Flotation mecanism

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IN THE NAME OF GOD
Flotation mechanism , circuit design and
effective parameter for enhancement flotation
recovery
Supervisor: Dr. Karimi
By: : Hamid Faramarzi
Imam Khomeini International University, Qazvin, Iran.

content
 Introduction
 Flotation mechanism
 Flotation Reagents
Effective parameter for increase recovery
 Operation parameters
 Hydrodynamic parameters
Conclusion
Reference

The flotation system includes many interrelated components, and
changes in one area will produce compensating effects in other areas [5]
Introduction

1. Each particle must achieve a level of hydrophobicity that will permit it to attach to a rising
bubble.
2. The particle must be suspended in the pulp phase of the cell.
3. The particle must collide with a rising bubble.
4. The particle must adhere to the bubble.
5. The particle must not detach from the bubble during passage through the pulp phase.
6. The particle must not detach from the bubble as the bubble leaves the pulp phase and
enters the froth phase.
7. The particle must not detach and drain from the froth during the passage of the froth to
the weir.

Flotation is necessary if particles are too fine for other separation processes [2].
Mineral flotation involves the use of bubbles to separate valuable minerals from
unwanted gangue material [1].
Separation is achieved by rendering the surface of the
mineral particle hydrophobic, usually with a collector,
so that it preferentially attaches to a bubble, which then
rises to the surface of the cell where it is collects as a
froth [1].
Flotation mechanism

Flotation mechanism
 only some materials are naturally hydrophobic enough for this process
 every particle has to get the chance to come in contact with an air bubble
only some processes will create a foam which is stable enough
in most cases, the minerals to be separated have similar hydrophobic properties
for all this reasons a very intelligent regime of the reagents [conditioning]
as well as a controlled hydrodynamic in the pulp is necessary [2].

Hydrodynamic parameters
For any given particle size, the effects of
impeller speed and bubble diameter can be
summarized as follows:
1. If the impeller speed is too low, the particles
are not maintained in suspension, but settle in
significant quantities at the base of the cell.
2. If the impeller speed is too high, the
turbulence in the cell is sufficient to rupture the
bond between the particle and bubble, and so
the recovery drops

3. If the bubble size is too low, the bubble are
too small to give sufficient buoyancy to the
particles to lift them to the top of the pulp.
4. If the bubble size is too large, the fewer will
be the number of bubbles created for a constant
air flow rate. Since the overall rate of flotation
depends on the number as well as the size of
the bubbles, the recovery will drop . [6]
Definition of the flotation process.[6]

In the turbulent condition of flotation cell, there are a number of sub-process
occur that include:
 Suspension of particles in the pulp.
Mixing of the aerated pulp for reagent distribution and conditioning
and to bring about particle-bubble collisions as the basic requirement
for bubble attachment
Rising of the loaded bubbles and removal of the froth [4].

Four states in which particles exist in a flotation cell.
flotation modeling

flotation modeling
Particle-bubble collisions
Not every particle in the path of a rising bubble will
collide with the bubble because, as the bubble
advances through the water, it forces the water
aside and this tends to carry the particles out of the
path of and around the bubble.
Stokes flow which applies when the bubble
Reynolds number is very much less than unity
and potential flow which applies when the
bubble Reynolds number is very much larger
than unity.

the streamlines show the trajectories that a
small neutrally buoyant particle will take during
the encounter with the bubbles.
Potential flow leads to much
higher collision efficiencies than Stokes flow
This agrees with intuition since a faster moving
bubble will sweep up particles in its path
more effectively than a slow moving bubble
flotation modeling

flotation modeling
Particle-bubble attachment
The attachment process requires significantly more complex modeling than the collision
process which, as shown in the previous section, is governed primarily by the fluid
dynamics close to the bubble.
When a particle collides with the bubble, the particle cannot immediately attach to the bubble
because a thin film of liquid between the particle and the bubble must first drain. When the
intervening film becomes sufficiently thin it can rupture allowing the particle to penetrate the
skin of the bubble.

If a stable three-phase contact has been
established before the fluid stream lines start to
diverge from the bubble, successful attachment is
achieved.
The accumulating collection of particles on the
lower surface gradually builds up until the whole
of the lower hemisphere of the bubble is covered
with adhering particles.
flotation modeling

flotation modeling
Particle Detachment
particles can become detached from a bubble
due to the effects of stresses that are induced
by the turbulence in the flotation cell.
Two forces are dominant in causing a particle
to become detached from a bubble. The
weight of the particle and the inertia of the
particle during the acceleration of the bubble
that is induced by turbulent eddies in the fluid

flotation modeling
The balance of forces can be altered by any factor which changes any of the
interfacial tensions. A new equilibrium position is established and a new contact
angle formed. The contact angle is a measure of how well the air bubble spreads
or wets the
solid surface. A low contact angle
(nominally less than 90°)
indicates a hydrophilic surface
while an angle greater than 90°
represents a hydrophobic surface.
A hydrophobic surface is one
which will favour contact with air
over water due to a lower
free energy and hence will
readily stick to an air
interface if one is available

