Flotation reagents-collectors
In flotation beneficiation plant, main euipments are important such as
ball mill, flotation machine, crushing machine etc. And the flotation reagents
are also important for flotation process, the reagents used in flotation are
usually divided into three classes:
Collectors: organic chemicals which make the surface hydrophobic and hence the mineral
is capable of being collected in the process.
Frothers: organic chemicals which reduce the surface tension of the water to
stabilize the bubbles into a froth layer at the top of the flotation cell to
make concentrate removal
easier.
Modifiers: organic or inorganic chemicals used to modify the slurry conditions to enhance
the difference in surface chemistry between the valuable and gangue minerals.
Let’s introduce collectors in this article
Collectors
Collectors are generally heteropolar
organics with a charged polar group and an uncharged non-polar group. The
non-polar group is typically a hydrocarbon chain and in the beginning of the flotation
process this hydrocarbon chain was provided in the form of oil. This oil flotation
was phased out in the early 1920's by the development of more selective
organics such as the xanthates and dithiophosphates. Oil in the form of
kerosene or diesel is still used as the principal collecting agent in the coal
and other industries. The process of collection can be illustrated by taking a
clean glass plate and placing a few drops of water onto the surface as shown in
Fig. 1.
Fig1. Spreading of water over a
hydrophilic clean glass surface.
The water spreads out over the plate
because glass is hydrophilic. In Fig. 2, a thin film of oil or grease is
smeared over the plate surface and a few drops of water are again placed on the
plate. In this case the water shrinks up into droplets as the oil film is
hydrophobic. The thin film of oil has converted the hydrophilic glass surface
to an hydrophobic surface.
Fig.2. Beading of water on an oiled
hydrophilic surface
Minimisation of the system free energy
is the driving force for the reduction of the amount of high energy oil/water
interface. Thus the water will shrink to minimize the contact area between the
water and oil. When an air interface is available as shown in Fig.3, the oil molecule,
represented by a stick figure will concentrate at the air interface and extend
into the air phase as much as possible. The molecule is represented as aligning
perpendicular to the air/water interface. The collectors used in flotation
contain a non-polar hydrocarbon chair with a polar group on the chain. The
polar group may be ionised and hydrophilic so that the organic may be water
soluble. The polar group is also modified to be specifically attracted to certain
minerals. At an air/water interface the hydrocarbon chain of the collector will
stick out into the air phase at right angles to the interface while the
hydrophilic polar group remains in the water phase (Fig.2). If a suitable
mineral surface is present and the polar group is attracted to the solid
surface, a raft of collector ions will be adsorbed onto the mineral surface, effectively
forming a thin film of oil on the mineral surface and hence making the surface hydrophobic,
through adsorption rather than a physical smearing (Fig.3B). If an air interface
is now provided, in the form of an air bubble, the hydrocarbon chain will
extend into the air phase and if the bond strength between the polar group and
the mineral surface is strong enough, the particle will be lifted to the
surface by the buoyancy of the air bubble (Fig.3C).
Fig3. A: Collector dissolved in the
aqueous phase, B: Adsorption onto a mineral surface and C: attachment of an air
bubble onto the hydrophobic surface.
Collectors may be non-ionic
(hydrocarbon oils) or ionised. The ionised collectors are either cationic,
(amines) or anionic (fatty acids or sulphydril compounds such as xanthates or dithiophosphates).
sinonine can also provide sand washing plant epc.
sinonine can also provide sand washing plant epc.
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