FLOTATION

Report
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Flotation process (sometimes called flotation
separation) is a method of separation widely
used in the wastewater treatment and mineral
processing industries.
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Mechanism of froth flotation are:
Attachment of a specific mineral particle to
air bubbles
Being carried by the water in the floth
Caught b/w particles in the froth
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In flotation concentration mineral is
transferred to the froth leaving the gangue in
the pulp. This is direct flotation.
In reverse flotation, gangue is separated into
the froth fraction. Air bubbles can only stick
to the mineral particles if they can displace
water from the mineral surface which means
that the mineral has to be hydrophobic. Air
bubbles can continue to support the mineral
particles at the surface only if they can form a
stable froth which is achieved by using
floatation reagents.
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Dissolved air flotation
Induced gas flotation
Froth flotation, typical in the mineral
processing industry
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Dissolved air flotation (DAF) is a water treatment process that
clarifies wastewaters (or other waters) by the removal of
suspended matter such as oil or solids. The removal is achieved
by dissolving air in the water or wastewater under pressure and
then releasing the air at atmospheric pressure in a flotation tank
or basin. The released air forms tiny bubbles which adhere to the
suspended matter causing the suspended matter to float to the
surface of the water where it may then be removed by a
skimming device.[
Dissolved air flotation is very widely used in treating the
industrial wastewater effluents from oil refineries, petrochemical
and chemical plants, natural gas processing plants, paper mills,
general water treatment and similar industrial facilities. A very
similar process known as induced gas flotation is also used for
wastewater treatment. Froth flotation is commonly used in the
processing of mineral ores.
In the oil industry, dissolved gas flotation (DGF) units do not use
air as the flotation medium due to the explosion risk. Natural gas
is used instead to create the bubbles.
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The feed water to the DAF float tank is often (but not
always) dosed with a coagulant (such as ferric chloride or
aluminum sulfate) to flocculate the suspended matter.
A portion of the clarified effluent water leaving the DAF
tank is pumped into a small pressure vessel (called the air
drum) into which compressed air is also introduced. This
results in saturating the pressurized effluent water with
air. The air-saturated water stream is recycled to the front
of the float tank and flows through a pressure reduction
valve just as it enters the front of the float tank, which
results in the air being released in the form of tiny
bubbles. The bubbles adhere to the suspended matter,
causing the suspended mater to float to the surface and
form a froth layer which is then removed by a skimmer.
The froth-free water exits the float tank as the clarified
effluent from the DAF unit.[1]
Some DAF unit designs utilize parallel plate packing
material, lamellas, to provide more separation surface and
therefore to enhance the separation efficiency of the unit.
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Induced Gas Flotation (IGF) is a water treatment process that
clarifies wastewaters (or other waters) by the removal of
suspended matter such as oil or solids. The removal is achieved
by injecting air bubbles into the water or wastewater in a
flotation tank or basin. The small bubbles adhere to the
suspended matter causing the suspended matter to float to the
surface of the water where it may then be removed by a
skimming device.
Induced Gas Flotation is very widely used in treating the
industrial wastewater effluents from oil refineries, petrochemical
and chemical plants, natural gas processing plants and similar
industrial facilities. A very similar process known as dissolved air
flotation is also used for waste water treatment. Froth flotation is
commonly used in the processing of mineral ores.
IGF Units in the oil industry do not use air as the flotation
medium due to the explosion risk. These IGF Units use natural
gas to create the bubbles.
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The feed water is to the IGF float tank is often (but
not always) dosed with a coagulant (such as ferric
chloride or aluminum sulfate) to flocculate the
suspended matter.
The bubbles may be generated by an impeller,
eductors or a sparger. The bubbles adhere to the
suspended matter, causing the suspended mater to
float to the surface and form a froth layer which is
then removed by a skimmer. The froth-free water
exits the float tank as the clarified effluent from the
IGF unit.[1]
Some IGF unit designs utilize parallel plate packing
material to provide more separation surface and
therefore to enhance the separation efficiency of the
unit.
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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.
Eg oxides-hematite,cassiterite;oxidisedmalachite,cerussite;non metallicfluorite,phosphate,fine coal;sulphidescopper,zinc,lead
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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. 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.
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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 hydrophobic contaminants 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]
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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]
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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 (see copper
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 mineralbearing 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.
