Purification of iron from haematite
Key feature of the production process
Iron is extraction from its ore which is called haematite and this process often happens in a blast furnace
- Limestone is added to the haematite (iron ore) this causes a reaction with silica which is the impurities from the iron ore.
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Then this reaction makes molten calcium silicate in the furnace which can be cold slag
- The slag floats on the iron liquid
- The iron ore is then heated with carbon to transform it to iron metal
Importance of physical and chemical properties of substances
Limestone
The limestone is important because it contains the carbon dioxide which is good in helping remove impurities
Oxygen
The oxygen is important because it burns the coke which allows heat to be created, carbon monoxide and carbon dioxide
The coke
It burns in the air and makes heat and makes carbon by reacting with carbon monoxide
The carbon monoxide
Really hot air is blown in the furnace which causes the carbon to burn quickly and that make carbon dioxide. So the temperature increases very quickly. The carbon dioxide then reacts with hot carbon to make carbon monoxide. The carbon monoxide is really important because it is this chemical that reduces the iron to the final iron metal.
Iron
Iron is not a very reactive metal, so, because its position in the reactivity series of metals, iron can be extracted using carbon in a blast furnace because iron is below carbon (iron is less reactive than carbon). Therefore, iron can be displaced from its e.g. its oxides, by heating with the theoretically 'more reactive' carbon in a sort of displacement reaction.
Iron is a good electricity and heat conductor with a boiling point of 2861° and a melting of 1,538° at this melting point, the iron is soft enough to be turned into many other objects with the help alloys. When mixed with alloy, it can be used to manufacture things like metal pans, scissors etc...
Iron rusts in damp air, dissolve in dilute acid.
The uses of the final product
Iron is mostly used to produce steel but is mostly used to manufacture many different parts of a car. Some types of steel are used to make materials such as cutting knife, drilling tools etc.
Why both metals require different method to be extracted
Extracting aluminium and iron cannot be done the same way because the extraction depends on their reactivity. Aluminium just like all the most reactive metals is often extracted using electrolysis while iron which is less reactive than aluminium is extracted by using the reduction method with carbon Monoxide or carbon
Electrolysis is the best way to extract aluminium because this method doesn’t damage the aluminium where as other methods do. The oxidisation of aluminium for example forms a cover around the aluminium that is being oxidised.
In order of reactivity, we have Aluminium followed by carbon and then further down the list we have iron. Because aluminium is more reactive than carbon according to its place on the reactivity series, it can’t be displaced by the aluminium by since carbon is above iron, it can be used for displacement.
Bauxite is by washed with a hot solution of sodium hydroxide, NaOH, at 175 °C, This then turns the aluminium oxide in the ore to soluble sodium aluminate, 2NaAlO2,
Chemical equation:
Al2O3 + 2 NaOH + 3 H2O → 2 NaAlO2
This treatment also dissolves silica; lime is added here, to precipitate the silica as calcium silicate. We purify the solution by filtering off the solid impurities. Originally, the alkaline solution was cooled and treated by bubbling carbon dioxide into it, through which aluminium hydroxide precipitates:
2 NaAlO2 + CO2 → 2 Al (OH)3 + + H2O
But later, this gave way to seeding the supersaturated solution with high-purity aluminium hydroxide (Al(OH)3) crystal, which helped removed the need for cooling the liquid and was more economically feasible:
2 H2O + NaAlO2 → Al(OH)3 + NaOH
Then, when heated to 980°C (), the aluminium hydroxide decomposes to aluminium oxide, giving off water vapour in the process:
2 Al(OH)3 → Al2O3 + 3 H2O
The left-over NaOH solution is then recycled. This, however, allows gallium and vanadium impurities to build up in the liquors, so these are extracted.
For bauxites having more than 10% silica, Bayer process becomes infeasible due to insoluble sodium aluminium silicate being formed, which reduces yield, and another process must be chosen.
A large amount of the aluminium oxide so produced is then subsequently smelted in the Hall–Héroult process in order to produce aluminium.
