General Principles and Process of Isolation of Metals

Extraction of Crude Metal from Concentrated Ore, Refining

  1. Concentrated ore is converted to a compound suitable for production of metal by either roasting or calcination.
    • An ore is heating in presence of air at below its melting point is called roasting
    • a) In roasting sulphide ore is converted in to oxides is called oxidizing roasting.
    • b) In roasting sulphide ore is converted in to sulphate on controlled conditions is called sulphadizing roasting.
    • c) In chloradizing roasting sulphide mineral is converted in to chloride.
  2. Smelting process is used for carbonate ores. Carbonate ores are heating in absence of air at below its melting point to escape CO2 like volatile gases is called roasting.
  3. Both calcination and roasting are performed in a reverberatory furnace.
  4. Ore is heated with reducing agent and flux during smelting. Smelting is performed in blast furnace.
  5. Metal oxide is subjected to reduction to obtain pure metal.
    • a) Auto reduction involves heating in air as for cinnabar (HgS)
    • b) Reduction by carbon:- Smelting coal or coke is used. Eg. For iron and zinc. Active metals like Na, Mg, Al or hydrogen gas are also used when carbon cannot.
    • c) Electrolytic reduction is used for reactive metals like Li, Na, Ca, Al. Carbon reduction is not possible for these metals as they form carbides on heating to high temperature.
  6. Refining:- Refining is the process of obtaining pure metals from reduced metal. The methods are
    • a) Liquation – Eg. Sn and Pb
    • b) Distillation – Eg. Zn
    • c) Electrolysis for highly electropositive metals like Cu, Ag, Au etc.
    • d) Hydro Metallurgy – Eg. Cyanide process for Ag, Au.
    • e) Chemical process – Mond's process Eg. Ni
  7. Higher degree of purity is obtained by
    • a) Van Arkel method. Eg: Titanium, Zirconium, and Thorium.
    • b) Zone refining – Eg. Germanium, Silicon etc.

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