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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]
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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.
s
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following steps are
followed:
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Grinding to liberate the mineral particles
Reagent conditioning to achieve hydrophobic surface
charges on the desired particles
Collection and upward transport by bubbles in an
intimate contact with air or nitrogen
Formation of a stable froth on the surface of the
flotation cell
Separation of the mineral laden froth from the bath
(flotation cell)
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1) pneumatic machines either use air
entrained by turbulent pulp addition(cascade
cells), or more commonly air either blown in
or induced, in which case air must be
dispersed either by baffles or some form of
permeable base within the cell. It gives low
grade concentration &little operating trouble.
The davcra cell is used for roughing or
cleaning operations.
Most resent is floatation column.
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Mechanical floatation characterized by a
mechanically driven impeller which agitates
the slurry and disperses the incoming air into
small bubbles.
Criterions for assessing cell performance are:
Metallurgical performance i.e. product
recovery & grade.
Capacity in tonnes treated per unit volume.
Power consumption/tonne.
economicali.e. initial, operation &
maintenance cost
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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.
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A composition and process are provided for the recovery of the
values of zinc, molybdenum, copper, lead, iron (pyrite), and
iron-containing small amounts of gold or uranium, or both, from
ores comprising these mineral sulfides. The aqueous
composition is the impure form of an alkali metal alkyl
trithiocarbonate compound. The process comprises employing
said aqueous composition as a collection agent for the above
minerals in an ore recovery process.
A process for the separation of zinc values from lead values from
an ore comprising both is provided by employing an alkali metal
alkyl trithiocarbonate compound as a collection agent for zinc.
In addition, both a composition and process are provided for the
recovery of the values of iron, copper, and lead from ores
comprising these values. The composition consists essentially of
a dispersant and an impure form of an alkali metal alkyl
trithiocarbonate compound. The process comprises employing
this composition as a collection agent for the above minerals in
an ore recovery process.
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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.
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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
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Frothers
Frothers produces stable bubbles for
hydrophobic particles to attach to.work in
liquid phase only and not to mineral surface.
It should have low collecting power.
Reduce surface tention.
Pine oil
Alcohols (MIBC)
Polyglycols
Polyoxyparafins|
Cresylic Acid (Xylenol)
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Modifiers
Modifiers as activators, depressants or pH
modifiers. Alters selectivity of the collectors.
It intensifies or reduces their water repellant
effect on the mineral surface.
Activator-soluble salts which ionizes in solution
Eg activation of sphalerite by cu in solution
Depressant-are used to increase the selectivity of
floatation by rendering certain minerals
hydrophilic thus preventing their floatation.
Eg slime coating
Cationic modifiers:
Ba2+, Ca2+, Cu+, Pb2+, Zn2+, Ag+
Anionic modifiers:
SiO32-, PO43-, CN-, CO32-, S2Organic modifers:
Dextrin, starch, glue, CMC
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pH modifier floatation is carried out at alkali
pH because most collector are stable at
higher pH & corrosion of cells, pipework is
minimized.
pH modifiers such as:
Lime CaO
Soda ash Na2CO3
Caustic soda NaOH
Acid H2SO4, HCl
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Specific ore applications
Sulfide ores
Copper (see copper extraction)
Copper-Molybdenum
Lead-Zinc
Lead-Zinc-Iron
Copper-Lead-Zinc-Iron
Gold-Silver
Oxide Copper and Lead
Nickel
Nickel-Copper
Nonsulfide ores
Fluorite
Tungsten
Lithium
Tantalum
Tin
Coal
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Ore Concentration by Froth Flotation
Remember that only 0.67% of the ore is copper.
The copper minerals and waste rock are
separated at the mill using froth flotation. The
copper ore slurry from the grinding mills is
mixed with milk of lime (simply water and
ground-up limestone) to give a basic pH, pine oil
(yes, it comes from trees -- a by-product of
paper mills) to make bubbles, an alcohol to
strengthen the bubbles, and a collector chemical
called potassium amyl xanthate (or the
potassium salt of an alkyl dithiocarbonate).
The xanthates are added to the slurry in relatively
small quantities. Xanthate is a long hydrocarbon
(5 carbons) chain molecule. One end of the chain
(the ionic dithiocarbonate) is polar and sticks to
sulfide minerals while the other end is nonpolar,
containing the hydrocarbon chain is hydrophobic
-- it hates being in the water and is attracted to
the nonpolar hydrocarbon pine oil molecules.
