, and they showed

good adsorption capacity.

Keywords: Water; Hybrid Clay; Adsorption; Phosphate; Nitrate; Fluoride

CHAPTER ONE

1.0. INTRODUCTION

Over 750 million people around the world lack access to potable water, and thus faced with

several water-related health challenges (WHO, 2014). Surface water sources are usually polluted

with dissolved solids, minerals, heavy metals, toxic anions, organic and inorganic substances

which have unfavourable effects on flora and fauna (Awuah et al., 2009). Various toxic anions

are present in water, some of which are; fluoride (F-), nitrate (NO3-), perchlorate (ClO4

-),

phosphate (PO43-

), and dichromate (Cr2O72-

). Fluoride intake at low concentration protects the

teeth from tooth decay but excess intake of this anion mainly from drinking water causes serious

health challenges such as; fluorosis, cancer, digestive and nervous disorders (Fawell et al., 2006).

On the other hand, nitrate is very soluble in water and excess of it causes methagblobinemia in

infants (Mirna et al., 2014). Furthermore, perchlorate has been reported to affect thyroid

hormone causing severe physical and mental disabilities in infants (Steinmaus et al., 2010). Also,

chromium has also been found to cause severe health problem like cancer of the lungs

(Khaldoun, 2012).

Different methods for the purification of water have been reported which include; precipitation,

reverse osmosis, coagulation, adsorption, ion exchange, ozonation, filtration and electrodialysis

(Loganathanet al., 2013). Among the several methods, adsorption is favoured because it is cost

effective, highly reliable, energy efficient, design flexible and the ability to easily regenerate

spent adsorbent (Bhatnagar et al., 2011). The common use of adsorption process in water

purification has led to the development of various materials (adsorbent) such as; activated carbon

(Dennise et al., 2013), hybrid clay (Unuabonah et al., 2013), chitosan (Viswanathan et al., 2010),

activated alumina (Maliyekkalet al., 2006), red mud (Tor et al., 2009), and ion-exchange resin

(Solangi et al., 2010).

Clay minerals have been widely used because of its favourable cationic exchange capacity, high

specific area, availability and its cost effectiveness (Du et al., 2006). However, clay minerals

have several drawbacks such as low bulk density and low flow rate when used in fixed-bed

systems. Modification of phyllosilicate materials employed for the adsorption of pollutants in

water is usually carried out to circumvent their undesirable properties. Research has shown that

modified clay mineral is more effective than the unmodified clay mineral (Xi et al., 2010).

Different materials such as metal oxides and surfactants have been used to modify clay minerals,

thereby increasing their efficiency and effectiveness.

Several research has been carried out using surfactants in modifying adsorbent materials, some

of which includes; the use of hexadecyltrimethylammoniumbromide (HDTMA-Br) as modifying

agents for bentonite, kaolinite, and halloysite clay; these modified clays were used for the

removal of nitrate in water (Xi et al., 2010). Other reported surfactant modified adsorbents are;

bolaform amphiphiles modified granular activated carbon for the removal of nitrate in water

(Dennise et al., 2013), and dodecyltrimethylammoniumbromide (DDTAB) modified

montmorillonite for the adsorption of phenolic compounds in water (Yuri et al., 2013).

1.1. Statement of Problem

The rate of technological advancement, growing industrialization, and extensive use of

chemicals has resulted in the release of unwanted contaminants (for example toxic anions:

fluoride, bromide, phosphate, perchlorate, nitrate, and dichromate) into various water

compartments. The continuous release of these contaminants has led to a decrease in drinking

water quality causing various water-borne diseases (Rajani, 2011). This worrying environmental

problem has been recognized as an issue of growing concern in recent years. To address this

challenge, it will be important to develop low-cost adsorbents that will possess high adsorption

capacity towards the removal of these contaminants from waste or polluted water system.

1.2. Aim and Objectives

The aim of this project is to develop low-cost adsorbents that will enhance the removal of toxic

anions in water systems. The objectives of this study are;

• Preparation of hybrid clay adsorbents (Kaolinite clay and Carica papaya seeds).

• Modification of the hybrid clay adsorbents with surfactants

• Characterization of the adsorbents using Fourier Transform Infrared Spectroscopy (FTIR)

and Point of Zero Charge.

• Application of the adsorbents for removal of anions (phosphate, nitrate, and fluoride) in

simulated water.

CHAPTER TWO

2.0. LITERATURE REVIEW

2.1. Water Pollution

The quality of various water compartments (drinking water, groundwater, and surface water) are

getting worse day by day due to contamination from different sources. Increases in

anthropogenic activities, technological advancement, and in world population, are some of the

factors that contribute to increasing water pollution (Gupta, 2013). It has been reported that

several people in the world lack access to potable water, however, they are left with the choice of

taking water that is polluted with chemicals and pathogens (UNICEF, 2008). Due to this,

millions die each year as a result of water-related health challenges, such as cholera, typhoid,

cryptosporidiosis, nervous disorder, and fluorosis (Fawell et al., 2006; Sobsey et al., 2008).

There are three main types of contaminants in water. They include chemical contaminants,

microbial contaminants and radiological contaminants (Yakub, 2012). The risks associated with

radioactive contaminants are minimal compared to that of chemical and biological contaminants

(WHO, 2011). Various chemical contaminants present in water includes: pesticides, halogenated

organics, fluoride, arsenic, phosphate, dichromate, perchlorate, mercury, lead, chloroform,

polychlorinated biphenyl, dioxins, dyes, polyaromatic hydrocarbon, chloride, nickel, cyanide,

iron, sulphides, cadmium, phenol, and bromide (Pradeep & Anshup, 2009).

Microbial contaminants includes: enteric bacteria like; Escherichia coli, Shigella. Spp, Vibrio

cholerae, Salmonella Typhic, Legionella spp, Mycobateria (non-tuberculosis) viruses like;

adenoviruses, astroviruses, enteroviruses, sapoviruses, rotaviruses, noroviruses, protozoa like;

Acanthamoebaspp, Cylosparacayetanensis, Entamoeba histolytica, and Naegleriafowleri (WHO,

2011).

2.2. Anions as Water Contaminants

Anions are negatively charged inorganic chemical contaminants. They include nitrate, fluoride,

phosphate, perchlorate, chloride, cyanide, and dichromate. These contaminants are of importance

to flora and fauna. However, when these contaminants are beyond permissible dose over a

prolonged period, they can cause detrimental effects to humans and aquatic environment. This

lead to the generation of limiting standards by various environmental bodies. The following are

common anions found in water: fluoride, phosphate, dichromate, perchlorate, nitrate, and

bromide.

2.2.1. Fluoride

Fluoride is one of the chemical contaminants that is found excess in the environment; surface

water and ground water. The presence of this contaminant in the environment may be as a result

of geochemical reactions or through anthropogenic activities such as disposal of industrial waste

waters (Habuda-Stanic et al., 2014).Fluoride is a fluorine ion, and it has the capability to behave

as a ligand and also to form different organic and inorganic compounds, in which most are

soluble in water (WHO, 2002). Research has shown that the presence of the naturally occurring

form of fluoride in drinking water enables its ease entrance into the human body through the

gastrointestinal tract (Yadav et al., 2007; Viswanathan et al., 2010). Asides from drinking water,

other sources of entry of fluoride into the body includes; drugs, cosmetics, industrial exposure,

and food (WHO, 2002; Habuda-Stanic et al., 2014).

The presence of naturally occurring fluoride and its concentration in water sources depends on

several factors such as; total dissolved solids, pH, alkalinity, acidity hardness, geochemical

composition of the aquifers, fluorine polluted waste water discharges usually by fertilizer

industry, aluminium and zinc smelters, glass and ceramics manufacturing processes, steel

production, and fluorinates textiles (Meenakshi et al., 2006; Mourad et al., 2009). Fluoride in

drinking water has a total effect on the teeth and bones; it strengthens the enamel (Mohapatra et

al., 2009). According to various environmental bodies, the concentration of fluoride in drinking

water should not be greater than 1.5mg/L. Continuous intake of fluoride greater than the standard

concentration can lead to various health challenges (Harrison, 2005). Health challenges related to

fluorine contaminated water includes; dental fluorosis (mottling and embrittlement), skeletal

fluorosis, crippling fluorosis, and change in DNA structure (Wang et al., 2004; Mohapatra et al.,

2009).

2.2.2. Nitrate

Nitrate is another chemical contaminant that is abundant in various environmental compartments.

It is a naturally occurring compound that is gotten after the decomposition of animal or human

waste (Aroke et al., 2014). Due to its high solubility in water, it is perhaps the widest spread

contaminant in the world (Bhatnagar et al., 2011). Nitrate is mostly available at moderate

concentrations in most natural waters; however, excessive use of fertilizers, pesticides, and

manure, has resulted in an increase in its concentration in the environment which has been

recognized as an issue of growing concern (Cengeloglu et al., 2006). Nitrate is a by-product of

septic systems, septics leaches down into the ground water resources and supply nearby water

bodies. However, water quality may be affected through groundwater resources that have a high

number of septic systems in their watershed (Aroke et al., 2014). High concentration of nitrate in

drinking water is associated with an increase of nitrosoproline levels in urine; also, nitrate

administered through drinking water have been proved to be directly related to the

concentrations of N-nitroso compounds in faces (Yang et al., 2007; Bryan et al., 2013).

The presence of high concentration of nitrate can be detrimental to the environment.

Environmental problems caused by high concentration of nitrate includes eutrophication, water

anoxia, methemoglobinemia (Blue baby) in new-born infants, production of nitrosamine which is

related to cancer, blood poisoning, and also other illnesses (Cengeloglu et al., 2006; Onyango et

al., 2010). Due to the various environmental problems related to the high concentration of nitrate

in drinking water, WHO set the standard permissible level of nitrate in drinking water to be

50mg/L (Onyango et al., 2010).

2.2.3 Perchlorate

Perchlorate is an anion that consists of a tetrahedral array of oxygen atoms around the central

chlorine atoms. It is a strong oxidizing agent that has been detected in various environmental

compartments. In most cases, perchlorate is found to be the anion associated with cations like

potassium, ammonium, and also sodium. It is usually found in the form of perchloric acid and its

salts; sodium perchlorate, ammonium perchlorate and also potassium perchlorate (Sellers et al.,

2006).

Perchlorate is a stable anion under normal atmospheric conditions and also non-volatile, due to

this, it can penetrate into drinking water aquifers (Sellers et al., 2006). Perchlorate salts are very

soluble, and due to their high solubility and non-complexing nature, it makes them very mobile

in the aqueous environment and does not give room for bioaccumulation (Mortzer, 2001;

Srinivasan et al., 2009). Furthermore, perchlorate has limited reactivity which is as a result of the

high strength of the chlorine-to-oxygen bonds; this makes perchlorate salt persist in the

environment and also makes it difficult for their removal by chemical reduction (Srinivasan et

al., 2009).There are several applications of perchlorate because it has an exceptional oxidizing

capacity. It is used as an oxidizer in explosives, flare, and fireworks, in the manufacturing of

munitions, in controlling of hyperthyroid conditions and graves diseases (Martino et al., 1986;

Srinivasan et al., 2009).

Some of the sources of perchlorate includes; release from defence and military operations, potash

ores, in corrosion control applications, in production of sodium hypochlorite (a breakdown

product), disposal of solid repellents, untreated liquid waste from hog out process, precipitation

from flame manufacturing sites, and certain fertilizers (Wilkin et al., 2007). The primary route of

human exposure to perchlorate is through the ingestion of perchlorate contaminated food or

contaminated water. Other routes include skin absorption, and inhalation of perchlorate (Shi et

al., 2007). High concentration of perchlorate in drinking water can affect the thyroid gland.

