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Adsorption of Lead (Ii) Ion Clay Using Clacined Okada Clay

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CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF STUDY
Removal of heavy metals such as cadmium, lead, nickel, chromium and copper from aqueous solution is necessary because of the hazardous effect it does on the environment ,thereby making environmental protection important, however waste solutions containing heavy metal elements need treatment systems that can remove these contaminants effectively (Harvey and Chantawong, 2001). Frequent appearance of these metals in waste streams from many industries, including electroplating, metal finishing, metallurgical, tannery, chemical manufacturing, mining and battery manufacturing. This problem has received considerable attention in recent years, primarily due to the concern that those heavy metals in waste streams can be readily adsorbed by marine animals and directly enter the human food chain, thus presenting a high health risk to consumers (Lin et al., 2000).
A number of technologies for treating contaminated effluents have been developed over the years. The most important of these techniques include chemical precipitation, filtration, ion- exchange, reverse osmosis and membrane systems. However, all these techniques have their inherent advantages and limitations in application. In the last few years, adsorption has been shown to be an alternative method for removing dissolved metal ions from liquid wastes (Bayat, 2002).
The removal of heavy metal ions from industrial wastes using different adsorbents is currently of great interest. However, in order to minimize processing costs, several recent investigations have focused on the use of low cost adsorbents [e.g. agricultural by-products (Samantaroy et al., 1997), waste materials (Namasivayam and Yamuna, 1995:561-578), biosorbents (Ülkϋ and I Haluk, 2001), and clay materials (Harvey and Chantawong, 2001). Adsorbents, mainly clay minerals, are readily available, inexpensive materials and offer a cost-effective alternative to conventional treatment of such mentioned waste streams (Sanchez et al., 2002).
In order to further such studies, the present research work deals with an investigation into the use of a thermal treated Okada clay (calcined clay) as adsorbent for the removal of Pb(II), Ni(II), Cr(VI) and Cu(II) from simulated waste solutions. In this investigation, calcined Okada clay has been chosen as the adsorbing material because of its excellent sorptive properties.
Heavy metals in solution can be present either as free-ions or complexed with organic and inorganic ligands (Alleoni et al., 2003). Therefore, the affinity of Pb²⁺ for calcined clay would be evaluated by single component heavy-metal solutions, whereas a multicomponent solution would be used to verify the affinity of each metal in the presence of competing pollutants (Brigatti et al., 2000).
In the current study, Okada clay would be used in the adsorption of Pb²⁺ aqueous solution. This is to know the capability and adsorption rate of this absorbent; also the equilibrium and kinetics of adsorption of the clay will be determined.

1.2 AIM AND OBJECTIVES
1.2.1 Aim
The aim of this study is to demonstrate the use of thermally treated Okada clay as an alternative media to the conventional activated carbon for adsorption of Lead (II) ions (Pb2+) from aqueous solutions.
1.2.2 The objectives of this work are to: i. Set up equilibrium batch studies of the adsorption of Pb2+ from aqueous solutions at various adsorbent dosage ii. Estimate the adsorption capacity of adsorbent iii. Characterize the clay in terms of the physical and chemical properties iv. Analyse the experimental data using different isotherm models 1.3 JUSTIFICATION
Commercial activated carbon is regarded as the most effective adsorbent for heavy metal. Due to its high cost however, alternative low cost adsorbents have attracted the attention of several investigators to provide an alternative. Such a newly mined, low-cost material, calcined Okada clay, would be used in this investigation as adsorbent for various heavy metals. However, its effectiveness.
1.4. SOPE OF WORK i. Collection, treatment and characterization of Okada clay. ii. Calcine clay sample at 500℃ iii. Evaluation of the effectiveness of the clay samples as adsorbents. iv. Laboratory batch study to evaluate the adsorption capacity. v. Analysis of isotherms models by linear regression analysis for the sorption of Pb2+ from aqueous solutions onto the clay sample.

CHAPTER TWO
LITERATURE REVIEW
2.0 INDUSTRIAL WASTEWATER
2.1 INTRODUCTION
Since the end of the last century a large amount of products, such as medicines, disinfectants, contrast media, laundry detergents, surfactants, pesticides, dyes, paints, preservatives, food additives, and personal care products, have been released by chemical and pharmaceutical industries threatening the environment and human health. Currently there is a growing awareness of the impact of these contaminants on groundwater, rivers, and lakes (Culp, 1978).

Industrialization has continued to threaten freshwater resources because industrial activities are synonymous with huge demands for freshwater. Industrial use accounts for around one-quarter of worldwide demand. Such demand has led to increasingly stringent environmental legislation and associated escalating costs of water supply and discharge.
Owing to the enormity of freshwater required for industrial processes and limitations on continuous dependence on this singular source, wastewater reuse is an option that is being accorded serious consideration by professionals in water industries. The reuse option is impeded by the stringent environmental legislation and high cost of treating wastewater to the level of reuse. Recycled wastewater could serve as a medium for solvents and heat transfer in industries. Large volumes of water and relatively low water quality are required for cooling processes but much higher quality water is needed for boiler operations and as a solvent because of the high deleterious effects of pollutants in the boiler systems. The higher water quality required for some industrial operations has imposed a higher process cost for recycling, but the end product water is nonetheless required only for physical heat transfer (Judd 1999).

Owing to the high cost necessary to recycle water for reuse, many industries opt for the use of freshwater which has continued to deplete the available water for domestic consumption. To stem this tide, an affordable recycling option is required for industries to fully embrace the wastewater reuse option. An array of materials has been explored as a low-cost treatment system for industrial wastewater treatment. It has been reported that peat is effective in the removal of textile dyes, and pesticides (Brown et al. 1979; Williams and Crawford 1983). Some applications using wood bark and peat have also been reported for both physicochemical and biological wastewater treatment (Lens et al. 1994).

