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SCHOOL OF MATERIALS AND MINERAL RESOURCES ENGINEERING

UNIVERSITY SAINS MALAYSIA

DEVELOPMENT OF MARCO-POROUS ECOTILES FROM FRESH

WATER SLUDGE FOR CADMIUM REMOVAL

YEOH KAR KEAT

Supervisor: ASSOC. PROF. DR. YEOH FEI YEE

Dissertation submitted in partial fulfilment of the requirements For the degree of Bachelor of engineering with honours

(MATERIALS ENGINEERING)

UNIVERSITI SAINS MALAYSIA

JUNE 2019

ACKNOWLEDGEMENT

First of all, I would like to wish a thousand thanks to Universiti Sains

Malaysia for giving me the opportunity the complete my degree of Bachelor of

Materials Engineering. Great thanks to School of Materials and Mineral Resources

Engineering to provide me adequate equipment and Laboratory to complete this research.

Secondly, I would like to thank my supervisor, Assoc. Prof. Dr Yeoh Fei Yee for giving me proper advice and guidance throughout my research despite his busy schedule. This research would not be done successfully without his support and supervision.

Besides that, I would also like to thank to all of the research team who have helped and contributed in this research, especially Ooi Chee Heong and Kelvin Heng which provide tones of helps throughout this experiment.

Great thanks to the technical staff in School of Materials And Mineral

Resources who have provided their service, help and advice along the progress of the experiment. Without their help, this research would not be successful.

Last but not least, I would like to thank my friends and family who gives me full support either directky or indirectly in this research. With their support and encouragement, I was able to complete my degree successfully.

Table of content

ACKNOWLEDGEMENT ...... i

LIST OF TABLES ...... vi

LIST OF FIGURES ...... vii

LIST OF ABBREVIATIONS ...... ix

ABSTRACT ...... x

ABSTRAK ...... xi

Chapter 1 Introduction ...... 1

1.1 Preface ...... 1

1.2 Introduction ...... 1

1.2 Problem statement ...... 5

1.3 Research objective...... 6

1.4 Scope of research ...... 6

CHAPTER 2 LITERATURE REVIEW ...... 7

2.1 Sludge Problem ...... 7

2.2 Coagulation of Sludge...... 8

2.3 Alternative Solution to Disposed Of Water Sludge ...... 11

2.4 Fabrication of Porous Ceramic Body ...... 15

2.5 Heavy Metal Adsorption ...... 18

2.6 Types of Cadmium Removal ...... 20

2.7 Porous medium for Cadmium Removal ...... 21

2.8 Urea Functionalisation of Clay ...... 23

2.9 Heavy Metal Adsorption by Chelating Agent, Urea ...... 25

CHAPTER 3 MATERIALS AND METHODOLOGY ...... 27

3.1 Introduction ...... 27

3.2 Preparation of Raw Materials ...... 28

3.2.1 Drying ...... 28

3.2.2 Grinding ...... 29

3.2.3 Sieving ...... 30

3.3 Slip Casting ...... 31

3.3.1 Mixing ...... 31

3.3.2 Casting ...... 33

3.3.3 Firing ...... 33

3.3.4 Determination of the parameter ...... 34

3.4 Physical Testing ...... 34

3.4.1 Modulus of Rupture Test ...... 34

3.4.2 Preparation of Urea Solution ...... 35

3.4.3 Functionalisation of Ecoclay ...... 35

3.5 Scanning Electron Microscope (SEM) ...... 36

3.6 X-ray Diffraction ...... 36

iii

3.5 Determining the Urea Functionalisation ...... 37

3.5.1 Fourier-transform infrared spectroscopy (FTIR) ...... 37

3.5.2 Urea Concentration Measurement ...... 37

3.6 Heavy metal Adsorption ...... 38

3.6.1 Determining Time Taken for Adsorption ...... 38

3.6.2 Determining How Porosity Affect Heavy Metal Adsorption ...... 39

3.6.3 Inductively coupled plasma - optical emission spectrometry (ICP-OES) .. 40

Chapter 4 Results and Discussion ...... 42

4.0 Introduction ...... 42

4.1 Ecoclay Tiles Characterisation ...... 42

4.1.1 Determination of the parameters ...... 42

4.1.2 Modulus of Rupture (MOR) Test ...... 46

4.1.2 FTIR result of Functionalised Ecoclay Tiles ...... 48

4.1.3 Urea Concentration Measurement ...... 51

4.1.4 X-ray Diffraction Analysis ...... 53

4.1.5 Scanning Electron Microscope ...... 61

4.2 Heavy Metal Adsorption Capability of Porous Ecoclay Tiles ...... 66

4.2.1 Time Taken to Reach Maximum Adsorption Capacity ...... 66

4.2.2 Effect of Amount of Pore-Forming Agent on the Cadmium Adsorption

Capacity ...... 68

Chapter 5 Conclusion and Recommendation ...... 72

5.1 Conclusion ...... 72

Future Recommendation ...... 73

References ...... 74

LIST OF TABLES

Table 2. 1 Chemical composition and physical test of different samples from different plants of alum sludge by X-ray fluorescence (XRF) ...... 8

Table 2. 2List of primary coagulant used for water treatment...... 10

Table 3. 1 Composition of clay body sample with different amount of sludge...... 31

Table 3. 2Composition of clay boy with difference amount of rice husk ...... 32

Table 4. 1MOR value for Ecoclay ...... 46

Table 4. 2 Amount of urea functionalised on to the ecoclay sample ...... 52

Table 4. 3 Position and relative intensity of XRD peak of sludge with respective d- spacing ...... 54

Table 4. 4 Position and relative intensity of XRD peak of fired clay with 30 wt% sludge with respective d-spacing ...... 56

Table 4. 5 Position and relative intensity of XRD peak of fired clay with 30 wt% sludge with respective d-spacing ...... 60

Table 4. 6 SEM result on porous Ecoclay sample ...... 62

Table 4. 7 SEM observation of Ecoclay sample with different amount of pore-forming agent ...... 63

Table 4. 8 Time Taken For the Ecoclay Sample To Reach Maximum Adsorption

Capacity ...... 66

LIST OF FIGURES

Figure 1. 1 drying of water sludge before disposed of to the landfill ...... 2

Figure 1. 2 Porous ceramic brick ...... 3

Figure 1. 3 Various ways of producing porous materials ...... 4

Figure 2. 1 Electric double layer ...... 9

Figure 2. 2 Compressive strength of the ceramic bodies burned at 1000ºC and 1050ºC temperature...... 13

Figure 2. 3 Effective porosity (We), total open porosity (Wr) and reserve pore volume

(R) of the ceramic bodies burned at 1000 ºC temperature...... 13

Figure 2. 4 The hardness trend of formulated bisque clay that comprised of 20-50 wt% water sludge...... 15

Figure 2. 5 Method of fabrication of endo-templating porous material...... 16

Figure 2. 6 Graph of shaking speed against removal efficiency...... 19

Figure 2. 7 Sorption of cadmium by using organic sorbent...... 23

Figure 2. 8 FTIR result of (a) urea; (b) Kaolin; (c) Urea- kaolin complex ...... 24

Figure 2. 9 Ethylenediamine serves as a chelating agent by binding via its two nitrogen atoms ...... 26

Figure 3. 1 (a) Dried sludge chunk (b) Rice husk ...... 28

Figure 3. 2 Mortar and pestle ...... 29

Figure 3. 3 Mini Grinder for grinding rice husk ...... 30

Figure 3. 4 Automatic Mechanical Mixer ...... 33

vii

Figure 3. 5 Modulus of Rupture ...... 35

Figure 3. 6 Portable FTIR Machine ...... 37

Figure 3. 7 Heavy metal adsorption process on the orbital shaker ...... 39

Figure 4. 1 1st batch of ecoclay sample with different sludge composition ...... 43

Figure 4. 2 shows the observation of the ecoclay sample after glazing...... 44

Figure 4. 3 Sample sticking to the mould...... 45

Figure 4. 4 graph of MOR against porosity ...... 47

Figure 4. 5 FTIR result of (a) unfunctionalised ecoclay, (b) Functionalised ecoclay, (c)

Comparison between result of unfunctionalised ecoclay and functionalised ecoclay. 49

Figure 4. 6 FTIR spectrum of pure urea...... 50

Figure 4. 7 Crystalline urea at the bottom of the beaker after functionalisation process.

...... 51

Figure 4. 8 Calibration graph for urea solution for UV-VIS ...... 52

Figure 4. 9 XRD diffractogram of sludge ...... 55

Figure 4. 10 XRD diffractogram of fired clay with 30 wt% sludge...... 57

Figure 4. 11 XRD diffractogram of functionalised clay...... 59

Figure 4. 12 Large irregular shape found in sample ES30-P20 ...... 65

Figure 4. 13 Time Taken To Reach Maximum Adsorption Capacity ...... 67

Figure 4. 14 Graph of heavy metal concentration against wt% of rice husk ...... 69

Figure 4. 15 Graph of wt% of rice husk against removal efficienc ...... 71

viii

LIST OF ABBREVIATIONS

SEM Scanning Electron Microscope

FTIR Fourier-transform infrared spectroscopy

POP Plaster of Paris

MOR Modulus of Rupture

XRD X-ray Diffraction

UV-VIS Ultraviolet–visible spectroscopy

ICP-OES Inductively coupled plasma - optical emission spectrometer

DEVELOPMENT OF MARCO-POROUS ECOTILES FROM FRESH

WATER SLUDGE FOR CADMIUM REMOVAL

ABSTRACT

In this research, investigation on the cadmium removal efficiency of a ecoclay product is explored. Fresh water sludge obtained from Sungai Dua Water treatment

Plant is used as a partial substitution of the raw material to fabricate a ceramic tiles.

