Market Survey on Copper - Indian Bureau of Mines

B) Concentration (Froth Flotation)
The copper minerals, particularly sulphides are intimately associated
with gangue minerals necessitating fine grinding to bring about fair liberation.
In addition, there is a little difference between specific gravity of sulphide
minerals of copper and sulphide minerals of associated base metals.
Concentration of copper ores can not be carried out by gravity separation
technique. Under these circumstances, froth flotation becomes a suitable option
for copper ore beneficiation.
Froth flotation as applied to copper ores, involves:
i) Conditioning of the ground ore pulp with flotation reagents to make
copper minerals hydrophobic without affecting other accompanying minerals
and
ii) Passing a dispersed stream of fine air bubbles up through the pulp
causing air bubble attachment to copper minerals with which they rise to the top
of the flotation cell in the form of mineral laden froth, other minerals being
unaffected are rejected as tailings.
(a) Rougher and Scavenger Flotation
Commercial flotation is a continuous operation which is carried out in
cells arranged in series. Overflow from classifiers/hydro cyclone forms feed to
flotation. The pulp (overflow) conditioned with different flotation reagents
enters the first cell where some valuable minerals are collected and the
remaining pulp passes to the second cell and so on until barren tailings leave
the last cell. The float from the last few cells is of comparatively lower grade
containing interlocked particles or free coarse materials. The flotation of readily
and rapidly floatable material is called rougher flotation whereas flotation of
mixed particles, coarse particles and very fine particles from the last few cells
is called scavenger flotation, i.e. in a commercial flotation circuit, the fast
floating material is recovered by scavenging.
Both scavenger concentrates and cleaner tails contain essentially slow
floating fine values as well as coarse mixed particles. Therefore, they are
classified. The fine classified product is recycled to the rougher circuit or
cleaned in a separate circuit and the coarse product is reground and returned
to the system with new feed.
b) Cleaner Flotation
It goes with saying that rougher concentrates seldom conform to the
smelters requirements as they are often contaminated with gangue minerals due
to mechanical entrapments. In order to drop out these gangue minerals, rougher
concentrate is cleaned number of times at lower pulp density.
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