STAGES IN MINERAL PROCESSING
LIBERATION: separating minerals into individual grains.
Primary liberation is carried out by crushing. This is done in a jaw crusher at the mine.
The grains are further liberated at a plant which is often on the mine site. Secondary
liberation takes place at the crushing plant. The grains are passed through a cone
crusher, a rod mill and finally a ball mill. At each stage the grains are screened and any
liberated grains are removed.
SEPARATION: The metallic minerals are separated from the gangue (waste).
Methods of separation:
Method
Suitable for:
PHYSICAL
Gravity separation (e.g. on shaking
tables)
X-ray separation
Magnetic separation
Electrical conductivity
CHEMICAL
Froth flotation – chemicals make mineral
grains water repellent, so grains float to
the surface of a pool. Chemicals used
depend on the nature of the mineral.
Concentrated ore is then removed from the site for
SMELTING: metal is heated to remove impurities such as sulphur. An ore melt forms as
well as a layer of slag. Other chemicals may be added to remove impurities, e.g. silica is
added to remove iron from copper melts, whilst limestone removes impurities from iron.
An example is the extraction of copper from Mt Isa in Australia. Read t he information
about the mine, study the diagram and draw a flow diagram to show the stages in copper
extraction.