The world is facing a global water quality crisis. Continuing population growth and urbanization, rapid industrialization, and expanding and intensifying food production are all putting pressure on water resources and increasing the unregulated or illegal discharge of contaminated water within and beyond national borders. This presents a global threat to human health and wellbeing, with both immediate and long term consequences for efforts to reduce poverty whilst sustaining the integrity of some of our most productive ecosystems (Osborn and Savelli. 2010). There are many causes driving this crisis, but it is clear that freshwater and coastal ecosystems across the globe, upon which humanity has depended for millennial, are increasingly threatened. It is equally clear that future demands for water cannot be met unless wastewater management is revolutionized.

Wastewater can be contaminated with a myriad of different components like pathogens, organic compounds, synthetic chemicals, nutrients, organic matter and heavy metals. They are either in solution or as particulate matter and are carried along in the water from different sources and affect water quality. These components can have bio-cumulative, persistent and synergistic characteristics affecting ecosystem health and function, food production, human health and well-being. Over 70 percent of the water has been used in other productive activities before entering urban areas. Wastewater management is a key component of health risk management (Pimentel, 2008).
Wastewater disposal is becoming a problem in developing countries as large quantities of municipal waste and industrial effluent are being produced due to increased urbanization and industrialization respectively (Alloway& Ayres, 1995). The major challenge is how to deal with the waste which is being released at a rate faster than its proper disposal.
2.1.2 TREATMENT
There is not a standard design to treat all wastewaters due to the characteristics of the process specific waste. Each site requires a design specific to the process at hand, but some combination of the following pretreatment, primary treatment, secondary treatment, and processing are normally used. As a rule of thumb, we would like to separate several pollutants in one step and use several steps to increase the degree of treatment.

2.1.2.1 TREATMENT PROCESSES
2.1.2.1.1 PRIMARY (MECHANICAL) TREATMENT
Primary treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as “mechanical treatment”, although chemicals are often used to accelerate the sedimentation process. Primary treatment can reduce the BOD of the incoming wastewater by 20-30% and the total suspended solids by some 50-60%. Primary treatment is usually the first stage of wastewater treatment. Many advanced wastewater treatment plants in industrialized countries have started with primary treatment, and have then added other treatment stages as wastewater load has grown, as the need for treatment has increased, and as resources have become available.

2.1.2.1.2 SECONDARY (BIOLOGICAL) TREATMENT
Secondary treatment removes the dissolved organic matter that escapes primary treatment. This is achieved by microbes consuming the organic matter as food, and converting it to carbon dioxide, water, and energy for their own growth and reproduction. The biological process is then followed by additional settling tanks (“secondary sedimentation", see photo) to remove more of the suspended solids. About 85% of the suspended solids and BOD can be removed by a well running plant with secondary treatment. Secondary treatment technologies include the basic activated sludge process, the variants of pond and constructed wetland systems, trickling filters and other forms of treatment which use biological activity to break down organic matter.
2.1.2.1.3 TERTIARY TREATMENT
Tertiary treatment is simply additional treatment beyond secondary.Tertiary treatment can remove more than 99 percent of all the impurities from sewage, producing an effluent of almost drinking-water quality. The related technology can be very expensive, requiring a high level of technical know-how and well trained treatment plant operators, a steady energy supply, and chemicals and specific equipment which may not be readily available. An example of a typical tertiary treatment process is the modification of a conventional secondary treatment plant to remove additional phosphorus and nitrogen.
Disinfection, typically with chlorine, can be the final step before discharge of the effluent. However, some environmental authorities are concerned that chlorine residuals in the effluent can be a problem in their own right, and have moved away from this process. Disinfection is frequently built into treatment plant design, but not effectively practiced, because of the high cost of chlorine, or the reduced effectiveness of ultraviolet radiation where the water is not sufficiently clear or free of particles.be discharged directly to surface or ground waters.
2.1.3 INDUSTRIAL WASTEWATER CHARACTERISTICS
The physical and chemical characterization presented below is valid for most wastewaters, both municipal and industrial.
2.1.3.1 PHYSICAL CHARACTERISTICS include:solids content,color,Odor,temperature
2.1.3.1 .1 SOLID CONTENT
The solids content in a wastewater consist of the insoluble or suspended solids and the soluble compounds dissolved in water. The suspended solids content is found by drying and weighing the residue removed by the filtering of the sample. When this residue is ignited the volatile solids are burned off. Volatile solids are presumed to be organic matter, although some organic matter will not burn and some inorganic salts break down at high temperatures. The organic matter consists mainly of proteins, carbohydrates and fats. Between 40 and 65 % of the solids in an average wastewater are suspended. Settleable solids, expressed as millilitres per litre, are those that can be removed by sedimentation. Usually about 60 % of the suspended solids in a municipal wastewater are settleable (Ron & George, 1998). Solids may be classified in another way as well: those that are volatilized at a high temperature (600 °C) and those that are not. The former are known as volatile solids, the latter as fixed solids. Usually, volatile solids are organic.

2.1.3.1.2. COLOUR
Colour is a qualitative characteristic that can be used to assess the general condition of wastewater. Wastewater that is light brown in colour is less than 6hours old, while a light-to-medium grey colour is characteristic of wastewaters that have undergone some degree of decomposition or that have been in the collection system for some time. Lastly, if the colour is dark grey or black, the wastewater is typically septic, having undergone extensive bacterial decomposition under anaerobic conditions. The blackening of wastewater is often due to the formation of various sulphides, particularly, ferrous sulphide. This results when hydrogen sulphide produced under anaerobic conditions combines with divalent metal, such as iron, which may be present. Colour is measured by comparison with standards
2.1.3.1.3 ODOUR
The determination of odour has become increasingly important, as the general public has become more concerned with the proper operation of wastewater treatment facilities. The odour of fresh wastewater is usually not offensive, but a variety of odorous compounds are released when wastewater is decomposed biologically under anaerobic conditions. The different unpleasant odours produced by certain industrial wastewater are presented in Table 1-1.
Table 1-1 Unpleasant odours in some industries (Brault, 1991) Industries | Origin of odours | Pharmaceutical industries | Fermentation produces | Food industries | Fermentation produces | Food industries (fish) | Amines, sulphides, mercaptans | Rubber industries | Sulphides, mercaptans | Textile industries | Phenolic compounds | Paper pulp industries | H2S, SO2 | Organics compost | Ammonia, sulphur compounds |

2.1.3.1.4 TEMPERATURE
The temperature of wastewater is commonly higher than that of the water supply because warm municipal water has been added. The measurement of temperature is important because most wastewater treatment schemes include biological processes that are temperature dependent. The temperature of wastewater will vary from season to season and also with geographic location. In cold regions the temperature will vary from about 7 to 18 °C, while in warmer regions the temperatures vary from 13 to 24°C (Ron & George, 1998).
2.1.4 CHEMICAL CHARCTERISTIC
2.1.4.1 MEASUREMENT OF ORGANIC CONTENT
Laboratory methods commonly used today to measure gross amounts of organic matter in wastewater include:Biochemical oxygen demand (BOD),Chemical oxygen demand (COD),Total organic carbon (TOC).
2.1.4.1.1 BIOCHEMICAL OXYGEN DEMAND (BOD)
Biochemical Oxygen Demand is not a specific pollutant. BOD is a measure of the amount of oxygen required by bacteria and other microorganisms to oxidize any organic matter in the water biochemically.BOD is an indirect measure of the concentration of organic contamination in the water. The more organic matter present, the greater the amount of oxygen that microorganisms will consume in oxidizing the wastes to CO2 and H2O.

2.1.4.1.2 CHEMICAL OXYGEN DEMAND (COD)
The equivalent amount of oxygen required to oxidize any organic matter in a water sample by means of a strong chemical oxidizing agent is called chemical oxygen demand.
2.1.4.1.3 TOTAL ORGANIC CARBON (TOC)
Another means for measuring the organic matter present in water is the TOC test, which is especially applicable to small concentrations of organic matter.
2.1.5 SOURCES OF WASTEWATER
Wastewater can originate from many sources such as; homes, businesses and industries. Storm water, surface water and ground water can enter the wastewater collection system and add to the volume of wastewater. The source of a wastewater will determine its characteristics and how it must be treated. For example, wastewater from homes and businesses (domestic wastewater) typically contains pollutants such as; fecal and vegetable matter, grease and scum, detergents, rags and sediment. On the other hand, wastewater from an industrial process (industrial wastewater) may include; toxic chemicals and metals, very strong organic wastes, radioactive wastes, large amounts of sediment, high temperature waste or acidic/caustic waste. Wastewater could even come from streets and parking lots during a rainstorm (storm wastewater) that could contain; motor oil, gasoline, pesticides, herbicides and sediment.
Most modern wastewater treatment facilities are designed to treat domestic wastewater. Industrial wastewaters that contain high strength waste, toxic waste or acid/caustic waste may have to be pretreated to make them safe to discharge to the collection system. If not, the processes at the wastewater treatment plant receiving the waste could be disrupted. Storm wastewater should be collected and treated (when necessary) separately from domestic and industrial wastewater.

2.2 HEAVY METALS
It is often used as a group name for metals and semimetals (metalloids) that have been associated with contamination and potential toxicity or ecotoxicity. Heavy metal is a member of a loosely defined subset of elements that exhibit metallic properties
The hazardous ill effects of heavy metals on the environment and public health is a matter of serious concern. Biosorption is emerging as a sustainable effective technology. Heavy metals in water resources are one of the most important environmental problems of countries. The intensification of industrial activity and environmental stress greatly contributes to the significant rise of heavy metal pollution in water resources making threats on terrestrial and aquatic life. The toxicity of metal pollution is slow and interminable, as these metal ions are non-bio-degradable. The adsorption capacity of Xanthium Pensylvanicum towards metal ions such as Pb2+, Cu2+, Zn2+, Cd2+, Ni2+, Co2+ and Fe3+, was studied. The adsorption capacity was performed by batch experiments as a function of process parameters (such as sorption time and pH). Experimental results showed that the removal percentages increasing of metal ions at pH=4, initial concentration of metal ions 10 mg/L, and after 90 min of shaking was: Zn2+ < Cd2+ < Cu2+ < Pb2+ < Ni2+ < Fe3+ < Co2+.

