Extraction of Lead

Extraction of Lead

Lead Atomic Number: 82
Lead Electronic configuration: [Xe]4f¹⁴4d¹⁰6s²6p²

Lead is extracted from galena (PbS) involving the following steps:

1. Concentration:
   The crushed, powdered ore is concentrated by the froth floatation process.
   
2. Reduction:
   The concentrated ore is reduced in two steps:
   1. Roasting:
      The concentrated ore is roasted in reverberatory furnace, where the ore is partially oxidised.
      
      2PbS + 3O₂  2PbO + 2SO₂
      
      PbS + 2O₂  PbSO₄
      
   2. Smelting: After roasting, the temperature of furnace is raised and air supply is reduced. Some more concentrated galena is added. PbS reacts with PbO and PbSO4 forming lead metal.
      
      2PbO + PbS  3Pb + SO₂
      
      PbSO₄ + PbS  2Pb = 2SO₂
      
      Molten lead is drawn off from the lower part of the furnace.
      
   3. Purification:
      Lead obtained from furnace still contains Bi, Sb, Cu, Fe, Ag, etc. as impurity. These impurities can be removed by the following processes.
      
      
      1. Softening process: The impure metal is melted on the hearth reveberatory furnace in a current of air. The base metals are oxidised and float over the surface of the molten mass as scum, which is removed.
         
      2. Desilverisation: The removal of silver is done by Parke's process or Pattinson's process.
         
      3. Electrolytic refining: The desilverised lead is further purified by electrolytic method.
         On passing current, pure lead is deposited on the cathode. The less electropositive metals like Ag, Au, Sb etc. collect below anode as anodic mud while more electropositive impurities like Zn, Fe, Ni etc. go into the solution.