mercury pollution
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Human activities such as burning coal, medical waste, and other materials containing mercury are major contributors to mercury pollution. Mercury enters the environment through air pollution and can harm human health, especially for fetuses and children. The largest source of mercury air pollution is coal-fired power plants, which emit around 70% of the mercury in the US. Capturing mercury from coal plant emissions is challenging given mercury's various chemical forms.
mercury pollution
- 1. MERCURY POLLUTION I. D. MALL Professor, Dept. of Chemical Engineering, Indian Institute of Technology, Roorkee Like all elements, the mercury has also existed on the planet since the Earth was formed. Mercury moves through the environment as a result of both natural and human activities. The human activities that are most responsible for causing mercury to enter the environment are burning materials (such as batteries), fuels (such as coal) that contain mercury, 171 and certain industrial processes. These activities produce air pollution containing mercury. HOW MERCURY ENTERS THE ENVIRONMENT Standard Information Atomic number : 80 Atomic symbol : Hg Atomic weight : 200.59 Group number : 12 Period number : 6 Standard state : liquid at 298 K Color : silvery white Highest specific gravity (among liquids) Temperature : Specific gravity 0oC : 13.595 20oC : 13.595 100oC : 13.352
- 2. Freezing point : -38.89oC Boiling point : 357.25oC Vapour pressure : 0oC : 0.00019 mm Hg 20oC : 0.0012 mm Hg Mercury Inorganic Mercury Compounds • Mercuric sulfide, • Mercuric chloride • Mercury oxide etc. 172 Heat of Vapourization: 16.46 KJ/mol Mercury has high ionization potential Ist 10.39 eV IInd 18.65 eV IIIrd 34.3 eV Due to this mercury forms various compounds with active reagents, such as, oxygen, acids etc. Mercury is a good conductor of heat. Mercury is a fair conductor of electricity. Mercury works well with other metals, especially the amalgams. High Electro – and heat conductivity, significant chemical stability Catalytic Properties: Production of acetaldehyde from acetylene, analysis of organic substances for the determination of nitrogen Mercury vapour density is around 7 times heavier than air. Vapourization: Colourless vapour in air, no odour, so illusion that it is not present in the air. Mercury vapour: Dermal rate penetration. As temperature rise from 20 to 30oC, vapour pressure increases and consequently increase in concentration of mercury in air by 2.32 times. 30 – 40oC – at its own surface, concentration of mercury exceeds the maximum permissible quantity for industrial sites 3000 – 6000 times. TYPES OF MERCURY COMPOUNDS Mercury is a naturally occurring element that is found in air, water and soil. It exists in several forms: Elemental/ or Metallic Mercury INORGANIC MERCURIC COMPOUNDS Organic Mercury Compounds •Methyl mercury •Ethyl mercury •Dimethyl mercury •Phenyl mercury These include mercuric sulfide (HgS), mercuric oxide (HgO) and mercuric chloride (HgCl2). Also called mercury salts. Most inorganic mercury compounds are white powders or crystals, except for mercuric sulphide, which is red and turns black after exposure to light.
- 3. Some mercury salts (such as HgCl2) are sufficiently volatile to exist as an 173 atmospheric gas. Water solubility and chemical reactivity of these inorganic (ionic) mercury gases lead to much more rapid deposition from the atmosphere than for elemental mercury. This results in significantly shorter atmospheric lifetimes for these ionic (e.g. divalent) mercury gases than for the elemental mercury gas. ORGANOMERCURIALS When mercury combines with carbon, the compounds formed are called organic mercury compounds or organomercurials. e.g. dimethyl mercury, phenyl mercury, ethyl mercury and methyl mercury). The most common organic mercury compound in the environment is methyl mercury. Like the inorganic mercury compounds, both methyl mercury and phenyl mercury exist as salts (for example, methyl mercuric chloride or phenyl mercuric acetate). When pure, most forms of methyl mercury and phenyl mercury are white crystalline solids. Dimethyl mercury, however, is a colourless liquid. HEALTH EFFECTS An exposure to the various forms of mercury will harm a person's health depends on a number of factors. The factors that determine how severe the health effects are from mercury exposure include these: the chemical form of mercury (methylmercury is more toxic than elemental mercury); the dose; the amount of chemical entering the body the age of the person exposed (the fetus is the most susceptible); the duration of exposure; the route of exposure -- inhalation, ingestion, dermal contact, etc.; and the health of the person exposed. MERCURY POISONING CAUSES impaired neurological development in fetuses, infants, and children impairment of the peripheral vision; disturbances in sensations (pins and needles feelings, usually in the hands, feet, and around the mouth); lack of coordination of movements; impairment of speech, hearing, walking; and muscle weakness Elemental mercury poisoning causes motional changes (e.g., mood swings, irritability, nervousness, excessive shyness); insomnia; neuromuscular changes (such as weakness, muscle atrophy, twitching); headaches; disturbances in sensations; changes in nerve responses; performance deficits on tests of cognitive function. At higher exposures there may be kidney effects, respiratory failure and death.
