FLUORIDE REMOVAL FROM WATER WITH ALUMINIUM OXIDE HYDROXIDE: A PILOT STUDY FOR HOUSEHOLD APPLICATION

ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES ENVIRONMENTAL SCIENCE PROGRAM

FLUORIDE REMOVAL FROM WATER WITH ALUMINIUM OXIDE HYDROXIDE: A PILOT STUDY FOR HOUSEHOLD APPLICATION

A Thesis Submitted to

The School of Graduate Studies of Addis Ababa University

in Partial Fulfillment of the Requirement for

the Degree of Master’s of Science

in Environmental Science

By

Yoseph Abebe Woldetsadik

July 2007

Declaration

I the undersigned declare that this Thesis is my original work and has not been presented for any degree in any university and all the resource of materials used for the Thesis have been duly acknowledged.

Name: Yoseph Abebe Woldetsadik

Signature: ------

This Thesis has been submitted for Examination with my approval as university advisor.

Name Signature

1. Dr. Feleke Zewge ------

2. Prof. B. S. Chandravanshi ------

Date and place of submission: Environmental Science Program

Addis Ababa University

July, 2007

ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES ENVIRONMENTAL SCIENCE PROGRAM

FLUORIDE REMOVAL FROM WATER WITH ALUMINIUM OXIDE HYDROXIDE: A PILOT STUDY FOR HOUSEHOLD APPLICATION

By Yoseph Abebe Woldetsadik Environmental Science program Faculty of Science

APPROVED BY EXAMINING BOARD: Signature

Advisors

Dr. Feleke Zewge ______

Prof. B. S. Chandravanshi ______

Examiners

1. Dr. Mesfin Redi ______

2. Dr. Seyoum Leta ______

ACKNOWLEDGEMENTS During my years as an M.Sc. student at the Addis Ababa University (AAU), many people have

contributed to my professional and personal growth. I wish to take this opportunity to thank all those

who assisted me in this research.

First and foremost, I wish to express my deepest gratitude to my advisors, Dr. Feleke Zewge and Prof. B.

S. Chandravanshi for their invaluable guidance, constant encouragement, priceless suggestions, indispensable support and sharing their rich experience during the entire course. I am obliged to them for the confidence they have shown in me and for the patience they have exercised during the entire course of work. Their modern outlook, meticulous supervision as well as cordial cooperation at any moment

within and outside of academic routine will always be an example in my life. Dr. Feleke Zewge

deserves additional credit for his usual genuine discussion and daily following up of my work, and for facilitating the X-ray diffraction analysis of adsorbent materials at the Technical University of Delft,

Netherlands.

I would like to thank Dr. Yonas Chebude for his kind cooperation for allowing me to use Furnace and

Prof. Masresh Fetene for allowing me to use a Sieve for the determination of the particle size. Special thanks also go to Eyobeal Mulgeta; his thoughtful suggestions were greatly appreciated. I would also

like to thank Ato Sahlemicael Deme and Ato H/Gebreal Mengesha, Department of Chemistry, Addis

Ababa University; Ato Bekele Tollosa, Quality and Standards Authority of Ethiopia, for the technical

assistance they gave me during my research work.

Secondly, I wish to thank my parents whose lot of personal sacrifice showed me the way of achieving

my goal. My brothers and sister also encouraged me during the tough life of all those years. I am

deeply thankful for that. Last but not least, a special note of thanks for my wife Misrak Girma for her

support and encouragement throughout my study.

Above all, I wish to thank God for his unlimited blessings.

- i -

Dedication: - To my kid, Kidus Yoseph Abebe

- ii -

TABLE OF CONTENTS Page Acknowledgements i

Dedication ii

Table of Contents iii

List of Figures v

List of Tables vii

List of Abbreviations and Symbols ix

Abstract xi

1. INTRODUCTION 1

Background 1

1.2 Domestic Defluoridation Units 5

1.3 Aluminium hydroxides 14

1.4 Fluoride adsorption in batch and continuous modes 17

1.4.1 Adsorption Isotherms 18

1.4.2 Adsorption in packed bed column 21

1.5 Objectives of the Research 23

2. MATERIALS AND METHODS 24

2.1 Preparation of Aluminium Oxide hydroxides 24

2.2 Characterization of Adsorbents 24

2.2.1 BET Surface Area and Pore Volume 24

- iii -

2.3 Batch Adsorption Studies 25

2.4 Laboratory Scale Column Experiment 25

2.5 Pilot Scale Column Experiment 27

2.6 Reagents and Standard Preparation 28

2.7 Effect of Cations on the Defluoridation Capacity of AlOOH 29

2.8 Fluoride Analysis 29

3. RESULTS AND DISCUSSION 31

3.1 Characterization of Adsorbents 31

3.2 Adsorption Isotherms 35

3.3 Breakthrough Study of Laboratory Scale column 46

3.4 Pilot Scale Column Study 49

3.5 Effect of Cations on the Defluoridation

Capacities of AlOOH 53

4. CONCLUSION 59

REFERENCES 62

APPENDIX 68

- iv –

LIST OF FIGURES Page

Fig.1. Activated alumina based defluoridation unit 7

Fig.2. Bone charcoal defluoridation units: (A) Bucket type system;

(B) Column type system 8

Fig.3. Stainless steel Candle Filter (Nalgonda Technique) 10

Fig.4. Stratified column of brick chips household defluoridator 11

Fig.5. Contact precipitation for household use 13

Fig.6. Classification of Aluminium hydroxides 14

Fig.7. Schematic design of column unit for laboratory scale experiment 26

Fig.8. Pilot Scale column diagram and column detail 27

Fig.9. XRD patterns of the sample produced (a) at 50 OC (pseudoboehmite) and

(b) at 200 OC (boehmite) 32

Fig.10. Pore size distribution of aluminium hydroxides produced under ordinary

conditions (pseudoboehmite) and treated at 300 oC (boehmite). 32

Fig.11. Langmuir equilibrium isotherm model of boehmite: Co = 50 mg/l,

pH = 7.0, Temp. = 25 oC 36

Fig.12. Langmuir equilibrium isotherm model of pseudoboehmite: Co = 50 mg/l,

pH = 7.0, Temp. = 25 oC 36

Fig.13. Dubinin-Radushkevich equilibrium isotherm model for the adsorption

o of fluoride ions onto pseudoboehmite, Co =50 mg/l, pH =7.0, Temp.=25 C 39

Fig.14. Dubinin-Radushkevich equilibrium isotherm model for the adsorption

o of fluoride ions onto boehmite, Co = 50 mg/l, pH = 7.0, Temp. = 25 C 39

Fig.15 Temkin equilibrium isotherm model for the adsorption of fluoride ions

o onto pseudoboehmite, Co = 50 mg/l, pH = 7.0, Temp. = 25 C 41

- v -

Fig.16. Temkin equilibrium isotherm model for the adsorption of fluoride ions

o onto boehmite, Co = 50 mg/l, pH = 7.0, Temp. = 25 C 42

Fig.17. Comparision of experimental breakthroughcurves, 92 ml min-1 (),

-1 o 23 ml min (c) ; Co=20 mg/l, h = 25cm , Temp. = 22 C 44

Fig.18. Schematic of inorganic ion (fluoride) transport from the bulk solution

onto porous metal oxides adsorbents (AlOOH) 46

Fig.19. Pilot column experimental breakthrough curve, 100.2 mg /l 48

Fig.20. N2 adsorption /desorption isotherm at 77 K, boehmite 69

Fig.21. N2 adsorption /desorption isotherm at 77 K, pseudoboehmite 70

- vi -

LIST OF TABLES page

Table 1. Structural properties of Oxides and Hydroxides 15

Table 2. BET N2 surface area, and Pore volume of boehmite and pseudoboehmite 35 Table 3. Langmuir Isotherm data of pseudoboehmite 37 Table 4. Langmuir Isotherm data of boehmite 38 Table 5. Dubinin-Radushkevich Isotherm data of pseudoboehmite 40 Table 6. Dubinin-Radushkevich Isotherm data of boehmite 41

Table 7. Temkin equilibrium isotherm data of pseudoboehmite 43

Table 8. Temkin equilibrium isotherm data of boehmite 43

Table 9. Summery of Freundlich ,Langmuir,Temkin and D-R isotherm model constants and correlation coefficients for adsorption of F- onto pseudoboehmite and boehmite 44 Table 10. Fixed bed column parameters for the removal of 20 mg l-1 of F- -1 -2 by AlOOH ,QL= 5.54 ml min cm , h = 25 cm , EBCT= 4.52 min 47 Table 11. Column parameters for pilot experiment 50 Table 12. Predicted and Observed Service time of household adsorption column at different initial fluoride concentration. 52 Table 13. Data of adsorption efficiency of aluminium hydroxides at different concentrations of anions (Adapted from [35]) 53 Table 14. Effects of Cations on fluoride adsorption of AlOOH at ambient pH 54 Table 15. Physicochemical analysis result of influent water and treated water, at room temperature 56 Table 16. Rough cost estimation for pilot defluoridator 57

Table 17. BJH desorption pore size distribution, pseudoboehmite 68 Table 18. BJH desorption pore size distribution, boehmite 69 Table 19. Raw data of effluent fluoride concentration (mg/ l) and treated water (ml) for laboratory scale experiment

(Qv = 92 ml/ min, Co =20 mg/l). 71

- vii -

Table 20. Raw data of effluent fluoride concentration (mg/ l) and treated water (ml) for pilot scale column experiment

(Qv = 100.2 ml /min, Co =20 mg/l). 71 Table 21. AAS result summery, Al, mg/l 78 Table 22. AAS result summery, Ca, mg/l 80 Table 23. AAS result summery, Mg, mg/l 81 Table 24. AAS result summery, Na, mg/l 84

Table 25. AAS result summery, K, mg/l 85

Table 26. AAS result summery, Fe, mg/l 87

Table 27. Varian AAS (SIPS 220) detection limit of analyzed metals 87

- viii -

List of Abbreviations and Symbols

AAS Atomic Absorption Spectrometer ASTM American Society for Testing and Materials BDST Bed depth service time BET Brunauer, Emmett, and Teller equation BJH Barret – Joyner - Halenda CC Calcium chloride CDTA 1, 2-cyclohexanedinitrilo tetraacetic acid EBCT Empty bed contact time EDTA Ethylene diamine tetra acetic acid DFT Density functional theory D–R Dubinin–Radushkevich ISE Ion selective Electrode ISO International Organization for Standardization MSP Monosodium phosphate NEERI National Environmental Engineering Research Institute of India ppm parts per million PVC Polyvinylchloride QSAE Quality and Standards Authority of Ethiopia TISAB Total ion strength adjustment buffer WHO World Health Organization XRD X-ray Diffraction B Langmuir constant (mg g-1) β Activity coefficient (mol2/J2)

1/bT Adsorption potential of the adsorbent -1 Cb Breakthrough fluoride concentration (mg l ) -1 Ce Equilibrium concentration of the adsorbate (mg l ) -1 Co Column influent or initial fluoride concentration (mg l )

Cx Intercept on the ordinate of BDST plot (h) ε Polanyi potential E Mean free energy of sorption per molecule of the sorbate (kJ mol-1) -1 -1 Ka Adsorption rate constant (L mg h ) -1 KF Adsorption capacity (mg g ) based on Freundlich isotherm

KT Temkin isotherm constant (L min mg) m Mass of adsorbent in column (g) -1 mx Slope of BDST plot (h cm ) n Freundlich adsorption equilibrium constant (dimensionless) -3 No Average adsorption capacity per volume of bed (mg cm ) -1 qo Maximum solid phase concentration of the solute (mg g ) -1 q e Amount of solute adsorbed per unit weight of material (mg g ) -1 qm Langmuir, maximum adsorption capacity (mg g )

- ix -

-1 qs D-R, maximum adsorption capacity (mg g ) -1 Qv Volumetric flow rate (ml min ) R Universal gas constant (kJ mol L-1) RL Langmuir equilibrium parameter 2 -1 SA Surface area (cm g ) t Service time at breakthrough point (h) T Absolute temperature (Kelvin) V Throughput volume (ml) Z Packed-bed column depth (cm)

-x-

Abstract

Health problems occurring due to high fluoride concentrations in drinking water are a widespread problem in the East African Rift system including the Ethiopian Rift Valley. Excessive fluoride in groundwater is the most serious water quality problem and many people are being affected by both dental and skeletal fluorosis. The WHO and national standard (ES 261:2001) permit only 1.5 mg/l as a safe limit for human consumption whereas several residents of Rift Valley region of Ethiopia are consuming water with fluoride concentration much more than the permissible limit.

Current methods of fluoride removal from water include adsorption onto activated alumina, bone char and clay, precipitation with lime, dolomite and aluminium sulfate, the Nalgonda technique, ion exchange and membrane processes such as reverse osmosis, electrodialysis and nano filtration. Most of the available materials for defluoridation are expensive and technically non-feasible in rural communities in Ethiopia. Hence the development of defluoridation method based on locally available materials is desirable. The technology must be technically simple, cost effective, easily transferable, use local resources and must be accessible to the rural community.

The present work has been undertaken to explore the feasibility of aluminium oxide hydroxide for the removal of fluoride from water. Aluminium hydroxide was prepared by the reaction between aluminium sulfate (Alum) and sodium hydroxide at room temperature. The white preciptate of aluminium hydroxide was dried at 50 oC in air circulated oven and heated at 300 oC in oxidizing atmosphere to produce two forms of aluminium hydroxides respectively. The products were characterized by XRD and BET SA measurements by BET-nitrogen method. A surface area of 110 m2/g and pore volume of 0.29 cm3/g was obtained for the sample prepared at 300 oC (Boehmite) where as a surface area of 37 m2/g and pore volume of 0.19 cm3/g was obtained for the sample prepared at ordinary conditions (Pseudo-boehmite structure).XRD results show that heat treated aluminium hydroxide comprised AlOOH as the major component and traces of FeO(OH), Fe (OH) 2 and Al2O3..

-2 -1 The Langmuir sorption capacity, qm, and adsorption coefficient, b, are 101.63 mg/g and 4.0 × 10 L mg for psedoboehmite and 72.72 mg/g and 2.11×10 –1 L mg -1 for boehmite, respectively. The D-R isotherm adsorption energy values of 6.04 and 13.35 kJ mol-1 are noted for F –adsorption onto pseudoboehmite and AlOOH, respectively which indicates the sorption process is predominantly physisorption. The Temkin constant, KT, of boehmite and pseudoboehmite for F - are 20,735.34 l mg -1 and 7,369.996 l mg -1, respectively indicating a lower adsorbent/fluoride ion potential (interaction) for pseudoboehmite. The Temkin adsorption potential, 1/bT, was 0.00742 and 0.00116 for AlOOH and pseudoboehmite, respectively. The relatively higher adsorption potential for AlOOH was probably due to the high surface coverage of F- ions onto its surface. - xi- .

The AlOOH media used has the capability of producing water with a residual fluoride concentration of less than 0.05 mg/l from an initial fluoride of 20.0 mg/l. In the previous fluoride adsorption studies using this material, the adsorption capacity of AlOOH for fluoride ions has been tested in batch and continuous mode and found out as 23.7 mg F - /g and 25.79 mg F -/g , respectively.

A comparable breakthrough time, t, was observed between a laboratory scale column (down flow) experiment and mini column(up flow) of the previous adsorption experimental results with breakthrough time values 1150 min and 1350 minutes, respectively.

The presence of certain cations may be effective in fluoride retention. Exchangeable cations such as Na, Ca and Mg may form solid precipitate with fluoride.

A domestic defluoridator has been developed and tested at a pilot domestic unit. AlOOH particles with 1.0 – 2.0 mm size were used as filter media in this unit. Upward flow technique has been used in the defluoridation process. The performance of the pilot defluoridator has been monitored at regular intervals to evaluate its fluoride removal performance. The pilot household defluoridator has a capacity of treating about 20 L of water and this quantity of water could be used by a family of five each consuming four liters per day for cooking and drinking purposes. About 0.785 Kg of AlOOH granules has reached breakthrough in 1.4 month when the fluoride concentration in water was around 20 mg/l. The defluoridation price per liter of water was estimated as 0.55 birr/L.

Hence it is concluded from the pilot study that the developed technology is simple, efficient, effective and feasible for defluoridation of water for fluoride affected regions both at the remote and rural settlements at large and urban households in Ethiopia.

Key words: Fluoride, defluoridation, Pseudo-boehmite, boehmite, adsorption, Bed Depth Service Time

- xii -

1. INTRODUCTION

1.1 Background

Water is one of the major elements essential for sustenance of all forms of life. The chemical nature of water is one of the most important criteria that determine its usefulness for a specific need and as such not all the waters are fit for drinking. Many water sources contain harmful substances in concentrations that make the water unsafe to drink or unfit for domestic use.

Deprived sections of society in the world consume contaminated water which may result in epidemics. The sources of water contamination may be by natural or human activities. One such contaminant is fluoride, which arises due to its natural presence from dissolution of fluoride containing rocks, or discharge by agricultural and industrial activities such as glass, electronics, steel, aluminum, pesticide and fertilizer manufactures [1, 2].