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Raising the pH causes the polar end to ionize more
and to preferentially stick to chalcopyrite (CuFeS2)
and leave the pyrite (FeS2) alone. Air is blown into the
tanks and agitated like a giant blender, producing a
foamy froth. The chalcopyrite grains become coated
with xanthate molecules with their hydrophobic ends
waving around trying desperately to get out of the
water.
They attach themselves to the oily air bubbles which
become coated with chalcopyrite grains as they rise
to the surface and flow over the edge of the tank. In
this manner through a series of steps the copper ore
is concentrated to an eventual value of over 28%
copper. Waste rock particles do not adhere to the
bubbles and drop to the bottom of the tank. The
waste material that comes out of the bottom of the
tanks at the tail end of this process is called
"tailings." It is nothing more than ground-up rock
with the copper minerals removed.
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The bubbles that flow over the edge of the first set of
flotation tanks (inside the mill building) end up in this
thickener. By then the bubbles have broken and the
slurry is poured into the center of this round tank.
The solid material settles to the gently sloping
bottom and is pushed toward the center by a systems
of rakes that slowly revolve around the tank.
The thickened slurry is pumped back into the mill for
further processing. The clarified water flows under
the small dam, that you can see just inside the
perimeter of this tank, flows over the side, and is
pumped back to the mill for reuse.
That stuff floating on top is "almost money" - just
chalcopyrite that hasn't sunk in the tan yet. A water
spray on the opposite side of that radial walkway
helps sink it.
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Text edited by Rob Vugteveen, Director,
Asarco Mineral Discovery Center
The graphic down shows an air bubble
surrounded by grains of chalcopyrite that has
been coated with xanthate. The pine oil acts
as a frother only, providing the air bubbles
that the xanthate sticks to.
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The earliest patent relating to the mineral flotation process
is that of Haynes in 1860. his recognition of the
differences in wettability of various minerals by water and
oil formed the basis for a number of “oil” flotation
processes. During the next fifty years, there principal
stages of flotation development occurred:
Bulk oil flotation used the fact minerals of metallic luster
are preferentially wetted by oil the presence of water –
consequently passing into the interface between the oil
and water – while the water – wetted gangue (worthless
rock) drops out. This process requires large amounts of oil
– usually one part for each part of are.
Skin flotation used the fact that when finely ground dry ore
was gently brought into contact with still water, the
metallic particles tended to float more than did the
gangue. This process was developed between 18901915. However, both skin and bulk oil flotation were made
obsolete by the froth flotation process.
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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 the early 1900s in
Australia by C.V Potter and around the same time by G.D Delprat[2]. Initially,
naturally occurring chemicals such as fatty 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.
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Beychok, Milton R. (1967). Aqueous Wastes from
Petroleum and Petrochemical Plants (1st ed.). John
Wiley & Sons. LCCN 67019834.
^ Lawrence K. Wang, Yung-Tse Hung, Howard H. Lo
and Constantine Yapijakis (2004). Handbook of
Industrial and Hazardous Wastes Treatment (2nd ed.).
CRC Press. ISBN 0-8247-4114-5.
^ Kiuru, H.; Vahala, R., eds (2000). "Dissolved air
flotation in water and waste water treatment".
^
a b
International conference on DAF in water and waste
water treatment No. 4, Helsinki, Finland. IWA
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Publishing, London. ISBN 1-900222-81-7.
Flotation Concentration
Asarco Mining Operations in Arizona,Mission Mine,
Tucson,Text edited by Rob Vugteveen, Director,
Asarco Mineral Discovery Center
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The Columbia Electronic Encyclopedia® Copyright © 2007,
Columbia University Press. Licensed from Columbia
University Press. All rights reserved.
www.cc.columbia.edu/cu/cup/
recovery process.
www.grandpolycoats.com
US Patent References:
Flotation reagents
Parlman et al. - March, 1984 - 4439314
Froth flotation process and collector composition
Wiechers - July, 1980 - 4211644
ORE FLOTATION PROCESS WITH POLY(ETHYLENEPROPYLENE)GLYCOL FROTHERS
Booth - July, 1971 - 3595390
Method of making tertiary alkyl trithiocarbonates
Crouch et al. - June, 1952 - 2600737
Flotation reagent
Ott - June, 1940 - 2203739

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