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ENVIRONMENTAL CHEMISTRY Chem. 3030

ENVIRONMENTAL CHEMISTRY Chem. 3030. The two terms ‘environmental chemistry’ and ‘pollution’ often seem to go together, yet environmental chemistry is much more than the study of chemical effects of pollution.

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ENVIRONMENTAL CHEMISTRY Chem. 3030

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  1. ENVIRONMENTAL CHEMISTRY Chem. 3030

  2. The two terms ‘environmental chemistry’ and ‘pollution’ often seem to go together, yet environmental chemistry is much more than the study of chemical effects of pollution. It is a multidisciplinary science of chemical phenomena in the environment involving chemistry, physics, life science, public health, engineering, etc.

  3. THE COURSE OUTLINE Stratospheric chemistry and the ozone layer; principles of photochemistry, light absorption by molecules, noncatalytic and catalytic process of ozone distraction, free radicals, Cl and Br as X catalysts, the ozone hole and its consequences, chlorofluorocarbons (CFCs). Ground-level (tropospheric) air chemistry; ground-level ozone and photochemical smog, oxidation of methane, hydrocarbons and atmospheric SO2, acid rain, ecological effects of outdoor air pollutants, indoor air pollution: formaldehyde, NO2, CO, tobacco smoke, asbestos, radioactivity from radon gas. The greenhouse effect and global warming; energy absorption, the major and minor greenhouse gases: CO2, water vapour, methane, N2O, CFCs. Environmental consequences of energy use: CO2 emissions,solar energy, conventional and alternative fuels, nuclear energy. The chemistry of natural waters; acid-base chemistry, CO2/carbonate system, ion concentations, alkalinity, seawater, redox chemistry in natural waters, oxygen demand, the pE scale, sulphur and nitrogen compounds, ion complexes, stratification, precipitation. Soil chemistry; soil components, weathering process, aerobic, anaerobic soils, water-sediment-soil system.

  4. Reading References: W. vanLoon, S. J. Duffy; Environmental Chemistry, a Global Perspective, 2nd ed. Colin Baird; Environmental Chemistry TG Spiro, WM Stigliani; Chemistry of the Environment Course notes

  5. THREE MAJOR ENVIRONMENTAL MEDIA: SURFACE WATERS, SUBSURFACE WATERS (SOIL AND GROUND WATER), AND THE ATMOSPHERE Each medium has its own distinct characteristics but they have also many similarities. Few chemicals are restricted in their movement to one medium only – chemical exchange must be considered.

  6. WATER WATER IS THE ELEMENT OF SELFLESS CONTRAST – IT PASSIVELY EXISTS FOR OTHERS … WATER’S EXISTENCE IS,THEREFORE, AN EXISTING-FOR-OTHERS …ITS FATE IS TO BE SOMETHING NOT YET SPECIALIZED … AND THUS IT SOON CAME TO BE CALLED ‘THE MOTHER OF ALL THAT SPECIAL’ Hegel, Philosophy of nature (1817)

  7. WATER PROPERTY MAGNITUDE CONSEQUENCE HEAT CAPACITYExceptionally high a). Slows down temp.changes. 4.19 kJ / kg K b). Heat transported around the globe by ocean currents. c). Influences climate LATENT HEAT OFExceedingly high Stops the water temp. from changing FUSION 333 kJ/ kg rapidly when is around zero – additional energy required to freeze the water. LATENT HEAT OFHighest of all substances Low water and heat loss to the EVAPORATION2260 kJ/kg atmosphere DENSITY Maximum density at 40C Ice floats, insulating the water below Decreases with from cold. increasing salinity. Stratification of non-flowing waters SURFACE Highest of all liquids Controls the size of raindrops, sea TENSION73 mN/m waves, sprays, etc. DISSOLVING Exceptionally good Dissolves nutrients and transports POWER them to plants. TRASPARENCYRelatively large Absorbs in the ultraviolet and infrared but transmits the visible radiation required for photosynthesis

  8. Ice crystal Model of water molecule

  9. The model of hydration sphere of sodium – an inner rigid water shell, an outer, somewhat rigid floating in the sea of ‘free’ water Polymers of water molecules demonstrating the ‘flickering clusters’ model

  10. STRATIFICATION EPILIMNION warmer, lower density, aerobic CO2 H2CO3 HCO3- SO42- NO32-- Fe(OH)3 THERMOCLINE HYPOLIMNION cooler, more dense, anaerobic CH4 H2S NH3 NH4+ Fe2+(ag) bacteria SEDIMENTS

  11. 1000g (1L) / 18g = 55.56 mol/L K = [H3O+] [OH-] / 55.56 or K x 55.56 = [H+] [OH-] = 10-14 (250C) KW and pKw = pH + pOH = 14 THE ACDITY OF WATER THE ACIDITY OF WATER AND ANY AQUEOUS SOLUTION – MEASURE OF CONCENTRATION OF HYDRONIUM IONS = pH pH = -log [H3O+] or simply pH = -log [H+] Autoprotolisis of water: 2H2O  H3O+ + OH- K = [H3O+] [OH-] / [H2O] = 1.8 x 10-16 (250C) What is the concentration of water in water?

