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Copper Smelting

Key Concepts

Physical Processes Chemical Processes
Mining Crushing Grinding Concentrating Roasting Smelting Conversion Refining

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Example: Extraction of Copper From Chalcopyrite (CuFeS2)

  1. Mining : digging or blasting to obtain the copper ore from the surrounding rock
  2. Crushing : mined copper ore is crushed into very small pieces
  3. Grinding : crushed copper ore is ground into a powder
  4. Concentrating by flotation (also known as froth flotation or as ore flotation).

    Mining produce ores containing 2% or less of copper.

    Concentrating the ore by froth flotation can result in ores with up to 35% copper.

    • A collector oil, such as an organic xanthate or thiophosphate, is added to the powdered ore and adheres strongly to the chalcopyrite 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 chalcopyrite 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 copper is skimmed off the surface and the now enriched or concentrated ore is taken away for roasting.
      The water bath mixture is recycled.
    • The concentrated (enriched) ore can contain up to 35% copper and a number of impurities such as antimony, arsenic, and lead.
  5. Roasting : reduces impurities in the copper ore and produces calcine (a mixture of products)*

    • Concentrated (enriched) ore is heated to between 500oC and 700oC in air.

      Some impurities in the ore, such as arsenic and antimony, are oxidized and form volatile gases which can be removed:

      4As + 3O2(g) → 2As2O3(g)

      4Sb + 3O2(g) → 2Sb2O3(g)

    • Roasting the ore containing chalcopyrite, CuFeS2, also produces sulfur dioxide gas and a mixture of compounds called calcine.

      One of the reactions in the formation of calcine is shown below:

      2CuFeS2(s) + 4O2(g) 2FeO(s) + Cu2S(s) + 3SO2(g)
      chalcopyrite+ oxygen calcine + sulfur dioxide

    • Calcine, a mixture of solids including copper oxides, sulfides and sulfates, can then be smelted.

      eg, copper(I) oxide can be produced from copper(I) sulfide:
      2Cu2S + 3O2(g) → 2Cu2O + 2SO2(g)

  6. Smelting with Fluxes*: converts the calcine to matte (a mixture of copper sulfides and iron sulfides)

      Calcine is heated to over 1200oC with fluxes such as silica (SiO2) and limestone (CaCO3).

    • Calcine melts and its compounds react with the fluxes.
    • Any copper(I) oxide present will be converted into copper(I) sulfide during the smelting process because copper has a higher affinity for sulfur than it does for oxygen.

      for example: Cu2O + FeS → Cu2S + FeO

    • Impurities form a slag which floats on the surface and is easily removed.

      One of the reactions to remove iron impurities is shown below:

      FeO + SiO2 FeO.SiO2
      iron impurity + silica slag

      (FeO.SiO2 can also represented as FeSiO3)

    • After the slag is removed, the resulting product, called matte, is a mixture of copper sulfides (mostly Cu2S) and impurities such as iron sulfides.
      This matte, containing about 40% copper, can then be fed to a converter.
  7. Conversion of Matte into Blister Copper (impure copper)

    • Air is blown through the molten matte which converts iron(II) sulfide to iron(II) oxide and sulfur dioxide

      2FeS + 3O2 → 2FeO + 2SO2(g)

      Iron(II) oxide, FeO, slag is skimmed off.

    • Relatively pure copper(I) sulfide, Cu2S, accumulates in the bottom of the converter.
    • Air is blasted through this copper(I) sulfide to reduce the copper and oxidize the sulfur to sulfur dioxide:

      reactionCu2S + O2 2Cu + SO2
      oxidation state (number) of copper+1 0 decrease in oxidation state:
      copper is reduced
      oxidation state (number) of sulfur-2 +4 increase in oxidation state:
      sulfur is oxidized

    • The impure copper produced by the converter is referred to as blister copper because bubbles of sulfur dioxide gas on the surface of the copper look like blisters.
    • Blister copper contains 97-98% copper.

      Impurities in blister copper can include gold, silver, antimony, arsenic, bismuth, iron, lead, nickel, selenium, sulfur, tellurium and zinc.

    • Blister copper can be caste into blocks to undergo electrorefining (electrolytic refining).
  8. Refining: increases the purity of the copper by removing impurities.
    (see electrorefining)

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*The reactions that take place and the compounds that are formed are dependent on many factors, including the type of smelter/converter in use!