Metal Extraction


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  • Created by: Melissa
  • Created on: 12-05-12 08:39

Which method?

  • Energy requirements
  • Cost of reductant
  • Metal purity required
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Rocks containing a high enough percentage of metal to be extracted commercially

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Most common types of metal compound's in Earth's c

Oxides and Sulphides

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Sulphides ---> Oxides

  • Roasting in air
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Nickel and Copper

Scarce in Eath's crust but occur in high grade ores in a few locations

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Aluminium and Iron

  • Most abundant metals in Earth's crust
  • Widely distributed
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  • Carbon is cheap and plentiful
  • Used in the form of coke (made by heating coal in the absence of air)
  • For some metals, the temperature required is excessively high (so uneconomic) and metal carbides are formed rather than the metal itself (e.g. aluminium, tungsten, titanium)
  • Used for extraction of IRON, MANGANESE and COPPER
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Extraction of Iron

  • Haematite is the main ore of iron and contains 
  • Coke is burned in hot air producing CO and lots of heat
  • High temperatures in furnace mean more coke is reacted with CO to produce CO
  • Reduced by carbon monoxide (most common):
  • Or, carbon (in hottest parts of furnace):
  • Limestone removes sandy impurities (forming **** -used in road making)
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Extraction of Manganese

  • Formed from reduction of manganese (IV) oxide with carbon:
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Extraction of Copper

  • Malachite contains        which on heating forms copper (II) oxide.
  • Copper can be formed by reduction with carbon:
  • Not much copper is made this way as newer, alternative methods from aqueous solutions have been developed which have environmental advantages.
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Reduction by Hydrogen

  • Tungsten cannot be heated with carbon because tungsten carbide is formed
  • Tugsten (VI) oxide (WO  ) is heated with hydrogen at 900C
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Electrolysis of Metals

  • Raw materials for the extraction of aluminium are purified aluminium oxide and cryolite (       )
  • Aluminium oxide must be molten or dissolved to conducts electricity, and so is dissolved in molten cryolite ( this requires a lower temp. than using molten aluminium oxide so has lower energy costs)
  • Electrodes are made from graphite (carbon)
  • Continuous process
  • Positive electrode burns due to O produced there ( forming CO ) so must be replaced frequently
  • Main cost is electricity so often built near hydroelectric power stations.
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Reduction by active metal (e.g. Ti)

  • If reacted with C, titanium carbide is formed which is very brittle.
  • Titanium is useful because it is abundant, has a low density and is corrosion resistant - used for making strong, low density alloys for use in aircraft, hip joints and nuclear reactors.
  • Must be very pure so electrolysis not suitable.
  • Must be reacted with a more reactive metal (Mg or Na)
  • TiO  (solid) is converted to TiCl (liquid) at 900C
  • TiCl  is purified by fractional distillation in an Ar atmosphere.
  • Ti is extracted by Mg or Na in an ARGON ATMOSPHERE at 1000C
  • Expensive due to heat, Na/Mg (made by electrolysis), Ar, and it is a batch process.
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Recycling Metals

  • Saves resources (metal ores)
  • Creates less waste (mining waste)
  • Saves energy resources
  • Reduces air pollution
  • However, there are costs both financial and energy costs) associated with sorting and transporting metals to be recycled.
  • RECYCLING COPPER - react scrap copper with sulphuric acid or a specific enzyme to form solutions containing Cu  (aq)
  • Copper can be extracted by reaction with scrap iron (this method can also be used to extract copper from low grade ores)
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