Project Abstract

<p> </p><p>The removal of Pb(II) ions from aqueous model solution using zeolite has been<br>investigated under different operational parameters like heavy metal ion<br>concentration, adsorbent amount and particle size. The zeolite used was<br>synthesized and characterized using SEM and XRD analysis. The equilibrium<br>adsorption capacity of zeolite used for lead removal were measured and the<br>experimental data analyzed by means of Freundlich and Langmuir isotherm<br>models. The adsorption efficiency of Zeolite in removing Pb2+ ions at room<br>temperature and 60 minute agitation time at pH&lt;10 was 98%. The results also<br>show that the adsorbent with the lowest particle size of 53.6μm had the highest<br>adsorption efficiency(98.33%) The concentration of metal ions were measured by<br>Atomic Absorption Spectroscopy (AAS). Overall, the results showed that synthetic<br>zeolite could be considered as a potential adsorbent for lead removal from aqueous<br>solutions.</p><p>&nbsp;</p><p><strong>&nbsp;</strong></p> <br><p></p>

Project Overview

<p> INTRODUCTION<br>In developing countries, rapid growth of urbanization and industrialization<br>has generated large volume of waste containing toxic heavy metals. Heavy metal<br>contamination exists in aqueous waste water streams of many industries such as<br>metal plating facilities, mining operations, tanneries etc1. Environmental pollution<br>due to these toxic metals have been of major concern to environmental engineers;<br>the ions from these heavy metals cause damage to humans e.g. cadmium poisoning<br>causes acute chronic disorders such as renal damage and hypertension, problem in<br>Haemoglobin synthesis, kidney, gastrointestinal tract, joints and reproductive<br>disorders. Acute or chronic dosage results in damage of the nervous system2.<br>Within the body, lead is absorbed and stored in the bones, blood, and tissues. It<br>does not stay there permanently, rather it is stored there as a source of continual<br>internal exposure 3. As time goes by, the bones demineralize and the internal<br>exposures may increase as a result of larger releases of lead from the bone tissue.<br>There is also concern that lead may mobilize from the bone among women<br>undergoing menopause4. Post menopausal women have been found to have higher<br>blood lead levels than pre-menopausal women5.<br>Lead poisoning occurs if a person is exposed to very high levels of lead over<br>a short period of time. When this happens, a person may feel abdominal pain,<br>14<br>constipated, tired, headachy, irritable, loss of appetite, memory loss, pain or<br>tingling in the hands and/or feet and weak.<br>Generally, lend affects children more that it does adults. Children tend to<br>show signs of sever lead toxicity at lower levels than adults. Neurological effects<br>and mental retardation have also occurred in children whose parents may have jobrelated<br>lead exposure6. The health effects from prolonged exposure to lead<br>included abdominal pain, depression, forgetfulness among others. Also, the<br>Department of Health and Human Services (DHHS), Environmental Protection<br>Agency (EPA), and the International Agency for Research on cancer (IARC) have<br>determined that lead is probably cancer-causing in human7.<br>Exposure to chromium results in asthma, chronic bronchitis, chronic<br>irritation, chronic pharyngitis, chronic rhinitis, congestion and hyperemia, polyps<br>of the upper respiratory tract, tracheobronchitis, and ulceration of the nasal mucosa<br>with possible septal perforation though zinc is considered to be relatively nontoxic,<br>particularly if taken only. However, manifestations of overt toxicity symptoms<br>(nausea, vomiting, epigastric pain, lethargy and fatique) will occur with extremely<br>high intakes 8.