Many epidemiological studies have shown that fluoride in drinking water has a narrow range between intakes that cause beneficial and detrimental health effects. Fluoride intake to humans is necessary as long as it does not exceed the limits. The World Health Organization (WHO) estimates the maximum allowable limit for fluoride uptake to human’s in drinking water as 1.5 mg l-1 [3]. Excess fluoride intake causes different types of fluorosis, primarily dental and skeletal fluorosis. White line striations followed by brown patches and, in severe cases, brittling of the enamel are common symptoms of dental fluorosis. Skeletal fluorosis first causes pain in the different joints, then limits joint movement and finally causes skeletal deformities, which become particularly acute if fluoride uptake occurs during growth. Since these ailments are incurable, fluorosis can only be mitigated by preventing intake of excess fluoride.

- 1 -

Ground water plays an important role in the supply of drinking-water to rural communities. The use of groundwater is usually regarded as being preferable to the use of surface water in that managed groundwater resources are less vulnerable to contamination and usually require a reduced level of treatment. [4]

Ethiopia is one of the 23 countries in the world [5] where the population suffers from the consumption of fluoride rich drinking water. In the Rift Valley areas, the fluoride concentration in natural ground water is excessively high and about 10 million people experience the effects of dental as well as skeletal fluorosis. [6] Where the high fluoride water is the only water source, it is necessary to use specialized processes to reduce the fluoride in the water to acceptable levels.

The high fluoride levels in drinking water and its impact on human health in many Rift Valley areas of Ethiopia have been given by concerned bodies in finding the most suitable and sustainable defluoridation technology.

The fluoride bearing minerals or fluoride rich minerals in the rocks and soils are the cause of high fluoride content in the groundwater. This problem of high concentrations of fluoride in natural water, especially ground water, is severe and widespread in Rift valley region of Ethiopia

[6-9].

The source of high fluoride concentrations is primarily associated with:

• Addition of fluoride by active volcanic and fumarolic activities;

• High water-rock interaction (interaction of water with fluoride bearing rocks, volcanic

and sedimentary such as acidic products like pumice, igmbrite, obsidian and rhyolite); and

• Low calcium concentration, which restricts the precipitation of fluoride as fluorite (CaF2).

- 2 -

Besides the Rift Valley region, there are a few isolated pockets in Oromiya region whose ground water contains a significant concentration of fluoride [10, 11]. In Somali region also there are some areas (e.g. Deghabour, Kebri Dehar, Jerer Valley, Hargele and Warder) where ground water supplies contain fluoride concentration well above the WHO guideline value and/or the national standard. Although details are not available on the factors responsible for the recorded high fluoride concentrations, it is believed to be of geological origin. According to a recent study [12], a total of 1,613 water samples were collected from 852 utility piped supplies, 292 boreholes, 155 dug wells and 313 protected springs and analysed for fluoride. The overall results obtained indicate that 1,519 samples (94.2 %) of the total samples analysed comply with the WHO guideline value and the national standard. Maximum concentrations found were up to 10.5 mg/ L.

For Oromiya region, almost all the water supplies whose fluoride concentration exceeds the

WHO guideline value and the national standard are from the East Shoa zone, which is located in the main Rift Valley system of Ethiopia. The results obtained in the project confirm completely with the historical water quality data and numerous study findings [6, 8, 9] pertaining to the zone that fluoride is indeed a major water quality problem.

Remedial measures have to be considered for the removal of fluoride, if it’s concentration in water source exceeds the permissible level. A wide range of treatment procedures has been reported for the removal of excess fluoride from water. These can be broadly divided into three categories: precipitation, adsorption and membrane based. Precipitation methods involve the addition of soluble chemicals to water. Fluoride is removed either by precipitation, co- precipitation or adsorption onto the formed precipitate [13–15]. Adsorption processes involve the passage of raw water through an adsorbent bed, where fluoride is removed by physical, ion

- 3 - exchange or surface chemical reactions with the solid matrix. A wide range of adsorbents, such as activated alumina, bone char, clay, zeolites, fly ash, brick and specific ion exchange resins, have been reported for fluoride removal [16–23]. Membrane based defluoridation methods include reverse osmosis, nanofiltration, electrodialysis and electrocoagulation [24–28].

It is difficult and expensive to reduce a high natural level of fluoride in water. This means that the first option should be to find an alternative source with lower fluoride levels. If there is no other possible or cost-effective source, defluoridation must be practiced to avoid the toxic effects. The best method depends on local circumstances, fluoride concentration and socio-economic factors.

The entire water demand is often ten times higher, and to defluoridate this would be too expensive, as well as producing a large amount of toxic sludge [29].

The World Health Organization (WHO) has identified and evaluated the most promising defluoridation methods, which can be used at both a central and a household level in developing countries. These include bone charcoal, contact precipitation, Nalgonda technique, clay and activated alumina based defluoridators [30].

Defluoridation of water by activated alumina is the method of choice due to its very high affinity for fluoride. It is a porous material with the surface comprised largely of active sites. It is

o prepared by dehydration of Al (OH)3 in the temperature of 300 – 600 C. Activated alumina is regarded as an excellent material for fluoride removal. However, pH and alkalinity are the factors which affect the sorption capacity. The exhausted material can be regenerated by washing with alkali followed by acid and finally with distilled water [31-33].

- 4 - Batch and laboratory scale fixed bed column experiments for fluoride adsorption have revealed that heat treated hydrated alumina produced at 300 oC of particle size 1.0 – 2.0 mm and with neutral pH condition is regarded as suitable for fixed bed adsorption provided that the charring temperature does not exceed 300 °C and the charring time is sufficient and appropriate [ 34,35].

It is therefore possible to manufacture of good quality treated hydrated alumina with appropriate particle size from a locally produced alum.

Most people affected by fluoride contamination in the Ethiopian Rift are poor, live in small communities and rely on underground water as a source of drinking water. They therefore need an appropriate method that is cheap, simple to use and adaptable to either a household or a village scale. One such method could involve the use of a readily available material, such as aluminium hydroxide in the form of boehmite (AlOOH).

1.2 Domestic Defluoridation Units

In the past decades, a wide range of defluoridation materials and methods have been investigated and analyzed, mainly on a laboratory scale. Insufficient removal efficiency, complicated maintenance and/ or unaffordable costs, particularly for rural populations, are the main reasons why these methods have rarely been implemented in developing countries, except in some areas.

Sorption on activated alumina, co-precipitation on aluminium hydroxide (known as the Nalgonda technique) and sorption on bone char are the most common defluoridation methods used in developing countries [36].

Different approaches have been practiced in developing countries to filter fluoride affected water through a column packed with a strong adsorbent, such as activated alumina (Al2O3), activated

- 5 - charcoal and clay; Nalgonda and contact precipitation for both community and household use.

Relatively expensive filters are commercially available based on packages of medium and a modification of the candle-type stainless steel domestic filters.

But the development and implementation of simple and sustainable defluoridation techniques are urgently needed, especially since groundwater will increasingly serve as a drinking water source.

As compared to community based filter units, household treatment options appear to offer greater potential for sustained use, in part because overall time commitments may be lower and also because the benefits to the user are more directly obvious. Promotion of household filter units as against community defluoridation units create a sense of ownership and therefore seem to be more successful. People may happily accept simple and relevant technologies, introduced with the help of local functionaries and field workers.

1.2.1 Activated Alumina Household Unit

Application of domestic defluoridation plant, based on activated alumina, has been launched by

UNICEF in rural India. The unit consists of two chambers (Fig. 1).The upper chamber is fitted with a water flow control device (removable circular ring) at the bottom. The average flow is 10 liters per hour. The main component of this unit is a PVC gasket containing 3 Kg of activated alumina with a bed depth of 17 cm. A perforated plate of either stainless steel or tin is placed on the top of activated alumina bed to facilitate uniform distribution of water. The top chamber is covered with a lid. Lower chamber is used for collection of treated water. It is fitted with a tap to draw the treated water. About 10 liters of water can be collected in 1 hour. Exhausted activated alumina can be regenerated by dip regeneration method [37].

- 6 - Activated alumina surface is amphoteric in nature and can exist as AlOH+, AlOH, and AlO-.

Fluoride binding to activated alumina is proposed to be due to exchange of surface hydroxyl groups, which can be represented by the following reactions [38]

+ - AlOH2 + F ------→ AlF + H2O (1)

AlOH + F------→ AlF + OH- (2)

Fig. 1. Activated alumina based defluoridation unit

1.2.2 Bone Charcoal Household Unit

The bone char method was practiced for use in rural areas of Tanzania. The bone charcoal defluoridation units; the bucket type and column type systems are described in fig. 2. In a bucket type system, plastic buckets of 20 litres were fitted with a tap near the bottom. About 4 to 5 kg of bone char was then put into the bucket. Water to be defluoridated was then filled in the bucket and allowed to percolate through the bone char media. A tap installed on the side near the bottom of the bucket is used to collect the defluoridated water. Bucket type defluoridators are cheaper because columns are omitted but not recommended due to poor fluoride removal. In such defluoridators the flow is down ward.

- 7 - In the column bone char packed method, columns of diameter of 15 cm and a height of 50 cm are taken to be standard columns. With those dimensions the column can accommodate 4 kg of bone char grains. The height of 50 cm is selected because it can be fed with water from a bucket placed on normal home tables, which have heights ranging from 70 to 90 cm thus avoiding extra costs of making special platform for raising the bucket of raw water for feeding the bone char column.

Water inside the columns flow upward to avoid overflowing in case the media get clogged. Water to be defluoridated is allowed to percolate upwards through the bone char media whereby fluoride is mainly adsorbed onto the bone char granules and some is removed by ion exchange process [39].

Bone charcoal has the specific ability to take up fluoride from water. This is believed to be due to its chemical composition, mainly as hydroxyapatite, Ca10(PO4)6(OH)2, where one or both the hydroxyl-groups can be replaced with fluoride. The principal reaction is hydroxyl-fluoride exchange of apatite:

– – Ca10(PO4)6 (OH)2 + 2F ------Æ Ca10(PO4)6 (F)2 + 2 OH (3)

A B

Fig. 2. Bone charcoal defluoridation units: (A) Bucket type system; (B) Column type system

- 8 - 1.2.3 Defluoridation by Nalgonda Technique

It involves addition of aluminium salt, lime and bleaching powder followed by rapid mixing, flocculation, sedimentation and filtration. Aluminium salt is responsible for removal of fluoride from water. The dose of aluminium salt increases with increase in the fluoride and alkalinity levels in the raw water. For domestic treatment, any container of 20-60 liter capacity is suitable and the required dose depends mainly on the alkalinity and initial fluoride content of the water.

Mixing time of 11 minutes and settling time from 1-2 hours were reported to be sufficient. The dose of lime is empirically 1/20th of the dose of alum. Lime facilities forming denser floc or rapid settling. [40].

During this flocculation process many kinds of micro-particles and negatively charged ions including fluoride are partially removed by electrostatic attachment to the flocs. (Equations 4–7):

Alum dissolution:

3+ 2– Al 2(SO4)3 .18H2 O ------Æ 2Al + 3SO4 + 18H2 O (4)

Aluminium precipitation (Acidic):

3+ + 2Al + 6H2O------Æ 2Al (OH)3 + 6H (5)

Co-precipitation (non-stoichiometric, undefined product):

– F + Al (OH)3 ------Æ Al–F complex + undefined product (6) pH adjustment:

+ 2+ 6Ca (OH)2 + 12H ------Æ 6Ca + 12H2 O (7)

The unit consists of two chambers of 300 mm diameter (Fig. 3). The upper chamber is fitted with two candle filters. The main component of this unit is a handle for mixing alum and lime. The denser flocs formed after alum and lime addition is allowed to settle for one hour [41].

- 9 - The water is filtered through the candle filters. Lower chamber is used for collection of treated water. It is fitted with a tap to draw the treated water. About 10 liters of water collected in 1.25 hours. The denser flocs formed will be removed by washing the upper chamber and the filter unit will be ready for next defluoridation.

The Nalgonda Technique has been applied in India, Tanzania, Ethiopia and Thailand at different levels. On household scale it is introduced in buckets or drums and at community scale in fill and draw plants. For larger communities a waterworks-like flow system is developed, where the various processes of mixing, flocculation and sedimentation are separated in different compartments. [42].

Handle for mixing

Stainless steel angular paddles

Filter Raw water candles Stainless steel vessel

Treated water

Fig. 3. Stainless steel Candle Filter (Nalgonda Technique)

- 10 - 1.2.4 Clay defluoridators

Fired clay chips are reported to have good fluoride removal capacity [43]. Domestic clay column filters are normally packed using clay chips found as waste from the manufacture of brick, pottery or tile. The filter is based on up-flow in order to allow for settling of suspended solids within the filter bed. The filter does not have a clean water reservoir and the filtration rate is controlled by slow withdrawal through the tap. (Fig. 4)

Depending on the raw water quality, and on the quality of the brick chips, such a post-filtration through charcoal may be a precondition to obtain good water quality. As charcoal has a low specific density, the pebbles stabilize the stratified bed and are necessary to avoid the escape of charcoal grains with the treated water [44].

Fig. 4. Stratified column of brick chips household defluoridator

- 11 - 1.2.5 Contact precipitation

Contact precipitation is a technique by which fluoride is removed from the water through addition of calcium and phosphate compounds and then bringing the water in contact with an already saturated bone charcoal medium. In solutions containing calcium, phosphate and fluoride, the precipitation of calcium fluoride and/or fluorapatite is theoretically feasible, but practically impossible due to slow reaction kinetics. It has recently been reported that the precipitation is easily catalysed in a contact bed that acts as a filter for the precipitate [45]. Using calcium chloride (CC) and sodium dihydrogenphosphate (MSP) or “monosodium phosphate” as chemicals, the following equations illustrate the removal:

Dissolution of CC:

2+ – CaCl2.2H2O (s) ______Ca + 2 Cl + 2H2O (8)

Dissolution of MSP:

3- + + NaH2PO4.H2O (s) ______PO4 + Na + 2 H + H2O (9)

Precipitation of calcium fluoride:

2+ – Ca + 2 F ______CaF2(s) (10)

Precipitation of fluorapatite:

2+ 3– – 10 Ca + 6 PO4 + 2 F ______Ca10(PO4)6 F2(s) (11)

The contact precipitation unit comprises a column, (Fig. 5) containing a relatively small, saturated bone charcoal contact bed. Gravel, or coarse grained bone charcoal, is used as a supporting medium. Above the bed a relatively large space is used for mixing the chemical with the raw water. From the bed the defluoridated water flows continuously by gravity to a shallow, but wide, clean water tank. One or more clean water taps are fitted at the bottom. The flow from

- 12 - the raw water tank to the clean water tank is constrained by a valve or a narrow tube arrangement to allow for appropriate contact time in the bed. Too short contact time would reduce the removal capacity and increase the escape of chemicals in the treated water. Too long contact time may result in precipitation of calcium phosphates in the upper parts of the filter bed, thus also reducing the removal efficiency. The optimum contact time is not yet known but contact times of

20 to 30 minutes have been shown to produce excellent operation.

Fig. 5. Contact precipitation for household use

- 13 - 1.3 Aluminum Hydroxides

A general classification of the various modifications of aluminum hydroxides is shown in Fig. 6.

The best defined crystalline forms are the three trihydroxides, Al (OH)3: gibbsite, bayerite, and nordstrandite, and two modifications of aluminum oxide hydroxide, AlO(OH): boehmite and diaspore. Besides these well-defined crystalline phases, several other forms have been described in the literature [46, 47]. Identification of the different hydroxides and oxides is best carried out by X-ray diffraction methods [47]. Structural data is listed in Tables 1.

Aluminium hydroxides

Crystalline Gelatinous

Trihydoxides Oxide-hydroxides X-ray indifferent Pseudo- Al(OH)3 AlOOH (Amorphous) boehmite (Gelatinous boehmite)

Boehmite (γ-aluminium oxide Diaspore (α-aluminium oxide hydroxide) hydroxide)

Gibbsite (γ-aluminium Bayerite(α-aluminium Nordstrandite (β-aluminium trihydroxide) trihydroxide) trihydroxide)

Fig. 6. Classification of Aluminium hydroxide

- 14 - Table 1. Structural properties of oxides and hydroxides [47]

Density, Phase Formula Crystal system g/cm3 Al(OH) Gibbsite 3 monoclinic 2.42

Al(OH) _ Gibbsite 3 triclinic

Bayerite Al(OH)3 monoclinic 2.53

Nordstrandite Al(OH) 3 triclinic -

Boehmite AlOOH orthorhombic 3.01

Diaspore AlOOH orthorhombic 3.44

Corundum Al(OH)3 hexahagonal (romb) 3.98

High surface area alumina’s are of wide use in industry as sorbents, catalysts and catalysts supports [48]. The improvement of the performance properties of these materials, which strongly depend on their porosity, will therefore have a great economical impact.

Recent studies (e.g., [49]) propose the use of microporous (pores<2 nm) and mesoporous (2–50 nm) materials as adsorbents for pollutants in aqueous systems. However, to utilize these materials for maximum economic and environmental benefits, relationships between physical properties

(e.g., specific surface area and pore structure) and surface chemistry (e.g., surface charge, adsorption behavior) must be elucidated.

1.3.1 Aluminum Oxide Hydroxides

Aluminium trihydroxide, Al(OH)3, and aluminium monohydroxide (AlOOH) exhibit polymorphism and exist in many structure forms [47]. The structure of all aluminium cations

- 15 - located in octahedrally coordinated interstices. The packing of oxygen ions inside the layer can be either hexagonal or cubic; where as the symmetry of the overall structure for each hydroxide is determined by the distribution of hydrogen. The relative distance between hydroxyl groups, both within and between the layers, has been suggested to control the mechanism of dehydration for the particular hydroxide [50].

Pseudoboehmite is formed during aging of X-ray indifferent hydroxide gels as a precursor of trihydroxide. The reflections of pseudoboehmite are broadened not only because of the very small particle size, but also because of variable distances of the AlO(OH) double chains, which form the structural element of pseudoboehmite as well as of well-crystallized boehmite. The lattice spacing in the direction of the c axis increases by 0.117 nm for each mole of excess water

[51].

Boehmite is the major constituent of many bauxite minerals. It can also be synthesized in the laboratory, for instance, by neutralizing aluminium salts at a temperature close to the boiling water of water, by treating activated aluminium with boiling water or by hydrothermal reaction.

The boehmite crystal structure consists of the cubic packed oxygen ions with the aluminium cations sandwiched between the adjacent layers. The distribution of hydrogen atom results in an orthorhombic unit cell that has been described by Cmcm space group. The lattice parameters of boehmite are a= 2.861 Å, b= 3.696 Å and c= 12.233 Å [52].

Aluminum oxide hydroxide has ion exchange ability. The hydroxyl groups on aluminum oxide hydroxide have selective adsorptivity for anions of interst and could be used for the removal of a given anion from water. The selectivity of anion adsorption onto aluminum oxide hydroxide was in the order of chloride, nitrate, hydrogen carbonate, fluoride, sulfate, and phosphate. This shows

- 16 - that aluminum oxide hydroxide could selectively adsorb phosphate ion better than the other anions in rivers, lakes, and the sea.

According to a study report [68], the adsorption rate of aluminum oxide hydroxide for phosphate was faster than that other adsorbates. Besides, the amount of phosphate adsorbed onto aluminum oxide hydroxide was influenced by pH and other competing anions. For instance the amount of phosphate adsorbed was greatest at pH 4, ranging with pH from 2 to 9. The selectivity of phosphate adsorption onto aluminum oxide hydroxide was evaluated based on the amount of phosphate ion adsorbed onto aluminum oxide hydroxide from several anion complex solutions. It is phosphate that aluminum oxide hydroxide can selectively adsorb. The selectivity of phosphate onto aluminum oxide hydroxide was about 7000 times that of chloride. This result indicated that the hydroxyl groups on aluminum oxide hydroxide have selective adsorptivity for phosphate and could be used for the removal of phosphate from seawater. Thus, a similar pattern of fluoride adsorption onto AlOOH would be expected.

1.4. Fluoride adsorption in batch and continuous modes

The contact between solid adsorbent and the liquid can be made by either batch contact system or fixed bed (up flow or down flow). Batch type sorption is usually limited to the treatment of small volumes of effluent, whereas fixed bed systems have an advantage over this limitation. In fixed bed the adsorbate is continuously in contact with a given quantity of fresh adsorbent thus providing the required concentration gradient between adsorbent and adsorbate for adsorption

[53].

- 17 - 1.4.1 Adsorption isotherms

Adsorption reactions can be described by various models. Empirical models provide descriptions of adsorption data. An adsorption isotherm indicates how the adsorption molecules distribute between the liquid phase and the solid phase when the adsorption process reaches an equilibrium state in batch investigations. The analysis of the isotherm data by fitting to different isotherm models is an important step to find the suitable model that can be used for design purposes [58].

The general purpose of adsorption isotherms are described as follows:

1.4.1.1 Langmuir isotherm

The Langmuir isotherm assumes monolayer adsorption onto a surface containing a finite number of adsorption sites of uniform strategies of adsorption with no transmigration of adsorbate in the plane of surface [59].

The Langmuir equation is useful for the estimation of maximum adsorption capacity corresponding to complete monolayer coverage expressed by:

qbCmax e q e = (12) 1 + bCe The linear form of Langmuir isotherm equation is given as:

CC1 ee=+ qqbq em m (13)

Where; Ce is the equilibrium concentration of the adsorbate (mg/l), qe is the amount of adsorbate adsorbed per unit mass of adsorbent (mg/g), qm and b are Langmuir constants related to adsorption capacity and rate of adsorption, respectively.

- 18 -

When Ce/qe was plotted against Ce, a straight line with slope of 1/qm was obtained. The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless equilibrium parameter (RL) [59], which is defined by:

1 RL = (14) 1 + bCo

Where b is the Langmuir constant and C0 is fluoride concentration (mg/l). The value of RL indicates the type of the isotherm to be either favorable (0 < RL < 1), unfavorable (RL > 1), linear

(RL = 1) or irreversible (RL = 0).

1.4.1.2 Temkin isotherm

The Temkin adsorption isotherm model is used to evaluate the adsorption potentials of the adsorbent for adsorbates. Temkin and Pyzhev considered the effects of indirect adsorbate/ adsorbent interactions on adsorption isotherms. The heat of adsorption of all the molecules in the layer would decrease linearly with coverage due to adsorbate/adsorbent interactions [60]. The

Temkin isotherm has been used in the form as follows:

RT qKCee= ln T (15) b T The linear form of the Temkin isotherm model as shown below can be plotted as qe against ln Ce

RT RT qKCee=+lnT ln (16) bbTT Where 1/bT is the adsorption potential of the adsorbent; and KT is the Temkin isotherm constant

- 19 - 1.4.1.3 Dubinin–Radushkevich isotherm (D-R isotherm)

The Dubinin – Radushkevich model is used to estimate the characteristic porosity and the apparent energy of adsorption. It is powerful and simple in concept and applications and can be employed from trace to saturation concentrations. The D–R isotherm assumes a fixed volume or

‘‘sorption space’’ close to the sorbent surface where sorption takes place. It describes heterogeneity of sorption energies within this space, independent of temperature.

2 lnqqe =− ln s βε (17) where qe and qs are sorbed concentration and maximum sorption capacity respectively at the sorbent surface, expressed in units of mg/g and, β is a constant (activity coefficient)related to energy, in units of mol2/J2 and ε is Polanyi potential , is the work required to remove a molecule or ion away from its location in the ‘‘sorption space’’. It is computed as

⎛⎞1 ε = RT ln⎜⎟ 1 + (18) ⎝⎠C e where R is the universal gas constant in kJ mol/L, T is the temperature in Kelvin and Ce is the

2 equilibrium concentration of sorbate in solution. When ln qe is plotted against ε , a straight line may be obtained if the sorption data follow the D–R isotherm.

The value of β can be correlated to sorption energy (E) using the following relationship [61]. The constant β gives the mean free energy E of sorption per molecule of the sorbate when it is transferred to the surface of the solid from infinity in the solution and can be computed by using the relationship:

- 20 - ⎡⎤1 E = ⎢⎥ (19) ⎣⎦2β

1.4.2 Adsorption in packed bed column

Several models were applied to simulate the breakthrough curves to predict the scaling-up of a unit plant. The Bed Depth Service Time model (BDST) is a simple model for predicting the relationship between bed depth (Z) and service time (t) in terms of concentration and adsorption parameters as: [62]

⎛⎞KNZao ⎛⎞Co F ln⎜⎟−= 1 ln ⎜⎟e −−1 K aoC t (20) ⎝⎠C ⎝⎠

[62]; where Co is the initial concentration of fluoride ions in the liquid phase (mg/l); Cb the

-1 breakthrough fluoride concentration (mg L ); F is the linear flow rate (m/h); N0 is the bed

-3 capacity (mg cm ); Ka is the rate constant in BDST model (L/mg h); t is the service time (h); and

Z is the bed depth of the column (m). Since the exponential term is usually much larger than unity, the term in the parentheses on the right hand side of equation (20) is often neglected.

Hutchins [63] then proposed a linear relationship between bed depth and service time given by eq. (21).

NCoo1 ⎛⎞ tZ= − ln⎜⎟− 1 (21) CFo KCao ⎝⎠ C

Equation (22) indicates the linear relationship between t and Z as

tm=−x Z C x (22)

- 21 - where mx is the slope of the BDST line and the intercept of this equation represents

1 ⎛⎞Co Cx = ln⎜⎟− 1 (23) KCao ⎝⎠ C

The slope of the BDST line, mx, represents the time required for the adsorption zone to travel a unit length through the adsorbent and is used to predict the performance of the bed. If there is a change in the initial adsorbate concentration, C0, to a new value of initial adsorbate concentration

1 1 ( C o ), the new slope ( mx ) can be written as:

1 C o mmxx= x (24) C o

And the new intercept can be written as:

1 ⎛⎞C o ln⎜⎟− 1 1 ⎛⎞C o ⎝⎠C C = C xx⎜⎟1 (25) ⎝⎠C o ⎛⎞C o ln⎜⎟− 1 ⎝⎠C

If the designed data are required for a change in flow rate of adsorbate to the adsorption system,

2 the intercept remains unchanged and the new slope ( m x ) can be written as [64].

2 ⎛⎞F mmxx= ⎜⎟ ⎝⎠F 1 (26)

- 22 - 1. 5 Objectives of the Research

The general objective of the research was to develop and test a domestic defluoridator in a pilot column unit to remove excess fluoride in drinking water using Aluminium Oxide Hydroxide as an adsorbent in order to minimize the effect of endemic fluorosis.

The specific objectives were as follows:

1. To determine the structure, porosity and surface area of the adsorbent.

2. To examine the applicability of various isotherm models (Langmuir, D-R and Temkin

models) for the adsorption of fluoride onto aluminium hydroxides (boehmite and

pseudoboehmite).

3. To evaluate scale up approaches of the pilot column through a laboratory scale column

experiment.

4. To investigate the effect of cations on the defluoridation capacity of aluminium oxide

hydroxide in the pilot column.

5. To investigate reaction mechanisms for the adsorption of fluoride onto aluminium oxide

hydroxides (boehmite and pseudoboehmite).

- 23 - 2. Materials and Methods

2.1 Preparation of Aluminium Oxide Hydroxide

Locally available Aluminium sulphate (Alum) was used as starting material for the production of aluminium oxide hydroxide. About 300 g of Al2(SO4)3.14H2O was mixed in 1500 ml of distilled water and stirred with magnetic stirrer in a 2 L conical flask until complete dissolution. The resulting lower pH (2.7) was adjusted to about pH of 7.00 by adding 2.0 M NaOH at room temperature while stirring vigorously. The precipitate (aluminium hydroxide) was then sun dried or oven dried at 50 oC until constant weight. The adsorbent was then placed in a furnace

(Calbolite, ELF Model) and heated at 300 oC for 1 h to produce treated aluminium hydroxide

[34].

The heat treated aluminium hydroxide (aluminium oxide hydroxide) was crushed and sieved to particles size range of 1-2 mm. This material was packed in a column to the required depth in a continuous defluoridation process.

2.2 Characterization of the adsorbents

2.2.1 BET Surface Area and Pore Volume

BET surface areas and pore size distributions of the produced aluminium hydroxides were determined from N2 isotherm data collected at 77 K using Quantachrome Autosorb-6B apparatus (Quantachrome Corporation, USA) at the Delft Technical Universty, Netherlands through Dr. Feleke Zewge. Prior to analysis, particles were out gassed overnight at 423 K. The density functional theory (DFT) was used to calculate micropore volumes, mesopore volumes

- 24 - and micropore size distributions from the N2 adsorption data (Vulcan kernel, PC software version

1.19, Quantachrome, Boynton Beach, FL).

2.3 Batch adsorption studies

Predetermined amounts of aluminium hydroxides (AlOOH and pseudoboehmite) were placed with a known volume of fluoride solution (20 mg F-/l) into a 1L Erlenmeyer flask under continuous mixing condition with magnetic stirrers at room temperature (23 ± 2 oC). The supernatant was filtered through a 0.2 µm filter paper (ADVATEC) and therefore an aliquot of filtered solution was analyzed by Orion Model, EA 940 Expandable Ion Analyzer [34].

In this procedure, a 20 mg F- / l solution was added to a glass vessel and the F- concentration was measured after 1 h and 12 h contact period.

2.4 Laboratory Scale Column Experiment

A schematic diagram for the experimental laboratory scale setup is shown in Fig 7. The adsorbent bed was made of Perspex tube of 4.5 cm i.d. and 40 cm height, closed at both ends with a rubber stopper.At the bottom of the adsorbent bed, 5.0 mm diameter glass beds were placed so as to provide a uniform inlet flow of solution into the column.

A weighed amount of adsorbent was packed well within the column, and an upper retaining cotton pad was inserted on top of the bed and firmly secured in place by glass beds for the even distribution of flow through the top of the column and also to prevent wash away of the adsorbent at the bottom.

- 25 - AlOOH Adsorbent column bed Cotton pad Glass Effluent beds reservoir Rubber stopper Glass column Pump

Influent reservoir

Fig. 7. Laboratory Scale Column Experimental apparatus and Column.

Water with fluoride content of 20 mg/l was prepared in a 25 L tank and homogenenized before

the commencement of defluoridation. The packed bed was initially washed with deionized water

to remove fine particles, by operating the column in down flow mode until the effluent water

become clear. The water was pumped in a down flow mode by a peristaltic pump (Heidolph

PUMPDRIVE 5006). Samples were withdrawn at the outlet of the column at 1 hour interval

using 25 cm3 measuring cylinder until the adsorbent bed become exhausted. The desired

-1 breakthrough concentration (Cb) was determined at 7.5 % of the initial concentration (20 mg L ),

which is 0.075 C/Co or 1.5 mg/l.

The experiment was carried out at room temperature (22 ± 2 0C). The pH of the inflow was

maintained at 7.4 throughout the experiment.

- 26 - 2.5 Pilot Scale Column Experiment

Pilot testing was conducted with fluoride spiked tap water. A pilot defluoridator was designed as a column (Fig. 8), provided with an attached down pipe arrangement, in order to allow for up flow adsorption of fluoride water through a medium of locally available aluminium oxide hydroxide. Upward flow ensures uniform flow across sectional area of the column.

Inlet tap ∅ 0.85 mm circular PVC plate Feed tank PVE tubing

Outlet tap AlOOH ∅ 0.25 mm bed nylon mesh

PVC column Perforated PVC pipe (∅ 75 mm, L=5cm) adsorbent support

Treated water collection tank

Fig. 8. Diagram of pilot adsorption column and column detail; arrows show the water feeding direction.

The unit is made of PVC pipe of 40 cm length and 10.3 cm diameter. The inner pipe is 1.0 cm in diameter with a circular perforated plate fixed at 5 cm from the base of the filter. The outlet is fixed 5 cm above the top of the filter. A piece of nylon mesh with the same diameter as the

- 27 - column was placed at both ends in the bottom and top of the adsorbent to prevent AlOOH particles passing through the perforated PVC plate. The filter unit is packed with AlOOH sizes 1-

2 mm up to a height of 25 cm. The column was fed by gravity from feedwater tank that was elevated 60 cm.The fluoride containing water was fed through the inlet pipe. At the beginning the filter unit is filled with distilled water and kept for at least 12 hours to obtain equilibrium.

Thereafter when fresh Fluoride rich water is fed through the inlet pipe an equal volume of defluoridated water comes out automatically through the outlet pipe. The treated water from the outlet was collected in separate reception tank to measure treated water volume. The volume of treated water was measured at 1 hr interval and the average flow rate was calculated based on these values. To account for any slight variation of the flow rate due to a higher flow resistance.

The desired breakthrough concentration (Cb) was set at 7.5 % of the initial concentrations (20 mg/l), which is 0.075 C/Co or 1.5 mg /l. The inlet concentration of fluoride was kept constant at

20 mg /l during the pilot study.

2.6 Reagents and Standard Solutions

A 1000 mg /l sodium fluoride stock solution (99.0% NaF, BDH chemicals Ltd Poole England) was prepared by using distilled water. Standards and samples at a required concentration range were prepared by appropriated dilution of the stock solution with distilled water.

The Ionic Strength Adjustment Buffer (TISAB) was prepared by following a recommended procedure, except that EDTA is replaced by CDTA [65] as follows; 57 ml of glacial acetic acid,

58 g of sodium chloride, 7 g of sodium citrate and 2 g of EDTA were added to 500 ml distilled water, allowed to dissolve, pH adjusted to 5.3 with 5.0 M Sodium hydroxide, and then make up to 1 L in a volumetric flask with distilled water [34].

- 28 -

2.7 Fluoride Measurement

Total solubilized fluoride was determined potentiometrically using Orion fluoride ion-selective electrode (ISE). A pH/ISE meter (Orion Model, EA 940 Expandable Ion Analyzer) equipped with combination fluoride-selective electrode (Orion Model 96-09) was employed.

The fluoride ion selective electrode was calibrated prior to each experiment in order to determine the slope and intercept of the electrode which were in turn used to convert the experimentally obtained potential-time diagram to concentration-time diagram by:

()− / SconsE C − 10 F = (27)

- Where C F is free fluoride concentration, E is potential, S is the slope of the calibration curve and const is its intercept.