Fresh water sludge is found to have similar chemical component and physical properties as the raw material of the ceramic tiles, hence sludge could be used as partial substitution of the clay composition in tiles making. Pore-forming agent, rice husk, were added into the composition to fabricate a porous ceramic tiles to further increase the surface area of the sample for the optimum cadmium removal efficiency.

Urea functionalisation is one of the key for a ceramic tiles to increase the removal efficiency on the cadmium solution. The results shows that functionalised ecoclay sample with 10 wt% pore-forming agent to have the best cadmium removal efficiency. The optimum time for the maximum cadmium removal efficiency is found to be 8 hours.

ABSTRAK

Dalam kajian ini, penyiasatan mengenai kecekapan penyingkiran kadmium produk ecoclay diteroka. Enapcemar air yang diperoleh dari Loji Rawatan Air Sungai Dua digunakan sebagai penggantian separa bahan mentah untuk menghasilkan jubin seramik. Enapcemar air didapati mempunyai komponen kimia yang sama dan sifat fizikal untuk diguna sebagai bahan mentah jubin seramik menjadikan enapcemar sebagai penggantian yang sesuai untuk tanah liat konvensional. Agen pembentuk liang, sekam padi, ditambah ke dalam komposisi untuk membuat jubin seramik berliang untuk meningkatkan lagi permukaan sampel untuk kecekapan penyingkiran kadmium yang optimum. Fungsi Urea adalah salah satu kunci untuk jubin seramik untuk meningkatkan kecekapan penyingkiran pada penyelesaian kadmium. Hasilnya menunjukkan bahawa sampel ecoclay yang berfungsi dengan 10 wt% ejen pembentuk liang untuk mempunyai kecekapan penyingkiran kadmium yang terbaik. Masa optimum untuk kecekapan penyingkiran kadmium maksimum didapati 8 jam.

Chapter 1 Introduction

1.1 Preface

Sludge is a by-product of water treatment plant which have a chemical composition similar to the building material. Due to this properties, sludge can be added in to building material like clay body or cement as a substitute for the raw material of the ceramic body. By using sludge as a building material, the problem of sludge disposal can also be solved. By using rice husk as pore-forming agent, a porous clay body can be formed and be used to adsorb heavy metal in industry waste water. Urea is used as a chelating agent to enhance the heavy metal adsorption capability of the clay body.

1.2 Introduction

As a basic necessity of our daily life, fresh water went through a series of process and purification in a fresh water treatment plant before reaching the final consumer. These process include pre-chlorination, coagulation, sedimentation, and filtration. Water sludge is a by-product of the purification process of fresh water processing plant. Large amount of water sludge is produced every year. The two main disposal method of water sludge includes: water sludge is accumulated at the landfills and the disposal of water sludge back to the river without any further treatment. Both disposal method may lead to serious environmental pollution and it is also going against the Malaysian government Environmental Act 1974 and Environmental Quality Regulations (Sewage) 2009. Therefore, an alternative method of water sludge disposal should be implemented as soon as possible to prevent any further damage done to the environment.

Figure 1. 1 drying of water sludge before disposed of to the landfill

One of the alternative method to dispose of the water sludge is to incorporate it in to building material such as brick and tiles. Water sludge is found to be having composition that is closely resemble to the composition of the clay. This enable water sludge to be added into the clay composition without altering the much of the clay structure (Benlalla et al., 2015). By using fresh water sludge as a building material, the problem of fresh water sludge disposal is solved. Besides that, the cost of building material could also be reduced by using fresh water sludge instead of raw material like clay and cement.

From previous studies, the water sludge is found to be consist of five main elements which is Oxygen (O), Silicon (Si), Aluminium (Al), Iron (Fe), and Carbon

(C) which exist in the form of SiO2, Al2O3, Fe2O3, Kaolinite, Quartz, Haematite, and cubic-zeolite (Ling et al., 2017). Sample that is crafted by using sludge were observed to have uniform shrinkage, no obvious crack detected with certain increases in

2 hardness. This opens up the possibility for fresh water sludge to partially replace conventional mineral clay as a green substituent.

By milling the fresh water sludge for a prolonged duration (~7h) a fine particle size (~107µm-150µm) water sludge can be obtain. The particle size after milling falls in the range of 107µm-150µm (Ling et al., 2018). The water sludge also exhibit a

27m2/g specific area with a 0.05cm3/g pore volume (Ling et al., 2018). The appearance of the fired clay have a reddish brown colour due to the existence of hematite content in the water sludge. Metal leakage from the water sludge is reduced significantly by adding bentonite or sodium silicate into the slip (Ling et al., 2018).

Figure 1. 2 Porous ceramic brick

Porosity is one of the most important properties of a ceramic material that is use for industrial application such as thermal insulator and lightweight building materials. (Obada et al., 2017). A lot of properties such as thermal conductivity, water absorption, bulk density and compressive strength can be altered by just changing the porosity of a ceramic material (Šveda et al., 2017). Therefore, careful manipulation of the porosity is required to obtain the optimum properties for every application.

Several properties like pore shape, size and distribution can be altered by using

3 different materials and manufacturing process. Different types of pore might serve in a different type of applications. For instance, micropore are suitable for the adsorption and purification of gaseous streams, on the other hand, macropores plays an important role in biomedical field (Colombo et al., 2010).

There are various kind of pore inducing agents available that could be used to induce porosity to a ceramic material. These pores inducing agent can be divided into

2 categories: combustible pore-forming agent and chemical additive (Šveda et al.,

2017). Combustible pore-forming agent normally consist of natural and carbon based materials such as saw dust, wheat particle, mesocarp fibre, rice husk, cotton, peas and seeds are mixed into the ceramic body and burnt away during the firing process leaving behind empty pores in the ceramic body (Obada et al., 2017). In this case, rice husk is used as a pore-forming agent in the ceramic body. Rice husk is selected because as one of the top 25 rice producing country in the world a lot of rice husk is generated from rice mill every year. Besides that, rice husk can be easily grinded in to powder form of desired particle size by using a mechanical grinder, making rice husk an excellent choice as a pore-forming agent.

Figure 1. 3 Various ways of producing porous materials

Cadmium is a heavy metal with symbol Cd and atomic number of 48.

Cadmium is commonly found in the environment from natural occurrence, anthropogenic activity and industrial activity (Chain, 2009). Following the aggravation of industry activity such as electroplating industry, pigment and battery manufacturing industry large amount of cadmium are discharged into the atmosphere, water and soil causing serious environmental pollution (Li et al., 2015).

Cd is a heavy metal hazardous to human. If accidentally inhaled or ingested, it could cause acute and chronic intoxications (Bernard, 2008). An important toxicologic feature of cadmium is mainly due to the long half-life of the heavy metal in human body. (approximately 10-30 years) Once Cd enters human body, it is accumulated in human body throughout the lifetime. Cadmium is a toxic heavy metal that could interfere with various biological system in human body. Some of the most common case of excessive exposure to cadmium can lead to the development of lung insufficiency, renal disturbances, and osteomalacia (Blainey et al., 1980). Cadmium is also found to be related to the development of hypertension and various kind of cancers (Bernard and Lauwerys, 1986).

1.2 Problem statement

Sludge disposal have always been a problem for water treatment plants.

Tonnes and tonnes of water sludge is produced from water treatment plant but there is limited landfills for the water sludge disposal. As an alternative, water sludge can be incorporated into clay body due to the similarity in their chemical composition.

Porosity caused by the organic component exists in sludge causing a porous clay body to form. The porosity properties of clay body with sludge might reduce the strength of

5 the clay body. However, the porous properties of clay body with sludge can be exploited by using it as an adsorbent. The heavy metal adsorbing power of clay body with sludge is investigated in this lab study with pore-forming agent and chelating agent to further increase the heavy metal adsorbing power of clay body with sludge.

1.3 Research objective

The main aim of this research is to determine the capability of using clay body with sludge in removing heavy metal from industrial waste water. To achieve the goal, two objectives are carried out:

I. To determine the optimum amount of pore-forming agent for heavy

metal removal using Clay body with sludge.

II. To determine the ability of chelating agent, Urea, on the effect of

heavy metal adsorption efficiency of clay body with sludge.

1.4 Scope of research

Clay body is produced with sludge and different amount of rice husk as pore- forming agent. The strength of clay body with different amount of pore-forming agent was tested by using MOR test.

The capability of functionalising the chelating agent, urea, on to the clay body is also investigated by using FTIR and by measuring urea remaining in beaker before and after functionalisation process. The time require for the clay body to reach its maximum adsorption capability and how the porosity and chelating agent affect the adsorption power of the clay body is determined by using ICP-OES test.

CHAPTER 2 LITERATURE REVIEW

2.1 Sludge Problem

Fresh water sludge is also known as drinking water sludge is a waste product from fresh water treatment plant. Water sludge is unsafely disposed of at a daily basis to the landfill and nearby river at a daily basis. Untreated water sludge is harmful to the environment and could cause serious water and land pollution due to the Al content. Besides that, disposal of untreated water sludge to the open environment also goes against Malaysian government Environmental Act 1974 and Environmental

Quality Regulations (Sewage) 2009 (Breesem et al., 2014).

Every year, over 2.0 million tons of fresh water sludge is produced by water treatment plant across Malaysia. Malaysia is not the only country that faces sludge disposal problem that causes land and water pollution. Sludge disposal is a global problem that the world faces everyday. A better alternative method to dispose of the water sludge is crucial as sludge contains chemical composition that is toxic towards the environment and aquatic system. Water sludge contains a lot potentially harmful substances like aluminium hydroxide and some other carcinogenic substances. The chemical composition of the water sludge varies depending on the water treatment plant. Table 2.1 shows the main composition of different water sludge from different water treatment plant.(Breesem et al., 2014)

Table 2. 1 Chemical composition and physical test of different samples from different plants of alum sludge by X-ray fluorescence (XRF)

2.2 Coagulation of Sludge

At Sungai Dua water treatment plant, coagulant is added to water to aid the removal of turbidity, colour, and micro-organisms from the fresh water. Coagulation process is a very common process in conventional fresh water treatment plant to separate impurities in water which will flocculate and form sludge that will settle to the bottom of the tank. The sludge can be easily removed later filtration or centrifuge to separate the sludge from the water (Verrelli et al., 2009).

