Liberation is
the release of the valuable mineral from the gangue.
·
Major objective of comminution process
·
By liberation energy can be saved in further processing
·
High liberation is essential, if high grade
solids are required
·
For leaching, it is necessary to
expose the required mineral only
·
In practical, complete liberation is seldom achieved
·
Particles of “locked” mineral and gangue are called middlings
Degree of liberation is the %age of mineral occurring as free particles
in the ore in relation to the total content.
- If there are weak
boundaries between mineral and gangue then there will be high degree of liberation
- If adhesion is strong
then this produces much middlings and low
degree of liberation
- To increase the degree
of liberation involves directing the breaking stresses at the mineral
crystal boundaries
- Degree of liberation is zero when valuable mineral
is completely enclosed with gangue
Methods of liberation:
Froth flotation requires as much as possible
mineral surface to be exposed
·
Most important and versatile mineral processing technique
·
Developed in 1906
·
Permitted for low grade, uneconomic minerals
·
Used only for specific minerals e.g. lead-zinc, copper-zinc etc.
Principle:
It
uses the difference in surface properties of mineral and gangue
·
It is a physico-chemical process
·
It involves three phases with many sub processes
1. selective attachment to air
bubbles or true flotation
2. entrainment in the water
which passes through the froth
3. physical entrapment between
particles in froth attached to air bubbles referred as aggregation
·
separation efficiency is dependent on the degree of entrainment and physical entrapment
·
Process can only be applied to fine particles
Chemical leaching requires a portion of
mineral must be exposed to provide a channel to the bulk of mineral
Classification is a process of separation
of particles on the basis of velocity with which they fall in a fluid.
·
Fluid is usually water
·
Applied to such a particles which are too fine
·
Velocity of particles is dependent on size, specific gravity and shape
of particles
·
If resistance of fluid is high and velocity of particles is low then it
is called viscous flow
·
When velocity is high and resistance is low then it is called turbulent flow
·
Free settling is sinking of particles in
a larger volume of liquid than that of particles
·
Particles are not apparent in free settling
·
When solid particles increased in pulp and particle crowding become
apparent then that is called hindered
settling
Magnetic separation used the difference in
magnetic properties of to separate the valuable mineral and gangue
·
There are two types of magnetic materials:
1. Diamagnetic materials are repelled along the
lines of force to a point where field intensity is smaller
·
Cannot be concentrated magnetically
1. Paramagnetic materials are attracted along the
magnetic lines of forces to points of greater field intensity