Perchlorate disrupts the uptake of iodide in the thyroid gland, and this is because perchlorate has

a similar ionic radius with iodide. Hence, it affects the production of thyroid hormone (Sellers et

al., 2006). The thyroid hormone plays a significant role in the development of the central

nervous system of infants (WRF, 2014). According to various environmental bodies, the

maximum concentration level of perchlorate in drinking water is between 1– 6µg/L (WRF,

2014).

2.2.4 Phosphate

Phosphate is a nutrient that is essential in the agricultural and aquatic environment. It is a

contaminant that is often present in drinking water and also surface water (Ma et al., 2006).

Some of the applications of phosphate include food additives, fertilizers, detergents products,

meat production, e.t.c (Lu et al., 2009). The primary sources of phosphate in surface water and

ground water are from the excessive application of fertilizer from agricultural feeds and also

discharge from wastewater treatment plants (Kumar, et al., 2010).

The continuous release of phosphate increases their concentration in water compartments, and

this can lead to an increase in eutrophication, reduction in biodiversity, excessive production of

photosynthetic aquatic microorganisms in freshwater and also marine ecosystems (Kumar, et al.,

2010). According to Environmental Protection Agency (EPA), the standard permissible level of

phosphate in water is 0.1mg/L (Akshay-Shende and Main, 2014). It is, therefore, desirable to

reduce the concentration of this contaminant below the permissible limit before discharging to

the environment due to its negative impact on the environment.

2.3 Water Treatment Techniques of Anions

Due to technological advancement leading to increasing industrial activities, there is a

continuous release of contaminants to various water compartments, causing various health

problems. Therefore, there is a need to bring down the concentration of these contaminants to an

acceptable level, so as to cause a reduction in death rate resulting from water-related diseases.

This has led to the development of various water treatment techniques (Mohapatra et al., 2009).

Various water treatment methods have been employed for the removal of contaminants in water.

The removal of contaminants in water may be best achieved at the point of use. The choice of

which water treatment technique to use depends on the water quality problems likely to be

present, and also the cost of the process (Yakub, 2012). The water treatment techniques that are

commonly used can be classified into filtration technologies and disinfection. They include

chemical coagulation or flocculation, sedimentation, chlorination and chlorine dioxide,

ozonation, solar disinfection, and ultraviolet radiation employed as disinfection techniques, while

reverse osmosis, electrodialysis, and adsorption used as filtration technologies (Sobsey et al.,

2008).

2.3.1 Chemical coagulation/flocculation

This technique involves the use of alum. Alum is made up of hydrated potassium aluminium

sulphate (KAl(SO4)2.12H2O), aluminium hydroxide (Al(OH)3) and iron salts. The alum

neutralizes the layer surrounding the suspended particles in the water, and this allows them to

flocculate together to form bigger particles. The coagulated particles can then be filtered out

(Sobsey et al., 2008). Advantages of this water treatment technique include its high efficiency

and also the commercial availability of the chemicals involved. Disadvantages include; pH

adjustment, it’s expensive, efficiency depends on the presence of other ions and pH of the water,

and there could be a possibility of formation of sludge with a high amount of toxic substances

(Habuda-Stanic et al., 2014).

2.3.2 Reverse osmosis

This treatment technique is a membrane process that can be applied to remove various

contaminants from water. It involves pushing the water under pressure through a semi-permeable

membrane that allows the passage of water and rejects the passage of dissolved constituents. It is

a process of osmosis in reverse (Lee et al., 2011). Reverse osmosis has been applied in cleaning

up waste water, treating sea water to drinking water, in recovering dissolved salts from industrial

processes (Kneen et al., 2005). It has been reported that the treatment of water with reverse

osmosis method can lead to the reduction of dissolved solids, suspended particles and variety of

ions like fluoride, nitrate, nitrite, and chloride (Kneen et al., 2005). Factors like pressure,

temperature, recovery and salt concentration of the water can influence the performance of

reverse osmosis. In the case of pressure, one of the factors that determine the amount of pressure

required is the concentration of salt in the water. The higher the salt concentration of the water,

the greater the amount of pressure needed to overcome the osmotic pressure (Lee et al., 2011).

Figure 2.1: The process of reverse osmosis (PIW, 2015)

Advantages of reverse osmosis include high efficiency, ability to remove a variety of

contaminants, no chemical is required, and no waste is produced. The drawbacks of reverse

osmosis include high capital in running and maintaining the process, there could be a problem of

clogging and fouling, and some of the membranes involved in this process are pH sensitive

(Loganathan et al., 2013; Habuda-Stanic et al., 2014).

2.3.3 Electro-dialysis

This water treatment technique is another membrane process that is applied for the removal of

ions from water across charged membranes using an electric field as the driving force (Fu et al.,

2011). In electrodialysis process, most of the membranes used are ion-exchange membranes.

They are of two types: cationic exchange membranes and the anionic exchange membranes

(Sadrzadeha et al., 2009). Electrodialysis has been reported to be widely employed for the

purification of seawater and brackish water into drinking and process water, treatment of

industrial effluents, and anions waste water treatment e.g. fluoride and salt production

(Sadrzadeha et al., 2009; Loganathan et al., 2013).Advantages of electrodialysis include

excellent removal, no requirement of chemicals, and also no production of waste. Its

disadvantages include high capital cost, the problem of polarization, high operational cost, and

requirement of skilled labour (Loganathan et al., 2013).

2.3.4 Ion-exchange

Ion exchange is a water treatment technique that involves the use of ion-exchange resins in the

removal of contaminants in water. Ion-exchange resins have the ability to exchange their anions

and cations with contaminants in the wastewater. Ion exchange resins are of two types; cationic

exchangers and anionic exchangers. Most cationic exchangers are resins with the sulfonic acid

functional groups while most anionic exchangers are resins with quaternary amine functional

groups (Fu et al., 2011). Several factors like pH, temperature, ionic charge, contact time, can

affect the efficiency of this technique (Gode et al., 2006).

Advantages of ion exchange process include high efficiency, high treatment capacity, and no

production of waste (Kang et al., 2004; Fu et al., 2011). Its drawbacks include high capital cost,

replacement of the resins after several regenerations, and low selectivity to some contaminants

(Habuda-Stanic et al., 2014).Among the several methods employed for water treatment,

adsorption has been reported to be the most attractive; because of its flexibility in design, ease of

operation, cost effectiveness compared to other methods, availability of wide range of

adsorbents, and ability to easily regenerate spent adsorbent (Bhatnagar et al., 2011).

2.4 Adsorption

Adsorption is a water treatment technique that has been established for treating domestic water,

urban wastewater, ground water remediation, and industrial effluents (Gupta et al., 2009). It

involves the deposition of substances on the surface of the material; it is a surface process (Vinod

et al., 2013). It can also be defined as a phase transfer process applied in removing substances

from fluid phases like gases and liquids. Adsorption is the enrichment of substances from fluid

phases like gases or liquids onto the surface of a material (Eckhard, 2012).

In adsorption, we have the adsorbate and the adsorbent. Adsorbate is the substance that is

accumulated on the surface of the material; it can also be called the pollutant. While adsorbent is

the material onto which, the substances are adsorbed on its surface. Adsorption process can be

operated in physical, chemical and biological systems (Eckhard, 2012). Furthermore, there are

several factors that can affect the efficiency of adsorption. They include pH, the presence of

other pollutants, temperature, the nature of the adsorbent, the nature of the adsorbate, the particle

size of the adsorbent, concentration of the adsorbate, surface area, contact time, and adsorbent

dosage (Vinod et al., 2013). Also, in enhancing adsorption efficiency, pre-filtration is required

as a result of the presence of suspended particles in the adsorbate and also oil and greases.

2.4.1 Types of adsorption

There are two different types of adsorption, depending on the type of attraction between the

adsorbent and the adsorbate; physisorption or physical adsorption and chemisorption or chemical

adsorption.

Physisorption: This is a type of adsorption in which the force of attraction that exists

between the adsorbent and adsorbate is a weak force (weak van der Waal force of

attraction). Physical adsorption is an exothermic process with a low enthalpy

(20-40kJ/mol), and this is due to the weak force of attraction, it is a process that is

reversible but not very specific. It usually takes place at a low temperature and decreases

as the temperature increases. Also, during physisorption, there is the formation of a

multilayer of the adsorbate on the adsorbent, the level of adsorption increases with

increase in the surface area of the adsorbent (Thommes et al., 2015).

Chemisorption: In this case, the type of force of attraction that exists between the

adsorbent and adsorbate are chemical forces or chemical bonds. It is also an exothermic

process but has a higher enthalpy value (80-240 kJ/mol), and this is as a result of the

strong force of attraction. It is an irreversible process but highly specific. Chemical

adsorption takes places with the formation of monomolecular layer (unilayer) of the

adsorbate on the adsorbent. It operates better at high temperature and an increase in

temperature results in an increase in chemisorption and later a decrease in chemisorption.

Finally, chemisorption also increases with increase in surface area (Kralik, 2014).

2.4.2 Modes of operation of adsorption

The mode of operation of adsorption is classified into two; batch flow system and column flow

system.

Batch Flow System: Batch Flow System: This type of adsorption operation involves the

agitation of the mixture of the adsorbent and the adsorbate for a period. A particular

weight of the adsorbent is used with a specific volume of the contaminant. After

agitation, the residual concentration is then quantified, and the material is regenerated for

subsequent use. Batch flow system in adsorption is mostly employed in the treatment of

a small volume of contaminants.

Column Flow System: In column flow system, it does not involve agitating the mixture

of the adsorbent or the adsorbate instead, the adsorbent is packed, and the adsorbate is

run continuously through it. A particular weight of the adsorbent is packed into a column,

and the contaminant is run continuously through it. In column flow system, there is room

for varying the flow rate of the contaminant through the adsorbent and also the spent

adsorbent can be regenerated for subsequent use. It can be applied in the treatment of a

large volume of water. The types of continuous flow system include: fixed bed adsorption

system, fluidized bed adsorption system and moving bed adsorption system.

2.4.3 Adsorbents

Adsorbents are materials that have the ability to stimulate the process of adsorption on their

surfaces. The process of adsorption has led to the production of various adsorbents. The most

widely used adsorbents for the removal of pollutants in water is activated carbon; this is

attributed to the fact that it is thermally stable, highly porous and also allows rapid adsorption.

(Dias et al., 2007).

Activated carbon is an environmentally friendly adsorbent that is employed by many industries.

It is a carbonaceous material; it has a large internal surface area and also a high degree of surface

reactivity that is available for adsorption process (Kalderis et al., 2008; Mohammad-Khan et al.,

2009). However, its use for water treatment at large scale is circumscribed as a result of high

associated cost of production and also its regeneration cost (Dias et al., 2007).

The use of activated carbon for water treatment has been widely studied. It has been applied for

the removal of heavy metals like mercury (Zhang et al., 2005), lead (Nadeem et al., 2006),

chromium (Liu et al., 2007), cadmium (Madhava-Rao et al., 2006), e.t.c. Activated carbon has

also been applied for the removal of anions like phosphate (Namasivayam et al., 2007), nitrate

(Namasivayam et al., 2007), perchlorate (Yoon et al., 2009), and fluoride (Daifullah et al.,

2007). However, high cost associated with the use of activated carbon, resulted in the utilization

of various materials that are less cost effective. They are called low-cost adsorbents.

2.4.4 Low cost adsorbents

Different types of low-cost adsorbents have been developed and applied for wastewater

treatment. Some of these adsorbents are prepared from agricultural waste and also industrial by-

products, hence, contributing to the minimization of waste, waste recovery and also waste reuse

(Gupta, 2013). Some of the low-cost adsorbents that have been developed include; sawdust, fly

ash, clay minerals, zeolites, metal oxides, chitosan, scrap tyres, hydroxides, rice hulls, coconut

shell, sugar cane bagasse, red mud, bark, and petroleum wastes.