There is two type of unwanted particle in the water, mineral (clays, aluminum and iron oxides and hydroxides, asbestos, silica) and organic particle (viruses, bacteria, protozoan cysts, algae). These particle is stable and have slow rate of flocculation or aggregation due to three reasons:

1. Electrostatic repulsive interactions due to diffuse electrical double layers

(EDL)

2. Hydrophilic effect of the particle at the particle surface.

3. Steric effects due to adsorbed macromolecules

Electric double layer is one of the most common phenomenon in the mechanism of electrostatic stabilisation of colloids. When a colloid is dispersed in a positively charged dispersion medium the colloidal particle will adsorb the positive electric charge on the particle surface. A electric double layer consist of three main factor:

1. Surface charge: the type of charge that is adsorb to the colloidal particle

surface.

2. Stern layer: counterions that is attracted and attached to the colloidal particle

by the charge on the colloidal particle surface through electrostatic force.

3. Diffuse layer: consist of free counterions which may be affected by the

electrostatic force of the charged particle.

Figure 2. 1 Electric double layer (Park and Seo, 2011)

If the colloidal particle is negatively charged then it will be attracted by the charged at the surface and coagulation happens (Park and Seo, 2011).

There are several types of coagulant available for water treatment process. Table 2.2 shows a list of primary coagulant use for water treatment (Edzwald, 1993).

Table 2. 2 List of primary coagulant used for water treatment (Edzwald, 1993).

Name Comments

ALUM Widely used

SODIUM ALUMINATE Used with alum; provide alkalinity and pH control

ALUMINIUM CHLORIDE Used in blends with organic polymers

POLYALUMINIUM Several formulations based on Al strength, [OH ]/ [AIT ],

CHLORIDE and anions and cations added

POLYALUMINIUM Produced on-site

SULPHATE

FERRITE CHLORIDE Widely used

FERRITE SULFATE Widely used

2.3 Alternative Solution to Disposed Of Water Sludge

Fresh water sludge have a physio-chemical characteristic that allows it to be used as a substitution for building materials. Dried water sludge can be reuse as raw material to fabricate several material for different application. Among those application includes concrete, cement mortar, clay material and fired ceramic product

(Breesem et al., 2014).

Ecoclay was an eco-friendly alternative solution for water sludge treatment without involving synthetic chemical. The name Ecoclay is derived from the clay product produced by using water sludge. Water sludge can be used as an alternative green material for clay, tiles, and ceramic to sanitary ware manufacturer(Ling et al.,

2017).

Several aspect need to be concern when using water sludge as raw material substitution for building materials. Two of the main properties of building material to be concern are the compressive strength and the shrinkage of the building material.

According to Torres et al. research, it is found to be appropriate to replace 10% of sand in ceramic brick by water sludge (Torres et al., 2012). By mixing various proportion of water sludge in to a clay brick sample and fired at different temperature,

Elangovan and Subramanian found that up to 205 of the raw material can be substituted with water sludge without compromising the strength of a commercial clay brick.(Elangovan and Subramanian, 2011) Besides that, water sludge can be used also as a colourant for clay brick beside as a clay substitute (Dunster et al., 2007). Due to the existence of large amount of iron oxide in the fresh water sludge, adding fresh water sludge to the ceramic body composition will change the physical appearance of the ceramic body. When grounded and dried the fresh water sludge have a light

11 yellow brown appearance. After firing at 1000ºC, the appearance of the sludge is found to be changed from light yellow brown to dark brown (Kizinievič et al., 2013).

Another research shows that by mixing the water sludge with rice husk ash, up to 75% of the raw material could be substituted by water sludge and rice husk ash mixture and obtain an optimum result. The clay brick with 75% water sludge and rice husk ask mixture is able to achieve the require value compressive strength, water absorption and efflorescence assigned by the standard specifications (Hegazy et al., 2012). With different type of water sludge substitution in to the clay body, the properties of the clay brick might differ greatly. Quesada et al. partially substitute the raw material of a ceramic brick with urban sewage sludge, bagasse, sludge from the brewing industry, olive mill wastewater and coffee grained residues (Eliche-Quesada et al., 2011). As a building material, the compressive strength is one of the most important properties to be consider. Addition of waste material like different kind of water sludge from different source can decrease the compressive strength of a building material.

However, the result of using different water sludge in the ceramic brick still falls in the standard specification range(Eliche-Quesada et al., 2011). According to all those study, same trend can be seen that addition of sludge to a ceramic body will also affect the physical properties of the ceramic body. As the composition of sludge in ceramic body increases from 5 wt% to 40 wt% the compressive strength of the ceramic body is found to be decreases from 53.8 MPa to 25.9 MPa (Kizinievič et al.,

2013). The decrease in compressive strength is mainly due to the porosity from the addition of sludge.

Figure 2. 2 Compressive strength of the ceramic bodies burned at 1000ºC and 1050ºC temperature (Kizinievič et al., 2013).

Besides that, porosity of a ceramic body can also be affected by the addition of sludge to a ceramic body. From Figure 2.3 we can see that effective porosity of a ceramic body consist of 5 wt% to 40 wt% of sludge composition can range from 20% to 40 % effective porosity (Kizinievič et al., 2013).

Figure 2. 3 Effective porosity (We), total open porosity (Wr) and reserve pore volume (R) of the ceramic bodies burned at 1000 ºC temperature (Kizinievič et al., 2013). The organic matter in the sludge is one of the main pore-forming agent that is burned off during the sintering process of ceramic body. The organic matter in sludge can

13 reach a maximum value of 10-12% (Rodríguez et al., 2010). However, increasing the composition of sludge in a ceramic body shows an opposite trend in hardness compared to its compressive strength. As the composition of water sludge increases from 20 wt% to 50 wt%, the hardness of the ceramic body increases from Vickers

Hardness of 45 Hv to 49 Hv (Ling et al., 2018).

Figure 2. 4 The hardness trend of formulated bisque clay that comprised of 20-50 wt% water sludge (Ling et al., 2018). Water sludge might have metal desorption when immersed in a solution. The metal ions includes Ti4+, Fe3+, Al3+, Mg2+, and K+ which can be dangerous at a high concentration. To reduce the metal desorption problem, various method have been used. The metal leakage of a water sludge clay product could be reduced by firing the clay product. Besides that, it is found that by adding bentonite and sodium silicate to the mix, the metal desorption from the clay body is lowered. This is because after firing, the movement of metal ions is restricted as strong bond form, reducing the metal leakage (Ling et al., 2018).

2.4 Fabrication of Porous Ceramic Body

Porous material plays a very important role in the industry due to its wide range of application. Some of the application that uses porous materials include catalysis, separation, lightweight building materials, biomaterials and so on. Different application may require different fabrication method to produce a porous material that matches the specification that matches their purposes (Tang et al., 2004).

There are various way of producing a porous ceramic body. Some of the methods include colloidal templating, biological templating, emulsion system, powder processing, and marcoporous polymeric foam (Colombo et al., 2010).

Templating method of creating porous ceramic material can be divided into two different categories, endo-templating and exo-templating. Endo-templating involve mixing the template into the ceramic body while mixing. The template will then be removed from the clay body either by dissolving away in a solvent or through firing process which the template will be burned away. On the other hand, exo- templating involve impregnating a porous structure by using the clay slip. Then the template is removed leaving behind a porous structure (Colombo et al., 2010). normally the template used is a “hard” object or particle which will not change shape throughout the shaping and forming process of the clay body (Tiemann, 2007).

Figure 2. 5 Method of fabrication of endo-templating porous material (Tang et al., 2004).

The structure of a porous material is highly dependent on the properties of the raw material used to fabricate the porous material. The suspension condition, particle size, and volume ration of the ceramic and the pore-forming agent are some of the crucial properties need to be consider when manufacturing a porous material. A well- dispersed suspension of the pore-forming agent must be ensure to prevent

16 agglomeration of the pore-forming agent which may disrupt the formation of desired porous structure (Tang et al., 2004).

Impregnating a polymeric foam is another way of creating a porous ceramic material. Polymer foams with different compositions, pore sizes and pore morphologies can be used as templates for the synthesis of large ceramics with tailor made hierarchical porosity. These templates are inexpensive, very versatile and quickly available (Colombo et al., 2010).

Besides that, biological template can also be uses as a pore-forming agent to create a porous ceramic body. Some of the advantages of using biological template is that they are inexpensive, abundant, renewable, and environmentally friendly. Those biological template including starch gel, wood, palm fibre, and cuttlebone (Greil,

2001). Biological template become one of the greatest material choice mainly due to its excellent strength and its specific stiffness. However, there is some limitation when using biological template due to there might be incompatibility between the biological template and the precursor (Valtchev et al., 2004). In this investigation, biological template, rice husk is used as the pore-forming agent. Rice husk is selected due to its high silica content.(Martin, 1938) In a paddy producing country like India, about 6.0 million tonnes of rice husk is thrown away as waste (Prasad et al., 2001). By using rice husk as biological template pore-forming agent in ceramic product, the waste can be reduced.

Some of the limiting factor for a hard colloidal template as pore-forming agent is its maximum pore size is limited to the size of the pore-forming agent. Besides that, by using hard template, crack might occur due to the shrinkage during the drying and densification of the ceramic body (Imhof and Pine, 1998). Templating strategy based

17 on the emulsion system is able to overcome the size limiting issue by the hard colloidal template. These technique uses meso–macroporous silica foams that follows the structure of inorganic precursor based on the emulsion structure. The template can be later removed by dissolving the template or evaporation before densification or firing process (Colombo et al., 2010).

