Vaal University of Technology

Faculty of Engineering and Technology

Department of Metallurgical Engineering

PRACTICAL 2: Froth flotation

Mineral Processing 3

Group 4

Complied by : Kg Matshitse 217230245

: P, Shikwambana 217238076

Complied for : Mr Jeli

Due Date : 11/06/2021
Subject code :
DECLARATION

We group 4 hereby declare that all the below information is correct and accurate. We

solemnly declare that all the information furnished in this document is free of errors
to the best of our knowledge. We hereby declare that all the information contained in
this documents is in accordance with facts or truths to our knowledge

Signature:
 KG Matshitse
 Mphelo LA 217247938
 Langa
 P Shikwambana

Date : 2021/06/10
1 ABSTRACT

In this experiment we deal with one of the various ways of separation which is
flotation of coke. Flotation It can be used to separate phases, such as removing solid
particles or oil drips from water. Flotation is widely used to separate particles with
various hydrophobicities. The ability of a material to be wetted with a liquid in the
presence of a gas phase is referred to as hydrophobicity. Hydrophilic solids are
those that can easily be wetted with water, whereas hydrophobic solids have a low
affinity for wetting. Because of their hydrophobicity, particles cling to gas bubbles,
generating a particle-air aggregate that is lighter than water and rises to the water's
surface. . A Denver flotation cell was prepared to conduct the experiment, and
reagents were prepared whereby paraffin and MIBC were used. Water phase in the
flotation cell was conditioned to promote the formation of a more or less stable froth.
The coal was crushed and pulverized (reduced to fine size and produced powder) in
other to prepare the feed for the flotation. Scrappers were used to obtain the
products from the flotation cell, and pans were used to receive the products. An oven
was used to dry up the products, and a Muffle furnace was used to burn the coal for
ash analysis.
Contents
1 ABSTRACT..................................................................................................................................3
2 INTRODUCTION.........................................................................................................................5
3 LITERATURE REVIEW..............................................................................................................6
3.1 Flotation phases..................................................................................................................6
3.2 Froth flotation in waste water treatment...........................................................................8
3.3 Kinetic approach to flotation modelling............................................................................8
3.4 Principles of flotation...........................................................................................................8
3.5 Flotation phases..................................................................................................................9
3.6 Collection in the froth layer..............................................................................................10
3.7 Reagents..............................................................................................................................10
3.8 Denver flotation cell............................................................................................................11
4. EXPERIMENTAL PROCEDURES...........................................................................................12
4 RESULTS AND DISCUSSON.................................................................................................14
5 CONCLUSION..........................................................................................................................17
6 RECOMMENDATION..............................................................................................................18
7 REFERANCES..........................................................................................................................19
2 INTRODUCTION

Flotation is a mineral processing method for separating and concentrating ores by

changing their surfaces to a hydrophobic or hydrophilic state, meaning that water
repels or attracts them. The aim of the experiment was to upgrade coal using
flotation, and also to find out the amount of ash through ash analysis.

Froth flotation this is a process where selectively separation of hydrophobic which is

water repelling or hydrophilic which have an affinity to water or favourable, this is a
process, further the flotation process describes density separation in this the lighter
material float to the surface of a salt solution, froth flotation depends on the density
of the material alone. The froth flotation process development has improved the
recovery of minerals such copper and lead bearing minerals.

Originally, natural chemicals like fatty acids and oil were used as flotation reagents in
a large sizes in order to increase hydrophobicity of the valuable minerals, however
the process can be applied to a wide range of material to be separated.
3 LITERATURE REVIEW

Flotation according To Wills (2006:267) “Flotation Is an Important Mineral Processing

Technique without Any Doubt, And It Is Being Used to Treat Greater Tonnages. It Is
A Physico-Chemical Separation Process That Utilises The Difference In Surface
Properties Of The Valuable Minerals And The Unwanted Gangue Minerals”. Flotation
Comprises Of Three Phases Namely: Water, Solids And Froth. Although the basic
principles of the flotation process are well understood, quantitative prediction models
that can be used to stimulate the function of flotation cells in normal industrial circuits
have proven to be exceedingly difficult to develop. A cloud of air bubbles around a
millimetre in size is introduced into an agitated slurry in a flotation cell to aerate it.

