C10 - Using Resources

• Humans use the Earth’s resources to provide warmth, shelter, food and transport. Natural resources, supplemented by agriculture, provide food, timber, clothing and fuels.
• Finite resources from the Earth, oceans and atmosphere are processed to provide energy and materials
• The human population is growing very quickly and many people argue that humans are using up the Earth's finite resources at a rate which is too fast and therefore unsustainable.
• Chemists try to improve agriculture and industrial processes to provide new products that allow humans to meet their needs. It is essential that this is done in a sustainable way. This means that future generations of humans must also be able to meet their own needs.
• Finite resources from the Earth's crust, oceans and atmosphere will one day run out. They can be processed to provide energy and useful materials. Renewable resources are those which will not run out in the foreseeable future.
• One of the most important finite resources in the crust is crude oil. Crude oil is processed through fractional distillation and cracking to produce a wide variety of useful chemicals.
• Sea water is a renewable resource because there is such a large amount of it that humans will not use it all up.
• Sometimes natural products can be supplemented or replaced by agricultural and synthetic products. For example, until 1910 all fertilisers were obtained from natural resources such as manure.
• However, the Haber process enabled humans to produce fertilisers from nitrogen in the air, and has allowed synthetic fertilisers to be produced.
• Synthetic fertilisers have allowed intensive farming to become widespread, which has meant that we can produce enough food to support the growing world population
• Water is essential for life. Water that is safe for humans to drink is called potable water. Potable water is not pure water because it almost always contains dissolved impurities.
• For water to be potable, it must have sufficiently low levels of dissolved salts and microbes. This is because:

  • Dissolved salts can sometimes be harmful
  • Microbes can cause illness
• The methods used to make water potable depend on where you live. Starting with fresh water is easier than sea water, as removing the large amount of sodium chloride present in sea water requires a lot of energy.
• In the UK, rain provides enough fresh water to meet the needs of the population. Sometimes during the summer months in some areas of the UK, water reserves run low and people are encouraged to conserve tap water by the use of hosepipe bans.
• Most potable water in the UK is produced from naturally occurring fresh water by:

  • passing the water through filter beds to remove insoluble particles
  • sterilising the water to kill microbes
• The methods used for sterilisation include chlorine, ozone and ultraviolet light.
• Potable water can be made from sea water, through a process known as desalination.
•  It is preferable to make potable water from fresh water reserves rather than from sea water. This is because removing the large amount of sodium chloride (35 grams in every kilogram of sea water) requires a lot of energy.
• Desalination can be done by distillation and by reverse osmosis.
• In distillation, Sea water is heated until it boils. The salt remains in the liquid, and the steam is pure water. The steam is cooled and condensed to make potable water.
• In reverse osmosis, Water is put under high pressure and passed through a membrane which has tiny pores (holes) in it. The pores allow water molecules through, but prevent most ions and molecules from passing through.
• Distillation requires a lot of energy to boil the water, and also to cool the steam down to condense it. The waste water is very salty and can be difficult to dispose of in a sustainable way which does not harm marine ecosystems.
• Reverse osmosis requires expensive membranes and also produces a large volume of waste water, so its efficiency is often quite low.
• Sewage treatment involves the following steps:

  • screening and grit removal to remove large particles
  • sedimentation allows tiny particles to settle out from still water, which produces sewage sludge and effluent (the liquid which remains on top)
  • the sewage sludge is digested anaerobically by specific bacteria
  • the effluent is treated with aerobic bacteria to reduce the volume of solid waste
• Here are some examples of pollutants which might be present in waste water:

  • Human waste - contains harmful bacteria and high levels of nitrogen compounds, which harm aquatic ecosystems
  • Industrial waste - which may contain harmful metal compounds
  • Agricultural waste - which may contain fertilisers or pesticide
• A life-cycle assessment or LCA is a 'cradle to grave' analysis of the impact of a manufactured product on the environment.
• The main stages of an LCA are:

  1. extracting and processing the raw materials needed
  2. manufacturing the product and its packaging
  3. using the product during its lifetime
  4. disposing of the product at the end of its useful life
• Raw Materials:

  All the raw materials we need come from the Earth's crust, atmosphere or oceans, or are due to living organisms. Obtaining these materials has an impact on the environment

  • using up limited resources (ores, crude oil)
  • damaging habitats (quarrying, mining)
• Manufacture:

  • Using up land for factories
  • The use of machines and people
• Use:

  The impact of a product on the environment during its use depends on the type of product. For example, a wooden chair has very little impact, unless it needs cleaning or repair. On the other hand, using a car will have a significant impact.
• Disposal

  • using up land for landfill sites
  • whether any or all of the product can be recycled or reused
• Criticisms of LCAs

  • some parts of a LCA require judgements, such as the effect of pollutants
  • who has completed the LCA and whether they have any bias
  • For example, if the LCA is completed by the company which is making and selling a product, they might only include some parts of the genuine environmental impact.
• Advantages of recycling:

  • fewer quarries and mines are needed to extract finite reserves of metal ores
  • less crude oil needs to be extracted from the crust as a raw material for making plastics
  • less energy is needed for recycling compared with making a new product from natural resources, so the emission of greenhouse gases is reduced
  • the amount of waste that is disposed of in landfill is reduced
• Disadvantages of recycling:

  • the collection and transport of used items needs organisation, workers, vehicles and fuel
  • it can be difficult to sort different metals from one another
  • the sorted metal may need to be transported to where it can be turned into ingots
• Metals, glass, building materials, clay ceramics and most plastics are made from limited natural resources. Some items made from these materials can be reused, and this saves the most energy and reduces the impact on the environment
• The amount of sorting required depends on the purity of the mixture of metals/materials, and also on how pure you need the final recycled metal to be.
• Biological Methods of Metal Extraction:

  • Phytomining
  • plants are grown on a low-grade ore
  • the plants absorb metal ions through their roots and concentrate these ions in their cells
  • the plants are harvested and burnt
  • the ash left behind contains metal compounds
  • Bioleaching
  • Certain bacteria can break down low-grade ores to produce an acidic solution containing copper ions. 
• Phytomining:

  • Plants absorb mineral ions through their roots. Phytomining (also known as phytoextraction) makes use of this:
  • plants are grown on a low-grade ore
  • the plants absorb metal ions through their roots and concentrate these ions in their cells
  • the plants are harvested and burnt
  • the ash left behind contains metal compounds
  • Phytomining is slow, but it:
  • reduces the need to obtain new ore by mining
  • conserves limited supplies of high-grade ores
  • reduces the amount of rock waste that must be disposed of after traditional mining
• Bioleaching:

  • Certain bacteria can break down low-grade ores to produce an acidic solution containing copper ions. The solution is called a leachate and the process is called bioleaching.
  • Bioleaching does not need high temperatures but it produces toxic substances, including sulfuric acid, which damage the environment.
• Iron is more reactive than copper. It can displace copper from the leachate. For example:

  iron + copper sulfate → iron(II) sulfate + copper

  Since iron is cheaper than copper, the use of scrap iron is a cost-effective way to produce copper from the leachate. Alternatively, the copper compounds can be dissolved and the solution electrolysed to produce copper metal.