Chemistry - Extraction of Metals

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  • Created by: Siana
  • Created on: 12-02-14 20:24
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  • Extraction of Metals
    • Different methods of extraction depend on:
      • Reactivity of metal
      • Cost of reactants compared to metal
      • Purity required
        • Some must be very pure, others are better impure
      • Energy costs
        • High temperatures and electrolysis are very expensive
      • Environmental issues
        • Pollutants
    • Sulphide Ores
      • Must be converted into oxide
        • Roasted in air
      • Advantages
        • Sulphur dioxide can be collected before it is released into the atmosphere - can be used to make sulphuric acid
      • Disadvantages
        • Produces large quantity of sulphur dioxide
          • Principal cause of acid rain
    • Reduction with Carbon
      • Metals below carbon in the reactivity series are often extracted from their ores with carbon and  carbon monoxide
        • Cheap and effective. e.g. iron
      • Extraction of Iron
        • Extracted from haematite by reaction with carbon monoxide in the blast furnace.
          • Coke, haematite and limestone are added continuously to the top of the blast furnace
          • Hot air blown into the base.
        • 1) Coke reacts with oxygen at the base. Exothermic reaction keeps furnace hot.
        • 2) Carbon dioxide rises up furnace, reacts with more coke, produces carbon monoxide (Exothermic reaction)
        • 3) carbon monoxide reduces haematite to iron. Liquid iron sinks to base and is tapped off. Some haematite is reduced directly by the carbon. The ore often contains other oxides of iron which are also reduced by the carbon.
    • Extraction of manganese and copper
      • Advantages
        • Raw materials are cheap
        • reaction is exothermic - less energy required to maintain heat
        • purity is sufficient for steel making purposes
        • Continuous process
      • Disadvantages
        • Carbon dioxide (greenhouse gas) is released
        • metals higher in the reactivity series than carbon cannot be extracted this way.
        • metals which react with carbon to form carbides cannot be extracted this way.
        • metals which require high purity cannot be produced this way, the metal produced always contains significant quantities of carbon

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