Occurrence and Extraction of Metals: Extraction of Metals: Calcination (For CBSE, ICSE, IAS, NET, NRA 2022)

Get unlimited access to the best preparation resource for competitive exams : get questions, notes, tests, video lectures and more- for all subjects of your exam.

Extraction of Metals

Calcination and Roasting of Ore

The concentrated ore is converted into metal oxide by calcination or roasting.

Calcination

  • Calcination involves heating of the concentrated ore in a limited supply of air so that it loses moisture, water of hydration and gaseous volatile substances.
  • The ore is heated to a temperature below its melting point.

For example:

1. Removal of water of hydration

2. Expulsion of from carbonate

Roasting

Roasting is a process in which the concentrated ore is heated in a free supply of air at a temperature insufficient to melt it.

For example:

1. Removal of the volatile impurities like arsenic, sulphur, phosphorus and organic matter

2. Conversion of the Sulphide ores into oxides

Reduction of Metal Oxides to Free Metal

Reduction is carried out after calcination or roasting of ores.

Smelting

Smelting is a process in which the oxide ore in molten state is reduced by carbon or other reducing agents to free metal.

By using carbon as a reducing agent:

  • This method is used for the isolation of iron, tin and zinc metals from their respective oxides.
  • Reduction occurs by the action of carbon and/or carbon monoxide which is produced by the partial combustion of coke or charcoal.

  • Concentrated ore also contains some amount of gangue material which is removed during reduction process by the addition of flux during smelting.
  • Flux is a chemical substance which combines with gangue at higher temperatures to form easily fusible material called slag which is not soluble in the molten metal.

Flux are of two types:

Basic Flux: Limestone on heating converted into calcium oxide used as basic flux which combines with acidic impurities like silica in metallurgy of iron and forms fusible calcium silicate .

(Limestone)

Acidic flux: is used as acidic flux to remove basic impurity of in metallurgy of .

Reduction by Other Reducing Agents

  • Oxide ores which cannot be reduced by carbon or metals which show affinity to carbon by forming metal carbides, are reduced by reducing agents like aluminum, sodium, magnesium or hydrogen.
  • Chromium oxide or manganese oxide are reduced by aluminum powder. This process is known as Goldschmidt՚s Alumina-thermite reduction method.

Self-Reduction

  • This method is applied to the Sulphide ores of copper, mercury and lead.
  • The ore are heated in air. A part of these Sulphide ores is changed into the oxide or sulphate which then reacts with the remaining part of the Sulphide ore to give the metal and Sulphur dioxide.

Following reaction show the extraction:

(Copper glance)

  • Copper produced is called Blister copper.
  • The evolution of Sulphur dioxide produces blisters on the surface of solidified copper metal.

Developed by: