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  1. 1. Regional government of KurdistanMinistry of Higher Education and Scientific research University of sulaimani School of science Chemistry department Determination of heavy metals In wastewaters Submitted to the chemistry department in the school of Science -University of Sulaimany- as a partial fulfillment Of the requirements for the degree of Bachelor of Science-B.Sc.- In Chemistry By ARAM I. Abdul rahman Mustafa Hassan Supervised by KOSAR HIKMAT HAMA AZIZ -2012- 1
  2. 2. Chapter oneA-Introduction(A-A) WastewaterWastewater is water that has been used and must be treated before it is released into anotherbody of water, so that it does not cause further pollution of water sources. Wastewater comesfrom a variety of sources. Everything that you flush down your toilet or rinse down the drainis wastewater. Rainwater and runoff, along with various pollutants, go down street guttersand eventually end up at a wastewater treatment facility. Wastewater can also come fromagricultural and industrial sources. Some wastewaters are more difficult to treat than others;for example, industrial wastewater can be difficult to treat, whereas domestic wastewater isrelatively easy to treat (though it is increasingly difficult to treat domestic waste, due toincreased amounts of pharmaceuticals and personal care products that are found in domesticwastewater. For more information about emerging contaminants (1.2.3) 1. Wastewater is simply water that has been used. It usually contains various pollutants, depending on what it was used for. It is classified into two major categories, by source: Domestic or sanitary wastewater. This comes from residential sources including toilets, sinks, bathing, and laundry. It can contain body wastes containing intestinal disease organisms. 2. Industrial wastewater. This is discharged by manufacturing processes and commercial enterprises. Process wastewater can contain rinse waters including such things as residual acids, plating metals, and toxic chemicals.Wastewater is treated to remove pollutants (contaminants). Wastewater treatment is aprocess to improve and purify the water, removing some or all of the contaminants, makingit fit for reuse or discharge back to the environment. Discharge may be to surface water, suchas rivers or the ocean, or to groundwater that lies beneath the land surface of the earth.Properly treating wastewater assures that acceptable overall water quality is maintained.In many parts of the world, including in the United States, health problems and diseaseshave often been caused by discharging untreated or inadequately treated wastewater. Such 2
  3. 3. discharges are called water pollution, and result in the spreading of disease, fish kills, anddestruction of other forms of aquatic life. The pollution of water has a serious impact on allliving creatures, and can negatively affect the use of water for drinking, household needs,recreation, fishing, transportation, and commerce. (4)The main reason care should be taken when dealing with waterwaste is to protect other watersources from becoming contaminated. Thus, most waterwaste is taken by sewer line to awater treatment facility. There, the solids and most biological organisms are removed fromthe water and the clean water is released as effluent, usually into another source of water,such as a river or lake. If the equipment at the water treatment facility is running properly,the water will pose no danger to the environment upon being released.Industrial water waste is often treated slightly differently than standard householdwaterwaste. Water that has only been used in the manufacturing process may be able to bereleased directly into the environment if a number of conditions are meant. This is oftenregulated heavily in many jurisdictions and those industrial facilities can be fined heavily iffound to be abusing the discharge terms. In some cases, even criminal action could be takenagainst those responsible. The water will likely contain some solids, especially metals. Thosemetals cannot be of types or in concentrations that are considered dangerous.Further, industrial waterwaste must not be mixed with any other type of water being flushedfrom the facility. For example, sewer lines that serve bathrooms and kitchens at suchfacilities cannot run into lines serving industrial uses. This protects the effluent from crosscontamination, thus making sure no harmful bacteria is released into an otherwise clean orsafe water supply.Waterwaste can also be considered runoff from streets and other areas after a rainfall. Thistype of water is sometimes not considered that dangerous, and is often funneled directly intoa natural body of water. Some communities and states have begun to change the rulesregarding this and feel oil and other contaminants on the roads surface can have a negativeimpact on the environment. To protect the environment, some have mandated special ponds,called drainage ponds, to collect the water and keep it separate from other water sources.This waterwaste is not meant to be treated, but may become cleaner over time due to naturalprocesses. 3