Effective parameter for increase recovery
Effective parameter for
increase recovery
Operation
parameters
Solid percent
PH
Kind of collector
Number of cell
Hydrodynamic
parameters
Impeller rotational speed
Impeller off-bottom clearance
0.3H, .04H , …

Operation parameters
Collector:
Flotation requires hydrophobicity of the mineral particle but
only a few mineral substances are naturally hydrophobic.
Therefore, there is a need to use various reagents, called
collectors[7].
Collectors can be defined as organic chemical substances in
which the molecular structure is divided into a non-polar and a
polar group [9].

Collector:
The non-polar portion of the collector molecule is a hydrocarbon radical, which does not
react with water and is therefore water-repellent.
Collector with long H-C chain in contrast to short H-C chain caused an increase recovery
and decrease grade.
[6]

Activators and depressants:
In some cases, a regulator reacts directly with the mineral surface and
provides conditions for interaction of this mineral with the collector
These reagents are known as activators.
Some regulators may reduce conditions for hydrophobization of a
particular mineral with the collector, or they can make the surface
hydrophilic. these reagents are called depressants [9,2].

Frothers:
frother are heteropolar surface-active compounds.
Lower the surface tension of water
Surface tension also affects the size of the air bubbles.
Have the ability to adsorb on the air bubble–water interface.
increases the film strength of the air bubbles.
providing better attachment of hydrophobic particles to the bubbles [9].

Stabilizes the air bubbles
Prevents that small bubbles combine together and become big bubbles
Destabilize the bubbles [froth] after leaving the flotation cell
Has no negative effect like collector or other regencies
Has no effect on pH-value and is not effected by pH-value [2].

Number of cell
• Some more flotation cell with low volume decrease the
flotation time.
• According to economic condition should used some less cell
with high volume.
• So, generally number of cell is between 8-14 [3].
impeller off-bottom
impeller off-bottom clearance in a wide range from 0.2H to 0.4H does not
change the recovery so much as compared to the previous observations in the
factorial experiments. This shows the poor effect of impeller off-bottom
clearance in this range

The detrimental effect starts beyond 0.4H. Increasing impeller off-bottom clearance beyond
0.4H sharply decreases the recovery of coarse particles due to the lack of efficient particles
suspension. The decreased recovery when the impeller was submerged deeper than 0.2H is
attributed to the lack of introduced air into the flotation cell.

75 micron
Effect of the particle size on gold and silver recovery [5].

Effect of impeller speed on gold and silver recovery [5].

Effect of collector loading on gold and silver recovery for
240-mm froth thickness [5].

Conclusion
 Mineral flotation involves the use of bubbles to separate valuable minerals from unwanted gangue
material .
 Reagent was used in flotation include: collector, frother, Depressants and activator.
 Flotation performance is expressed by the relationship of two parameter: grade and recovery.
The effective parameter in recovery include:
Number of cell
Kind of collector
 Solid percent
 PH
 Impeller rotational speed
 Impeller off-bottom clearance

• [1]. Mixing and case dispersion in mineral flotation cell.
• [2]. Flotation “separation by different surface washability”.
• . 3[. نعمت اللهی حسین، کانه آرایی، جلد 2، موسسه انتشارات و چاپ دانشگاه تهران، چاپ پنجم، 1387 [
• [4]. Investigation of the reasons for copper and gold loss in the cleaner tail at ok tedi, PNG.
• [5]. J.R. Parga, J.L. Valenzuela and S. Aguayo “ Bacis flotation cell for gold- and silver-beard
pyrite recovery” Society for Mining, Metallurgy, and Exploration, Inc, 2009.
• [6]. A. Gupta and D.S. Yan, “Mineral processing design and operation: An introduction ” 2006.
• [7]. Jan Drzymala, “mineral processing” 2007.
• [8]. B.A wills, “mineral processing technology” 2006.
• [9]. Srdjan M. Bulatovic “Handbook of Flotation Reagents” 2007.
• [10] Bianca Newcombe ⇑, D. Bradshaw, E. Wightman “ The hydrodynamics of an operating
flash flotation cell “Minerals Engineering 41 (2013) 86–96
• [11] Optimization of the performance of the hydrodynamic parameters on the flotation
performance of coarse coal particles using design expert (DX8) software A. Dashti a, M.
Eskandari Nasab Fuel 107 (2013) 593–600
References

Flotation mecanism

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