- To make iron, it is first nece**ary to mine iron ore.
- Iron ore is simply rock with a high concentration of iron within it. Usually the ores are mixed into rocks which contain silica.
- From the table above, it is evident that the iron ores contain oxygen.
- In order to make the iron from the ore, the oxygen must first be removed. This can be achieved using a blast furnace in which a series of reduction reactions occur.
- Ores of iron greater than 5mm can be placed straight into the blast furnace; however these are in short supply and so the iron first goes through agglomerating proce**es (fuse together the smaller lumps of ore) such as sintering or pelletising. These proce**es involve mixing together the iron with controlled quantities of fluxes.
- Iron, limestone and coke are fed into the top of the blast furnace. The limestone is melted to become the ****, which removes impurities such as sulphur.
- The main fuel used in the blast furnace is coke. This is made by heating carbon in the absence of oxygen. The coke is burnt in heated air (1,100 K to 1,600K) and then blown into the furnace at the bottom. The coke reacts with oxygen in the hot air blast to form carbon monoxide:
2C(s) + O2(g) 2CO(g)
- Hydrocarbons can also be used as a fuel, and these react similarly to produce carbon monoxide and hydrogen.
CH4(g) + 0.5O2(g) CO(g) + 2H2(g)
- The gases move up the blast furnace where they reduce the iron oxides (at different temperatures):
Fe2O3(s) + 3CO(g) 3CO2(g) + 2Fe(s)
Fe2O3(s) + 3C(s) 2Fe(s)+ 3CO(g)
- The products formed from the reactions above begin to melt and trickle down to the bottom of the blast furnace.
- The limestone also descends to the bottom of the blast furnace where it is thermally decomposed:
CaCO3(s) CaO(s) + CO2(g)
- The basic calcium oxide produced in this reaction then goes on to react with acidic impurities in the iron:
FeS(s) + CaO(s) + C(s) CaS(s) + FeO(s) + CO(s)
CaO(s) + SiO2(g) CaSiO3(s)
- The CaS and CaSiO3 become the ****, which also contains other impurities such as MgO, CaO, SiO2and Al2O3. The liquid **** is le** dense than iron and so it floats on top of the molten iron at the bottom of the furnace.
- The molten iron and liquid **** are removed from the furnace through the tap holes at the base.
- The **** can be used to make bi-products such as cement. The hot gases produced are cleaned and are then burned as a fuel in the hot blast stoves that are used to preheat the air that is blown into the furnace.
The Basic Oxygen Steel making (BOS) Proce**
- In the UK, steel is made using the BOS proce**…