Metallurgical operations

• Some important ores


  • Iron - Haematite - Fe2O3
  • Iron - Magnesite - Fe3O4
  • Copper - Chalcopyrite - CuFeS2
  • Aluminum - Bauxite - Al2O3.xH2O
  • Sodium - Halite - NaCl
  • Lead - Galena - PbS
  • Zinc - Zinc blende - ZnS
  • Mercury - Cinnabar - HgS
  • Chromium - Chromite - FeO.Cr₂O
  • Tin - Cassiterite - Sno₂
  • Silicon - Silica - Sto
• Metals are important for structural applications, cooking utensils, bolts, electrical wires, and many other things
• Almost all metals in nature are found in the form of their compounds
• Minerals


  Naturally occurring metallic compounds
• Gangue


  The debris attached with the mineral such as sand, rock, and clay
• An ore is a solid deposit containing a sufficiently high percentage of a mineral to make extraction of metal economically feasible
• Metallurgy


  The process of separating a metal from its ore and preparing it for use
• Main steps in metallurgy

  1. Crushing, grinding or pulverizing of the ore

  2. Concentration of the ore

  3. Extraction of metal

  4. Refining of metal
• Concentration


  After crushing, grinding, or pulverizing, the ore is converted into powder. The mineral is separated from gangue by physical methods
• Magnetic Separation


  Used for magnetic ore where a magnet is used to remove the mineral, leaving the gangue behind
• Cyclone Separation


  Used when large density differences exist between ore and impurities. Air under high pressure is blown through the pulverized ore, separating the gangue from the mineral-rich particles
• Flotation Process


  Used for sulphide ores. Pulverized ore is fed into a tank containing water and an oil-detergent mixture. The mineral particles rise to the top as a froth, while gangue particles fall to the bottom
• Flotation process for the concentration of sulphide ores

  1. Mixture is agitated with air

  2. Detergents wet the mineral particles but not the silicate gangue

  3. Mineral particles rise to the top of the mixture as a forth, from where they are skimmed off

  4. Particles of the gangue fall down to the bottom

  5. Copper ore is concentrated generally by flotation process
• Roasting


  • Roasting for zincblende (ZnS)
  • Roasting for cinnabar (HgS)
• Smelting


  1. The method to reduce metal ions to free metal

  2. Roasted copper ore is heated with coke and sand at about 1100°C, materials melt and separate into two layers: matte and silicate slag

  3. Bessemerization: air is blown through the molten copper matte in a Bessemer converter, iron sulplide (FeS) is oxidized and removed as slag, cuprous sulphide (Cu₂S) is oxidized to cuprous oxide
• Blister copper is about 97 to 99% pure Cu, with entrapped bubbles of gas
• Refining or purification of metals


  The metal obtained as a result of smelting contains some impurities, so it must be refined