2.4.4.1 Red mud

Red mud is a waste material that is produced during the production of alumina. It composes of

iron oxide, alumina, sodium oxide, and also silica (Gupta, 2013). The adsorption of fluoride from

aqueous solution with the use of red mud has been studied (Cengeloglu et al., 2002). It showed

good adsorption capacity and the mechanism for the removal of the pollutant was attributed to

ligand exchange between fluoride and the hydroxyl group on the surface of the adsorbent.

Another study was carried out on the removal of phosphate by red mud activated with heat

treatment and acid-heat treatment (Liu et al., 2007). It was reported that the red mud adsorbent

activated with acid-heat treatment performed better than the red mud adsorbent activated with

heat treatment. Also, the adsorption of phosphate was pH dependent; maximum removal was

observed at pH 5.5.Wei et al. (2009) investigated the modification of red mud with aluminium

chloride and heat activation. They both showed good adsorption capacity that is greater than the

use of ordinary red mud as an adsorbent; modified adsorbent with aluminium chloride possessed

an adsorption capacity of 68.07mg/g while that activated by heat possessed an adsorption

capacity of 91.28mg/g. It was also reported that the adsorption process was affected by pH;

highest defluoridation capacity was observed between pH 7-8.

Cengeloglu et al. (2006) examined the adsorption of nitrate with the use of ordinary red mud and

also acid activated red mud. From the study, the removal efficiency of the acid activated

adsorbent was higher than the ordinary red mud adsorbent with adsorption capacity of 5.858 and

1.859mmol/g respectively. The mechanism for the removal of nitrate was similar to that of

fluoride as reported by Cengeloglu et al. (2002). It was attributed to the chemical nature of the

adsorbent and also the interaction between the adsorbate and the metal oxides o the surface of the

adsorbent.

2.4.4.2 Chitin and chitosan

They are materials that are found in exoskeletons of crabs and also other arthropods. They are

inexpensive and also effective in nature (Gupta, 2013). Chitosan is a derivative of chitin, and it is

produced from chitin through deacetylation. Deacetylation of chitin leads to the generation of

free amino groups, and this enhances the chelating capacity of chitosan to be greater than that of

chitin (Gupta, 2013).

The adsorption of fluoride from synthetic water on chitosan was examined by Sahli et al. (2007).

It was reported that the adsorption process was rapid and affected by pH. Also, the adsorption of

fluoride from brackish water was also studied, and it was reported that the selectivity of fluoride

by the adsorbent was higher compared to other co-existing anions. Furthermore, the adsorption

of nitrate with the use of chitosan hydrogel beads was examined (Chatterjee et al., 2009). The

chitosan beads were modified with epichlorohydrin, and its surface was conditioned with sodium

bisulphate. It was observed that there was an increase in the adsorption capacity of the modified

chitosan beads compared to the unmodified chitosan beads; adsorption capacity of 104.0mg/g

and 90.7mg/g respectively. Also, it was reported that the adsorption process was temperature

dependent; an increase in temperature resulted in a decrease in the adsorption capacity of the

adsorbent.

Ma et al. (2007) prepared a magnetite-chitosan adsorbent and applied on the removal of fluoride

using batch adsorption. It was reported that the adsorption capacity was even higher than that of

the commercial activated alumina. Also from the study, it was concluded that amine and iron

oxides group on the surface of the adsorbent were the main groups involved in the adsorption

process. Chitosan/Hydrotalcite composite was prepared and applied for the adsorption of fluoride

(Viswanathan et al., 2010). It was observed that the use of the composite for adsorption of

fluoride gave a higher adsorption capacity compared with the use of hydrotalcite or chitosan

alone, with adsorption capacity of 1255mgF-/kg, 1030mgF-/kg and 52mgF-/kg respectively. This

shows that the incorporation of chitosan on hydrotalcite brought about the enhancement of the

adsorbent.

The defluoridation study of drinking water with the use of chitin, chitosan, and lanthanum-

modified chitosan was carried out by Kamble et al. (2007). Also, the uptake of fluoride was also

compared between distilled water and field water. It was observed that the lanthanum chitosan

adsorbent showed higher defluoridation capacity compared to chitin and chitosan. Furthermore,

it was reported that the adsorption process was pH dependent and also on the concentration of

other anions present. Also, from the study, there was a comparison with the use of distilled water

and field water. The defluoridation capacity was higher with the use of distilled water compared

to field water and this was concluded to be as a result of coexisting anions that are present in the

field water.

Liu et al. (2015) examined the removal of phosphate with the use of modified chitosan beads.

The chitosan beads were modified with zirconium ions. It was reported that the adsorbent

showed a good adsorption capacity of 60.6mg/g and the mechanism for the adsorption process

was as a result of electrostatic attraction and also the exchange of ions between the adsorbent and

the phosphate ions. The adsorbent was regenerated and was re-used, which gave an effective

result.

2.4.4.3 Rice husk

Rice husk is an agricultural waste product that has been widely employed for the production of

low-cost adsorbents. Several properties like its insolubility in water, high mechanical strength,

and excellent chemical stability makes this agricultural waste be a suitable adsorbent material for

the treatment of various contaminants from water (Ahmaruzzaman et al., 2011). Rice husk as an

agricultural waste can serve as a precursor for the production of activated carbon, hence,

providing a potential inexpensive material as an alternative to the commercially sold activated

carbons and also in reducing the cost of waste disposal (Ahmaruzzaman et al., 2011).

The use of rice husk ash for the removal of fluoride has been examined (Tantijaroonroj et al.,

2009). From the study, three different adsorbents were used (egg shell, activated carbon and rice

husk ash. The removal efficiencies for egg shell activated carbon and rice husk were 61.8%,

53.4%, and 42.5% respectively. Another study was carried out by Deshmukh et al. (2009)

employing the use of rice husk for the removal of fluoride in water. The rice husk was

impregnated chemically and then physically activated. A removal efficiency of about 75% was

reported, and the adsorption process was pH dependent; at a lower pH, defluoridation capacity

was higher. It was suggested by the authors to carry out the adsorption of fluoride at a lower

water pH.

Abdul et al. (2005) compared the adsorption of phosphate with the use of three adsorbents;

activated charcoal produced from rice husk, groundnut shell, and corncobs. From the study, the

three adsorbent showed good adsorption capacity, although activated charcoal produced from

corncob was the most efficient.Rice husk ash was doped with aluminium to produce aluminium

doped rice husk ash derived silica, and its uptake of phosphate from wastewater was investigated

(Salsuwanda et al., 2009). The modification of rice husk enhanced the adsorption capacity of the

material and also its adsorption kinetics study. It was reported that the adsorbent was

regenerated, and its re-use also showed a good adsorption capacity.

Ketal et al. (2012) studied the modification of rice husk for the adsorption of nitrate in water and

wastewater. From the study, a good removal efficiency of 93.4% was recorded, and the presence

of other anions affected the adsorption process. The material was also regenerated and reused,

and a static adsorption capacity was observed till its seventh cycle.

2.4.4.4 Fly ash

This is a waste material that can be obtained from discharges from sugar industries, thermal

power plants. It comprises of iron oxide, silica, carbon, alumina, and other micro-constituents

(Gupta, 2013). Fly ash is a material that is readily available; it can be applied in the production of

cement, bricks and also for road construction (Gupta et al., 2009).

The uptake of phosphate with the use of fly ash using a crossflow microfiltration system was

examined by Yildiz (2004). It was reported that the pH of the adsorbent and adsorbate and also

the concentration of the adsorbate are the most parameters to be considered for phosphate

removal. Also, the uptake of phosphate is dependent on the formation of insoluble calcium and

aluminium phosphate. Another study was carried out on the use of a medium calcium fly as with

calcium oxide content of about 11.57% for the adsorption of phosphate. It was reported that the

mechanism of removal was by precipitation, ion exchange and also weak physical interactions

between the metallic salts of phosphate and the surface of the adsorbent (Oguz, 2005).

Chen et al. (2007) examined the uptake of phosphate with the use of different fly ash (high

calcium fly ash, medium calcium fly ash, and low calcium fly ash). The three adsorbents showed

good adsorption capacity. For high-calcium fly ash, removal of phosphate was higher under

alkaline conditions. For medium-calcium fly ash, the removal of phosphate was higher at neutral

pH levels. For the low-calcium fly ash, the immobilization of the adsorbate occurred at all pH

levels. These activities were explicated by the reaction of the adsorbate with iron and calcium

components in the adsorbent. The adsorption of fluoride from aqueous solution on magnesia-

loaded fly ash cenospheres was studied by Xu et al. (2011). The adsorbent was prepared by

impregnating the cenospheres of fly ash with magnesium chloride solution. The adsorbent

showed a good defluoridation capacity of 6.0mg/g; however, the adsorption capacity was

affected by the presence of co-existing ions and also the pH. It was also concluded that fly ash is

a potential adsorbent for the removal of fluoride in waste water.

Fly ash has also been applied for the removal of nitrate from the effluent of paper mill industry

(Ugurlu, 2009). From the study, three different adsorbents were used; fly ash, raw sepiolite, and

heat-activated sepiolite. Fly ash had a good adsorption capacity, although, the heat-activated

sepiolite was more active compared with ordinary fly ash. The pH of both the adsorbate and

adsorbent played a major role in the adsorption process and also, there was an increase in the

adsorption of nitrate with a decrease in particle size.

2.4.5 Clay minerals

These are natural materials; they are generally referred to as aluminosilicate minerals. They have

particles size in the micron range and also exhibit good cation exchange attributes (Ozcan et al.,

2005). Clay minerals are generated as a result of in situ alteration of erosional cycle, they can

also be generated as a result of deposition inform of sediment during erosion cycle (Reeves et al.,

2006).There are several clay minerals; they are classified based on the stacking of the octahedral

and tetrahedral sheets into layers. When there is an attachment of an octahedral sheet between

two tetrahedral sheets; such clay is called 2:1 clay, for example, montmorillonite, and illite.

However, when there is just one tetrahedral sheet and octahedral sheet bounded together by

hydrogen bonds; such clay is called 1:1 clay, for example kaolinite (WHO, 2005).

Figure 2.2: Mineralogical classifications associated with clay minerals (Shackelford et al., 2008)

Clay minerals have various advantages among the natural minerals and over alternative

adsorbents. Clay minerals are readily available, they are relatively cheap, they are non-toxic,

they possess good adsorption properties, and also good ion exchange property for pollutants that

are charged (Du et al., 2006). Also, there can be introduction of other materials into the inner

layers of these natural materials, thus, used as new functional materials.

Clay minerals suffer drawbacks like low bulk density, clogging and also flowrate when

employed in fixed-bed systems; this led to the modification of clay minerals with materials like

surfactants, metal oxides, also acid and base treatment (Xi et al., 2010). Several clay minerals

have been examined and applied as low-cost adsorbent for the treatment of water and

wastewater. They include zeolite, kaolinite, bentonite, montmorillonite, sepiolite, and llite.

2.4.5.1 Zeolite

Zeolites are hydrated alumino silicate minerals that possess high adsorptive selectivity feature.

They are generated by connecting SiO2 and AlO4 tetrahedral sheet (Ng et al., 2008). They are

created as a result of the chemical reaction that occurs between saline water and volcanic lava.

They have a net negative charge on their surfaces. The most abundant of the zeolite species is

clinoptilolite (Gupta, 2013).

Figure 2.3: Structure of Zeolite (Bilgi, 2014)

The use of zeolite for water and wastewater treatment has been widely studied. A natural

Mexican-clinoptilolite has been evaluated for the adsorption of fluoride by Diaz-Nava et al.

(2002). The material was treated with sodium, calcium, europium and lanthanum. Their effects,

pH and also the particle size of the material on the adsorption of fluoride were investigated. It

was reported that the retention of fluoride on both the untreated and treated materials were

similar. The retention of the adsorbate was then proposed to be as a result of occlusion and

adsorption of the adsorbate on the adsorbent.

Another study was carried out by Samatya et al. (2007). They investigated the use of modified

Turkish zeolite with metal ions (aluminium, lanthanum, and zirconium dioxide) for the

adsorption of fluoride. It was reported that prior to the modification of the adsorbent, it was pre-

conditioned with nitric acid, sodium nitrate and deionized water. The adsorbent that was pre-

conditioned with nitric acid and modified with zirconium dioxide had the highest adsorption

capacity, followed by that of lanthanum and aluminium.

The use of zeolite for the adsorption of chromate has also been investigated. Campos et al.

(2007) studied the use of modified zeolite for chromate adsorption. Zeolite was modified with

hexadecyltrimethylammonium (HDTMA) and ethylhexadecyldimethylammonium (EHDDMA).

From the study, the adsorption capacity of HDTMA-zeolite was higher than EHDDMA-zeolite,

and the adsorption of chromate on HDTMA-zeolite was reported to be as a result of the

combination of hydrophobic effects, entropic, HDTMA counter ion and coulombic effects.

2.4.5.2 Bentonite

Bentonite is a clay based

mineral of high colloidal and plastic clays that comprises of majorly montmorillonite. Bentonite

is generated by the in situ devitrification of the volcanic ash. Bentonite has found uses in

improving the properties of drilling muds, pelletizing taconite iron ore, in absorbing oil and

grease and also animal wastes, treatment of water and wastewater (WHO, 2005).

Figure 2.4: Structure of Bentonite (James, 2013)

Xi et al. (2010) examined the use of modified bentonite clay for the adsorption of nitrate. The

clay mineral was modified with surfactant; hexadecyltrimethylammonium bromide. It was

reported that modifying the adsorbent gave the possibility of its use for the adsorption of nitrate,

and it showed a good adsorption capacity, although, a decrease in the surface area of the

adsorbent was observed when the modification occurred. The use of a zero-valent iron and

pillared bentonite for the removal of nitrate has been examined (Li et al., 2010). Pillared and

zero-valent iron bentonite was prepared by intercalating poly(hydroxo Al(III)) cations with zero-

valent iron into the interlayers of the clay based material. It was reported that the modified

material gave a better adsorption capacity compared with the unmodified material, and a

distinguishable high removal of nitrate was observed when a uniform mixture of the modifiers

was used. Ma et al. (2012) prepared a novel bentonite-based adsorbent for the removal of

anionic pollutants from water. Bentonite was modified with calcium oxide to produce a novel

adsorbent. The material was used for the adsorption of phosphate, fluoride, and other anionic

contaminants using a batch adsorption process. The material showed good adsorption capacity

for both fluoride and phosphate and the mechanism of adsorption was reported to be an

anion/hydroxyl (anion/OH-) exchange reaction.

Magnesium chloride was incorporated on bentonite clay and applied for the removal of fluoride

(Thakre et al., 2010). Bentonite was chemically modified using magnesium chloride to enhance

the defluoridation capacity of the material. It was reported that the material performed well over

a wide range of pH and also showed a good defluoridation capacity. Also, through the

thermodynamic study, it was suggested that the process was endothermic and spontaneous. The

spent material was regenerated and reused, a decrease in defluoridation capacity was observed.

Yan et al. (2010) investigated the adsorption of phosphate using hydroxyl-aluminium, hydroxyl-

iron, and hydroxyl-iron-aluminium pillared bentonites. From the study, the hydroxyl-aluminium

bentonite gave the highest adsorption capacity followed by hydroxyl-iron bentonite and the

mixture-bentonite. Form the thermodynamic study; it was proposed that the adsorption process

was spontaneous in nature and also endothermic. Finally, the adsorption of phosphate on the

adsorbent significantly enhanced the pH, which suggested that the mechanism of adsorption was

an anion/hydroxyl (anion/OH-) exchange reaction.

2.4.5.3 Montmorillonite

Montmorillonite clay is a clay mineral that consists of several layers (2:1 clay system). Each

layer of the clay mineral consists of one octahedral alumina sheet organized between two

tetrahedral silica sheets. Due to the presence of other metal elements, montmorillonite may occur

in various colours like white, yellow-white, grey and also yellow-green (Navjeet et al., 2012).

Also, this clay mineral as found uses as a catalyst, an inorganic support for reagents utilized in

organic synthesis, as an adsorbent used in water and wastewater treatment (Navjeet et al., 2012).

Figure 2.5: Structure of montmorillonite (Micheal, 2010)

The use of montmorillonite for the adsorption of fluoride from aqueous solution has been studied

(Tor, 2006). The study was carried out using a batch equilibration technique. The mechanism for

the adsorption of the adsorbate was proposed to be as a result of interaction between the

adsorbate ions and the metal oxides that are present on the surface of the adsorbate. The material

was regenerated and reused, a slight decrease in adsorption efficiency was observed.

In 2012, Bhardwaj et al. examined the removal of nitrate with the use of surfactant-modified

montmorillonite adsorbent. hexadecyltrimethylammonium bromide (HDTMAB) and

dioctadecyldimethylammonium bromide (DODMAB) were the surfactants used. It was reported

that the modified adsorbents showed higher adsorption capacities compared with the unmodified

adsorbent. Also, the surfactant modification and increase in the surfactant loading concentration

stimulated the nitrate anion retaining capacity of the adsorbents.

Perassi et al. (2014) investigated the removal of phosphate onto calcium carbonate modified

montmorillonite using a batch adsorption process. It was reported that the adsorption process was

dependent on pH; as the pH decreases, adsorption increases. They also examined the adsorption

of phosphate in the presence of humic acid (competitor), it was observed that there was a

reduction in the adsorption capacity which revealed that both ions were in competition for the

active sites on the adsorbent.

The use of inorganic-organic montmorillonites for the adsorption of phosphate, phenol and Cd

(II) using a single and multiple systems has been examined (Ma et al., 2016). The inorganic-

organic montmorillonites were obtained by modifying polyhydroxy-aluminium pillared

montmorillonite with cationic (hexadecyltrimethylammonium bromide) and zwitterionic

surfactant (hexadecyldimethyl (3-sulphonatopropyl) ammonium). The adsorbents modified with

cationic surfactant showed the highest adsorption capacity compared with adsorbents modified

with the zwitterionic surfactant. For the multiple systems, it was reported that the adsorption of

each adsorbate was not affected by other components.

Huang et al. (2014) studied the use of pillared montmorillonite adsorbents for the removal of

phosphate. Zirconium and zirconium/aluminium polyhydroxy-cations were intercalated onto

natural montmorillonite to give zirconium-pillared montmorillonite and zirconium/aluminium

pillared montmorillonite. It was observed that the adsorption capacity of zirconium/aluminium

pillared montmorillonite was higher compared with the zirconium pillared montmorillonite

because it possesses higher positive chares on its surface. Also, it was revealed that the process

of adsorption of the adsorbate was spontaneous and endothermic in nature.

Gatti et al. (2016) examined the use of aminopropyltrimethoxysilane and

aminopropyltrimethoxysilane-silver modified montmorillonite for the adsorption of nitrate. It

was reported that the chemical modification of natural montmorillonite with the silane material

produced an effective adsorbent for retention of nitrate. Also, the modified adsorbents with or

without silver possessed a good adsorption capacity, especially at low pH and from the

thermodynamic study, the process of adsorption was said to be exothermic. Montmorillonite clay

was modified with hexadecylpyridinium chloride and used for the adsorption of nitrate and

perchlorate in water (Bagherifam et al., 2014). The adsorbent showed maximum adsorption

capacities of 0.67 and 1.11mmol/g for both nitrate and perchlorate respectively. It was also

reported that the removal of the adsorbates were highly selective in the presence of naturally

occurring anions like chloride, carbonate, and also sulphate. It was proposed that the adsorbent

can be utilized as an efficient material for the separation of nitrate and perchlorate from water

compartments.

Bia et al. (2012) studied the use of iron-modified montmorillonite on the removal of fluoride.

The study was carried out using batch adsorption method. Operational variables like pH, effect

of competitive anion, ionic strength were evaluated. It was observed that there was an increase in

defluoridation capacity with an increase in adsorbate concentration and decrease in pH. In the

case of the effect of competitive anion, phosphate was used. It was reported that the effect of

phosphate on the defluoridation capacity was dependent on the order of adsorbate addition.

When the adsorbates were introduced simultaneously, higher defluoridation capacity was

observed, but when the adsorbates were added one before another, a lower defluoridation

capacity was observed. Also, it was revealed that both adsorbates competed for common active

sites on the surface of the material.

Ramdani et al. (2010) investigated the use of montmorillonite clay for the removal of fluoride

from Saharan brackish water in Algeria using the potentiometric method. Two types of

montmorillonite clay were used; montmorillonite with high percentage of calcium and

montmorillonite without calcium. Both adsorbents were activated thermally and chemically.

From the study, the material that was chemically activated showed a high percentage removal of

88% compared with the material that was thermally activated, possessing a percentage removal

of 5%. From the thermodynamics study, it was proposed that the adsorption process was

exothermic. Also, the removal of the adsorbate was also proposed to be an ionic exchange mode.

2.4.5.4 Kaolinite

Kaolinite is a 1:1 layered clay mineral generated as a result of rock weathering. It consists of tiny

sheets of triclinic crystals with a pseudo-hexagonal morphology. It is structured in a way that its

tetrahedral silica sheet is alternated with an alumina octahedral sheet; hence, its silica

tetrahedrons and the adjacent layer of the octahedral sheet form a common layer. Kaolinite clay

possesses good cation exchange capacity (WHO, 2005).

Figure 2.6: Structure of Kaolinite (IHRDC, 2016)

Deng and Shi (2015) synthesized Mg-Al hydrotalcite loaded on kaolin clay through

co-precipitation and applied on the adsorption of phosphate in aqueous solution. It was reported

that a high uptake of phosphate by the material was observed over a wide pH range of 2.5-9.5.

Also, a maximum adsorption capacity of about 11.92 mg/g was recorded. From the obtained

thermodynamic results, the adsorption process of phosphate onto the adsorbate was deduced to

be a spontaneous and an exothermic process. The use of kaolinite clay for removal of fluoride

from aqueous solution has been examined (Meenakshi et al., 2008). The clay was activated

mechanically using an oscillatory disc mill; an increase in surface area of the adsorbent

compared to raw kaolinite was recorded (15.11 m2/g – 32.43 m

2/g). A defluoridation capacity of

0.106 mg/g for the activated kaolinite was reported compared with a defluoridation capacity of

0.096 mg/g for raw kaolinite. .

Adsorption of phosphate and also chromium (VI) onto supported kaolin clay was studied by

Deng et al. (2014). Mg-Al Hydrotalcite was used to modify the clay material using ultrasound-

assisted co-precipitation method. The adsorption behaviours of both contaminants from single

and binary solutions were investigated. The adsorption capacities for phosphate and chromium

(VI) in individual solutions were 605.75 mmol/kg and 309.60 mmol/kg respectively while for

binary solutions were 461.61 mmol/kg and 145.38 mmol/kg respectively. A reduction of the

adsorption capacities in the binary solutions was proposed to be as a result of competitive

adsorption of the contaminants. Also, the adsorbent was regenerated, and regeneration efficiency

after the third cycle of 69.6% and 71.9% was recorded for phosphate and chromium (VI)

respectively.

Aroke et al. (2014) investigated the removal of nitrate and chromate with the use of surfactant

modified kaolin clay. Hexadecyltrimethylammonium bromide (HDTMA) was the surfactant used

to modify kaolin clay and used for the removal of these contaminants from simulated water. It

was reported that the material was in three categories; bilayer surface modified clay (BMC),

monolayer surface modified clay (MMC) and unmodified kaolin clay (UKC). Percentage

removal efficiencies for BMC, MMC and UKC were 82.50%, 40.33% and 11.98% respectively

while for chromate were 43.21%, 26.34% and 5.17% respectively. It was concluded that the

modification of kaolin with cationic surfactant enhanced the affinity of the material towards

adsorption of oxyanions.

The adsorption of hexavalent chromium on kaolinite clay and illite has been evaluated (Ajouyed

et al., 2011). From the study, parameters such as pH, ionic strength and also initial concentration

strongly influenced the adsorption of the adsorbate by the adsorbents. For kaolinite, the optimum

pH range for the adsorption of the contaminant was 2 - 4 while for illite was 2 - 2.6. The

maximum adsorption capacity for both kaolinite and illite were 0.571 mg/g and 0.276 mg/g

respectively.

Moharami and Jalali (2015) studied the use of modified clays for the adsorption of phosphorus

from aqueous solutions. Kaolinite with other clay minerals like bentonite, calcite and zeolite

were modified with FeCl3, CaCl2, and NaCl and applied for the removal of phosphorus. Amongst

all, adsorbents modified with FeCl3 gave the best adsorption capacity. The adsorption capacities

for Fe- modified kaolinite, bentonite, calcite and zeolite were 1.31 mg/g, 1.31 mg/g, 1.97 mg/g,

and 1.58 mg/g respectively. It was also reported from the study that ionic strength had a minute

effect at different pH during the adsorption study.

A new hybrid clay adsorbent (HYCA) was firstly prepared by Unuabonah et al. (2013). This

adsorbent is based on the use of kaolinite clay and Carica papaya seeds. The adsorbent has found

usage for the adsorption of heavy metal ions from aqueous systems, but its use for the removal of

anions has not been reported. The modification of this hybrid clay adsorbent with surfactants for

adsorption of anions is investigated.

CHAPTER THREE

3.0 MATERIALS AND METHODS

3.1 Materials and Equipment

Kaolinite clay (Redemption Camp), Carica papaya seeds (Open Market), N-1-

Napthylethylenediaminedihydrochloride (Chemistry Laboratory), Ortho-Phenylenediamine

(Chemistry Laboratory), distilled water, Millipore water, sodium fluoride, sodium nitrate,

sodium bicarbonate, sodium carbonate, potassium dihydrogen phosphate (MRS Scientific),

ammonium heptamolybdate (Merck), ammonium metavanadate (Sure-Chem), beakers,

Erlenmeyer flasks, pipettes, funnels, Ultra-Violet Spectroscopy (UV-Spectroscopy) (Shimazu),

Ion Chromatography (Metrohm), Fourier Transform Infrared Spectroscopy (FTIR) (Shimazu)

3.2 Methods

3.2.1 Preparation of hybrid clay adsorbent (furnace-calcined)

Raw kaolinite clay was obtained from Redemption Camp, Mowe, Ogun State. After collection,

heavy particles were removed from the sample. The clay was crushed and sieved through a mesh

sieve having a mesh size of 45 microns. Some parts of the kaolin clay were dispersed in doubly

deionized water in a container for several hours. Moore and Reynolds's method was used in

purifying the clay. The clay was soaked in 30 % Hydrogen Peroxide (oxidizing agent) in a

container for 24 h to remove organic matter from the material; it was stirred intermittently with

stirring rods and washed with deionized water. The Carica papaya seeds were sun dried until all

fleshy part of the fruit has dried off the seed.

An equal weight of purified kaolinite clay and dried Carica papaya seed (20 g) was weighed into

a beaker with 250 mL of 0.1 M NaOH and stirred. The mixture was left standing for 3 d with

irregular stirring after which it was transferred into an oven and heated at 105 oC until the

samples are dried. Samples of the dried mixture were weighed into a crucible and calcined at 300

oC for 6 h in a furnace. The resulting powdery material was washed several times with distilled

water to remove excess NaOH from the surface of the composite and was subsequently dried to

remove all moisture. The dried samples were stored in an air tight container and subsequently

referred to as Furnace- Calcined Hybrid Clay Adsorbent (F-HYCA) (Adebowale et al., 2005;

Unuabonah et al., 2013).

3.2.2 Preparation of hybrid clay adsorbent (vacuum-calcined)

An equal weight of purified kaolinite clay and dried Carica papaya seed (20 g) was weighed into

a beaker with 250 mL of 0.1 M NaOH and stirred. The mixture will be left standing for 3days

with irregular stirring after which it was transferred into an oven and heated at 105 oC until the

samples are dried. Samples of the dried mixture were weighed into a crucible and calcined at200

oC for 8 h in a vacuum oven. The resulting powdery material was washed several times with

distilled water to remove excess NaOH from the surface of the composite and was subsequently

dried to remove all moisture. The dried samples were stored in an air tight container and

subsequently referred to as Vacuum-Calcined Hybrid Clay Adsorbent (V- HYCA)

3.2.3 Preparation of modified hyca adsorbents

According to Unuabonah et al.(2013) the net charge on the surface of HYCA (parent material) is

negatively charge. In order to enable the adsorption of toxic anions in water, the surface of the

adsorbent was functionalized to create a positive environment on its surface.

Two modifiers (diamine salts) were used:

N-1-Napthylethylenediaminedihydrochloride (NEDD)

Ortho-Phenylenediamine (OP)

3.2.3.1 Synthesis of n-1-napthylethylenediaminedihydrochloride modified adsorbent (NEDD)

Three different concentrations of the modifier were used; 25 mg/L, 50 mg/L, and 100 mg/L. A

specific weight of HYCA (5 g) was weighed, and 100 mL of the diamine salt stock solution was

added. The solution was shaken for 6 h using a shaker. After shaking, the solution was filtered

and washed to remove unbounded materials. It was then oven dried at 90 oC.

3.2.3.2. Synthesis of o-phenylenediamine modified adsorbent (OP)

Three different concentrations of the modifier were used; 25 mg/L, 50 mg/L and 100 mg/L. The

solution was acidified to a pH of 3 to protonate the modifier using 0.01 M H2SO4. A specific

weight of HYCA (5 g) was weighed, and 100mL of the diamine salt stock solution was added.

The solution was shaken for 6 h using a shaker. After shaking, the solution was filtered and

washed to remove unbounded materials. It was then oven dried at 90 oC.

The following modified HYCA adsorbents were obtained: NEDD-VHYCA (25), OP-VHYCA

(25), NEDD-VHYCA (50), OP-VHYCA (50), NEDD-VHYCA (100), OP-VHYCA (100),

NEDD-FHYCA (25), OP-FHYCA (25), NEDD-FHYCA (50) and OP-FHYCA (50).

3.3 Characterization of Modified Adsorbents

Fourier Transformed Infrared Spectroscopy (FTIR) was employed in characterizing the modified

adsorbents. FTIR analyses were performed on the materials to determine the functional groups

present.

3.4 Determination of pHpzc (Point of Zero Charge) of the Adsorbents

The pH-pzc of the adsorbents was determined using the salt addition method. A solution of0.01

M NaCl was prepared, and its pH was be adjusted using a pH meter to be between 2 and 12

using 0.01 M HCl and0.01 M NaOH solutions. 30 mg of the adsorbent was weighed, and 10 mL

of 0.01 M NaCl solutions having different pH was added in an erlenmeyer flask. It was placed on

a mechanical shaker for 24 h after which the equilibrium (final) pHof the solutions was recorded.

Δ pH (the difference between initial and final pH values) was plotted against their initial pH. The

pHinitialat which Δ pH is zero was considered aspHpzc(Dayanandaet al., 2015).

3.5 Preparation of Standard Reagents

Fluoride standard:1000 mg/L of this reagent was prepared by dissolving 2.2100 g of sodium

fluoride in distilled water and diluted to 1L.

Nitrate standard:1000 mg/L of nitrate standard was prepared by dissolving 6.0679 g of sodium

nitrate in distilled water and diluted to 1L.

Phosphate standard: 1000 mg/L of phosphate standard was prepared by dissolving 4.3937 g of

potassium dihydrogen phosphate in distilled water and diluted to 1L.

Colour developing reagent: 2.5g of ammonium heptamolybdate was weighed into a beaker

containing 30ml of distilled water (Solution A). 0.125 g of ammonium metavanadate was

weighed into a beaker containing 30 mL of distilled water, heated to boiling, allowed to cool and

33mL of concentrated hydrochloric acid was added (Solution B). Solution A was added to B and

diluted to 100 mL.

Eluent: 0.2856 g of sodium bicarbonate (NaHCO3) and 0.3816 g of sodiumcarbonate (Na2CO3)

will be dissolved in deionized water and diluted to 2L.

3.6 Adsorption Studies

3.6.1 Adsorption isotherm studies

Adsorption isotherm studies are carried out to determine the adsorption equilibrium; which is the

ratio between the adsorbed concentration of the adsorbate with the concentration of adsorbate

remaining in the solution (Foo et al., 2010). An adsorption isotherm is a valuable curve that

describes the processes involved in the release, retention or mobility of an adsorbate from an

aqueous system onto an adsorbent at a constant temperature and pH (Foo et al., 2010).

The most widely used technique in predicting the optimum isotherm is the search for the best-fit

adsorption isotherm using the method of least squares (Shahmohammadi-Kalalagh et al., 2013).

Without doubt, linear regression analysis has often been utilized in accessing the quality of fits

and adsorption performance, due to its wide usefulness in a variety of adsorption data. However,

in the past few years, utilization of non-linear optimization modelling, as an alternative to the

linear form, has been reported (Prasad et al., 2009). In this present study, three adsorption

isotherm models are applied; Freundlich, Brouers-Sotolongo, and Jovanovic.

3.6.1.1. Freundlich isotherm

This model describes the non-ideal and reversible adsorption, not restricted to the formation of

monolayer. It can be applied to multilayer adsorption; with non-uniform distribution of

adsorption heat and affinities over the heterogeneous surface (Foo et al., 2010). Its expression is

given by;

…………………………………………………………………….(1)

Where:

qe = maximum adsorption capacity (mg/g)

nF = Freundlich isotherm constants related to adsorption intensity

Kf = Freundlich isotherm constants related to adsorption capacity (mg/g)

Ce= equilibrium concentration of adsorbate (mg/L)

3.6.1.2. Brouers-sotolongo isotherm

This isotherm is given by a deformed exponential (Weibull) function (Altenor et al., 2009). Its

expression is given by;

………………………………………………………(2)

Where:

qe = maximum adsorption capacity (mg/g)

qmax = saturation value

Kw = KF/qmax; where KF is the low Ce Freundlich constant, for a given temperature

Ce= equilibrium concentration of adsorbate (mg/L)

α = is a measure of the width of the sorption energy distribution and therefore of the energy

heterogeneity of the adsorbent surface.

3.6.1.3 Jovanovic isotherm

The assumption of this isotherm is similar to that considered by Langmuir isotherm which

assumes monolayer adsorption on the surface of the adsorbent. Jovanovic is represented by

another approximation for monolayer localized adsorption without lateral interactions (Hossain

et al., 2012).