2.5 Heavy Metal Adsorption

Heavy metal adsorption can be divided into two categories: physisorption and chemisorption. Physisorption is mainly the adsorption of heavy metal particle to the adsorbent surface by Van de Waal forces. Chemisorption of heavy metal mainly involve the attraction of positively charged heavy metal ions to the negatively charged adsorbent surface. However, the heavy metal adsorption sequence does not always follows the same order as their electronegativity value. Cadmium which have a lower electronegativity value than Cu and Pb, is found to be one of the most adsorbed heavy metal on to the adsorbent (Park et al., 2016).

There is several factor that can affect the removal efficiency of a sorbent. One of the factor that will affect the removal efficiency is the shaking speed of the heavy metal solution. Shaking induced extra kinetic energy to the heavy metal molecule in the solution increasing the removal efficiency.

Figure 2. 6 Graph of shaking speed against removal efficiency (Argun et al., 2007). From the graph in Figure 2.6, the removal efficiency of the sorbent shows an increasing trend as the shaking speed of the heavy metal solution increases. The increase in shaking speed will cause the heavy metal molecule in the solution to move vigorously. This will increase the rate of collision between the sorbent and the sorbate and increase the removal efficiency. Besides that shaking also cause the concentration of heavy metal solution at the adsorption boundary between the sorbent and sorbate which decreases the boundary layer near the sorbent allowing more heavy metal ions to diffused in to the sorbent. However, further increasing the shaking speed above the optimum shaking speed, a slight decrease of heavy metal removal efficiency is observed. This is due to the vigorous shaking provides enough energy to break the newly formed bond between the sorbate and the sorbent (Argun et al., 2007).

Besides that, by using the same amount of sorbent in a fixed heavy metal concentration the rate of adsorption will also change with the contact time. The adsorption rate can be categorised into 3 part. Initially the adsorption rate increases rapidly which represent the optimal removal efficiency of the sorbent. Then, the heavy metal removal efficiency slowly decreases as the adsorption capacity of the sorbent approaches its maximum value. Further increase in the contact time of the

19 sorbent and sorbate will cause the heavy metal removal efficiency to slightly decrease.

This phenomenon happens is mainly due to the saturation of sorbate on the surface of the sorbent causing desorption to happen (Argun et al., 2007).

Another factor that can affect the heavy metal removal efficiency is the pH of the heavy metal solution. The heavy metal removal efficiency is found to be increases as the pH value increases. The optimum pH for heavy metal removal is pH 8. Further increase in pH, the heavy metal removal efficiency will start to decreases. At lower pH, in the acidic heavy metal solution, the saturation of H+ ions compete with the heavy metal ions to be adsorbed to the sorbent surface, decreasing the removal efficiency of heavy metal. At higher pH, the heavy metal ions starts to precipitate causing the removal efficiency to decrease (Gadde and Laitinen, 1974).

2.6 Types of Cadmium Removal

Cadmium is extremely toxic to human health even in a small concentration (Li et al., 2003). The permittable concentration if cadmium in drinking water according to the World Health Organisation guideline is less than 0.005 mg l-1 (Mohan and Singh,

2002). Long-term exposure to cadmium could cause nausea, salivation, diarrhea, muscular cramps, renal degradation, lung insufficiency, bone lesions, cancer and hypertension in human (Mohan and Singh, 2002). Several types of method that is used to remove cadmium from wastewater includes chemical precipitation, ion- exchange and adsorption (Li et al., 2003).

Chemical precipitation of cadmium from wastewater include flocculation and sedimentation of the targeted element, cadmium for easy removal. The optimum pH for chemical coagulation and precipitation by lime treatment for cadmium removal requires the pH to be greater than 10.5. The use of chemical precipitation appears to

20 be feasible but the cost of the removal system should be consider for larger scale removal (Charerntanyarak, 1999).

Ion-exchange is another method for cadmium removal. The cadmium uptake of the adsorbent can be affected by various mechanism of ion-exchange process.

Cadmium ions had to move through the pores of the zeolite mass, but also through channels of the lattice, and they had to replace exchangeable cation (mainly sodium and calcium). The diffusion of the ions will be retarded when the ions move through a smaller diameter channels. The cadmium uptake is mainly attributed to the ion- exchange reaction on the surface of the sorbent (Ćurković et al., 1997).

Adsorption in one of the most cost effective and widely used method for cadmium removal. Variety of adsorbent such as hematite, activated carbon, and holly oak is found to exhibit good cadmium removal efficiency by adsorption. The surface area and the pore specific volume of the sorbent can affect the cadmium removal efficiency of the sorbent. Besides that, functionalisation of the sorbent surface could further increase the cadmium removal efficiency of the sorbent (Li et al., 2003).

2.7 Porous medium for Cadmium Removal

There are several mediums that have been used to remove cadmium from a solution. Most of them involve a porous medium which have a large surface area in order to increase the capability of cadmium removal. This is due to the contact surface of a sorbent to the sorbate is one of the most important aspect in adsorption

(Benguella and Benaissa, 2002).

One of the material that can be used for cadmium removal is chitin. Research shows that chitin flakes can be uses to remove cadmium from a solution. Chitin is a

21 natural polymer that is normally found in cell wall as the component responsible for metal biosorption. The amino group in the glucose ring in the chitin structure provide electron pair for the metal biosorption. The adsorption capacity of chitin is directly affected by the concentration of the cadmium solution and the particle size of the chitin used for cadmium removal (Benguella and Benaissa, 2002).

Besides that, activated carbon is also another material that is suitable for cadmium removal. The cadmium removal capability of activated carbon is directly affected by the pH of the adsorption column. The decrease in pH of the column cause the decrease of OH- on the surface and inside the porous structure of the activated carbon. With this, the cadmium removal capability will decrease as the pH value decrease. By adding alkaline solution like NaOH to the column, the adsorption capability of the column is found to have a significant improvement due to the increase in the OH- available at the surface and pore liquid (Reed et al., 1994).

Surface area of the activated carbon also plays an important role in affecting the heavy metal removal efficiency of activated carbon. Higher surface area resulting in more adsorption site for the adsorbent to bind to the adsorbate.

Organic sorbent also plays an important role in cadmium removal. Crushed coconut shell is able to remove 80% of cadmium from the 500µg/l standard cadmium solution in a 24h time period. Raw rice husk however does not show a significant result in cadmium removal compared to crushed coconut shell. Raw rice husk only remove up to 62% in 24 hour, but after activating the rice husk, the cadmium removal is found to be increases to 94.4% within 24h. The low adsorption capability maybe due to the low density of the raw rice husk cause the rice husk to not mixed well with

22 the sorbate causing the rice husk unable to be in full contact with the sorbate for adsorption to occur (Bhattacharya and Venkobachar, 1984).

Figure 2. 7 Sorption of cadmium by using organic sorbent.(Bhattacharya and Venkobachar, 1984)

2.8 Urea Functionalisation of Clay

Chelating agent is a type of compound that could allow the same metal ions to attach to their molecule structure to form a ring structure or two (Flora et al., 2015).

Urea is a good chelating agent that could be used to remove heavy metal from an aqueous solution (Mureseanu et al., 2010). Besides that, urea can be obtain easily and at a low cost as large amount of urea can be found in the waste product of dialysis process (Amin et al., 2014). By functionalising a clay product with urea, the heavy metal adsorption capability of the clay body will be enhanced. From Figure 2.8, the

FTIR result on kaolin, urea and kaolin-urea complex shows that urea can be used to functionalise a clay body. The FTIR result shows that kaolin have two sharp band at

3694cm-1 and 3625cm-1. These result is cause by vibrational coupling of three surface of hydroxyl in the primitive cell and the dipole oscillation in perpendicular to the layer and hydroxyl group lie within lamellae in plane common to both the tetrahedral and octahedral sheets respectively. When kaolin is functionalised with urea, the intensity of the 2 band found to be decreased and shift to a lower frequency. New band at 3503cm-1 formed due to the hydrogen bond between kaolinite layers causing the formation of new band. The bond form between urea and kaolin can be observed through the band at 3440cm-1 and 3444cm-1. These bond form due to the formation of

H-bond between NH2 group from the tetrahedral sheet of oxygen and urea for the kaolinite structure (Husssein et al., 2015).

Figure 2. 8 FTIR result of (a) urea; (b) Kaolin; (c) Urea- kaolin complex (Husssein et al., 2015).

2.9 Heavy Metal Adsorption by Chelating Agent, Urea

Urea on the surface of the clay body provide a lot of amino group on the clay body surface which increase the adsorption free energy of the clay body significantly.

The adsorption free energy and the porous ceramic body is the main factor in heavy metal removal capability of a clay body. The more –NH- and NH2 group coated on the surface of the clay body the higher the adsorption capability of the clay body (Wei et al., 2016).

Figure 2. 9 Ethylenediamine serves as a chelating agent by binding via its two nitrogen atoms (lumenlearning.com) Although urea is a nitrogenous compound which may cause eutrophication in surface water if used in excess, it is still a good choice as compare to heavy metal that exhibit toxic and carcinogenic properties, urea does not have any known toxic effect

(Khokhotva and Waara, 2010).

CHAPTER 3 MATERIALS AND METHODOLOGY

3.1 Introduction

To achieve the objective of this investigation, the research is divided in to four main section.

The first section of the research is preparing the raw materials required to fabricate the ecoclay product. The composition of the clay body is determined and the variable of the research is set to be the pore-forming agent, rice husk to be added in to the clay body. Sludge and rice husk is grinded to under a specific particle size and sieving is done to ensure the particle size of the raw material.