  12. ACIDITY OF THE SOLUTION • IDENTIFY THE SPECIES IN SOLUTION • ex.sol. NaCl in water sol. HCl in water • HOW CONCENTRATIONS OF IONS DEPEND ON EACH OTHER • ex.Ka, Kb, Kw for HCl and NaOH sol. • MASS BALANCE • ex. For the fixed volume V  m ~ c • CHARGE BALANCE • ve+ = ve- • SOLUBILITY OF GASES • X(g) = X(aq) • KH = [X(aq)] / px - Henry’s Law

  13. ACID-BASE CHEMISTRY IN NATURAL WATERS THE CO2 / CARBONATE SYSTEM CO32-  H2CO3 moderately weak strong base acid CO2 + H2O  H2CO3  2H+ + CO32- LIME ROCKS – SOURCE OF CARBONATE IONS

  14. The proportion of the carbonate present in all its possible forms

  15. CO32- + H2O HCO3- + OH- H2CO3 HCO3- + H+ AIR WATER ROCK SOIL SEDIMENTS NATURAL AIR,WATER,ROCK SYSTEM CO2 H20 + Ca2+ CaCO3

  16. EQUILIBRIUM: WATER / CaCO3 1. CaCO3  Ca2+ + CO32- Ksp = [Ca2+] [CO32-] = 4.6 X 10 –9 (250C) [Ca2+] = [CO32-] = S - solubility, Ksp = S2, S = (Ksp)1/2 = 6.8x 10-5M 2. CO32- + H2O  HCO3- + OH- K = [HCO3-][OH- ] / [CO32-] 3. = (1 + 2) CaCO3 + H2O Ca2+ + HCO32- + OH- and KT = Ksp + K Ka (HCO3-) = 4.7 x 10-11 and Ka x Kb = KW = 10-14 Kb (CO32-) = KW / Ka = 2.1 x 10-4 conjugate base KT = [Ca2+] [HCO3-] [OH- ] and S = [Ca2+] = [HCO3-] = [OH- ] KT = S3 = 9.7 x 10-13 S = 9.9 x 10-5 GREATER SOLUBILITY BECAUSE CO32 REACTS WITH WATER

  17. EQUILIBRIUM: WATER / CaCO3 / CO2 (ATMOSPHERIC) CaCO3 + CO2 + H2O  H2CO3  Ca2+ + 2HCO3- with K = Ksp x Kax Kb x KH/ KW = 1.5 x 10-6 M3/L3atm   and K = [Ca2+] [HCO3-]2 / p CO2 = S x (2S)2 / p CO2 p CO2 – partial pressure of atmospheric CO2 = 0.00036 atm S3 = 1.3 X 10-10 and S = 5.1 x 10-4 M / L Compare:water with CO2without CO2 [Ca2+] 5.1 x 10-4 M / L 9.9 x 10-5 M / L WATER WITH DISSOLVED CO2 MORE READILY DISSOLVES CaCO3

  18. ACIDITY OF NATURAL WATERS – normal and acid rain (1) (1) pH = 5.6

  19. ACIDITY OF NATURAL WATERS – sea water

  20. 1 2 3 4 5 6 5 7 2 ACIDITY OF NATURAL WATERS - seawater

  21. 1 pH = 8.4

  22. Cl- Hg2+ + Cl- HgCl+ HgCl+ + Cl- HgCl2 and HgCl3-HgCl42- OH- HgCl+ + OH-  HgOHCl and HgOHxClyz METAL COMPLEXES IN NATURAL WATERS APPLICATION OF CHEMISTRY OF SIMPLE METAL - LIGAND SYSTEMS TO MUCH MORE COMPLEX ENVIRONMENTAL SYSTEMS EX: Inorganic Hg complexes in sea water Conditions: pH = 8.4 – OH- , major anion Cl- Large number of equilibrium reactions are occurring in water In order to assess the environmental impact of trace metals in water body predictions have to be made as to which species are present in solution. Solutions: Complicated computer modeling and/or graphical representations