  4. 4. Any of the following acts or omissions, whether willful or negligent, shall constitute the wasteof water: A. Causing or permitting water to discharge, flow or run to waste into any gutter,sanitary sewer, watercourse or storm drain, or to any adjacent property, from any tap, hose,faucet, pipe, sprinkler, or nozzle. In the case of irrigation, “discharge,” “flow” or “run towaste” means that the earth intended to be irrigated has been saturated with water to thepoint that excess water flows over the earth to waste. In the case of washing, “discharge,”“flow” or “run to waste” means that water in excess of that necessary to wash, wet or cleanthe dirty or dusty object, such as an automobile, sidewalk, or parking area, flows to waste. B. Allowing water fixtures or heating or cooling devices to leak or discharge. C. Maintaining ponds, waterways, decorative basins or swimming pools withoutwater recirculation devices. D. Backwashing so as to discharge to waste swimming pools, decorative basins orponds in excess of the frequency necessary to ensure the healthful condition of the water orin excess of that required by standards for professionally administered maintenance or toaddress structural considerations, as determined by the director or his or her designee. E. Operation of an irrigation system that applies water to an impervious surface orthat is in disrepair. F. Use of a water hose not equipped with a control nozzle capable of completelyshutting off the flow of water except when positive pressure is applied. G. Irrigation of landscaping during rainfall. H. Overfilling of any pond, pool ,fountain which results in water discharging towaste.(5) 4
  5. 5. (A-B)Source ofWaste WaterWastewater can be defined as the flow of used water discharged from homes,businesses,industries, commercial activities and institutions which is directed to treatmentplants by acarefully designed and engineered network of pipes. This wastewater is furthercategorizedand defined according to its sources of origin. The term “domestic wastewater”refers to flowsdischarged principally from residential sources generated by such activities asfoodpreparation, laundry, cleaning and personal hygiene. Industrial/commercial wastewateris flowgenerated and discharged from manufacturing and commercial activities suchasPrinting, foodand beverage processing and production to name a few.InstitutionalWastewater characterizeswastewater generated by large institutions such ashospitals and educational facilities.Typically 200 to 500 liters of wastewater are generatedfor every person connected to thesystem each day. The amount of flow handled by atreatment plant varies with the time of dayand with the season of the year.(Major Components) 1. Domestic: food, soap and detergents, bathroom (fecal and urine), and paper. 2. Commercial: bathroom and food from restaurants and other “stores.” 3. Industrial: highly variable, dependent on industry, controlled by pre-treatment regulations. 4. Runoff from streets: sand and petroleum and tire residues (infiltration, not a direct discharge). (6)(A-C)Heavy MetalsHeavy metals are a major concern in the treatment of water due to the toxic and other detrimentaleffects these materials can produce. In general, heavy metals are considered to be the followingelements: Copper, Silver, Zinc, Cadmium, Gold, Mercury, Lead, Chromium, Iron, Nickel, Tin,Arsenic, Selenium, Molybdenum, Cobalt, Manganese, and Aluminum.The term heavy metalrefers to any metallic chemical element that has a relatively high density and is toxic or poisonousat low concentrations.Heavy metals can be found in varying concentrations in any natural source of water, but themain treatment problems exist in the process water of the following industries: Metal mining and smelting operations Foundries Metal planting and finishing Metal fabricating plants such as automotive manufacturing, etc. 5
  6. 6. While not all heavy metals are involved, research has shown that certain metals such asmercury, lead and chromium are toxic to aquatic life in relatively low concentrations. Forexample, 20 ppm of chromium is fatal to trout after 8 days exposure. If 100 gallons of normalchromium planting solution is discharged into a waterway it will be toxic to allmicroorganisms in the food cycle, even if diluted by 100,000,000 gallons of water.In larger concentrations these metals may have detrimental health effects on man. Heavymetals are a cumulative toxin that the body cannot dispose of and they accumulate toharmful levels with repeated exposure.The presence of heavy metals in a waste stream caninterfere and even destroy the effectiveness or normal waste treatment operations. Activatedsludge secondary treatment plants are especially affected since heavy metals can kill thenecessary bacteria.Heavy metals in water can make it unsuitable for many uses such asdrinking, boiler feed, or process uses where high degree purities are required.