Second section of the research is clay body fabrication including slip casting and firing of the clay body. Slip is prepared from the raw material prepared and cast into a selected mould. The shape of the mould is important as a tile shape mould allow the characterisation testing to be done easily. After casting, the green body is then fired using a furnace.

Third section of the research is the chelating agent functionalisation of the

Ecoclay body. Urea is selected as the chelating agent to further increase the heavy metal adsorption efficiency of the Ecoclay. FTIR test and Urea remaining in the functionalisation beaker is tested to determine the amount of urea functionalised on to the Ecoclay body.

The last section of the research involve the heavy metal adsorption of the

Ecoclay sample. Both Ecoclay sample with and without is tested for the time taken for them to reach the maximum adsorption capacity. Then, the duration for the Ecoclay to

27 reach its maximum adsorption capacity is use to determine the effect of porosity of the Ecoclay body on heavy metal adsorption.

3.2 Preparation of Raw Materials

3.2.1 Drying

Water sludge that was collected from Sungai Dua PBA Water Treatment Plant and rice husk was dried by placing them outdoor under the hot sun. Dried sludge chunk and rice husk was shown at Figure 3.1 (a) and (b) below. The purpose of drying process was to remove moisture in the sludge and rice husk to prevent agglomeration during grinding process.

(a) (b)

Figure 3. 1 (a) Dried sludge chunk (b) Rice husk

3.2.2 Grinding

Water sludge chunk was crushed by using a mallet in to smaller size

(approximately 0.5cm in diameter). The water sludge is then grind in to powder form by using mortar and pestle. Each batch of water sludge was grinded for 20 min to obtain a fine particle size.

Figure 3. 2 Mortar and pestle Rice husk was grinded using a mini grinder. A 100 micron sieve was place at the output hole of the mini grinder to ensure only particle smaller than 100 micron was collected at the plastic bag place at the output hole.100 micron particle size was selected to ensure the better packing with the same particle size of pore-forming agent and the sludge powder. Rice husk was fed slowly into the mini grinder to ensure complete grinding of the rice husk. The mini grinder was operated for 10 min with a 5 min stop interval to prevent it from overheating.

Figure 3. 3 Mini Grinder for grinding rice husk

3.2.3 Sieving

Sludge powder that have been grinded in to powder form was then sieved using a sieve shaker machine. The sludge powder was poured into a 100 micron sieve and placed on the sieve shaker machine with a collecting tray at the bottom of the sieve. The sieve shaker machine was set to shake for 20 min at an amplitude of level 6.

100 micron particle size was selected because as the particle size decreases the hardness of the sample increases.(Ling et al., 2018)

3.3 Slip Casting

3.3.1 Mixing

The composition of clay body consist of ball clay, feldspar, silica, water sludge and rice husk. The composition of each sample was shown in Table 3.1 and 3.2 below.

Table 3. 1 Composition of clay body sample with different amount of sludge.

Sample

Material ES10 ES20 ES30 ES40 ES50

Ball clay 49.5% 44% 38.5% 33% 27.5%

Feldspar 27% 24% 21% 18% 15%

Silica 13.5% 12% 10.5% 9% 7.5%

Sludge 10% 20% 30% 40% 50%

Table 3. 2 Composition of clay boy with difference amount of rice husk

sample (%) materials

ES30-R00 ES30-R10 ES30-R20 ES30-R30 ES30-R40 ES30-R50 ball clay 38.5 34.65 30.8 26.95 23.1 19.25 feldspar 21 18.9 16.8 14.7 12.6 10.5

silica 10.5 9.45 8.4 7.35 6.3 5.25 sludge 30 27 24 21 18 15 rice husk 0 10 20 30 40 50

The raw material was prepared in a 500ml plastic beaker and weighted by using an electric balance. Water was added to the clay composition at the ratio of 1:1.

Then, the clay composition was stirred using a mechanical overhead stirrer. Small amount of Sodium Silicate (0.3wt% of the dry weight of clay body) was added to ensure a suitable viscosity was achieved for slip casting. The mixture is stirred for 2 hour with a mechanical overhead stirrer at a speed of 400 rpm for 2 hours to ensure a homogeneous mixture. After stirring for 2 hours, the mixture was removed from the mechanical stirrer and left to set for 30 minute. This will let the air bubble trapped in the mixture while stirring to escape.

Figure 3. 4 Automatic Mechanical Mixer

3.3.2 Casting

A Plaster of Paris (POP) mould of the desired shape of casting is prepared.

The slip mixture that have been prepared was then poured into the mould through a filter to remove any agglomerated particle. The cast was then let to dry in the mould to form green body. The green body can be removed from the mould when there was a clear gap form between the green body and the POP mould (approximately 30mins).

The green body was then dried at room temperature for 1 day.

3.3.3 Firing

The green body after drying was placed in Nabertherm Furnace for sintering.

The heating rate of the furnace was set at 5ºC/min. The sample was soaked at 1080ºC for 4 hour to ensure complete firing of the sample. The sample was cooled down slowly in the furnace to prevent cracking due to thermal shock.

3.3.4 Determination of the parameter

The slip prepared by adding 5 different amount of sludge in to the slip before casting. The amount of sludge added was 10, 20, 30, 40, 50 wt% respectively. The sample was allow to be cooled down in the furnace to room temperature before removing from the furnace. After that glaze was applied on to the ecoclay sample then the sample was glaze fired to ensure that the sample is compatible with glazing process.

After obtaining the optimum slip composition and firing parameter, another batch of slip was prepared for casting with different amount of pore-forming agent, rice husk added. The rice husk was grinded in to powder form before added in to the slip and then mixed homogenously. 10, 20 ,30, 40, 50 wt% of pore-forming agent was added to the slip before the casting process and mixed homogeneously before casting.

3.4 Physical Testing

3.4.1 Modulus of Rupture Test

The dimension of the sample was measured by using a Vernier Caliper. The lower support of the MOR machine is set to have a gap of 6cm. the sample is placed carefully on to the lower support. Then a bar is lowered down to the centre of the sample. The force value was shown at the display of the MOR machine. The sample was then carefully remove from the MOR machine. The MOR value was then calculate using the formula in Figure 3.5

Figure 3. 5 Modulus of Rupture

3.4.2 Preparation of Urea Solution

Urea is a chelating agent which facilitates the adsorption of heavy metal on the ecoclay sample. In this case, concentration of urea in the dialysate is used as reference for the urea solution used to functionalise the ecoclay product. A concentration of

0.014mol/L of urea was prepare by adding 0.85g of urea powder to 1 litre of

Deionised Water in a 1 litre volumetric flask. The urea powder was weighted using

Satorious Electrical Balance.

3.4.3 Functionalisation of Ecoclay

Ecoclay sample was functionalised by heating the ecoclay sample at high temperature in urea solution. 100ml of pre-prepared urea solution was poured into a

250ml beaker with ecoclay sample in it. The beaker was then put into a drying oven to heat at 90ºC. The urea solution was heated in drying oven until all the urea have dried.

The drying process will approximately take 12 hours to completely evaporate 100ml of urea solution. Then the sample was carefully removed from the beaker.

3.5 Scanning Electron Microscope (SEM)

The microstructure of the fired clay with rice husk as pore-forming agent was observed by using the Field Emission Scanning Electron Microscope (FESEM). The clay sample was cut into small fragment in the size of 2mm x 2mm x 2mm. This was to make sure that the sample can fit in to the vacuum chamber of the SEM. 1cm of carbon tape was cut and stick on the sample holder followed by the clay sample.

Shake the sample softly to ensure the sample was stick securely on to the sample holder and to remove any extra residue. Then, the sample aws sent for gold coating by using a SEM Sputter Coating System to prevent charging on the sample when using

SEM.

The prepared sample was then place in the SEM vacuum chamber and the vacuum pump was turned on. After the vacuum chamber is completely vacuumed, the sample was scanned by copper anode with 5kV as accelerating voltage. Sample was observed at 500x, 1000x, and 5000x.

3.6 X-ray Diffraction

The crystal structure of the sludge powder was determined by using the bruker

Axs D8 Advance X-ray diffractometer with Cu Ka radiation. The scaning range (2θº) was set from 10º to 90º with the step size of 0.030º and 38.4 second as step size. The

XRD patern was then analized by using Xpert Highscore Plus to identify the phase and mineral present in the sample.

3.5 Determining the Urea Functionalisation

3.5.1 Fourier-transform infrared spectroscopy (FTIR)

Perkin-Elmer Spectrum One Fourier Transformation Infrared Spectrometer was used to detect the infrared spectrum that is absorbed or emitted by the solid, liquid or gas sample. FTIR can be used to determine the functional group in a sample.

The sample tiles that have been functionalised with urea is place on the stage of the

FTIR spectrometer. A probe was tighten on the sample to secure the sample on the stage. The sample was scanned using reflection method between the wavelength of

400-4000cm-1 with a scan rate of 16 cycles.

3.5.2 Urea Concentration Measurement

After drying the urea solution in the oven some amount of urea is not coated on to the sample and form urea crystal at the bottom of the beaker. To determine the

amount of urea functionalised on to the sample, the urea crystal in the beaker was dissolved using 100ml of deionised water. Sample solution was then collected and the

concentration of urea is determined by using UV-VIS spectrometer.

Figure 3. 6 Portable FTIR Machine

The clay sample functionalised with urea was also dissolved in 100 ml of DI water to determined how much urea will dissolved out of the sample when immersed in water. Sample solution was collected and the concentration of urea dissolved out of the clay sample was determined using UV-VIS spectrometer.