  23. COMPLEXES COMPLEXES Hg Pb Ag Cu Cu Hg Ni Pb ADSORBED ADSORBED Na Ag Na Ni K K FRESHWATER SEAWATER THE MAJOR COMPLEXES OF TRACE METALS IN WATERS FREE IONS FREE IONS

  24. ELEMENT MAJOR SPECIES ELEMENTS PREDICTED TO HAVE SIMILAR SPECIATION IN FRESH AND SEAWATER ELEMENTS PREDICTED TO HAVE DIFFERENT SPECIATION IN FRESH AND SEAWATER FRESHWATER BOTH SEAWATER

  25. The oxidation of water H2O = O2 + 4H+ + 4e- log K = - 83.1 K = pO2 [H+]4 [e-]4 and pE = 20.75 -pH The reduction of water 2H+ + 2e- = H2 log K =0 K = pH2/ [H+]2 [e-]2 and pE = -pH pE pE pH pH REDOX CHEMISTRY IN NATURAL WATERS The concentration of electrons control redox processes in the environment pE = -log [e-] Most common measure of electron activity is EH, the electrode potentialmeasured against SHE The natural limits of redox in natural waters pE and EH are linearly related: pE = (F/ 2.3RT) EH

  26. REDOX AND ACIDITY CONDITIONS IN NATURAL WATERS

  27. pE – pH (or EH - pH) DIAGRAMS (Pourbaix diagrams)

  28. pE – pH (or EH - pH) DIAGRAMS (Pourbaix diagrams)

  29. WATER CHEMISTRY... AND SOIL Soil composition 1. Inorganic mineral matter (defined as soil material made up mostly of oxygen, silicon, and aluminum (many other metals in small quantities may be included) 2. Organic mineral matter (defined as soil material having derived mostly from plant residues and made up mostly of carbon, oxygen, and hydrogen) 3. Solutes (refers to the portion of soil composed of water and mostly dissolved salts (plant nutrients) 4. Air (refers to the gaseous portion of soil composed of the same gases found in the atmosphere (oxygen, nitrogen, and carbon dioxide) but in different proportions)

  30. WATER CHEMISTRY... AND SOIL Soil modifies water chemistry or quality through the processes of: 1. Surface-exchange hydrolysis 2. Dispersion by monovalent metal ions 3. Soil's catalytic role in many chemical and/or electrochemical reactions 4. Precipitation reactions of heavy metals through hydroxylation 5. Oxidation reactions of organics and inorganics 6. Hydrolysis reactions of organics and inorganics 7. Condensation reactions of organics 8. Physical adsorption of metals and metalloids 9. Chemical reactions with metalloids 10. Soil-dissolution reactions Overall, soil systems behave as complex biomolecular sieves.

  31. Soil – polymeric structures of silicates – extended networks Si4+ can be replaced by Al3+ Other major cations: H+, K+, Na+, Mg2+, Ca2+, Fe2+ Structural units in silicate minerals

  32. ION EXCHANGE EQUILIBRIA ON THE SURFACE OF SOIL-CLAY PARTICLE Clay minerals – particles <2µm. They bond electrostatically cations – natural ion exchangers

  33. Organic matter – humus: decompose by organisms plant material in forms of cellulose and hemicellulose undecomposed –protein and lignin and its polimerized and partly oxidized forms containing carboxylic groups –COOH: fulvic and humic acids Fulvic acid – soluble in alkaline and acidic solution Humic acid - soluble in alkaline, not soluble in acidic solution Humic materials have great affinity to heavy metal cations and extract them from waters by ion exchange process – formation of complexes by –COOH groups in fulvic and humic acids CEC – Cation Exchange Capacity – quantity of cations that are reversibly adsorbed per unit mass of a dry soil – number of moles of positive charge

  34. WEARTHERING PROCESS

  35. SUSPENDED SEDIMENTS WATER SEDIMENTATION DISSOLUTION RESUSPENSIBLE BOTTOM SEDIMENTS BOTTOM SEDIMENTS DISSOLUTION AND DEPOSITION PROCESSES THE INTERCHANGE OF MATERIAL BETWEEN SEDIMENTS AND WATER