(7)The most commonly encountered toxic heavy metals include: Arsenic Lead Mercury Cadmium Iron AluminumOther heavy metals of concern include:(Antimony,Chromium/chrome,Cobalt,Copper,Manganese,Nickel,Uranium,Vanadium,Zinc)Most common heavy metals are lead(Pb), mercury(Hg), cadmium(Cd) and arsenic(As)Heavy metals become toxic when they are not metabolized by the body and accumulate inthe soft tissues. Heavy metals may enter the human body through food, water, air, orabsorption through the skin when they come in contact with humans in agriculture and inmanufacturing, pharmaceutical, industrial, or residential settings.(8)(A-D)Effect of Heavy Metals OnHealth and Environment 6
  7. 7. Heavy metals are dangerous because they tend to bio accumulate. Bioaccumulation meansan increase in the concentration of a chemical in a biological organism over time, comparedto the chemicals concentration in the environment. Compounds accumulate in living thingsany time they are taken up and stored faster than they are broken down (metabolized) orexcreted.Heavy metals can enter a water supply by industrial and consumer waste, or even from acidicrain breaking down soils and releasing heavy metals into streams, lakes, rivers, andgroundwater. Now we are going to describe the kinds of heavy metals, their dangerous levelsand the effects of these heavy metals to human health and environment.The most pollutans heavy metals are Lead, Cadmium, Copper, Chromium, Selenium andMercury.(9)(A-D-A)Lead  Has a very low melting point of 327 degrees C  Used as a structural metal in ancient times and for weather proofing buildings  Romans used it in water ducts and in cooking vessels  Analysis of ice-core samples from Greenland indicate that atmospheric lead concentration reached a peak in roman times that was not equaled again until the renaissance Sources of lead  Commonly used in the building industry for roofing and flashing and for soundproofing  Used in pipes  When combined with tin, it forms solder, used in electronics and in other applications to make connections between solid metals  Lead is also used in ammunition  Note: Lead shots have been banned in United States, Canada, Netherlands, Norway and Denmark  Lead is used in batteries and sinkers in fishing Health effects of lead 7
  8. 8.  At high levels, inorganic lead is a general metabolic poison  Lead poisoning effects the neurological and reproductive systems, example: downfall of roman empire  Lead breaks the blood-brain barrier and interferes with the normal development of brain in infants Environmental effects of leadLead accumulates in the bodies of water organisms and soil organismsHealth effects on shellfish can take place even when only very small concentrations of leadare presentBody functions of phytoplankton can be disturbed when lead interferes.Phytoplankton is an important source of oxygen production in seas and many larger sea-animals eat itThat is why we now begin to wonder whether lead pollution can influenceglobal balances(A-D-B) Mercury  Most volatile of all metals  Highly toxic in vapor form  Liquid mercury itself is not highly toxic, and most of that ingested is excreted Sources of Mercury  Elemental mercury is employed in many applications due to its unusual property of being a liquid that conducts electricity  Used in electrical switches, fluorescent light bulbs and mercury lamps  Emission of mercury vapor from large industrial operations  Unregulated burning of coal and fuel oil  Incineration of municipal wastes  Emissions from mercury containing products :batteries, thermometers, etc.  Mercury amalgams: dental fillings Health effects of mercury 8
  9. 9.  Disruption of the nervous system  Damage to brain functions  DNA damage and chromosomal damage  Allergic reactions, resulting in skin rashes, tiredness and headaches  Negative reproductive effects, such as sperm damage, birth defects and miscarriages Environmental effects of mercury  Fish are organisms that absorb great amounts of methyl mercury from surface waters every day (mercury can accumulate in fish and in the food chains)  The effects that mercury has on animals are:kidneys damage, stomach disruption, damage to intestines, reproductive failure and DNA alteration(A-D-C) Cadmium  Cadmium lies in the same subgroup of the periodic table as zinc and mercury, but is more similar to zinc  Coal burning is the main source of environmental cadmium  Incineration of wastes containing cadmium is an important source of the metal in the environment  Cadmium is most toxic in its ionic form unlike mercury Note: Mercury is most toxic in vapor form and lead, cadmium and arsenic are most toxic in their ionic forms. Sources of Cadmium  Cadmium is used as an electrode in “nicad” batteries  Cadmium is used as a pigment in paints(yellow color)  It is also used in photovoltaic devices and in TV screens  Cigarette smoke  Fertilizers and pesticides Note: The greatest proportion of our exposure to cadmium comes from our food supply- seafood, organ meats, particularly kidneys, and also from potatoes, rice, and other grains. 9