- 4. Symptoms of high exposures to inorganic mercury include: skin rashes and dermatitis; mood swings; memory loss; mental disturbances; and muscle weakness HLL closed the factory in May 2001 after the local people, led by environmental groups, brought to the notice of the Tamil Nadu Pollution Control Board (TNPCB) the fact that the company had dumped 7.4 tonnes of mercury-contaminated glass waste at its scrapyard, in the slopes in Munjikal, below the rear wall of the factory. One gram of mercury let into a 10-hectare lake for a few years can poison it completely.) The scrap yard is located in a crowded area of the town. Subsequently, the TNPCB issued notice to the company to refrain from carrying out any activity at the plant site. It also cut water and power supply to the factory The Factories Act, 1948 : The second schedule Permissible Levels of certain Chemical substances in work Environment Permissible limits of exposure (mg/m3) Short term exposure limit (15 min) Time weighted avg. concentration (8h) Substance Mercury (as Hg) – skin (i) Alkyl compounds 0.01 0.03 174 Mercury-contaminated glass waste being packed at HLL's scrapyard for shipment to the United States, on the orders of the Tamil Nadu Pollution Control Board in March. The glass waste in the scrapyard at HLL (ii) All forms except 0.05 - alkyl vapour
- 5. EPA daily exposure limit of Methyl Mercury microgram (μg) /per kilogram (2.2 lbs)/ per day. Assumes inhalation or ingestion, and not INJECTION. Also assumes low background exposures not large bolus doses. Different Emission Sources Causes Mercury Pollution Combustion Manufacturing Miscellaneous Utility Boilers Chlor-alkali production Paints use Commercial/industrial boilers Lime manufacturing Mercury catalysts 175 Electric lamp breakage Carbon Hazardous waste black production combustors Landfills Electrical apparatus Turf products manufacturing Sewage sludge incinerators Agricultural burning Geothermal power plants Mobile sources Medical waste incinerators Battery production Explosives manufacturing Mercury compounds production Dental Municipal waste combustors preparations Primary mercury Pigment production production Laboratory use Residential boilers Oil shale retorting Area Point
- 6. Area Point Combustion Manufacturing Sludge application Byproduct coke production Total amount of mercury Number of units produced 450,000 70 tonnes Some leading mercury users in India (1998-2001) Sector Mercury (Hg) content per unit About 200 gm mercury used per tonne of caustic tonnes/year soda produced. All this mercury is passed on to the environment through emissions and products. Varies between 0.6 to 1 gm. 8957,0002 7.2 tonnes Chlor-alkali Thermo meters Batteries • Alkaline Not more than 25 mg NA Total 33 to 50 per cent by weight of the battery 1,650 million3 25 tonnes5 Mercury Zinc Total 1per cent Hg by (LeClanche) weight of the battery NA Zinc Carbon Fluorescent lamps 0.0252 to 0.080 gm / lamp6 150 million3 7.89 tonnes Between 3 gm to 6gm6 4051,0004 18.23 tonnes Thermostat switches Average 0.6 or 0.7 gm per unit 1481,0002 0.96 tonnes Alarm clocks 0.4 gm per unit6 95,5003 0.04 tonnes Hearing aids Average annual mercury emissions between 1991-92 and 2000-2001 176 Primary copper smelting Cement manufacturing Petroleum refininga Instrument manufacturing Secondary mercury production Zinc mininga Fluorescent lamp recycling Pulp and paper mills Wood-fired boilers Residential woodstoves Crematories Source: 1. Environmental Rating of Indian Caustic-Chlorine Sector, Green Rating Project ,(2002),Centre for Science and Environment. 2. Industrial Handbook, Centre for Industrial Economic Research (Delhi), 1998 3. Industrial Handbook, Centre for Industrial Economic Research (Delhi), 2000-01 4. http://www.indiainfoline.com/auto/db01.html 5. Telephonic conversation with Battery Industry official 6. Draft Wisconsin Mercury Sourcebook, Wisconsin Department of Natural Resources (USEPA grant), May 1997
