Metallurgy

Definition

• Metallurgy is the process of obtaining pure metals from ores.

Steps in Metallurgy

1. Crushing and Grinding of Ores

   • Ores are crushed into fine powder using big jaw crushers and ball mills.
   • This process is known as pulverization.

2. Concentration of Ores

   • Ores are concentrated based on impurities and their proportions.
   • Removal of impurities results in concentrated ores.
   • Three methods of concentration:
     • Centrifugation:
       • Used when densities of ore and impurities differ.
       • Fine powder of ore placed on a moving table; metal particles remain in slots due to centrifugal force.
       • Dense particles settle in grooves, while lighter impurities are separated.
     • Froth Flotation:
       • Concentrates sulfide ores (e.g., copper, lead, zinc).
       • Ore mixed with water and oil, agitated with air.
       • Sulfide ore separates as froth; impurities settle at the bottom.
     • Magnetic Separation:
       • Pulverized ore placed on a conveyor belt with magnetic wheels.
       • Magnetic particles are attracted to the wheels, separating them from non-magnetic particles.

3. Conversion of Concentrated Ore into Metal Oxide

   • Methods include roasting, calcination, and smelting:
     • Roasting: Heating concentrated ore in excess air.
     • Calcination: Heating in absence of air without melting the ore.
     • Smelting: Melting operation to extract metal.

4. Reduction of Metals

   • Reduction can be done using reducing agents or electrolysis.
   • Reducing agents like carbon or carbon monoxide are used for metals like zinc, iron, lead, and copper.
   • Active metals require electrochemical reduction since they attract more oxygen than carbon.

5. Refining of Metals

   • Further refining methods include:
     • Electrolysis:
       • Impure metal anode, pure metal cathode, using a water-soluble salt as electrolyte.
       • Impure metal dissolves, and pure metal deposits on the cathode.
       • Insoluble impurities form anode mud at the bottom.
     • Liquefaction:
       • Uses a furnace slightly above melting point of the metal.
       • Metal melts and collects below; impurities remain solid.
     • Fractional Crystallization:
       • Used for trace impurities.
     • Zone Refining:
       • For semimetals (e.g., silicon, boron).
       • Impurities crystallize out as the molten metal cools down.