  10. 10. Health effectsof Cadmium  Severe pain in joints  Bone diseases  Kidney problems  Its lifetime in the body is several years  Areas of greatest risk are Japan and central Europe  In very high levels it poses serious health problems related to bones, liver and kidneys and can eventually cause death.Environmental effects of cadmium  Cadmium can be transported over great distances when it is absorbed by sludge  This cadmium-rich sludge can pollute surface waters as well as soils  Cadmium strongly adsorbs to organic matter in soils  When cadmium is present in soils it can be extremely dangerous, as the uptake through food will increase  Soils that are acidified enhance the cadmium uptake by plants  This is a potential danger to the animals that are dependent upon the plants for survival – Cadmium can accumulate in their bodies, especially when they eat multiple plants (10,11). 10
  11. 11. (A-E)Methods ForRemoving Heavy Metals From Waste Water.Heavy Metals Removal: Conventional TechnologiesA number of techniques for the treatment of heavy metal-containing waste waters have been developedin recentyears, in order to both decrease the amount of metal-containing waste watersproduced by industrial activities andimprove the quality of treated effluents.Various treatments,such aschemical precipitation, coagulation–flocculation,flotation, ion exchange,electrochemical treatment process by Using Peat, byAdsorption onto Activated Carbon andmembranefiltration, can be utilized to remove heavy metals from contaminated waste waters, each withtheir owninherent advantages and limitations in application.(A-E-A)Chemical PrecipitationChemical precipitation is the most common technology used to remove dissolved (ionic) metalsfrom water solutions,such as process waste waters containing toxic metals. The ionic metals areconverted to an insoluble form (particle) bythe chemical reaction between the soluble metal compoundsand the precipitating reagent. Typically, the metalprecipitated from the solution is in theform of hydroxide. The conceptual mechanism of heavy metal removal bychemical precipitationis represented aswhere M(OH)nis insoluble metal hydroxide and Mn+and OH- represent dissolved metal ions andprecipitant,respectively. Therefore, the optimum pH for precipitation of one metal may causeanother metal to solubilize, or startto go back into solution. Most process waste waters containmixed metals and hence precipitating these differentmetals as hydroxides can be a tricky process.Chemical precipitation requires large amounts of chemicals to reduce theconcentration ofmetals to an acceptable level for discharging waste waters into the environment. Other drawbacksofthis method are related to the excessive sludge production that requires further treatments,the cost of sludgedisposal, the slow kinetics of metal precipitation, the poor settling ofmetal hydroxides, the aggregation of metalprecipitates, and the long-term environmental impactof sludge disposal. 11
  12. 12. The single component and multi-component hydroxide precipitation andadsorption were studied for different heavymetals namely Iron (III), Chromium(III), Copper (II), Lead (II), Nickel (II), and Cadmium (II) from aqueoussolutions.By using the jar tester Magnesia (MgO) was used as a precipitator at differentdoses and compared withother chemicals like lime (CaO) and caustic soda(NaOH). The treatment involves the addition of either magnesia orlime-waterSuspensions (combined with cationic polyelectrolyte, CPE) in various doses, 1.0 –5.0 g/l for the metalsamples to study the effect of varying doses on the treatmentefficiency. The results show that the percent removal ofmetal ions increases toabout 99 % with increasing the MgO dose to some limits. The optimum values ofMgO doseswere found to be 1.5-3.0 g/l. The pH value ranges are 9.5 to 10 withMgO precipitant and pH of 11.5 to 12 with CaOprecipitantwas the most favorable speed of rapid mixing and the slow mixing speed of 15-30rpm, G of (14-35 s-1), fortwenty minutes gave the best results.At the best operatingconditions of the pilot plant, the removal efficiency of metalions was more than97% at doses of MgO (1.0-4.0 g/l). (12)(A-E-B) Ion ExchangeIon exchange is a reversible chemical reaction wherein an ion present in solution is exchanged witha similarly charged ion bound to a stationary solid phase (resin). Ion exchange can also be used forrecovering valuable heavy metals from inorganic effluents. After separating the loaded resin, metalscan be recovered in a more concentrated solution by eluting with suitable reagents.Since the acidic functional groups of the resins consist of sulfonic acid,it is assumed that thephysico-chemical interactions occurring during metal removal can be expressed as follows:where (–RSO3-) and Mn+represent the anionic group attached to the ion-exchange resin and themetalcation,respectively, while n is the coefficient of the reaction component, depending on theoxidation state of metal ions.Selecting the optimum dosage level depends mainly on the quality offinished water required, considering botheconomic and operating factors. Depending on the characteristicsof the ion exchanger, heavy metal removal by ion 12
