Market Survey on Copper - Indian Bureau of Mines

c) Flotation Reagents
The most important reagents in copper ore flotation are collectors,
frothers, pH regulators and depressants.
i) Collectors: The reagents which create the hydrophobic surfaces on
minerals are called collectors. They are hetropolar organic compounds, i.e.
collector molecule contains a non-polar hydrocarbon group and a polar
(charged) group. The non-polar hydrocarbon radical has pronounced waterrepellant
properties whereas polar group has affinity for water. The collectors
absorb on the mineral surface with non-polar end oriented outwards. It is this
orientation which imparts hydrophobicity to the mineral particles.
The most widely used collectors for sulphide flotation are xanthates
(sulphydryl type) which have polar bivalent sulphur. The other sulphur- bearing
collectors are thiono carbonates, dithiophosphates (Aerofloat) and
pthilocarbonitides. The dithiophosphates are not as widely used as xanthates,
but are still important reagents in sulphide flotation. They have pentavalent
phosphorus in polar group. Sodium ethyl xanthate has a typical structure.
The reaction of xanthate with oxidation product of sulphide surface
through ion exchange process is considered to be a major adsorption mechanism
for flotation of sulphides. However, a high degree of surface oxidation
accompanied by formation of sulphates readily reacts with xanthates. As the
metal xanthates so formed scale off the mineral surface, the solubility of copper,
lead, silver and mercury in xanthate is very low whereas solubility of iron and
zinc xanthates is much higher. There fore sphalerite activation by copper
sulphate is necessary. The alkali earth metal xanthates (Ca, Ba, Mg) are very
soluble and they have no collector action on the minerals of such metals nor on
oxides, silicates or alumino-silicates. This phenomenon permits extremely
selective flotation of sulphides from gangue minerals. Xanthates are normally
used in weakly alkaline pulps, since they decompose in acid media and at high
pH hydroxyl ions can displace xanthate ions from the mineral surface.
Sodium isopropyl xanthate is the universal collector used in the copper
flotation plants. Sodium isopropyl xanthate is often replaced by amyl xanathate
as it yields pyrite-rich copper concentrate suitable for flash smelting. The
performance of combination of two or more xanthates/collectors has been
found much superior to those of individual collectors and therefore copper
flotation plants are employing combination of two to four collectors.
ii) Frothers: When the mineral surface has been rendered hydrophobic by
the use of a collector, stability of bubble attachment especially at the pulp
surface depends to a considerable extent on the efficiency of the frother.
Frothers are generally surface-active hetropolar organic reagents capable of
being adsorbed on air-water interface. When frother molecules react with
water, the water dipoles combine readily with polar groups and hydrate them.
But there is practically no reaction with the non-polar hydrocarbon group, the
tendency being to force the latter into the airphase. Thus, hetropolar structure
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