- 7. Point Source Estimate of Mercury Discharge in the U.S. Source: U.S. EPA, Office of Air Quality Planning and Standards. 1999 National EmissionsInventory for Hazardous Air Pollutants. http://www.epa.gov/ttn/chief/net/1999inventory.html#final3haps MERCURY EMISSIONS FROM COAL -FIRED POWER PLANTS Interesting facts about Coal-fired Power Plants and Mercury Pollution Coal-fired power plants are the single largest source of mercury pollution According to the US National Wildlife Federation (NWF), a single 100 megawatt (MW) coal-fired power plant emits approximately 25 pounds of mercury a year. According to the US Center for Clean Air Policy, 50% of the mercury emitted from coal-fired power plants can travel up to 600 miles from the power plant. According to NWF, as little as 0.002 pounds of mercury a year can contaminate a 25-acre lake to the point where fish are unsafe to eat. Coal Plants are Largest Mercury Source Methylmercury contamination in food sources as low as one part per million has been shown to cause death in some some animals. The majority of the mercury entering lakes, streams, rivers, and oceans comes from the atmosphere (i.e. air deposition) 85% of mercury emissions come from smokestacks, primarily power plants and municipal and medical waste incinerators 177
- 8. 33% of all mercury emissions comes from utility boilers (coal- and oil-fired), Source Tons/yr Percent(%) Asia 860 58 Africa 197 13 Europe 186 13 N. America 105 7 Australia 100 7 S. America 27 2 178 the largest unregulated source. Mercury Pollution Per Year 70% from Coal-fired Power Plants ENVIRONMENTAL ISSUES WITH COAL AS FUEL Burning coal without increasing global carbon dioxide levels is a major technological challenge Coal when burnt gives rise to a variety of wastes which must be accounted and controlled Mercury, NOx, SOx and Solid Particulate Matters in the form of ash are the main pollutants Solid and fly ash quantify as high as 50% of Indian Coal Global warming associated with emission of CO2, NOx is a major issue with world community Burning coal without increasing global carbon dioxide levels is a major technological challenge
- 9. Coal when burnt gives rise to a variety of wastes which must be accounted and Year 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Consumption 332.2 358.5 362.9 375.4 406.1 413.6 430.6 430.6 N/A N/A 179 controlled Worldwide Distribution of Mercury Emissions Source: United Nations Environment Programme Global Mercury Assessment, 2002, Mercury in Coal Coal Production and Consumption in India, 1996-2005 (in millions of short tons) n/a - not applicable N/A – not available 412.95 n/a 382.61 24.34 389.20 n/a 361.24 27.96 367.29 n/a 341.27 26.02 352.60 n/a 327.79 24.81 337.94 n/a 313.69 24.25 326.58 n/a 304.10 22.48 319.93 n/a 296.51 23.42 323.63 n/a 300.40 22.23 311.96 n/a 289.32 22.64 295.56 n/a 273.41 22.15 Production Anthracite Bituminous Lignite
- 10. note: components may not add to total due to rounding Source: Government of India Behavior of Mercury in Coal-fired Boilers APCD Entrained PM Inlet 140 °C HCl N2 Hg Mercury Partitioning Mass Fraction Hgo, Hg2+ compounds, particulate mercury Hg(p) 180 1500 °C Hg° Coal MERCURY CAPTURE CO2 H2O SO2 NOx Thermochemical Equilibrium Calculations HgCl Hg° 2 HgO 0 300 600 900 1200 Temperature, °C Factors Affecting Speciation Type and properties of coal Time/temperature profile Composition of flue gas Fly ash and sorbent properties Flue gas cleaning conditions Hg(p) easily captured by electrostatic precipitators (ESPs) and fabric filters (FFs) Hg 2+ compounds are relatively soluble and can generally be captured in scrubbers Hg° is insoluble and must be adsorbed onto solids or converted to Hg 2+ for capture by scrubbing Typical Hg2+ to Hg° ratio in flue gas: bituminous coal subbituminous coal lignite SOURCE OF MERCURY IN COAL-FIRED THERMAL POWER PLANT Mercury exists in trace amounts in fossil fuels (e.g., natural gas, oil, and coal), vegetation, crustal material, and waste products. Through combustion, mercury vapor can be released to the atmosphere, where it can drift for a year or more, spreading with air currents over vast regions of the globe. In 1995, an estimated 5,500 tons of mercury was emitted globally from both natural and anthropogenic sources.
