Iron extraction

Iron extraction

Iron is a transition

Second most abundant metal after aluminium

Iron extraction may be done from the following ores.

Haematite Fe2O3

Magnetite Fe3O4

Siderite FeCO3

Ores of iron mainly contain silica (SiO2) and aluminium oxide as impurity

Extraction

Iron extraction is from its oxide or siderite

Siderite is first roasted in air to convert it to iron (III) oxide

FeCO3 (s)    → FeO (s)     + CO2 (g)

Iron (II) oxide is then oxidized by oxygen in the atmosphere to iron (III) oxide

4FeO (s) +  O2 (g)   → 2Fe2O3 (s)

 

Iron extraction

Blast furnace is about 30m high

Made of steel lined with bricks made from magnesium oxide which conserve heat energy in order to maintain the optimum temperature for the reduction process

The furnace is fed with a mixture of iron (III) oxide powder, limestone, and coke from the top

The mixture is then heated by a blast of air at temperature of about 800oC – 1000oC from the bottom of the furnace

At the bottom of the furnace, coke is oxidized to carbon (IV) oxide

The reaction is exothermic and raises the temperature of the furnace to about 1600oC

C (s) +   O2 (g)   → CO2 (g)

In the middle part oxygen in the air is in limited supply and carbon (IV) oxide formed at the lower part is reduced by coke to carbon (II) oxide

CO2 (g) +   O2 (g)  → 2CO (g)

At the upper part of the furnace, where temperatures are about 700oC, iron (III) oxide is reduced to iron by carbon and carbon (II) oxide

2Fe2O3 (s)    +   3C (s) → 4Fe (l)     +       3 CO2 (g)

2Fe2O3 (s) + 3CO (s) → 4Fe (l)     +       3 CO2 (g)

The carbon (IV) oxide produced is recycled

Calcium carbonate is decomposed to calcium oxide and carbon (IV) oxide

CaCO3 (s)   → CaO (s)    +   CO2 (g)

Calcium oxide being basic reacts with acidic and amphoteric oxides to form slag

CaO (s)  +   SiO2(s)  → CaSiO3 (l)

CaO (s)  +   Al2O3 (s) →CaAl2O4 (l)

The slag formed is tapped off at a higher level of the furnace because of its lower density compared to molten iron. Hence it floats on iron

Iron obtained is 90 – 95% pure and known as pig iron




The main Impurities include carbon, silicon, manganese, sulphur and phosphorous

These impurities make iron to be less hard as well as brittle and lowering its melting point

Cast iron (pig iron)

It is iron obtained from blast furnace

Contains about 3-5% carbon, 1% silicon and 2% phosphorous

It is brittle but extremely hard hence used in making

Furnaces, Railing, Drainage pipes, Engine block, Iron boxes

Manufacture of wrought iron and steel

Wrought iron

Contains 1% carbon. It is malleable and thus can be easily forged (molded) and welded.

Used in

Making iron nails, Iron sheets, Horse shoes, Agricultural implements

Steel

These are alloys of iron where the main component is iron

Other substances may be carbon, vanadium, manganese, tungsten, nickel and chromium

Mild steel contains about 0.3% carbon

Mild steel

Making

Nails, Car bodies, Railway lines, Ships bodies, Gliders, Rods for reinforced concrete, Pipes

Mild steel is easily worked on

Stainless steel

Contains 74% iron, 18% chromium and 8% nickel

Containing 10-12% chromium is used in making cutlery, sinks, and vats

Containing 5-18% tungsten is used in making high speed cutting and drilling tools because it is tough and hard

Cobalt steel

Contains 97.5% and 2.5% cobalt

It is highly magnetic and so it is to make electromagnets



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