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Environmental Chemistry

Environmental Chemistry. Some Chemical Equations. Environmental chemistry. study of the effect of human activity on the chemical processes in the environment concerns political and natural borders global issues applied chemistry. carbon monoxide : reduction (1). Lean burn engines :

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Environmental Chemistry

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  1. Environmental Chemistry Some Chemical Equations

  2. Environmental chemistry • study of the effect of human activity on the chemical processes in the environment • concerns political and natural borders • global issues • applied chemistry

  3. carbon monoxide: reduction (1) Lean burn engines: Decrease fuel /air ratio, from 1:14.7 (stoichiometric ratio/green band in diagram) to 1:18. Why? (or increase air /fuel ratio to 18:1)

  4. Catalytic converter

  5. Car Exhaust Reduction catalytic converter in car exhaust system: • reduction of nitrogen oxide • oxidation of CO and un-burnt hydrocarbons/VOCs • equations: CO (g) + O2(g) CO2(g) NO (g) + CO (g) CO2(g) + N2 (g) C8H18(g) + O2(g) CO2(g) + H2O(g)

  6. carbon monoxide: reduction (2) CO (g) + O2(g) CO2(g) NO (g) + CO (g) CO2(g) + N2 (g) C8H18(g) + O2(g) CO2(g) + H2O(g)

  7. sulphur oxides: sources • Natural: • volcanoes • sea spray • biological decay of organic matter that contains sulphur • reduction of sulphates • Man-made: • coal-burning power stations (equation starting from S in coal) • roasting of metal sulphides e.g. ZnS and Cu2S (equation)

  8. sulphur oxides: health effects • acidic oxides • formation of sulphuricacid

  9. sulphur oxides: methods of reduction • use of “low-sulphur content” fuels or removal of sulphur before burning coal/oil • removal of SO2from fumes before they are released: • limestone based fluidised bed(equations showing decomposition of calcium CaCO3reaction of CaO with SO2) • alkaline scrubbing (wet scrubber) (also called flue gas desulphurization, FGD): (equations showing reaction of CaO and Mg(OH)2)

  10. sulphur oxides: methods of reduction • limestone based fluidised bed(equations showing decomposition of calcium CaCO3reaction of CaO with SO2 • Treatment of basic solutions with sulfur dioxide affords sulfite salts: • SO2 + NaOH → Na2SO3 + H2O • calcium oxide (lime) reacts with sulfur dioxide to form calcium sulfite: • CaO + SO2 → CaSO3

  11. Sulphur oxides: reduction (1) Wet scrubber

  12. sulphur oxides: methods of reduction • alkaline scrubbing (wet scrubber) (also called flue gas desulphurization, FGD): (equations showing reaction of CaO and Mg(OH)2)

  13. Controls on CO2 • CO2 is controlled by a global scale feedback loop with a time scale of >10,000 years • Consider the following reactions: Generic Weathering Reaction Generic Precipitation Reactions Generic Mantle Reactions

  14. Global O2 • oxidation is long-term sink of atmospheric O (e.g., oxygen stored as SO42-or CO32-salts) • C & S most important • model past O2 from these reactions

  15. OxidationReduced species react with free O2

  16. Oxidative Pyrite Weathering

  17. Acidic Hydrolysis Reaction H+ replaces cations in mineral structure Main acid sources: • carbonic acid (H2CO3 from CO2 dissociation in natural waters) • organic acids (from CO2 respiration in soils) • sulfuric acid (volcanic, anthropogenic H2S) …typical mechanism of silicate dissolution.

  18. Feldspar Hydrolysis Solid - Clay (“Secondary Mineral”) Dissolved Species Similar for: Anorthite (Ca2Al2Si2O8) K-Feldspar (KAlSi3O8) Most common weathering reactions on Earth…

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