A calibration curve was plotted by preparing a 1 mol of 10ml urea solution and then diluting the solution 20 times. Each dilution cuts the concentration of the urea solution by half and then 5 ml of solution is extracted by using a 5ml micro pipette to be inspected by using UV-VIS spectrometer. The data was collected and plotted into a graph. The gradient of the graph was then determined and form the calibration equation shown as below:

Equation 3.1 Equation for the urea calibration curve

3.6 Heavy metal Adsorption

3.6.1 Determining Time Taken for Adsorption

The time taken for the ecoclay sample to reach its maximum heavy metal adsorption capacity was determined by dipping the sample in a heavy metal solution and sample solution was collected for each time interval. Cadmium heavy metal solution was prepared by using Aldrich Cadmium Nitrate Tetrahydrate 98%. 370.18 mg of

Cadmium Nitrate Tetrahydrate was weighted by using Satorious Electrical Balance.

Then, it was added into a 1L volumetric flask together with 1L of deionised water to form cadmium solution with concentration of 135mg/L concentration. 100ml of the

38 cadmium solution was poured in to a 250ml beaker and ecoclay sample with 0% rich husk was suspended in the solution. The ecoclay sample should be fully immersed in the cadmium solution. The beaker was then shake at 100 rpm using a Daihan SHO-D1

Orbital Shaker. 5ml of sample solution was taken from the beaker at 5mim, 15min,

30min, 1hr, 2hr, 4hr, 8hr, and 24hr time interval. The step was repeated for ecoclay sample that was functionalised with urea. The sample solution was stored in a plastic sample bottle for ICP-OES testing.

Figure 3. 7 Heavy metal adsorption process on the orbital shaker

3.6.2 Determining How Porosity Affect Heavy Metal Adsorption

50ml of the Cadmium solution prepared in 3.6.1 was poured into a 50ml centrifuge tube. The ecoclay tiles was cut into 2cm x 2cm x 0.5cm size by using tiles cutter then each sample is weighted using digital balance. The ecoclay sample tiles with 0% rice husk was then added in to the centrifuge tube containing the solution.

The centrifuge tube was capped tightly to prevent leakage. Then the centrifuge tube was placed on the Daihan SHO-D1 Orbital Shaker to shake for a duration determined in 3.6.1. The step was repeated with sample with 10% and 20% rice husk both with and without urea functionalisation

3.6.3 Inductively coupled plasma - optical emission spectrometry (ICP-OES)

ICP-OES is a method use to examine the composition of elements is liquid samples by using plasma and a spectrometer. The solution to analyze was conducted by a peristaltic pump though a nebulizer into a spray chamber. The produced aerosol was lead into an argon plasma. Plasma is the forth state of matter, next to the solid, liquid and gaseous state. In the ICP-OES the plasma was generated at the end of a quarts torch by a cooled induction coil through which a high frequency alternate current flows. As a consequence, an alternate magnetic field is induced which accelerated electrons into a circular trajectory. Due to collision between the argon atom and the electrons ionization occurs, giving rise to a stable plasma. The plasma is extremely hot, 6000-7000 K. In the induction zone it can even reach 10000 K. In the torch desolvation, atomization and ionizations of the sample takes place. Due to the thermic energy taken up by the electrons, they reach a higher "excited" state. When the electrons drop back to ground level energy is liberated as light (photons). Each element has an own characteristic emission spectrum that is measured with a spectrometer. The light intensity on the wavelength is measured and with the calibration calculated into a concentration.

Each sample solution was tested by inserting the probe into the solution which extract a small amount of liquid to be analyse by the ICP-OES. Data of the element

40 concentration in the solution can be obtain from the computer connected to the ICP-

OES machine.

Chapter 4 Results and Discussion

4.0 Introduction

The result of this investigation can be categorised into two part: ecoclay tiles characterisation and heavy metal adsorption capability of porous ecoclay tiles. These results will discussed in detail in 4.1 and 4.2 respectively.

4.1 Ecoclay Tiles Characterisation

Tiles that is fabricated using sludge as additive and rice husk as pore-forming agent.

The phase of the raw material of the tiles and the final product itself is determined using XRD. The functionalisation of chelating agent, urea on the Ecoclay tiles is determined using FTIR Spectroscopy. The physical structure of the Ecoclay tiles is observed by using SEM. The strength of the ecoclay tiles with different porosity is also tested using the MOR machine.

4.1.1 Determination of the parameters

The 1st batch of sample is inspected through visual inspection after the 1st firing sequence and before the glaze firing sequence. Figure 4.1 shows the observation of the 1st batch of ecoclay sample with different sludge composition.

Figure 4. 1 1st batch of ecoclay sample with different sludge composition From Figure 4.1, as the composition of the sludge increases from 110 wt% to

50 wt %, there is a few differences in the physical appearance of the ecoclay sample that can be found. Firstly, the colour of the ecoclay sample is found to be turning more and more reddish brown as the composition of the sludge increases. This is mainly due to the existence of hematite in the sludge(Ling et al., 2017). Besides that, the porosity of the ecoclay sample increases with the increase in sludge composition.

This is because there is some organic component in the sludge (Rodríguez et al.,

2010).

Pinhole

10 wt % sludge 20 wt % sludge

Crack

Pinhole

30 wt % sludge 40 wt % sludge

Crack

50 wt % sludge Figure 4. 2 shows the observation of the ecoclay sample after glazing.

Figure 4.2 shows the observation of the ecoclay samples after glazing process.

From the observation, as the composition of the sludge increases from 10 wt % to 30 wt %, the pinholes on the glaze increases. Ecoclay sample with sludge composition more than 40 wt %, crack starts to form on the glaze. The crack become more obvious as the composition of sludge increases from 40 wt % to 50 wt %. This phenomenon maybe due to the increases in the sludge content cause the coefficient of expansion of the ecoclay sample to be differ from the glaze. As more sludge is added, the greater the difference the coefficient of expansion between the sample and the glaze. Hence, as the composition of the sludge increases, the greater the defect on the glaze.

Figure 4. 3 Sample sticking to the mould. The slip with pore-forming agent was cast into a mould to produce the porous ecoclay sample. As the composition of the pore-forming agent increase, the sample become harder to be remove from the mould. Sample with 30 wt% pore-forming agent stuck to the mould and could not be removed without breaking the green body of the sample as shown in Figure 4.3. The reason that the sample stuck to the mould is that the sample is too damp to be removed from the mould due to the excessive pore-

45 forming agent that traps moisture in the sample green body. The pore-forming agent, rice husk, is mainly consist of fibre which can soak up moisture and prevent the moisture to be absorb by the plaster of paris mould. Hence, the green body is not dry enough and adhere to the mould even after 1 day of drying at normal room condition.

Therefore, only sample with maximum pore-forming agent up to 20 wt% is successfully produced.

4.1.2 Modulus of Rupture (MOR) Test

Modulus of Rupture test is done on ecoclay sample with different amount of pore-forming agent. This test is to determine the strength of the ecoclay tiles with different amount of pore-forming agent. Table 4.1 shows the result for the MOR test for the ecoclay sample.

Table 4. 1MOR value for Ecoclay

Sample Code Breaking Sample Sample MOR value

Load, F thickness, d Width, b (cm) (MPa)

(MPa) (cm)

ES30-R00 125 0.9 3.3 4.21

ES30-R10 71.9 0.75 3.3 3.49

ES30-R20 99.8 0.9 3.3 3.36

WT%

Figure 4. 4 Graph of MOR against porosity From table 4.1 we found that the MOR value of the ecoclay tiles sample decreases from 4.2 MPa to 3.3 MPa when the pore-inducing agent, rice husk weight percent increases from 0 wt% to 20 wt%. According to Ryshkewitch’s model the relative strength of a porous material is equal to the ratio of minimum solid area to the cell area normal to the reference stress (Chen et al., 2013). As the pore-inducing agent in the ecoclay sample increase, porosity of the ecoclay sample increases. In this case the increase in porosity will decrease the solid area of the ecoclay sample which is normal to the reference stress. Besides that, porosity also act as the stress concentration point when an external force is exerted on to the eocclay sample. The higher the porosity indicate more stress concentration point in the ecoclay sample further decreasing the strength of the ecoclay sample. However, the decreasing trend slows down as the wt% of pore-forming agent increases from 10 wt% to 20 wt%. According to research, the strength is supposes to follow a fairly linear decreasing trend (Le Huec et al., 1995).

The different in the trend may be cause by the agglomeration of the pore-forming

47 agent during the casting process. The agglomeration of the pore-forming agent can be observed in the SEM observation.

4.1.2 FTIR result of Functionalised Ecoclay Tiles

After the ecoclay sample is functionalised by using urea solution, the ecoclay samples is inspected for the effect of urea functionalisation on ecoclay sample by using FTIR

Spectroscopy. Figure 4.5 (a), (b), (c) shows the results of original ecoclay sample, ecoclay sample functionalised with urea and the comparison between both of the sample.

(a)

C=O N-H C-N N-H

(b)

C=O N-H C-N N-H

(c)

Figure 4. 5 FTIR result of (a) unfunctionalised ecoclay, (b) Functionalised ecoclay, (c) Comparison between result of unfunctionalised ecoclay and functionalised ecoclay.

From the FTIR result we can observed that there is some peaks that represent different functional group is detected in the FTIR spectrum. According to the pure urea FTIR spectrum shown in figure 4.3 those functional group are C=O, N-H, and C-

N functional groups.

Figure 4. 6 FTIR spectrum of pure urea (Manivannan and Rajendran, 2011).

From the FTIR spectrum of functionalised ecoclay shown in figure 4.5 (b), the stretching frequency of N-H functional group in urea functionalised on to the ecoclay appear at two wavelength which is which is 1598 cm-1 and 3435 cm-1. The C-N and

C=O functional group stretching frequency appears at 1466 cm-1 and 1684 cm-1 respectively. The FTIR spectrum result shows that there is traces of urea found in the functionalised ecoclay indicating the success of bonding the urea on to the ecoclay.