3.1 Flotation phases

 The pulp phase is aerated, which causes bubbles to continually develop and
ascend through the pulp as a cloud. The bubbles are going upward relative to
the pulp at their local rise velocity and the particles are going downward at
their local settling velocity at any point in the pulp phase.
 The bubble phase consists of a cloud of bubbles that rise through the pulp
phase. The process of bubble-particle collision and particle attachment moves
a particle from the pulp to the bubble phase. As the bubble goes through the
pulp, it becomes more heavily loaded with attached particles.
 Froth phase; particles enter the froth phase when a bubble carrying the
particles crosses the pulp-froth interface. Bubbles that burst through the pulp
phase's surface generate the froth phase, which floats on top of the pulp
phase.
 Water phase in the flotation cell is conditioned to promote the formation of a
more or less stable froth. When the bubbles cross the interface, they do not
burst, and each one transports a layer of water into the froth phase. The
bubbles travel close together, with only a thin layer of liquid separating them.

In mineral processing froth flotation is explained as the process in which the

separation of minerals from gangue by using the minerals differences in
hydrophobicity as advantage, through the use of surfactants and wetting agents the
hydrophobicity variation in valuable minerals and waste gangue are increased. The
separation of these minerals selectively makes the processing complex feasible. On
the other hand flotation is whereby there is a separation of large range of sulphides,
carbonates and oxides before further refinement. Others purified by flotation are the
phosphates and coal

Froth flotation is commonly used in mines , this process or technique separates the
mineral of focus from the liquid phase this resulting as the difference in the ability of
air bubbles which is to selectively adhere to surface particles with its hydrophobicity
taken into account, the air bubbles together with the hydrophobic particles attached
are carried to the surface, whereby there is a formation of froth that can be
removed , meanwhile the hydrophilic minerals stay in liquid phase [CITATION Qui17 \l
1033 ].

3.2 Froth flotation in waste water treatment

In industrial waste water treatment plants the process of froth flotation is used to
remove fats, oils and grease from solid suspended in waste water, in the units known
as dissolved air flotation these are used to remove oil in waste water effluents of oil
refineries, petrochemical and chemical plants
3.3 Kinetic approach to flotation modelling

Flotation is a kinetic process. In order for a particle to be recovered in the froth phase
it must successfully complete the following steps:

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

The particles in the flotation cell exists in four states

Particles suspended in pulp phase.

Particles attached to bubble phase.

Particles attached to the froth phase.

Particles retained in the plateau border.

3.4 Principles of flotation

The process of material being recovered by flotation from the pulp comprises
three mechanism:

1. Selective attachment to air bubbles (true flotation),

2. Entrainment in the water which passes through the froth, and

 3. Physical entrapment between particles in the froth attached to air bubbles.
True flotation is the dominant mechanism for the recovery of valuable minerals,
and the separation efficiency between valuable minerals and gangue is
dependent on the degree of entrainment and physical entrapment. For flotation to
occur, an air bubble must be able to attach itself to a particle, and lift it to the
water surface.

3.5 Flotation phases

 The pulp phase is aerated so that bubbles are formed continuously and rise
through the pulp as an upward moving cloud. At any point in the pulp phase
the bubbles are moving upward relative to the pulp at their local rise velocity
and the particles are moving downward at their local settling velocity. Particles
can leave the pulp phase through one of the two routes; by collision with and
attachment to a bubble or direct to the froth phase by entrainment at the pulp-
froth interface.
 The bubble phase consists of a cloud of bubbles that rise through the pulp
phase. A particle transfers from the pulp to the bubble phase by a process of
bubble-particle collision and particle attachment. Bubbles become more
heavily loaded with attached particles as the bubble passes through the pulp.
 Froth phase; particles enter the froth phase when a bubble carrying the
particles crosses the pulp-froth interface. The froth phase floats on top of the
pulp phase and is formed by bubbles that break through the surface of the
pulp phase.

