Mechanical Separation topic.

1. FLOTATION
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23-Jan-15
Presents by Group 6

2. History
Introduction
Basic Principles
Mechanics of Flotation
Chemicals of Flotation
Advantages and Disadvantages
References
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3. HISTORY
 1869 - WILLIAM HAYNES patented a process of
separation of minerals and gangue using oil, which he
called “Bulk Flotation”.
 1896-97 - FRANK ELMORE and STANLEY ELMORE
set up the “Glasdir Copper Mine” at Llanelltyd, Dolgellau
in North Wales, where they carried out the world’s first
commercial Flotation process in 1897.
 1900(s) - In this era, C.V.PATTER and
G.D.DELPRAT independently, in Australia,
invented the “Modern Froth Flotation” process, in
which initially fatty acids and oil were the flotation
reagents to enhance hydrophobicity of the valuable
minerals.
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4. 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.
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5. 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. 5

6. 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

7. AIR IN
MINERALISED
FROTH
PULP
AIR
BUBBLE
CELL
AGITATOR
MINERALS’ PARTICLES ATTACHED TO BUBBLE
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8. 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. 8

9. Floatation Column
 Typical industrial column cell
comprises a steel tank equipped with
a feed inlet pipe near the top of the
column, a system of internal and
external launders to collect and
remove froth and a slurry outlet near
the bottom of the tank to remove
non-floating material.
 Drain nozzle and a series of re-
pulping nozzles are also located at
the bottom
 Depending on the tank geometry, it
may contain several internal baffles
to control the mixing characteristics
within the tank.
 A gas sparging system used to
generate the bubbles required for the
flotation process is located at the
bottom of the vessel. A froth
washing system, used to cleanse the
froth of entrained impurities, is
installed at the top of the tank.
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10. Cont…
 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 10

11. CHEMICALS OF FLOTATION
 Chemicals are required,
1. To control the relative Hydrophobicities between the
particles.
2. To maintain proper froth characteristics.
 The different types of chemicals involved are
 COLLECTORS
 FROTHERS
 REGULATORS,
 ACTIVATORS
 DEPRESSANTS
 pH MODIFIERS 11

12. Collectors
 These are Organic compounds used for enhancing the
Hydrophobicities of the selected minerals, by Adsorption
of its molecules or ions to the mineral surface and
reducing the stability of the hydrated surface separating
the mineral surface and air bubble.
 They are added to the Pulp, and sufficient time for
adsorption is provided during agitation. This period is
known as the CONDITIONING PERIOD.
 The different types of Collectors are tabulated as
follows,
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13. NON-IONISING IONISING
ANIONIC CATIONIC
(LIQUID NON-POLAR HYDROCARBONS,
INSOLUBLE IN WATER.)
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14.  These are required to enhance the hydrophobicities of
the partially hydrophobic minerals surfaces (e.g. coal),
by selectively adsorbing on their surface.
 Fuel and Kerosene oil are some of the non-ionic
collectors.
 These have complex molecules, which are assymetric in
nature and are Heteropolar, i.e., molecules have a non-
polar hydrocarbon group (which is water repellant in
nature) and a polar group (which reacts with water).
 Ionic collectors are classed into:-
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15.  These collectors possess non-polar and a polar group in
the Anionic part, and the Cationic part has no significant
role in the reagent-surface reaction.
 Carboxylates (OXYHYDRYL):-
 These are also called Fatty Acids or Soaps.
 Examples are salts of oleic acid and linoleic acid.
 Soaps have an advantage over other ionic collectors
that though they have long carbon chains, they are
soluble in water.
 These are strong in nature and have low selectivity.
 They are used for flotation of Ca, Ba, Sr, Mg and salts
of alkali and alkaline earth metals. 15

16. POLAR
GROUP
NON-POLAR GROUP
CATIONANION
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17. CATIONANION
POLAR GROUPNON-POLAR GROUP
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18.  These collectors have the Cationic part as their
significant role player in the reagent-surface reaction.
 The Polar group is based on PENTAVALENT NITROGEN
(commonly amines).
 They follow the principle of Physisorption and attach to
the mineral surface through electrostatic attraction.
Hence, they are weak collectors.
 Active in slightly acidic solutions and inactive in strongly
alkaline and acidic media.
 There requirement can be reduced by adding a non-
polar agent (eg. Kerosene), that gets pre-adsorbed.
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19. Frothers
 These are heteropolar surface-active reagents capable
of being adsorbed on the air-water interface.
 This chemical has the following functions:
1.To stabilize the formation of bubble in the Pulp phase.
2.To create a stable froth to allow selective drainage
from the froth of entrained gangue .
To increase the flotation kinetics.
 A good Frother should have negligible collecting
properties and should form such a froth, which is stable
enough to transfer of floated mineral from cell to the
collecting launder. They should have enough solubility in
water, so that they are evenly distributed & effective. 19

20. 20

21.  The most effective frothers include Hydroxyl, Carboxyl,
Carbonyl, Amino group and Sulpho group in their
composition. Alcohols having no collector properties is
preferred over other frothers.
 There are two types of frothers,
 NATURAL (eg. Pine Oil, Cresol etc.)
 SYNTHETIC (eg. MIBC [Methyl IsoButyl Carbinol],
Cytec Oreprep 549)
 The synthetic frothers are much stable in their
composition and thus advantageous over the natural.
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22.  These reagents Activate the mineral surface towards the
action of the Collectors, by altering their chemical
properties. Thus, they are referred as the FRIENDS of
Collectors.
 They are soluble salts which get ionised easily and the
ions react with the mineral surface.
 A classical eg. of Activation is in case of the SPHALERITE
ORE.
 Xanthates cannot effectively float the ZnS ore
particles, due to the formation of readily soluble
Zinc- Xanthate compound on the surface.
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23.  These reagents Deactivate the mineral surface towards
the action of Collectors, by altering their chemical
properties. Hence, they are referred as the ENEMIES of
the Collectors.
 Their typical use is to increase the Selectivity of
flotation, by preventing one mineral from flotation while
allowing other mineral to float unimpeded.
 There are mainly two categories of depressants,
 INORGANIC [eg. Sodium cyanide, Zinc sulphate
etc.]
 ORGANIC (or POLYMERIC) [eg. Starch, tannin,
Quebracho, Dextrin etc.]
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24.  Cyanides are the most commonly used in the selective
flotation of Lead-Copper-Zinc and Copper-Zinc systems
as Depressants for Sphalerite and pyrite ores.
 An eg. of the Cu-Zn system can be considered to
understand the action of a Depressant,
 The Cu ions present in the mineral leads to
unintetional activation of the Sphalerite (i.e. Zn
mineral) and thereby preventing selective flotation.
 Hence, Sodium Cyanide is added to Desorb the
surface Copper and react with the Copper ions in the
solution to form soluble complexes.
 The reactions proceed as follows, 24

25.  These are advantageous as they are less hazardous than
the inorganic ones.
 They do not ionize in the solution, but prevent flotation
forming a thin coating over the mineral particles.
 They are used in less amounts for depressing Talc,
Graphite and Calcite.
 Starch and Dextrin also act as supplementary Lead
depressants in Copper-Lead systems.
 Other applications include the selective depression of
polymetallic sulphide ores in the processing of iron ore.
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26.  The selectivity in complex flotation processes is dependent
on a delicate balance between the reagent concentration and
the pH.
 This pH factor is modified with the help of the substances
called pH MODIFIERS. Alkalinity in a solution is maintained by
the addition of Lime, Sodium carbonate, and to a lesser
extent NaOH and Ammonia. Sulphurous and Sulphuric acids
are used to lower the pH.
 Lime is widely used in the form of Milk of Lime, to maintain
the pulp alkalinity. It is added to the slurry prior to the
flotation. It precipitates heavy metal ions from the solution
thereby acting as Deactivators. But they dissociate to a
greater extent into OH- and Hydrogen ions, which further
modify the zeta potential and hence, the floatability of the
mineral.
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27.  For any concentration of Collector, there is a CRITICAL
pH value, below which a given mineral will float and
above which it will not.
 This critical value depends on the mineral’s nature,
collector’s nature and concentration, and the
temperature.
COLLECTOR’S
CONCENTRATION(inmg/L)
pH VALUE
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28. 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.
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29. DISADVANTAGES
 Capital costs
 Energy, operating costs
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30. REFERENCES
 Wills, B.A. and Napier-Munn Tim, “Mineral Processing
Technology”, Elsevier(2005)
 Kavatra, S.K., “Flotation Fundamentals”
 Ray, H.S. and Sridhar, R., “Extraction of Non-
Ferrous Metals”
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