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Carbon Reduction Method for Extracting Metals from their Oxides

Key Concepts

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Example: Extracting Lead from Cerussite

  1. Mining : digging or blasting to obtain the lead ore from the surrounding rock
  2. Crushing : mined lead ore is crushed into very small pieces
  3. Grinding : crushed lead ore is ground into a powder
  4. Concentrating by flotation (also known as froth flotation or as ore flotation).
    Concentrating the ore by froth flotation increases the percentage of lead in the ore by removing many of the minerals that do not contain lead.

    • A collector oil, such as an organic xanthate or thiophosphate, is added to the powdered ore and adheres strongly to the cerussite particles making them water repellant.
      This collector oil does not adsorb so strongly on other minerals such as silicate minerals so these particles will not repel water.
    • This mixture is fed into a water bath containing a foaming agent such as crude cresol or pine oil (soap is not a suitable foaming agent in this case).
    • Jets of air are forced through the water bath.
    • Water repellant cerussite particles stick to the foam bubbles and float to the surface making a froth.
      Gangue (waste) falls to the bottom and is removed.
    • The froth which contains the lead is skimmed off the surface and the now enriched or concentrated ore is taken away for roasting.
      The water bath mixture is recycled.
  5. Thermal Decompostion of the Cerussite to Produce Lead(II) Oxide:

    The lead(II) carbonate that makes up the mineral cerussite is not very stable.

    On heating, lead(II) carbonate decomposes into lead(II) oxide and carbon dioxide:

    PbCO3(s) → PbO(s) + CO2(g)

    The lead(II) oxide produced in this way can then be reduced to metallic lead using heat and carbon because lead is less active than carbon.

  6. Reduction of Lead Using Carbon and Heat:

    On heating with carbon, the carbon is oxidized to carbon dioxide (or carbon monoxide) while lead is reduced from a positive "ion" in lead(II) oxide to the neutral metallic element:

    Chemical Reaction 2PbO + C 2Pb + CO2
    Pb : Oxidation State +2 0 Oxidation state has decreased.
    Lead has been reduced.
    C : Oxidation State 0 +4 Oxidation state has increased.
    Carbon has been oxidized.

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* In a blast furnace, the carbon fuel will be oxidized before the metal in the oxide is reduced. The metal in the oxide is then reduced by carbon monoxide and the product of the reaction will be metal and carbon dioxide.
metal oxide + carbon monoxide → metal + carbon dioxide

** The chemistry of metal extraction is very complicated, so when we simplify the reactions it is not really possible to be accurate about what the exact nature of the reactants and products will be.