Water phase in the flotation cell is conditioned to promote the formation of a more
or less stable froth. The bubbles do not burst when they cross the interface and
each one carries of skin of water into the froth phase. The bubbles move close
together, with a single film of liquid separating the individual bubbles.

3.6 Collection in the froth layer.

Once a particle and bubble have come in contact, the bubble must be large enough
for its buoyancy to lift the particle to the surface. This is obviously easier if the
particles are low density (as is the case for coal) than if they are high-density (such
as lead sulphide). The particle and bubble must remain attached while they move up
into the froth layer at the top of the cell. The froth layer must persist long enough to
either flow over the discharge lip of the cell by gravity, or to be removed by
mechanical froth scrapers. If the froth is insufficiently stable, the bubbles will break
and drop the hydrophobic particles back into the slurry prematurely. However, the
froth should not be so stable as to become persistent foam, as a foam is difficult to
convey and pump through the plant. The surface area of the bubbles in the froth is
also important. Since particles are carried into the froth by attachment to bubble
surfaces, increasing amounts of bubble surface area allows a more rapid flotation
rate of particles. At the same time, increased surface area also carries more water
into the froth as the film between the bubbles. Since fine particles that are not
attached to air bubbles will be unselectively carried into the froth along with the water
(entrainment), excessive amounts of water in the froth can result in significant
contamination of the product with gangue minerals.

3.7 Reagents

MIBC (Methyl Isobutyl Carbinol) is an excellent chemical reagent used as

foaming reagent both for non-ferrous metal and non-metallic ores. It's mainly
used in the flotation plant of non-ferrous oxide ores or fine-grained sulphide ores
with a large quantity of soil grade. It is widely applied in flotation treatment of
lead-zinc ore copper- molybdenum copper-gold ore and mineral processing of
copper-gold ore with particular effect on improving the quality of concentrate and
efficiency of mine recovery
3.8 Denver flotation cell

Figure 2: Denver cell (www.sepor.com)

The Denver cell is equipped with 250, 500, 1000 and 2000 grams of stainless steel
tanks and one 1000 grams of clear acrylic tank, two inter-changeable adapting
impellers and diffusing parts.

D-12 machines are prewired with toggle switch and cable with plug wired for 115vac,
1 phase. Speed of the machine is adjusted by turning the knob located directly
above the motor and connected to the variable speed sheave. To increase speed,
turn the knob counter clockwise. To decrease speed, turn the knob clockwise. Adjust
speed only when machine is running. The nominal speed required for each test is a
factor within the control of the operator who by observation will quickly determine the
proper speed for each operation. Machines furnished with tachometers are ideal for
obtaining nominal speed during specific tests and can be used for setting speeds for
comparative tests. Normal operating speeds are as follows: 250-, 500-, or 1000-
gram tests - Approximately 1300 rpm. 2000-gram tests - Approximately 1200 rpm.
The machine produces its own air so it is not necessary to have an external air
source. However, pressurized air can be added if desired. The air valve at the top of
the standpipe is used for aeration control during the aeration and flotation operation.
The valve is closed during conditioning and opened during the aeration and flotation
period.
4. EXPERIMENTAL PROCEDURES

APPARATUS
 Weighing balance
 Collecting pans
 Paraffin oil
 Denver cell
 Stopwatch
 Micro pipette
 Pulverizing mill
 MIBC solution
 Coal sample
 Glass beaker

PREPARATION OF REAGENTS

 250g was weighed

 Particle size was reduced by pulverizer
 1ml of paraffin oil was measured and 10ml of water added and mixed on
magnetic stirrer
 0.5ml of MIBC and 10ml of water were added and mixed on magnetic stirrer