- 11. ENVIRONMENTAL IMPACT OF CEMENT MANUFACTURE 181 INTRODUCTION Major environmental issues are dust pollution of the atmosphere and emission of Green House Gases (GHG), ecological concern arising from the degradation of mined-out areas, noise transport pollution and emission of mercury. GHG emission from cement industries is about 1.4 x 103 million tonne of CO2 equivalent against the total world greenhouse gas emissions of 44 x 103 million tonne of CO2 equivalent. Cement related GHG emissions originate from fossil fuel combustion at cement manufacturing operation (40%) transport activities (5%) combustion of fossil fuel that is required to make the electricity (5%). manufacturing process (about 50%) Cement consumption 1985-2020E (million t) Continent 1985 2003 2020 % pa growth 03 -20 Developed countries 323 410.5 475 0.80 % Developing countries 363.7 1202.5 2586.5 4.30 % Total 686.7 1612.9 3061.5 3.60 %
- 12. PRODUCT LIFE CYCLE OF CEMENT Environmental Impact of Cement Manufacture Energy Energy EIA/LCA MERCURY EMISSION FROM POWER PLANTS Case study: Mercury Emissions from Thermal Power Plants, Singhrauli, M.P. The Singhrauli area is a major site of thermal power generation in the country at Present. Govind Ballabh Paant Sagar lake is surrounded by the super thermal powerPlants(STPP) namely Singhrauli STPP, Vindhayachal SSTP, Rihand STPP, Anpara A B STPP, Renusagar STPP. Besides Hindalco, High Tech Carbon and Kanoria Chemical Industrial Units, which contribute towards thermal, chemical and industrial effluents alongwith airborne pollutants. The Power Plant Combustion Waste Stream (CW) 182 RAW MATERIAL MINING CLINKER PRODUCTION CLINKER PRODUCTION TRANSPORATION CONCRETE STRUCTURE ITS USE DEMOLITION RECYCLE Energy Energy Energy Waste Waste Waste Waste Waste AIR POLLUTION: Particulate and Fugitive emission,SOx, NOx. PLANT PROCESS Raw Material Preparation, Crushing and Grinding, Pyroprocessing, Clinker Cooling, Clinker and Gypsum grinding. RAW MATERIAL MINING Lime Stone, Laterite, Bauxite, Gypsum, Coal. STORAGE AND TRANSPORTATION OF FINISHED PRODUCT AIR POLLUTION: Particulates, Fugitive emission,SOx, NOx. SOLID WASTE: Fly Ash, ETP Sludge, rejects. ACIDIFICATION CO2 EMMISSION WATER POLLUTION: BOD, COD, TSS. AIR POLLUTION: Particulate and Fugitive emission.
- 13. This waste stream already contains about 40% of the mercury in coal mined for 20 g Elemental Hg (v) 60 g HgCl2 (v) 20 g HgCl2 (particle-bound) 183 power production. Considerable evidence suggest that federal and state regulation of how these wastes are managed does not adequately protect the environment. Small amounts of mercury are contained in several waste types: Flyash Scrubber sludge Active mercury control sorbents Bottom ash How Far does Mercury Travel in the Atmosphere emitted by coal-fired thermal power plant? EPA estimates 7 to 45% of mercury released from power plants is deposited within a 30-mile radius. The stack height at each plant, the chemical species of the mercury, and the amount of rainfall at a given site all affect how much mercury is deposited around the plant. As shown in the table (next slide), power plants with shorter stacks will have more local deposition than those with taller stacks, and more mercury is deposited locally in a humid site compared to an arid site. EPA’s Mercury Emissions Partitioning Assume 100 g Total Hg Global Cycle 64% Loss Global Cycle 99% Loss 40.8 g HgCl2 (v) Deposited Only 48.2 g Total Hg Deposited 7.2 g HgCl2 (p-b) Deposited Global Cycle 32% Loss 1% 0.2 g Elemental Hg (v) Deposited Hazardous Waste Combustion Facility 36% 68% Emission Rates Hg0 = 0.2% of Total Hg HgCl2 = 48% of Total Hg Vapor Phase Fractions, Fv Fv for Hg0 (0.2/0.2) = 1.0 Fv for HgCl2 (40.8/48.0) = 0.85
- 14. Elemental Mercury Phase, Upon Deposition Hg0 (v) = 0.2% of Total Hg Emitted Negligible Contribution to Soils, Water Bodies, and Plants Assumed Only Direct Inhalation of Vapor is Evaluated for Elemental Mercury Mercuric Chloride Phases, Upon Deposition HgCl2 (v, particle-bound) = 48% of Total Hg emitted Significant Contribution to Soils and Water Direct Inhalation and Indirect Pathways are Evaluated for Mercuric Chloride MERCURY TRANSPORT FATE: AFTER DEPOSITION Deposition to Soils Water Body = (7.2g HgCl2)pb + (40.8g HgCl2 + 0.2 g Hg0)v Runoff Ksr Points in controlling Mercury pollution in coal-fired thermal power plant The capture of mercury across existing air pollution control devices (APCD) can vary significantly based on coal properties, fly ash properties including unburned carbon, specific APCD configurations, and other factors. ICR data indicates that for For pulverized coal (PC) units (the predominant technology currently used for electricity generation) the greatest co-benefit mercury control is realized for bituminous-fired units equipped with a fabric-filter baghouse (FF) for PM control and either wet flue gas desulfurization (FGD) or spray dryer absorber (SDA) for SO2 control. 184 Volatilization Ksv Leaching Ksl Soil Losses Ks = Ksg + Kse + Ksr + Ksl + Ksv Runoff Load Lri + Lr Erosion Load Le Cs 98% HgCl2 2% MeHg Cw 85% HgCl2 15% MeHg Erosion Kse Total Load to Water Body Ltotal = Ldep + Ldiff + Lri + Lr + Le Prior to Soil Losses 47g HgCl2; 0.96g MeHg Prior to Loads from Soils 40.8g HgCl2; 7.2g MeHg
