Extraction of Metals from its Ore

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Extraction of Metals from Its Ore

Extraction of Metals

Metals usually exist as compounds or mixed with other substances, such as rocks and dirt.
Compounds containing metals are also known as ore or mineral and exist as metal oxides, metal sulphides or metal carbonate.
Non reactive metals such as gold and silver do not need to be extracted because they exist as metal elements.
Reactive metals like iron and aluminium require a particular way to be extracted from their respective ores.
The methods for extracting reactive metals are based on the position of the metal in the reactivity series of metal.
Two of the most common ways to extract metals from their respective ores are:

The image is an educational graphic titled ‘Ways to Extract Metals from Their Ores.’ It is divided into two sections. The left section, labeled ‘Electrolysis,’ states, ‘For metals that are more reactive than carbon.’ The right section, labeled ‘Reduction by Carbon,’ states, ‘For metals that are less reactive than carbon.’The background is white, and the text is in blue and red.

Extraction of Metals from Its Ore through the Process of Electrolysis

Reactive metals like aluminium, Al can be extracted from its ore using electrolysis.
In the extraction of aluminium, Al, aluminium ore or bauxite is firstly purified to obtain aluminium oxide, \(Al_2O_3\), which is then melted down to enable the process of molten electrolysis to be conducted.
The melting process uses an extremely high energy since the melting point of aluminium oxide, \(Al_2O_3\) is 2000 °C.
To overcome this problem, cryolite, \(Na_3AlF_6\) is melted together with aluminium oxide, \(Al_2O_3\) to lower its melting point.
The extraction of aluminium from molten aluminium oxide, \(Al_2O_3\) by electrolysis using electrolysis process is as shown as below:

The extraction of aluminium using electrolysis is a redox reaction.

Electrode	Anode	Cathode
Reaction	Oxidation	Reduction
Substance that undergoes reaction	Oxide ion, \(O^{2-}\)	Aluminium ion, \(Al^{3+}\)
Product	Oxygen molecule, \(O_2\)	Molten aluminium
Half equation	\(2O^{2-}(l) \rightarrow O_2(g) + 4e^-\)	\(Al^{3+}(l) + 3e^- \rightarrow Al(l)\)

Molten aluminium sinks to the bottom of the layer because its density is higher, and then is drained out through a designated channel.
The entire process of aluminium extraction consumes a huge amount of electricity.
During the process of electrolysis for molten aluminium oxide, \(Al_2O_3\), carbon dioxide, \(CO_2\) is also formed, which negatively affects the environment.
Apart from that, the purification process of bauxite also creates a residue in a form of red sludge that is toxic.
Therefore, as consumers, we must recycle aluminium to reduce pollution on the environment.

Extraction of Metals from Its Ore through the Process of Carbon Reduction

Iron metal, which is less reactive than carbon, C can be extracted by carbon, C reduction process.
This process is carried out in a blast furnace by heating up iron ore or hematite (\(Fe_2O_3\)) with coke, C and limestone, \(CaCO_3\) as shown below:

There are several important reactions involved in this extraction process as shown below:

Reaction	Explaination
Zone 1 Coke, C reacts with oxygen, \(O_2\) from the hot air to form carbon dioxide, \(CO_2\). \(C(s) + O_2(g) \rightarrow CO_2(g)\)	This is a redox exothermic reaction that makes the temperature of the blast furnace reach 1600 °C.
Zone 2 The produced carbon dioxide, \(CO_2\) reacts with the remaining coal. \(C(s) + CO_2(g) \rightarrow 2CO(g)\)	Carbon monoxide, \(CO\) is the reducing agent for the subsequent reaction. This is an endothermic reaction that lowers the temperature in Zone 2.
Zone 3 Coke, C and carbon monoxide, \(CO\) function as reducing agents and reduce iron(III) oxide, \(Fe_2O_3\) or iron ore to molten iron. \(2Fe_2O_3(s) + 3C(s) \rightarrow 4Fe(l) + 3CO_2(g)\) \(Fe_2O_3(s) + 3CO(s) \rightarrow 2Fe(l) + 3CO_2(g)\)	Iron(III) oxide, \(Fe_2O_3\) is reduced by carbon monoxide, \(CO\). Iron deposits are formed at the bottom of the blast furnace.
At high temperature, calcium carbonate, \(CaCO_3\) decomposes to form calcium oxide, \(CaO\) (quicklime) and carbon dioxide, \(CO_2\). \(CaCO_3(s) \rightarrow CaO(s) + CO_2(g)\) Impurities in the iron ore like silicon(IV) oxide, \(SiO_2\) react with calcium oxide to form slag or calcium silicate, \(CaSiO_3\). \(CaO(s) + SiO_2(s) \rightarrow CaSiO_3(l)\)	Calcium oxide, CaO is a base and can neutralise the acidic silicone(IV) oxide, \(SiO_2\). This reaction is important to separate the impurities from molten iron. The difference in density causes the slag to be at the top layer of the molten iron, which makes the separation process easier.

Extraction Using A More Reactive Metal

When metals are heated together, the more reactive metal can extract the less reactive metal from its metal oxide.
This reaction releases large amounts of heat that produce metal in molten state.
For example, in a thermite reaction, aluminium powder, Al is heated together with iron(III) oxide powder, \(Fe_2O_3\).
The more reactive aluminium, Al reduces iron(III) oxide, \(Fe_2O_3\) to produce molten iron, Fe.
This is a very useful reaction in producing small quantities of molten iron for welding railway tracks.
The following is the equation for the thermite reaction;
- \(Fe_2O_3(s) + 2Al(s) → Al_2O_3(s) + 2Fe(l)\)
Some other metals like chromium, Cr and titanium, Ti can be extracted from their respective metal oxides using reduction by more reactive metals.
Reactivity series of metal is as shown below:

Reactivity Series of Metal

Very reactive metals.

The best way to extract the metal from its ore is by electrolysis.

Moderately reactive metals.

The best way to extract the metal from its ore is reduction by carbon.

Less reactive metal.

Metal is extracted from its ore by direct heating in air.

Unreactive metal.

Exists as an element.