Froth 

flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is
used in several processing industries. Historically this was first used in the mining industry.

History

William Haynes in 1869 patented a process for separating sulfide and gangue minerals using oil and
called it bulk-oil flotation.

The first successful commercial flotation process for mineral sulphides was invented by Frank
Elmore[1] who worked on the development with his brother, Stanley. The Glasdir copper mine at
Llanellyd, near Dolgellau, in North Wales was bought in 1896 by the Elmore brothers in conjunction
with their father, William Elmore. In 1897, the Elmore brothers installed the world's first industrial
size commercial flotation process for mineral beneficiation at the Glasdir copper mine. The process
was not froth flotation but used oil to agglomerate pulverised sulphides and buoy them to the surface,
and was patented in 1898 with a description of the process published in 1903 in the Engineering and
Mining Journal. By this time they had recognized the importance of air bubbles in assisting the oil to
carry away the mineral particles. The Elmores had formed a company known as the Ore Concentration
Syndicate Ltd to promote the commercial use of the process worldwide. However developments
elsewhere, particularly in Australia by Minerals Separation Ltd, led to decades of hard fought legal
battles and litigations which, ultimately, were lost as the process was superseded by more advanced
techniques.

The modern froth flotation process was independently invented in the early 1900s in Australia by C.V
Potter and around the same time by G.D Delprat.[2] Initially, naturally occurring chemicals such asfatty
acids and oils were used as flotation reagents in a large quantity to increase the hydrophobicity of the
valuable minerals. Since then, the process has been adapted and applied to a wide variety of materials
to be separated, and additional collector agents, including surfactants and synthetic compounds have
been adopted for various applications.

In the 1960s the froth flotation technique was adapted for deinking recycled paper.

Industries
Mining

Froth flotation to separate plastics,Argonne National Laboratory

 Froth flotation cells to concentrate copper and nickel sulfide minerals, Falconbridge, Ontario.

Froth flotation is a process for separating minerals from gangue by taking advantage of differences in

theirhydrophobicity. Hydrophobicity differences between valuable minerals and waste gangue are
increased through the use of surfactants and wetting agents. The selective separation of the minerals
makes processing complex (that is, mixed) ores economically feasible. The flotation process is used
for the separation of a large range of sulfides,carbonates and oxides prior to further
refinement. Phosphates and coal are also processed upgraded by flotation technology.

Waste water treatment

The flotation process is also widely used in industrial waste water treatment plants, where it removes
fats, oil, grease and suspended solids from waste water. These units are called Dissolved air
flotation (DAF) units.[3] In particular, dissolved air flotation units are used in removing oil from the
wastewater effluents of oil refineries,petrochemical and chemical plants, natural gas processing
plants and similar industrial facilities.

Paper recycling

Froth flotation is one of the processes used to recover recycled paper. In the paper industry this step is
called deinking or just flotation. The target is to release and remove the hydrophobiccontaminants
from the recycled paper. The contaminants are mostly printing ink and stickies. Normally the setup is
a two stage system with 3,4 or 5 flotation cells in series.[4]

Principle of operation

Froth flotation commences by comminution (that is, crushing and grinding), which is used to increase
the surface area of the ore for subsequent processing and break the rocks into the desired mineral and
gangue in a process known as liberation, which then has to be separated from the desired mineral.
The ore is ground into a fine powder and mixed with water to form a slurry. The desired mineral is
rendered hydrophobic by the addition of a surfactant or collector chemical. The particular chemical
depends on which mineral is being refined. As an example, pine oil is used to
extract copper (seecopper extraction). This slurry (more properly called the pulp) of hydrophobic
mineral-bearing ore and hydrophilic gangue is then introduced to a water bath which is aerated,
creating bubbles. The hydrophobic grains of mineral-bearing ore escape the water by attaching to the
air bubbles, which rise to the surface, forming a foam or a scum (more properly called a froth). The
froth is removed and the concentrated mineral is further refined.

Science of flotation

To be effective on a given ore slurry, the surfactants are chosen based upon their selective wetting of
the types of particles to be separated. A good surfactant candidate will completely wet one of the types
of particles, while partially wetting the other type, which allows bubbles to attach to them and lift
them into a froth. The wetting activity of a surfactant on a particle can be quantified by measuring
the contact angles that the liquid/bubble interface makes with it. For complete wetting the contact
angle is zero.

Another consideration, especially important for heavy particles, is to balance the weight of the particle
with the surfactant adhesion and buoyant forces of the bubbles that would lift it.

For typical values of metal densities and surface tensions, if the bubbles are larger than the ore
particles, and the particles are equal to or less than 1 mm radius, then particles will rise into the froth
layer if:[5]

where   is the radius of the particles,   is the average surface tension between the three pairs of
phases (particle, flotation solution, air),   is the mass density of the particles, and   is the acceleration
of gravity (9.81 m/s2).

