Iron is extracted from its ore (rocks rich in iron oxide) in a blast furnace. The iron ore is mixed with coke (a refined form of coal with a very high carbon content) and limestone. This mixture is baked into a crusty mixture known as sinter (that has a very high surface area) before being loaded into a huge brick-lined furnace. Hot air is blasted through the mixture, raising the temperature to 1800 °C. At this temperature several different reactions occur resulting in liquid iron and a molten waste product called slag.
The furnace is run 24 hours a day to make sure that the iron does not solidify. The slag is allowed to cool and can be used for road building and to make abrasives (like sandpaper).
Reactions
There are four main reactions that take place within the furnace. The first is the thermal decomposition of the limestone (calcium carbonate).
Secondly, carbon dioxide reacts with the coke (carbon) to produce carbon monoxide. Carbon monoxide is a better reducing agent than carbon so it can reduce the iron oxide to iron more easily.
Thirdly the iron ore (iron oxide) is reduced to produce molten iron.
Finally, the major impurity in iron ore, sand (silicon oxide) reacts with quicklime (calcium oxide) left over from the thermal decomposition of limestone to produce slag (calcium silicate).
Questions…
- Suggest another compound that thermally decomposes.
- Name (a) a metal element and (b) a non-metal element mentioned in the text above.
- Non-metal oxides tend to be acidic when dissolved in water. Give an example from the compounds mentioned above.
- Metal oxides are all bases. Give an example from the compounds above.
- What substance is oxidised in the reaction that produces iron?
- From the clues above, what type of reaction is the one that produces slag?
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