C5.4 How can we extract useful materials from minerals?
The lithosphere contains many naturally occurring elements and compounds called minerals. Ores are rocks that contain varying amounts of minerals, from which metals can be extracted.
Sometimes very large amounts of ores need to mined in order to recover a small percentage of 
valuable minerals – e.g. copper. The method of extraction depends on the metal’s position in the reactivity series.
Metals such as zinc, iron and copper are metals that can be extracted by heating their oxides with carbon.
For example:
Zinc can be extracted from zinc oxide by heating it with carbon – zinc oxide is reduced because it loses oxygen – carbon is oxidised because it gains oxygen:
When a metal oxide loses oxygen it is reduced while the carbon gains oxygen and is oxidised.
Some metals are so reactive that their oxides cannot be reduced by carbon
All chemical reactions follow the same simple rule: the mass of the reactants is equal to the mass of the products – this means there must be the same number of atoms on both sides of the equation.
S= solid l = liquid g = gas aq = aqueous (dissolved in water)
Atoms are too small for their actual atomic mass to be of much use to us – we therefore use the relative atomic mass (RAM) – This is the number that compares the mass of one atom to the mass of other atoms.
Each element in the periodic table has two numbers – the larger of the two is the mass number which also doubles up as the relative atomic mass.
The relative formula mass (RFM) of a compound is the relative atomic masses of all its elements added together.
If you are given its formula, you can calculate the mass of metal that can be extracted from a substance. Follow these steps:
Electrolysis is the decomposition of an electrolyte (a solution that conducts electricity) using an electric current. The process is used in industry to extract reactive materials from their ores. Electrolytes include molten ionic compounds – ionic compounds will only conduct electricity when their ions are free to move.
This occurs when the compound is either molten or dissolved in solution; the electrostatic forces between the charged ions are broken. The crystal lattice is broken down and the ions are free to move.
During electrolysis, metals form at the negative electrode and non-metals form at the positive electrode.
Aluminium is the most abundant metal on Earth – despite this, it is expensive, largely because of the amount of electricity used up in the extraction process.
Aluminium must be obtained from its ore by electrolysis because it is too reactive to be extracted by heating with carbon.
These are the steps
❶ Aluminium ore (bauxite) is purified to leave aluminium oxide
❷ Aluminium oxide is mixed with cryolite (a compound of aluminium) to lower its melting point
❸ The mixture of aluminium oxide and cryolite is melted so that the ions can move
❹ When a current passes through the molten mixture, positively charged aluminium ions move towards the negative electrode (the cathode) to become neutral atoms and aluminium is formed. Negatively charged oxide ions move towards the positive electrode (the anode) to become neutral atoms and oxygen is formed
❺ This cause the positive electrodes to burn away quickly – they have to be replaced frequently
In the extraction of aluminium, this is the equation for the equation at the negative electrode:
Al3+ + 3e− → Al
In the extraction of aluminium, this is the equation for the equation at the positive electrode:
2O2− → O2 + 4e−
Generally , metals are strong and malleable (they can be beaten or pressed into thin sheets), have high melting points and can conduct electricity.
The properties of a metal can be explained by its structure – the force of attraction that keeps the structure together is known as the metallic bond – strong bonds.
In a metal crystalline structure, the positively charged ions are held closely together by a ‘sea’ of electrons that are free to move.
- Strength – the ions are arranged in a lattice structure – metal ions are closely packed in a lattice structure
- High melting point – a lot of energy is needed to break the strong force of attraction between the metal ions and the sea of electrons
- Malleable – Rows of ions can slide over each other – this results in the metal being ‘bendy’ and can be dented
- Conducts electricity – moving electrons can carry the electric charge – electrons are free to move throughout the structure. When an electrical force is applied, the electrons move along the metal in one direction
In order to assess the impact on environment of extracting and using metals – a life cycle assessment of metal products needs to be carried out.
However many impacts on the environment can arise including:
