Metallurgy

Minerals

Metallic compounds that occur naturally on the Earth's crust.

Ores

Minerals from which metals can be extracted easily and profitably

Limestone

CaCO3

Bauxite

Al2O3.2H2O

Cryolite

Na3AlF6

Corundum

Al2O3

Red haematite

Fe2O3

Brown haematite

Fe2O3.3H2O

Magnetite

Fe3O4

Iron Pyrites

FeS2

Siderite

FeCO3

Zinc blende

ZnS

Zincite

ZnO

Calamine

ZnCO3

Fluorspar

CaF2

Alumina

Al2O3

Gangue

Earthly impurities

Magnetic seperation

Dressing of iron ores

Hydraulic/Hydrolytic washing (or) Gravity separation

Dressing of lead ores

Froth floatation

Dressing of Sulphide ores

Baeyer’s process

• Chemical method

• Dressing of Aluminium ores

  1. Al2O3.2H2O + NaOH —> 2NaAlO2 + 3H2O

  2. NaAlO2 + H2O —> NaOH + Al(OH)3

  3. Al(OH)3 —> Al2O3 + 3H2O

Stages of extraction

Ore —> Pulverisation —> Dressing/Concentration(Removal of gangue) —> Conversion to oxide(Roasting/Calcination) —> Reduction(Metal Oxide to Metal) —> Purification

Calcination

Heating ore in absence of oxygen

Roasting

Heating ore in presence of oxygen

Reduction of ZnO

• chemical method

• Reducing agent - Coke(C)

Reduction of Fe2O3

• Chemical method

• Reducing agent - CO

Reduction of PbO

• Chemical method

• Reducing agent - NH3

Reduction of CuO

• Chemical method

• H2

Reduction by electrolyis

K2O, Na2O, CaO, MgO, Al2O3

Reduction by chemical methods

ZnO, CuO, PbO, Fe2O3

Reduction by thermal decomposition

HgO

Hall-Heroult’s process

• Electrolytic reduction of alumina to aluminium

• Electrolysis is used because bond between aluminium and oxygen is very strong.

Graphite rods are replaced periodically during Hall-Heroult’s process

Oxygen reacts with graphite and converts it to CO2 OR CO

Why is coke sprinkled over the electrolyte in hall-heroult’s process

• Prevents burning of the anode

• Reduces heat loss

Role of cryolite and fluorspar in Hall-Heroult’s process

• Increases conductivity

• Reduces fusion temperature from 2050 to 950

• Act as solvent

Alloys

A homogenous mixture of metals in fixed ratios

Duralumin

• Al, Cu, Mg, Mn

• Making aircrafts

• Light tools

Magnalium

• Al, Mg

• Light tools

Brass

• Cu, Zn

• Electrical fittings

• Decorative articles

Bronze

• Statues, medals, coins

• Cu, Sn, Zn

Solder

• Pb, Sn

• Electrical fuse soldering purposes

Stainless steel

• Fe, Cr, Ni, C

• Utensils, cutlery, surgical instruments