<br>Arsenic and mercury are other heavy metals that are highly toxic even on<br>minimal exposure. Arsenic is classified as a metalloid usually found combined<br>with oxygen, chlorine, and sulphur. Exposure to arsenic include sore throat and<br>15<br>irritated lungs as much as skin effects. Longer exposure at lower concentrations<br>can lead to circulatory and peripheral nervous disorders as well as high risk of lung<br>cancer 9. Health effect of mercury include hydrargyria or mercurialism. Elemental<br>mercury does cause damage by blocking blood vessels, damage to the brain,<br>kidneys and lungs 10. Mercury poisoning can result in several diseases, including<br>acrodynia (pink disease)11, Hunter–Russell syndrome and minamata disease<br>chronic exposure to excessive manganese levels can lead to variety of psychiatric<br>and motor disturbances, termed manganism. Generally, exposure to ambient<br>manganese air concentrations in excess of 5 micrograms Mn/m3 can lead to Mninduced<br>symptoms 12.<br>Adsorption of these metal ions from industrial effluent before discharged<br>into the environment is of great importance so as to control the risk and<br>endangerment they cause. To achieve this i.e. elimination or adsorption of heavy<br>metals from industrial effluents, adsorbents such as zeolites are employed for<br>effective adsorption of heavy metals from waste water or industrial effluents so as<br>to free the effluents of the heavy metal ions such as Pb ions, Cd ions, Cr ions etc<br>before they are discharged or released into the environment13.<br>16<br>1.0 BACKGROUND OF STUDY<br>1.1 HEAVY METAL TOXICITY<br>Heavy metal is a metal with a fairly high relative atomic mass, and specific<br>gravity greater than 5.0 especially those that are significantly toxic (e.g., lead,<br>cadmium, mercury).They persist in the environment and can accumulate in plant<br>and animal tissues. Mining and industrial wastes and sewage sludge are potential<br>sources of heavy metal pollution16.<br>With the rapid development of industries such as metal plating facilities,<br>mining operations, fertilizer industries, tanneries, batteries, paper industries and<br>pesticides etc, heavy metal wastewaters are directly or indirectly discharged into<br>the environment increasingly, especially in developing countries such as Nigeria.<br>Unlike organic contaminants, heavy metals are not biodegradable and tend to<br>accumulate in living organisms and many heavy metal ions are known to be toxic<br>or carcinogenic. Toxic heavy metals of particular concern in the treatment of<br>industrial waste waters include zinc, copper, nickel, mercury, cadmium, lead and<br>chromium.<br>Now-a-days heavy metals are the environmental priority pollutants and are<br>becoming one of the most serious environmental problems. So these toxic heavy<br>metals should be removed from industrial waste water or effluents to protect the<br>people and the environment.<br>17<br>1.2 METHODS OF HEAVY METAL REMOVAL<br>Many methods that are been used to remove heavy metal ions include<br>chemical precipitation17, sulfide precipitation18 investigated pyrite and synthetic<br>iron sulphide for removal of lead and copper. Ion-exchange processes have been<br>widely employed to remove heavy metals from effluents due to their many<br>advantages, such as high treatment capacity, high removal efficiency and fast<br>kinetics19-21.<br>Adsorption additives22, tannic acids23, magnesium24, surfactants25 and<br>activated carbon composite could be effective adsorbents for heavy metals.<br>Agricultural waste materials as potential adsorbent for sequestering heavy metal<br>ions from aqueous solutions26, membrane filtration27, nanofiltration (NF) used for<br>nickel28,29 performed a new working system of investigate the removal of<br>hexavalent chromium ions using electrolysis electrochemical treatment<br>technologies, etc30 studied the performance of an electrochemical treatment<br>technologies system with aluminum electrodes for removal of metal ions from<br>water.<br>1.3 TYPES OF HEAVY METAL ADSORBENTS<br>Various types of adsorbent used in heavy metal removal are activated<br>carbon31, clay minerals32,33, biomaterials34, zeolites35,36, and some industrial solid<br>18<br>wastes37,38 have been widely used as adsorbents for adsorption of ions and organics<br>in waste water treatment.<br>Adsorption is now recognized as an effective and economic method for<br>heavy metal removal in waste water treatment. The adsorption process offer<br>flexibility in design and operation and in many cases will produce high-quality<br>treated effluent. In addition, because adsorption is sometimes reversible,<br>adsorbents can be regenerated by suitable desorption process. In this work, zeolite<br>will be used as the adsorbent in removal of lead ions from simulated waste water.<br>1.3.1 Zeolites<br>Zeolites are microporous, alumino silicate minerals commonly used as<br>commercial adsorbents39. Some zeolites occur naturally while others are synthetic.<br>Zeolite has a three-dimensional structure with pores.<br>The zeolite history began with the discovery of stilbite by Crönstedt, a Swedish<br>mineralogist in year 1756. Upon heating the zeolite released occluded water, which<br>gave the materials their general name, zeolite, after the Greek words, “ξειv” (zeo) ,<br>to boil, and “λιϑoς” (lithos), stone. A representative empirical formula of a zeolite<br>is<br>M2/nO . Al2O3 . xSiO2. yH2O<br>where M represents the exchangeable cation of valence n. M is generally a Group I<br>or II ion, although other metal, non-metal and organic cations may also balance the<br>19<br>negative charge created by the presence of Al in the structure. The framework may<br>contain cages and channels of discrete size, which are normally occupied by water.<br>It consists of silicon, aluminium and oxygen ions. The silicon ions are neutrally<br>charged in the crystal structure. Aluminium ions create negative places. To keep<br>the cargo in balance, a counter ion (Na+, K+) or a proton (H+) is present in the<br>pores. One type of zeolite have just as large pores through the entire crystal<br>structures. All natural zeolites contain aluminium and are hydrophilic in nature40.<br>Zeolites are widely used in industries for water purification, as catalysts, for<br>the preparation of advanced materials and in nuclear processing. Their biggest use<br>is in the production of laundry detergents. Zeolites are also used in medicine and in<br>agriculture.<br>Zeolites have a porous structure that can accommodate a wide variety of<br>cations such as Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather<br>loosely held and can readily be exchanged for others in a contact solution. Some of<br>the more common mineral Zeolites are Analcine, Chabazite, Clinoptiloite,<br>Heulandites, Natrolite, Phillipsite and Stilbite. An example mineral formula is<br>Na2Al2Si3O10.2H2O, the formula for natrolite.<br>Natural zeolites form where volcanic rocks and ash layers react with alkaline<br>ground water. Zeolites also crystallize in post-depositional environments over<br>periods ranging from thousands to millions of years in shallow marine basins.<br>20<br>Naturally occurring zeolites are rarely pure and are contaminated to varying<br>degrees by other minerals, metals, quartz, or other zeolites. For this reason,<br>naturally occurring zeolites are excluded from many important commercial<br>applications where uniformity and purity are essential.<br>Zeolites are the aluminosilicate members of the family of microporous solids<br>known as “molecular sieves”. The term molecular sieve refers to a particular<br>property of these materials, i.e. the ability to selectively sort molecules based<br>primarily on a size exclusion process. This is due to a very regular pore structure of<br>molecular dimensions. The maximum size of the molecular or ionic species that<br>can enter the pores of a zeolite is controlled by the dimensions of the channels.<br>These are conventionally defined by the ring size of the aperture, where, for<br>example, the term “8-ring” refers to a closed loop that is built from 8-tetrahedrally<br>coordinated silicon (or aluminium) atoms and 8 oxygen atoms. These rings are not<br>always perfectly symmetrical due to a variety of effects, including strain induced<br>by the bonding between units that are needed to produce the overall structure, or<br>coordination.<br>1.3.2 Use of Synthetic Zeolite for Wastewater Treatment<br>The use of synthetic zeolite for the environmental protection is stimulated by<br>its good physico-chemical properties e.g. selective sorption,its non-toxic nature<br>and availability. A great deal of research on zeolite has focused on a wide range of<br>21<br>applications including waste water treatment or purification with emphasis on the<br>ammonia and heavy metal removal41, removal of radioactive 137Cs and 90Sr from<br>low-level waste streams of nuclear installations42, and recently also for the removal<br>of organic pollutants, like hydrochloroflourocarbons (HCFCs) from petroleum<br>products from water43. They can be used as barriers to contaminant migration or as<br>binders in waste solidification systems.