Getting Metals from Rocks

Ores contain enough metal to make extraction worth while
1. In many cases the ore is an oxide of the metal. For example the main aluminium ore is called bauxite its aluminium oxide
2. Most metals need to be extracted using a chemical reaction
3. The economics (profitability) of metal extraction can change over time.
  1. If the market price of a metal drops a lot it might not be worth extracting it. If the price increases a lot then it might be worth extracting more of it
  2. As technology improves it becomes possible to extract more metal from a sample rock than was originally possible. So it might now be worth extracting metal that wasnt worth extracting in the past
Metals are extracted from their ores chemically
1. A metal can be extracted from its ore chemically by reduction or electrolysis
2. Some ores may have to be concentrated before the metal is extracted this just involves getting rid of the unwanted rocky material
3. Electrolysis can also be used to purify the extracted metal
The reactivity series
1. Some metals can be extracted by reduction with carbon
  1. When an ore is reduced oxygen is removed from it
    1. 2Fe2O3 + 3C to 4Fe + 3CO2
      1. Iron(3)oxide + carbon to iron + carbon dioxide
  2. The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon
    1. The reactivity series
      1. Potassium, Sodium, Calcium, Magnesium, Aluminium
        More reactive than carbon so extracted by electrolysis
        CARBON
        Zinc, Iron, Tin, Copper
        Less reactive than carbon so are extracted by reduction using carbon
  3. Metals higher in the reactivity series have to be extracted using electrolysis which is expensive
  4. Metals below carbon in the reactivity series can be extracted by reduction using carbon. This is because carbon can only take the oxygen from metals which are less reactive that itself
Some metals have to be extracted by electrolysis
1. Metals that are more reactive than carbon have to be extracted using electrolysis
  1. e.g. aluminium
2. Much more expensive and uses a lot of energy
3. Electrolysis means splitting up with electricity
  1. It requires a liquid to conduct the electricity called the electrolyte
    1. Electrolytes are often metal salt solutions made from the ore or molten metal oxides
      1. The electrolyte has free ions - these conduct the electricity and allow the whole thing to work
        Electrons are taken away by the positive electrode and given away by the negative electrode
  2. Heres how electrolysis is used to get copper:
    1. Electrons are pulled off the copper atoms at the positive electrode causing them to go into solution Cu2+ ions
      1. Cu2+ ions near the negative electrode gain electrons and turn back into copper atoms
        The impurities are dropped at the positive electrode as sludge whilst pure copper atoms bond to the negative electrode
Copper is purified by electrolysis
1. Copper can be easily extracted by reduction with carbon. The ore is heated in a furnace this is called smelting
  1. However the copper produced this way is impure and impure copper doesnt conduct electricity well. This isnt very useful because a lot of copper is used to make electrical wiring
    1. So electrolysis is also used to purify it even though its expensive
A displacement reaction can be used to extract copper
1. If you put a reactive metal into a solution of a dissolved metal compound the reactive metal will replace the less reactive metal in the compound
  1. This is because the more reactive metal bonds more strongly to the non-metal bit of the compound and pushes out the less reactive metal
    1. E.g. Scrap iron can be used to displace copper from solution this is really useful because iron is cheap but copper is expensive. If some ion is put in a solution of copper sulfate the more reactive iron will "kick out" the less reactive copper from the solution. You end up with iron sulfate solution and copper metal
      1. Copper sulfate + iron to iron sulfate + copper
      2. If a piece of silver metal is put into a solution of copper sulfate nothing happens. The more reactive copper is already in the solution
Copper-rich ores are in short supply
1. The supply for copper-rich ores is limited so it needs to be recycled
  1. The demand for copper is growing and this may lead to shortages in the future
2. Scientists are looking into new ways of extracting copper from low-grade ores or from the waste that is currently produced when copper is extracted
  1. Examples of two new methods
    1. Bioleaching
      1. This used bacteria to separate copper from copper sulfide. The bacteria get energy from the bond between copper and sulfur separating out the copper from the ore in the process. The leachate (solution produced) contains copper which can be extracted by filetering
    2. Phytomining
      1. This involves growing plants in soil that contains copper. The plants cant use or get rid of the copper so it gradually builds up in the leaves. The plants can be harvested, dried and burned in a furnace. The copper can be collected from the ash
    3. Traditional methods of copper mining are pretty damaging to the environment. These new methods of extraction have a smaller impact but the disadvantage is that they are slow
Metal extraction is bad for the environment
1. People have to balance the social, economic and environmental effects of mining the ores
2. Mining metal ores is good because it means that useful products can be made. It also provides local people with jobs and brings money into the area
3. Mining ores is bad for the environment as it causes noise, scarring of the landscape and loss of habitats. Deep mine shafts can also be dangerous for a long time after the mine has been abandoned
Recycling metals is important
1. 1. Mining and extracting metals takes a lot of energy most of which comes from burning fossil fuels
  1. 2. Fossil fuels are running out so its important to conserve them. Burning them also contributes to acid rain, global dimming and climate change
    1. 3. Recycling metal only uses a small fraction of energy needed to mine and extract new metal
      1. 4. Energy doesnt come cheap so recycling saves money to
        5. Also theres a finite amount of each metal in the earth. Recycling conserves this
        6. Recycling metal cuts down on the amount of rubbish that gets sent to the landfill. Landfill takes up space and pollutes the surroundings. If all the aluminium cans in the UK were recycled thered be 14 million fewer dustbins to empty each year

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	Criado por sian.allison quase 11 anos atrás