…………………………………………………………………..(3)

Where:

qe = maximum adsorption capacity (mg/g)

qm = saturation value

Ce= equilibrium concentration of adsorbate (mg/L)

KJ= Jovanovic isotherm constant

3.6.2. Adsorption of phosphate

Adsorption of phosphate was carried out using batch adsorption method. A specific weight of the

adsorbent was weighed (30 mg) into an Erlenmeyer flask and a specific volume of the adsorbate

(50 mL) was added. The concentration of the adsorbate was between 10 mg/L – 500 mg/L. The

mixture was shaken for 2 h using a shaker at a speed of 200 rpm and then filtered to determine

the residual concentration of the adsorbate using UV spectroscopy at 420nm. The adsorption

capacity was estimated using the relationship qe in mg/g;

………. …………………………………………………………(4)

Where:

Ci= initial concentration of anions (mg/L)

Cf = residual concentration of anions (mg/L)

V = volume of the solution (L)

W = mass of dry adsorbent used (g).

Figure 3.1: Phosphate calibration curve

3.6.3 Adsorption of nitrate and fluoride

The modified vacuum-calcined materials were applied for the adsorption of nitrate and fluoride.

Adsorption of nitrate and fluoride was carried out using batch adsorption method. A specific

weight of the adsorbent was weighed (1 g and 30 mg respectively) into an Erlenmeyer flask and

a specific volume of the adsorbate (100 mL and 10 mL respectively) was added. The

concentration of the adsorbate was between 10 – 30 mg/L. The mixture was shaken for 2 h using

a shaker at a speed of 200 rpm and then filtered to determine the residual concentration of the

adsorbate using Ion Chromatography. The adsorption capacity was also estimated as stated

above.

CHAPTER FOUR

4.0 RESULTS AND DISCUSSION

4.1. PHYSICOCHEMICAL CHARACTERIZATION

4.1.1. Fourier Transform Infrared Characterization (FTIR)

NEDD-VCHYCA Adsorbent

Figure 4.1 shows the Fourier Infrared spectra (FT-IR) of the parent material (HYCA) previously

prepared by Unuabonah et al. (2013) and the surface modified hybrid clay (NEDD-VHYCA).

The infrared spectra of HYCA showed a peak at 1047 cm-1

, 1616 cm-1

, 3619 cm-1

and 3699 cm-1

.

The peak at 1047 cm-1

is attributed to the presence of Si – O group (Si -O bending vibration).

1616 cm-1

peak is observed to be an –N-H stretching vibration of an amine. At 3619 cm-1

, the

inner hydroxyl group –O-H stretching of kaolinite clay is observed (Unuabonah et al., 2013).

The peak at 3699 cm-1

is as a result of the presence of –O-H group present at the octahedral

surface of the layers of the clay mineral which is related to the bands that are coupled to the

asymmetric and symmetric vibrations of –O-H (Unuabonah et al., 2013).

There is a significant difference between the infrared spectra of HYCA and surface modified

HYCA which suggests that modification of the HYCA has occurred. However, with an increase

in the concentration of the modifier, there is no significant difference between the spectra

(Figure. 4.1).

4000 3500 3000 2500 2000 1500 1000 500

wavenumber (cm-1

)

3432

1616

1033

1047

16321746

3622

36993619

VHYCA

2926 28553698

NEDD-VHYCA (25)

1515

1446

NEDD-VHYCA (50)

3698

36222926

2855

NEDD-VHYCA (100)

36983622 2926

2855

Figure 4.1: Fourier Transform Infrared spectra of N-1-Napthylethylenediamine dihydrochloride

modified HYCA adsorbent under Vacuum (NEDD-VCHYCA)

The infrared spectra of NEDD modified VHYCA showed the following peaks: 3698 cm-1

,

3622 cm-1

, 3432 cm-1

, 2926 cm-1

, 2855 cm-1

, 1746 cm-1

, 1632 cm-1

, 1515 cm-1

, 1446 cm-1

, and

1033cm-1

. The peaks at 3698 cm-1

and 3622cm-1

are as a result of the presence of hydroxyl group

on the surface of kaolinite clay and inner hydroxyl groups between the layers of the clay

(Unuabonah et al., 2013). The presence of –N-H stretching vibration at 3432 cm-1

indicates that

the modification with the NEDD modifier (with N atoms in it) was successful, although there

could be some contributions from Carica papaya seed as reported by Unuabonah et al. (2013).

The twin peaks at 2926 cm-1

and 2855 cm-1

are -C-H stretch peaks that are assigned to methyl and

methylene –CH2 from the modifier (Unnithan et al., 2004; Yang et al., 2013). The presence of

the peak at 1746 cm-1

signify the presence of–C=O stretching vibration of an ester group (Pavia et

al., 2001). The two peaks at 1632 cm-1

and 1515 cm-1

are as a result of the presence of

ammonium groups proposed to be from the modifier (Bacsik et al., 2011). The presence of

methylene fragments is responsible for the adsorption band at 1446 cm-1

(Bacsik et al., 2011).

There was a red shift from 1047 cm-1

(Si-O- stretching vibration) to 1033 cm-1

when HYCA was

modified with NEDD modifier (Unuabonah et al., 2013).

OP-VHYCA Adsorbent

Figure 4.2 illustrates the Infrared spectra of HYCA and OP-VHYCA. The changes in the

Infrared spectra of both HYCA and the surface modified material (OP-VHYCA) signify that

surface modification of HYCA was effective.

The surface modified material exhibited the following peaks; 3697 cm-1

, 3622 cm-1

,

3446 cm-1

, 2926 cm-1

, 2854 cm-1

, 1752 cm-1

, 1646 cm-1

, 1525 cm-1

, 1460 cm-1

and 1033 cm-1

.

The two peaks at 3697 cm-1

and 3622 cm-1

are assigned to –O-H stretching vibration on the

surface and inner portions of kaolinite clay between the tetrahedral and octahedral layer of the

clay mineral (Unuabonah et al., 2013). The presence of an -N-H stretching group is observed at

3446 cm-1

which is suggested to be as a result of the modification and also the papaya seeds

(Unuabonah et al., 2013).

4000 3500 3000 2500 2000 1500 1000 500

wavenumber (cm-1

)

1033

3699

3619 1616 1047

VHYCA

3697

3622

34462854

2926

1752

1646

OP-VHYCA (25)

1525

1460

OP-VHYCA (50)

3697

3622

29262854

OP-VHYCA (100)

3697

36222926

2854

Figure 4.2: Fourier Transform Infrared spectra of Ortho-phenylenediamine-modified HYCA

adsorbent under Vacuum (OP-VCHYCA)

The absorption band observed at 2926 cm-1

and 2854 cm-1

are indicative of a -C-H stretching

group of -CH2, suggested to be from the methyl and methylene group of the modifier (Unnithan

et al., 2004; Yang et al., 2013). The peak at 1752 cm-1

reveals the presence of –C=O stretching

vibration of an ester group (Pavia et al., 2001). Ammonium groups are observed at two

adsorption bands (1646 cm-1

and 1525 cm-1

) when HYCA was modified. The band at 1460 cm-1

suggests the presence of methylene fragments (Bacsik et al., 2011). A significant shift which

indicates the presence of Si-O group from HYCA was noticed from 1047 cm-1

– 1033 cm-1

which

can be attributed to the effect of the modification.

NEDD-FHYCA Adsorbent

Figure 4.3 describes the Fourier Transform Infrared characterization (FT-IR) of HYCA and its

modified material (NEDD-FHYCA). The presence of hydroxyl groups on the surface of the clay

material and inner hydroxyl groups between the layers of the clay material is responsible for the

two peaks at 3697 cm-1

and 3622 cm-1

respectively (Unuabonah et al., 2013). Another peak can

be observed at 3434 cm-1

which can be attributed to the presence of an –N-H stretching vibration

from the modifier and also the Carica papaya seed (Unuabonah et al., 2013). The absorbance

band at 1634 cm-1

is as a result of the presence of ammonium groups, proposed to be from the

modifier (Bacsik et al., 2013). The peak at 1033 cm-1

is attributable to the presence of a Si-O

bending vibration from HYCA, although a shift in peak was observed when compared to HYCA

adsorbent.

4000 3500 3000 2500 2000 1500 1000 500

wavenumber (cm-1

)

3699

36191616

1047

1033

FHYCA

3697

3622

3434 1634

1033NEDD-FHYCA (25)

34343697

3622

1634

NEDD-FHYCA (50)

Figure 4.3a: Fourier Transform Infrared spectra of N-1-Napthylethylenediamine

dihydrochloride modified HYCA adsorbent under Furnace (NEDD-FHYCA)

An elaboration of data between 2840 and 2960 cm-1 for data used to make the spectra in figure

4.3a reveals the presence of 2920 cm-1

and 2851 cm-1

for 25-NEED and 2853cm-1

and 2927 cm-1

for 50-NEED (Figure. 4.3b) which are typical peaks for –C-H stretching vibrations of –CH2 of

methyl and methylene (Unnithan et al., 2004; Yang et al., 2013) probably originating from the

modifiers used in the modification of these adsorbents.

2960 2940 2920 2900 2880 2860 2840

wavenumber (cm-1)

NEDD-FHYCA (25)

2851

2920

2927

NEDD-FHYCA (50)

2853

Figure 4.3b: Fourier Transform Infrared spectra of N-1-Napthylethylenediamine

dihydrochloride modified HYCA adsorbent under Furnace (NEDD-FHYCA)

OP-FHYCA Adsorbent

Figure 4.4 describes the infrared spectra of HYCA and the surface-modified adsorbent (OP-

FHYCA). The adsorption band at 3698 cm-1

and 3616 cm-1

reveals the presence of –O-H on the

surface of kaolinite clay and inner hydroxyl groups between the layers of the clay mineral

(Unuabonah et al., 2013). The presence of an –N-H stretching vibration from the modifier and

also the Carica Papaya seed is what is responsible for the peak at 3428 cm-1

. The band at 1623

cm-1

suggests the presence of ammonium group on the surface of material after modification

(Bacsik et al., 2013). There was a significant shift from 1047 cm-1

(Si-O- stretching vibration) to

1036 cm-1

when HYCA was modified.

4000 3500 3000 2500 2000 1500 1000 500

wavenunmber (cm-1)

36993619

16161047

FHYCA

3698

3616

34281623

1036

1036

OP-FHYCA (25)

3698

3616

34281623

OP-FHYCA (50)

Figure 4.4a: Fourier Transform Infrared spectra of Ortho-phenylenediamine modified HYCA

adsorbent under Furnace (OP-FHYCA)

An elaboration of data between 2840 and 2960 cm-1 for data used to make the spectra in figure

4.3a reveals the presence of 2930 cm-1

and 2856 cm-1

for 25-OP and 2855cm-1

and 2929 cm-1

for

50-NEED (Figure. 4.4b) which are typical peaks for –C-H stretching vibrations of –CH2 of

methyl and methylene (Unnithan et al., 2004; Yang et al., 2013) probably originating from the

modifiers used in the modification of these adsorbents. However, these peaks are less intense

compared with those of NEDD modified adsorbents as shown in figure 4.3b.

2840 2860 2880 2900 2920 2940 2960

wavenumber (cm-1)

OP-FHYCA (25)

2930

2856

OP-FHYCA (50)

2929

2855

Figure 4.4b: Fourier Transform Infrared spectra of Ortho-phenylenediamine modified HYCA

adsorbent under Furnace (OP-FHYCA)

4.1.2 PHpzc Characterization (Point of Zero Charge)

The point of zero charge is one of the essential attributes of adsorbent surfaces. This is the pH at

which the total sum of charges on the surface of a material is zero. The pHpzc of a material is used

to determine how easy an adsorbent can adsorb the contaminants present in water (Dayananda et

al., 2015). When the pH of the solution is below the pHpzc of the adsorbent, the net surface charge

on the surface of the material is positive as a result of adsorption of excess hydrogen ions (H+),

while when the pH of the solution is above the pHpzc of the adsorbent, the net surface charge on

the surface of the material is negative due to the desorption of hydrogen ions (H+) (Dayananda et

al., 2015).