<br>There are increasing demands for healthier environment, with the emphasis<br>on high-quality drinking water and on the removal of contaminants from industrial,<br>agricultural and municipal waste waters. Most technologies using zeolites for water<br>and soil purification are based on the unique cation-exchange behaviour of zeolites<br>through which dissolved cations are removed from water or soil by exchanging<br>with cations in zeolites exchange sites. The most common cation in waters<br>affecting human and animal health is NH4<br>+. It can be replaced with biologically<br>accepted cations, like Na+, K+ or Ca2+ in the zeolite. Ammonia removal is very<br>important to prevent oxygen depletion and algae bloom and due to its extreme<br>toxicity to most fish species44. Additionally, it has detrimental effects on<br>disinfection of water supplies and corrosive action on certain metals and<br>construction materials. Nitric oxides, nitrates and ammonia/ammonium are very<br>soluble in water and can quickly end up in ground and drinking water. Some<br>naturally occurring zeolite such as chabazite and clinoptilolite showed the best<br>22<br>results for ammonia removal. Heavy metals are well known for their toxicity and<br>their disposal is a significant industrial waste problem. Pb2+, Cu2+, Fe3+, Cd2+ and<br>Cr3+ are especially common metals in industrial wastes that tend to accumulate in<br>organisms, causing numerous diseases and disorders45.<br>1.3.3 Mechanisms of Heavy Metal Removal from Industrial Waste Water<br>The contamination with heavy metals exists in aqueous waste streams of<br>many industries such as metal plating industries, dyes and textile industries, mining<br>operations etc. The amount of heavy metal waste is increasing on yearly basis; they<br>tend to accumulate in living organisms. Treatment processes for the removal of<br>heavy metals from waste water include coagulation, carbon adsorption, ion<br>exchange, reverse Osmosis etc46. The sorption processes are the most attractive<br>since their application is simple, and they require mild operating conditions. The<br>limiting factor could be the regeneration of the sorbing materials.<br>The sorption of heavy metals by zeolites is a complex process because of the<br>inner and outer charged surfaces, imperfections on the surfaces, mineralogical<br>heterogeneity among others that can also contribute to the overall sorption<br>capacity. The extensive research of adsorption isotherms revealed that ion<br>exchange or chemisorptions on zeolites governs the immobilization of metal<br>cations especially in natural zeolites tuffs47.<br>23<br>Following the ion exchange mechanism, ions present in the pores of zeolite<br>crystalline lattices, like Na+, K+, Ca2+ etc are substituted by metal ions from the<br>solution. The chemisorption always results in the formation of stable inner-sphere<br>or outer-sphere complexes, where functional groups on the zeolite framework<br>(mainly OH-) form strong chemical bonds with the metal ions. In clinoptilolite and<br>the majority of zeolites, ion-exchange processes generally dominate over<br>chemisorption. The sorption of heavy metal by the zeolite is directly related to the<br>charge of the zeolite framework, i.e the quantity of aluminium present in the<br>zeolite framework, the nature and concentration of the cationic species, the size<br>and distribution of zeolite tuff particles, the solvent and the temperature.48<br>1.4 ADSORPTION<br>Adsorption refers to the adhesion of atoms, ions or molecules from a gas,<br>liquid or dissolved solid to a surface 49. This process creates a film of the adsorbate<br>on the surface of the adsorbent. This process differs from absorption in which a<br>fluid (the absorbate) permeates or is dissolved by a liquid or solid (the absorbent)50.