2. INTRODUCTION
Flotation is the separation of particles from a mixture by causing some particles to
collect on the surface of bubbles.
Floatation is an extractive process where various minerals can be selectively extracted.
For example, in poly-metal ores such as Pb-Zn-Cu, floatation allows separate extraction
of Pb, Cu and Zn.
The process of separation of mineral includes three important mechanisms :
1. TRUE FLOTATION, i.e., selective attachment to air bubbles.
2. ENTRAINMENT in the water which passes through the froth.
3. AGGREGATION, i.e. physical entrapment between the particles in froth.
3. CONT…
True flotation dominates the recovery of the valuable minerals and the other two decide
the separation efficiency between the valuable and the gangue.
FLOTATION process can be applied to relatively fine particles, because if the particles
are coarse and heavy, their weight will be greater than the adhesion between the
particle and the air bubble and the particle will detach from the bubble.
There are two ways of flotation :
1. DIRECT FLOTATION- In which the mineral is attached to the froth and the gangue
remains in the tailing.
2. REVERSE FLOTATION- in which the gangue is attached to the froth and minerals
remain in tailing.
4. BASIC PRINCIPLES
This process commences with Comminution (to increase the surface area of the
ore).
The ore is ground to fine powder and wetted with water to form a Slurry.
A Surfactant chemical (known as COLLECTOR) is mixed with slurry to render the
desired mineral HYDROPHOBIC.
This slurry (now PULP) is then placed in the water bath containing FROTHER,
which is aerated to create bubbles.
The desired mineral escape water by getting attached to the air bubbles, which
rise to the surface and form what is called FROTH. This Froth is then removed
and the concentrated mineral is refined.
6. MECHANICS OF FLOTATION
The basis of Froth Flotation is the difference in the WETTABILITY of the mineral
and gangue particles.
On the basis of Wettability of particles are classified as HYDROPHOBIC and
HYDROPHILIC.
The valuable minerals can attach to the air bubbles , only if they are
Hydrophobic. Once they reach the surface, due to the buoyancy of the air
bubbles, the particle-bubble contact can sustain only if they form a stable froth.
The stability of the froth depends on the strength of the attachment of the
bubble to the mineral surface. This strength can be estimated with the help of
YOUNG-DUPRE EQUATION, which relates the strength of attachment to the
interfacial energies.
7. This process is used for sulphide ores. Oils can wet
sulphides. Oil floats on water. Sulphide ores are
first ground to powder and water is added.
Then pine oil is added and the emulsion is agitated
by passing compressed air. Oil and froth float on
the surface along with the sulphide ore.
The gangue particles being insoluble in oil remain
at the bottom of the water tank. The froth is
removed and allowed to settle down
This is called the froth-floating process. This
process is used for sulphide ores of Cu, Pb and Zn
8.
9. ADVANTAGES OF FLOTATION OVER
SEDIMENTATION
High rise velocity permits small tankage.
Ability to handle variable solids loading (can adjust air flow).
Can provide high float concentration (good thickening).
Can remove low density particles which would require long settling
periods.