2.2.1 LEAD
Lead has environmental importance due to its well-known toxicity and intensive use in industries such as storage-battery manufacture, printing, pigment manufacturing, petrochemicals, fuel combustion and photographic materials. Assimilation in the human body of relatively small amounts of Pb(II) over a long period of time can Lead to malfunctioning of certain organs and chronic toxicity. Pb(II) is one of these heavy metals, and can be introduced into liquid wastes from different industries. In water, Pb(II) tends to accumulate in aquatic organisms through the food chain and by direct uptake. It can damage practically all tissues, particularly the kidneys and the immune system. Intense exposure to high Pb(II) levels (from 100 to 200 gram/day) causes encephalopathy with the following symptoms: vertigo, insomnia, migraine, irritability, and even convulsions, seizures, and coma. Sixty percent of Pb(II) is used for the manufacturing of batteries (automobile batteries, in particular), while the remainder is used in the production of pigments, glazes, solder, plastics, cable sheathing, ammunition, weights, gasoline additive, and a variety of other products. Such industries continue to pose a significant risk to workers, as well as surrounding communities. There is a need to treat the waste water to bring the concentration of toxic elements below the recommended release limit.
2.2.2. NICKEL
Nickel is a toxic heavy metal that is widely used in silver refineries, electroplating, zinc base casting and storage battery industries. The chronic toxicity of nickel to humans and the environment has been well documented. For example, high concentration of Nickel (II) causes cancer of lungs, nose and bone. It is essential to remove Ni(II) from industrial wastewater before being discharged. For this reason, it is generally used the advanced treatment processes such as chemical reduction, ion exchange, reverse osmosis, electro dialysis, and activated carbon adsorption. Since the cost of these processes are rather expensive, the use of agricultural residues or industrial by-product having biological activities have been received with considerable attention (Halil Hasar, 2003). Thus, many materials have been examined.

2.2.3. VARIOUS EFFECTS OF HEAVY METALS
Heavy metal pollution is one of the problems of the ecosystem. Toxic metal compounds coming to the earth's surface not only reach the earth's waters (seas, lakes, ponds and reservoirs), but can also contaminate underground water in trace amounts by leaking from the soil after rain and snow. Therefore, the earth's waters may contain various toxic metals.
Drinking water is obtained from springs which may be contaminated by various toxic metals. One of the most important problems is the accumulation of toxic metals in food structures. As a result of accumulation, the concentrations of metals can be more than those in water and air. The contaminated food can cause poisoning in humans and animals.
Although some heavy metals are necessary for the growth of plants, after certain concentrations heavy metals become poisonous for both plants and heavy metal microorganisms.
Another important risk concerning contamination is the accumulation of these substances in the soil in the long term. Heavy metals are held in soil as a result of adsorption, chemical reaction and ion exchange of soil. Heavy metals have an effect on the enzymes. It has been determined that various metal ions hinder various enzymes responsible for mineralization of organic compounds in the earth. Therefore, studies on the removal of heavy metal pollution are increasing.
Adsorption is usually described through isotherms, that is, functions which connect the amount of adsorbate on the adsorbent, with its pressure (if gas) or concentration (if liquid).models describing process of adsorption, namely: Freundlich isotherm, Langmuir isotherm, BET isotherm, etc.
2.3 WATER TREATMENT
Water treatment is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water. The goal of this process is to produce water fit for a specific purpose. Most water is disinfected for human consumption (drinking water) but water purification may also be designed for a variety of other purposes, including meeting the requirements of medical, pharmacological, chemical and industrial applications. (World Health Organization, 2007).
2.4 ADSORPTION
Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a molecular or atomic film (the adsorbate). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution. Adsorption can perform many separations that are impossible or impractical by convential techniques, such as distillation, absorption, and even membrane-based system. Lately, applications for adsorption have expanded rapidly because of sharply rising environmental or quality requirements. Likewise, advances in adsorbent technology have made it possible to meet many of those demands. Recently developed adsorbents are now available “off-the-shelf “and in most cases they can perform satisfactorily. Nevertheless, new adsorbents are constantly being synthesized that have dramatically improved properties which translate into better performance. A new adsorbent may take months or years to perfect, however, so a rule-of –thumb is that there is never enough time to develop a new adsorbent for an urgent new applications. Advanced Engineers and scientist have developed a better understanding of the mechanisms of adsorption. In fact, this has led to faster and more accurate simulations and designs of adsorption processes. For the past thirty years, it has been possible to solve the relevant equations numerically. Recently, that ability has been augmented by faster, more accessible machines, as well as modes that are able to isolate the relevant effects without being bogged down by too many fitted parameters. The best known application of adsorption fall in the category of purification, e.g. municipal water treatment to remove traces of pollutants, as well as “taste” or “odor.” Another widespread application, although much smaller in terms of adsorbent consumption, is the pressure-swing air dryer found on semis for their air–brake systems. Adsorption is becoming more popular as a unit operation, as a means for separating fluid mixtures. The term sorption encompasses both processes, while desorption is the reverse process. Adsorption is operative in most natural physical, biological, and chemical systems, and is widely used in industrial applications such as activated charcoal, synthetic resins and water purification.
Similar to surface tension, adsorption is a consequence of surface energy. In a bulk material, all the bonding requirements (be they ionic, covalent or metallic) of the constituent atoms of the material are filled. But atoms on the (clean) surface experience a bond deficiency, because they are not wholly surrounded by other atoms. Thus it is energetically favorable for them to bond with whatever happens to be available. The exact nature of the bonding depends on the details of the species involved, but the adsorbed material is generally classified as exhibiting physisorption or chemisorption.
2.4.1 TYPES OF ADSORPTION 1. Physisorption or Physical adsorption 2. Chemisorption or Chemical adsorption
2.4.1.1 Physisorption or physical adsorption is a type of adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular) interactions, which are also responsible for the non-ideal behavior of real gases.
2.4.1.2 Chemisorption is a type of adsorption whereby a molecule adheres to a surface through the formation of a chemical bond, as opposed to the Van der Waals forces which cause physisorption.
2.4.2. FACTORS ON WHICH ADSORPTION DEPENDS 1. Surface area of adsorbent: the greater the surface area of adsorbent, the greater the volume 2. Nature of gas being absorbed: the higher the critical temperature of gas, greater is the amount of gas adsorbed 3. Temperature: adsorption decreases with increase in temperature and vice-versa 4. Pressure: adsorption of gas increase with increase of pressure because on applying pressure gas close to each other

2.5 ADORBENT
An adsorbent is a substance, usually porous in nature and with a high surface area that can absorb substances onto its surface by intermolecular forces. Only at very low concentrations is the adsorption isotherm linear, at higher concentrations the adsorption isotherm may be Langmuir or Freundlich in nature (Matsumura, M. et al,1996). Due to the fact that the solutes can distribute between the adsorbent surface and a mobile phase, adsorbents are used as a stationary phases in gas-solid and liquid-solid chromatography. Adsorbents are also used for extraction purposes removing traces of organic materials from large volumes of water very efficiently (Zeldowitsch J. et al, 1934). Typical adsorbents used in gas-solid chromatography are silica gel, alumina, carbon and bonded phases. These are mostly used in the separation of the permanent gases and the low molecular weight hydrocarbon gasses (M.I. El-Khaiary, et al, 2008). Adsorbents used in liquid solid chromatography are mostly silica gel and various types of bonded phases. Adsorbents in liquid-solid chromatography have a very wide variety of application areas. Activated carbon remains the most widely studied adsorbent, and it has been found to adsorb a variety of materials such as metals, dyes, phenols, and a host of other organic compounds and bio-organisms, and is therefore used for the removal of pollutants from wastewaters by adsorption (Navrot J and Banin A. et al, 1986). The design and operation of the process is convenient and can be handled easily,and the operational costs are therefore comparatively low. As a result, the cost of the adsorbent, and the additional costs of regeneration if have therefore been made by many research workers in the field of waste management to look for alternative adsorbents that are cheaper than activated carbons required, can be a significant fraction of the overall process costs. Aluminosili-cate and oxide minerals are capable of removing many metals over a wider pH range and to muchlower dissolved levels than precipitation. Therefore, one promising option is the use of regionally available low-cost materials that may offer a solution to purify industrial wastewaters. It is well known that some clays are able to strongly adsorb organic compounds and many studies have been carried out to assess their industrial, environmental and pharmaceutical, etc. Applications (Mortland et al., 1986; Barrer, 1989; Zhang & Sparks, 1993; La et al., 1997). Several studies on soil chemistry have demonstrated the ability of soil clays and oxides to selectively adsorb metal cations
Table 2.1The Table of Adsorbents and Their Uses ADSORBENTS | USES | Silica gel | Drying of gases, refrigerants, organic solvents,Adsorption of heavy (polar) hydrocarbons from natural gas, transformer oils etc. | Activated alumina | Drying of gases, organic solvents, transformer oils, removal of HCL from Hydrogen | activated carbon | Adsorption of organic substances and non-polar adsorbatesWaste gas (and waste water treatments. | Zeolites | Drying of process airCO2 removal from natural gasCO removal from reforming gasAir separationCatalytic crackingCatalytic synthesis and Reforming | Polymers and resins | | Clay | Treatment of edible oilsRemoval of organic pigmentsRefining of mineral oilsRemoval of polychlorinated biphenyls (PCBs) | Proteins | Adsorption of biomaterials |

2.5.1 LOW-COST ADSORBENT The materials that have been investigated for this purpose include both natural materials and wastes and byproducts generated from many industries(Gupta, V.K.; GUPTA, M. and Sharma, S. et al, 2001). These materials have been used as such and sometimes after some minor treatment, and are widely known as low-cost adsorbents (LCAs). It is worthwhile noting here that these materials are usually called substitutes for activated carbons because of their wide use and especially for their application in treating wastewater, which is usually done by activated carbons; however, in a broad and clearer way, they are basically substitutes for all expensive adsorbents (Kurniawan, T.A. et al, 2004). These low-cost alternative adsorbents may be classified in two ways, either on basis of their availability (i.e., natural materials such as wood, peat, coal, lignite, etc.; industrial / agricultural / domestic wastes or byproducts such as slag, sludge, fly ash, bagasse flyash, red mud, etc; and synthesized products) or depending on their nature (i.e., inorganic and organic). Though both classifications are good, we are adopting the first for discussing the materials in brief.