However, due to the low intensity of the spectroscopy result, not all of the urea in the urea solution prepared is bonded to the ecoclay during the functionalisation process.

Only a small amount of urea is bonded to the ecoclay sample.

4.1.3 Urea Concentration Measurement

Figure 4.7 shows that there is urea crystal left in the beaker after functionalising the ecoclay by using the drying method. The amount of urea left in the beaker is determined by measuring the urea solution that is dissolved from the urea left in the beaker with a UV-Vis spectroscopy.

Ecoclay sample

Crystalline urea

Figure 4. 7 Crystalline urea at the bottom of the beaker after functionalisation process. By using the calibration curve obtain from the calibration done by diluting a 2 mole urea solution 30 times, a calibration equation is obtained from the gradient of the trendline of the graph.

Calibration graph for urea concentration 1.4 y = 1.2038x + 0.0706 1.2 R² = 0.9893

0.8

0.6 Intensity (A) Intensity 0.4

0.2

0 0 0.2 0.4 0.6 0.8 1 Concentration (g/l)

Figure 4. 8 Calibration graph for urea solution for UV-VIS Table 4. 2 Amount of urea functionalised on to the ecoclay sample

Intensity (A) Concentration (g/l)

Initial urea solution - 0.661 concentration

Urea crystal remain in the 0.616 0.453 beaker

Urea desorption from the 0.149 0.066 ecoclay sample

Urea coated on to the - 0.141 ecoclay sample

Table 4.2 shows that there is large amount of urea remain in the beaker and not coated on to the ecoclay sample. 0.045 g of urea solution is left in the beaker which is 73.55% of the initial urea weight used to prepare the urea solution. Besides that, some of the urea coated on to the ecoclay sample might also dissolved out when

52 immersed in water. 0.066g of urea is dissolved out when immersed into 100ml of DI

Position (2theta) d-spacing (Ǟ) Relative intensity (%) Minerals name water which is 9.96% of the initial urea weight. After the desorption of urea, only

0.014g of urea have been coated on to the 6.5g of ecoclay sample.

4.1.4 X-ray Diffraction Analysis

The XRD pattern of the sludge is shown in Figure 4.9. After analysing the peak by using a computer programme, Xpert Highscore, the mineral compound found in the water sludge from Sungai Dua water treatment plant is identified as Quartz

(SiO2), Zeolite (SiO2), Hematite (Fe2O3), Dickite (Al2 (Si2O5) (OH)4), Kaolinite (Al4

(OH)8 (Si4O10)). The result obtained differs from the composition found in the sludge sample from Campos dos Goytacazes, State of Rio de Janeiro, Brazil, which consist of mineral compound such as kaolinite, quartz, gibbsite and goethite (Monteiro et al.,

2008). The difference in the mineral composition of the sludge is mainly due to the different in the water source that generated the sludge.

12.4917 7.08978 36.51 Dickite

18.5317 4.74889 1.3 Zeolite

20.0958 4.42376 23.53 Quartz

21.0624 4.21888 44.37 Dickite

25.0596 3.55358 38.32 Quartz

26.8501 3.32094 100 Zeolite

35.1765 2.54817 25.55 Hematite

36.1305 2.48085 12.95 Hematite

36.7773 2.44456 12.9 Zeolite

38.6634 2.32702 19.77 Zeolite

42.6413 2.11866 7.5 Quartz

45.7659 1.98198 6.63 Hematite

50.3668 1.81035 8.34 Quartz

60.1265 1.53759 8.74 Kaolinite

62.5742 1.48248 9.1 Zeolite

68.4466 1.36913 4.75 Quartz

Table 4. 3 Position and relative intensity of XRD peak of sludge with respective d- spacing

Figure 4. 9 XRD diffractogram of sludge Figure 4.9 XRD diffractogram of sludge the mineral compound detected from the XRD pattern result, the main mineral compound found in the sludge is Kaolinite, which comprise of 48.5 % of the sludge mineral compound composition. The second highest mineral content in the sludge is Dickite, which composed of 29.2 % of the sludge mineral compound composition. Other composition includes quartz, zeolite and hematite which consist of 9.1 %, 7.5%, and 5.6 % of the sludge composition respectively. Majority of the mineral composition matches the composition of the building materials, making sludge a suitable replacement material of the raw material of a building material.(Rodrigues and Holanda, 2015) The presence of hematite in the sludge which explains the reddish brown colour of the sludge and the tiles sample manufactured using sludge(Ling et al., 2017). Zeolite is a crystaline hydrated and

5- 4- microporous aluminosilicate which consist of AlO4 and SiO4 with tetrahedral crystal structure. The additional negative charge can be balanced out by the cations that is in the porous structure (Rios et al., 2009).

Table 4. 4 Position and relative intensity of XRD peak of fired clay with 30 wt% sludge with respective d-spacing

Pos. [°2Th.] d-spacing [Å] Rel. Int. [%] Mineral name

16.388 5.40645 4.72 Mullite

20.8527 4.26049 16.55 Quartz low

26.1713 3.39714 8.95 Mullite

26.6421 3.34662 100 Quartz low

27.481 3.2442 5.09 Leucite high

30.9029 2.89389 1.66 Mullite

33.1934 2.70128 2.88 Mullite

35.2051 2.54447 3.46 Leucite high

36.5248 2.4586 5.48 Quartz low

39.4519 2.28274 5.44 Quartz low

40.799 2.21351 3.68 Mullite

42.4372 2.12902 4.71 Quartz low

45.7735 1.98095 1.4 Quartz low

50.1173 1.81883 11.37 Quartz low

54.8893 1.67253 2.23 Quartz low

57.4018 1.60488 1.01 Mullite

59.9389 1.54227 4.32 Quartz low

60.5652 1.53188 1.96 Mullite

64.4371 1.44636 1 Mullite

68.2309 1.37255 3.26 Quartz low

79.9189 1.20022 1.62 Quartz low

81.3234 1.18434 1.15 Quartz low

Figure 4. 10 XRD diffractogram of fired clay with 30 wt% sludge. Figure 4.10 shows the XRD diffractogram of the fired clay with 30 wt% sludge (ES30). After analysing the diffractogram with computer programme, Xpert

Highscore, the sample ES30 is found to be consist of Quartz (SiO2), Mullite

(Al4.68Si1.32O9.66), Leucite (Na.15K.85AlSi2O6), and Hematite (Fe2O3). By comparing the result obtain from the XRD analysis of sludge and sample ES30, a few mineral phases in sludge is not found in sample ES30 which contain 30 wt% of the sludge. This is because there is phase changes during the firing process. Kaolinite phases that is found in the sludge is transformed in to the mullite phase during the firing process of sample ES30. The transformation of kaolinite to mullite phase at firing temperature above 1050℃ can be can be separated into several reaction. When kaolinite is heated to temperature of 400~500℃, dehydroxylation happens and H2O is liberated forming metakaolinite (Eqn 4.1). During dehydroxylation, the octahedral sheet of the

Al(O,OH)6 might be disturbed. However, the SiO4 tetrahedral sheet is not affected due to the more stable hydroxyl group. After the firing temperature achieved 950℃, the SiO4 group combined with the AlO6 group, forming a short range order structure called Al-Si spinel (Eqn 4.2) (Chen et al., 2004). The Al-Si spinel phase maybe

57 formed due to the opotatic transformation of metakaolinite (Brindley and Nakahira,

1959). Mullite phase started formed at 1000 °C and bearing the similar crystallographic structure of Al–Si spinel phase and metakaolinite, causing the c axis of mullite crystal is parallel to the <110> orientation of the Al–Si spinel phase.

Instantaneous nucleation process and the short distance diffusioncan further accelerate the growth of the mullite phase at temperature above 1050℃ (Eqn 4.3) (Chen et al.,

2004). Eqn 4.1

Eqn 4.2

Eqn 4.3

From the XRD diffractogram analysis, the main mineral compound found in the sample ES30 is Mullite which consist of 48 % of the composition of sample ES30.

Mullite is formed when the kaolinite which is the main composition in the raw material of the sample which is ball clay and sludge undergoes phase transformation during the firing process. Quartz is the second most abundant mineral compound in the sample ES30 consist of 34.7% of the composition of sample ES30. Quartz is mainly formed when the silica in the raw material undergoes phase change during the firing process. Other minor mineral in the sample ES30 is Leucite and hematite which consist of 8.9% and 8.4% respectively. Leucite is a member of the feldspathoid group which act as a fluxing material that is added to the sample to reduce the firing temperature of a ceramic. Hematite is a component from the sludge which gives the reddish brown colour to the sample ES30 (Ling et al., 2017).

Figure 4. 11 XRD diffractogram of urea functionalised clay.

Table 4. 5 Position and relative intensity of XRD peak of fired clay with 30 wt% sludge with respective d-spacing

Pos. [°2Th.] d-spacing [Å] Rel. Int. [%] Mineral name 16.688 5.3114 5.28 Mullite 21.1508 4.20295 22.2 Quartz low 26.9281 3.30687 96.44 Hematite 27.8128 3.21722 7.08 Carbamide (urea) 31.2259 2.86794 4.42 Mullite 33.4879 2.67846 4.96 Mullite 35.4642 2.5308 5.59 Mullite 36.8374 2.43868 8.56 Hematite 39.7672 2.27195 8.3 Leucite high 41.083 2.19852 4.8 Mullite 42.7241 2.11586 6.27 Quartz low 46.056 1.96955 3.38 Leucite high 50.405 1.81455 8.79 Carbamide (urea) 54.2804 1.69005 1.33 Mullite 55.1539 1.66533 3.64 Quartz low 57.663 1.60232 1.32 Quartz low 60.2107 1.53617 6.14 Quartz low 60.8707 1.5203 2.64 Hematite 64.6502 1.44096 1.39 Mullite 68.4987 1.36803 5.09 Quartz low 80.1849 1.19887 1.21 Leucite high 81.5536 1.18181 1.33 Quartz low

Figure 4.12 shows the XRD diffractogram of the functionalised ecoclay sample. The composition of the sample is determined by analysing the XRD diffractogram by using Xpert Highscore. The sample is consist of Quartz (SiO2),

Mullite (Al4.68Si1.32O9.66), Leucite (Na.15K.85AlSi2O6), Hematite (Fe2O3) and Carbamide

(CO (NH2)2). The composition of functionalised ecoclay sample is the same as the sample ES30 but with the addition composition of carbamide, which is a type of urea.