<br>Adsorption is a surface-based process while absorption involves the whole volume<br>of the material. The term sorption encompasses both processes, while desorption is<br>the reverse of it. Adsorption is a surface phenomenon. Adsorption is present in<br>many natural, physical, biological and chemical systems, and is widely applied in<br>industrial processes such as activated charcoal, capturing and using waste heat to<br>24<br>provide cold water for air conditioning and other process requirements (adsorption<br>chillers), synthetic resins and water purification. The word “adsorption” was<br>coined in 1881 by German physicist Heinrich Kayser 51.<br>1.4.1 Adsorption Isotherms<br>Adsorption is usually described through isotherm, that is, the amount of<br>adsorbate on the adsorbent as a function of its pressure (if gas) or concentration (if<br>liquid) at constant temperatures. The quantity adsorbed is nearly always<br>normalized by the mass of the adsorbent to allow comparison of different<br>materials.<br>The equilibrium distribution of metal ions between the sorbent and the<br>solution is important in determining the maximum sorption capacity. Several<br>isotherm models are available to describe the equilibrium sorption distribution in<br>which two models are used to fit the experimental data: Langmuir and Freundlich<br>models. The linear form of Langmuir model52 is given as:<br>ıı ıı ı = ı1<br>ııı ıı. ııı+ ıı<br>ııı ıı<br>Where qe is metal concentration on the zeolite at equilibrium (mg of metal<br>ion/g of zeolite), Qmax (mg/g) and KL (1/mg) are Langmuir constants related to the<br>maximum adsorption capacity corresponding to complete coverage of available<br>adsorption sites and a measure of adsorption energy (equilibrium adsorption<br>25<br>constant) respectively. These constants are found from the slope and intercept of<br>Ce/qe Vs Ce linear plot so that Qmax = 1/slope and KL = slope/intercept.<br>The linear form of the Freundlich model53 is given as:<br>lnqe = In KF + (1/n) In Ce<br>Where KF and n are Freundlich constants determined from the slope and intercept<br>of plotting In qe vs In Ce.<br>Amount of metal ion adsorbed on zeolite is calculated at the difference between<br>initial and final concentrations at equilibrium.<br>qe = (Ci-Ce)/S<br>Where qe is the ion concentration adsorbed on the zeolite at equilibrium (mg of<br>ion/g of zeolite). Ci is the initial concentration of ions in the solution (mg/L). The<br>slurry concentration, S, is expressed by :<br>S = m/v<br>Where v is the initial volume of ions solution used (L) and m is the mass of zeolite<br>used (g). The percent adsorption (%) is calculated using the equation.<br>% adsorption = (Ci -Ce/Ci) x 100%<br>1.5 STATEMENT OF PROBLEMS<br>With the rapid development of industries such as metal plating facilities,<br>mining operations, fertilizer industries, tanneries, batteries, paper and pesticide<br>industries, heavy metal wastewaters are directly or indirectly discharged into the<br>environment increasingly, especially in developing countries such as Nigeria.<br>26<br>Unlike organic contaminants, heavy metals are not biodegradable and tend to<br>accumulate in living organisms and many heavy metal ions are known to be toxic<br>or carcinogenic.<br>Despite the very useful collection of verified synthesis of zeolite materials,<br>recipes for zeolite synthesis are often difficult to follow.<br>1.6 OBJECTIVE OF THE STUDY<br>The aim of the research is to study the adsorption capacity of synthetic<br>zeolite synthesized from aluminosilicate solutions and gels. To achieve this, a<br>study was carried out with the following objectives:<br>i. To synthesize zeolite X from sodium aluminosilicate solution via<br>hydrothermal sol gel process.<br>ii. To characterize the synthesized zeolite via Scanning Electron Microscopy<br>and X-ray diffraction.<br>iii. To evaluate the potential of the produced synthetic zeolite on its capacity as<br>an adsorbent for adsorption of Pb ions from waste water<br>1.7 JUSTIFICATION OF THE STUDY<br>The hydrothermal approach used to synthesize the zeolitic adsorbent not<br>only proffered acheaper route and lower reaction time for synthesis, it also gave<br>high yield of the product with high purity hence its efficacy in removal of metallic<br>lead ions in waste water.<br>27 <br></p>