2.5.1.1 NATURAL MATERIAL
Materials occurring in nature and used as such or with minor treatment and having little or no use falls in this category. Some of the materials used are as follows:
2.5.1.1.1 WOOD
In an attempt to overcome the economic disadvantages of activated carbon, ( Poots et al, 2003) investigated wood as an adsorbent for the removal of telon blue. The adsorbent was studied without any pretreatment and was sieved into different size ranges prior to use. The kinetics of the process was found to be dependent on the particle size, being minimum (> 3h) for small particle size (150–250 μm) and maximum (> 6h) for large particle sizes (710–1000 μm). It was suggested that because of its low cost, the wood adsorbent does not need to be regenerated after use and maybe disposed by burning, and the heat so evolved can be used for generating steam.
2.5.1.1.2. COAL
Natural coal was studied as an adsorbent for the removal of dyes by Mittal et al,(2001). The coal was not used as adsorbent as such but sulfonated and heated in a water bath. Sorption and desorption of two basic dyes, rhodamine B and methylene blue, and the acidic dye sand olarhodine were studied. The potential of brown young coals Ilgin and Beysehir lignite to remove copper (Cu²⁺), lead (Pb²⁺), and nickel (Ni²⁺) from aqueous solutions was studied as a function of pH, contact time, metal concentration, and temperature ( Pehlivan and Arsalan, 2003)
2.5.1.1.3 PEAT
This is one of the natural materials most widely studied as an alternative adsorbent by a number of researchers. (Poots et al, 1999) used peat as an adsorbent without any pretreatment and studied the adsorption of telon blue on it.
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2.6. INDUSTRIAL/AGRICULTURAL/DOMESTIC WASTES OR BYPRODUCTS
A number of agricultural wastes / byproducts has also been investigated as adsorbents for the removal of pollutants by a number of workers.
2.6.1 PEANUT HULL
Peanut shell has been used (Chamarthy et al, 2006) who prepared adsorbents by heat treatment in the presence of phosphoric or citric acid and used it for the adsorption of Cd²⁺, Cu²⁺, Ni²⁺, Pb²⁺, and Zn²⁺. Their investigations showed that phosphoric acid-modified shells adsorbed metal ions in larger amounts compared to citric acid modified shells. Besides them, the potential of peanut hull pellets to capture metal ions Cu²⁺, Cd²⁺, Zn²⁺, and Pb²⁺ from wastewater and their performance comparison to that of raw peanut hulls and a commercial grade ion-exchange resin has been carried out ( Brown et al, 2007 ) as well
2.6.2 SUNFLOWER STALKS AND MAIZE COB
The feasibility of utilizing sunflower stalks, a renewable agricultural waste available at low cost, was explored (Sun and Shi, 2008). The source material was sieved, and adsorption of Cu²⁺, Zn ²⁺, Cd²⁺ and Cr³⁺ was studied. Sunflower stalks were also studied as adsorbents for basic and direct dyes in aqueous solutions with equilibrium isotherms and kinetic adsorptions. The authors suggested that because sunflower stalks consist of cellulose, it is the polyol structure of cellulose-based materials that has relatively strong chemical adsorption of cations such as metal ions and organic bases as well as physical adsorption of other materials such as acidic and anionic compounds.
2.6.3 RED MUD
Red mud is a waste from the aluminum industry and has also been investigated as an adsorbent (Shiao and Akashi, 2003). The mud was treated with acid and activated at various temperatures, and its capacity was found to be equivalent to that of alumina. Red mud treated with seawater has been used as an adsorbent for arsenate removal from water (Genç et al, 2005). The adsorption was found to follow the Langmuir model and increased with decreasing pH, higher adsorbent dosages, and lower initial arsenate concentrations.

2.6.4 STRAW, USED TIRES
Straw and used rubber tires were investigated (Streat et al, 1998 ) for the sorption of phenol and p-chlorophenol from water. The source material was carbonized in a tube furnace in a stream of oxygen free nitrogen and followed by activation using a stream of moisture-laden nitrogen. Pseudo equilibrium sorption of phenol and p-chlorophenol obeyed a Freundlich type adsorption isotherm, and the sorption half – times were found to be 2.1 and 2.5 min for phenol sorption on tire and straw, respectively.
2.6.5 FERTILIZER INDUSTRY WASTE
A waste carbon slurry generated during liquid fuel combustion in fertilizer plants has been converted into an inexpensive carbonaceous adsorbent (Srivastava et al, 2002). The material was converted into adsorbent by treating first with hydrogen peroxide and further activating it in air at 450°C, resulting in an adsorbent having a surface area of 630 m²g¯¹. The material so prepared was utilized for the removal of Cr (VI), Hg (II), Pb (II), Cu (II), and Mo (II) from metallurgical and electroplating wastewaters. The same product also exhibited good adsorption potential for substituted phenols.
2.6.6 WASTE PAPER
Waste newsprint paper has also been put to use for preparing alternative adsorbents. (Shimada et al, 2007) used newspaper as raw material for the production of activated carbon. Waste newsprint paper was mixed with 8% phenol resin, and the material was heated at 150°C for 10 min and was further carbonized at 800°C for 2hour under nitrogen gas followed by the activation at 900°C for 1h under CO₂ atmosphere to get activated carbon. The activated carbon so produced possessed good surface area (1000 m² g¯¹) and the yield was 40%. In view of its high surface area, this product functioned as a good adsorbent, as evidenced by high iodine (1310mgg¯¹) and methylene blue number (326mgg¯¹).
Besides these, various other materials such as human hair, sewage sludge, fly ash, palm oil ash, saw dust, lignin, bagasses, pine needles, cactus leaves, polymer materials, ZnS, MnO2, black tea leaves, tree fern, pyrite and synthetic iron sulphide, alum-impregnated activated alumina, sorel's cement, calcined-alunite, coconut copra meal, zeolitized pumice waste, refinery residue, rosacanina seeds, limestone and GAC mixture, and wheat bran have also been explored as adsorbents.
2.7. CLAY
The term clay refers to a naturally occurring material composed primarily of fine-grained mineral which is generally plastic when wet and hardens when dried or fried (Bailey, 1980).
The ‘’naturally occurring” requirement of clay consist of hydrated aluminum silicate, quartz and organic fragment and occurs as sedimentary rocks, soils and other deposits. It becomes plastic when moist but hardens on heating and is used in the manufacture of bricks, cement, ceramics etc.
The property of clay been plastic when wet simple means the ability of the materials to be molded to any shape. Plasticity is a property that is greatly affected by the chemical composition of the material. For example, some species of mica can remain non-plastic upon grinding macroscopic flakes even when more than 10% of the material is less than 0.002mm (equivalent spherical diameter) which than make micas become plastic upon grinding macroscopic flakes where 3% of the materials is less than 0.002mm.
2.7.1 CLAY MATERIALS
Clay minerals are layer silicates that are formed usually as products of chemical weathering of other silicate minerals at the earth’s surface (Guggenheim and Martin, 1995). They are found most often in shale’s, the most common types of sedimentary rock.
Soils are made up of a complex mixture of solids, liquid and gases. The solid fraction of soils is made up of organic and inorganic components. The inorganic component of the soil makes up more than 90% of the soil solids.
Inorganic components occur mainly in limited number of compounds with definite crystalline structure minerals. The inorganic component includes both primary and secondary minerals. The secondary minerals normally are found in the clay fraction of the soil solids which is less than micro or 0.002mm clay minerals are mineral which mainly occur in the clay sized fraction of the soil.
2.7.2 ORIGIN OF CLAY MATERIALS
Clay minerals are formed weathering a variety of minerals. The two main processes involve slight physical and chemical alteration or decomposition and recrystallization (Rhoads, 1986). Clay mineral types are normally determined by the types of minerals and acidity of the leaching water.
2.7.3 IMPORTANCE OF CLAY MATERIALS
The clay minerals and soil organic matter are colloids. The most important property of colloids is their small size and large surface area. The total colloidal area of small colloids may range from 10m²/g to more than 80m²/g depending the external and internal surface of the colloid (Kittrick and Hope, 1963).
Soil colloids also carry negative or positive change on their external and internal surfaces. The presence of charge influences their ability to attract or repulse change ions to or from surfaces.
2.7.4 CHARGE DEVELOPMENT ON CLAY MATERIALS
Two main sources of charges in clay minerals are isomorphous institution and pH-dependents charges.Charge development of on silicate clays is mainly due to isomorphous substitution. This is the substitution of one element for another in ionic crystals without change of the structure. It takes places during crystallization and is not subject to change afterward. It takes places only between ions differing by less than about 10% to 15% in crystal radii. In tetrahedral coordination, AL³⁺ for Si⁴⁺ and in octahedral co-ordination Mg²⁺, Fe²⁺, Fe³⁺ for Al³⁺. Charges developed as a result of isomorphous substitution are permanent and not pH-dependent. In allophones, some silicate clays, e.g. kaolinite, and the metal oxides the main source of change are termed pH-dependent charges because these charges are variable and may either be positive or negative depending on the pH of the soil. In the metal oxides acid soils tends to develop positive charges because of the protonation of the solid on the oxide surface.
Clays are well known and familiar to mankind from the earliest days of civilization. Owing to their low cost, abundance, high sorption properties and potential for ion-exchange, clay materials are a strong candidate as adsorbents. There are various type of clays such as ball clay, bentonite, common clay, fire clay, Fuller's earth, and kaolin. The adsorption capabilities of clays generally result from a net negative charge on the structure of minerals. This negative charge gives clay the capability to adsorb positively charged species. In recent years, there has been an increasing interest in utilizing clay minerals and in modified form to adsorb not only inorganic but also organic molecules.
2.7.5 CALCINED CLAY
The word calcining refers to the treatment of a mineral product at a very high temperature such as 800 to 1000 degrees centigrade. The word is derived from the process of converting calcium carbonate to calcium oxide. When the word calcination is used together with the word clay, there is no calcium involved; rather the word calcination is used only because similar equipment as used for calcium carbonate can be used to prepare anhydrous clay. Intense heating of ‘kaolin clay’ drives off water of hydration and yields a bright anhydrous clay product in which individual platelets of the mineral are fused together

