Extraction of Iron

ChemistryGeneral Principles And Processes Of Isolation Of ElementsFor JEE aspirants

Ores

Magnetite $F e_{3} O_{4}$

Red Haematite $F e_{2} O_{3}$

Limonite $F e_{2} O_{3} .3 H_{2} O$

Iron pyrites $F e S_{2}$

Copper pyrites $C u F e S_{2}$

Siderite FeCO₃

Extraction of iron

Dressing of the ore: Iron ore is first broken into small pieces of 3 – 5 cm in size.

Roasting and calcination: During roasting S, As, etc. are oxidized to the respective oxides.

$S + O_{2} S O_{2} ↑$

$4 A s + 3 O_{2} 2 A s_{2} O_{3} ↑$ .

$F e C O_{3}$ decomposes as

$F e C O_{3} F e O + C O_{2} ↑$

$F e_{2} O_{3} .3 H_{2} O L oses w a t er$

$F e_{2} O_{3} .3 H_{2} O F e_{2} O_{3} + 3 H_{2} O$

$F e_{3} O_{4}$ is decomposed to ferrous oxide and ferric oxide.

$F e_{3} O_{4} F e O + F e_{2} O_{3}$

Ferrous oxide reacts with silica to form ferrous silicate at high temperature.

$F e O + S i O_{2} F e S i O_{3}$

The conversion of FeO into $F e_{2} O_{3}$ will prevent the formation of $F e S i O_{3} .$ Thus mass of the ore becomes porous causing the increase in the effective surface area.

Smelting in the Blast furnace

Reactions:

(i) Zone of combustion

$C + O_{2} C O_{2}$ (1500-1600°C)

(coke)

(ii) Zone of reduction

$F e_{2} O_{3} + 3 C O 2 F e + 3 C O_{2}$ (300-700°C)

$F e O + C O F e + C O_{2}$

(iii) Zone of slag formation

$C a C O_{3} C a O + C O_{2}$ (800-1000°C)

(limestone)

$C a O + S i O_{2} C a S i O_{3}$

fusible slag

(iv) Zone of fusion (lower part of furnace)

Molten iron is heavier than molten slag. The two liquids are periodically tapped off and solidified into blocks called pigs.

Preparation of wrought iron:

This is done by heating cast iron with haematite $(F e_{2} O_{3})$ which oxidises C to CO, S to $S O_{2},$ Si to Si to $S i O_{2}, P t o P_{4} O_{10} & M n$ to MnO

$F e_{2} O_{3} + 3 C 2 F e + 3 C O$

Where $C O & S O_{2}$ escapes, manganous oxide (MnO) and Silica $(S i O_{2})$ combine to form slag.

$M n O + S i O_{2} M n S i O_{3}$

Similarly phosphorus pentoxide combines with haematite to form ferric phosphate slag.

$2 F e_{2} O_{3} + P_{4} O_{10} 4 F e P O_{4}$

Manufacturing Process:

Casts iron takes in piddling furnace and melted by hot blast of air. The chemical reactions which occur are:-

$S + O_{2} S O_{2} ↑$

$3 S + 2 F e_{2} O_{3} 4 F e + 3 S O_{2} ↑$

$3 S i + 2 F e_{2} O_{3} 4 F e + 3 S i O_{2}$

$M n + F e_{2} O_{3} 2 F e + 3 M n O$

$M n O + F e_{2} O_{3} M n S i O_{3} (s l a g)$

$3 C + F e_{2} O_{3} 2 F e + 3 C O$

$4 P + 5 O_{2} 2 P_{2} O_{5}$

$F e_{2} O_{3} + P_{2} O_{5} 2 F e P O_{4} (s l a g)$

On removing impurities, the melting point rises and it becomes a semi solid mass. The metal is taken out of the furnace in the form of balls which are then beaten under hammer to separate out the slag. The product thus formed is thus called wrought iron.

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