2.8 Effect of Cations on the Defluoridation Capacity of AlOOH

The effect of cations on the adsorption of F- was studied in a continuous mode by determining the residual F- concentration of simulated tap water comprising Na+, K+, Mg++ and Ca++ and Fe3+ ions. The effects of such ions were determined at ambient pH and initial fluoride content of 20 mg /l in a fixed bed column of internal diameter 46 mm, bed height of 250 mm, and flow rate of

92 ml min-1. The amount of adsorbent packed in the column was 150.32 g. Residual fluoride was determined at 1 h time interval until breakthrough point was reached.

Water samples were taken at three different intervals randomly (beginning, middle and near breakthrough points) for cations analysis. Similar analysis was also made for the influent water.

- 29 - All water samples collected for selected metal analysis were preserved using nitric acid

(Assay=69.0 - 71.0 %, Specific gravity=1.42, LABORT FINE CHEM PVT LTD). A Varian

SpectrAA-220 atomic absorption spectrometer (Varian Australia Pty Ltd) was used for analyzing the samples for dissolved metal content. The analytical wavelengths and experimental conditions used in the SpectrAA-220 AAS measurements are summarized in appendix part of this paper.

Standard test methods were employed for the determination of metals in the Water samples. ISO:

9964-1, 9964-2:1993, ISO 7980:1996, ASTM D 1068-90 and ASTM: D 857-89 were the methodologies for the determination of sodium, potassium, calcium and magnesium, iron and aluminium, respectively.

Standard solutions were prepared using 1000 mg/l reference solution supplied by Fisher

Scientific Limited; the required concentrations were obtained by diluting with distilled water to concentrations of interest. These were used in obtaining calibration curves for the concentration range used in the experiment. Single element hollow cathode lamp of sodium, potassium, calcium, magnesium, iron and aluminium were used as a light source while air –acetylene and/or nitrous oxide-acetylene flame was used to atomize the samples.

After the determination of each cations of interest, their prospective effects were assessed with respect to their initial influent concentration. The efficiency of the adsorbent was calculated based on the measurement of residual fluoride concentration.

Besides the major cations, residual aluminium content was determined so as to investigate its release during the adsorption process.

- 30 - 3. RESULTS AND DISCUSSION

3.1 Characterization of the adsorbents

In designing an adsorption column, the characterization of adsorbents should be done prior to experiments. In particular, one should know not only the specific area but also the pore size distribution of the adsorbent in order to confirm that it would be proper for the given purpose.

The XRD of the adsorbents were carried out and X-ray diffraction patterns for the aluminium hydroxide dried at 50 oC and after being thermally activated at 300 oC were analyzed. A less ordered structure with no sharp peaks was observed in the XRD powder patterns of aluminium hydroxide dried at 50 oC as shown in Figure 9 that seems the characteristic of gelatinous aluminium hydroxides .It also indicates such solids do not exhibit long-range crystalline order.

The aluminium hydroxide prepared in the same procedure but thermally activated at 300 oC produced a more ordered structure with sharper and more intense lines as shown in Figure 9 which corresponds to the pattern of boehmite. It also showed higher specific surface area and larger crystallite size than those of the heat untreated aluminium hydroxide powder. The study result is supported by Wefers [47] stating that such occurrence corresponds to an improvement in crystallinity due to the local hydrothermal environment related to the evaporation of water on drying.

Studies also indicated that [66] well-crystallized hydroxides such as boehmite are always formed at a slow rate, presumably because crystallization occurs by dissolution and reprecipitation which is a slow process for a compound of low solubility. By contrast pseudo- boehmite is formed rapidly. It exhibits some evidence of crystallinity (i.e., X-ray diffraction), but a small particle size and a slow rate of further crystallization.

- 31 - The X-ray diffraction pattern also indicates that in pseudoboehmite the crystal size is extremely small, less than l00 Å and probably no more than a few lattice parameters only (Fig. 9).

300

250

200 AlOOH

y Pseudoboehmite 150 Intensit

100

50

0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 2-Theta

Fig. 9. XRD patterns of sample produced at 50 OC (pseudoboehmite) and sample produced at 300 OC (AlOOH)

Textural characterization of heat treated aluminium hydroxide comprised AlOOH as the major component and traces of FeO (OH), Fe (OH) 2 and Al2O3.

Porosity and surface area are important characteristics of solid materials that highly determine the properties and performance of adsorbets. Physical and chemical gas adsorption as well as mercury intrusion porosimetry are the most widely used techniques to characterize the above- mentioned parameters.

- 32 - Nitrogen adsorption is frequently used at 77 K to probe porosity and surface area and to be a standard procedure for the characterization of porosity texture of adsorbents. The adsorption isotherm is the information source about the porous structure of the adsorbent, heat of adsorption, characteristic of physical and chemistry and so on. It can be seen from Fig. 10 that the sample prepared at 50 oC has quite narrow micropore size distribution than the heat treated sample.

0.35

0.3 Pseudoboehmite [cc/g] 0.25 AlOOH [cc/g]

0.2

0.15

0.1

Desorption Dv (log d) (cc/g) d) Dv (log Desorption 0.05

0 1 10 100 1000 10000

Pore diameter (Ao)

Fig. 10. Pore size distribution of aluminium hydroxides produced at 50 oC (pseudoboehmite)

and treated at 300 oC (boehmite).

An increase in the pore volume of AlOOH may result from the activation on the microporosity. It is further confirmed that the heat treated aluminium hydroxide has larger micropore volume and

BET surface area than the one that was produced at 50 oC. The micropore volume and BET surface area of both adsorbents are summarized in Table 2.

- 33 - Table 2. BET surface areas and Pore volumes for AlOOH and Pseudoboehmite

BET surface Total pore Micro pore External surface Sample area,m2/g volume,cm3/g volume,cm3/g area,m2/g

AlOOH 110 0.29 0.0021 104

Pseudoboehmite 37 0.19 0.0019 32

The typical N2 adsorption-desorption isotherms (Figs. 20 and 21) shows that a fairly mesoporous characterstics is observed in the aluminium hydroxide produced at 50 oC where as the heat treated aluminium hydroxide shows microporous characterstics with total pore volume and BET surface area of 0.29 cm3/g and 110 m2/g, respectively.

For amorphous aluminium oxides it is important to understand the level of detail of the surface area characterization, since quantification of the internal porosity is expected to substantially affect the final surface area value and our capability to understand the reactivity of these products. Despite the importance of charge properties to sorption of ionic and neutral solutes, pH- dependent surface charge of synthetic mesoporous materials has not been investigated in detail.

Without this information it is difficult to assess whether compound sorption differences between porous and non-porous materials are due to porosity itself or to co-varying differences in reactive site density. For instance, a study [49] observed a significantly greater adsorption of 2, 4- dichlorophenoxyacetic acid to mesoporous alumina, relative to non-porous alumina, in surface normalized batch adsorption experiments. However, it is unclear if these differences were attributable to mesoporosity or increased reactive site density present on the porous alumina surface. In addition, a thorough understanding of points of zero charge, active site density and

- 34 - reactivity, as affected by porosity will enable researchers to select porous materials for specific applications to aqueous systems (e.g., ion or contaminant adsorption).

The AlOOH derived from aluminium sulphate (17 % Al2O3) contained relatively small surface area and total pore volume as compared to AlOOH (obtained from AlCl3) used for the adsorption of phosphate ions from sea water with values 297 m2/g and 0.402 cm3/g [68].

3.2 Adsorption isotherms

Adsorption equilibra provides fundamental physicochemical data for evaluating the applicability of adsorption processes as a unit operation usually described by isotherm models whose parameters express the surface properties and affinity of the adsorbent, at fixed operating conditions. In the previous studies dealing with fluoride adsorption onto AlOOH [34], it was noted that the experimental data was fitted to Freundlich model. The freundlich constants KF and

1/n of the adsorption isotherm was 23.72 and 0.2875 for AlOOH (boehmite) and 7.03 and 0.6133 for the gelatinous aluminium hydroxide (pseudoboehmite), respectively. The correlation coefficient in the freundlich plots was 0.9721 and 0.9873 for AlOOH (boehmite) and gelatinous aluminium hydroxide, respectively.

In order to get additional information about the fluoride adsorption characteristics, it is considered to evaluate other adsorption models such as Langmuir, Dubinin Radushkevich (D–R), and Temkin models. The adsorption isotherms (Langmuir, D-R, Temkin) of fluoride onto boehmite and pseudoboehmite are shown in Figs. 11 – 16.

- 35 - Langmuir Model

- The plots of specific sorption (Ce/qe) against the equilibrium concentration (Ce) for F ions are shown in Figure 11 and 12. The sorption capacity, qm, which is a measure of the maximum sorption capacity corresponding to complete monolayer coverage for psedoboehmite is 101.63 mg/g and that of boehmite is 72.72 mg/g.

The adsorption coefficient, b that is related to the apparent energy of sorption for F- onto AlOOH is 2.11×10–1 L mg-1 and that of pseudoboehmite is 4.0 × 10-2 L mg-1. This observation showed that the energy of adsorption onto psedoboehmite is lower than that of boehmite which is probably due to the less availability of adsorption sites on the adsorbent. The higher b the higher is the affinity of the sorbent for the sorbate. The value of RL was also found to be 0.0862 and

0.3390 for AlOOH and pseudoboehmite respectively at 25 oC.

0.50 Ce/qe = 0.24863 + 0.00984Ce

2 0.45 R = 0.92032

0.40

,g/L e /q

e 0.35 C

0.30

0.25

5 1015202530 C ,m g/L e

Fig. 11. Langmuir equilibrium isotherm model of pseudoboehmite; Co = 50 mg/l, pH = 7.0,

Temp. = 25 oC

- 36 - 0.45

0.40 Ce/qe = 0.06502 + 0.01375Ce 0.35

R2 = 0.97289 0.30

0.25 ,g/L e

/q 0.20 e

C 0.15

0.10

0.05

0.00 0 5 10 15 20 25 30 C ,m g/L e

Fig. 12. Langmuir equilibrium isotherm model of AlOOH ;Co = 50 mg/l, pH = 7.0,

Temp. = 25 oC

Table 3. Langmuir Isotherm data of pseudoboehmite.

Dose (g/l) Ce (mg/l) qe (mg/g) Ce/qe (g/l) 0.4 27.37 58.26 0.47 0.6 22.67 46.67 0.49 0.8 18.27 40.50 0.45 1 14.67 36.00 0.41 1.2 13.10 31.31 0.42 1.4 10.02 29.04 0.35 1.6 8.73 26.21 0.33 1.8 7.65 23.90 0.32 2 5.87 22.40 0.26

- 37 - Table 4. Langmuir Isotherm data of AlOOH

Dose (g/l) Ce,(mg/l) qe,(mg/g) Ce/ qe, (g/l)

0.4 28.5 70.3 0.41

0.6 21.5 58.5 0.37

0.8 16.4 50.3 0.33

1 11.7 44.9 0.26

1.2 8.1 40.4 0.2

1.4 4.9 36.9 0.13

1.6 3.8 33 0.12

1.8 2.4 30.1 0.08

2 1.2 27.7 0.04

Dubinin-Radushkevich Isotherm

The linear Dubinin-Radushkevich isotherm plot for the adsorption of fluoride ions onto psedoboehmite and boehmite (AlOOH) are presented in Figures 13 and 14. Examination of the data shows that the Dubinin- Radushkevich isotherm also provides an accurate description of the data for the fluoride ions over the concentration range studied (Tables 5 and 6). The adsorption processes have adsorption energy values of 6.04 and 13.35 kJ mol-1 for F- ions onto pseudoboehmite and AlOOH respectively. Physisorption processes have adsorption energies less than 40 kJ mol–1 and the energy values for fluoride ions sorption on AlOOH and pseudoboehmite indicates that the sorption process is predominantly physisorption.

- 38 - Besides, the values are the orders of an ion-exchange mechanism, in which the sorption energy lies within 8–16 kJ/mol [69, 70]. The sorption capacity, qs in the D-R equation was found to be

123.68 mg/g for F- sorption onto AlOOH and 312.62 mg/g for F- sorption onto pseudoboehmite.

The difference may arise due to the fact that fluoride molecules in the pseudoboehmite diffuse through the mesoporous to microporous faster than that of boehmite that results the internal pores of the adsorbent (pseudoboehmite) to trap in more fluoride ions on its surface. On the other hand, the reduction in fluoride adsorption capacity onto AlOOH surface may be attributed due to the fact that parts of the available micropores are occupied by fluoride molecules. The above results are in good agreement with earlier reports pertaining to fluoride adsorption studies with dolomite

[71].

2 ln qe= -4.1071- 6.7913 E-9 ε

-5.8 R2= -0.98211

-6.0

-6.2

,mol/g e -6.4

q ln

-6.6

-6.8

2.70E+008 3.00E+008 3.30E+008 3.60E+008 3.90E+008 4.20E+008

2 2 -2 ε , J mol

Fig. 13. Dubinin-Radushkevich equilibrium isotherm model for the adsorption of fluoride ions

o onto pseudoboehmite, Co = 50 mg/l, pH = 7.0, Temp. = 25 C

- 39 -

2 ln qe= -5.0344 – 2.80361 E-9 ε -5.6 R2= -0.9547 -5.8

-6.0

mol/g e, -6.2

ln q

-6.4

-6.6

2.80E+008 3.50E+008 4.20E+008 4.90E+008 5.60E+008

ε2, J2 mol-2 Fig. 14. Dubinin-Radushkevich equilibrium isotherm model for the adsorption of fluoride ions

o onto AlOOH, Co = 50 mg/l, pH = 7.0, Temp. = 25 C

Table 5. Dubinin-Radushkevich Isotherm data of pseudoboehmite.

qe qe, ln qe, Ce Ce, 1/Ce, ln 1/Ce, RT, ε ε2 mg/g mole/g mole/g mg/l mole/l L/mole L/mole J/mole

58.26 0.00307 -5.79 27.37 0.00144 694.44 6.54 2478.819116211.482.63E+08

46.67 0.00246 -6.01 22.67 0.00119 840.34 6.73 2478.819116682.452.78E+08

40.50 0.00213 -6.15 18.27 0.00096 1041.67 6.95 2478.819117227.792.97E+08

36.00 0.00189 -6.27 14.67 0.00077 1298.70 7.17 2478.819117773.133.16E+08

31.31 0.00165 -6.41 13.10 0.00069 1449.28 7.28 2478.819118045.803.26E+08

29.04 0.00153 -6.48 10.02 0.00053 1886.79 7.54 2478.819118690.303.49E+08

26.21 0.00138 -6.59 8.73 0.00046 2173.91 7.68 2478.819119037.333.62E+08

23.90 0.00126 -6.68 7.65 0.00040 2500.00 7.82 2478.819119384.373.76E+08

22.40 0.00118 -6.74 5.87 0.00031 3225.81 8.08 2478.819120028.864.01E+08

- 40 - Table 6:- Dubinin-Radushkevich Isotherm data of AlOOH

qe, qe, ln qe, Ce, Ce, 1/Ce, ln1/Ce, RT, ε ε2 mg/g mole/g mole/g mg/l mole/l L/mole L/mole J/mole

70.3 0.0037 -5.599 28.5 0.00150 666.67 6.50 2478.8191 16118.01 2.60E+08

58.5 0.0031 -5.783 21.5 0.00113 884.96 6.79 2478.8191 16820.13 2.83E+08

50.3 0.0027 -5.934 16.4 0.00086 1162.79 7.06 2478.8191 17496.94 3.06E+08

44.9 0.0024 -6.048 11.7 0.00062 1612.9 7.39 2478.8191 18308.04 3.35E+08

40.4 0.0021 -6.154 8.1 0.00043 2325.58 7.75 2478.8191 19215.12 3.69E+08

36.9 0.0019 -6.244 4.9 0.00026 3846.15 8.25 2478.8191 20462.23 4.19E+08

33 0.0017 -6.356 3.8 0.00020 5000 8.52 2478.8191 21112.58 4.46E+08

30.1 0.0016 -6.448 2.4 0.00013 7692.31 8.95 2478.8191 22180.41 4.92E+08

27.7 0.0015 -6.531 1.2 0.00006 16666.67 9.72 2478.8191 24097.01 5.81E+08

Temkin Isotherm Model

Figures 15 and 16 shows the Temkin isotherm plot for the adsorption of fluoride ions onto

- pseudoboehmite and AlOOH .The Temkin constant, KT, of boehmite and pseudoboehmite for F are 20,735.34 l mg-1 and 7,369.996 l mg-1 ,respectively indicating a lower adsorbent/fluoride ion potential (interaction) for pseudoboehmite. The Temkin adsorption potential, 1/bT, related to heat of sorption for the fluoride ions, as expressed RT/bT was 0.00742 and 0.00116 for AlOOH and pseudoboehmite, respectively. The relatively higher adsorption potential for AlOOH was probably due to the high surface coverage of F- ions onto its surface.

The Temkin isotherm described the experimental data successfully with R2 values 0.9272 and

0.9557, respectively (Tables 7 and 8). However, the plots ln Ce vs qe remain most frequently

- 41 - curvilinear [72]. In this study, the plots were found to be curvilinear at the pH value of 7 .Despite non-linearity of plots for fluoride adsorption experiments, Bache and Williams [73] considered this model to be convenient because the curves approach linearly over a wide concentration range.

0.0035

0.0030

0.0025 qe = 0.00116 ln Ce + 0.01033

2 ,mol/g

e R = 0.95567

q 0.0020

0.0015

0.0010 -8.2 -8.0 -7.8 -7.6 -7.4 -7.2 -7.0 -6.8 -6.6 -6.4 ln C ,m ol/L e Fig.15. Temkin equilibrium isotherm model for the adsorption of fluoride ions onto

o psedoboehmite, Co = 50 mg/l, pH = 7.0, Temp. = 25 C

0.0040

qe= 0.00742 ln Ce + 6.4931 E-4 0.0035 2 R = 0.92743 0.0030

0.0025 ,mol/g

e q

0.0020

0.0015

-10.0 -9.5 -9.0 -8.5 -8.0 -7.5 -7.0 -6.5 -6.0 Fig. 16. Temkin equilibrium isotherm modelln for C the,mol/L adsorption of fluoride ions onto AlOOH, e

- 42 - o Co = 50 mg/l, pH = 7.0, Temp. = 25 C

Table 7. Temkin equilibrium isotherm data of psedoboehmite qe (mg/g) qe (mole/g) Ce (mg/l) Ce (mole/l) ln Ce(mole/l)

58.26 0.0031 27.37 0.00144 -6.54

46.67 0.0025 22.67 0.00119 -6.73

40.50 0.0021 18.27 0.00096 -6.95

36.00 0.0019 14.67 0.00077 -7.17

31.31 0.0017 13.10 0.00069 -7.28

29.04 0.0015 10.02 0.00053 -7.54

26.21 0.0014 8.73 0.00046 -7.68

23.90 0.0013 7.65 0.00040 -7.82

22.40 0.0012 5.87 0.00031 -8.08

Table 8. Temkin equilibrium isotherm data of AlOOH qe (mg/g) qe(mole/g) Ce, mg/l Ce(mole/l) lnCe(mole/l)

70.3 0.0037 28.5 0.00150 -6.50

58.5 0.0031 21.5 0.00113 -6.79

50.3 0.0027 16.4 0.00086 -7.06

44.9 0.0024 11.7 0.00062 -7.39

40.4 0.0021 8.1 0.00043 -7.75

36.9 0.0019 4.9 0.00026 -8.25

33 0.0017 3.8 0.00020 -8.52

- 43 - 30.1 0.0016 2.4 0.00013 -8.95

27.7 0.0015 1.2 0.00006 -9.72

Table 9. Summary of Freundlich, Langmuir, Temkin and Dubinin–Radushkevich isotherm model constants and correlation coefficients for adsorption of fluoride onto AlOOH &pseudoboehmite.

Isotherms Adsorbent Constants R2

q (mg/g) b (l/mg) m Langmuir: 72.72 0.211 Ce/ qe =1/ qmb +1/qmCe Boehmite 0.9729 pseudoboehmite 101.63 0.04 0.9203

KF (mg/g 1/n (l/mg)1/n) Freundlich: 23.72 0.2875 log qe = logKF + (1/n) logCe Boehmite 0.9721 pseudoboehmite 7.03 0.6133 0.9873

qs (mg/g) E, kJ/mol Dubinin-Radushkevich: 2 qe = qs exp(−Bε ) Boehmite 123.68 13.35 0.9547 2 ln qe = ln qs - Bε pseudoboehmite 312.62 6.04 0.9821

KT (l/mg) RT/bT Temkin: qe = (RT/bT) ln(KTCe) Boehmite 20735.43 0.00742 0.9274 qe= RT/bTln KT + RT/bT ln Ce pseudoboehmite 7369.996 0.00116 0.9557

- 44 - The equilibrium adsorption isotherm models of the Langmuir, D-R, and Temkin, equations were used to fit the batch experimental data in order to understand the mechanism of fluoride adsorption at the surface of AlOOH and pseudoboehmite. Isotherm parameters and the correlation coefficients (R2) obtained from the linear curves of each isotherm model are summerized in Table 9. Within the concentration range studied, the R2 values suggest that the

Langmuir isotherm provide a good model for the sorption of F- ions on to AlOOH. While the

Temkin and Dubinin-Radushkevich isotherms produce a reasonable fit to the experimental data for pseudoboehmite.

Consideration of the comparative magnitudes of the R2 values, suggest that the Temkin and D-R isotherm models provide additional information about the AlOOH/pseudoboehmite to F- ions sorption system.

Reaction mechanism for fluoride adsorption onto aluminum oxide hydroxides

Fluoride occurs mostly at active sites on aluminum species (aluminum oxides/ hydroxides) deposited on the surface and/or in the pores. Two mechanisms may occur in the adsorption process. Firstly, fluoride species may be adsorbed on the ionic AlOOH surface. Such a mechanism can be observed for many sorbents with a considerable surface area such as activated carbons, porous silicas, activated alumina and resin. Clearly, the parameter of sorbent surface area plays a key role in this mechanism. A second mechanism involves anion exchange and is unique for a sorbent of anion AlOOH. Flouride ions that exhibit anionic properties can enter the interlayer region of the AlOOH by anion exchange with hydroxide groups. This will give rise to a significant increase in the fluoride removal ability of the sorbent. The high efficiency by the sorbent in the removal of fluoride may be explained by the combination of these two mechanisms.

- 45 - In the lower pH range, coulombic attraction can readily occur in conjunction with specific chemical adsorption due to an exchange reaction. In the higher pH range, the concentration of hydroxide groups is too high, competing strongly with fluoride for the active sites. Aluminum oxide hydroxide has ion exchange ability. The fluoride reacts with hydroxyl groups on zeolite[79]. Both zeolite and aluminum oxide hydroxide are clays. Hence, the amount of fluoride adsorbed onto aluminum oxide hydroxide increased with increased equilibrium concentration.

The adsorption mechanism would be changed in real water situation due to the presence of many anions and cations that may affect the adsorption of F- ions onto AlOOH surface.

The above proposal is in agreement with Hao and Huang [33] that anion adsorption sites onto

+ alumina are aquo groups (AlOH2 ) and hydroxo groups (AlOH) therefore fluoride can be adsorbed by a positively charged or neutral surface as the following equations:

≡AlOH + F------> ≡AlF + OH- (28)

- - - ≡AlOH + 2F ------> ≡AlF2 + OH (29)

+ - ≡AlOH2 + F ------> ≡AlF + H2O (30)

The mechanism of charge formation on the surface of alumina is based on the phenomenon of adsorption and desorption of protons by active surface centers.

3.2 Break through Study of the Laboratory Scale Column

A fixed-bed down-flow column, packed with 1.6 g granular AlOOH and with a flow rate 92 ml/min. was studied. The result was compared with that of the previous up flow mode mini column breakthrough study [36]. Breakthrough time, t for a flow velocity of 92 ml min-1 occurred at 1150 min while that of the mini column with flow velocity 23 ml min-1 was 1350 minutes.

Figure 17 shows the breakthrough curves of fluoride adsorption onto heat treated aluminium

- 46 - hydroxide in a laboratory scale column and mini column of previous adsorption experiment. The

results indicate that the breakthrough time, t, for both column experiments is comparable. The

adsorption of fluoride onto AlOOH is presented in the form of breakthrough curves where the

concentration ratio C / Co is plotted versus time.

- Table 10:- Fixed bed column parameters for the removal of 20 mg/l of F by AlOOH, QL= 5.54 ml min-1cm-2, h = 25 cm, EBCT= 4.52 min, at different flow modes.

Weight of Q , flow rate D, bed depth Bed volume EBRT V t Adsorbent Flow L adsorbent b exhaustion pattern (ml min-1cm-2) (cm) (cm3) (min) (L) (h) rate(g L-1) m (g) Up 5.54 25 103.87 37.5 4.52 30.998 22.5 1.21 flow Down

flow 5.54 25 415 150.3 4.52 105.71 19.1 1.42

1.0  4.6 cm column (down flow) ^ 2.3 cm column (up flow)

0.8

0.6

o

C/C 0.4

0.2

0.0 0 102030405060 Time,h Fig. 17. Comparison of experimental breakthrough curve, 92 ml min-1(), 23 ml min-1 (^); (Co = 20 mg/l, h = 25 cm).

- 47 - The operating parameters for the column are given in Table 10. Based on the findings of the previous continous column experiment, the linear flow rate through the bed depth, particle size, and bed height were similar to that of the mini-column results and the internal diameter was increased by one fold. [35].

The breakthrough curves for both experimental flow patterns indicated an approaching characteristic S shape profile produced in ideal adsorption systems, suggesting that adsorption of fluoride onto AlOOH is probably mass transfer controlling [35]. Furthermore, with in porous adsorbent particles in adsorption column, the fundamental mass transport mechanisms can be limited by external film, pore and surface diffusion, assuming that there is good mixing and no axial dispersion inside the column. Internal diffusion is an important mass transport process during the removal of inorganic ions by porous metal oxides/hydroxides. [71].

The column was operated for 3 – 6 hours and stopped for 18- 21 hours and the on-off pump operation was continued until the complete exhaustion of the column. The fluoride breakthrough profile is illustrated in Fig. 17. After the first short-term shutdown period, effluent fluoride concentrations were lower than that of prior to shutdown. Subsequent on-off pump cycles resulted in the same trend of increased fluoride adsorption after the shutdown period. This may be explained as follows. The off-pump cycle allows fluoride diffusion along the internal pore surfaces and adsorption at binding sites, results a decrease in fluoride concentration in the stagnant layer around the particle. While restarting the system, a higher concentration gradient exists between liquid and solid surface fluoride concentrations which facilitate rapid removal of fluoride from solution. These observations suggest that fluoride adsorption onto porous adsorbents are intraparticle diffusion limited.

- 48 - Fb Fs

Fig. 18. Schematic of inorganic ion (fluoride) transport from the bulk solution onto porous metal

oxides adsorbents (AlOOH) (adapted from [72]).

3.4 Pilot studies

After bench scale isotherm tests have provided a sufficient data for the media (AlOOH), pilot tests can verify the characteristics of the breakthrough curve at selected process parameters, such as surface loading rate and empty bed contact time.

A pilot defluoridation unit was initially designed on the assumption that 20 litres of treated water was the daily requirement for cooking and drinking for a family of five, each consuming 4 liters per day. With this criterion, it was expected that 2.5 Kg AlOOH granules can be used for 2 to 3 months if fluoride concentration in water is around 20 mg/l.

Based on the previous scale up procedure [35], a column of internal diameter 10.3 cm packed with 753.65 g of AlOOH granules and an EBCT 4.52 min was prepared to produce 20 L/day of treated water for one month. But, the theoretically assumed flow rate was too high so that there would be a possibility of fracture and/or dissolution of the adsorbent material besides the

- 49 - shortening of the bed life. Thus, the flow rate was reduced by 1/4th for a better service time of the adsorbent bed. When the flow rate decreases the contact time in the column is longer, intra- particulate diffusion then becomes effective. Thus the adsorbate will have more time to diffuse in to the particles of the adsorbent and a better adsorption capacity can be obtained.

Table 11 . Column parameters for pilot experiment ;(*)-theoretically assumed flow rate.

Theoritically Theoritically Parameter Unit assumed Pilot assumed Pilot Working Pilot column column colum Service time month 3 1 1.45 Fluoride concentration mg/l 20 20 20 Grain size mm 1.0 – 2.0 1.0 – 2.0 1.0 – 2.0 Mass of AlOOH g 2578.14 861.33 753.65 Flow rate ml/min 1577.8 527.16 (460.86*) 100.2 Diameter of column cm 19.07 11.01 10.3 Height of AlOOH bed cm 25 25 25 Bedvolume cm3 7137.87 2384.5 2083.07 EBCT min 4.52 4.52 20.79

The BDST model can be applied to predict the service time of the pilot scale adsorption bed by

-3 -1 -1 -3 considering BDST parameters, K(9.48 x10 L mg h ) and No(9.31 mg cm ) that were

calculated from mini-column experiments. It was found out that a service time, t, 144 hr is

calculated using Eq. (20) for a column design with fluoride concentration 20 mg/l, 25 cm bed

depth and 1.21 linear flow rate which is almost equal to the experimental value, 138.54 hr.

(Table 12). In reality, both intra particle adsorption and external resistance do play an important

role in the adsorption process along the column. Thus, due to a number of factors like

irreversibility of the sorption process at high sorbent solid phase loadings, dispersion and

uneven flow pattern through the bed ;an increase in contact time hadn’t lengthen the service

time of the bed as it was assumed.

- 50 - 0.16

0.14

0.12

0.10

o 0.08 C/C

0.06

0.04

0.02

0.00 0 20 40 60 80 100 120 140 Time,h

-1 Fig.19. Pilot column experimental breakthrough curve, 100.2 ml min , Co = 20 mg /l, h = 25 cm.

The possibility to predict the service time of large scale adsorption bed based on the parameters from the mini-column tests were suggested in the previous work [35].To scale-up the system, the linear flow rate through the bed depth is similar to mini-column results and the internal diameter and the bed depth would increase while keeping constant their ratio.

For design purposes, the operational capacity has to be investigated first. Based on the results of the pilot column, it can be possible to predict the service time of adsoption column, if is assumed

- 51 - that on average an Ethiopian family of five, consume 20 liter per day for cooking and drinking purpose while each consuming 4 liters per day.

The design configuration used in this study suggested for application of AlOOH granules as adsorbent in a column type defluoridator seem to be appropriate and efficient. One of the advantages of up flow column unit is that, the flow resembles plug flow, where the lower parts of the packed bed become saturated at a time where the upper parts are still fresh. Then the saturation zone moves slowly towards the upper treated water point. This kind of flow allows for saturation of the medium with respect to the high fluoride raw water, hence the high capacity utilization in the column systems.

It was found out that the adsorbent exhaustion rate for the pilot column was lower (0.9045 g.L-1) and a longer EBRT (20.83 min.) was required to attain such a rate. This implies a smaller amount of adsorbent is needed per unit volume of feed treated that acquires a lower operating cost. As

McKay and Bino [74] proposed that the capital and operation costs of the adsorption system for a fixed liquid flow rate, feed concentration and adsorbent characteristics were almost entirely dependent on EBRT and adsorbent exhaustion rate only.

Table 12. Predicted and Observed Service time of household adsorption column at different initial fluoride concentration.

Predicted Service Time of the Observed Bed Service Z (cm) ,C ( mg /l) , o Bed (t) Time (t) F (cm min-1) (Months) (Months)

[25,20,1.203] 1.44 1.39

[25,10,1.203] 3.22 -

[25,5, 1.203] 6.24 -

- 52 -

3.5 Effect of Cations on defluoridation capacity of AlOOH

It was reported that the fluoride removal efficiency of a fixed amount aluminum salt depends on pH, alkalinity, the type of the co-existing anions, and other characteristics of the treated water

[33].

- - 3- 2- Previously [35], the effect of anions (Cl , HCO3 , PO4 and SO4 ) on the adsorption of fluoride onto the aluminium hydroxides (AlOOH and psedoboehmite) were studied in batch mode, and

- 2- the result showed that Cl and SO4 have very little effect on the fluoride removal capacity of

- 3- both adsorbents but HCO3 and PO4 had an effect on the removal capacity of the adsorbent, due to competitive nature of the two ions onto adsorption site.

The results in Table 12 showed that, the fluoride removal efficiency in the absence of anions in both AlOOH and pseudoboehmite is above 90 %, but it declines to 70.5 % (pseudoboehmite) and

- 73.9 % (AlOOH) for the one which contain 500 ppm of HCO3 and for the solution containing

3- 500 ppm of PO4 it declines to 79.5 % (pseudoboehmite) and 71.3 % (AlOOH).

- 53 - Table 13. Data of adsorption efficiency of aluminium hydroxides at different concentrations of anions (Adapted from [35]).

Anion Conc.(mg/L) pseudoboehmite AlOOH Effi. (%) pHi pHf Effi (%) pHi pHf - HCO3 0 90.7 6.30 6.00 93.1 6.25 6.12 100 85.1 8.45 7.62 87.6 8.42 7.59 200 76.9 8.63 7.81 83.4 8.60 8.10 300 75.0 8.68 8.26 78.9 8.68 8.27 400 72.5 8.69 8.11 74.8 8.67 8.37 500 70.5 8.70 8.37 73.9 8.71 8.47 2- SO4 0 90.0 7.07 6.29 94.6 7.07 5.94 100 91.3 7.04 6.24 93.7 7.13 6.02 200 90.9 7.04 6.30 92.5 7.05 6.18 300 89.8 7.06 6.32 92.0 7.12 6.15 400 88.2 7.16 6.41 91.9 7.11 6.14 500 88.6 7.10 6.38 92.0 7.08 6.09 Cl- 0 90.7 5.98 5.96 93.7 6.32 5.65 100 91.1 6.32 5.94 93.8 6.23 5.69 200 89.5 6.34 5.97 93.5 6.17 5.69 300 90.1 6.40 5.96 94.5 6.17 5.57 400 91.9 6.38 5.90 93.8 6.14 5.69 500 90.5 6.25 5.98 93.7 5.88 5.68 3- PO4 0 90.1 6.89 6.19 93.5 6.53 6.24 100 84.7 5.66 5.99 78.8 5.50 7.09 200 83.1 5.42 5.87 75.4 5.17 6.86 300 81.9 5.16 5.84 75.6 5.11 6.68 400 79.9 5.18 5.80 71.6 5.19 6.63 500 79.5 5.00 5.76 71.3 5.23 6.53

The chemical content of certain cations such as Mg 2+, Al3+, Fe3+, Ni2+, Mn2+, and Fe2+ produce an impact on the chemical adsorption of F- [75]. The results obtained for the effect of sodium, potassium, calcium, magnesium, and iron on fluoride adsorption on the AlOOH at ambient pH are shown in Table 14 below.

