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.

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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].




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



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.

flotation modeling



Potential flow leads to much

higher collision efficiencies than Stokes flow

the streamlines show the trajectories that a

small neutrally buoyant particle will take during

the encounter with the bubbles.

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



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.

flotation modeling



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



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



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






Solid percent

PH

Kind of collector

Number of cell


Impeller rotational speed

Impeller off-bottom clearance 0.3H, .04H , …



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 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

impeller off-bottom



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.




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

75 micron




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 ganguematerial .

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”.

• .1387، موسسه انتشارات و چاپ دانشگاه تهران، چاپ پنجم، 2نعمت اللهی حسین، کانه آرایی، جلد [. 3]

• [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