4.1.5 Scanning Electron Microscope

The fired clay with rice husk is observed under the SEM to observe the microstructure of the ecoclay sample. The Sample was observed under 3 magnification of 500x, 1000x, and 5000x. Table 4.6 shows the result of SEM observation on the sample.

From the observation below, we can see that fired bond formed between the clay particles after fired at 1080ºC for a soaking time of 4 hour. The fired bond form provide physical strength for the final product. Some pores was observed where the pore-forming agent, rice husk is burned away during the sintering process. The pores formed in the sample reduces the sample density and also increases the surface area of contact for the cadmium removal application.

Table 4. 6 SEM result on porous Ecoclay sample

Magnification Observation

500x

1000x

5000x

Table 4. 7 SEM observation of Ecoclay sample with different amount of pore-forming agent

Sample Observation

ES30-R00

Pores

ES30-R10

Pores

ES30-R20

Pores

From the observation shown in table 4.7, the SEM image shown that there is an increase in the numbers of pores per unit area as the weight percent of the pore- forming agent added into the slip increases. The pore-forming agent in this case act as an endo-templating method of fabricating a porous material. The pore-forming agent in the ecoclay sample is burned away during the firing process of the ecoclay sample leaving behind an empty void in the sample which becomes the pores in the sample.

From the observation in table 4.3, the pores in sample ES30-R00 and ES30-R10 is have a relatively uniform round shape compared to sample ES30-R20.

Figure 4.13 shows the pore size of ecoclay sample with different amount of pore-forming agent. Small size pores (average radius of 125µm) is observed from sample ES30-P00 which have 0 wt% of pore-forming agent added. The formation of the small size pores is due to there is some organic matters in the sludge which burned off during firing forming pores in the ES30-P00 sample which have 0 wt% pore- forming agent added. For both sample ES30-P10 and ES30-P20, pores with the same size (average radius of 640µm) is found. The formation of the bigger pores is due to the addition of pore-forming agent to the ecoclay body which the pore-forming agent is burned off during the firing process. Large size pores with irregular shape is observed only in the ES30-P20 sample. The large size irregular shape exist in ES30-

P20 sample is speculated to formed due to the agglomeration of the pore-forming agent in the slip during the casting process.

Figure 4. 12 Large irregular shape found in sample ES30-P20

4.2 Heavy Metal Adsorption Capability of Porous Ecoclay Tiles

4.2.1 Time Taken to Reach Maximum Adsorption Capacity

Sample with 0wt% pore-inducing agent is used to test for the time taken for the ecoclay sample to reach its maximum adsorption capacity. Both functionalised and unfunctionalised ecoclay sample is tested and the result is shown in Table 4.8 and

Figure 4.15 below.

Table 4. 8 Time Taken For the Ecoclay Sample To Reach Maximum Adsorption Capacity

Original Urea hour min diluted actual diluted actual

0 0.1 135 135

0.08333 5 56.08 112.16 43.88 87.76

0.25 15 52.29 104.58 50.02 100.04

0.5 30 53.17 106.34 47.39 94.78

1 60 58.2 116.4 31.59 63.18

2 120 48.91 97.82 29.47 58.94

4 240 54.3 108.6 25.06 50.12

8 480 59.41 118.82 21.44 42.88

24 1440 55.04 110.08 41.59 83.18

140

120

100

Original 60 Urea

40 Concentration mg/l)urea Concentrationmg/l)urea functionalisationthe 20

0 0 200 400 600 800 1000 1200 1400 1600

Time (min)

Figure 4. 13 Time Taken To Reach Maximum Adsorption Uptake

From figure 4.15, the graph shows that there is a great difference between the adsorption capability between functionalised and unfunctionalised ecoclay sample.

Ecoclay sample functionalised with urea shows a significant increase in the cadmium adsorption capability. The adsorption capacity for a 6g functionalised ecoclay sample reached its maximum capacity when 92.12 mg/l of cadmium is removed from the 135 mg/l cadmium solution in 8 hour, leaving behind 42.88 mg/l cadmium solution. The maximum adsorption capacity of the ecoclay sample functionalised with urea is 15.35 mg/l/g of ecoclay sample. The graph also shows that the optimum adsorption time for the functionalised Ecoclay sample is 8 hours. Any further increase in the time of contact between the ecoclay sample and the cadmium solution will cause desorption to happen and decrease in adsorption efficiency.

4.2.2 Effect of Amount of Pore-Forming Agent on the Cadmium Adsorption

Capacity

Different amount of pore-forming agent is added to the ecoclay composition to determine the effect of porosity on the cadmium removal efficiency of ecoclay sample.

From the graph shown in Figure 4.16, the cadmium removal efficiency of functionalised ecoclay sample is found to be decrease as the wt% of pore-forming agent increases. This result is due to the different in pore size of the adsorption medium. The most common pore size use for heavy metal adsorption is mesoporous materials which have pore size ranging from 2nm to 50nm (McManamon et al., 2012).

The organic composition in the sludge form small pores in the ecoclay sample providing increased surface area for adsorption to take place. The pore-forming agent, rice husk added produce a larger size pores which reduces the available surface area

68 for adsorption. Hence, as the pore-forming agent wt% increases, the adsorption efficiency of the ecoclay sample decreases.

160 initial concentration

140

120 100 Ecoclay 80 60 Urea functionalised

40 ecoclay concetration(mg/l) 20 0 0 5 10 15 20 25 wt% of rice husk (wt%)

Figure 4. 14 Reduction of cadmium by ecoclay and functionalised ecoclay at 10 wt% and 20 wt% rice husk fabrication.

Table 4.9 and 4.10 and Figure 4.17 shows the weight of each ecoclay sample used for cadmium removal and the removal efficiency per gram of each sample. From the graph in Figure 4.17, the adsorption efficiency per gram of both functionalised and non-functionalised ecoclay increases when the amount of rice husk increases from

0wt% to 10 wt%. The introduce of rice husk produce a large pore in the ecoclay sample which increases the surface area for the adsorption to occur (Jin et al., 2017).

However, as the wt% of rich husk increases from 10 wt% to 20 wt%, the cadmium removal efficiency did not follow the increasing trend. This is cause by the agglomeration of the rice husk during the casting process.

Table 4. 9 Weight of ecoclay sample and the removal efficiency per gram of ecoclay sample

Rich sample Husk type (wt%) sample 1 sample 2 sample 3

removal removal removal efficiency efficiency efficiency per gram sample removal per gram of sample removal per gram of removal of weight efficiency sample weight efficiency sample sample efficiency sample (g) (mg/l) (mg/l/g) (g) (mg/l) (mg/l/g) weight (g) (mg/l) (mg/l/g) 0 6.85 56.20 8.20 6.09 41.90 6.89 6.03 40.20 6.66 Original 10 4.16 58.50 14.07 3.90 43.10 11.04 3.65 45.90 12.59 20 2.86 38.40 13.43 4.43 46.60 10.51 3.99 50.20 12.57 0 6.53 113.10 17.31 6.13 71.00 11.58 6.24 48.00 7.69 Urea 10 4.18 78.70 18.82 3.80 87.60 23.08 4.73 53.60 11.32 20 3.62 98.00 27.06 3.38 44.60 13.19 3.38 45.80 13.53

Figure 4. 15 Graph of wt% of rice husk against removal efficiency per gram of ecoclay

Chapter 5 Conclusion and Recommendation

5.1 Conclusion

The objective of this study have been achieved. The pore-forming agent content in the clay body is optimized at 10 wt%. By functionalising the ecoclay tiles with urea, the cadmium removal capability can be enhanced.

The porosity of the ecoclay sample increases as the amount of the pore- forming agent added to the sample increases. At 20 wt% pore-forming agent, the pores in the ecoclay sample ES30-R20 is found to be bigger than that of in sample

ES30-R10 which both using the same pore-forming agent. This phenomenon is cause by the agglomeration of the pore-forming agent during the casting process. Even though ecoclay sample ES30-R10 and ES30-R20 both are porous material with different amount of pore-forming agent, the increase in the pore-forming agent does not increase the cadmium removal efficiency. The optimum amount of pore-forming agent for maximum adsorption efficiency is 10 wt% of the clay composition. The optimum time of contact between the functionalised ecoclay sample and the cadmium solution is 8 hour. Longer time of contact will cause desorption to happen which slightly decreases the cadmium removal efficiency.

Future Recommendation

For future study on developing a porous ecoclay product for heavy metal removal, several recommendation for improvement is suggested below to further increase the yield of the product.

i. A bigger mould with simple shape is used for the casting process to

ensure easy removal of the green body.

ii. Dedicated deflocculant can be added to the slip correspond to the type

of pore-forming agent used to prevent agglomeration and proper

distribution of pore-forming agent during the casting process.

iii. Improved urea functionalisation process can be used instead of drying

the urea solution in an oven onto the ecoclay sample to reduce the

energy consumption for the functionalisation process.

iv. Different concentration of heavy metal solution can be used to

determine the adsorption isotherm of the functionalised ecoclay sample.

v. The firing condition of the ecoclay product with organic pore-forming

agent can be modified to convert the organic pore-forming agent in the

porous ecoclay sample into corresponding activated carbon to further

increase the heavy metal removal efficiency.

References

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