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प्रश्न
How is iron extracted from its ores?
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उत्तर
Iron is extracted as cast iron mostly from haematite ore. The extraction is carried out in the following steps.
1) Concentration: The ore is crushed into small pieces that range in size from 2.5 to 5.0 cm. The ore is often rich enough to not need additional concentration. On the other hand, the ore is sometimes washed with a stream of water and, if required, concentrated using a magnetic separation technique.
2) Preliminary Roasting or Calcination: Large open heaps or special kilns are used to heat the concentrated ore while air is present. The following changes occur during the initial roasting or calcination process.
i. Moisture is removed and the ore gets dried.
ii. Sulphur, arsenic, phosphorus, and other impurities undergo oxidation and are removed as their volatile oxides.
\[\ce{S + O2 -> SO2 \uparrow}\]
\[\ce{4As + 3O2 -> 2As2O3 \uparrow}\]
\[\ce{4P + 5O2 -> 2P2O5 \uparrow}\]
iii. If there is ferrous oxide, it oxidizes to ferric oxide. This stops ferrous silicate, or slag, from forming during the smelting process.
\[\ce{4FeO + O2 -> 2Fe2O3}\]
iv. The ore becomes porous. This helps in its reduction at a later stage.
Smelting: The calcined or roasted ore is placed into a blast furnace along with coke and limestone. The ore undergoes smelting in this furnace. A blast furnace is a huge steel cylindrical furnace with fire bricks lining the interior. Both the top and bottom halves are thin. It features a cup and concentric arrangement for the charge introduction and an outlet for waste gas outflow at the top.
