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Extraction of Moderately Reactive Metals

The metal such as iron, zinc, lead and copper are moderately reactive. They are usually present as sulphides or carbonates in nature.



Roasting is the process of strongly heating a concentrated ore in excess air. Sulphide ores are usually roasted and converted to the oxide or sulphate form.





Calcination is the process of heating a concentrated ore in a controlled supply of air, whereby organic matter and volatile impurities are removed.


Generally, carbonate, hydroxide and hydrated oxide ores are calcined in a reverberatory furnace. 



Reduction to Metal :-
After calcination or roasting, the oxide formed is reduced to the metal state. For example iron oxide is reduced to iron in a blast furnace and zinc oxide is reduced by carbon to metallic zinc in a fire clay retort.

Blast Furnace
The calcined ore mixed with coke (C) and limestone (CaCO3) is fed into the top of a blast furnace. A blast of hot air is blown in at the bottom of the furnace. The falling coke burns and intense heat is generated. Temperature around 1900

C + O2  CO2 + heat


CO2 + C  2 CO


Carbon monoxide (CO) thus produced acts as a reducing agent and reduces iron oxides to iron.
In the middle of the furnace, limestone decomposes to quicklime (CaO), which reacts with silicaceous impurities to form calcium silicate (slag).


In the lower part of the furnace, the molten iron sinks to the bottom and forms a layer below the slag. It is removed periodically from a low hole and deposited in sand moulds. It is called cast iron or pig iron. A single blast furnace produces about 3000 to 6000 tonnes of iron daily.

Reduction to Zinc Oxide in a Fire Clay Retort



Thus, zinc oxide (ZnO) and lead oxide (PbO) are reduced with coke (C).

The highly reactive metals such as sodium, calcium and aluminium are used as reducing agents because they can displace metals of lower reactivity. When manganese dioxide is heated with aluminium powder a highly exothermic reaction takes place and Mn is obtained in the molten state
3MnO2(s) + 4 Al(s)  3Mn(l) + 2Al2O3(s) + Heat
The reduction of a metal oxide to form metal by using aluminium powder as a reducing agent is called thermite reaction. The reactions of metal oxides with aluminium powder to produce metals are highly exothermic ithnat is a large amount of heat is evolved. In fact, the amount of heat evolved is so large that the metals are produced in the molten state. This property of reduction by aluminium is made use of in thermite welding for joining the broken pieces of heavy iron objects like girders, railway tracks or cracked machine parts.
A mixture of iron (III) oxide and aluminium powder is ignited with a burning magnesium ribbon. Aluminium reduces iron oxide to produce iron metal with the evolution of a lot of heat. Due to this heat, iron (metal) is produced in the molten state.

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