- 54 - Table 14. Effect of cations on fluoride adsorption of AlOOH at ambient pH; where Co, C1, C2, C3

are sampling points: initial metal ion conc., beginning, middle and near breakthrough

respectively. (*):- mean of triplicate reading

Conc., mg/l Sample taken Cation Mean value of triplicates* Mean Value C * o 10.5990 10.5990 C1* 7.4890 Ca2+ C2* 6.6995 7.0038 C3* 6.8230 Co* 2.2285 2.2285 C1* 1.8990 Mg 2+ C2* 1.9990 1.9323 C3* 1.8990 Co* 40.915 40.915 C1* 46.160 Na+ C2* 48.610 46.970 C3* 46.140 Co* 6.665 6.665 C1* 6.735 K+ C2* 7.245 6.435 C3* 5.320 Co* 0.0518 0.0518 C1* 0.0484 Fe3+ C2* 0.0356 0.0438 C3* 0.0474 Co* 0.0339 0.0339 C1* 0.3459 Al3+ C2* 0.5092 0.4488 C3* 0.4914

- 55 - The slight decline in concentration of iron ions may be explained as follows: aluminum oxy hydroxide structures have some similarities with those of iron oxy hydroxides and, therefore, a significant amount of Fe3+ can probably replace Al3+ in the boehmite crystal lattice during adsorption process. In addition to this, the adsorption of fluoride on ferric oxide surface is mainly a process in which coordinated OH- exchanges with F- as specific adsorption [76].

When electrolyte ions (cations and anions) approach the particle surface, they weaken or activate the Al-OH bonds that are already on the surface. Consequently, the protonation and deprotonation reactions take place easily. At high C0, the Al-OH bonds on the particle surface become more activated in such a way that the thermodynamic equilibrium of the protonation and deprotonation reactions described as the following equations shifts to the right [77].

+ + HOHAl ←+− ⎯→ − OHAl 2 Protonation (32)

− − OHOHAl ←+− ⎯→ +− 2OHOAl Deprotonation (33)

The interaction of cations and anions with the surface hydroxyl groups may also involve binding of cations and anions at specific sites on particle surfaces. These binding reactions are considered to proceed as follows:

+ − −+ AlOH 2 An ←+ ⎯→ 2 AnAlOH (34)

− + +− CatAlO ←+ ⎯→ CatAlO (35)

At low concentrations, the adsorption of metal ions on aluminum oxides and hydroxides can be considered as a bimolecular adsorption/desorption reaction in which a metal ion is bound by an aluminol group, releasing a proton to solution, i.e.

AlOH + Ca2+ ------Æ AlOCa+ + H+ (36) AlOH + Mg2+ ------Æ AlOMg+ + H+ (37)

- 56 - The above suggestion is further supported by the physico-chemical property of the water before and after treatment, specifically pH value, described in Table 15.

Table 15. Physico-chemical analysis result of influent water and treated water, at 21 OC.

Parameters Sample type TDS, mg/l pH Conductivity,μS/cm Distilled water 0.0 5.72 1.2 Tap water 50.0 7.49 106 20 mg/l F- water 96 7.48 202 Treated water 99 6.93 209

Besides this, precipitation of fluoride ions as insoluble magnesium fluoride and calcium fluoride is expected to lower the fluoride ion concentration in the water. Narkis et al. [78] supports the assumption as the capacity of anion removal by activated alumina increases when Ca 2+and Mg2+ are present in the wastewater due to precipitation on the alumina surface.

The relatively higher residual concentration of sodium in the treated water may arise from the the chemicals (NaF and NaOH) used to prepare the simulated water sample and adsorbent material respectively.

The presence of aluminium residuals in the treated water may be due to the probable dissolution of the AlOOH during the ion exchange process with other constituents. The presence of certain cations may be effective in fluoride retention. Exchangeable cations such as Na and Ca may form solid precipitate with fluoride. The adsorption of fluoride might be hindered by the presence of metals. Detailed studies will be needed to further evaluate ion exchange processes that take place between AlOOH surface and major cations in terms of their retententive characterstics and /or effects on fluoride removal efficiency besides their reaction chemistry.

- 57 - Price estimation of pilot household defluoridator

A rough estimation of defluoridation cost for the pilot household defluoridator is shown in Table

16. Estimations for initial capital cost include costs of power, chemicals, material and labour.

Table 16. Rough cost estimation for pilot defluoridator.

Approx. Serial No. Item price, Birr

1 ∅110 mm PVC pipe 50

2 ∅ 10 mm PVC tubing 15

3 ∅ 102 mm perforated circular PVC plate 20

4 ∅ 75 mm PVC pipe 30

5 Transparent Silicon paste 40

6 15 mm thickness flat PVC plate 65

7 ¼ inch chrome plated tap 60

8 2.0 kg NaOH granules 100

9 3 kg Aluminium sulfate 60

10 5 KWh Electricity 5

11 Labour cost 40

Total cost 455

AlOOH granules (about 0.8 kg) packed the pilot column defluoridated 833.22 L of water during its service time. Assuming consumption for drinking and cooking of four liters per capita per day

(l/cd) and an average of five people per household, the treatment cost is about 0.55 birr per liter at

20 mg/l of influent fluoride.

- 58 - Treatment cost = 455 birr / 833.22 liter ≅ 0.55 birr per liter

The cost of treated water seems to be unaffordable to the poor fluoride affected community. Thus based on this rough cost estimate, various options have to be designed so as to minimize the initial capital cost of defluoridation, either:

⇒ Non governmental support agencies have play a bigger role in terms of financing the

developed household defluoridation technology.

⇒ If there exists a 50 to 50 cost sharing arrangement between beneficiaries and NGO’s, the

scheme would ensure the involvement of users and the supporting agencies thereby

reduces the down time of installations and reducing initial capital costs.

⇒ If a project is launched to upscale the defluoridation practice, the cost of production of the

adsorbent material (AlOOH ) will be expected to fall with a significant level.

4. Conclusion

The values of BET surface area, total pore volume, micro pore volume and external surface area are 110 m2/g, 0.29 cm3/g, 0.0021 m2/g, 104 cm3/g, respectively for AlOOH and 37 m2/g, 0019 cm3/g, 32 m2/g, respectively for pseudoboehmite. XRD results show that heat treated aluminium hydroxide comprised AlOOH as the major component and traces of FeO (OH), Fe (OH) 2 and

Al2O3. It can be seen from Fig. 10 that the sample prepared at ordinary conditions has quite narrow micropore size distribution than the heat treated sample. An increase in the pore volume of AlOOH may result from the activation on the microporosity.

- 59 - The equilibrium adsorption isotherm models of the Langmuir, D-R and Temkin, equations were used to fit the batch experimental data in order to understand the mechanism of fluoride adsorption at the surface of AlOOH and pseudoboehmite.

-2 -1 The sorption capacity, qm, and adsorption coefficient, b, is 101.63 mg/g and 4.0 × 10 L mg for psedoboehmite and 72.72 mg/g and 2.11×10–1 L mg-1 for boehmite, respectively. Energy of adsorption onto psedoboehmite is lower than that of boehmite which is probably due to the less availability of adsorption sites on the adsorbent.

Examination of batch adsorption data showed that the Dubinin- Radushkevich isotherm also provides an accurate description of the data for the fluoride ions over the concentration range studied. The adsorption processes have adsorption energy values of 6.04 and 13.35 kJ mol-1 for F- ions onto pseudoboehmite and AlOOH, respectively which indicates the sorption process is predominantly physisorption.

- -1 The Temkin constant, KT, of boehmite and pseudoboehmite for F are 20,735.34 l mg and

7,369.996 l mg-1 respectively, indicating a lower adsorbent/fluoride ion potential (interaction) for pseudoboehmite. The Temkin adsorption potential, 1/bT, was 0.00742 and 0.00116 for AlOOH and pseudoboehmite, respectively. The relatively higher adsorption potential for AlOOH was probably due to the high surface coverage of F- ions onto its surface.

Within the concentration range studied, the R2 values suggest that the Langmuir isotherm provide a good model for the sorption of F- ions on to AlOOH. While the Temkin and Dubinin-

Radushkevich isotherms produce a reasonable fit to the experimental data for pseudoboehmite.

Aluminum oxide hydroxide has ion exchange ability. The fluoride reacts with hydroxyl groups on aluminum oxide hydroxide. Hence, the amount of fluoride adsorbed onto aluminum oxide

- 60 - hydroxide increased with increased equilibrium concentration. Anion adsorption sites onto

+ aluminium oxide/hydroxides are aquo groups (AlOH2 ) and hydroxo groups (AlOH) therefore fluoride can be adsorbed by a positively charged or neutral surface.

Breakthrough study results for fluoride adsorption onto heat treated aluminium hydroxide in a laboratory scale column(down flow) and mini column(up flow) of previous adsorption experiment showed that breakthrough time for a flow velocity of 92 ml min-1 occurred at 1150 min while that of the mini column with flow rate of 23 ml min-1 was 1350 minutes. The results indicate that the breakthrough time, t, for both column experiments is comparable.

The pilot household defluoridator has a capacity of treating about 20 L of water and this quantity of water could be used by a family of five each consuming four liters per day for cooking and drinking purposes. About 0.785 Kg of AlOOH granules has reached breakthrough in one and half month when the fluoride concentration in water was around 20 mg/l.

The presence of certain cations may be effective in fluoride retention. Exchangeable cations such as Na, Ca and Mg may form solid precipitate with fluoride.

The defluoridation price per liter of water was estimated as 0.55 birr/L, in which the household defluoridator would have to be subsidized so as to make it appropriate for use.

This process differs from the known processes in its simplicity and very low traces of residual aluminum in outlet water. It is a practical approach, especially for rural population in Ethiopia

From the previous and present experimental findings; it could be possible to conclude that

AlOOH granulars can be exploited for applications at a household level and/ or community level fluoride treatment of potable water.

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C. Surface Charge of Variable Porosity Al2O3(s) and SiO2(s) Adsorbents; Journal of Porous Materials , 2002;9: 243–256 50. Gitzen, W. H. Alumina as a Ceramics Material, Columbus, OH, American Ceramic Society,1970. 51. Hart, D. L.; Alumina Chemicals Science and Technology Handbook, Society of Mining Engineers (AIME), New York, 1984. 52. Chun and Hendel ;H. V. D. X-ray Spectroscopic Study of Chemical Bonds in Oxides, Naturforsch, 1967; 22a:1401- 1407. 53. Kumar, V.; K. Subanandam, V. Ramamurthi and Sivanesan S. Solid Liquid Adsorption for Wastewater Treatment: Principle Design and Operation; Anna university, in Chennai-India, February 2004. 54. Kenny MB, Sing KSW, Theocharis C., Proc. 4th Int. Conf. on Fundamentals of Adsorption, Kodansha, Tokyo, 1993: 323. 55. Kaneko K. Equilibria and Dynamics of Gas Adsorption on Heterogeneous Solid Surfaces, Elsevier, Amsterdam, 1997:679. 56. Jufang W. Modeling adsorption of organic compounds on activated carbon, A multivariate approach, 2004; Umeå, Sweden

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- 67 - APPENDEX

Table 17. BJH Desorption pore size distribution, pseudoboehmite

Diameter Vcum dV/dd Pseudoboehmite Å [cc/g] [cc/Å/g] [cc/g] 19.32 0.0002568 2.09E-04 0.009306 20.56 0.0005024 1.98E-04 0.009369 21.81 0.0007152 1.67E-04 0.008366 23.09 0.001135 3.27E-04 0.0174 24.43 0.001406 1.94E-04 0.01093 25.83 0.001694 2.05E-04 0.01217 27.29 0.002009 2.10E-04 0.01322 28.82 0.002319 1.97E-04 0.01308 30.43 0.002575 1.56E-04 0.01094 32.15 0.002641 3.64E-05 0.002691 34.02 0.002987 1.79E-04 0.01403 36 0.003289 1.48E-04 0.01223 38.16 0.003834 2.40E-04 0.02107 40.49 0.004476 2.70E-04 0.02517 42.99 0.004855 1.44E-04 0.01425 45.76 0.00522 1.25E-04 0.01319 48.82 0.005534 9.80E-05 0.01101 52.26 0.005806 7.43E-05 0.008942 56.1 0.006408 1.50E-04 0.01934 60.52 0.007086 1.41E-04 0.0196 65.62 0.008126 1.93E-04 0.02917 71.64 0.008992 1.30E-04 0.02143 78.92 0.0106 2.04E-04 0.037 87.77 0.01299 2.44E-04 0.04931 98.62 0.01607 2.58E-04 0.05849 110.96 0.01967 2.83E-04 0.07214 130.79 0.02796 3.08E-04 0.09247 153.91 0.0343 3.28E-04 0.1159 184.26 0.04825 3.37E-04 0.1426 242.62 0.07185 3.13E-04 0.1735 359.32 0.1111 2.48E-04 0.2022 530.78 0.1585 2.56E-04 0.31 771.74 0.2038 1.53E-04 0.2679 1125.45 0.2401 8.83E-05 0.2261 2032.74 0.2876 3.39E-05 0.152

- 68 - 200 180 Volume [cc/g] STP 160 140 120 100 80 Volume (cc/g) Volume 60 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Relative pressure (P/Po)

Fig. 20. N2 adsorption /desorption isotherm at 77 K, AlOOH

Table 18. BJH Desorption pore size distribution, AlOOH

BJH Desorption Pore Size Distribution,AlOOH Diameter Vcum dV/dd dV/dlogd Å [cc/g] [cc/Å/g] [cc/g] 19.4 1.65E-03 1.34E-03 6.00E-02 20.63 3.34E-03 1.36E-03 6.48E-02 21.9 4.99E-03 1.28E-03 6.46E-02 23.2 7.01E-03 1.54E-03 8.22E-02 24.53 9.04E-03 1.49E-03 8.42E-02 25.93 1.11E-02 1.42E-03 8.45E-02 27.39 1.31E-02 1.33E-03 8.37E-02 28.94 1.49E-02 1.16E-03 7.71E-02 30.61 1.73E-02 1.39E-03 9.79E-02 32.38 2.03E-02 1.63E-03 1.22E-01 34.27 2.43E-02 2.04E-03 1.61E-01 36.27 2.86E-02 2.11E-03 1.77E-01 38.37 3.19E-02 1.52E-03 1.34E-01 40.69 3.49E-02 1.24E-03 1.16E-01 43.24 3.80E-02 1.17E-03 1.16E-01 46.05 4.11E-02 1.06E-03 1.12E-01 49.16 4.42E-02 9.47E-04 1.07E-01 52.68 4.74E-02 8.40E-04 1.02E-01 56.66 5.13E-02 9.24E-04 1.21E-01 61.16 5.54E-02 8.58E-04 1.21E-01 66.38 6.00E-02 8.22E-04 1.26E-01

- 69 - 72.58 6.53E-02 7.85E-04 1.31E-01 79.91 7.17E-02 8.04E-04 1.48E-01 88.75 7.85E-02 7.02E-04 1.43E-01 99.98 8.64E-02 6.20E-04 1.43E-01 114.06 9.57E-02 5.98E-04 1.57E-01 131.05 1.05E-01 5.17E-04 1.56E-01 150.04 1.14E-01 4.46E-04 1.54E-01 184.26 1.28E-01 2.92E-04 1.23E-01 242.41 1.45E-01 2.42E-04 1.34E-01 349.98 1.84E-01 2.66E-04 2.11E-01 527.34 2.33E-01 2.37E-04 2.84E-01 730.29 2.69E-01 1.81E-04 3.02E-01 1030.93 3.23E-01 1.34E-04 3.13E-01 1811.34 3.55E-01 2.79E-05 1.12E-01

260 240 220 200 180 160 140 120 100 Volume (cc/g) Volume 80 60 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 Relative pressure (P/Po)

Fig. 21. N2 adsorption /desorption isotherm at 77 K , pseudoboehmite

- 70 -

Continuous Packed-bed column experiment:

Flow Mode: - Down flow Contact time: - 4.52 minutes Material: AlOOH (THA) Bed depth: 25 cm Internal diameter of the column: 4.6 cm Mass of THA: 150.32g - Particle size: 1-2 mm [F ] initial: 20.0 (± 0.1 mg/l) Flow rate: 92 ml/min Room temp. : - 20 oC (± 2 oC) Effluent volume: 325.05 L Column length: 40 cm Breakthrough time: 1146min Fluoride containing water:-Tap water Slope of fluoride ion analyzer = -59.1 mV/DEC

Table 19. Raw data of effluent fluoride concentration (mgL-1) treated water (L) for laboratory -1 scale experiment (Qv = 92 ml min , Co =20 mg/l).

Treated Treated Time (h) Residual [F-],mg/l C/C o water (ml) water (L) 0.5 0.0459 0.00230 2740 2.74 1 0.0709 0.00355 5520 5.52 2 0.0836 0.00418 5550 11.07 3 0.0955 0.00478 5490 16.56 4 0.0993 0.00497 5580 22.14 5 0.102 0.0051 5540 27.68 6 0.108 0.0054 5520 33.20 7 0.132 0.0066 5570 38.77 8 0.141 0.0071 5500 44.27 9 0.198 0.0099 5490 49.76 10 0.271 0.0136 5500 55.26 11 0.149 0.0075 5520 60.78 12 0.441 0.0221 5510 66.29 13 0.559 0.0280 5480 71.77 14 0.405 0.0203 5510 77.28 15 0.634 0.0317 5490 82.77 16 0.703 0.0352 5500 88.27 17 0.869 0.0435 5500 93.77 18 1.04 0.0520 5540 99.31 19 1.39 0.0695 5480 104.79 19.1 1.51 0.0751 916 105.71 20 1.91 0.0950 5500 110.29 21 1.03 0.0515 5490 115.78 22 1.66 0.0830 5560 121.34 23 2.98 0.1490 5540 126.88 24 3.84 0.1920 5500 132.38

- 71 - 25 4.77 0.2385 5510 137.89 26 5.86 0.2930 5500 143.39 27 6.23 0.3115 5490 148.88 28 5.33 0.2665 5540 154.42 29 7.34 0.3670 5500 159.92 30 8.01 0.4001 5510 165.43 31 8.77 0.4385 5490 170.92 32 9.92 0.4960 5540 176.46 33 10.2 0.5100 5450 181.91 34 10.9 0.5450 5500 187.41 35 9.89 0.4920 5560 192.97 36 12.0 0.5970 5570 198.54

37 12.8 0.6368 5540 204.11

38 13.2 0.6567 5550 209.66

39 13.9 0.6965 5510 215.17

40 12.4 0.6169 5500 220.67 41 12.6 0.6269 5490 226.16 42 14.1 0.7015 5490 231.65 43 14.8 0.7363 5510 237.16 44 15.2 0.7562 5500 242.66 45 14.5 0.7214 5510 248.17 46 14.8 0.7363 5490 253.66 47 15.5 0.7711 5500 259.16 48 16.0 0.7960 5470 264.63 49 16.4 0.8159 5500 270.13 50 16.9 0.8408 5500 275.63 51 17.3 0.8607 5460 281.09 52 17.8 0.8856 5500 286.59 53 18.4 0.9154 5480 292.07 54 17.2 0.8557 5490 297.56 55 18.9 0.9403 5550 303.11 56 19.2 0.9552 5510 308.62 57 19.4 0.9652 5500 314.12 58 19.5 0.9701 5460 319.58 59 19.8 0.9851 5470 325.05

PILOT SCALE COLUMN EXPERIMENT

Flow Mode: - Up flow Contact time: - 20.83 minutes Material: THA Length of column bed: 25 cm Internal diameter of the column: 10.3 cm Mass of THA: 753.65g - Particle size: 1-2 mm [F ] initial: 20.0 (± 0.1 mg/l) Flow rate: 100 ml/min (Average) Room temp. : - 20 oC (± 2 oC Column length: 40 cm Estimated service time: 30 days Fluoride containing water:-Tap water Slope of fluoride ion analyzer = -59.4 mV/DEC

- 72 - Table 20. Raw data of effluent fluoride concentration (mg/l) and treated water (L) for

pilot scale column experiment (Qv = 100.2 ml min-1, Co =20 mg/l).

Treated Treated Day Time (h) Residual [F-],mg/l C/C o water (ml) water (L) 1 0.0303 0.00152 6010 6.010 2 0.0318 0.00159 6080 12.090 1 3 0.0336 0.00168 5990 18.080 3.19 0.0339 0.00170 1995 20.075 1 0.0377 0.00189 6005 26.080 2 0.0385 0.00193 6030 32.110 2 3 0.0401 0.00201 6010 38.120 3.21 0.0406 0.00203 1975 40.095 1 0.0439 0.00220 6040 46.135 2 0.0476 0.00238 6010 52.145 3 3 0.0507 0.00254 5985 58.130 3.20 0.0509 0.00255 2005 60.135 1 0.0633 0.00317 6020 66.155 2 0.0679 0.00340 6030 72.185 4 3 0.0726 0.00363 5990 78.175 3.22 0.0728 0.00364 2020 80.195 1 0.0753 0.00377 6005 86.200 2 0.0784 0.00392 6070 92.270 5 3 0.0806 0.00403 6000 98.270 3.20 0.0807 0.00404 1990 100.260 1 0.0821 0.00411 6025 106.285 2 0.0863 0.00432 6030 112.315 6 3 0.0870 0.00435 5995 118.310 3.21 0.0870 0.00435 2010 120.320 1 0.0861 0.00431 6005 126.325 2 0.0869 0.00435 6030 132.355 7 3 0.0878 0.00439 6010 138.365 3.19 0.0878 0.00439 1980 140.345 1 0.0877 0.00439 6010 146.355 2 0.0889 0.00445 6000 152.355 8 3 0.0898 0.00449 6005 158.360 3.20 0.0899 0.00450 1990 160.350 1 0.0888 0.00444 6030 166.380 2 0.0906 0.00453 6040 172.420 9 3 0.0927 0.00464 6005 178.425 3.18 0.0929 0.00465 1990 180.415 1 0.0917 0.00459 6000 186.415 10 2 0.0932 0.00466 6010 192.425 3 0.0941 0.00471 5990 198.415

- 73 - 3.20 0.0941 0.00471 2010 200.425 1 0.0956 0.00478 6010 206.435 2 0.0968 0.00484 6000 212.435 11 3 0.0979 0.00490 6005 218.440 3.20 0.0980 0.00490 1990 220.430 1 0.0916 0.00458 6020 226.450 2 0.0997 0.00499 6005 232.455 12 3 0.102 0.00510 6010 238.465 3.19 0.102 0.00510 2000 240.465 1 0.0999 0.00500 6005 246.470 2 0.104 0.00520 6010 252.480 13 3 0.108 0.00540 6015 258.495 3.18 0.108 0.00540 1970 260.465 1 0.0987 0.00494 6015 266.480 2 0.105 0.00525 6005 272.485 14 3 0.110 0.00550 6010 278.495 3.19 0.110 0.00550 1980 280.475 1 0.107 0.00535 6000 286.475 2 0.112 0.00560 6020 292.495 15 3 0.114 0.00570 6010 298.505 3.18 0.114 0.00570 1975 300.480 1 0.106 0.00530 6030 306.510 2 0.111 0.00555 6010 312.520 16 3 0.117 0.00585 6005 318.525 3.18 0.117 0.00585 1950 320.475 1 0.115 0.00575 6020 326.495 2 0.119 0.00595 6015 332.510 17 3 0.122 0.00610 6005 338.515 3.19 0.122 0.00610 1990 340.505 1 0.118 0.00590 6015 346.520 2 0.123 0.00615 6020 352.540 18 3 0.127 0.00635 5990 358.530 3.19 0.127 0.00635 1990 360.520 1 0.121 0.00605 6025 366.545 2 0.126 0.00630 6020 372.565 19 3 0.131 0.00655 6005 378.570 3.17 0.130 0.00650 1960 380.530 1 0.130 0.00650 6010 386.540 2 0.135 0.00675 6005 392.545 20 3 0.141 0.00705 6000 398.545 3.19 0.141 0.00705 2000 400.545 1 0.137 0.00685 6015 406.560 2 0.143 0.00715 6005 412.565 21 3 0.149 0.00745 5990 418.555 3.19 0.149 0.00745 1995 420.550

- 74 - 1 0.147 0.00735 6005 426.555 2 0.151 0.00755 6010 432.565 22 3 0.154 0.00770 6000 438.565 3.18 0.154 0.00770 1990 440.555 1 0.148 0.00740 6030 446.585 2 0.155 0.00775 6015 452.600 23 3 0.159 0.00795 5980 458.580 3.18 0.159 0.00795 1980 460.560 1 0.154 0.00770 6000 466.560 2 0.161 0.00805 6010 472.570 24 3 0.169 0.00845 6015 478.585 3.19 0.170 0.00850 1990 480.575 1 0.171 0.00855 6010 486.585 2 0.189 0.00945 6020 492.605 25 3 0.197 0.00985 6000 498.605 3.18 0.198 0.00990 1980 500.585 1 0.194 0.00970 6005 506.590 2 0.211 0.01055 6015 512.605 26 3 0.242 0.01210 6005 518.610 3.19 0.244 0.01220 1985 520.595 1 0.239 0.01195 6030 526.625 2 0.251 0.01255 6020 532.645 27 3 0.277 0.01385 6000 538.645 3.17 0.278 0.01390 1960 540.605 1 0.263 0.01315 6025 546.630 2 0.281 0.01405 6005 552.635 28 3 0.297 0.01485 6000 558.635 3.18 0.299 0.01495 1980 560.615 1 0.284 0.01420 6015 566.630 2 0.303 0.01515 6005 572.635 29 3 0.332 0.01660 5990 578.625 3.20 0.334 0.01670 2000 580.625 1 0.312 0.01560 6010 586.635 2 0.338 0.01690 6005 592.640 30 3 0.377 0.01885 6000 598.640 3.19 0.379 0.01895 1990 600.630 1 0.361 0.01805 6020 606.650 2 0.383 0.01915 6005 612.655 31 3 0.409 0.02045 5990 618.645 3.18 0.410 0.02050 1995 620.640 1 0.404 0.02020 6010 626.650 2 0.419 0.02095 6000 632.650 32 3 0.428 0.02140 6005 638.655 3.19 0.430 0.02150 2005 640.660 33 1 0.424 0.02120 6015 646.675

- 75 - 2 0.443 0.02215 6005 652.680 3 0.458 0.02290 6000 658.680 3.17 0.459 0.02295 1980 660.660 1 0.445 0.02225 6005 666.665 2 0.468 0.02340 6010 672.675 34 3 0.476 0.02380 6005 678.680 3.18 0.478 0.02390 1985 680.665 1 0.461 0.02305 6000 686.675 2 0.482 0.02410 6020 692.675 35 3 0.495 0.02475 6005 698.680 3.18 0.496 0.02480 1980 700.685 1 0.482 0.02410 6000 706.700 2 0.512 0.02560 6010 712.705 36 3 0.541 0.02705 6005 718.705 3.19 0.543 0.02715 1990 720.685 1 0.548 0.02740 6010 726.695 2 0.637 0.03185 6000 732.695 37 3 0.679 0.03395 6010 738.705 3.18 0.683 0.03415 1980 740.685 1 0.675 0.03375 6005 746.690 2 0.739 0.03695 6010 752.700 38 3 0.798 0.03990 5990 758.690 3.19 0.816 0.04080 2005 760.695 1 0.809 0.04025 6000 766.695 2 0.849 0.04224 6005 772.700 39 3 0.896 0.04458 6010 778.710 3.18 0.943 0.04692 1990 780.700 1 0.907 0.04512 5990 786.690 2 0.952 0.04736 6005 792.695 40 3 0.998 0.04990 6000 798.695 3.19 1.00 0.05000 2010 800.705 1 0.978 0.04890 6005 806.710 2 1.05 0.05250 6010 812.720 41 3 1.37 0.06850 5980 818.700 3.19 1.39 0.06950 2010 820.710 1 1.29 0.06450 6005 826.715 2 1.48 0.07400 6010 832.725 42 2.05 1.51 0.07550 495 833.220 3 1.59 0.07950 5985 838.710 3.19 1.70 0.08500 2005 840.715 1 1.76 0.08800 6000 846.715 2 2.20 0.11000 6005 852.720 43 3 2.89 0.14450 6005 858.725 3.20 2.97 0.14850 2000 860.725

- 76 - Standard Test method for Aluminium in Water (ASTM: D 857-89) Direct flame atomic absorption determination of Al in nitrous oxide-acetylene flame. Apparatus: Varian SpectrAA Flame Atomic Absorption Spectrometer, SIPS-220 (Varian Australia Pty Ltd) Aluminium Hollow Cathode Lamp Oxidant, Nitrous Oxide (99.5 %); Newfield ind. EST. Tunstall, UK LTD Fuel, locally (Chora industrials Plc.) produced acetylene Pressure reducing regulators Experimental -The sample was filtered in a retentive filter paper (whatman # 542) prior to analysis. -10 ml KCl is added to give a final conc of 2000 μg/ml of K to overcome enhancement interference from other alkali metals.

Method Development:

Name: Water,Column experiment Analyst: Yoseph Abebe W/tsadik Comments: Det. of Al Analysis started 12:29:14 02/02/07 (AA Online)

Method: Al (Flame)

Instrument settings: Wavelength: 309.3 nm, Slit Width: 0.5 nm, Lamp Current:10.0 mA, Background Correction: BC On

Measurement settings: Calibration Mode: Concentration, Measurement Mode: Integrate, Smoothing: 5 point Replicates Standard: 3, Replicates Sample: 3, Measurement Time: 5.0 s

Flame settings: Flame Type: N2O/Acetylene, N2O Flow: 12.55 L/min, Acet. Flow: 7.35 L/min Burner Height: 0.0 mm

Instrument Zero [Postread=-0.0039Abs, Gain=23%]

Sample ID Conc mg/l %RSD Mean Abs BG Abs Readings CAL: CAL ZERO 0.0000 45.4 -0.0025 0.0026 -0.0014 -0.0037 CAL: STANDARD 1 4.0000 2.4 0.0142 0.0062 0.0144 0.0138 CAL: STANDARD 2 8.0000 2.7 0.0288 0.0064 0.0297 0.0281 CAL: STANDARD 3 12.0000 2.5 0.0422 0.0071 0.0411 0.0423 CAL: STANDARD 4 16.0000 1.2 0.0550 0.0084 0.0543 0.0556 CAL: STANDARD 5 20.0000 1.6 0.0690 0.0078 0.0690 0.0701

- 77 - New Rational-Cal. Set 1

0.08 0.07 R2 = 0.998 0.06 0.05 0.04

Absorbance 0.03 0.02 0.01 0.0000 5.0000 10.0000 15.0000 20.0000 25.0000 Al,mg/L

Sample ID Conc mg/l %RSD Mean Abs BG Abs Readings

1:Top Std (20 mg/l) 20.5379 1.0 0.0702 0.0070 0.0708 0.0694 2: Blank 0.2957 68.8 0.0011 0.0048 0.0017 0.0011 3: Co A 0.3201 90.3 0.0011 0.0055 0.0019 -0.0000 4: Co B 0.1939 >100 0.0007 0.0059 0.0008 -0.0001 5: Co C 0.4749 34.2 0.0017 0.0048 0.0013 0.0014 6: C1 A 0.8071 23.3 0.0029 0.0056 0.0035 0.0029 7: C1 B 0.5836 39.5 0.0021 0.0063 0.0028 0.0022 8: C1 C 0.5340 47.8 0.0019 0.0067 0.0027 0.0009 9: C2 A 0.6310 27.1 0.0022 0.0062 0.0019 0.0019 10: C2 B 1.1876 16.2 0.0042 0.0044 0.0046 0.0046 11: C2 C 0.5961 24.8 0.0021 0.0064 0.0025 0.0023 12: C3 A 1.0237 9.6 0.0036 0.0051 0.0040 0.0036 13: C3 B 0.7610 20.6 0.0027 0.0060 0.0030 0.0030 14: C3 C 0.5765 37.5 0.0021 0.0067 0.0015 0.0017 15:Check Std(20 mg/l)19.7887 2.1 0.0583 0.0089 0.0592 0.0588 Table 21. Result Summery, Al, mg/l.

Mean Al Conc., Sample code Final conc.-Blank Mean of sample mg/l Blank 0.2957 - - Co 0.3296 0.0339 0.0339 mg/l C1 0.6416 0.3459 C2 0.8049 0.5092 0.4488 mg/l C3 0.7871 0.4914

Water Quality-Determination of Ca and Mg –Atomic Absorption Spectrometric method (ISO 7980:1996)

-Vol. of sample taken=20 mL/100 mL volumetric flask. -10 mL CsCl is added to give a final conc of 2000-5000 μg/mL of Cs to overcome interferences.

- 78 - Method: Ca (Flame)

Instrument settings: Wavelength: 422.7 nm, Slit Width: 0.5 nm, Lamp Current:10.0 mA, Background Correction :BC Off

Measurement settings: Calibration Mode: Concentration, Measurement Mode: Integrate, Smoothing: 5 point Replicates Standard: 3, Replicates Sample: 3, Measurement Time: 5.0 s

Flame settings: Flame Type: N2O/Acetylene, N2O Flow: 10.00 L/min, Acet. Flow: 7.04 L/min Burner Height: 0.0 mm

Instrument Zero [Postread=-0.0035Abs, Gain=23%]

Sample ID Conc mg/l %RSD Mean Abs Readings CAL: CAL ZERO 0.0000 10.9 -0.0031 -0.0027 -0.0033 CAL: STANDARD 1 0.2000 2.7 0.0177 0.0178 0.0181 CAL: STANDARD 2 0.4000 0.7 0.0358 0.0356 0.0359 CAL: STANDARD 3 0.6000 0.9 0.0516 0.0514 0.0513 CAL: STANDARD 4 0.8000 0.5 0.0677 0.0682 0.0676 CAL: STANDARD 5 1.0000 1.3 0.0836 0.0824 0.0844

New Rational-Cal. Set 1

0.09 R2 = 0.9971 0.08 0.07 0.06 0.05 0.04 0.03 Absorbance 0.02 0.01 0 0.0000 0.2000 0.4000 0.6000 0.8000 1.0000 1.2000 Ca,mg/L

1: Top 1.0788 1.2 0.0441 0.0440 0.0447 2: Blank 0.2072 4.5 0.0184 0.0178 0.0180 3: Co-A 2.4353 1.0 0.0458 0.0460 0.0461 4: Co-B 2.3035 1.5 0.0444 0.0451 0.0441 5: Co-C 2.2423 0.5 0.0436 0.0434 0.0437 6: C-1A 1.6868 1.1 0.0420 0.0425 0.0416

- 79 - 7: C-1B 1.7257 3.4 0.0425 0.0411 0.0426 8: C-1C 1.7024 2.3 0.0421 0.0419 0.0432 9: C-2A 1.6313 1.5 0.0420 0.0424 0.0422 10: C-2B 1.5196 2.3 0.0400 0.0410 0.0395 11: C-2C 1.4905 0.9 0.0405 0.0409 0.0404 12: Check 0.8438 0.8 0.0716 0.0709 0.0720 13: C-3A 1.5947 2.0 0.0436 0.0428 0.0445 14: C-3B 1.5614 2.1 0.0410 0.0410 0.0419 15: C-3C 1.5592 0.9 0.0406 0.0411 0.0404

Table 22. Result Summery, Ca, mg/l.

Mean Ca Conc., Final conc.- Dil. Factor(x50) Sample code Mean of sample mg/l Blank Blank 0.2072 - - - Co 2.3270 2.1198 2.1198 10.5990 mg/l C1 1.7050 C2 1.5471 1.6080 1.4008 7.0040 mg/l C3 1.5718

Method: Mg (Flame)

Instrument settings: Wavelength: 285.2 nm, Slit Width: 0.5 nm, Lamp Current: 4.0 mA, Background Correction:BC On

Measurement settings: Calibration Mode: Concentration, Measurement Mode: Integrate, Smoothing: 5 point Replicates Standard: 3, Replicates Sample: 3, Measurement Time: 5.0 s

Flame settings: Flame Type: N2O/Acetylene, N2O Flow: 11.00 L/min, Acet. Flow: 6.63 L/min Burner Height: 0.0 mm

Instrument Zero [Postread=-0.0007Abs, Gain=24%]

Sample ID Conc mg/l %RSD Mean Abs BG Abs Readings

CAL ZERO 0.0000 97.0 -0.0006 0.0003 -0.0009 -0.0009 STANDARD 1 0.2000 1.0 0.0349 0.0043 0.0353 0.0346 STANDARD 2 0.4000 0.3 0.0645 0.0050 0.0643 0.0646 STANDARD 3 0.6000 0.3 0.0934 0.0052 0.0931 0.0936 STANDARD 4 0.8000 0.2 0.1214 0.0061 0.1212 0.1217 STANDARD 5 1.0000 0.7 0.1486 0.0065 0.1493 0.1474

- 80 - New Rational-Cal. Set 1

0.16 0.14 R2 = 0.9979 0.12 0.1 0.08 0.06

Absorbance 0.04 0.02 0 0.0000 0.2000 0.4000 0.6000 0.8000 1.0000 1.2000 Mg,mg/L

1: Top(1 mg/l)0.9712 1.2 0.0780 0.0053 0.0791 0.0777 2: Blank 0.0185 13.7 0.0032 0.0044 0.0027 0.0034 3: Co-A 0.4664 0.7 0.0751 0.0054 0.0750 0.0756 4: Co-B 0.4645 0.6 0.0748 0.0054 0.0753 0.0746 5: Co-C 0.4618 0.3 0.0744 0.0055 0.0742 0.0742 6: C-1A 0.3955 0.8 0.0645 0.0052 0.0640 0.0650 7: C-1B 0.3981 0.6 0.0649 0.0053 0.0649 0.0644 8: C-1C 0.4013 0.3 0.0653 0.0053 0.0652 0.0656 9: C-2A 0.4174 0.3 0.0678 0.0054 0.0680 0.0676 10: C-2B 0.4159 0.9 0.0676 0.0053 0.0682 0.0672 11: C-2C 0.4216 0.0 0.0684 0.0056 0.0684 0.0684 12: Check (1 mg/l) 0.9775 0.4 0.1448 0.0068 0.1443 0.1447 13: C-3A 0.3977 0.2 0.0648 0.0057 0.0647 0.0648 14: C-3B 0.3990 0.5 0.0650 0.0054 0.0652 0.0652 15: C-3C 0.3983 0.8 0.0649 0.0054 0.0655 0.0647

Table 23. Result Summery, Mg, mg/l.

Mean Mg Conc., Sample code Mean of sample Final conc.-Blank Dil. Factor(x50) mg/l

Blank 0.0185 - - - Co 0.4642 0.4642 0.4457 2.2285 mg/l C1 0.3983 C2 0.4183 0.4050 0.3865 1.9325 mg/l C3 0.3983

Standard Test method for the determination of Sodium and Potassium in Water (ISO: 9964-1, 9964-2:1993; Direct flame atomic absorption determination of Na and K in water using air - acetylene flame.

- 81 - Principle:-Addition of CsCl solution (25 g/ 50 ml of conc. HCl and diluted to the mark of 1000 ml volumetric flask) to the sample as an ionization suppressant. Aspiration of the sample directly into the air/acetylene flame of an AAS. Measurement of the absorbance at λ of 589.0 nm.

Reagents: HCl (Assay=36%, AVONCHEM, UK) HNO3 (Assay=69.0 - 71.0 %, LABORT FINE CHEM PVT LTD, India) CsCl (Assay=99.99 %, WINLAB, UK) NaCl (Assay=Min. 99.99 %, NICE PVT LTD, India) KCl (Assay=Min. 99.99 %, EXCELAR, UK) Distilled Water (pH=5.65, Conductivity= μS)

Apparatus: Varian SpectrAA Flame Atomic Absorption Spectrometer, SIPS-220 (Varian Australia Pty Ltd) Sodium Hollow Cathode Lamp Potassium Hollow Cathode Lamp Fuel, locally (Chora industrials Plc.) produced acetylene Pressure reducing regulators Experimental -The sample was filtered in a retentive filter paper (whatman # 542) prior to analysis. - 2 ml of each sample was taken in a 100ml volumetric flask. -10 mL CsCl was added to give a final conc of 2000 μg/mL of Cs to overcome enhancement interference from other alkali metals.

Method Development: Worksheet created 13:58:46 07/02/07 Worksheet details: Name: Water (Packed bed column exp’t) Analyst: Yoseph Abebe Woldetsadik Comments: Determination of Na and K

Analysis started 14:54:24 07/02/07 (AA Online)

Method: Na (Flame)

Instrument settings: Wavelength: 589.0 nm, Slit Width: 0.5 nm, Lamp Current: 5.0 mA, Background Correction: BC Off

Measurement settings: Calibration Mode: Concentration, Measurement Mode: Integrate, Smoothing: 5 point Replicates Standard: 3, Replicates Sample: 3, Measurement Time: 5.0 s

Flame settings: Flame Type: Air/Acetylene, Air Flow: 18.45 L/min, Acetylene Flow: 2.03 L/min

- 82 - Burner Height: 0.0 mm

Instrument Zero [Postread=-0.0072Abs, Gain=25%]

Sample ID Conc mg/l %RSD Mean Abs Readings CAL: CAL ZERO 0.0000 23.9 -0.0069 -0.0061 -0.0058 -0.0088 CAL: STANDARD 1 0.2000 1.5 0.0956 0.0950 0.0972 0.0945 CAL: STANDARD 2 0.4000 0.5 0.1762 0.1753 0.1767 0.1767 CAL: STANDARD 3 0.6000 1.0 0.2399 0.2426 0.2382 0.2388 CAL: STANDARD 4 0.8000 1.2 0.2941 0.2976 0.2938 0.2907 CAL: STANDARD 5 1.0000 0.6 0.3403 0.3408 0.3421 0.3379

New Rational,Cal. Set-1

0.4 e R2 = 0.9786 0.3 0.2 0.1

Absorbanc 0 0.0000 0.5000 1.0000 Na,mg/L

1: Top(1.0 mg/l) 0.9867 0.8 0.2087 0.2088 0.2071 0.2104 2: Blank -0.6081 0.0 -0.2931 -0.2930 -0.2931 -0.2931 3: CoA 0.8153 0.4 0.2994 0.3008 0.2987 0.2986 4: CoB 0.8483 0.6 0.3068 0.3083 0.3046 0.3074 5: CoC 0.7913 0.8 0.2938 0.2926 0.2965 0.2922 6: C1A 0.9361 0.9 0.3251 0.3233 0.3285 0.3235 7: C1B 0.9381 0.5 0.3255 0.3236 0.3263 0.3267 8: C1C 0.8953 0.9 0.3168 0.3167 0.3139 0.3199 9: C2A 0.9858 1.2 0.3347 0.3375 0.3300 0.3366 10: C2B 0.9435 1.5 0.2028 0.1998 0.2057 0.2029 11: C2C 0.9874 0.6 0.3350 0.3373 0.3343 0.3333 12: C3A 0.9218 0.7 0.3223 0.3238 0.3233 0.3196 13: C3B 0.9106 1.4 0.3200 0.3165 0.3183 0.3252 14: C3C 0.9360 1.3 0.3251 0.3248 0.3211 0.3295 15: Check(1.0 mg/l)0.9806 1.8 0.2092 0.2049 0.2117 0.2109

- 83 - Table 24. Result Summery: - Na, mg/L.

Mean Na Conc., Final conc.- Sample code Mean of sample Dil. Factor(x50) mg/l Blank

Blank - - - - Co 0.8183 0.8183 0.8183 40.915 mg/l C1 0.9232 C2 0.9722 0.9394 0.9394 46.970 mg/l C3 0.9228

Analysis started 15:15:50 07/02/07 (AA Online)

Method: K (Flame)

Instrument settings: Wavelength: 766.5 nm, Slit Width: 1.0 nm, Lamp Current: 5.0 mA, Background Correction: BC Off Measurement settings: Calibration Mode: Concentration, Measurement Mode: Integrate, Smoothing: 5 point Replicates Standard: 3, Replicates Sample: 3, Measurement Time: 5.0 s

Flame settings: Flame Type: Air/Acetylene, Air Flow: 18.25 L/min, Acetylene Flow: 2.00 L/min Burner Height: 0.0 mm

Instrument Zero [Postread=0.0021Abs, Gain=60%]

Sample ID Conc mg/l %RSD Mean Abs Reading CAL: CAL ZERO 0.0000 8.1 0.0066 0.0065 0.0061 0.0072 CAL: STANDARD 1 0.2000 1.5 0.0962 0.0963 0.0976 0.0948 CAL: STANDARD 2 0.4000 0.9 0.1778 0.1791 0.1784 0.1761 CAL: STANDARD 3 0.6000 0.8 0.2579 0.2583 0.2555 0.2598 CAL: STANDARD 4 0.8000 0.6 0.3299 0.3282 0.3321 0.3292 CAL: STANDARD 5 1.0000 0.4 0.4059 0.4047 0.4077 0.4053

- 84 - New Rational,Cal. Set-1

0.6 2 0.4 R = 0.9987 0.2

Absorbance 0 0.0000 0.2000 0.4000 0.6000 0.8000 1.0000 K,mg/L

1:Top(1.0 mg/l) 0.9966 0.5 0.4010 0.4021 0.3985 0.4025 2: Blank -0.0251 3.0 -0.0122 -0.0121 -0.0119 -0.0126 3: CoA 0.1328 0.9 0.0629 0.0626 0.0626 0.0636 4: CoB 0.1335 0.8 0.0633 0.0627 0.0634 0.0637 5: CoC 0.1335 0.9 0.0633 0.0639 0.0628 0.0631 6: C1A 0.1328 1.0 0.0629 0.0623 0.0629 0.0635 7: C1B 0.1351 0.5 0.0640 0.0644 0.0639 0.0638 8: C1C 0.1363 0.7 0.0646 0.0641 0.0650 0.0646 9: C2A 0.1844 0.7 0.0865 0.0858 0.0866 0.0870 10: C2B 0.1254 1.1 0.0595 0.0600 0.0598 0.0587 11: C2C 0.1248 0.1 0.0593 0.0593 0.0593 0.0592 12: C3A 0.1248 1.7 0.0593 0.0583 0.0593 0.0602 13: C3B 0.0974 1.1 0.0465 0.0465 0.0460 0.0470 14: C3C 0.0970 2.6 0.0463 0.0477 0.0455 0.0458 15: Check (1.0 mg/l)0.9425 0.8 0.3829 0.3860 0.3800 0.3825

Table 25. Result summery, K, mg/l.

Mean K Conc., Final conc.- Sample code Mean of sample Dil. Factor(x50) mg/l Blank

Blank - - - - Co 0.1333 0.1333 0.1333 6.665 mg/l C1 0.1347 C2 0.1449 0.1287 0.1287 6.435 mg/l C3 0.1064

- 85 - Standard Test method for the determination of Iron in Water (ASTM D 1068-90) Direct flame atomic absorption determination of dissolved iron in water using air - acetylene flame. Principle:-Atomization of filtered sample directly into an air-acetylene flame with no pre- treatment. Reagents: HCl(Assay=36%,Specific gravity=1.18,AVONCHEM) HNO3 (Assay=69.0 - 71.0 %, Specific gravity=1.42, LABORT FINE CHEM PVT LTD) Distilled Water (pH=5.65, Conductivity= μS)

Apparatus: Varian SpectrAA Flame Atomic Absorption Spectrometer, SIPS-220 (Varian Australia Pty Ltd) Iron Hollow Cathode Lamp Fuel, locally (Chora industrials Plc.) produced acetylene Pressure reducing regulators

Method: Fe (Flame)

Instrument settings: Wavelength: 248.3 nm, Slit Width: 0.2 nm, Lamp Current:5.0 mA, Background Correction: BC On

Measurement settings: Calibration Mode: Concentration, Measurement Mode: Integrate, Smoothing: 5 point Replicates Standard: 3, Replicates Sample: 3, Measurement Time: 5.0 s

Flame settings: Flame Type: Air/Acetylene, Air Flow: 18.90 L/min, Acetylene Flow: 2.18 L/min Burner Height: 0.0 mm

Instrument Zero [Postread=0.0011Abs, Gain=57%]

Sample ID Conc mg/l %RSD Mean Abs BG Abs Readings CAL ZERO 0.0000 27.9 -0.0020 0.0025 -0.0019 -0.0015 -0.0026 STANDARD 1 1.0000 0.7 0.0512 0.0050 0.0508 0.0515 0.0513 STANDARD 2 2.0000 0.7 0.1050 0.0052 0.1056 0.1053 0.1041 STANDARD 3 3.0000 0.6 0.1575 0.0058 0.1569 0.1586 0.1571 STANDARD 4 4.0000 1.1 0.2076 0.0061 0.2051 0.2091 0.2087 STANDARD 5 5.0000 0.2 0.2540 0.0060 0.2541 0.2536 0.2544

- 86 - 0.003

0 003 New Rational,Cal. Set-1 0.3000 e R2 = 0.9993 0.2000

0.1000 bsorbanc A 0.0000 0.0000 2.0000 4.0000 6.0000 Fe,mg/L

1: Top(5.0 mg/l) 4.9599 0.2 0.2528 0.0062 0.2526 0.2525 0.2534 2: Blank 0.0053 >100 0.0003 0.0048 0.0012 -0.0008 0.0004 3: CoA 0.0623 25.3 0.0032 0.0040 0.0041 0.0029 0.0025 4: CoB 0.0575 6.4 0.0029 0.0034 0.0030 0.0027 0.0030 5: CoC 0.0366 71.0 0.0019 0.0041 0.0019 0.0032 0.0005 6: C1A 0.0424 34.4 0.0022 0.0036 0.0017 0.0018 0.0030 7: C1B 0.0603 25.7 0.0031 0.0032 0.0025 0.0040 0.0027 8: C1C 0.0434 17.2 0.0022 0.0042 0.0018 0.0026 0.0023 9: C2A 0.0367 32.1 0.0019 0.0043 0.0013 0.0019 0.0025 10: C2B 0.0354 43.1 0.0018 0.0046 0.0009 0.0023 0.0022 11: C2C 0.0356 27.4 0.0018 0.0045 0.0015 0.0024 0.0016 12: C3A 0.0497 15.0 0.0025 0.0035 0.0022 0.0029 0.0025 13: C3B 0.0473 19.8 0.0024 0.0039 0.0029 0.0023 0.0020 14: C3C 0.0461 30.9 0.0023 0.0041 0.0015 0.0027 0.0028 15: Check(5mg/l)4.8685 0.3 0.2486 0.0061 0.2484 0.2481 0.2494

Table 26. Result summery, Fe, mg/l.

Mean Fe Conc., Sample code Mean of sample Final conc.,mg/l mg/l Blank 0.0053 0.0053 - Co 0.0521 0.0521 0.0521 C1 0.0487 C2 0.0359 0.0441 0.0441 C3 0.0477

Table 27. Varian AAS (SIPS 220) Detection Limit of analyzed elements.

Instrument detection Element limit Al 0.0300 mg/l Ca 0.0010 mg/l Fe 0.0060 mg/l K 0.0030 mg/l Mg 0.0003 mg/l Na 0.0002 mg/l

- 87 -