Isolation of Phosphorus and Compounds of Phosphorus

Isolation of Phosphorus and Compounds of Phosphorus

Isolation of Phosphorus:

  1. Retort process

  2. Electrothermal process
  1. Retort Process:

    Step - 1: Phosphorite [Ca3(PO4)2] minerals is reacted with H2SO4; forming insoluble calcium sulphate and orthophosphoric acid (H3PO4)

    Ca3(PO4)2 + 3H2SO4  3CaSO4 + 2H3PO4

    Step - 2
    : Liquid which separated from insoluble residue is evaporated when it converts into metaphosphoric acid.

    H3PO4  HPO3 + H2[Note : HPO3 always exist in cyclic polymeric state]
    Metaphosphoric acid

    Step - 3
    : Metaphosphoric acid is reduced to phosphorus by carbon which comes out as vapourised form which is then condensed.

    4HPO+ 10C  P4 + 10CO + 2H2O

  2. Electrochemical Method:

    Mineral Phosphorite (Ca3(PO4)2) is treated with carbon in presence of silica. This mixture is dried and then placed in electric furnance.

    The mixture is heated at 1400 - 1500oC by discharge of alternating current between carbon electrodes.

    Silica reacts with calcium phosphate Ca3(PO4)and forms phosphorus pentoxide which is further reduced by carbon into P.

    2Ca3(PO4)2 + 6SiO2 + 10C  6CaSiO3 + P+ 10CO

    Red phosphorus is obtained by heating white phosphorus at 540-570 K in an inert atmosphere (CO2 or coal gas) for several hours.

     

    Like white phosphorus, red phosphorus also exists as P4 tetrahedral but these are joined together through covalent bonds to give a polymeric structure.

    Because of its polymeric structure, its melting point (883 K) is much higher than that of white phosphorus (317 K).

Compounds of Phosphorus

  1. Oxides of Phosphorus
  2. Oxyacids of Phosphorus (H3PO3 & H3PO4)
  3. Phosphine (PH3)

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