Topic 10: Earth's Resources and Sustainable Development

• natural resources

  resources supplemented from agriculture
• finite resources

  resources that are being used up faster than they can be made eg. crude oil, limestone, metal ores
• renewable resources

  resources that can be replaced at the same rate that they are used up eg. biofuels
• sustainable development

  development which meets the needs of current generations without compromising the needs of future generations
• Synthetic (man-made) Alternatives:

  • Polyester: alternative to cotton and wool, can be used in clothes
  • Polymers: alternative to rubber, can be used in tyres
  • MDF (medium-density fibreboard): alternative to wood, can be used in construction
• Reasons for Estimating using Order of Magnitude:

  • Can be uncertainty when estimating
  • Rate of future consumption is uncertain
  • Possibility of discovering new deposits
  • New technologies could burn more fossil fuels
• potable water

  impure water that is safe to drink, containing low levels of dissolved salts and microbes, a pH between 6.5 and 8.5 and not containing any microorganisms
• fresh water

  found in lakes, rivers, ice caps, glaciers, underground streams and aquifers; contains low levels of dissolved salts and microbes
• ground water

  found in underground streams and aquifers; contains low levels of dissolved salts and ordinary levels of microbes
• sea water

  found in the sea; contains high levels of dissolved salts and microbes
• waste water

  produced through homes, industry and agriculture; contains high levels of dissolved salts and microbes
• pure water

  water not containing dissolved salts or microbes
• Water Treatment Plant (used for fresh and ground water):

  1. Wire mesh filters out large solids
  2. Gravel or sand filter beds remove small insoluble solids
  3. Disinfecting sterilises by killing bacteria
  4. Adding fluoride improves dental health
• Methods of Sterilisation:

  • Chlorine gas: dissolves in water to kill microorganisms as it is a powerful oxidising agent - it is toxic and has evaporated by the time it reaches us
  • Ozone (O3): made by exposing oxygen to sparks; not as soluble as chlorine but is an equally powerful oxidising agent and isn't toxic (Equation: 3O2 -spark- 2O3)
  • Ultraviolet (UV) light: causes mutations in the bacteria's DNA so they can't replicate and therefore die out - not as effective as other methods
• Desalination Methods (used on sea water):

  • Distillation: water is boiled in boiling chamber and it evaporates then condenses in the condensing dome - requires a lot of energy
  • Reverse Osmosis: external pressure is used to force water through a semi-permeable membrane to separate salts - requires energy but not as much as distillation

  Both processes are expensive
• Waste water treatment:

  1. Sewage sent through pumping station
  2. Screening grit removes large solids
  3. Primary sedimentation splits sewage into sludge containing human waste (solid) and effluent (liquid)
  4. Effluent digested aerobically, sterilised and released into rivers or as drinking water - rapidly breaks biomass into CO2, O2; requires lots of energy as oxygen is bubbled through sewage at an ambient temperature
  5. Sludge digested anaerobically at 36°C over 30 days - biomass broken down into CH4 which is used as fuel as it is rich in minerals and has no pathogens as well as CO2, H2O
• Why treat waste water?

  • Contains large amounts of microbes allowing the spread of pathogens such as cholera
  • Contains high levels of nitrates, phosphates and other minerals that promote excessive algae growth leading to eutrophication as the algae compete with and kill other water based plants
• Bioleaching Copper:

  1. Ore containing 0.1% of CuFeS2
  2. Ore crushed to a fine powder
  3. Water and bacteria are added and left in a tank for 6 days
  4. CuFeS2 is oxidised to CuSO4, which is soluble
  5. The solution of CuSO4 is collected and electrolysed
  6. Pure copper is obtained
• Mining and Smelting of Copper:

  1. Copper ore is mined from earth
  2. Copper ore is heated in a furnace with carbon (smelting), which produces impure copper
  3. The copper is purified by electrolysis
  4. Pure copper is produced
• Copper Purification: Electrolysis

  • Pure copper and impure copper electrodes: made from copper from the extraction process
  • Solution of Cu2+ used
  • Copper atoms form Cu2+ ions and move from the impure copper to the pure copper electrode to become pure copper metal again
  • Lots of energy required: expensive
• Copper Purification: Displacement

  • Copper displaced from solution using scrap iron as it is cheap and abundant
  • Copper sulfate + iron = iron sulfate + copper
  • CuSO4(aq) + Fe(s) = FeSO4(aq) + Cu(s)
  • Not as efficient as electrolysis
• Phytomining:

  • Plants grown on soil containing low grade ores
  • Plants absorb copper compounds from soil
  • Plants are burned - the ash contains copper compounds
  • Copper is extracted from a solution made from the ash by electrolysis
  • Pure copper is produced
• Copper Mining Advantages:

  • Quicker
  • Extracts more copper
  • More economically viable

  Disadvantages:

  • Supply of copper rich ore is limited
  • Causes dust and noise pollution
  • Requires more energy
  • Destruction of landscapes and habitats
  • Large amounts of waste rock
  • Releases more carbon dioxide contributing to global warming
  • Releases sulfur dioxide causing acid rain
• Bioleaching Advantages:

  • Extracts copper from low grade oils
  • Conserves copper rich oils
  • Doesn’t destroy landscape and produces less pollutants
  • Lower energy costs

  Disadvantages:

  • Slow
  • Less efficient
  • Produces toxic waste (not as much as smelting)
  • Less economically viable
• Phytomining Advantages:

  • Extracts copper from low grade ores
  • Conserves copper rich ores
  • Doesn’t destroy landscapes and produces less pollutants
  • Lower energy costs

  Disadvantages:

  • Produces smaller amount of copper per unit mass
  • Takes up a lot of space
  • Growing plants takes tine
  • Produces carbon dioxide when plants burn
  • Land can’t be used to grow food
• How should I write a 6 mark question on life cycle assessments?

