Metallurgy

Metallurgy and Steel
Extraction of metals: Extraction of Chromium from oxide ore, Nickel from sulphide ore,
beryllium from silicate ore, gold and platinum from native ores. Refining techniques: zone
refining and vapour phase refining.
Powder metallurgy: Importance, metal powder production and application. Production of
tungsten from wolframite.
Steel: Iron - carbon phase diagram. Explanation for austinite, cementite , ferrite and pearlite
based on phase diagram.
Alloy steels: Influence of Si, Mn, Cr , Ni, Ti, and W on the properties of steel.
Ferro alloys: Production of ferrochrome, ferro manganese and ferrosilicon.
Heat treatment of steel - Hardening, case hardening, carbiding and nitriding, tempering and
annealing.

Mineral — Naturally occurring form of the metal (metal can be in free or combined state)
Ore — Mineral from which the metal can be extracted economically.
Metallurgy — Can be regarded as the science and technology involved in the extraction of
metals from their ore.
Gangue — Undesirable materials in an ore.
Flux — Material added to combine with gangue to form fusible material called slag.
Acidic fluxes: SiO2. Al2O3, Basic Fluxes: CaO. MgO, Neutral Fluxes: CaF 2.
Na2SO4
Slag— Fusible material formed by the combination of gangue and suitable flux
Gangue + Flux Slag (Lighter than molten metal, easily separated)

Important metallurgical processes are:
(i) Concentration of the ore
(ii) Extraction of crude metal
(iii) Refining
(i) Concentration of the ore
(a) Gravity separation /Hydraulic washing / levigation
(b) Froth Flotation
(c) Magnetic separation
(ii) Extraction of crude metals
(a) Pyrometallurgy
(b) Hydrometallurgy
(c) Electrometallurgy
(iii) Refining
Process of purification of crude metals to get extra pure metals is called refining of metals
(a) Electrolytic refining
(b) Vapor phase refining
(c) Zone refining




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, Extraction of Chromium from Chromite ore (Oxide ore)

Ore of Chromium: Chromite, FeOCr2O3
 Concentration:
The ore is concentrated by gravity separation method.
Powdered ore is suspended in water and taken in a hydraulic
classifier. Water under pressure is pumped from the bottom
and powdered ore introduced from the top of the tower.
Heavier ore particles settle down while the lighter gangue
particles get washed away with water.
 Roasting:
Concentrated ore is mixed with excess of sodium carbonate
heated at high temperature in a reverberatory furnace in a free
supply of air. The chromium oxide (Cr2O3) present in the
chromite ore is converted into sodium chromate.
4FeOCr2O3 + 8Na2CO3 + 7O2 → 2Fe2O3 + 8 Na2 CrO4 + 8CO2
 Extraction with water:
The roasted mass is extracted with water when Na2CrO4 goes into solution leaving behind
insoluble Fe2O3.The sodium chromate solution is treated with calculated amount of sulphuric
acid to convert the chromate to dichromate.
2Na2 CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4 + H2O
 Fractional crystallization:
Sodium sulphate and sodium dichromate present in the above solution are separated by
fractional crystallization. The solution is concentrated when the less soluble sodium sulphate
crystallizes first leaving behind sodium dichromate.
After separating sodium sulphate crystals the solution is further concentrated to obtain solid
sodium dichromate.
 Reduction of sodium dichromate to chromic oxide:
Sodium dichromate is heated with sulphur to obtain Cr2O3
Na2Cr2O7 + S → Na2SO4 + Cr2O3
 Reduction of chromic oxide by aluminothermite process:
Chromic oxide is finally reduced to chromium by aluminothermite process.
Aluminium at high temperature reduces Cr2O3 to Cr.
Cr2O3 and Al powder are mixed and taken in a fireclay
crucible. A mixture of barium peroxide and
aluminum powder is ignited using Mg ribbon as a fuse.
Cr2O3 is reduced to chromium.
Cr2O3 +Al → Cr + Al2O3
The large amount of heat liberated in the highly
exothermic reaction melts the chromium which collects
as liquid at the bottom of the crucible (92% purity.)
Refining:
The metal is refined electrolytically using chromium chloride as the electrolyte. Mercury is
used as the cathode while impure chromium acts as anode. Chromium amalgam formed at the



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