2.8 ADSORPTION ISOTHERM STUDIES
If the adsorbent and adsorbate are contacted long enough, equilibrium will be established between the amount of adsorbate adsorbed and the amount of adsorbate in solution. The equilibrium relationship is described by adsorption isotherms.
In general, an adsorption isotherm is a curve relating the equilibrium concentration of a solute on the surface of an adsorbent, qe, to the concentration of the solute in the liquid, Ce, with which it is in contact.
The adsorption isotherm is also an equation relating the amounts of adsorbate (x) adsorbed on the surface of the adsorbent and the pressure (if gas) or concentration (if liquid) at constant temperature.
There are various types of isotherm studies- the linear isotherm, the Freundlich isotherm, Langmuir isotherm, BET isotherm etc.

Fig 2. 1 A Graph of Langmuir, Freundlich and linear isotherm
2.8.1 FREUNDLICH EQUATION
The most common shape of the graph of amount adsorbed per unit weight of adsorbent versus the concentration in the fluid in equilibrium is:

Fig 2.2 Typical Adsorption Isotherm

This graph very closely resembles that for microbial specific growth rate coefficient versus substrate concentration. These data often fit nicely the empirical equation proposed by Freundlich: q = Kf Cn .......................................................................................................................................... (2.1)
Where:
* Kf and n are coefficients * q = weight adsorbed per unit wt of adsorbent * C = concentration in fluid
Taking logs and rearranging: log q = log Kf + n log C……………………………………………………………..(2.2)
The coefficients Kf and n can be estimated from slopes and by substituting values from a line fitted to a graph of log q versus log C. With a personal computer handy, the method of least squares can be used to get a statistical fit, however outlying data points are not as obvious as with a graph.
2.8.2 LANGMUIR ISOTHERM
In 1916, Irving Langmuir published an isotherm for gases adsorbed on solids, which retained his name. It is an empirical isotherm derived from a proposed kinetic mechanism.
It is based on four hypotheses:
1. The surface of the adsorbent is uniform, that is, all the adsorption sites are equal.
2. Adsorbed molecules do not interact.
3. All adsorption occurs through the same mechanism.
4. At the maximum adsorption, only a monolayer is formed: molecules of adsorbate do not deposit on other, already adsorbed, molecules of adsorbate, only on the free surface of the adsorbent.
2.8.3 LANGMUIR EQUATION
Langmuir derived a relationship for q and C based on some quite reasonable assumptions.
These are: a uniform surface, a single layer of adsorbed material, and constant temperature. The rate of attachment to the surface should be proportional to a driving force times an area. The driving force is the concentration in the fluid, and the area is the amount of bare surface. If the fraction of covered surface is F, the rate per unit of surface is:
Rate going on = k1 C (1 - F)…………………………………………………………… (2.3)
The evaporation from the surface is proportional to the amount of surface covered:
Rate leaving = k2 F………………………………………………………………….. (2.4)
Where
* k1 and k2 are rate coefficients * C = concentration in the fluid * F = fraction of the surface covered
2.8.3.1 ANIMATION OF FINDING ADSORPTION SITES
At equilibrium, the two rates are equal, and we find that:

……………………………………………………………………………..……… (2.5)

……………………………………………………………………………..……… (2.5)

By dividing the numerator and denominator by k1, and making use of the fact that q will be proportional to F, the useful form of the equation is:
…………………….……………………………..…………… (2.6)
Where
* qm = q for a complete monolayer * Ka = a coefficient
Taking reciprocals and rearranging:
…………………………………………………………. (2.7)
A plot of versus should indicate a straight line of slope and an intercept of. The graph shows data points and lines fitted to both Freundlich and Langmuir equations.
2.8.4. B.E.T. EQUATION
A different equation is more likely to describe adsorption where the adsorbate exceeds a monolayer.
The Brunauer-Emmett-Teller (BET) equation is:
…………………………………………………… (2.8)
Where
* Cs = concentration at which all layers are filled * Kb = a coefficient
Its assumptions are: * Adsorbed molecules stay put * Enthalpy of adsorption is the same for any layer Energy of adsorption is the same for layers other than the first * A new layer can start before another is finished.
It is important that many unusual adsorptions isotherms are fitted well by the BET equation. This is to be expected when there are three coefficients to manipulate. The maximum loading, Qm, just multiplies to move the entire curve up and down. The coefficient, Kb, has a major effect on shape. The concentration at which all sites are saturated (maybe several layers) can be adjusted to get a portion of the isotherm. In other words, you can look at just part of the curve. As C approaches Cs, the denominator of the equation becomes small, and the curve shoots up.

CHAPTER 3
MATERIALS AND METHODS
3.1 MATERIALS
The sample to be collected from the clay deposits at Okada, and at depths of up to 10 cm with the aid of a plastic shovel and digger and hand-picked to minimize the possibility of contamination. The clay sample to will be placed in small polythene bags and then dried, pulverized and sieved screened to obtain geometric sizes of 0.02mm or less before analysis.
The salt to be used for the preparation of the aqueous solutions is lead (II) Sulphate. Other chemicals to be used are: Ethanol, Ammonium acetate and Potassium chloride all reagents used would be of analytical grade. Distilled water would be used for dilution and preparing stock solutions.
3.2 METHODS
3.2.1. PREPARATION OF AQUEOUS SOLUTIONS
Stock solutions (1000mg/L) of Pb2+ would be prepared by dissolving appropriate amounts of analytical grade lead (II) Sulphate in distilled water. All working solutions would be obtained by diluting the stock solutions with appropriate amounts of distilled water. The concentration of metal ions in solutions would be analysed by Atomic Absorption Spectrophotometer. A duplicate measurement would be analysed for every sample to track experimental error and show capability of reproducing results (Marshall and Champagne, 1995).

3.2.2 CHARACTERIZATION OF OKADA CLAY

3.2.2.1 DETERMINATION OF CATION EXCHANGE CAPACITY (CEC)
The cation exchange capacity (CEC) of the clay sample would be determined by the procedure described by Chapman (1961).

3.2.2.2 DETERMINATION OF MINERALS IN CLAY
The mineralogical composition of the clay would be obtained by XRD studies

3.2.2.3 DETERMINATION OF CHEMICAL BONDS IN CLAY
Fourier transform infrared spectroscopy (FTIR) of the adsorbent would be done by using an FTIR spectrometer. This would be to determine functional groups present in the clay samples.

3.2.2.4 DETERMINATION OF THE MICROSTRUCTURES, COMPOSITION AND MORPHOLOGY OF THE CLAY
The microstructure and morphology of the clay samples would be determined through scanning electron microscope.
3.2.2.5 CALCINING OF CLAY
The clay has to be heated up to a temperature of 500℃ in a furnance

3.2.6 ADSORPTION STUDIES
The adsorption studies for evaluation of Okada clay for removal of heavy metal from aqueous solutions would be carried-out in triplicate using the batch adsorption procedure (Brasil et al., 2006; Lima et al., 2007). For these experiments varying amount of adsorbents (0.4, 0.8, 1.2, 1.6 and 2g) would be placed in a 250 ml conical flasks containing 50.0 ml of heavy metal solutions with metal ion concentration of 20mg/l, for a time of 120 minutes at room temperature. The adsorbents would be separated from solution by filtering with Whatman filter paper No. 42. The residual metallic ion concentrations would also be determined using an Atomic Absorption Spectrophotometer
The amount of the metal ion sorbed and percentage of removal of metal ion by the adsorbent were calculated by applying the Equations (1) and (2), respectively:

q=Co-Cfm.V………………………………………..……………………………… (3.1)
% Removal =Co-CfCo.100………………………………………………………….. (3.2)
Where:
q = the amount of metal ion sorbed by the adsorbent (mg/g)
C0 = the initial ion concentration put in contact with the adsorbent (mg/L)
Cf = the final concentration (mg/L) after the batch adsorption procedure.
V = the volume of aqueous solution (L) put in contact with the adsorbent. m = the mass (g) of adsorbent.

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