  1. Extracting and processing raw materials - how much is the local environment being damaged through habitat destruction, use of energy and release of pollutants?
  2. Manufacturing and packaging the product - energy use? release of pollutants? quantity of waste products and ease of their disposal?
  3. Using and reusing the product - how much damage does it do over its lifetime? how long can it be used for?
  4. Disposing of the product - how much space does it take up? how many pollutants are released? how much energy is used?
  5. Final judgement
• Limitations of Life Cycle Assessments:

  • Not easy to quantify effects of pollutants as we aren't sure what the total effect will be, so we have to make a value judgement (however we can quantify the use of water, resources, energy and production of waste)
  • Value judgements are subjective which makes it harder to make a final judgement
  • Some companies use selective/abbreviated LCAs to make their products appear more environmentally friendly in advertising - therefore it is important that they are peer reviewed
• Plastic Bags:

  • Raw materials: Crude oil (not sustainable)
  • Obtaining raw materials: Lots of energy needed to extract oil
  • Transporting raw materials: Fuels produce pollution eg. carbon dioxide; possible damage from spillages
  • Manufacture: Lots of energy needed to separate fractions, cracking and polymerisation
  • Transporting for use: Fuels produce pollution eg. carbon dioxide
  • Disposal: Landfill (doesn't rot), incinerator (gives off carbon dioxide), recycling (energy and fuel needed for transport and melting)
• Paper Bags:

  • Raw materials: Trees (can be replanted but deforestation releases carbon dioxide)
  • Obtaining raw materials: Habitats destroyed when trees cut down
  • Transporting raw materials: Fuels produce pollutants eg. carbon dioxide
  • Manufacture: Uses lots of water and chemicals eg. bleaches that can harm the environment
  • Disposal: Landfill (rots giving off methane), incinerator (gives off carbon dioxide), recycling (uses energy and fuel for transport and melting)
• hardness

  how easily a material can resist being scratched or indented
• brittleness

  how easily a material breaks when a force is applied
• stiffness

  how well a material can resist bending
• Ceramics:

  • Materials which are typically hard, brittle, heat-resistant and corrosion-resistant
  • Made by shaping and firing a non-metallic material at a high temperature
  • 2 main groups: clay ceramics and glass
  • Clay ceramics eg. china, brick, porcelain are made by shaping wet clay when soft then heating in a high furnace so it hardens - have a high compressive strength
  • Glass is made by heating a mixture of sand, sodium carbonate and limestone then allowing the molten liquid to solidify - transparent, strong, good thermal insulator
• Formulations/Composites:

  • Made of multiple materials with different properties that have been combined to produce a material with more desirable properties
  • Usually made from 2 components: the reinforcement (usually long solid fibres or fragments) and the matrix (binds the reinforcement together; starts soft then hardens)
• Polymers:

  • Large molecules of high relative molecular mass
  • Made by linking together large numbers of smaller monomers
  • Properties dependent on properties of monomers and conditions of reaction
  • Properties: flexible, easily shaped, good insulators of heat and electricity
• Low density vs High density poly(ethene):

  • Both made from ethene monomers

  Low density:

  • Made in moderate temperatures (100 - 300 °C) with a high pressure (150 MPa) and an oxygen catalyst
  • More flexible, more transparent, weaker
  • Used in carrier bags
  • Polymers are disorganised so intermolecular forces are weaker

  High density:

  • Made in low temperatures (50 °C) with a low pressure (0.1 MPa) and an aluminium oxide catalyst
  • More rigid but stronger
  • Used in drainpipes
  • Polymers are organised so intermolecular forces are stronger
• Thermosoftening polymers:

  • Made from lots of polymer chains
  • Held together by weak intermolecular forces (no covalent bonds)
  • Break easily when heated and melt the polymer
  • Can be remoulded into a different shape
  • Will harden again when cooled
• Thermosetting polymers:

  • Made from lots of polymer chains
  • Held together by strong covalent bonds in the form of crosslinks between polymer chains
  • Require lots of energy to break so don't soften when heated: have to be burned to break and cannot be remoulded
  • Hard, strong and rigid
• Metals vs Alloys:

  • Metals: malleable, ductile (not brittle), good conductors of heat and electricity, high melting and boiling points
  • Alloys: stronger and less malleable
• corrosion

  the process by which metals are slowly broken down by reacting with substances in their environment eg. rusting