For particles larger than the bubbles, they too can rise into the froth, each buoyed by a swarm of
bubbles, under similar conditions as those expressed in the inequality.[5]

Flotation equipment

Diagram of froth flotation cell. Numbered triangles show direction of stream flow. A mixture of ore
and water called pulp [1] enters the cell from a conditioner, and flows to the bottom of the cell. Air [2]
or nitrogen is passed down a vertical impeller where shearing forces break the air stream into small
bubbles. The mineral concentrate froth is collected from the top of the cell [3], while the pulp [4]
flows to another cell.

Flotation can be performed in rectangular or cylindrical mechanically agitated cells or tanks, flotation
columns, Jameson cells or deinking flotation machines.

Mechanical cells use a large mixer and diffuser mechanism at the bottom of the mixing tank to
introduce air and provide mixing action. Flotation columns use air spargers to introduce air at the
bottom of a tall column while introducing slurry above. The countercurrent motion of the slurry
flowing down and the air flowing up provides mixing action. Mechanical cells generally have a higher
throughput rate, but produce material that is of lower quality, while flotation columns generally have a
low throughput rate but produce higher quality material.

The Jameson cell uses neither impellers nor spargers, instead combining the slurry with air in a
downcomer where high shear creates the turbulent conditions required for bubble particle contacting.

Mechanics of flotation

The following steps are followed, following grinding to liberate the mineral particles:

1. Reagent conditioning to achieve hydrophobic surface charges on the desired particles

2. Collection and upward transport by bubbles in an intimate contact with air or nitrogen
3. Formation of a stable froth on the surface of the flotation cell
4. Separation of the mineral laden froth from the bath (flotation cell)

Simple flotation circuit for mineral concentration. Numbered triangles show direction of stream
flow, Various flotation reagents are added to a mixture of ore and water (called pulp) in a conditioning
tank. The flow rate and tank size are designed to give the minerals enough time to be activated. The
conditioner pulp [1] is fed to a bank of rougher cells which remove most of the desired minerals as a
concentrate. The rougher pulp [2] passes to a bank of scavenger cells where additional reagents may
be added. The scavenger cell froth [3] is usually returned to the rougher cells for additional treatment,
but in some cases may be sent to special cleaner cells. The scavenger pulp is usually barren enough to
be discarded as tails. More complex flotation circuits have several sets of cleaner and re-cleaner cells,
and intermediate re-grinding of pulp or concentrate.

Chemicals of flotation
1. Collectors

Collectors either chemically bond (chemisorption) on a hydrophobic mineral surface,

or adsorb onto the surface in the case of, for example, coal flotation through physisorption.
Collectors increase the natural hydrophobicity of the surface, increasing the separability of the
hydrophobic and hydrophilic particles.

Xanthates

 Potassium amyl xanthate (PAX)

 Potassium isobutyl xanthate (PIBX)
 Potassium ethyl xanthate (KEX)
 Sodium isobutyl xanthate (SIBX)
 Sodium isopropyl xanthate (SIPX)
 Sodium ethyl xanthate (SEX)

Dithiophosphates

 Thiocarbamates  
 Xanthogen Formates  
 Thionocarbamates  
 Thiocarbanilide  

2. Frothers

 Pine oil
 Alcohols (methyl isobutyl carbinol (MIBC))
 Polyglycols
 Polyoxyparafins|
 Cresylic Acid (Xylenol)
 3. Modifiers

pH modifiers such as:

 Lime CaO
 Soda ash Na2CO3
 Caustic soda NaOH
 Acid H2SO4, HCl

Cationic modifiers:

 Ba2+, Ca2+, Cu+, Pb2+, Zn2+, Ag+

Anionic modifiers:

 SiO32-, PO43-, CN-, CO32-, S2-

Organic modifers:

 Dextrin, starch, glue, CMC

Chemicals for deinking of recycled paper

 pH control: sodium silicate and sodium hydroxide

 Calcium ion source: hard water, lime or calcium chloride
 Collector: fatty acid, fatty acid emulsion, fatty acid soap and/or organo-modified siloxane[6]

Specific ore applications

Sulfide ores
 Copper (see copper  Copper-
 Lead-Zinc  
extraction)   Molybdenum  
 Copper-Lead-Zinc-
 Lead-Zinc-Iron    Gold-Silver  
Iron  
 Nickel-
 Oxide Copper and Lead    Nickel  
Copper  
Nonsulfide ores
 Fluorite    Tungsten    Lithium  
 Tantalum    Tin    Coal  

References

1. ^ "Wales - The birthplace of Flotation". Retrieved 2010-01-13.

2. ^ "Historical Note". Minerals Separation Ltd. Retrieved 2007-12-30.
3. ^ Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical
Plants (1st ed.). John Wiley & Sons Ltd.. LCCN 67019834.
4. ^ Voith EcoCell flotation
plant http://www.voithpaper.com/applications/productsearch/files/594_VPR-PB-07-
0001-GB-07.pdf
5. ^ a b De Gennes, P. et al. (2004). Capillarity and Wetting Phenomena (1st ed.).
Springer-Verlag New York, Inc.. ISBN 0-387-00592-7.