- 15. The worst performing bituminous-fired PC units were equipped only with a hot-side electrostatic precipitator (ESP). Units burning subbituminous and lignite coals frequently demonstrated significantly worse mercury capture than a similarly equipped bituminous-fired unit. For example, Figure 3 on previous slide presents the percent mercury removal for bituminous, lignite, and subbituminous coal-fired plants with cold-side ESPs. Plants that burn bituminous coal typically have higher levels of oxidized mercury than plants that burn lignite or subbituminous coal, possibly due to the higher chlorine and/or sulfur content of bituminous coal. 185 Control technologies in use today On average across U.S. coal-fired power plants, current technologies being used to reduce particulate, NOx and SO2 emissions capture about 40% of the mercury that enters the boilers with the coal. However, the removal rate of mercury for any particular plant can vary from 10% to over 90%, depending on the type of coal and the air pollution control device used. In addition, a significant fraction of the eastern bituminous coal burned in power plants is cleaned before it is shipped to the plant, and this process removes, on average, 25-35% of the mercury in the coal. Effectiveness of these technologies in reducing mercury emissions The primary factors that affect the capture of mercury by existing air pollution controls are the coal burned and the type of air pollution (NOx, SO2, particulate) controls used at the plant. Mercury in the flue gas appears as a mix of elemental (or metallic, non-water soluble) and oxidized (water soluble) mercury, depending primarily on the coal and to a lesser extent on the design of the boiler. Some controls, such as scrubbers for SO2 reduction, capture only oxidized mercury. In some cases, selective catalytic reduction (SCR) for NOx control may increase the percent of the mercury that is in the oxidized form, enabling a downstream scrubber (if present at the power plant) to capture more of the mercury. Coals and boilers that result in increased levels of carbon leaving the boiler unburned tend to produce a fly ash that may adsorb some of the mercury. The amount that would be adsorbed and subsequently captured by the particulate control depends on the technology used – electrostatic precipitators or bag houses – due to the difference in how the fly ash and flue gases contact each other in these devices. All these interactions depend on complex chemical reactions between various species in the flue gas, especially chlorine, but we do not yet totally understand this chemistry.
- 16. 186 Key findings of ITRC, Lucknow Out of total 100 vegetable samples. 23% samples had mercury levels higher than permissible limit Mean mercury level; were significantly higher (p 001) food crops obtained from Singhrauli region than mean levels of the samples collected from the control areas. Out of forty samples of drinking water collected from Singhrauli region, Six samples showed higher values than the permissible level of 1 μg/l. The mean mercury values of (30 samples) of mercury in fish collected from Singrauli region were significantly higher (p 001) than the mean values of fish collected from control areas. 19 milk samples out of 22 samples collected from the Singhrauli region had mercury levels higher than the permissible levels of 3 μg/l. http://www.cseindia.org/dte-supplement/70-71SPR.PDF
- 17. Summary of Pollution Sources Control : Techniques for Mercury 187 Restriction without pretreatment like recycling/sanitar y-land fill, etc. Solid waste dumping Process change/restrictio n in use of Hg Process Pulp paper change/use of ventury scrubber Chlor-alkali industries Air pollution control Air borned Hg particulate deposition Ion exchange/neutra lization sedimentation Mining smelting battery Mercury E/P bughouse Battery cell Restriction in use in agriculture Use as herbicide Insecticide Process change/properly designed tailings disposal sys. Chlor-alkali industries Conditioning of Hg in refrigeration unit followed by EP Hg Mining smelting Control measures Control Soil pollution measures Water pollution source Control measures Air pollution source