Extracting metals from their ores

Rocks containing a considerable amount of a metal are called ores. The metal in the ore is present in its impure form as compounds of that element.

These compounds are often metal oxides or metal sulphides.

Reactivity

Reactivity plays a major role in deciding the method of extracting metal from their ores.

Metals those are quite reactive (such as potassium, sodium, calcium, magnesium and aluminium) are extracted from their ores by electrolysis of a molten compound.

For less reactive metals such as zinc, a chemical reducing agent (typically carbon or carbon monoxide) is used to extract them from their ores.

Extraction of iron

Iron is a very important metal. It has uses almost everywhere, making it one of the most used metals.

As iron is a less reactive than carbon, it needs to be extracted using the reactions in the blast furnace.

Unlike gold, iron is not found native; it needs to be extracted from its ores. The major ore of iron is hematite (Iron(II)oxide).

Process of extracting iron using the blast furnace

Iron is extracted using the blast furnace. Here is the process of extracting iron from hematite:

A mixture of hematite, limestone and coke is added at the top of the blast furnace
Hot air is blown into the furnace to encourage complete combustion of the coke
This produces large amounts of heat and carbon dioxide
Higher up the furnace, the oxygen is used up and thus the carbon dioxide decomposes to carbon monoxide.
This reduces the iron ore (hematite) to iron, that flows down to the bottom of the blast furnace.

 

Purifying the iron
Iron ore contains an impurity: silicon (V) oxide. This is removed by the addition of limestone.
Limestone decomposes due to the heat to calcium oxide
The calcium oxide reacts with the impurity (silicon (V) oxide) to produce slag.  

 

Iron produced from the blast furnace separates from the slag by sinking to the bottom; slag is less dense than iron.

It is then tapped of and used commercially for many applications and uses.

The slag is cooled down and used by builders to construct roads.

Zinc

  • Ore: Zinc blende (Zinc sulphide- ZnS)
  • Method of extraction- reduction in a blast furnace
  • Reducing Agent: Carbon

Process of extracting zinc using the blast furnace

  1. Zinc blende is roasted in air to form zinc oxide and sulphur dioxide:
  2. Zinc oxide is heated with carbon, where it is reduced to zinc:
  3. Zinc escapes through the blast furnace as zinc vapour and is cooled down in condensation trays.

Uses of metals

Metals can have many uses in various industries. The uses of some of the most commonly used metals are listed below:

Metal Use
Zinc Used for making alloys such as brass

Used for rust prevention by galvanizing and sacrificial process

Aluminium Aircraft construction (because it has low density)

Food containers (as it resists corrosion)

Copper Electrical wires (as it is an excellent conductor of electricity and is ductile)

Cooking utensils (as it is malleable)

 

Alloys

An alloy is a mixture of two or more metals. Alloys are made to enhance the properties of a metal for a particular use.

For example, iron gets rusted easily when in contact with oxygen and water; to overcome this, it is mixed with chromium and nickel to form ‘stainless’ steel that doesn’t rust.

Examples of alloys

  • Brass: A mixture of zinc and copper
  • Stainless steel: a mixture of iron, chromium and nickel

 

 

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