2 4 6 8 10 12

-5

-4

-3

-2

-1

0

1

2

3

p

H

pHInitial

25 NEDD

25 OP

50 NEDD

50 OP

100 NEDD

100 OP

Figure 4.5: Plot of pHpzc of modified VHYCA

Figure 4.5 shows the pHpzc characterization of modified VHYCA. The pHpzc values of 25-NEDD,

50-NEDD, 100-NEDD, 25-OP, 50-OP, and 100-OP are observed to be 7.31, 7.49, 7.77, 7.42,

6.73, and 7.07 respectively. From the values obtained, it can be proposed that these materials will

exhibit good adsorption capacities for the removal of anions, coupled with the fact that an

average pH of 6.04 was used for the adsorption processes in this study.

The plot of pHpzc of modified FHYCA is illustrated in figure 4.6. The pHpzc values of 25-NEDD,

50-NEDD, 25-OP, and 50-NEDD are ascertained to be 6.25, 6.62, 6.75, and 7.23 respectively.

These values indicate that these materials possess good adsorption capacities for potential

adsorption of anions from water.

2 4 6 8 10 12

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

p

H

pHInitial

25 NEDD

25 OP

50 NEDD

50 OP

Figure 4.6: Plot of pHpzc of modified FHYCA

An average pH of about 6.04 was used in the adsorption process which is lower than the pHpzc

values of the adsorbents. This indicates a possibility of the adsorbents to be favoured by the

adsorption process for the removal of anions.

4.2 Adsorption OF Phosphate

The obtained equilibrium data were analysed and fitted into three different isotherm models;

Freundlich, Brouers-Sotolongo, and Jovanovic.

Figures 4.7 to 4.17 below shows the non-linear curve fits of the adsorption isotherms data of

phosphate on the unmodified and modified adsorbents by the three models stated above. The

values of the maximum adsorption amount (qmax), correlation coefficient (R2), error (E) and other

parameters are given in tables 4.1 and 4.2 respectively. The correlation coefficient and error are

used to compare the adequacy of the models to describe experimental data obtained.

The data of table 4.3 shows that Brouers-Sotolongo is the most suited model for fitting

adsorption isotherms of phosphate adsorbed on both unmodified and modified adsorbents. The

order for the adsorption of phosphate on the adsorbents is Brouers-Sotolongo model > Javanovic

model > Freundlich model.

For the Freundlich isotherm model, the nF parameter (homogeneity factor), can be used to

indicate whether the adsorption is linear (nF= 1), or a chemical process (nF< 1), or a physical

process (nF> 1) (Vargas et al., 2012). As it can be observed in table 4.3, the nF values for the

various adsorbents are 1.26, 1.72, 1.96, 1.52, 1.59, 1.37, 1.30, 1.25, 1.29, 1.16, and 1.14

respectively for V-HYCA, NEDD-FHYCA (25), NEDD-FHYCA (50), OP-FHYCA (25), OP-

FHYCA (5O), NEDD-VHYCA (25), NEDD-VHYCA (50), NEDD-VHYCA (100), OP-VHYCA

(25), OP-VHYCA (50), and OP-VHYCA (100), which indicates that the mechanism for the

removal of phosphate from aqueous solution using these adsorbents is physisorption.

Considering the various adsorbents used in this study, the amount of adsorbed phosphate is

higher in the modified adsorbents compared with the unmodified adsorbent. The best performing

material in the category of modified VHYCA materials (OP (50)) shows an adsorption capacity

of 97.75 mg/g compared with unmodified VHYCA which exhibits an adsorption capacity

of 68.06 mg/g. This indicates that modification of the material enhanced the adsorption

capacity of the material.

Furthermore, looking at the variable concentrations of the modifiers; for NEDD-modified

adsorbents, NEDD (50) and NEDD (25) performed better for both V-HYCA and F-HYCA

respectively, exhibiting adsorption capacities of 84.11 mg/g and 85.19 mg/g with correlation

coefficient of 0.9783 and 0.9867 respectively. Furthermore, for OP-modified adsorbents, OP

(50) and OP (25) showed high adsorption capacities of 97.75 mg/g and 138.22 mg/g with

correlation coefficients of 0.9773 and 0.9767 for V-HYCA and F-HYCA respectively.

Also, in comparing the adsorption capacities of the modifiers, OP-modified adsorbents

performed better compared with NEDD-modified adsorbents for both vacuumed calcined HYCA

(VHYCA) and furnace calcined HYCA (FHYCA). Among the modified VHYCA adsorbents,

OP (50) shows the highest adsorption capacity of 97.75 mg/g for removal of phosphate from

aqueous solution with a coefficient correlation of 0.9773, while for FHYCA adsorbents, OP (25)

exhibits the highest adsorption capacity of 138.22 mg/g with correlation coefficient of 0.9767.

On the other hand, NEDD (50) and NEDD (25) reveals good adsorption capacities of 84.11 mg/g

and 85.19 mg/g for VHYCA and FHYCA respectively with correlation coefficient of 0.9783 and

0.9867 respectively. It is proposed that OP-modified adsorbents performed better than the

NEDD-modified adsorbents because of the bulkiness of NEDD modifier which may have led to

over-crowding of the active sites compared to OP modifier that is less bulky.

In addition, it is observed that modified-VHYCA adsorbents and modified-FHYCA adsorbents

performed differently. Modified-FHYCA adsorbents performed better than the modified-

VHYCA adsorbents with OP-FHYCA (25) exhibiting the highest adsorption capacity of 138.22

mg/g with correlation coefficient of 0.9767 as against OP-VHYCA (50) which shows an

adsorption capacity of 97.75 mg/g with correlation coefficient of 0.9773 as the best performing

material for modified-VHYCA adsorbents. It can be assumed that the reason for this dissimilar

behaviour may be as a result of the oxidation surface active sites in FHYCA adsorbents as a

result of calcining in air (O2) as against VHYCA adsorbents prepared under pressure in vacuum

(in the absence of air).

Table 4.1: Equilibrium isotherm analysis of the adsorption process

Freundlich Brouers-Sotolongo Javanovic

Adsorbent kf 1/n qmax kBS α qmax kJ

V-HYCA 0.5820 1.2616 68.0571 2.87×10-4

1.5788 95.8538 2.96×10-3

NEDD-VHYCA (25) 0.8120 1.3693 73.4068 1.84×10-3

1.1775 86.0347 3.48×10-3

NEDD-VHYCA (50) 0.7804 1.2984 84.1072 8.29×10-4

1.3444 111.1087 3.02×10-3

NEDD-VHYCA (100) 0.6430 1.2511 78.2452 9.77×10-5

1.7793 113.8936 2.78×10-3

OP-VHYCA (25) 0.5729 1.2881 93.7528 2.53×10-3

1.0016 94.0644 2.54×10-3

OP-VHYCA (50) 0.4291 1.1640 97.7539 1.04×10-3

1.2029 146.9487 1.73×10-3

OP-VHYCA (100) 0.4185 1.1419 81.8496 2.83×10-5

1.9817 151.6964 1.83×10-3

NEDD-FHYCA (25) 2.1175 1.7242 85.1881 1.06×10-2

0.8330 72.0989 6.33×10-3

NEDD-FHYCA (50) 3.5167 1.9634 75.2203 1.45×10-2

0.8793 70.3627 9.98×10-3

OP-FHYCA (25) 1.0632 1.5219 138.2183 6.57×10-2

0.8192 98.3839 4.34×10-3

OP-FHYCA (50) 1.7814 1.5941 81.3005 5.22×10-3

1.0240 82.6882 5.67×10-3

kf = Freundlich isotherm constant (mg/g) (dm3/g)n related to adsorption capacity; 1/n = Freundlich isotherm constants related to adsorption intensity

qmax = amount of adsorbate in the adsorbent at equilibrium (mg/g); kBS, α = Brouers-Sotolongo isotherm constants; kJ = Jovanovic isotherm constant

Freundlich Brouers-Sotolongo Javanovic

Adsorbent R2

Error R2

Error R2

Error

VHYCA 0.9418 43.9444 0.9859 12.1299 0.9645 26.7899

NEDD-VHYCA (25) 0.9767 15.3736 0.9970 2.1927 0.9940 3.9219

NEDD-VHYCA (50) 0.9531 45.3650 0.9783 23.9616 0.9700 29.0030

NEDD-VHYCA (100) 0.9419 55.9631 0.9920 8.7445 0.9636 34.9903

OP-VHYCA (25) 0.9834 9.2585 0.9883 7.4852 0.9883 6.5497

OP-VHYCA (50) 0.9687 26.9186 0.9773 22.2592 0.9746 21.8625

OP-VHYCA (100) 0.9435 58.1171 0.9850 17.5743 0.9555 45.7626

NEDD-FHYCA (25) 0.9770 15.2847 0.9867 10.1328 0.9823 11.7406

NEDD-FHYCA (50)

OP-FHYCA (25)

0.9058

0.9735

77.3861

25.5206

0.9293

0.9767

66.3591

25.6666

0.9273

0.9727

59.7392

26.3074

OP-FHYCA (50)

R2 = correlation coefficient

0.9440 49.4532 0.9661 34.2090 0.9660 30.0002

Table 4.2:

Equilibrium isotherm analysis showing the R2 and Error data of the adsorption process

74

Table 4.3: Comparison of maximum adsorption capacity (Qm) for phosphate with other

adsorbents

Adsorbent Qm (mg/g) Isotherm

Reference

HO-CaBen (Bentonite based adsorbent) 29.1 Langmuir Ma et al., 2012

Modified inorganic - bentonite 12.7 Langmuir Yan et al., 2010

Zirconium-pillared montmorillonite 17.2 Langmuir Ma et al., 2016

Mg-Al hydrotalcite-kaolin 11.92 Langmuir Deng and Shi, 2015

Fe-modified kaolinite 1.31 Freundlich Moharami and Jalali, 2015

OP-FHYCA (25) 138.22 Brouers-

Sotolongo

This work

OP-VHYCA (50) 97.75 Brouers-

Sotolongo

This work

The results illustrated in table 4.4, shows that surfactant modified-HYCA can be considered to be

a potential adsorbent for adsorption of anions from aqueous solution especially phosphate.

75

0 100 200 300 400 5000

10

20

30

40

50

60

70

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

0 100 200 300 400 5000

10

20

30

40

50

60

70

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

Figure 4.7: Isotherm models for adsorption of phosphate on VHYCA

Figure 4.8: Isotherm models for adsorption of phosphate on NEDD-VHYCA (25)

76

0 100 200 300 400 5000

20

40

60

80

100

Ce (mg/L)

qe

(m

g/g

)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

0 100 200 300 400 5000

20

40

60

80

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

Figure 4.9: Isotherm models for adsorption of phosphate on NEDD-VHYCA (50)

77

0 100 200 300 400 5000

10

20

30

40

50

60

70

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

0 100 200 300 400 5000

20

40

60

80

100

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

Figure 4.10: Isotherm models for adsorption of phosphate on NEDD-VHYCA (100)

Figure 4.11: Isotherm models for adsorption of phosphate on OP-

VHYCA (25)

78

0 100 200 300 400 5000

20

40

60

80

100

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

0 100 200 300 400 5000

20

40

60

80

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

Figure 4.12: Isotherm models for adsorption of phosphate on OP-VHYCA (50)

Figure 4.13: Isotherm models for adsorption of phosphate on OP-VHYCA (100)

79

0 100 200 300 400 5000

20

40

60

80

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-Sotolongo

...... Jovanovic

0 100 200 300 400 5000

20

40

60

80

100

Ce (mg/L)

qe (

mg

/g)

experimental data

___ Freundlich

----- Brouers-sotolongo

...... Jovanovic

Figure 4.14: Isotherm models for adsorption of phosphate on NEDD-FHYCA (25)

Figure 4.15: Isotherm

models for adsorption of

phosphate on NEDD-FHYCA

(50)

80

0 100 200 300 400 5000

20

40

60

80

Ce (mg/L)

qe (

mg

/g)

experimental data

___Freundlich

----- Brouers-Sotolongo

...... Jovanovic

Figure 4.16: Isotherm models for adsorption of phosphate on OP-FHYCA (25)

Figure 4.17: Isotherm models for adsorption of phosphate on OP-

FHYCA (50)

81

4.3 ADSORPTION OF NITRATE AND FLUORIDE

4.3.2 Adsorption of Nitrate

Figure 4.18 shows the chart of NO3- adsorption on modified V-HYCA adsorbents; NEDD-

VHYCA (50) and OP-VHYCA (50). From the bar chart it can be deduced that NEDD-VHYCA

adsorbent performed better than OP-VHYCA adsorbent in the removal of NO3- from aqueous

solution containing various concentrations of NO3- ranging from 10-30 mg/L.

82

100

31.3

98.6

41.8

69.7

52.6

5 10 15 20 25 30 35

0

20

40

60

80

100

% R

em

oval

Initial Concentration (mg/L)

NEDD-VHYCA (50)

OP-VHYCA (50)

Figure 4.18: Adsorption of nitrate on NEDD-VHYCA (50) and OP-VHYCA (50)

4.3.1 Adsorption of Fluoride

Figure 4.18 describes the chart of the adsorption of fluoride in aqueous solution on NEDD-

VHYCA (25) and OP-VHYCA (25) adsorbents. It is observed that the NEDD-modified

adsorbent has a higher percentage removal compared with OP-modified adsorbent in the removal

of fluoride from aqueous solution.

83

6.9

4.1

19.6 19.8 20.0 20.2 20.4

0

1

2

3

4

5

6

7

% R

em

oval

Initial concentration (mg/L)

NEDD-VHYCA (25)

OP-VHYCA (25)

Figure 4.19: Adsorption of fluoride on NEDD-VHYCA (25) and OP-VHYCA (25)

CHAPTER FIVE

5.1 CONCLUSION AND RECOMMENDATION

Modified Kaolinite clay adsorbents (FHYCA and VHYCA) modified with surfactants (NEDD

and OP) through surface modification were applied for the removal of anions in aqueous

solutions. The modification process is simple. Fourier Transform Infrared spectroscopy suggests

that modification was successful. The presence of an ammonium head (NH4+) was observed

between 1515 cm-1

to 1646 cm-1

which could be responsible for the removal of anions when the

84

materials are used. The pHpzc values of 7.31, 7.49, 7.77, 7.42, 6.73, 7.07, 6.25, 6.62, 6.75, and

7.23 were observed for NEDD-VHYCA (25), NEDD-VHYCA (50), NEDD-VHYCA (100), OP-

VHYCA (25), OP-VHYCA (50), OP-VHYCA (100), NEDD-FHYCA (25), NEDD-FHYCA

(50), OP-FHYCA (25), and OP-HYCA (50) adsorbents respectively. This suggested that the

reaction was feasible, since the pH of the adsorption process used in the study was lower than the

pHpzc of the materials.

Adsorption of three toxic anions (phosphate, nitrate, and fluoride) in aqueous solutions were

carried out in this work. Three different isotherm models (Freundlich, Brouers-Sotolongo, and

Jovanovic) were applied to the experimental data obtained on the adsorption of phosphate.

Brouers-Sotolongo isotherm model was found to be the most suitable to explain the adsorption

process of the adsorbate onto the adsorbents.

The adsorption capacities found by the isotherm were 68.06 mg/g, 73.41 mg/g, 84.11 mg/g,

78.25 mg/g, 93.75 mg/g, 97.75 mg/g, 81.85 mg/g, 85.19 mg/g, 75.22 mg/g, 138.22 mg/g, and

81.30 mg/g with correlation coefficient of 0.9859, 0.9970, 0.9783, 0.9920, 0.9883, 0.9773,

0.9850, 0.9867, 0.9293, 0.9767, and 0.9661 for VHYCA, NEDD-VHYCA (25), NEDD-VHYCA

(50), NEDD-VHYCA (100), OP-VHYCA (25), OP-VHYCA (50), OP-VHYCA (100), NEDD-

FHYCA (25), NEDD-FHYCA (50), OP-FHYCA (25), and OP-FHYCA (50) respectively. It was

observed that the furnace–calcined adsorbents (FHYCA) performed better than the vacuum-

calcined adsorbents (VHYCA) with OP-modified adsorbents been the best performing material

for both VHYCA and FHYCA respectively. On the other hand, for adsorption of nitrate and

fluoride in aqueous solutions, NEDD-VHYCA adsorbents performed better compared with OP-

VHYCA.

85

The results obtained in this study indicate that surfactant modified HYCA can be utilized as a

potential adsorbent for anions removal form drinking water. Further research can be carried out

in evaluating various operational variables effect (time, pH, temperature, and competitive anions)

on the materials in order to determine the suitable conditions that provides the materials with the

best efficiency for toxic anions removal from aqueous solution.

86

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APPENDIX

Table A1: pHPZC of Modified VHYCA Adsorbents

Initial pH 25-NEDD 25-OP 50-NEDD 50-OP 100-NEDD 100-OP

2 -0.11 -0.33 -0.08 -0.11 -0.04 -0.06

4 -3.35 -3.62 -3.30 -2.53 -1.81 -4.64

6 -1.16 -2.13 -1.55 -0.68 -0.68 -1.25

8 0.58 0.87 0.49 1.12 0.06 1.08

10 2.02 2.45 2.30 2.83 2.94 1.72

12 0.31 0.35 0.26 0.16 1.13 1.53

Table A2: pHPZC of Modified FHYCA Adsorbents

Initial pH 25-NEDD 25-OP 50-NEDD 50-OP

2 -0.17 -0.06 -0.17 -0.88

4 -0.25 -0.8 -0.22 -0.65

6 -0.30 -0.94 -0.52 -0.11

8 2.16 2.08 0.86 0.71

10 2.59 2.37 1.28 2.29

12 1.86 1.86 0.98 0.79

98

Table A3: Adsorption of Nitrate

Adsorbent Ci(mg/L) Cf (mg/L) Ce(mg/L) qe(mg/g)

50-NEDD 10 0.000 10.00 1.00

50-NEDD 20 13.74 6.26 0.63

50-NEDD 30 0.43 29.57 2.96

50-OP 10 5.816 4.184 0.42

50-OP 20 6.057 13.943 1.39

50-OP 30 14.22 15.78 1.58

Table A4: Adsorption of Fluoride

Adsorbent Ci(mg/L) Cf (mg/L) Ce(mg/L) qe(mg/g)

50-NEDD 20 18.617 1.383 0.461

50-NEDD 20 19.562 0.438 0.15

50-NEDD 20 19.175 0.825 0.28

99

Table A5: Phosphate Calibration Table

Concentration (mg/L) Absorbance (nm)

0 0

2 0.083

4 0.161

6 0.225

8 0.304

10 0.394

20 0.819

50 1.995

100 4.090

Table A6: Adsorption of phosphate on VHYCA

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 9.66 0.34 0.56

20 19.04 0.96 1.60

30 27.48 2.52 4.20

40 37.21 2.79 4.65

50 44.52 5.48 9.13

100 90.46 9.54 15.90

200 171.15 28.85 48.08

300 267.85 32.15 53.58

500 458.63 41.37 68.95

100

Table A7: Adsorption of phosphate on NEDD-VHYCA (25)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 8.36 1.64 2.37

20 17.68 2.32 3.87

30 26.67 3.33 5.55

40 36.50 3.50 5.83

50 43.15 6.85 11.42

100 86.06 13.94 23.23

200 175.31 24.69 41.15

300 268.28 31.72 52.86

500 459.29 40.71 67.85

Table A8: Adsorption of phosphate on NEDD-VHYCA (50)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 8.04 1.96 3.27

20 17.80 2.20 3.67

30 26.55 3.45 5.75

40 36.23 3.77 6.28

50 41.49 8.51 14.18

100 89.48 10.52 17.53

200 167.24 32.76 54.6

300 263.77 36.23 60.38

500 451.23 48.77 81.28

101

Table A9: Adsorption of phosphate on NEDD-VHYCA (100)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 8.43 1.57 2.62

20 17.01 2.99 4.98

30 26.89 3.11 5.18

40 36.84 3.16 5.27

50 44.25 5.75 9.58

100 90.70 9.30 15.5

200 171.15 28.85 48.08

300 259.43 40.57 67.62

500 453.63 46.37 77.28

Table A10: Adsorption of phosphate on OP-VHYCA (25)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 8.99 1.01 1.68

20 17.92 2.08 3.47

30 26.77 3.23 5.38

40 36.30 3.70 6.16

50 44.57 5.43 9.05

100 87.28 12.72 21.20

200 177.23 22.77 37.95

300 274.54 25.46 42.43

500 460.38 39.62 66.03

102

Table A11: Adsorption of phosphate on OP-VHYCA (50)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 8.77 1.23 2.05

20 18.72 1.28 2.13

30 28.14 1.86 3.10

40 35.77 4.23 7.05

50 44.30 5.70 9.50

100 89.73 10.27 17.11

200 171.15 28.85 48.08

300 270.00 30.00 50.00

500 451.89 48.11 80.18

Table A12: Adsorption of phosphate on OP-VHYCA (100)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 8.77 0.95 1.58

20 18.72 1.64 2.73

30 28.14 2.45 4.08

40 35.77 4.92 8.20

50 44.30 5.34 8.90

100 89.73 5.87 9.78

200 171.15 27.87 46.45

300 259.86 40.14 66.90

500 451.23 48.77 81.28

103

Table A13: Adsorption of phosphate on NEDD-FHYCA (25)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 6.99 3.01 5.01

20 16.28 3.72 6.20

30 25.23 4.77 7.95

40 31.64 8.36 13.93

50 38.11 11.89 19.81

100 80.68 19.32 32.20

200 171.88 28.12 46.87

300 268.28 31.72 52.87

500 456.89 43.11 71.85

Table A14: Adsorption of phosphate on NEDD-FHYCA (50)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 8.77 1.23 2.05

20 16.79 3.21 5.35

30 25.92 4.08 6.80

40 28.63 11.37 18.95

50 27.11 22.89 38.15

100 75.55 24.45 40.75

200 167.24 32.76 54.60

300 265.48 34.52 57.53

500 454.28 45.72 76.20

104

Table A15: Adsorption of phosphate on OP-FHYCA (25)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 7.48 2.52 4.20

20 17.20 2.80 4.67

30 24.30 5.70 9.50

40 29.95 10.05 16.75

50 37.79 12.21 20.35

100 84.10 15.90 26.50

200 166.01 33.99 56.65

300 265.26 34.74 57.90

500 447.31 52.69 87.82

Table A16: Adsorption of phosphate on OP-FHYCA (50)

Ci (mg/L) Ce (mg/L) Cf (mg/L) Qe (mg/g)

10 9.60 0.4 0.67

20 16.52 3.48 5.80

30 26.33 3.67 6.12

40 34.49 5.51 9.18

50 33.37 16.63 27.72

100 80.93 19.07 31.78

200 166.75 33.25 55.41

300 265.48 34.52 57.53

500 452.77 47.23 78.72