  36. SOIL CHEMISTRY TRRESTIAL CHEMISTRY WATER-SOIL CHEMISTRY BIOGEOCHEMISTRY

  37. DISSOLUTION AND DEPOSITION PROCESSES: • SOLUBILITY AND PRECIPITATION • CHEMICAL WEATHERING - BY HYDROLISIS (SILICATES) • - BY OXIDATION (IRON MINERALS, S2-) • COLLOIDS AND THEIR AGGREGATION - HYDROPHILIC COLLOIDS (LARGE MOLECULES WHICH INTERACT STRONGLY WITH WATER) - HYDROFOBIC COLLOIDS (INTERACT LESS STRONGLY BUT ARE STABLE BECAUSE PARTICLES REPEL EACH OTHER - ASSOCIATION COLLOIDS (MICELLES)

  38. CONCENTRATION OF IONS IN SOIL SOLUTIONS IS DETERMINED BY MANY PROCESSESS DEPENDENT ON EACH OTHER REDUCTION DESORPTION PRECIPITATION OXIDATION ACID-BASE REACTION COMPLEX FORMATION ADSORPTION OTHER CONNECTIONS….?

  39. REMOVING COLLOIDAL MATERIAL  TO AGGREGATE COLLOIDS  TO DESTABILIZE COLLOIDS 

  40. ACID MINE DRAINAGE

  41. ACID MINE DRAINAGE

  42. This reaction is catalyzed by bacteria. • The pollution associated with AMD is characterized by: • Seeping from mines acidified water and rust-coloured iron hydroxide • The concentrated acid liberate toxic heavy metals from their ores in the mine, further adding to the pollution.

  43. CHEMICAL SPECIATION OF HEAVY METALSTHE NEED FOR SPECIATION • DISTRIBUTION, MOBILITY AND BIOLOGICAL AVAILABILITY OF CHEMICAL ELEMENTS DEPENDS NOT SIMPLY ON THEIR CONCENTRATIONS BUT, CRITICALLY, ON THE CHEMICAL AND PHYSICAL ASSOCIATIONS WHICH THEY UNDERGO IN NATURAL SYSTEMS. • CHANGES IN ENVIRONMENTAL CONDITIONS (NATURAL AND ANTHROPOGENIC) CAN STRONGLY INFLUENCE THE BEHAVIOUR OF BOTH ESSENTIAL AND TOXIC ELEMENTS BY ALTERING THE FORMS IN WHICH THEY OCCUR. • THE MOST IMPORTANT CONTROLING FACTORS INCLUDE pH, REDOX POTENTIAL, AND AVAILABILITY OF ‘REACTIVE SPECIES’ SUCH AS COMPLEXING LIGANDS (ORGANIC AND INORGANIC), PARTICLE SURFACES FOR ADSORPTION, AND COLLOIDAL MATTER. SPECIATION SCIENCE SEEKS TO CHARACTERISE, AT LEAST SOME OF, THE MOST IMPORTANT FORMS OF AN ELEMENT, IN ORDER TO UNDERSTAND THE TRANSFORMATIONS BETWEEN FORMS WHICH CAN OCCUR, AND TO INFER FROM SUCH INFORMATION THE LIKELY ENVIRONMENTAL CONSEQUENCES.

  44. CHEMICAL SPECIATION CLASSES OF CHEMICAL SPECIATION SCREENING SPECIATION (identification and quantification of different species of an element, e.g. free ions, complexes) REDOX SPECIATION (identification and quantification of different oxidation states of an element) ISOTOPIC SPECIATION (mostly for medical purposes or to trace sources of contaminants) DISTRIBUTION SPECIATION (e.g. biological uptake, transport in soils, distribution in water column)

  45. CHEMICAL SPECIATION OF HEAVY METALSFUTURE DEVELOPMENTS AND REQUIREMENTS • STANDARIZATION OF SPECIATION SCHEMES • DEVELOPMENT OF NEW IN SITU ANALYTICAL METHODS FOR SPECIES DETERMINATION • DEVELOPMENT OF INTELLECTUAL TOOLS NECESSARY TO FILL THE GAP BETWEEN THE MOLECULAR AND THE MACROSCOPIC LEVELS • IMPROVEMENT OF THE IDENTIFICATION AND QUANTIFICATION OF ‘ORGANIC MATERIALS’ • STUDY OF THE BEHAVIOUR AND PROPOERTIES OF COLLOIDAL MATTER • STUDY OD THE ROLE PLAYED BY LIVING ORGANISMS IN TRACE METAL CONTROL • DEVELOPMENT OF CHEMICAL SPECIATION SCHEMES WHICH CAN BE DIRECTLY RELATED TO MEASURES OF BIOAVAILABILITY

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