PROCEDURE DURING EXPERIMENT

Coal was crushed and added to a mill for further grinding and obtain micron size
powder for the flotation process. 250g of coal from the mill was weighed and
prepared as flotation feed and remained mass was used for ash analysis. 1200ml of
water was added into the flotation tank and the cell was turned on with 1200rpm
operating speed and the 250g of coal was added to agitate for 5 minutes. After two
minutes, 0.8g/ml of oil was added using a micro pipette and continued with agitation
for two minutes.
After 3 minutes, 0.8g/ml of MIBC was added and the agitation continued for 1
minute. After 1 minute, the valve was slowly open and collection of froth as
concentrate 1 began. After collection, the valve was closed again for 2 minutes to
allow agitation and opened again the valve for collection of concentration 2, this
routine was followed for the collection of concentrate 3 and 4. All the collected
concentrates were put in oven for a few hours (overnight) to dry the water and have
remains of concentrate masses. All the different concentrate collected were then
measured for analysis.
4 RESULTS AND DISCUSSON

Concentrates Mass(g) Mass (%) Cumulative Time(s)

(%)
1 4.7 36.7186 36.7186 60
2 2.4 18.75 55.46875 120
3 2.6 20.3125 39.0625 180
4 3.11 24.21875 44.53125 240
Total 12.8 100 124.12875 360

Graph of Time vs Cumulative (%)

Calculations
The amount of oil (cm3) needed.
0.3g=1kg
Mass=0.25kg
The amount of MIBC (cm3) needed
0.15g=1kg
Mass=0.25kg
=0.8g/ml

(Please discuss according to graph)

Discussion
During the first
5 CONCLUSION

Froth flotation is the best preferred operation in the coal industry because it is good
and versatile and economically friendly for large operations. Every operations has its
pullbacks and for froth is losing more courser particles and some tailings and also
limited from oxidized coal, but overall it is a good and metallurgical trusted and
preferred route.
The main reason for froth flotation was achieved and observed during the
experiment, separating hydrophobic from hydrophilic materials.
6 RECOMMENDATION
The flother MIBC is used to improve the coal flotation performance. It has a low flash point.
As a results it can results in many incidents like a fire during coal processing. Due to this
incidents it is wise to conceder a flother that will provide equal or better flotation results for
continued performance. This flother needs must be safer and environmental friendly than
MIBC. And it must have at least a higher flash point. During our investigation or rather
research it discovered that Pine oil and Dowfroth 250 have a higher flash point hence we
recommend them for this experiment. Pine oil has the potential to be used as a stand-alone
reagent for coal flotation that would remove the need for a potentially hazardous collector
making it safer on site. Dowfroth 250 has also possesses the dual frothing and collecting
properties, and has a high flash point double of MIBC making it the safer than MIBC.
7 REFERANCES

 Crawford, C. Blair, Quinn, B. 2017. in Microplastic Pollutants, Microplastic

separation techniques

 Sutherland, K.L., 1948. Physical chemistry of flotation. XI. Kinetics of the

flotation process. The Journal of Physical Chemistry, 52(2), pp.394-425.

 Rubio, J., Souza, M.L. and Smith, R.W., 2002. Overview of flotation as a
wastewater treatment technique. Minerals engineering, 15(3), pp.139-155.

 Matis, K.A. ed., 1994. Flotation science and engineering. CRC press.

 Shen, H., Forssberg, E. and Pugh, R.J., 2001. Selective flotation separation of
plastics by particle control. Resources, Conservation and Recycling, 33(1),
pp.37-50.

 Wang, C.Q., Wang, H., Fu, J.G. and Liu, Y.N., 2015. Flotation separation of
waste plastics for recycling—A review. Waste Management, 41, pp.28-38.

 Shibata, J., Matsumoto, S., Yamamoto, H. and Kusaka, E., 1996. Flotation
separation of plastics using selective depressants. International Journal of
Mineral Processing, 48(3-4), pp.127-134.

 da Rosa, J.J. and Rubio, J., 2005. The FF (flocculation–flotation)

process. Minerals Engineering, 18(7), pp.701-707.
 Gharai, M. and Venugopal, R., 2016. Modeling of flotation process—an
overview of different approaches. Mineral Processing and Extractive
Metallurgy Review, 37(2), pp.120-133.