  13. 13. exchange is effective in acidic conditionswith pH ranging from 2 to 6. However, ion exchange also has somelimitations in treating wastewaters containing heavy metals. Prior to ion exchange, appropriate pretreatment systemsfor secondaryeffluent such as the removal of suspended solids from waste water are required. In addition,Suitable ion-exchange resins are not available for all heavy metals and the capital and operationalCosts are high.A-E-C) Electrochemical Treatment TechniquesElectro-dialysis (ED) is a membrane separation technique in which ionized species in the solutionare passed throughan ion-exchange membrane by applying an electric potential. The membranesare thin sheets of plastic materials witheither anionic or cationic charge. When a solution containingionic species passes through the cell compartments, theanions migrate toward the anode and thecations migrate toward the cathode, crossing the anion-exchange andcation-exchange membranes.Since ED is a membrane process, it requires clean feed, careful operation, and periodicmaintenanceto prevent any damage to the membranes.In conclusion, it is possible to say that physico-chemicaltreatments offer various advantages buttheir benefits are counterbalanced by a number of drawbacks such as theirhigh operational costs dueto the chemicals used, high energy consumption, and handling costs for sludge disposal. (1-17 )(A-E-D) Metal Removal from Wastewater Using PeatPeat has been investigated by several researchers as a sorbent for the capture of dissolved metals from waste streams.The mechanism of metal ion binding to peat remains a controversial area with ion-exchange, complexation, andsurface adsorption being the prevalent theories. Factors affecting adsorption include pH, loading rates, and thepresence of competing metals. The optimum pH range for metals capture is generally 3.5–6.5. Although the presenceof more than one metal in a solution creates competition for sorption sites and less of a particular ion may be bound,the total sorption capacity has been found to increase. Studies have also shown that metals removal is most efficientwhen the loading rates are low. In addition, recovery of metals and regeneration of the peat is possible using acidelution with little effect on peat’s sorption capacity.14 13
  14. 14. Advantages: This method is simple, effective and economical means of pollution remediation. Peat is plentiful and inexpensive(A-E-E) Removal of Heavy Metals from Industrial Wastewaters by Adsorption onto Activated CarbonPrepared From an Agricultural Solid WasteActivated carbon was prepared from coir pith by a chemical activation method and characterized. The adsorption oftoxic heavy metals, Hg(II), Pb(II), Cd(II), Ni(II), and Cu(II) was studied using synthetic solutions and was reportedelsewhere. In the present work the adsorption of toxic heavy metals from industrial wastewaters onto coir pith carbonwas studied. The percent adsorption increased with increase in pH from 2 to 6 and remained constant up to 10. Ascoir pith is discarded as waste from coir processing industries, the resulting carbon is expected to be an economicalproduct for the removal of toxic heavy metals from industrial wastewaters.15 14
  15. 15. Chapter TwoMethod for the determination of heavy metals such as 1) Voltammeter 2) Chromatography 3) Atomic absorption 4) Atomic emission ICPIntroduction 1) VoltammetryIs a category of electro analytical methods used in analytical chemistry and variousindustrial processes. In voltammetry, information about an analyte is obtained bymeasuring the current as the potential is varied (16)Voltammetry experiments investigate the half cell reactivity of an analyte. Voltammetry isthe study of current as a function of applied potential. These curves I = f (E) are calledvoltammograms. The potential is varied arbitrarily either step by step or continuously, orthe actual current value is measured as the dependent variable. The opposite, i.e.,amperometry, is also possible but not common. The shape of the curves depends on thespeed of potential variation (nature of driving force) and on whether the solution is stirredor quiescent (mass transfer). Most experiments control the potential (volts) of an electrodein contact with the analyte while measuring the resulting current (amperes) (17)To conduct such an experiment requires at least two electrodes. The working electrode,which makes contact with the analyte, must apply the desired potential in a controlled wayand facilitate the transfer of charge to and from the analyte. A second electrode acts as theother half of the cell. This second electrode must have a known potential with which togauge the potential of the working electrode, furthermore it must balance the charge addedor removed by the working electrode. While this is a viable setup, it has a number ofshortcomings. Most significantly, it is extremely difficult for an electrode to maintain aconstant potential while passing current to counter redox events at the working electrode.To solve this problem, the role of supplying electrons and referencing potential has beendivided between two separate electrodes. The reference electrode is a half cell with aknown reduction potential. Its only role is to act as reference in measuring and controllingthe working electrodes potential and at no point does it pass any current. The auxiliary 15
  16. 16. electrode passes all the current needed to balance the current observed at the workingelectrode. To achieve this current, the auxiliary will often swing to extreme potentials atthe edges of the solvent window, where it oxidizes or reduces the solvent or supportingelectrolyte. These electrodes, the working, reference, and auxiliary make up the modernthree electrode system.There are many systems which have more electrodes, but their design principles aregenerally the same as the three electrode system. For example, the rotating ring-diskelectrode has two distinct and separate working electrodes, a disk and a ring, which can beused to scan or hold potentials independently of each other. Both of these electrodes arebalanced by a single reference and auxiliary combination for an overall four electrodedesign. More complicated experiments may add working electrodes as required and attimes reference or auxiliary electrodes.In practice it can be very important to have a working electrode with known dimensionsand surface characteristics. As a result, it is common to clean and polish workingelectrodes regularly. The auxiliary electrode can be almost anything as long as it doesntreact with the bulk of the analyte solution and conducts well. The reference is the mostcomplex of the three electrodes; there are a variety of standards used and it is worthinvestigating elsewhere. For non-aqueous work, IUPAC recommends the use of theferrocene/ferrocenium couple as an internal standard. In most voltammetry experiments,a bulk electrolyte (also known as a supporting electrolyte) is used to minimize solutionresistance. It is possible to run an experiment without a bulk electrolyte, but the addedresistance greatly reduces the accuracy of the results. With room temperature ionic liquids,the solvent can act as the electrolyte.(18) 2) Chromatographic analysesChromatographic analyses were carried out on a metal-free high-pressure ionchromatograph, model 2010i (Dionex, Sunnyvale, CA, USA), which is equipped with anisocratic pump, a post-column pneumatic controller for post-column reagent addition(equipped with a semi permeable membrane reactor), and a variable-wavelengthabsorbance detector (at 520 nm). The ion chromatograph was interfaced to an integratorunit Spectra-Physics model SP4270 (Spectra-Physics, San Jose, CA USA) for collectingchromatographic data Three ionic separation column systems were used during theexperimental tests: (1) a cationic separation column (2) an anionic separation column (3) abifunctional mixed-bed ion-exchange columnThe separation column systems were protected from fouling problems by fixing theirrespective guard columnsAll the experimental tests were carried out under isocratic eluent flow-rate conditions andat room temperature. A 100-ml sample loop was used for all measurements. At thesampling site, groundwater samples were pre-filtered through a filter-membrane (19) 16
  17. 17. Chemical reagents and standardsAll chemical reagents were analytical grade and contained negligible concentrations oftrace metals Nitric and hydrochloric acids were ultra-pure reagents (Merck, Mexico).Pyridine-2,6-dicarboxylicacid (PDCA) and PAR monosodium salt were obtained fromAldrich. Oxalic acid, citric acid, D tartaric acid, lithium hydroxide, sodium hydroxideammonium hydroxide (30%), and acetic acid were also analytical reagent grade (Baker,Mexico).Working standard solutions of metals ranging from0.00195 to 100 mg/ l (1.9 to1310 mg/ l) were prepared each working day by serial dilution of certified AAS standardsolutions of each metal containing 1000 mg/ l (Merck). Deionized water with conductivitylower than 0.1 mS was used. Normal precautions for trace analysis were taken, e.g., allglassware material was carefully cleaned in concentrated nitric acid and vigorously washedwith deionized water.(20) 17